Gas turbines could be the technology of choice for the future as the laws on emission standards get tougher by the day.
Gas-based power capacity addition in India has been hit badly owing to factors like ù the cost of power, cost of transporting gas, and non-availability of gas. A decade back there were major initiatives by different stakeholders to put up gas-based power plants thinking that the fuel will be available in plenty from domestic production. The matrix changed when the domestic output dipped considerably and running the plants on imported fuel making it expensive.
Natural gas is a clean fuel as compared to coal. A developing country like India depends mostly on thermal power plants, particularly coal-based ones, to meet its ever growing power demand. While coal-fired power contributes to 61 per cent of the energy mix of the country, gas-based power contribution is only 9 per cent. According to the Central Electricity Authority (CEA) data as on 31 March 2016, the installed gas based capacity in the country is 24,508 MW. And if we go by reports, close to 15,000 MW of gas based plants are stalled. Reduction in domestic gas output is stated to be the major reason for this. The gas-based power being more expensive than the coal-fired one, utilities are keeping away from the former. It is true that power is available for `3/ unit for short term contract through the year. It is natural for utilities to overlook the more expensive gas based power. The government said in a report, ´Considering the drop in production of domestic natural gas, plant load factors (PLFs) of about 54.5 per cent in 2012 of gas-based plants has come down. How CIL is set to go fully digital ver, it is expected that the situation is likely to improve in the coming years/ decades.´
The effect of all this had trickled down to the turbine/ component manufactures. In the second half of the last decade when gas-based capacity additions were awarded, the equipment/ turbine manufactures in the country have ramped up their capacities. The segment is dominated by the state-owned Bharat Heavy Electricals Limited (BHEL).
The boom in power capacity addition that started in 2006-2007 has resulted in formation of the numerous joint ventures. Domestic companies like JSW, L&T, Thermax and Bharat Forge joined hands with the global giants like Toshiba, MHI Boilers, Babcock & Wilcox Energy Solutions and Alstom respectively resulting in an average investment of Rs.5,000 to Rs.7,000 crore. These companies have a combined capacity of 16,000 MW, with BHEL having similar capacity, which is completely under-utilised. A total of 36,000 MW of equipment capacity is available in the country at present.
Before the 2008 global financial meltdown, India had robust economy which was growing close to double digits. To support the economic growth, the Central Government has decided to allow private sector companies to develop power generation capacity in India. That boosted additions to the power generation capacity to 10,000 MW per annum in the beginning, and gradually to the current 20,000 MW per annum levels. When the domestic companies failed to meet the equipment demand, Chinese and Korean companies filled the gap.
And this boom time triggered the formation of major JV´s and investments in power equipment segment. By the time the capacities came up, the scenario had changed completely, and the demand for electricity fell considerably.
The companies which have put up the facilities have been on a wait and watch for the last couple of years hoping for a revival.
ôWe are unlikely to see a revival of fortunes for the gas-based power plants in the near future. Trends are not in favour of expensive power at least for the next three years. The revival will largely depend on the initiatives taken by the government to encourage gas-based power production,´ said Prakash Gaurav Goel, Research Analyst - Utilities, Coal and Fertilisers, ICICI Securities Ltd.
Gas-based power is stable and cleaner than coal. Globally, there is an urge for clean energy and thus reducing emission. This global initiative is intended to fight the impending danger of climate change. India is world´s third largest emitter of Green House Gases (GHG) after the US and China.
And power plants lead the list of major pollutants in the country. In the month of October 2016, India has been party to a global decision in mitigating climate change by ratifying the Paris Accord.
The country has taken major steps in mitigating climate change sources by promoting generation of power from green sources like wind and solar. However, these energy sources are non-dependable and the output is inconsistent.
The government had earlier planned to integrate gas-based power plants as gap-fillers for the inconsistent renewable energy.
But this plan failed to take-off. About 90 per cent of the power demand comes from the domestic consumers, while 10 per cent comes from the city commercials. One of the major challenges faced by the utilities is the peaking power issue. ´Gas plants are considered to be the best solution to address the peaking power issue - a) These plants can be used at any time of the day or night as it is easy to switch-on and switch-off; b) Islanding is possible; c) these can be put up anywhere, even in the middle of a city (small size) as there is very low pollution,´ added Goel.
The other possibility of a revival in gas plants is, if the global commodity prices spiral back to higher levels: crude back to above $150 and coal $200. In such a scenario, the price of gas-based power will be equivalent or less than the coal fired one. That will trigger a faster bounce back for gas power plants in India.
While the research firm Markets and Markets in one of its report said that the global gas turbines market is expected to clock a compounded annual growth rate (CAGR) of 3.9 per cent from 2015 to 2020, from the value of US$15.9 billion in 2014.
Frost & Sullivan, another consulting firm puts the global gas and steam turbine Markets to touch US$43.5 billion in 2020, from over US$32.5 billion in 2013.
The power equipment manufacturing capacities in the country are intended to cater to the domestic requirement. India has been successful in developing a strong manufacturing base for the heavy electrical equipment with subcritical technology with a unit capacity of 660 MW and in the process of adopting super-critical technology for unit size of 800 MW and above. While the said technologies are for coal-based power plants, it also has manufacturing capabilities of gas turbines of up to 260 MW of unit capacity. Apart from BHEL which has the largest installed capacity, there are other manufacturers in the private sector, who are manufacturing turbines for power generation and industrial use.
Globally, various factors are driving the gas turbines market. These include shale gas boom; increasing demand for electric power worldwide; and subsequent investments in creating new generating capacity, need for high efficiency, low carbon emission etc. In addition, various countries have already raised their concerns about resource depletion, increase in harmful emissions. And majority of the countries have started announcing stricter regulations for climate change mitigation by increasing focus on technologies that can produce power in a much cleaner and efficient manner. The high efficiency and durability of gas turbines also is another key driver for the market. Combined with stringent carbon emission regulations, the focus has now shifted to high performance and lower power generation cost. This is forcing people to look at highly efficient gas turbines. Gas turbines are an essential part of distributed power technologies product portfolio along with diesel and gas reciprocating engines, solar panels, fuel cells, and small wind turbines. Thus, growth of distributed power systems will translate into an increased demand for gas turbines ´Power for All´ by 2020, is the ambitious plan of India government to provide electricity to households in the country. It is understood that to achieve this, one has to look beyond the large power grid. In other words, distributed power generation systems are gaining momentum. In India, these systems, as of now refer only to solar or wind power. Gas- based power plants can also be considered under this initiative. However, the cost of transporting gas is the dithering factor. The distributed distribution islands normally have a capacity in the range of 1 MW to 100 MW.
Efficiency, reliability and environmental compatibility, giving low life-cycle costs are the best characteristics of gas turbines. Work-wise, the gas turbine technology is matured with a wide range of capacity products available, making it the most sought after.
a) Open Cycle Gas Turbines
This is the most widely used technology. In the open cycle turbines, air is taken from the atmosphere, compressed in a centrifugal or axial-flow compressor, and then fed into a combustion chamber. The fuel is added and burned at an essentially constant pressure with a portion of the air. The open cycle gas turbine consists of a compressor, combustion chamber and a turbine. The compressor takes in ambient fresh air and raises its pressure. Heat is added to the air in the combustion chamber by burning the fuel and raises its temperature.
Typically these gas turbines are available in the capacity range of 5 - 375 MW. The efficiency is better with the larger models. According to reports the efficiency of these gas turbines are between 35-40 per cent, and can go to as high as 46 per cent.Advantages
It has only three components - compressor, combustion chamber and turbine. The combustion chamber is inexpensive, light weight and small with a high rate of heat release. It can be designed to burn almost all hydrocarbon fuels ranging from gasoline to heavy diesel oil.
- Low weight and size - It has lower specific weight and requires less space per unit of power output.
- No warm-up period - it can accelerate from a cold start to a full load without a warm-up period.
- Low capital cost - Since it has only a minimum number of components and has low weight and size, the capital cost is low compared to other plants.
- Sensitivity - it is sensitive to changes in the component efficiencies. A reduction in the efficiencies of compressor and turbine will lower the efficiency of the cycle. An increase in atmospheric temperature lowers the thermal efficiency.
- High air rate - It has a very high air rate. This high air rate is not a disadvantage in most of the applications like aviation field, but is a prime factor in marine applications.
b) Combined Cycle
According to General Electric (GE), one of the largest manufacturers of combined cycle gas turbines, this technology compresses air and mixes it with fuel and is heated to a very high temperature. The hot air-fuel mixture moves through the gas turbine blades, making them spin.
The fast-spinning turbine drives the generator that converts a portion of the spinning energy into electricity. A Heat Recovery Steam Generator (HRSG) captures exhaust heat from the gas turbine that would otherwise escape through the exhaust stack. The HRSG creates steam from the gas turbine exhaust heat and delivers it to the steam turbine. Steam turbine delivers additional electricity. The steam turbine sends its energy to the generator drive shaft, where it is converted into additional electricity.
- Size - Smaller in size and weight as compared to and equivalent steam power plant. The gas turbine plants are subjected to less vibration.
- Fuel- Cheaper and cleaner fossil fuel natural gas. There are no standby losses in gas turbine plants. These plants can be built relatively quicker and requires less space. Can run on a wide variety of fuels.
- Cost of setting up -Installation and maintenance costs are less than that of thermal power plants.
- Operation- It can be started quickly
- Emissions -Exhaust of gas turbine is free from smoke. Very low toxic emissions of CO and HC due to presence of excess air in the process.
- Reliability - Greater reliability, particularly in applications where sustained high power output is required.
- The part load efficiency is poor.
- The unit is operated at a high temperature and pressure so special metals are required to maintain the unit.
- Major part of the work, about 66 per cent, is developed in the turbine is used to travel in the drive to the compressor.
- The devices that are operated at high temperature are complicated.
The turbine manufactures had taken the brunt of India´s dip in gas-based capacity addition. The green shoot is that the sector experts expect the government to push gas-based power generation as there is large capacity of renewable energy entering the grid. For grid stability, they may look at gas-based power. Difficulties in mining coal, depleting coal sources globally, and discarding of old coal-based power plants put together can trigger a momentum for gas-based power plants in another five years´ timeframe.
But availability of natural gas either from domestic sources or through imports would be a pre-condition for this revival.
Though on the back foot now, gas turbines, going forward could be the technology of choice for future capacity additions. As the law get stringent on the emission standards, the gas turbines will have the field day.
- Renjini Liza Varghese