JP2014095485A - Boiler with feed water preheating device and operation method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow a boiler to continue proper operation as much as possible by preventing degradation in combustion state in the boiler due to accumulation of water in the bottom part within a feed water preheating device.SOLUTION: There is provided a boiler 1 with a feed water preheating device 7 in which heat transfer tubes 3 for flowing feed water to the boiler 1 is provided in an exhaust gas passage 2 for flowing combustion exhaust gas from the boiler 1 and which preheats the feed water to the boiler 1 by heating the heat transfer tubes 3 with the combustion exhaust gas. The exhaust gas passage part for flowing the combustion exhaust gas, within the feed water preheating device 7 includes a drain discharging port 6 and a drain discharging pipe 5 for discharging water accumulated in the exhaust gas passage part, and further includes a pressure detecting device 4 for detecting a pressure of the combustion exhaust gas flow flowing in the exhaust gas passage. When an increasing of pressure loss at the exhaust gas passage is detected with the pressure detecting device 4, the occurrence of abnormal state is notified and water in the feed water preheating device is discharged.

Description

  The present invention relates to a boiler having a feed water preheating device for preheating boiler feed water using heat of combustion exhaust gas discharged from a boiler, and an operation method thereof.

  There exists a boiler which heats the boiler water which flows through the inside of a heat exchanger tube installed in a combustion furnace or a flue from the outer side of a heat exchanger tube, as it also exists in patent 2911014 gazette. In such a boiler, a feed water preheating device is provided in an exhaust gas passage through which combustion exhaust gas whose temperature has decreased by heating a heat transfer tube in a combustion furnace, and the boiler feed water is preheated by the combustion exhaust gas, thereby improving the efficiency of the boiler. It is widely done. In the feed water preheating device, heat exchange is performed between the combustion exhaust gas in the exhaust gas passage and the boiler feed water flowing in the heat transfer pipe provided in the exhaust gas passage, and the amount of heat absorbed by the heat transfer pipe from the combustion exhaust gas increases. The temperature of the boiler can be raised, and the efficiency of the boiler is improved. When the exhaust gas outlet position in the boiler is in a relatively high place, the feed water preheating device will be folded at the bottom, and a heat transfer tube will be installed at the part where the exhaust gas flow is lowered. convenient.

  In the patent of Japanese Patent No. 2911014, in a boiler in which a heat transfer tube is heated by the heat of combustion gas, incombustibles or dust adheres to the surface of the heat transfer tube and the heat exchange efficiency is remarkably reduced. Mentions that it is necessary to clean the heat transfer tubes. The contamination in the heat transfer tube is determined based on the pressure value in the furnace. In other words, if non-combustible material such as soot adheres to the surface of the heat transfer tube, the flow area of the flue gas flowing through the heat transfer tube group decreases, the resistance of the flue gas flow increases, and the furnace pressure increases. The internal pressure value is detected. However, the increase in the furnace pressure due to the incombustible material adhering to the surface of the heat transfer surface gradually increases over a long period of time, and the heat transfer tubes are cleaned at intervals much shorter than that. For this reason, if heat transfer tube cleaning is performed appropriately, there is not much opportunity to detect contamination of the heat transfer tube based on the furnace pressure.

  To clean the heat transfer tubes, install the heat transfer tube cleaning water injection section above the portion where the heat transfer tubes of the feed water preheating device are installed, and spray the cleaning water from the heat transfer tube cleaning water injection section toward the heat transfer tubes. Do that. In addition, since cleaning wastewater is generated when the heat transfer pipe is cleaned, a drain discharge port and a drain discharge pipe are provided at the bottom of the feed water preheating device, and the cleaning drainage is discharged from the drain discharge port to the outside through the drain drain pipe. If the flow path is open when the heat transfer pipe is not cleaned, the drain drain pipe is normally closed because the flue gas flowing in the exhaust gas passage leaks out, and only opens when the heat transfer pipe is cleaned. I have to.

  By the way, since the exhaust gas passage discharges combustion exhaust gas to the outdoors, the tip is naturally opened to the outdoors. Although the structure is such that rain does not easily enter at the end of the exhaust gas passage, water sometimes enters the exhaust gas passage due to rain blowing. Since the feed water preheating device is installed at the lowermost part of the exhaust gas passage, the water that has entered the exhaust gas passage accumulates in the exhaust gas passage portion at the bottom of the feed water preheating device as shown in FIG.

  When water accumulates in the exhaust gas passage portion in the feed water preheating device, the flow area of the combustion exhaust gas in the feed water preheating device is reduced. If the flow path area is reduced, it becomes a resistance when the combustion exhaust gas flows, and the combustion exhaust gas becomes difficult to flow. Then, since the combustion exhaust gas cannot escape in the boiler, the furnace pressure rises, and when the furnace pressure increases, it becomes difficult for combustion air to enter the boiler. The supply amount of combustion air is set so as to be optimal at the normal furnace pressure, so if it becomes higher than the assumed furnace pressure and a predetermined amount of combustion air cannot be supplied, The state changed and vibrational combustion and many harmful substances were generated during combustion. When the boiler is unable to perform normal combustion, the boiler has to be stopped. Therefore, there is a problem that the steam supply is insufficient due to the abnormal stop of the boiler, which may affect the operation of the factory.

Japanese Patent No. 2911014

  The problem to be solved by the present invention is to prevent the deterioration of the combustion state in the boiler due to the accumulation of water at the bottom of the feed water preheating device, and to keep the proper operation as much as possible. The purpose is to provide a boiler with a preheating device.

  According to the first aspect of the present invention, a heat transfer pipe through which water is supplied to the boiler is provided in an exhaust gas passage through which combustion exhaust gas from the boiler passes, and the water supply to the boiler is preheated by heating the heat transfer pipe with the combustion exhaust gas. A boiler having a feed water preheating device, wherein the exhaust gas passage portion through which the combustion exhaust gas in the feed water preheating device passes is provided with a drain discharge port and a drain drain pipe for discharging water accumulated in the exhaust gas passage portion, and further an exhaust gas passage When a pressure detection device for detecting the pressure of the combustion exhaust gas flow flowing through the exhaust gas passage is provided and an increase in pressure loss in the exhaust gas passage is detected by the pressure detection device, an abnormality is notified and the water supply preheating device It is characterized by controlling the discharge of water.

  According to a second aspect of the present invention, in the boiler having the feed water preheating device, a cleaning device for cleaning the drain discharge pipe is provided, and drainage from the exhaust gas passage portion of the feed water preheating device is performed by increasing pressure loss. However, when the pressure detected by the pressure detection device does not drop, the drain discharge pipe is controlled to be cleaned.

  According to a third aspect of the present invention, in the boiler having the feed water preheating device, the pressure detected by the pressure detection device is reduced even if drainage from the exhaust gas passage portion of the feed water preheating device is performed due to an increase in pressure loss. If not, control is performed to reduce the combustion amount of the boiler.

  According to a fourth aspect of the present invention, a heat transfer pipe for passing water to the boiler is provided in an exhaust gas passage for passing combustion exhaust gas from the boiler, and the water supply to the boiler is preheated by heating the heat transfer pipe with the combustion exhaust gas. The boiler has a feed water preheating device, and a drain discharge port and a drain drain pipe for discharging water accumulated in the exhaust gas passage portion are provided in the exhaust gas passage portion through which the combustion exhaust gas in the feed water preheating device passes, and the exhaust gas passage is further provided. A pressure detection device for detecting the pressure of the flowing flue gas flow is provided, and when the pressure loss increase in the exhaust gas passage is detected by the pressure detection device, an operation of discharging water at the bottom of the feed water preheating device is performed. It is characterized by.

The invention according to claim 5 is an operation method of a boiler having the feed water preheating device,
The boiler is equipped with a cleaning device that cleans the drain discharge pipe, and the pressure detected by the pressure detection device did not drop even when the drainage operation was performed from the exhaust gas passage of the feed water preheating device due to increased pressure loss. In this case, the operation is performed to clean the drain discharge pipe.

  According to the sixth aspect of the present invention, in the operation method of the boiler having the feed water preheating device, even if drainage from the exhaust gas passage portion of the feed water preheating device is performed due to an increase in pressure loss, the pressure detection device detects it. When the pressure does not decrease, an operation is performed to reduce the combustion amount of the boiler.

  By implementing the present invention, even if the flow path of the combustion exhaust gas is narrowed due to accumulation of water at the bottom of the feed water preheating device, the boiler can be operated in an appropriate state as much as possible.

Flow chart in one embodiment of the present invention Flow chart in another embodiment of the present invention

  An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a flow chart of a boiler implementing the present invention, and FIG. 2 is a flow chart of a boiler in another embodiment. In the boiler 1, a large amount of air is required for combustion, and the furnace pressure rises due to combustion in the combustion chamber inside the boiler, so that it is necessary to send air to a location with high pressure. Therefore, a blower is installed, and air whose pressure is increased by the blower is supplied. The supply of combustion air by the blower is set to an optimal air volume corresponding to the combustion volume in consideration of the furnace pressure during combustion. In recent boilers, high-load combustion is performed in a small space, and it is not necessary to simply send the amount of air necessary for combustion, and it is high while keeping the generation amount of harmful substances such as CO and NOx low. In order to obtain efficiency, precise air supply control is performed.

  In the boiler, the boiler water is heated by the high-temperature gas generated by combustion to generate steam. The flue gas whose temperature has been lowered by exchanging heat with the boiler water is discharged through the flue gas passage 2 connected to the combustion chamber. However, since this combustion exhaust gas is sufficiently hot compared with the feed water temperature to the boiler, a feed water preheating device 7 is provided in the middle of the exhaust gas passage 2 to preheat the feed water with the exhausted combustion exhaust gas. A large number of heat transfer tubes 3 extending in the horizontal direction are provided in the feed water preheating device 7, and the combustion exhaust gas flows downward between the heat transfer tubes 3 in the feed water preheating device 7 and is turned at the lower portion in the feed water preheating device 7. It is set as the structure taken out more. The heat transfer pipes in the water supply preheating device 7 are connected to form a water supply flow path, and water supply into the water supply preheating device is performed from the lowermost heat transfer tube of the heat transfer tube group. The boiler water flow in the feed water preheater sequentially passes from the lower heat transfer pipe and reaches the uppermost heat transfer pipe while being heated. Although not shown, the preheated boiler water is taken out of the feed water preheater and is supplied to the boiler 1. Water is supplied. Many heat absorption fins are provided on the outer surface of the heat transfer tube of the feed water preheating device 7. The heat absorption fins are provided in the entire circumference in the circumferential direction from the surface of the heat transfer tube, and by installing the heat absorption fins, the area in contact with the combustion gas can be increased, so heat absorption in the heat transfer tube The amount can be increased.

  The combustion exhaust gas reaching the feed water preheating device 7 from the boiler exchanges heat with the heat transfer pipe 3 of the feed water preheating device. In the heat transfer tube 3, the area in contact with the combustion exhaust gas is increased by the heat absorption fins. Therefore, the heat of the combustion exhaust gas is absorbed by the large heat transfer surface, and the boiler feed water flowing in the heat transfer tube is heated. The combustion exhaust gas flows toward the lower part while heating the heat transfer tube, and the temperature gradually decreases by heating the heat transfer tube.

  If soot or the like contained in the combustion exhaust gas adheres to the heat transfer tube 3, the heat transfer efficiency is lowered. Therefore, a cleaning device for injecting cleaning water to the heat transfer tube 3 is provided to perform periodic cleaning. I have to. The heat transfer tube cleaning device injects boiler blow water from the upper part of the heat transfer tube, and the heat transfer tube cleaning water injection unit 9 is installed above the portion where the heat transfer tube 3 is installed. A drain discharge port 6 and a drain drain pipe 5 are provided at the bottom of the feed water preheating device 7 in order to discharge the cleaning waste water generated during cleaning. The drain valve 11 provided in the drain drain pipe 5 is normally closed, and when the heat transfer pipe 3 is cleaned, the drain valve 11 is opened so that the cleaning water is discharged from the drain outlet 6 through the drain drain pipe 5 to the outside. A flush outlet 10 is also provided directly above the drain outlet 6 provided at the bottom of the feed water preheating device 7, and the flush water is directed from directly above the drain outlet 6 toward the drain outlet 6. So that it can be injected.

  A pressure detection device 4 is provided in the exhaust gas passage 2. The pressure detection device 4 is for detecting an increase in pressure loss at the combustion exhaust gas turn portion at the bottom of the feed water preheating device 7. When the pressure loss increases in the feed water preheating device 7, the pressure increases in the exhaust gas passage 2 on the primary side of the feed water preheating device. For this reason, the pressure detection device 4 in FIG. 1 detects the pressure in the exhaust gas passage 2 upstream of the feed water preheating device, and by detecting the pressure increase in the exhaust gas passage 2, the pressure loss increases. To detect. The pressure value detected by the pressure detection device 4 is output to the operation control device 8 that controls the operation of the boiler.

  Further, the pressure detection device 4 may directly detect the pressure in the exhaust gas passage 2, but if the pressure loss in the feed water preheating device is detected, the primary side and the secondary side of the feed water preheating device 7 are used. It is also possible to detect the differential pressure at. In the embodiment of FIG. 2, the pressure detection device 4 has a pressure detection pipe connected to the inlet side and the outlet side of the feed water preheating device 7 so as to detect the differential pressure between the two. When detecting a pressure loss change in the feed water preheating device 7, it is clearer to detect a differential pressure before and after the feed water preheating device. Also in this case, the pressure value detected by the pressure detection device 4 is output to the operation control device 8 that controls the operation of the boiler.

  The exhaust gas passage 2 is open to the outdoors, and the tip of the exhaust gas passage 2 has a structure that prevents rain from entering. However, when rain enters the exhaust gas passage 2, the rain flows downward in the exhaust gas passage 2, so that it enters the feed water preheating device 7 provided at the bottom of the exhaust gas passage 2 and accumulates at the bottom of the feed water preheating device 7. . A drain drain pipe 5 is connected to the bottom of the feed water preheating device in order to drain cleaning waste water generated when the heat transfer pipe 3 is washed. However, since it is normally closed, boiler feed water leaked from the heat transfer pipe 3 Will accumulate at the bottom of the feed water preheater. When the water level accumulated at the bottom of the feed water preheating device becomes higher, the water blocks the exhaust gas passage at the bottom of the feed water preheating device, and the flow area of the exhaust gas is reduced.

  When the flow passage cross-sectional area of the exhaust gas passage is reduced, resistance when the combustion exhaust gas passes increases and it becomes difficult to discharge the combustion exhaust gas. Therefore, the pressure rises in the exhaust gas passage 2 upstream of the feed water preheating device 7. In the pressure detection device 4, information on the pressure increase in the exhaust gas passage on the upstream side of the feed water preheating device, that is, information for detecting an increase in pressure loss in the feed water preheating device 7 is sent to the operation control device 8. The operation control device 8 that has received the information about the pressure loss increase notifies the abnormality of the pressure rise and opens the drain valve of the drain drain pipe 5 to discharge the water accumulated in the feed water preheating device 7. As a method for notifying an increase in pressure loss, it is possible to turn on an abnormal indicator lamp or to display a character on a display device. Drainage from the feed water preheating device 7 may be performed automatically by the operation control device 8, or may be performed manually after confirming abnormality notification in the operation control device. If the water in the feed water preheating device 7 disappears by opening the drain valve 11 and the area of the exhaust gas passage is enlarged, the combustion exhaust gas flows smoothly, so the furnace pressure of the boiler is lowered.

  Further, when the drain discharge port 6 or the drain drain pipe 5 is clogged, drainage cannot be performed even if the drain valve 11 is opened. When the heat transfer pipe 3 of the feed water preheating device 7 is washed, soot that has adhered to the heat transfer pipe 3 may flow down and clog the drain drain pipe 5, so that the drain drain pipe 5 is clogged. Even if the drain valve 11 is opened, the water level at the bottom of the feed water preheating device does not decrease. The clogging of the drain discharge port 6 and the drain drain pipe 5 is solved by injecting cleaning water from the discharge water cleaning unit 10 for the discharge port to the drain discharge port 6. If the drain drain pipe 5 is not clogged by flushing the clog of the soot by the washing water injection section 10 for the discharge port, the water accumulated at the bottom of the feed water preheating device can be discharged from the drain drain pipe 5.

  If the pressure in the exhaust gas passage 2 does not decrease even if the drainage operation is performed, control is performed to reduce the combustion amount of the boiler 1. If the boiler 1 performs three-position control of high combustion, low combustion, and stop, the combustion amount can be limited by controlling at two positions of low combustion and stop without performing high combustion. If the boiler 1 performs four-position control of high combustion, medium combustion, low combustion, and stop, control is performed at three positions of medium combustion, low combustion, and stop, or two positions of low combustion and stop. . Further, if the boiler performs proportional control, combustion is limited to a predetermined combustion amount set to a value lower than the rated combustion amount. By doing so, the operation is performed without increasing the combustion amount in the boiler.

  In the operation control device 8, the limit range of the combustion amount may be changed in accordance with the pressure loss increase amount in the pressure detection device 4. When the pressure loss increase amount in the feed water preheating device is small, the amount that reduces the combustion amount of the boiler may be small, and if the pressure loss increase amount is large, the amount that restricts the combustion amount may be increased. . In that case, it can be done by setting the limit value of the combustion amount corresponding to the increase amount of the pressure loss, and the increase amount of the pressure loss becomes larger, than the combustion stop set value that is the limit value that can perform normal combustion. However, the setting may be such that the boiler is not operated.

  If the pressure in the exhaust gas passage 2 remains high even after the drainage operation is performed, the furnace pressure remains high because the exhaust of the combustion exhaust gas from the boiler 1 is hindered. In that case, if the combustion state changes due to hindering the supply of combustion air, a large amount of harmful substances such as vibration combustion and NOx may be generated. In that case, since there is a problem if the boiler is operated as it is, the boiler is forced to stop the operation. However, even in that case, if the combustion amount is reduced and the generation amount of combustion exhaust gas is reduced, the magnitude of the pressure loss can be reduced even if the flow path area in the feed water preheating device portion is reduced. Even when the furnace pressure rises due to an increase in ventilation resistance, the furnace pressure can be kept low by keeping the amount of combustion in the boiler low, so when the pressure loss in the feed water preheater increases, combustion in the boiler By not increasing the amount, the operation of the boiler can be continued as much as possible without deteriorating the combustion state.

  In addition, even if the pressure loss is detected by detecting an increase in pressure loss with the pressure detection device and the pressure loss is reduced by reducing the combustion amount of the boiler, the pressure loss increases if the water level in the feed water preheating device increases significantly. . In that case, if the combustion amount of the boiler is reduced as the pressure loss increases, the combustion of the boiler can be continued to the limit. If the limit value at which proper combustion cannot be performed even if the combustion amount is reduced is exceeded, the operation of the boiler is stopped to prevent vibration combustion and generation of harmful substances.

  In addition, when the pressure increase in the exhaust gas passage 2 occurs due to the reduction of the combustion exhaust gas passage, the case where the passage area is reduced in the heat transfer tube group portion due to adhesion of soot to the heat transfer tube 3, and the above description As described above, there may be a case where the flow path area of the passage portion is reduced. The reduction of the channel area due to soot adhesion on the heat transfer tube gradually increases over a long time, and the reduction of the channel area in the passage portion occurs in a relatively short time. Therefore, by measuring the time required for the pressure rise, it is possible to determine which factor is caused. In the case of a pressure increase due to soot adhesion on the heat transfer tube, it is effective to clean the heat transfer tube, and in the case of a pressure increase due to accumulation of water at the bottom of the water supply preheating device, it is effective to perform drainage.

  The present invention is not limited to the embodiments described above, and many modifications can be made by those having ordinary knowledge in the art within the technical idea of the present invention.

DESCRIPTION OF SYMBOLS 1 Boiler 2 Exhaust gas passage 3 Heat transfer pipe 4 Pressure detection apparatus 5 Drain drain pipe 6 Drain discharge port 7 Water supply preheating apparatus 8 Operation control apparatus
9 Washing water injection part for heat transfer tubes
10 Washing water injection part for discharge port
11 Drain valve

Claims (6)

  In the exhaust gas passage that passes the combustion exhaust gas from the boiler, a heat transfer tube that passes the feed water to the boiler is installed, and the boiler with a feed water preheating device that preheats the feed water to the boiler by heating the heat transfer tube with the combustion exhaust gas The exhaust gas passage portion through which the combustion exhaust gas in the feed water preheating device passes is provided with a drain discharge port for discharging water accumulated in the exhaust gas passage portion and a drain drain pipe, and further the pressure of the combustion exhaust gas flow flowing in the exhaust gas passage is adjusted. A pressure detection device is provided to detect an increase in pressure loss in the exhaust gas passage and to control the discharge of water in the feed water preheating device when the pressure detection device detects an increase in pressure loss. A boiler having a feed water preheating device.   A boiler having the feed water preheating device according to claim 1, wherein a cleaning device for cleaning the drain discharge pipe is provided, and the pressure detection device even if drainage from the exhaust gas passage portion of the feed water preheating device is performed due to an increase in pressure loss A boiler having a feed water preheating device, which performs control to clean the drain discharge pipe when the pressure detected in step 3 does not drop.   In the boiler having the feed water preheating device according to claim 1 or 2, when the pressure detected by the pressure detection device does not drop even if drainage from the exhaust gas passage portion of the feed water preheating device is performed due to an increase in pressure loss. A boiler having a feed water preheating device, characterized in that control is performed to keep the combustion amount of the boiler low.   In the exhaust gas passage that passes the combustion exhaust gas from the boiler, a heat transfer tube that passes the feed water to the boiler is installed, and the boiler with a feed water preheating device that preheats the feed water to the boiler by heating the heat transfer tube with the combustion exhaust gas The exhaust gas passage portion through which the combustion exhaust gas in the feed water preheating device passes is provided with a drain discharge port for discharging water accumulated in the exhaust gas passage portion and a drain drain pipe, and further detects the pressure of the combustion exhaust gas flow flowing through the exhaust gas passage A pressure detection device is provided, and when a pressure loss increase in the exhaust gas passage is detected by the pressure detection device, an operation for discharging water at the bottom of the water supply preheating device is performed. How to operate the boiler.   The operation method of the boiler with the feed water preheating device according to claim 4, wherein the boiler is provided with a cleaning device for cleaning the drain discharge pipe, and drainage operation from the exhaust gas passage portion of the feed water preheating device due to an increase in pressure loss A method for operating a boiler having a feed water preheating device, characterized in that if the pressure detected by the pressure detection device does not drop even after the operation, the drain discharge pipe is washed. 6. The operation method of a boiler having a feed water preheating device according to claim 4 or 5, wherein the pressure detected by the pressure detection device decreases even if drainage from the exhaust gas passage portion of the feed water preheating device is performed due to an increase in pressure loss. If not, a method for operating a boiler having a feed water preheating device, characterized in that an operation for reducing the combustion amount of the boiler is performed.

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