Natural Gas Fired Plants : Technology / Performance / Environment / Design Trends

turbineonline-40mw cogeneration plant for TATA Chemicals

Home

90 MW Cogeneration
Power plant for Indian
Petrochemicals,
Gandhar

46 MW captive power plant for Gujarat Cements, Piparav

Turbine Details :

Natural Gas Fired Plants : Technology / Performance / Environment / Design Trends

Market Demand Contract awards for the last five years for fossil fuel-fired power plants (above 50 MW) averaged 63 GW per year and, sales are forecasted to average about 67 GW per year over the period 1999-2004. The market in Asia Pacific is declining, while that of Europe is showing moderate growth (from a low level). Strong growth in North America is reflected in the growth of the 60Hz market. In the past, the proportion of power plants with gas turbines, i.e., open cycle and combined cycle (combining gas and steam turbines) was around 54% of total fossil fuel fired power plants. For the next five years (until 2005), this proportion is expected to rise to 63%. For open and combined cycle power plants, this means that sales are expected to grow from 34 GW per annum to 42 GW per annum. This growth is predominantly due to market developments in North America. In addition, open and combined cycle gas turbine plants are expected to take an ever increasing share of the power market in developing countries where low cost natural gas is available.

In comparison with coal fired power plants, open and closed cycle power plants are characterized by lower capital investment costs. On the other hand, fuel costs play a relatively more important role.

Over the last 50 years, the efficiencies of gas turbines have increased from 33% to 38% (LHV) and those of combined cycle plant from 48% to 58%. At present, there are a rather small number of global manufacturers and suppliers offering GT products covering a wide range of power output. The products of the different suppliers can be grouped in clusters by comparable output. For all major manufacturers, small (50 MW) and medium classes (50 to 200 MW) includes proven existing GT models with lower efficiencies and operating temperatures, but with robust and reliable performance; the large classes (above 200MW) are those that deliver higher performance. The latest gas turbine technology also reflects the expertise of aero jet engine manufacturers. As a result, using pressure ratios of around 17, performance features have been achieved for heat rates in the range of 9,400-9,800 kJ/kWh and for efficiencies up to 38%.

These performance improvements have been achieved through :

Improved compressor design.
Higher turbine inlet temperature (approximately 1250°C ISO)
Advanced blading (design, materials, coating).
Optimal design of the turbine blade cooling system, with or without need for external coolers.
Improved cooling of the combustion system sections (chamber, canes, transitions)
Less pressure drop in the turbine exhaust.

Less than 25 ppm NOx emissions can be expected from these plants. This compares with the maximum allowable levels of 60 ppm for GTs fired with natural gas as set out in the World Bank's "Thermal Power Guidelines for New Plants". Because of better materials (alloys and coatings), with a higher resistance to high temperature oxidation and corrosion, combined with better cooling techniques, gas turbines are expected to reach a unit capacity of around 250 MW to 350 MW) and efficiencies of 40% over the next years . In conjunction with optimized main steam parameters and with improved plant component efficiencies, this in turn will increase CC plant capacity to the 375 MW 500 MW range, with CC efficiencies around 60%. (See also Figure 1). From a plant aspect, plant construction time has been shortened by the concept of predesigning, introduction of modules and by advanced project management and scheduling?. Inter alia, this was effected by simplification of the electrical and instrumentation and control systems as well as the foundation and overall civil works construction requirements. In addition, plant operation has been simplified by, for example, allowing full 100% steam bypass operation in the event of steam turbine malfunctions.

Upgrading Fossil-Fueled Power Plants :

The operators of established power plants often seek to improve plant performance beyond what can be achieved through routine maintenance; in particular, operators look for higher output, additional heat extraction, improved pollution control and improved plant control.. A common approach is to incorporate a gas turbine into an existing fossil fired steam generation system. The most common configuration is called parallel powering, where gas turbine exhausts are used in the existing steam cycle. This is achieved by feeding the exhausts into a heat-recovery steam generator (HRSG) which provides additional steam to the existing steam turbine. Typically, parallel powering requires the addition of a gas turbine, associated electrical and instrumentation and control equipment, civil engineering, HRSG, additional piping and pumps as well upgrading the steam turbine. Generally, parallel powering can be undertaken fairly separately from the existing part of the plant, with a final integration phase and a plant down time of 1.5 to 2 months.

7Back

Topé