JPH0799243B2 - Waste heat recovery equipment - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a waste heat recovery device, and more particularly to an auxiliary fuel injection type waste heat recovery device suitable for operation in a wide load region.

(Prior Art) In order to operate a steam turbine for power generation and driving an auxiliary machine with high efficiency, it is necessary to increase the temperature and pressure of the steam used. On the other hand, in the case of a waste heat recovery device that recovers the heat from the exhaust gas of a gas turbine and obtains steam, a system that inputs auxiliary fuel is often adopted to obtain the required amount of steam regardless of the load of the gas turbine. ing. The conventional waste heat recovery device is
As shown in FIG. 2, an exhaust gas 10 is introduced into a furnace 1 (hereinafter referred to as a water-cooled wall furnace) having a water-cooled wall, and fuel is injected from a furnace burner 2. The retained heat of the exhaust gas 10 and the combustion heat of the fuel to be introduced are recovered through the steam superheater 3, the steam generator 4, and the economizer 5 at the downstream side, and finally the exhaust gas 10 is released to the atmosphere via the exhaust stack 6. Is dissipated to. In this case, the water-cooled wall furnace 1 mainly receives radiant heat, and the steam superheater 3 mainly receives convective heat to raise the temperature. Normally, for example, when the exhaust gas 10 uses a gas turbine as a generation source, even if the load on the gas turbine side changes, the gas amount of the exhaust gas 10 does not change so much, and therefore the evaporation amount of the steam 13 is a considerable amount. However, the steam temperature does not rise to the required temperature. In order to improve the efficiency of the steam turbine or to prevent entry into the wet steam region inside the steam turbine, it is necessary to raise the steam temperature to above and below 500 ° C, even though the exhaust gas temperature is around 400 ° C. Yes, the exhaust gas temperature is raised by the combustion of auxiliary fuel. On the other hand, when the required evaporation amount of the steam 13 is small, the auxiliary fuel is injected to burn the steam in order to maintain the steam temperature, and the surplus exhaust gas is diffused from the bypass chimney 7 into the atmosphere.

(Problems to be Solved by the Invention) In the above conventional technology, the temperature of the exhaust gas introduced is low,
Moreover, at the time of so-called low load operation in which the required evaporation amount of the steam 13 is small, even if it is desired to throttle the fuel supplied to the waste heat recovery device, the heat absorption by the water-cooled wall furnace is large and the gas temperature at the inlet of the steam superheater 3 is As a result, the high temperature steam 13 cannot be obtained. On the contrary, at the time of high load that requires a large amount of vapor evaporation, the high temperature gas is absorbed by the water-cooled wall furnace 1, which also has the advantage of preventing the steam superheater 3 from overheating. Regarding the increase of surplus gas emission and the increase of fuel consumption,
I had to accept it as unavoidable. The present invention has been made for the purpose of solving the above problems and reducing the amount of surplus exhaust gas emission and the amount of fuel consumption at the time of low load operation of a waste heat recovery device.

(Means for solving the problem) The above-mentioned purpose is to prevent burner and steam superheat outside the water cooling wall furnace in addition to those inside the waste heat recovery device so as not to be affected by heat absorption by the water cooling wall of the furnace. It is achieved by providing a container.

(Function) Even if the temperature of the introduced exhaust gas is low, the temperature of the inside of the furnace rises without being absorbed by the water cooling wall due to the combustion of the duct burner arranged outside the water cooling wall furnace, and the gas temperature at the steam superheater inlet Does not drop, and steam with the required temperature and pressure can be generated, thus eliminating the need to charge excess fuel.

(Embodiment) An embodiment of the present invention will be described with reference to FIG.

In FIG. 2 and FIG. 2, those having the same reference numeral in the prior art indicate the same functional product. The introduced exhaust gas 10 is combusted and heated by a duct burner 8 installed in the duct, passes through a steam superheater 9 in the duct, and is further combusted and heated by a furnace burner 2 to enter a water-cooled wall furnace 1. After the heat is absorbed by the water-cooled wall furnace 1, the heat is recovered via the steam superheater 3, the steam evaporator 4 and the economizer 5, and is discharged to the atmosphere by the exhaust chimney 6. In the system of this waste heat recovery device, when a large amount of steam 13 is required, that is, at the time of high load operation, the furnace burner 2 having a larger capacity than the duct burner 8 burns the fuel, and the heat absorption from the water-cooled wall furnace 1 is also effective. Therefore, the conditions for selecting the material for the steam superheater 3 are relaxed, and conversely, the fuel flowing to the furnace burner 2 is operated during low load operation. The passage is shut off, fuel is injected only into the duct burner 8 and the exhaust gas temperature is raised by a small amount of fuel consumption, and the exhaust gas is introduced into the steam superheater 9 as it is. That is, by adjusting the openings of the flow ratio adjusting valves 14 and 15 provided in the flow path of the auxiliary fuel 11, the flow ratio of the auxiliary fuel 11 is adjusted according to the required steam amount and temperature generated in the waste heat recovery device. can do. The main valve 16 is a valve that adjusts the auxiliary fuel supply amount according to the temperature of the outlet duct of the waste heat recovery device.

In this way, by selectively using the furnace burner 2 and the duct burner 8, the waste heat recovery device is operated in a wide range of load areas, the steam temperature is effectively maintained at a high temperature, the fuel consumption amount is minimized, and surplus fuel is injected. Therefore, the amount of exhaust gas emitted from the bypass chimney 7 can also be minimized.

(Effect of the invention) As described above, by carrying out the present invention, even when the waste heat recovery device is operated at a low load, heat is not absorbed by the water-cooled wall furnace, so that an excessive amount of auxiliary fuel is not charged,
The required temperature of the steam superheater is maintained and heat is recovered, and the effect that the fuel consumption at the time of low load can be minimized is obtained.

[Brief description of drawings]

FIG. 1 is a system diagram of a waste heat recovery system according to an embodiment of the present invention, and FIG. 2 is a system diagram of a conventional waste heat recovery system. 1 ... Water-cooled wall furnace, 2 ... Furnace burner 3 ... Steam superheater, 4 ... Steam generator 5 ... Economizer, 6 ... Exhaust stack 7 ... Bypass stack, 8 ... Duct burner 9 ... Inside duct Steam superheater, 10 ...... Exhaust gas 11 …… Auxiliary fuel, 12 …… Water supply 13 …… Steam, 14, 15, …… Flow ratio adjusting valve 16 …… Main valve

Claims (1)

[Claims] 1. Waste heat comprising a furnace having a water cooling wall, a furnace burner facing the furnace, a steam generator for combusting exhaust gas introduced into the furnace with auxiliary fuel to generate steam, and a steam superheater. In the recovery device, a waste heat recovery device comprising a duct burner in a duct for introducing the exhaust gas, and a steam superheater different from the steam superheater in the middle of the duct burner and the furnace burner.