Abstract

Three cogeneration plants, totaling 24 megawatts of electric power output and 750 million Btu/h of steam generation, have been placed in service in Chevron enhanced oil recovery operations in Kern County, California. Two of the plants, each with 10 MW of electricity generation capacity, use conventional gas turbines with supplementary-fired waste heat recovery steam generators. The third plant, with 4 MW of electricity generation, uses plant, with 4 MW of electricity generation, uses a steam topping turbine to extract power from steam as it expands from high steam generator output pressures down to lower steam injection well pressures.

The two gas turbine plants have proven to be reliable, flexible and economic. The topping turbine operation and economics are still being proven. proven

Introduction

In Kern County, California, Chevron operations presently require about 35 MW of electric power presently require about 35 MW of electric power and about 3.5 billion Btu/h of steam. The steam, primarily used for steam drive applications, primarily used for steam drive applications, is typically generated at pressures ranging from 400 to 800 psi and at qualities ranging from 30% to 80%. The electricity is primarily used in producing operations, including pumping units, gas plants, steam generators (blowers and pumps), compressors, water cleaning facilities, and a small refinery.

The decision to use cogeneration to meet part of the electricity requirements was based part of the electricity requirements was based on the following needs:

  1. Uncertainty about the utility's ability to provide electric power requirements needed for expansion of production facilities.

  2. Maximum fuel use efficiency in production operations.

  3. High rates of return on invested capital.

  4. A desire to obtain cogeneration experience in production operations.

COGENERATION PLANT LOCATION AND TYPE

The location of steam and electricity requirements, as well as the type of fuel available in the different areas, defined the location and type of each cogeneration plant. As shown in Figure 1, production is concentrated in three widely separated areas. In two of the areas (Taft and Cymric) natural gas is readily and economically available as a fuel. The availability of gas in these areas allowed gas turbine-generator units with waste heat recovery steam generators to be considered. Previous experience with these units in offshore use had also been satisfactory. Based primarily on these considerations, gas-turbine-based cogeneration systems were selected for the Taft and Cymric sites. A system schematic of these cogeneration units is shown in Figure 2.

In the third area (Kern River) natural gas was not economically available. Crude oil, with an API gravity in the 12–14 range was the primary steam generator fuel. No proven gas turbine designs appeared to be available which could use this crude as a fuel.

As an alternative to a gas turbine plant, a steam topping turbine electric generation plant was considered. A system schematic of this steam turbine system is shown in Figure 3. Using the steam turbine involves raising steam generator outlet pressures from 600 to 1500 psi, separating the steam and liquid phases of the 80% (maximum) quality steam, and expanding the 1500 psi saturated steam phase down to 600 psi through a steam turbine. The steam turbine exhaust is remixed with the water phase that had been separated upstream of the turbine.

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