Lecture Objectives:

• Finish with absorption cooling

• Power generation • Rankine cycles

• Connect power generation with heating and cooling

–CHP–CCHP

Useful information about LiBr absorption chiller

• http://www.cibse.org/content/documents/Groups/CHP/Datasheet%207%20-%20Absorption%20Cooling.pdf

Practical Tips for Implementation of absorption chillers • Identify and resolve any pre-existing problems with a cooling system, heat

rejection system, water treatment etc, before installing an absorption chiller, or it may be unfairly blamed.

• Select an absorption chiller for full load operation (by the incorporation of thermal stores if necessary) as COP will drop by up to 33% at part-load.

• Consider VSD control of absorbent pump to improve the COP at low load.

System with no pump(Platen-Munter system)

• H2O-NH3 + hydrogen

http://www.youtube.com/watch?v=34K61ECbGD4

Power generation

Power generation in steam turbines(Rankine cycle)

Pump

Nuclear

Coal

Steam powered turbine

Ideal Rankine Cycle

1-2 isentropic pump 2-3 constant pressure heat addition

3-4 isentropic turbine 4-1 constant pressure heat rejection

Ideal Rankine Cycle

h1=hf saturated liquid

Wpump (ideal)=h2-h1=vf(Phigh-Plow)vf=specific volume of saturated liquid at low pressure

qin=h3-h2 heat added in boiler Usually either qin will be specified or else the high temperature and pressure (so you can find h3)

qout=h4-h1 heat removed from condenser)

wturbine=h3-h4 turbine work

Deviations from Ideal in Real Cycles• Pump is not ideal

• Turbine is not ideal

• There is a pressure drop across the boiler and condenser

• We need to sub-cool the liquid in the condenser to prevent cavitation in the pump.

pump

factual

actual

idealpump

PPvWW

W 12

ideal

actualturbine W

W

For increasing system efficiency of Rankine Cycle

• Lower condenser pressure• We should have at least 10°C T between condenser

and cooling water or air temperature for effective heat transfer

• The quality at exit to prevent turbine problems shouldn’t go less than about 88%

• Superheat the steam more• Tmax ~ 620° due to material stress

• Increase boiler pressure (with same Tmax)• Pmax ~ 30 MPa• This affects the quality at exit!

Reheat Cycle

• It allows increase boiler pressure without problems of low quality at turbine exit

Regeneration• Preheats steam entering boiler using a feed-water

heater, improving efficiency

Further improvements

Analogy with cooling cycles

Gas powered turbine

http://www.youtube.com/watch?feature=player_embedded&v=rxps0sZ8T3Y

Combustion product gas powered turbines

• Limited to gas or oil as a major source of fuel

• Approximately 55 to 65% of the power produced by the turbine is used for compressor.

• Gas temperatures at the turbine inlet can be 1200ºC to 1400ºC

• Because of the power required to drive the compressor, energy conversion efficiency for a simple cycle gas turbine plant is ~ 30%

Combined Cycle(gas and steam)

http://www.youtube.com/watch?feature=player_embedded&v=D406Liwm1Jc

Combined heat and power(cogeneration CHP or three generation CCHP)

Here, we use thermal energy for heating and/or cooling

Other method for CHPHere, we use mechanical energy for poweringvapor compressioncooling systems