OCR Text |
Show 3 (3) higher net plant efficiency on CO 2 recovery -higher gross plant efficiency by minimizing dry gas loss -lower energy penalty on CO2 recovery The authors also suggested that the 02/C02 combustion system was more economical than the conventional CO2 scrubbing process, as shown in Fig.3. Consequently, the 02/C02 combustion system is expected to be one of the promissing 'system on CO2 recovery from pulverized coal fired power stations. Firstly, an attempt was made to conduct an experimental works by a drop tube (electrically heated) furnace to study the characteristics of 02/C02 combustion, fundamentally. By the substitution of CO2 for N2 in air, NOx conversion decreased and it's effectiveness was counted to be 10-20%, while the char burnout was not affected. On 02/C02 combustion, the increase of 02 conc. in the oxidant enhanced the char burnout and the it's effect was found to become significant at the condition of reduced 02/fuel ratio to fuel rich. NOx conversion, which was briefly estimated from fuel-N content with ignoring thermal-NOx, decreased in the fuel rich 02 combustion, otherwise increased in the fuel lean O2 combustion, with the increase of O2 conc. of the oxidant. The fate of NOx ' in the oxidant -gas was also analyzed, taking into considerations of actual flue gas recycle. NOx was greatly decomposed into molecular N2 by reducing 02/fuel ratio, and it's reduction rate was estimated more than 90% at 02/fuel ratio of 0.8. This behavior was recognized to be similar reaction mechanism as the in-furnace NOx reduction. Consequently, the results on the drop tube furnace showed that 02/C02 combustion had a better char burnout and lower NOx emissions on comparison with the conventinal air combustion. Especially, NOx conversion could be reduced to 2%, which corresponded wi th about 40-50 ppm on air combustion. As a next research step, accordingly, an attempt was made to conduct a bench-scale test by a tunnel type test furnace. The paper described the experimental results on the bench-scale testing. |