Numerical Analysis of Nitric Oxide Emission from a Sulfur Recovery Unit Thermal Reactor Using Rounded Corners, a Choke Ring or a Vector Wall

具流線化轉角、阻氣環或向量壁之硫回收單元熱反應爐氮氧化物生成數值研究

葉俊郎(Chun-Lang Yeh)

《中國機械工程學刊》 41卷4期 (2020/08) Pp. 427-439

摘要

Sulfur recovery unit (SRU) thermal reactor is important equipment in a sulfur plant. Its operating temperature can exceed 1600oC and thus lead to the formation of nitrogen oxides (NOx). In this paper, NOx produced by an industrial-scale SRU thermal reactor is analyzed. Both the prototype reactor and its modifications, including modifying the zone 1 corner geometry, modifying the choke ring, and using a vector wall, are compared to seek a feasible way of reducing NOx emission. From the simulation results, it is found that the SRU thermal reactor with a radius of curvature 1m at the zone 1 corner has the lowest nitric oxide (NO) emission among the radii of curvature at the zone 1 corner investigated. Among the choke ring heights investigated, the SRU thermal reactor having a choke ring height of 1.11m has the highest NO emission while the one having a choke ring height of 0.74m has a lower NO emission. Further, among the choke ring positions investigated, the SRU thermal reactor having a choke ring away from the zone 1 corner by 6m has the lowest NO emission while the one having a choke ring away from the zone 1 corner by 3m has the highest NO emission. The NO concentration at the reactor exit using a vector wall is higher than that using a choke ring. Among the SRU thermal reactors investigated in this study, the one without a choke ring has the lowest NO emission. However, it has the highest zone 2 temperature and this is harmful to the downstream heat exchanger tubes. Although a vector wall produces more sulfur, its NO emission is also higher. In summary, a SRU thermal reactor using a choke ring of 0.74m in height and 6m away from the zone 1 corner is a feasible compromise among the sulfur production, the operating temperature (service life consideration) and the NO emission.

關鍵字

sulfur recovery unit ； thermal reactor ； nitrogen oxides ； zone 1 corner geometry ； choke ring ； vector wall

並列摘要

本文旨在針對硫回收單元熱反應爐內部流場進行詳細的數值模擬，並進行汙染分析，以期提升其操作效能並避免過度的汙染排放，探討內容包含以下三項因素對於氮氧化物生成之影響：（1）反應爐幾何形狀之影響、（2）阻氣環之影響、（3）向量壁之影響。由研究結果發現，在反應爐第一區轉角流線化方面，當流線化曲率半徑為1m時，出口一氧化氮濃度最低。在阻氣環高度方面，當阻氣環高度為1.11m時，出口一氧化氮濃度最高，而當阻氣環高度為0.74m時，其出口一氧化氮濃度較低。在阻氣環位置方面，當阻氣環位於第一區轉角下游6m處時，出口一氧化氮濃度最低，在另一方面，當阻氣環位於第一區轉角下游3m處時，出口一氧化氮濃度最高。使用向量壁比使用阻氣環之硫回收單元熱反應爐出口一氧化氮濃度高。在本研究所探討之熱反應爐中，當無阻氣環時，出口一氧化氮濃度最低，然而，其第二區溫度最高，這對於下游的熱交換管有害。雖然向量壁可產生較多的硫，但其一氧化氮排放濃度亦較高。綜合來看，考量硫的產量、流場溫度（與使用壽命相關）、以及一氧化氮排放量等因素，具有高度0.74m、且位於第一區轉角下游6m處阻氣環之硫回收單元熱反應爐為最佳設計。