a steam generator (boiler);
a steam turbine;
balance-of-plant (bop) equipment;
and
particulate removal equipment;
typically electrostatic precipitator (ESP).
Thermal power technologies involve combustion or gasification of oil, natural gas or coal to produce electricity. The sections below provide information on the various thermal power conversion technologies, including a description of each technology, performance issues, time for construction, suitability for developing countries, and deployment issues; bibliographical information is also provided for further reference.
*Source: "Clean Coal Technologies for Developing Countries," World Bank Technical Paper No. 286, Energy Series, E. Stratos Tavoulareas and Jean-Pierre Charpentier, July 1995
The conventional steam plant is a mature technology used widely throughout the world. It consists of:
a steam generator (boiler);
a steam turbine;
balance-of-plant (bop) equipment;
and
particulate removal equipment;
typically electrostatic precipitator (ESP).
Although steam plants up to 1,300 MW and supercritical steam conditions of 24 MPa STET have been built, in recent years most PC plants range in size between 300 and 900 MW with steam outlet conditions 16 MPa (2,400 psi), 565°C/565°C (1050°F/1050°F) and overall plant efficiency in the 34 to 38 percent range. Supercritical steam plants have been used in some countries (Denmark and Japan) and have achieved efficiencies in the 38 to 42 percent range.
Steam plants burn all types of coals (anthracite, bituminous, subbituminous, lignites, and brown coals), oil, natural gas, and biomass independently or in combination. However, the power plant needs to be designed for the available fuels.
Source: "Clean Coal Technologies for Developing Countries," World Bank Technical Paper No. 286, Energy Series, E. Stratos Tavoulareas and Jean-Pierre Charpentier, July 1995
The pulverized coal-fired (PC) plant is a conventional steam plant firing pulverized coal. Additional equipment required is:
coal handling (usually, a direct-firing
system for pulverized coal)
coal preparation including pulverizers
particulate removal equipment;
typically electrostatic precipitator (ESP), and
solid waste handling and disposal.
Capital costs for PC plants with ESP range from 800 to 1000 $/kW depending upon the size, fuel characteristics, site-specific requirements, and environmental regulations.
Pulverized Coal-Fired Plant Sub-Sections:
AFBC technologies are adaptable to both new and existing installations, work well in combination with other technologies, and are suitable for many local coals. However, their acceptance in many developing countries has been slowed by a lack of regulations requiring high removal of SO2.
Eight PFBC plants are operating or under construction in Europe, Japan, and the United States.
Because of its high cost and early stage of development, IGCC technology is, for the near future, an unlikely choice of technology for developing countries with lenient SO2 removal and NOx emission regulations. However, it is one of the few technologies (the others being supercritical pulverized coal and PFBC) that significantly increases power plant efficiency and will have a beneficial effect in reducing emissions of CO2. As such, IGCC, like PFBC, is a technology that may be used in developing countries in the long term.
Coproduction of Electricity and Clean Fuels
The modern power gas turbine is a high-technology package that is comprised of a compressor, combustor, power turbine, and generator, as shown in the figure "Simple-Cycle Gas Turbine".
In a gas turbine, large volumes of air are compressed to high pressure in a multistage compressor for distribution to one or more combustion gases from the combustion chambers power an axial turbine that drives the compressor and the generator before exhausting to atmosphere. In this way, the combustion gases in a gas turbine power the turbine directly, rather than requiring heat transfer to a water/steam cycle to power a steam turbine, as in the steam plant. The latest gas turbine designs use turbine inlet temperatures of 1,500C (2,730F) and compression ratios as high as 30:1 (for aeroderivatives) giving thermal efficiencies of 35 percent or more for a simple-cycle gas turbine.
Source: William & Larson, "Aeroderivative Turbines for Stationary Power", The Center for Energy and Environmental Studies, Princeton University, May 1988.
The combined-cycle unit combines the Rankine (steam turbine) and Brayton (gas turbine) thermodynamic cycles by using heat recovery boilers to capture the energy in the gas turbine exhaust gases for steam production to supply a steam turbine as shown in the figure "Combined-Cycle Cogeneration Unit". Process steam can be also provided for industrial purposes.
Gas Combined Cycle Sub-Sections
Source: William & Larson, Aeroderivative Turbines for Stationary Power", The Center for Energy and Environmental Studies, Princeton University, May 1988.
Diesel is a reciprocating engine which uses diesel fuel (distillate) for high-speed or heavy oil (residual for mid- and low-speed engines. Also, dual-fuel (gas and oil) engines are available.
Diesel engine sizes vary from larger, low-speed (100-200 rpm), two-cycle, multi-cylinder, 50 MW 1500-ton engines several stories high, through medium speed (400-700 rpm), four cycle, 2 to 25 MW engines, to small high speed (1000 rpm or more), four -cycle 0.2 to 2 MW engines, with variations of these three basis engine types. Engine lives, assuming average annual operation of 5000 hours, are typically five years for high-speed engines increasing to 20 years for low-speed engines.
Diesel generators, remain a reliable, low initial cost, short term power source. These advantages are bought at the cost of use of restricted types of fuel and relatively high maintenance requirements.
The maturity, modularity and simplicity of field installation makes diesel technology a predominant choice for small remote systems of 100 MW or less.
The medium speed diesel efficiency is comparable to modern gas turbine but are limited to much lower combined cycle efficiencies. Diesel waste heat may be used for hot water, space heating, etc.
Diesel generators play an important role as local reserve, particularly where the transmission tie is radial or of marginal reliability for other reasons.
The environmental assessment should include an analysis of reasonable alternatives to meet the ultimate objectives of the project. The analysis may lead to alternatives that are more sound from an environmental, sociocultural, and economic point of view than the originally proposed project. A number of alternatives need to be considered:
no action (i.e., examine the
consequences of taking no action to meet the expected demand needs)
alternative fuels
energy efficiency and load management
(DSM) alternatives
site location alternatives
alternative heat rejection systems
alternative water supply/intake
alternatives
plant and sanitary waste discharge
alternatives
engineering and pollution control
equipment alternatives
solid waste disposal alternatives