多孔介質燃燒室應用於小瓦數固態氧化物燃料電池之研究

Abstract

多孔介質燃燒(porous medium combustion, PMC)已被證實具有比一般燃燒更高的燃燒效率、更高的燃料釋放熱功率、更低的貧油可燃極限及廢氣汙染，因此將多孔介質燃燒室與固態氧化物燃料電池系統結合，做剩餘燃料及廢熱再利用，能大幅改善系統燃料使用效率及廢氣汙染，本文探討兩段式多孔介質燃燒室在小瓦數固態氧化物燃料電池系統中的應用，以氫氣為燃料，使用泡沫陶瓷為多孔介質，陶瓷分為上游孔密度40ppi及下游15ppi兩部分，並且替換氧化鋯、碳化矽、氧化鋁三種常見泡沫陶瓷材料，各別測試比較三種材料對於燃燒效果以及廢氣排放的影響，顯示使用氧化鋁的燃燒室平均溫度最高，殘餘氫氣量也十分稀少，也發現陶瓷之比熱比起熱傳導係數對於燃燒有更大的影響，比熱如果較高燃燒溫度也較高，另外泡沫陶瓷孔洞的不均勻性會增加回火的機率，甚至在理論上不會發生的情況下依然發生，因此在預熱區改用孔洞均勻的蜂窩陶瓷將能提高捕焰的能力，此外燃燒室口徑過小容易使火焰反應區超出多孔介質降低燃燒效果，因此恰當的口徑尺寸配合使用孔洞分佈均勻的陶瓷，將能提升燃燒效果。

Porous medium combustion has showed better performance than free flame in efficiency, power, lean flammability limit and emission, so the combination of porous media burner and SOFC system will improve the efficiency and emission of whole system by recover residual fuel and heat of SOFC. This research studied the two-section porous medium burner of low wattage SOFC system and used hydrogen as fuel. The porous media was ceramic foam with 40ppi upstream section and 10ppi downstream section. Three kinds of ceramic foam including ZrO2, SiC and Al2O3 were tested individually. Results show that Al2O3 burner has the highest burning temperature, and the specific heat of ceramic has a greater impact on temperature than thermal conductivity of ceramic. Burning temperature increases with specific heat. The concentration of unburned hydrogen is low. The nonuniformity of ceramic foam will occasionally cause flashback even in the estimated value, so using more uniform ceramic honeycomb may reduce flashback. Besides, small burner diameter will stretch flame reaction zone and cause ineffective combustion. So, suitable burner diameter and uniform porous ceramic are beneficial to porous medium combustion.