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Lecture20 Exercises on heat recovery

Now assume that the heat exchanger is not used coal

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Unformatted text preview: arged in the environment. This illustrates that preheating of air not only save fuel but also reduces carbon emission into the environment. Now assume that the heat exchanger is not used. Coal is burned with a mixture of cold air 25O C and oxygen. Excess of oxygen (air + pure oxygen combined) over theoretical for combustion will be kept same as with preheater. Calculate the amount of oxygen required in kg/hr to obtain the same fuel consumption as obtained with the heat exchanger Pre‐heater adds 9833 kJ sensible heat into furnace. When pre‐heater is not used, nitrogen of air must be reduced so that heat taken out by nitrogen equal to 9833 kJ Let Y kg mol oxygen is required, this corresponds to 3.76Y of nitrogen Thus 3.76Y x 41620 9833 Y 0.0628 kg mole which gives 691 kg/hr of oxygen. This problem illustrates the method of reduction of fuel by adopting technologies like preheating of air and oxygen enrichment of air. Both the technologies are in use to reduce the fuel consumption in industrial practice. Which technology suits has to be evaluated locally keeping in view the available resources and expertise. Exercise‐4 A heat balance for a continuous metallurgical process gives the following data: Heat input % of total Combustion of fuel 100 Heat output % of total Process requirements 25 Sensible heat in flue gases 50 Heat loss 25 The installation o...
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