Temperature control method and apparatus for the air supply in P

Power plants – Combustion products used as motive fluid

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Details

60 3912, 60728, F02C 326, F02C 7143

Patent

active

054351227

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

To ensure satisfactory function of the turbine units in a PFBC plant, it is required that the temperature of the air when it passes through compressors is maintained within certain given limits. If this is not done, compressors may, for example, reach a working range where surge occurs.
PFBC plants have been described in a number of patent specifications, technical papers etc. In this description, therefore, only the parts of such a plant which are needed to describe the air system will be briefly described. The Swedish patent application SE 9102651-8 entitled "Air flow control system in PFBC plants", filed concurrently herewith, describes in detail, in addition to the PFBC plant as such, how an air system is built up. It also describes the important limitations that such a system entails and how these are overcome with the aid of controls overriding each other.


SUMMARY OF THE INVENTION

The present invention comprises methods and devices for controlling and limiting the temperature of the air on the output of the high-pressure compressor, that is, before the air is passed into the pressure vessel and the combustor of the PFBC plant, and also for limiting the temperature of the air on the input of the high-pressure compressor both during stationary operation and during load change.
A PFBC plant which includes the air temperature control according to the present invention comprises a twin spool gas turbine unit. To the low-pressure shaft there are connected a low-pressure compressor and a low-pressure turbine, and to the high-pressure shaft there are connected a high-pressure compressor and a high-pressure turbine. Air is sucked via the inlet duct into the low-pressure compressor and is passed on via an intermediate cooler to the high-pressure compressor. The air which thereby passes through the high-pressure compressor is pressed into the boiler of the PFBC plant. The return flow from there first passes through the high-pressure turbine and then through the low-pressure turbine and is then released into the free environment.
In order for an air supply system to function satisfactorily, certain limitations must be introduced with regard to the temperature of the air, in addition to the limiting controls described in the above-mentioned "Air flow control system in PFBC plants", and the purpose of the invention, as mentioned above, is to maintain the temperature both downstream and upstream of the high-pressure compressor within permissible limits.
In the Swedish patent application dealing with air flow control, it is stated that in the air passage between the low-pressure compressor and the high-pressure compressor there is provided an intermediate cooler with the implicit but obvious task of cooling the air flow. Swedish patent SE 8602003-9, "A method for operation of a turbine unit", describes both an external intermediate cooler and an internal intermediate cooler arranged in the connection between the low-pressure compressor and the high-pressure compressor. These intermediate coolers are arranged for heat exchange between the air in the compressor circuit and the condensate from the condenser (or similar medium). This patent specification further states that "By the intermediate cooling the temperature of the air to the high-pressure compressor is reduced while at the same time the condensate to the feedwater tank is heated in the internal intermediate cooler". However, no temperature control is mentioned in this connection.
The maximum permissible temperature at the output of the high-pressure compressor is determined by the maximum permissible temperature of the interdependent systems during stationary operation. To be able to limit this temperature, the air out from the high-pressure compressor is temperature-controlled by means of the intermediate cooler. The intermediate cooler may, for example, be of cross-flow type with cooling water on the tube side. A constant water flow is maintained by a circulation pump and the temperature of the water in the intermediate coole

REFERENCES:
patent: 4362462 (1982-12-01), Blotenberg
patent: 4530207 (1985-07-01), Brannstrom
patent: 4584949 (1986-04-01), Brannstrom
patent: 4893466 (1990-01-01), Egnell et al.

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