JP2003074310A - Exhaust recombustion type combined cycle plant - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust recombustion type combined cycle plant in which a starting time is short. SOLUTION: The plant comprises: a once-through boiler 1; a gas turbine 18 for supplying an exhaust gas as an air for combustion to the boiler 1 through a gas turbine exhaust gas cooler 19 (hereafter: the cooler 19); a water system for supplying a boiler water to the cooler 19 and feeding the water heated by a turbine exhaust gas to the boiler 1; a boiler starting circulation system circulating a boiler inside fluid before starting of the boiler 1, and including a steam separator 3, a drain tank 4, and a pump 5. In the plant, reciprocation passages (each passage of point A→C, D→B) for feeding/returning the boiler inside fluid to/from the cooler 19 by branching from the boiler starting circulation system are provided, the boiler inside fluid before starting of the boiler 1 is made to flow between the boiler starting circulation system and the cooler 19 via the reciprocation passages, and a coolant of the cooler 19 after ignition of the boiler 1 is switched from the boiler inside fluid to the boiler water of the water system.

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steam / gas turbine combined cycle, in which exhaust gas of a gas turbine is supplied to a boiler for generating steam and used as combustion air. The present invention relates to a mold combined cycle plant, and more particularly to a plant system configuration suitable for shortening the startup time of a boiler, and eventually reducing the startup time of a plant. 2. Description of the Related Art A schematic configuration of a conventional exhaust refueling type combined cycle will be described with reference to FIG. It should be noted that the detailed configuration will be described later in the section of the embodiments of the present invention. A conventional exhaust reburning combined cycle plant is configured by combining a boiler 1 for supplying steam to a steam turbine and a gas turbine 18. One of the water supply systems to the boiler 1 is a system for supplying water to the boiler 1 from a condenser through a low-pressure feed water heater 9, a high-pressure feed water heater 6, a economizer 2, and the like, and another water supply system. Is a system for feeding water from the condenser to the boiler 1 through the low-pressure gas feedwater heater 11, the high-pressure gas feedwater heater 10, the gas turbine exhaust gas cooler 19, the economizer 2, and the like. Each feed water heater 9, 6 extracts the air from the boiler 1,
The gas feed water heaters 11 and 10 use the boiler exhaust gas for heating, and the gas turbine exhaust gas cooler 19 uses the gas turbine exhaust gas for heating. One of the systems for supplying combustion air to the boiler 1 is a system for supplying air to the boiler 1 via an air preheater 15, and the other system is a turbine exhaust (hereinafter, referred to as a turbine exhaust) discharged from a gas turbine 18. This is a system that cools the gas by a gas turbine exhaust gas cooler 19 and sends it to the boiler 1 as combustion air. The air preheater 15 uses boiler exhaust gas for heating. [0003] On the other hand, in the case of a variable-pressure once-through boiler of a boiler type, the internal fluid of the boiler 1 is usually circulated at the time of startup.
For the purpose of heat recovery, a boiler starting circulation system is installed, which branches off from the boiler 1, passes through the brackish water separator 3, the brackish water separator drain tank 4, and the boiler circulation pump 5, and joins the water supply system of the boiler. I have. This boiler startup circulation system
The boiler water supply system via the gas feed water heaters 10 and 11 and the gas turbine exhaust gas cooler 19 is an independent system. That is, the boiler internal fluid that has passed through the boiler circulation pump 5 has a system in which the entire amount flows to the economizer 2 side. For this reason, the heat recovery of the gas turbine exhaust gas at the time of the gas turbine pre-start is mainly performed on the boiler feed water by the gas turbine exhaust gas cooler 19, and the boiler internal fluid is not directly heated. [0004] As described above, in the conventional exhaust gas reburning type combined cycle plant,
When the gas turbine pre-starts, especially when the temperature of the boiler internal fluid is low, there is no means for directly heating the boiler internal fluid flowing through the boiler startup circulation system, so it takes time to start the boiler, and thus the plant startup time is long In addition, there has been a lack of consideration for effectively using the heat of the exhaust gas from the gas turbine for the purpose of shortening the startup time of the combined cycle plant. SUMMARY OF THE INVENTION An object of the present invention is to reduce the start-up time of an exhaust gas recirculation type combined cycle plant by recovering heat of gas turbine exhaust gas directly into a boiler internal fluid flowing through a boiler startup circulation system in an exhaust gas recirculation type combined cycle plant. Is to do. [0006] To achieve the above object, an exhaust gas reburning combined cycle plant according to the present invention comprises a once-through boiler for supplying steam to a steam turbine, and a gas as combustion air for the once-through boiler. A gas turbine that supplies turbine exhaust gas via a gas turbine exhaust gas cooler,
A water supply system that supplies boiler feed water as a cooling medium to a gas turbine exhaust gas cooler and forms a flow path that feeds water heated by turbine exhaust gas to a once-through boiler, and a boiler internal fluid in the once-through boiler before starting the once-through boiler Recirculating type combined cycle system having a boiler starting circulation system that forms a circulation flow path that branches off from the boiler to take out to the outside and returns to the inside again, the gas turbine that branches off from the circulation flow path of the boiler starting circulation system A reciprocating flow path for feeding and returning the boiler internal fluid as a cooling medium to the exhaust gas cooler is provided, and before starting the once-through boiler, the boiler internal fluid is circulated between the circulation flow path and the gas turbine exhaust gas cooler through the reciprocating flow path. Switches the cooling medium of gas turbine exhaust gas cooler from boiler internal fluid to boiler feedwater of water supply system after ignition of once-through boiler Characterized in that a changing means. In the exhaust gas reburning combined cycle plant configured as described above, the switching means branches the boiler internal fluid in the boiler start-up circulation system through the reciprocating flow path in a state in which the gas turbine is pre-started before starting the boiler. Since the gas flows into the gas turbine exhaust gas cooler, the temperature of the fluid inside the boiler rises before the boiler starts, and the boiler startup time until the fluid temperature in the boiler rises to a predetermined temperature after ignition of the boiler can be shortened. In addition, the start-up time of the exhaust gas reburning combined cycle plant can be reduced. [0008] Embodiments of the present invention will be described below. FIG. 1 is a system configuration diagram of an exhaust gas reburning combined cycle plant according to an embodiment. [0009] The exhaust gas reburning combined cycle plant is a heat engine combining a boiler for supplying steam to a steam turbine for power generation and a gas turbine for power generation. [0010] There are two water supply systems to the boiler 1. One water supply system is a low-pressure feed water heater 9 sequentially from the condenser,
The feed water heaters 9 and 6 pass through a deaerator 8, a boiler feed pump 7, and a high-pressure feed water heater 6, and then feed water to the boiler 1 via a economizer 2 provided in a flue of the boiler 1. Uses the extracted air of the boiler 1 for heating the feedwater, and the economizer 2 uses the boiler exhaust gas for heating the feedwater. The other water supply system passes through the low-pressure gas feed water heater 11, the deaerator 8, the boiler feed pump 7, the high pressure gas feed water heater 10, the gas turbine exhaust gas cooler 19, and the gas saver 2 sequentially from the condenser. In a system for supplying water to the boiler 1 through the system, each gas feed water heater 11, 10 uses boiler exhaust gas for heating the boiler feed water, and a gas turbine exhaust gas cooler 19 uses exhaust gas from the gas turbine 18 for heating the boiler feed water. Use. The two water supply systems are boiler 1
Before entering, join and connect to the economizer 2. The boiler exhaust gas is discharged from the flue of the boiler 1, and is sequentially denitrated 14 and the high-pressure gas feed water heater 1.
0, the gas is supplied to the outside air from the chimney 13 via the low-pressure gas feed water heater 11 and the induction ventilator 12, and the boiler feed water is heated by the gas feed water heaters 10, 11 as described above. Two systems for supplying combustion air to the boiler 1 are provided. One system is a system for supplying air to the boiler 1 via a pressurized ventilator 16 and an air preheater 15, and the air preheater 15 is a flow of boiler exhaust gas passing through a high pressure gas feed water heater 10 and a low pressure gas feed water heater 11. It is installed in a channel provided in parallel with the road. Another combustion air supply system is a system for cooling turbine exhaust (also referred to as turbine exhaust gas) discharged from the gas turbine 18 by a gas turbine exhaust gas cooler 19 and sending it to the boiler 1 as combustion air. As described above, the gas turbine exhaust gas cooler 19 exchanges heat with the boiler feed water to heat the boiler feed water. The turbine exhaust gas is supplied to the boiler 1, and is branched off at the outlet side of the gas turbine exhaust gas cooler 19 and finally discharged from the chimney 13 through a branch path connected to the denitration device 14 at the discharge side of the boiler exhaust gas. Is done. Symbol 1 in the figure
Reference numeral 7 denotes a compressor for sending compressed high-temperature compressed gas to the turbine. When the type of the boiler 1 is a variable-pressure once-through boiler, when the variable-pressure once-through boiler is started / stopped, the boiler 1 is turned off.
In order to circulate the internal fluid of the boiler 1, it branches off from the boiler 1, passes through the brackish water separator 3, the brackish water separator drain tank 4, the boiler circulation pump 5, joins the boiler water supply system, and passes through the boiler 2 A boiler startup circulation system returning to 1 is installed. In the exhaust gas recirculation type combined cycle plant of the present invention, when the boiler 1 is started, the fluid in the boiler start-up circulation system is guided to the gas turbine exhaust gas cooler 19, and the fluid exchanges heat with the gas turbine exhaust gas to raise the temperature and return to the boiler 1. This is the feature of the present invention. That is, in order to accelerate the boiler startup, the fluid circulating in the boiler startup circulation system is supplied to the outlet side of the boiler circulation pump 5 (A shown in FIG. 1).
At the point (point), the gas is fed into the gas turbine exhaust gas cooler 19 via the water supply outlet side (point C) of the high-pressure gas feed water heater 10, heated there, and circulated from the water supply outlet side (point D) of the gas turbine exhaust gas cooler 19. A boiler start-up acceleration circulation system is installed, which is returned to the downstream side (point B) from the point A on the outlet side of the pump 5 and then returned to the boiler 1 through the economizer 2. In addition,
The flow of the fluid from the gas turbine exhaust gas cooler 19 to the boiler start-up circulation system through a system passing through the points D and B is as follows.
This is because fluids with different positional relationships and temperatures between the boiler start-up circulation system, the gas turbine exhaust gas cooler system, and the boiler water supply system can be merged without any problem. Need not be branched to form a system that joins at point B. Next, the operation of the exhaust reburning combined cycle plant will be described. At the time of the steam only operation, the entire amount of the boiler feedwater flows to one feedwater system including the low-pressure feedwater heater 9 and the high-pressure feedwater heater 6, but at the time of the exhaust refueling combined cycle operation, together with the one feedwater system, the low-pressure gas feedwater heater 11, Since a part of the boiler feedwater flows into another feedwater system including the high-pressure gas feedwater heater 10 and the gas turbine exhaust gas cooler 19, it is used for the high-pressure feedwater heater 6 and the low-pressure feedwater heater 9 in one feedwater system. The steam amount of the turbine bleed is reduced, and the plant efficiency is improved. Now, the exhaust gas reburning combined cycle plant according to the present invention has a configuration in which the starting time of the boiler 1 is reduced in the operation of starting the gas turbine 18 in advance, igniting the boiler 1 and ventilating the steam turbine. Has become. If the temperature of the fluid inside the boiler 1 is low before the gas turbine 18 is started and before the boiler 1 is started, the fluid inside the boiler 1 branches off from the boiler startup circulation system to the gas turbine exhaust gas cooler 19. The gas is then exchanged with high-temperature gas turbine exhaust gas in the gas turbine exhaust gas cooler 19 to raise the temperature of the boiler internal fluid, and is returned to the boiler 1 via the boiler startup circulation system again. When the internal fluid reaches a certain temperature in the boiler 1 and the boiler 1 is ignited, the flow path between the boiler starting system and the gas turbine exhaust gas cooler 19 is closed, and the cooling medium of the gas turbine exhaust gas cooler 19 is removed from the boiler internal fluid. Switch to boiler water supply from condenser. That is, the low pressure gas feed water heater 11, the high pressure gas feed water heater 1
The water supply is switched to another water supply system including 0, 19, and the like. As a system switching unit, for example, a switching valve is disposed at an appropriate position in a pipe forming a flow path between the boiler startup circulation system and the gas turbine exhaust gas cooler 19 and another water supply system, and the temperature of the fluid inside the boiler is measured. It may be activated by a temperature detector. As described above, the temperature of the boiler internal fluid is first raised by the gas turbine exhaust gas, so that the gas turbine 18
Then, by effectively recovering heat, and thereafter heating the boiler feed water by boiler ignition, the temperature rise of the boiler 1 can be accelerated, and the startup time can be shortened. On the other hand, after the boiler is ignited, the boiler feedwater can also be heated by the gas feedwater heater before venting the turbine. As described above, since both the boiler internal fluid and the feedwater heating are performed at an early stage of startup, the temperature of the boiler can be raised in a short time, so that the heat recovery is performed only in the water supply system of the boiler. Startup time can be reduced. When the temperature of the internal fluid of the boiler is sufficiently raised, the cooling medium of the gas turbine exhaust gas cooler 19 is switched from the internal fluid of the boiler to the supply water of the boiler. There is no trouble. According to the present invention, since the internal fluid of the boiler can be heated by the heat of the gas turbine exhaust gas at the time of starting the gas turbine, the system configuration can recover heat only in the conventional boiler feedwater. It is possible to accelerate the temperature rise characteristics of the boiler, so that the time from gas turbine ignition to steam turbine ventilation can be shortened, and the time from exhaust gas reburning combined cycle plant to full load can be shortened. In addition, the startup loss is also reduced.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a system configuration diagram of an exhaust gas reburning combined cycle of the present invention. FIG. 2 is an example of a system configuration of a conventional exhaust gas reburning combined cycle. [Description of Signs] 1 Boiler 2 Energy saving device 3 Steam separator 4 Steam separator drain tank 5 Boiler circulation pump 6 High pressure feed water heater 7 Boiler feed pump 8 Deaerator 9 Low pressure feed water heater 10 High pressure gas feed water heating Heater 11 Low-pressure gas feed water heater 12 Induction ventilator 13 Chimney 14 Denitration device 15 Air preheater 16 Push-in ventilator 17 Compressor 18 Gas turbine 19 Gas turbine exhaust gas cooler

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F01D 19/00 F01D 19/00 R F01K 13/02 F01K 13/02 B F02C 6/18 F02C 6/18 B F22B 1/18 F22B 1/18 C E 33/02 33/02 Z F22D 1/36 F22D 1/36 11/00 11/00 E

Claims (1)

Claims: 1. A once-through boiler that supplies steam to a steam turbine, a gas turbine that supplies gas turbine exhaust gas as combustion air to the once-through boiler via a gas turbine exhaust gas cooler, and the gas turbine. A water supply system for supplying boiler feed water as a cooling medium to an exhaust gas cooler and forming a flow path for supplying feed water heated by the turbine exhaust gas to the once-through boiler; and a boiler inside the once-through boiler before the start of the once-through boiler A recirculation type combined cycle plant having a boiler starting circulation system for forming a circulation flow path for branching out the fluid from the boiler and taking it out to the outside and returning it to the inside again. A reciprocating flow path for feeding and returning the boiler internal fluid as a cooling medium to the gas turbine exhaust gas cooler; Before starting the once-through boiler, the boiler internal fluid is caused to flow between the circulation flow path and the gas turbine exhaust gas cooler through the reciprocating flow path, and after igniting the once-through boiler, the cooling medium of the gas turbine exhaust gas cooler is discharged. An exhaust reburn type combined cycle plant, comprising: switching means for switching from boiler internal fluid to boiler feedwater of the water supply system.