The 1980 MW Sipat coal fired power plant is a new generation of plant for India. It is the first supercritical power plant in the country, and has been given ‘Mega Project’ status in the government’s attempt to plug the gap between power supply and demand.
India’s failure to meet its demand shortfall over the last decade has been well documented. The main stumbling block in power sector development has been the poor financial state of many of the state electricity boards (SEBs) combined with slow sector reform. Investment in the sector has consequently suffered, with India seeing the abandonment of many major projects.
Taen supercritical power plant, Korea
There are signs, however, that the country may be turning the corner. At the beginning of 2002, the first foundation stone was laid at Sipat, the largest coal fired plant currently under construction in the country. In addition to being the largest coal fired project in the country, the plant will also be the first in India to use supercritical technology.
The 1980 MW Sipat stage 1 thermal power project, located in Sipat, Bilaspur district in Chhattisgarh state is a new generation of project aimed at helping the government in its effort to increase new generating capacity.
With the Ministry of Power awarding the plant ‘Mega Project’ status, Sipat will become eligible for various fiscal concessions such as zero customs duty, a ten-year tax holiday and exemption from sales tax and local levies, as is given to other mega projects.
Sipat is the first power project of National Thermal Power Corporation (NTPC) to have thermal sets with supercritical parameters. In the private sector, the 3960 MW Hirma mega power project of Reliance Power and Southern Electric USA, is another project which has been planned with supercritical parameters.
Figure 2. The boiler will be fabricated at Doosan’s facilities in Changwon, Korea before being shipped to site
When the revised mega project power policy was announced in 1998, the ministry received several requests from various IPPs including Enron Power Corporation (for its Dabhol project), for recognition as a mega power project. These requests, however, were all rejected. While approving the list of 19 mega power projects, the ministry had taken a decision not to add any new projects to the list. This was because the ability of Power Trading Corporation (PTC) – the sole buyer of power from mega projects – to absorb power from projects was completely dependent on the willingness of states to buy the power at the current rates.
The location of the Sipat plant was therefore an important factor in the plant being given mega project status. Chhattisgarh has large reserves of coal and power plants developed there would produce cheap power. It is also one of the few profit-making SEBs (see box, page 20).
Following a feasibility study, NTPC put out a tender about three years ago for a supercritical plant at Sipat. The plant will consist of Stage 1, three units of 660 MW each; and Stage 2, two units of 500 MW each. The site has been prepared for five units, although three units will be installed at this stage.
Three bidders were short listed for Sipat Stage 1: a consortium of Alstom and Bharat Heavy Electricals Ltd (BHEL); Technopromexport, Russia; and Doosan, Korea. After submitting the lowest bid, Doosan won the contract to supply the steam generators and auxiliaries. Doosan’s project manager, Ho Jun Hyun Doosan commented: “NTPC opted for supercritical technology because of the high efficiency and resulting lower emissions when compared to conventional coal plant. According to our studies, although supercritical plants are 2-3 per cent more expensive in terms of capital costs, by increasing steam pressure to 240 bar at 568à‚°C, plant efficiency is increased by about 1.8 per cent. This translates into about 4 per cent lower coal consumption.”
Doosan also has a great deal of experience with supercritical boilers, with over 10 years of experience with supercritical steam generators in operation at 10 plants in Korea alone.
Doosan will design, manufacture and test the steam generators. These will be built at Doosan’s factory in Changwon, South Korea and shipped to the site. At the site, Doosan will be responsible for testing and commissioning of the boilers and their auxiliaries.
Figure 3. Overview of Sipat supercritical boiler
Local installation of the units will be carried out by an Indian construction company, Larsen & Toubro. The single steam turbine will be supplied by Power Machines of Russia. Balance of plant equipment and power evacuation will be supplied by NTPC and local companies, which will also carry out civil works, etc. The boiler is designed to reduce dust to 200-300 g/m3. This will be further reduced to 40 mg/m3 through the use of electrostatic precipitators supplied by BHEL, India.
Civil work is already underway at the site and structural steel erection work is scheduled to begin in February or March 2005. Erection of pressure parts is scheduled to begin in October this year and hydro testing will begin a year later. Initial firing of the first unit is scheduled for 15 May 2007, with synchronization following four months later in September. Commercial operation of Unit 1 is planned for 15 February 2008. This a total of 46 months from the Notice of Award. The remaining units will come on line at six month intervals after this, with the final unit entering commercial operation in February 2009.
“This is a tight time schedule… and there will be penalties if the schedule is not met. This could be up to 5 per cent of the contract price,” said Hyun.
Currently, Doosan is performing computer modelling during the design phase. Hyun explained: “Although Doosan has 20 supercritical units in operation, we have not had much experience with high ash coals. We are therefore carrying out simulation modelling in the US to measure gas flows and particle distributions etc. Boiler designs will be adjusted according to the results. We expect to finish simulations this year.”
The plant will burn Indian bituminous coal from a site about 40 km away. The coal has medium sulphur content but fairly high ash content (about 43 per cent). According to Doosan, coal with such a high ash content is unique in India and can pose a challenge to boiler designers. “Ash can cause erosion and wear. To counteract this, you have to ensure even gas flows with velocities of about 10 m/s.” Even gas flows will be achieved by the use of flow distribution baffles at the top of the backpass. This will avoid localized erosion. Erosion protection plates will also be used on the erosive area in the backpass. Tube bends will also have shield plates for protection from erosion.
Coal will be transported to the plant by rail. On arrival, it will be stored in the coal yard for use as the primary fuel. Fuel oil will be used for startup of the steam generators, coal flame stabilization and low load operation. The plant is designed to operate in base load with sliding pressure, two-shift operation. This is according to demand which will see high and frequent load swings.
Coal from the bunker is transported via coal feeders to pulverizers, supplied by Doosan, which grind the coal to the required fineness before being fed to the boilers. There are 10 pulverizers per boiler.
The three boiler units are identical although units 1 and 2 have a common stack, while unit 3 has its own stack. Each boiler has 40 burners located in the corners of each boiler at 10 levels. The burners are low NOx tangential burners which limit NOx to a maximum of 260 g/GJ. The burners can also be tilted for easy and quick reheater steam control.
Figure 4. Long life high performance mills
The boilers are of the once-through design and can deliver 2250 t/h of steam at a pressure of 255 kg/cm2 (250 bar) and a temperature of 540à‚°C.
The evaporator is spiral wound, a design which is normally used for supercritical boilers to achieve minimum waterwall flow, which in turn protects waterwall tubes from overheating regardless of the unit size and low load operation. It also ensures even heat absorption along the waterwalls and hence reduces fluid temperature differences in adjacent tubes.
The boiler has a two-pass type layout which is an economic design for a boiler with low height. It also allows economical plant layout. In the first pass there is a three stage superheater and final reheater. The second pass consists of primary reheater and economizer Boiler steam conditions are shown in Table 3. The boiler pressure parts will use high strength alloys and stainless steels which have been field proven in Korea.
The boilers use a startup system and re-circulating pump at low load (below 30 per cent). The startup system ensures sufficient cooling of the economizer and evaporator and maintains the mass flow required for the stability of the evaporator through the use of the re-circulating pump. It also ensures minimum heat and water losses during the startup phase.
Figure 5. Low NOx burners are arranged at four corners
Steam from the boilers is fed to a single 660 MW steam turbine. The turbine is a 4-cylinder unit for supercritical parameters with intermediate steam reheating. Fresh steam pressure is 247 kg/cm2 g at a temperature of 537à‚°C. Steam temperature after reheating is 565à‚°C.
The HP section has two casings and two carriers. The inner casing of the HP turbine (HPT) is fixed in relation to the outer casing by a system of transverse and vertical keys that do not hinder thermal expansion of the casing. The HPT flow path consists of a control stage and 16 reactive-type pressure stages. The connection of the branch pipes of the inner and outer casings is of a telescopic design, sealed with piston rings. The steam is extracted for feed water heating after the second HPT stages and from the HPT exhaust.
The intermediate pressure turbine (IPT) is a double-wall cylinder. Steam is admitted to the IPT through four pipes and four governing valves.
The low pressure turbine (LPT) is a double-flow cylinder having five stages in each flow. Steam is admitted to the LPT through four pipes. The LPT has outer and inner casings of a welded design. The outer casing consists of three sections – a middle section and two exhaust sections. The inner casing is installed in the outer casings with arms and fixed by a system of longitudinal and transverse keys, to allow the inner casing to expand freely.
Figure 6. Tilting burners allow reheater temperature control
The HP, IP and LP rotors are solid forged rotors. The connecting couplings of the turbine and generator rotors are of a rigid design. Safety margins for blading rotor components are designed for shaft over-speed of 20 per cent.
To ensure dynamic and static strength of blading, especially at transient speeds and variable conditions, Power Machines has performed vibration tests on experimental turbine sets and commercial size tests at power stations. According to the company, low levels of dynamic stresses have demonstrated high vibration reliability. The main proof of reliability and efficiency of the steam path, however, has been obtained from extensive experience of operation of the blading used in the turbine. Moving blades of the LPT last stages have been tuned in another machine. Vibration control is necessary for all moving blades for frequencies below 300 Hz.
Moving blades of the HP and IP cylinders and the first two stages of the LP cylinder feature T-shape roots. The third, fourth and fifth stage blades of the LP cylinder feature fir-tree tails. Moving blades of the HP, IP and LP cylinders have integrally milled shrouds. The LPT last stage moving blades are protected from erosion by plates brazed to the blade inlet edges.
The turbine shaft rests on eight bearings, one of which – a journal-thrust bearing – is a spherical self-adjusting bearing. The remaining bearings are not self-adjusting. All bearing shells are made of steel.
Figure 7. The startup system maintains the mass flow required for the stability of the evaporator startup
The HPT and IPT shaft glands and diaphragm seals are elastic, labyrinth seals. LPT glands are of the straight-through elastic type. The segments of sealing rings with sealing strips are spring-loaded with flat springs. Gland holders ensure alignment is maintained during turbine warming. Turbine equipment supports are designed to maintain their structural integrity when subjected to seismic loading. Maximum seismic acceleration at the upper plate of the turbine-generator foundation for which the equipment is designed to keep its structural integrity is 0.35g.
Delivery of the steam turbine is scheduled for 2006, well ahead of initial firing of the first steam generation in May 2007.
An important step for India
The Indian Ministry of Power has set itself a target of electrifying the remaining 80 000 villages in the country by providing power for all by 2012. This will require an additional 100 000 MW over the current (2002-2007) and next (2007-2012) Five Year Plans. During the first Plan, 41 000 MW is planned – 22 500 MW from federal government-owned companies, 11 400 MW to be built by SEBs and the remainder by the private sector. During the second Plan, a further 49 000 MW is required and, according to the Central Electricity Authority, there will be strong emphasis on hydropower.
As the first power station in India to have a single unit with a capacity of more than 500 MW, the government has declared Sipat as the Model Mega Project in India. Hopefully, the project will instil confidence in the Indian power sector by demonstrating that large advanced technology projects can be built successfully and to schedule in the country.
Chhattisgarh: a hub for India
Chhattisgarh is in an ideal position to play a pivotal role in India’s plans for adding new generation. Development plans may focus on cheap, pithead power-producing states like Chhattisgarh, which has the potential to produce up to 50 000 MW.
On 3 March, 2001, in a meeting of chief ministers on power sector reforms, the Indian prime minister welcomed an offer from the state minister for Chhattisgarh to become the power hub of India. This offer is now becoming a reality. NTPC has since begun construction on the Sipat Super Thermal Plant and another 600 MW plant in Korba. Several other states are also interested. Power will be wheeled to the respective states. Private sector MoUs total another 1500 MW and more projects are in the pipeline.
Chhattisgarh has an excellent power export infrastructure. It can transport and sell power to deficit areas in any part of India. The Chhattisgarh State Electricity Board (CSEB) levies minimal wheeling charges. An added reason for investing in Chhattisgarh’s power generation sector is what the state describes as a “progressive power policy, that allows third party sales to buyers outside the state, with or without wheeling from CSEB”. This also overcomes the usual escrow/guarantee bottleneck.
CSEB is one of the few profit making SEBs. Power sector reforms are underway in Chhattisgarh. The ‘user-pays’ regime has been adopted, meaning there is no free power in the state. Subsidies, where applicable, are targeted. The process of tariff rationalization is in place and a project to achieve 100 per cent electronic metering has been started.
The state has 44 per cent forest cover; even so, Chhattisgarh Environment Protection Board pursues proactive policies so that power generation is environmentally sustainable. Non-conventional energy sources have been accorded very high priority. A special agency called CREDA (Chhattisgarh Renewable Energy Development Agency) has been set up, and over 1200 villages in dense forests are being electrified using off-grid energy. Micro hydropower potential is also being tapped in a big way, and several projects have been identified for viable private investment.
Labour relations are very cordial in the power generating plants, with man-days lost being the lowest in the country. Private sector power generation investors are welcome as Chhattisgarh is inviting investment in greenfield power projects with the cheapest cost of production in the country.
The government has claimed it sees “Chhattisgarh emerging as the power hub of India, with the capacity to cover half the demand-supply gap in the entire country”.