Waste heat recuperators

Fig. 9.2 shows how a simple open circuit gas turbine can be used as a cogeneration plant (a) with a waste heat recuperator (WHR) and (b) with a waste heat boiler (WHB). Since the products from combustion have excess air, supplementary fuel may be burnt downstream of the turbine in the second case. In these illustrations, the overall efficiency of the gas turbine is taken to be quite low ((tjo)cg = ccJf ca 0.25), where the subscript CG indicates that the gas turbine is used as a recuperative cogeneration plant. 

Fig. 9.2. Cogeneration plants (a) with waste heat recuperator (WHR) and (b) with waste heat boiler (WHB).

For the operation of induction furnaces, BAT is to melt clean scrap use good practice measures for the charging and operation use medium frequency power and, when installing a new furnace, to change any mains frequency furnace to medium frequency to evaluate the possibility of waste heat recuperation and under specific conditions to implement a heat recovery system. For exhaust capture and treatment fi om induction furnaces, BAT is to use a hood, lip extraction or cover extraction on each induction furnace to capture the furnace off-gas and maximise the off-gas collection during the full working cycle to use dry flue-gas cleaning and to keep dust emissions below 0.2 kg/toime molten iron. 

Smelting. The fuel suppHed to the reverberatory furnace is in the range of 5—6 GJ/t (4.7-5.7 x 10 Btu/t) concentrate. Steam produced in the waste heat boiler is equal to ca 60% of the energy suppHed by the fuel. The additional heat recovered from the exit gases in the recuperator to preheat the combustion air is equal to ca 10% of the energy from the fuel. Hence, the heat recovered from the furnace is equal to ca 70% of the heat from the fuels. 

FIG. 27-57 Diagram of a metallic radiation recuperator. (From Goldstick Waste Heat Recovery, Faiimont Press, Atlanta, 1986. )... 

Furnaces are large users of energy, and in order to reduce costs, such equipment should be well insulated, used to maximum capacity and most of the waste heat in both the flue gases and product recovered. It should be possible to recover the waste heat in the flue gases down to at least 200°C. Specialist equipment for such waste heat recovery is available in the form of recuperators and regenerators. 

Chemical Recuperation of Waste Heat by Utilizing Organic Chemical Hydrides... 

At present, waste heat exhausted from the ICE is removed with any efficient radiator system through direct apparent heat exchanging. On the contrary, organic chemical hydrides can recuperate the chemical energy of endothermic reaction heat during exhausted heat removal. Heat transfers accompanying the phase change of evaporation and condensation of aromatic products and unconverted reactants will certainly facilitate the removal of heat from the ICE parts, with adoption of any new radiator system compelled. 

One-pass conversion obtained in the continuous dehydrogenation reactor equipped with an external condenser (Figures 13.18 and 13.22) gives the extent of energy recuperation from the ICE waste heat through hydrogen generation, because induction of heat from the external thermo-reservoir to the catalyst layer must be consumed stationarily to allot the supplied heat to the endothermic reaction heat as well as the evaporation heat. 

The onboard hydrogen supplied from organic chemical hydrides will be utilized well in the ICE vehicles. Even for stationary use of hydrogen, distribution of organic chemical hydrides will play an important role at stations or sites, where waste heat at modest temperatures is dissipated in vain without chemical recuperation. 

Recent studies by Thermo Electron Corporation have shown that certain forms of waste heat utilization (e.g., recuperators or process steam boilers) provide a better return on investment than that obtainable from bottoming cycle generators. The optimum choice of heat recovery strategy depends, in part, upon the temperature of exhaust heat available. 

Limpt, H., and Beerkens, R., Energy Recovery from Waste Heat in the Glass Industry and Thermochemical Recuperator , pp. 3-15,73 Glass Prohlems Conf., Oct., 2013. 

Recuperators are usually employed to heat an incoming fluid with waste heat from a process. For example a waste-heat boiler is, in principle, a heat exchanger using the waste heat from probably a blast furnace to evaporate water to steam. In other cases recuperators heat incoming fluid and cool outgoing fluid simultaneously. On a steamgenerating plant flue gases are often used in economizers to heat the feed water to the boiler. 

ENERGY RECOVERY FROM WASTE HEAT IN THE GLASS INDUSTRY AND THERMOCHEMICAL RECUPERATOR... 

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