Its All About Power Sector

For a country like India where major generation is based on thermal units and where coal is being used as a fuel source, the need to control the emissions is a necessary for future generations to sustain on the same technology. The control over emissions from burning coal can only be improved with use of better technologically sophisticated equipment that can improve operational efficiencies of power plants. In this view a brief of the supercritical technology implementation in India is detailed below.

The critical point of water is defined as 220.6 bar & 374°C. The power plants operating above this point are called Super Critical Power Plants and the power plants operating below this point are called Sub Critical Power Plants. At super critical parameters, the Latent heat of Vaporization is Zero, hence, water directly becomes steam without boiling.

Power Plants operating at Super Critical parameters have higher efficiency compared to that of Sub Critical plants and therefore have lower Emissions and lower specific Fuel consumption.Conventional sub critical steam power plants operate at a steam pressures in the range of 170 bar or below. The new generation Super Critical power plants of NTPC operate in the pressure range of 247 kg/cm2 and temperature of 565 to 593°C.

World Scenario in Implementaion of Super Critical Technology: Supercritical power plants first came into commercial operation in the US and they employed very ambitious steam parameters. (110 MW Philo 6 came online in 1957, retired in 1975 and had main steam turbine inlet pressure of 316.4 kg/cm2 (4500 psi) and Temperature of 621°C (1150°F). Eddystone 1 (in 1960), a 325 MW unit with main steam turbine inlet pressure of 352 kg/cm2 (5000 psi) , temperature of 649°C (1200° F). About 160 plus supercritical units came in the US during 1960s and 1970s. Commercially best available technology today employs temperature in the range of 600°C to 620°C with highest parameters for modern plant being used in Japan and Europe. Japan and Europe are the clear leaders in the material technology commercially available in the market. World leaders in adoption of super critical units are the US, Japan, China, Germany, countries of former USSR, South Korea and Italy. Former USSR constructed several units of 300 MW capacity with Supercritical parameters and had maximum total installed capacity of Supercritical units. Europe was developing materials suitable for 700°C class under AD 700 program - which has not been abandoned. US launched its own program (DOE, EPRI and Ohio Coal development office) to develop materials suitable up to 1400°F (760°C) class. Today majority of coal fired plants in the world are sub-critical, however by a rough estimate more than 500 units representing an estimated 300 GW (22% of total capacity) utilised super critical and Ultra Supercritical steam conditions by the end of 2007.

Power Plant Technology in India so far: Power generation in India is dominated by thermal power generation, which is predominantly based on sub-critical coal fired technology. Efficiency of a coal based unit strongly depends upon the steam parameters being used. With sufficient operating experience gained through operation of 500 MW sub-critical units in the country, newer units based on super critical parameters were commissioned in India during the XI plan.

Advantages of Super Critical Technology: Capital cost of a super critical plant is higher than that of sub-critical plant due to its higher operating pressure and also because of use of superior materials in boiler and turbine. This additional capital cost may be offset by saving in fuel cost. If the fuel cost is high, then saving due to efficiency improvement is more. This saving in operational expenses may compensate the increased capital expenditure of supercritical units. Further techno-economy for supercritical units may be achieved by increasing the unit size. Further, modern super-critical plants are also known tohavebetter load following capabilities as once-through design of these boilers have fewer thick section components than the conventional drum type boilers used for sub-critical plants. The cost of a super critical plant is approximately 2-3% higher than the cost of a conventional plant.

Supercritical Units in NTPC: Looking at the global concerns on CO2 emissions, NTPC took initiative to introduce supercritical technology for power plants in India. Under this effort NTPC ordered 660 MW super critical units for Sipat-I and Barh-I in 2003-04. The steam parameters adopted for these plants were 247 Kg/cm2 / 537°C / 565°C - as against 170 kg/cm2 / 537°C / 537°C. This resulted in turbine heat rate improvement of about 10% over that of Singrauli-I (5x200 MW).

NTPC has further raised the steam parameters for Barh-ll units and the upcoming supercritical units under 660 MW and 800 MW bulk tender to 247 Kg/cm2 / 565°C / 593 °C. This will result in turbine heat rate improvement by about 12% with reference to that of Singrauli-I (5x200 MW).

So far, NTPC has commissioned three super critical units of 660 MW at Sipat-I and synchronized first super critical unit of NTPC with higher steam parameters of 660 MW at Barh-ll (2x660 MW).

With abundant coal reserves, coal has been and is likely to remain mainstay fuel in India for power generation for many more years to come. Therefore, in order to further address the challenge of Global warming and fast capacity addition at affordable price, it is essential to install coal based plants with further elevated steam parameters leading to adoption of advanced and ultra supercritical units in the country.

Material Development for Ultra Supercritical: The main barrier or enabler for Supercritical and Ultra Supercritical plants has been development of high temperature materials. World wide research has resulted in numerous high strength steels and alloys for heavy section piping, boiler tubes, and steam turbine rotors.

Low alloy carbon steels have proved their worth for sub critical units with temperatures upto 540°C. Newly developed high creep strength martensitic 9% to 12% chromium steels such as P91, P92 (NF-616) and P122 (HCM 12A) used for thick section boiler components and steam pipes - are the key new materials that have enabled supercritical units to operate at temperatures approaching 1100°F (593°C). Research, development and demonstration programs underway in Europe and Japan aimed to produce materials capable of withstanding 1300°F (700°C).

Government of India also launched Mission 2017, a program to develop Advance Ultra Super Critical (Adv-USC) technology for power plants operating at 310 kg/cm2 and 700°C steam parameters with indigenously developed materials and equipment. Mission intends to utilize core strengths of organizations such as IGCAR (Indira Gandhi Centre for Atomic Research), NTPC and BHEL. Co-operation from other national/international consultants/institutions/laboratories will be sought, as required. After development of Adv-USC technology, mission proposes to establish an 800 MW Adv-USC Demo plant based on indigenous technology. Mission has a time frame of seven years (2.5 years for R&D and 4.5 years for setting up of Demo plant) from the time the funding for the project is cleared by the Government of India.

Indigenous Supercritical Manufacturing Capacity Building: Government of India envisaged Bulk Tendering of Steam Generator and Steam Turbine Generator of various projects with an objective to develop indigenous capability and capacity for manufacturing of supercritical units in the country. In this regard Ministry of Power conveyed to NTPC the approval of Government of India for induction of supercritical technology through bulk ordering of supercritical units.

The Gol directive outlines important eligibility criteria for the boiler and turbine bidders. As per the directive, setting up of manufacturing facility of supercritical units in India is a mandatory condition for the bidders desirous of participating in the tender. The directive puts great emphasis on creation of manufacturing facilities in India by the technology providers/Original Equipment Manufacturers (OEM), either through a Subsidiary/JV Company incorporated in India or through an Indian licensee. These efforts resulted in establishment of multiple players each in manufacturing of supercritical boiler and turbines in India based on above initiative of Gol, NTPC has so far issued tenders for 11 units of 660 MW and 9 units of 800 MW, out of this orders have been placed for 11 units of 660 MW (9 for NTPC and 2 for DVC) and 7 units of 800 MW (all for NTPC).

Issues relating to super critical technology: The challenge is not to install the super critical power plant but to operate and maintain it with high availability. About 160 plus supercritical units came in the US during 1960s and 1970s. After that the supercritical technology suffered the setback due to problems associated with material suitability for such high steam parameters.

With increase in coal cost and emphasis on climate issues, Super Critical technology is attracting renewed interest and adoption of super critical technology in India is also gaining momentum. Nearly 50% of the total capacity to be installed during XII plan and nearly 90% of the capacity addition during XIII plan is expected to be from supercritical. Bulk tendering of super critical units with an aim to develop indigenous manufacturing capacity for super critical units and Mission 2017 to develop indigenous advanced Ultra Supercritical technology are the steps taken towards the challenge of faster capacity addition and mitigating global warming concerns.

Source: Cerebral Business Research Pvt. Ltd