Descripción: vibrating screen and its working...
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
Solid Separation Systems for the Pig Industry
Case Study 4 –Vibrating Screen
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 µm to 5.6 mm.
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Solid Separation Systems for the Pig Industry
Case Study 4 –Vibrating Screen
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:
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Solid Separation Systems for the Pig Industry
Case Study 4 –Vibrating Screen
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. •
Manufacturer’s 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%
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Solid Separation Systems for the Pig Industry
Case Study 4 –Vibrating Screen
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 Parameter Units Flow removal TS removal TS of output VS removal BOD COD
0.12 0.2 2.5 5.7 3.3 -
% of inflow % of inflow % wb % of inflow % of inflow % of inflow
(ii) Loading rate – 67 L/min Parameter Units Flow removal TS removal TS of output VS removal BOD COD
% of inflow % of inflow % wb % of inflow % of inflow % of inflow
% of inflow % of inflow % wb % of inflow % of inflow % of inflow
0.39 0.4 12.6 12.2 4.3 10.0
0.12 1.2 13.8 8.5 18.5 -
Size of Opening (mm) 0.17 0.21 0.7 0.7 14.0 9.8 10.9 10.8 17.0 12.9 2.4 15.3 8.9
0.39 0.6 22.2 16.4 28.1 16.1
0.12 2.1 18.7 4.8 42.8 -
Size of Opening (mm) 0.17 0.21 0.8 0.9 1.8 7.0 1.9 4.8 2.4 9.0 3.9 12.5 10.7
0.39 1.6 12.3 4.9 17.2 12.2
(iii) Loading rate – 110 L/min Parameter Units Flow removal TS removal TS of output VS removal BOD COD
Size of Opening (mm) 0.17 0.21 0.5 2.8 5.8 14.3 3.9 8.7 8.4 12.4 4.5 3.3 16.3
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
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Solid Separation Systems for the Pig Industry
Case Study 4 –Vibrating Screen
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)
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Solid Separation Systems for the Pig Industry 4.4.3
Case Study 4 –Vibrating Screen
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 manufacturer’s 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 Slurry Concentration Influent % TS Effluent % TS TS % removed Removed % TS solids Influent g/L COD Effluent g/L COD COD % removed Flowrate L/min range
April 2002
0.83
1.57
0.64
2.88 2.75 5.0
1.83 1.34 27.0
0.83 Low 1.52 1.36 10.0
High 2.86 2.56 10.0
1.57 1.55 1.51 3.0
19.3
20.9
20.9
18.4
16.9
29.7
21.5
20.4
13.7
12.9
25.4
20.7
15.4
13.6
12.2
14.0
4.0
24.0
1.0
6.0
15-35
53-126
37-57
37-108
37-103
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Solid Separation Systems for the Pig Industry 4.4.4
Case Study 4 –Vibrating Screen
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, 1470% 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
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Solid Separation Systems for the Pig Industry
Case Study 4 –Vibrating Screen
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
