JPH01315321A - Waste heat recovery heat exchanger - Google Patents

Abstract

PURPOSE:To prevent the unreacted reducing agent from being discharged to the atmosphere by detecting the temp. of exhaust gas at the inlet and outlet of denitration catalyst, and calculating the optimum injection amount of the catalyst by the output signal of the detected temp. to control the injection amount. CONSTITUTION:NH3 is injected into the exhaust gas from a reducing agent injection nozzle 10, and the gas exchanges heat at a superheater 2 and at an evaporator 3, and then enters into the denitration catalyst 4 where NOx is reduced to be removed, and enters into a fuel economizer 5 where heat is exchanged again, and then the gas is discharged to the atmosphere from a stack. In this case, the temp. of the exhaust gas is detected at the catalyst inlet side and at the catalyst outlet side by temp. detectors 20, 21, and the temp. signals are inputted into an arithmetic unit 22 where the injection amount of NH3 suitable for the temp. of the catalyst is calculated from the injection amount of NH3 calculated at an NH3 injection amount calculator 24 calculating from the signal 23 concerning NOx content, so that an adjusting valve 15 is controlled.

Description

[Detailed description of the invention] [Object of the invention] (Industrial application field) The present invention uses exhaust gas from a gas turbine device as a heat source to generate driving steam for other steam engines, steam for processes, or hot water. The present invention relates to an exhaust heat recovery heat exchanger that generates nitrogen oxides, and particularly relates to an exhaust heat recovery heat exchanger that reduces the temperature of nitrogen oxides in exhaust gas.

(Prior art) In general, in a combined cycle power generation system or a cogeneration power generation system, exhaust gas from a gas turbine or diesel engine is used as a heat source to generate driving steam for a steam turbine or steam hot water for a process. Although a recovery heat exchanger is installed, the exhaust gas from gas turbines, diesel engines, etc. contains harmful nitrogen oxides, so measures are being taken to reduce them in order to protect the environment. .

FIG. 5 is a diagram showing a schematic configuration of a conventional exhaust heat recovery heat exchanger. Inside the casing 1 of the exhaust heat recovery heat exchanger, a gas is supplied from a gas turbine or a diesel engine (not shown), etc. A superheater 2 from the upstream side with respect to the flow of exhaust gas,
An evaporator 3, a denitrification catalyst 4, and a carbon saver 5 are provided.

Therefore, the exhaust gas supplied from the gas turbine etc. to the exhaust heat recovery heat exchanger is heat exchanged with water flowing through the superheater 2 etc. in the superheater 2, evaporator 3, and energy saver 5 in sequence. , is released into the atmosphere from a chimney (not shown). On the other hand, water to be heat exchanged with the exhaust gas is sent to the economizer 5 through a water supply pipe from a water supply pump (not shown), heated, and then introduced into the lower part of the steam drum 7. The canned water in the steam drum 7 is then sent to the evaporator 3 by the circulation pump 8, where it is evaporated, returned to the steam drum 7 again, where the moisture is separated, and then turned into superheated steam in the superheater 2. The water is supplied to a steam turbine, process equipment, etc. (not shown) through the

By the way, the fuel is supplied to the exhaust heat recovery heat exchanger as described above using LN.
If exhaust gas from a gas turbine equipment named G flows in, this exhaust gas will contain about 150 ppm of nitrogen oxides if no treatment is taken, and in order to satisfy environmental standards, Normally, water or steam is injected into the gas turbine combustor to suppress the amount of nitrogen oxides generated, and a denitrification device 4 installed in the exhaust gas stream is used to reduce the amount of nitrogen oxides. The dry selective catalytic reduction method, which is one of the methods of this denitration equipment, decomposes nitrogen oxides into nitrogen and water by injecting ammonia as a reducing agent into the exhaust gas, and the reaction is carried out using an iron oxide catalyst. This is done when passing through the layer (see Japanese Patent Publication No. 35908/1983).

The denitrification rate in this method largely depends on the reaction temperature in the catalyst layer, as shown in FIG.

In other words, the denitrification rate increases rapidly as the reaction temperature rises from 200°C to 300°C, and increases from 350°C to 40°C.
It reaches its maximum value between 0°C and decreases again after 450°C. For this reason, in exhaust heat recovery heat exchangers for combined cycle power generation and cogeneration power generation, which have a wide operating load range, the denitrification equipment is installed at a position where a high denitrification rate can be obtained in the entire load range. As shown in FIG. 5, the denitrification catalyst 4 is generally installed downstream of the evaporator 3, and a reducing agent injection nozzle 10 is installed to inject ammonia, which is a reducing agent.
is placed on the upstream side.

In addition, as mentioned above, there is an appropriate temperature range for the denitrification reaction, and if ammonia is injected at a temperature other than that, the amount of unreacted ammonia released into the atmosphere will increase, which is undesirable from an environmental conservation perspective, especially during startup. This is an important problem in combined cycle power generation, which has a high frequency of outages.

In order to deal with this problem, in the conventional exhaust heat recovery heat exchanger, two methods as shown in FIG. 5 are used in combination as ammonia injection control methods. The first method is to control the start and end of ammonia injection, and in the apparatus shown in FIG. The opening/closing of a cutoff valve 13 provided in the ammonia injection system 12 is controlled by the signal. For example, when the temperature of the exhaust gas flow at the inlet of the denitrification catalyst 4 exceeds a certain value during startup, the shutoff valve 13 of the ammonia injection system 12 is changed from fully open to fully open by a signal from the ammonia injection control device 11, and the ammonia injection is stopped. It is about to start. The second method is to control the amount of ammonia injected, and the amount of ammonia injected necessary for reducing the nitrogen oxides contained in the exhaust gas stream is controlled by a signal related to the nitrogen oxide content of the exhaust gas, such as the exhaust gas flow rate. , Calculate the amount of ammonia injection using the bag 4 and 14 based on the temperature, etc.
The control valve 15 is actuated by the signal from the ammonia injection amount calculation device 14 to control the inflow amount of ammonia.

(Problem to be solved by the invention) However, denitrification catalysts are generally made of iron or other structures with a catalyst layer fixed on the surface, and the overall weight of the catalyst is large, resulting in a considerably large heat capacity. . For this reason,
When the load fluctuation range is large, such as during startup, there is a considerable time delay between the temperature change on the downstream side of the catalyst and the gas temperature change on the upstream side of the catalyst. FIG. 7 is a diagram showing an example of a change in exhaust gas temperature at the catalyst inlet/outlet portion during startup;
In response to changes in the exhaust gas temperature at the gas turbine outlet (-dotted chain line), the exhaust gas temperature at the catalyst inlet changes as shown by the solid line, and the exhaust gas temperature at the catalyst outlet changes as shown by the dotted line. . Therefore, in this case, the time required for the denitrification reaction temperature to reach the practical lower limit of 250° C. is approximately 30 minutes longer on the outlet side than on the inlet side. In other words, the temperature of the entire catalyst finally reaches the lower limit of the denitrification reaction temperature range 30 minutes after the exhaust gas temperature at the catalyst inlet reaches 250°C.

Therefore, when the timing of ammonia injection is controlled according to the exhaust gas temperature at the denitrification catalyst inlet, as in the conventional exhaust heat recovery heat exchanger, the entire catalyst is There is a problem that a considerable portion of the ammonia injected into the exhaust gas until the temperature reaches the above temperature range is released into the atmosphere without reacting.

On the other hand, as a method to prevent unreacted ammonia from being released into the atmosphere,
A method of controlling ammonia injection using the exhaust gas temperature at the outlet of the denitrification catalyst is also considered.

However, in the case of this method, as is clear from the exhaust gas temperature characteristics at startup in Figure 7, when the exhaust gas temperature at the catalyst outlet reaches a temperature range suitable for the denitrification reaction, the entire catalyst is suitable for the denitrification reaction. Since the temperature range is within a certain range, it is possible to prevent unreacted ammonia from being released into the atmosphere as described above. However, since ammonia is not injected until the entire catalyst reaches the temperature range for the denitrification reaction, there are problems such as nitrogen oxides in the exhaust gas during this time are not removed at all and are released into the atmosphere.

In view of these points, the present invention aims to provide an exhaust heat recovery heat exchanger that can minimize the release of nitrogen oxides during startup, etc., and prevent unreacted reducing agent from being released into the atmosphere. purpose.

(Means for Solving the Problems) The present invention includes a denitrification catalyst that renders nitrogen oxides contained in exhaust gas serving as a heat source harmless through catalytic reductive decomposition, and a reducing agent injection device provided upstream of the denitrification catalyst. In the exhaust heat recovery heat exchanger, an exhaust gas temperature detector that detects the exhaust gas temperature at the inlet and outlet of the denitrification catalyst, or the exhaust gas temperature at the inlet of each stage of the multi-stage denitrification catalyst and the exhaust gas temperature at the exit of the final stage; , and a computing unit that calculates the optimum injection amount of the reducing agent based on the output signal of the exhaust gas temperature detector and outputs a control signal to a control valve provided in the reducing agent injection system.

(Function) During the operation of the exhaust heat recovery heat exchanger, when the exhaust gas temperature at the inlet and outlet of the denitrification catalyst or the exhaust gas temperature at the outlet of each stage of the multi-stage denitrification catalyst is detected, the detected temperature The area of the catalyst that has reached the reaction temperature is calculated by the calculator, and the optimum amount of reducing agent to be injected is calculated accordingly.The control valve of the reducing agent injection system is controlled by the output signal, and the optimum amount is calculated. A reducing agent is injected into the heat exchanger.

(Embodiments) Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a schematic configuration diagram showing an example of the exhaust heat recovery heat exchanger of the present invention, in which the exhaust gas discharged from a gas turbine, diesel engine, etc. Flows into the heat exchanger from the superheater 2,
After exchanging heat in the evaporator 3, the nitrogen oxides in the exhaust gas enter the denitrification catalyst 4 and are decomposed by reacting with ammonia, which is a reducing agent, and are reduced to a predetermined concentration. And then the economizer 5
It exchanges heat again and is released into the atmosphere from a chimney (not shown).

Incidentally, a catalyst inlet side temperature detector 20 and a catalyst outlet side temperature detector 21 are provided at the inlet and outlet of the denitrification catalyst 4, respectively, and the temperature signals detected by both temperature detectors 20 and 21 are sent to a computer. It will be man-powered on the 22nd. In addition, the arithmetic unit 22 uses a signal 23 related to the nitrogen oxide content in the exhaust gas at the outlet of the gas turbine device, etc., such as signals such as exhaust gas temperature and exhaust gas flow rate, to respond only to the current state of the exhaust gas. A signal from an ammonia injection amount calculation device 24 that calculates the ammonia injection amount is also input.

On the other hand, the arithmetic unit 22 is composed of an input/output circuit, a central processing unit, a storage device, etc., and calculates the temperature of the catalyst layer from the output signal of the catalyst inlet temperature detector 20 and the output signal of the catalyst outlet temperature detector 21. Calculate the area that has reached a temperature suitable for reaction, for example, the surface area of the catalyst that has reached a temperature suitable for reaction, and then calculate the correction coefficient defined by the ratio of this value to the entire area of the catalyst layer, for example, the total surface area. By multiplying the signal from the ammonia injection amount calculation device 24, the optimum ammonia injection amount is calculated taking into account the current temperature state of the catalyst, and this is converted into a valve opening signal to control the control valve 15. Outputs a control signal to control.

The details of the operation of the arithmetic unit 22 will be explained below based on FIG.

FIG. 2 is a flowchart showing the processing carried out by the computing unit 22 at a certain time during operation of the exhaust heat recovery heat exchanger of the present invention, and the release of unreacted ammonia into the atmosphere becomes a problem mainly at the time of startup. and during load fluctuations, but here we will proceed with the explanation assuming the startup time.

First, the lower limit T of the reaction temperature of the catalyst at Pl is 111
Set n. This value remains constant throughout all operating conditions.

Next, the catalyst inlet gas temperature T1 and the catalyst outlet gas temperature T2 at the current time are read in P2, and in P3, the higher one of these two temperature signals is Ht - the lower one is Tt.
, set to . MAX [T1. T2] is T1 and T
The larger one of 2 is shown, and MEN rTl, T2 shows the smaller one of T1 and T2. Here, since the catalyst inlet side gas temperature T1 is higher than the catalyst outlet side gas temperature T2 at the time of startup, TH-T1. It becomes TL-T2.

Subsequently, in P4, the ammonia injection ff1A, which has not been corrected regarding the temperature variation distribution within the catalyst, from the ammonia injection amount calculation device 24 is read. After this T1□ (-
The catalyst inlet side temperature T't) is compared with the reaction temperature lower limit value T, and if TIt<Twin, the process branches to P9. In this case, since the catalyst inlet side gas temperature T1 has not reached the reaction temperature lower limit value Tm1n, it is determined that the entire denitration catalyst has not reached the reaction temperature, and true ammonia injection ff1A-0 is performed.

On the other hand, TH≧Tl11n, that is, the catalyst inlet temperature T
1 is equal to or higher than the reaction temperature lower limit Tm1n, P
Proceed to step 2 and compare TL (catalyst outlet side temperature T2) with reaction lower limit temperature "m1n".At this time, TL≧"win"
In other words, when the catalyst outlet side temperature T2 is also equal to or higher than the reaction temperature lower limit value, it is determined that the entire denitrification catalyst has reached the reaction temperature, so the ammonia injection amount is not corrected and A-Ao
(P to).

On the other hand, if T < T, the process branches to P7. This L
In the case of mIn, the catalyst inlet temperature T1 has reached the reaction temperature, and the catalyst outlet temperature T2 has not reached the reaction temperature, so it is determined that the denitrification catalyst has partially reached the reaction temperature.

Then, the value A calculated by the ammonia injection amount calculation device 24. Calculate the correction coefficient α for . Here, the correction coefficient α represents the ratio of the portion of the catalyst layer that has reached the reaction temperature range to the total catalyst, and is a function of the catalyst inlet temperature T 1 and the catalyst outlet temperature T2.

As an example of this function, the simplest form is T - T T, -72 L (at startup), which approximates the temperature distribution between the catalyst inlet and outlet using a linear equation.

Subsequently, the corrected true ammonia injection amount 1iIA is calculated by multiplying the uncorrected ammonia injection amount Ao by α calculated in the above P7 (P8).

In this way, the true ammonia injection amount A determined in each of the above steps is converted into an opening signal of the control valve 15, and the opening signal is output to the control valve 15 (P, □,
Pl. ).

Even when the load fluctuates, the optimum ammonia injection amount is calculated using a process similar to the flowchart shown in FIG.

In this way, during start-up and load fluctuations, the amount of ammonia injection, which was conventionally determined only from the exhaust gas condition of the gas turbine, etc., can be adjusted from the denitration catalyst inlet and outlet gas temperature to the area of the catalyst that has reached the reaction temperature. Since the amount of ammonia is calculated and the correction is made based on this, an appropriate amount of ammonia is injected into the exhaust gas, minimizing the amount of nitrogen oxides released into the atmosphere, and releasing unreacted ammonia into the atmosphere. This can be prevented.

FIG. 3 is a diagram showing another embodiment of the present invention, in which the denitrification catalyst is provided in multiple stages in the flow direction, and one denitrification device is formed by the multiple stages. has been done. That is, between the evaporator 3 and the economizer 5, from the upstream side of the exhaust gas flow, first-stage denitrification catalysts 25a, . . .
... An n-th stage denitrification catalyst 25n is provided, and on the inlet side of each stage, a first stage inlet side exhaust gas temperature detector 26a,
A second stage inlet side exhaust gas temperature detector 26b..., an nth stage inlet side exhaust gas temperature detector 26n are provided respectively, and the nth stage outlet exhaust gas temperature detector 26b is provided at the outlet of the nth stage denitrification catalyst. A detector 26r is provided. The temperature detectors on the inlet side from the second stage to the nth stage are also used as the temperature detectors on the outlet side of the denitrification catalyst in the previous stage, and these n+
The output signal of one temperature sensor is input to the calculator 22.

The arithmetic unit 22 also receives input from the ammonia injection amount calculation device 24 which calculates the ammonia injection amount using the signal 23 regarding the nitrogen oxide content in the exhaust gas, as in the first embodiment. The number of stages of the catalyst that has reached the reaction temperature is determined from the signal of the exhaust gas temperature sensor, the correction coefficient α defined by the ratio of this to the total number of stages is calculated, and the uncorrected ammonia injection ff1Ao is multiplied to calculate the true ammonia Calculate the injection EIA and apply this value to the control valve 1.
5, and the signal is applied to the control valve 15 as a control signal.

FIG. 4 is a flowchart showing the processing performed by the computing unit 22 at a certain time in the above embodiment. First, the lower limit value Tll11n of the catalyst reaction temperature is set with P. Subsequently, at P2, the ammonia injection amount Ao, which has not been corrected regarding the catalyst anti-temperature distribution, is read from the ammonia injection amount calculation device 24.

At P, a loop counter that controls the loop from P to Plo is set to 1, and a counter i that counts catalysts that have reached the reaction temperature are both set to O.

At P, loop k is added by 1, and at P5, the outlet side gas temperature TK is the same as the catalyst inlet side gas temperature TK1 of the second stage.
Read □, and in the following P6, set the higher one of TKl and T to T and the lower one to TL.
11. Here, since T > T at startup, T11
KI K2 is the inlet side gas temperature TK2, TL is the outlet side gas temperature TK2
is set.

Then, in P7, TH is compared with the lower limit value T of the catalyst reaction temperature, and TH T is determined. In this case, 11n has not reached the reaction temperature, so it branches to Plo and the loop continues. On the other hand, if TH>T1°, TI has reached the reaction temperature, and then proceeds to P and TL
and T, 1n are compared.

At this time, if Tt≧Tm1n, both the catalyst population and the outlet of that stage have reached the reaction temperature, so the counter i is 1.
will be added. On the other hand, if Tt, ≧T, and l11n are not satisfied, TL has not reached the reaction temperature, so counting is not performed and the process proceeds to P. Then, at Plo, P4 to P until the loop counter k reaches the total number of catalyst stages n.
1o is looped.

When the loop ends in this way, the number i of catalyst stages that have reached the reaction temperature has been counted, and the true ammonia injection amount A corrected by Pll is A - A.

Calculate by n. And the above true ammonia injection amount A
is converted into an opening degree signal of the control valve 15, and output to the control valve 15 (P1□"13).

In this way, the operation of the calculator 22 is basically the same as in the first embodiment, but in the first embodiment, the temperature distribution inside the catalyst is predicted based on the exhaust gas temperature at the entrance and exit of the catalyst, and the correction coefficient is calculated. On the other hand, in the second embodiment, the number of stages in which both the inlet and outlet temperatures have reached the reaction temperature among all stages of the denitrification catalyst is counted, and the correction coefficient α is calculated by α-1/n. It's different.

Therefore, in this example as well, an appropriate amount of denitrification ammonia is injected into the catalyst portion that has reached the reaction temperature, so that unreacted ammonia is released into the atmosphere while minimizing the amount of nitrogen oxides released into the atmosphere. can be suppressed. Furthermore, in this embodiment, there is a large amount of temperature information that can be used for calculation in the computing unit 22, so it is expected that reliability will be improved compared to the first embodiment. It is also possible to improve the accuracy of the ammonia injection amount by applying the first embodiment to each stage.

〔Effect of the invention〕

As explained above, the present invention detects the exhaust gas temperature at the inlet and outlet of the denitrification catalyst, determines the temperature range where the reaction temperature is reached, and injects the optimal amount of reducing agent accordingly. Therefore, the release of unreacted reducing agent into the atmosphere can be minimized, and there is no need to wait until the denitrification catalyst has completely reached the reaction temperature before injecting the reducing agent, reducing the amount of nitrogen oxide released into the atmosphere. can be minimized.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of the exhaust heat recovery heat exchanger of the present invention, FIG. 2 is a flowchart showing the operation of the computing unit, FIG. 3 is a schematic configuration diagram showing another embodiment of the present invention, The figure is a flowchart showing the operation of the computing unit in the above other embodiment, Figure 5 is a schematic configuration diagram of a conventional exhaust heat recovery heat exchanger, Figure 6 is a temperature characteristic diagram of the denitrification rate in the denitrification device, and Figure 7 is FIG. 2 is a state explanatory diagram showing changes in exhaust gas temperature at the gas turbine outlet, the denitrification catalyst population, and the denitrification catalyst outlet. 2... Superheater, 3... Evaporator, 4... Denitrification catalyst,
5. Economizer, 10. Reducing agent injection nozzle, 15.
...Control valve, 20...Catalyst inlet side temperature sensor, 21.
...Catalyst outlet side temperature detector, 22...Arithmetic unit, 24.
...Ammonia injection amount calculation device. Applicant's agent: Yu Sato Figure 2 Figure 5 Figure 6

Claims (1)

[Scope of Claims] 1. Exhaust heat recovery heat exchange that includes a denitrification catalyst that renders nitrogen oxides contained in exhaust gas as a heat source harmless through catalytic reductive decomposition, and a reducing agent injection device provided upstream of the denitrification catalyst. In the denitration catalyst, an exhaust gas temperature detector detects the exhaust gas temperature at the inlet and outlet of the denitrification catalyst, and an output signal from the exhaust gas temperature detector is used to calculate the optimal injection amount of the reducing agent. 1. An exhaust heat recovery heat exchanger comprising: a computing unit that outputs a control signal to a control valve; 2. In the exhaust heat recovery heat exchanger, which has a denitrification catalyst that detoxifies nitrogen oxides contained in the exhaust gas as a heat source through catalytic reductive decomposition, and a reducing agent injection device installed upstream of the denitrification catalyst, the flow of the exhaust gas is Denitrification catalysts installed in multiple stages in the direction, exhaust gas temperature detectors that detect the exhaust gas temperature at the inlet side of the denitrification catalyst in each stage and the exhaust gas temperature at the outlet of the final stage denitrification catalyst, and each temperature detector. It is characterized by having an arithmetic unit that determines the catalyst stage that has reached the reaction temperature based on the output signal, calculates the corresponding optimal reducing agent injection amount, and outputs a control signal to the control valve installed in the reducing agent injection system. This is an exhaust heat recovery heat exchanger.