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Heat Exchanger recuperators

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Heat Exchanger recuperators

  1. 1. A Presentation recupretor Submitted to: Dr. Erfan Uckan Associate Professor
  2. 2.  Heat exchangers are practical devices used to transfer energy from one fluid to another  To get fluid streams to the right temperature for the next process – reactions often require feeds at high temp.  To condense vapours  To evaporate liquids  To recover heat to use elsewhere  To reject low-grade heat  To drive a power cycle What are heat exchangers for?
  3. 3. what is Recupretor A recupretor is a one in which the two fluids are separated at all time by a solid barrier. A recuperator 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 Recuperators are often used in association with the burner portion of a heat engine, to increase the overall efficiency. For example, in a gas turbine engine, air is compressed, mixed with fuel, which is then burned and used to drive a turbine. The recuperator transfers some of the waste heat in the exhaust to the compressed air, thus preheating it before entering the fuel burner stage. Since the gases have been pre-heated, less fuel is needed to heat the gases up to the turbine inlet temperature. By recovering some of the energy usually lost as waste heat, the recuperator can make a heat engine or gas turbine significantly more efficient.
  4. 4. Heat exchangers Recuperators Regenerators Wall separating streams Direct contact  Most heat exchangers have two streams, hot and cold, but some have more than two Main Categories Of Exchanger
  5. 5. Recuperators/Regenerators
  6. 6. Other types of gas-to-gas heat exchangers - Run around coil -Thermal wheel, or rotary heat exchanger (including - enthalpy wheel and desiccant wheel) - Heat pipe - Radiation Recuperator - Convection Recuperator
  7. 7. Heat Recuperators Air-to-Air, Air-Liquid-Air
  8. 8. The aim in a heat recuperator is to transfer the heat contained in the dryer exhaust air to preheat the drying air. In principle, there are two types of heat recuperating systems: · Air-to-Air · Air-Liquid-Air - Process-Therm - Hex-Tube Both systems are incorporated after the cyclones. However, incorporating a bag filter prior to the heat recuperator increases the efficiency, as deposits on the heat surface cannot be completely avoided even with correctly selected air velocities in the dust-loaded air. It is possible to operate the recuperator several days without cleaning, but should it prove necessary to clean the equipment, this is done by means of a built-in CIP system. Heat Recuperators
  9. 9. Niro offers two types of Air-Liquid-Air heat recuperators: • Process-Therm heat exchanger • Hex-Tube heat exchanger These units are much more flexible with respect to retrofit installations. The air- liquid-air heat recovery units consists of two heat exchangers, one for heat transfer between the dryer exhaust air and the other, a finned tube heat exchanger for preheating the inlet air to the dryer. Typically water or water-glycol solution is re-circulated between the two heat exchangers as the heat transfer liquid. In this type of heat recuperator the exhaust air heat exchanger is placed after a bag filter or a wet scrubber and the finned tube heat exchanger is located after the main inlet air filter to the dyer. Both the Hex-Tube heat exchanger and the Process-Therm heat recuperator units can be cleaned during operation or shut down and are supplied with CIP nozzles and CIP manifold to connect to the dryer CIP system.
  10. 10. The thermal plates are assembled vertically in compact plate banks with separation between the plates. Exhaust air is passed down between the plates and the heat transfer liquid is re-circulated within the plates. Heat transfer is a function of the turbulence achieved in the gas stream; the closer the plates , the higher the turbulence and thus the heat transfer. A variable gap allows the use of optimum conditions avoiding the risk of plugging. The use of individual liquid connectors allow the plates to be isolated singly. This offers ease of maintenance and operation but also avoids the expense of total bank Process-Therm installation Individual plate connections
  11. 11. Energy transfer process Normally the heat transfer between airstreams provided by the device is termed as 'sensible', which is the exchange of energy, or enthalpy, resulting in a change in temperature of the medium (air in this case), but with no change in moisture content. However, if moisture or relative humidity levels in the return air stream are high enough to allow condensation to take place in the device, then this will cause 'latent' heat to be released and the heat transfer material will be covered with a film of water. Despite a corresponding absorption of latent heat, as some of the water film is evaporated in the opposite airstream, the water will reduce the thermal resistance of the boundary layer of the heat exchanger material and thus improve the heat transfer coefficient of the device, and hence increase efficiency. The energy exchange of such devices now comprises both sensible and latent heat transfer; in addition to a change in temperature, there is also a change in moisture content of the exhaust air stream. However, the film of condensation will also slightly increase pressure drop through the device, and depending upon the spacing of the matrix material, this can increase resistance by up to 30%. If the unit is not laid to falls, and the condensate not allowed to drain properly, this will increase fan energy consumption and reduce the seasonal efficiency of the device.
  12. 12. · Objectives: – Design a lightweight recuperator applicable to FTT’s Advanced Engine Concept – Perform a mock build of a recuperator demonstrator · What is heat transfer? – The process of heat exchange between two fluids operating under different temperatures – A device that implements this process is a heat exchanger · What is a recuperator? – Waste heat recovery heat exchanger – Utilizes the hot turbine exit gases to heat a portion of cooler compressor discharge air and returns it to the combustor – Reduces heat losses and therefore increases efficiency
  13. 13. Recuperators and regenerators recover heat from the turbine exhaust and use it to preheat the air from the compressor before it enters the combustor, thereby saving fuel. This heat transfer While recuperators and regenerators are quite similar thermodynamically, they are totally different in design. Recuperators are conventional heat exchangers in which hot and cold gases flow steadily on opposite sides of a solid (usually metal) wall. Regenerators are periodic-flow devices. Fluid streams flow in opposite directions through passages in a wheel with heat storage walls. The wheel rotates, transferring heat from one stream to the other. Regenerators usually use a nest of very small parallel passages oriented axially on a wheel which rotates
  14. 14. In a similar manner, turbine reheat can be used to increase the power output of a large-pressure-ratio turbine. This is the thermodynamic principle in turbojet afterburner firing. Turbine reheat increases power, but decreases efficiency unless the turbine exhaust heat is used for additional power generation, as is the case with a combined cycle, or is used with a recuperator to preheat combustor inlet air. Intercoolers and reheat burners increase the temperature difference between the compressor and turbine discharges, thereby increasing the opportunity to use a recuperator to preheat the burner air with exhaust heat. An intercooled recuperated (ICR) machine is at present in development. The efficiency decrease at part load of an ICR gas turbine is much less than of conventional simple cycle machines. Small gas turbines have uncooled turbine blades as a result of the difficulty in manufacturing extremely small cooling passages in small blades. This results in low efficiencies, making it difficult for such turbines to compete with high-volume production (low-cost) reciprocating (piston) engines. The low-pressureratio recuperated cycle has greater efficiency, although at higher cost. The recuperated cycle is finding favor in programs for small (under 300-kW) gas turbines used for stationary power. Because of their compact size, low emissions, and light weight, gas turbines are also being considered for hybrid engine-battery vehicles. Proponents are pursuing the low-pressure-ratio recuperated gas turbine as the way to obtain high efficiency and low emissions in a compact power plant. An ingenious gas turbine cycle is the closed cycle in which the working fluid is sealed in the system. Heat is added to the fluid with an externally fired heater and extracted from the fluid through heat exchangers. The working fluid may be any gas, and the density of the gas may be varied—to vary the power delivered by the machine—by using a gas storage cylinder connected to the compressor discharge
  15. 15. Use in metallurgical furnaces Recuperators have also been used to recover heat from waste gasses to preheat combustion air and fuel for many years by metallic recuperators to reduce energy costs and carbon footprint of operation. Compared to alternatives such as regenerative furnaces, initial costs are lesser, there are no valves to be switching back and forth, there are no induced-draft fans and it does not require a web of gas ducts spread up all over the furnace. Historically the recovery ratios of recuperators compared to regenerative burners were low. However, recent improvements to technology have allowed recuperators to recover 70-80% of the waste heat and pre-heated air up to 850-900 deg C is now possible.
  16. 16. Use in microturbines Recuperators can be used to increase the efficiency of gas turbines for power generation, provided the exhaust gas is hotter than the compressor outlet temperature. The exhaust heat from the turbine is used to pre-heat the air from the compressor before further heating in the combustor, reducing the fuel input required. The larger the temperature difference between turbine out and compressor out, the greater the benefit from the recuperator. [1] Therefore, microturbines (<1MW), which typically have low pressure ratios, have the most to gain from the use of a recuperator. In practice, a doubling of efficiency is possible through the use of a recuperator.[2] The major practical challenge for a recuperator in microturbine applications is coping with the exhaust gas temperature, which can exceed 750C.
  17. 17. Use in ventilation systems In heating, ventilation and air-conditioning systems, HVAC, recuperators are commonly used to re-use waste heat from exhaust air normally expelled to atmosphere. Devices typically comprises a series of parallel plates of aluminium, plastic, stainless steel, or synthetic fibre, alternate pairs of which are enclosed on two sides to form twin sets of ducts at right angles to each other, and which contain the supply and extract air streams. In this manner heat from the exhaust air stream is transferred through the separating plates, and into the supply air stream. Manufacturers claim gross efficiencies of up to 80% depending upon the specification of the unit. The characteristics of this device are attributable to the relationship between the physical size of the unit, in particular the air path distance, and the spacing of the plates. For an equal air pressure drop through the device, a small unit will have a narrower plate spacing and a lower air

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