應用靜態混合器來改善原油脫鹽以降低蒸餾塔頂腐蝕

原油脫鹽包括兩個步驟：油／水的混合與分離。在混合階段，藉著混合裝置將注入的洗滌水打散成無數的小水滴均勻分散在原油中。水滴的大小與分佈也是影響脫鹽效率的重要因素。水滴太大，無法有效脫鹽；太小則不易合併，易造成脫後原油帶水及脫鹽廢水帶油等問題。其間有一最適尺寸分佈範圍。對一定的界面面積，混合裝置若能產生尺寸大小較均一、粒徑分佈較窄的水滴，則可得到最短的合併時間，以及最佳洗滌和沈降效果。脫鹽常用的油／水混合裝置有混合閥（mixing valve）及靜態混合器（static mixer）。混合閥所形成的水滴分佈較寬，水滴的聚併及沉降效率較差。靜態混合器對流體的剪切程度較小，所形成的水滴分佈較窄，尺寸較均一，較不會產生過小的水滴。為適應不同煉量與類型原油的脫鹽，建議將混合閥與靜態混合器一起搭配使用。為降低一蒸餾工場主塔頂部空冷器的腐蝕，建議利用歲修時在其兩段脫鹽槽現有混合閥後面的管線上各加裝了一支Komax的靜態混合器來改善脫鹽效率，進而降低塔頂腐蝕。比較加裝靜態混合器前、後兩操作週期的數據，主要結果如下：（1）原油脫鹽後鹽含量的平均值由1.12ptb降為0.84ptb；脫鹽不合格的月數由之前週期的13次大幅降為5次。加裝後的週期脫鹽結果確有明顯的改善。（2）塔頂迴流槽水腳冷凝水的氯離子（Cl^–）平均濃度由62.80ppm降為41.25ppm；總鐵離子（T-Fe）含量的平均值也由1.15ppm降至0.99ppm。

關鍵字

靜態混合器；原油脫鹽；蒸餾工場塔頂腐蝕控制

並列摘要

Crude desalting consists of two steps: oil-water mixing and separation. In the mixing step, a swarm of washing water droplets is formed and a homogeneous distribution of aqueous phase in the oil phase is created. Droplet size is an important factor influencing desalting efficiency. A process optimum exists between large droplets which do not desalt effectively and small droplets that do not coalesce and cause excessive carryover and carryunder. A uniform water droplet size will have the lowest coalescence time for a given interphase surface area and gives the best attainable combination of washing and settling. For controlled mixing, mixing devices such as static in-line mixers and/or mixing valves are commonly applied. The viscous shear levels in static mixers are much lower than in mixing valve. The static mixers produce a more narrow droplet size distribution and the droplet sizes do not become so small. To allow operation in a range of crude types and feed rates, combinations of static mixers and a controllable mixing valve are recommended. For reducing the tower overhead corrosion of a crude distillation unit (CDU), two Komax static mixers were installed downstream of the existing mixing valves of the two-stage desalters respectively during a turnaround to improve the salt removal efficiency. Major indexes were compared before and after the installation of static mixers as following:. (1) The averaged salt content in desalted crude was better than the one of last operating run, it decreased from 1.12 to 0.84ptb, and the monthly qualified ratios of desalted crudes were improved significantly. (2) The average chloride level (Cl^-) in crude tower overhead accumulator water decreased from 62.80 to 41.25ppm, and consequently the average iron content (Fe^(+2)+Fe^(+3)) in tail water, one of the overhead corrosion indicators, decreased from 1.15 to 0.99ppm.

並列關鍵字

Static Mixers ； Crude Desalting ； Overhead Corrosion Control of CDU

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應用靜態混合器來改善原油脫鹽以降低蒸餾塔頂腐蝕

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