JP2014085054A - Waste heat recovery boiler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a waste heat recovery boiler having an economizer and a water tank heat exchanger on a downstream side of a boiler heat transmission part and pre-heating boiler feed water by utilizing exhaust gas, which prevents the economizer from boiling the boiler feed water.SOLUTION: The waste heat recovery boiler comprises: a boiler heat transmission part 1 for heating boiler feed water and generating steam; a water tank 10 for storing the boiler feed water to be fed to the boiler heat transmission part 1; a water tank heat exchanger 3 for pre-heating the boiler feed water stored in the water tank 10; and an economizer 6 for pre-heating the boiler feed water to be fed to the boiler heat transmission part 1. The water tank heat exchanger 3 and the economizer 6 heat boiler feed water or boiler supply water by utilizing heat of high-temperature exhaust gas emitted from the boiler heat transmission part. The water tank heat exchanger 3 heats boiler feed water by utilizing the exhaust gas which has underwent heat recovery at the boiler heat transmission part 1 and the economizer 6 heats boiler supply water by utilizing the exhaust gas which has underwent heat recovery at the water tank heat exchanger 3.

Description

  The present invention relates to an exhaust heat recovery boiler, and more particularly to an exhaust heat recovery boiler that preheats boiler water using exhaust gas after heat exchange in a boiler heat transfer section.

  Japanese Patent Application Laid-Open No. 2011-122742 discloses a boiler heat transfer section that heats boiler water to generate steam, an economizer that preheats water supplied to the boiler heat transfer section downstream of the exhaust gas flow of the boiler heat transfer section, and an economizer Further, there is a description of a boiler in which a water tank heat exchanger for preheating water stored in the water supply tank is installed on the downstream side while circulating water between the water supply tank and the water supply tank.

  Heating in the boiler is performed by passing high-temperature gas around the heat transfer tube, and the high-temperature gas flows in the order of the heat transfer section of the boiler body, the economizer, and the heat exchanger for the feed water tank. Go. The temperature of the high-temperature gas that heats the boiler water decreases as the boiler water is heated at each location. Therefore, the gas temperature for heating the boiler water with the economizer is lower than the temperature at the boiler heat transfer section, and the gas temperature for heating the boiler water with the heat exchanger for the feed water tank is further lower than the temperature at the economizer section. In this case, the temperature of the feed water rises first by the heat exchanger for the feed water tank, and then the temperature rises further by passing through the economizer, so that hot water can be supplied to the boiler heat transfer section.

  In the boiler heat transfer section, steam is generated by heating the boiler water, but if the boiler feed water temperature is high, the required amount of heating in the boiler heat transfer section is reduced, and if the same heat is generated, more steam is generated. be able to. By installing a heat exchanger for the water tank in addition to the economizer and preheating the boiler water before entering the economizer, the amount of heat absorbed by the entire system increases, Efficiency can be improved.

  The above-described configuration can also be performed by an exhaust heat boiler that generates steam by using high-temperature exhaust gas generated by a gas turbine or an engine without having its own heat generation device. By using cogeneration such as generating electricity with a gas turbine and generating steam with a waste heat boiler, the overall efficiency increases, so exhaust heat boilers are widely used. Can also increase the efficiency.

  However, since the exhaust heat boiler does not control the temperature and amount of the high-temperature gas for supplying heat by itself, the amount of supplied heat increases or decreases depending on the load factor at the heat generation source. When the amount of heat supplied increases, the amount of heat absorbed by the economizer and the heat exchanger for the water supply tank increases, and the temperature of the boiler water supply rises. Furthermore, when the water supply to the boiler heat transfer section is ON / OFF controlled, the boiler feedwater staying in the economizer due to the stoppage of the water supply will continue to be heated for a long time by the high temperature exhaust gas. The temperature increased and steam was sometimes generated in the economizer. If the feed water sent from the economizer to the boiler heat transfer section becomes steam, the boiler heat transfer section cannot detect the water level correctly and cannot operate the boiler appropriately.

JP 2011-122742 A

  The problem to be solved by the present invention is that an economizer and a water tank heat exchanger are installed on the downstream side of the boiler heat transfer section, and the boiler uses the exhaust gas after heat exchange in the boiler heat transfer section. An object of the present invention is to provide an exhaust heat recovery boiler that can prevent boiler water from boiling by the economizer because the amount of heating in the economizer becomes excessive in a boiler that preheats water.

  Boiler heat transfer section that generates steam by heating boiler water, water supply tank for storing boiler water for supplying to the boiler heat transfer section, and water supply tank for preheating boiler water stored in the water supply tank A heat exchanger and an economizer for preheating boiler feed water to be supplied to the boiler heat transfer section, and the heat exchanger for the feed water tank and the economizer use the heat of the hot exhaust gas discharged from the boiler heat transfer section and Boiler feed water is heated, and the heat exchanger for the feed water tank heats the boiler water using the exhaust gas after heat recovery at the boiler heat transfer section, and the economizer is a heat exchanger for the feed water tank. The boiler feed water is heated using the exhaust gas after the heat recovery.

  If the water tank heat exchanger is installed upstream of the economizer in the exhaust gas flow, the temperature of the exhaust gas is lowered by the water tank heat exchanger before reaching the economizer. Therefore, the temperature of the exhaust gas reaching the economizer can be adjusted, and the boiler water can be prevented from boiling in the economizer. Further, since the heat exchanger for the feed water tank is heated by the higher temperature exhaust gas, the amount of heat recovered in the heat exchanger for the feed water tank increases, and the temperature in the feed water tank increases. If the temperature of the boiler feed water that is stored in the water supply tank becomes high and the rate of heat recovery in the economizer decreases, the fluctuation range of the boiler feed water temperature supplied to the boiler heat transfer section decreases. The temperature of the feed water can be stabilized.

Flow chart of exhaust heat recovery boiler implementing the present invention

  An embodiment of the present invention will be described with reference to the drawings. FIG. 1 recovers heat from high-temperature exhaust gas generated in a gas turbine, an engine, etc., and has exhaust heat recovery having an economizer 6 and a water tank heat exchanger 3 in addition to a boiler heat transfer section 1. It is a flowchart of a boiler. Water supply to the boiler heat transfer section 1 is performed from a water supply tank 10 having a water level adjusting device. The water level adjusting device of the water supply tank 10 supplies water to the water supply tank 10 when the water level in the water supply tank 10 becomes lower than the set water level, and supplies water to the water supply tank 10 when the water level in the water supply tank 10 becomes higher than the set water level. As a water level control device, a float valve is widely used because it is inexpensive.

  A circulation pipe 5 for preheating boiler water stored in the water supply tank 10 is connected to the water supply tank 10 before being supplied to the boiler heat transfer section 1. The circulation pipe 5 circulates boiler water between the water supply tank heat exchanger 3 provided in the exhaust gas passage 2, and both ends of the circulation pipe 5 are connected to the water supply tank 10. Are provided with a circulation pump 9 and a water supply tank heat exchanger 3. The heat exchanger 3 for the feed water tank is installed in the exhaust gas passage 2 downstream from the boiler heat transfer section 1 and further heats from the exhaust gas whose temperature has been lowered by the heat absorption by the boiler heat transfer section 1. It tries to collect. The circulation pipe 5 operates the circulation pump 9 to send water stored in the water supply tank 10 to the heat exchanger 3 for the water supply tank, and performs heat exchange with the exhaust gas by the heat exchanger 3 for the water supply tank. The pre-heated boiler water is returned to the water supply tank 10. The circulation pump 9 continuously supplies water with a constant amount of water, and circulates the boiler water in the water supply tank 10 between the heat exchanger 3 for the water supply tank.

  Water supply to the boiler heat transfer section 1 is performed through a boiler water supply pipe 8. The boiler water supply pipe 8 is a pipe having one end connected to the water supply tank 10 and the other end connected to the boiler heat transfer section 1, and a water supply pump 4 and an economizer 6 are installed in the middle thereof. The boiler heat transfer section 1 detects the water level of the boiler water, outputs an operation command to the feed water pump 4 when the water level drops to the feed water start water level, and to the feed water pump 4 when the water level rises to the feed water stop water level. Output a stop command. The water supply pump 4 starts water supply when receiving an operation command, and stops water supply when receiving a stop command, and is repeatedly operated and stopped to keep the water level in the boiler at a predetermined value.

  In FIG. 1, the exhaust gas is supplied from the left side toward the exhaust gas passage 2 and flows in the right direction. In the exhaust gas passage 2, a boiler heat transfer section 1, a water supply tank heat exchanger 3, and an economizer 6 are installed in this order from the upstream side of the exhaust gas flow. The exhaust gas flow flowing from the left side to the right side performs heat exchange in the order of the boiler heat transfer unit 1, the water supply tank heat exchanger 3, and the economizer 6, and the temperature is lowered every time heat exchange is performed.

  In the figure, an example of the temperature is described. The raw water supplied through the raw water pipe 7 is 25 ° C., and the temperature of the exhaust gas is 500 ° C. In the example shown in the figure, the exhaust gas supplied at 500 ° C. consumes heat by heating the boiler water in the boiler heat transfer section 1 and generating steam. The exhaust gas whose temperature has been reduced in the boiler heat transfer section 1 is 200 ° C. downstream of the boiler heat transfer section, and the 200 ° C. exhaust gas then heats the tank water flowing in the water supply tank heat exchanger 3. . The temperature of the exhaust gas is lowered also in the heat exchanger 3 for the feed water tank, and is 170 ° C. downstream of the heat exchanger 3 for the feed water tank. The exhaust gas at 170 ° C. flows to the economizer 6 installed further downstream of the exhaust gas passage 2, and the economizer also heats boiler feed water. The exhaust gas whose temperature has been lowered also in the economizer 6 is discharged through the exhaust gas passage 2.

  Water supply to the boiler heat transfer section 1 is performed by supplying boiler water stored in the water supply tank 10 through the raw water pipe 7. In addition to the boiler water supply pipe 8 through which water is supplied to the boiler heat transfer section 1, a circulation pipe 5 for circulating boiler water between the water supply tank heat exchanger 3 is connected to the water supply tank 10. . The circulation pipe 5 is provided with a circulation pump 9 on the way, and the circulation water is circulated between the feed water tank 10 and the feed water heat exchanger 3 by operating the circulation pump 9. When boiler water is sent from the feed water tank 10 to the feed water heat exchanger 3, the feed water heat exchanger 3 exchanges heat between the boiler water and the exhaust gas, and the boiler water absorbs heat and raises the temperature. . In the case of the example shown in the figure, when 70 ° C. boiler water is sent to the water supply tank heat exchanger 3, the water supply tank heat exchanger rises to 95 ° C., and the 95 ° C. circulating water returns to the water supply tank 10. It has become. At this time, the operation of the circulation pump 9 is continuously performed, and the feed water tank heat exchanger 3 continuously flows the circulating water without stagnation, so that the heat absorption efficiency of the feed water tank heat exchanger 3 is high. Can be maintained.

  In the boiler heat transfer section 1, water supply is started when the water level in the boiler decreases to the water supply start water level, and water supply is stopped when the water level in the boiler rises to the water supply stop water level. Water is supplied through the water supply pipe 8 by operating the water supply pump 4. Although the boiler water was 70 ° C. in the water supply tank 10, it was raised to 120 ° C. by heating with the economizer 6 provided in the middle of the water supply pipe 8. Since the pressure is high inside the boiler, the boiler feed water 8 does not boil at this temperature, and the boiler feed water enters the boiler heat transfer section 1 in a liquid state. Since the temperature of the exhaust gas that heats the economizer 6 is lowered by the heat exchanger 3 for the water supply tank, the temperature rise in the economizer 6 is suppressed, and the boiler water does not boil. In the boiler, steam is not mixed with the feed water, so that the water level in the boiler can be detected correctly and stable operation can be performed.

  In an exhaust heat recovery boiler with a large variation in the amount of heat supplied, if an economizer is provided immediately downstream of the boiler, the amount of heat of exhaust gas supplied to the economizer may be higher than expected. And since the water supply to a boiler starts and stops according to the water level in a boiler, the boiler water supply in an economizer repeats a flow and a stop. Therefore, the temperature of the boiler feed water after preheating with the economizer 6 greatly increases or decreases depending on the situation. In some cases, the boiler feed water boils in the economizer, and the boiler feed water containing steam is supplied to the boiler. There was a case. However, when the water supply tank heat exchanger 3 is provided between the boiler heat transfer section 1 and the economizer 6 as in the present invention, the exhaust gas temperature is lowered in the water supply tank heat exchanger 3. It is possible to prevent the boiler water from boiling.

  Moreover, in the heat exchanger 3 for water supply tanks which became upstream, since the exhaust gas temperature supplied becomes high, a heating amount becomes large. However, the water supply tank heat exchanger 3 continuously circulates the boiler water with the water supply tank 10, and the recovered heat is sent to the water supply tank 10 to raise the temperature of the boiler water. Therefore, the temperature change width in the water supply tank 10 is smaller than the fluctuation of the boiler water supply temperature on the downstream side of the economizer that is starting and stopping the water supply. Since the feed water temperature sent to the economizer 6 is leveled at a high level, the feed water to the boiler heat transfer section 1 is stabilized at a high state level, and the exhaust heat is used efficiently.

  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.

1 Boiler heat transfer section
2 Exhaust gas passage
3 Heat exchanger for water supply tank
4 Water supply pump
5 Circulation piping
6 economizer
7 Raw water piping
8 Boiler feed piping
9 Circulation pump
10 Water tank
11 Steam piping

Claims (1)

Boiler heat transfer section that generates steam by heating boiler water, water supply tank for storing boiler water for supplying to the boiler heat transfer section, and water supply tank for preheating boiler water stored in the water supply tank A heat exchanger and an economizer for preheating boiler feed water to be supplied to the boiler heat transfer section are used. Boiler feed water is heated, and the heat exchanger for the feed water tank heats the boiler water using the exhaust gas after heat recovery at the boiler heat transfer section, and the economizer is a heat exchanger for the feed water tank. An exhaust heat recovery boiler, wherein the boiler feed water is heated using the exhaust gas after the heat recovery.

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