Sustainable management of wastes through co-processing in cement kilns

A variety of wastes get generated in large quantities during the societal, industrial and agricultural activities undertaken by mankind. These wastes have hazardous & non-hazardous characteristics and cause substantial damage to the environment. Most of these wastes can be converted into useful resources through the pre-processing and can be gainfully utilized as Alternative Fuels and Raw materials (AFRs) in the clinker manufacturing process through co-processing. Cement kiln co-processing facilitates to manage these wastes in an ecologically sustaining manner while conserving the fossil fuels & raw materials. The high temperature, alkaline environment and large residence time available in the cement kilns facilitates their environmentally sound management. Also, the heavy metals present in the waste streams get embedded in the crystalline structure of the clinker making them non-leachable. The organic content in the waste gets utilized as alternative fuel and the inorganic content gets utilized as alternative raw material. Wastes therefore get gainfully utilized in clinkering process without generating ash.  Hence, cement kiln co-processing offers a solution that is higher in waste management hierarchy as compared to incineration and landfilling.
The level of utilization of Alternative Fuels varies from <1% in some plants to >90% in some other plants. There are several learnings related to co-processing of wastes in cement kilns and vary depending upon the level of AFR used. This learning includes various aspects associated with sourcing, handling, transportation, pre-processing & co-processing of wastes. They also pertain to various other aspects such as health & safety, process impacts, community perceptions, statutory compliances, etc. that need to be dealt with suitably in the design of the pre-processing and co-processing facilities and also need to be addressed suitably during the pre-processing and co-processing operation.  This article provides an insight into these learnings through case studies experienced in India where the plants have ramped up their TSR levels from <1%  to >20%.

Author: U. Parlikar

Section: Waste utilization

Keywords: alternative fuels and raw materials, cement kiln, co-processing, waste utilization, thermal substitution rate