CHARACTERISTICS

The efficiency of a turbine depends on its condition relative to its design. With use, the condition of the turbine deteriorates, and its efficiency deteriorates proportionately. Efficiency can be improved by evaluating the design and operating condition of the turbine. Improvements can be made in one or more of three areas: (1) combustion to improve fuel utilization and minimize environmental impact; (2) heat transfer and aerodynamics to improve turbine blade life and performance; and (3) materials to permit longer life and higher operating temperatures for more efficient systems. For maximum efficiency in utility applications, a steam turbine can be added to convert steam to electricity; adding a second cycle can increase efficiency to 45-53%.

Turbine improvements can improve the heat rate, thereby decreasing economic cost and improving efficiency of operation. With greater efficiency, emissions of GHGs will be avoided. Because of the widespread deployment of turbines, turbine improvements are an area with large potential for reducing GHG emissions with the added benefit of decreasing turbine operating costs.

SIZE:
Turbines range in size from micro (<5 MW) to large (100 MW and larger)
Combined Cycles: 50-800 MW_e

FEATURES:
Specific aspects to be evaluated include: poorly maintained steam seals, eroded/damaged first stage nozzle block; damaged rotating elements and diaphragms; feedwater heaters in/out of service; reduced load operation; manual control of turbine; valve and horizontal joint leakages; operation of turbine at unusually low steam flows to support the district heating system; operating low pressure turbines in condensing mode. Also, steam turbines can be re-bladed to improve turbine efficiency. Other turbine cycle improvements could include a program to monitor leaking valves and replace them when necessary (valve cycle isolation).

COST:
Natural gas - $480 to $570/kW (120 to 440 MW_e); lower costs have recently been reported; Distillate fuel oil - $540 to $580/kW (120 to 210MW_e). Investment costs are approximately 30% less than for a conventional steam power plant, and costs may decrease over the next 2 decades.

CURRENT USAGE:
Gaseous and liquid fueled-turbines are widely used. Advanced turbines systems with efficiencies >60% and NO_x emissions in the single digits (ppm) are under development.

POTENTIAL USAGE:
Demand for electricity all over world is rapidly increasing; demand is estimated at close to 4500 GW by 2020–approximately one-third of this will be filled by gas turbines.

ISSUES ASSOCIATED WITH IMPLEMENTING ACTION

• May not be technically feasible to upgrade from a simple to a combined cycle application due to space limitations and technical incompatibilities (steam turbine inlet pressure and temperature).
• Only feasible where gas (or low cost liquid fuels) are available and economically competitive.

CLIMATE CHANGE IMPACT

EMISSION EFFECT:
    

CONDITIONS FOR EMISSIONS MITIGATION:

• Emissions will decrease in proportion to heat rate improvements.

EMISSION ESTIMATE:
Natural gas-fired turbines emit about 425 gCO₂/kWh; Oil-fired turbines emit about 550 gCO₂/kWh

COST-EFFECTIVENESS:
Increasing efficiency of turbines will decrease fuel costs.

SECONDARY EFFECTS:
Turbines emit the following air pollutants: SO₂: 0.5 to 0.7 g/kWh for high-sulfur distillate fuel oil NO_X: 0.4 to 1.3 g/kWh for natural gas or distillate oil CO : 0.07 to 0.12 g/kWh for natural gas 0.8 to 0.2 g/kWh level for distillate fuel oil Particulates: 0.01 to 0.03 g/kWh. VOCs: 0.03 to 0.07 g/kWh.

RESOURCES

• Electric Power Research Institute, Heat Rate Improvement Guidelines For Existing Fossil Plants, Report No. CS-4554.

CONTACTS

Association of Energy Engineers
Atlanta, Georgia
Tel: (770) 447-5083
Fax: (770) 446-3969
http://www.aeecenter.org

Gas Turbine Association
Jeff Abboud
Washington, DC
Tel: (202) 298-1806
Fax: (202) 338-2416
Advocates@erols.com
http://www.gasturbine.org