Mathematical Modeling and Deign of Gypsum Dryer

Abstract

The present work aims in encountering the problem associated with drying of chemical gypsum used by JK Lakshmi cement, Moti Bhoyan, Kalol Plant. JK Lakshmi cement's Moti Bhoyan Plant is a grinding unit which uses the chemical gypsum as a raw material in cement making process. The Chemical gypsum - containing high amount of moisture - is a waste product coming from nearby plants. The moisture is causing problem in transportation of gypsum during the process. The problem can be solved by removing moisture from gypsum up to 10% w/w. The plant is using direct sun drying as a drying technique although being an inefficient process. Moreover, plant needs at least 70 ton/day gypsum drying resulting in a requirement of a big drying area. Hence a new technique of Inclined Rotary drum drying is suggested. To design an Inclined Drum Dryer a mathematical model is generated. The mathematical model is divided in to two parts sizing model and rating model. The sizing of dryer is done by making heat balance and mass balance between gypsum and air. The result of it gives mass flow rate of air required for drying. The mass flow rate and velocity of air gives the required size of drum. The diameter of drum and hold up of drum gives the size of flights and number of flights required for required heat transfer to achieved. The size of flight and number of flights calculated by model is used to optimize the size of drum. The sizing model gives Length and Diameter of drum, Size and Number of Flights and Air flow rate required to reduce the moisture contain up to 10%. The rating model takes input of geometrical parameters calculated from sizing model. The drum is divided in to small control volume (CV) and energy and mass balance is applied to each control volume. The output of one CV is input to the constrictive CV. The temperature and mass flow rate are taken as input parameters for each control volume. The mathematical model links each control volume to give actual Length of dryer required for specified output moisture contain. The model also give output moisture contain of air and temperature of gypsum as well as air. The dryer is designed by combining sizing and rating model. The drum dryer is designed for 0.001m diameter particle size. Air temperature of 350 ○ C, moisture contain and temperature of solid as 30% w/w and 30 C as input parameters for final gypsum moisture of 10 % and 65 ○ C. A C++ program for sizing model and rating model is generated. The sizing model code gives length of drum as 15.694 m and diameter of 1.889 m making L/D ratio as 8.30. The flight size as 0.51 m and number of flight as 19 is been selected to get above results. For rating model length of drum is taken as 8 m and diameter as 1 m making L/D ration 8. The rating model gives required length of drum as 8 m. The output of rating model gives the final moisture contain of air as 0.1089 w/w, the final product temperature is 63.87 ○ C, air temperature of 77.96 ○ C and final product moisture contain as 0.10 w/w. The study shows that with change in size of particle the required size of drum changes, to compensate the change the flight hold up must be changed.