Combined Heat and Power

Transcription

1 Lecture 12 Combined Heat and Power Combustion Turbines and Co-generation Combustion Turbines and Combined Heat and Power (CHP) Systems See B. K. Hodge, Chapter 5 and Chapter 11. ISBN:

2 Combustion Turbines 2

3 Gas/Combustion Turbine Power Plants Gas Turbine Power Plants are lighter and more compact than vapor power plants. The favorable power-output-to- weight ratio for gas turbines make them suitable for transportation. Air-standard Brayton Cycle Regenerative Gas Turbines 3

4 Regenerative Gas Turbines table_05_02 4

5 LM 2500 Gas Turbine (GE Energy) 5

6 table_05_04 6

7 Cogeneration Defined Process Cogeneration is the simultaneous generation of two or more types of energy from a single fuel source Combined Heat and Power When combustion engines are used only for generating electricity, most of the usable energy from fuel combustion is lost in the form of heat - resulting in systems that are only 20-30% efficient. Generating systems can be made greater than 70% efficient by recovering and using waste heat from the combustion process - this strategy is more commonly known as "Cogeneration" or "Combined Heat and Power." 7

8 Useful Energy From Conventional Electric Generation Useful Energy From Cogeneration Typical cogeneration reaches efficiencies of 75%, while conventional electricity generation operates at efficiencies around 33% 8

9 Attractive Load Profile for Cogeneration The following diagram illustrates how use of Combined Heat & Power can increase efficiency: 9

10 Combined Cycle Co-generation System Combined Cycle GT Heat Recovery Boiler Steam Turbine Inlet Air Combustor GS Steam Condenser Compressor Gas Turbine Turbine Feed Pump 10

11 Start here Monday 11

12 DHC Cogeneration Heat Recovery Boiler Inlet Air Combustor Building Loads Compressor Turbine Feed Pump MIT Campus System Layout Steam System To MIT Campus Boiler 3 Boiler 4 Boiler 5 HRSG Combustion Turbine GS Generator To Chilling Plant 12

13 Typical Cycle Efficiencies 80% 70% 60% 50% 40% 30% 20% 10% 0% Simple GT Rankine CCGT DHC GT 13

14 fig_11_05 14

15 15

16 *******CGT & HRSG Diagram Dual Fuel Supplementary Firing 21 kg/s Steam 1000 degree exhaust Combustion Turbine GS 22 MW(e) CO Catalyst Bed EV Dual-Cone Combustor 16

17 Emission Control Techniques Water injection to reduce flame temperature Bypass air for temperature air control Pilot fuel ratio variation CO oxidation in exhaust Water Tube Boilers 17

18 Combined Cycle Heat Balance Oct 23 18

19 Temperature Profile in Heat Recovery Boiler Steam Turbine Assisted Co-generation (allows better matching of heat and electricity loads) 19

20 CGT & HRSG Diagram Dual Fuel Supplementary Firing 21 kg/s Steam 1000 degree exhaust Combustion Turbine GS 22 MW(e) CO Catalyst Bed fig_11_04 20

21 21

22 PINCH POINT ANALYSIS PINCH POINT PINCH POINT ANALYSIS 200 kg/s Superheated Steam Saturated Steam PINCH POINT Sub-cooled Liquid 22

23 23

24 32.45 kg/s 24

25 PINCH POINT 25

26 Other Types of Co-generation Heat and Power Fuel Cell Micro Gas Turbine IC Engine Fuel Cell Micro Gas Turbine IC Engine 26

27 27

28 ******Diesel Engine Co-gen 28

29 29

30 fig_11_13 Thermal Cooling Technologies Traditional Conventional Vapour-Compression (non-thermal Common Types of Thermal Air Conditioning Absorption Chillers Adsorption Chillers Desiccant Dehumidifiers/Evaporative Coolers 30

31 Absorption Chiller 31

32 Absorption Chiller Refrigeration Cycle The basic cooling cycle is the same for the absorption and electric chillers. Both systems use a lowtemperature liquid refrigerant that absorbs heat from the water to be cooled and converts to a vapour phase (in the evaporator section). The refrigerant vapours are then compressed to a higher pressure (by a compressor or a generator), converted back into a liquid by rejecting heat to the external surroundings (in the condenser section), and then expanded to a low- pressure mixture of liquid and vapour (in the expander section) that goes back to the evaporator section and the cycle is repeated. The basic difference between the electric chillers and absorption chillers is that an electric chiller uses an electric motor for operating a compressor used for raising the pressure of refrigerant vapors and an absorption chiller uses heat for compressing refrigerant vapours to a high-pressure. The rejected heat from the power-generation equipment (e.g. turbines, microturbines, and engines) may be used with an absorption chiller to provide the cooling in a CHP system. The basic absorption cycle employs two fluids, the absorbate or refrigerant, and the absorbent. The most commonly fluids are water as the refrigerant and lithium bromide as the absorbent. These fluids are separated and recombined in the absorption cycle. In the absorption cycle the low-pressure refrigerant vapour is absorbed into the absorbent releasing a large amount of heat. The liquid refrigerant/absorbent solution is pumped to a high-operating pressure generator using significantly less electricity than that for compressing the refrigerant for an electric chiller. Heat is added at the high-pressure generator from a gas burner, steam, hot water or hot gases. The added heat causes the refrigerant to desorb from the absorbent and vaporize. The vapours flow to a condenser, where heat is rejected and condense to a high-pressure liquid. The liquid is then throttled though an expansion valve to the lower pressure in the evaporator where it evaporates by absorbing heat and provides useful cooling. The remaining liquid absorbent, in the generator passes through a valve, where its pressure is reduced, and then is recombined with the low-pressure refrigerant vapours returning from the evaporator so the cycle can be repeated. Absorption chillers are used to generate cold water (44 F) that is circulated to air handlers in the distribution system for air conditioning. 32