JPS6031898A - Control apparatus of digestion tank - Google Patents

Abstract

PURPOSE:To obtain a stable methane gas generating amount, by providing an estimating operation apparatus of methane gas generated in a digestion tank and an operation apparatus for outputting a control signal on the basis of the comparative operation of the estimated value and the methane gas generating amount in the digestion tank. CONSTITUTION:The amount and concn. of sludge charged into a digestion tank 1 in the preceding time are measured by a charged sludge flow meter 8 and a charged sludge densitometer 7 and the measured values are inputted to an estimating operation apparatus 11 where the amount of a sludge solid substance is calculated to input the estimated methane gas generating amount of charged sludge to a comparing operation apparatus 13. Digestion gases from the digestion tank 1 and a digestion tank 2 due to the preceding sludge charging result are sent to a gas tank 4 but the concn. of the methane gas and the flow amount thereof in the digestion gas are measured by a digestion gas meter 9 and the measured values are inputted to a generation amount operation apparatus 12. In this case, a methane gas amount during a determined time from the preceding sludge charging to this time sludge charging is inputted to a calculation and comparison operating apparatus 13.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a control device for a sludge digestion tank in a sewage treatment plant.

[Technical background of the invention and its problems]

Raw sludge and surplus sludge from the water treatment facility of a sewage treatment plant are concentrated in a thickening tank and then fed into a sludge digestion tank.In the digestion tank, the organic matter in the sludge is decomposed by the action of anaerobic bacteria, resulting in methane gas. It is then gasified as carbon dioxide gas, led to a storage tank, and used as fuel. Digested sludge is extracted from the digestion tank and sent to dewatering equipment. Methane-producing bacteria among the anaerobic bacteria, which are important in the decomposition reaction of the anaerobic bacteria, are extremely susceptible to temperature, ionization concentration, etc. Regarding temperature control,
As long as the digestion tank is well insulated, such as by installing heat insulators, no special controls are required as long as it is heated normally. In addition, if the ionization concentration of the input sludge itself fluctuates, it is necessary to adjust the ionization concentration by tilting forward.

The most important thing is that the ionization concentration varies depending on the state of digestion in the digester. That is, as the load on the digestion tank increases, the concentration of fatty acids produced by decomposition in the first digestion stage increases, the ionization concentration in the digestion tank becomes acidic, the activity of methane-producing bacteria decreases, and the amount of methane gas generated decreases. Therefore, it is very important to control the amount of load on the digester so that the methanogens can react efficiently with the digester.

The conventional method of controlling the amount of sludge input is not particularly controlled, and the number of days for digestion is determined by the numerical value used when designing the capacity of the digester, and a gas flow meter is not installed. Therefore, it was not determined that the digestive status was normal.

Currently, as an issue of energy conservation in sewage treatment plants, the use of generators or power drives using gas engines that utilize digestion gas is expected to be effective.

In order to fully demonstrate its effect, it is necessary to stably obtain the amount of digestion gas, that is, methane gas. An increase in the amount of methane gas means that the content of organic matter in the digested sludge will decrease, and the capacity will also decrease. It was expected that the volume and amount of chemicals injected would also be reduced.

[Purpose of the invention]

The present invention aims to eliminate the above-mentioned drawbacks, and by measuring the amount of methane gas generated from the digester, the situation of the digester can be judged and the amount of sludge input can be controlled, and a stable amount of digested gas can be obtained. The purpose is to promote weight loss.

[Summary of the invention]

The present invention provides a digestion tank that decomposes, liquefies and gasifies organic matter in sludge through the action of anaerobic bacteria, an input sludge flow rate needle that measures the amount of solid matter in sludge input into the digestion tank, and this input sludge flow rate needle. a prediction calculation device that predicts and calculates the amount of methane gas generated in the digestion tank based on the flow rate output from the sludge and the concentration of the sludge; a digestion gas flowmeter that measures the flow rate of methane gas generated from the digestion tank; and a digestion gas flow meter that measures the concentration of this methane gas. a methane gas concentration needle, a generation amount calculation device that calculates the amount of methane gas generated based on the concentration signal from the methane gas concentration meter and the flow rate signal from the digestion gas flow rate needle, and an actual output signal and prediction calculation device of the generation amount calculation device. This digester control device consists of a comparison calculation device that inputs the predicted output signal, which is the output of the A calculation device that measures the amount of solid matter in the sludge put into the digester and predicts the amount of methane gas generated from the digester, and compares the amount generated with the amount of methane gas actually generated from the digester. This is a digester control device that controls the amount of sludge to be input at this time according to the difference in the amount of methane gas generated.

[Embodiments of the invention]

Next, examples of the present invention will be described. Figure 1 shows a digestion tank 1 that decomposes, liquefies and gasifies organic matter in sludge by the action of anaerobic bacteria, an input sludge flow meter 7 that measures the amount of solid matter in sludge input into the digestion tank 1, and an input sludge flowmeter 7. A prediction calculation device 11 that predicts and calculates the amount of methane gas generated in the digestion tank 1 based on the flow rate output from the flow meter 7 and the concentration of sludge; a digestion gas flow rate needle 9 that measures the flow rate of methane gas generated from the digestion tank 1; A methane gas concentration meter 10 that measures the concentration of this methane gas, a generation amount calculation device 12 that calculates the amount of methane gas generated based on the concentration signal co from the methane gas concentration needle 10 and the flow rate signal Qa from the digestion gas flowmeter 9, and the amount of generation The figure shows a digester control device comprising a comparison calculation device 13 that inputs an actual output signal 12a of the calculation device 12 and a predicted output signal tta which is an output of the prediction calculation device 11, performs a comparison operation, and outputs a control signal 13a. .

That is, the present invention measures the solid matter of the sludge that is introduced into the digestion tank 1 in a sludge digestion tank in a sewage treatment plant, and determines whether the sludge is injected according to the amount of methane gas per solid matter determined by an experiment. This sludge digestion equipment is characterized in that it predicts the amount of methane gas generated by the process, compares it with the amount of methane gas actually generated from the digestion tanks 1 and 2, and controls the amount of sludge to be introduced at this time based on the result. .

Figure 1 shows a digestion tank 1 in which organic matter in sludge is decomposed and liquefied and gasified by the action of anaerobic bacteria, a digestion tank 2 in which the sludge in the digestion tank 1 is introduced via a connecting pipe and separated by sedimentation, and A gas tank 4 that stores methane gas generated from the tank 2 and the digestion tank 1, and a gas stirring blower 5 that stirs the anaerobic bacteria and sludge in the digestion tank 1 and at the same time equalizes the temperature inside the digestion tank 1. , a steam boiler 6 that supplies heating steam to the digestion tank 1, an input sludge flowmeter 7 that measures the volume of sludge charged into the digestion tank 1, and a steam boiler 6 that supplies steam for heating to the digestion tank 1; In a sludge digestion device consisting of an input sludge concentration meter 8 for measurement and a sludge input pump 3 for inputting sludge into the digestion tank 1, the input is determined by the flow rate signal QC of the input sludge flow meter 7 and the concentration signal of the input sludge concentration meter 8. a prediction calculation device 11 that calculates a predicted value of the amount of methane gas generated from the sludge by integrating the solids obtained, a digestion gas flow meter 9 that measures the flow rate of digestion gas generated from the digestion tanks 1 and 2; a methane gas concentration meter 10 that measures the methane gas concentration in the gas;
The actual amount of methane gas generated is calculated from the digestion gas flow rate Qe measured by the digestion gas flow meter 9 and the methane gas concentration CG measured by the methane gas concentration meter 10 at a predetermined time until the sludge input as a result of sludge injection. The generation amount calculation bag @ 12 is used as a comparison calculation device 13 which compares and calculates the measured amount which is the output of the generation amount calculation device 12 and the predicted amount which is the output of the prediction calculation device 11, and the output of the comparison calculation device 13. A sludge digester is shown that includes an operation control device 14 that controls the operating time or speed of the sludge input pump 3 to control the amount of sludge input.

FIG. 2 is a diagram showing the amount of gas generated depending on the amount of sludge input.

Figure 2 is determined experimentally at each sewage treatment plant because it varies depending on the type of sludge in the sewage treatment plant, that is, the amount of organic matter contained in it, and the composition of the organic matter that makes up the sludge. The rate of change is small unless the quality of the sewage is different. According to Figure 2, calculate the amount of methane gas generated after one hour from the amount of sludge solids introduced.

Figure 1 (- shows the control system for the amount of sludge input. The amount and concentration of sludge that was previously input into the digestion tank 1 are measured by the input sludge flow meter 8 and the input sludge concentration meter 7, and are input to the prediction calculation device 11. A prediction calculation device 11 measures the amount of solid matter in the sludge, and a predicted amount of methane gas generated from the input sludge is input to a comparison calculation device 13.

The digestion gas from the digestion tanks 1 and 2 according to the results of the previous sludge injection is sent to the gas tank 4, but the methane gas concentration and gas flow rate in the digestion gas are measured with the digestion gas concentration meter 10 and the digestion gas flow meter 9. The amount of methane gas generated during a predetermined period of time from the previous sludge injection to the current sludge injection is input to the calculation/comparison calculation device 13.

The comparison calculation device 13 compares the predicted methane gas generation amount due to the previous sludge injection obtained from the prediction calculation device 11 with the actual methane gas generation amount obtained from the generation amount calculation device 12. Based on the result, the device 14 controls the input sludge pump and the amount of sludge input based on the current input sludge flow rate and concentration (: solid content amount).

The state of the control is shown in Fig. 3. Points A, B, and C indicate the time when sludge is introduced, and the amount of methane gas generated is accumulated until the next time when sludge is introduced. The predicted value P is the value shown at the final point, and the actual measured value is shown as a solid line. In the case of example a, since the predicted value P and the actual measured value almost match at the final point, the amount of sludge input this time is the same as the previous one. For example, since the value is higher than the predicted value, it is judged that the condition of the digester tank is good, so the same amount of sludge as the last time is input this time. In the case of example C, the actual measured value is lower than the predicted value P by width 1, so it can be determined that the condition of the digester is poor. reduce As a result, if the current predicted value P is the same as or exceeds the actual value, the amount of sludge introduced last time will be returned to:
Two controls.

The calculation formula in the calculator is shown below. The prediction calculation device calculates the amount of solid matter in the input sludge and further calculates the predicted amount of methane gas generated based on FIG. 2, which is expressed by equation (1).

However, Σcc - Qc = W (amount of solids) is a value that is determined to some extent depending on the capacity of the digestion tank.Vmu = VT ・Σcc
-Qc ・・・・・・・・・(1) Generation amount calculation device 1
2 is for calculating the amount of methane gas generated from the time when sludge is added until the next time, and is expressed by equation (2).

VB=ΣCa・QG The computing unit calculates the difference between the predicted methane gas generation amount ■A and the measured methane gas generation amount ■O, and outputs the plow operation amount to the control bag [14] based on the result of the following equation.

(al VB -VA + O without control bl'vIl
-vm=10△V No control +CI VB-VA
In the case of =-△■, V, =Vd-ΣCc+”QctC
Reduce the amount of sludge input so that =

However, if ΣCc''Qc decreases from the originally planned input amount and the final methane gas generation amount matches the predicted value for the input amount, or if it increases, the input is controlled by returning to the previous input amount.

〔Effect of the invention〕

Since the present invention is configured as described above, the condition of the digester becomes stable, so a stable amount of methane gas is generated, which increases the value of using methane gas as energy, and further reduces the amount of sludge that is extracted. This has the effect of reducing the load on backup dewatering equipment.

[Brief explanation of the drawing]

Figure 1 shows the flow of a digester tank showing an embodiment of the present invention (V-)
An explanatory diagram, FIG. 2 is an explanatory diagram showing the relationship between the amount of methane gas generated per input sludge solid material depending on the number of days for digestion, and FIG. 3 is an explanatory diagram showing the state of control of the amount of methane gas generated according to the present invention.1 ... Digestion tank 2 ... Digestion tank 3 ... Sludge injection pump 4 ... Gas tank 5 ...
Gas stirring blower 6... Steam boiler 7... Input sludge flow meter 8... Input sludge concentration meter 9... Digestion gas flow meter 10... Methane gas concentration meter 11... Prediction calculation device 12...・Generation amount calculation device 13...Comparison calculation device 14...Sludge injection pump control device Representative Patent attorney Noriyuki Chika (and one other person)

Claims (1)

[Claims] A digestion tank that decomposes organic matter in sludge and liquefies and gasifies it by the action of anaerobic bacteria, an input sludge flow meter that measures the amount of solids in the sludge input into the digestion tank, and a flow meter that measures the amount of solid matter output from this input sludge flow rate needle. a prediction calculation device that predicts and calculates the amount of methane gas generated in the digestion tank based on the flow rate and the concentration of the sludge; a digestion gas flow meter that measures the flow rate of the methane gas generated from the digestion tank; and a digestion gas flowmeter that measures the concentration of the methane gas. A methane gas concentration meter, a generation amount calculation device that calculates the amount of methane gas generated based on the concentration signal from the methane gas concentration needle and the flow rate signal from the digestion gas flow rate needle, and an actual output signal of the generation amount calculation device and the predicted calculation. A digester control device comprising a comparison calculation device that inputs a predicted output signal, which is the output of the device, performs comparison calculations and outputs a control signal.