Sludge treatment system, sludge treatment control apparatus, and sludge treatment method

Abstract

To provide reduction of greenhouse gas emissions by effectively utilizing waste heat of digestion gas power generation.SOLUTION: A sludge treatment system includes: a first heating part that feeds concentrated sludge into the digestion tank for anaerobic digestion, generates gas power using the digestion gas generated as fuel, adds coagulant to the digested sludge drawn from the digestion tank, coagulates and dehydrates the sludge and discharges the dehydrated sludge, and uses the waste heat from combustion exhaust gas generated during gas power generation to heat the excess concentrated sludge to a first predetermined temperature; a second heating part that heats the digestion tank to a second predetermined temperature using the waste heat from the combustion exhaust gas; a third heating part that heats the digested sludge to a temperature below a third predetermined temperature using the waste heat from the combustion exhaust gas and heats the digested sludge to a temperature below a fourth predetermined temperature; a first calculation part that calculates the amount of waste heat; a second calculation part that calculates the amount of required heating heat for each heating part; and a control part that controls the implementation of heating by at least one of the heating and the heating temperature so that the total amount of heating heat required for the entire heating part is less than the waste heat from combustion exhaust gas waste.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] An embodiment of the present invention relates to a sludge treatment system, a sludge treatment control device, and a sludge treatment method. [Background technology]

[0002] 2. Description of the Related Art Digestion gas power generation using digestion gas generated from sewage sludge has been known as one of the means for recovering energy from sewage sludge.

[0003] Sewage sludge contains about 80% organic matter, and anaerobic digestion produces digester gas containing about 60% methane. Because digester gas is a carbon-neutral fuel that is not derived from fossil fuels, electricity generated by digester gas power generation is considered to be renewable energy and does not increase greenhouse gas emissions.

[0004] In addition, the use of renewable energy reduces the amount of energy used that is derived from fossil fuels, which contributes to the reduction of greenhouse gas emissions. Reducing greenhouse gas emissions is a global issue, and reduction targets have been set. Therefore, it is expected that digester gas power generation will become more widespread and expand in the future. In addition, it is expected that technologies such as sludge solubilization, which allows more digester gas to be recovered from sewage sludge, will be adopted. In other words, it is expected that the amount of power generation using digester gas will increase in the future. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2015-131263 A [Patent Document 2] JP 2017-213479 A [Patent Document 3] JP 2017-213479 A Summary of the Invention [Problem to be solved by the invention]

[0006] In digestion gas power generation, the digestion gas is burned, and combustion exhaust gas is generated during power generation. This combustion exhaust gas is high-temperature thermal energy (waste heat) at several hundred degrees, and the waste heat of the combustion exhaust gas is used to heat the digestion tank, as a heat source for cooling and heating, and to supply hot water via an exhaust gas heat exchanger or waste heat boiler. As mentioned above, if the amount of power generated from digester gas increases in the future with the aim of reducing greenhouse gas emissions, the amount of waste heat from combustion exhaust gas will also increase proportionately. However, there is a concern that if waste heat utilization continues as in the past, the increased amount of waste heat from combustion exhaust gas will not be consumed.

[0007] The present invention has been made in consideration of the above, and aims to provide a sludge treatment system, a sludge treatment control device, and a sludge treatment method that effectively utilize the waste heat from combustion exhaust gas generated in digester gas power generation and can reduce greenhouse gas emissions more than conventional methods. [Means for solving the problem]

[0008] A sludge treatment system according to an embodiment of the present invention is a sludge treatment system that performs anaerobic digestion of concentrated sludge, which is generated in sewage treatment and contains concentrated primary settling sludge and excess sludge, by feeding the concentrated sludge into a digestion tank, and generating power from the digestion gas using the generated digestion gas as fuel. The system also adds a coagulant to the digested sludge extracted from the digestion tank to coagulate and dehydrate the digested sludge and discharge dehydrated sludge. The system includes a first heating unit that heats the concentrated excess sludge, which is obtained by concentrating the excess sludge, to a first predetermined temperature using waste heat from the combustion exhaust gas generated in the gas-fired power generation, a second heating unit that heats the digestion tank to a second predetermined temperature using the waste heat from the combustion exhaust gas, and a third heating unit that heats the digestion tank to a second predetermined temperature using the waste heat from the combustion exhaust gas. The system includes a third heating unit that heats the sludge until the temperature of the sludge becomes equal to or lower than a third predetermined temperature and the temperature change reaches a fourth predetermined temperature; a first calculation unit that calculates the amount of waste heat of the combustion exhaust gas waste heat; a second calculation unit that calculates the amount of heating heat required in each of the first heating unit, the second heating unit, and the third heating unit; and a control unit that controls the heating and heating temperature by at least one of the first heating unit to the third heating unit so that the total amount of heating heat required by the first heating unit, the second heating unit, and the third heating unit is less than the amount of waste heat of the combustion exhaust gas waste heat. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic block diagram of a sludge treatment system according to an embodiment. [Diagram 2] FIG. 2 is an explanatory diagram of the results of a heat treatment experiment on thickened excess sludge. [Diagram 3] FIG. 3 is an explanatory diagram of the results of the continuous digestion test. [Figure 4] FIG. 4 is an explanatory diagram of the results of the coagulation dehydration experiment. [Diagram 5] FIG. 5 is an explanatory diagram of the model treatment plant. [Figure 6] FIG. 6 is a diagram illustrating the relationship between the amount of waste heat from the combustion exhaust gas and the amount of waste heat consumed during heating. [Figure 7] FIG. 7 is an explanatory diagram of the amount of CO2 emissions reduced when heating is performed. [Figure 8]FIG. 8 is a diagram illustrating the relationship between the amount of waste heat from combustion exhaust gas and the total amount of heating heat associated with a combination of heat treatments using the waste heat from combustion exhaust gas. [Figure 9] FIG. 9 is an explanatory diagram of the relationship between the amount of waste heat from combustion exhaust gas, the total amount of heating heat associated with a combination of heat treatments using the waste heat from combustion exhaust gas, and the amount of CO2 emission reduction. [Figure 10] FIG. 10 is an explanatory diagram of the control process of the sludge treatment system according to the embodiment. [Figure 11] FIG. 11 is an explanatory diagram of a calculation process of the CO2 reduction amount in the sludge treatment system according to the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Next, the embodiment will be described in detail with reference to the drawings. FIG. 1 is a schematic block diagram of a sludge treatment system according to an embodiment. The sludge treatment system 10 includes a thickening equipment (gravity type) 11, a thickening equipment (mechanical type) 12, a first heat exchanger 13, a first flow meter 14, a first valve 15, a first thickened excess sludge thermometer 16, a thickened sludge tank 17, a second thickened excess sludge thermometer 18, a thickened sludge thermometer 19, a digester tank 20, a digester tank thermometer 21, a second heat exchanger 22, a second flow meter 23, a second valve 24, a digester gas flow meter 25, a gas generator 26, a combustion exhaust gas thermometer 27, a waste heat boiler 28, a pump 29, a third valve 30, a third flow meter 31, a third heat exchanger 32, a fourth flow meter 33, a fourth valve 34, a digester sludge thermometer 35, a sludge coagulation tank 36, a sludge dewatering machine 37, and a system controller 38.

[0011] The thickening equipment (gravity type) 11 treats sewage using a standard activated sludge process, and performs gravity thickening on the primary sludge extracted from the primary sedimentation obtained in the first settling tank to produce thickened primary sludge. The thickening equipment (mechanical) 12 reacts the sewage discharged from the first settling tank in a reaction tank, and then mechanically thickens the final settling sludge extracted from the final settling obtained in the second settling tank to produce thickened excess sludge.

[0012] The first heat exchanger 13 performs heat exchange to heat the thickened excess sludge with hot water from the waste heat boiler . The first flow meter detects the flow rate of the hot water supplied from the waste heat boiler to the first heat exchanger 13, and outputs a first flow rate detection signal F1 to the system controller .

[0013] The first valve 15 adjusts the flow rate of hot water supplied from the waste heat boiler to the first heat exchanger 13 based on a valve control signal VC1 under the control of the system controller . The first thickened excess sludge thermometer 16 measures the temperature of the thickened excess sludge supplied from the thickening equipment 12 and outputs a first thickened excess sludge temperature signal T1 to the system controller .

[0014] The thickened sludge tank 17 stores the thickened primary sludge supplied from the thickening equipment 11 and the thickened excess sludge supplied from the thickening equipment 12 . The second thickened excess sludge thermometer 18 measures the temperature of the thickened excess sludge supplied from the thickening equipment 12 after it has been heated by the first heat exchanger 13, and outputs a second thickened excess sludge temperature signal T2 to the system controller 38.

[0015] The thickened sludge thermometer 19 measures the temperature of the thickened sludge (= thickened primary settling sludge and thickened excess sludge) supplied from the thickened sludge tank 17 to the digester tank 20, and outputs the thickened sludge temperature T3 to the system controller . The digester 20 performs microbial treatment on the supplied thickened sludge under anaerobic conditions with little oxygen, and digests the sludge by decomposing it into digestion gas containing methane gas, carbon dioxide, and the like through methane fermentation.

[0016] The digester thermometer 21 measures the temperature inside the digester 20 and outputs the digester temperature T4 to the system controller 38. The second heat exchanger 22 performs heat exchange to heat the undigested thickened sludge in the digester 20 with hot water from the waste heat boiler 28.

[0017] The second flow meter detects the flow rate of the hot water supplied from the waste heat boiler to the second heat exchanger 22, and outputs a second flow rate detection signal F2 to the system controller . The second valve 24 adjusts the flow rate of hot water supplied from the waste heat boiler 28 to the second heat exchanger 22 based on a valve control signal VC2 under the control of the system controller 38.

[0018] The digestion gas flow meter 25 detects the flow rate of digestion gas such as methane gas generated during digestion in the digestion tank 20, and outputs a third flow rate detection signal F3 to the system controller . The gas generator 26 generates electricity by driving a gas engine using the supplied digestion gas. The combustion exhaust gas thermometer 27 detects the temperature of the combustion exhaust gas from the gas generator 26 and outputs the exhaust gas temperature T5 to the system controller .

[0019] The waste heat boiler 28 is supplied with the combustion exhaust gas generated in the gas generator 26, and recovers heat to generate water for heating. The pump 29 performs a pumping operation for supplying the heating water generated by the waste heat boiler 28 to the first heat exchanger 13, the second heat exchanger 22, and the third heat exchanger 32.

[0020] The third valve 30 adjusts the flow rate of heating water supplied from the waste heat boiler 28 to the first heat exchanger 13, the second heat exchanger 22 and the third heat exchanger 32 as a whole, based on a valve control signal VC3 under the control of the system controller 38. The third flow meter 31 detects the flow rate of heating water supplied from the waste heat boiler 28 to the first heat exchanger 13, the second heat exchanger 22 and the third heat exchanger 32 as a whole, and outputs a fourth flow rate detection signal F4 to the system controller 38.

[0021] The third heat exchanger 32 performs heat exchange to heat the digested sludge obtained by digestion in the digester 20 with hot water from the waste heat boiler 28. The fourth flow meter 33 detects the flow rate of the hot water supplied from the waste heat boiler to the third heat exchanger 32, and outputs a fifth flow rate detection signal F5 to the system controller . The fourth valve 34 adjusts the flow rate of hot water supplied from the waste heat boiler 28 to the third heat exchanger 32 based on a valve control signal VC4 under the control of the system controller 38. The digested sludge thermometer 35 detects the temperature of the digested sludge heated by the third heat exchanger 32 and outputs the digested sludge temperature T6 to the system controller 38. The sludge coagulation tank 36 adds appropriate amounts of polyferric sulfate and polymer coagulant to the supplied digested sludge to coagulate it. The sludge dewatering machine 37 dewaters the sludge flocculated in the sludge flocculation tank 36 to produce treated sludge. The system controller 38 generates valve control signals VC1 to VC4 based on the input first thickened excess sludge temperature signal T1, second thickened excess sludge temperature signal T2, thickened sludge temperature T3, digester tank temperature T4, exhaust gas temperature T5, digested sludge temperature T6 and first flow rate detection signal F1 to fifth flow rate detection signal F5, and controls the entire sludge treatment system 10.

[0022] First, prior to describing the operation of the embodiment, a preliminary experiment that led to the embodiment will be described. As a preliminary experiment, the following three types of treatment, (A) to (C), were carried out. (A) Heat treatment of thickened excess sludge (B) Heat treatment in digesters (C) Heat treatment of digested sludge (coagulation and dehydration treatment)

[0023] Each experiment will be described in detail below. (A) Heat treatment experiment of thickened excess sludge A digestion test was conducted on the heat-treated excess sludge, and the amount of digestion gas generated per amount of organic matter (VS amount) of the heat-treated excess sludge was calculated as the gas generation rate. Further, the increase in the gas generation rate of the digestion gas relative to the gas generation rate of untreated sludge was calculated as the increase in digestion gas.

[0024] FIG. 2 is an explanatory diagram of the results of a heat treatment experiment on thickened excess sludge. As shown in Figure 2, the increase in digestion gas increased up to 50°C. In addition, although the increase in digestion gas decreased after 50°C, the gas generation rate was still higher than when the material was not heated. Heat treatment up to 50℃ improves the digestibility of excess sludge and increases the gas generation rate to 30Nm 3 When this result is converted to thickened sludge consisting of a mixture of thickened excess sludge and thickened primary settling sludge, the gas generation rate is 12 Nm 3 / t-Equivalent to an increase in VS. Therefore, when the digestion rate was calculated from this gas generation rate, it was found that heating the excess sludge to 50°C increased the digestion rate by 1.2 points.

[0025] (B) Heat treatment experiment in digester According to sewage statistics, 70% of sewage treatment plants in Japan use so-called mesophilic digestion, with a digestion temperature of 30 to 40°C, and the average is 36°C.

[0026] Based on the inventors' findings, in the temperature range of 40 to 50°C, which is between mesophilic digestion and thermophilic digestion (digestion temperature = 50 to 60°C), the activity of methanogens decreases; however, it is assumed that the effect of promoting the hydrolysis rate of sludge due to the increase in temperature exceeds the effect of the decrease in activity of methanogens, and it was predicted that gas production would increase even in the digestion temperature range of 40 to 50°C. Therefore, continuous digestion tests were carried out at digestion temperatures of 36°C and 44°C, respectively.

[0027] FIG. 3 is an explanatory diagram of the results of the continuous digestion test. After one month from the start of operation, gas generation stabilized in all cases, and the amount of gas generated per unit of thickened sludge volume (gas generation rate) was 300 to 400 Nm3 at a digestion temperature of 36°C. 3 It fluctuated in the range of / t-VS. Also, when the digestion temperature is 44℃, the digestion temperature is 350 to 560Nm 3 It fluctuated in the range of / t-VS. Furthermore, when comparing the average values ​​for the final week, the average value when the digestion temperature was 44°C was approximately 55Nm higher than the average value when the digestion temperature was 36°C. 3 / t-VS showed a high gas generation rate. In addition, when the digestion rate was calculated from the obtained gas generation rate, the digestion rate was found to be 5.6 points higher when the digestion temperature was 44°C than when the digestion temperature was 36°C.

[0028] (C) Heat treatment experiment of digested sludge (flocculation and dehydration experiment) When treated sludge is heated during sludge dewatering, the viscosity of the sludge decreases and the settling property improves. As a result, it was predicted that heating the treated sludge would decrease the moisture content of the dewatered sludge. Therefore, a heating coagulation and dehydration experiment was conducted on digested sludge extracted from the digester. A simulation experiment was carried out assuming that the coagulation dewatering was performed using a two-liquid conditioning method in which polyferric sulfate and a polymer coagulant were added as coagulants. The coagulation and dewatering experiment was carried out three times using different digested sludge and heating temperatures.

[0029] FIG. 4 is an explanatory diagram of the results of a coagulation and dehydration experiment in which digested sludge is heated. As shown in Figure 4, although the moisture content of the dewatered sludge differs from test to test because the properties of the digested sludge differ for each test, it was found that within the same test, up to 70°C, the moisture content of the dewatered sludge tends to decrease as the heating temperature increases.

[0030] Incidentally, since an object of this embodiment is to reduce greenhouse gas emissions more than in the past, it would be counterproductive if the moisture content of the dewatered sludge was reduced but greenhouse gas emissions increased due to heating. Therefore, in this embodiment, the amount of waste heat from combustion exhaust gas generated by gas power generation and the amount of heat from digested sludge required to heat the digested sludge were estimated for a "model treatment plant" described in detail below, and it was estimated that it would be possible to heat the digested sludge up to +20°C (equivalent to the fourth specified temperature) if approximately 1 / 3 of the waste heat from combustion exhaust gas was allocated to the amount of heat from digested sludge heating and no increase in greenhouse gases was caused by heating.

[0031] Taking these factors into consideration, it was suggested that heating the digested sludge to be coagulated and dewatered to a temperature of +20°C (corresponding to the fourth specified temperature) up to a maximum of 70°C (corresponding to the third specified temperature) would improve the dewaterability and reduce the moisture content of the dewatered sludge.

[0032] (4) Model treatment plant In order to calculate the heat usage and greenhouse gas emissions when the above-mentioned heat treatment of thickened excess sludge, heat treatment of the digester, and heat treatment of digested sludge are carried out, a "model treatment plant" was constructed based on a sewage treatment plant with a daily treatment capacity of 50,000 tons. In this case, the model treatment plant was constructed based on the most general process considered from sewerage statistics, "Sewerage Construction Planning and Design Guidelines and Commentary", etc.

[0033] FIG. 5 is an explanatory diagram of the model treatment plant. The model treatment plant in FIG. 5 is assumed to be a sewage treatment plant that does not carry out the above-mentioned heat treatment of thickened excess sludge, heat treatment in the digester, and coagulation and dehydration treatment.

[0034] The sludge treatment system 100 of the model treatment plant comprises a sedimentation tank (primary sedimentation tank) 101, a reaction tank 102, a sedimentation tank (final sedimentation tank) 103, a thickening equipment (gravity type) 104, a thickening equipment (mechanical type) 105, a first heat exchanger 106, a digester 107, a second heat exchanger 108, a third heat exchanger 109, a generator 110, a waste heat boiler 111, and a sludge dewatering machine 112.

[0035] In the sludge treatment system 100 of the model treatment plant, sewage is treated by the standard activated sludge process, and primary sludge withdrawn from the primary sedimentation obtained in a settling tank 101 and excess sludge withdrawn from the final sedimentation obtained in a settling tank 103 after a reaction in a reaction tank 102 are thickened and mixed to produce thickened sludge, which is then fed into a digester tank 107 for anaerobic digestion. The generated digester gas is used as fuel to generate gas-fired electricity, and the generated combustion exhaust gas waste heat is used to heat the digester tank 107 via a waste heat boiler 111 and a second heat exchanger 108.

[0036] In this case, the digestion temperature in the digester 107 is 36°C, and the gas generation rate is 564 Nm 3 / t-VS, digestion rate was assumed to be 65.4%. In addition, the digested sludge withdrawn from the digestion tank 107 was dewatered by adding a flocculant (polyferric sulfate and polymer flocculant). Furthermore, the total solids (TS) of the digested sludge was 1.88% and the amount of dewatered sludge was 22.83 t / day.

[0037] (5) Calculation of heat and greenhouse gas emissions The results of each experiment, namely (A) heat treatment of thickened excess sludge, (B) heat treatment in the digester, and (C) heat treatment of digested sludge (coagulation and dehydration treatment), were applied to the model treatment plant shown in Figure 5, and the amount of heat and greenhouse gas emissions were calculated.

[0038] In this case, the amount of heat was calculated by calculating the amount of waste heat from the combustion exhaust gas, the amount of heat for heating the excess sludge and the amount of heat for heating the digested sludge were calculated by calculating the amount of heat used to heat the sludge, and the amount of heat for heating the digester tank was calculated as the sum of the amount of heat used to heat the sludge and the amount of heat dissipated from the digester tank.

[0039] Greenhouse gas emissions are calculated based on the following items [1] to [4] in accordance with the "Guidelines for Sewage Sludge Energy Technology": 2 The amount of emissions was calculated as [1] Emissions associated with the consumption of energy, such as electricity and fuel [2] Emissions from each treatment process during the operation of the facility [3] Emissions from drinking water, industrial water, and pharmaceutical consumption [4] Reducing emissions through effective use of sewerage resources

[0040] First, [1] we will explain emissions associated with the consumption of energy such as electricity and fuel. For "[1] Emissions associated with the consumption of energy, such as electricity and fuel," calculate the "quantity of waste heat from the combustion exhaust gas of the gas generator, Q" and the "quantity of heat q required for heating each of (A) the heating treatment of the concentrated excess sludge, (B) the heating treatment of the digester, and (C) the heating treatment of the digested sludge (flocculation and dehydration treatment)." And when q < Q, the heating for each of (A) heat treatment of concentrated excess sludge, (B) heat treatment of the digester, and (C) heat treatment of digested sludge (coagulation and dewatering treatment) can be covered by the waste heat energy of the combustion exhaust gas. In this case, "use of electricity provided by others" (purchasing electricity) is not involved, and the CO 2 emission amount is 0.

[0041] Also, when q > Q, the amount of waste heat of the combustion exhaust gas required for heating each of (A) heat treatment of concentrated excess sludge, (B) heat treatment of the digester, and (C) heat treatment of digested sludge (coagulation and dewatering treatment) is insufficient. In this case, assuming that the shortage (q - Q) is compensated by purchasing electricity, the CO 2 emission amount was calculated using the following formula (1).

[0042] CO 2 emission amount [kg-CO 2 / year] = 0.587 [kg-CO 2 / kWh] × (q - Q) [MJ / h] × 24 × 365 ÷ 3.6... Formula (1)

[0043] Next, [2] The emissions from each treatment process associated with the operation of the facility will be described. "Emissions from each treatment process associated with the operation of [2] the facility" are assumed to incinerate dewatered sludge, and using the following formulas (2) and (3), the CO 2 emission amount was calculated from the amount of dewatered sludge using Formula (4).

[0044] CH 4 emission amount [kg-CH 4 / year] = 0.0097 [kg-CH 4 / wet-t] × amount of dewatered sludge (wet) [t / day] × 365... Formula (2)

[0045] N 2 O emission amount [kg-N 2 O / year] = 1.11 [kg-N 2 O / wet-t] × amount of dewatered sludge (wet) [t / day] × 365... Formula (3)

[0046] CO 2 Emissions [kg-CO 2 / year] =CH 4 Emissions [kg-CH 4 / year]×25 +N 2 O emissions [kg-N 2 O / year]×298 ……Formula (4)

[0047] Next, [3] we will explain emissions associated with the consumption of drinking water, industrial water, and chemicals. [3] Emissions from consumption of drinking water, industrial water, and chemicals are calculated by using the following equations (5) to (7) to calculate CO emissions from digested sludge TS, assuming that polyferric sulfate and polymer coagulants are used for sludge dewatering. 2 Emissions were calculated.

[0048] Polyferric sulfate CO 2 Emissions [kg-CO 2 / year] =0.0308[kg-CO 2 / kg] ×Polyferric sulfate injection amount [kg / day] × 365 ……Equation (5)

[0049] Polymer flocculant CO 2 Emissions [kg-CO 2 / year] = 6.5 [kg-CO 2 / kg] × Polymer coagulant injection amount [kg / day] × 365 …… Equation (6)

[0050] CO 2 Emissions [kg-CO 2 / year] = Polyferric sulfate CO 2 emissions +CO of polymer flocculant 2 Emission amount...Equation (7)

[0051] [4] Reduction of emissions through effective use of sewage resources is calculated using Equation (8) assuming that the electricity generated by digester gas power generation will be used within the facility, thereby reducing the corresponding amount of "electricity supplied by others" (purchased electricity). 2 The amount of reduction was calculated. CO 2 Reduction [kg-CO 2 / year] =0.587[kg-CO 2 / kWh] × Digestion gas power generation amount [kWh / day] × 365……Equation (8)

[0052] FIG. 6 is a diagram illustrating the relationship between the amount of waste heat from the combustion exhaust gas and the amount of waste heat consumed during heating. Figure 7 shows the CO 2 FIG. 1 is an explanatory diagram of emission reduction amounts. In FIG. 7, CO 2 Emissions reductions are expressed as negative values.

[0053] (A) As a heat treatment for thickened excess sludge, the excess sludge is heated to 50°C. The thickened excess sludge is heated to 50°C, and the gas generation rate of the thickened sludge in the digester is 12 Nm 3 By increasing / t-VS, the amount of digestion gas generated is increased by 117m 3 / day, and as shown in Figure 6, the amount of waste heat from the combustion exhaust gas increased by 39 MJ / h.

[0054] On the other hand, the amount of heat required to heat the thickened excess sludge was 441 MJ / h, as shown in Figure 6. However, because the thickened excess sludge was heated in advance, the amount of heat required to heat the digester decreased by 441 MJ / h, and the total amount of heat consumed did not change.

[0055] As a result of the increase in digestion gas generation, the amount of electricity generated increased by 238 kWh / day, and as shown in Figure 7, this resulted in a reduction in the amount of CO 2 Emissions are 50,000 kg-CO 2 / year decrease. As the digestion rate increased by 1.2 points, the TS of the digested sludge decreased by 0.05 points, and the amount of dewatered sludge decreased by 0.57 t / day, the amount of polyferric sulfate injected decreased by 19 kg / day, and the amount of polymer coagulant injected decreased by 2 kg / day.

[0056] In addition, as shown in Figure 7, the amount of CO in [2] decreases with the decrease in the amount of dewatered sludge. 2 Emissions amount to 70,000 kg-CO 2 / year. The reduction in the amount of coagulant injected has led to a decrease in the amount of CO 2 Emissions are 10,000 kg-CO 2 / year decrease.

[0057] (A) By heating the excess sludge to 50°C as a heat treatment for thickened excess sludge, the amount of digestion gas generated increases and the volume of dewatered sludge decreases without increasing the amount of heat required for heating. As shown in Figure 7, the amount of CO emitted from the sludge treatment process is reduced. 2 Total emissions of 130,000 kg-CO 2 / year reduction could be achieved.

[0058] (B) As a heat treatment for the digester, the digester is heated to 44°C, and the gas generation rate of the thickened sludge in the digester is 55Nm 3 By increasing / t-VS, the amount of digestion gas generated is increased by 537 m 3 / day, and as shown in Figure 6, the amount of waste heat from the combustion exhaust gas increased by 180 MJ / h.

[0059] On the other hand, the amount of heat required to heat the digester to 44°C increased by 442 MJ / h, and the total heat consumption became 1220 MJ / h, as shown in Figure 6. However, this amount could be covered by the waste heat of the combustion exhaust gas of 2020 MJ / h.

[0060] As a result of the generation of digester gas, the amount of electricity generated increased by 1,089 kWh / day, and as shown in Figure 7, this resulted in a reduction in the amount of CO 2 Emissions: 240,000 kg-CO 2 The digestion rate increased by 5.6 points, which resulted in a 0.22 point decrease in the TS of the digested sludge, and a 2.68 t / day decrease in the amount of dewatered sludge, 87 kg / day decrease in the amount of polyferric sulfate injected, and 11 kg / day decrease in the amount of polymer coagulant injected. As shown in Figure 7, the reduction in the amount of dewatered sludge resulted in a reduction in the amount of CO 2 Emissions: 320,000 kg-CO 2 / year decrease.

[0061] As shown in Figure 7, the reduction in the amount of coagulant injected resulted in a decrease in the amount of CO 2 Emissions: 30,000 kg-CO 2 / year decrease.

[0062] (B) By heating the digester to 44°C, the heat required to heat the digester increases by 442 MJ / h, but this can be met by the waste heat from the combustion exhaust gas. 2 There is no increase in emissions.

[0063] On the other hand, by applying 44°C heating to the digester, the amount of digestion gas generated increases and the amount of dewatered sludge decreases, so as shown in Figure 7, the amount of CO emitted from the sludge treatment process is reduced. 2 Total emissions of 590,000 kg-CO 2 / year reduction could be achieved.

[0064] (C) By applying +20°C heating to the digested sludge, the digested sludge was heated to +20°C, 56°C, and coagulated and dehydrated, and the moisture content of the dehydrated sludge decreased by 1.5 percentage points, resulting in a reduction in the amount of dehydrated sludge by 1.83 t / day. As shown in Figure 6, the amount of heat required to heat the digested sludge to +20°C was 650 MJ / h.

[0065] As shown in Figure 6, the total heat consumption was 1,428 MJ / h, including the 778 MJ / h required to heat the digester to 36°C. However, this amount could be covered by the 1,840 MJ / h waste heat from the combustion exhaust gas. As shown in Figure 7, the reduction in the amount of dewatered sludge reduces CO emissions by [2]. 2 Emissions: 220,000 kg-CO 2 / year decrease.

[0066] (C) By applying +20°C heating to the digested sludge, the amount of heat required to heat the digested sludge increases by 650 MJ / h as shown in Figure 6. However, this can be met by the waste heat from the combustion exhaust gas. As shown in Figure 7, the CO reduction in [1] 2 There is no increase in emissions. On the other hand, the amount of dewatered sludge is reduced, so CO emissions from the sludge treatment process are reduced.2 As shown in Figure 7, the total emissions are 220,000 kg-CO 2 / year reduction could be achieved.

[0067] (6) The total amount of heat generated by (A) the heating treatment of thickened excess sludge, (B) the heating treatment of the digester, and (C) the heating treatment of digested sludge (flocculation and dehydration treatment). FIG. 8 is a diagram illustrating the relationship between the amount of waste heat from combustion exhaust gas and the total amount of heating heat associated with a combination of heat treatments using the waste heat from combustion exhaust gas. Figure 8 shows the total amount of waste heat from combustion exhaust gas, the total amount of heating heat, and the difference between them when (A) heating treatment of thickened excess sludge, (B) heating treatment in the digester, and (C) heating treatment of digested sludge (flocculation and dehydration treatment) are carried out in combination.

[0068] Figure 9 shows the total amount of heat generated by the combination of the waste heat from combustion exhaust gas and the heat treatment using the waste heat from combustion exhaust gas, and the amount of CO 2 FIG. 2 is an explanatory diagram of the relationship between the amount of emission reduction and In Figure 8, the difference is smaller in the right column, which indicates that waste heat is being used effectively. Figure 8 shows that waste heat can be used to simultaneously carry out (A) heating treatment of thickened excess sludge, (B) heating treatment in the digester, and (C) heating treatment of digested sludge (coagulation and dehydration treatment). In this case, as shown in Figure 9, 940,000 kg-CO 2 It has been suggested that this could reduce greenhouse gas emissions by 100% per year.

[0069] In this case, the amount of waste heat from the combustion exhaust gas is an estimated value under specific conditions, and if the amount of concentrated sludge or sludge concentration (TS) input into the digester tank decreases due to seasonal fluctuations or other reasons, it is expected to fall below the total amount of heating heat.

[0070] Therefore, in the embodiment, the amount of waste heat is calculated based on the process value of the sludge treatment process, and (A) heating treatment of concentrated excess sludge, (B) heating treatment of the digester tank, and (C) heating treatment of digested sludge (coagulation and dehydration treatment) are carried out in a combination that results in the total amount of heating heat being less than the amount of waste heat and minimizing the difference, thereby making it possible to effectively utilize the waste heat and reduce greenhouse gas emissions.

[0071] FIG. 10 is an explanatory diagram of the control process of the sludge treatment system according to the embodiment. FIG. 11 shows the CO 2 FIG. 11 is an explanatory diagram of a calculation process of a reduction amount. Hereinafter, the operation of the sludge treatment system 10 of the embodiment will be described with reference to FIGS.

[0072] The thickening equipment (gravity type) 11 of the sludge treatment system 10 of the embodiment treats sewage using a standard activated sludge process, and performs gravity thickening on the primary sedimentation sludge extracted from the primary sedimentation obtained in the first sedimentation tank, supplying the resulting thickened primary sedimentation sludge to the thickened sludge tank 17.

[0073] In addition, the thickening equipment (mechanical) 12 reacts the sewage discharged from the first sedimentation tank in a reaction tank, and then mechanically thickens the final sedimentation sludge extracted from the final sedimentation obtained in the second sedimentation tank, and supplies the resulting thickened excess sludge to the thickened sludge tank 17.

[0074] The thickened sludge tank 17 stores the thickened primary sludge supplied from the thickening equipment 11 and the thickened excess sludge supplied from the thickening equipment 12, and supplies them to the digestion tank 20.

[0075] The digester 20 treats the thickened sludge supplied from the thickened sludge tank 17 with microorganisms under anaerobic conditions with little oxygen, and digests the sludge by decomposing it into digester gas containing methane gas, carbon dioxide, etc. through methane fermentation. The digester gas is then supplied to a gas generator 26 via a digester gas flow meter 25.

[0076] The gas generator 26 generates electricity by driving a gas engine using the digestion gas supplied from the digester 20. At this time, the digestion gas flow meter 25 detects the flow rate of digestion gas such as methane gas generated by digestion in the digestion tank 20, and outputs a third flow rate detection signal F3 to the system controller .

[0077] Further, the combustion exhaust gas thermometer 27 detects the temperature of the combustion exhaust gas from the gas generator 26 and outputs the exhaust gas temperature T5 to the system controller . As a result, the system controller 38 functions as a first calculation unit, and calculates the amount of waste heat from the combustion exhaust gas based on the flow rate of the digestion gas and the temperature of the combustion exhaust gas from the gas generator 26, as shown in FIG. 10 (step S11).

[0078] The waste heat boiler 28 is supplied with the combustion exhaust gas generated in the gas generator 26, and recovers heat to generate water for heating. The heating water produced by the waste heat boiler 28 is supplied to a pump 29, which supplies the heating water produced by the waste heat boiler 28 to the first heat exchanger 13, the second heat exchanger 22, and the third heat exchanger 32.

[0079] The first heat exchanger 13 performs heat exchange to heat the thickened excess sludge with hot water from the waste heat boiler .

[0080] At this time, the first thickened excess sludge thermometer 16 measures the temperature of the thickened excess sludge supplied from the thickening equipment 12 and outputs a first thickened excess sludge temperature signal T1 to the system controller 38. Similarly, the second thickened excess sludge thermometer 18 measures the temperature of the thickened excess sludge supplied from the thickening equipment 12 and after it has been heated by the first heat exchanger 13, and outputs a second thickened excess sludge temperature signal T2 to the system controller 38. As a result, the system controller 38 functions as a second calculation unit and calculates the excess sludge heating heat quantity in the heating treatment of the thickened excess sludge, as shown in Figure 10, based on the first thickened excess sludge temperature signal T1 and the second thickened excess sludge temperature signal T2 (step S12).

[0081] In addition, the thickened sludge thermometer 19 measures the temperature of the thickened sludge (= thickened primary settling sludge and thickened excess sludge) supplied from the thickened sludge tank 17 to the digester tank 20, and outputs the thickened sludge temperature T3 to the system controller . The digester thermometer 21 measures the temperature inside the digester 20 and outputs the digester temperature T4 to the system controller 38. As a result, the system controller 38 functions as a second calculation unit and calculates the amount of heat required to heat the digester in the heating treatment of the digester (B) as shown in Figure 10, based on the thickened sludge temperature T3 and the digester temperature T4 (step S13).

[0082] Furthermore, the digested sludge thermometer 35 detects the temperature of the digested sludge heated by the third heat exchanger 32 and outputs the digested sludge temperature T6 to the system controller 38. As a result, the system controller 38 functions as a second calculation unit and calculates the amount of heat required to heat the digested sludge in the heating treatment (coagulation and dehydration treatment) of the digested sludge (C) based on the digestion tank temperature T4 and the digested sludge temperature T6, as shown in Figure 10 (step S14).

[0083] As a result, the system controller 38 functions as a control unit and controls the heating and heating temperature by at least one of the heat exchangers (heating units) among the first heat exchanger 13, the second heat exchanger 22, and the third heat exchanger 32, so that the total amount of heating heat required by the first heat exchanger 13 functioning as the first heating unit, the second heat exchanger 22 functioning as the second heating unit, and the third heat exchanger 32 functioning as the third heating unit for (A) heating treatment of concentrated excess sludge, (B) heating treatment of the digester tank, and (C) heating treatment of digested sludge (coagulation and dehydration treatment) is less than the amount of waste heat from the combustion exhaust gas (step S15).

[0084] That is, when (A) performing heating treatment of thickened excess sludge, the system controller 38 controls the opening of the first valve 15 using a valve control signal VC1 based on the first thickened excess sludge temperature signal T1 from the first thickened excess sludge thermometer 16, the second thickened excess sludge temperature signal T2 from the second thickened excess sludge thermometer 18, and the first flow rate detection signal F1 from the first flow meter 14, and adjusts the flow rate of hot water supplied from the waste heat boiler 28 to the first heat exchanger 13, thereby controlling the heating temperature of the thickened excess sludge by the first heat exchanger 13.

[0085] Similarly, (B) when performing heating treatment of the digester tank, the opening of the second valve 24 is controlled by a valve control signal VC2 based on the digester tank temperature T4 from the digester tank thermometer 21 and the second flow rate detection signal F2 from the second flow meter 23, and the flow rate of hot water supplied from the waste heat boiler 28 to the second heat exchanger 22 is adjusted, thereby controlling the heating temperature of the digester tank 20 by the second heat exchanger 22.

[0086] In addition, when (C) heating treatment (coagulation and dehydration treatment) of digested sludge is performed, the opening of the fourth valve 34 is controlled by a valve control signal VC4 based on the digested sludge temperature T6 from the digested sludge thermometer 35 and the fifth flow detection signal F5 from the fourth flow meter 33, and the flow rate of hot water supplied from the waste heat boiler 28 to the third heat exchanger 32 is adjusted, thereby controlling the heating temperature of the digested sludge by the third heat exchanger 32.

[0087] In parallel with the above processing, the system controller 38 calculates the amount of carbon dioxide emissions in the above-mentioned "[1] Emissions associated with energy consumption such as electricity, fuel, etc." based on the amount of waste heat from the combustion exhaust gas calculated in step S11 of Figure 10, the amount of heat from heating the excess sludge calculated in step S12, the amount of heat from heating the digester tank calculated in step S13, and the amount of heat from heating the digested sludge calculated in step S14 (step S21 of Figure 11).

[0088] Similarly, the system controller 38 calculates the amount of carbon dioxide emissions in the above-mentioned "[2] Emissions from each treatment process associated with the operation of the facility" based on the dewatered sludge volume (t / day), which is the actual sludge treatment result (step S22 in Figure 11).

[0089] Furthermore, the system controller 38 calculates the amount of carbon dioxide emissions in the above-mentioned "[3] Emissions associated with the consumption of drinking water, industrial water, and chemicals" based on the dewatered sludge volume (t / day), which is the actual result of sludge treatment (step S23 in Figure 11).

[0090] Furthermore, the system controller 38 calculates the amount of carbon dioxide emissions reduced in the above-mentioned "[4] Reducing emissions through effective use of sewerage resources" based on the amount of digestive gas electricity generated (kWh / day) in the gas generator 26 (step S24 in Figure 11).

[0091] Then, the system controller 38 subtracts the amount of carbon dioxide emission reduction calculated in step S24 from the sum of the amounts of carbon dioxide emission calculated in steps S21 to S23 to obtain the effective annual carbon dioxide emission (unit: kg-CO 2 / year) is calculated (step S25 in FIG. 11).

[0092] It is then possible to visually present this information to the operator of the sludge treatment system 10. Furthermore, according to the sludge treatment system of the embodiment, control is performed to minimize the difference between the amount of waste heat generated by gas-fired power generation using digestion gas generated by digesting sludge, the amount of heat used to heat concentrated excess sludge to a first predetermined temperature using this waste heat, the amount of heat used to heat the digester tank to a second predetermined temperature, and the total amount of heat used to heat the digested sludge until the temperature of the digested sludge is below a third predetermined temperature and the temperature change reaches a fourth predetermined temperature, thereby suppressing the generation of new greenhouse gases due to these heating operations.

[0093] Therefore, according to the sludge treatment system 10 of the embodiment, it is possible to reduce greenhouse gas emissions more than ever before while reliably grasping the effective utilization of the waste heat from the combustion exhaust gas generated in the digestion gas power generation.

[0094] The system controller of the sludge treatment system of this embodiment is equipped with a control device such as a CPU, a storage device such as a ROM (Read Only Memory) or RAM, an external storage device such as a semiconductor memory device, for example an HDD, a USB memory, or an SSD (Solid State Drive), a display device such as a display device that displays various information, and input devices such as a keyboard and a mouse, and has a hardware configuration that utilizes a conventional computer.

[0095] The program executed by the system controller of this embodiment is provided as a file in an installable or executable format recorded on a computer-readable recording medium such as a USB memory, a semiconductor memory device such as an SSD (Solid State Drive), or a DVD (Digital Versatile Disk).

[0096] The program executed by the system controller of this embodiment may be stored on a computer connected to a network such as the Internet and provided by downloading it via the network. The program executed by the device of this embodiment may be provided or distributed via a network such as the Internet.

[0097] The program for the system controller of this embodiment may be provided in a state where it is pre-installed in a ROM or the like.

[0098] The program executed by the system controller of this embodiment has a modular structure including the above-mentioned units (first calculation unit, second calculation unit, control unit), and in terms of actual hardware, the CPU (processor) reads the program from the above-mentioned storage medium and executes it, thereby loading the above-mentioned units onto the main memory device, and the first calculation unit, second calculation unit, and control unit are generated on the main memory device.

[0099] Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and spirit of the invention, and are included in the scope of the invention and its equivalents described in the claims. [Explanation of symbols]

[0100] 10 Sludge treatment system 11 Concentration equipment 12 Concentration equipment 13 1st heat exchanger 14 1st flow meter 15 First valve 16 First thickened excess sludge thermometer 17 Thickened sludge tank 18 Second thickened excess sludge thermometer 19 Thickened sludge thermometer 20 Digester 21 Digester thermometer 22 Second heat exchanger 23 2nd flow meter 24 Second Valve 25 Digestion gas flow meter 26 Gas Generator 27 Combustion exhaust gas thermometer 28 Waste heat boiler 29 Pump 30 3rd valve 31 3rd flow meter 32 Third heat exchanger 33 4th flow meter 34 4th valve 35 Digested sludge thermometer 36 Sludge coagulation tank 37 Sludge dewatering machine 38 System Controller F1~F5 1st flow rate detection signal~5th flow rate detection signal T1 First thickened excess sludge temperature signal T2 Second thickened excess sludge temperature signal T3 Thickened sludge temperature T4 Digester temperature T5 Exhaust gas temperature T6 Digested sludge temperature VC1~VC4 Valve control signals

Claims

1. A sludge treatment system which: generates sewage treatment and contains concentrated primary sludge and excess sludge, and introduces the concentrated sludge into a digestion tank for anaerobically digesting it; introduces the concentrated sludge into the digestion tank for anaerobically digesting it; generates gas power using the generated digestion gas as fuel; and adds a flocculant to the digested sludge extracted from the digestion tank to flocculate and dehydrate it, and discharges dehydrated sludge; a first heating unit that heats the concentrated excess sludge obtained by concentrating the excess sludge using waste heat from the combustion exhaust gas generated in the gas-fired power generation to a first predetermined temperature; a second heating section that heats the digester tank to a second predetermined temperature using the waste heat from the combustion exhaust gas; a third heating section that heats the digested sludge by using the waste heat from the combustion exhaust gas until the temperature of the digested sludge becomes equal to or lower than a third predetermined temperature and the temperature change of the digested sludge becomes equal to or lower than a fourth predetermined temperature; A first calculation unit that calculates a waste heat amount of the combustion exhaust gas waste heat; a second calculation unit that calculates a heating amount required in each of the first heating unit, the second heating unit, and the third heating unit; a control unit that controls heating and a heating temperature by at least one of the first heating unit to the third heating unit so that a total amount of heating heat required by the first heating unit, the second heating unit, and the third heating unit is less than an amount of waste heat of the combustion exhaust gas; A sludge treatment system comprising:

2. The control unit controls the first heating unit to perform heating at the first predetermined temperature of up to 50° C. The sludge treatment system according to claim 1.

3. The control unit controls the second heating unit to perform heating at the second predetermined temperature within a temperature range of 40° C. to 50° C. The sludge treatment system according to claim 1.

4. The control unit controls the third heating unit so that the third predetermined temperature is a maximum of 70° C. and heating is performed until the fourth predetermined temperature becomes 20° C. The sludge treatment system according to claim 1.

5. A sludge treatment control device controls a sludge treatment system in which thickened sludge, which is generated in sewage treatment and contains thickened primary sludge and excess sludge, is fed into a digestion tank for anaerobically digesting the thickened sludge, the thickened sludge is fed into the digestion tank for anaerobically digesting the thickened sludge, gas power generation is performed using the generated digestion gas as fuel, and a flocculant is added to the digested sludge extracted from the digestion tank to flocculate and dehydrate it, and the dehydrated sludge is discharged, The sludge treatment system includes a first heating unit that heats concentrated excess sludge obtained by concentrating excess sludge using waste heat from combustion exhaust gas generated in the gas-fired power generation to a first predetermined temperature, a second heating unit that heats the digester tank to a second predetermined temperature using the waste heat from combustion exhaust gas, and a third heating unit that heats the digested sludge using the waste heat from combustion exhaust gas until the temperature of the digested sludge is equal to or lower than a third predetermined temperature and the temperature change reaches a fourth predetermined temperature; The sludge treatment control device includes a first calculation unit that calculates an amount of waste heat of the combustion exhaust gas waste heat; a second calculation unit that calculates a heating amount required in each of the first heating unit, the second heating unit, and the third heating unit; a control unit that controls heating and a heating temperature by at least one of the first heating unit to the third heating unit so that a total amount of heating heat required by the first heating unit, the second heating unit, and the third heating unit is less than an amount of waste heat of the combustion exhaust gas; A sludge treatment control device comprising:

6. A sludge treatment method comprising the steps of: feeding concentrated sludge, which is generated in sewage treatment and contains concentrated primary sludge and excess sludge, into a digestion tank for anaerobically digesting the concentrated sludge; feeding the concentrated sludge into the digestion tank for anaerobically digesting the concentrated sludge; generating gas power using the generated digestion gas as fuel; and adding a flocculant to the digested sludge extracted from the digestion tank for flocculation and dehydration, and discharging dehydrated sludge, a first heating step of heating the concentrated excess sludge obtained by concentrating the excess sludge using waste heat from the combustion exhaust gas generated in the gas-fired power generation to a first predetermined temperature; a second heating step of heating the digester tank to a second predetermined temperature using the waste heat from the combustion exhaust gas; a third heating step of heating the digested sludge using the waste heat from the combustion exhaust gas until the temperature of the digested sludge is equal to or lower than a third predetermined temperature and the temperature change of the digested sludge reaches a fourth predetermined temperature; A first calculation step of calculating a waste heat amount of the combustion exhaust gas waste heat; a second calculation step of calculating an amount of heating heat required in each of the first heating step, the second heating step, and the third heating step; a control process for controlling the implementation and heating temperature of at least one of the first heating process to the third heating process so that a total amount of heating heat required in the first heating process, the second heating process, and the entire heating process is less than an amount of waste heat of the combustion exhaust gas; The sludge treatment method comprises:

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