Approach analysis and strategy suggestions for clean utilization technology of medium and low temperature pyrolysis gas heat

High temperature tar-containing pyrolysis gas carries a large amount of sensible heat and latent heat,and the efficient heat recycling of this part is crucial for the energy efficiency improvement of the whole process.In order to promote the efficient recycling of residual heat resources in the medium and low temperature pyrolysis process,this paper reviewed the main technical characteristics and shortcomings of the cooling and waste heat utilization methods of medium and low temperature pyrolysis gas,such as waste heat utilization from chilling process and exhaust heat boiler.This paper also summarized the research status and characteristics of high-temperature pyrolysis gas heat utilization technology,including waste heat recovery in the upper part of the primary cooler,circulating aqueous ammonia and upward pipes.The main technical difficulties in the process of heat recycle from medium and low temperature pyrolysis gas,such as tar adhesion happened in condensation process of tar-containing high temperature pyrolysis gas,low-temperature and low-pressure gas heat capture and efficient utilization,were also analyzed.Based on the technical limitations and the phase-change heat transfer technologies,took the condensation-heat transfer characteristics of tar-containing pyrolysis gas as the scientific basis,an integrated technology coupling pyrolysis gas multi-stage condensation and phase-change heat transfer for energy cascade recovery and utilization was proposed.Based on the dew point difference and precipitation characteristics from different components of tar steam,such technology forms a temperature gradien t-based classifying and condensation process of pyrolysis gas,recycles the heat contained in pyrolysis gas step by step,and realizes on-line quality recovery of tar products in different distillation ranges. At the same time,it takes advantages of coupling and composites phase-change heat transfer technology,the heat transferring medium and pyrolysis gas implementes classifying and counterflow heat transfer,purposefully recycled sensible heat from pyrolysis gas and latent heat from low-grade pyrolysis gas,to achieve the integration of grading condensation and heat cascade recycling of oil-containing pyrolysis gas,thereby to achieve the dual effects of heat efficiency and product quality improvement of the pyrolysis system. Taking 1 million t/a fluidized bed pyrolysis process as an example,the heat recovery technical route of medium and low temperature pyrolysis gas was proposed,and the heat balance was calculated.The results indicate that an 81.17%heat utilization rate of medium and low temperature pyrolysis gas could be achieved in this technical route,which shows its feasibility initially.The efficient recycling of residual heat resources in the pyrolysis process will be the main direction and potential of resource-saving and environment-friendly pyrolysis industry development.