Waste Heat recovery.pptxWaste Heat Recovery, Cogeneration and Tri-generation

Waste Heat Recovery, Cogeneration and Tri-generation

1. Waste Heat Recovery, Cogeneration and Tri-generation

2. Unit No. 4 Waste Heat Recovery, Cogeneration and Tri-generation Department of Mechanical Engineering Prof. Kokare A.Y. Babasaheb Phadtare Polytechnic, Kalamb-Walchandnagar Subject- Power Plant Engineering

3. Unit No. 4 Waste Heat Recovery, Cogeneration and Tri-generation Course Outcome (CO): Measure waste heat recovery in a typical thermal power plants.

4. Waste Heat Recovery Introduction A waste heat recovery unit (WHRU) isan energy recovery heat exchanger that transfers heat from process outputs at high temperature to another part of the process for some purpose, usually increased efficiency. The WHRU is a tool involved in cogeneration. Waste heat may be extracted from sources such as hot flue gases from a diesel generator, steam from cooling towers, or even waste water from cooling processes such as in steel cooling. 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. The essential quality of heat is not the amount but rather its “value”. The strategy of how to recover this heat depends in part on the temperature of the waste Waste heat found in the exhaust gas of various processes or even from the exhaust stream of a conditioning unit can be used to preheat the incoming gas. This is one of the basic methods for recovery of waste heat. Many steel making plants use this process as an economic method to increase the production of the plant with lower fuel demand.

5. Classification of WHRS on Temperature Range Bases High Temperature Heat Recovery The following Table 8.2 gives temperatures of waste gases from industrial process equipment in the high temperature range. All of these results from direct fuel fired processes. Medium Temperature Heat Recovery The following Table 8.3 gives the temperatures of waste gases from process equipment in the medium temperature range. Most of the waste heat in this temperature range comes from the exhaust of directly fired process units. Low Temperature Heat Recovery The following Table 8.4 lists some heat sources in the low temperature range. In this range it is usually not practical to extract work from the source, though steam production may not be completely excluded if there is a need for low- pressure steam. Low temperature waste heat may be useful in a supplementary way for preheating purposes.

6. Classification of WHRS on Temperature Range Bases Low Temperature Heat Recovery The following Table 8.4 lists some heat sources in the low temperature range. In this range it is usually not practical to extract work from the source, though steam production may not be completely excluded if there is a need for low- pressure steam. Low temperature waste heat may be useful in a supplementary way for preheating purposes.

7. Benefits of Waste Heat Recovery Direct Benefits: Recovery of waste heat has a direct effect on the efficiency of the process. This is reflected by reduction in the utility consumption & costs, and process cost. Indirect Benefits: 1 . Reduction in pollution: A number of toxic combustible wastes such as carbon monoxide gas, sour gas, carbon black off gases, oil sludge, Acrylonitrile and other plastic chemicals etc., releasing to atmosphere if/when burnt in the incinerators serves dual purpose i.e. recovers heat and reduces the environmental pollution levels. 2. Reduction in equipment sizes: Waste heat recovery reduces the fuel consumption, which leads to reduction in the flue gas produced. This results in reduction in equipment sizes of all flue gas handling equipment's such as fans, stacks, ducts, burners, etc .

8. Benefits of Waste Heat Recovery 3 . To reduce operating costs: By recycling and reusing the waste heat energy, there will be less consumption of fuel. reduce the operating cost of industry. 4. To make huge savings and earn high profit : By switching to the most energy-efficient technology available, companies can make huge savings and significantly reduce environmental impact. In other words, industry will gain higher profit. 5. Increased demand: In the "World Energy Outlook" report the International Energy Agency (IEA) predicts world energy demand to increase by 45% over the next 20 years. 6. To challenge and face higher energy prices: Day by day, prices of fossil fuels and other sources of energy are increasing. Therefore, if energy is not saved and conserved by adopting various technologies including the waste heat recovery method.

9. Heat pipe exchanger : They have the ability to transfer heat hundred times more than copper. Heat pipes are mainly known in renewable energy technology as being used in evacuated tube collectors. The heat pipe is mainly used in space, process or air heating, in waste heat from a process is being transferred to the surrounding due to its transfer mechanism. Thermal Wheel or rotary heat exchanger : consists of a circular honeycomb matrix of heat absorbing material, which is slowly rotated within the supply and exhaust air streams of an air handling system. Economizer : In case of process boilers, waste heat in the exhaust gas is passed along a recuperators that carries the inlet fluid for the boiler and thus decreases thermal energy intake of the inlet fluid

10. Sr. No Source of Waste Heat Quality 1. Heat in flue gases. High grade. The higher the temperature, the greater the potential value for heat energy. 2. Heat in vapour streams High grade. The higher the temperature, the greater the potential value for heat energy. When these vapour streams are condensed, latent heat is also recoverable. 3. Convective and radiant heat lost Law grade if recovered, it may be used for space heating or air preheating 4. Heat losses in cooling water Low grade If recovered, these heat losses offer useful gains when heat is exchanged with incoming fresh water 5. Heat losses in providing chilled water . or in the disposal of chilled water High grade, if it can be utilized to reduced demand for refrigeration Low grade, if refrigeration unit is used as a form of heat pump

11. Heat Recovery Methods 1. Recuperator Recuperators is a special purpose counter-flow energy recovery heat exchanger positioned within the supply and exhaust air streams of an air handling system, or in the exhaust gases of an industrial process, in order to recover the waste heat. Generally, they are used to extract heat from the exhaust and use it to preheat air entering the combustion system. 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. A recuperator for recovering waste heat from flue gases is shown in Figure . The inner tube carries the hot exhaust gases while the external annulus carries the combustion air from the atmosphere to the air inlets of the furnace burners.

12. waste heat recovery boiler (WHRB) W a st e Heat Recovery Boiler (WHRB)

13. Principle of Working: . "Waste heat recovery boilers are those boilers, which either uses waste heat in the gases coming out of diesel engine or gas turbines at high temperature or uses the waste fuel in the incinerators. Incinerator is an apparatus for burning waste fuel at high temperatures . Use of waste heat recovery better is the most convenient and widely used 1 low installation cost 2. Compact in se 3. No operating problems W a st e Heat Recovery Boiler (WHRB)

14. LATENT HEAT RECOVERY METHOD 1. Waste heat recovery boilers especially designed for capturing latent heat: They are found in any size. 2. Working fluids having less boiling point temperature than water: Latent heat recovery from low temperature streams for example, refrigerants, brine solutions) is possible by the use of working fluids having boiling point less than water. ADVANTAGES OF SENSIBLE HEAT RECOVERY Advantages of sensible heat recovered are , 1. Sensible heat recovered from the waste flue gases can be used either for winter air conditioning or preheating the air, which is required for combustion of fuel. 2 . Sensible heat recovered from the hot gases leaving the metal furnaces can be used for heating the steel scraps.

15. ADVANTAGES OF WASTE HEAT RECOVERY FOR INDUSTRIAL SECTOR 1. Waste heat recovery increases to the overall efficiency of the industrial process. 2 . Waste heat recovery reduces fuel consumption and so decreases both the cost of fuel and energy consumption. 3. Waste heat recovery reduces harmful emissions containing carbon dioxide, oxides of nitrogen etc . 4. Waste heat recovery helps to reduce the equipment size. Due to reduced size of equipment, fuel consumption reduces. It also reduces the requirements for handling the fuel, pumps, filters, fan etc.

16. BENEFITS OR ADVANTAGES OR USES OF WASTE HEAT RECOVERED Direct Benefits of Waste Heat Recovery, To heat the air, which is used for the purpose of combustion. 2 . To heat the air, which is used in winter air conditioning. 3. In case of metal furnaces used for melting steel scrap, waste heat can be used for heating the air up to 300°C, 4. Waste heat of low temperature range (0 to 120°C) can be used for the production of bio-fuels by growing algae farms or can be used in green houses or in eco-industrial parts . 5 . High grade waste heat (more than 650°C) can be used for generation of electricity or mechanical work.

17. APPLICATIONS OF WASTE HEAT RECOVERED Common applications of waste heat recovered are : 1. Pre-heating combustion air for boilers, ovens and furnaces. 2 . Pre-heating fresh air used to ventilate the building. 3 . Hot water generation including pre-heating boiler feed water. 4 . Direct steam generation for process or power generation. 5 . Space heating 6. Drying. Special applications of waste heat recovered are: Animal shelters. 2 . Aqua-cultural uses. 3 . Green houses. 4. Agricultural uses . 5. Process heating

18. ANIMAL SHELTERS • The growth rate of some animals is strongly influenced by atmospheric temperature. • Proper control of temperature using waste heat can increase the productivity as well as it can decrease the fuel consumed to create artificial temperature. This is particularly more effective for farms of small animals. For example: Poultry farm.

19. AQUA CULTURAL USES An artificial pond , where temperature is controlled with the help of waste heat recovered from the exhaust steam of thermal power plant • It is observed that the fish yield increases to 1000 kg per acre per year as compared to 50 to 300 kg per acre per year in a pond with phosphorous fertilizer. • In addition to temperature dissolved oxygen and nutritional adequacy are the other factors Lake or pond responsible for their growth rate.

20. GREEN HOUSES A greenhouse (also called a glasshouse) is a building, in which, plants are grown. The waste heat can be used to produce green house climate, where air temperature and relative humidity required for different vegetables can be controlled. The favorable conditions for the vegetables like tomatoes, onions and egg plants are 20 to 75oC during day time and 15 to 70°C during night time, which can be controlled easily by means of green house climates.

21. PROCESS HEATING: Some of the applications of process heating in industries are listed below. Preheating of air required for combustion in boiler furnace. 2 . Reheating of fresh air for hot air driers. 3 . Waste heat recovered from furnace can be used as heat source for oven, 4 . Waste heat recovered from the flue gases can be used for preheating of boiler feed water in economizer . 5 . Drying, curing and baking ovens. 6 . Heating, ventilating and air conditioning system.

22. Thermal wheel/ Heat Wheel A thermal wheel , also known as a rotary heat exchanger , or rotary air-to-air enthalpy wheel , or heat recovery wheel , is a type of energy recovery heat exchanger positioned within the supply and exhaust air streams of an air-handling system or in the exhaust gases of an industrial process, in order to recover the heat energy. Other variants include enthalpy wheels and desiccant wheels . A cooling-specific thermal wheel is sometimes referred to as a Kyoto wheel .

23. COGENERATION .Cogeneration or Combined Heat and Power (CHP) may be defined as, "the sequential generation of two different forms of useful energy from a single primary energy source, typically mechanical energy and thermal energy

24. NEED FOR COGENERATION A cogeneration plant produces both, electrical power and process heat simultaneous 1. Process heat . There are several industries such as paper mills textile mills, chemical industry, processing units sugar factories rice mills oil production and refining, heating or and so on, where saturated steam at the desired temperature is required for heating, drying etc. For constant temperature heating (or drying ). 2 . Electrical power: Apart from the process heat the factory also needs power to drive various machines, for lighting and other purposes. Therefore , two separate units were required for generating steam of two qualities. But, having two separate units for process heat and power is wasteful. Therefore, the idea of cogeneration came into existence. Dnyan , Kala, Krida and Krishi Prathisthan’s

25. Principle and Advantages of Cogeneration Cogeneration or Combined Heat and Power (CHP) is defined as the sequential generation of two different forms of useful energy from a single primary energy source , typically mechanical energy and thermal energy . Mechanical energy may be used either to drive an alternator for producing electricity, or rotating equipment such as motor, compressor, pump or fan for delivering various services. Thermal energy can be used either for direct process applications or for indirectly producing steam, hot water, hot air for dryer or chilled water for process cooling. Cogeneration provides a wide range of technologies for application in various domains of economic activities. The overall efficiency of energy use in cogeneration mode can be up to 85 per cent and above in some cases. 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 . Cogeneration makes sense from both macro and micro perspectives . At the macro level , it allows a part of the financial burden of the national power utility to be shared by the private sector ; in addition, indigenous energy sources are conserved . At the micro level , the overall energy bill of the users can be reduced , particularly when there is a simultaneous need for both power and heat at the site , and a rational energy tariff is practiced in the country Dnyan , Kala, Krida and Krishi Prathisthan’s Department of Mechanical Engineering Prof. Kokare A.Y.

26. Dnyan , Kala, Krida and Krishi Prathisthan’s Department of Mechanical Engineering Prof. Kokare A.Y.

27. Dnyan , Kala, Krida and Krishi Prathisthan’s Department of Mechanical Engineering Prof. Kokare A.Y.

28. Classification Of Cogeneration Systems Topping cycle or Topping system or Topping cycle CHP plant. 2 . Bottoming cycle or Bottoming or Bottoming cycle CHP plant. TOPPING CYCLE topping cycle, the fuel supplied is first used to produce power (i.e. electricity) and then thermal energy (process heat). The thermal energy (waste heat) produced is a by-product of the thermodynamic cycle, which is used to satisfy process heat or other thermal requirements , such as heating of water and buildings. In a topping cycle, cogeneration plant generates electrical or mechanical power first followed by the heat recovery boiler to create low pressure process steam or to drive a secondary steam turbine. TYPES OF TOPPING CYCLE COGENERATION SYSTEMS Combined cycle topping system, 2 . Gas turbine topping system, 3 . Steam turbine topping system, 4 . Heat recovery topping system.

29. Combined Cycle Topping System It produces mechanical energy. This mechanical energy drives an electric generator , which generates electrical energy (electricity). Exhaust gases released by gas turbine Steam contain large amount of heat. Therefore, exhaust gas can be either used to provide heat to various domestic and industrial applications or they can be sent to a heat recovery system (steam generator or boiler) to generate steam, which may be further used to drive a secondary steam turbine.

30. Gas Turbine Topping System In Gas turbine CHP Plant, gas turbine is used to drive a synchronous generator to produce energy (electricity), The exhaust gases leaving the gas turbine are sent to a heat recovery boiler, where heat contained by exhaust gases can generate steam or it can be used as process heat . Advantages of Gas Turbine Topping Compressor 1. Good fuel efficiency. 2. Simple plant 3. Less civil construction cost, 4. Less impact on environment. 5. High flexibility in operation.

31. Steam Turbine Topping System Steam turbine CHP plant is used to generate electrical energy (electricity) using a steam turbine and an electric generator. The exhaust steam leaving the steam turbine is High pressure steam then used as low-pressure process steam to heat water for various purposes. Advantages of Steam Turbine Topping System: Simple in construction, 2 . Easy to operate . 3 . Suitable for low quality fuel

32. Bottoming System In a bottoming cycle, the primary fuel is utilized for generating high temperature thermal energy. The heat rejected from the process (waste heat) is used to generate electrical power through a waste heat recovery boiler and a turbine coupled with electric generator

33. Advantages and Disadvantages of Cogeneration Plant (CHP) 1 Cogeneration helps to improve the efficiency of the plant 2. Lower emissions to the environment, particularly carbon dioxide (CO), the main greenhouse gas. 3 . In addition to carbon dioxide (CO), cogeneration reduces emissions of particulate matter, nitrous oxides , sulphur dioxide, mercury etc , which would otherwise lead to increased pollution 4 . Cogeneration reduces cost of production and improve productivity 5 . Cogeneration is more economical as compared to conventional power plant 6 . Cogeneration reduces the manufacturing price and enhances output. .

34. Advantages and Disadvantages of Cogeneration Plant (CHP) 7. Cogeneration helps to conserve utilization of water as well as the cost of water. 8. Cogeneration optimizes the energy supply to all types of consumers 9 . Increased efficiency of energy conversion and use cogeneration is the most effective and efficient form of power generation 10 . Cogeneration results in large cost savings 11 . Cogeneration has increased competitiveness amongst the energy generation companies and forced or limit the energy prices, 12 . Cogeneration has increased employment opportunities.

35. Advantages and Disadvantages of Cogeneration Plant (CHP) 13 . Enhancing operational efficiency to lower overhead costs. 14 . Reducing energy waste, thereby increasing energy efficiency, utility grid for energy demands, 15 . Being an alternative source of energy generation, cogeneration reduces the dependency of electric 16. Cogeneration allows companies to replace aging infrastructure Disadvantages of Cogeneration Plant (CHP): High capital cost, 2 . Moderate efficiency, if it runs at part load instead of full load .

36. Dnyan , Kala, Krida and Krishi Prathisthan’s Department of Mechanical Engineering Prof. Kokare A.Y.

37. Dnyan , Kala, Krida and Krishi Prathisthan’s Department of Mechanical Engineering Prof. Kokare A.Y. TRI-GENERATION Trigeneration can be defined as, "the simultaneous process of cooling, heating and power generation from only one fuel input".

38. Dnyan , Kala, Krida and Krishi Prathisthan’s Department of Mechanical Engineering Prof. Kokare A.Y.

39. Dnyan , Kala, Krida and Krishi Prathisthan’s Department of Mechanical Engineering Prof. Kokare A.Y.

40. Dnyan , Kala, Krida and Krishi Prathisthan’s Department of Mechanical Engineering Prof. Kokare A.Y.

41. Dnyan , Kala, Krida and Krishi Prathisthan’s Department of Mechanical Engineering Prof. Kokare A.Y.

42. Need of Tri-generation Plant (CCHP) 5.Trigeneration gives lower emissions to the environment , particularly carbon dioxide (CO2), which is the main greenhouse gas. 6. In addition to carbon dioxide (CO ), trigeneration also reduces the emissions of particulate matter, nitrous oxides, sulphur dioxide, mercury etc., which results in reduced pollution. 7. Efficiency of trigeneration power plant is 90%, whereas, efficiencies or conventional power plant and cogeneration are 35% and 80% respectively . 8. Transmission line losses are reduced to greater extent.

43. Sr. No Comparative Point Trigeneration Cogeneration 1. Definition simultaneous process of cooling, heating and power from ne fuel Source. Cogeneration is sequential generation of two cooling, heating from fuel. 2. Alternative name Combined Heating, Cooling and Power (CCHP). Combined Heat and Power (CHP) 3. Forms of energies Electricity, Heating and Cooling. Electricity and Heating 4. Efficiency 90%. 80%. 5. Absorption refrigeration system Needed Not Needed

44. Advantages of Tri-generation Plant (CCHP) 1. Low payback period 2. Protection against electricity cost and outages 3. Replacing thermal energy 4. Energy efficiency 5. Environmentally sustainable 6. Savings on energy costs 7. Less emissions of greenhouse gases 8. Back-up power to the site 9. Independence from the grid 10. Energy prices are rising 11. Low maintenance cost 12. Sale of electricity 13. Increased power reliability

45. Disadvantages and Application of Tri-generation DISADVANTAGES OF TRIGENERATION 1 . High capital cost . 2. More research work is needed. 3. Intense planning is required for designing tri-generation systems for projects. 4. Applicability differs with each project. APPLICATIONS OF TRIGENERATION 1 . Data centers. 2 . Food processing industries. 3. Manufacturing units. 4. Colleges and universities. 5. Military complexes. 6. Schools, colleges. 7 . Office buildings. 8. Shopping centers and Supermarkets. 9 . Manufacturing plants. 10 . Refrigerated warehouses, 11 . Theatres. 12 . Airports. 13 . Golf/country clubs. 14 . Casinos. 15 . Resorts.