The Hindu Business Line : Greening coal-fired power plants

India could have been at the forefront of developing technologies to enhance the combustion efficiency of coal-fired boilers. Due to inadequate support from industry and the utilities, such improvements did not take root.

It is imperative for technologists and policy-makers to see what best can be done to use coal and yet minimise pollution.

M. R. Ganesan

India needs to add power capacity — lots and lots of it. Since the cheapest and most abundant fuel we have is coal, its use for generating electricity is a reality that cannot be wished away, despite environmental concerns. Given this, it is imperative for technologists and policy makers to see what best can be done to use coal and yet minimise pollution. The heart of a power plant is the boiler, which is also where the pollutants from fuel, unless captured, make the ir way into the atmosphere.

Obviously, there are two ways to reduce emissions — burn less coal per unit of electricity generated and use technologies to capture pollutants.

RAISE EFFICIENCY

Efficiency increases — less coal for the same output of electricity — can be achieved by raising the temperature and pressure of steam in the boiler. While supercritical technology is now making some headway into India, the country needs to leapfrog the technology range to those that give much higher efficiencies. Ultra supercritical technology, with steam parameters of 300 Bar and about 600{+o}C are now established, but technologists are working on ‘advanced ultra supercritical technologies’, where the steam temperature is about 750{+o}C. For every 20{+o} increase in superheat temperature, the plant efficiency improves by one percentage point.

However, raising pressure and temperature of steam in the boiler is not without its challenges. Austenitic steel with high chromium content and nickel-based alloys are required to withstand the stresses due to very high pressure and temperature. In addition, these must be resistant to high corrosion and have good wieldable and formable characteristics. This is another area where India can take the lead in developing the technologies concerned.

BURN COAL COMPLETELY

The boiler is at the epicentre of the ‘emission conundrum’. To burn coal completely, you need to admit more air into the boiler so that there is sufficient oxygen for thorough combustion. But when you introduce air, the nitrogen in the air forms nitrous oxides. So what do you do? Admit only oxygen into the boiler, instead of air, right? Then, you would have to factor in the economics of separating oxygen from the air. Experts have estimated that separation of oxygen from air chips away as much as six percentage points out of efficiency. Yet, looking at it from an environmental angle, it is worth it.

A good way to address this is to mandate the integration of a renewable energy project with a coal-based project. For example, a 1,000 MW coal-fired power project could be asked to put up, say, a 50 MW wind project, if possible at site, or otherwise elsewhere. For sure, there is a cost to it, but it should be viewed as the cost of cleaning up the environment. Oxy-firing is clearly an area that India could lead in research. Another area for research is the improvements that can be made in fluidised bed combustion (FBC) and circulating fluidised bed combustion boilers (CBFC). In these boilers, air is pumped in at the bottom and the coals ‘bubble’ in mid-air, which helps in complete combustion of the fuel.

While this technology is by no means new, the capacities are on the lower side. The biggest CFBC boiler in the world with supercritical parameters is that of Foster Wheeler in Poland, with a capacity of 460 MW. CFBC boilers of 300 MW size are prevalent in the US.

CFBC boilers have considerably lower combustion temperatures and hence are not suitable for ultra supercritical system applications. India should take the initiative to develop supercritical CFBC technologies to fire lower grade fuels leaving better coal to be fired in conventional supercritical systems.

MISSED OPPORTUNITIES

Bharat Heavy Electricals Ltd was once in the vanguard of developments in FBC technology. If the company had persisted with its research, it would have been the world leader in not only FBC, but also CFBC technology. This did not happen because there was no patronage, or support, from the utility /industry sector. Consequently, India has to still depend upon overseas companies for CFBC technology.

The mistakes of the 1970s should not be repeated in supporting IGCC technology-based power projects. BHEL initiated research activities on IGCC during the early 1980s and has been running a small-scale (6.5 MW) demonstration plant in Tiruchirapalli for several years. BHEL has successfully developed pressurised fluid bed gasification technology to handle high ash coals. Yet there have been no takers for this.

With part-funding from the Union Government, APGENCO and BHEL recently came forward to install a commercial scale 185 MWe IGCC system. But it is understood that even after a year of the agreement between APGENCO and BHEL, work is yet to begin on this project. Elsewhere in the globe, development activities commenced during the 1980s ;today a couple of 250/300 MWe IGCC plants have been in operation for over a decade. A 900 MWe system is in design stage.

JOINT EFFORT

India is presented with a splendid opportunity to seize the technology initiative and become a global leader in certain technologies, thanks to the de-carbonisation of the global economy. For this, it would require joint efforts of major companies. It is imperative that various ministries, steel companies, power equipment manufacturers and power utility companies, join hands for collaborative research into areas like metallurgy and emissions, with the objective of achieving energy security. The results of the research would be useful chips while India negotiates at climate talks. While a concerted effort to home-grow technologies is imperative, it is equally important that once developed, such technologies are adequately supported, perhaps with government support.

If the users keep asking for reference plants, be it Advanced SC systems, CFBCs, or IGCCs, we will get nowhere. After all, the pioneers of any technology are able to progress because somebody used their technology placing trust in them.

(The author is a former Executive Director, BHEL. blfeedback@thehindu.co.in)

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