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close this bookEnvironmental Handbook Volume II: Agriculture, Mining/Energy, Trade/Industry (GTZ, 1995, 736 p.)
close this folderMining and energy
close this folder41. Thermal power stations
View the document1. Scope
View the document2. Environmental impacts and protective measures
View the document3. Notes on the analysis and evaluation of environmental impacts
View the document4. Interaction with other sectors
View the document5. Summary assessment of environmental relevance
View the document6. References
View the document7. Appendices

3. Notes on the analysis and evaluation of environmental impacts

3.1 Immissions Limits for Air

As already explained in section 2, the decisive atmosphere-specific environmental impact parameter is "ground-level pollution", i.e., the effects of air pollution on humans, animals, plants and inanimate objects. In evaluating the environmental consequences of thermal power plants, air pollution is normally of central interest. With the exception of CO2, the main pollutants are increasingly regulated by the particular immission limits adopted by different countries. In actual practice, concrete projects must attach primary importance to abiding by the applicable standards. In some countries, those standards are even more stringent than those stipulated by Germany's TA-Luft (Technical Instructions on Air Quality Control). To the extent that the relevant standards have not yet been set or have been set too high, recourse should be taken to the long-term standards prescribed by TA-Luft with regard to impairment of human health and, in part, to the protection of vegetation, materials, water bodies, etc. (cf. Appendix A-4).

If in connection with a concrete project the relevant standards will obviously be exceeded by the baseline pollution load or foreseeable developments, then the promotion of thermal power plants must be ruled out from the beginning on environmental grounds. According to TA-Luft, exceptions can be made for new power plants if the additional burden attributable to the planned facility will not exceed 1 % of the long-term immission limits (irrelevance clause).

If an existing power plant contributes considerably toward substantial transgression of the relevant immission limits, the first step to take is to investigate the possibility of its - economically feasible - relocation. If the results of the study indicate retention of the existing site, the annual relevant pollutant concentrations attributable to the power plant must be significantly reduced in absolute terms by appropriate rehabilitation measures. If the contribution of the existing power plant toward the overall pollutive burden does not exceed 1 % of the standard values after rehabilitation, the irrelevance clause may be applied by way of analogy to the exemption provisions for new plants.

Whenever the relevant standards are significantly exceeded, care must be taken to prepare an appropriate sanitation concept for the affected sphere of influence. Such a concept must provide for the reduction of pollution from sources not standing in direct connection with the project of interest.

With regard to the immission limits listed in Appendix A-4, the reader's attention is called to the fact that the particulate, sulfur dioxide and nitrogen oxide values serve as vitally important indicators for the environmental consequences of thermal power plants. The limit values for hydrogen chloride, cadmium and lead gain significance, when those elements are more abundantly present than normal in the fuel. In such cases, all considerations concerning the environmental relevance of the thermal power plant must be made subject to an analysis of the fuel to be used.

As far as German immission limits are concerned, it should be noted that they only come to bear in increasingly rare cases, because steady cuts in pollutant releases have enabled extensive compliance in most areas in recent years. Any requirements exceeding the immediately prophylactic scope are substantiated on the basis of the pollution prevention principle. Pollution limits are not schematically transferable to other situations and other countries, because, for example, the sensitivity of the local vegetation, the prevailing climatic and weather conditions, and the composition of the local soil(s) can be wholely different, hence justifying either more stringent or more lenient standards. Those specified in TA-Luft give due account to the protection of human health. As such, they are more stringent for clean-air areas than for regions in which high levels of baseline pollution already prevail.

3.2 Emission limits for air

As explained in section 3.1, the premier measure for limiting the environmental consequences of thermal power plants is adherence to the pertinent immission limits. Nonetheless, power plant emissions also should be appropriately limited - since an ounce of prevention is better than a pound of cure. As mentioned in section 2, there are a number of tried & tested commercial-scale pollution control technologies, each with its own particular benefits and drawbacks. One frequent drawback is the relatively high cost of efficient technology. The extent to which a less complex and therefore less expensive approach could significantly reduce the adverse environmental impacts of a thermal power plant should be ascertained in advance.

For example, it certainly would make sense to eliminate particulate emissions with a relatively low-cost cyclone instead of a more efficient and accordingly more expensive electrostatic precipitator or fabric filter, particularly since the high cost of the latter could be regarded as prohibitive, with the result that, ultimately, no dust control effect whatsoever is achieved. According to that same line of reasoning, it would be better to install a single-field electrostatic precipitator than none at all on the grounds that a multiple-field unit would be too expensive. Moreover, the use of more elementary processes has the added advantage of simplifying the operation, maintenance and repair of the equipment while offering a higher level of operational reliability.

Appendix A-5 lists the main laws, rules and regulations governing the release of power plant emissions to the air, water and soil in the Federal Republic of Germany.

As a rule of thumb for concrete projects, the emission limits adopted by the developing country or countries in question should be adhered to. In some cases, of course, this could result in transgression of the comparatively strict emission limits prevailing in the Federal Republic of Germany. Depending on the general context, though, that still could be regarded as tolerable. Nevertheless, the pollution prevention principle dictates that every attempt be made to install appropriate emission control technologies, even on a stage-by-stage basis if necessary, e.g., by first installing a cyclone separator and leaving room for the eventual retrofitting of an electrostatic precipitator.

Appendix A-6 summarizes the essential emission limits for airborne pollution from large-scale combustion plant in the Federal Republic of Germany.

As the table shows, the requirements differ according to type of fuel and size of installation (the latter expressed in terms of thermal output), whereas the larger installations generally are expected to satisfy more stringent environmental protection standards.

Other European Countries go by emission limits similar to those applying in Germany, particularly by way of EC Directive 88/609, most notably for SO2. The Japanese and U.S. American emission limits are also comparable, but how stringently they are enforced depends on local circumstances (competent authorities, baseline pollution levels, etc.). Appendix A-6 also lists the emission standards for new, large-scale coal-fired power plants in selected countries, along with the corresponding EC standards, for the indicators SOx, NOx and particulate emissions. Also included is a conversion chart for converting SO2 and NOx units from mg/m³STP to ppm or lb/106 BTU.

The limit values prescribed in Appendix A-6 can be achieved at justifiable expense for favorable fuels, i.e., for those with high calorific values and low sulfur contents. For unfavorable fuels, however the stipulation of low emission limits can be rather problematic. For example, according to table 2, it would take a separation efficiency of roughly 98 % to limit the SOx emission level to 400 mg SO2/m³STP for a raw gas concentration of roughly 18 000 mg SO2/m³STP. For such fuels, however, stipulation of an 85 - 95 % degree of desulfurization corresponding to the justifiable techno-economic expenditures would be more advantageous.

In some countries, the only available fuels are of such inferior quality that the emission levels listed in Appendix A-6 cannot be adhered to, and higher levels are therefore permitted.

It would be inappropriate to simply transfer the emission limits of, say, the Federal Republic of Germany to other countries, since identical limitations in combination with inferior fuels would call for more sophisticated purification technology than that required in Germany. To maintain a like level of expenditures, one must work from the given emission levels and automatically arrive at higher limit values. It should be noted in that connection, that some of the fuel used in the Federal Republic of Germany does not meet standard German specifications.

From the standpoint of environmental protection, emission limits serve merely as expedients denoting a certain state of technological development under a certain set of boundary conditions. The primary purpose of environmental protection, however, must be to protect human health, the vegetation, water bodies, etc. In other words, the primary objective of such provisions is to comply with the immission limits (cf. section 3.1). The factors governing ground-level pollution were discussed in section 2.

3.3 Monitoring of pollution levels

As a rule, it takes very sensitive instruments to accurately measure pollutant concentrations, since the levels in question can be situated several orders of magnitude below the emission concentrations. Still, certain conclusions can be drawn concerning past pollution by studying the proposed site and its surroundings. The baseline pollution level will be all the higher, of course, if other power plants and/or emission-intensive industries are located in the near vicinity or if the proposed site borders on a major traffic artery. A conflict of purposes could arise in that cogeneration, for example, as its high efficiency and accordingly low emission levels requires a nearby consumer, normally some form of industrial enterprise. If the consumer is characterized by relatively high emissions, the correspondingly high baseline pollution level could partially or even entirely counteract the environmental merits of cogeneration.

With regard to emission measurement, care should be taken to ensure that the scope of supply for the power plant includes instruments for measuring dust, SOx and NOx emissions. Such pollutants are relatively easy to monitor with the aid of mobile local instruments applied to flues or breeching. The requisite gas analyzers operate according to different principles. Differentiation is made between photometric and physicochemical measuring processes.

Photometric processes operate on a purely physical basis (nondispersive infrared process, nondispersive ultraviolet process), while the physico-chemical processes are based on a chemical reaction. Such instruments offer resolutions extending to 1 ppm.

Particulate concentration levels are monitored primarily by physical techniques, e.g., using graphimetric and radiometric instruments.

3.4 Emission limits for wastewater/effluent

In the Federal Republic of Germany, effluent from water treatment and cooling systems is subject to discharge limitations pursuant to section 7a Wasserhaushaltsgesetz - WHG (Federal Water Act) and Appendix 31 of the Rahmen-Abwasser VWV General Administrative Framework Regulation on Wastewater as listed in table 3.

Table 3 - Discharge limitations for effluent from water treatment and cooling systems
Closed-loop systems of:

Power plants

Industrial processes

Other steam-generating sources

Random sample

Settleable solids





Available chlorine










2-hour composite sample

Chemical oxygen demand






Phosphorus (Ptot)















Source: Rahmen-Abwasser VWV (General Administrative Framework Regulation on Wastewater), Appendix 31 (Aug. 13, 1983)

To the extent that a flue-gas desulfurizing system produces wastewater, the minimum discharge requirements put forth in Appendix 47 of the General Administrative Framework Regulation on Wastewater as per section 7a Federal Water Act dating from Sept. 8, 1989, shall apply (cf. Appendix A-4).

The discharge of effluents other than those described in section 2.2 is governed by additional appendices to the General Administrative Framework Regulation as per section 7a of the Federal Water Act; its Appendix 49, for example, applies to oily wastewater.

The above requirements are in line with the stringent provisions of the German Federal Water Act, which stresses the importance of prevention and prescribes limits based on the hazard levels of the respective substances. Moreover, the Abwasserabgabengesetz (Wastewater Charges Act) rewards users who satisfy the requirements of section 7a, WHG (75 % lower wastewater charge) or who maintain existing facilities at least 20% below the prescribed limits (setting off the cost of investment against the past three years' wastewater charges.

For a concrete project, the type and nature of tolerable water pollution naturally depends on the size, quality and manner of utilization of the receiving water. Weak, sensitive recipient bodies must be analyzed in any case. Particularly in tropical countries, the water flow rate can vary widely on a seasonable basis - a fact that must be given due consideration. In that connection, consideration must be given to either relocating the plant or, as discussed in section 2.2, installing a dry cooling tower. Apart from the pollution load, the tolerable thermal load on the receiving body must be critically examined for each concrete project. According to the recommendation of the German Ler working group on water LAWA, the maximum temperature increase of a receiving body in a temperate climate zone should not exceed 3 K.

3.5 Noise

Depending on the local situation, the noise immission requirements for power plants can differ widely. According to the TA-L (Technical Instructions on Noise Abatement) in the Federal Republic of Germany, the following noise immission limits (guide values) should be complied with:

day dB (A)

night dB (A)

areas containing only nonresidential buildings areas containing primarily nonresidential buildings areas containing nonresidential and residential buildings areas containing primarily residential buildings areas containing exclusively residential buildings areas containing health resorts, hospitals, nursing homes

70 65 60 55 50 45

70 50 45 40 35 35

The concrete-case values also depend on the baseline noise-immission levels.

As a rule, power plants should be located as far as possible from residential areas. According to the North-Rhine/Westphalian spacing ordinance Abstandserla/I>, a distance of 800 m or more means that the power plant can be expected to cause no impairment. In a number of German cities, power plants are situated much closer to residential areas, particularly in the case of cogenerating facilities, since the district heat produced by the power plant suffers substantial transmission losses with increasing distance to the consumer heat sinks.

The distance between a power plant and the nearest residential area depends primarily on the noise immission levels encountered at the points of interest, i.e., where the noise is measured. Noise immissions from the boiler and turbine plant can be substantially reduced by the application of noise control measures to the fae.

The delivery of fuel and process materials and the hauling away of residues (incl. the loading and unloading of trucks, railroad cars, barges, etc.) contribute substantially to the overall noise pollution levels from a power plant. For a coal-fired plant, the noise caused by the coaling system must also be allowed for. Consequently, delivery and removal activities, as well as operation of the coaling system, often have to be restricted to the daytime hours.