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Report | October 2012

AV Krishnan, executive director, BHEL gives .....

AV Krishnan, Executive director, BHEL gives an insight on boiler technology in India

Which are the key boiler technologies in the market? What are their technical parameters (steam cycle, etc)?
Subcritical-Drum type boilers where operating Steam Pressure is below 225Kg/cm2 and Once-through Supercritical boilers where Steam Pressure is above 247 Kg/cm2 are the two key boiler technologies offered in the market.

Up to 2008 BHEL was offering steam generators for power generation in the subcritical segment with unit ratings ranging from 110 MW to 600 MW with turbine throttle pressure of 150 Kg/cm2 for 210/250 MW and 170 kg/cm2 for 500/600 MW units.

After supplying more than 950 boilers, BHEL is currently adopting Advanced Steam Cycles with turbine throttle pressure of 247 kg/cm2 for 660 MW and 800 MW units to improve the environmental and economic performance of IndiaƆs power generation. In addition to this, Circulating Fluidised Bed Combustion technology (CFBC) is offered by BHEL to take care firing of Lignite which is hard to burn in the conventional type of boilers as furnace temperatures are higher than ash fusion temperatures.

CFBC technology is highly handy for efficiently burning low grade fuel such as Lignite, petcoke, washery rejects and host of other fuels.The CFB technology has demonstrated an unparalleled ability to achieve low Nitrogen Oxide and Sulphur dioxide by adding lime powder directly to the combustor.

CFBC technology has been credited with environment friendly operations and high flexibility for fuel variants.In 1999, BHEL has commissioned two units of 125 MW CFBC Boilers for Gujarat Industrial Power Corporation limited at Surat in Gujarat, which was then the largest CFBC plant in whole of the Southeast Asia.

Once again BHEL has proved its mettle by commissioning 250 MW CFBC power plant for Neyveli Lignite Corporation at Neyveli in Tamil Nadu.

This has placed India among a select few nations who have such large scale CFB units along with Germany, USA, China, France and Poland.

Which is the most popular boiler technology currently being deployed in power plants?
Once-through supercritical boiler technology is the most popular boiler technology currently being deployed in power plant.

Here, Supercritical conditions occur when the boiler pressure increases above the critical pressure of 221.2 kg/cm2. In the process, supercritical boilers can ensure that the overall plant can operate at cycle efficiencies improved by 4 per cent to 5 per cent.

In once-through boilers, the water and steam generated in the furnace waterwalls pass through only once, without recirculation.

BHEL striving in its path to offer the best to the nation and customers, after mastering the sub-critical, conventional drum-type boilers, BHEL is now offering Once-Through Supercritical Boiler backed up with the vast experience of the world leader in the field of power equipment, Alstom.

Once-through supercritical technology for higher unit ratings of 660 MW to 1,000 MW offers various benefits including increased efficiency; Lower Fuel consumption; Lower emission levels of CO2, NOX and SOX; Lower operating costs and Greater operational flexibility.

As the demand for coal is ever increasing, it becomes paramount importance to increase the efficiency of the boiler. As such, OTSC boiler with 4 per cent to 5 per cent more efficient than the convention sub-critical boilers is the most preferred one.

Also, Government of India is giving thrust to more efficient technologies for coal linkages, as such utility companies give preference to Once through supercriticalPower plants.

How much was BHEL's boiler sales during 2011-12? What are its boiler capacity addition plans in the next few years?
In power generation segment, BHEL is the largest manufacturer in India supplying a wide range of products and systems for thermal, nuclear, gas and hydro-based utility and captive power plants and providing services from concept to commissioning to meet customer requirements. BHEL supplied sets have crossed 1,00,000 MW, including 75,495 MW of thermal sets maintaining the record of nearly three-fourth of the power generated in India.

BHEL Tiruchirappalli Complex which comprises High Pressure Boiler Plant & Seamless Steel Tube at Tiruchirappalli; Piping Centre in Chennai and Industrial Valves Plant in Goindwal has achieved a record turnover of Rs 14,600 crore during the year 2011-12. For the current year, the Complex is all set to cross a turnover of Rs 17,500 crore.

With 15 manufacturing units, the company has the capacity to deliver 20,000 MW per annum of power plant equipment including 15,000 MW of steam generator equipment. The company ranks among the most important power equipment manufacturers in the world.

What are the new measures being taken to enhance boiler efficiency?
For improving the power plant cycle efficiency, BHEL designs boilers for high pressure; high Super heater and Reheater temperature; and higher feed water temperature.

BHEL is also taking continuous efforts to improve the efficiency of the boilers through various measures. These includes release of minimum flue gas temperature at air heater outlet; minimum excess air at air heater outlet; minimum super heater spray (if tapped off before feed heaters); minimum reheater spray; maintaining minimum unburnt carbon loss; and reduced auxiliary power consumption.

What initiatives/modifications are being carried out in boiler design to enable blending of coal?
Considering the coal shortage in the country and also as per CEA directives, BHEL boilers are designed to consider a 70:30 (70 per cent Indian: 30 per cent imported) blend of coals.

The furnace, superheater/reheater/economiser and windboxand firingsystem design, mill sizing etc are suitably designed by BHEL to handle blended coals. BHEL boilers earlier designed for 100 per cent Indian coals are currently capable of handling blended coals also. Utilities like Reliance Infra (BSES)/Dahanu, Hindustan Zinc Limited, GSECL, etc have successfully blended and fired in BHEL boilers.

What role is BHEL playing in emerging boiler technologies like advanced ultra supercritical and IGCC?
Advanced Ultra super -critical boilers: In order to secure energy security through efficient firing of coal, BHEL has joined hands with Indira Gandhi Centre for Atomic Research and NTPC to design, develop and build Advanced Ultra super-critical boilers under National Mission on Clean Coal Technologies, its ninth under the National Action Plan for Climate Change. The Mission will foster work on Advanced Ultra Supercritical technology, Integrated Gasification Combined Cycle (IGCC) and Carbon Capture and Sequestration, among other areas.

Here, BHEL will design, manufacture and commission advanced Ultra super-critical boilers. Plants operating with Advanced Ultra supercritical boilers can achieve a still higher efficiency than that of plants with supercritical boilers. The MoU was signed on August 26,2010. The power plant design will be made to withstand 300 kg/cm2 and 700oC. This will be developed by the year 2017.

Integrated Gasification Combined Cycle (IGCC) technology: BHEL is one of the few companies worldwide, involved in the development of Integrated Gasification Combined Cycle (IGCC) technology which would usher in clean technology.

It is different from conventional Boiler Technology. In boiler, coal is burnt in a combustion chamber under stoichiometric conditions to produce Steam which operates a steam turbine for power generation, whereas in IGCC, the coal is gasified in a gasifier under sub-stoichiometric conditions to produce Synthetic gas which operates the gas turbine in a combined cycle plant to generate power.

Towards this, a 6.2 MW IGCC research facility has been set-up at the Unit and further field trials at large scale carried are being carried out. The trials done at the research facility reflect typical situation that may come in a larger commercial plants of higher capacities. BHEL has established the relevant technology for gasification of high ash Indian coals and the development is totally in-house.

What is the progress on the IGCC boiler technology in India? When can we expect the first commercial project to be commissioned?
In India, the gasification technology suitable for the high ash Indian coals has been developed totally in-house by BHEL and is ready for commercialisation. In fact, BHEL has taken up establishment of high capacity IGCC power plant as one of its mission projects. With suitable governmental support, as is done in almost all the foreign countries, BHEL will establish the commercial IGCC plant soon in India.

What is the status of R&D on advanced supercritical technology?
To realise the mission of realising much higher efficient boilers than the existing once through supercritical boilers, BHEL has already set up the-state-of-the-art once-through supercritical test facility for developing advanced ultra supercritical technology.

This is one of the six test facilities in the world of its kind. This facility helps to carry out tests at ultra and advanced ultra-supercritical conditions with a maximum fluid condition of 400 kg/cm2, 700oC, mass flux of 3,500 kg/cm2 and heat flux of 1,000 kw/m2.

Welding Research Institute of BHEL which carries out Research and Development on various welding processes and technologies, Metallurgical investigations, dissemination of knowledge in welding and consultancy services is doing the research & development for establishing manufacturing technology of various critical components systems using special materials for advanced ultra-supercritical boilers.

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