JPH0510564B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a soot blower control device for a recovery boiler, and particularly to a soot blower control device suitable for reducing cleaning media such as steam and air consumed by the soot blower. It is.

[Conventional technology]

At a kraft pulp mill, the recovery boiler, which recovers chemicals from black liquor and recovers energy as generated steam, requires the largest initial investment of all processes, is difficult to operate, and is an equipment that affects the efficiency of the entire plant. be.

FIG. 5 is a schematic system diagram showing the black liquor, air, and exhaust gas systems in a conventional recovery boiler.

Solid content 60-70 in an evaporator (not shown)
% concentrated black liquor is transferred to superheater 1, evaporation water pipe 2,
It is injected from the oscillator 6 into the furnace 5 of the recovery boiler 4 having a heat transfer surface such as the economizer 3, adheres to the furnace wall 7, dries, is thermally decomposed, and then falls onto the hearth 8. The carbon material in the black liquor is pressed by the primary air from the primary air port 9 opened in the furnace wall 7 near the furnace wall 8, and the carbon material in the black liquor forms a chamber bed 10 and undergoes reductive combustion. Oxidative combustion is carried out by secondary air and tertiary air from 12. The inorganic substances in the black liquor are melted and discharged from the smelt spout 13 as smelt. In order for these reactions to take place satisfactorily, the area directly above the hearth 8 must be maintained in a reduced state, and the area above it must be maintained in an oxidized state.

In this reduction zone, sodium sulfate is reduced to sodium sulfite with high efficiency, increasing the efficiency of chemical reduction. At the same time, this reduces the generation of sulfur dioxide gas and fume, increases the amount of steam generated, and improves the efficiency of the steam generator. This will lead to improvement.

As described above, the inside of the furnace 5 is divided into three zones: a reduction zone, a dry pyrolysis zone, and an oxidation zone, and each zone plays a respective role to efficiently recover chemicals from black liquor.

The above describes the general structure of a recovery boiler, and black liquor and combustion air are supplied as follows.

The black liquor is heated in the black liquor heater 14 using steam for preheating the black liquor.
After being heated to about 100°C and pressurized by a black liquor jet pump (not shown) in the black liquor piping 15, the oscillator 6
The fuel enters the furnace 5 and is sprayed and dispersed from the oscillator 6 shown in FIG. 5 into the furnace 5. With this oscillator 6,
The black liquor sprayed and spread within the furnace 5 is sprayed onto the furnace wall 7 on the opposing surface, and while moving within the furnace 5, some of the water in the black liquor is dehydrated. After adhering to the furnace wall 7, it is dried and thermally decomposed by the radiant heat of the furnace, and is deposited in a coarse particle state (hereinafter referred to as "chire") on the furnace bed 1 at the bottom of the furnace.
Accumulate to 0.

On the other hand, air is passed through an air duct 17 by a forced draft fan 16 to the primary air port 9 and the secondary air port 1.
Air is supplied into the furnace 5 from the first and third air ports 12.

The primary air and secondary air from the primary and secondary air ports 9 and 11 reduce the chemicals (Na ₂ SO ₄ ) in the chamber bed 10 and turn the inorganic components in the black liquor into smelt, which is then released into the smelt spout. After dissolving in water, it is causticized and recovered as a cooking chemical.
In addition, the organic components in the black liquor are oxidized and burned in the oxidation zone mainly by the tertiary air from the tertiary air port 12, and the heat transfer tubes such as the furnace wall 7, superheater 1, evaporator water tube 2, and economizer 3 Waste heat is recovered as steam.

On the other hand, dust is removed from the exhaust gas from the recovery boiler 4 by an electrostatic precipitator 19 in an exhaust gas duct 18, and the exhaust gas is discharged into the atmosphere from an induced draft fan 20.

In addition, as shown in Fig. 5, the recovery boiler 4 is composed of a energy saver 3 that heats the feed water to near the saturation temperature, an evaporation water pipe 2 that evaporates the saturated temperature water, and a superheater 1 that generates superheated steam. The boiler 4 is followed by an electrostatic precipitator 19 for removing dust, a spray device 21 for adjusting the temperature of superheated steam, and a soot blower 22.

In order to remove dust attached to the heat transfer surfaces of the superheater 1, evaporative water pipe 2, and economizer 3 of the recovery boiler 4,
A soot blower 22 using steam, compressed air, or the like as a spraying medium is used to clean dust adhering to the heat transfer surface.

Since the recovery boiler 4 generates a large amount of dust, the soot blower 22 is normally operated at all times, or the operator sets the time from the end of operation of one soot blower 22 to the start of operation of the next soot blower 22 (hereinafter referred to as an interval). The cleaning work using the soot blower 22 is performed in accordance with a predetermined blowing order of the soot blower 22 while maintaining the operation interval for this interval.

However, with this kind of control, even if there are load fluctuations in the recovery boiler 4 or changes in operating conditions, the soot blower 22 is not controlled in response to these changes, so dust adhesion progresses and excessive steam and Since compressed air is used, proper control cannot be expected.

In addition, the soot blower 22 may be damaged due to dirt on the heat transfer surface.
As an example of changing the operation of a boiler, a method has been proposed in which a group of soot blowers appropriately arranged in a boiler is activated in response to changes in boiler water, steam, etc. (Japanese Patent Publication No. 43-8489). The control of the soot blower 22 is such that the soot blower is started using a change in the state of the boiler, for example, when the degree of contamination of the heat transfer surface exceeds a certain threshold value, and the soot blower is activated. It is not preferable for items with a large amount of dust like No. 4.

On the other hand, since the amount of steam that can be supplied from the recovery boiler 4 for soot blowing is limited, it is impossible to operate a large number of soot blowers 22 at once.

[Problem that the invention seeks to solve]

In this way, in the conventional soot blower operation control based on constant dirt level control, even if the recovery boiler load fluctuates or the operating conditions change, the control is constant based on the dirt level, so dust adhesion may progress too much or There was a drawback that the amount of cleaning medium for soot blowing was consumed more than necessary.

The present invention aims to eliminate such conventional drawbacks, and aims to enable the soot blower to be started at intervals that can follow the load fluctuations and operating conditions of the recovery boiler, and to reduce the consumption of cleaning media by the soot blower. The present invention provides a soot blower control device with a small amount of use.

[Means for solving problems]

In order to achieve the above-mentioned object, the present invention includes a first computing unit that computes a dirt deviation interval signal from a dirtiness deviation signal, a second computing unit that computes a gas differential pressure interval signal from a detection signal, and a gas outlet temperature A third arithmetic unit for calculating interval signals is provided, and a comparator is provided for comparing the interval signals from these first, second, and third arithmetic units to calculate the minimum interval signal. It is designed to control a soot blower.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

Fig. 1 is a soot blower control system diagram of a recovery boiler according to an embodiment of the present invention, Fig. 2 is a characteristic curve diagram of the second computing unit, Fig. 3 is a characteristic curve diagram of the third computing unit, Fig. 4 a, b is a characteristic curve diagram showing the relationship between the degree of contamination and time, and between the soot blower interval and time.

In Fig. 1, 22 is a soot blower, 23 is a detector for detecting process values such as the feed water flow rate, feed water temperature, pressure, exhaust gas temperature, and steam temperature of the recovery boiler 4, 24 is a detection signal, and 25 is a design heat transmission coefficient setting. 26 is a dirt level calculator, 27 is a dirt level calculation signal, 28 is a dirt level setting signal, 29 is a dirt level deviation signal, 30 is a first calculator that calculates the dirt level interval signal 31, 32 is a gas differential pressure interval signal 33
34 is a third computing unit that computes the outlet gas temperature interval signal 35; 36 is the contamination level interval signal 31; and the differential pressure interval signal 3.
3. A comparator that calculates the minimum interval signal 37 from the outlet gas temperature interval signal 35.

In such a structure, as shown in FIG. 1, as a control device for a soot blower 22 according to the present invention, a detection signal 24 of each part of the recovery boiler 4 indicating the degree of contamination of the heat transfer surface is detected by a detector 23. , the amount of heat absorbed is calculated by the dirt degree calculator 26. In FIG. 1, the energy saver 3 will be explained as an example, but the amount of heat absorbed can be determined by the following equation.

ΔQ=(Cpwo−Cpwi)×Mw……(1) Here, Cpwo: specific heat of the outlet water of the economizer 3 Cpwi: Specific heat of inlet water of economizer 3 Mw: Water supply flow rate ΔQ: Endothermic amount shows.

Cpwo and Cpwi in equation (1) are uniquely determined by the detection signal 24 from the detector 23 for the supply water temperature and pressure.

On the other hand, the amount of heat absorbed ΔQ has the following relationship.

ΔQ=Hs・Uc・ΔTen ……(2) ΔTen=[(TGi−Two)−(T _Gp −Twi)]/en[(T _Gi −Two)/(T _G o−Twi)] ……(3 ) Here, Hs: Boiler heat transfer area Uc: Heat transmission coefficient ΔTen: Logarithmic average temperature difference T _G i: Inlet gas temperature of economizer 3 T _G o: Outlet gas temperature of economizer 3 Two: Economizer 3 outlet water supply temperature Twi: Indicates the inlet water supply temperature of the energy saver 3.

T _G i, T _G o, Twi, and Two in equation (3) are the detector 2
3, and from these and equations (1) to (3), the heat transfer coefficient (Uc) can be determined. Since this heat transfer coefficient (Uc) is affected by boiler load fluctuations, etc., it is normalized by taking the ratio with the design heat transfer coefficient (Ud) setting signal 25.
This is called the degree of contamination.

CF _C = Uc/Ud...(4) Here, CFc: indicates the degree of contamination.

Contamination degree deviation signal (CF _c ) obtained in this way
27 and the contamination degree setting signal (CF _D ) 28 is calculated as a contamination degree deviation signal 29, and based on the degree of this contamination degree deviation signal 29, the first computing unit 30 determines the interval contamination of the soot blower 22. The interval signal 31 is increased or decreased.

In addition, in FIG. 1, the second and third computing units 3
2 and 34, control of the gas differential pressure interval signal 33 in temperature monitoring, and the control of the outlet gas temperature interval signal 35 depend on the recovery boiler 4.
An example is shown below.

In the differential pressure excessive monitoring by the second computing unit 32, the design pressure loss of the recovery boiler 4 of the embodiment is 50 mmAq, and the capacity of the induced draft fan 20 of FIG. 5 is set to have a margin of 30%.
Can be used up to 65mmAq. Therefore, in this example, as shown in Fig. 2, the boiler differential pressure is 55 mmAq.
Up to this point, excessive differential pressure monitoring is ignored, and when the differential pressure exceeds this level, the gas differential pressure interval signal 33 is set to zero and continuous soot blowing is performed.

On the other hand, as an example of temperature monitoring of the third computing unit 34, the relationship between the interval and the outlet temperature of the economizer 3 for controlling the outlet temperature of the economizer 3 is shown in FIG. The curve in FIG. 3 was obtained by changing the interval under constant load conditions and performing an operation to find an interval value such that the outlet gas temperature of the economizer 3 does not change while changing the load. If the soot blower 22 is operated with the outlet gas temperature interval signal 35 shown below the curve in FIG. There is no damage to the electrostatic precipitator 19 shown in FIG. 5, etc.

In this way, the first, second, third computing units 30, 32,
34 contamination degree interval signal 31, gas differential pressure interval signal 33, outlet gas temperature interval signal 3
5 is input to a comparator 36, and the comparator 36 controls the soot blower 22 using the smallest interval signal 37 among these interval signals 31, 33, and 35.

In this way, the first, second, third computing units 30, 32,
The reason why the minimum interval signal 37 from 34 is used to control the soot blower 22 is that black liquor, which is the fuel for the recovery boiler, has a different calorific value depending on whether the wood that is the raw material for papermaking is hardwood or softwood. This is because the switching of the wood type is performed separately without being linked to the operation of the recovery boiler 4.

Therefore, even if the black liquor flow rate is constant, the amount of heat supplied to the recovery boiler 4 may change. In such a case, the conventional soot blower control based on a constant level of contamination is insufficient to maintain the temperature of each part of the recovery boiler 4. Adjustment may not be possible. Therefore, when the amount of heat absorbed in the recovery boiler 4 is small and the outlet gas temperature of the economizer 3 tends to rise, it is necessary to shorten the interval of the soot blower 22, in addition to controlling based on the degree of contamination. Normally, as shown in FIG. 5, the maximum operating temperature of the electrostatic precipitator 19 is about 200° C., so it is controlled so that it does not exceed this temperature.

Furthermore, in the superheater 1, a water spray device 21 is used to adjust the temperature of the superheated steam as shown in FIG. If the temperature of the superheated steam becomes low, the amount of water sprayed by the spray device 21 may become zero, and the temperature of the superheated steam may further decrease. In such a case as well, it is necessary to shorten the soot blow interval of the superheater 1 regardless of the contamination degree constant control.

Therefore, in the embodiment of the present invention, a dirt level interval signal 31 determined from the dirt level, a gas differential pressure interval signal 33 determined from the gas draft, and an outlet gas temperature interval signal 35 determined from the outlet gas temperature of the economizer 3 are compared. The soot blower 22 is started by comparing the interval signals 37 with the soot blower 36 and setting the minimum interval signal 37 as the interval of the soot blower 22 at that time.

4a and 4b show actual measured values when the minimum interval signal 37 is the dirtiness interval signal 31. FIG.

In the figure, A is a dirt level deviation signal (CF _C ), B is a dirt level setting signal (CF _D ), and C is a conventional dirt level setting signal (CF _D ).

Figures 4a and 4b show how the contamination degree setting signal (CF _D ) 28 is converted into the conventional contamination degree setting signal C in the recovery boiler 4.
This figure shows the step response when changing the dirt setting signal B from 0.6 to 0.5. Since the contamination level setting signal 28 is lowered from 0.6 to 0.5, the soot blower interval increases by the deviation as shown in FIG. 4b, and the operating interval of the soot blower 22 is thereby shortened. Approximately 3 hours (horizontal axis
After 180 minutes), the dirt level setting signal B and the dirt level deviation signal A match and there is no deviation, so the soot blower interval becomes constant and becomes longer as before.

In this way, in the conventional soot blower control based only on the degree of contamination, changing the soot blow interval in accordance with an increase or decrease in the degree of contamination is based on the premise that dust adheres uniformly to the heat transfer surface. However, in reality, dust often adheres locally to the recovery boiler 4. This is because the dust, which has become semi-molten due to combustion, moves within the recovery boiler 4 while being cooled, so that it tends to accumulate in the temperature range where the dust solidifies. When dust is locally attached like this, the heat transfer surface may be kept clean as a whole. By taking into consideration the gas draft and outlet exhaust gas temperature, which correspond to localized dust accumulation, the heat transfer surface can be cleaned in accordance with the load fluctuation of the recovery boiler 4 and the type of fuel. The amount of media is also small.

〔Effect of the invention〕

According to the present invention, the soot blower can be started at intervals that can follow the load fluctuations and operating conditions of the recovery boiler, and cleaning work can be performed with less consumption of cleaning media.

[Brief explanation of drawings]

Fig. 1 is a soot blower control system diagram of a recovery boiler according to an embodiment of the present invention, Fig. 2 is a characteristic curve diagram of the second computing unit, Fig. 3 is a characteristic curve diagram of the third computing unit, Fig. 4 a, b is a characteristic curve diagram showing the relationship between the degree of contamination and time, and the relationship between the soot blower interval and time, and FIG. 5 is a schematic configuration diagram of the recovery boiler. 1... Superheater, 2... Evaporative water pipe, 3... Energy saver, 4... Recovery boiler, 22... Soot blower,
24...Detection signal, 26...Contamination degree calculator, 27
...Contamination degree calculation signal, 28...Contamination degree setting signal,
29...Contamination degree deviation signal, 30...First computing unit,
31... Contamination degree interval signal, 32... Second computing unit, 33... Gas differential pressure interval signal, 34...
...Third computing unit, 35...Outlet gas temperature interval signal, 36...Comparator, 37...Minimum interval signal.

Claims (1)

[Claims] 1. A contamination degree calculation unit is provided which calculates the degree of contamination of the heat transfer surface based on the detection signal from the recovery boiler, and the soot blower is operated based on the contamination degree deviation signal between the contamination degree calculation signal from the contamination degree calculation unit and the contamination degree setting signal. In the device that is activated to clean the heat transfer surface, a first computing unit that computes a dirt deviation interval signal from the dirtiness deviation signal, a second computing unit that computes a gas differential pressure interval signal from the detection signal, and a gas outlet. A third computing unit is provided to compute the temperature interval signal, and a comparator is provided to compare the interval signals from the first, second, and third computing units to compute the minimum interval signal. A soot blower control device for a recovery boiler, characterized in that the soot blower is controlled by the soot blower.