It's not exactly a glamorous piece of equipment. But in industrial locations notorious for high levels of pollution - especially of suspended particulate matter (SPM) - the installation of Electro Static Precipitator (ESP) makes life that much less messy for the residents, as it controls emissions of the particulate

per cubic metre to 115 mg per cubic metre, the HWB had few options but to initiate a search for new technology. As things had stood, the ESP at its coal-fired captive power plant at Manuguru, Andhra Pradesh, had a serious problem in bringing emissions down to even the 150 mg per cubic

to some improvement, they failed to yield the desired results. Moreover, the Ashworth system was highly capital intensive, and the Board was looking for a cheaper solution. And so, Dr R.R. Sonde, chief engineer, process, at Heavy Water Board's Mumbai plant, was put on task. Sonde conceived of an alternative ammonia dosing method. The ash characterisation in the lab indicated that ammonia would be the right choice for maintaining the appropriate resistivity. "Several trial runs showed that ammonia dosing with the ESP fine-tuning yields

matter from the coal-fired boilers. Unfortunately, precipitator efficiency depends on the coal quality and the resistivity, an electro-chemical property of ash. If ash resistivity is high the collection efficiency of the precipitator is low, because the ash particles, which are not adequately charged, move sluggishly towards the electrodes.

This is not a favourable situation for India, which has high coal reserves but of low quality and high ash content. Much of the country's power is produced from the coal fired thermal plants, which are a cheaper source of electricity.

SPM levels as low as 20 mg per cubic metre, which is lower than the USEPS norm of 30-50 mg, depending on the location," saysSonde.

How does the solution rank cost-wise? Says Sanjay Trivedi, managing director, Chemithon Engineers Ltd, an Indian subsidiary of US $225 million Chemithon Group: "There are several solutions, of which this is the cheapest. For example one option would be to add a new ESP that would require an investment of Rs25 crore to Rs30-crore for a power plant of 200 MW. A retro-fitting option, on the

However, with ever stricter particulate emission norms, thermal power plants have been falling out of favour. This may now change.

Controlled ammonia injection technology, recently developed at the Heavy Water Board (HWB), Department Of Atomic Energy, will, if adopted, entirely change public outlook towards thermal power plants, known for their uncontrolled fly ash emissions. Provided, of course, that the technology delivers what it promises. It claims to reduce suspended particulate matter from 650 to 700 mg per cubic metre to around 20 mg per cubic metre — lower than the US Environmental Protection Standards.

When the Andhra Pradesh Pollution Control Board (APPCB) lowered the old SPM emission norm of 150 mg

metre standard. Actual performance was in the range of 300-700 mg per cubic metre. It was, clearly, time to research a solution.

"The review pointed towards a low resistivity of the ash particles as the main culprit for the poor performance of ESP," says H.S. Kamath, chairman and chief executive, HWB. An exhaustive literature review was done as a first step towards understanding the resistivity problem. The search led to a paper presented by Ashworth et at at the joint ASME-IFEE Power Generation Conference in 1992, which concluded that with flue gas humidification, the ESP efficiencies could be improved to over 99.8 per cent.

While the experiments based on these findings at the Manuguru Plant did lead

other hand, would require investments of Rs7 crore to Rs10 crore for a power plant of the same size. An alternative approach would be to go for single conditioning by chemical dosing, either by mixing sulphur trioxide or vapourised ammonia with flue gas. In which case, there would be just the mixing cost and nothing else. With the former, this would be Rs2.5 crore to Rs3.0 crore and with the latter, Rs1 crore."

Chemithon, which specialises in sulphur trioxide dosing, has signed an MoU with the Heavy Water Board to commercialise the technology in India. Meanwhile, the Board is applying for an international patent. At the current rate of projected power sector growth, the annual business potential for the technology is estimated at Rs30-35 crore. In terms of pollution control, the technology could prove invaluable.