JPS5926779B2 - Method for controlling nitrogen oxide emissions in gas turbine plants - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to (a) a method for controlling nitrogen oxide NOx emissions in a gas turbine plant.

A major component of popular pollutants from fossil fuel combustion equipment is hydrocarbons, the unburned emissions of the fuel.
C, carbon monoxide CO, and sulfur oxide SO
X and nitrogen oxide NOx.

In the case of a gas turbine combustor, the combustion is continuous at a high temperature with an air volume that is much larger than the stoichiometric air ratio, so the amounts of unburned emissions HC and Co are almost non-problematic, and the amount of sulfur Although the oxide SOX can be lowered by reducing the sulfur content in the fuel, the amount of NOx emissions is large and extensive reduction measures are required.

NOx is generated by the oxidation of nitrogen in the combustion air in the high temperature region of the flame (thermal NOx), and by the oxidation of nitrogen other than the fuel (fuel NOx), and the former is temperature dependent. is very large and increases significantly as the temperature increases, and the latter is affected by the partial pressure of nitrogen and oxygen in the fuel.
The higher the amount of nitrogen and excess oxygen, the higher the amount of NOx outside of nitrogen in the fuel.
The amount of conversion to will be large.

Conventionally, methods for reducing NOx in gas turbine plants include the water injection method, in which water or steam is injected directly into the combustor to cool the high-temperature region of the flame, and the other method is to inject a reducing agent into the gas turbine exhaust gas. However, a flue gas denitrification method that decomposes NOx into nitrogen and water is known.

The NOx reduction amount by the water injection method is controlled by the water injection amount W, which is the [NOx] concentration when water is injected and the [NOx] concentration when water is not injected.

Concentration ratio of concentration to concentration [NOx]/[NOx].

For example, if the water injection amount is W and the fuel flow rate is F, the following equation holds.

[NOx]/[NOx].

-exp(-k-) Here, k is a constant determined by the nitrogen content in the fuel, and becomes smaller as the nitrogen content increases.

In general gas turbines for power generation, the maximum value of W/F is determined by the amount of generalized carbon generated, and this value is approximately W/F.
F = ranges from 1.2 to 1.5.

On the other hand, the increase in power generation cost due to water injection is due to the amount of water consumed and the heat loss corresponding to the latent heat of vaporization of water, which increases approximately in proportion to the amount of water injection, and when W/F = 1. 5～
This is the second section.

In the conventional control of the water injection amount W, that is, the control of the amount of NOx discharged, the water injection amount W is changed in response to an increase or decrease in the fuel flow rate F so that W/F remains approximately constant. The water injection amount is not controlled so as to meet the target value.

By the way, NOx emission regulations are moving toward total volume regulation, and each power generation plant has to determine the optimal amount of power generation that corresponds to the demand for electricity that changes from time to time and the amount of NOx emission regulations, and the amount of power that is permissible at that time. The value of the NOx emission amount will be commanded.

In this case, in the conventional water injection method, since the W/F is controlled to be substantially constant, the amount of NOx discharged cannot be arbitrarily controlled with respect to the amount of power generated by the gas turbine.

Therefore, if the NOx emission reduction command value is relatively lenient, excessive water injection will be performed, resulting in an increase in the power generation cost corresponding to the extra amount of water injection, resulting in economically disadvantageous power generation. It turns out.

On the other hand, extremely strict NOx emission regulation values, such as 90%
It is impossible to meet this value using only the water injection method, and it is necessary to reduce the power generation capacity or use another NOx reduction method.
We will have to rely on reduction methods.

The above-mentioned flue gas denitrification method is considered as a method that greatly exceeds the NOx reduction value achieved by the water injection method.

This method decomposes NOx in the gas phase by the action of a reducing agent, and although the reducing agent is consumed, there is almost no pressure loss in the denitrification device, and it is suitable for denitration of gas turbines with a large amount of exhaust gas.

For example, when hydrazine is used as a reducing agent, the temperature of 400 to 600
In the range of °C, a NOx reduction rate of about a factor of 90 has been obtained.

This NOx reduction rate is determined by [reducing agent injection amount]/
It is uniquely determined by [NOx amount].

Although this denitrification method can significantly reduce NOx,
Furthermore, by combining this with the water injection method, 98%
This makes it possible to reduce NOx to a certain extent, and the amount of NOx emissions can actually be reduced to a negligible value.

However, in the denitrification method, the cost of power generation increases due to the consumption of the reducing agent, and as long as a reducing agent is used, the increase in the cost of power generation for the same NOx reduction rate is considerably higher than that of the water injection method.

In order to suppress this increase in power generation costs, it is necessary to reduce N in the combustor.
It is necessary to suppress the amount of o￥ generated as much as possible, to lower the NOx concentration in the exhaust gas, and to set and control the injection amount of the reducing agent so as to appropriately satisfy the set amount of NOx emission.

In addition, in gas turbine plants equipped with both the water injection method and the denitrification method, the amount of water injection is and the reducing agent injection amount must be set.

The purpose of the present invention is to minimize the increase in power generation costs in a gas turbine plant equipped with both the water injection method and the flue gas denitrification method, and to accurately satisfy the required value for reducing NOx emissions. It is an object of the present invention to provide a method for controlling the amount of NOx in which the amount of water injection and/or the amount of reducing agent injection is controlled.

In order to achieve such an objective, the present invention measures the NOx emission amount at a certain output value of the gas turbine, thereby simulating the relationship between the power generation output of the gas turbine and the NOx emission amount, and comparing the actual Determine the amount of emitted NOx at the operating output value, determine the NOx reduction rate from this amount and the NOx regulation value, and in order to satisfy this NOx reduction rate, first use the water injection method to determine the amount of water injection that satisfies the above reduction rate. If the NOx reduction rate cannot be achieved even if the amount is set to the maximum limit, set the water injection amount to the maximum limit, use the flue gas denitrification method in combination to find the reducing agent injection amount that satisfies the NOx reduction rate, and apply the water injection method. NOx is reduced by combining exhaust gas denitrification method.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

Gas turbine NOx emissions are determined by the fuel and air flow rate ratio,
It is influenced by the type of fuel, the amount of nitrogen content, combustor pressure, atmospheric humidity, temperature, combustor inlet air temperature, etc., but the relationship between NO and emissions due to each factor can be approximated as a certain functional form.

Therefore, NOx at a certain output value of the gas turbine
By measuring the concentration, we know the changes in each factor with respect to the gas turbine load, so we can accurately measure the amount of NOx emissions over the entire load range of the gas turbine, that is, simulate the power generation output and NOx emission concentration. be able to.

FIG. 1 shows experimentally determined changes in NOx emissions depending on the plant output using the nitrogen content in the fuel as a parameter, and the nitrogen content has a relationship of N1>N2>N3.

In addition to these factors, NOx emissions are affected by popular conditions (temperature, humidity), but the influence of atmospheric conditions is smaller than the influence of plant output and nitrogen content in fuel, and the amount of NOx emitted is The amount can be represented by nitrogen content and plant load.

Next, we will show the relationship between η and the water injection amount W using the nitrogen content in the fuel as a parameter when the plant output, that is, the NOx reduction rate η7 based on the water injection method is defined as when the power generation power is constant. Figure 2 shows this.

Reduction of NOx by water injection is mainly effective in reducing the generation of thermal NOx, but is less effective in preventing the generation of fuel NOx, so the effect is most pronounced in fuels with a low nitrogen content.

However, if the water injection amount is too large, HC and CO will be generated in large quantities, and there is a limit Wl beyond which it is impossible to increase the amount any further.

Therefore, depending on the amount of nitrogen in the fuel, the limit B
1. B2. There is B3.

FIG. 3 shows the relationship between η and reducing agent injection amount H when the NoX reduction rate η□ by the flue gas denitrification method is defined as η and the nitrogen content as a parameter.

FIGS. 2 and 3 show the characteristics at the values of the power generation output, and it has been confirmed that the characteristics shown in the figure are shown except in the region where the output is low, for example, the region of 30 or less.

Therefore, when the set power generation output A1 of the gas turbine and the NOx emission regulation value are commanded to be nl, and the NOx emission amount n at the power generation output is measured, the regulation value can be adjusted to satisfy nl as follows. The water injection amount W or W and the reducing agent injection amount H can be determined.

First, from the current power generation output as the first snap and the measured NOx emissions, the relationship between the nitrogen content in the fuel and the NOx emissions at full load can be simulated based on the characteristics shown in FIG.

In other words, if the actual power generation output is A and the measured NOx emissions are n, then the characteristic N3 passing through the intersection of A and n indicates the characteristics of the NOx emissions at full load using fuel at this time. .

Figure 1 shows N1. N2. Although the three characteristics of N3 are shown as representatives, in reality many characteristics are determined in advance, so the intersection of n and A is always on one of the characteristic curves. Become.

Therefore, if n and A are determined from the characteristics shown in FIG. 1, one characteristic with the nitrogen content as a parameter can be determined.

The next step is to set the power generation output A from the characteristics determined.
The NOx emission amount n1 at No. 1 is determined from FIG.

That is, the NOx emission amount n1 when the power generation output of the plant is set to the set value A1 is predicted, and the required NOx reduction rate η is calculated from this predicted value using the previously given NOx regulation value.

seek. That is, Calculate.

Next, from the characteristics of FIG. 2, the limit reduction rate B3 due to water injection is determined using the characteristics of N3.

If ≦B3, η.

-η is obtained from the N3 characteristic diagram in FIG.

η.

〉B3, calculate the reducing agent injection amount H that is ηOB3 - η□ from the N3 characteristic in Fig. 3, and use both methods together to reduce NOx using the water injection amount W2 and the reducing agent injection amount H. Make a reduction.

The characteristics shown in Figs. 2 and 3 differ from those shown in the figures where the power generation output of the plant is extremely small. Therefore, in such operating regions, the conventional method should be used without implementing the method of the present invention. good.

Figure 4 shows the relationship between the NOx reduction rate and the increase in power generation costs.The flue gas denitrification method is higher than the water injection method in terms of the increase in power generation costs, and the limits of each NOx reduction rate are C, If B (C>B), the request reduction rate is 0-B
If the case is B-C, the increase in costs can be reduced by reducing up to B with the water injection method and reducing the rest with the flue gas denitrification method.

Point B in FIG. 4 is shown in FIG. 2 as B1°B2. B3, and its value can be determined if the nitrogen content in the fuel and the limit water injection amount Wl (determined by the fuel used) are determined.

FIG. 5 shows the configuration of an embodiment of a control device that implements the above-mentioned control method, in which 1 is a compressor, 2 is a combustor, and 3 is a combustor.
1 is a turbine, 4 is a generator, and 5 is an exhaust duct, which constitute a gas turbine power generation plant.

6 is a central command unit, 7 is an arithmetic controller, 8 is a NOx monitor, 9 is a fuel tank, 10 is a fuel adjustment valve, 11 is a water tank, 12 is a water flow rate adjustment valve, 13 is a reducing agent tank,
14 is a reducing agent flow rate adjustment valve, 15 is a reducing agent injector, 1
6 is an exhaust gas sampling tube, 17 is a sample gas, 18
indicates a pump.

In such a configuration, the NOx value under a certain operating condition of the gas turbine is measured by the NOx monitor 8 by taking out the sample gas 17 from the exhaust gas sampling pipe 16, and is inputted to the arithmetic controller 7 as the NOx concentration signal 103. Ru.

The arithmetic controller 7 outputs a power generation output signal 10 of the gas turbine.
1 and the NOx concentration signal 1030 input signals, the predicted values of the power generation output and NOx emissions of the gas turbine as shown in FIG. 7, and the gas turbine NOx is
The value is controlled so that it satisfies the specifications.

At this time, if the gas turbine is in a low NOx operation using both water injection and reducing agent injection, the water injection amount setting signal 105 and the reducing agent injection amount setting signal 106 are used, respectively. The NOx reduction rate is calculated by the arithmetic controller 7 from the flow rate of This section describes the NOx control method when changing the power generation output of the gas turbine and the NOx regulation value based on the operating conditions.

A command signal for increasing or decreasing the power generation output of the gas turbine is input from the central command device 6 to the arithmetic controller 7 as a power generation output command signal 101, and a signal 1 of the NOx regulation value at this time is inputted to the arithmetic controller 7.
02 is similarly input to the arithmetic controller 7.

The arithmetic controller 7 calculates the NOx emissions after the change in the gas turbine power output based on the simulation of the gas turbine power output and NOx emissions shown in FIG. The required NOx reduction rate is calculated.

Then, the NOx reduction rate after the change in the power generation output of the gas turbine is simulated as a function similar to that shown in Figures 2 and 3, and the required water injection amount and reducing agent injection amount are calculated, and Regarding the former, it is determined whether the required water injection amount is within an allowable value.

Here, the same NOx reduction rate is used as the basis for both low NOx
If the increase in power generation costs due to water injection is smaller than that of smoke denitrification, that is, when the relationship shown in Figure 4 exists, even if the required NOx reduction rate is within the limit B of water injection. For example, the required water injection amount calculated by the arithmetic controller 7 is set by operating the water flow rate adjustment valve 12 using the setting signal 105.

Furthermore, if the required NOx reduction rate is C, which exceeds the water injection limit in Figure 4, the water injection is set to the water injection amount that gives the limit reduction rate B, and the water injection amount is set to the amount necessary to satisfy the required NOx value. By calculating the NOx reduction efficiency of flue gas denitrification, the required amount of nitrogen injected is determined from a simulation similar to that shown in FIG.

The Kowara water injection amount and reducing agent injection amount are each set to signal 1.
The flow rate is set by operating the water flow adjustment valve 12 and the reducing agent injection valve 14 at 05°106.

By controlling NOx emissions in this way, we can accurately keep the NOx emissions, which change in response to the required power generation amount of the gas turbine, which changes over time, within the required regulatory values, and create conditions that minimize power generation costs. It becomes possible to control the

In this case, the signal 103 of the exhaust gas NOx monitor 8
The accuracy of NOx control can be further improved by incorporating feedback control between the signal 102 and the NOx emission control amount signal 102.

As described above, according to the present invention, the NOx emission regulation amount can be accurately and smoothly controlled so that the increase in power generation costs is minimized.

[Brief explanation of the drawing]

The figures are all related to the present invention; Figure 1 is a simulation diagram of power generation output and NOx emissions, Figure 2 is a simulation diagram of water injection amount W and NOx reduction rate η, and Figure 3 is a simulation diagram of reducing agent injection. Fig. 4 is a simulation diagram of the NOx reduction rate η and increase in power generation costs, and Fig. 5 is a configuration diagram of an embodiment of a device that realizes the NOx control method. be. 2... Combustor, 3... Turbine, 4...
... Generator, 6 ... Central command unit, γ.
... Arithmetic controller, 8... NOx monitor,
12...Water flow rate adjustment valve, 14...
Reducing agent flow rate adjustment valve, 101...Power generation output request signal, 102...NOx emission regulation signal.

Claims (1)

[Claims] 1 Measure nitrogen oxide emissions at a certain power generation output value of the gas turbine, and simulate the relationship between the power generation output and nitrogen oxide emissions of the gas turbine and the amount of nitrogen in the fuel, and set the From the power generation output, determine the amount of nitrogen oxide emissions and nitrogen in the fuel at the set power generation output from the relationship between the power generation output and nitrogen oxide emissions, and calculate the nitrogen oxide emissions and nitrogen at the set power output. The required nitrogen oxide reduction rate is determined from the amount of oxide emissions, and the relationship between the nitrogen oxide reduction rate and the water injection amount and reduction injection amount is simulated using parameters other than nitrogen in the fuel, and the above-mentioned required nitrogen oxide reduction rate is calculated. When the nitrogen oxide reduction rate is less than or equal to the maximum limit reduction rate obtained by water injection, determine the amount of water injection so that the reduction rate obtained by water injection is equal to the required reduction rate, and calculate the required reduction. Nitrogen oxidation in a gas turbine plant characterized by determining the injection amount of reducing agent so that when the rate is large, the amount exceeding the maximum limit reduction rate due to water injection is reduced by combined use of flue gas denitrification method. Method for controlling the amount of waste discharged.