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Combined heat power plant (chp)
- 1. Combined Heat and Power Plant (CHP) Lecture 6
- 2. Combined Heat and Power Combined heat-and-power, also known as “cogeneration,” refers to the use of recovered exhaust heat of any production unit for another process requirement. This in turn results in improvement in the energy utilization of the unit. By so doing, the overall thermal efficiency of generation may be raised from 40–50% to 70–90%. The upper limit of 90% holds for large installations with a very well-defined and constant heat demand.
- 3. Combined heat-and-power does not have to be a renewable source of energy; in fact, many CHP installations use natural gas as a source. The use of biomass as a source is the only renewable form of CHP. The direct combustion of organic matter to produce steam or electricity is the most advanced of the different CHP processes and, when carried out under controlled conditions, is probably the most efficient.
- 4. Large CHP installations are used for production of steam in industrial installations, for space heating in the agriculture, and for district heating. Agricultural CHP is very common in the Netherlands and in Denmark, where about 25% of electricity comes from CHP. Recently, incentives toward smaller generation units have resulted in a growth in CHP in some countries. Micro CHP plants used for space heating and electricity receiving a lot of attention. Possible applications are domestic heating, hotels shopping centers and offices. For example, a somewhat larger unit produces 105kW electricity and 172kW heat. A market for much smaller units may be emerging, intended for heating of domestic premises. An example is a unit that produces 1 kW electricity together with 7.5– 12kW heat.
- 5. Categories of CHP applications Four categories of CHP applications: small-scale CHP schemes: to meet space and water heating requirements in buildings, based on spark ignition reciprocating engines large-scale CHP schemes: for steam raising in industrial and large buildings, based on compression ignition reciprocating engines, steam turbines or gas turbines large scale CHP schemes for district heating: based around a power station or waste incinerator with heat recovery supplying a local heating network CHP schemes fuelled by RES: these may be at any scale
- 20. Energy Distribution in a combined cycle system
- 24. Features Very mature technology Size: 0.5 – 30+ MW Efficiency: electricity (20 – 45%), cogeneration (80 – 90%) Installed cost ($/kW): 400 – 1,200 O&M cost ($/kWh): 0.003 – 0.008 Fuel: natural gas, biogas, propane Emission: approximately 150 – 300 ppm NOx (uncontrolled) below approximately 6 ppm NOx (controlled) Cogeneration: yes (steam) Commercial Status: widely available Three main components: compressor, combustor, turbine Start-up time range: 2 – 5 minutes Natural gas pressure range: 160 – 610 psig Nominal operating temperature: 59 F Combustion Gas Turbines24
- 25. Combustion Gas Turbines Combustor Power Converter Compressor air fuel Power Turbine Generator HRSG (Heat Recovery Steam Generator)Feed water Process steam Fig. 1 Block diagram of Combustion Gas Turbine System. 25
- 26. CHP Technologies
- 27. Advantages High efficiency and low cost (particularly in large systems) Readily available over a wide range of power output Marketing and customer serving channels are well established High power-to-weight ratio Proven reliability and availability Disadvantages Reduced efficiencies at part load Sensitivity to ambient conditions (temperature, altitude) Small system cost and efficiency not as good as larger systems Advantages & Disadvantages Combustion Gas Turbines 27
- 28. Comparison CHP
- 29. Micro-turbines29
- 30. Size: 25 – 500 kW Efficiency: unrecuperated (15%), recuperated (20 – 30%), with heat recovery (up to 85%) Installed cost ($/kW): 1,200 – 1,700 O&M cost ($/kWh): 0.005 – 0.016 Fuel: natural gas, hydrogen, biogas, propane, diesel Emission: below approximately 9 - 50 ppm NOx Cogeneration: yes (50 – 80C water) Commercial Status: small volume production, commercial prototypes now Rotating speed: 90,000 – 120,000 Maintenance interval: 5,000 – 8,000 hrs Micro-turbines Features 30
- 31. Advantages Small number of moving parts Compact size Light-weight Good efficiencies in cogeneration Low emissions Can utilize waste fuels Long maintenance intervals Disadvantages Low fuel to electricity efficiencies Micro-turbines Advantages & Disadvantages 31
- 32. Overview of CHP Technologies Technology Pros Cons Fuel Cell - Very low emission - Exempt from air and permitting in some areas - Comes in a complete “ready to connect” package - High initial investment - Limited number of commercially available units Gas Turbine - Excellent service contracts - Steam generation capabilities - Mature technology - Requires air permit - The size and shape of generator package is relatively large Micro-turbine - Lower initial investment - High redundancy - Low maintenance cost - Relative small size and installation flexibility - Relatively new technology - Requires air permit - Synchronization problems possible for large installations Recip. Engine - Low initial investment - Mature technology - Relatively small size - High maintenance costs - Low redundancy
- 33. Benefits of CHP High Efficiency, On-Site Generation Means Improved Reliability Lower Energy Costs Lower Emissions (including CO2) Conserve Natural Resources Support Grid Infrastructure Fewer T&D Constraints Defer Costly Grid Upgrades Price Stability Facilitates Deployment of New Clean Energy Technologies 33
- 34. Factors for CHP Suitability High Thermal Loads-(Cooling, Heating) Cost of buying electric power from the grid versus to cost of natural gas (Spark Spread) Long operating hours (> 3000 hr/yr) Need for high power quality and reliability Large size building/facility Access to Fuels (Natural Gas or Byproducts) 34
- 35. Generators Two Types of Generators Induction • Requires Grid Power Source to Operate • When Grid Goes Down, CHP System Goes Down • Less Complicated & Less Costly to Interconnect • Preferred by Utilities Synchronous • Self Excited (Does Not Need Grid to Operate) • CHP System can Continue to Operate thru Grid Outages • More Complicated & Costly to Interconnect (Safety) • Preferred by Customers 35
- 36. Environmental Benefits of CHP (NOx)36
- 37. 186 lb/MMBtu Power Station Fuel (U.S. Fossil Mix) 117 CHP Fuel (Gas) Lb/MMBtu CO2 Emissions Reductions from CHP 39,000 Tons CO2 Saved/Year Power Plant 6.0 MWe 70,000 pphSteamBoiler117 Boiler Fuel ( Gas) Lb/MMBtu CO2 Emissions 56k Tons/yr CO2 Emissions 43k Tons/yr …TOTAL ANNUAL CO2 EMISSIONS…95k Tons 56k Tons CO2 Emissions 52k Tons/yr Conventional Generation Combined Heat & Power: Taurus 65 Gas TurbineEfficiency: 31% Steam Efficiency: 80% Efficiency: 82.5 %
- 38. CHP and Energy Assurance Combined Heat & Power (CHP) can Keep Critical Facilities Up & Operating During Outages For Example, CHP can Restore Power and Avoid: – Loss of lights & critical air handling – Failure of water supply – Closure of healthcare facilities – Closure of key businesses 38