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 et%207%20-%20Absorption%20Cooling.pdfhttp:// et%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) H 2 O-NH 3 + hydrogen

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 h 1 =h f saturated liquid W pump (ideal) =h 2 -h 1 =v f (P high -P low ) v f =specific volume of saturated liquid at low pressure q in =h 3 -h 2 heat added in boiler Usually either q in will be specified or else the high temperature and pressure (so you can find h 3 ) q out =h 4 -h 1 heat removed from condenser) w turbine =h 3 -h 4 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.

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 T max ~ 620° due to material stress Increase boiler pressure (with same T max ) P max ~ 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

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) yer_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 CHP Here, we use mechanical energy for powering vapor compression cooling systems