Multi-Stage Control of Waste Heat Recovery from High Temperature Slags Based on Time Temperature Transformation Curves

Yongqi Sun,Xidong Wang,Lili Liu,Zuotai Zhang

doi:10.3390/en7031673

Abstract

This paper presents a significant method and a basic idea of waste heat recovery from high temperature slags based on Time Temperature Transformation (TTT) curves. Three samples with a fixed CaO/SiO2 ratio of 1.05 and different levels of Al2O3 were designed and isothermal experiments were performed using a Single Hot Thermocouple Technique (SHTT). The TTT curves established through SHTT experiments described well the variation of slag properties during isothermal processes. In this study, we propose a multi-stage control method for waste heat recovery from high temperature slags, in which the whole temperature range from 1500 °C to 25 °C was divided into three regions, i.e., Liquid region, Crystallization region and Solid region, based on the TTT curves. Accordingly, we put forward an industrial prototype plant for the purpose of waste heat recovery and the potential of waste heat recovery was then calculated. The multi-stage control method provided not only a significant prototype, but also a basic idea to simultaneously extract high quality waste heat and obtain glassy phases on high temperature slags, which may fill the gap between slag properties and practical waste heat recovery processes.

Highlights

It is well known that the steel industry is energy intensive, consuming around 9% of anthropogenic energy [1] and emitting large quantities of CO2 into the atmosphere [2]
Multi-Stage Control of Waste Heat Recovery Based on Temperature Transformation (TTT) Curves
As the slag melt was quenched from 1500 °C, the crystallization was not observed when it was higher than the break temperature, indicating that the waste heat recovery from the slags can last a long time during this temperature interval

Summary

Introduction

It is well known that the steel industry is energy intensive, consuming around 9% of anthropogenic energy [1] and emitting large quantities of CO2 into the atmosphere [2]. With the acceleration of global warming nowadays, energy saving and CO2 emission reduction in the steel industry is attracting more and more attention, the energy efficiency has already been substantially improved by implementing extensive advanced technologies. According to the previous estimations [3,4], high temperature (1450–1550 °C) slags, carrying a substantial amount of high quality heat, represent the last potential source for energy reduction in the steel industry. BF slags can be treated through two methods: gradually cooled by air in a slag pit [9] or rapidly quenched by water [10]. Air-gradually-cooled slags have low utilization values because of their weak hydraulicity due to the high content of crystalline phases [11], while water quenched BF slags are increasingly utilized as cementitious materials because of the glassy phases [11]

Methods

Results

Conclusion