Gas turbine combined cycle system

Abstract

In a combined cycle gas turbine configuration having at least two power blocks, stack emissions (particularly nitrous oxides or NOx but also carbon monoxide CO and unburned hydrocarbons, UHC) are controlled concurrently with part load power output. In one power block a combined cycle power plant has a relatively large heavy-duty industrial gas turbine fired to about 1,700° C. at the turbine inlet leading to a first heat recovery system. A second power block with a smaller gas turbine has a second heat recovery system. A controller adjusts coupling of flue gas and steam paths from the second power block to the first power block to meet load demand in compliance with applicable emissions regulations.

Description

CROSS-REFERENCE TO RELATED APPLICATION[0001]This application claims the benefit of U.S. Provisional Application No. 61 / 820,901, filed May 8, 2013.FIELD[0002]This disclosure concerns the field of gas turbines and in particular provides methods and apparatus for managing stack emissions (e.g., nitrous oxides (NOx), carbon monoxide (CO), unburned hydrocarbons (UHC) and the like), while concurrently controlling load power output. The invention is particularly applicable to combined cycle power plants with heavy-duty industrial gas turbines, fired, for example, to 1,700° C. (3,092° F.) at the turbine inlet.BACKGROUND[0003]The term “combined cycle” generally refers to an assembly of two or more engines driven from the same source of heat, converting heat energy into mechanical energy, usually to drive one or more electrical generators. In gas turbine (GT) combined cycle plants, expansion of product gas resulting from combustion of fuel turns a gas turbine. Hot exhaust gases from the gas t...

AI Technical Summary

Benefits of technology

This patent describes a way to reduce harmful emissions, specifically NOx, from a gas turbine engine. The system includes a flue gas compressor that takes part of the exhaust gas from the added power block and injects it into the combustor of the gas turbine of the first power block. This high temperature gas helps increase power generation efficiency, but without causing excessive levels of harmful emissions. The system also ensures a high temperature in the first power block for optimal efficiency, but without producing too much unwanted exhaust emissions.

Problems solved by technology

The design of high efficiency, high temperature gas turbines presents challenges including (1) cooling of the turbine hot gas path (HGP) components operating at such high temperatures; and (2) control of NOx and CO emissions.

Turbine HGP cooling by compressor extraction air is detrimental to gas turbine performance in at least two aspects.

Thus, in order to achieve a desired firing temperature, the gas turbine combustor needs to be fired that much harder, with direct impact on NOx emissions.

Another aspect of air cooling is that the air used to cool the stage 1 rotor does not produce useful shaft work.

The cooling air limits the desired impact of higher firing temperatures.

Such developments remain a major challenge.

But commercialization seems to be decades off.

One drawback of steam cooling technology is a lack of “flexibility”.

Specifically, the availability of steam (or the lack of it) during the early phase of combined cycle startup slows down the process until enough steam is generated in the HRSG to supply the gas turbine.

An auxiliary boiler might be utilized instead to provide cooling steam during startup, but at the expense of additional startup fuel consumption and emissions, and at additional capital cost.

Apart from cooling problems, NOx emissions remain an obstacle in the path of ever-rising TITs.

Once the IGVs reach their fully closed position (i.e., minimum airflow), further reduction in output is achieved by reducing the fuel flow, and exhaust temperature starts going down, with further detrimental impact on the contribution of the bottoming cycle.

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