JPH043801A - Boiler controller - Google Patents

Abstract

PURPOSE:To maintain the numerical values for performance of a plant by using a parameter that is given by the brand, etc. of used fuel and inputting measured values of the exhaust gas temperature at the furnace outlet, set temperatures, and total fuel quantity instruction value of boiler in order to calculate the fuel quantity instruction value of each burner. CONSTITUTION:The brand of coal is given by a signal setting element 207 and a function element 209 which receives a load instruction 101 and brand setting 208 gives the temperature at the furnace outlet for the boiler load. A signal 202 gives actual measured values of temperature at the outlet of the furnace measured by a gas thermometer. And a first calculator 211 receives signals 202, 210, 208 and a fuel instruction 151 to calculate fuel instructions 212 and 213 at the maximum capacity of each burner and in the range of turndown. Pulverized coal volume instructions 212 and 213 are compared with the actual flow rates 204 and 206 and the drive signals 216 and 217 for a supply coal feeder are given in order to make the deviation in said comparison zero. With this arrangement the shortcomings in steam pressure control are eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a boiler control device suitable for burning different brands of coal.

[Conventional technology]

FIG. 3 shows pulverized coal production equipment 56, 57, steam turbine 19, 23, and generator 25 that constitute the boiler equipment to which the present invention is applied. These facilities are combined with the conventional control device shown in FIG. 4, and operate as a total system as a thermal power plant that follows the load command signal 101 shown in FIG.

Hereinafter, the outline of the boiler equipment and its control device shown in FIGS. 3 and 4 will be explained.

a) The current generated power signal 27 is the command (load command signal)
The opening degree of the turbine control valve 17 is changed so that it matches 101.

That is, if the command 101 gives an increase in load, the control valve drive signal 1 is increased until the actual power generation amount (generated power signal) 27 follows.
8 increases due to the proportional-integral adjustment effect.

b) According to the increase/decrease in the load command 101, the water supply command 147 is obtained via the function 104 giving the load/water ratio.

However, since the furnace water wall 5 receives the most intense radiation heat transfer in the boiler, in order to protect the heat transfer tubes, the setting element 112 provides a minimum water supply amount to drive the water supply flow rate control valve 2.

The purpose of this protection is to prevent the heat transfer coefficient on the inner surface of the heat exchanger tube from rapidly decreasing when the flow velocity inside the electric heating tube decreases, and the heat exchanger tube is no longer cooled. However, it is uniformly set from the viewpoint of securing the flow velocity in the pipe, and corresponds to securing water supply with priority over control of the water/fuel ratio of the boiler, which will be described later.

C) If the amount of water supplied to the boiler exceeds the amount necessary to maintain the load at the time in order to protect the ice wall (furnace ice wall) 5, fuel is input according to the load, so the water Steam and water are mixed at the outlet of the wall 5, and moisture is recovered as a drain 7 by a steam and water separator 6. Normally, although not shown, the drain is returned to the boiler feed water by a recirculation pump, or returned to the upstream of the feed water pump 1 after heating the feed water by a heat exchanger. is called "circulation mode". Conversely, the water supply corresponding to the load command 101 is
When the setting (setting element) 112 is exceeded, the fuel also reflects the command 101, so the outlet of the water wall 5 becomes dry steam, and the drain recirculation as described above does not occur.
This is called "through-flow mode."

Signal switching elements 107, 115 both provide signals as shown in FIG. 4 in the "through-flow mode" and in the "circulation mode".
In , it switches to the side indicated by the arrow. The determination of such mode is given by the function element 108 based on the load command.

d) The main steam pressure of the boiler is input by signal 16 and set value 1 given by function 105 in response to load command 101
According to the deviation from
A correction signal is given to.

This is because the boiler steam pressure basically depends on the density of the retained steam, and in order to increase the pressure, the amount of evaporation must be increased, but in "circulation mode", increasing the fuel command 151 increases the amount of evaporation. On the other hand, in the "through-flow mode", the ice wall outlet is already in the dry steam region, so increasing the water supply command 147 will increase the amount of evaporation.

e) The fuel quantity command 151 is basically the water/fuel ratio function 113
As mentioned above, in the "circulation mode", a correction signal 149. based on the steam pressure deviation is given. In the "throughflow mode", it is corrected by the deviation from the set value 148 of the signal 59 giving the next week's steam temperature at the outlet of the heater. This is because in areas where the exit of the ice wall is dry, the excess or deficiency of fuel is reflected in the steam temperature. Directive 151 is for pulverized coal production equipment in operation 56.5
According to the number of machines such as 7, etc., it is divided by the value of the setting 118, and the amount of coal fed per production facility is adjusted by the drive signal 29, 36, etc.

f) The air flow rate command 43 is obtained by correcting the value given by the fuel/air ratio function 125 so that the oxygen concentration signal 51 in the waste gas at the outlet of the economizer 4 is maintained at the set value.

g) The main steam temperature is input as a signal 14, and according to the deviation from the set value 153, water is injected into the superheater desuperheater for control.
At this time, in order to ensure a sufficient amount of water injection amount reduction when the steam temperature decreases, the boiler heat transfer surface distribution is previously designed with a steady water injection amount according to the load, and this value is given by the function element 139. .

h) Reheat steam temperature is input with signal 61 and set value 152
According to the deviation signal 157 from
Adjust the amount of gas recirculation by correcting.

Here, the reason why the element 130 is not made to exert an integral action is to prevent mutual interference of the integral action by the element 141 for controlling the reheat steam temperature using the signal 48, which will be described later.

Reheating steam temperature control by gas recirculation utilizes the positional relationship between the hanging superheater 12 and the hanging reheater 22.

In other words, the form of heat transfer from the combustion gas to the heat exchanger is
It is known that the former is proportional to the fourth power of the absolute gas temperature, and the latter is proportional to the gas volumetric flow rate to the 0.6 power.

Therefore, the superheater 12 on the gas high-temperature side is designed to use "radiation" to obtain a predetermined performance, and similarly, the reheater 22 has a high rate of heat transfer by "convection". Here, if the amount of gas recirculation is increased, the amount of gas passing through the heat transfer surface 12.22 will increase, but since the proportion of low temperature gas at the outlet of the economizer 4 being mixed into the furnace will increase, the gas temperature will decrease. descend.

Therefore, an increase in gas recirculation decreases "radiation" and increases "convection", so the amount of heat absorbed by the superheater (suspended superheater 12), which has a large proportion of the former, decreases, and the amount of heat absorbed by the reheater (suspended Reheater 2
2) will increase. Therefore, it is possible to control the temperature of the reheated steam by adjusting the amount of heat absorbed by the reheater 22 according to the deviation 157, but such a method essentially causes disturbance to the temperature of the main steam passing through the superheater 12. give.

However, on the main steam side, water injection into the attemperator 9, which is a powerful temperature control means, can be actively used without causing a decrease in plant efficiency, so it is advantageous to be able to absorb such disturbances. Since water injection into the reheater 22 is avoided because it causes a significant drop in plant efficiency, gas recirculation is positioned as a quick-response control method that can adjust the heat absorption of the suspended heat transfer surface near the boiler outlet.

i) Although gas recirculation is effective in controlling the temperature of reheated steam as described above, since the exhaust gas is blown from the furnace hopper, it inevitably affects combustion, and excessive recirculation can cause fuel instability and unburned content (soot). ) will increase, and if it is too small, harmful nitrogen oxides will increase in the exhaust gas.

Therefore, the gas recirculation damper can only be opened and closed within the upper and lower limits given by the setting elements 133 and 135, and is actually positioned as a means for reducing transient reheat steam temperature fluctuations. The main reheat steam temperature control uses gas dampers 47 and 45 to distribute the amount of gas passing through the horizontal reheater 21 and horizontal superheater 8, respectively, based on the deviation signal 157, giving priority to the reheat steam temperature, so to speak. Disturbances to the steam temperature will be resolved by injecting water into the desuperheater 9. The above control using the horizontal heat transfer surface gas path damper has the advantage of not having any adverse effects on combustion, and eliminating the need for a special increase in ventilation power to eliminate steady-state deviations, but it is controlled on the heat transfer surface far from the steam extraction position from the boiler. The biggest drawback is that the response is slow.

Therefore, good reheat steam temperature control can only be achieved in combination with the above-mentioned gas recirculation.

In FIG. 4, function 142 gives the base position of the reheater damper drive signal at each load, and subtractor 145 operates the superheater damper (gas damper) 45 inversely to the reheater damper (gas damper) 47, so that the reference Subtraction is performed from the position setting 144.

[Problem to be solved by the invention]

Compared to oil and gas fuels, coal has a lower volatile content, calorific value,
There are very wide differences in properties in terms of crushability, moisture content, etc., and when multiple types of coal are burned in the boiler equipment shown in Figure 3, the following problems arise.

1-a) In general, coal with a high volatile content burns quickly in the furnace, and the opposite is true for coal with a low volatile content, and the distribution of heat is biased towards the furnace exit, so the temperature of the furnace exit gas depends on the volatile content. Inverse correlation with size (if volatile content is small, outlet gas temperature is high)
have. Generally, the following equation holds for the amount of heat absorbed by a furnace.

Qw = Ct −Gy To ・Cg ・(G
y 1Q, +Gr) - (1) Qo: Furnace heat absorption per unit time C1 Fuel calorific value per two units of input Gf Fuel input per two units of input T9: Furnace outlet gas temperature C9: Combustion gas Average gas specific heat G1: Air input amount per unit time Gr 2 Gas recirculation amount per unit time If the boiler load is the same, there is no big difference in C2 and GtO values regardless of the fuel properties, but T, Since there is a range of values, it is shown that Q is quite different. This is the conventional technique (c),
This adversely affects the circulation/throughflow switching control described in sections (d) and (e).

That is, if the load command 101 is the same, the boiler feed water will be approximately the same, but since the heat absorption of the furnace is different, the load at which the outlet of the furnace water wall 5 turns into dry steam will vary considerably depending on the fuel properties. As described in the related art, the operation of the control device must be switched depending on the difference in circulation/throughflow mode, but if the actual wetness/dryness of the outlet of the water wall 5 does not match, the following problems will occur.

b) If once-through mode control is performed even though the actual plant is humid, the increase in water supply in response to the drop in steam pressure will make the ice wall outlet even more humid, reducing the amount of evaporation and further increasing the steam pressure. descend.

(Example) If circulation mode control is performed even though the actual plant is dry, the increase in fuel corresponding to the drop in steam pressure will only increase the steam temperature at the outlet of the ice wall and will not increase the amount of evaporation, causing mischief. This only causes a disturbance to the steam temperature control.

Therefore, in a boiler that burns multiple types of coal, it is not possible to switch between the circulation mode and the once-through mode based on the load alone, as in the function element 108, unless some measure is taken.

In addition, it is difficult to realize a method for detecting wetness/dryness in an actual plant because the dryness (mass ratio of saturated water and saturated steam) itself does not directly affect physical quantities that are easy to measure, such as the temperature and pressure of the air-water mixture. .

1-b) As mentioned in the previous section, the temperature of the furnace exit gas differs depending on the type of coal used, and the difference in moisture and hydrogen content in the fuel changes the amount of water vapor in the combustion gas, which affects the temperature of the superheater and reheater. Radiative heat transfer is influenced by both the gas temperature itself and the radiation parameters.

The basis of the above mechanism is as explained in h) of the previous section. The most essential way to change the ratio of radiation/convection heat transfer is to adjust the amount of gas recirculation.
Currently, as mentioned in i) of the previous section, in order to maintain good combustion, gas recirculation is performed at an amount between the upper and lower limits, and the gas path damper is adjusted so that the reheated steam temperature reaches the specified value, and the steam temperature fluctuations are adjusted. At the time of occurrence, a control philosophy must be adopted in which only transient fluctuations that cannot be followed by control by the gas path damper depend on gas recirculation changes.

Therefore, depending on the type of coal, the gas pass damper 45.4
There are cases where the opening degree of 7 is forced to be operated in a range where the controllability is extremely poor (response linearity is impaired and the sensitivity is far from the design point), such as fully open or close to the open position.

Of course, if the control deviation cannot be reduced even if the damper is fully opened and inspected, the plant will not be able to maintain its performance values.

[Means to solve the problem]

As described above, in order for the boiler device and the boiler control device to exhibit good performance, the furnace outlet gas temperature is required to be at a predetermined value in the same load zone regardless of the type of coal.

In short, the present invention results in adjusting the fuel distribution of each burner so that the estimated or actually measured furnace outlet gas temperature at the relevant point in time becomes a predetermined value given according to the load.

The temperature of the gas at the exit of the furnace can be determined by measuring the gas temperature using thermocouples, radiant light, ultrasonic propagation speed, etc., or by actually measuring the gas temperature at the exit of the economizer, and determining the temperature on the steam side of each heat transfer surface. From the pressure and flow rate, calculate the amount of heat lost by the combustion gas in the section from the furnace outlet to the economizer outlet, calculate the gas temperature base, and add this to the gas temperature at the economizer 4 output to determine the furnace exit gas temperature. There are ways to maintain this.

[Effect]

In general, combustion gas generated from a burner located far from the furnace outlet is cooled to a large extent by ice walls due to radiation heat transfer while it remains in the furnace.

Therefore, if the furnace outlet gas temperature is lower than a predetermined value, the gas temperature difference can be eliminated by burning more gas at a position closer to the furnace outlet.

Similarly, when there is a high gas temperature deviation, combustion will occur mainly in the burner far from the outlet.In other words, in the present invention, the volatile content is small, the outlet gas temperature tends to rise, and the ice wall heat absorption tends to decrease. Coal has the effect of realizing burner fuel distribution that increases residence time.

〔Example〕

FIG. 1 shows an embodiment of the present invention. This is intended to control the boiler equipment shown in FIG. 3, and is configured in combination with the conventional control device shown in FIG. 4. The same parts as in FIGS. 3 and 4 are given the same numbers and their explanations will be omitted. Furthermore, there are some parts that are the same as those in FIGS. 3 and 4 and whose description in FIG. 1 has been omitted if there is no room for misunderstanding about their existence in FIG.

The signal setting element 207 gives the brand of coal, and the function element 20
9 receives the load command 101 and the brand setting 208 and provides an appropriate furnace outlet gas temperature for the boiler load. This is because the amount of generated gas (in other words, the amount of air required for combustion) to obtain the same amount of heat varies depending on the chemical composition of the coal (ratio of carbon and hydrogen). This is because, in order to maintain the absorption amount at an appropriate value, the furnace outlet gas temperature setting must be changed depending on the type of coal (the setting should be lower for coal that produces a large amount of gas).

The signal 202 gives the actual value of the furnace outlet gas temperature measured by a gas thermometer, but as described in the section on means for solving the problem, this signal may be grasped and substituted by a means that does not directly measure it. . The first calculation means 211 uses the above signal 202
, 210, 208 and Fuel Directive 151, the maximum capacity of each burner, turndown (minimum air volume by ensuring flow velocity to prevent burner backfire, and coal/air ratio of coal dust explosion limit) are determined. , the minimum amount of fuel that allows safe operation).

An embodiment of the first calculation means 211 is shown in FIG.

In FIG. 2, the fuel command 151 is given on the basis of the total calorific value per unit time, so it is divided by the calorific value signal 290 per unit mass determined by the type of coal to obtain the total pulverized coal amount signal 292. A command for the furnace outlet gas temperature is given by a signal 254, and a pulverized coal reference gradient distribution signal 255 for each burner is determined according to the command temperature and the coal type signal 208.
get.

Signal 255 indicates which burner near the furnace outlet and which burner farthest from the furnace outlet should be used in order to maintain the designed furnace outlet gas temperature when the specified fuel is applied throughout the entire load range for each type of coal during boiler commissioning adjustment. A function 254 is determined and given depending on the tendency of how much pulverized coal should be distributed in a gradient manner. of course,
At the time of actual operation, the boiler operating state will be different from that at the time of trial run adjustment, so it is generally impossible to operate in accordance with the command value with only signal 255. Therefore, the actual measured gas temperature 202 and command 21
Depending on the deviation from 0, if the slope distribution rate is positive, fuel will be increased to the burner near the furnace outlet, if it is 0, it will be distributed evenly, if it is negative, it will be increased to the burner far from the furnace outlet, and if the actual temperature 202 is high. If the command 210 cannot be reached, the allocation rate is increased. This function uses the function 252 to change the signal 2 because the correction width of the allocation ratio differs depending on the coal type and the degree of deviation.
53 is obtained and added to the basic signal 255 to obtain a slope distribution ratio 257. Note that in the following explanation, the value of the gradient distribution ratio will be expressed as d.

The pulverized coal distribution calculation elements 258 to 261 are prepared by 2n sets of burners that individually increase or decrease fuel, and sequentially from the burner closest to the furnace outlet, (1+nd)/(2n), [1+
(n-1)d)/(2n).

(1-nd)/(2n), (1(n-1)) from the burner furthest from the furnace outlet.
d) / (2n) , -------, is given.

In other words, elements 258 to 261 have the function of multiplying the total pulverized coal amount 292 by the above distribution coefficients, and the sum of these distribution coefficients is always 1 regardless of the value of d, so the pulverized coal amount command for each burner is The sum of 262 to 265 is always the total amount of pulverized coal 292
, and the desired slope distribution can be achieved depending on the value of d.

As mentioned above, each burner has a permissible maximum value 277 and minimum value 278 for the amount of pulverized coal supplied, which is determined by the type of coal.
Signals 262 to 265 are subject to such upper and lower limits, resulting in final command values of 212,287°288.213.

At this time, if the upper and lower limits are applied, the total signal amount will be 2
92, the excess/deficiency related to the upper and lower limits is calculated using elements 266 to 268, and the excess/deficiency is transferred to the nearest burner. This is the correction signal 269~
271 to addition elements 266 to 268. Although such "wrinkling" makes it impossible to achieve the ideal slope distribution, as long as the wrinkling is done to the nearest burner, the effect is small, and with this method, it is possible to achieve the ideal slope distribution, at least by considering the upper and lower capacity limits of the burner. Close slope distribution can be achieved.

The pulverized coal amount commands 212 and 213 for each burner are compared with the actual flow rates 204 and 206, respectively, and coal feeder drive signals 216 and 217 are set so that the deviation is zero. that time,
Since the pulverizability differs depending on the type of coal and the way in which the amount of correction for the deviation is given differs, the second calculation means 214 and 215 that calculates the drive signal takes the coal type signal 208 into consideration.

In this embodiment, measuring means 203°205 are used to grasp the actual amount of pulverized coal.
is used. These can be realized with a device that utilizes transmission and reflection of ultrasonic waves, microwaves, etc., and the coal output of the mill shown in Japanese Patent Application No. 1983-1.31342 “Pulverized Coal Boiler Control Device” by the present applicant can be realized. A method of estimation using a characteristic model may also be used.

〔Effect of the invention〕

The present invention has the following effects.

(2) Due to differences in furnace heat absorption characteristics related to differences in coal properties, problems in steam pressure control caused by changes in plant load where the ice wall outlet switches between dry steam and wet steam can be resolved.

2) A problem where the reheat steam temperature control operation end is stuck at the upper and lower limits of the variable range based on changes in the ratio of radiant heat transfer and convection heat transfer in superheaters and reheaters related to differences in coal properties, resulting in a significant decrease in controllability. can be resolved.

[Brief explanation of drawings]

Fig. 1 is a system configuration diagram of a boiler equipment according to an embodiment of the present invention, Fig. 2 is a detailed block diagram of the first calculation means in Fig. 1, and Fig. 3 is a boiler equipment to which the present invention is applied. FIG. 4 is a block diagram of a conventional boiler control device. 211...First calculation means. 2082IO Figure 15/ 2/3 Figure 3

Claims (1)

[Claims] A boiler of boiler equipment having a furnace surrounded by evaporation tubes and equipped with a plurality of burners that can adjust the amount of fuel individually or in groups, and a steam superheater and a steam reheater installed in the furnace exhaust gas flow path. In the control device, input the measured value or estimated value of the furnace outlet exhaust gas temperature, the temperature setting value, and the boiler total fuel amount command value at the relevant time using parameters given by the brand of fuel used or analysis data,
A boiler control device comprising a first calculation means for calculating a fuel quantity command value for each burner or burner group.