Thermodynamic and Economic Analysis of 1.4 MWe Rice-Husk Fired Cogeneration in Thailand

Abstract

Rice husk is a residue from rice milling process. Rice husk can be used in an economical way to meet the energy demand within the rice milling industry by using rice husk as fuel for heat and power production to supply the heat and electricity in the processes, and to produce surplus electricity for selling to the national grid. Two cases of the study: thermal-match and rice husk-match of different energy utilization are considered for economic evaluation of power plants to meet different demand categories. The capacity of the plant is 576 tons paddy/day. The total load of thermal energy consumption is 1,062 MJ/ton paddy and the electrical energy consumption of the rice mill is 6,518 MWh/year. The total capital cost of the thermal-match cogeneration plant is 1 million US$ while the total capital cost of the rice husk-match cogeneration is 1.24 million US$. Results show that the rice husk-match cogeneration is more economically feasible than the thermal-match cogeneration. The capacity of back pressure steam-fired boiler is 18 tons/hour of steam at 25 bar (absolute) and 400^oC. The rice husk-match cogeneration can generate power of 1,432 kW while the thermal-match cogeneration can produce power only 923 kW. The economic analyses in terms of the net present value (NPV), simple pay-back period (PBP), and internal rate of return (IRR) are also evaluated. Results show that the rice husk-match cogeneration has NPV of 0.30 million US$/year, PBP of 3.7 years and IRR of 27%, while the thermal-match cogeneration has NPV of 0.18 million US$/year, PBP of 5.5 years and IRR of 17%. The two cases of the study are based on 180 days/year of operation of rice mill cogeneration. Results of the study also show that rice husk-match cogeneration is more profitable than the thermal-match cogeneration.