Operation characteristics of waste heat recovery from high-temperature particles under varying temperatures and flow rates

High-temperature particles produced from metallurgy, building materials, and chemical industry are mostly characterized by wide variations in temperature and flow rate, and the waste heat recovery processes from these particles are essentially unsteady. The heat transfer characteristics in a gas–solid countercurrent moving bed under periodic variation of inlet particle flow rate and temperature are investigated. The wide variation of inlet particle flow rate and temperature causes wide variation in input heat capacity ratio. However, their effects are different. The inlet particle temperature variation has slight effects on the instant outlet particle temperature and heat recovery efficiency, but great on that of air for the simulated cases. The variation amplitude of outlet air temperature is up to 431.41 K under the wide temperature variation of 600 K and long duration of 2.5τp (τp is the particle residence time). Improving technique should be adopted to maintain the temperature level of outlet air under wide temperature variation according to the utilization of the recovered heat. Meanwhile, the wide variation of flow rate affects the instant outlet particle and air temperatures. The variation amplitudes of outlet particle and air temperature are 88.90 K and 203.35 K, respectively. Furthermore, instant heat recovery efficiency decreases 9.6% under the wide flow rate variation that ranges from 46.58 to 19.96 t/h and long duration of 2.5τp. Varying the flow rate of air flow with an accordance variation range and duration of particle may be an efficient way if the instant heat recovery efficiency and temperature level of outlet air are requested.