Consultation on waste heat recovery from coke oven flue gas
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Question: The flue gas volume from the coke oven is 150,000 standard cubic meters per hour on a wet basis, with a humidity level of 10%. The requirements are that the temperature of the flue gas at the inlet of the waste heat recovery unit be 225°C, the temperature at the outlet be 150°C, and the saturated steam pressure be 0.64 MPa (gauge pressure). The inlet water is softened water at 20°C. Is it possible to achieve this? The temperature of saturated steam at 0.64 MPa (gauge pressure) is approximately 168°C. Can the flue gas be cooled to such a low temperature? Or, if it can be reduced to 150°C, its economic efficiency in terms of design is very poor.
It is possible to do so, but a design that reduces the temperature to 150°C would indeed reduce economic efficiency. This is because the lower the flue gas temperature, the lower the efficiency of waste heat recovery; moreover, a larger heat exchange area and more complex equipment are required to ensure heat recovery, which in turn increases costs. .
Based on the calculations, this is not feasible; the temperature difference at the narrow areas is essentially 0, so heat exchange can no longer take place. There are two solutions: 1 is to appropriately increase the exhaust temperature to 150. 2 is to reduce the steam pressure to below 0.4 MPa, so that the temperature at the narrow point can be maintained above ~15°C.
It’s completely achievable; just draw two curves to see it – the inlet water temperature is 20°C, the steam temperature is 168°C, and the flue gas temperature ranges from 225°C to 150°C. It can be said that this level of recovery isn’t the best, but it’s sufficient. It mainly depends on what kind of recycling device you use. Evaluate the cost-effectiveness and the payback period for investment.
I once developed a plan for waste heat recovery in a sponge titanium hot blast furnace; I forgot how to upload it
Lowering the temperature to 150°C is no problem at all; it’s simple – just preheat the water supply, and the result will be excellent.
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