Purification of coke

Abstract

A process and apparatus are disclosed for purification of petroleum coke to produce an economical low sulfur product suitable for electrode production. Finely ground green coke is treated on an enclosed circular grate apparatus and subjected to sequential treatments in which hot gases are passed through a deep permeable bed of coke on the grate in a series of separate treating zones including a preheat zone, a heating and calcining zone, a desulfurizing zone in which hydrogen rich gas is passed through the heated bed, a reduction gas generation zone in which hydrocarbon and steam pass through hot coke to form hydrogen, and a cooling zone. Adequate temperatures for calcination and desulfurization are achieved and the proper heating rate is obtained without overheating the metal parts of the hearth by use of radiant and hot gas heating means in the calcining zone and in the desulfurizing zone and by introducing the air and/or fuel gas near the bottom of the coke bed. Air is passed through the grate at a controlled rate to provide an oxygen deficient atmosphere during calcining, thereby avoiding unwanted coke combustion and high loss of coke fines due to combustion. The fines problem is solved by recycling flue gases through the coke bed which acts as a gas filter and by using sized coke free from fines on the top and bottom of the coke bed. The circular grate apparatus is designed to provide a deep coke bed which results in greater efficiency and significant reductions in capital investment and operating costs, particularly for desulfurizing calcining which requires longer calcining times than ordinary calcining.