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Calculation of sludge dewatering capacity of belt filter press

1 Introduction
Belt-type pressure filter sludge dewatering machine is based on chemical flocculation contact filtration and mechanical extrusion principle and made of high efficiency solid-liquid separation equipment, because of its simple process, high degree of automation, continuous operation, easy control and work process Adjustable and a series of advantages, and save the sludge concentration pool, to a certain extent, save the construction funds, is being more and more widely used.
The flocculated sludge first enters the gravity dewatering zone, and most of the free water is filtered through the filter belt under the action of gravity. With the operation of the filter belt, the sludge enters the wedge region composed of two filter belts, The sludge is slowly pressurized, the sludge is gradually thickened, the fluidity is reduced, the transition to the press area; in the press area, the sludge is subjected to the increasing pressing force and the shear force generated by the alternation of the upper and lower positions of the two filter belts The majority of the residual water and the interstitial water remaining in the sludge are filtered out and the sludge becomes a low-grade sheet filter cake. The upper and lower filter belts are separated by a discharge roller, and by changing the curvature of the filter tape Scraper will filter off the cake to achieve the solid-liquid separation of materials, and the upper and lower filter belt after re-use, the next cycle of concentrated pressure filter.
Belt filter press in the practical engineering applications involved in the main technical and economic indicators are:
① processing capacity,
② mud cake moisture content,
③ chemical dosage,
④ power consumption,
⑤ flushing water consumption,
⑥ with tension,
⑦ effective bandwidth,
⑧ filter running speed
⑨ gas pressure and other key indicators.
Which processing capacity is to evaluate the overall performance of belt filter press the primary indicators. There are many factors that affect the processing capacity of the belt filter press, but mainly in the gravity dehydration area, the press zone and its filter belt running speed, filter belt tension, roll diameter (size, wrap angle and center distance), filter belt ) Selection, dosing conditioning effect, etc., but also belt filter press structure design, manufacturing and other quality of the comprehensive embodiment. Therefore, the calculation method of the processing capacity of the belt filter press has certain guiding significance for the optimization design of the belt filter press, the choice of the operating parameters and the reasonable dosage.
2, the processing capacity of the calculation
According to the calculated wet mud cake production, and then calculate the amount of feed (that is, processing capacity), the formula is as follows: the thickness of the wet mud cake,
Q wet cake = B • ξ • δ • v • s • γ • β
Where: Q wet mud cake - wet mud cake output t / h
B - filter width m
Ξ - filter belt width utilization factor, generally take 0.85 ~ 0.9
Δ - wet mud cake thickness m, generally take 6 ~ 10mm (0.006 ~ 0.01m)
V - pressure filter belt with the actual working speed m / min, generally take 3 ~ 6m / min
S - unit time 60min / h
Γ - wet mud cake weight t / m3, generally take 1.03t / m3
Β - solid phase recovery, generally take ≥ 95%
Q Amount of feed = (wet cake with solid / feed solids) × Q wet cake (t / h)
It can be seen from the above calculation formula that the calculation method is to use the belt filter press to produce the thickness of the wet mud cake as the main calculation parameters, and the formation of wet mud cake on the one hand with the belt filter operating parameters such as filter belt Running speed, filtration pressure has a great relationship; on the other hand with the nature of the sludge such as solid concentration, viscosity, dosing sludge after the resistance is also a great relationship; wet mud cake thickness formation also depends on the The structure of the filter press design, such as the length of the concentrated section, the capacity of the concentrated section, the pressure filtration time and the filtration cycle, the choice of the permeability of the filter belt. In the formula, the Q wet mud cake is linearly related to the thickness of the wet mud cake δ, 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 width Nor uneven.
So the calculation method is not with the concentrated section, the main technical parameters of the squeeze section and the main parameters of the combination of sludge parameters, did not reflect the effect of sludge dosing treatment, filter design parameters, operating parameters, such as changes in factors Belt filter presses, and the calculated range of Q wet mud cake is large. It is generally suitable for the design selection of belt filter press, the optimized structure design of belt filter press, the guiding operation, etc. It is not meaningful.
For the sludge dewatering system of the municipal wastewater treatment plant, the specific resistance of the sludge is controlled by (1 ~ 4) × 1012m / kg (the laboratory is determined by the r value to determine the more economical dosage) (1 ~ 3) × 1012m / kg (centrifugal dehydration r = (2 ~ 4) × 1012m / kg) for the belt filter press, the laboratory generally through the dosing sludge after the specific resistance r. When the ambient temperature is 20 ℃, the kinematic viscosity of the sludge is μ = 0.001Pa • s.
For the press section, the pressure P is calculated by the belt tension, the press roll and the contact area of ​​the filter belt, and the concentration C0 into the press section is the concentration of the concentrated sludge (8 to 10%), Ck is the final cake concentration (25% (T = ts / T2), ts for the actual filter time (press the filter belt and press roll contact length, press the filter belt running Speed), T is the filter press cycle (squeeze section of the running time).
The sum of the treated amount of the concentrated section and the pressing section is the processing amount of the belt type filter press. Because the filter does not take into account the filter medium filter impedance Rf, and the filter impedance Rf and filter belt material, ventilation [generally selected 8000 ~ 10000m3 / (h • m2)] and so on, so the final treatment capacity should be Is the calculated amount of processing multiplied by a coefficient K (K generally take 0.9 ~ 0.95) is the belt filter press the amount of processing.
3, the conclusion
Although the second algorithm is more complicated than the first algorithm, the calculation method includes the influence of structural design parameters, sludge parameters and operating parameters on the treatment capacity of the belt filter. The design of the machine, the dosage of reasonable dosage and the choice of running parameters have certain guiding significance to improve the processing capacity of belt filter press. And through the example of calculation, the processing capacity of the concentrated section of the belt filter press processing capacity play a major role.

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