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Emission Standards

Stationary Engines—World Bank Guidelines


In 1998, the World Bank Group has issued Thermal Power: Guidelines for New Plants, which define procedures for establishing maximum emission levels for fossil-fuel based thermal power plants with a capacity of 50 or more megawatts of electricity (MWe) that use coal, fuel oil, or natural gas. The guidelines include emission limits for particulate matter, SO2 and NOx for various types of power plants, including engine-driven power plants. The guidelines also include ambient air quality standards, as well as provisions applicable to noise, liquid effluents, and solid wastes from power plants.

The guidelines have been adopted to assist the World Bank in making funding decisions for new power plants. However, internationally, the World Bank’s guidelines have been widely used as the minimum norm if the host country does not have its own specific legislation for engine-driven power plants.

Engine Emission Standards

The maximum emission levels are expressed as concentrations, to facilitate monitoring. The emission limits are to be achieved through a variety of control and fuel technologies, as well as through good maintenance practice. Dilution of air emissions to achieve the limits is not acceptable.

The following are emission limits for engine driven power plants:

  • Particulate matter. PM emissions (all sizes) should not exceed 50 mg/Nm3.
  • Sulfur dioxide. Total SO2 emissions should be less than 0.20 metric tons per day (tpd) per MWe of capacity for the first 500 MWe, plus 0.10 tpd for each additional MWe of capacity over 500 MWe. In addition, the SO2 concentration in flue gases should not exceed 2,000 mg/Nm3, with a maximum emissions level of 500 tpd.
  • Nitrogen oxides. Provided that the resultant maximum ambient levels of nitrogen dioxide are less than 150 µg/m3 (24-hour average), the NOx emissions levels should be less than 2,000 mg/Nm3 (or 13 g/kWh, dry at 15% O2). In all other cases, the maximum NOx emission level is 400 mg/Nm3 (dry at 15% O2).

Ambient Air Quality

The guidelines for ambient air quality in thermal power plants are summarized in Table 1.

Table 1. Ambient Exposure Limits, µg/m3
Pollutant24-hour averageAnnual average
Total suspended particulates (TSP)a23080
a - Measurement of PM10 is preferable to measurement of TSP