CN104359223B - System and method for using steam turbine exhaust steam as heat medium of power plant boiler heater - Google Patents

Abstract

The invention provides a kind of system and method using exhaust steam in steam turbine as steam air heater of utility boiler thermal medium, comprise steam turbine, condenser, air inlet adjustment valve, steam air heater and water pump, be connected by pipeline between steam turbine with condenser, pick out a road in the throat of condenser and take out exhaust steam pipeline, be provided with air inlet adjustment valve taking out on exhaust steam pipeline, take out exhaust steam pipeline to be connected with the steam side import of steam air heater, the condensate outlet of steam air heater is connected with water pump.The exhaust steam amount entering steam air heater is controlled by the air inlet adjustment valve taken out on exhaust steam pipeline as required.Part exhaust steam in steam turbine is introduced Boiler Air Heater's as thermal medium by this system, be used for heating the cold air of air preheater import, effectively make use of the heat of exhaust steam, improve unit efficiency, exhaust steam amount simultaneously owing to entering condenser reduces, reduce the thermic load of condenser, be conducive to reducing turbine back pressure, thus further raising unit efficiency.

Description

System and method for using steam turbine exhaust steam as heat medium of power plant boiler heater

technical field

The invention relates to a system and a method for using exhaust steam of a steam turbine as the heat medium of a boiler heater of a power station, and belongs to the technical field of waste heat utilization of a coal-fired power plant.

Background technique

The function of the power station air heater is to increase the temperature of the cold air at the inlet of the air preheater, so that the wall temperature of the heated surface of the cold section of the air preheater is higher than the acid dew point temperature of the flue gas, and reduce low-temperature corrosion. The boiler heater of the power station is a tube heat exchanger, the cold medium outside the tube is air, and the heat medium inside the tube is steam. the goal of. The heat medium of boiler heaters in conventional coal-fired power plants is steam turbine low-pressure extraction steam, which needs to consume a certain flow of steam, which increases the heat consumption rate of the unit.

The structure of the traditional utility boiler heater belongs to the prior art. For example, a utility boiler heater is disclosed in the document CN200979291Y, in which several spiral finned tubes are arranged in the frame to form several groups of spiral fins arranged crosswise. Tube bundle, the upper header is installed on the top of the frame, and the lower header is installed below. The upper and lower ends of the spiral finned tube are connected with the upper and lower headers respectively, forming a steam channel in the spiral finned tube, and outside the spiral finned tube 1. The inner cavity of the frame forms an air channel to be heated. The side single pieces are arranged on the surfaces of both sides of the frame, and the middle single piece is arranged on the middle surface. A steam inlet is arranged on the upper header, and a drain outlet is arranged at the bottom of the frame. Hanging rings are installed on the frame. Spiral finned tubes are formed by spiral fins wrapped around a tube. During operation, steam enters the spiral fin tube 5 from the steam inlet, the air to be heated passes through the spiral fin tube 5, heat is conducted from the pipe 13 to the spiral fin 12, and the spiral fin 12 heats the air through radiation convection. When using, according to the size of the air duct, side monoliths can be arranged on both sides of the frame, and several middle monoliths can be arranged in the middle. This arrangement has the characteristics of good heat transfer effect, small resistance, firmness and durability, and convenient installation and maintenance. The spiral finned tube bundles can be galvanized as a whole, and the inside and outside of the frame can be painted with heat-resistant paint. There are gaskets between the parallel sheets and the connection between the heater and the air duct to improve the anti-rust, anti-corrosion and sealing performance of the heater. . The layout form can be selected according to the air duct conditions of the power plant: when the air duct is arranged horizontally, type I or type III air heaters can be selected; when the air duct is vertical to the horizon, type II heaters can be selected. Each piece of the air heater has bolt holes for connection. When the air heater is connected to the air duct, it is connected by bolts through the flange. The heat exchange element is welded into a spiral fin tube by high-frequency resistance. This fin tube has the advantages of compact structure, small resistance, large heat dissipation area, firm welding, and not easy to accumulate dust. The air heater uses the low-pressure extraction steam of the steam turbine as the heat source to heat the air. After the air heater is used at the inlet of the air preheater of the power plant boiler, it can avoid the oxygen corrosion caused by the metal surface of the preheater and the sulfuric acid corrosion caused by sulfur trioxide. The ash accumulation on the metal wall is greatly reduced, and the air resistance will not increase due to ash blocking, thereby greatly prolonging the service life of the air preheater and ensuring the safe operation of the unit.

Document CN201531899U discloses a dynamic air heater for power plant boilers, which includes a support frame and multiple sets of heat exchange elements located in the support frame. The two ends of the heat exchange elements are respectively movably connected with inlet and outlet headers, and the inlet header passes through the steam inlet hollow. The support shaft is connected to the inlet pipe, and the outlet header is connected to the outlet pipe through the hydrophobic hollow support shaft; the cross-section of the heat exchange element is a parallelogram structure, and the short diagonal of the heat exchange element must be in line with the short side of the heat exchange element in the shape of a parallelogram Vertical, and adjacent heat exchange elements are closely arranged. The steam inlet hollow support shaft and the hydrophobic hollow support shaft are respectively connected to the inlet and outlet pipes through flanges, and an operating handle connected to the heat exchange element is installed on the flange of the steam inlet hollow support shaft pipe. The support frame is mainly composed of flanges connecting the inlet and outlet of the air duct, the outer casing of the air heater, and the support for strengthening the rigidity of the air heater. The outer casing is provided with an inlet and outlet shaft hole. A sealing gland is set at the place, and a heater supporting and hanging device is welded on the outer wall of the supporting frame, which is used for on-site supporting and hanging of the air heater; the main function of the whole supporting frame is to support the rotating heat exchange element group and form the air duct wall. Each group of heat exchange element groups is connected by flanges. The heat exchange element is the key part of the heater for heat exchange, and its heat exchange area is determined by calculation according to the actual situation; the function of the inlet and outlet flanges is to connect the steam inlet pipe and the drainage pipe, and an operating handle is welded on the steam inlet flange , to facilitate the rotating operation of the air heater; the steam inlet hollow support shaft is used as a steam guide pipe and guide bearing journal, and the drain drainage hollow support shaft is used to drain the drain pipe and support the bearing journal; the function of the inlet header is to transfer steam Evenly distributed to the heat exchange element tube group, the function of the outlet header is to collect water. The heat exchange element is welded to the inlet and outlet headers, and the heat exchange element is a rotatable component. In order to facilitate the rotation of the heat exchange element group and reduce the cross-sectional area of the cold air corridor as much as possible, the heater heat exchange element group is arranged in a parallelogram. To ensure reliable rotation of the heat exchange element, the diagonal line of the heat exchange element must be perpendicular to the short side of the parallelogram heat exchange element. A position indication plate and a detachable limit pin are installed on the shell of the support frame, and a limit sealing plate is arranged in the support frame. The position sign is used to indicate the position of the heat exchange element; a limit pin is set on the outer casing of the support frame to avoid excessive rotation angle. During running operation, the air heater is out of operation in the high temperature season, and the wide surface of the heat exchange element is parallel to the wind direction. Turn the heat exchange element of the air heater through 90°, and then connect the flanges. In order to avoid steam leakage from the flanges, the gaskets of the flanges should be replaced during each operation. The rotation direction of each group of air heaters should be consistent. To avoid large resistance To reduce the impact on the system, heaters should be turned on and off sequentially, several sets of heat exchange elements are not allowed to operate at the same time, the action should be slow during operation, there should be operating personnel present on site, and keep in touch with the central control room, strictly Monitor system wind pressure and fan current changes. The air heater can be arranged at the outlet or entrance of the air duct of the fan. According to the layout of the air duct and the flow direction of the steam inlet and outlet, the heat exchange elements of the air heater are arranged as follows: (1) When the air heater is arranged in a horizontal air duct, The air heater can be arranged vertically, the steam passes through the heat exchange element from top to bottom, and the steam inlet and outlet positions are on the same axis; (2) When the air heater is arranged in a vertical air duct, the air heater can be arranged obliquely, and the steam Pass through the heat exchange element from left to right or from front to back, the steam inlet and outlet positions are on the same axis, and the inlet position is higher than the outlet position.

The heat of exhaust steam discharged from the steam turbine to the condenser is one of the largest waste heat losses in the production of thermal power plants. The exhaust steam is condensed into condensed water after exchanging heat with circulating water or cooling air in the condenser. The heat released during the condensation process of the exhaust steam is discharged to the environment through the cooling tower or air-cooling fan, and the lost heat accounts for about About 60%, becoming the bottleneck restricting the improvement of unit efficiency. How to utilize the exhaust heat of steam turbines has always been the focus and difficulty of research in the field of waste heat utilization technology in power plants.

Contents of the invention

The invention proposes a system and method for using the exhaust steam of a steam turbine as the heat medium of a boiler heater of a power station. Part of the exhaust steam of the steam turbine is introduced into the boiler heater as heat medium to heat the cold air at the inlet of the air preheater, which effectively utilizes the heat of the exhaust steam and improves the efficiency of the unit. At the same time, the amount of exhaust steam entering the condenser is reduced , which reduces the heat load of the condenser, which is beneficial to reduce the back pressure of the steam turbine, thereby further improving the efficiency of the unit. pressure, thereby further improving the efficiency of the unit.

In order to achieve the above object, the present invention provides a system that uses the exhaust steam of the steam turbine as the heat medium of the heater of the power plant boiler, including a steam turbine, a condenser, an air inlet regulating valve, a heater and a water pump, and the steam turbine and the condenser Through pipeline connection, a pipeline for extracting exhausted steam is connected to the throat of the condenser, and an air intake regulating valve is installed on the exhausted steam pipeline, and the exhausted steam pipeline is connected with the steam side inlet of the heater, and the exhausted steam pipeline is connected to the steam inlet of the heater. The condensed water outlet is connected with the water pump.

The amount of exhaust steam entering the heater is controlled by the intake regulating valve on the exhaust exhaust pipeline as required.

The water pump communicates with the steam turbine condensate system.

It also includes a condensate pump, the water inlet of the condensate pump is connected with the water outlet of the condenser, and the water outlet of the condensate pump is connected with the condensate system of the steam turbine.

It also includes a blower fan and an air preheater, and the blower fan, the air heater and the air preheater are connected through an air pipeline.

A part of the exhaust steam after doing work in the steam turbine is discharged into the condenser; the exhaust steam exchanges heat with the cooling water in the condenser, and transfers the heat to the cooling water to increase the temperature of the cooling water. A phase change occurs, and after heat release, it condenses into condensed water, and the condensed water enters the condensed water system after being boosted by the condensed water pump.

A exhausted steam pipeline is connected to the steam side inlet of the heater at the throat of the condenser; an air intake regulating valve is installed on the exhausted steam pipeline to adjust the steam extraction volume of the exhausted steam; a part of the exhausted steam is exhausted It is drawn from the throat of the condenser, and is transported to the steam side inlet of the heater through the exhaust steam pipeline, and exchanges heat with the cold air in the heater to increase the temperature of the cold air, and at the same time, the exhaust steam is released due to heat A phase change occurs, and after heat release, it condenses into condensed water, which enters the condensed water system after being boosted by the water pump, and is discharged together with the condensed water from the condenser.

The cold air enters the fan, is pressurized by the fan, enters the heater, and exchanges heat with exhaust steam in the heater. After preheating and absorbing the heat of the exhaust steam, the exhaust steam undergoes a phase change due to heat release, and after the heat release, it condenses into condensate water, which enters the condensate water system after being boosted by the water pump, and is discharged together with the condensate water from the condenser; After the cold air is heated by exhaust steam, it enters the air preheater to further heat up.

The role of the air intake regulating valve on the exhaust steam extraction pipeline is to control and adjust the exhaust steam entering the heater according to needs. When the flow of cold air delivered by the fan increases or the temperature of the cold air entering the air preheater is high, increase the opening of the intake regulating valve to increase the exhaust steam flow through the intake regulating valve, so that More exhaust steam enters the heater to participate in heat exchange, and the cold air absorbs more heat from the exhaust steam, thereby further increasing the temperature of the cold air; at this time, the flow of exhaust steam entering the condenser becomes smaller, and the exhaust steam condenses The heat released in the process is discharged to the environment through the cooling tower or the air cooling fan, and the heat lost in the environment is correspondingly reduced.

When the flow of cold air delivered by the fan becomes smaller or the temperature of the cold air entering the heater is already high, the opening of the intake regulating valve can be reduced to reduce the exhaust steam flow through the intake regulating valve, so that Less exhaust steam enters the heater to participate in heat exchange, and the cold air absorbs less exhaust steam heat; at this time, the exhaust steam flow into the condenser is large.

The air heater can take various forms, and is typically installed in the air duct before or after the blower, including a support frame and multiple sets of heat exchange elements located in the support frame, and the two ends of the heat exchange elements are respectively connected with an inlet header and an outlet header.

Placing the air heater in the middle of the fan will increase the resistance of the air duct and the power consumption of the fan; at the same time, because the air sucked into the fan contains a lot of impurities, it is generally difficult for these impurities to exchange heat through the heater after entering the air duct. Components, most of them are deposited on the heat exchange elements on the windward side of the heater. As time accumulates, more and more impurities are deposited, the resistance of the heater is also increasing, and the power consumption of the fan is further increased. Therefore, in the design of the air duct, it is usually necessary to minimize the resistance loss caused by the air heater to the air duct.

The present invention also provides a method for using the exhaust steam of the steam turbine as the heat medium of the boiler heater of the power station, including a steam turbine, a condenser, an air intake regulating valve, a heater and a water pump, and the steam turbine and the condenser are connected through pipelines, A exhausted steam pipeline is connected to the throat of the condenser, and an intake regulating valve is installed on the exhausted steam pipeline. The exhausted steam pipeline is connected with the steam side inlet of the heater, and the condensed water outlet of the heater is Connected with the water pump; the exhausted steam after working in the steam turbine is discharged into the condenser; a part of the exhausted steam is condensed in the condenser and becomes condensed water after heat release; The exhaust steam condenses into water after releasing heat in the air heater, and enters the condensate water system after being boosted by the water pump; the cold air enters the air heater after being pressurized by the fan, and enters the air heater after being heated by the exhaust steam in the air heater. The air preheater further heats up the temperature.

The amount of exhaust steam entering the heater is controlled by the regulating valve on the exhaust exhaust pipeline as required.

Description of drawings

Fig. 1 is an overall schematic diagram of a system using exhaust steam from a steam turbine as the heat medium of a utility boiler heater described in the present application.

Detailed ways

As shown in Figure 1, the system using exhaust steam from the steam turbine as the heat medium of the boiler heater of the power station includes a steam turbine 1, an air intake control valve 2, a heater 3, a water pump 4, and a condenser 5, and the steam turbine 1 and the condenser 5 They are connected through pipelines, and a exhaust steam pipeline is connected to the throat of the condenser 5, and an air intake regulating valve 2 is arranged on the exhaust steam pipeline, and the exhaust steam pipeline is connected with the steam side inlet of the heater 3 , The condensed water outlet of the air heater 3 is connected with the water pump 4 . The water pump 4 communicates with the steam turbine condensate system.

The system also includes a condensate pump 6, the water inlet of the condensate pump 6 is connected with the water outlet of the condenser 5, and the water outlet of the condensate pump 6 is connected with the steam turbine condensate system.

The system also includes a fan 7 and an air preheater 8, and the fan 7, the heater 3 and the air preheater 8 are connected through an air pipeline.

The system works as follows:

A part of the exhaust steam after working in the steam turbine 1 is discharged into the condenser 5, and the heat is exchanged with the cooling water in the condenser 5, and the heat is transferred to the cooling water, so that the temperature of the cooling water rises, and the exhaust steam is condensed The condensed water in the boiler 5 becomes condensed water after condensing and releasing heat, and the condensed water enters the condensed water system after being boosted by the condensed water pump 6 .

A exhausted steam pipeline is connected to the steam side inlet of the heater 3 at the throat of the condenser 5; an intake regulating valve 2 is installed on the exhausted steam pipeline to adjust the steam extraction volume of the exhausted steam; a part The exhausted steam is extracted from the throat of the condenser, and transported to the steam side inlet of the heater through the exhausted steam pipeline, and exchanges heat with the cold air in the heater 3, so that the temperature of the cold air rises, and the exhausted steam The steam undergoes a phase change due to heat release, and after heat release, it condenses into condensed water, which enters the condensed water system after being boosted by the water pump 4, and is discharged together with the condensed water from the condenser.

The cold air enters the fan 7, and enters the heater 3 after being pressurized by the fan 7, and exchanges heat with exhaust steam in the heater 3. Preheated by the exhaust steam inside, after absorbing the heat of the exhaust steam, the exhaust steam undergoes a phase change due to heat release, and after the heat release, it condenses into condensate water, which enters the condensate water system after being boosted by the water pump, and gathers with the condensate water from the condenser The cold air is heated by exhaust steam and then enters the air preheater for further heating.

The role of the air intake regulating valve on the exhaust steam extraction pipeline is to control and adjust the exhaust steam entering the heater according to needs. When the flow of cold air delivered by the fan increases or the temperature of the cold air entering the air preheater is high, increase the opening of the intake regulating valve to increase the exhaust steam flow through the intake regulating valve, so that More exhaust steam enters the heater to participate in heat exchange, and the cold air absorbs more heat from the exhaust steam, thereby further increasing the temperature of the cold air; at this time, the flow of exhaust steam entering the condenser becomes smaller, and the exhaust steam condenses The heat released in the process is discharged to the environment through the cooling tower or the air cooling fan, and the heat lost in the environment is correspondingly reduced.

When the flow of cold air delivered by the fan becomes smaller or the temperature of the cold air entering the heater is already high, the opening of the intake regulating valve can be reduced to reduce the exhaust steam flow through the intake regulating valve, so that Less exhaust steam enters the heater to participate in heat exchange, and the cold air absorbs less exhaust steam heat; at this time, the exhaust steam flow into the condenser is large.

The air heater can take various forms, and is typically installed in the air duct before or after the blower, including a support frame and multiple sets of heat exchange elements located in the support frame, and the two ends of the heat exchange elements are respectively connected with an inlet header and an outlet header.

Placing the air heater in the middle of the fan will increase the resistance of the air duct and the power consumption of the fan; at the same time, because the air sucked into the fan contains a lot of impurities, it is generally difficult for these impurities to exchange heat through the heater after entering the air duct. Components, most of them are deposited on the heat exchange elements on the windward side of the heater. As time accumulates, more and more impurities are deposited, the resistance of the heater is also increasing, and the power consumption of the fan is further increased. Therefore, in the design of the air duct, it is usually necessary to minimize the resistance loss caused by the air heater to the air duct.

The invention uses the exhaust steam heat of the steam turbine to heat the cold air at the inlet of the air preheater, recycles the heat of the exhaust steam, cancels the steam extraction of the steam turbine in the existing air heater system, and improves the efficiency of the unit.

The invention has the advantages of simple system, cascaded utilization of waste steam waste heat, and improved unit efficiency.

The system approach of the present invention has been illustrated and explained with reference to schematic process diagrams. Based on the above description, additional variations and modifications will be obvious to those skilled in the art, all of which fall within the protection scope of the present application, and the protection scope of the present invention is determined by the appended claims.

Claims (2)

1. the system using exhaust steam in steam turbine as steam air heater of utility boiler thermal medium, comprise steam turbine, condenser, air inlet adjustment valve, steam air heater and water pump, be connected by pipeline between steam turbine with condenser, pick out a road in the throat of condenser and take out exhaust steam pipeline, be provided with air inlet adjustment valve taking out on exhaust steam pipeline, take out exhaust steam pipeline to be connected with the steam side import of steam air heater, the condensate outlet of steam air heater is connected with water pump; The exhaust steam amount entering steam air heater is controlled by the air inlet adjustment valve taken out on exhaust steam pipeline as required; Water pump is communicated with steam turbine condensate system; Also comprise blower fan and air preheater, blower fan, to be connected by air duct between steam air heater and air preheater; Described steam air heater comprises support frame and is positioned at many groups heat exchange element of support frame, and heat exchange element two ends are connected to inlet header and outlet header; In air channel before described steam air heater is arranged on blower fan or after blower fan, cold air enters steam air heater after blower fan pressurization, in steam air heater, carry out heat exchange with exhaust steam; Cold air enters the further heat temperature raising of air preheater after being raised by exhaust steam heating-up temperature; When the cold air flows of blower fan conveying becomes large time, strengthen the aperture of air inlet adjustment valve; When the cold air flows of blower fan conveying diminishes time, reduce the aperture of air inlet adjustment valve; Also comprise condensate pump, the water inlet of condensate pump is connected with the delivery port at condenser, and the delivery port of condensate pump is communicated with steam turbine condensate system.

2. the method using exhaust steam in steam turbine as steam air heater of utility boiler thermal medium, is characterized in that, adopt the system using exhaust steam in steam turbine as steam air heater of utility boiler thermal medium as claimed in claim 1, the exhaust steam in steam turbine after acting enters condenser; Part exhaust steam becomes condensate water after condensation heat in condenser; Another part exhaust steam is by taking out exhaust steam pipeline and air inlet adjustment valve enters steam air heater, and exhaust steam is condensed into water after heat release in steam air heater, after water pump boosting, enter condensate system; Cold air enters steam air heater after blower fan pressurization, enters the further heat temperature raising of air preheater in steam air heater by exhaust steam after being heated; The exhaust steam amount entering steam air heater is controlled by the control valve taken out on exhaust steam pipeline as required; When the cold air flows of blower fan conveying becomes large time, strengthen the aperture of air inlet adjustment valve, make to become large by the exhaust steam flow of air inlet adjustment valve; When the cold air flows of blower fan conveying diminishes time, reduce the aperture of air inlet adjustment valve.