Design &Types of Design &Types of Steam TurbinesSteam Turbines

Prof. Osama El Masry

elmasryo@yahoo.com

Design Characteristics for Design Characteristics for a Steam Turbinea Steam TurbineCustom designThermal outputFuel flexibility Reliability and life Size range Emissions

Performance and Performance and Efficiency EnhancementsEfficiency Enhancements

Electrical EfficiencyThermodynamic Efficiency Efficiency Enhancements

Condensing TurbineCondensing TurbineThe condensing turbine processes result in

maximum power and electrical generation efficiency from the steam supply and boiler fuel

Inlet pressure is relatively highand exhaust pressure is largely reduced

• The power output of condensing turbines is sensitive to

ambient conditions

Condensing TurbineCondensing Turbine Increasing

condensation temp. from 38 oC to 45°C, gives 6.5% less power output

When condensation temp. is reduced to 27°C the power output is increased by 9.5%

Example 5.1Example 5.1

In a condensing turbine cycle, the turbine generates 3.5 MW of Electric power with inlet steam at 27 bar & 71oC of superheat, the turbine efficiency is 75%, and the condenser pressure is 0.07 bar. The plant has also a separate low-pressure boiler, which generates saturated steam at 2.7 bar from feed water at 130oC and the boiler provides the heating capacity of 70x103 MJ/h. Calculate the steam mass flow rate and heat added in the two boilers if the boiler efficiency is 84% in both boilers.

SolutionSolution

For the condensing turbineE=3.5 x 1000=ms1(h1-h2)ηT

h1= 3000 kJ/kg h2=2o65 kJ/kgms1= 5 kg/sQ1= ms1(h1-h`pc)/ηb=5(3000-163.4)/0.84=16.88

MWFor the heating boilerH=70 x 106/3600== ms2 (h3-h4) = ms2(2720-130x

4.187)ms2=8.94kg/sQ2= ms2(h3-h4)/ηb=70 x 106/3600 x 0.84=23.1 MWmtotal=13.94 kg/sQtotal=40 MW

Back-pressure TurbineBack-pressure TurbineThe term “back-pressure” refers to turbines

that exhaust steam at atmospheric pressures and above

A back-pressure turbine exhausts its entire flow of steam to the industrial or facility process

Back-pressure TurbineBack-pressure TurbineCombined Heat and Power is the main

applicationFor industrial plants: H.P steam flows

through the turbine to a low pressure steam tank and then desuperheated (by small jet) to dry and saturated condition and then allowed to flow to the process where it gives off its latent heat

Example 5.2Example 5.2

For the plant in example 5.1 if a back pressure turbine is used under the same inlet steam conditions, exit pressure is 1.4 bar and turbine efficiency is 75%. If the exhaust steam is used in the heating process and heating capacity needed is 70x103 MJ/h, calculate the steam mass flow rate, the power generated and the heat added in the boiler. Assume that the boiler efficiency is 84%, and the heating condensate is returned back to the boiler as saturated liquid.

h1=3000kJ/kg h2s=2333kJ/kg h2=2500kJ/kg h3=458.5kJ/kg

H=70 x 106/3600== ms (h2 –h3) =

ms= 9.52 kg/s

Power(E)= ms(h1-h2)=4760 kW

Neglecting the pump powerQadd= ms(h1-h3)/ηb

=24195 kW

Extraction TurbineExtraction Turbine The extraction turbine has opening(s) in its casing for

extraction of a portion of the steam at some intermediate pressure before condensing the remaining steam

Extraction TurbineExtraction TurbineAt steam extraction locations there are

usually steam flow control valves that control system flow rates and cost.

used in conjunction with a multistage turbine in cases where the exhaust is not sufficient to develop the power required

Mixed Pressure TurbineMixed Pressure Turbine

A heat accumulator in its simple form, is a cylindrical vessel where exhaust steam is led to submerged orifices,

The steam condenses by direct contact with water. The water absorbs its latent heat, thus its sensible heat increases, and the pressure of steam above it rises.

When the turbine consumes more steam than is coming, there is a slight reduction of pressure in the steam space which causes the water to evaporate, thus causing the pressure to fall gradually and the water looses sensible heat so on……..

The first operation is called storage period while the second is called the generation period. The steam consumption and the pressure of the steam in the accumulator is shown next

Mixed Pressure TurbineMixed Pressure Turbine

Mixed Pressure TurbineMixed Pressure Turbine

Mixed Pressure TurbineMixed Pressure Turbine

-Case (1) Power from H.P. turbine work only,

Power1 = m x Δ hHP

where m is the steam consumption in H.P. turbine work only

-Case (2) Power from L.P. turbine work only Power2 = m1 x Δ hLP

Where m1 is the steam consumption in L.P. turbine work only

 

Case (3) Power from both L.P & H.P.

turbine work

h3M(m+m1) =m h2+m1h3