A combined cycle waste heat boiler L-shaped flue gas passage system and method

Abstract

The present invention provides a combined cycle waste heat boiler L-shaped flue gas passage system and method, which includes a compressor. The compressor transfers the compressed air to a combustion chamber, and the combustion chamber transfers the flue gas after combustion to a gas turbine. The high-temperature flue gas expands and does work in the gas turbine and then enters the waste heat boiler. The waste heat boiler includes a horizontal flue gas passage and a vertical flue gas duct. An L-shaped flue duct turning space is provided at the contact of the horizontal flue gas passage and the vertical flue gas duct to form an L-shaped flue duct. An evaporator and an economizer are arranged in the vertical passage. The evaporator and the economizer are connected to a chimney. The steam working medium heated by the flue gas is first heated in the economizer and the evaporator, then enters a superheater and a reheater, and finally enters a steam turbine to do work. By adjusting the pressure and temperature of the main flue and evenly distributing the flue gas flow in the superheated steam section, the operation economy of the combined cycle under partial load conditions is optimized, and its peak shaving performance is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of gas-steam combined cycle waste heat boilers in the energy and power industry, and particularly relates to a combined cycle waste heat boiler L-shaped flue gas passage system and method. Background Art

[0002] Gas-steam combined cycle units mostly participate in the peak shaving of the power grid and operate under part-load conditions. However, as the load of the gas turbine decreases, its heat rate increases and its economy decreases. Therefore, improving the off-design operation efficiency of gas-steam combined cycle units has become an important research topic. Gas turbine units with higher parameter levels of exhaust steam from gas turbines have better off-design performance. The pressure, temperature, and flow rate of the main flue gas entering the waste heat boiler need to have a larger adjustable range, and accordingly, the structural layout of each part of the heating surface of the waste heat boiler also needs to be adjusted.

[0003] On the one hand, for the currently operating triple-pressure waste heat boilers, they have high, medium, and low-pressure superheaters, triple-pressure evaporators, and triple-pressure economizers. The superheaters also share the flue gas duct in parallel with the reheaters. Their heat transfer surface layout is huge and complex. Whether it is a horizontal or vertical structure, it is difficult to repair and maintain the internal coils of the heating surface, with a long cycle and relatively high costs. Moreover, currently, the high parameters of the flue gas discharged from the gas turbine of the combined cycle unit into the waste heat boiler can reach 630°C / 1.045 MPa. The flue gas inlet pressure of the waste heat boiler is 3 kPa higher than the atmospheric pressure and is in a positive pressure operation state, with a risk of flue gas leakage. A laser or infrared imaging alarm system is required, and the horizontal and vertical flue gas duct structures lack space for arranging optical instruments. Although some units use induced draft fans to reduce the positive pressure of the flue gas, the induced draft fans are arranged at the tail of the chimney, and the flue gas induced draft fans consume a large amount of electric energy with extremely low efficiency.

[0004] On the other hand, from the perspective of unit performance optimization, using IGV (Inlet Guide Vane) adjustment is a widely used off-design adjustment method, that is, by gradually closing the IGV angle to reduce the compressor inlet flow rate to lower the gas turbine load, which can increase the gas temperature at the turbine inlet to improve the off-design efficiency. However, the unit cannot always adjust the load by closing the IGV angle. Otherwise, the gas flow will further decrease, the expansion ratio of the last stage of the gas turbine will decrease, and the turbine exhaust temperature will exceed the limit. Moreover, currently, the gas temperature at the turbine inlet of the gas turbine generally cannot be directly measured, causing certain difficulties in controlling the temperature range of the gas turbine exhaust.

[0005] Currently, the background art has not proposed solutions to the above problems. Summary of the Invention

[0006] In order to overcome the problems existing in the above-mentioned prior art, the object of the present invention is to provide a combined cycle waste heat boiler L-shaped flue gas channel system and method, which comprehensively adjusts the output of the top cycle and the bottom cycle of the gas-steam combined cycle by regulating the pressure and temperature of the main flue and evenly distributing the flue gas flow in the superheated steam section, optimizes the operation economy of the combined cycle under partial load conditions, and improves its peak shaving performance.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] A combined cycle waste heat boiler L-shaped flue gas channel system includes a waste heat boiler 4, the waste heat boiler 4 includes a horizontal flue gas channel and a vertical flue gas duct, an L-shaped flue turning space 12 is arranged at the contact position between the horizontal flue gas channel and the vertical flue gas duct to form an L-shaped flue, an evaporator 7 and an economizer 8 are arranged in the vertical channel, the evaporator 7 and the economizer 8 are connected to a chimney 14, and the chimney 14 is used to discharge flue gas into the atmosphere. The steam working medium heated by the flue gas is first heated in the economizer 8 and the evaporator 7, then enters the superheater 5 and the reheater 6, and finally enters the steam turbine 15 to do work.

[0009] The horizontal flue gas channel is two parallel flues, in which a superheater 5 and a reheater 6 are respectively arranged. Flue gas baffles 10 and flue duct baffles 11 are respectively arranged at the outlet positions of the flues where the superheater 5 and the reheater 6 are located. The flue gas of the superheater 5 and the reheater 6 converges into the L-shaped flue turning space 12.

[0010] A steam-driven induced draft fan 9 is arranged in the L-shaped flue turning space 12, and a drone hole door 13 is opened on the furnace wall surface and an infrared thermal imager 16 is arranged.

[0011] The steam-driven induced draft fan 9 is arranged on the ground, and the power source is the extraction steam from the steam turbine 15.

[0012] Pressure measuring points are arranged at the inlet of the waste heat boiler 4 to monitor the inlet flue gas temperature and pressure. Since the pressure loss from the gas turbine exhaust to the waste heat boiler inlet can be ignored, the gas turbine exhaust pressure can be indirectly measured. Temperature measuring points are arranged at the inlet ends of the superheater 5 and the reheater 6 of the waste heat boiler 4. A pressure measuring point is arranged on the outlet side of the steam-driven induced draft fan 9. Using the infrared thermal imager 16 in the L-shaped flue turning space 12, the combustion situation in the furnace is monitored by infrared imaging, and the infrared thermal imaging diagram and temperature information in the horizontal section flue are monitored by a computer.

[0013] An operation method of a combined cycle waste heat boiler L-shaped flue gas channel system includes the following steps;

[0014] When the unit load decreases from full load, the intake air volume of the compressor 1 is regulated by the IGV, and at the same time, the natural gas volume of the combustion chamber 2 is regulated to keep the exhaust gas temperature of the gas turbine 3 unchanged. As the load decreases, the exhaust gas temperature of the gas turbine 3 rises. When it is about to exceed the off-design temperature, the power of the steam-driven induced draft fan 9 is increased;

[0015] By adjusting the angles of the flue gas damper 10 and the flue duct damper 11, the flow distribution path of the flue gas can be flexibly changed. When the superheater 5 is overheated, the opening degree of the corresponding flue gas damper 10 should be reduced. When the reheater 6 is overheated, the opening degree of the corresponding flue duct damper 11 is reduced, and the excess flue gas will flow into the non-overheated side flue until the working medium temperatures of the superheater 5 and the reheater flue 6 of the waste heat boiler reach the design condition values, thus ensuring an even distribution of the flue gas flow;

[0016] By comprehensively adjusting the opening degrees of the flue gas damper 10 and the flue duct damper 11 and the power of the steam-driven induced draft fan 9, the flue gas pressure at the inlet of the waste heat boiler is controlled to be negative, and the flue gas pressure sent to the chimney 14 after being pressurized by the steam-driven induced draft fan 9 is normal pressure;

[0017] Enter and carry out shutdown maintenance through the unmanned aerial vehicle access door 13 in the turning space 12 of the L-shaped flue, which is convenient for the maintenance of the superheater 5, reheater 6, evaporator 7, economizer 8 and steam-driven induced draft fan 9 of the waste heat boiler, and does not require high-altitude operations or damage to the heating surface.

[0018] The beneficial effects of the present invention:

[0019] The present invention provides an L-shaped flue system for a waste heat boiler in a combined cycle power station. By arranging an induced draft fan at the turning of the L-shaped flue of the waste heat boiler, the flue gas at the inlet of the waste heat boiler operates at a negative pressure relative to the atmospheric pressure, preventing flue gas leakage and improving safety. A horizontal double flue with the superheater and reheater arranged in parallel and separated is provided, and flue duct dampers are respectively arranged at the outlets of the double flues. An unmanned aerial vehicle access door 13 is also provided at the turning of the L-shaped flue for easy access for maintenance and inspection.

[0020] After adopting the structure of the present invention, due to the arrangement of the L-shaped flue, compared with the traditional vertical waste heat boiler, there are two additional flue gas dampers for specifically regulating the steam working medium temperatures of the superheater and reheater, as well as an unmanned aerial vehicle access door for maintenance and an infrared thermal imager for measuring high temperatures. Compared with the traditional horizontal waste heat boiler, the heating surface is moved upward, and the chimney is above the heating surface, greatly saving the floor area and improving the space utilization rate. Therefore, the structure of the L-shaped flue can simplify the layout structure of the heating surface, not only saving the site, but also reducing the cost and shortening the cycle.

[0021] The unique advantages of the L-shaped flue system of the present invention are as follows:

[0022] For the horizontal part of the superheater and the reheater, the parallel double flue gas ducts are respectively equipped with flue gas dampers to regulate the flue gas flow. If the flue duct of either the superheater or the reheater is overheated or underheated, the flue gas damper can be used for regulation, saving the traditional desuperheating water injection device.

[0023] At the bent part of the L-shaped structure, a forced draft fan is put into operation to blow the flue gas to flow, so that the flue gas at the inlet of the waste heat boiler is reduced to atmospheric pressure or negative pressure, which can completely avoid flue gas leakage. By comprehensively adjusting the opening degrees of the flue gas damper 10 and the flue duct damper 11 and the power of the steam-driven forced draft fan 9, the negative pressure range of the flue gas pressure at the inlet of the waste heat boiler can be adjusted to cooperate with the fluctuations of the air and fuel flow rates under variable operating conditions.

[0024] The flue gas pressure after being pressurized by the steam-driven forced draft fan 9 is normal pressure, and it is exhausted through the chimney effect of the vertical flue duct to reduce the loss of the flue gas pressure, which is beneficial to the improvement of the waste heat boiler efficiency under variable operating conditions;

[0025] Because the forced draft fan is arranged at a relatively low position, it is very convenient to use the extraction steam of the steam turbine to drive the steam-driven forced draft fan, saving the plant's electricity energy and having good economy.

[0026] Aiming at the problems that the thermal efficiency of the gas turbine combined cycle is relatively low during low-load operation and the IGV cannot fully utilize to regulate the output of the combined cycle, by arranging a steam-driven forced draft fan and a rotatable flue gas damper in the L-shaped waste heat boiler flue duct, the main flue duct pressure during variable operating conditions of the unit is regulated, the output range of the unit is expanded, and the thermal efficiency of the combined cycle is improved.

[0027] The L-shaped flue duct system uses a forced draft fan to reduce the flue gas pressure at the inlet of the waste heat boiler, which can ensure that the exhaust gas of the gas turbine turbine does not overheat. Compared with the traditional unit, when the air and natural gas flow rates are certain, the reduction of the gas turbine back pressure increases the output, the inlet temperature range of the waste heat boiler is expanded, and it can smoothly reach higher parameters during partial load operation of the unit, which is beneficial to the improvement of the waste heat boiler efficiency and the improvement of the operating economy of the unit. Brief Description of the Drawings

[0028] Figure 1 It is a schematic diagram of the L-shaped flue duct system of the gas-steam combined cycle waste heat boiler.

[0029] The intake and exhaust of the gas turbine are represented by thick arrows, and the steam is represented by thin arrows. Detailed Embodiment

[0030] The present invention will be further described in detail below with reference to the drawings.

[0031] As Figure 1As shown in the figure: The system mainly includes a compressor 1, a combustion chamber 2, a gas turbine 3, a waste heat boiler 4, horizontal flue gas heating surfaces (superheater 5 and reheater 6), vertical flue gas heating surfaces (evaporator 7 and economizer 8), a steam-driven induced draft fan 9, a flue gas damper 10 and a flue damper 11, a manhole 13, and a chimney 14, etc.

[0032] The compressor 1 transfers the compressed air to the combustion chamber 2, and the combustion chamber 2 transfers the combustion flue gas to the gas turbine 3. The high-temperature flue gas enters the waste heat boiler 4 after expanding and doing work in the gas turbine 3.

[0033] The L-shaped flue for combined cycle is characterized in that: The air enters the combustion chamber 2 after being compressed by the compressor 1, the flue gas after the fuel burns in the combustion chamber 2 enters the gas turbine 3, the high-temperature flue gas enters the waste heat boiler 4 after expanding and doing work in the gas turbine 3. The horizontal flue gas channels of the waste heat boiler 4 are respectively set as the superheater 5 and the reheater 6 in parallel. The flue gas is separated into two flue gas channels, and then the flue gas of the superheater 5 and the reheater 6 converges into the turning space 12 of the L-shaped flue. A steam-driven induced draft fan 9 is arranged in the turning space 12 of the L-shaped flue, and a drone manhole 13 is opened in the furnace and an infrared thermal imager 16 is arranged. The flue gas flows through the induced draft fan 9 and is pressurized, and the pressure rises to be equivalent to the ambient pressure, and then is sent into the vertical flue gas duct. The evaporator 7 and the economizer 8 are arranged in the vertical channel, and finally connected to the chimney 14 to discharge the flue gas into the atmosphere. The steam working medium heated by the flue gas is first heated in the economizer 8 and the evaporator 7, then enters the superheater 5 and the reheater 6, and finally enters the steam turbine 15 to do work.

[0034] A further detailed description is made for the waste heat boiler flue in the form of "L":

[0035] The L-shaped flue includes a vertical flue and a horizontal flue. In the vertical flue, the high, medium, and low pressure evaporators 7 and the triple-pressure economizer 8 are installed in a staggered manner. The horizontal flue is divided into two parallel flues. In one flue, the high, medium, and low pressure superheaters 5 are installed, and in the other flue, the reheater 6 is installed, including the heating surfaces of the cold section and the hot section of the reheater. The horizontal flue is arranged with parallel superheater and reheater heating surfaces, and at the same time, the flue gas damper 10 and the flue damper 11 are set to adjust the flue gas flow in the parallel superheater and reheater flues respectively to prevent the superheater or the reheater from overheating. The end of the horizontal flue is the turning space 12 of the L-shaped flue, the end of the vertical flue is the chimney 14 flue gas outlet, and the L-shaped tail flue is vertically installed on the ground. The lower end of the turning space 12 of the L-shaped flue is the ground, and the steam-driven induced draft fan 9 is arranged on the ground, and the power source is the extraction steam from the steam turbine 15.

[0036] Pressure measuring points are arranged at the inlet of the waste heat boiler 4 to monitor the temperature and pressure of the inlet flue gas. Since the pressure loss from the exhaust of the gas turbine to the inlet of the waste heat boiler can be ignored, the exhaust pressure of the gas turbine can be indirectly measured. Temperature measuring points are arranged at the inlet ends of the superheater 5 and the reheater 6 of the waste heat boiler 4. Pressure measuring points are arranged on the outlet side of the steam-driven induced draft fan.

[0037] The combustion condition in the horizontal section of the furnace is monitored by infrared imaging using the turning space 12 of the L-shaped flue, and the infrared thermal imaging diagram and temperature information in the horizontal section of the flue are monitored by a computer.

[0038] The operation method of the present invention includes the following steps:

[0039] The implementation mode will be described below with reference to examples.

[0040] When the unit load drops from full load, the intake air volume of the compressor 1 is regulated by IGV, and at the same time, the fuel quantity in the combustion chamber 2 is regulated to maintain the constant gas temperature at the inlet of the gas turbine 3. As the load decreases, the exhaust gas temperature of the gas turbine 3 rises. When it is about to overheat, the steam-driven induced draft fan 9 is started, and the flue gas is discharged from the chimney 14 after being pressurized by the induced draft fan. At this time, by regulating the power of the induced draft fan 9, the exhaust back pressure of the gas turbine 3 is further regulated;

[0041] By adjusting the angles of the flue gas damper 10 and the flue damper 11, the flow distribution path of the flue gas can be flexibly changed. When any side of the superheater 5 or the reheater 6 is overheated, the opening degree of the corresponding flue damper is reduced until the working medium temperature of the superheater 5 and the reheater 6 is at the design condition value, so as to reduce the flue gas flow rate on the overheated side and distribute the excess flue gas flow rate to the non-overheated side flue;

[0042] By comprehensively adjusting the opening degrees of the flue gas damper 10 and the flue damper 11 and the power of the steam-driven induced draft fan 9, the inlet flue gas of the waste heat boiler is controlled to be negative pressure, and the flue gas after being pressurized by the steam-driven induced draft fan 9 is at normal pressure, so as to avoid causing flue gas pressure loss and is beneficial to improving the efficiency of the waste heat boiler;

[0043] Maintenance during shutdown is carried out by entering through the drone access door 13 in the turning space 12 of the L-shaped flue, which is convenient for the maintenance of all heating surfaces of the waste heat boiler, namely the superheater 5, the reheater 6, the evaporator 7, the economizer 8 and the steam-driven induced draft fan 9, without the need for high-altitude operations or damage to the heating surfaces.

Claims

1. A combined cycle waste heat boiler L-shaped flue gas passage system, comprising a waste heat boiler (4), wherein the waste heat boiler (4) includes a horizontal flue gas passage and a vertical flue gas duct. An L-shaped flue duct turning space (12) is provided at the contact between the horizontal flue gas passage and the vertical flue gas passage, forming an L-shaped flue duct. An evaporator (7) and an economizer (8) are arranged in the vertical flue gas duct. The evaporator (7) and the economizer (8) are connected to a chimney (14), and the chimney (14) is used to discharge flue gas into the atmosphere. The steam working medium heated by the flue gas is first heated in the economizer (8) and the evaporator (7), then enters a superheater (5) and a reheater (6), and finally enters a steam turbine (15) to do work; A steam-driven induced draft fan (9) is arranged in the L-shaped flue duct turning space (12), and a drone manhole door (13) is opened on the furnace wall surface and an infrared thermal imager (16) is arranged; Pressure measuring points are arranged at the inlet of the waste heat boiler (4) to monitor the inlet flue gas temperature and pressure. Temperature measuring points are arranged at the inlet ends of the superheater (5) and the reheater (6) of the waste heat boiler (4). Pressure measuring points are arranged on the outlet side of the steam-driven induced draft fan (9). The infrared thermal imager (16) in the L-shaped flue duct turning space (12) is used to monitor the combustion condition in the furnace through infrared imaging; The horizontal flue gas passage is composed of two parallel flue ducts, in which a superheater (5) and a reheater (6) are respectively arranged. A flue gas baffle (10) and a flue duct baffle (11) are respectively arranged at the outlet positions of the flue ducts where the superheater (5) and the reheater (6) are located. The flue gas of the superheater (5) and the reheater (6) converges into the L-shaped flue duct turning space (12); The steam-driven induced draft fan (9) is arranged on the ground; The evaporator (7) and the economizer (8) are arranged in a staggered manner in the vertical flue gas duct.

2. The L-shaped flue gas passage system of a combined cycle waste heat boiler according to claim 1, wherein The power source is the extraction steam from the steam turbine (15).

3. A method for operating an L-shaped flue gas passage system of a combined cycle waste heat boiler according to any one of claims 1-2, characterized in that, It includes the following steps; When the unit load drops from full load, the intake air volume of the compressor (1) is adjusted by the IGV, and at the same time, the natural gas volume of the combustion chamber (2) is adjusted to keep the exhaust gas temperature of the gas turbine (3) unchanged. As the load decreases, the exhaust gas temperature of the gas turbine (3) rises. When it is about to exceed the off-design temperature, the power of the steam-driven induced draft fan (9) is increased; By adjusting the angles of the flue gas baffle (10) and the flue duct baffle (11), the flow distribution path of the flue gas is flexibly changed. When the superheater (5) is overheated, the opening degree of the corresponding flue gas baffle (10) should be reduced. When the reheater (6) is overheated, the opening degree of the corresponding flue duct baffle (11) is reduced until the working medium temperature of the flue ducts of the superheater (5) and the reheater (6) of the waste heat boiler is the design condition value; By comprehensively adjusting the opening degrees of the flue gas baffle (10), the flue duct baffle (11) and the power of the steam-driven induced draft fan (9), the inlet flue gas pressure of the waste heat boiler is controlled to be negative pressure, and the flue gas pressure sent to the chimney (14) after being pressurized by the steam-driven induced draft fan (9) is normal pressure; Enter through the drone manhole door (13) in the L-shaped flue duct turning space (12) to carry out shutdown maintenance, which is convenient for the maintenance of the superheater (5), the reheater (6), the evaporator (7), the economizer (8) and the steam-driven induced draft fan (9) of the waste heat boiler.

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