Solar fired combined cycle with supercritical turbine

Abstract

Mechanical work for electric power generation is obtained from thermal energy in a plant arranged for introduction of solar energy, available intermittently, by reflecting and concentrating solar radiation to directly heat a flow medium such as the exhaust gas from a combustion turbine directed into a steam generating boiler / evaporator. Steam generators and staged turbines recover and extract energy optimally at particular temperature, pressure and flow parameters in a closed thermodynamic cycle. Solar energy that is available intermittently is injected into the cycle to elevate the energy of the flow medium, in particular to produce supercritical steam. A steam turbine optimized for expanding supercritical steam is deployed during periods of available solar radiation by a controllable clutch and other switching and valve arrangements. The exhaust from the supercritical steam turbine can be coupled to downstream staged turbines optimized for successively lower pressures and higher flow rates.

Description

FIELD OF THE INVENTION[0001]This invention provides methods and apparatus wherein concentrated solar energy is used, when sunlight is available, to heat the exhaust gas from a gas turbine to temperatures high enough for supercritical steam production in a heat recovery steam generator. The additional supercritical steam is expanded in a steam turbine for electric power generation at the highest possible thermal efficiency.BACKGROUND OF THE INVENTION[0002]Like many renewable power generation technologies, Concentrated Solar Power (CSP) suffers from intermittence and unpredictability, which can render the technology difficult to justify and to deploy efficiently for meeting a constant demand for power. There are possible means to alleviate the discontinuous nature of energy supplied by an intermittent source, such as to provide thermal energy storage facilities, but that can add to plant size and cost appreciably. Another remedy is to supplement the solar thermal energy input by an on...

AI Technical Summary

Benefits of technology

The invention provides a new way to use solar energy in a gas turbine plant to improve efficiency. Instead of adding solar energy to the plant at a separate location, it is directly introduced into the gas turbine and steam generator. This allows for optimal performance regardless of whether solar energy is available or not. The high temperature and pressure of the solar energy is used to generate supercritical steam, which is then expanded in a turbine to extract mechanical work. This work is then converted into electric power by a main steam turbine. The system also includes a solar concentrator that increases the energy state of the flow medium, resulting in higher efficiency compared to current technology.

Problems solved by technology

Like many renewable power generation technologies, Concentrated Solar Power (CSP) suffers from intermittence and unpredictability, which can render the technology difficult to justify and to deploy efficiently for meeting a constant demand for power.

There are possible means to alleviate the discontinuous nature of energy supplied by an intermittent source, such as to provide thermal energy storage facilities, but that can add to plant size and cost appreciably.

Another remedy is to supplement the solar thermal energy input by an on-demand energy source, for example by burning a fossil fuel when solar radiation is unavailable, but that runs against the purpose of deploying renewable energy technologies in the first place.

In all these concepts, solar thermal energy accounts for only a small fraction of the total generation capacity (for example 10%) at a considerable expense and complexity.

The plant cost is further increased by the need for equipment to handle complex integration issues such as a switching and control philosophy during solar thermal start and shutdown, among other challenges.

A main drawback of such solar trough technology is that the maximum achievable steam temperature is limited to about 745° F. by HTF availability.

This is one of the two limiting factors in solar power augmentation; the other is the increase in the condenser pressure with increasing low pressure turbine exhaust steam flow (a typical alarm limit is 5 inches of mercury).

This is a particularly critical item for plants with air-cooled condensers, which are very expensive in terms of capital expenditure and parasitic power consumption (power consumed by large fans driving the airflow through the condenser cells).

While the condenser pressure limitation can be overcome (e.g., by adding extra air cooled condenser cells to be deployed when low pressure exhaust flow is increased), the high pressure throttle pressure limit is not so straightforward to accommodate.

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