Combination of Waste Polymers and Lignocellulosic Biomass as Additives in Cokemaking

Abstract

Introduction: The demand for steel has increased markedly in recent years and is expected to continue to do so up to around 2050. At the same time, the blast-furnace route is responsible for 70 % of world steel production, while metallurgical coke is essential for the proper functioning of the blast furnace. The steel industry is a carbon-based process due to its high consumption of coal and coke and therefore is responsible for a large proportion of anthropogenic CO2 emissions. The coking process is can also be used to recycle high carbon content wastes such as plastics, tyres, biomass etc. As a consequence, recycling in coke ovens can serve as a way to reduce CO2 emissions through the inclusion of biomass and other wastes as raw materials, in this way contributing to a circular economy. The study of coking pressure produced by a coal during the coking process is of great importance because this pressure may result in the permanent deformation of, and damage to, the walls of the oven with drastic economic consequences for the industry. For this reason, it is important to establish the influence of these alternative raw materials on coking pressure and coke quality. Aim: The aim of this work is to improve waste recycling in the cokemaking industry by using a combination of various high carbon content materials with contrasting effects. Coke quality and coking pressure of the blends will be the focus of this study. Methods: A bituminous coal normally used by the cokemaking industry was employed as raw material together with pine sawdust (PS), hydrothermally treated PS, waste polyethylene and waste tyres. The fluidity of the blends was studied by means of the Gieseler test (ASTM D2639-74). The thermal decomposition of the blends was investigated by means of thermogravimetric analysis (TGA). The effect of the additives on the coking pressure developed by the coal was determined by means of the Koppers-INCAR test. The mechanical strength and reactivity to CO2 of cokes produced al laboratory scale were also studied by subjecting them to a microstrength test and ECE-INCAR test, respectively. The existence of synergy between the blend components was assessed on the basis of the devolatilization curves obtained by TGA. The percentage of each waste in the blend was determined as a function of the modification of the fluidity and the contraction of the coal. Results: The results of the TGA indicated the existence of some degree of synergism between the additives that helped in the explanation of their effect on coking pressure. The effect of the additives on coal fluidity was low. Conclusion: It was possible to combine various types of additives in order to minimize their effect on coking pressure and coke quality