JPS6238610B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to the control of SOx emissions in exhaust gas from a boiler, and in particular, in a boiler that uses multiple fuels, the amount of sulfur in the fuel is controlled by controlling the usage ratio of each fuel. This is related to the control of SOx emissions in exhaust gas.

In the operation of power plants, social regulations regarding environmental pollution have become stricter, and in addition to K-value regulations, especially regarding SOx in exhaust gas from boilers,
SOx emissions are being regulated.

To deal with this, power plants have adopted methods such as removing SOx from exhaust gas using flue gas desulfurization equipment and using fuel with low sulfur content.

In the latter method, since low-sulfur fuel is more expensive than high-sulfur fuel, low-sulfur fuel and high-sulfur fuel are blended, and the sulfur content in the fuel is adjusted to an appropriate level. By adjusting the value, we can control the amount of expensive low-sulfur fuel used and adjust SOx emissions in the exhaust gas from the boiler to be within the regulated value, resulting in the most economical operation within the constraints of environmental regulations. I try to do this.

Conventionally, in such cases, the SOx concentration and exhaust gas flow rate in the exhaust gas from the boiler are measured, and from this the SOx emissions in the exhaust gas are calculated, and the sulfur content in the fuel and the fuel flow rate are measured. Calculate the amount of SOx emissions in the exhaust gas, compare this value with the regulation value from time to time, and if the SOx emission amount is greater than the regulation value, increase the blend ratio of fuel with a low sulfur content, and
If emissions are lower than the regulation value, adjustments are made by increasing the blending ratio of fuel with a high sulfur content.

FIG. 1 shows an example of a method for controlling the amount of SOx discharged from the exhaust gas from a boiler according to this prior art. In the figure, 1 indicates the amount of SOx in the exhaust gas based on the measurement signals of the SOx concentration in the exhaust gas and the exhaust gas flow rate.
2 is a setting device that sets the target value of SOx emissions in exhaust gas; 3 is a signal from setting device 2 (target value of SOx emissions in exhaust gas) and a signal from calculator 1. A subtractor that calculates the deviation of the signal (measured value of SOx emissions in exhaust gas), 4 is a calculator that calculates the manipulated variable of the amount of sulfur in the fuel from the deviation of SOx emissions, 5 is a general fuel with a high sulfur content. a calculator that calculates the difference between the sulfur concentration and the sulfur concentration in the low sulfur fuel based on the measurement signals, and calculates the amount of change in the sulfur content in the fuel when the unit amount of fuel is changed; 6 corrects the fuel based on the signal from the calculator 4 (manipulated amount of sulfur in the fuel) and the signal from the calculator 5 (changer for changing the amount of sulfur in the fuel when the unit amount of fuel is changed) A calculator that calculates the manipulated variable, 7 a limiter that limits the modified manipulated variable, 8 a fuel quantity command value transmitter, and 9 a signal from 8 (fuel quantity command value) and a signal from 7 (fuel modified manipulated variable). Adder 10 calculates the fuel quantity command value for more general fuel, and 10 calculates the fuel quantity command value for low sulfur content fuel from the signal from 8 (fuel quantity command value) and the signal from 7 (fuel correction operation amount). It is a subtractor. In the control system shown in the figure, when a deviation occurs between the target value and the measured value of SOx emissions in exhaust gas, the fuel amount command values for general fuel and low-sulfur fuel are revised according to the amount of deviation, and the SOx emissions are reduced. It is controlled to match the target value.

In the conventional control method described above, control is performed from time to time in response to deviations in the amount of SOx discharged from the exhaust gas from the boiler. On the other hand, environmental regulations are regulated based on the cumulative value of SOx emissions over a specified period of time (usually one hour), and conventional control methods have the drawback of not being able to fully comply with environmental regulations.

The purpose of the present invention is to eliminate the drawbacks of the above-mentioned conventional method, and to create a system based on integrated values that comply with environmental regulations.
The purpose is to provide a control device for SOx emissions.

To control SOx emissions based on integrated values, it is necessary to predict changes in SOx emissions in exhaust gas,
It is necessary to find the predicted value of the cumulative value of SOx emissions over the specified time, compare this with the regulation value, and calculate the corrected operation amount.

SOx in exhaust gas is generated by the combustion of sulfur in fuel, and the fluctuations in the amount of SOx emissions in exhaust gas respond to fluctuations in the amount of sulfur in fuel as shown in Figure 2.

Figure 2a shows the fluctuations in the amount of sulfur in the fuel, and Figure 2b shows the fluctuations in the amount of SOx emissions in the exhaust gas.

From the figure, the amount of sulfur in the fuel is Δ before t ₁ from the current time.
When S(t ₁ ) fluctuates, the resulting fluctuation in the amount of SOx discharged in the exhaust gas at the current time is expressed by the following equation.

Also, t ₁ before the current time, the amount of sulfur in the fuel is ΔS
The variation in the amount of SOx emissions in the exhaust gas due to the change in SOx (t ₁ ) after t ₂ from the current time is expressed by the following formula.

From this, when the amount of sulfur in the fuel fluctuates by ΔS(t ₁ ) before t ₁ from the current time, the fluctuation in the amount of SOx emissions after t ₂ from the current time is expressed by the following equation.

ΔSOxF (t ₁ , t ₂ ) = ΔSOx (t ₁ , t ₂ ) −ΔSOx (t ₀ , 0) Future fluctuations in SOx emissions due to changes in the amount of sulfur in the fuel will be Since it _is the sum of future changes in SOx emissions due to changes in the amount of sulfur in the
The predicted value of emissions is expressed by the following formula.

SOx (t ₂ ) = SOx (0) + ∫ΔSOx × F (t ₁ , t ₂ ) dt ₁ where SOx (0): instantaneous value of SOx emissions at present The above formula is based on past actual measurements and boiler fuel Because it is a function of the response characteristics of the fluctuations in SOx emissions in the exhaust gas (dead time t ₂ and first-order lag time constant T ₁ ) to fluctuations in the amount of sulfur in the fuel, the fluctuation in the amount of sulfur in the fuel up to the current time If you memorize the progress, you can easily calculate it.

Note that when t ₁ becomes sufficiently large, ΔSOxF(t ₁ , t ₂ )
is close to 0, so it is only necessary to consider a certain period of time t ₁ starting from the present moment. Also, if t ₂ becomes sufficiently large, SOx (t ₂ ) approaches a constant value, so if t ₂ is calculated for a certain period, it can be approximated by assuming that a constant SOx emission continues after that.

Based on the predicted value of the SOx emission amount (instantaneous value) calculated above, a predicted value of the integrated value of the SOx emission amount for a specified time is determined.

Figure 3 shows an overview of the method for calculating the predicted value of the cumulative value of SOx emissions. In the figure, the horizontal axis indicates the time axis, t ₀ indicates the current time, and T indicates the specified time. Further, the vertical axis SOx (t) indicates the instantaneous value of the SOx emission amount at each time. (The area under the curve representing the instantaneous value of the SOx emission amount corresponds to the integrated value.) Then, S _T (t) indicates the integrated value of the SOx emission amount up to time t. In the figure, the cumulative value of SOx emissions up to the current time t ₀ is expressed by the following formula and obtained as known data.

S _T (t ₀ ) = ∫ ^t0 ₀ SOx (t) dt On the other hand, the predicted value of the SOx emission amount (instantaneous value) after the current time is the SOx emission amount at the current time t ₀ and,
Based on the above considerations, it can be calculated using the following formula from the fluctuation history of the amount of sulfur in the fuel up to the current time.

SOx (t) = SOx (t ₀ ) + ∫ ^t0 _t0 - _Tx ΔSOxF (t ₁ , t) dt ₁ where T _x : ΔSOxF (t ₁ , t) can be ignored t ₁ The right-hand side of the above equation is all the current time It can be obtained from the actual measured values up to t ₀ .

From this, the predicted value of the cumulative amount of SOx emissions after the specified time has elapsed can be calculated using the following formula.

S _T (T)=∫ ^t0 ₀ SOx(t)dt+∫ ^T0 _t0 SOx(
t)
dt = S _T (t ₀ ) + SOx (t ₀ ) (T-t ₀ ) +∫ ^T0 _T0 ∫ ^t0 _t0-Tx ΔSOxF (t ₁ , t) dt
₁ dt The predicted value of the cumulative value of SOx emissions calculated above is the predicted value when no correction operation is performed at the current time t ₀ , and this value and the predicted value at the specified time
The amount of sulfur in the fuel may be corrected so as to eliminate the deviation of the regulation value of the integrated value of SOx emissions.

If this correction operation amount is ΔS, the amount of variation in the amount of SOx emissions at time t after the current time is expressed by the following formula.

When this correction operation is performed, the predicted value of the integrated value of SOx emissions becomes equal to the regulation value, so the following equation holds true.

From this, the corrected operation amount can be determined by the following formula.

Here, if the sulfur content of the general fuel is S _a and the sulfur content of the low sulfur fuel is S _b , then in the fuel when the blend ratio is changed by decreasing the unit amount of the general fuel and increasing the low sulfur fuel by the same amount. The variation in the amount of sulfur in is shown by the following formula.

S _ab = S _a −S _b Accordingly, the fuel operation amount for changing the blend ratio to make the integrated value of SOx emissions equal to the regulation value is calculated by the following formula.

ΔF=ΔS/S _a −S _b As described above, according to the present invention, the cumulative value of SOx emissions from the start time of the specified time to the current time, the instantaneous value of SOx emissions at the current time, and the current Based on the changes in the amount of sulfur in the fuel up to that point in time, a predicted value of the cumulative SOx emissions over a specified period of time is calculated, and based on this, a corrective operation amount for the fuel blend ratio is determined and controlled. ,
It is possible to control the cumulative value of SOx emissions to match environmental regulation values.

The above example describes the case where the amount of SOx emissions in exhaust gas is calculated from the SOx concentration in exhaust gas from a boiler and the exhaust gas flow rate.
Instead of using the measured value of SOx emissions, the amount of sulfur in the fuel is calculated from the sulfur content in the fuel and the fuel flow rate, and from this, the amount of SOx emissions in the exhaust gas is approximated by equivalent conversion and monitored and controlled. be.

In this case, there is a proportional relationship between the amount of sulfur in the fuel and the amount of SOx emitted in the exhaust gas, which corresponds to the case where T _L =0 and T ₁ =0 in FIG. 2.

When this value is substituted into the above-mentioned calculation formula, the fuel operation amount for changing the blend ratio to make the integrated value of SOx emissions equal to the regulation value becomes the following formula.

ΔF=1/S _a −S _b・S _TA −S _T (t ₀ )−SOx(t ₀ )(T−t
₀ )/K ₀ (T-t ₀ ) As shown above, when calculating the amount of sulfur in the fuel from the sulfur content in the fuel and the fuel flow rate, and approximating the amount of SOx emissions in the exhaust gas from this by equivalent conversion,
By calculating the fuel correction operation amount for changing the blend ratio from the cumulative value of SOx emissions up to the current time, the instantaneous value of SOx emissions at the current time, and the remaining time until the specified time, the present invention can be easily applied. Control based on principles can be implemented.

FIG. 4 shows a block diagram of an embodiment in which the above control is carried out using a computer, and FIG. 5 shows a flowchart of the contents of the control processing by the computer at that time.

In FIG. 4, the low sulfur content fuel is supplied from the low sulfur content supply line 41, and the high sulfur content fuel is supplied from the high sulfur content supply line 4.
It is line blended with high sulfur content fuel supplied from 2, and is burned in a boiler 48 via a fuel supply line 47. The amount of fuel supplied to the boiler 48 is controlled by a fuel control device 50 according to the boiler load requirements. The flow rate signal from the flowmeter 46 is input to the control device 50 for this purpose, and at the same time, it is also input to the computer system 53 for SOx emission control.
The flow rate of the low sulfur fuel is regulated by a flow control valve 43 driven by a control valve drive device 56 based on a command from a computer system 53. Flowmeter 44
The signal is taken into the computer system 53 for this purpose. In this process, the flow rate of high sulfur fuel is
It is obtained by subtracting the low sulfur content fuel flow rate (value of flow meter 44) from the amount of fuel supplied to the boiler (value of flow meter 46). On the other hand, the exhaust gas flow rate from the chimney 49 is determined by the exhaust gas flow rate detector 52 and the SOx in the exhaust gas.
The concentrations are each measured by SOx concentration detectors 51 and taken into the computer system 53. Note that the exhaust gas flow rate can also be calculated by the computer system 53. The sulfur content in the fuel is set in the low sulfur fuel sulfur content setter 54 and the high sulfur fuel sulfur content setter 55 based on the analysis results, and is taken into the computer system. In the computer system 53, SOx emission control is executed according to the process shown in FIG. 5 based on this information. This process is repeatedly executed at a predetermined period, but if there is a control deviation when the control period approaches the end of the relevant time period (when t ₀ approaches T), S _TA - S _T (if there is t ₀ )) the manipulated variable becomes large and control becomes unstable. Therefore, in this control method, near the end point of the time period, the above operation amount is calculated using the following formula ΔF=1/S _a −S _b・S _{TA −ST} (t ₀ )−SOx(t ₀ ) (t-t
₀ )/K ₀ (T−t ₀ ) is dealt with by setting the following limit.

When T-t ₀ α, T-t ₀ =α α: Constant The above processing is performed in block 90 in FIG.

According to this control method, the SOx
Since emissions can be controlled accurately, the consumption of expensive low-sulfur fuel can be reduced, which has the effect of reducing boiler fuel costs.

[Brief explanation of the drawing]

FIG. 1 is a block diagram for explaining the prior art, FIGS. 2 and 3 are graphs for explaining the present invention, and FIG. 4 is a block diagram for explaining an embodiment of the present invention. , FIG. 5 is the same flowchart. 41...Low sulfur content fuel supply line, 42...High sulfur content fuel supply line, 43...Flow rate control valve, 44...Flow meter, 45...Flow rate control valve, 46...Flow meter, 47...
Fuel supply line, 48...boiler, 49...chimney, 5
3...Computer system.

Claims (1)

[Claims] 1. Detecting the flow rate of exhaust gas from the boiler in a boiler having a fuel supply section capable of supplying a plurality of types of fuel and a fuel supply amount control means for controlling the amounts of various fuels supplied from the fuel supply section. The system is equipped with exhaust gas flow rate detection means a, detection means b for SOx concentration in exhaust gas, fuel supply amount detection means c for detecting the supply amount of each fuel, and fuel component detection means d for detecting the sulfur content of each fuel. from the evaluation start time to the current time
The amount of SOx emissions is determined based on the detected values of the exhaust gas flow rate and SOx concentration at each time detected by means a and b, or the amount of fuel supplied at each time detected by means c and d. By calculating and integrating the SOx emissions at each time based on the detected value of the amount of sulfur contained in the fuel, the detected values of the exhaust gas flow rate and SOx concentration detected by means a and b are integrated. is calculated based on the instantaneous value of SOx emissions at the current time calculated based on the amount of fuel supplied at each time detected by means c and means d and the detected value of the amount of sulfur contained in each fuel. Based on the amount of change in the amount of sulfur in the fuel up to the current time, the trend in SOx emissions after the current time is predicted by calculation according to a predetermined calculation formula, and based on the integration results and the prediction results. , according to a predetermined calculation formula, during the environmental regulation evaluation period.
The predicted value of SOx emissions is calculated, and the amount of sulfur in the fuel is corrected according to the deviation between this predicted value and the regulation value of SOx emissions so as to eliminate the deviation between the predicted value and the regulation value. A method for controlling SOx emissions in exhaust gas, characterized in that supply ratios of various fuels are corrected and controlled by giving control command values to each of the fuel supply amount control means. 2 SOx in exhaust gas described in claim 1
In the emission control method, when the current time is close to the end point of the environmental regulation evaluation period, a predetermined value is used to calculate the corrected control amount for each fuel supply amount based on the deviation between the predicted value of SOx emissions and the regulation value during the environmental regulation evaluation period. SOx in exhaust gas characterized by setting a limit of
Emission control methods.