PRECIP 
NEWSLETTER 

December 2009
No. 407

In recent years, the power industry in India has been developing quickly. The total installed capacity, which was slightly more than 100,000 MW in 2001, is expected to reach around 215,000 MW in 2011. At ICESP XI, Lin Guoxin, Fujian Longking Co., Ltd., China, noted that this means an increase of about 6000 MW per year in India.

So far, 95 percent of the Indian coal-fired boilers are equipped with electrostatic precipitators. In 2005, the dust emission standard for 210 MW sized plants and above was 150 mg/Nm³. At that time, among the 83 coal-fired power plants, 27 plants, or about 32.5 percent, had emissions which did not meet the required standard. The current emission standard in India has since been raised. This shows that there is a substantial ESP market in India and at present, quite a number of Chinese enterprises are undertaking construction of coal-fired power plants there. As a result, Chinese environmental protection enterprises have also entered the Indian market. They must face the problem of how to solve the emission problems from firing Indian coal, which can generate ash that is difficult to collect.

For example, Balco Power Plant, which belongs to Bharat Aluminum Co., Ltd. is located at Korba in India. There are four units of 135 MW each, which were supplied in succession from 2005 to 2006. Due to the difference between the burned coal and the designed coal, the original ESP was unable to meet the required emission standard. In order to solve the issue, an SO₃ conditioning system was installed in March 2007. Although the emissions were reduced, in most cases they still exceeded the stipulated requirement.

The design SCA for the ESP at the Balco plant was 120 m²/m³/s of flue gas flow. This was far from the 180 m²/m³/s that should have been designed for the actual conditions. Inadequate SCA was the major reason for poor performance.

Flue gas conditioning (FGC) can enhance the performance of ESPs. Testing with SO₃ and NH₃ was conducted at the Balco plant. The test results showed that the outlet particle concentration was reduced by 50 percent when using SO₃ alone and by 65 percent when using both SO₃ and NH₃. Practice thus indicates that flue gas conditioning can improve the performance of an ESP collecting Indian coal ash. However, the improvement has a limit. It is necessary to have a certain minimum SCA before FGC can help to actually meet the emission requirements.

Fujian Longking began to study an ESP combined with a fabric filter in 2003. It consists of two parts in series, an ESP area at the front and a filter bag area at the rear. The structure is known as an Electrostatic Fabric Organic Integrated Precipitator (EFOIP).

In this process, dust is charged and most of it is collected in the front electrostatic precipitator area. The amount of dust entering the filter bag area is small in quantity but fine in size. As a result, the gas flow resistance in the filter bag area is largely reduced, the cleaning period is extended much longer, and the abrasion of the filter bags caused by scouring of coarse grain can be avoided. Practice indicates that the outlet particle concentration of EFOIP is less than 50 mg/Nm³ and the life of a filter bag is longer than four years. However, filter bags require a lot of maintenance.

Capital investment and operation costs depend on the mode of dust removal and precipitator size, as well as coal characteristics. For example, consider a 500-MW unit fired with typical Indian coal. Because of the typical Indian coal used in this project, with 0.25 percent sulfur content, high silica and a high inlet particle concentration of up to 97.7 g/Nm³, it is necessary to use an ESP with an SCA larger than 200 m²/m³/s of gas flow. This requires 4 parallel ESPs each with 2 chambers and 8 fields, with gas velocity lower than 0.65 m/s. If FGC plus the ESP is adopted, considering the limitation of SO₃ conditioning for achieving the 100 mg/Nm³ outlet requirement, the plant would need to use 6.5 fields of the above-mentioned ESP as the basic requirement. If EFOIP is adopted, it only needs to keep 2 fields of the above-mentioned ESP, and use 2.5 fields of space as the filter bag area. When compared with the above-mentioned ESP, an investment of 3.5 fields ESP can be saved. Therefore, the capital investment of EFOIP is the lowest and the ESP is the highest.

As for operating costs, considering power consumption, sulfur consumption and maintenance costs, the three modes of dust removal are comparable. Large maintenance for the filter bags and troubles of replacement are the disadvantages of EFOIP. However, EFOIP can assure performance of dust removal on economic terms.

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