JPH0125881Y2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field] The present invention is a system for supplying primary air to a mill that crushes coal to be used as fuel for a boiler. Regarding a control device.

[Conventional technology]

Coal pulverized by a mill contains moisture, and the amount of moisture varies depending on the type of coal. High-temperature air is supplied to the mill for high-moisture coal that has a large amount of water, and low-temperature air is supplied to the mill for low-moisture coal that has a small amount of water. The air supplied to such a mill is obtained by mixing air heated by an air preheater and cold air that bypasses the air preheater. This primary air heating system will be explained using diagrams.

FIG. 2 is a system diagram of a conventional primary air heating system. In the figure, 1 is a forced draft fan (hereinafter referred to as FDF), 2 is a secondary air preheater (hereinafter referred to as SAH) that heats the air sent from FDF 1, and 3 is the exhaust gas G from the boiler. A tri-sector air preheater (hereinafter referred to as AH) was used. 4 is a primary air fan (hereinafter referred to as PAF), and 5A and 5B are mills for crushing coal. 6
A and 6b are cold air dampers that adjust the amount of cold air supplied to the mills 5A and 5B, respectively, and 7a and 7b are hot air dampers that adjust the amount of hot air from AH3 that is supplied to the mills 5A and 5B, respectively. . 8 is a wind box that supplies combustion air to the boiler.

The air pressurized by the FDF 1 is heated by the SAH 2 and then heated by the high temperature exhaust gas G discharged from the boiler in the AH 3, and this heated air is supplied to the wind box 8 as combustion air. On the other hand, the primary air for mills to be supplied to mills 5A and 5B is branched at the outlet of FDF1 and
4 and is boosted. This pressurized part of the air is heated in AH3, and the hot air damper 7a,
It is supplied to mills 5A and 5B via 7b. or,
Among the pressurized air, unheated cold air that bypasses AH3 is mixed with hot air via cold air dampers 6a and 6b, and is supplied to mills 5A and 5B.

The amount of heat of the air supplied to the mills 5A, 5B is the amount of heat that the mills 5A, 5B require for drying the coal, and this is the amount of heat that the mills 5A, 5B require to dry the coal.
b, and by adjusting the opening degrees of hot air dampers 7a and 7b. Therefore, the amount of heating of air in AH3 is also controlled by these cold air dampers 6a and 6b and hot air dampers 7a and 7b. .

By the way, in such a primary air heating system, if the moisture content of the coal used does not change much, the amount of primary air heating in AH3 can be sufficiently controlled by the above means, but if the moisture content of the coal used, for example, If there is a difference of 10% or more, the above method will be out of its control range. and,
In order to be able to control even high moisture coal, AH3
Although it is possible to adopt measures to increase the
When AH3 is increased, when using low moisture coal, the amount of bypass air is increased and the amount of primary air passing through AH3 is reduced.
The disadvantage is that the temperature of the 3-outlet gas increases and the boiler efficiency decreases.

FIG. 3 is a system diagram of another conventional primary air heating system. In the figure, parts that are the same as those shown in FIG. 2 are given the same reference numerals, and explanations thereof will be omitted. 9 is a secondary air preheater (hereinafter referred to as secondary AH) that heats the air sent from the FDF 1 using exhaust gas from the boiler, and the air heated here is supplied to the wind box 8 as combustion air. . 1
0 is a primary air preheater (hereinafter referred to as primary AH) that heats the air sent from PAF 4 with exhaust gas G, like the secondary AH9, and the heated air is sent to the mill 5A, via hot air dampers 7a and 7b. 5
B is supplied. 11 is an exit gas damper for exhaust gas passing through the secondary AH 9, and 12 is an exit gas damper for exhaust gas passing through the primary AH 10.

Next, the operation of this heating system will be explained with reference to the graphs shown in FIGS. 4a to 4c. FDF
The air pressurized in step 1 is heated in secondary AH 9 and then introduced into wind box 8. On the other hand, the primary air supplied to the mills 5A and 5B is branched at the outlet of FDF1 and pressurized at PAF4. A portion of the pressurized air is heated in the primary AH 10 and supplied to the mills 5A, 5B via hot air dampers 7a, 7b. Further, unheated cold air bypassing the primary AH 10 is mixed with hot air via cold air dampers 6a, 6b, and is supplied to the mills 5A, 5B.

The amount of heat of the air supplied to the mills 5A, 5B is the amount of heat that the mills 5A, 5B require for drying the coal, and this is the amount of heat that the mills 5A, 5B require to dry the coal.
12, and the cold air dampers 6a, 6b and hot air dampers 7a, 7b adjust the amount of air passing through the primary AH 10 and the amount of bypass air. In such control, the smaller the amount of bypass air in the primary AH10, the better the heat exchange efficiency in the primary AH10, so the amount of exhaust gas flowing into the primary AH10 is:
The opening degrees of the cold air dampers 6a and 6b are distributed so that the opening degrees can be set to the lower limit value of the controllable range (minimum opening degree for control purposes).

[Problem that the invention attempts to solve]

Here, regarding the graphs shown in Figures 4a to 4c, the horizontal axis of each figure indicates the moisture content of the coal used,
Also, the vertical axis of FIG. 4a shows cold air dampers 6a and 6b.
The opening degrees of the hot air dampers 7a and 7b are determined, and the vertical axis in FIG. 4b shows the outlet gas dampers 11 and 1.
The opening degree of 2 is plotted, and the temperature is plotted on the vertical axis of FIG. 4c. Furthermore, in the figure, the solid line part is the primary
The state of each part is shown when the low temperature end average metal temperature of AH10 is not maintained above the sulfuric acid condensation temperature, and the broken line portion shows the state of each part when the low temperature end average metal temperature is maintained above the sulfuric acid condensation temperature.
Now, if the moisture content of the coal used is low, the amount of heat in the air supplied to the mill must be suppressed, and for this reason,
The outlet gas damper 12 is placed in the closed direction as shown in FIG. 4b, and the amount of exhaust gas flowing into the primary AH 10 is reduced. Therefore, the outlet gas temperature of the primary AH10 decreases as shown by the solid line in Figure 4c, and
Below this point, the average metal temperature at the low temperature end of the primary AH10 is below the maximum condensation temperature of sulfuric acid. As a result, sulfuric acid corrosion occurs in the primary AH10, especially when a denitrification device is installed in the boiler equipment.
Acid corrosion products become the core of acidic ammonium sulfate adhesion and become primary
There is a possibility that the clogging of AH10 will be further exacerbated, making it impossible to continue operation. And primary AH10
In order to maintain the average metal temperature at the low temperature end of the primary AH above the maximum condensation temperature of sulfuric acid, the opening degree of the outlet gas damper 12 should be increased as shown by the broken line in Figure 4b.
It is necessary to increase the amount of exhaust gas flowing into the air filter 10, but in that case, the amount of flowing exhaust gas will exceed the required amount, and as shown by the broken line in Figure 4a, the cold air damper will be in the open direction and the hot air damper will be in the closed direction. As a result, the amount of cold air increases and
The heat exchange efficiency in AH10 decreases significantly between points A and B shown in FIG. Furthermore, when coal with lower moisture content is used, the cold air damper must be fully opened below point B for the above reasons, making it impossible to control the mill outlet air temperature.

On the other hand, if the coal used has a high moisture content, the primary AH10
Due to the increased amount of heating required in the secondary AH9
The outlet gas damper 11 is adjusted in the closing direction as shown by the dashed line in FIG. If coal with even higher moisture content is used, the cold air damper must be fully closed from the lower limit of its opening to point D as shown in Figure 4a. It becomes impossible to control the outlet air temperature.

As mentioned above, conventional primary air heating systems have the disadvantage that if there is a considerable change in the moisture content of the coal used, the heat exchange efficiency in the air preheater will decrease, which in turn will reduce the boiler efficiency. Ta. Furthermore, when coal with extremely low moisture content or coal with extremely high moisture content is used, the hot air damper and cold air damper must be fully open or fully closed, making it impossible to control the temperature of the primary air. There was also a drawback.

The present invention was developed in view of these circumstances, and its purpose is to prevent a decrease in boiler efficiency and to control the primary air temperature with good responsiveness to a wide range of coal moisture content. The object of the present invention is to provide a primary air temperature control device for a mill that can perform the following steps.

[Means for solving problems]

To achieve the above object, the present invention comprises at least one mill, a primary air preheater for heating the air supplied to the mill, and a damper for regulating the amount of cold air supplied to the mill. A steam air preheater disposed upstream of the primary air preheater, an opening detection device for detecting the opening of the damper, and a minimum opening detected by the opening detection device and a preset value. The present invention is characterized in that it is provided with a comparison means for comparing the minimum opening degree and a control means for controlling the amount of heating of air by the steam air preheater according to the comparison result of the comparison means.

[Effect]

The minimum opening of the cold air damper provided in one or more mills is compared with a preset minimum opening, and the detected minimum opening is determined as the set minimum opening. When the temperature is higher than the temperature, the throttle of the steam air preheater is increased, and when the temperature is lower than the temperature, the throttle is decreased.

〔Example〕

Hereinafter, the present invention will be explained based on the illustrated embodiments.

FIG. 1 is a system diagram of a primary air heating system according to a first embodiment of the present invention. In the figure, parts that are the same as those shown in FIG. 2 are given the same reference numerals, and explanations thereof will be omitted. 15 is a steam air preheater for primary air (hereinafter referred to as primary air preheater) installed between PAF4 and AH3.
(referred to as SAH), which heats the primary air pressurized by PAF4 with steam. 16 is primary SAH
This is a primary SAH inlet steam valve (hereinafter referred to as a steam valve) that adjusts the amount of steam sent to SAH 15. 18a,1
Reference numeral 8b indicates an opening degree detector that detects the opening degree of the cold air dampers 6a and 6b, respectively. In this system, the amount of heat required by mills 5A and 5B is reduced to AH3.
However, unless this division is properly adjusted, the same drawbacks as in the past will occur. This will be explained with reference to the graphs shown in FIGS. 5a and 5b. In Figure 5a, the horizontal axis shows the moisture content of the coal used, and the vertical axis shows the amount of cold air.
In addition, in FIG. 5b, the horizontal axis shows the water content of the used coal, and the vertical axis shows the temperature. Now, assuming that the primary SAH 15 is operated at a constant capacity and the amount of heat of the primary air is adjusted by the amount of bypass air, the amount of heat of the primary air may be small when using low moisture coal, so the cold air damper 6 is used.
a and 6b are opened to increase the amount of cold air as shown in FIG. 5a, thereby increasing the exhaust gas temperature at the outlet of AH3 and reducing the boiler efficiency. To avoid this efficiency loss, primary SAH is applied only when high moisture coal is used.
Even if SAH 15 is operated, the coal used in several mills does not have the same properties at the same time, and the primary air supply conditions are usually different for each mill, so in this case, primary SAH 15 is used. Judgment as to whether or not this is the case must rely solely on the intuition of the operator, making it extremely difficult to make an appropriate judgment. Therefore, in this embodiment, the primary
The purpose is to control the amount of steam in the SAH 15 in relation to the opening degrees of the cold air dampers 6a and 6b to achieve the intended purpose.

FIG. 6 is a block diagram of a control device for the primary air heating system shown in FIG. 1. 18a and 18b are opening degree detectors of the cold air damper shown in FIG.
20 is a minimum opening degree discriminator that selects the smallest opening degree among the opening degrees detected by each opening degree detector 18a, 18b. 21 is a minimum opening setting device for setting the controllable minimum operational opening of the cold air dampers 6a and 6b;
22 is a comparator that compares the value of the minimum opening degree discriminator 20 and the value of the minimum opening degree setter 21.

If the moisture content of the coal used in each mill 5A, 5B is different, the cold air damper 6 of each mill 5A, 5B
The opening degrees of a and 6b are different. The minimum opening degree discriminator 20 extracts the smaller opening degree of the opening degrees of both the cold air dampers 6a and 6b, and compares it with the minimum opening degree set in the minimum opening degree setting device 21 in the comparator 22. As a result of the comparison, if the opening degree of the smaller one of the cold air dampers 6a, 6b is larger than the minimum opening degree set in the minimum opening degree setting device 21, the amount of heated steam of the primary SAH 15 is adjusted as follows. For example, when coal with low moisture content is used, the opening degree of the cold air damper is large, and therefore the difference from the set minimum opening degree is large, and the signal from the comparator 22 determines the primary SAH1
The steam valve 16 of No. 5 is gradually throttled from the open state.
As a result, the amount of heating steam in the primary SAH 15 decreases. On the other hand, due to this decrease in the amount of heating steam, the primary air temperature at the entrances of mills 5A and 5B decreases, this temperature is detected by a temperature detector (not shown), and the cold air damper is throttled based on this detected value. Eventually, the opening degree becomes the one set in the minimum opening degree setting device 21. The comparator 22 ensures that the opening degree of this cold air damper does not become less than the set minimum opening degree. In extreme cases, the steam valve 16 is completely closed and the primary
SAH15 becomes unused.

Conversely, when coal with high moisture content is used, it is necessary to increase the amount of heat required at the mill inlet, so the cold air damper is closed and its opening is close to the set minimum opening. Therefore, the throttle of the steam valve 16 of the primary SAH 15 due to the signal from the comparator 22 is slight, and this slight throttle causes the cold air damper to further close, and finally the minimum opening setting device 2
It becomes equal to the opening degree set to 1. The broken line shown in FIG. 5 indicates the value when control is performed using the primary SAH 15 as described above.

As described above, in this embodiment, the minimum opening degree of the cold air damper is set, and the primary SAH is adjusted so that the minimum of the detected cold air damper opening degrees becomes the set minimum opening degree. Since the steam valve is controlled, the amount of bypass air in the AH can be reduced and exhaust gas heat recovery can be performed effectively.
The amount of heating steam for the SAH can also be reduced to the necessary minimum, thereby preventing a decrease in boiler efficiency. Further, regardless of the amount of moisture in the coal used, the cold air damper is never fully closed or fully opened, and therefore the temperature of the primary air can be controlled with good responsiveness. Furthermore, since the amount of bypass air is small, the cold air duct etc. can be made small, and equipment costs can be reduced.

FIG. 7 is a system diagram of a primary air heating system according to a second embodiment of the present invention. In the figure, the same parts as those shown in FIG. 3 are given the same reference numerals.
18a and 18b are cold air dampers 6a and 6, respectively.
This is an opening degree detector that detects the opening degree of b, and is the same as that shown in the previous embodiment. 24 is primary AH1
This is a temperature detector that detects the low temperature end average metal temperature of 0. 25 is a steam air preheater for primary air (primary air preheater) installed between PAF4 and primary AH10.
SAH), 26 is a steam valve that adjusts the amount of steam in the primary SAH 15. 27 is an opening detector for detecting the damper opening of the outlet gas damper 11 of the secondary AH9. Here, the area ratio of the heat transfer areas of the primary AH 10 and the primary SAH 25 is determined so as to satisfy various conditions such as weight and draft loss, and to achieve an optimal distribution at low cost for the entire system. FIG. 8 is a characteristic curve of the cost versus the area ratio of the primary AH and the primary SAH, where the broken line represents the cost of the primary AH, the dashed line represents the cost of the primary SAH, and the solid line represents the total cost. The area ratio between a% and b% is the range in which the total cost is minimized.

FIG. 9 is a block diagram of a control device for the primary air heating system shown in FIG. 7. In the figure, the same parts as those shown in FIG. 7 are given the same reference numerals. 2
8 is an opening detector 18 for the cold air dampers 6a and 6b.
This is a minimum opening degree discriminator that selects the minimum opening degree from among the opening degrees detected at a and 18b. Reference numeral 29 denotes a minimum opening degree setting device for setting the controllable minimum operational opening degree of the cold air dampers 6a, 6b. A comparator 30 compares the minimum opening determined by the minimum opening discriminator 28 and the set opening set in the minimum opening setting device 29. 31 is normally in the cutoff state, and the opening detector 2
Reference numeral 7 denotes a switch that is brought into conduction when the minimum opening degree of the outlet gas damper 11 of the secondary AH9 is detected.
32 is a sulfuric acid maximum condensation temperature setter that sets the maximum condensation temperature of sulfuric acid, and 33 is a comparator that compares the temperature detected by the temperature detector 24 and the temperature set in the sulfuric acid maximum condensation temperature setter 32.

The operation of the control device of this embodiment will be explained with reference to the graphs shown in FIGS. 10a to 10d. 10th
Figures a to c are graphs corresponding to Figures 3 a to c, respectively, and in Figure 10 d, the horizontal axis represents the water content of the coal used, and the vertical axis represents the amount of steam in the primary SAH.
First, a case will be described in which the coal used is low moisture coal below point A' shown in FIG. In this case, since the primary air supplied to the mill does not require a large amount of heat, the gas damper 11 is opened and the gas damper 12 is throttled, as shown in FIG. supply will be restricted. As a result, the temperature of the primary air is kept low, and if no other measures are taken,
The average metal temperature at the low temperature end of the primary AH10 is below the maximum condensation temperature of sulfuric acid, as shown by the solid line in FIG. 10c, resulting in the above-mentioned drawbacks. However, in this embodiment, the comparator 33 compares the low temperature end average metal temperature detected by the temperature detector 24 with the maximum sulfuric acid condensation temperature set in the setting device 32, and the low temperature end average metal temperature is determined by the maximum sulfuric acid condensation temperature. When the temperature is below the temperature, a signal is output from the comparator 33, and the steam valve 26 is opened to supply steam to the primary SAH 25 as shown in FIG. 10d. For this reason, the primary air is heated in the primary SAH 25 and flows into the primary AH 10, so
The average metal temperature at the low temperature end of the primary AH10 rises as shown by the broken line in Figure 10c, and never falls below the maximum condensation temperature of sulfuric acid. When the primary air is heated by the primary SAH 25, the cold air damper is in the open direction, but by setting the outlet gas damper 12 of the primary AH 10 in the closing direction, the cold air damper is not in the open direction, as shown in FIG. 10a. In this way, the opening degree is maintained at the lower limit value for control, and a control margin for the cold air damper can be secured. Note that when the coal used is low moisture coal as described above, the outlet gas damper 11 of the secondary AH is open and the opening degree is greater than the minimum opening, so the switch 31
is in a cutoff state, and the signal from the comparator 30 is cut off and does not affect the opening degree of the steam valve 26. Furthermore, when the moisture content of the coal used is between points A' and C' shown in FIG. 11 is in the closed direction as shown in FIG.
During C', the steam valve 26 is in a closed state.

If the moisture content of the coal used is above point C' shown in Figure 10, the amount of heat required by the primary air will increase,
The outlet gas damper 11 of the secondary AH9 has the minimum opening degree, and more exhaust gas G is introduced into the primary AH10. As the gas damper 11 reaches its minimum opening degree, the switch 31 becomes conductive. Primary AH10
By supplying more exhaust gas G to the primary air, the amount of heat given by the primary AH 10 to the primary air increases, but when the moisture content of the coal used is above point C', the amount of heat is insufficient. In this embodiment, the minimum opening degree among the opening degrees of the cold air damper is determined by the minimum opening degree discriminator 28,
This is compared with the minimum opening degree set in the setter 29 (an opening degree smaller than the lower limit opening degree on the control).
As a result, a signal is output from the comparator 30, and this signal passes through the switch 31, which is in a conductive state, to the steam valve 2.
6 in the open direction, and as shown in FIG. 10d, steam is supplied to the primary SAH 25 to heat the primary air, thereby sufficiently compensating for the insufficient amount of heat.

In this example, when low-moisture coal is used, the cold air damper is held at the lower limit opening for control, and when the average metal temperature at the low temperature end of the primary AH falls below the maximum condensation temperature of sulfuric acid, the primary SAH The average metal temperature at the low temperature end is maintained above the maximum condensation temperature of sulfuric acid by supplying steam to However, since steam was supplied to the primary SAH to compensate for the insufficient amount of heat, the same effect as in the previous embodiment is achieved.

[Effect of idea]

As described above, in this embodiment, a steam air preheater is placed before the primary air preheater, and the opening degree of the cold air damper is detected and compared with the preset minimum opening degree. The amount of heating of the primary air by the steam air preheater is controlled according to the results of this comparison, so the opening degree of the cold air damper is reduced to effectively recover heat from the exhaust gas and reduce the drop in boiler efficiency. The primary air temperature can be controlled with good responsiveness over a wide range of coal moisture content.

[Brief explanation of the drawing]

Fig. 1 is a system diagram of a primary air heating system according to the first embodiment of the present invention, Figs. 2 and 3 are system diagrams of a conventional primary air heating system, and Figs.
b and c are characteristic diagrams of the system shown in Fig. 3; Figs. 5 a and b are characteristic diagrams of the system shown in Fig. 1; Fig. 6 is a block diagram of the control device of the system shown in Fig. 1; The figure is a system diagram of the primary air heating system according to the second embodiment of the present invention, and FIG. 8 is a graph showing the relationship between the area ratio and cost of the primary air preheater and the steam air preheater shown in FIG. 7. , FIG. 9 is a block diagram of the control device of the system shown in FIG. 7, and FIGS. 10 a, b, c, and d are graphs explaining the operation of the system shown in FIG. 7 and the control device shown in FIG. be. 3... Tri-sector air preheater, 5A, 5B
...Mil, 6a, 6b...Cold air damper, 7a,
7b...Hot air damper, 9...Secondary air preheater,
10... Primary air preheater, 11, 12... Gas damper, 15, 25... Steam preheater for primary air,
16, 26... Steam valve, 18a, 18b... Cold air damper opening detector, 20, 28... Minimum opening degree discriminator, 21, 29... Minimum opening setting device, 22, 3
0, 33... Comparator, 24... Low temperature end average metal temperature detector, 27... Gas damper opening degree detector, 3
1... Switch, 32... Sulfuric acid maximum condensation temperature setting device.

Claims (1)

[Scope of utility model registration request] A device comprising at least one mill, a primary air preheater that heats air supplied to the mill, and a damper that adjusts the amount of cold air supplied to the mill, disposed upstream of the primary air preheater. a steam-type air preheater, an opening detection device for detecting the opening of the damper, and comparison means for comparing the minimum opening detected by the opening detection device with a preset minimum opening. A primary air temperature control device for a mill, comprising: a control means for controlling the amount of air heated by the steam air preheater according to the comparison result of the comparison means.