Case Study Vibrating Screen

Solid Separation Systems for the Pig Industry Case Study 4 Vibrating Screen

Case Study 4 VIBRATING SCREEN

Contents CASE STUDY 4 VIBRATING SCREEN ........................................................ 4-1

4.1 Description of the System............................................................................. 4-2 4.2 Manufacturer / Distributor ........................................................................... 4-3 4.3 Information Sources....................................................................................... 4-4 4.4 Performance Data ........................................................................................... 4-4 4.4.1 Shutt et al. (1975) Piggery wastewater (2 screen types) ....................... 4-4 4.4.2 Pain et al. (1978) Cow and piggery wastewaters and slurries ............ 4-6 4.4.3 Hegg et al. (1981) Animal wastewaters (3 screen types) ...................... 4-7 4.4.4 Holmberg et al. (1983) Piggery wastewater........................................... 4-8 4.4.5 Abery (1994) Piggery wastewater .......................................................... 4-8 4.4.6 Charles (2000) Piggery wastewater (2 screen types)............................ 4-9 4.4.7 Summary of performance data ................................................................ 4-10 4.5 Running Costs and Maintenance .............................................................. 4-11 4.6 Practical Operating Issues........................................................................... 4-11 4.7 Piggery Case Studies.................................................................................... 4-11 4.8 Summary Selection Criteria..................................................................... 4-12 4.8.1 Solids removed........................................................................................... 4-13 4.8.2 Capital cost ................................................................................................. 4-13 4.8.3 Operating costs .......................................................................................... 4-13 4.8.4 Ease of operation........................................................................................ 4-13 4.8.5 Solids management options ..................................................................... 4-13 4.9 References ...................................................................................................... 4-14

List of Figures

Figure 4-1 Schematic diagram of a Vibrating Screen................................................... 4-2 Figure 4-2 Flamingo Quad-deck Vibrating Screen ...................................................... 4-3 Figure 4-3 TS removal vs influent TS content for cow slurry - Pain et al. (1978) ..... 4-6 Figure 4-4 TS content of removed solids vs solids removal rate (all data)............. 4-10

List of Tables Table 4-1 - Vibrating screen performance - Shutt et al. (1975) ...................................... 4-5 Table 4-2 Vibrating Screen data - Hegg et al. (1981)..................................................... 4-7 Table 4-3 Flamingo screen performance Charles (2000) .......................................... 4-9 Table 4-4 Capital and operating costs of Vibrating Screens ..................................... 4-12

April 2002 FSA Environmental Page No.4-1


FIGURE 4-1 SCHEMATIC DIAGRAM OF A VIBRATING SCREEN

4.1 Description of the System A vibrating screen is similar to a static rundown screen except that the liquid for separation is poured onto a rapidly vibrating horizontal screen (see Figure 4-1). The solids slide to the edge of the screen, while the liquid passes through the screen. A vibrating screen consists of one to four plates (mesh or cloth screen bases) in series, driven by a vertical electric motor. An adjustable, eccentric weighted arm controls the motion of the unit. Adjusting the arm changes the frequency of vibration of the screens, varying the vertical, horizontal and inclinational motion. By changing the weights and their position, the flow of materials can be directed either towards or away from the centre of the screens. Solids are removed via a discharge outlet extending from the perimeter of each screen deck. In Australia, the only vibrating screen known to have been tested in the pig industry is the Flamingo (see Section 4.2). The manufacturers claim that the screens are `easy to operate, easy to change the screen cloth and easy to clean. Anti-blinding devices keep the screen clean during all operations. The screen units are `highly efficient, have an elegant design, are durable and available for any powder and viscous liquid. Screen cloths are available in a range of apertures from 32 m to 5.6 mm.



FIGURE 4-2 FLAMINGO QUAD-DECK VIBRATING SCREEN The key features of the Flamingo Vibratory Screen are claimed to be:

Suitable for sifting, granulating and liquid filtration Waste water treatment Contact parts stainless steel (Grade 304) Screens can be changed quickly and easily by changing the mesh only Units fitted with tapping balls as standard Lids standard Discharge control gate Galvanised base A large number of sieves available ex stock. Screens are available from 450 mm diameter to 1430 mm diameter and from one to three layers. Power requirements range from 0.37 kW to 2.2 kW.

4.2 Manufacturer / Distributor Lao Soung Machinery Co. Ltd of Taiwan developed the equipment. Information is available at www.commerce.com.tw/c/029900668. It is claimed that these screens are used extensively in piggeries in Taiwan and other parts of Asia. In Australia, the equipment is distributed by:



Ernst Fleming Flamingo Products 79 Derby St, Silverwater NSW 2128 Ph: 02 9648 3308 Facsimile: 02 9648 5441 Email: [email protected]

Further information is available at www.flamingoproducts.com. Other manufacturers of vibrating screens are Sweco and Kason.

4.3 Information Sources The information presented in this case study is derived from the following sources. No site visits were undertaken to see an operating vibrating screen.

Manufacturers product information (Flamingo). Shutt et al. (1975) Solid separation pf piggery wastewater using screens. Pain et al. (1978) Solid separation of piggery and cow wastewater and slurries. Hegg et al. (1981) Solid separation of animal wastewater. Holmberg et al. (1983) Solids separation of piggery wastewater. Abery (1994) Solids separation of piggery wastewater. Charles (2000) - PRDC Group Demonstration Project No 1667

4.4 Performance Data

4.4.1 Shutt et al. (1975) Piggery wastewater (2 screen types) Shutt et al. (1975) compared the solids removal efficiencies of stationary rundown screens and vibrating screens with different-sized screen openings. Piggery wastewater with a TS content of 0.2-0.7%, and a range of flow rates were used for the comparisons. The wastewater was flushed out of pig fattening barns by discharging large quantities of water down the gutters. The manufacturer of the screen was not specified but the unit had one deck, 460 mm in diameter, with a surface area of 0.164 m2. The screen was operated at three flow rates (41 L/min, 67 L/min and 110 L/min) using four different screen opening apertures (0.12 mm, 0.17 mm, 0.21 mm and 0.39 mm) (see Table 4-1). No mention was made of changes to or settings of the vibratory motion of the unit. The best result was achieved with the largest screen size (0.39 mm) and a flow rate of 0.0011 m3.s-1. This removed 0.6% of the influent volume, 22.2% of the TS, 28.1% of the VS and 16.1% of the BOD. The TS concentration of the solids removed was 16.4%



wb. For the other vibrating screen opening sizes, performance was optimised at the same flow rate. Because screen sizes and flow rates were different for the stationary and vibrating screens, direct comparisons are difficult. However, for a given flow rate, it was concluded that static rundown screens would be more effective than vibrating screens at removing solids.

TABLE 4-1 - VIBRATING SCREEN PERFORMANCE - SHUTT ET AL. (1975) Solids removal performance (percent of indicated parameter retained in screened fraction) (i) Loading rate 41 L/min

Size of Opening (mm) Parameter Units 0.12 0.17 0.21 0.39

Flow removal % of inflow 0.2 0.5 2.8 0.4 TS removal % of inflow 2.5 5.8 14.3 12.6 TS of output % wb 5.7 3.9 8.7 12.2 VS removal % of inflow 3.3 8.4 12.4 4.3 BOD % of inflow - - 4.5 - COD % of inflow - 3.3 16.3 10.0 (ii) Loading rate 67 L/min


Flow removal % of inflow 1.2 0.7 0.7 0.6 TS removal % of inflow 13.8 14.0 9.8 22.2 TS of output % wb 8.5 10.9 10.8 16.4 VS removal % of inflow 18.5 17.0 12.9 28.1 BOD % of inflow - - 2.4 - COD % of inflow - 15.3 8.9 16.1 (iii) Loading rate 110 L/min


Flow removal % of inflow 2.1 0.8 0.9 1.6 TS removal % of inflow 18.7 1.8 7.0 12.3 TS of output % wb 4.8 1.9 4.8 4.9 VS removal % of inflow 42.8 2.4 9.0 17.2 BOD % of inflow - - 3.9 - COD % of inflow - 12.5 10.7 12.2 The data highlights the need to select the optimum flow rate and mesh size combinations to achieve the best recovery results. High flow rates (110 L/min) increased the water content of the solids fraction substantially. Similarly, the use of a small aperture cloth (0.12 mm) and a low flow rate tended to blind the screen, increasing the water content of the solids. The best TS content of separated solids



was 16.4%, with a flow rate of 67 L/min and the largest screen aperture of 0.39 mm.. These solids would be spadeable for composting purposes.

4.4.2 Pain et al. (1978) Cow and piggery wastewaters and slurries Pain et al. (1978) evaluated the use of a vibrating screen (and other devices) for cow and piggery wastewaters and slurries containing from 4% to 15% TS. They were evaluating practical devices suitable for use in Britain. No details are given on the influent characteristics or history and there is no particle size distribution of the solids. The differences between the cow and pig wastewaters are not stated. The configuration of the vibrating screen was similar to Figure 4-1. Woven stainless steel screens with nominal mesh sizes of 0.75 mm and 1.5 mm were used. Neither screen diameter nor manufacturer was specified. The authors only reported on the performance of the screen on cow wastewater and slurry. They found that the screens were ineffective when the influent solids content was above 8%, because the slurry accumulated on top of the screen. At influent solids of about 7%, the device removed up to 50% of TS, but this rapidly declined as influent TS content declined. At about 4% TS influent, removal efficiency was only 15% of TS (see Figure 4-3). They noted that a very wet solid was produced and therefore a considerable amount of seepage from the stack occurred. The removed solids were in the range of 11% to 13% TS (thick slurry).

FIGURE 4-3 TS REMOVAL VS INFLUENT TS CONTENT FOR COW SLURRY - PAIN ET AL. (1978)



4.4.3 Hegg et al. (1981) Animal wastewaters (3 screen types) The objective of this study was to determine potential amounts of TS and COD removable from manure wastewaters using three types of commercially available screens. They tested rotating, static and vibrating screens. The vibrating screen was similar in configuration to Figure 4-1. It was a 457 mm diameter, Sweco single deck device. Three mesh sizes were tested (1.57 mm, 0.83 mm and 0.64 mm). Operating performance was optimised using manufacturers recommendations. The pig wastewater was from finishing pigs fed a pelleted, corn-soybean ration. Detailed particle size analysis is given. However, the particle size appears large compared to other literature, 53.5% > .42 mm (see Part A report Table 5-2). For each test, a grab sample of influent, effluent and separated solids was collected and analysed. The TS removal rate was based on a ratio of the difference between TS in influent, minus TS in effluent (screened solids), divided by the TS of the influent. All of this data is expressed as a concentration and no mention is made of measuring flow rates. Hence, TS removal rates are not based on mass balance. Table 4-2 provides a summary of their data. The percentage TS removed ranged from 3% to 27% for the 1.5 mm and 0.63 mm mesh respectively. The COD removal rates were also larger for the finer mesh. The finer mesh did not produce TS concentrations of solids because the screen was partially plugged with pig hair. This data illustrates that the outcome of the experiment is linked to how appropriately the experiment is designed to match the device characteristics. For example, the highest solids recovery of 27% may be due to reduced flow rate (not just opening size). It also produced the driest solids (20.9%). Overtopping the screen with too high a flow rate substantially diluted the solids recovered. The TS content of the screened solids varied (in this experiment) from 16.9% to 20.9%. This is spadeable and possibly stackable.

TABLE 4-2 VIBRATING SCREEN DATA - HEGG ET AL. (1981)

Mesh Size Mm 0.83 1.57 0.64 0.83 1.57 Slurry Concentration High Low Influent % TS 2.86 2.88 1.83 1.52 1.55 Effluent % TS 2.56 2.75 1.34 1.36 1.51 TS removed

% 10.0 5.0 27.0 10.0 3.0

Removed solids

% TS 19.3 20.9 20.9 18.4 16.9

Influent COD

g/L 29.7 21.5 20.4 13.7 12.9

Effluent COD

g/L 25.4 20.7 15.4 13.6 12.2

COD removed

% 14.0 4.0 24.0 1.0 6.0

Flowrate range

L/min 15-35 53-126 37-57 37-108 37-103



4.4.4 Holmberg et al. (1983) Piggery wastewater Holmberg et al. (1983) tested the feasibility of using a vibrating screen to concentrate flushed piggery wastewater for use in an anaerobic digester. Four flow rates (37.5, 75, 112.5 and 150 L/min) and five screen mesh sizes (0.10 mm, 0.23 mm, 0.52 mm, 0.98 mm and 2.4 mm) were tested. The device used as a 457 mm Sweco device similar to that used by Hegg et al. (1981). The wastewater was obtained from a finishing house that was flushed daily and collected in a sump before being pumped to the screen. Analysis of the flushed effluent, and the solid and liquid separated components included TS, VS, FS, TC (total carbon), COD, total Kjeldahl nitrogen, ammonia nitrogen, total phosphorus and ortho-phosphorus. Mass balances were used to determine solids reductions. The TS of the flushed effluent varied from less than 1.5% to 5.4% with an average of 2.92%. In this wastewater, the fraction of the TS that was FS, VS and TC were consistent and averaged 17%, 83% and 44% respectively. Complete analyses are provided. The data shows that, over the range of flow rates and screen sizes, the solid fraction (as a percentage of the inflow) contained from 1-45% of the flow, 11-67% of TS, 14-70% of VS, 11-69% of TC, 2-58% of COD, 9-57% of ortho-phosphorus, 2-58% of total phosphorus, 2-51% of total Kjeldahl nitrogen and 2-51% of ammonia nitrogen. Complete analyses of the solid and liquid fractions are presented. The TS content of the solid fraction ranged from 2.4% to 18.1%. The wettest solids came from the finest screens that also had the highest solids recovery. The ratio of VS to TS in the solids varied slightly from 86-96%. This wide range of performance efficiencies again reflects the importance of matching device performance to inflow rate. As with other experiments, improved TS recovery is achieved with a finer mesh, but this results in a wetter solid fraction.

4.4.5 Abery (1994) Piggery wastewater Avery (1994) tested sedimentation, centrifugation, screening and dissolved air floatation as methods of removing solids from piggery effluent at Bunge, Corowa. The screens were already part of the effluent treatment system but no technical details are provided in the report. They are simply described as two-layer, vibrating mesh screens with an inflow rate of 20 L/s. The screens used a 3.75 kW motor. Effluent was flushed into a sump from which it was pumped to the screens. The pit pump used a 15 kW motor and the sediment pump (agitator) used a 4 kW motor. Only one test was conducted using the screens as the sole separation system. The TS of the influent was 0.57%. In this case, the screens removed 0.2% of the total inflow and only 6.7% of the TS inflow. The TS of the separated solids was 21.1%. It was estimated that the cost of electricity was $40.63 per ML treated. They noted that the main advantage of this process is its simplicity, being able to operate 24-hours per



day with very little monitoring, and it is unaffected by the start/stop operation which occurs at night when the raw effluent flow is low.

4.4.6 Charles (2000) Piggery wastewater (2 screen types) The objective of this project was to compare the performance of a vibratory screen with a static rundown screen. The wastewater was flushed from a piggery, with a TS concentration of 1.02%. Detailed particle size analyses of the wastewater were provided and only 6% of the TS had particle sizes greater than 0.5 mm. This would indicate that it had been through a chopper type pump of had degraded into smaller particles before separation. The equipment used was a 2-deck Flamingo system, with a 450 mm screen diameter (see Figure 4-2). Screen mesh sizes tested were 0.074 mm, 0.104 mm, 0.147 mm, 0.175 mm and 0.246 mm, with a flow rate of


4.4.7 Summary of performance data The following conclusions can be drawn from the above data.

a. Performance of vibrating screens is highly variable as it depends on TS of influent, influent characteristics, screen mesh size, flow rate, manufacturers settings and other factors.

b. In the literature, the range of performance data includes:

TS removal from 1.8% to 67% VS removal from 2% to 70% COD removal from 1% to 59% TS content of separated solids from 1.9% to 21%.

c. Generally, there is a trade-off between solids removal efficiency and the

quality of the solids that are removed (see Figure 4-4).

d. Solids removal efficiency is strongly related the TS content of the influent.

e. Generally, vibrating screens work better with TS in the influent that is below 7% to prevent clogging but over 1% to improve removal efficiency.

f. Clogging or blinding of the screen openings due to slimy effluents is a major

problem and frequent cleaning is often required.

g. Figure 4-4 shows the combined data of Shutt et al (1975), Hegg et al (1981), Avery (1994) and Charles (2000). There is a general trend of reduced solids content in the separated solids versus increased solids removal efficiency but the performance data is erratic and unpredictable.

FIGURE 4-4 TS CONTENT OF REMOVED SOLIDS VS SOLIDS REMOVAL RATE (ALL DATA)



4.5 Running Costs and Maintenance

No information has been provided by the manufacturer on running costs other than power required to run the system (2 kW per hr).

Maintenance is replacement of mesh (fine mesh 6 months to 1 year, coarse mesh 2 to 4 years depending on abrasiveness of slurry)

In practice the screens need to be washed preferably twice daily In practice with an average daily flow rate of 22,000L using a 2.2 kW motor

over 11 hours operation, $4.00 of power was used. Because of the moving parts, vibrating screens have higher maintenance and power requirements than stationary rundown screen (Kruger et al. 1995). While vibrating sometimes helps to prevent blinding (Mukhtar et al. 1999; Fulhage & Pfost 1993), regular cleaning is still required to maintain high efficiencies. Performance of vibrating screens is affected by both the flow rate and the TS concentration of the wastewater. Therefore, to optimise performance, the TS concentration and the flow rate should remain constant. Accordingly a sump, agitator and lift pump should be included in the running costs of a stationary screen.

4.6 Practical Operating Issues It is generally reported that vibrating screens have a low requirement for regular monitoring and maintenance. However, some authors mention problems with screen blinding. It appears that a problem with these devices is the correct matching of influent quality and quantity to device performance. Another issue is the water content of the separated solids. This is often reported as being too wet. Separated solids that are not stackable and they leak water after separation, presenting handling and odour problems.

4.7 Piggery Case Studies Four piggery case studies have been analysed. These are a 200-sow and a 2000-sow unit operated under low flushing (5 L/SPU/day) and high flushing (25 L/SPU/day) regimes. Capital and operating costs were estimated using data supplied by the manufacturer. It was assumed that power costs $0.13/kWhr and labour costs are $25/hr. The power costs calculated below are similar to that those proposed by Abery (1994). Table 4-4 provides summarised capital and operating costs. They offered two screen sizes. The finer screen with the lower flow rate was used in the analysis. A major issue with this analysis is selection of the appropriate solids removal efficiency. We have used 10% for the low TS effluent and 20% for the higher TS effluent. Sumps, pumps and agitators have been built into the capital and operating cost of the screen.



TABLE 4-4 CAPITAL AND OPERATING COSTS OF VIBRATING SCREENS

Item Units 200-sow low-flush

200-sow high flush

2000-sow low-flush

2000-sow high flush

No of pigs SPU 2,134 2,134 21,340 21,340 Flushing L/SPU/day 5 25 5 25 Hosing L/SPU/day 1 2 1 2 Total effluent a ML/yr 9 25 85 250 Effluent flow (24 hr)

L/s 0.27 0.79 2.7 7.9

Solids content of effluent

% TS 3.1 1.2 3.3 1.2

Solids t/yr 270 290 2,800 2,940 Flamingo Vibrating Screen Data Flowrate L/s 1.8 2.5 8.3 16.7 Operation hrs/day 3.5 7.6 7.8 11.4 hrs/yr 1,300 2,780 2,850 4,160 Solids Removal b

% 20 10 20 10

t/yr 54 29 560 294 Capital cost c $ 31,000 34,000 68,500 107,000 $/ML treated

/yr 3,630 1,360 800 430

$/t solids removed /yr

580 1,170 120 360

Operating Cost

kWhr/yr 13,920 31,920 67,230 113,2400

$/yr (power) 1,810 4,150 8,740 14,720 Labour hr/day 0.2 0.2 0.3 0.4 $/yr (labour) d 1,830 1,830 2,7400 3,650 $/yr (main.) e 1,000 1,000 2,000 2,000 Total $/yr 4,630 6,970 13,480 20,370 Operating $/ML treated 540 280 160 82 $/t solids

removed 86 240 24 69

a Total wastewater includes flushing water, hosing water, manure and drinking water wastage. b This figure is adopted until better data is available. c Capital cost includes a manure collection sump with pumps and agitator. d Labour for monitoring and maintenance costed at $ 25/hr e Routine maintenance of pumps and agitators

4.8 Summary Selection Criteria The vibrating screen is an advance on the static rundown screen. Solid separation occurs due the liquid component passing through a screen. Mechanical reliability appears good, but clogging of screens seems to be an issue when inappropriate flow rates are used. Chemical additives do not improve performance, but gravity thickening to a TS concentration of above 3% may.



4.8.1 Solids removed Solid removal efficiencies reported in the literature vary widely. Assuming that the device is correctly matched to the inflow rate, then it would be appropriate to assume that 10% of solids are removed with the influent at 1.2% TS and 20% with the influent at 3.1% TS. These results indicate that gravity thickening to a concentration of above 3% would improve the operational efficiency of vibrating screens.

4.8.2 Capital cost From Table 4-4, the capital cost could be $31,000 to $34,000 for a 200-sow piggery and $68,500 to $107,000 for a 2000-sow piggery. This includes the single vibrating screens for the 200-sow case studies, 2 screens for the 2000-sow low flush case study and 4 screens for the 2000-sow high flush case study. The capital cost also includes collection sumps, agitators and pumps.

4.8.3 Operating costs From Table 4-4, the operating costs could range from $280 to $540/ML of effluent treated for the 200-sow case studies and $80 to $160/ML of effluent treated for the 2000-sow case studies. Operating costs per tonne of dry solids removed range from $86 to $240 for a 200 sow piggery and $24 to $69 for a 2000 sow piggery. The lower costs reflect economies of scale with larger piggeries. The lower costs reflect economies of scale with larger piggeries. Vibrating screens have more maintenance requirements that static rundown screens.

4.8.4 Ease of operation The device is reported as easy to operate with little monitoring, provided that the flow rate and TS concentration of the wastewater have been matched to the screen size. However, pressure hosing would be required on a regular basis (daily) to remove biofilms from the screens.

4.8.5 Solids management options If the flow rate and TS concentrations are correctly matched to the screens used, then spadeable solids suitable for composting can be obtained (>15%). A bulking agent (straw or sawdust) could be added to solids that are spadeable but not stackable, to absorb any seepage during composting. Wetter slurries (greater than 5% but less than 15%) would be difficult to pump or spade, and would be prone to odour generation.



4.9 References Abery R. 1994. An evaluation of methods of effluent treatment at Module 5,

Corowa. Bunge Meat Industries, Corowa, NSW. Charles J. 2000. Solid separation using a Vibrating Sieve No. 1667. Pig Research and

Development Corporation Group Demonstration Project. Fulhage C. and Pfost D.L. 1993. Mechanical solid/liquid separation for dairy waste.

University of Missouri. Accessed on-line 23/01/2000. Hegg R.O., Larson R.E. and Moore J.A. 1981. Mechanical liquid-solid separation in

beef, dairy and swine waste slurries. Transactions of the American Society of Agricultural Engineers 24(1):159-63.

Kruger I., Taylor G. and Ferrier M. 1995. Effluent at Work. Australian Pig Housing

Series. New South Wales Agriculture, Tamworth NSW Australia. Mukhtar S., Sweeten J.M. and Auvermann B.W. 1999. Solid-liquid separation of

animal manure and wastewater. Texas Agricultural Extension Service publication E-13. Texas A&M University System. 5pp.

Shutt J.W., White R.K., Taiganides E.P. and Mote C.R. 1975. Evaluation of solids

separation devices. Managing Livestock Wastes. Proceedings of 3rd International Symposium on Agricultural Wastes, American Society of Agricultural Engineers Urbana, Illinois, USA. pp 463-467.


Vibrating ScreenDescription of the SystemManufacturer / DistributorInformation SourcesPerformance DataShutt et al. $1975$ Piggery wastewater $Pain et al. \(1978$ Cow and piggery wastewaHegg et al. $1981$ Animal wastewaters $3 Holmberg et al. \(1983$ Piggery wastewaterAbery $1994$ Piggery wastewaterCharles $2000$ Piggery wastewater \(2 scrSummary of performance data

Running Costs and MaintenancePractical Operating IssuesPiggery Case StudiesFlamingo Vibrating Screen Data

Summary Selection CriteriaSolids removedCapital costOperating costsEase of operationSolids management options

References

Case Study Vibrating Screen

Documents

screen types

vibrating screen case

vibrating screen data

piggery wastewaters

piggery case studies

summary of performance

pig industry case study

list of figures figure