JP7680263B2 - Fly ash circulation type exhaust gas treatment equipment and fly ash circulation type exhaust gas treatment method - Google Patents

Description

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 portion of the fly ash captured by a bag filter is returned to the upstream side of the bag filter and circulated.

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

Patent Document 1 discloses an exhaust gas treatment system that includes a bag filter installed in the flue gas duct through which the exhaust gas flows, a neutralizing agent supplying device that supplies a neutralizing agent to the upstream side of the bag filter, and an induction fan installed downstream of the bag filter.

In the exhaust gas treatment equipment of Patent Document 1, reaction products are generated by the reaction of the acid gas in the exhaust gas with the neutralizing agent. The reaction products are introduced into the bag filter as fly ash together with the soot and unreacted neutralizing agent in the exhaust gas due to the attraction effect caused by the operation of the induction fan. The introduced fly ash (soot + reaction products + unreacted neutralizing agent) is collected by a filter cloth installed in the bag filter. In this way, the acid gas in the exhaust gas is removed.

Patent Document 2 discloses an exhaust gas treatment system with a similar basic configuration to that of Patent Document 1, which implements 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 some of the removed fly ash is returned to the flue on the bag filter inlet side.

JP 2017-213499 A JP 2014-24052 A

In the exhaust gas treatment equipment of Patent Document 1, the fly ash collected by the bag filter sometimes contained a large amount of unreacted neutralizing agent, and the neutralizing agent was not used efficiently.

In the device implementing the fly ash circulation type exhaust gas treatment method of Patent Document 2, a portion 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 reaction with the acid gas, and the neutralizing agent can be used efficiently. However, in the device of Patent Document 2, when the pressure loss in the bag filter increases as the fly ash circulation rate increases, the power loss of the induced draft fan increases. Therefore, while the cost of the neutralizing agent can be reduced, the fan power cost increases. Conversely, if the fly ash circulation rate is reduced, the pressure loss in the bag filter decreases and the power loss of the induced draft fan can be suppressed, but the utilization efficiency of the neutralizing agent decreases and the cost of the neutralizing agent increases.

As mentioned above, reducing the cost of neutralizing agents and reducing the cost of powering fans are in a contradictory relationship, but there is a demand for comprehensive economic efficiency in terms of the overall running costs, including the cost of neutralizing agents and the cost of powering fans.

The present invention has been made in consideration of the above problems, and aims to provide a fly ash circulation type flue gas treatment facility 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.

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.

With this fly ash circulation type flue gas treatment system, 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 fan power cost of the induction fan, are minimized, so that the overall running costs, including the cost of the neutralizing agent and the fan power cost, can be reduced.

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

According to the fly ash circulation type exhaust 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 exhaust 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 at which the sum of the calculated chemical cost of the neutralizing agent and the fan power cost of the induced draft fan is minimized, 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 that minimizes running costs, including the cost of the neutralizing agent and the fan power cost of the induction fan. Therefore, the overall running costs can be reliably reduced.

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.

According to this fly ash circulation type exhaust gas treatment method, a fly ash circulation rate control process is carried out in the fly ash circulation process to control the fly ash circulation rate so that the running costs, including the cost of the neutralizing agent and the fan power cost of the induction fan, are minimized, so that the overall running costs, including the cost of the neutralizing agent and the fan power cost, can be reduced.

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

According to the fly ash circulation type exhaust gas treatment method of this configuration, the chemical cost of the neutralizing agent for the fly ash circulation rate is calculated in the chemical cost calculation step from the amount of neutralizing agent 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 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, in the fan power cost calculation step, 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. 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, 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 in the fly ash circulation rate adjustment step so that the fly ash circulation rate approaches the target fly ash circulation rate. This allows the fly ash circulation rate to be reliably brought close to the target fly ash circulation rate that minimizes running costs, including the cost of the neutralizing agent and the fan power cost of the induction fan. Therefore, the overall running costs can be reliably reduced.

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. 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. 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. FIG. 4 is a graph showing the relationship between the differential pressure coefficient and the fly ash circulation rate. 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. 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.

The present invention will now 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.

<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 equipment 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 equipment 20 for treating the flue gas discharged from the temperature reducing tower 9.

<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.

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 arranged alternately in a stepped manner, and a drying stoker that forms the drying stage, a combustion stoker that forms the combustion stage, and a post-combustion stoker that forms the 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 to each other 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 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 that distributes and supplies pressurized air from the bottom of a bed of particles such as silica sand, causing the heat-storing silica sand to flow while burning the material to be combusted within it.

The boiler 5 uses the heat of the exhaust gas to generate steam, the economizer 7 uses the residual heat of the exhaust gas to heat the water supplied to the boiler 5, and the cooling tower 9 cools the exhaust gas from the economizer 7 to a predetermined temperature.

<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.

<Bag 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.

The fly ash circulation type flue gas treatment equipment 20 further includes a neutralizing agent supply device 30 and a fly ash circulation device 40.

<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 such as slaked lime or a sodium bicarbonate-based agent (slaked lime in this example) 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.

In the neutralizing agent supply device 30, the neutralizing agent stored in the agent tank 35 is supplied into the agent transport pipe 31 by the feeder 37 while a forced airflow is generated in the agent 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 agent transport pipe 31, and the neutralizing agent can be supplied to the upstream side of the bag filter 21.

<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.

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 portion 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.

The fly ash supply unit 50 is a device that supplies fly ash to the upstream side of the bag filter 21, and mainly comprises 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 receives and stores fly ash sent from the sorting conveyor 45 via 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.

In the fly ash supply section 50, a forced airflow is generated in the fly ash transport pipe 51 by operating the pressure blower 53, while the fly ash stored in the fly ash tank 55 is supplied into the fly ash transport pipe 51 by the 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 upstream of the bag filter 21.

The fly ash circulation type exhaust 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. 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.

<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.

In the fly ash circulation type exhaust 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, and 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 acidic gas in the exhaust gas. The reaction product generated by the reaction between the acidic 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 installed in the bag filter 21. In this way, the acidic gas in the exhaust gas is removed.

In the bag filter 21, when the pressure difference between the inlet side and the outlet side 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 at the bottom of the casing of the bag filter 21. The fly ash stored at 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 via the delivery pipe 17 connected to one end side of the distribution conveyor 45, and the remainder is discharged to the outside of the system via the discharge pipe 19 connected to the other end side of the distribution conveyor 45.

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 there. The fly ash stored in the fly ash tank 55 is supplied into the fly ash transport pipe 51 by the feeder 57. The fly ash supplied 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 supplied to the upstream side of the bag filter 21. In this way, by returning a portion of the fly ash taken out from the bottom of the bag filter 21 to the inlet duct of the bag filter 21 and circulating it, 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.

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 total amount of fly ash, which is the total amount of soot generated by 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. In other words, if the total amount of fly ash, which is the total amount of soot generated by 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 x 100 (%). The procedure of the fly ash circulation rate control process performed by the control device 70 will be described in detail below.

Figure 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 Figure 2, the symbol "S" represents a step. Figure 3 is a graph showing the relationship between the acid gas removal rate of the flue gas and the neutralization agent equivalence ratio at a predetermined fly ash circulation rate. In the graph of Figure 3, the value of the equivalence ratio on the vertical axis and the value of the acid gas removal rate on the horizontal axis each increase in the direction of the arrow. A predetermined program for executing the procedure shown in the flow chart of Figure 2 and data related to the graph of Figure 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 Figure 3 is automatically updated periodically based on the actual operating data of the fly ash circulation type flue gas treatment equipment 20.

<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 given 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 acid gas (HCl) measured by the inlet acid gas concentration meter 61 and the concentration of 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 can be 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.

The amount of hydrated lime used is calculated using a specified 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 hydrated lime used and the chemical unit price. An example of the calculation result is shown in Table 2.

In this way, the cost of the neutralizing agent for a 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 exhaust gas at a specified fly ash circulation rate and the neutralizing agent equivalent ratio, so that the cost of the neutralizing agent for a fly ash circulation rate can be accurately calculated.

Figure 4 is a graph showing the relationship between the differential pressure coefficient and the fly ash circulation rate. In the graph of Figure 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 each increase in the direction of the arrow. Data related to the graph of Figure 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 Figure 4 is automatically updated periodically based on actual operating data of the fly ash circulation type flue gas treatment equipment 20.

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, calculated from the measured 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.

In the graph of Fig. 4, when the fly ash circulation rate increases from R ₁₀ % to R ₂₀ %, the differential pressure coefficient decreases. This is because, as the fly ash circulation rate increases from R ₁₀ % to R ₂₀ %, the fly ash becomes larger in size and the average particle size increases, so that the airflow resistance 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. When the fly ash circulation rate exceeds R ₂₀ %, the airflow resistance increase effect due to the increase in the fly ash circulation amount becomes dominant over the airflow resistance reduction effect due to the increase in the average particle size of the fly ash, so the differential pressure coefficient increases with the increase in the fly ash circulation rate. Thus, the circulation rate and the differential pressure coefficient have a downward convex function relationship in which the differential pressure coefficient is a downward convex function of the fly ash circulation rate.

<Step S2: Fan power cost calculation process>
In step S2 of the flow chart of 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 of Fig. 4. An example of the calculated differential pressure coefficient with respect to the fly ash circulation rate is shown in Table 3.

The fan power cost is calculated using a predetermined formula based on the differential pressure coefficient shown in Table 3 and the measured value of the exhaust gas flow meter 69. An example of the calculation result is shown in Table 4.

In this way, the fan power cost of the induction fan 23 for the fly ash circulation rate is calculated by the fan power cost calculation unit 73 based on 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 induction fan 23 for the fly ash circulation rate can be accurately determined.

Figure 5 is a graph showing the relationship between the total cost of chemicals and fan power costs and the fly ash circulation rate.

<Step S3: Cost-minimizing fly ash circulation rate calculation step>
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 the fan power cost (see Table 4). That is, the minimum cost fly ash circulation rate which minimizes the sum of the chemical cost and the 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 the 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 Fig. 5).

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

<Step S5: Fly ash circulation rate adjustment step>
In step S5, the fly ash circulation rate adjusting unit 79 adjusts the fly ash circulation rate of the fly ash circulating device 40 so that it approaches the target fly ash circulation rate ( _R33 % in this example). That is, the fly ash circulation rate adjusting unit 79 controls the amount of chemical sent out by the feeder 57 and/or the amount of chemical pumped by the pump 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.

In this way, the minimum cost fly ash circulation rate that minimizes the sum of the calculated chemical cost of the neutralizing agent and the fan power cost of the induction 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 that it approaches 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 that minimizes the running cost including the chemical cost of the neutralizing agent and the fan power cost of the induction fan, so that the overall running cost can be reliably reduced.

As shown in the graph of Fig. 3, when the fly ash circulation rate is increased from R ₁₀ %, R ₂₀ %, R ₃₀ %, and R ₄₀ % in order, the equivalence ratio decreases, so that increasing the fly ash circulation rate reduces the chemical cost. On the other hand, as shown in the graph of Fig. 4, when the fly ash circulation rate increases from R ₁₀ % to R ₂₀ %, the differential pressure coefficient decreases, and when the fly ash circulation rate exceeds R ₂₀ %, the differential pressure coefficient increases with increasing 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 indicates that the fan power cost is minimum at a certain fly ash circulation rate in a certain range of the fly ash circulation rate (in this example, R ₁₀ % to R ₄₀ %). The present invention has been made based on the finding that by appropriately matching the relationship shown in the graph of FIG. 3 with the relationship shown in the graph of FIG. 4, it is possible to obtain a minimum-cost fly ash circulation rate (R ₃₃ % in this example) at which the total of the chemical cost and the fan power cost is minimized between a low level value (e.g., R ₁₀ %) and a high level value (e.g., R ₄₀ %) of the fly ash circulation rate.

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 changed as appropriate within the scope of the spirit of the present invention.

(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 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. In the following, the description will be focused on the parts unique to the other embodiment.

In the combustion treatment facility 1 shown in Figure 6, the duct 11 is configured with 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, which are connected in this order from the upstream side to the downstream side of the exhaust gas flow.

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

<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 .

The transfer conveyor 46 is configured to send the fly ash transported 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 outside the system via the discharge pipe 19 connected to the transport direction end of the transfer conveyor 46.

The fly ash supply section 50 mainly comprises 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 under natural flow into the upstream vertical duct section 11b, and the fly ash can be supplied to the upstream side of the bag filter 21. Here, the supply position of the feeder 57 to the upstream vertical duct section 11b is set downstream of the exhaust gas flow from the supply position of the feeder 37 to the upstream vertical duct section 11b.

The alternative embodiment shown in FIG. 6 described above can also provide the same effects as the embodiment shown in FIG. 1.

The fly ash circulation type flue gas treatment equipment and the fly ash circulation type flue gas treatment method of the present invention can be used, for example, to remove acid gases such as hydrogen chloride (HCl) and sulfur oxides (SOx) contained in the flue gas discharged from a waste incinerator or a biomass incinerator, thereby rendering the flue gas released into the atmosphere harmless.

REFERENCE SIGNS LIST 1 Combustion treatment facility 20 Fly ash circulation type exhaust gas treatment equipment 21 Bag filter 23 Induction fan 30 Neutralizing agent supply device 40 Fly ash circulation device 70 Control device 71 Agent cost calculation section 73 Fan power cost calculation section 75 Cost minimum fly ash circulation rate calculation section 77 Target fly ash circulation rate setting section 79 Fly ash circulation rate adjustment section

Claims (4)

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. 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: 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. 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:

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