JPH0611379B2 - Exhaust heat recovery heat exchanger - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Industrial field of use) The present invention uses exhaust gas from a gas turbine device or the like as a heat source for driving steam for another steam engine, steam for process, or hot water. The present invention relates to an exhaust heat recovery heat exchanger, and more particularly to an exhaust heat recovery heat exchanger configured to reduce the temperature of nitrogen oxides in exhaust gas.

(Prior Art) Generally, in a combined cycle power generation system or a combined heat and power generation system, exhaust heat recovery for generating driving steam for a steam turbine or steam hot water for a process by using exhaust gas of a gas turbine or a diesel engine as a heat source. Although a heat exchanger is provided, since harmful nitrogen oxides are contained in the exhaust gas of a gas turbine, a diesel engine, etc., a means for reducing the same is adopted from the viewpoint of environmental protection.

FIG. 5 is a diagram showing a schematic configuration of a conventional exhaust heat recovery heat exchanger, and the casing 1 of the exhaust heat recovery heat exchanger is supplied from a gas turbine, a diesel engine or the like (not shown). From the upstream side of the exhaust gas flow, the superheater 2,
An evaporator 3, a denitration catalyst 4, and a economizer 5 are provided.

Thus, the exhaust gas supplied from the gas turbine or the like to the exhaust heat recovery heat exchanger is heat-exchanged with the water flowing through the superheater 2 or the like in the superheater 2, the evaporator 3, and the economizer 5 in order. , Is emitted into the atmosphere from a chimney (not shown). On the other hand, the water that is heat-exchanged with the exhaust gas is sent from a water supply pump (not shown) to the economizer 5 through the water supply pipe, heated, and then introduced into the lower portion of the steam drum 7. Then, the canned water of the steam drum 7 is sent to the evaporator 3 by the circulation pump 8, and is steamed there, and returns to the steam drum 7 again to separate moisture, and then becomes superheated steam in the superheater 2 and becomes the main steam pipe 9 And is supplied to a steam turbine, a process device, or the like (not shown).

By the way, in the exhaust heat recovery heat exchanger as described above, the fuel is LN
When the exhaust gas from the gas turbine device, which is designated as G, flows in, the exhaust gas contains about 150 ppm of nitrogen oxides unless any measures are taken, and in order to satisfy the environmental standard, In general, water or steam is injected into a gas turbine combustor to suppress the amount of nitrogen oxides generated, and a denitration device 4 installed in the exhaust gas flow.
The reduction is being carried out. The dry selective catalytic reduction method, which is one of the methods of this denitration device, is to inject ammonia as a reducing agent into exhaust gas to decompose nitrogen oxides into nitrogen and water, and the reaction is an iron oxide-based catalyst. This is carried out when passing through the layer (see Japanese Examined Patent Publication No. 50-35908).

The denitrification rate in this method largely depends on the reaction temperature in the catalyst layer as shown in FIG. That is, the denitrification rate rapidly increases as the reaction temperature rises from 200 ° C to 300 ° C, reaches a maximum value between 350 ° C and 400 ° C, and decreases again after passing 450 ° C.
From this, in the exhaust heat recovery heat exchanger for combined cycle power generation and co-generation with a wide operating load range, the denitration device is installed at a position where a high denitration rate can be obtained in the entire load zone. As shown in FIG. 5, the denitration catalyst 4 is generally installed on the downstream side of the evaporator 3, and the reducing agent injection nozzle 10 for injecting ammonia as a reducing agent is arranged on the upstream side thereof.

Further, as described above, there is an appropriate temperature range for the denitration reaction, and if ammonia is injected in a temperature range other than that, it increases the amount of unreacted ammonia released into the atmosphere, which is not preferable from the standpoint of environmental protection, and especially it is started. This is an important issue in combined cycle power generation, which is frequently stopped.

In order to deal with this problem, in the conventional exhaust heat recovery heat exchanger, two methods as shown in FIG. 5 are used together as a method for controlling the injection of ammonia. The first method is a method of controlling the start and end of the injection of ammonia, and in the apparatus shown in FIG. 5, the temperature of the exhaust gas flow at the inlet of the denitration catalyst 4 is input to the ammonia injection control apparatus 11, from which The opening / closing of the shutoff valve 13 provided in the ammonia injection system 12 is controlled by this signal. Therefore, for example, when the temperature of the exhaust gas flow at the inlet of the denitration catalyst 4 exceeds a certain value at the time of startup, the shutoff valve 13 of the ammonia injection system 12 is changed from fully closed to fully opened by a signal from the ammonia injection control device 11, and ammonia injection is performed. Is about to start. The second method is a method of controlling the injection amount of ammonia, and the injection amount of ammonia required for the reduction of nitrogen oxides contained in the exhaust gas flow is determined by a signal related to the nitrogen oxide content of the exhaust gas, for example, the exhaust gas flow rate. Calculated from the temperature, temperature, etc. by the ammonia injection amount calculation device 14,
The control valve 15 is operated by a signal from the ammonia injection amount calculation device 14 to control the inflow amount of ammonia.

(Problems to be solved by the invention) However, as a denitration catalyst, a catalyst having a catalyst layer fixed on the surface of a structure such as iron is generally used, and since the weight of the entire catalyst is large, the heat capacity becomes considerably large. . For this reason,
When the load fluctuation range is large, such as at startup, there is a considerable time delay in the temperature change on the catalyst downstream side with respect to the gas temperature change on the catalyst upstream side. FIG. 7 is a diagram showing an example of changes in exhaust gas temperature at the catalyst inlet / outlet portion at startup,
Corresponding to the change in the exhaust gas temperature (dashed line) at the gas turbine outlet, 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 to reach the practical lower limit of the denitration reaction temperature of 250 ° C. is about 30 minutes longer on the outlet side than on the inlet side. In other words, 30 minutes after the exhaust gas temperature at the catalyst inlet reaches 250 ° C., the temperature of the entire catalyst finally becomes the lower limit of the denitration reaction temperature range.

Therefore, when the injection timing of ammonia is controlled by the exhaust gas temperature at the denitration catalyst inlet as in the conventional exhaust heat recovery heat exchanger, the entire catalyst is reached after the denitration catalyst inlet gas temperature reaches the temperature range suitable for the reaction. Ammonia injected into the exhaust gas before the temperature reaches the above temperature range has a problem that a considerable part is released into the atmosphere without being reacted.

On the other hand, as a method to prevent atmospheric release of unreacted ammonia,
A method of controlling the injection of ammonia using the exhaust gas temperature at the denitration catalyst outlet is also conceivable. However, in the case of this method, as is clear from the exhaust gas temperature characteristics at startup in FIG. 7, when the exhaust gas temperature at the catalyst outlet reaches the temperature range suitable for the denitration reaction, the entire catalyst is suitable for the denitration reaction. Since the temperature is within the above range, it is possible to prevent the unreacted ammonia from being released into the atmosphere as described above. However, since ammonia is not injected until the temperature of the entire catalyst reaches the temperature range of the denitration reaction, there is a problem that nitrogen oxide in the exhaust gas during this period is not removed at all and is released into the atmosphere.

In view of these points, the present invention aims to obtain an exhaust heat recovery heat exchanger capable of minimizing the release of nitrogen oxides at the time of startup and preventing the release of unreacted reducing agent to the atmosphere. To aim.

(Means for Solving the Problem) The present invention has a denitration catalyst for detoxifying nitrogen oxides contained in exhaust gas which is a heat source by catalytic reduction decomposition, and a reducing agent injection device provided on the upstream side thereof. In the exhaust heat recovery heat exchanger, an exhaust gas temperature detector for detecting the exhaust gas temperature at the inlet and the outlet of the denitration catalyst, or the exhaust gas temperature at the inlet of each stage of the denitration catalyst and the exhaust gas temperature at the outlet of the final stage. And an arithmetic unit for calculating an optimum injection amount of the reducing agent based on the output signal of the exhaust gas temperature detector and outputting a control signal to a control valve provided in the reducing agent injection system.

(Operation) When the exhaust gas temperature at the inlet and outlet of the NOx removal catalyst or the exhaust gas temperature at each stage of the NOx removal catalyst is detected during operation of the exhaust heat recovery heat exchanger, the detected temperature The area of the catalyst that has reached the reaction temperature is calculated by the computing unit, the optimal injection amount of the reducing agent is calculated accordingly, and the control signal of the reducing agent injection system is controlled by the output signal, so that the optimal amount of the reducing agent is obtained. Are injected into the heat exchanger.

Embodiments Embodiments of the present invention will be described below 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, and the exhaust gas discharged from a gas turbine, a diesel engine, or the like is an inlet port portion provided with a reducing agent injection nozzle 10. Flows into the heat exchanger from the superheater 2,
After exchanging heat with the evaporator 3, the nitrogen oxide in the exhaust gas enters the denitration catalyst 4 and is decomposed by reacting with ammonia as a reducing agent to be reduced to a predetermined concentration. And then the economizer 5
After that, heat is exchanged again, and the heat is released from the chimney (not shown) into the atmosphere.

By the way, a catalyst inlet side temperature detector 20 and a catalyst outlet side temperature detector 21 are provided at the inlet and the outlet of the denitration catalyst 4, respectively, and the temperature signals detected by the temperature detectors 20 and 21 are calculated by a calculator. 22 is input. Further, the computing unit 22 uses only the signal 23 relating to the nitrogen oxide content in the exhaust gas at the outlet of the gas turbine device, for example, the signal of the exhaust gas temperature, the exhaust gas flow rate, etc., to correspond to the current exhaust gas state only. A signal from the ammonia injection amount calculation device 24 for calculating the ammonia injection amount to be input is also input.

On the other hand, the computing unit 22 is composed of an input / output circuit, a central processing unit, a storage unit, and the like, and uses the output signal of the catalyst inlet temperature detector 20 and the output signal of the catalyst outlet side temperature detector 21 to determine the catalyst layer. Of the area in which the temperature suitable for the reaction is reached, for example, the surface area reaching the temperature suitable for the reaction of the catalyst is calculated, and the correction coefficient defined by the ratio of this value and the entire area of the catalyst layer, for example, the total surface area Is multiplied by a signal from the ammonia injection amount calculation device 24 to calculate an optimum ammonia injection amount in consideration of the current temperature state of the catalyst, and this is converted into a valve opening signal to adjust the control valve 15 Output a control signal for controlling.

The details of the operation of the computing unit 22 will be described below with reference to FIG.

FIG. 2 is a flow chart showing the processing performed by the computing unit 22 at a certain time during the operation of the exhaust heat recovery heat exchanger of the present invention. The release of unreacted ammonia into the atmosphere is a problem mainly at startup. Also, although the load is changed, the description will proceed here assuming the start-up.

First, the lower limit value T _min of the reaction temperature of the catalyst is set at P ₁ . This value is constant throughout all operating conditions.

Subsequently, the catalyst inlet gas temperature T ₁ and the catalyst outlet gas temperature T ₂ at the current time are read in P ₂ , and in P ₃ , the higher one of these two temperature signals is _HL and the lower one is _TL.
Set to. MAX [T ₁ , T ₂ ] in the figure are T ₁ and T _2.
, MIN [T ₁ , T ₂ ] is T ₁ and T ₂
The smaller one is shown. Here, since the catalyst inlet side gas temperature T ₁ is higher than the catalyst outlet side gas temperature T ₂ at the time of startup, T _H = T ₁ and T _L = T ₂ .

Subsequently, at P ₄ , the ammonia injection amount A _O from the ammonia injection amount calculation device 24, which is not corrected for the temperature distribution in the catalyst, is read. After that, _TH (= catalyst inlet side temperature T ₁ ) is compared with the reaction temperature lower limit value T _min, and _TH <T
If _min , branch to P ₉ . In this case, since the catalyst inlet gas temperature T ₁ has not reached the reaction temperature lower limit value T _min , it is determined that the entire denitration catalyst has not reached the reaction temperature, and the true ammonia injection amount A = 0.

On the other hand, if T _H ≧ T _min, that is, if the catalyst inlet temperature T ₁ is equal to or higher than the reaction temperature lower limit value T _min , the process proceeds to P ₆ and T _L (catalyst outlet side temperature T ₂ ) and the reaction lower limit value temperature T _min. Compare with. At this time, if T _L ≧ T _min, that is, the catalyst outlet side temperature T ₂ is also the reaction temperature lower limit value or more,
Since it is determined that the entire denitration catalyst has reached the reaction temperature, the ammonia injection amount is not corrected and A = A ₀ (P
₁₀ ).

On the other hand, if T _L <T _min , the process branches to P ₇ . In this case, the catalyst inlet side temperature T ₁ has reached the reaction temperature, and the catalyst outlet side temperature T ₂ has not reached the reaction temperature, and it is judged that the denitration catalyst has partially reached the reaction temperature. .

Then, the correction coefficient α is calculated for the value A ₀ calculated by the ammonia injection amount calculation device 24. Here, the correction coefficient α represents the ratio of the portion reaching the reaction temperature range in the catalyst layer to all the catalysts, and is a function of the catalyst inlet temperature T ₁ and the catalyst outlet temperature T ₂ . As an example of this function, the temperature distribution between the catalyst inlet and outlet was approximated by a linear equation. Can be given as the simplest form.

Next, the corrected true ammonia injection amount A is calculated by multiplying the uncorrected ammonia injection amount A ₀ by α calculated in P ₇ (P ₈ ).

In this way, the true ammonia injection amount A determined in each of the above steps is converted into the opening signal of the control valve 15, and the opening signal is output to the control valve 15 (P ₁₁ , P
₁₂ ).

Even when the load changes, the optimum ammonia injection amount is calculated by the same process as the flowchart shown in FIG.

In this way, at the time of startup or load change, the area of the catalyst that has reached the reaction temperature from the denitration catalyst inlet / outlet gas temperature to the ammonia injection amount that was conventionally determined only from the exhaust gas state of the gas turbine etc. Since it is calculated and corrected by this, an appropriate amount of ammonia is injected into the exhaust gas, the amount of nitrogen oxides released into the atmosphere is minimized, and unreacted ammonia is released into the atmosphere. Can be prevented.

FIG. 3 is a view showing another embodiment of the present invention. In this exhaust heat recovery heat exchanger, a plurality of stages of denitration catalysts are provided in the flow direction, and a plurality of stages form one denitration device. Has been done. That is, between the evaporator 3 and the economizer 5, the first stage denitration catalyst 25a, ..., The nth stage denitration catalyst 25n are provided from the upstream side of the exhaust gas flow, and the inlet side of each stage is provided. Is provided with 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. At the outlet, the second stage outlet exhaust gas temperature detector 26
r is provided. The inlet side temperature detectors from the second stage to the nth stage are also used as the outlet side temperature detectors of the denitration catalyst of the preceding stage, and the output signals of these n + 1 temperature detectors are calculated by the calculator 22. Entered in.

The calculator 22 is also input from the ammonia injection amount calculation device 24 that calculates the ammonia injection amount using the signal 23 relating to the nitrogen oxide content in the exhaust gas as in the first embodiment, where n + 1 The number of catalyst stages reaching the reaction temperature is obtained from the signal of the exhaust gas temperature detector, the correction coefficient α defined by the ratio of this to the total number of stages is calculated, and the uncorrected ammonia injection amount A ₀ is multiplied to obtain the true value. Is calculated, and this value is converted into an opening degree signal of the control valve 15, and the signal is added to the control valve 15 as a control signal.

FIG. 4 is a flow chart showing the processing performed by the computing unit 22 at a certain time in the above-mentioned embodiment. First, the lower limit value T _min of the catalyst reaction temperature is set at P ₁ . Next, P ₂
Ammonia injection amount A ₀ not corrected by the ammonia injection amount calculation device 24 regarding the temperature distribution in the catalyst
Read.

At P ₃ , both the loop counter k that controls the loop from P ₄ to P ₁₀ and the counter i that counts the catalyst that has reached the reaction temperature are set to O.

At P ₄ , the loop k is incremented by 1, and at P ₅ , the catalyst inlet side gas temperature T _{K1 as} well as the outlet side gas temperature T _K2 is read, and at P ₆ that follows, the higher of T _K1 and T _K2 . T to
Set _{H 2} and the lower one to T _L. Here when starting up, T _K1 ＞
T inlet side gas temperature because it is _K2 to _{T H} T _{K2, T L} the outlet gas temperature T _K2 is set.

Then, performs comparison between T _H and the catalyst reaction temperature lower limit value T _min at P _7, since in the case of T H _{<T min} is not reached the reaction temperature, it is loop branches to P ₁₀ continues. On the other hand, when T _H > T _min , T _H has reached the reaction temperature, and then the process proceeds to P ₈ to compare T _L and T _min . At this time, if T _L ≧ T _min , the counter i is incremented by 1 because both the catalyst inlet and outlet of that stage have reached the reaction temperature. On the other hand, if T _L ≧ T _min is not satisfied, T _L has not reached the reaction temperature and counting is not performed and the process proceeds to P ₁₀ . Then, at P ₁₀ , P _{4 to} P ₁₀ are looped until the loop counter k reaches the total catalyst stage number n.

When the loop is completed in this way, the stage number i of the catalyst reaching the reaction temperature has been counted,
The true ammonia injection amount A corrected in P ₁₁ Calculate by And the above true ammonia injection amount A
Is converted into an opening signal of the control valve 15 and output to the control valve 15 (P _{12 ′} , P ₁₃ ).

As described above, the operation of the calculator 22 is basically the same as that of the first embodiment, but in the first embodiment, the correction coefficient is estimated by predicting the temperature distribution in the catalyst according to the exhaust gas temperature at the inlet and outlet of the catalyst. In contrast to the above, the second embodiment counts the number of stages of the denitration catalysts of all stages in which both the inlet and outlet temperatures reach the counter temperature, and obtains the correction coefficient α by α = i / n. It's different.

Therefore, also in this example, since an appropriate amount of ammonia for denitration corresponding to the catalyst portion that has reached the reaction temperature is injected, the atmospheric release of unreacted ammonia is minimized while minimizing the atmospheric release of nitrogen oxides. Can be suppressed. Further, in the present embodiment, since the temperature information that can be used for the calculation in the arithmetic unit 22 increases, the reliability can be expected to be improved as compared with the first embodiment. Further, when the number of stages of the denitration catalyst is relatively small, the accuracy of the ammonia injection amount can be increased by applying the first embodiment to each stage.

〔The invention's effect〕

As described above, the present invention detects the exhaust gas temperature at the inlet and outlet of the denitration catalyst and determines the temperature range where the reaction temperature is reached, so that the optimal amount of reducing agent is injected accordingly. Therefore, it is possible to minimize the release of unreacted reducing agent into the atmosphere, and it is not necessary to wait for the reducing agent to be injected until the denitration catalyst reaches the reaction temperature completely. Can be minimized.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an exhaust heat recovery heat exchanger of the present invention, FIG. 2 is a flow chart showing an operation of a computing unit, FIG. 3 is a schematic configuration diagram showing another embodiment of the present invention, and FIG. FIG. 7 is a flow chart showing the operation of the calculator in the other embodiment, FIG. 5 is a schematic configuration diagram of a conventional exhaust heat recovery heat exchanger, FIG. 6 is a temperature characteristic diagram of the denitration rate in the denitration device, and FIG. FIG. 4 is a state explanatory view showing changes in exhaust gas temperature at a gas turbine outlet, a denitration catalyst inlet and a denitration catalyst outlet. 2 ... Superheater, 3 ... Evaporator, 4 ... Denitration catalyst, 5 ...
Economizer, 10 ... reducing agent injection nozzle, 15 ... control valve,
20 ... Catalyst inlet side temperature detector, 21 ... Catalyst outlet side temperature detector, 22 ... Calculator, 24 ... Ammonia injection amount calculation device.

Claims (2)

[Claims] 1. An exhaust heat recovery heat exchanger comprising a denitration catalyst for detoxifying nitrogen oxides contained in exhaust gas, which is a heat source, by catalytic reduction decomposition, and a reducing agent injection device provided on the upstream side thereof. An exhaust gas temperature detector that detects the exhaust gas temperature at the inlet and outlet of the denitration catalyst, and calculate the optimal injection amount of the reducing agent by the output signal of the exhaust gas temperature detector,
An exhaust heat recovery heat exchanger, comprising: a calculator that outputs a control signal to a control valve provided in a reducing agent injection system. 2. An exhaust heat recovery heat exchanger comprising a denitration catalyst for detoxifying nitrogen oxides contained in exhaust gas, which is a heat source, by catalytic reduction decomposition, and a reducing agent injection device installed on the upstream side thereof. A denitration catalyst installed in multiple stages in the exhaust gas flow direction, an exhaust gas temperature detector that detects the exhaust gas temperature at the inlet side of each stage denitration catalyst and the exhaust gas temperature at the exit of the final stage denitration catalyst, and the respective temperatures. It has a calculator that calculates the catalyst stage that has reached the reaction temperature from the output signal of the detector, calculates the optimal reducing agent injection amount corresponding to it, and outputs a control signal to the control valve installed in the reducing agent injection system. An exhaust heat recovery heat exchanger characterized by the above.