Fly ash circulation type exhaust gas treatment equipment and fly ash circulation type exhaust gas treatment method

Abstract

To provide a fly ash circulation type exhaust gas treatment facility where whole running cost including neutralizing agent cost and fan power cost can be suppressed.SOLUTION: A fly ash circulation type exhaust gas treatment facility 20 comprises: a bag filter 21 where an exhaust gas is introduced; a neutralizing agent feeder 30 feeding a neutralizing agent to an upstream side of the bag filter 21; an induction fan 23 disposed at a downstream side of the bag filter 21; a fly ash circulation device 40 where a part of fly ash containing the unreacted neutralization agent collected by the bag filter 21 is returned to the upstream side of the bag filter 21 and circulated; and a control unit 70 controlling a circulation rate of the fly ash circulated by the fly ash circulation device 40 so that running cost including the agent cost of the neutralizing agent and the fan power cost of the induction fan 23 becomes minimum.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a fly ash circulation type flue gas treatment system and a fly ash circulation type flue gas treatment method in which a part of fly ash collected by a bag filter is returned to the upstream side of the bag filter and circulated. [Background technology]

[0002] The exhaust gas generated when waste materials, etc. are burned in a combustion furnace contains soot and dust. In addition, if the waste materials, etc. being burned contain chlorine (Cl) or sulfur (S) components, the exhaust gas also contains acidic gases, such as hydrogen chloride (HCl) and sulfur oxides (SOx). As a method for removing these acidic gases, a method is known in which the acidic gases are reacted with neutralizing agents, such as hydrated lime or sodium bicarbonate-based agents, to remove them (see, for example, Patent Documents 1 and 2).

[0003] Patent Document 1 discloses an exhaust gas treatment system including a bag filter installed midway through a flue gas flow, a neutralizing agent supplying device that supplies a neutralizing agent to the upstream side of the bag filter, and an induced draft fan installed downstream of the bag filter.

[0004] In the exhaust gas treatment equipment of Patent Document 1, a reaction product is generated by the reaction between the acid gas in the exhaust gas and the neutralizing agent. The reaction product is introduced into a bag filter as fly ash together with the soot and unreacted neutralizing agent in the exhaust gas by the induction action caused by the operation of an induction fan. The introduced fly ash (soot + reaction product + unreacted neutralizing agent) is collected by a filter cloth provided in the bag filter. In this way, the acid gas in the exhaust gas is removed.

[0005] Patent Document 2 discloses an exhaust gas treatment system having the same basic configuration as that of Patent Document 1, which performs a fly ash circulation type exhaust gas treatment method in which fly ash collected by a bag filter is removed from the bottom of the bag filter and a portion of the removed fly ash is returned to the flue on the inlet side of the bag filter. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2017-213499 A [Patent Document 2] JP 2014-24052 A Summary of the Invention [Problem to be solved by the invention]

[0007] In the flue gas treatment equipment of Patent Document 1, the fly ash collected by the bag filter sometimes contains a large amount of unreacted neutralizing agent, and the neutralizing agent is sometimes not used efficiently.

[0008] In the apparatus for carrying out the fly ash circulation type exhaust gas treatment method of Patent Document 2, a part of the fly ash taken out from the bottom of the bag filter is returned to the flue on the bag filter inlet side and circulated, so that the unreacted neutralizing agent contained in the fly ash is subjected to a reaction with the acid gas, and the neutralizing agent can be used efficiently. However, in the apparatus of Patent Document 2, when the pressure loss in the bag filter increases with an increase in the fly ash circulation rate, the power loss of the induced draft fan increases. Therefore, while the chemical cost of the neutralizing agent can be reduced, the fan power cost increases. Conversely, if the circulation rate of the fly ash is reduced, the pressure loss in the bag filter is reduced and the power loss of the induced draft fan can be suppressed, but the utilization efficiency of the neutralizing agent decreases and the chemical cost of the neutralizing agent increases.

[0009] As described above, reduction in the cost of neutralizing agents and reduction in the cost of powering the fan are in a contradictory relationship, but there is a demand for overall economy in terms of the overall running costs, including the cost of neutralizing agents and the cost of powering the fan.

[0010] The present invention has been made in consideration of the above problems, and has an object to provide a fly ash circulation type flue gas treatment system and a fly ash circulation type flue gas treatment method that can reduce overall running costs, including the cost of neutralizing agents and the cost of fan power. [Means for solving the problem]

[0011] The fly ash circulation type flue gas treatment equipment according to the present invention for solving the above problems has the following characteristic configuration: A fly ash circulation type flue gas treatment facility including a bag filter into which exhaust gas is introduced, a neutralizing agent supplying device that supplies a neutralizing agent to the upstream side of the bag filter, an induction fan disposed downstream of the bag filter, and a fly ash circulation device that returns a portion of the fly ash containing the unreacted neutralizing agent captured by the bag filter to the upstream side of the bag filter and circulates the portion, The fly ash circulating device is provided with a control device for controlling a circulation rate of the fly ash circulated by the fly ash circulating device so as to minimize running costs including the chemical cost of the neutralizing chemical and the fan power cost of the induction fan.

[0012] In the fly ash circulation type flue gas treatment equipment of this configuration, the circulation rate of the fly ash circulated by the fly ash circulation device is controlled by the control device so that the running costs, including the cost of the neutralizing agent and the power cost of the induced draft fan, are minimized, so that the overall running costs, including the cost of the neutralizing agent and the power cost of the fan, can be reduced.

[0013] In the fly ash circulation type flue gas treatment equipment according to the present invention, The control device includes: a chemical cost calculation unit that calculates the chemical cost of the neutralizing chemical from the amount of the neutralizing chemical used that is calculated based on the relationship between the acid gas removal rate of the flue gas at a predetermined fly ash circulation rate and the neutralizing chemical equivalent ratio; a fan power cost calculation unit that calculates a fan power cost of the induced draft fan relative to the fly ash circulation rate based on a relationship between a differential pressure coefficient relating to a pressure difference between an inlet side and an outlet side of the bag filter and a fly ash circulation rate; a cost minimum fly ash circulation rate calculation unit that calculates a cost minimum fly ash circulation rate that minimizes the sum of the calculated chemical cost and the fan power cost; a target fly ash circulation rate setting unit for setting the minimum cost fly ash circulation rate to a target fly ash circulation rate; a fly ash circulation rate adjusting unit that adjusts the fly ash circulation rate of the fly ash circulating device so as to approach the target fly ash circulation rate; It is preferred that the compound contains

[0014] In the fly ash circulation type flue gas treatment equipment of this configuration, the chemical cost of the neutralizing agent for the fly ash circulation rate is calculated by the chemical cost calculation unit from the amount of neutralizing agent used, which is calculated based on the relationship between the acid gas removal rate of the flue gas at a predetermined fly ash circulation rate and the neutralizing agent equivalent ratio. This makes it possible to accurately calculate the chemical cost of the neutralizing agent for the fly ash circulation rate. In addition, the fan power cost of the induced draft fan for the fly ash circulation rate is calculated by the fan power cost calculation unit based on the relationship between the fly ash circulation rate and the differential pressure coefficient related to the differential pressure between the inlet side and the outlet side of the bag filter. This makes it possible to accurately calculate the fan power cost of the induced draft fan for the fly ash circulation rate. Then, the minimum cost fly ash circulation rate calculation unit calculates the minimum cost fly ash circulation rate, which minimizes the sum of the calculated chemical cost of the neutralizing agent and the fan power cost of the induced draft fan, and the calculated minimum cost fly ash circulation rate is set as the target fly ash circulation rate by the target fly ash circulation rate setting unit, and the fly ash circulation rate of the fly ash circulation device is adjusted by the fly ash circulation rate adjustment unit so that it approaches the target fly ash circulation rate. This allows the fly ash circulation rate of the fly ash circulation device to reliably approach the target fly ash circulation rate at which the running costs, including the chemical cost of the neutralizing chemical and the fan power cost of the induction fan, are minimized, thereby reliably reducing the overall running costs.

[0015] Next, the characteristic configuration of the fly ash circulation type flue gas treatment method according to the present invention for solving the above problems is as follows: A fly ash circulation type flue gas treatment method including a neutralizing agent supplying step of supplying a neutralizing agent to an upstream side of a bag filter into which exhaust gas is introduced, an exhaust gas introducing step of introducing the exhaust gas containing the neutralizing agent into the bag filter by an induction action of an induction fan provided downstream of the bag filter, and a fly ash circulation step of returning a portion of the fly ash containing the unreacted neutralizing agent collected by the bag filter to the upstream side of the bag filter and circulating the same, In the fly ash circulation step, a fly ash circulation rate control step is carried out to control the circulation rate of the fly ash so that running costs including the chemical cost of the neutralizing chemical and the fan power cost of the induction fan are minimized.

[0016] According to the fly ash circulation type flue gas treatment method of the present configuration, in the fly ash circulation step, a fly ash circulation rate control step is carried out to control the circulation rate of the fly ash so as to minimize the running costs, including the costs of the neutralizing agent and the power costs of the induction fan, so that the overall running costs, including the costs of the neutralizing agent and the power costs of the fan, can be reduced.

[0017] In the fly ash circulation type flue gas treatment method according to the present invention, The fly ash circulation rate control step includes: A chemical cost calculation step of calculating the chemical cost of the neutralizing agent from the amount of the neutralizing agent used that is calculated based on the relationship between the acid gas removal rate of the flue gas at a predetermined fly ash circulation rate and the neutralizing agent equivalent ratio; a fan power cost calculation step of calculating a fan power cost of the induced draft fan with respect to a fly ash circulation rate based on a relationship between a differential pressure coefficient relating to a pressure difference between an inlet side and an outlet side of the bag filter and a fly ash circulation rate; a cost-minimizing fly ash circulation rate calculation step of calculating a cost-minimizing fly ash circulation rate that minimizes the sum of the calculated chemical cost and the fan power cost; a target fly ash circulation rate setting step of setting the cost minimum fly ash circulation rate to a target fly ash circulation rate; a fly ash circulation rate adjusting step of adjusting the fly ash circulation rate so as to approach the target fly ash circulation rate; It is preferred that the compound contains

[0018] According to the fly ash circulation type flue gas treatment method of this configuration, the chemical cost of the neutralizing agent for the fly ash circulation rate is calculated from the amount of neutralizing agent used, which is calculated based on the relationship between the acid gas removal rate of the flue gas at a predetermined fly ash circulation rate and the neutralizing agent equivalent ratio, in the chemical cost calculation step. This allows the chemical cost of the neutralizing agent for the fly ash circulation rate to be accurately calculated. In addition, the fan power cost of the induced draft fan for the fly ash circulation rate is calculated based on the relationship between the fly ash circulation rate and the differential pressure coefficient related to the differential pressure between the inlet side and the outlet side of the bag filter in the fan power cost calculation step. This allows the fan power cost of the induced draft fan for the fly ash circulation rate to be accurately calculated. Then, the minimum cost fly ash circulation rate, which minimizes the sum of the calculated chemical cost of the neutralizing agent and the fan power cost of the induced draft fan, is calculated in the minimum cost fly ash circulation rate calculation step, and the calculated minimum cost fly ash circulation rate is set as the target fly ash circulation rate in the target fly ash circulation rate setting step, and the fly ash circulation rate is adjusted to approach the target fly ash circulation rate in the fly ash circulation rate adjustment step. This allows the fly ash circulation rate to reliably approach the target fly ash circulation rate at which the running costs, including the cost of the neutralizing agent and the power cost of the induction fan, are minimized, thereby making it possible to reliably reduce the overall running costs. [Brief description of the drawings]

[0019] [Figure 1] FIG. 1 is a block diagram showing a schematic configuration of a combustion treatment facility equipped with a fly ash circulation type flue gas treatment system according to one embodiment of the present invention. [Diagram 2] FIG. 2 is a flow chart showing the procedure of a fly ash circulation rate control step carried out by a control device in a fly ash circulation type flue gas treatment facility according to one embodiment of the present invention. [Diagram 3] FIG. 3 is a graph showing the relationship between the acid gas removal rate of the flue gas and the neutralizing agent equivalent ratio at a given fly ash circulation rate. [Figure 4] FIG. 4 is a graph showing the relationship between the differential pressure coefficient and the fly ash circulation rate. [Diagram 5] FIG. 5 is a graph showing the relationship between the total cost of chemicals and the cost of powering the fan and the fly ash circulation rate. [Figure 6] FIG. 6 is a block diagram showing a schematic configuration of a combustion treatment facility equipped with a fly ash circulation type flue gas treatment system according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Hereinafter, the present invention will be described with reference to the drawings. However, the present invention is not intended to be limited to the embodiments described below or the configurations shown in the drawings.

[0021] <Outline of the combustion treatment facility> Fig. 1 is a block diagram showing a schematic configuration of a combustion treatment facility 1 equipped with a fly ash circulation type flue gas treatment system 20 according to one embodiment of the present invention. The combustion treatment facility 1 shown in Fig. 1 includes a combustion furnace 3 for burning materials to be combusted, such as waste materials such as municipal waste and biomass fuels, a boiler 5 to which flue gas generated by combustion in the combustion furnace 3 is introduced, an economizer 7, and a temperature reducing tower 9, and a fly ash circulation type flue gas treatment system 20 for treating the flue gas discharged from the temperature reducing tower 9.

[0022] <Combustion furnace> The type of the combustion furnace 3 is not limited, but examples thereof include a stoker type combustion furnace and a fluidized bed type combustion furnace.

[0023] A stoker-type combustion furnace is a type of combustion furnace in which a stoker placed inside the furnace is moved, combustion air is sent from the bottom of the stoker, and the material to be combusted is dried, combusted, and post-combusted. Here, examples of the stoker include a stepped stoker and a traveling stoker. A stepped stoker is a furnace in which movable grates and fixed grates are alternately arranged in a stepped manner, and a drying stoker that forms a drying stage, a combustion stoker that forms a combustion stage, and a post-combustion stoker that forms a post-combustion stage are divided in order from the upstream side to the downstream side in the direction of feeding the material to be combusted. On the other hand, a traveling stoker is configured by wrapping and mounting an annular grate body, which is made of multiple grates connected in a ring shape so that they can rotate freely, around a driving wheel and a driven wheel that are arranged at a predetermined interval in the direction in which the material to be combusted is moved in the furnace. In a traveling stoker, the annular grate body is driven to move in an orbit, and the material to be combusted from the material to be combusted input device that is received by the annular grate body is moved and combusted on the annular grate body. A fluidized bed combustion furnace is a type of combustion furnace in which pressurized air is dispersed and supplied from the bottom of a layer of particles such as silica sand to fluidize the heat-storing silica sand and burn the material to be combusted within it.

[0024] In the boiler 5, the heat of the exhaust gas is used to generate steam, in the economizer 7, the water to be supplied to the boiler 5 is heated using the residual heat of the exhaust gas, and in the cooling tower 9, the exhaust gas from the economizer 7 is cooled to a predetermined temperature.

[0025] <Fly ash circulation exhaust gas treatment equipment> The fly ash circulation type flue gas treatment equipment 20 includes a bag filter 21 disposed downstream of the exhaust gas flow of the temperature reducing tower 9, an induced draft fan 23 disposed downstream of the exhaust gas flow of the bag filter 21, and a chimney 25 disposed downstream of the exhaust gas flow of the induced draft fan 23. The temperature reducing tower 9, the bag filter 21, the induced draft fan 23, and the chimney 25 are connected to each other by ducts (flues) 11, 13, and 15. In the fly ash circulation type flue gas treatment equipment 20, the exhaust gas from the temperature reducing tower 9 is introduced into the bag filter 21 through the duct 11 by the induction action caused by the operation of the induced draft fan 23, and the exhaust gas after the dust removal treatment in the bag filter 21 is released into the atmosphere through the duct 13, the induced draft fan 23, the duct 15, and the chimney 25.

[0026] <Bug filter> The bag filter 21 is configured by incorporating a required filter cloth into a casing and providing a brush-off device. The inside of the casing is divided into upper and lower parts by a cage plate, and the inside of the casing is partitioned into a pre-filtration exhaust gas chamber below the cage plate and a post-filtration exhaust gas chamber above the cage plate. The pre-filtration exhaust gas chamber is connected to the cooling tower 9 via a duct 11. The post-filtration exhaust gas chamber is connected to an induction fan 23 via a duct 13. The cage plate is provided with a required number of openings for suspending the filter cloth, and the filter cloth is suspended and supported from each opening so as to be disposed in the pre-filtration exhaust gas chamber. The filter cloth is a cylindrical bag body, and one closed end (lower end) is inserted into the pre-filtration exhaust gas chamber, while the other open end (upper end) is disposed facing the post-filtration exhaust gas chamber, and aggregate is incorporated into the filter cloth to maintain its cylindrical shape. The brush-off device is configured to inject compressed air from an air compressor through piping and a required injection nozzle onto the inner surface of the filter cloth to be brushed off (backwashed) when the differential pressure between the inlet and outlet sides of the bag filter 21 reaches or exceeds a predetermined value, or at regular intervals regardless of the value of the differential pressure, thereby blowing off and brushing away the fly ash that has adhered to and accumulated on the outer surface of the filter cloth.

[0027] The fly ash circulation type flue gas treatment facility 20 further includes a neutralizing agent supplying device 30 and a fly ash circulation device 40.

[0028] <Neutralizing agent supply device> The neutralizing agent supplying device 30 is a device that supplies a neutralizing agent to the upstream side of the bag filter 21, and mainly includes a chemical transport pipe 31, a pressure blower 33, a chemical tank 35, and a feeder 37. The chemical transport pipe 31 is connected to the duct 11 on the inlet side of the bag filter 21. The pressure blower 33 generates a forced airflow toward the duct 11 in the chemical transport pipe 31. The chemical tank 35 stores a neutralizing agent (in this example, hydrated lime) such as a hydrated lime or a sodium bicarbonate-based agent for neutralizing acid gas in the exhaust gas. The feeder 37 supplies the neutralizing agent stored in the chemical tank 35 into the chemical transport pipe 31.

[0029] In the neutralizing drug supply device 30, a forced airflow is generated in the drug transport pipe 31 by operating the pressure blower 33, while the neutralizing drug stored in the drug tank 35 is supplied into the drug transport pipe 31 by the feeder 37, so that the forced airflow in the drug transport pipe 31 blows the neutralizing drug into the duct 11 on the inlet side of the bag filter 21, and the neutralizing drug can be supplied to the upstream side of the bag filter 21.

[0030] <Fly ash circulation device> The fly ash circulation device 40 is a device that returns a portion of the fly ash containing unreacted neutralizing agent captured by the bag filter 21 to the upstream side of the bag filter 21 and circulates it, and is mainly equipped with a discharge conveyor 41, a sorting conveyor 45, and a fly ash supply section 50.

[0031] The discharge conveyor 41 discharges the fly ash stored at the bottom of the casing of the bag filter 21. The sorting conveyor 45 sorts the fly ash discharged from the bag filter 21 by the discharge conveyor 41 to one end side and the other end side of the discharge conveyor 41, and sends a part of the fly ash to the fly ash supply section 50 via the delivery pipe 17 connected to one end side of the discharge conveyor 41, and discharges the remainder to the outside of the system via the discharge pipe 19 connected to the other end side of the discharge conveyor 41.

[0032] The fly ash supplying section 50 is a device for supplying fly ash to the upstream side of the bag filter 21, and mainly includes a fly ash transport pipe 51, a pressure blower 53, a fly ash tank 55, and a feeder 57. The fly ash transport pipe 51 is connected to the duct 11 on the inlet side of the bag filter 21 at a position downstream of the exhaust gas flow from the position where the chemical transport pipe 31 is connected. The pressure blower 53 generates a forced air current toward the duct 11 in the fly ash transport pipe 51. The fly ash tank 55 introduces and stores the fly ash sent from the sorting conveyor 45 through the delivery pipe 17. The feeder 57 supplies the fly ash stored in the fly ash tank 55 into the fly ash transport pipe 51.

[0033] In the fly ash supply section 50, a forced airflow is generated in the fly ash transport pipe 51 by the operation of a pressure blower 53 while the fly ash stored in the fly ash tank 55 is supplied into the fly ash transport pipe 51 by a feeder 57. The forced airflow in the fly ash transport pipe 51 blows the fly ash into the duct 11 on the inlet side of the bag filter 21, so that the fly ash can be supplied to the upstream side of the bag filter 21.

[0034] The fly ash circulation type flue gas treatment equipment 20 further includes an inlet side acid gas concentration meter (continuous analyzer) 61, an outlet side acid gas concentration meter (continuous analyzer) 63, an inlet side pressure gauge 65, an outlet side pressure gauge 67, and an exhaust gas flow meter 69. The inlet side acid gas concentration meter 61 measures the concentration of acid gas (HCl, SOx, etc.) in the exhaust gas flowing in the duct 11 on the inlet side of the bag filter 21, upstream of the position where the chemical transport pipe 31 is connected in the duct 11. The outlet side acid gas concentration meter 63 measures the concentration of acid gas in the exhaust gas flowing in the duct 13 on the outlet side of the bag filter 21. The inlet side pressure gauge 65 measures the pressure on the inlet side of the bag filter 21. The outlet side pressure gauge 67 measures the pressure on the outlet side of the bag filter 21. The exhaust gas flow meter 69 measures the flow rate of the exhaust gas flowing in the duct 13 on the outlet side of the bag filter 21.

[0035] <Control device> The fly ash circulation type flue gas treatment facility 20 further includes a control device 70 for controlling the circulation rate of the fly ash circulated by the fly ash circulation device 40. The control device 70 is mainly composed of a computer capable of controlling the fly ash circulation device 40, and by executing a predetermined program, the control device 70 performs the functions of a chemical cost calculation unit 71, a fan power cost calculation unit 73, a cost minimum fly ash circulation rate calculation unit 75, a target fly ash circulation rate setting unit 77, and a fly ash circulation rate adjustment unit 79.

[0036] In the fly ash circulation type flue gas treatment equipment 20 in the combustion treatment facility 1 configured as described above, the neutralizing agent stored in the chemical tank 35 is supplied to the chemical transport pipe 31 by the feeder 37 while the forced airflow is generated in the chemical transport pipe 31 by the operation of the pressure blower 33, so that the neutralizing agent is blown into the duct 11 on the inlet side of the bag filter 21 by the forced airflow in the chemical transport pipe 31. The neutralizing agent blown into the duct 11 reacts with the acid gas in the exhaust gas. The reaction product generated by the reaction between the acid gas and the neutralizing agent is introduced into the bag filter 21 as fly ash together with the soot and unreacted neutralizing agent in the exhaust gas by the induction action caused by the operation of the induction fan 23. The introduced fly ash (soot + reaction product + unreacted neutralizing agent) is collected by the filter cloth provided in the bag filter 21. In this way, the acid gas in the exhaust gas is removed.

[0037] In the bag filter 21, when the pressure difference between the inlet side and the outlet side becomes equal to or exceeds a predetermined value, or at regular intervals regardless of the pressure difference, the brushing device operates to brush off the fly ash that has adhered to and accumulated on the outer surface of the filter cloth. The brushed-off fly ash is stored in the bottom of the casing of the bag filter 21. The fly ash stored in the bottom of the bag filter 21 is discharged by the discharge conveyor 41. The discharged fly ash is distributed by the distribution conveyor 45 to one end side and the other end side of the distribution conveyor 45. Then, a part of the fly ash is sent to the fly ash supply section 50 through the delivery pipe 17 connected to one end side of the distribution conveyor 45, and the remaining part is discharged to the outside of the system through the discharge pipe 19 connected to the other end side of the distribution conveyor 45.

[0038] The fly ash sent out from one end of the sorting conveyor 45 through the delivery pipe 17 is introduced into the fly ash tank 55 in the fly ash supply section 50 and temporarily stored therein. The fly ash stored in the fly ash tank 55 is fed into the fly ash transport pipe 51 by the feeder 57. The fly ash fed into the fly ash transport pipe 51 is blown into the inlet duct 11 of the bag filter 21 by the forced airflow generated in the fly ash transport pipe 51 by the operation of the pressure blower 53, and is fed to the upstream side of the bag filter 21. In this way, a part of the fly ash taken out from the bottom of the bag filter 21 is returned to the inlet duct of the bag filter 21 for circulation, so that the unreacted neutralizing agent contained in the fly ash is subjected to a reaction with the acid gas, and the neutralizing agent can be efficiently used.

[0039] The control device 70 controls the circulation rate of the fly ash circulated by the fly ash circulation device 40. Here, the fly ash circulation rate is the ratio of the amount of recirculated fly ash to the amount of fly ash totaling the soot generated by the combustion in the combustion furnace 3, the neutralizing agent supplied by the neutralizing agent supply device 30, and the increase due to the neutralization reaction. That is, if the amount of fly ash totaling the soot generated by the combustion in the combustion furnace 3, the neutralizing agent supplied into the duct 11 through the agent transport pipe 31, and the increase due to the neutralization reaction between the supplied neutralizing agent and the acid gas is a, and the amount of fly ash supplied into the duct 11 through the fly ash transport pipe 51 is b, the fly ash circulation rate is calculated as b / a × 100 (%). Hereinafter, the procedure of the fly ash circulation rate control process performed by the control device 70 will be described in detail.

[0040] FIG. 2 is a flow chart showing the procedure of the fly ash circulation rate control process performed by the control device 70 in the fly ash circulation type flue gas treatment equipment 20 according to one embodiment of the present invention. In FIG. 2, the symbol "S" represents a step. FIG. 3 is a graph showing the relationship between the acid gas removal rate of the flue gas and the neutralizing agent equivalent ratio at a predetermined fly ash circulation rate. In the graph of FIG. 3, the value of the equivalence ratio on the vertical axis and the value of the acid gas removal rate on the horizontal axis increase as they proceed in the direction of the arrows. A predetermined program for executing the procedure shown in the flow chart of FIG. 2 and data related to the graph of FIG. 3 are stored in advance in the memory of the control device 70 and are read out as necessary when performing calculations, etc. In addition, the data related to the graph of FIG. 3 is automatically updated periodically based on the actual operating data of the fly ash circulation type flue gas treatment equipment 20.

[0041] <Step S1: Drug cost calculation process> In step S1 of the flow chart in Fig. 2, the chemical cost calculation unit 71 calculates the chemical cost of the neutralizing chemical (slaked lime in this example) for the fly ash circulation rate from the amount of neutralizing chemical used, which is calculated based on the relationship between the acid gas removal rate of the exhaust gas at a predetermined fly ash circulation rate and the neutralizing chemical equivalent ratio, as shown in the graph in Fig. 3. That is, when the HCl removal rate calculated from the concentration of the acid gas (HCl) measured by the inlet acid gas concentration meter 61 and the concentration of the acid gas (HCl) measured by the outlet acid gas concentration meter 63 is k%, the neutralizing chemical equivalent ratio for the fly ash circulation rate is calculated from the graph in Fig. 3. An example of the neutralizing chemical equivalent ratio for each fly ash circulation rate is shown in Table 1.

[0042] [Table 1]

[0043] The amount of slaked lime used is calculated using a prescribed formula based on the equivalence ratio shown in Table 1, the HCl concentration and SOx concentration measured by the inlet acid gas concentration meter 61, the gas volume measured by the exhaust gas flow meter 69, etc., and the chemical cost is calculated from the calculated amount of slaked lime used and the chemical unit price. An example of the calculation result is shown in Table 2.

[0044] [Table 2]

[0045] In this way, the cost of the neutralizing agent for the fly ash circulation rate is calculated by the agent cost calculation unit 71 from the amount of neutralizing agent used, which is determined based on the relationship between the acid gas removal rate of the flue gas at a specified fly ash circulation rate and the neutralizing agent equivalent ratio, so that the cost of the neutralizing agent for the fly ash circulation rate can be accurately determined.

[0046] Fig. 4 is a graph showing the relationship between the differential pressure coefficient and the fly ash circulation rate. In the graph of Fig. 4, the value of the differential pressure coefficient on the vertical axis and the value of the fly ash circulation rate on the horizontal axis increase in the direction of the arrow. Data related to the graph of Fig. 4 is pre-stored in the memory of the control device 70 and is read out as necessary when performing calculations, etc. In addition, the data related to the graph of Fig. 4 is automatically updated periodically based on the actual operating data of the fly ash circulation type flue gas treatment equipment 20.

[0047] The differential pressure coefficient on the vertical axis of the graph shown in Figure 4 is the pressure difference between the inlet and outlet sides of the bag filter 21, obtained from the measurement values ​​of the inlet pressure gauge 65 and the outlet pressure gauge 67, divided by the amount of treated gas, i.e., the amount of gas measured by the exhaust gas flow meter 69.

[0048] In the graph of Figure 4, the fly ash circulation rate is R 10 % to R 20 %, the differential pressure coefficient decreases because the fly ash circulation rate increases to R 10 % to R 20 %, the fly ash becomes larger in size and the average particle size becomes larger, so that the resistance to airflow of the fly ash layer on the filter cloth in the bag filter decreases, and the fly ash is easily brushed off from the filter cloth, so that the air permeability of the filter cloth is maintained good. 20%, the differential pressure coefficient increases with an increase in the fly ash circulation rate, because the increased air resistance due to the increased fly ash circulation volume becomes dominant over the reduced air resistance due to the increased average particle size of the fly ash. In this way, the circulation rate and the differential pressure coefficient have a downward convex function relationship with the fly ash circulation rate.

[0049] <Step S2: Fan power cost calculation process> In step S2 of the flowchart in Fig. 2, the fan power cost calculation unit 73 calculates the fan power cost of the induced draft fan 23 based on the relationship between the differential pressure coefficient and the fly ash circulation rate, more specifically, based on the relationship in which the differential pressure coefficient is a downward convex function with respect to the fly ash circulation rate, as shown in the graph in Fig. 4. An example of the calculated differential pressure coefficient with respect to the fly ash circulation rate is shown in Table 3.

[0050] [Table 3]

[0051] Using the differential pressure coefficient shown in Table 3 and the measurement value of the exhaust gas flow meter 69, etc., a specified calculation formula is used. Calculate the fan power cost. An example of the calculation results is shown in Table 4.

[0052] [Table 4]

[0053] In this way, the fan power cost of the induced draft fan 23 for the fly ash circulation rate is calculated by the fan power cost calculation unit 73 on the basis of the relationship between the fly ash circulation rate and the differential pressure coefficient relating to the pressure difference between the inlet and outlet sides of the bag filter 21, so that the fan power cost of the induced draft fan 23 for the fly ash circulation rate can be accurately determined.

[0054] FIG. 5 is a graph showing the relationship between the total cost of chemicals and the cost of powering the fan and the fly ash circulation rate.

[0055] <Step S3: Cost-minimizing fly ash circulation rate calculation process> In step S3 of the flow chart in Fig. 2, the minimum cost fly ash circulation rate calculation unit 75 calculates the minimum cost fly ash circulation rate which minimizes the sum of the calculated chemical cost (see Table 2) and fan power cost (see Table 4). That is, the minimum cost fly ash circulation rate which minimizes the sum of the chemical cost and fan power cost is calculated from an approximation formula obtained based on the relationship shown in the graph in Fig. 5 obtained from the data on the chemical cost and fan power cost (see Table 5) with respect to the fly ash circulation rate. In this example, the minimum cost fly ash circulation rate is R 33 % (see Figure 5).

[0056] [Table 5]

[0057] <Step S4: Target fly ash circulation rate setting process> In step S4 of the flowchart in FIG. 2, the target fly ash circulation rate setting unit 77 sets the cost minimum fly ash circulation rate calculated by the cost minimum fly ash circulation rate calculation unit 75 (in this example, R 33 %) is set as the target fly ash circulation rate.

[0058] <Step S5: Fly ash circulation rate adjustment process> Then, in step S5, the fly ash circulation rate adjusting unit 79 adjusts the fly ash circulation rate of the fly ash circulation device 40 to the target fly ash circulation rate (in this example, R 33 %). That is, the fly ash circulation rate adjusting unit 79 controls the amount of chemical agent delivered by the feeder 57 and / or the amount of chemical agent pumped by the pumping blower 53 by feedback control according to the difference between the target fly ash circulation rate and the current fly ash circulation rate so as to bring the difference closer to zero.

[0059] In this way, the minimum cost fly ash circulation rate which minimizes the sum of the calculated chemical cost of the neutralizing agent and the fan power cost of the induced draft fan 23 is calculated by the minimum cost fly ash circulation rate calculation unit 75, the calculated minimum cost fly ash circulation rate is set as the target fly ash circulation rate by the target fly ash circulation rate setting unit 77, and the fly ash circulation rate of the fly ash circulating device 40 is adjusted by the fly ash circulation rate adjustment unit 79 so as to approach the target fly ash circulation rate. Therefore, the fly ash circulation rate of the fly ash circulating device 40 can be reliably brought close to the target fly ash circulation rate which minimizes the running cost including the chemical cost of the neutralizing agent and the fan power cost of the induced draft fan, so that the overall running cost can be reliably suppressed.

[0060] As shown in the graph in Figure 3, the fly ash circulation rate is R 10 %, R 20 %, R 30 %, R 40 %, the equivalence ratio decreases, so increasing the fly ash circulation rate reduces the chemical cost. On the other hand, as shown in the graph in Figure 4, when the fly ash circulation rate is R 10 % to R 20 %, the differential pressure coefficient decreases and the fly ash circulation rate increases to R 20 %, the differential pressure coefficient increases with the increase in the fly ash circulation rate. In this way, the fly ash circulation rate and the differential pressure coefficient have a downward convex function relationship with respect to the fly ash circulation rate. This is because, with regard to the fan power cost, the differential pressure coefficient increases with the increase in the fly ash circulation rate (in this example, R 10 %~R 40 %), the fly ash circulation rate is minimized at a predetermined value. The present invention appropriately matches the relationship shown in the graph of FIG. 3 with the relationship shown in the graph of FIG. 4, thereby making it possible to reduce the fly ash circulation rate to a low level (for example, R 10 %) and high level values ​​(e.g., R 40 %), the minimum cost fly ash circulation rate (in this example, R 33 This was based on the finding that it is possible to obtain the .

[0061] The fly ash circulation type flue gas treatment equipment and the fly ash circulation type flue gas treatment method of the present invention have been described above based on one embodiment, but the present invention is not limited to the configuration described in the above embodiment, and the configuration can be appropriately changed within the scope of the invention.

[0062] (Another embodiment) Fig. 6 is a block diagram showing a schematic configuration of a combustion treatment facility 1 equipped with a fly ash circulation type flue gas treatment equipment 20 according to another embodiment of the present invention. In the other embodiment shown in Fig. 6, the same or similar parts as those in the embodiment shown in Fig. 1 are simply given the same reference numerals in the figure and detailed description thereof is omitted, and the following description will focus on the parts unique to the other embodiment.

[0063] In the combustion treatment facility 1 shown in Figure 6, the duct 11 is configured by connecting an upstream horizontal duct section 11a, an upstream vertical duct section 11b, a turning duct section 11c, a downstream vertical duct section 11d, and a downstream horizontal duct section 11e in the order listed from the upstream side to the downstream side of the exhaust gas flow.

[0064] <Neutralizing agent supply device> The neutralizing agent supplying device 30 mainly comprises a chemical tank 35 and a feeder 37, and is configured so that the neutralizing agent stored in the chemical tank 35 is supplied to the upstream vertical duct section 11b by the feeder 37, thereby sending the neutralizing agent into the upstream vertical duct section 11b under natural flow, and thereby supplying the neutralizing agent to the upstream side of the bag filter 21.

[0065] <Fly ash circulation device> The fly ash circulating device 40 mainly includes a discharge conveyor 41, a fly ash transport conveyor 46, and a fly ash supply section 50.

[0066] The transfer conveyor 46 is configured to transport the fly ash removed from the bag filter 21 by the discharge conveyor 41 to the fly ash tank 55 in the fly ash supply section 50 via the delivery pipe 17 connected to the transfer conveyor 46 midway along the transport path, and to discharge any fly ash that does not fit into the fly ash tank 55 and overflows therefrom outside the system via the discharge pipe 19 connected to the end of the transfer conveyor 46 in the transport direction.

[0067] The fly ash supplying section 50 mainly includes a fly ash tank 55 and a feeder 57, and is configured so that the fly ash stored in the fly ash tank 55 is supplied to the upstream vertical duct section 11b by the feeder 57, whereby the fly ash is sent into the upstream vertical duct section 11b under gravity flow, and the fly ash can be supplied to the upstream side of the bag filter 21. Here, the supply position of the feeder 57 relative to the upstream vertical duct section 11b is set downstream of the exhaust gas flow from the supply position of the feeder 37 relative to the upstream vertical duct section 11b.

[0068] The other embodiment shown in FIG. 6 described above can also provide the same effects as the embodiment shown in FIG. [Industrial Applicability]

[0069] The fly ash circulation type flue gas treatment system and the fly ash circulation type flue gas treatment method of the present invention can be used, for example, in applications for removing acidic gases such as hydrogen chloride (HCl) and sulfur oxides (SOx) contained in flue gas discharged from a waste incineration furnace, a biomass incineration furnace, or the like, and rendering the flue gas released into the atmosphere harmless. [Explanation of symbols]

[0070] 1. Combustion treatment facility 20 Fly ash circulation exhaust gas treatment equipment 21 Bag filter 23 Attracting Fans 30 Neutralizing agent supply device 40 Fly ash circulation device 70 Control device 71 Drug Cost Calculation Department 73 Fan power consumption calculation unit 75 Cost-minimized fly ash circulation rate calculation unit 77 Target fly ash circulation rate setting unit 79 Fly ash circulation rate adjustment unit

Claims

1. A fly ash circulation type flue gas treatment facility including a bag filter into which exhaust gas is introduced, a neutralizing agent supplying device that supplies a neutralizing agent to the upstream side of the bag filter, an induction fan disposed downstream of the bag filter, and a fly ash circulation device that returns a portion of the fly ash containing the unreacted neutralizing agent captured by the bag filter to the upstream side of the bag filter and circulates the portion, A fly ash circulation type flue gas treatment facility comprising a control device that controls a circulation rate of the fly ash circulated by the fly ash circulation device so as to minimize running costs including the chemical cost of the neutralizing chemical and the fan power cost of the induction fan.

2. The control device includes: a chemical cost calculation unit that calculates the chemical cost of the neutralizing chemical from the amount of the neutralizing chemical used that is calculated based on the relationship between the acid gas removal rate of the flue gas at a predetermined fly ash circulation rate and the neutralizing chemical equivalent ratio; a fan power cost calculation unit that calculates a fan power cost of the induced draft fan relative to the fly ash circulation rate based on a relationship between a differential pressure coefficient, which is a value obtained by dividing a differential pressure between an inlet side and an outlet side of the bag filter by a flow rate of exhaust gas on the outlet side of the bag filter, and a fly ash circulation rate; a cost minimum fly ash circulation rate calculation unit that calculates a cost minimum fly ash circulation rate that minimizes the sum of the calculated chemical cost and the fan power cost; a target fly ash circulation rate setting unit for setting the minimum cost fly ash circulation rate to a target fly ash circulation rate; a fly ash circulation rate adjusting unit that adjusts the fly ash circulation rate of the fly ash circulating device so as to approach the target fly ash circulation rate; The fly ash circulation type flue gas treatment facility according to claim 1, comprising:

3. A fly ash circulation type flue gas treatment method including a neutralizing agent supplying step of supplying a neutralizing agent to an upstream side of a bag filter into which exhaust gas is introduced, an exhaust gas introducing step of introducing the exhaust gas containing the neutralizing agent into the bag filter by an induction action of an induction fan provided downstream of the bag filter, and a fly ash circulation step of returning a portion of the fly ash containing the unreacted neutralizing agent collected by the bag filter to the upstream side of the bag filter and circulating the same, A fly ash circulation type flue gas treatment method comprising: a fly ash circulation rate control step of controlling the circulation rate of the fly ash so as to minimize running costs including the chemical cost of the neutralizing chemical and the fan power cost of the induction fan in the fly ash circulation step.

4. The fly ash circulation rate control step includes: A chemical cost calculation step of calculating the chemical cost of the neutralizing agent from the amount of the neutralizing agent used that is calculated based on the relationship between the acid gas removal rate of the flue gas at a predetermined fly ash circulation rate and the neutralizing agent equivalent ratio; a fan power cost calculation step of calculating a fan power cost of the induced draft fan relative to a fly ash circulation rate based on a relationship between a differential pressure coefficient, which is a value obtained by dividing a differential pressure between an inlet side and an outlet side of the bag filter by a flow rate of exhaust gas at the outlet side of the bag filter, and a fly ash circulation rate; a cost-minimizing fly ash circulation rate calculation step of calculating a cost-minimizing fly ash circulation rate that minimizes the sum of the calculated chemical cost and the fan power cost; a target fly ash circulation rate setting step of setting the cost minimum fly ash circulation rate to a target fly ash circulation rate; a fly ash circulation rate adjusting step of adjusting the fly ash circulation rate so as to approach the target fly ash circulation rate; The fly ash circulation type exhaust gas treatment method according to claim 3, comprising the steps of:

Images