| 摘要: | 本論文實作改良一合成氣低氮氧化物(NOx)燃燒器，以Bédat & Cheng (1995)所提出之弱漩渦噴流燃燒器(weak swirl jet burner, WSJB)的設計概念為基礎，在燃燒器上游出口設置弱漩渦噴流產生器，它乃由四支20度向上斜角設計之切邊小噴嘴所構成，可在燃燒器出口下游處，形成一均勻擴張流場(diverging flow field)，使原本本生燈噴流預混火焰可呈一碗狀預混火焰。氣化合成氣主要成份為一氧化碳和氫，為氣化複循環發電技術(Integrated Gasification Combined Cycles，IGCC)之重要燃料。國際間大多數的合成氣燃燒特性之研究，大多侷限在層流條件下，對於紊流條件下之合成氣燃燒速度研究仍然缺乏。因此，以本實驗室先前所設計之快速混合裝置及貧油紊流燃燒技術，針對挾帶床氣化爐所產出之合成氣(成份為65%CO/35%H2)，進行當量比=0.5與0.7貧油合成氣預混燃料之紊流燃燒速度(turbulent burning velocities, ST)量測及其相關排放物之量測，以建立合成氣低氮氧化物燃燒技術。我們探討在固定燃料配比條件下當量比對於火焰特性與燃燒器的穩定操作範圍之影響，並且應用質點影像測速技術(particle image velocimetry, PIV)和氣體分析儀分別量測在不同流量下之紊流燃燒速度和NOx及CO污染物濃度排放量測。實驗結果顯示：當量比=0.7有較寬廣的操作範圍，氫氣濃度增加可擴展混合燃氣之可燃極限並提高ST值；又ST值及紊流強度(turbulent intensity, u'）會隨著噴流雷諾數（Rej）增加而增加；此一合成氣低氮氧化物燃燒器所量得之[NOx]值均低於10 ppm，在當量比= 0.5的燃燒條件中[NOx]值更低於5 ppm以下。本研究成果將有助於瞭解煤氣化合成氣之燃燒特性與其應用限制，對未來發展氣化複循環發電技術有所助益。 The basic design concept of weak-swirl-jet burner (WSJB) is coming from Bédat & Cheng (1995). To settle a weak jet swirl generator in advance position, produce a stable diverging flow field at the lower reaches and a bowl-shaped premixed turbulent flame. Then, this generator is made by 4 tangential weak air jets at 20 degree_inclination. Syngas, a mixture of mainly carbon monoxide (CO) and hydrogen (H2), is an important fuel in Integrated Gasification Combined Cycles. The most of previous studies in the feature of syngas combustion are limited in the laminar flame regime, and it’s scanty of studies to focus on turbulence combustion of syngas. However, utilizing the fast mixing apparatus and the lean turbulent combustion technique developed in our laboratory, we investigated the turbulent burning velocities (ST) and the exhaust emissions of the premixed lean syngas flames in the WSJB at two equivalence ratios of equivalence rate = 0.5 and equivalence rate = 0.7. The syngas used is the product from fluidized bed, with 65% CO and 35% H2. We identified the stable operation regime of the burner. Using particle image velocimetry and a gas analyzer, we measured the turbulent burning velocities and the emissions of NOx and CO under different equivalence ratios, mixture flow rates (characterized by the jet Reynolds number Rej ), and swirl strength (characterized by the swirl number S). The main results from our experiments include: (1) On the (Rej , S) plane, the stable operation region for equivalence rate equivalence rate = 0.7 is broader than that for equivalence rate = 0.5; (2) Increasing the concentration of H2 extends the flammable limits of the syngas and increases the ST ; (3) Both ST and turbulent intensity increase with the increase of Rej ; (4) Turbulent burning velocities normalized by the laminar burning velocity, ST/SL, of the bowl-shaped flames in the WSJB are higher than the turbulent spherical flames under the same conditions; and (5) Over the range of Rej and S explored, the NOx emission is always below 10 ppm, with the minimum below 5 ppm for equivalence rate = 0.5. Our experiment demonstrated that the WSJB is superb burner in terms of reducing NOx emission. Moreover, our study improves to understanding the turbulent flame of syngas feature and practical apply limitation. That benefits the development of Integrated Gasification Combined Cycles (IGCC). |
