Energy Analysis in Rice Mills for Cogeneration in Thailand

Abstract

Three types of rice mills are studied: the white rice mills that use only electricity, the white rice mills that use electricity and steam engines and the par-boiled rice mills that use electricity and steam in the par-boiled process. The white rice mills and par-boiled rice mills use steam in heating process or paddy drying. Electrical energy consumption in the milling process of white rice mill and par-boiled rice mill are approximately 110 MJ/ton paddy and 129MJ/ton paddy respectively. Electrical energy consumption of white rice mill is spent 43% in whitening and polishing process, 26% in screening and blowing process, 23% in bucket and conveyor process, and 8% in husking process. Electrical energy consumption in the milling process of par-boiled rice mill is spent 43% in whitening and polishing process, 38% in screening, bucket and conveyor process, 14% in blowing process, and 5% in husking process. The thermal energy consumption for par-boiled rice process in 2,410 MJ/ton paddy, of which 8% for soaking process, 6% for cooking process and 86% for paddy drying process. In the paddy drying process, the moisture content of the grain is reduced from 34% w.b. 14% and thermal energy used is 10 MJ/kg water evaporated. The result of the analysis show that the total electrical energy consumption: milling process, drying process, improving and packing process, office and boiler in the white rice mill is approximately 190 MJ/ton paddy and 238 MJ/ton paddy in par-boiled rice mill. Assuming that steam turbine cogeneration is used, the electrical energy generated from 312 rice mill is therefore, 217 MW, of which 57% is used within the rice mills and 43% is left. The thermal energy generated from the rice mills is 3.16x10¹⁰ MJ/year, of which 5.37x10⁹ MJ/year is used within the rice mills and 2.62x10¹⁰ MJ/year is left However, optimization of cogeneration system may help to reduce the amount of steam left.