การปรับปรุงการเผาไหม้ของเตาเผาเบดนิ่งแบบไหลขึ้น สาหรับหม้อต้มน้าร้อน

Abstract

This research aims to improve combustion efficiency in an updraft fixed-bed furnace for hot water boilers using corncob as fuel by controlling the fuel feeding and air flow rates and minimizing the CO emission to below 690 ppm with retaining the boiler temperature. Initial efficiency data of the combustion furnace were collected with a combustion chamber volume of 11.46 m3, a diameter of 1.8 m, and a height of 4.5 m. Combustion employed a 2-point aeration technique with primary and secondary air fans using the flow rate of 81.47 and 44.05 m3 g-1, respectively. Corn cob with the size of 15 cm was fed to the combustion chamber with a feeding rate of 17.67 kg min-1. The data on corncob combustion revealed that the average CO emission was 1,859 ppm. The equivalent ratio of the initial condition was 0.54, indicating that the oxygen level in the combustion system was too high. This problem leads to the study on the airflow rate of 75.31 m3 min–1 with the flow rate of 4.88 and 26.43 m3 min-1 at the primary and secondary air fan, respectively. The study was divided into two parts. The first part was to study the fuel consumption rate of corn cobs before size reduction and the aeration rate. The corn cob feed rate varied from 8.02, 8.82, 9.62, 11.23, 12.83, and 14.43 kg min-1. The second part was to investigate the fuel consumption rate of corncobs after size reduction together with the aeration rate. The cob feed rate of 3.97 and 5.95 kg min-1 were studied to find the optimum conditions for using corncob fuel in the combustion furnace. It should be noted that the water temperature was controlled between 65 C but not exceeding 90 C, while CO concentration in the exhaust gas should not exceed 690 ppm. In the first part, the studies revealed that the temperature of boiled water could not be exceeded 65 °C when the corncob with no size reduction was used with the feed rates of 8.02 and 8.82 kg min-1 studied. The concentration of CO in exhaust gas were 1,382.61 and 836.50 ppm, respectively. When the feed rate of corn cobs with no size reduction was increased to 9.62 and 11.23 kg min-1, the hot water temperature increased to 65 but not more than 90 °C. Meanwhile, the CO concentration in the exhaust gas decreased to 631.94 and 430.74 ppm, respectively. Finally, the increase in the corncob feed rate with no size reduction to 12.83 and 14.43 kg min-1, the boiling water temperature exceeded 90 °C. The CO concentration of the exhaust gas was dramatically reduced to 94.87 and 56.68 ppm, respectively. The study of the optimum conditions for using in K.P. company’s furnace found that the average temperature at R1 was 400 - 450 °C before entering the heat exchanger. The feed rate of corncobs with no size reduction was 9.62 kg min-1. Consequently, the fuel consumption was reduced by approximately 45.56%. The CO gas content in exhaust gas was 631.94 ppm, decreased by 66%, and is lower than the Department of Industrial Works standard. The optimal hot water temperature could be achieved and could continuously work for 24 hours with the continuous feed of fuels. In the second part, the corncob with the size reduction was employed. The feed rate of corncobs of 3.97 kg min-1 enables boiling the water to reach the temperature of 65 but not more than 90 °C. The CO concentration in exhaust gas was 408 ppm. When the feed rate of corncobs is increased to 5.95 kg min-1, the temperature exceeding 65 °C was achieved but more than 90 °C. The CO concentration in exhaust gas was 268 ppm. Some problems related to using corncobs with the size reduction could be addressed. Fine fuel fragments are blown onto the heat exchanger and vacuum systems resulting in clogged hot water pipes. Since the corn cob reduction is a Hammer mill, thus lightweight, fine and unburned corncobs are readily blown. Therefore, the aeration rate must be reduced to as low as 75.31 m3 min-1. In conclusion, the studies were accomplished to improve the combustion efficiency of updraft fixed-bed furnaces for hot water boilers, find the optimal fuel feed rate, and reduce the CO concentration in the exhaust gas to less than 690 ppm. In addition, this optimized condition for updraft fixed-bed furnaces could practically heat the hot water, which the temperature can exceed 65 °C. In addition, the excess hot water produced from the plant, apart from the utilization, can be further used in other activities and add value to the business.