Effective waste heat recovery from industrial high-temperature granules: A Moving Bed Indirect Heat Exchanger with embedded agitation

Abstract

Substantial contact heat resistance exists among granules in traditional Moving Bed Indirect Heat Exchanger (MBIHE), leading to poor heat transfer. To address that issue, a novel MBIHE with embedded agitator is developed, where the agitation can induce granule migration. The migrating granule serves as heat carrier to “carry” its heat directly to heat transfer surface, which accordingly enhances the heat efficiency. Through simulating the agitating process based on Discrete Element Method, horizontal migrations of granules are observed. Migrativity (0 ≤ σ ≤ 1) is defined to describe the horizontal mixing intensity of granules, which in turn represents the ability of heat transfer enhancement by the granule migration. σ increases with the agitator’s rotational number Nr and approaches to 1 when Nr > 60. Due to the granule migration, poor contact between granules and the lower part of heat transfer tube in a stagnant bed is addressed, and the heat transfer area is increased by ∼20%. A pilot-scale MBIHE with granule capacity of 60–120 kg/h is built to conduct heat recovery experiments. The heat transfer coefficient is enhanced by 2–3 times owing to the granule mixing in MBIHE, and the heat recovery efficiency is up to 60–80%.