Turbine efficience

Improve Steam Turbine Efficiency
Understand the factors that affect steam consumption
Steam are a major energy consumer. Optimising process operating conditions can considerably improve turbine water rate, which in turn will significantly reduce energy requirement. Various operating parameters affect condensing and back pressure turbine steam consumption and efficiency. Why Important Theindustrial sector is the largest energy consumer, accounting for about 30 % of total energy used. Fuel and energy prices are continuously rising. With the present trend of energy prices and scarcity of hydrocarbon resources lowering energy requirement is a top priority. Energy conservation benefits depend on the adopting minor or major modifications and using the latest technology. Energy conservationdoes not mean curtailing energy use at the cost of industrial and economic growth. In the large process industries, steam turbines are the main energy consumers. Savings achieved here will be significant, with a better return on investment than for most other equipment. Effect of operating conditions on steam turbines A condensing turbine system is shown in figure 1. Turbine exhaust operating belowatmosphere, is condensed in a shell and tube exchanger called surface condenser. Condensate flows in the shell side of the condenser and steam is condensed by the cooling water. Vacuum in the surface condenser i.e. turbine exhaust vacuum is controlled/ maintained by vacuum ejector system of the surface condenser.

Turbine

Vent

Condenser CWR CWS Inter/after condenser Boiler CWR CWSMotive Steam BFW Pump

Figure 1 : Diagrammatic details of a condensing type turbine Contd..2/-

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Turbines are designed for a particular operating conditions like steam inlet pressure, steam inlet temperature and turbine exhaust pressure/ exhaust vacuum, which affects the performance of the turbines in a significant way. Variations in these parameters affects the steam consumption in theturbines and also the turbine efficiency. Theoretical turbine efficiency is calculated as workdone by the turbine to the heat supplied to generate the steam. Efforts are made to show the impact of various operating conditions by considering the following steam conditions as illustration.

Condensing Type turbine Steam inlet pressure Steam inlet temperature Exhaust vacuum Turbine rated BHP Steamconsumption
40 kg/cm2a 350 deg C 657 mm Hg 10000 HP 27785

Back pressure type turbine
Steam inlet pressure Steam inlet temperature Exhaust pressure Turbine rated BHP Steam consumption 40 kg/cm2a 350 deg C 4.5 kg/cm2a 10000 HP 57960

In the above referred turbines, 1 % reduction in steam consumption saves around $ 47000 annually for condensing turbines and around $ 84000 annually in backpressure turbine. LHV of the fuel for generating steam is considered as 10500 kcal/kg and boiler efficiency is taken as 87 %. Effect of various operating parameters is illustrated in the succeeding paragraphs. 2.1 Effect of Steam inlet pressure Steam inlet pressure of the turbine also effects the turbine performance. All the turbines are designed for a specified steam inlet pressure. For obtaining thedesign efficiency, steam inlet pressure shall be maintained at design level. Lowering the steam inlet pressure will hampers the turbine efficiency and steam consumption in the turbine will increase. Similarly at higher steam inlet pressure energy available to run the turbine will be high, which in turn will reduce the steam consumption in the turbine. Figure - 2a & 2b represents the effects of steaminlet pressure on steam consumption and turbine efficiency respectively, keeping all other factors constant for the condensing type turbine.

Contd..3/-

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99.9 99.6 Steam consumption, % 99.3 99 98.7 98.4 98.1 97.8 Turbine efficiency, % 35 36 37 38 39 40 41 42 43 44 45

34.2 34 33.8 33.6 33.4 33.2 33 35 36 37 38 39 40 41 42 43 44 45 Steam pressure, kg/cm2 Steam pressure, kg/cm2...