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The belt filter press is a high-efficiency solid-liquid separation device based on the principle of chemical flocculation contact filtration and mechanical extrusion, because of its simple process flow, high degree of automation, continuous operation, simple control operation and adjustable working process. The advantages of the series, and the elimination of the sludge concentration tank, to some extent save construction funds, is getting more and more widely used.

      The flocculated sludge first enters the gravity dewatering zone, and most of the free water is filtered by the filter belt under gravity; as the filter belt runs, the sludge enters a wedge-shaped zone composed of two filter belts, two filter belts. The sludge is slowly pressurized, the sludge is gradually thickened, the fluidity is reduced, and the transition to the pressing zone; in the pressing zone, the sludge is subjected to the increasing pressing force and the shearing force generated by the alternating upper and lower positions of the two filter belts. The role of most of the free water and interstitial water remaining in the sludge is filtered out, the sludge becomes a flake cake with a lower water content; the upper and lower filter belts are separated by a discharge roller, and the curvature of the filter belt is utilized and utilized. The scraper scrapes off the filter cake to achieve solid-liquid separation of the material, and the upper and lower filter belts are washed and reused for the next cycle of concentrated pressure filtration.

       The main technical and economic indicators involved in the actual engineering application of the belt filter press are:

       1 processing power,

       2 mud cake moisture content,

       3 chemical dosage,

       4 power consumption,

       5 flushing water consumption,

       6 with tension,

       7 effective bandwidth,

       8 filter belt running speed

       9 main indicators such as gas source pressure.

      The processing capacity is the primary indicator for evaluating the overall performance of the belt filter press. There are many factors affecting the processing capacity of the belt filter press, but it is mainly reflected in the gravity dewatering zone, the press zone and its belt running speed, the filter belt tension, the roll diameter (size, wrap angle and center distance), and the filter belt (breathing capacity). The selection, dosing and conditioning effects are also a comprehensive reflection of the quality of the belt filter press structure design, manufacturing and so on. Therefore, understanding the calculation method of the belt filter press processing capacity has certain guiding significance for the optimization design of the belt filter press, the selection of operating parameters, and the reasonable dosage.

2, the calculation of processing power

     The thickness of the wet mud cake produced by the belt filter press is taken as the main calculation parameter, and the feed amount (ie, processing capacity) is calculated according to the calculated wet mud cake yield. The calculation formula is as follows:

     Q wet mud cake = B•ξ•δ•v•s•γ•β

     Where: Q wet mud cake - wet mud cake output t / h

      B——filter belt width m

      ξ——The filter belt width utilization factor is generally 0.85~0.9

      Δ——wet mud cake thickness m, generally take 6~10mm (0.006~0.01m)

      v——The actual working speed of the filter belt is m/min, generally 3~6m/min

      S——unit time 60min/h

      Γ——wet mud cake specific gravity t/m3, generally take 1.03t/m3

      β - solid phase recovery rate, generally ≥ 95%

     Q feed amount = (wet mud cake solid content / feed solid content) × Q wet mud cake (t / h)

      It can be seen from the above formula that the calculation method is based on the thickness of the wet cake produced by the belt filter press, and the thickness of the wet cake is formed on the one hand with the operating parameters of the belt filter, such as the filter belt. The running speed and filtration pressure have a great relationship; on the other hand, it also has a great relationship with the properties of sludge such as solid concentration, viscosity, and specific resistance of sludge after dosing; the key to the formation of wet mud cake thickness depends on The structural design of the filter press is such as the length of the concentration section, the capacity of the concentration section, the filter press time and the filter press cycle, and the selection of the filter belt permeability. In the calculation formula, the Q wet mud cake has a linear relationship with the thickness δ of the wet mud cake. The thickness of the wet mud cake is selected from 3 to 10 mm, and the thickness of the wet mud cake formed in the actual operation of many belt filter presses is within the filter belt width. Not uniform.

      Therefore, this calculation method is not combined with the main technical parameters of the concentration section and the pressing section and the main property parameters of the sludge, and does not reflect the factors such as the effect of sludge dosing conditioning, the design of the filter filter structure parameters, and the changes of operating parameters. The influence of the processing capacity of the belt filter press, and the calculated range of Q wet mud cake is large, generally suitable for the design and selection of belt filter press, optimized structure design and guiding operation of the belt filter press. It is not meaningful.

      For the municipal sewage sludge dewatering system, after the sludge is conditioned, the specific resistance of the sludge is controlled at (1~4)×1012m/kg (the laboratory determines the economical dosage by measuring the r value) For the belt filter press, the specific resistance r of the sludge in the laboratory is generally adjusted to be (1 to 3) × 1012 m / kg (centrifugal dehydration r = (2 ~ 4) × 1012 m / kg). When the ambient temperature is 20 ° C, the kinematic viscosity of the sludge μ = 0.001 Pa•s.

      For the press section, the pressure P is calculated by the tension of the filter belt, the contact area between the press roll and the filter belt, and the concentration C0 entering the press section is the concentrated sludge concentration (8-10%), and Ck is the final filter cake concentration (25%). ～20%), filter press time t=m/T, m=ts/T (ie t=ts/T2), ts is the actual filter press time (contact length of press belt and press roll in press section, filter belt operation in press section) The speed is obtained), and T is the filter press cycle (pressing section running time).

      The sum of the treatment amounts of the concentration section and the press section is the throughput of the belt filter press. Since the impedance Rf of the filter medium filter belt is not considered in the calculation, the impedance Rf of the filter belt is related to the material of the filter belt and the aeration amount [generally selected from 8000 to 10000 m3/(h•m2)], so the final treatment amount should be The amount of processing calculated above is multiplied by a coefficient K (K is generally 0.9 to 0.95), which is the throughput of the belt filter press.

3. Conclusion

      Although the above second algorithm is more complicated than the previous algorithm, the calculation method includes the structural design parameters of the belt filter press, the sludge property parameters, the operating parameters, etc., and the effect on the throughput, and the optimized belt filter press The structural design, the reasonable dosage and the selection of operating parameters have certain guiding significance for improving the processing capacity of the belt filter press. And through the calculation of the example, the processing amount of the concentration section plays a major role in the processing capacity of the belt filter press.

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