Highly Supercharged Gas Turbine Generating System

Abstract

A highly supercharged gas-turbine generation system include a gas turbine power plant that is supercharged to a high inlet pressure, preferably over about 1.15 pressure ratio and preferably includes a transmission system with refrigerated transformers for increased output. The gas turbine power plant includes a precompressor that supercharges to a design pressure ratio of about 1.20 to 10, with a preferred pressure ratio of about 2. For high supercharging pressures, a pressure-reducer is located downstream of the gas turbine to maintain turbine outlet pressure that is close to the inlet pressure. The pressure-reducer is preferably an expander, but can alternatively be an orifice. A torque-limiting coupling on the shaft between the gas turbine and the generator prevents transient overload of the shaft. Capacity of the gas turbine plant is preferably controlled by varying supercharging pressure. The expander preferably has variable-pitch blades to allow efficient variation of turbine outlet pressure. For combined-cycle embodiments, a heat-recovery steam generator (HRSG) may be placed between the gas turbine and a downstream expander. For highest combined cycle output, a single-pressure steam system with high inlet temperature to the HRSG is preferred. The high temperature is preferably provided by supplemental firing between the gas turbine and the HRSG. An expander may be inserted between the supplemental firing and the HRSG to further improve cycle efficiency and to reduce pressure in the HRSG. For retrofit applications with limited supercharging, a refrigeration system for generator cooling may be added to increase generator output to match that available from the supercharged gas turbine.

Description

[0001]Applicants claim benefit of provisional application No. 60 / 368,987, entitled “High-Output Gas-Turbine Power Plant,” filed on Apr. 2, 2002, provisional application No. 60 / 382,753, entitled “High-pressure supercharging system”, filed on May 22, 2002, and provisional application No. 60 / 431,616, entitled “High-Output Gas-Turbine Power Plant,” filed on Dec. 8, 2002.BACKGROUND[0002]1. Field of Invention[0003]The invention is in the field power generation systems, specifically gas turbines and combined-cycle plants with high-pressure supercharging and cooling systems.[0004]2. Description of Prior Art[0005]A basic problem with performance of power-transmission and generation systems is that the peak demand on such systems usually occurs during a maximum ambient temperature condition, which corresponds to a maximum air-conditioning load, while the capacity of the generators and transformers generally decreases as ambient temperature increases. In addition, prime movers such as combusti...

AI Technical Summary

Benefits of technology

[0024]In accordance with the present invention, an electric generation system includes a highly supercharged gas turbine. In addition the system preferably includes a high air velocity

Problems solved by technology

A basic problem with performance of power-transmission and generation systems is that the peak demand on such systems usually occurs during a maximum ambient temperature condition, which corresponds to a maximum air-conditioning load, while the capacity of the generators and transformers generally decreases as ambient temperature increases.

In addition, prime movers such as combustion turbines and combined-cycle plants generally have reduced power capacity at higher ambient temperature conditions.

This problem means that the system capacity is lowest at the same the demand is the highest.

Consequently, power generation and transmission systems designed to meet anticipated peak demands for power at maximum ambient temperature conditions by definition will have an excess capacity at lower ambient temperatures (when demand is lower) that is simply wasted.

However, none of these efforts has addressed the problem of reduced capacity during peak demand at maximum ambient temperatures as explained above.

Despite these advantages, developing combined-cycle plants face difficulties.

Chilling systems can provide more of a capacity increase but are limited to cooling to a temperature of about 45 to 50° F. to prevent possible icing problems.

Overspray and water injection system have also been used and can achieve significant capacity increases of up to 20 to 25% in some cases, but potential compressor damage and flame stability issues frequently limit the available output to smaller increases.

This system is complicated and requires the use of expensive steam-driven refrigeration equipment.

In addition, the system requires the use of a steam power that could be used to generate electricity, which is a real disadvantage for modern combined-cycle power plants.

For these reasons, the Foster-Pegg system has not been commercialized.

A problem with Bronicki is that it is unable to fully utilize available turbine capacity.

This limited pressure ratio, combined with the limited inlet cooling, creates an upper limit for the available capacity increase.

This limited capacity increase means that Bronicki is unable to increase the turbine capacity to the full value corresponding the shaft torque limit for the gas turbine.

This performance penalty creates another opportunity for increasing turbine capacity with supercharging.

This limitation of Bronicki is especially great in turbines of modern design because they are much less responsive to inlet pressure rise compared to older designs.

Another problem with designs found in the prior art is related to size of ducts and heat exchangers used to cooling air exiting the supercharging fan.

This large duct size creates a large space requirement and greatly increases material and labor costs for assembly of these supercharging systems Electric power plants, transmission, and distribution system represent a huge investment that has taken place over many decades.

Yet despite these investments, there are significant problems that remain.

The effect of ambient temperature on capacity of generators and transformers is another important problem.

Since temperature limits of electrical insulation and related components limit the output of generators and transformers, higher ambient temperatures reduce electrical capacity.

A related problem is a limited ability to increase capacity of electrical equipment to meet changing needs.

For transformers, cooling capacity can be increased through the addition of cooling fans to improved heat transfer, but is otherwise limited by thermal considerations.

Foster-Pegg also lacks a means for cooling the generator without operation of the chiller, which limits operation of the combustion turbine.

These cooling systems are complicated, extremely expensive and require specially design insulation in order to function.

They are not suitable for use with conventional generators and transformers.

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