With its higher thermodynamic efficiency and a lower power-to-weight ratio, steam turbine is revolutionising the power sector
Steam turbine is a mechanical device that converts thermal energy in pressurised steam and uses it to do mechanical work on a rotating output shaft. The original steam engine, largely powered the industrial revolution was based on reciprocating pistons. This has now been almost totally replaced by the steam turbine because the steam turbine has a higher thermodynamic efficiency and a lower power-to-weight ratio.
Steam turbine as industrial applicationSteam turbine systems are very commonly found in paper mills as there is usually a variety of waste fuels from hog fuel to black liquor recovery. Chemical plants are the next most common industrial user of steam turbines followed by primary metals. There are a variety of other industrial applications including the food industry, particularly sugar mills. There are commercial applications as well. Many universities have coal-powered CHP (Combined Heat and Power) generating power with steam turbines. Some of the facilities are blending biomass to reduce their environmental impact.
Choosing steam turbinesWhile steam turbines are competitively priced compared to other prime movers, the costs of complete boiler or steam turbine systems are relatively high on a per kW of capacity. This is because of their low power-to- heat ratio, the costs of the boiler, fuel handling and overall steam systems, and customisation of most installations. Thus, steam turbines are well-suited to medium- and large-scale industrial and institutional applications where inexpensive fuels are available.
Steam turbines for power sectorThe steam turbine is ideal for the very large power configurations used in power stations. The steam turbine derives much of its better thermodynamic efficiency because of the use of multiple stages in the expansion of the steam. This results in a closer approach to the ideal reversible process.
Electrical power stations use large steam turbines driving electric generators to produce most (about 80 per cent) of the world’s electricity. The advent of large steam turbines made central-station electricity generation practical as reciprocating steam engines of large rating became very bulky and operated at slow speeds.
Steam turbines can also be used directly to drive large centrifugal pumps, such as feedwater pumps at a thermal power plant.
While talking about the importance of steam turbines in power sector, Navin Dewaji, Vice President – Power Generation Division, Energy Sector, Siemens Ltd., shares how Siemens’ small steam turbines are benefiting industry like its compact design minimises space requirements of installation as well as low maintenance costs due to easy access to mechanical components.
ChallengesThere are some challenges when it comes to operation and maintenance of these turbines. “Turbine operation can get affected if it is not handled as prescribed,” says Mr Dewaji. “Poor inlet steam quality can cause scaling which affects normal turbine operation. Also, running turbine at parameters which are outside the allowed limits can cause damage to sensitive components of turbine and may cause damage.”
Changing trendsThese days the industry is observing some changing trends. These are:
Customers are moving towards higher MW ratings as average size of production firm is increasing
More focus on energy efficiency of steam turbine
Increasing use of small steam turbines for waste heat recovery
More focus on eco-friendly power generation, suiting steam turbine by using biomass or solid waste as fuel.