Utilization of cement rotary kiln waste heat for calcination of phosphogypsum

The cement industry nowadays is giving thrust to replace and reduce fossil fuel-based energy through recovery of waste heat, utilization of wastes (Alternative fuels) and adoption of renewable energy sources like wind energy, solar PV systems etc. In cement plants, high temperature heat is released into the atmosphere through exhaust flue gases, radiation and convection heat from hot and exposed surfaces like rotary kiln. A lot has already been explored about recovery of waste heat from exhaust hot flue gases. Many Indian cement plants have installed Waste Heat Recovery Systems (WHRS) at their facility for generating electricity by using heat energy in hot flue gases. At present cumulative generation capacity is estimated as similar to 344 MW from such WHRS facilities in Indian cement plants. Indian cement industry is facing issues about limited availability of the mineral gypsum. This is going to be more critical with possible restrictions over mineral gypsum import in India. On the other hand, the huge inventory of phosphogypsum is a challenge for phosphoric acid manufacturing plants. Phosphogypsum can't be used without processing in the cement production process due to adverse impact on cement properties. Processing of Phosphogypsum requires high temperature and if the temperature is raised through fossil fuel combustion then it will add to extra cost and associated Green House Gas (GHG) emissions. Heat recovery from kiln hot shell surfaces can be explored for phosphogypsum calcination purpose here. A feasibility concept of phosphogypsum calcination through kiln waste heat recovery is discussed in this paper.