5. Emission Reduction Measures

  Successful measures used to reduce local air pollution in urban areas have included the regulation of fuel for domestic heating (e.g., low-sulfur oils and coals) introduction of natural gas instead of coal and oil, development of district heating, and restrictions to the use of cars in city centers. Furthermore, fly ash and dust removal installations in industrial sources and large boilers have resulted in major improvements, while cost-effective energy conservation measures and the substitution of fossil fuels for renewable energy sources offer further potential for the reduction of emissions.

These measures have been particularly successful in reducing SO2 and particulate concentrations in the air. However, there has been little evidence of similar downward trends in NOx concentrations.

5.1. Technological measures
  Many countries have begun to pass more stringent air quality regulations which require improved efficiency in pollutant removal. Technologies that ensure the removal of these pollutants and develop by-products from them, besides dealing with the sludge produced, are likely to grow in importance.
Flue Gas Desulfurization The technology most commonly used to remove SO2 is known as flue gas desulfurization (FGD). Desulfurization of stack gas is commonplace in Japan, the US and Germany. In Japan, more than 1,800 such units operate alone. This is largely because of the strict emission regulations whereby a tax is imposed on a factory that emits even below the SO2 standard. As a result, FGD facilities have been installed even for small boilers. Fewer numbers of FGD units are used in the US owing to its less stringent air pollution standards.
Dust Removal The most commonly used dust-cleaning systems are "dry types" - electrostatic precipitators and bag filters. Not only in the SILAQ countries but across the CEE region, these have most commonly been used in recent years in the metallurgical and energy sectors. The "wet-absorption type" systems are most commonly found in the chemical industries, where recycling of absorbent is possible or further technological treatment is applied to extract and/or use some of the components or by-products.

It has been shown that the efficiency of electrostatic precipitators in the SILAQ countries is relatively high with a cleaning rate in the range of 97-98 percent. When bag filters are used as alternatives to electrical precipitators, the dust content far exceeds EU standards and is usually it is within the range of 5-10 mg/m3 . The wet dust type cleaning systems can give better results, but problems with secondary pollution and the use of by-products can result in the need for further treatment.

The selection of an air filtering system should therefore consider a number of separate issues, the most important of which include:

  • Selection of dry or wet type cleaning systems (sorbent or chemosorbent type), and in particular the cleaning rate, cost, selectivity, capacity, heat balance, availability of sorbent, etc;
  • Selection on the basis of implications from possible secondary pollution such as wastewater discharges, waste suspension or solid wastes;
  • Selection on the basis of the by-products released and the possibility for their direct use, recycling, and other means for utilization, disposal costs, environmental and human risks;
  • Selection of a total universal cleaning system that offers opportunity for the removal of most or all harmful components from waste gases - SO2, NOx, dust etc.

Preventive Measures Besides "end-of-pipe" technologies there are also other ways to reduce the air pollution caused by combustion processes. Such examples include:

  • Changing the fuel mix, and using additives;

  • Increasing the conversion efficiency;

  • Introducing low emission combustion or conversion processes;

  • Fuel cleaning.

Flue gas cleaning systems have been implemented world-wide and such systems have been introduced more recently in the SILAQ countries. The feasibility studies performed and national environmental action plans all target considerable investment in the coming years for such systems. A list of the conventional air cleaning systems are given in Table 14.
TABLE 14: Conventional Air Cleaning Systems
Process type Removal target: By-products Problems, Remarks
SO2 SO3 NOx
WET WORKING
   Lime-Limestone YES NO NO Gypsum, CaSO3/CaSO4 Demand for Gypsum
   Magnesium Hydroxide YES NO NO MgSO4, SO2, MgO Availability of sorbent
   Lime-Fly Ash YES NO NO CaSO3/CaSO4/Fly Ash Demand for the by-product
   Dual-alkali: primary - NaOH
secondary - Lime and Limestone		 YES NO NO CaSO3 / CaSO4 Demand for the by-product
   Sea water YES NO NO Wastewater Availability of sea water
   Wellman-Lord Na2SO3 YES NO NO S, SO2, H2SO4 Cost of sorbent, corrosion
   Ammonia scrubbing, GEESI Process YES YES NO NH4/2SO4 Corrosion, wastewater
   LINDE, C10H22O5 YES YES NO S, SO2, H2SO4 Expensive sorbent
   ispra-MARK 13A-Bromine YES YES YES H2, H2SO4 Expensive sorbent
   Hydrogen Peroxides YES YES YES HNO3 and H2SO4 Expensive sorbent
   Wet electrostatic precipitator NO YES NO Wastewater Need for caustic and wastewater treatment
SPRAY DRYING
   FLAKT Lime injection YES YES NO CaSO3/CaSO4/Fly Ash Demand for and utilization of the by-product
   ROCKWELL, Na2SO3 YES YES NO Na2 SO3,/Na2SO4, Fly Ash Utilization of the by-product
DRY WORKING
   UHDE/BPV Activated Carbon YES YES YES S, H2SO4, SO2 Expensive sorbent
   DAS/CDAS, Limestone, Lime and slacked Lime YES YES NO CaSO3/CaSO4 and Fly Ash Utilization of by-product
   Electron Beam YES YES YES NH4/2SO4 and NH4NO3 Energy consumption

  The performance targets of flue gas cleaning systems vary considerably, while different kinds of plants and the requirements regarding SO2 removal efficiency will also have a bearing on the results of such processes. The type and composition of the fuels are further factors that can affect performance. Table 15 summarizes the various levels of SO2 found in the flue gases of different kinds of thermal power stations. Among other issues to be considered when selecting an FGD unit are the operational costs, environmental and health benefits, and whether any other similar actions have already taken place.
TABLE 15: Sulfur Dioxide Content in the Fuel Gases of Worldwide Thermal Power Stations
Country Location Flow rate Nm3/h Content SO2 ppm
Bulgaria Maritza East 1,500,000 5,500
Germany Heilbrunn 1,225,000 1,125
Germany Goldenberg 1,680,000 1,820
UK Drax No. 1 1,680,000 1,546
USA Georgia Power 2,534,000 1,800
Czech Republic Prunenov No. 2 1,100,000 2,600
Poland Polaniec No. 5 2,200,000 1,225
Croatia Plomin PS 830,000 1,480
China Luohuang 1,087,000 3,700
Japan Matsuura 2,450,000 993

  Such variations in flue gas concentrations are related not only to SO2 content, but also to water vapor, SO3, NOx and other pollutants. Being aware of the level of such contents is essential for optimizing the performance of the cleaning systems, and therefore feasibility studies are of great importance for successful project implementation.
SILAQ Practice Within the SILAQ countries, different cleaning systems are operating or are in the process of being implemented. Wet working lime-limestone systems tend to be more commonplace, however dry cleaning systems tend to offer a number of clear advantages, indicating interest in these systems in the near future will grow. They do, for example, meet those standards otherwise achieved through "clean technologies" and are consistent with the goals of sustainable development.

Further studies concerning the efficiency of newly implemented installations in the SILAQ countries and others in the coming years may help to show new trends and indicate the values of certain cleaning systems over others. For example, while common in the US, gas reburning and sorbent injection methods, either separate or combined, are not widely used in the SILAQ countries. While they might be advantageous, the application of gas-reburning and integrated technologies would require modification to existing power plant equipment and the related capital and operating costs would have to depend on a number of site-specific factors. Some data related to the performance and cost of such systems is given in Table 16.
TABLE 16: Nominal Performance and Costs of Gas Reburning and Integrated Technologies
System type Emission control, % Cost factors
NOx SO2 Capital cost
(USD/kW)		 Capital and operating costs
(mills/kWh)		 Pollutant removal
(USD/ton)
Gas Reburning (GS) 60 18 30 2.8 254
Gas Reburning - Sorbent Injection (GR-SI) 60 50 90 8.0 388
Gas Reburning - Low-NOx Burners (GR-LNB) 70 18 50 3.3 270
Based on 1 USD/106 Btu coal to gas differential
Source: Clean Coal Technology , NO3, September 1993

   
Capital Requirements It is obvious that feasibility studies should be made on a case-by-case basis since the economic efficiencies of all the available technologies may vary widely. This could be the focus of future SILAQ studies.

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