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This data involves a number of assumptions and limitations, and you are cautioned not to give undue weight to such estimates. In addition, projections, assumptions and estimates of our future performance and the future performance of the markets in which we operate are necessarily subject to a high degree of uncertainty and risk. Granite Point Investment Highlights. The U. Strong cash flow profile supporting an attractive common stock dividend yield 1 See footnote 1 on p.

Commercial Real Estate Market Overview. Investment Strategy and Origination Platform. Data from to Data from the first quarter of through the fourth quarter of Census Bureau. Loan structure committed upfront to ensure Sponsor. Lender rights. Proactive monitoring. Borrower dialogue Some of these data, such as bulk density, are quantitative and should be measured following procedures which are meaningful for the paiticular application being considered.

Others are assessed "characteristics," about which qualitative statements, for exam- ple, "very sticky," are made. Second, it was unclear which of these descrip- tors of the materials were most significant in the design and trouble-free operation of systems. Finally, a need existed to provide an engineering basis for the evalu- ation and field testing of existing conveyor assemblies at existing re- sour. These con- siderations provided the basis for the objectives of this investiga- tion.

Its objec- tives were to: - determine, for commonly encountered waste ma- terials, i. The determination or measure- ment of properties and qualitative observations were made in the laboratory or on a test conveyor rig installed at NCRR's Resource Recovery Laboratory at Upper Marl- boro, MD. Engineering analysis and criteria development were done concurrently with the experimental work. Within the scope of this first phase of the work, belt conveyors horizontal and inclined , vibrat- ing conveyors and apron conveyors were considered.

Additionally, a test plan for a pneumatic conveyor rig was defined. In the present paper, to allow more room for a discussion of the approach taken, its rationale and detailed results on six waste ma- terials from MSW, it was decided to limit the discussion to two types of solids conveyors; - belt conveyor hori- zontal and inclined - vibrating conveyor.

Its design was based on several considerations: - ability to circulate a constant or quasi- constant mass flow rate; - easy access for sampling; and - flexibility to incline or decline, or inter- change test conveyors. To maintain a constant mass flow rate, the mass of material on the loop was changed at different speeds of the conveyors. It was experimentally verified that a con- stant mass flow rate was indeed realized along the loop. An attempt had earlier been made to use a surge hopper with a variable speed conveyor to keep a constant feedrate, but this procedure was abandoned because it resulted in surging and poor feedrate control.

The various components of the test rig are identified in Figure 2. Table 1 lists the specifica- tions for each conveyor. Worthy of note, conveyor 2a Table 1 , which is the test belt conveyor, was modified for testing with new idlers, belts and a variable drive motor to provide a range of speed from 0. Testing con- veyor 2b, of vibrating type, was luipped with a variable speed rive and interchangeable cam lafts to change stroke length. It was leased from Carman Industries, Inc.

Among the many properties affecting conveyability, some of the most important might be: bulk density, moisture, particle size, angle of surcharge, cohesiveneas, angle of internal friction, etc. Table 2 shows a complete list of bulk material properties affecting conveyability, according to the Con- veyor Equipment Manufacturers Asso- ciation CEMA 3. Asterisks indi- cate those which were considered to be unrelated to the conveyability of waste on solids conveyors.

Pan 2b Vibt. Vari-Speed Feeder Apron Conv. Recirculating test riq layout. Incline Speed Manufacturer Feed Apron 0. Return conveyor 0. Ample of maximum inclination of a belt 5. Angle of repose 6. Angle of slide 7. Angle of surcharge 8. Bulk density - loose 9. Bulk density - vibrated Elevated temperaturet Lumps - size - weight Specific gravityt Moisture content Screen analysis and-particle size consist Sized and unsized, material Characteristics assessed.

Aeration - fluidityt 2. Becomes plastic or tends to softent 3. Builds up and hardens 4. Corrosive 5. Generates static electricityt 6. Degradable - size breakdown 7. Deteriorates in storage - decomposition 8. Dusty 9. Explosiveness Flwmnability Harmful dust, toxic gas or fumes Hygroscopict Interlocks, oats and agglomerates Oils or fats presentt Packs under pressure Particle shape Stickiness - adhesion Contaminable-t Properties Measured and Results A complete description of test methods and procedures is given elsewhere 4 and would be too lengthy to reproduce here.

The dis- cussion will be limited to general comments and results, and to applicable properties or character- istics. The development of new, re- liable procedures was found to be outside the budget and time limits of this investigation. Some effort was spent on determining mass loss on two types of material - aluminum sheet and belt rubber lining - being impacted by the solids over a stan- dard time interval; results were in- conclusive, The angles of internal and external friction are doubtless of significance to the overall problem of conveying over the equip- ment lifetime, but were not needed in the engineering evaluation de- scribed below.

Angle of Maximum Inclination On a belt conveyor, the angle. It was observed to be dependent upon mass flow race and belt speed. For a "central" value of mass flow rate - which we estimated to be the middle of the range for each of the materials listed and for a nor- malized belt speed of 0.

The belt was mm IB in. Angles are se. Angle of Repose The angle-of repose for bulk. The results are - shown in Table 4. It is noted that, for each ma- terial , i range of values is reported should be expected, the angle of repose: for a given material varies due to irregularities in particle shape, size and their relative dis- tribution in tUe pile. A qualitative observation is that nar- rower ranges are observed for rela- tively more homogeneous fractions, such as d-RDF or the ferrous frac- tion.

A:igie of surcharge. Table 6 lists the observed values of the maximum angle of sur- charges for six materials and two idler angles. Loose Bulk Density Under actual conditions of use, MSW or its processed fractions may be less compacted or "looser" than could be inferred from measurements on a vibrated or tapped mass of the material.

Accordingly, the loose bulk density, thought to be similar to the "as conveyed" density, was mea- sured in a test in. Al- though there exist several published standards for determining bulk den- sity 3 , the American Society for the Testing and Materials ASTM methods suitable for aggregates and coke cannot be applied towards bulk density determination of solid waste fractions. The procedure developed by NCRR for this work is detailed elsewhere 4.

Basically, the mass and volume of the cone were measured to determine the loose or "as conveyed" bulk density. Results are given in Table 7. Its weight is ex- pressed in pounds of the maximum size lump 2. Particle size. Yet, pliable materials such as textiles and plastics might be much larger than the nominal grate or sieve size, and streams with significant amounts of these components are more prone to spillage. Considerable work re- mains to be done in characterizing MSW and its processed fractions as to the actual "size" of its com- ponents seen by the conveyor belt.

Moisture Content In the moisture content, only the absorbed and adsorbed water, measured by drying and evaporation, are considered. Due to the varia- bility of moisture in solid waste fractions, the values reported in Table 9 should be taken as no more than general indicators. Those materials with high moi- sture content, such as MSW or HF, may prove over long periods of time to cause-maintenance problems due to corrosion by salt and moisture.

The material was subjected-to a standard shaking action, and the percentage by weight retained oh each screen of a series of test screens was measured. The biggest opening screen was on top and the smallest on the bottom.

Results of the particle size analy- sis for all five fractions are given in Figure 4. Belt Conveyors: Analysis of the Basis of Spillage Rate Belt' conveyors are widely used in mining, construction and process- ing plants. Compared to other types, they often have the advan- tage of being economical, relatively simple to operate and able to con- vey materials of varying composi- tion, size and moisture.

They can be operated in the horizontal, in- clined or'declined mode. In spite of the simplicity of the operation and design of such systems, operating experience at resource recovery plants shows that many problems still beset belt con- veyors: spillage, jams, blow-back or roll-back, dusting, etc. Therefore, the variables or parameters on which some degree of control exists at the design stage, or in opera- tion need to be "fine-tuned" for a specific location and type of ma- terial.

After an 8-hour shift, 0. On each side of the belt, this would be equivalent of a layer Such rate of spil- lage would obviously be intolerable in steady operation. Other desirable althouah pos- sibly less cruci il features of a belt conveyor system of known geome- try, carrying a given material, are: a high throughput for a given size as measured by the width of the belt ; b low power consumption; c high reliability and troi'ble-free operation; d low levels of dust emissions: and e ease of transfer of material to and from t'..

It should be kept in mind, however, that high power consumption might be one of. High reliability and trouble- free operation, item c , can only be ascertained after much longer periods of time than would be possi- ble in this test program.

Still, whenever possible and justified, in- cidents of operation, jamming of equipirent or other incidents were noted and documented. As explained below, dust levels, item d , were recorded and evaluated in a relative, and to some extent, absolute manner. These levels were obtained at various "typical" locations near transfer points, in the middle of a straight run, etc.

First, by observing and recording trajectories of the material at the discharge point from the conveyor. Secondly, experimental jDservations, largely qualitative, and ad hoc improvements made during the course of the tests should serve as a guide for assessing the "pro- per" mode of feeding the belt with a variety of feedstocks.

Choice of Test Variables and Parameters A schematic representation of the conveyor belt system is shown in Figure 5. Schematic of belt conveyor system. Thir would appear as? First, the in- put mass flow rate, min defined above and shown in Figure 5, is assumed to be known and constant.

Second, the rate of spillage is' con- strued to be proportional to the belt length. For long, straight runs, i. More will be said about these limitations when discussing the experiments and test results. Let ma bfc! Thus, to-some extent, the choice of threshold "sm-x" is in- fluenced by the material conveyed, the characteristics of the experi- mental setup and the attainable ranges of test parameters, such as capacity, belt speed, etc.

In the discussion, the material being conveyed is assumed to be iven, from among the fractions- isted and described above. Its properties and characteristics, in the sense explained previously, have been measured and recorded. The size and geometric charac- teristics of the conveyor belt are assumed to be known. In the present case, as shown in Figure 6, this amounts to giving the belt.

S is' the idler ,angle. The spacing between idlers is i. The static capacity is deter- mined as follows. Along a length of belt sufficiently lono to be able to ignore end effects, the ma- terial under study is piled up on the belt, at rest, so that the edge of the pile, on either side, touches the edge of the belt.

Cross-section o4' loi'ed belt at rest. If in the experi. The reduc- tion in capacity resulting from- the motion is then assessed by a reduction coefficient: which itself is a function of the dynamic parameters, as described hereunder, and of the prescribed de- gree of spillage. Intuitively, it is obvious that the dynamic capacity would, all other factors being equal, be expressed by a larger num- ber if the allowed rate of spillage is larger.

The geometry, si2e of the sys- tem, and the conveyed material are given. Among other properties, its loose bulk density in the "conical" mode has been determined. It is assumed that the variations of this density with the speed and loading "of the belt are small and neglected a fact confirmed by observations. Increasing it might increase the conveyor carrying capacity, but this is not uniformly true.. Exces- sive speeds would increase spillage beyond tolerable limits, due to blow-back and mechanical shocks and vibrations.

Similarly, we could select Cdyn of the material on the belt, as an independent variable, and attempt to increase i. Again, this might only be possible to a point, due to ex- cessive "macs spillage" from the crumbling, sloughing slopes of the moving. Finally, the throughput m and belt speed V could be varied, but the dynamic capacity, calculated from equation 1 would still need to be related to the observed spil- lage rate.

For eyery pair mj, V , the spillage rate s will be measured as the de- pendent variable. Other sub- sidiary quantities, such as the dy- namic capacity or coefficient of reduction in dynamic capacity, can then be computed from the previous ones. Functional Dependence of Spillage and Mass Flev Rate on Velocity On physical grounds, the ex- pected dependence of the spillage rate on belt speed and mass flow rate could be obtained.

At very low speeds, this quantity is expected to be-smaller than, but on the or- der of, 1. At very high speeds, on the other hand, the whole mass being conveyed will be spilled, due to aerodynamic effects, vibrations and shocks on the idlers. Thus, for a given ipillage rate, there should exist: an optimal velocity, for which throughput is maximized. If a number of plots such as Figure 7 are drawn, a fami- ly Of curves corresponding to vari- ous mass flow rates can be obtained.

From these, in turn, curves, giving the spillage rate vs. For convenience, these curves will be labeled the curves shown in Figure 8. Shape of curves of dynamic reduction coeffi- cient vs. Spillage Rate. Examples of use of "d " curves. The forward motion of the material on the supporting inclined belt becomes impossible. From the results given above, it is observed that threshold c-TH is significantly lower than the an- gle of slide on the conveyor belt- ing material.

The angles selected for in- clin. As explained above, the belt speed V and mass flow rate m were selected as independe. The dependent variable will again be: S, spillage rate, per unit mass of throughput and unit length of belt as previously defined]. If so, the curves giving the spillage rate vs. The "steepness" of the sides, value of the optimum speed leading to minimum spillage and generally, position of the curve in the plane of representa- tion are expected, obviously, to depart from those corresponding to the horizontal case.

In the horizontal case, at relatively "low" V, the increase in carrying cross-section or dynamic section necessary to carry the same mass flow rate m at lower speed 's accompanies by an increase in spillage rate, A similar effect can be presumed to exist if the belt is ir. An increase in mass flow rate, when conveying a given material on a belt of given inclination a running at a given speed V, entails an increase in area of the cross- section on the belt occupied by ma- terial.

This should cause an in- crease in spillage rate, as illus- trated in Figure Operating Point. In the example illustrated in Figure 11, point Q is preferable to point P, since it allows a larger increase in mass flow rate before the maximum admissible level, smax is reached. In such cases, it would be more efficient to oper- ate in this range, for lower spil- lages under deliberate or acciden- tal variations of belt speed and mass flow rates about the nominal design conditions.

Increase in vertical cross section with inclination. Optimum Speed V4 and preferred operating range, at inclination a. Physically, aerodynamic "detach- ment" and "vibrations" should not depend to any degree on inclina- tion at small angles to the hori- zontal.

Thus, the level of spil- lage, all other factors being equal, should not vary much with the in- clination if the material is flat and self-compacting, as is the case with RDF. However, waste or frac- tions thereof containing a fair percentage of spherical or cylin- drical pieces likely to roll down the inclined belt, should show a rapid increase of spillage with speed, in the upper range of speeds.

To guide the material fed to the belt, a feed chute and 1. Test results are given and discussed below. Complete details on these tests may be found else- where 4. Horizontal Mode Test Results A certain fixed mass was placed on the test conveyor, at the chosen belt speed, providing a quasi-constant mass flow rate, over sufficiently short test durations and in the absence of excessive spillaqes 4. All spillage. The sides of the test conveyor were isolated wich plastic sheets to avoid includ- ing spillage caused by the return and feed conveyors.

Based on these complete re- sults, the analysis performed prior to the tests and outlined above was indeed confirmed. High spillage rates are observed at lower belt speeds. Upon increasing the belt' speed from a very low value, the rate of spillage for a constant mass flow rate decreases to a mini- mum value, then gradua.

Higher mass flow rates, for a given material and belt speed, lead to higher spillages, and the location of the minimum spillage point move3 towards higher belt speeds. Although all the solid waste "fractions show similar patterns of behavior, the specific values of spillage rates for each individual fraction are dependent on its pro- perties and characteristics.

For example, it was observed that d-RDF, being relatively uniform, showed a much lower spillage, all other fac- tors being equal, than more coarse, heterogeneous fractions 4. Noteworthy is the fact that, except at negligible throughputs, conveying will always generate some spilJage.

Shredded MSW. Spillage vs. RDF sample. The distribution of the spilled material along the section length was also recorded. The test conveyor was divided into four sec- tions labeled 1 to 4 of lrngth l. Spil- lage was separately collected and weighed for each of these sections at a given mass flow rate and for different belt. Table 12 i3 an fcxample for each of this d. It is seen that at 0. In section 1, the The spillage in section 2 At a higher speed of 1.

On the other hand, a higher percentage In summary, the amount and distribution of spillage area re- sult from non-uniform feed, very low or very high belt speed, im- proper feed and skirting arrange- ments, and carryover of adhesive, sticky material around the head pulley. Trajectories, or discharge paths of the material after the end pulley, were nr sured at a given, capacity and different speed by a direct observation technique, re- cording the fall height vs.

In actuality, the material, depending on the belt ve- locity, is discharged from the head pulley in the form of a band. The trajectories in these figures have been derived from plotting from the band's mid-stream points, at exam- ple is given in Figure The ex- perimental values were compared to the theoretical discharge trajec- tory, also plotted in Figure The theoretical and experimen- tal values correspond reasonably well.

This suggests that the method, provided by CEMA, for theo- retical trajectory calculations, could be successfully used to pre- dict solid waste trajectories accurately. This negligible change in power consumption - despite extreme vari- ations in such conveying conditions as speed, gravitational load, etc. The dis- advantage of using a skirtboard across the whole length of a loiig ' belt conveyor would be to increase the frictional resistance and, ' therefore, the horsepower require- ment.

Specific information for de- tailed horsepower calculations can be obtained from reference 2. Inclined Mode: Test Results The tests measured spillage vs. Overall experiments corroborated the speculation, from analysis, that higher spillages will be encountered on increasing the belt inclination, and that a preferred speid exists at given mass flow rate and inclination. An attempt was made to determine if any relationship between the extent of dust generated for parameters such as the test belt's angle of incli- nation, its velocity and mass flow rate of the material existed.

This, sampler measured the quantity of dust generated at the turbulent feed end of the belt conveyor. A second dust sampler was located approximately 6. The re- sults of the second sampler were in- consistent and unreliable, possibly due to background dust interferences in the testing area.

It was not possible to reduce or completely re- move the laboratory dust levels within a reasonable time on comple- tion of a test run; therefore, only tha dust loadings measured by the sampler located at the conveyor feed end were reported.

The test results provided the total suspended dust 4. Particle size distribution or any further characterization of the dust was not attempted. The test method and cal- culations are described elsewhere 4. For more complete details on dust sampling methods and proce- dures, the reader should refer to ASTM D and D standards. No consistent trends were rea- dily apparent, but a tendency to- wards greater dust concentration, was indeed observed for higher mass flow rates and belt conveyor inclina- tions.

Only the main re- sults and conclusions of the work described in reference 4 will be reported here. The theoretical principle of their- operation, illustrated in Figure 17, shows that during the first part of the acceleration of the pan, a par- ticle resting on it. A higher stroke amplitude might accelerate the material in a two- cycle jump, but this would require a much higher energy input. The test vibrating conveyor, 4. Two re- placeable, eccentric cams allowed the stroke "to be changed, either Dynamical balance also re- quires a balancing weight and the removal or addition of leaf springs, for a fixed stroke and frequency Figure Test results show that considerably more work is needed to rationally design a conveyor of appropriate stroke length and fre- quency for a given.

Within the finite scope of the program, it was not possible to un- dertake a systematic study of this complex mechanical system and its dynamics. The operating range was selected on an empirical basis, adopting as a reasonable operating criterion that the measured vibra- tion of the base not exceed 3. All points correspond- ing to a pan vibration of This limited the range of oporating fre- quencies to 4 30 - cpm Ihe tests conducted determined for the twc values of the stroke specified, the maximum carrying ca- pacity and conveying speed for fixed mass flow rate vs.

These re- sults are graphed in reference 4. A sample set of result curves is given in Figure The following conclusions could be drawn from the complete- series of tests: - For all fractions examined, over the range of frequency investigated, the carrying capacity increases with both frequency and stroke. However, on physical grounds, the capacity curve is expected to reach a saturation level- at some higher, undetermined fre- quency.

At cpm, in- creasing the amplitude from Vibrating conveyor principle. Schematic of vibrating conveyor. Carrying capacity of test vibratincr conveyor vs. At cpm, speeds on the order oC 0. RDF, for example. Experiments were carried out for the For the six fractions, a decrease in conveying speed with increasing burden depth was observed.

This indicates that the energy imparted by the vi- brating pan is absorbed rather than transmitted, as is the case for denser fractions. The percent lowering of burden height over 4. Thus, there is a definite tendency for the solid waste fraction to compact due to the vibra- tional activity of the pan. Most solid waste fractions are composites of varying bulk density components. A test was conducted to determine if varying components of a solid waste fraction segregate out, due to vast bulk density dif- ferences.

A particle size distribution was performed on a "top" and a "bottom" layer to determine the ex- tent of segregation. The frequency was fixed at Without repro- ducing detailed results given elsewhere 4 , and to summarize, it was ob- served that the smaller particles in MSW and HF did indeed concentrate in the bottom layer.

Such was not the case for RDF, presumably due to the ten- dency of fine particles to adhere on paper flakes. Conveying vs. This vas probably due to a loss'in physical inte- grity and gain in bulk density with increased moisture content. For most materials, dust level6 were higher for the larger stroke They ranged from a low of 0. In the present paper, the emphasis was put more specifically on belt conveyors and vibrating pan I.

The main results and' conclusions of the study are: - Properties and charac- teristics. Where sensi- ble and feasible, these - properties or charac- teristics were measured 2. The experi- mental values are reported. An analysis was made of the dependence to be expected, on a belt conveyor, be- tween spillage rate, ca- pacity and belt speed.

Experimental results on six waste fractions con- firmed these predictions.. A procedure for a rational choice of operating con- ditions at various flow rates was defined, in which the maximum admissible spillage is selected as the design criterion. Within the range of parameters inves- tigated, they underline the importance and show the effects of frequency, stroke amplitude, bulk density, moisture content on carrying capacity, con- veying speed, segregation in the depth and dust emissions.

The results indicate trends and 3ensi- tivities and should prove. How- ever, they strongly sug- gest that significantly n. Felago, S. Fischer, R. Pease, J. Quinn, and P. Depart- ment of Energy, Mitre Corp. Classification and Definitions of Bulk Materials. Khan, 2. An Engineering and Experiments] Evaluation of Conveyors for.

Final Report, Contract R, U. Environmental Protection Agency, Municipal Envircrimen-. Air Force, Engineer- ing and Services Laboratory. Center for Resource Recovery, Inc. Department of Labor. R from the U. Thanks are due to Mr. William Horton of Carmen Industries, for his co- operation in providing the test vi- brating- conveyor. Dia2, G. Trezek Cal Recovery Systems, Inc.

Methods of testing, criteria for evaluation, operating condi- tions, and assessment of atr classifier performance are described. Topics that are ger- mane to the design and operation of air classifiers are also covered. Comparisons presented herein enable judgements to be made as to the? Introduction --even air classification systems with nominai throughputs ranging from 4 to EPA [A].

During the course of the work, characterization pa- rameters were developed that enabled the comparison of all air classifiers on an equivalent basis. Constant light fraction split is defined as that value of the light frac- tion split. The invariant nature of ma- ter. The seven air classifiers tested in this study, their locations, and their general descriptions are given in Table 1.

Further details concerning the geo- metrical configuration of the air Classi- fiers are available in the final report to tne. An examination of some of the key characteristics of the solid waste en- countered during the air classifier test- ing program shows tne importance of nor- malizing tne performance parameters In terms of the air classifier infeed com- position. As can be seen from the en- tries in Table 2, there are wide varia- tions in the waste characteristics from site to site.

For example, the paper and plastic content of the infeed to the Los Angeles air classifier averaged The relative breakdown of air classifier feed material into light and heavy fractions. The- energy required by a unit or system and reported on an as-processed ton basis kWh per Metric ton. The cross-sectional area of the zone of separation of light and heavy materials.

The column area is perpen- dicular to the air stream and generally is reported as the maximum column area up-stream of the lights discharge. The volumetric air flow through the separation zone oivioed by the column area. The percentage of paper and plastic in the lignt fraction on an air-dry weight basis.

Light fraction Quality is a measure of the amount of the primary combustible consti- tuents ir, the light fraction. Defined 6S the product of the light fraction Quality and the liqht fraction split both. Combustible yield is a measure of the amount of pa- per and plastic recovered in the lignt fraction end repor- ted in terms of a unit input of feed material to the air classifier. A dimensionless term defineG as the mass flowrate of air divided by tr.

A low value of trie critical column loading parameter indicates tne need for relative!. Defined as the weight of paper and plastic on an air-dry basis recovered in the light fraction divided by me weight of paper ano plastic present in tne air classifier feed. A nigh recovery percentage of paper anc plastic is desirable to provide hign hejting value components for the light fraction.

Defined as the energy recovered in. Being a auelitative parameter, retained ash is a measure of tne aoility of an 3ir classifier to drop out in tne neavy fraction components that are high in ash content. The weight of mesh fines in the light, fraction divided oy the weight of 'fines in the air classifier feed, on an air dry basis.

Particle size of the heavy and light fractions was used to deterr,. Materials used for size distribution and composition analy- ses consisted of suosamples from the sam- ples of heavy and light fractions collec- ted for mass flowrate measurements. Tne size of the latter samples generally ranged from 10 to 50 kg.

The sample sizes for the size distribution and com- position analyses were in the range of 2. The general procedure involvied set- ting a particular air flow through the classifier, wnicn was accomplished through varying the rpm of the air clas- sifier fans or adjusting a damper. Sub- sequently, samples of heavy anc light fractions were collecteo simultaneously for a number of different!

Samples of : heavy and light fractions were collected from conveyors downstream of the classi- fier. These samples served the dual pur- pose of allowing calculation of the flow- rate of heavy ana light fractions while providing the material from wnich repre- sentative samples were chosen for later laboratory analyses. All material was completely removed from a given length of conveyor belting, thus a 1 leviatirig the problem of stratification of components in the flow stream whicn night have skewed tne results had onij "grab" sam- ples been collected.

Laboratory analysis consisted of air crying, screening, ana manually sorting the light ana heavy fractions, except for tne Ames air classifier testing in which it was oily possible to collect infeed and heav samples. In addition, heating value determinations and ash analyses were carried out on light and. Both manual and mechanical screening were used to determine the size distribution of the samples.

Size dis- tribution analyses were carried out in order to determine the amount of fines minus 14 mesh in the heavy and light fractions and aiso to provide a quantita- tive means of describii g the particle C i 7P of hp air cljStif IS? Manual sorting of the samples consisted of separating ferrous, paper and plastic, ana nonferrous components from the heavy ana light fractions. The composition and size data were used suo- sequently to develop the characterization parameters.

Also as part of tne test program, both air flow ana system power require- ments were measured tor eacn operating setpoint i. Results ana Discussion A sumnary matrix of the operating parameters aetenmned for each air clas- sifier is shown in Table 4. Data are Shown for eacn of tne three air flow set- tings usea during the test program at each site.

The air flow settings usea during the test program at eacn site are oenotea as "High", "Mecium", aria "Low". The volumetric air flows corresponaing to the high, meaium, and lew air flow set- tings are reported iii tne final report. Conse- quently, they were not exhibiting tneir best performance for eacn air flow set- ting. These parameters, all cased upon material characteristics, are reported in Table 5 in aisoltte ana nor- malized terms.

For reasons previously discussed, the normalized values re- ported as percent of component retained 1n light fractions. Table 5 are '. Due to tne differ- ing characteristics of the air classifier infeed material among tne different sites, the absolute values of the perfor- mance parameters colums A through k are only of value whenustJ to judge individ- ual air classifier performance and not to compare air classifiers among.

In addition, the use of the abso- lute values for evaluating air classifier performance at a pjrticular site presup- poses that the waste composition is in- variant ever the duration of tiie a questionable assumption. I 13 TnrwaL". CU 2iU2 1. M low tl. D 3ti. H oiy7 IB. Many comparisons ana conclusions can De , drawn rtYom the data. For example", an ex- amination of the data ir. As a second example, it may De noted that the percentage of paper and plastic in the heavy fraction column B ranged from 0.

The lignt fraction oDtaineo in Los Angeles also has a rela- tively nign heating value. However, the nign valu? An examina- tion of the heating value of the air classifier feeo at Los Angeles Taole 2 shows that the waste also has a rela- tively hign heating value. Hence, -the heating value of the Los Angeles light fraction is partly a conseouence of tne relatively high. From the standpoint of establishing criteria for air classifier evaluation, two Key ratios can he suggested.

The for. Retained Fines Tacoma Higr. High S Akron High 15 On tne otner njno, for recovery of a refuse derive; fut! Where pos- sible, only heating value ana asn oata for the same samples were used in tne calculat'ons as sno'wn for all sues ex- cept Ames. Consequently, tne values lis- ted in Taole 7 generally will differ from Tnose tnat would De calculated oy using ;he RE ana RA values listed in Taole 5, except for the Ames air classifier.

Some y tne cri- tical througnput for eacn air classifier at us optimum air flow setting, as ae- tailea in Taole A Cumpanson of air Classifiers is possiole using the data presented in TaDle 9. For example, the Tacoma air classifier uses tne '. However, tne RDF quality s. Retainer Asn T acoma Low 0. J Ames Hign As pre- viously discussed, other starting points are possible. The subse- quent determination of tne performance parameters would tnen follow similarly to that previously oesci ibeo for the case of characterizing RDF recovery, ;.

Conclusions Tne testing and performance charac- terization of seven air classifiers has shown the ranges of operating conditions ana performance tnat can oe expected for each air classifier, n aoainon, mctn- ojs nave ceen presented tor comparing different types of air classifiers oper- ating under different air anu material flows and handling snrediiea refuse of differing composition.

Thei-e is no absolute means of comparing air classi- fier periormance. However, u is now possiDle to judge air classifier per- formance on a relative oasis if tne judg- ing parameters are judiciously chosen so as to allow an eouitaole comparison, i. Hopefully, the methods and data presenter nere will prove useful in the evaluation of otner air classifiers.

Recovered Energy Avg. Results of all seven field tests taken collectively enable an overall, or aver- age, value of certain parameters to be calculated as shown in Tab'e Such average values subsequently can be used for calculation of mass and energy bal- ances on an air els' ''ier system.

Campbell Marc L. An un- derstanding of the operations and inter-relations of these vavious pieces of equipment is critical to proper design and functioning of the enLire system. A review of recent and ongoing research and evaluation programs for each of these processes is provided in this paper.

In a second section, analysis is made of the technical and economical feasi- bility of a d-RDF system for small community. ThP approach first defines thr affordable cost, on a breaiceven basis, fct the equipment and plant needed to provide a RDF feedstock to a TJensification module. A RDF pro- duction scheme is outlined and a preliminary facility.

This discussion oj. This example will illus- trate. In turn, ther;e are a large number of process flows Jthat have been applied or proposed for RDF production. These unit processes are scaled-up, and coml" ined in a number of commercial- scale RDF preparation plants. How- ever, in the first applications to solid waste, these systems generally have not functioned well and have fallen short of meeting operating expectations and product specifica- tions.

Subsequent efforts to evalu- ate, trouble-shoot or improve the performance of individual processes or plants as a whole were compli- cated by the fact that outputs of one process affected the performance of other processes as well as the rest of the system. The difficul- ties appear attributable to a lack of understanding of capabilities and limitations of the individual unit processes and to absence of signifi- cant bench, pilot or commercial operating experience using solid waste feedstock with this equip- ment.

In recognition of the need for basie knowledge of unit processes to advance the understanding and appli- cation of RDF preparation systems, the Environmental Protection Agency EPA had initiated a number of fun- damental, and experimental research programs. The following sections summarize descriptions, status and results of these research programs in the areas of shredding, air clas- sification, screening, densifica- tion and, material handling. While funding has been limited and priori- ties shifting in fact, the Depart- ment of Energy DOE now has sole responsibility for RDF process re- search , these research activities or in some cases the absence of such activities are highlighted to emphasize the type of analytical and experimental programs necessary to develop more basic knowledge on unit processes.

This could permit improved design, scaling, opera- tions, costing and evaluation of waste-to-energy systems, and speci- fication and pricing of RDF prod- ucts. It is beyond the scope of this paper to cover the results of all these projects in detail; the reader is directed to the refer- ences cited in this paper for addi- tional information.

Size Reduction Shredders are applied to un- processed or processed solid waste to produce a smaller, more uniform- ly sized, homogeneous product which is more easily handled and sepa- rated in follow'-on processing. Primary shredding refers to size reduction of unprocessed MSW uti- lizing hammermill horizontal and vertical axi'- , shear or flail mill types of shredders. Secondary shredding refers to the size reduc- tion, usually by a hammermill or knife mill, 6f a processed waste fraction - typically air-classified light fraction.

The earliest shredder perfor- mance testing was in EPA-supported field studies in the late 's and early "s in Gainesville, Florida and Madison, Wisconsin 1,2. A more fundamental pilot plant program by Cal Recovery Systems, Inc. A com- preliensive follow-on field test program by the same firm again under EPA support was then ini- tiated to make comparative perfor- mance evaluations of nine large commercial shredder installations 4.

More recently, a field test program concerned with production capacity and product characteris- tics from parallel and sequential shredding of trommeled, air- classified light fraction was run with a vertical shaft shredder and horizontal shaft shredder at the Maryland Environmental Service facility in Cockeysville, Maryland 5. Results on dependence of par- ticle size, throughput, power con- sumption and the effects of mois- ture and hammer wear for a vertical shaft hammermill were obtained at the Pompano Beach, Florida solid waste facility and reported recently 6.

The first two of these devices are of particular interest for the type of small-scale RDF processing systems considered in the example below. In a typical application, a flail mill is used to coarsely shred raw waste to break bags and liberate contents prior to separ-- tion or screening. No reported equipment investigations and only minimum experimental data on flail mill- product' characteristics are available to assist designers in using this equipment for waste- processing systems.

A primary-shredded, air- classified light fraction must be further reduced in size prior to densificaticjn in order to minimize milling action on the densifier, attendant increases in power con- sumption and wear and decreased mill capacity. Knife mills have recently been applied particularly in Europe or considered for size re- duction in preparation of densifier feedstock 7,8.

The presumed benefits of the knife mill have been the positive size control of tex- tiles and the increased product den- sity less de-fiberized or fluffy. However, data are not available to answer these or other questions sudi as capacity of existing models, sen- sitivity to 'damage from tramp metals and wear on the knives and grates. Shear shredders have :wo slow- speed, counter-rotating rotors with interme:3hed hammers.

They have found a growing market for indus- trial residues such as waste rub- ber and vood and are frequently mentioned as alternatives to hammer- mills for primary shredding. The advantages cited for the shear shredder are reductions in power consumption, wear and explosion hazard, but no documented investi- gations verify or disprove these claims. Air Classification Air classification is an aero- dynamic process to separate loosely- mixed fractions of material based on individual component size, shape and density in relation to the equipment configuration and air flew parameters.

There are several styles of air classifiers including straight column, zig-zag, horizon- tal vibrating, rotary drum and con- centric tubes. As applied to solid waste, the air classification pro- cess is most frequently employed on shredded waste to produce, a. In general, the expectations and predictions fcr separation efficiency and relia- bility have not been met in actual operation. Unit process research on air- classification equipment has pri- marily been in the form of field evaluations of pilot- and full- scale equipment.

Midwest Research Institute has reported on an exten- sive field test on 7- air classifiers of various styles and sizes 9. The tests documented performance and operating characteristics at several, operating conditions. In particular, experiments were run at varying air flows on both units and with varying internal geometry in the case of the zig-zag unit.

Few investigations directed at more basic understand- ing of the air-classification pro-- cess, the principles for design, scaling and operation have been undertaken or reported. Along these lines the work by M. Tels and M. Senden 11,12 should be cited. Also, the aerodynamic characterization of elements in.

An example of such a device is a tramp material separa- tor. The recent move away from shredder and air-classification systems and the increased use of flails and screening has reduced cost and complexity of waste pro- cessing systems, but it has not eliminated the need for.

The application of such a tramp materi- al separator is illustrated in this paper in the example of a small facility processing system. The efforts at development of such a device, which ia the subject of an upcoming research task at NCRR spon- sored by DOE 14 , unfortunately, cannot benefit from the extensive operating and performance data logged on 'nearly a dozen air clas- sifier systems in the test programs cited above.

Rather, for example, information on the applicability of theoretical and analytical models for air classifier performance should be assessed; a controlled pilot-scale parametrical test pro- gram should be undertaken; and data obtained on characterization of waste components by size, shape and mass relationships. Topical discus- sion and outlines of a number of these more fundamental types of unit process research programs are provided in a report on research goals prepared by NCRR for EPA Screening Flat or vibratory , rotary trommel or disc screens have been considered or applied for size separation of unprocessed waste and a variety of processed fractions.

Recent interest in preparation of RDF has been in the use of a rotary screen ahead of the primary shred- der. The objective is to remove undersize material, particularly abrasive inorganics, prior to shredding to reduce the loading wear and power consumption. Flat, rotary or disc screens may also be placed after the shredder or air classifier to remove ash-causing inorganic fines and pof-ntially troublesome oversize aateiLai from RDF.. For either location or screen type, screening has the promise of offering a relatively inexpensive, efficient approach to upgrading RDF.

Few reports of analytical or experimental efforts on flat screen- ing of solid wastes have been pub- lished. In an experimental program at NCRR, rome operating experience was gained, and associated data were reported on flat screening of shredded HSW and air-classified light fraction.

The testing, how- ever, was aimed at characterizing the particular devices being used and not at evaluating the screening process for various pieces of equip- ment and a range of input condi- tions The results indicated that, due to the presence of flat and flexible materials that ride on the screen and block the openings, flat screens would have to be un- usually large for effective MSW or RDF processing.

A tumbling action, as occurs in rotary screens, appears to offer improvement. DOE recently initiated an ex- tensive research effort on the mechanism and performance of rotary screens applied to RDF preparation. Studies of the tromroel hardware systems the structure and drive , the economics of full-scale trommels and an eval- uation of trommels for small-scale systems are all part of the DOE program.

The particular approach which NCRR has adopted to develop predic- tive relationships oYi trommel operation and performance was de- veloped as'part of em aforemen- tioned study for EPA on processing research topics 15, Concur- rent to that study, the first eval- uation of a full-scale trommel was conducted as part of an EPA test and evaluation program at the Re- source Recovery Demonstration Facility in New Orleans, Louisiana A disc screen is a horizontal assembly of rotating shafts with circular or elliptical interlocking discs arranged to form an aperture through which undersize material may pass.

Oversize material is carried across and off the screen by the,rotating discs. In one of the first applications to waste fuel processing, disc screens were installed in the RDF production plant in Ames, Iowa, for removal of grit, fine inorganics to reduce the load and wear on the secondary shredder and materials handling equipment and reduce tho ash content of the RDF. Unfor- tunately, data could not be obtained to indicate the change in fuel yield after the installation of the disc screens and show the proportion of organics loss with the grit product.

Densification For reasons of combustion, feeding, handling or storability, a densified form of RDF may be re- quired for a particular fuel market. Such applications are typically. Equipment types, include pelletizers, cubers, extruders and briquetters.

Some of the earliest and most extensively report experiences on the preparation, properties, handl- ing and economics of densification occurred at NCRR between and , under EPA's sponsorship 8. This project covered an operation and performance evaluation of a shredder and pelletizer subsystem designed to produce d-RDF from shredded, air-classified light frac- tion. Over Ms of pellets were produced for test firing in two different stoker-boiler facilities 24, Other experimental activi- ties at the NCRR densification plant included an investigation of the effect on throughput, power consumption and pellet quality from addition of waste.

The bench-scale testinq was the first of its kind and provided insights into the dynamics of pel- let formation and elements of the energy requirements for palletiza- tion. The results determined the effects of die configuration and suggested explanations for exces- sive die wear and decreasing spe- cific energy requirements for in- creasing mass throughput as ob- served in commercial pellet mills.

Material Handling Material handling processes in RDF preparation systems include mechanical and pneumatic conveyors. Although not contributing directly to the RDF refinement process, proper selection, design and opera- tion of this equipment is vital to reliable, clean and economical operation of the system, although problems with material handling equipment have been, prevalent in most of the first generation RDF processing plants, it was not until recently that a research effort on material handling systems has been initiated.

At NCTtR, the first phase of a research project studying the parameters affecting conveyability of waste fractions and testing various processed waste fractions on a series of belt and vibrating conveyor test rigs was just com- pleted Unfortunately, the additional phases which included field testing at full-scale commer- cial installations were a casualty of EPA's shift out of waste pro- cessing research programs. Pneumatic conveying systems are found at nearly every RDF facility, yet little knowledge of operating parameters and perfor- mance is available.

As part of the first phase conveyor project, the scope, facility requirements and cost oi a pneumatic test rig experi-. Tfcntal program have been assessed. Implementation of the program, how- ever, was not covered in the first phase funding and is not planned at this time. The relative -cost of scaling down sys- tem s'i2e and the' requirements for a variety of skilled labor might be seen as serious impediments.

In the following discussion, an example will be treated Ln which the technical and econonic aspects of producing d-RDF in a small com- munity plant are analyzed. This example follows the general ap- proach and procedures developed by the authors in a more detailed con- tract report 8.

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Sports betting odds today The experi- mental values are reported. This con- cern 1s broad, however, and not conclusive. Tests on belt conveyors horizontal or inclined and vibrating con- veyors were carried sz ital msw betting for six waste fractions, using a specially assem- bled, closed-loop test rig. Its design was based on several considerations: - ability to circulate a constant or quasi- constant mass flow rate; - easy access for sampling; and - flexibility to incline or decline, or inter- change test conveyors. The deployed panels have been restrained vlth hinges in mm cases and vlth various cable tether arrangements in other tests. The Veterans Health Administration's traumatic brain injury clinical reminder screen and evaluation: Practice patterns.
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Granite Point Investment Highlights. The U. Strong cash flow profile supporting an attractive common stock dividend yield 1 See footnote 1 on p. Commercial Real Estate Market Overview. Investment Strategy and Origination Platform. Data from to Data from the first quarter of through the fourth quarter of Census Bureau.

Loan structure committed upfront to ensure Sponsor. Lender rights. Proactive monitoring. Borrower dialogue Portfolio Overview. All projected changes in annualized net interest income are measured as the change from our 18 projected annualized net interest income based off of current performance returns on portfolio as it existed on March 31, This situation may also be viewed in terms of the following two cases.

In the first case, 2. Degree of sire reduction as a function of the ratio of grate opening to characteristic feed size for ACLI". Degree of size reduction as a function of the ratio of grate opening to characteristic feed size for SIF. The second case assumes the same grate spacing, 2. How- ever, the SLF yields considerably lower Z0 values ano a considerably higher value of Eo tfan those for the other two materials.

Studies designed to evaluate ma- chine wear were also conducted in Doth the laboratory and field tests. A com- parative evaluation of hardfacing mate- rials in terms of the degree of size re- duction of raw and screened light frac- tion is shown in Figure 5.

Information on hiwmer wear obtained from the field tests is summarized In TaDle A. A con- venient method for representing test data githered at different sites is shown in Figure 6. This method allows for a comparison of wear data collected from equipment shredding where different types of solid waste unoer various oper- ating conditions. The general conclu- sion that can be drawn from the data in the figure is that hard alloys yield significant reduction in hammer wear. For an equivalent amount of material worn front the hammers, this 60 percent reduction in wear for hammers that are coated with the harder alloy corresponds to an oper- ating time that 1s percent of that for hammers coated with the softer alloy.

Conclusions A systematic research program on refuse size reduction has been conducted during the past several years. The re- search was conducted on ooth pilot and full-scale plants. The pilot-scale research was aimed at establishing fundamental principles ano relationships between key variables in refuse sue reduction.

The full- scale test program involved the verifi- cation of the relationships developed in the pilot plant studies. Furthermore, the tests were designed such that tne results would serve the needs of tne refuse processing industry, information acquired as a result of these studies included evaluation techniques and de- Sign criteria.

In the course of the research, equipment especially designed to measure power consumption was developed. Non-dimensional parameters nave also Deen developed to allow for the com- parison of various types of shredders. Maintenance and operating costs, par- ticularly those related to power con- sumption and wear, have been identified. The next phase of this work will deal with tne preparation of designs aimed at fulfilling the needs of the user community.

Zalosh and John P. The ft m mock-up simulates a hori- zontal shaft hammermill Including rotating shaft, discs, and hammers with a large In- clined feed hood. Varying auounts of propane have been Injected Into the shredder and the resulting gas concentrations generated by rotor-Induced mixing have been measured.

Results of gas mixing tests with unobstructed feed and discharge areas Indicate that gas accumulations in the flasnable range are most likely to occur at the ends of the shredder shaft. Teat results Indi- cate that peak pressures of about 5 pslg 34 kPa can occur vlth this venting configura- tion if the entire shredder Is filled with a propane-air mixture in the range 3. Further tests will be conducted before generating recommended explosion venting guidelines. The refuse through- put entering these MSV shredders is often too large to permit thorough screening of the input stream to reaove all dangerous aaterlala.

Impact sparks or hot spots generated during shred- ding hammering can Ignite these materials and cause an explosion. So far, there have been veil over reported'shredder ex- ploalona resulting in property damage or In- Jury. As a result of these explosions, shred- der manufacturers and operators have started Implementing traditional protection meas- ures for Industrial explosion hazards.

The most popular of these protection measures Is explosion venting. Explosion venting is a technique for limiting structural damage caused by deflagrations. The basic explosion vent- ing concept is to allow an Incipient pres- sure rise to actuate blowout panels so as to vent unburnt gas and combustion products before damaging pressures develop in the enclosure shredder. To be effective, the - vent deployment pressure, area, and loca- tion, muBt accomodate the volume generation rate of gaseous combustion products.

Existing explosion venting design cri- teria are based on tests vlth simple struc- tures such as rooms or spherical or cylin- drical pressure vessels. Internal -obstructions shaft, homers, breaker plates, traah, etc. Since these effects esca- late the rate of pressure rise and may also reduce vented gas flow rates, they should be accounted for In shredder explosion vent design guidelines.

The approach has been to perform explosion tests In a realistic full-scale nock shredder outfitted with different explosion vent configurations. Explosion test data are being compared to design-basis explosion pressures suggested in existing vent design guidelines. This paper represents a progress report on work performed through November The project Is currently scheduled to be completed and a draft final report submitted In April Drawings of the mock-up are shown here in Figure 1.

The nock-up Is 27 ft 6. The steel frame and sheet metal clad plywood wall panels are deslgturd to withstand an internal explosion pressure of 5 pslg together vlth thrust loads caused by vented gas. Some of the 4-ft x 4-ft 1. The nisaber of deployed panels and the deployment 07erpressure can be varied in accord with the desired test conditions. The deployed panels have been restrained vlth hinges in mm cases and vlth various cable tether arrangements in other tests. The perform- ance of these restraints is discussed under Explosion Test Procedure and Instruaenta- lon.

As illustrated In Figure lb', the ham- Be rmlll shaft has been outfitted with 24 In. Four simulated haamers In the form of in. However, only 16 ham- mere have been installed so far In order to Unit the torque and horsepower requirements of the hanmermlll motor. Tests reported here have been conducted with a 3-hp 2. The shaft speed has been varied from to rpm. As of this vrltlng the 3-hp motor Is being replaced by a hp motor with a fixed speed transmission driving the shaft at rpm.

Although there are no inlet or dis- charge conveyors, the discharge area of the shredder mock-up Is designed to be repre- sentative of typical MSW shredder Instal- lations. There is a semi-cylindrical steel grating In the ln. The confinement associated vlth this configuration simulates the dis- charge conveyor section under an operating MSW shredder. No attempt has been made to put any crash throughput Into the shredder mock-up.

By obstructing inlet and discharge areas, trash throughput In a real MSW shredder mey affect the combustible gas accumulation process prior to an explosion and vented gas flow rates during the explosion. This had been simulated in the mock-up by obstructing the inlet and discharge areas with poly- ethylene sheets in some tests.

Rotor-Induced air flow diluted the propane sad governed the formation of the resulting propane-air mix- ture. The specific objective of the gas mixing tests was to determine the spatial and temporal extent of f Issuable propar-e- alr mixtures generated by this Injection and mixing process.

Shredder Mockup. The rationale for selecting these Injection locations was to simulate release from a propane cylinder or similar liquefied gas container ruptured by a hammer during the shredding process. Propane concentrations vere measured with an Anarad AR Infrared gas analyzer calibrated for a range of Z propane by volume.

The analyzer vas mounted directly on the shredder structural frame in order to keep Instrument response time down to s, depending on sample location. The output signal from the analyzer was recorded on an oscillograph in the Instrumentation trailer about ft 61 a away from the shredder.

Propane concentration histories at two locations during gas mixing test 7. For example, tf. Peak concentrations at sample location A at the end of the shaft were consistent- ly higher than at locations D ard D' midway along the shaft. This Is probably because of the lower Induced air velocity at the end of the shaft.

In the absence f such an air sweep- ing device, location A is a consistent po- tential I5r. Concentration data for repeat tests Testa 5 and 7, and Tests S and 9 differed by as such as a factor of 2. This lack of repeatability nay be due to randan tur- bulent fluctuations or less likely to the influence of ambient wluda.

Perhaps :he stoat striking feature of the data obtained for tests with the open discharge area 1b that the peak concentra- tions were under the lower flamable llalt at ail locations except A and E in one test. Cbs mix- tures for the first two rests were formed by rotor-Induced mixing with open Inlet and discharge areas.

However, this unrestrained mixing resulted in a very weak explosion in the firBt test and in no explosion at all after three attempts In the second tesc. Therefore, subsequent tests have beDn con- ducted by confining the gas mixture with polyethylene sheets.

An electric match was used for the ig- nition source in all but the last two teats which were fired by a condenser spark dis- charge. The electric match in the first.. In subsequent tests with a more uniform gas mixture, the Ignition source was at location D, which Is closer to the center of the hao- mermlll. Explosion pressures have been measured with tvo Dynlaoo Model PT strain gage transducers with a calibrated range of pslg.

One transducer labeled Gage B, was mounted on one side wall of the shredder, 41 in. Vent deployment pressures were varied from test to test, as were the panel restraining tech- niques. Some panels were hinged only, some were tethered by aircraft cabte, and ethers were both hinged and cabled. In the lore violent explosions, such as the last test, none of these restraining methods were com- pletely successful. If we Ignore the variations In propane concentration There Is only a minor change In laminar burning velocity In the range 3.

Although no for- mal analysis of variance has been concucted, It Is clear from the data In Table i- that all three Independent variables significant- ly affect the maximum overpressure, For sample,. The higher nominal vent deployment pressure In Test 3 0. Similarly, Increases In shaft speed and mixture volume also reiiulted in substantial increases in The vent release pressure data In Table 2 Indicate that the actual pressure at which the vert is fully deployed is several times hlghet than the static deployment pressure based on the ratings of the explosion vent fasteners.

This may be due either tc the higher release pressure of the fasteners under dynamic loads, or to the Inertia of the heavy vent panels after they have been released. The trace for Test 3 has one major peak corresponding to the time at which the vent panels are fully deployed. The first peak in Figure 5 occurs when the vent panels lire fully deployed, while the higher peak at msec probably occurs when all of the combustible gas mix- ture has been burnt.

Peak pressures measured by Cage A at the top of the shredder were consistently higher by 4-S4J than the values of Pnax measured by Gaga B. In the hammer circle region of the shredder. The reason for this difference in peak pressures is not Immed- iately apparent. The test sequence Indicated in Table 2 has been generally increasing in explosion severity. The last test conducted so far Test 7 was considerably more violent than the preceding tests. There was minor damage to some plywood panels, vent panel re- straints, and some welds on the structural frame.

The damage has now been repaired and preparations are under way to go to more severe test conditions In che form of a higher shaft speed rpm , more hammers 48 , and propane concentrations of 4,0- 5. Existing explosion venting design guidelines are based upon a worst-case gas mixture about 5. As discussed previously, test conditions to date have been somewhat less severe than this hypo- thetical worBt-case scenario. Nevertheless, It Is interesting to make a preliminary com- parison of our data with the existing explo- sion vent design guidelines.

In particular, we have compared our peak pressure data from the lsst two tests with a gas mixture filling the entire hanr mermlll , with pressures estimated from the Runes Equation and the Bartk. These nomographs are presented in teraa of enclosure volume, which, in the case of a shredder, can be calculated either with or without the volume of the inlet hood. If the inlet hood volume is neglected, Che hydrogen nomograph estimates a peak pressure of about J psig 0.

In both cases, the only vent area credited has been the vent panel area at the top of the shredder. Further explosion testing le planned, not only to explore the range of validity of thene preliminary results, but also to Investigate vent ducting effectB.

Plans have been formulated to Install a ft 4. Flammable vapor releases of 2 lb 1 kg'. If inlet and discharge areas are obstructed and a propanc-alr mixture in the range 3. In the absence of any venting, considerably higher prtsscies would be expected. Levis, V. Academic Press, p. NTPA Explosion Venting Nollet, A.

Sherwln, and K. Solberg, D. Pappas, and E. Zalosh, R. Explosion Protection in Refuse Shredding. Wiener and J. Assessment of Ex- plosion Hazards in Refuse Shredders. ERDA AlChE Loss Prevention. Vol 13, pp. Washington, D. This paper discusses the materials properties and charac- teristics Affecting the conveyability of MSW rnd its- processed fractions, and reports on experimentally determined values or observed characteris- tics.

Tests on belt conveyors horizontal or inclined and vibrating con- veyors were carried out for six waste fractions, using a specially assem- bled, closed-loop test rig. A procedure for the selection and operation of belt conveyors based on an admissible spillage rate is proposed, ana- lyzed and corroborated by test results. Experiments performed on a vibrating pan conveyor are also described.

Results discussed indicate trends and sensitivities over the range of frequency, amplitude and materials investigated. Figure 1. As sketched, these operations are carried out either, in series or in parallel. Such parallel or alternate streams might ba provided for the sole purpose of improving reliability or availabil- ity, on a permanent or emergency basis.

Mining, Inc. Thus, it is imperative that conveyor sys- tems for municipal solid waste MSW and its processed fractions be designed for reliability, low maintenance and low spillage, and yet not be specified so conserva- tively as to be grossly oversized and too costly. A recent study of research needs in resource recovery was per- formed for the Department of Energy by A. Scaramelli et al. Resource recovery system schematic. Chicago's problems with pneumatic line plugs are similar to those at Ames Hamilton has experienced" bridging at tran- sition points The screw conveyor at Lane County was too small, causing jamming and bridging Yet, with the possible exception of glass cullet, no such information is given or is availa- ble on the properties or conveya- biiity of MSW and its processed fractions.

As a result, design choices and the selection of equipment in existing recovery plants were made on an ad hoc basis, possibly based on as little as a name, a compacted bulk density, a desired capacity and some idea of the largest size of particles conveyed. If problems developed in operation, the symp- toms were more readily apparent than the causes.

Many processing plants show examples of ingenuity in "fixing" a troublesome part of the conveying system, such as a special belt wiper or an unusual cleat arrangement. These field modifications are actually after- thoughts , attempting to remedy a problem not anticipated in the use of an unfamiliar and relatively heterogeneous material.

There is little argument that to the maximum extent possible, trouble in operation should be an-v ticipated and prevented by sound design. However, the design engineer or equipment vendor might be lacking, even unknowingly, infor- mation or data vitally needed for this task.

Some of these data, such as bulk density, are quantitative and should be measured following procedures which are meaningful for the paiticular application being considered. Others are assessed "characteristics," about which qualitative statements, for exam- ple, "very sticky," are made.

Second, it was unclear which of these descrip- tors of the materials were most significant in the design and trouble-free operation of systems. Finally, a need existed to provide an engineering basis for the evalu- ation and field testing of existing conveyor assemblies at existing re- sour. These con- siderations provided the basis for the objectives of this investiga- tion.

Its objec- tives were to: - determine, for commonly encountered waste ma- terials, i. The determination or measure- ment of properties and qualitative observations were made in the laboratory or on a test conveyor rig installed at NCRR's Resource Recovery Laboratory at Upper Marl- boro, MD.

Engineering analysis and criteria development were done concurrently with the experimental work. Within the scope of this first phase of the work, belt conveyors horizontal and inclined , vibrat- ing conveyors and apron conveyors were considered. Additionally, a test plan for a pneumatic conveyor rig was defined. In the present paper, to allow more room for a discussion of the approach taken, its rationale and detailed results on six waste ma- terials from MSW, it was decided to limit the discussion to two types of solids conveyors; - belt conveyor hori- zontal and inclined - vibrating conveyor.

Its design was based on several considerations: - ability to circulate a constant or quasi- constant mass flow rate; - easy access for sampling; and - flexibility to incline or decline, or inter- change test conveyors. To maintain a constant mass flow rate, the mass of material on the loop was changed at different speeds of the conveyors.

It was experimentally verified that a con- stant mass flow rate was indeed realized along the loop. An attempt had earlier been made to use a surge hopper with a variable speed conveyor to keep a constant feedrate, but this procedure was abandoned because it resulted in surging and poor feedrate control. The various components of the test rig are identified in Figure 2.

Table 1 lists the specifica- tions for each conveyor. Worthy of note, conveyor 2a Table 1 , which is the test belt conveyor, was modified for testing with new idlers, belts and a variable drive motor to provide a range of speed from 0.

Testing con- veyor 2b, of vibrating type, was luipped with a variable speed rive and interchangeable cam lafts to change stroke length. It was leased from Carman Industries, Inc. Among the many properties affecting conveyability, some of the most important might be: bulk density, moisture, particle size, angle of surcharge, cohesiveneas, angle of internal friction, etc.

Table 2 shows a complete list of bulk material properties affecting conveyability, according to the Con- veyor Equipment Manufacturers Asso- ciation CEMA 3. Asterisks indi- cate those which were considered to be unrelated to the conveyability of waste on solids conveyors. Pan 2b Vibt. Vari-Speed Feeder Apron Conv. Recirculating test riq layout. Incline Speed Manufacturer Feed Apron 0. Return conveyor 0. Ample of maximum inclination of a belt 5. Angle of repose 6. Angle of slide 7. Angle of surcharge 8.

Bulk density - loose 9. Bulk density - vibrated Elevated temperaturet Lumps - size - weight Specific gravityt Moisture content Screen analysis and-particle size consist Sized and unsized, material Characteristics assessed. Aeration - fluidityt 2. Becomes plastic or tends to softent 3. Builds up and hardens 4. Corrosive 5.

Generates static electricityt 6. Degradable - size breakdown 7. Deteriorates in storage - decomposition 8. Dusty 9. Explosiveness Flwmnability Harmful dust, toxic gas or fumes Hygroscopict Interlocks, oats and agglomerates Oils or fats presentt Packs under pressure Particle shape Stickiness - adhesion Contaminable-t Properties Measured and Results A complete description of test methods and procedures is given elsewhere 4 and would be too lengthy to reproduce here.

The dis- cussion will be limited to general comments and results, and to applicable properties or character- istics. The development of new, re- liable procedures was found to be outside the budget and time limits of this investigation. Some effort was spent on determining mass loss on two types of material - aluminum sheet and belt rubber lining - being impacted by the solids over a stan- dard time interval; results were in- conclusive, The angles of internal and external friction are doubtless of significance to the overall problem of conveying over the equip- ment lifetime, but were not needed in the engineering evaluation de- scribed below.

Angle of Maximum Inclination On a belt conveyor, the angle. It was observed to be dependent upon mass flow race and belt speed. For a "central" value of mass flow rate - which we estimated to be the middle of the range for each of the materials listed and for a nor- malized belt speed of 0.

The belt was mm IB in. Angles are se. Angle of Repose The angle-of repose for bulk. The results are - shown in Table 4. It is noted that, for each ma- terial , i range of values is reported should be expected, the angle of repose: for a given material varies due to irregularities in particle shape, size and their relative dis- tribution in tUe pile.

A qualitative observation is that nar- rower ranges are observed for rela- tively more homogeneous fractions, such as d-RDF or the ferrous frac- tion. A:igie of surcharge. Table 6 lists the observed values of the maximum angle of sur- charges for six materials and two idler angles. Loose Bulk Density Under actual conditions of use, MSW or its processed fractions may be less compacted or "looser" than could be inferred from measurements on a vibrated or tapped mass of the material.

Accordingly, the loose bulk density, thought to be similar to the "as conveyed" density, was mea- sured in a test in. Al- though there exist several published standards for determining bulk den- sity 3 , the American Society for the Testing and Materials ASTM methods suitable for aggregates and coke cannot be applied towards bulk density determination of solid waste fractions.

The procedure developed by NCRR for this work is detailed elsewhere 4. Basically, the mass and volume of the cone were measured to determine the loose or "as conveyed" bulk density. Results are given in Table 7. Its weight is ex- pressed in pounds of the maximum size lump 2. Particle size. Yet, pliable materials such as textiles and plastics might be much larger than the nominal grate or sieve size, and streams with significant amounts of these components are more prone to spillage.

Considerable work re- mains to be done in characterizing MSW and its processed fractions as to the actual "size" of its com- ponents seen by the conveyor belt. Moisture Content In the moisture content, only the absorbed and adsorbed water, measured by drying and evaporation, are considered.

Due to the varia- bility of moisture in solid waste fractions, the values reported in Table 9 should be taken as no more than general indicators. Those materials with high moi- sture content, such as MSW or HF, may prove over long periods of time to cause-maintenance problems due to corrosion by salt and moisture.

The material was subjected-to a standard shaking action, and the percentage by weight retained oh each screen of a series of test screens was measured. The biggest opening screen was on top and the smallest on the bottom. Results of the particle size analy- sis for all five fractions are given in Figure 4.

Belt Conveyors: Analysis of the Basis of Spillage Rate Belt' conveyors are widely used in mining, construction and process- ing plants. Compared to other types, they often have the advan- tage of being economical, relatively simple to operate and able to con- vey materials of varying composi- tion, size and moisture. They can be operated in the horizontal, in- clined or'declined mode.

In spite of the simplicity of the operation and design of such systems, operating experience at resource recovery plants shows that many problems still beset belt con- veyors: spillage, jams, blow-back or roll-back, dusting, etc.

Therefore, the variables or parameters on which some degree of control exists at the design stage, or in opera- tion need to be "fine-tuned" for a specific location and type of ma- terial. After an 8-hour shift, 0. On each side of the belt, this would be equivalent of a layer Such rate of spil- lage would obviously be intolerable in steady operation.

Other desirable althouah pos- sibly less cruci il features of a belt conveyor system of known geome- try, carrying a given material, are: a high throughput for a given size as measured by the width of the belt ; b low power consumption; c high reliability and troi'ble-free operation; d low levels of dust emissions: and e ease of transfer of material to and from t'..

It should be kept in mind, however, that high power consumption might be one of. High reliability and trouble- free operation, item c , can only be ascertained after much longer periods of time than would be possi- ble in this test program. Still, whenever possible and justified, in- cidents of operation, jamming of equipirent or other incidents were noted and documented.

As explained below, dust levels, item d , were recorded and evaluated in a relative, and to some extent, absolute manner. These levels were obtained at various "typical" locations near transfer points, in the middle of a straight run, etc. First, by observing and recording trajectories of the material at the discharge point from the conveyor. Secondly, experimental jDservations, largely qualitative, and ad hoc improvements made during the course of the tests should serve as a guide for assessing the "pro- per" mode of feeding the belt with a variety of feedstocks.

Choice of Test Variables and Parameters A schematic representation of the conveyor belt system is shown in Figure 5. Schematic of belt conveyor system. Thir would appear as? First, the in- put mass flow rate, min defined above and shown in Figure 5, is assumed to be known and constant. Second, the rate of spillage is' con- strued to be proportional to the belt length. For long, straight runs, i. More will be said about these limitations when discussing the experiments and test results.

Let ma bfc! Thus, to-some extent, the choice of threshold "sm-x" is in- fluenced by the material conveyed, the characteristics of the experi- mental setup and the attainable ranges of test parameters, such as capacity, belt speed, etc. In the discussion, the material being conveyed is assumed to be iven, from among the fractions- isted and described above.

Its properties and characteristics, in the sense explained previously, have been measured and recorded. The size and geometric charac- teristics of the conveyor belt are assumed to be known. In the present case, as shown in Figure 6, this amounts to giving the belt. S is' the idler ,angle. The spacing between idlers is i. The static capacity is deter- mined as follows.

Along a length of belt sufficiently lono to be able to ignore end effects, the ma- terial under study is piled up on the belt, at rest, so that the edge of the pile, on either side, touches the edge of the belt. Cross-section o4' loi'ed belt at rest. If in the experi. The reduc- tion in capacity resulting from- the motion is then assessed by a reduction coefficient: which itself is a function of the dynamic parameters, as described hereunder, and of the prescribed de- gree of spillage.

Intuitively, it is obvious that the dynamic capacity would, all other factors being equal, be expressed by a larger num- ber if the allowed rate of spillage is larger. The geometry, si2e of the sys- tem, and the conveyed material are given. Among other properties, its loose bulk density in the "conical" mode has been determined. It is assumed that the variations of this density with the speed and loading "of the belt are small and neglected a fact confirmed by observations.

Increasing it might increase the conveyor carrying capacity, but this is not uniformly true.. Exces- sive speeds would increase spillage beyond tolerable limits, due to blow-back and mechanical shocks and vibrations. Similarly, we could select Cdyn of the material on the belt, as an independent variable, and attempt to increase i.

Again, this might only be possible to a point, due to ex- cessive "macs spillage" from the crumbling, sloughing slopes of the moving. Finally, the throughput m and belt speed V could be varied, but the dynamic capacity, calculated from equation 1 would still need to be related to the observed spil- lage rate.

For eyery pair mj, V , the spillage rate s will be measured as the de- pendent variable. Other sub- sidiary quantities, such as the dy- namic capacity or coefficient of reduction in dynamic capacity, can then be computed from the previous ones. Functional Dependence of Spillage and Mass Flev Rate on Velocity On physical grounds, the ex- pected dependence of the spillage rate on belt speed and mass flow rate could be obtained.

At very low speeds, this quantity is expected to be-smaller than, but on the or- der of, 1. At very high speeds, on the other hand, the whole mass being conveyed will be spilled, due to aerodynamic effects, vibrations and shocks on the idlers.

Thus, for a given ipillage rate, there should exist: an optimal velocity, for which throughput is maximized. If a number of plots such as Figure 7 are drawn, a fami- ly Of curves corresponding to vari- ous mass flow rates can be obtained. From these, in turn, curves, giving the spillage rate vs. For convenience, these curves will be labeled the curves shown in Figure 8. Shape of curves of dynamic reduction coeffi- cient vs. Spillage Rate.

Examples of use of "d " curves. The forward motion of the material on the supporting inclined belt becomes impossible. From the results given above, it is observed that threshold c-TH is significantly lower than the an- gle of slide on the conveyor belt- ing material. The angles selected for in- clin. As explained above, the belt speed V and mass flow rate m were selected as independe. The dependent variable will again be: S, spillage rate, per unit mass of throughput and unit length of belt as previously defined].

If so, the curves giving the spillage rate vs. The "steepness" of the sides, value of the optimum speed leading to minimum spillage and generally, position of the curve in the plane of representa- tion are expected, obviously, to depart from those corresponding to the horizontal case.

In the horizontal case, at relatively "low" V, the increase in carrying cross-section or dynamic section necessary to carry the same mass flow rate m at lower speed 's accompanies by an increase in spillage rate, A similar effect can be presumed to exist if the belt is ir. An increase in mass flow rate, when conveying a given material on a belt of given inclination a running at a given speed V, entails an increase in area of the cross- section on the belt occupied by ma- terial.

This should cause an in- crease in spillage rate, as illus- trated in Figure Operating Point. In the example illustrated in Figure 11, point Q is preferable to point P, since it allows a larger increase in mass flow rate before the maximum admissible level, smax is reached.

In such cases, it would be more efficient to oper- ate in this range, for lower spil- lages under deliberate or acciden- tal variations of belt speed and mass flow rates about the nominal design conditions. Increase in vertical cross section with inclination. Optimum Speed V4 and preferred operating range, at inclination a. Physically, aerodynamic "detach- ment" and "vibrations" should not depend to any degree on inclina- tion at small angles to the hori- zontal.

Thus, the level of spil- lage, all other factors being equal, should not vary much with the in- clination if the material is flat and self-compacting, as is the case with RDF. However, waste or frac- tions thereof containing a fair percentage of spherical or cylin- drical pieces likely to roll down the inclined belt, should show a rapid increase of spillage with speed, in the upper range of speeds. To guide the material fed to the belt, a feed chute and 1.

Test results are given and discussed below. Complete details on these tests may be found else- where 4. Horizontal Mode Test Results A certain fixed mass was placed on the test conveyor, at the chosen belt speed, providing a quasi-constant mass flow rate, over sufficiently short test durations and in the absence of excessive spillaqes 4. All spillage. The sides of the test conveyor were isolated wich plastic sheets to avoid includ- ing spillage caused by the return and feed conveyors.

Based on these complete re- sults, the analysis performed prior to the tests and outlined above was indeed confirmed. High spillage rates are observed at lower belt speeds. Upon increasing the belt' speed from a very low value, the rate of spillage for a constant mass flow rate decreases to a mini- mum value, then gradua. Higher mass flow rates, for a given material and belt speed, lead to higher spillages, and the location of the minimum spillage point move3 towards higher belt speeds.

Although all the solid waste "fractions show similar patterns of behavior, the specific values of spillage rates for each individual fraction are dependent on its pro- perties and characteristics. For example, it was observed that d-RDF, being relatively uniform, showed a much lower spillage, all other fac- tors being equal, than more coarse, heterogeneous fractions 4.

Noteworthy is the fact that, except at negligible throughputs, conveying will always generate some spilJage. Shredded MSW. Spillage vs. RDF sample. The distribution of the spilled material along the section length was also recorded.

The test conveyor was divided into four sec- tions labeled 1 to 4 of lrngth l. Spil- lage was separately collected and weighed for each of these sections at a given mass flow rate and for different belt. Table 12 i3 an fcxample for each of this d.

It is seen that at 0. In section 1, the The spillage in section 2 At a higher speed of 1. On the other hand, a higher percentage In summary, the amount and distribution of spillage area re- sult from non-uniform feed, very low or very high belt speed, im- proper feed and skirting arrange- ments, and carryover of adhesive, sticky material around the head pulley.

Trajectories, or discharge paths of the material after the end pulley, were nr sured at a given, capacity and different speed by a direct observation technique, re- cording the fall height vs. In actuality, the material, depending on the belt ve- locity, is discharged from the head pulley in the form of a band. The trajectories in these figures have been derived from plotting from the band's mid-stream points, at exam- ple is given in Figure The ex- perimental values were compared to the theoretical discharge trajec- tory, also plotted in Figure The theoretical and experimen- tal values correspond reasonably well.

This suggests that the method, provided by CEMA, for theo- retical trajectory calculations, could be successfully used to pre- dict solid waste trajectories accurately. This negligible change in power consumption - despite extreme vari- ations in such conveying conditions as speed, gravitational load, etc.

The dis- advantage of using a skirtboard across the whole length of a loiig ' belt conveyor would be to increase the frictional resistance and, ' therefore, the horsepower require- ment. Specific information for de- tailed horsepower calculations can be obtained from reference 2.

Inclined Mode: Test Results The tests measured spillage vs. Overall experiments corroborated the speculation, from analysis, that higher spillages will be encountered on increasing the belt inclination, and that a preferred speid exists at given mass flow rate and inclination. An attempt was made to determine if any relationship between the extent of dust generated for parameters such as the test belt's angle of incli- nation, its velocity and mass flow rate of the material existed.

This, sampler measured the quantity of dust generated at the turbulent feed end of the belt conveyor. A second dust sampler was located approximately 6. The re- sults of the second sampler were in- consistent and unreliable, possibly due to background dust interferences in the testing area. It was not possible to reduce or completely re- move the laboratory dust levels within a reasonable time on comple- tion of a test run; therefore, only tha dust loadings measured by the sampler located at the conveyor feed end were reported.

The test results provided the total suspended dust 4. Particle size distribution or any further characterization of the dust was not attempted. The test method and cal- culations are described elsewhere 4. For more complete details on dust sampling methods and proce- dures, the reader should refer to ASTM D and D standards. No consistent trends were rea- dily apparent, but a tendency to- wards greater dust concentration, was indeed observed for higher mass flow rates and belt conveyor inclina- tions.

Only the main re- sults and conclusions of the work described in reference 4 will be reported here. The theoretical principle of their- operation, illustrated in Figure 17, shows that during the first part of the acceleration of the pan, a par- ticle resting on it. A higher stroke amplitude might accelerate the material in a two- cycle jump, but this would require a much higher energy input.

The test vibrating conveyor, 4. Two re- placeable, eccentric cams allowed the stroke "to be changed, either Dynamical balance also re- quires a balancing weight and the removal or addition of leaf springs, for a fixed stroke and frequency Figure Test results show that considerably more work is needed to rationally design a conveyor of appropriate stroke length and fre- quency for a given.

Within the finite scope of the program, it was not possible to un- dertake a systematic study of this complex mechanical system and its dynamics. The operating range was selected on an empirical basis, adopting as a reasonable operating criterion that the measured vibra- tion of the base not exceed 3.

All points correspond- ing to a pan vibration of This limited the range of oporating fre- quencies to 4 30 - cpm Ihe tests conducted determined for the twc values of the stroke specified, the maximum carrying ca- pacity and conveying speed for fixed mass flow rate vs.

These re- sults are graphed in reference 4. A sample set of result curves is given in Figure The following conclusions could be drawn from the complete- series of tests: - For all fractions examined, over the range of frequency investigated, the carrying capacity increases with both frequency and stroke. However, on physical grounds, the capacity curve is expected to reach a saturation level- at some higher, undetermined fre- quency.

At cpm, in- creasing the amplitude from Vibrating conveyor principle. Schematic of vibrating conveyor. Carrying capacity of test vibratincr conveyor vs. At cpm, speeds on the order oC 0. RDF, for example. Experiments were carried out for the For the six fractions, a decrease in conveying speed with increasing burden depth was observed. This indicates that the energy imparted by the vi- brating pan is absorbed rather than transmitted, as is the case for denser fractions.

The percent lowering of burden height over 4. Thus, there is a definite tendency for the solid waste fraction to compact due to the vibra- tional activity of the pan. Most solid waste fractions are composites of varying bulk density components. A test was conducted to determine if varying components of a solid waste fraction segregate out, due to vast bulk density dif- ferences. A particle size distribution was performed on a "top" and a "bottom" layer to determine the ex- tent of segregation.

The frequency was fixed at Without repro- ducing detailed results given elsewhere 4 , and to summarize, it was ob- served that the smaller particles in MSW and HF did indeed concentrate in the bottom layer. Such was not the case for RDF, presumably due to the ten- dency of fine particles to adhere on paper flakes. Conveying vs. This vas probably due to a loss'in physical inte- grity and gain in bulk density with increased moisture content. For most materials, dust level6 were higher for the larger stroke They ranged from a low of 0.

In the present paper, the emphasis was put more specifically on belt conveyors and vibrating pan I. The main results and' conclusions of the study are: - Properties and charac- teristics. Where sensi- ble and feasible, these - properties or charac- teristics were measured 2. The experi- mental values are reported. An analysis was made of the dependence to be expected, on a belt conveyor, be- tween spillage rate, ca- pacity and belt speed.

Experimental results on six waste fractions con- firmed these predictions.. A procedure for a rational choice of operating con- ditions at various flow rates was defined, in which the maximum admissible spillage is selected as the design criterion. Within the range of parameters inves- tigated, they underline the importance and show the effects of frequency, stroke amplitude, bulk density, moisture content on carrying capacity, con- veying speed, segregation in the depth and dust emissions.

The results indicate trends and 3ensi- tivities and should prove. How- ever, they strongly sug- gest that significantly n. Felago, S. Fischer, R. Pease, J. Quinn, and P. Depart- ment of Energy, Mitre Corp. Classification and Definitions of Bulk Materials. Khan, 2. An Engineering and Experiments] Evaluation of Conveyors for. Final Report, Contract R, U. Environmental Protection Agency, Municipal Envircrimen-. Air Force, Engineer- ing and Services Laboratory.

Center for Resource Recovery, Inc. Department of Labor. R from the U. Thanks are due to Mr. William Horton of Carmen Industries, for his co- operation in providing the test vi- brating- conveyor. Dia2, G. Trezek Cal Recovery Systems, Inc. Methods of testing, criteria for evaluation, operating condi- tions, and assessment of atr classifier performance are described.

Topics that are ger- mane to the design and operation of air classifiers are also covered. Comparisons presented herein enable judgements to be made as to the? Introduction --even air classification systems with nominai throughputs ranging from 4 to EPA [A]. During the course of the work, characterization pa- rameters were developed that enabled the comparison of all air classifiers on an equivalent basis.

Constant light fraction split is defined as that value of the light frac- tion split. The invariant nature of ma- ter. The seven air classifiers tested in this study, their locations, and their general descriptions are given in Table 1. Further details concerning the geo- metrical configuration of the air Classi- fiers are available in the final report to tne. An examination of some of the key characteristics of the solid waste en- countered during the air classifier test- ing program shows tne importance of nor- malizing tne performance parameters In terms of the air classifier infeed com- position.

As can be seen from the en- tries in Table 2, there are wide varia- tions in the waste characteristics from site to site. For example, the paper and plastic content of the infeed to the Los Angeles air classifier averaged The relative breakdown of air classifier feed material into light and heavy fractions. The- energy required by a unit or system and reported on an as-processed ton basis kWh per Metric ton. The cross-sectional area of the zone of separation of light and heavy materials.

The column area is perpen- dicular to the air stream and generally is reported as the maximum column area up-stream of the lights discharge. The volumetric air flow through the separation zone oivioed by the column area. The percentage of paper and plastic in the lignt fraction on an air-dry weight basis.

Light fraction Quality is a measure of the amount of the primary combustible consti- tuents ir, the light fraction. Defined 6S the product of the light fraction Quality and the liqht fraction split both. Combustible yield is a measure of the amount of pa- per and plastic recovered in the lignt fraction end repor- ted in terms of a unit input of feed material to the air classifier.

A dimensionless term defineG as the mass flowrate of air divided by tr. A low value of trie critical column loading parameter indicates tne need for relative!. Defined as the weight of paper and plastic on an air-dry basis recovered in the light fraction divided by me weight of paper ano plastic present in tne air classifier feed.

A nigh recovery percentage of paper anc plastic is desirable to provide hign hejting value components for the light fraction. Defined as the energy recovered in. Being a auelitative parameter, retained ash is a measure of tne aoility of an 3ir classifier to drop out in tne neavy fraction components that are high in ash content.

The weight of mesh fines in the light, fraction divided oy the weight of 'fines in the air classifier feed, on an air dry basis. Particle size of the heavy and light fractions was used to deterr,.

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