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This document discusses various topics related to cogeneration and waste heat recovery. It begins with an overview of cogeneration, including its need, applications, advantages, and classifications. It then covers waste heat recovery classifications and applications, as well as potential savings. The document also discusses technical options for cogeneration systems like steam turbines, gas turbines, and reciprocating engines. Key factors that influence cogeneration choice are then summarized such as heat-to-power ratios and matching thermal or electrical loads.

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Energy Audit & Management Cogeneration & Waste Heat Recovery : Unit 6
Outline • Cogeneration – Need – Applications – Advantages – Classification – The cogeneration design process • Waste heat recovery – Classification and application – Potential for waste-heat recovery in Industry – Commercial WHR devices – Saving potential • CDM projects and carbon credit calculations
DG set system Syllabus Diesel Generating system Factors affecting selection Energy performance assessment of diesel conservation avenues
How Diesel Cycle works ?
A.C. Generator Controls Diesel Engine Load Accessories Excitation Control Fuel Control Foundation Fig-9.2 DG Set System A DG set should be considered as a system
Specific fuel consumption • The specific fuel consumption has come down from a value of 220 g/kWh in the 1970s to a value around 160 g/kWh in present times. Slow speed diesel engine, with its flat fuel consumption curve over a wide load range (50%-100%), compares very favourably over other prime movers such as medium speed diesel engine, With high efficiency turbochargers, it is possible to use an exhaust gas driven turbine generator to further increase the engine rated output. Turbocharger
Advantages of adopting Diesel Power Plants are: • Low installation cost • Short delivery periods and installation period • Higher efficiency (as high as 43 -45 %) • More efficient plant performance under part loads • Suitable for different type of fuels such as low sulphur – heavy stock and heavy fuel oil in case of large capacities. • Minimum cooling water requirements, • Adopted with air cooled heat exchanger in areas • where water is not available • Short start up time
Altitude and Intake Temperature Corrections Correction Factors For Engine Output Altitude Correction Temperature Correction Altitude Meters over MSL Non Super Charged Super Charged Intake oC Correction Factor 610 0.980 0.980 32 1.000 915 0.935 0.950 35 0.986 1220 0.895 0.915 38 0.974 1525 0.855 0.882 41 0.962 1830 0.820 0.850 43 0.950 2130 0.780 0.820 46 0.937 2450 0.745 0.790 49 0.925 2750 0.712 0.765 52 0.913 3050 0.680 0.740 54 0.900 3660 0.612 0.685
Derating due to Air Inter Cooler Water Inlet Temperature Water Temperature oC Flow % Derating % 25 100 0 30 125 3 35 166 5 40 166 8
Power Factor: The load power factor is entirely dependent on the load. The A.C. generator is designed for the power factor of 0.8 lag as specified by standards. Lower power factor demands higher excitation currents and results in increased losses. Over sizing A.C. generators for operation at lower power factors results in lower operating efficiency and higher costs.
- Unbalanced Load: Unbalanced loads on A.C. generator leads to unbalanced set of voltages and additional heating in A.C. generator. Hence, the load on the A.C. generators should be balanced as far as possible. Transient Loading: On many occasions to contain transient voltage dip arising due to transient load application, a specially designed generator may have to be selected.
Energy Balance & Waste Heat Recovery in DG Sets A typical energy balance in a DG set indicates following break-up: Input :100% Thermal Energy Outputs :35% Electrical Output : 4% Alternator Losses :33% Stack Loss through Flue Gases :24% Coolant Losses : 4% Radiation Losses
Typical Format for DG Set Monitoring DG Set No. Electricity Generating Capacity (Site), kW Derated Electricity Generating Capacity, kW Type of Fuel used Average Load as % of Derated Capacity Specific Fuel Cons. Lit/kWh Specific Lube Oil Cons. Lit/kWh 1. 480 300 LDO 89 0.335 0.007 2. 480 300 LDO 110 0.334 0.024 3. 292 230 LDO 84 0.356 0.006 4. 200 160 HSD 89 0.325 0.003 5. 200 160 HSD 106 0.338 0.003 18. 880 750 LDO 78 0.345 0.007 19. 800 640 HSD 74 0.324 0.002
Energy Saving Measures for DG Sets  Ensure steady load conditions on the DG set, and provide cold, dust free air at intake  Improve air filtration.  Ensure fuel oil storage, handling and preparation as per manufacturers’ guidelines/oil company data.  Calibrate fuel injection pumps frequently.  Ensure compliance with maintenance checklist.  Ensure steady load conditions, avoiding fluctuations, imbalance in phases, harmonic loads.  For base load operation, consider waste heat recovery system steam generation or vapour absorption system adoption.  Consider parallel operation among the DG sets for improved loading .  Carryout regular field trials to monitor DG set performance, and maintenance planning as per requirements.
Cogeneration Need
Cogeneration Applications
Cogeneration Advantages
Cogeneration Classifications
Cogeneration The Design Process
Waste Heat Recovery Classification and Applications
Waste Heat Recovery Potential of Heat Recovery in Industry
Waste Heat Recovery Commercial Devices
Waste Heat Recovery Saving Potentials
CDM Projects
Energy Efficient Technologies
Maximum Demand
MD controller
Automatic Power Factor Controllers
Energy Efficient Motors
Design changes Table 10.1 Watt Loss Area and Efficiency Improvement {PRIVATE}Watts Loss Area Efficiency Improvement 1. Iron Use of thinner gauge, lower loss core steel reduces eddy current losses. Longer core adds more steel to the design, which reduces losses due to lower operating flux densities. 2. Stator I 2 R Use of more copper and larger conductors increases cross sectional area of stator windings. This lowers resistance (R) of the windings and reduces losses due to current flow (I). 3. Rotor I 2 R Use of larger rotor conductor bars increases size of cross section, lowering conductor resistance (R) and losses due to current flow (I). 4. Friction & Windage Use of low loss fan design reduces losses due to air movement. 5. Stray Load Loss Use of optimised design and strict quality control procedures minimizes stray load losses.
Technical aspects of Energy Efficient Motors • Energy-efficient motors last longer, and may require less maintenance. At lower temperatures, bearing grease lasts longer; required time between re-greasing increases. Lower temperatures translate to long lasting insulation. Generally, motor life doubles for each 10°C reduction in operating temperature. • Electrical power problems, especially poor incoming power quality can affect the operation of energy-efficient motors. • Speed control is crucial in some applications. In polyphase induction motors, slip is a measure of motor winding losses. The lower the slip, the higher the efficiency. Less slippage in energy efficient motors results in speeds about 1% faster than in standard counterparts. • Starting torque for efficient motors may be lower than for standard motors. Facility managers should be careful when applying efficient motors to high torque applications.
Soft Starters
Characteristics
Variable Frequency Drives Motors connected to VFD provide variable speed mechanical output with high efficiency. These devices are capable of up to a 9:1 speed reduction ratio (11 percent of full speed), and a 3:1 speed increase (300 percent of full speed).
Variable Torque Vs. Constant Torque • Variable torque loads include centrifugal pumps and fans, which make up the majority of HVAC applications. • Constant torque loads include vibrating conveyors, punch presses, rock crushers, machine tools, and other applications where the drive follows a constant V/Hz ratio. Typical full-load efficiencies are 95% and higher
Fluid coupling
Energy Efficient Transformers 1600 kVA Amorphous Core Transformer
Electronic Ballast
Energy Efficient Lighting Controls • Occupancy Sensors • Timed Based Control • Daylight Linked Control • Localized Switching
COGENERATION
Need for cogeneration
Principle of Cogeneration Through separate heat and power route primary energy input in power plant will be 60 units (24/0.40) If a separate boiler is used for steam generation then the fuel input to boiler will be 40 units (34/0.85). If the plant had cogeneration then the fuel input will be only 68 units (24+34)/0.85 to meet both electrical and thermal energy requirements It can be observed that the losses, which were 42 units in the case of, separate heat and power has reduced to 10 units in cogeneration mode Along with the saving of fossil fuels, cogeneration also allows to reduce the emission of greenhouse gases (particularly CO2 emission). The production of electricity being on-site, the burden on the utility network is reduced and the transmission line losses eliminated
Technical Options for Cogeneration • Cogeneration technologies that have been widely commercialized include – extraction/back pressure steam turbines – gas turbine with heat recovery boiler (with or without bottoming steam turbine) – reciprocating engines with heat recovery boiler
Steam turbine cogeneration systems
Steam turbine cogeneration features • The choice between backpressure turbine and extraction- condensing turbine depends mainly on the quantities of power and heat, quality of heat, and economic factors • option for using a wide variety of conventional as well as alternative fuels such as coal, natural gas, fuel oil and biomass • power generation efficiency of the cycle may be sacrificed to some extent in order to optimize heat supply • In backpressure cogeneration plants, there is no need for large cooling towers • Steam turbines are mostly used where the demand for electricity is greater than one MW up to a few hundreds of MW • Due to the system inertia, their operation is not suitable for sites with intermittent energy demand
Gas turbine cogeneration systems
Gas turbine cogeneration features • natural gas is most commonly used; other fuels such as light fuel oil or diesel can also be employed • The typical range of gas turbines varies from a fraction of a MW to around 100 MW • the gestation period for developing a project is shorter and the equipment can be delivered in a modular manner • Gas turbine has a short start-up time and provides the flexibility of intermittent operation • If the heat output is less than that required by the user, it is possible to have supplementary natural gas firing • if more power is required at the site, it is possible to adopt a combined cycle that is a combination of gas turbine and steam turbine cogeneration
Reciprocating engine cogeneration systems
Reciprocating engine cogeneration features • high power generation efficiencies in comparison with other prime movers • There are two sources of heat for recovery: exhaust gas at high temperature and engine jacket cooling water system at low temperature • more popular with smaller energy consuming facilities, particularly those having a greater need for electricity than thermal energy • diesel has been the most common fuel in the past, the prime movers can also operate with heavy fuel oil or natural gas • ideal for intermittent operation and their performance is not as sensitive to the changes in ambient temperatures as the gas turbines • Though the initial investment on these machines is low, their operating and maintenance costs are high due to high wear and tear
Classification of Cogeneration Systems • A cogeneration system can be classified as either a topping or a bottoming cycle on the basis of the sequence of energy use • In a topping cycle, the fuel supplied is used to first produce power and then thermal energy, which is the by- product of the cycle and is used to satisfy process heat or other thermal requirements • In a bottoming cycle, the primary fuel produces high temperature thermal energy and the heat rejected from the process is used to generate power through a recovery boiler and a turbine generator
Combined-cycle topping system
Steam-turbine topping system
Diesel engine topping cycle
Gas-turbine topping system
Bottoming Cycle
Factors Influencing Cogeneration Choice
Base electrical load matching • the cogeneration plant is sized to meet the minimum electricity demand of the site based on the historical demand curve • rest of the needed power is purchased from the utility grid • thermal energy requirement of the site could be met by the cogeneration system alone or by additional boilers • If the thermal energy generated with the base electrical load exceeds the plant’s demand and if the situation permits, excess thermal energy can be exported to neighbouring customers
Base thermal load matching • the cogeneration system is sized to supply the minimum thermal energy requirement of the site. Stand-by boilers or burners are operated during periods when the demand for heat is higher • The prime mover installed operates at full load at all times • If the electricity demand of the site exceeds that which can be provided by the prime mover, then the remaining amount can be purchased from the grid • Likewise, if local laws permit, the excess electricity can be sold to the power utility
Electrical load matching • the facility is totally independent of the power utility grid • All the power requirements of the site, including the reserves needed during scheduled and unscheduled maintenance, are to be taken into account while sizing the system • This is also referred to as a “stand-alone” system • If the thermal energy demand of the site is higher than that generated by the cogeneration system, auxiliary boilers are used • On the other hand, when the thermal energy demand is low, some thermal energy is wasted • If there is a possibility, excess thermal energy can be exported to neighbouring facilities
Thermal load matching • The cogeneration system is designed to meet the thermal energy requirement of the site at any time • The prime movers are operated following the thermal demand • During the period when the electricity demand exceeds the generation capacity, the deficit can be compensated by power purchased from the grid • Similarly, if the local legislation permits, electricity produced in excess at any time may be sold to the utility
Important Technical Parameters for Cogeneration
Heat-to-power ratio • Heat-to-power ratio is one of the most important technical parameters influencing the selection of the type of cogeneration system • The heat-to-power ratio of a facility should match with the characteristics of the cogeneration system to be installed • It is defined as the ratio of thermal energy to electricity required by the energy consuming facility • Though it can be expressed in different units such as Btu/kWh, kcal/kWh, lb./hr/kW, etc., here it is presented on the basis of the same energy unit (kW) • The steam turbine cogeneration system can offer a large range of heat-to- power ratios. • The proportions of heat and power needed (heat: power ratio) vary from site to site, so the type of plant must be selected carefully and appropriate operating schemes must be established to match demands as closely as possible
Heat-to-power ratios and other parameters of cogeneration systems Cogeneration System Heat-to-power ratio (kWth / kWe) Power output (as per cent of fuel input) Overall efficiency (per cent) Back-pressure steam turbine 4.0-14.3 14-28 84-92 Extraction-condensing steam turbine 2.0-10.0 22-40 60-80 Gas turbine 1.3-2.0 24-35 70-85 Combined cycle 1.0-1.7 34-40 69-83 Reciprocating engine 1.1-2.5 33-53 75-85
Typical Heat: Power Ratios for Certain Energy Intensive Industries Industry Minimum Maximum Average Breweries 1.1 4.5 3.1 Pharmaceuticals 1.5 2.5 2.0 Fertilizer 0.8 3.0 2.0 Food 0.8 2.5 1.2 Paper 1.5 2.5 1.9
Cogeneration is likely to be most attractive if • The demand for both steam and power is balanced i.e. consistent with the range of steam: power output ratios that can be obtained from a suitable cogeneration plant. • A single plant or group of plants has sufficient demand for steam and power to permit economies of scale to be achieved. • Peaks and troughs in demand can be managed or, in the case of electricity, adequate backup supplies can be obtained from the utility company
Quality of thermal energy needed • The quality of thermal energy required (temperature and pressure) also determines the type of cogeneration system • For a sugar mill needing thermal energy at about 120°C, a topping cycle cogeneration system can meet the heat demand • On the other hand, for a cement plant requiring thermal energy at about 1450°C, a bottoming cycle cogeneration system can meet both high quality thermal energy and electricity demands of the plant
Load patterns
Fuels available • Depending on the availability of fuels, some potential cogeneration systems may have to be rejected • The availability of cheap fuels or waste products that can be used as fuels at a site is one of the major factors in the technical consideration because it determines the competitiveness of the cogeneration system. • A rice mill needs mechanical power for milling and heat for paddy drying. • If a cogeneration system were considered, the steam turbine system would be the first priority because it can use the rice husk as the fuel, which is available as waste product from the mill.
System reliability • Some energy consuming facilities require very reliable power and/or heat • for instance, a pulp and paper industry cannot operate with a prolonged unavailability of process steam • In such instances, the cogeneration system to be installed must be modular, i.e. it should consist of more than one unit so that shut down of a specific unit cannot seriously affect the energy supply
Grid dependent system versus independent system • A grid-dependent system has access to the grid to buy or sell electricity • The grid-independent system is also known as a “stand- alone” system that meets all the energy demands of the site • It is obvious that for the same energy consuming facility, the technical configuration of the cogeneration system designed as a grid dependent system would be different from that of a stand-alone system.
Retrofit versus new installation • If the cogeneration system is installed as a retrofit, the system must be designed so that the existing energy conversion systems, such as boilers, can still be used • In such a circumstance, the options for cogeneration system would depend on whether the system is a retrofit or a new installation
Electricity buy-back • The technical consideration of cogeneration system must take into account whether the local regulations permit electric utilities to buy electricity from the cogenerators or not • The size and type of cogeneration system could be significantly different if one were to allow the export of electricity to the grid
Local environmental regulation • The local environmental regulations can limit the choice of fuels to be used for the proposed cogeneration systems • If the local environmental regulations are stringent, some available fuels cannot be considered because of the high treatment cost of the polluted exhaust gas and in some cases, the fuel itself
Prime Movers for Cogeneration
Steam Turbine
Back pressure Steam Turbine
Extraction condensing Steam Turbine
Gas Turbine
Reciprocating Engine Systems
Typical Cogeneration Performance Parameters Efficiencies, % Prime Mover in Cogen. Package Nominal Range (Electrical) Electrical Generation Heat Rate (kCal / kWH Electrical Conversion Thermal Recovery Overall Cogenerati on Smaller Reciprocating Engines 10 – 500 kW 2650 - 6300 20-32 50 74-82 Larger Reciprocating Engines 500 – 3000 kW 2400 - 3275 26-36 50 76-86 Diesel Engines 10-3000 kW 2770 - 3775 23-38 50 73-88 Smaller Gas Turbines 800-10000 kW 2770-3525 24-31 50 74-81 Larger Gas Turbines 10-20 MW 2770-3275 26-31 50 78-81 Steam Turbines 10-100 MW 2520-5040 17-34 - - Note: Adapted from Cogeneration Handbook California Energy Commission, 1982
Relative Merits of Cogeneration Systems Variant Advantages Disadvantages Back pressure - High fuel efficiency rating - Little flexibility indesign and operation Steam turbine & fuel firing in boiler Simple plant Well-suited to low quality fuels More capital investment Low fuel efficiency rating High cooling water demand More impact on environment High civil const. cost due to complicated foundations Gas turbine with waste heat recovery boiler Good fuel efficiency Simple plant Low civil const. Cost Less delivery period Less impact on environment High flexibility in operation Moderate part load efficiency Limited suitability for low quality fuels Combined gas & steam turbine with waste heat recovery boiler Optimum fuel efficiency rating Low relative capital cost Less gestation period Quick start up & stoppage Less impact on environment High flexibility in operation Average to moderate part-load efficiency Limited suitability for low quality fuels Diesel Engine & waste heat recovery Boiler & cooling water heat exchanger Low civil const. Cost due to block foundations & least no. of auxiliaries High Power efficiency Better suitability as stand by power source Low overall efficiency Limited suitability for low quality fuels Availability of low temperature steam Highly maintenance prone.
Waste Heat Recovery (WHR)
8.1 Introduction What is waste heat? • Waste heat is heat, which is generated in a process by way of fuel combustion or chemical reaction, and then “dumped” into the environment even though it could still be reused for some useful and economic purpose.
Sources of Waste Heat • Boilers • Kilns • Ovens • Furnaces • DG Sets • Thermic Fluid Heaters • Low temperature process streams
Factors determining WHR • Heat Loss Quality Quantity
8.2 Classification and Application Source Quality Heat in flue gases. The higher the temperature, the greater the potential value for heat recovery Heat in vapour streams. As above but when condensed, latent heat also recoverable. Convective and radiant heat lost from exterior of equipment Low grade – if collected may be used for space heating or air preheats. Heat losses in cooling water. Low grade – useful gains if heat is exchanged with incoming fresh water.
Classification and Application Source Quality Heat losses in providing chilled water or in the disposal of chilled water. a) High grade if it can be utilized to reduce demand for refrigeration. b) Low grade if refrigeration unit used as a form of heat pump. Heat stored in products leaving the process Quality depends upon temperature. Heat in gaseous and liquid effluents leaving process. Poor if heavily contaminated and thus requiring alloy heat exchanger.
High Temperature Heat Recovery Types of Device Temperature, oC Nickel refining furnace 1370 –1650 Aluminium refining furnace 650-760 Zinc refining furnace 760-1100 Copper reverberatory furnace 900-1100 Cement kiln (Dry process) 620- 730 Glass melting furnace 1000-1550
Medium Temperature Heat Recovery Types of Device Temperature, oC Steam boiler exhausts 230-480 Gas turbine exhausts 370-540 Reciprocating engine exhausts 315-600 Heat treating furnaces 425 - 650 Catalytic crackers 425 - 650 Annealing furnace cooling systems 425 - 650
Low Temperature Heat Recovery Source Temperature, oC Process steam condensate 55-88 Cooling water from: Furnace doors 32-55 Annealing furnaces 66-230 Air compressors 27-50 Air conditioning and refrigeration condensers 32–43
Benefits of WHR • Direct benefits • Indirect benefits Reduction in Pollution Reduction in equipment sizes Reduction in auxiliary Energy consumption
Development of Waste Heat Recovery System • Understand the process – Sources and uses of waste heat – Upset conditions occurring in the plant due to heat recovery – Availability of space – Any other constraint, such as dew point occurring in an equipment, etc. • Economic evaluation of WHR System
Commercial WHR Devices • Recuperator • Regenerator • Heat Wheel • Heat Pipe • Economiser • Shell and tube heat exchanger • Waste heat boiler • Heat Pump • Thermocompressor • Direct contact heat exchanger
Recuperator In a recuperator, heat exchange takes place between the flue gases and the air through metallic or ceramic walls. Duct or tubes carry the air for combustion to be pre-heated, the other side contains the waste heat stream.
Metallic Radiation Recuperator The radiation recuperator gets its name from the fact that a substantial portion of the heat transfer from the hot gases to the surface of the inner tube takes place by radiative heat transfer Figure 8.2 Metallic Radiation Recuperator
Convective Recuperator The hot gases are carried through a number of parallel small diameter tubes, while the incoming air to be heated enters a shell surrounding the tubes and passes over the hot tubes one or more times in a direction normal to their axes.
Convective Radiative Recuperator For maximum effectiveness of heat transfer, combinations of radiation and convective designs are used, with the high-temperature radiation recuperator being first followed by convection type.
Ceramic Recuperator • In order to overcome the temperature limitation of metallic recuperators which is about 1000oC on the gas side, ceramic tube recuperators have been developed. • The materials of ceramic recuperators allow operation on the gas side up to 1300 oC and on the preheated air side up to 850 oC.
Regenerator The Regeneration which is preferable for large capacities has been very widely used in glass and steel melting furnaces. Important relations exist between the size of the regenerator, time between reversals, thickness of brick, conductivity of brick and heat storage ratio of the brick.
Heat Wheels Widely used in low to medium temperature waste heat recovery systems. A disk rotates between two side-by-side ducts: one a cold gas duct, the other a hot gas duct. As the disk slowly rotates, sensible heat (moisture that contains latent heat) is transferred to the disk by the hot air and, as the disk rotates, from the disk to the cold air.
Heat Pipe Heat pipe is a thermal energy absorbing and transferring system and have no moving parts and hence require minimum maintenance. wall
Economiser Widely used in a boiler system 1. To pre-heat the boiler feed water. 2. To pre-heat the combustion air. by utilizing the heat in the flue gas.
Shell and Tube Heat Exchanger When the medium containing waste heat is a liquid or a vapor which heats another liquid, then the shell and tube heat exchanger must be used since both paths must be sealed to contain the pressures of their respective fluids.
Plate Heat Exchanger The cost of heat exchange surfaces is a major factor when the temperature differences are not large. In such case this is used. Hot liquid passing through a bottom port in the head is permitted to pass upwards between every second plate while cold liquid at the top of the head is permitted to pass downwards between the odd plates. When the directions of hot & cold fluids are opposite, the arrangement is described as counter current Figure 8.10 Plate Heat Exchanger
Waste Heat Boilers Waste heat boilers are ordinarily water tube boilers in which the hot exhaust gases from gas turbines, incinerators, etc., pass over a number of parallel tubes containing water. The water is vaporized in the tubes and collected in a steam drum from which it is drawn off for use as heating or processing steam
Heat Pumps
Heat pump processes : 1. In the evaporator the heat is extracted from the heat source to boil the circulating substance; 2. The circulating substance is compressed by the compressor, raising its pressure and temperature; The low temperature vapor is compressed by a compressor, which requires external work. The work done on the vapor raises its pressure and temperature to a level where its energy becomes available for use 3. The heat is delivered to the condenser; 4. The pressure of the circulating substance (working fluid) is reduced back to the evaporator condition in the throttling valve, where the cycle repeats. The heat pump was developed as a space heating system The heat pumps have the ability to upgrade heat to a value more than twice that of the energy consumed by the device
Thermocompressor SUCTION STEAM L.P. Discharge Steam M.P Motive Steam H.P The thermocompressor is a simple equipment with a nozzle where HP steam is accelerated into a high velocity fluid. This entrains the LP steam by momentum transfer and then recompresses in a divergent venturi.
Direct Contact Heat Exchanger COLD WATER IN VENT L.P. STEAM HOT WATER Low pressure steam may also be used to preheat the feed water or some other fluid where miscibility is acceptable. This principle is used here.

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Unit_No_6.pptx

  • 1.
    Energy Audit &Management Cogeneration & Waste Heat Recovery : Unit 6
  • 2.
    Outline • Cogeneration – Need –Applications – Advantages – Classification – The cogeneration design process • Waste heat recovery – Classification and application – Potential for waste-heat recovery in Industry – Commercial WHR devices – Saving potential • CDM projects and carbon credit calculations
  • 3.
    DG set system Syllabus DieselGenerating system Factors affecting selection Energy performance assessment of diesel conservation avenues
  • 4.
  • 5.
    A.C. Generator Controls DieselEngine Load Accessories Excitation Control Fuel Control Foundation Fig-9.2 DG Set System A DG set should be considered as a system
  • 6.
    Specific fuel consumption •The specific fuel consumption has come down from a value of 220 g/kWh in the 1970s to a value around 160 g/kWh in present times. Slow speed diesel engine, with its flat fuel consumption curve over a wide load range (50%-100%), compares very favourably over other prime movers such as medium speed diesel engine, With high efficiency turbochargers, it is possible to use an exhaust gas driven turbine generator to further increase the engine rated output. Turbocharger
  • 7.
    Advantages of adoptingDiesel Power Plants are: • Low installation cost • Short delivery periods and installation period • Higher efficiency (as high as 43 -45 %) • More efficient plant performance under part loads • Suitable for different type of fuels such as low sulphur – heavy stock and heavy fuel oil in case of large capacities. • Minimum cooling water requirements, • Adopted with air cooled heat exchanger in areas • where water is not available • Short start up time
  • 8.
    Altitude and IntakeTemperature Corrections Correction Factors For Engine Output Altitude Correction Temperature Correction Altitude Meters over MSL Non Super Charged Super Charged Intake oC Correction Factor 610 0.980 0.980 32 1.000 915 0.935 0.950 35 0.986 1220 0.895 0.915 38 0.974 1525 0.855 0.882 41 0.962 1830 0.820 0.850 43 0.950 2130 0.780 0.820 46 0.937 2450 0.745 0.790 49 0.925 2750 0.712 0.765 52 0.913 3050 0.680 0.740 54 0.900 3660 0.612 0.685
  • 9.
    Derating due toAir Inter Cooler Water Inlet Temperature Water Temperature oC Flow % Derating % 25 100 0 30 125 3 35 166 5 40 166 8
  • 10.
    Power Factor: The loadpower factor is entirely dependent on the load. The A.C. generator is designed for the power factor of 0.8 lag as specified by standards. Lower power factor demands higher excitation currents and results in increased losses. Over sizing A.C. generators for operation at lower power factors results in lower operating efficiency and higher costs.
  • 11.
    - Unbalanced Load: Unbalancedloads on A.C. generator leads to unbalanced set of voltages and additional heating in A.C. generator. Hence, the load on the A.C. generators should be balanced as far as possible. Transient Loading: On many occasions to contain transient voltage dip arising due to transient load application, a specially designed generator may have to be selected.
  • 12.
    Energy Balance & WasteHeat Recovery in DG Sets A typical energy balance in a DG set indicates following break-up: Input :100% Thermal Energy Outputs :35% Electrical Output : 4% Alternator Losses :33% Stack Loss through Flue Gases :24% Coolant Losses : 4% Radiation Losses
  • 13.
    Typical Format forDG Set Monitoring DG Set No. Electricity Generating Capacity (Site), kW Derated Electricity Generating Capacity, kW Type of Fuel used Average Load as % of Derated Capacity Specific Fuel Cons. Lit/kWh Specific Lube Oil Cons. Lit/kWh 1. 480 300 LDO 89 0.335 0.007 2. 480 300 LDO 110 0.334 0.024 3. 292 230 LDO 84 0.356 0.006 4. 200 160 HSD 89 0.325 0.003 5. 200 160 HSD 106 0.338 0.003 18. 880 750 LDO 78 0.345 0.007 19. 800 640 HSD 74 0.324 0.002
  • 14.
    Energy Saving Measuresfor DG Sets  Ensure steady load conditions on the DG set, and provide cold, dust free air at intake  Improve air filtration.  Ensure fuel oil storage, handling and preparation as per manufacturers’ guidelines/oil company data.  Calibrate fuel injection pumps frequently.  Ensure compliance with maintenance checklist.  Ensure steady load conditions, avoiding fluctuations, imbalance in phases, harmonic loads.  For base load operation, consider waste heat recovery system steam generation or vapour absorption system adoption.  Consider parallel operation among the DG sets for improved loading .  Carryout regular field trials to monitor DG set performance, and maintenance planning as per requirements.
  • 15.
  • 16.
  • 17.
  • 18.
  • 19.
  • 20.
  • 21.
    Waste Heat Recovery Potentialof Heat Recovery in Industry
  • 22.
  • 23.
  • 24.
  • 26.
  • 27.
  • 28.
  • 29.
  • 30.
  • 31.
    Design changes Table 10.1Watt Loss Area and Efficiency Improvement {PRIVATE}Watts Loss Area Efficiency Improvement 1. Iron Use of thinner gauge, lower loss core steel reduces eddy current losses. Longer core adds more steel to the design, which reduces losses due to lower operating flux densities. 2. Stator I 2 R Use of more copper and larger conductors increases cross sectional area of stator windings. This lowers resistance (R) of the windings and reduces losses due to current flow (I). 3. Rotor I 2 R Use of larger rotor conductor bars increases size of cross section, lowering conductor resistance (R) and losses due to current flow (I). 4. Friction & Windage Use of low loss fan design reduces losses due to air movement. 5. Stray Load Loss Use of optimised design and strict quality control procedures minimizes stray load losses.
  • 33.
    Technical aspects ofEnergy Efficient Motors • Energy-efficient motors last longer, and may require less maintenance. At lower temperatures, bearing grease lasts longer; required time between re-greasing increases. Lower temperatures translate to long lasting insulation. Generally, motor life doubles for each 10°C reduction in operating temperature. • Electrical power problems, especially poor incoming power quality can affect the operation of energy-efficient motors. • Speed control is crucial in some applications. In polyphase induction motors, slip is a measure of motor winding losses. The lower the slip, the higher the efficiency. Less slippage in energy efficient motors results in speeds about 1% faster than in standard counterparts. • Starting torque for efficient motors may be lower than for standard motors. Facility managers should be careful when applying efficient motors to high torque applications.
  • 34.
  • 35.
  • 36.
    Variable Frequency Drives Motorsconnected to VFD provide variable speed mechanical output with high efficiency. These devices are capable of up to a 9:1 speed reduction ratio (11 percent of full speed), and a 3:1 speed increase (300 percent of full speed).
  • 37.
    Variable Torque Vs.Constant Torque • Variable torque loads include centrifugal pumps and fans, which make up the majority of HVAC applications. • Constant torque loads include vibrating conveyors, punch presses, rock crushers, machine tools, and other applications where the drive follows a constant V/Hz ratio. Typical full-load efficiencies are 95% and higher
  • 38.
  • 39.
    Energy Efficient Transformers 1600kVA Amorphous Core Transformer
  • 40.
  • 41.
    Energy Efficient LightingControls • Occupancy Sensors • Timed Based Control • Daylight Linked Control • Localized Switching
  • 42.
  • 43.
  • 44.
    Principle of Cogeneration Throughseparate heat and power route primary energy input in power plant will be 60 units (24/0.40) If a separate boiler is used for steam generation then the fuel input to boiler will be 40 units (34/0.85). If the plant had cogeneration then the fuel input will be only 68 units (24+34)/0.85 to meet both electrical and thermal energy requirements It can be observed that the losses, which were 42 units in the case of, separate heat and power has reduced to 10 units in cogeneration mode Along with the saving of fossil fuels, cogeneration also allows to reduce the emission of greenhouse gases (particularly CO2 emission). The production of electricity being on-site, the burden on the utility network is reduced and the transmission line losses eliminated
  • 45.
    Technical Options forCogeneration • Cogeneration technologies that have been widely commercialized include – extraction/back pressure steam turbines – gas turbine with heat recovery boiler (with or without bottoming steam turbine) – reciprocating engines with heat recovery boiler
  • 46.
  • 47.
    Steam turbine cogenerationfeatures • The choice between backpressure turbine and extraction- condensing turbine depends mainly on the quantities of power and heat, quality of heat, and economic factors • option for using a wide variety of conventional as well as alternative fuels such as coal, natural gas, fuel oil and biomass • power generation efficiency of the cycle may be sacrificed to some extent in order to optimize heat supply • In backpressure cogeneration plants, there is no need for large cooling towers • Steam turbines are mostly used where the demand for electricity is greater than one MW up to a few hundreds of MW • Due to the system inertia, their operation is not suitable for sites with intermittent energy demand
  • 48.
  • 49.
    Gas turbine cogenerationfeatures • natural gas is most commonly used; other fuels such as light fuel oil or diesel can also be employed • The typical range of gas turbines varies from a fraction of a MW to around 100 MW • the gestation period for developing a project is shorter and the equipment can be delivered in a modular manner • Gas turbine has a short start-up time and provides the flexibility of intermittent operation • If the heat output is less than that required by the user, it is possible to have supplementary natural gas firing • if more power is required at the site, it is possible to adopt a combined cycle that is a combination of gas turbine and steam turbine cogeneration
  • 50.
  • 51.
    Reciprocating engine cogenerationfeatures • high power generation efficiencies in comparison with other prime movers • There are two sources of heat for recovery: exhaust gas at high temperature and engine jacket cooling water system at low temperature • more popular with smaller energy consuming facilities, particularly those having a greater need for electricity than thermal energy • diesel has been the most common fuel in the past, the prime movers can also operate with heavy fuel oil or natural gas • ideal for intermittent operation and their performance is not as sensitive to the changes in ambient temperatures as the gas turbines • Though the initial investment on these machines is low, their operating and maintenance costs are high due to high wear and tear
  • 52.
    Classification of CogenerationSystems • A cogeneration system can be classified as either a topping or a bottoming cycle on the basis of the sequence of energy use • In a topping cycle, the fuel supplied is used to first produce power and then thermal energy, which is the by- product of the cycle and is used to satisfy process heat or other thermal requirements • In a bottoming cycle, the primary fuel produces high temperature thermal energy and the heat rejected from the process is used to generate power through a recovery boiler and a turbine generator
  • 53.
  • 54.
  • 55.
  • 56.
  • 57.
  • 58.
  • 59.
    Base electrical loadmatching • the cogeneration plant is sized to meet the minimum electricity demand of the site based on the historical demand curve • rest of the needed power is purchased from the utility grid • thermal energy requirement of the site could be met by the cogeneration system alone or by additional boilers • If the thermal energy generated with the base electrical load exceeds the plant’s demand and if the situation permits, excess thermal energy can be exported to neighbouring customers
  • 60.
    Base thermal loadmatching • the cogeneration system is sized to supply the minimum thermal energy requirement of the site. Stand-by boilers or burners are operated during periods when the demand for heat is higher • The prime mover installed operates at full load at all times • If the electricity demand of the site exceeds that which can be provided by the prime mover, then the remaining amount can be purchased from the grid • Likewise, if local laws permit, the excess electricity can be sold to the power utility
  • 61.
    Electrical load matching •the facility is totally independent of the power utility grid • All the power requirements of the site, including the reserves needed during scheduled and unscheduled maintenance, are to be taken into account while sizing the system • This is also referred to as a “stand-alone” system • If the thermal energy demand of the site is higher than that generated by the cogeneration system, auxiliary boilers are used • On the other hand, when the thermal energy demand is low, some thermal energy is wasted • If there is a possibility, excess thermal energy can be exported to neighbouring facilities
  • 62.
    Thermal load matching •The cogeneration system is designed to meet the thermal energy requirement of the site at any time • The prime movers are operated following the thermal demand • During the period when the electricity demand exceeds the generation capacity, the deficit can be compensated by power purchased from the grid • Similarly, if the local legislation permits, electricity produced in excess at any time may be sold to the utility
  • 63.
  • 64.
    Heat-to-power ratio • Heat-to-powerratio is one of the most important technical parameters influencing the selection of the type of cogeneration system • The heat-to-power ratio of a facility should match with the characteristics of the cogeneration system to be installed • It is defined as the ratio of thermal energy to electricity required by the energy consuming facility • Though it can be expressed in different units such as Btu/kWh, kcal/kWh, lb./hr/kW, etc., here it is presented on the basis of the same energy unit (kW) • The steam turbine cogeneration system can offer a large range of heat-to- power ratios. • The proportions of heat and power needed (heat: power ratio) vary from site to site, so the type of plant must be selected carefully and appropriate operating schemes must be established to match demands as closely as possible
  • 65.
    Heat-to-power ratios andother parameters of cogeneration systems Cogeneration System Heat-to-power ratio (kWth / kWe) Power output (as per cent of fuel input) Overall efficiency (per cent) Back-pressure steam turbine 4.0-14.3 14-28 84-92 Extraction-condensing steam turbine 2.0-10.0 22-40 60-80 Gas turbine 1.3-2.0 24-35 70-85 Combined cycle 1.0-1.7 34-40 69-83 Reciprocating engine 1.1-2.5 33-53 75-85
  • 66.
    Typical Heat: PowerRatios for Certain Energy Intensive Industries Industry Minimum Maximum Average Breweries 1.1 4.5 3.1 Pharmaceuticals 1.5 2.5 2.0 Fertilizer 0.8 3.0 2.0 Food 0.8 2.5 1.2 Paper 1.5 2.5 1.9
  • 67.
    Cogeneration is likelyto be most attractive if • The demand for both steam and power is balanced i.e. consistent with the range of steam: power output ratios that can be obtained from a suitable cogeneration plant. • A single plant or group of plants has sufficient demand for steam and power to permit economies of scale to be achieved. • Peaks and troughs in demand can be managed or, in the case of electricity, adequate backup supplies can be obtained from the utility company
  • 68.
    Quality of thermalenergy needed • The quality of thermal energy required (temperature and pressure) also determines the type of cogeneration system • For a sugar mill needing thermal energy at about 120°C, a topping cycle cogeneration system can meet the heat demand • On the other hand, for a cement plant requiring thermal energy at about 1450°C, a bottoming cycle cogeneration system can meet both high quality thermal energy and electricity demands of the plant
  • 69.
  • 70.
    Fuels available • Dependingon the availability of fuels, some potential cogeneration systems may have to be rejected • The availability of cheap fuels or waste products that can be used as fuels at a site is one of the major factors in the technical consideration because it determines the competitiveness of the cogeneration system. • A rice mill needs mechanical power for milling and heat for paddy drying. • If a cogeneration system were considered, the steam turbine system would be the first priority because it can use the rice husk as the fuel, which is available as waste product from the mill.
  • 71.
    System reliability • Someenergy consuming facilities require very reliable power and/or heat • for instance, a pulp and paper industry cannot operate with a prolonged unavailability of process steam • In such instances, the cogeneration system to be installed must be modular, i.e. it should consist of more than one unit so that shut down of a specific unit cannot seriously affect the energy supply
  • 72.
    Grid dependent systemversus independent system • A grid-dependent system has access to the grid to buy or sell electricity • The grid-independent system is also known as a “stand- alone” system that meets all the energy demands of the site • It is obvious that for the same energy consuming facility, the technical configuration of the cogeneration system designed as a grid dependent system would be different from that of a stand-alone system.
  • 73.
    Retrofit versus newinstallation • If the cogeneration system is installed as a retrofit, the system must be designed so that the existing energy conversion systems, such as boilers, can still be used • In such a circumstance, the options for cogeneration system would depend on whether the system is a retrofit or a new installation
  • 74.
    Electricity buy-back • Thetechnical consideration of cogeneration system must take into account whether the local regulations permit electric utilities to buy electricity from the cogenerators or not • The size and type of cogeneration system could be significantly different if one were to allow the export of electricity to the grid
  • 75.
    Local environmental regulation •The local environmental regulations can limit the choice of fuels to be used for the proposed cogeneration systems • If the local environmental regulations are stringent, some available fuels cannot be considered because of the high treatment cost of the polluted exhaust gas and in some cases, the fuel itself
  • 76.
    Prime Movers forCogeneration
  • 77.
  • 78.
  • 79.
  • 80.
  • 81.
  • 82.
    Typical Cogeneration PerformanceParameters Efficiencies, % Prime Mover in Cogen. Package Nominal Range (Electrical) Electrical Generation Heat Rate (kCal / kWH Electrical Conversion Thermal Recovery Overall Cogenerati on Smaller Reciprocating Engines 10 – 500 kW 2650 - 6300 20-32 50 74-82 Larger Reciprocating Engines 500 – 3000 kW 2400 - 3275 26-36 50 76-86 Diesel Engines 10-3000 kW 2770 - 3775 23-38 50 73-88 Smaller Gas Turbines 800-10000 kW 2770-3525 24-31 50 74-81 Larger Gas Turbines 10-20 MW 2770-3275 26-31 50 78-81 Steam Turbines 10-100 MW 2520-5040 17-34 - - Note: Adapted from Cogeneration Handbook California Energy Commission, 1982
  • 83.
    Relative Merits ofCogeneration Systems Variant Advantages Disadvantages Back pressure - High fuel efficiency rating - Little flexibility indesign and operation Steam turbine & fuel firing in boiler Simple plant Well-suited to low quality fuels More capital investment Low fuel efficiency rating High cooling water demand More impact on environment High civil const. cost due to complicated foundations Gas turbine with waste heat recovery boiler Good fuel efficiency Simple plant Low civil const. Cost Less delivery period Less impact on environment High flexibility in operation Moderate part load efficiency Limited suitability for low quality fuels Combined gas & steam turbine with waste heat recovery boiler Optimum fuel efficiency rating Low relative capital cost Less gestation period Quick start up & stoppage Less impact on environment High flexibility in operation Average to moderate part-load efficiency Limited suitability for low quality fuels Diesel Engine & waste heat recovery Boiler & cooling water heat exchanger Low civil const. Cost due to block foundations & least no. of auxiliaries High Power efficiency Better suitability as stand by power source Low overall efficiency Limited suitability for low quality fuels Availability of low temperature steam Highly maintenance prone.
  • 84.
  • 85.
    8.1 Introduction What iswaste heat? • Waste heat is heat, which is generated in a process by way of fuel combustion or chemical reaction, and then “dumped” into the environment even though it could still be reused for some useful and economic purpose.
  • 86.
    Sources of WasteHeat • Boilers • Kilns • Ovens • Furnaces • DG Sets • Thermic Fluid Heaters • Low temperature process streams
  • 87.
    Factors determining WHR •Heat Loss Quality Quantity
  • 88.
    8.2 Classification andApplication Source Quality Heat in flue gases. The higher the temperature, the greater the potential value for heat recovery Heat in vapour streams. As above but when condensed, latent heat also recoverable. Convective and radiant heat lost from exterior of equipment Low grade – if collected may be used for space heating or air preheats. Heat losses in cooling water. Low grade – useful gains if heat is exchanged with incoming fresh water.
  • 89.
    Classification and Application SourceQuality Heat losses in providing chilled water or in the disposal of chilled water. a) High grade if it can be utilized to reduce demand for refrigeration. b) Low grade if refrigeration unit used as a form of heat pump. Heat stored in products leaving the process Quality depends upon temperature. Heat in gaseous and liquid effluents leaving process. Poor if heavily contaminated and thus requiring alloy heat exchanger.
  • 90.
    High Temperature HeatRecovery Types of Device Temperature, oC Nickel refining furnace 1370 –1650 Aluminium refining furnace 650-760 Zinc refining furnace 760-1100 Copper reverberatory furnace 900-1100 Cement kiln (Dry process) 620- 730 Glass melting furnace 1000-1550
  • 91.
    Medium Temperature HeatRecovery Types of Device Temperature, oC Steam boiler exhausts 230-480 Gas turbine exhausts 370-540 Reciprocating engine exhausts 315-600 Heat treating furnaces 425 - 650 Catalytic crackers 425 - 650 Annealing furnace cooling systems 425 - 650
  • 92.
    Low Temperature HeatRecovery Source Temperature, oC Process steam condensate 55-88 Cooling water from: Furnace doors 32-55 Annealing furnaces 66-230 Air compressors 27-50 Air conditioning and refrigeration condensers 32–43
  • 93.
    Benefits of WHR •Direct benefits • Indirect benefits Reduction in Pollution Reduction in equipment sizes Reduction in auxiliary Energy consumption
  • 94.
    Development of WasteHeat Recovery System • Understand the process – Sources and uses of waste heat – Upset conditions occurring in the plant due to heat recovery – Availability of space – Any other constraint, such as dew point occurring in an equipment, etc. • Economic evaluation of WHR System
  • 95.
    Commercial WHR Devices •Recuperator • Regenerator • Heat Wheel • Heat Pipe • Economiser • Shell and tube heat exchanger • Waste heat boiler • Heat Pump • Thermocompressor • Direct contact heat exchanger
  • 96.
    Recuperator In a recuperator,heat exchange takes place between the flue gases and the air through metallic or ceramic walls. Duct or tubes carry the air for combustion to be pre-heated, the other side contains the waste heat stream.
  • 97.
    Metallic Radiation Recuperator Theradiation recuperator gets its name from the fact that a substantial portion of the heat transfer from the hot gases to the surface of the inner tube takes place by radiative heat transfer Figure 8.2 Metallic Radiation Recuperator
  • 98.
    Convective Recuperator The hotgases are carried through a number of parallel small diameter tubes, while the incoming air to be heated enters a shell surrounding the tubes and passes over the hot tubes one or more times in a direction normal to their axes.
  • 99.
    Convective Radiative Recuperator Formaximum effectiveness of heat transfer, combinations of radiation and convective designs are used, with the high-temperature radiation recuperator being first followed by convection type.
  • 100.
    Ceramic Recuperator • Inorder to overcome the temperature limitation of metallic recuperators which is about 1000oC on the gas side, ceramic tube recuperators have been developed. • The materials of ceramic recuperators allow operation on the gas side up to 1300 oC and on the preheated air side up to 850 oC.
  • 101.
    Regenerator The Regeneration whichis preferable for large capacities has been very widely used in glass and steel melting furnaces. Important relations exist between the size of the regenerator, time between reversals, thickness of brick, conductivity of brick and heat storage ratio of the brick.
  • 102.
    Heat Wheels Widely usedin low to medium temperature waste heat recovery systems. A disk rotates between two side-by-side ducts: one a cold gas duct, the other a hot gas duct. As the disk slowly rotates, sensible heat (moisture that contains latent heat) is transferred to the disk by the hot air and, as the disk rotates, from the disk to the cold air.
  • 103.
    Heat Pipe Heat pipeis a thermal energy absorbing and transferring system and have no moving parts and hence require minimum maintenance. wall
  • 104.
    Economiser Widely used ina boiler system 1. To pre-heat the boiler feed water. 2. To pre-heat the combustion air. by utilizing the heat in the flue gas.
  • 105.
    Shell and TubeHeat Exchanger When the medium containing waste heat is a liquid or a vapor which heats another liquid, then the shell and tube heat exchanger must be used since both paths must be sealed to contain the pressures of their respective fluids.
  • 106.
    Plate Heat Exchanger Thecost of heat exchange surfaces is a major factor when the temperature differences are not large. In such case this is used. Hot liquid passing through a bottom port in the head is permitted to pass upwards between every second plate while cold liquid at the top of the head is permitted to pass downwards between the odd plates. When the directions of hot & cold fluids are opposite, the arrangement is described as counter current Figure 8.10 Plate Heat Exchanger
  • 107.
    Waste Heat Boilers Wasteheat boilers are ordinarily water tube boilers in which the hot exhaust gases from gas turbines, incinerators, etc., pass over a number of parallel tubes containing water. The water is vaporized in the tubes and collected in a steam drum from which it is drawn off for use as heating or processing steam
  • 108.
  • 109.
    Heat pump processes: 1. In the evaporator the heat is extracted from the heat source to boil the circulating substance; 2. The circulating substance is compressed by the compressor, raising its pressure and temperature; The low temperature vapor is compressed by a compressor, which requires external work. The work done on the vapor raises its pressure and temperature to a level where its energy becomes available for use 3. The heat is delivered to the condenser; 4. The pressure of the circulating substance (working fluid) is reduced back to the evaporator condition in the throttling valve, where the cycle repeats. The heat pump was developed as a space heating system The heat pumps have the ability to upgrade heat to a value more than twice that of the energy consumed by the device
  • 110.
    Thermocompressor SUCTION STEAM L.P. Discharge Steam M.P Motive Steam H.P The thermocompressoris a simple equipment with a nozzle where HP steam is accelerated into a high velocity fluid. This entrains the LP steam by momentum transfer and then recompresses in a divergent venturi.
  • 111.
    Direct Contact HeatExchanger COLD WATER IN VENT L.P. STEAM HOT WATER Low pressure steam may also be used to preheat the feed water or some other fluid where miscibility is acceptable. This principle is used here.