Application of grey decision to atmospheric-vacuum distillation unit exchangers rebuilding

The exchangers on the top of atmospheric-vacuum distillation tower were exposed to washing erosion seriously when a refinery processed Middle-East sour crude oil.The rebuilding schemes are general shell-and-tube heat exchangers and helix-baffled structure,and tube materials are 20 carbon steel with TH847 coating,20 carbon steel aluminizing,316L and dual phase steel.Considering heat transfer efficiency,manufacture cost,maintenance cost,safety and manufacture difficulty,grey system theory was used to do grey target decision.Considering the corrosion resistance of the material,for various programs specific quantitative indicators,the grey correlation decision was done.Grey target decision,grey correlation decision and grey variable weight decision all show that helix-baffled structure with 20 carbon steel aluminizing tube is the optimum program.Helix-baffled structure is better than general bow-shaped baffle plate structure,and the advanced manufacturing technology should be adopted to lower the fabricating difficulty of helix-baffled heat exchanger.