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Low Carbon Conversion and Nuclear Power Energy Conservation and Management in Buildings

NBSLM03E (2010) Low Carbon Technologies and Solutions: Sections 1 - 5 N.K. Tovey ( 杜伟贤 ) M.A, PhD, CEng, MICE, CEnv. Low Carbon Conversion and Nuclear Power Energy Conservation and Management in Buildings Renewable Energy. Low Carbon Technologies and Solutions.

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Low Carbon Conversion and Nuclear Power Energy Conservation and Management in Buildings

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  1. NBSLM03E (2010) Low Carbon Technologies and Solutions: Sections 1 - 5 N.K. Tovey (杜伟贤) M.A, PhD, CEng, MICE, CEnv • Low Carbon Conversion and Nuclear Power • Energy Conservation and Management in Buildings • Renewable Energy

  2. Low Carbon Technologies and Solutions Low Carbon Solutions may be achieved by: • Improving the overall energy efficiency in the production and distribution of energy. • Using low carbon energy sources and conversion technologies. • Using Nuclear Power • Using Renewable Energy • Improving end use conversion efficiency through • Improving appliance efficiency/technology • Improving insulation and related issues in buildings • Enhancing Energy Management and analysis • Awareness Raising

  3. Improving the overall energy efficiency in the production and distribution of energy. • Energy is consumed in extracting energy, processing it and delivering it. • Primary Energy Ratio The Ratio of Energy as it exists in the ground to the energy delivered at point of final use (see NBSLM01E handout). • Improvements in Electricity Generation Efficiency can significantly reduce energy losses and carbon emissions

  4. Using low carbon energy sources Different Fossil Fuels as a result of their chemical composition have a higher or lower proportion of their mass as carbon. Burning natural gas (mostly methane CH4 ) produces CO2 and water. Coal on the other hand is mostly carbon and produces most CO2 when burnt. Typical emission factors from the combustion of a fuel (Gross CV): In electricity generation it is common to raise steam for the turbine. If this is done using gas then the carbon emissions will be only 183.58 / 310.05 = 59.2% of those emissions using the same technology and coal. Gas generation can exploit more efficient technologies resulting in further reduction.

  5. Section 2: Low Carbon Energy CONVERSION Solutions Heat In Q1 Work Out W Heat Out Q2 Schematic Representation of a Power Unit Schematic Representation of a Power Unit Revision from Module NBSLM01E: Generation of Work/Electricity First Law: W = Q1 - Q2 so efficiency Heat Engine But Carnot saw that Heat  Temperature We saw there was only limited scope for improving efficiency so long as we used steam as the primary fluid in electricity generation. What about Combined Cycle Gas turbines?

  6. Section 2: Low Carbon Energy CONVERSION Solutions Work IN W Heat In Q2 Schematic Representation of a Heat Pump Revision from Module NBSLM01E: Heat Pumps Heat Pumps A Heat Pump is a reversed Heat Engine: NOT a reversed Refrigerator Heat Out Q1 Heat Pump Coefficients of Performance of 3 – 5 are possible. Significant savings are possible as a Heat Pump works with Thermodynamics not against it as in a Heat Engine.

  7. Section 3: Combined Cycle Gas Turbines • An open cycle gas turbine ~ A jet engine • High T1 but also high T2 • so efficiency is low ~ 23% Exhaust Gases @ ~ 600oC Air Intake/Filter Fuel In Generator Combustion Gas Turbine Compressor

  8. Section 3: Combined Cycle Gas Turbines Multiple Shaft Machines Steam Turbine Air Intake/Filter Generator Generator Combustion Compressor Condenser Fuel In Gas Turbine Condenser

  9. Section 3: Combined Cycle Gas Turbines Multiple Shaft Machines Waste Heat Combined Cycle Gas Turbine Practical Efficiencies:- Gas Turbine alone 20 - 25% Steam Turbine alone 35 - 38% CCGT 47 - 52% 9

  10. Section 3: Combined Cycle Gas Turbines Multiple Shaft Machines – a worked example 0.22 0.23 1.0 Generator Gas Turbine 0.77 0.01 0.15 Waste Heat Boiler 0.02 0.28 0.62 0.30 Generator Steam Turbine 0.32 Condenser Gas turbine T1 = 950oC = 1223 K T2 = 500oC = 823K Electricity Steam turbine T1 = 500oC = 773 K T2 = 30oC = 303K Electricity Isentropic efficiency ~ 80% • Output from Gas Turbine: 0.23 units of power to generator and 0.77 units to WHB • Generator is ~ 95% efficient so output ~ 0.22 units • Waste Heat boiler is ~ 80% efficient so there will be ~ 0.15 units lost with 0.8*0.77=0.62 • units effective for raising steam. • Shaft power from Steam turbine = 0.62 * 0.486 = 0.30 units with 0.32 units to condenser • Total electrical output = 0.22 + 0.28 = 0.50units of which 0.03 units are used on station • Overall efficiency = 47% 10

  11. Section 3: Combined Cycle Gas Turbines Single Shaft Machines Air Intake/Filter Compressor Steam Turbine Condenser Exhaust Gases < 100oC Exhaust Gases 600oC Fuel In Generator Combustion Gas Turbine 11 Condenser

  12. Section 3: Combined Cycle Gas Turbines • Early CCGTs had multiple shafts with separate generators attached to gas turbines • Some had two or more gas turbines providing heat to waste heat boilers which powered a single steam turbine • Modern CCGT’s tend to have a common shaft with a gas turbine and steam turbine turning a single generator. • Advantages of single shaft machines: • tend to have lower capital cost • Tend to have higher overall efficiencies up to 55/56% - e.g. Great Yarmouth • Disavantages: • No option to run gas turbine by itself • Gas Turbines can reach full output in a matter of minutes. • Steam turbines take 6 - 8 hours or more • Gas Turbines tend to have higher NOx emissions and special provision is needed to reduce these levels – e.g. injecting steam into gas turbine.

  13. Section 4: Combined Heat and Power Engine Generator 13

  14. First Law of Thermodynamics: we can neither create or destroy energy ie Work out = Heat in – Heat Out Second Law states we must always reject Heat and efficiency = If we could utilise all of rejected heat The 1947 Act stated Electricity must be generated as efficiently as possible i.e. Work/Electricity (not energy) was King Section 4: Applications of Thermodynamics Combined Heat and Power (1) 14

  15. Section 4: Applications of Thermodynamics Combined Heat and Power (2) • Heat is normally rejected at ~ 30oC from a steam turbine • Too low a temperature for useful space heating • Reject heat at 100oC • i.e. Less electricity is generated, but heat is now useful • Typically there are boiler and other losses before steam is raised • Assume only 80% of energy available in coal is available. • And technical (isentropic efficiency) is 75% • Then for 1 unit of coal - electricity generated • case 1 = 0.8*0.75*0.639 = 0.38 units • case 2 = 0.8*0.75*0.555 = 0.33 units + up to 0.47 units of heat • or up to 0.8 units in total. Typically 10% of heat is lost so 0.73 units available.

  16. Section 4: Combined Heat and Power (3) Boiler Heat Exchanger To District Heat Main ~ 90oC GT Heat Exchanger Gas in To District Heat Main ~ 90oC Boiler Heat Exchanger Normal Condenser Back Pressure Steam Turbine To District Heat Main ~ 90oC ITOC or Pass out Steam Turbine Problem: For most CHP plant, electrical output will be limited if there is no requirement for heat. ITOC provides greater flexibility Although capital cost is greater Gas Turbine with CHP also Diesel/gas engine with CHP 16

  17. Section 4: Combined Heat and Power (4) Process Integrated Electricity Generation, Process Heat, Space Heat and Air compression at ICI Wallerscote Plant in late 1970s

  18. Section 4: CCGT with CHP Heat Lost 24 MW Fuel in 239 MW Steam Turbine GT Temp 1127oC Generator Generator Electricity 62 MW Electricity 55 MW Gas Turbine Useful Heat 98 MW

  19. Section 4: Combined Heat and Power Example of a Small Scale Scheme (1) Unless there is an industrial heat load, CHP plant capacity should be based on an approximate summer time heat load with supplementary heating provided by normal boilers in coldest months of year. summertime heat demand will affect summertime electricity generation

  20. Section 4: Example of a Small Scale CHP Scheme (2) Hot water and process heat demand is constant over the year at 4000 kW Heat loss rate for buildings is 1000 kW oC-1 Existing Heating provided by gas (80% efficiency). Mean space heat demand in January = (15.5 – 1.9) * 1000 = 13 600 kW This is the balance temperature – we shall discuss this in section 11.. A CHP scheme in a large building complex – e.g. a University/Hospital has installed 6000 kW of CHP electrical generation capacity. This is supplemented by supplementary boilers for peak winter heat demand. The actual electricity demands are shown. Note in some months these are greater than the installed capacity

  21. Section 4: Example of a Small Scale CHP Scheme (3) Column [4] values = col[3] + 4000 The 4000 is hot water and process heat requirement. Column [5] is electricity demand from Previous Sheet Column [6] indicates the potential amount of heat which would be available. Typically it is around 1.4 times the electricity generation so Col [6] = 1.4 * col [5] subject to a maximum electricity generation of 6000 kW i.e. when electrical demand > 6000kW, only 6000 * 1.4 = 8400 kW will be available for heat. Col [7] is actual amount of heat that can be usefully used. i.e if col [6] is less than heat demand Col [7] = Col[6] If Col[6] is greater than heat demand then the useful amount = heat demand Column 3 values = (15.5 – col [2])* 1000 15.5oC is the balance or neutral temperature at which no heating is required. Incidental gains from appliance heat and body heat increase temperature to comfort level. Maximum generation = 6000 kW electrical

  22. Section 4: Example of a Small Scale CHP Scheme (4) Column [9] is actual electricity that can be generated. If the heat demand is greater than 8400, then units can be run at full output – i.e. 6000 kW. If heat requirement is less than 8400kW, then output of generators will be restricted to a maximum of Col [7] / 1.4 Column [8] is supplementary heat required from back up boilers Col [8] = col [4] – col [7] Column [10] is additional electricity needed. Note: highest import occurs when electricity demand is least. The totals represent the total amount of heat or electricity generated or required over the year. Using 30 day months the totals in each column will be: mean values * 24 * 30

  23. Electricity generation in summer is restricted and import is highest when demand is least Section 4: Example of a Small Scale CHP Scheme (5) 23

  24. Section 4: CCGT with CHP – Large Scale (1) 1.0 Gas Turbine Waste Heat Boiler Generator Steam Turbine Station Electricity Use Heat Out Condenser Heat Losses from Mains Generator Electricity Out Irrecoverable Losses Useful Heat 24

  25. Section 4: CCGT with CHP – Large Scale (2) Gas Turbine 0.2375 Electricity 1.0 0.0125 Waste Heat Boiler Generator 0.25 0.75 0.125 Irrecoverable Losses 0.625 Gas turbine efficiency Electricity generated: 0.25 * 0.95 = 0.2375 Energy to Steam Turbine = 0.75 – 0.125 = 0.625 25

  26. Section 4: CCGT with CHP – Large Scale (3) Gas Turbine 0.2375 0.25 1.0 0.0125 0.75 Waste Heat Boiler 0.125 Irrecoverable Losses 0.0133 0.625 0.2523 0.2656 Generator Steam Turbine Condenser Generator Mechanical power to generator = 0.425 * 0.625 = 0.2656 Heat to Condenser = 0.625 – 0.2656 = 0.3594 Electricity out = 0.95 * 0.2656 = 0.2523 0.3594 steam turbine efficiency 26

  27. Section 4: CCGT with CHP – Large Scale (4) Gas Turbine 0.2375 0.25 1.0 Electricity Out 0.0125 0.75 Waste Heat Boiler 0.125 0.470 Irrecoverable Losses 0.0133 0.625 0.2523 0.2656 Generator Steam Turbine Station Electricity Use 0.3594 Heat Out 0.0196 Useful Heat 0.3594 Condenser 0.3048 Generator Heat Losses from Mains Station use of electricity = (0.2375 + 0.25230) * 0.04 = 0.196 Useful Heat = 0.3594*(1 – 0.152) = 0.3048 0.0546 27

  28. Section 4: CCGT with CHP – Large Scale (5) Summary of Scheme For each unit of fuel • Electricity available = 0.470 units • Heat sent out = 0.3594 units • Station efficiency = 0.470 + 0.3594 = 82.9% • But heat is lost form mains so only 0.3048 is actually useful • Overall system efficiency = 0.47 + 0.3048 = 77.5%

  29. NBSLM03E (2010) Low Carbon Technologies and Solutions N.K. Tovey (杜伟贤) M.A, PhD, CEng, MICE, CEnv Section 5: Heat Recovery Systems and Heat Pumps

  30. Section 5: Heat Recovery Systems and Heat Pumps • Parallel Plate Heat Exchanger Hot Fluid In Cold Fluid In

  31. Section 5: Heat Recovery Systems and Heat Pumps Hot Fluid In Cold Fluid In Parallel Flow Shell and Tube Exchanger Hot Fluid Temperature Cold Fluid Distance Inefficient: maximum temperature achieved is ~ 50% of temperature difference

  32. Section 5: Heat Recovery Systems and Heat Pumps Hot Fluid In Cold Fluid In Contra Flow Shell and Tube Exchanger Hot Fluid Temperature Temperature of heated fluid slightly less than original effluent hot fluid – more efficient Cold Fluid Distance

  33. Section 5: Regenerative Heat Exchangers Fresh Air Fresh Air Stale Air Stale Air Operation of Regenerative Heat Exchangers Stale air passes through Exchanger A and heats it up before exhausting to atmosphere Fresh Air is heated by exchanger B before going into building B A After ~ 90 seconds the flaps switch over. B Stale air passes through Exchanger B and heats it up before exhausting to atmosphere Fresh Air is heated by exchanger A before going into building A 33

  34. Section 5: Refrigerators andHeat Pumps Condenser Throttle Valve Compressor Evaporator A heat pump or refrigerator consists of four parts:- 1) an evaporator (operating under low pressure and temperature) 2) a compressor to raise the pressure of the working fluid 3) a condenser (operating under high pressure and temperature) 4) a throttle value to reduce the pressure from high to low. 34

  35. Section 5: Heat Pumps • Any low grade source of heat may be used • Typically coils buried in garden • Bore holes • Water bodies • Air • Example of roof solar panel with Heat Pump • Heat recovery in industrial processes A heat pump delivers 3, 4, or even 5 times as much heat as electricity put in. Working with thermodynamics not against it! 35

  36. Section 5: Heat Pumps • Performance is measured by Coefficient of Performance • (COP) • Theoretical Performance is defined by Carnot Relationship and may be large 6 – 10 as much heat is delivered as energy (electricity) input. • Practical COP in excess of 3. • i.e. Three times as much heat is obtained as work put in. • Remaining heat comes from the environment • The closer the temperature difference, the better the COP • Can be used for efficient heat recovery • Can recover the energy lost in electricity generation • Will out perform even a gas condensing boiler • Working with Thermodynamics - NOT against it 36

  37. The Norwich Heat Pump – 1944-6 Original Paper by John Sumner Proc. Institution of Mechanical Engineers (1947): Vol 156 p 338 37

  38. The Norwich Heat Pump – 1944-6 The History of the Site • The building was unique - the very first heat pump in the UK. • Installed during in early 1940s during the War. • Built from individual components which were not ideal. • Compressor was second hand built in early 1920’s ! for Ice making. • The evaporator and condenser had to be built specifically on site. • Refrigerant choice was limited during War - only sulphur dioxide was possible. • A COP of 3.45 was obtained - as measured over 2 years. • Even in 1940s, the heat pump was shown to perform better than older coal fired boiler.

  39. The Norwich Heat Pump – 1944-6 Condenser Compressor Evaporator The History of the Site • The Norwich Heat Pump - note the shape of the columns

  40. The Norwich Heat Pump – 1944-6 The History of the Site Schematic of the Norwich Heat Pump - from John Sumner’s Book - Heat Pumps 40

  41. The Norwich Heat Pump Building as it is today 41

  42. 13.6Types of Heat Pump For Space Heating Purposes: The heat source with water and the ground will involve laying coils of pipes in the relevant medium passing water, with anti-freeze to the heat exchanger. In air-source heat pumps, air can be passed directly through the heat exchanger. For Process Heat Schemes: the source may be a heat exchanger in the effluent of one process

  43. 13.6Types of Heat Pump Some Examples

  44. Advantages of Water as a heat source Readily Available Air Sources Heat Pumps are generally cheaper Disadvantages of Air as a heat source Noise on external fans Source temperature low when most heat needed: hence performance inferior at times of greatest need Source temperature varies greatly:- hence cannot optimise design External Heat Exchanger can freeze and provision must be made for defrosting. Generally heat pumps are not as robust as with other heat sources Section 5: Heat Pumps – Heat Sources 44

  45. Advantages of Water as a heat source source temperature normally higher than air or ground in winter: hence improved COP source temperature nearly constant: hence design can be optimised Can be either a water body or pumped from a bore hole Disadvantages of Water as a heat source not readily available size of water body must be consistent with total heat demand – e.g. a small pond would freeze rapidly and negate many advantages – large pond/lake/river avoid this issue. Section 5: Heat Pumps – Heat Sources 45

  46. Advantages of Ground as a heat source reasonable availability moderate source temperature - better than air, worse than water limited variation in source temperature: optimisation of design possible ground source heat pumps are more robust than air-source devices. can be used to store heat rejected from cooling in summer to accelerate ground heat recharge and improve CO{P in early part of following winter. Disadvantages of Ground as a heat source capital cost is great if retro-fitted land area can be large - for a carefully engineered system an area 1.5 – twice the total floor area of the building is required for systems in UK. Some contractors try to reduce area of heat source resulting in inadequate heat provision in severe weather. Section 5: Heat Pumps – Heat Sources 46

  47. Advantages of Air as a heat supply medium relatively low temperature: hence good COP possibility of heat recovery using mechanical ventilation. Possibility of use with air-conditioning and inter-seasonal heat store if used with ground source. Disadvantages of Air as a heat supply medium can only be fitted into warm air systems which require large ducts and less easy to install restrospectively than small bore hot water systems.. cannot be used with most current Central Heating systems in UK. Section 5: Heat Pumps – Heat Supply 47

  48. Advantages of Water as a heat supply medium more compact: can be incorporated with existing systems in use in UK Disadvantages of Water as a heat supply medium high operating temperature: hence lower COP Difficult to incorporate heat recovery Section 5: Heat Pumps – Heat Supply 48

  49. Advantages of under floor heating as a heat supply medium Low temperature ~35o C compared to ~ 60o C for hot water systems Possibility of using heat store in fabric. Disadvantages of under floor heating as a heat supply medium Cannot be fitted retrospectively: must be installed at time of construction. Difficult to incorporate ventilation heat recovery Section 5: Heat Pumps – Heat Supply 49

  50. Section 5: The Winnington – Tovey Heat Pump Waste Water Under floor Heating Condenser Solar Compressor Air Heating Ground Loop Stale Air 50

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