JPS58128200A - Control device of purifying tank - Google Patents

Abstract

PURPOSE:To maintain the alkalinity of washed sludge constant by determining the ratio of flow rate of washing water basing on the alkalinity of inflow sludge, the alkalinity of washing water and the set alkalinity of the washing water, and controlling the flow rate of the washing water in accordance with the ratio of flow rate of the washing water and the amt. of the inflow sludge. CONSTITUTION:The difference between the alkalinity Ab of inflow sludge 2 measured with an alkalinity meter 3 and the set value Aa of the alkalinity is determined with a subtractor 13, and the difference between the set value Aa of the alkalinity and the alkalinity Aw of washing water 5 is determined with a subtractor 14. The difference determined with both subtractors 13, 14 is applied to a controller 15 which determines the ratio of flow rate R of the washing water. The ratio R and the flow rate Fb of the inflow sludge measured with a flowmeter 4 are multiplied to obtain a command F'w for the flow rate of washing water to input to a controller 17. The controller 17 compares the command F'w and the flow rate Fw of the washing water measured with a flowmeter 8, and controls the opening of a water flow control valve 17. Thus, the flow rate of the washing water 5 to be applied to a washing tank 1 is controlled in such a way that the alkalinity of the washed sludge attains the set value Aa.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a washing tank control device for washing digested sludge, and more particularly, to a washing tank control device for controlling the alkalinity of digested sludge in percent.

In the sludge treatment process at sewage treatment plants, flocculants are added to digested sludge before it is dehydrated. Digested sludge generally has a high alkalinity of about 2000 to 3000 mg/z, and requires a large amount of flocculant. Figure 1 shows changes in the transit rate of the dehydrator due to changes in the alkalinity of the sludge and the amount of flocculant added.

Therefore, by washing the digested sludge with water with low alkalinity, the alkalinity of the sludge is lowered, and the highly compressible K slime, which is an obstacle to dewatering, is washed away, thereby saving on coagulant and making it easier for the dehydrator to pass. A cleaning process is provided to improve efficiency.

Conventionally, the amount of washing water for washing digested sludge has been controlled by a ratio injection control method based on the amount of inflowing sludge. Generally, the amount of washing water is 4 to 5 times the amount of inflowing sludge. However, in the ratio injection control method, when the alkalinity of the inflowing sludge changes, the alkalinity of the washed sludge also changes. Figure 2 shows that the alkalinity of the inflowing sludge is 3000m
The washing water amount ratio and alkalinity of washed sludge in the case of g/4 and 2000 mg/l are shown. The alkalinity of the nine-dashi washing water is ssomg/z. As shown in Figure 2, when the washing water ratio is set to 5, the alkalinity of the inflowing sludge is 20.
When the alkalinity of the washed sludge is 625 alt/l (Characteristic L2), the alkalinity of the washed sludge is 625 alt/l (Characteristic L2). The degree changes to 7291 ng/l.

This change in alkalinity results in a change in the transit rate of water dewatering, which does not significantly change the amount of excess flocculant added as shown in FIG.

For this reason, it is difficult to manage the operation of the dehydrators, and it is especially difficult to control the number of dehydrators in #1, where the number of dehydrators increases.

An object of the present invention is to provide a cleaning tank control device that can keep the transient efficiency of a dehydrator constant.

The present invention calculates the washing water amount ratio (from the alkalinity of the inflowing sludge, the alkalinity of the washing water, and the set alkalinity of the washing water), and controls the washing water amount based on this washing water amount ratio and the amount of inflowing sludge to increase the alkalinity of the washed sludge. is kept constant.

An embodiment of the present invention will be described below with reference to FIG. There are two types of cleaning methods, such as a one-stage cleaning method and a two-stage countercurrent cleaning method. This can be realized in the same way as the stage cleaning method.

In FIG. 3, inflowing sludge 2 enters a washing tank l and is washed with washing water 5, which is added as described in FIG.

Washing water 5 added to the washing tank 1 is regulated by a water amount control valve 7. The washed sludge IO is added to a dehydrator (not shown), and the washed wastewater 9 flows out from the top.

The alkalinity A- and the flow rate Fb' of the inflowing sludge 2 are measured by an alkaline change course 3 and a flow meter 4. Similarly, the alkalinity A1 and the flow rate F of the cleaning water 5 are measured by the alkaline needle 6 and the flow meter 8. The measured values of the alkaline needles 3 and 6 and the flowmeters 4 and 7 are added to the wash water calculation circuit 11. The wash water calculation circuit 11 includes an alkalinity setting device 12° subtractors 13, 14, . Divider 1
5. It consists of a multiplier 16 and a controller 17.

Next, the operation will be explained.

The difference between the inflow sludge alkalinity Ah measured by the alkaline needle changer 3 and the alkaline setting value A is determined by the subtractor 13. Further, the difference between the alkalinity set value A and the washing water alkalinity is determined by the subtractor 14. The difference determined by both subtracters 13 and 14 is added to the divider 15, and the cleaning flow rate ratio R is determined by the following formula.

h −Am R wealth □ ・・・・・・(1) aA
- However, R is the washing water amount ratio multiplier 16 which multiplies the washing water amount ratio R obtained by the divider 15 by the inflow sludge amount F- measured by the am meter 4, and the washing water amount command F
The washing water amount command F4 that outputs - becomes an input to the controller 17. The controller 17 compares the washing water amount command F' with the washing water amount X measured by the flow meter 8, and controls the opening degree of the water amount regulating valve 7. When p'v>p, the water flow control valve 7t is operated in the closing direction, and when pL<F, it is operated in the opening direction. At this time, the amount of washing water 5 added to the digestion tank 1 is controlled so that the alkalinity of the washed sludge becomes the set value A.

As described above, the alkalinity of the washed sludge can be controlled to be constant.

As described above, according to the present invention, the alkalinity of the washed sludge can be kept constant, so the transient efficiency of the dehydrator can be kept constant. Therefore, operation management of the dehydrator becomes easier.

[Brief explanation of drawings]

Figure 1 is a characteristic diagram showing changes in filtration efficiency of the dehydrator due to changes in sludge alkalinity and flocculant addition lid. Figure 2 is a characteristic diagram showing changes in washing water volume ratio and alkalinity to washed sludge. The figure is a configuration diagram showing an embodiment of the present invention. l...Washing tank, 2...Inflow sludge, 3...Inflow sludge alkaline needle change, 4...Inflow sludge placement needle, 5...Washing water, 6...Washing water alkaline placement needle, 7...・Washing water amount regulator, 8...Washing water amount needle, 9...Washing waste water, 1o
...Washing sludge, 11...Washing water calculation circuit, 12...
・Alkalinity setting device, 13.14...Subtractor, 15・
...divider, 16...controller, 17...comparator,
Water flow control valve.

Claims (1)

[Claims] 1. A washing tank for washing sludge by adding washing water, a water amount adjusting means for adjusting the amount of washing water added to this washing tank, and a washing water amount ratio according to the alkalinity and alkalinity setting value of the above-mentioned inflow sludge and washing water. means for determining the amount of water, a water amount commanding means for issuing a washing water amount command (based on the above-mentioned inflow sludge flow rate and washing water amount), and an adjustment needle for operating the water amount regulating means based on this washing water amount command, so as to maintain the alkalinity of the washed sludge at a constant value. 9. Control device for cleaning tank.