JP5627254B2 - Once-through boiler - Google Patents

Description

  The present invention relates to a once-through boiler in which a water level is set in the middle of a heat transfer tube and steam is generated by heating the heat transfer tube.

  Several vertical heat transfer tubes are installed, water is supplied from the lower part of the heat transfer tube, steam is generated by heating the boiler water in the heat transfer tube while the boiler water ascends the heat transfer tube, and from the upper part of the heat transfer tube Through-flow boilers for taking out steam are widely used, and in recent years, large-capacity once-through boilers are also increasing. Since the once-through boiler sets the water level in the middle of the heat transfer tube, the amount of boiler water is smaller than that of other types of boilers. Therefore, since the amount of heat held by the boiler is reduced, the damage is limited even if an accident occurs, and there is an advantage that the steaming time when starting from a cold can is shortened.

  However, in the once-through boiler that sets the water level in the middle of the heat transfer tube, severe water level control is required. In the part higher than the water level at the top of the heat transfer tube, it is cooled by the boiler water that is lifted by boiling in the heat transfer tube vigorously. The upper part of the heat transfer tube is overheated. Also, if the water level in the heat transfer tube is too high, the amount of boiler water lifted to the top of the heat transfer tube will increase, causing carryover in which a large amount of boiler water that could not be separated is taken out together with the steam, leading to a drop in steam quality Become. Therefore, water level control is important for once-through boilers.

  The appropriate water level also changes depending on the amount of combustion in the boiler. If the amount of combustion can be increased or decreased, such as high combustion, low combustion, high combustion, medium combustion, or low combustion, each fuel amount The proper water level is different. In the case of high combustion with a large amount of combustion, the boiling of boiler water increases in the heat transfer tube, so carryover occurs unless the water level is kept low, and in the case of low combustion with a small amount of combustion, heat transfer Since the boiling of boiler water in the pipe becomes small, the heat transfer pipe will overheat unless the water level is raised.

  Japanese Patent No. 294080 discloses that the water level is set corresponding to each of 100% combustion, 65% combustion, and 30% combustion, and the water level is changed in accordance with the amount of combustion. In Japanese Patent No. 294080, the water level in the water level detection container is low between Hb and Hc during 100% combustion, and the water level in the water level detection container is between Hc and Hd during 65% combustion. In the middle and 30% combustion, the water level in the water level detection container is set to a high level between Hd and He to change the water level in the heat transfer tube. Japanese Patent Application Laid-Open No. 55-31273 discloses a case where the water level control pipe column is connected to the steam separator and the pressure loss between the boiler body and the steam separator is used to increase the combustion amount. When the water level in the heat transfer tube is lowered and the amount of combustion is small, the water level in the heat transfer tube is increased. In this case, when the combustion amount increases, the amount of steam generated increases, so the pressure loss between the boiler body and the steam separator increases. That is, as the combustion amount increases, the pressure in the boiler body becomes larger than the pressure in the water level control pipe column, so the water level in the heat transfer pipe becomes lower than the detected water level in the water level control pipe column. Therefore, if water supply control is performed so that the water level control pipe column has a constant water level, the water level in the heat transfer pipe can be lowered as the combustion amount naturally increases.

  In this way, when the combustion amount changes, the water level in the heat transfer tube is changed according to the combustion amount, so that the heat transfer tube overheating and carryover do not occur even when the combustion amount changes. However, in a once-through boiler having a large capacity, the heat transfer tube may overheat or carry over immediately after the combustion amount is changed, and it is necessary to solve these problems.

Japanese Patent No. 294080

  The problem to be solved by the present invention is to provide a once-through boiler capable of preventing the balance between the combustion amount and the water level in the heat transfer tube from being lost and causing problems such as overheating and carryover of the heat transfer tube. .

The invention according to claim 1 is a once-through boiler in which the water level is set in the middle of the heat transfer tube, and the combustion amount of the boiler is set in multiple stages to set the middle combustion between the high combustion and the low combustion. The operation control device controls the amount of fuel supplied to the combustion device and the amount of combustion air by operating the fuel supply amount control device, the blower, and the air flow control device, and adjusts the combustion amount. The appropriate amount of water level in the heat transfer tube varies depending on the amount of combustion, and the appropriate water level decreases in the order of the appropriate water level for low combustion, the appropriate water level for medium combustion, and the appropriate water level for high combustion, and was determined based on the steam pressure value. In a once-through boiler that controls the operation of the boiler so that the amount of combustion is the same, when increasing the combustion amount from the state of combustion, it is necessary to increase the combustion amount from low combustion to high combustion by two or more stages. There is medium combustion from low combustion that has been done earlier Even if it is necessary to increase the combustion amount again in a short time after the increase in the combustion amount, the intermediate combustion is performed by increasing the combustion amount step by step, and the intermediate combustion increased by one step. The combustion amount is maintained for a predetermined time T1, and the combustion level is maintained for a predetermined time T1 with the intermediate combustion increased by one step, thereby setting the water level in the heat transfer tube to an appropriate level for intermediate combustion. It is characterized in that it performs an operation to shift to the combustion level one level above.

In the invention according to claim 2, in the once-through boiler, it is necessary to reduce the combustion amount by two or more stages from high combustion to low combustion, or from the reduction in the combustion amount from the high combustion to the middle combustion performed previously. Even when it is necessary to reduce the combustion amount again in a short time, the combustion amount is decreased by one step to perform intermediate combustion, and the combustion amount is maintained for a predetermined time T2 with the intermediate combustion decreased by one step. And by maintaining the combustion amount for a predetermined time T2 with medium combustion reduced by one step, the water level in the heat transfer tube is changed to an appropriate water level for medium combustion, and then the combustion amount is shifted to a lower combustion level. Although the operation is performed, the combustion amount is not held for a predetermined time T2 when the combustion is stopped.

  When changing from high combustion to low combustion, or when changing from low combustion to high combustion, do not change the combustion amount at a stretch, but set the time to perform combustion with the intermediate combustion amount and set the combustion amount By dividing the change, it is possible to reduce the difference between the combustion amount at the time of changing the combustion amount and the water level in the heat transfer pipe. If the combustion level is high and the water level in the heat transfer tube is low, or if the combustion level is low and the water level in the heat transfer tube is high, the combustion amount is Due to the large discrepancy between the water levels in the heat transfer tubes, overheating and carryover of the heat transfer tubes were supposed to occur, but if the difference between intermediate combustion and high combustion or low combustion in the middle is the difference between the combustion amount and the heat transfer tube Since the divergence of the water level is reduced, it is possible to prevent the heat transfer tube from being overheated and carryover.

Outline diagram of boiler implementing the present invention Explanatory drawing which showed the fluctuation state of the combustion state in this invention, and the water level in a heat exchanger tube

  An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram of a boiler for carrying out the present invention. At the upper part of the boiler, a combustion device 2 with a variable combustion amount for generating a downward flame is provided, and the flame is burned in the combustion chamber 3 in the center of the boiler. Combustion air used in the combustion device 2 is supplied by a blower 5 connected to the combustion device 2 through a blower passage. An air flow control device 8 for controlling the amount of air supplied from the blower 5 to the combustion device 2 is provided, and the air supply amount for combustion is adjusted by the air flow control device 8. A fuel supply control device 7 is also provided in the fuel supply pipe 4 for supplying fuel to the combustion device 2 so that the amount of fuel supplied to the combustion device 2 can also be adjusted by the fuel supply control device 7. The boiler supplies water from the lower part by operating a water supply pump 10 provided in the lower water supply pipe, generates steam by heating the boiler water in the heat transfer pipe, and takes out the steam through the upper steam extraction pipe 12. . In the heat transfer tube during the combustion of the boiler, the boiler water boils violently, and the steam taken out through the steam take-out pipe 12 contains the boiler water that has boiled up. Only steam is taken out, and the separated boiler water is refluxed to the bottom of the boiler.

  The boiler water supply control is performed based on the water level in the water level detection device 9 connected to the steam separator. The water level detection device 9 detects the water level by detecting the presence or absence of water with a plurality of electrode rods installed at different height positions. The water supply control is performed by starting the operation of the water supply pump 10 when the water level in the water level detection device falls to the water supply start water level, and stopping the operation of the water supply pump 10 when the water level rises to the water supply stop water level due to the water supply. The boiler is operated based on the steam pressure value detected by the pressure detection device 1 that detects the steam pressure value of the boiler. When the steam pressure value is low, the combustion amount is increased, and when the steam pressure value is high, the combustion amount is decreased to keep the steam pressure within a predetermined range. The water level information detected by the water level detection device 9 and the steam pressure value detected by the pressure detection device 1 are sent to the operation control device 6 that controls the operation of the boiler. The operation control device 6 is connected to each of the blower 5, the air flow control device 8, the fuel supply control device 7, and the feed water pump 10, and the operation control device 6 controls the operation of the boiler.

  The operation control device 6 controls the combustion amount at four positions of high combustion, medium combustion, low combustion, and combustion stop based on the steam pressure value. When the combustion amount for high combustion is 100% and the combustion amount for low combustion is 20%, intermediate combustion is an intermediate value, and about 50% to 70% is appropriate. The operation control device 6 controls the fuel amount supplied to the combustion device 2 and the combustion air amount by operating the fuel supply control device 7, the blower 5, and the air flow control device 8, and the combustion amount in the combustion device 2. Adjust.

  In addition, when the operation control device 6 increases the amount of combustion from a state where low combustion is being performed, the operation control device 6 is low even if a command for directly shifting from low combustion to high combustion is output, or even if intermediate combustion is being performed. When a command to shift to high combustion is output within a predetermined time from the end of combustion, during the set time T1, the transition to high combustion is performed after performing combustion at an intermediate combustion amount. Even when reducing the amount of combustion from the current state, if a command to shift directly from high combustion to low combustion is output, or even if going through intermediate combustion, low combustion within a predetermined time from the end of high combustion When the command to shift to is output, it is assumed that during the set time T2, the transition to low combustion is performed after performing combustion at an intermediate combustion amount. When the combustion is stopped from high combustion, or when the combustion is stopped from middle combustion, the combustion is stopped, so the heat transfer tube cannot be overheated even if the water level in the heat transfer tube is low. Therefore, when the combustion is stopped, the combustion amount is not held for the predetermined time T2 even if the combustion amount is decreased by two or more stages.

  If the pressure value that increases the combustion amount and the pressure value that decreases the combustion amount are set to the same value, a phenomenon called hunting that repeats the increase in the combustion amount and the decrease in the combustion amount may occur with slight pressure fluctuations. is there. Therefore, the occurrence of hunting is prevented by providing a difference (differential) between when the combustion amount is increased and when the combustion amount is decreased. If the pressure value that decreases the combustion amount is set higher than the pressure value that increases the combustion amount, the combustion amount is not changed until the difference pressure changes, so the combustion amount is repeatedly increased and decreased in a very short time. This is no longer the case.

  The water level in the water level detection device 9 is determined by the amount of water held by the boiler and the pressure at the water level detection device 9 portion. Since the water level detection device 9 is connected to the steam / water separator 11, the water level in the water level detection device 9 is influenced by the pressure in the steam / water separator 11, not the pressure in the boiler body. The steam / water separator 11 and the boiler body are connected by a steam take-out pipe 12. When steam flows through the steam take-out pipe 12, pressure loss occurs. Therefore, the boiler body and the steam / water separator 11 have a pressure. A difference occurs, and the pressure in the boiler body is higher than the pressure in the steam separator 11 by the pressure loss in the steam take-out pipe 12. Therefore, the water level in the heat transfer tube having a high pressure is lower than the water level in the water level detecting device 9 having a low pressure.

  Further, since the pressure loss in the steam take-out pipe 12 increases as the amount of steam flowing through the steam take-out pipe 12 increases, the pressure difference between the boiler main body and the steam / water separator 11 is low combustion / medium combustion / high combustion. It grows in order. That is, when water supply control is performed so that the water level in the water level detection device 9 is kept constant, the water level in the heat transfer tube is high during low combustion, and the water level in the heat transfer tube is low during high combustion.

  In the case of low combustion with a small amount of combustion, it is necessary to increase the water level in the heat transfer tube because the amount of boiling of the boiler water decreases. Conversely, in the case of high combustion with a large amount of combustion, boiling of the boiler water In order to increase the amount of increase, the water level in the heat transfer tube needs to be lowered. However, if the pressure loss in the steam extraction tube 12 is set to be appropriate, the water supply start water level set by the water level detection device 9 is set. By starting the operation of the water supply pump 10 and performing control to stop the operation of the water supply pump 10 at the water supply stop water level, the water level in the heat transfer tube can be automatically set to an appropriate water level that matches the combustion amount.

  FIG. 2 is an explanatory view schematically showing the fluctuation state of the combustion state and the water level in the heat transfer tube in the present invention. In the water supply control, the operation of the water supply pump 10 is started when the water level in the water level detection device 9 is lowered to the water supply start water level, and the operation of the water supply pump 10 is stopped when the water level is increased to the water supply stop water level. The water level in the heat pipe also rises and falls repeatedly. The appropriate amount of water level in the heat transfer tube varies depending on the amount of combustion, and the appropriate water level decreases in the order of low combustion, medium combustion, and high combustion. The water levels a to e shown in FIG. 2 indicate the height positions in the heat transfer tube of FIG. 1, the appropriate water level for high combustion is a to c, the appropriate water level for medium combustion is b to d, and low. It is assumed that the appropriate water level for combustion is c to e.

  In FIG. 2, the combustion determined from the steam pressure value is high combustion, and the boiler starts from a state where high combustion is being performed. The water level in the heat transfer tube at this time is between a and c, and is maintained at an appropriate water level at high combustion. Thereafter, the combustion amount determined from the steam pressure value at time A changes to low combustion. In this case, the operation control device 6 does not suddenly change the combustion amount to low combustion, but performs intermediate combustion that is intermediate 50% combustion. When the combustion amount is changed from high combustion to medium combustion at time A, the amount of steam passing through the steam extraction pipe 12 is reduced by one stage because the combustion amount is reduced. Therefore, the water level of the water level detection device 9 and the water level in the heat transfer pipe are reduced. The difference is reduced by one step. The operation control device 7 performs water supply control so that the water level detected by the water level detection device 9 is maintained within a certain range, but the pressure difference between the pressure in the boiler body and the water level detection device 9 is reduced. Thus, the water level in the heat transfer tube is one step higher, and is between b and d, which is an appropriate water level in medium combustion. In the operation control device 7, the middle combustion started at the time A is performed for the set time T2, and at the time B when the set time T2 ends, the operation control device 7 shifts to low combustion, which is the original combustion amount determined from the steam pressure value. If the combustion amount is shifted from medium combustion to low combustion and the amount of steam generation is reduced, the difference between the water level of the water level detection device 9 and the water level in the heat transfer tube is reduced by one step here, so the water level in the heat transfer tube is also increased by one step. It is between ce which is the appropriate water level in low combustion.

  Thereafter, the combustion amount determined from the steam pressure value at time C changes from low combustion to medium combustion, and at time D, it further changes to high combustion. In the operation control device 7, from time C, medium combustion, which is a combustion amount determined from the steam pressure value, is set, but at time D, the elapsed time after changing from low combustion to medium combustion at time C becomes the set time T1. Since it has not reached, the medium combustion is continued. Even if the combustion amount determined from the steam pressure value changes to high combustion, the operation control device 7 does not immediately start high combustion as before, but the elapsed time from the time C at which the middle combustion is started becomes the set time T1. Maintain medium combustion until it reaches, then change to high combustion. By shifting the combustion amount from low combustion to medium combustion and performing medium combustion for the set time T1, the water level in the heat transfer tube is lowered by one step and becomes between b and d, which is the appropriate water level in the medium combustion, and the set time At time E when T1 ends, when the state shifts to high combustion, which is a combustion amount determined from the steam pressure value, the water level in the heat transfer pipe is further lowered by one stage, and becomes the water level at high combustion.

  Thereafter, the boiler stopped operating at time F. When the operation is stopped, the combustion is immediately stopped even if the amount of combustion up to that point is high. In the case of combustion stop, combustion is not performed after that, so the heat transfer tube will not be overheated no matter where the water level in the heat transfer tube is, and it is necessary to perform an operation to adjust the water level in the heat transfer tube to the amount of combustion Absent. Water supply is not performed after time F, but when combustion is stopped and steam supply is lost, the pressure in the boiler decreases, and thus the water level in the heat transfer pipe rises.

  The amount of combustion in the boiler is determined from the steam pressure value detected by the pressure detection device 1, and the amount of combustion determined from the steam pressure value shifts from high combustion of 100% combustion to low combustion of 20% in a short time. Or, conversely, there is a case where the low combustion of 20% combustion shifts to the high combustion of 100% combustion in a short time. Although the transition of the combustion amount is performed in a relatively short time, the water level in the heat transfer tube changes in the amount of steam flowing through the steam take-out pipe 12 due to the change in the combustion amount, and thus in the boiler body and the water level detection device 9. Since the pressure difference changes and the water level in the heat transfer tube becomes a water level suitable for the combustion amount, it takes a relatively long time for the water level in the heat transfer tube to shift to an appropriate water level. Therefore, if the combustion amount is changed between high combustion and low combustion, the combustion level is high, but the water level in the heat transfer tube remains at the low combustion level, or the combustion amount is low. However, since the water level in the heat transfer tube remains at the level at the time of high combustion, the balance between the combustion amount and the water level in the heat transfer tube is lost, and the heat transfer tube may overheat or carry over. In addition, even when the medium combustion is passed, if the medium combustion is passed in a very short time, the balance between the combustion amount and the water level in the heat transfer tube is the same as when the combustion amount is changed between high combustion and low combustion. Sometimes collapsed. This is because the difference in the amount of combustion between the high combustion and the low combustion is large, so that the deviation of the water level in the heat transfer tube from the appropriate water level is large.

  When changing from high combustion to low combustion with a large difference in combustion amount, or changing from low combustion to high combustion, intermediate intermediate combustion is performed for a set time T or more and the combustion amount is changed in two stages. After changing the water level to an intermediate water level, change to the desired combustion amount. Even if the combustion amount and the water level in the heat transfer tube are different by setting the combustion amount to medium combustion and the water level in the heat transfer tube to the water level in medium combustion, the combustion amount is medium combustion and the water level in the heat transfer tube is low The water level in the heat transfer tube is high during combustion, the water level in the heat transfer tube is the water level during medium combustion, the combustion amount is medium combustion, the water level in the heat transfer tube is high during combustion, the combustion amount is low, and the water level in the heat transfer tube is medium combustion. One of the water levels of the time. Therefore, although the combustion amount is high, the water level in the heat transfer tube remains at the low combustion level, or the combustion level is low, but the water level in the heat transfer tube is the water level during high combustion. As it is, the combustion amount and the water level in the heat transfer tube are not extremely shifted. By preventing the deviation of the water level in the heat transfer tube from the appropriate water level from becoming large, the balance between the combustion amount and the water level in the heat transfer tube will not be lost, so it is possible to prevent the heat transfer tube from overheating and carryover.

1 Pressure detection device 2 Combustion device
3 Combustion chamber 4 Fuel supply piping 5 Blower 6 Operation control device
7 Fuel Supply Control Device 8 Air Flow Control Device 9 Water Level Detection Device 10 Water Supply Pump 11 Steam / Water Separator 12 Steam Extraction Pipe

Claims (2)

It is a once-through boiler that sets the water level in the middle of the heat transfer tube, and the combustion quantity of the boiler is set in multiple stages and medium combustion is set between high combustion and low combustion. supply amount control apparatus, the blower, which air volume control device controls the amount of fuel and the combustion air amount supplied to the combustion apparatus by operating the adjusting the combustion amount, the proper amount of heat transfer tube water level combustion Depending on the amount, the appropriate water level decreases in the order of the appropriate water level for low combustion, the appropriate water level for medium combustion, and the appropriate water level for high combustion. In the once-through boiler that controls the combustion, when increasing the combustion amount from the state of combustion, it is necessary to increase the combustion amount from two stages or more from low combustion to high combustion, or low combustion performed earlier From the increase in combustion volume from medium to medium combustion Even if it is necessary to increase the combustion amount again in step 1, the combustion amount is increased by one step to perform intermediate combustion, and the intermediate amount increased by one step and the combustion amount is maintained for a predetermined time T1. After maintaining the combustion level for a predetermined time T1 with medium combustion increased by one stage, the water level in the heat transfer tube is set to an appropriate level for medium combustion, and then the combustion level is further shifted to a higher level. A once-through boiler characterized in that the operation is performed. The once-through boiler according to claim 1, wherein it is necessary to reduce the combustion amount by two or more stages from high combustion to low combustion, or combustion again in a short time from the reduction in combustion amount from high combustion to medium combustion performed previously. Even when it is necessary to reduce the amount, the combustion amount is decreased by one step to perform intermediate combustion, and the intermediate amount decreased by one step and the combustion amount is maintained for a predetermined time T2. In addition, by performing the operation of shifting the combustion level to a lower combustion level after making the water level in the heat transfer tube an appropriate level for the middle combustion by holding the combustion amount for a predetermined time T2 in the middle combustion reduced by one step, When the combustion is stopped, the once-through boiler is characterized in that the combustion amount is not maintained for a predetermined time T2.

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