Study On Glycol Dehydration And Desalting Technology In Offshore Gas Field

In the process of offshore natural gas transportation,natural gas hydrate is easy to form,which leads to pipeline blockage and affects the normal natural gas transportation.The addition of Mono-ethylene glycol(MEG)can effectively inhibit the formation of natural gas hydrate.The MEG that absorbs part of the produced liquid contains a large amount of water,salt,a small amount of hydrocarbons and carbon dioxide(called MEG rich liquid).The MEG rich liquid can be effectively separated by the Mono-ethylene glycol regeneration and recovery unit(MRU),so that the MEG can reach the standard of recycling.Re-conveying back to the underwater injection point for recycling of MEG.At present,MRU mainly has traditional process,full-stream reclamation process,slip-stream reclamation process and ion exchange desalination process.The traditional process is not desalted and is only suitable for land gas fields.The slip-stream reclamation process equipment is complex and covers a wide area.Ion exchange desalination process is not mature in MRU.The full-stream reclamation process has higher investment in the early stage,and desalting and dehydrating are carried out in two units,which covers a large area.In order to effectively prevent corrosion and scaling,reduce operation cost and footprint,a new idea of one-step dehydration and desalting of distillation column with side line production is proposed in this paper.The specific research contents are as follows:(1)In order to investigate the feasibility of the new process,by Aspen Plus software design meet the requirements of the process rectification tower,determine the best theoretical plate number is 12,best feed position in 9 pieces of plate,the best side in 11 pieces of plate production location,at the same time,discusses the effect of feeding hot condition for rectification,choose the way to feed for the cold liquid feed.(2)Compared with the full-stream reclamation process,the annual total cost(TAC)of the one-step desalting process is reduced by 11.5% under the condition of the same treatment capacity and the same product target concentration.At the same time,under the conditions of different feed flow,water content in MEG rich solution and salt concentration of produced water,the TAC of one-step dehydration desalination process is lower than that of full-stream reclamation process,which is more cost-effective.(3)The effects of different pressure,water content and salt content on the distillation process and results were discussed.The results show that each index can meet the technological requirements under different conditions,and at the same time,in the long period of operation,each index can meet the requirements of injection and stable operation.The simulation results are in good agreement with the experimental results,which shows the feasibility of the design and the stability of the experiment.(4)According to the basic data provided by the simulation calculation and the pilot test,the selection,diameter and height parameters of the pilot test distillation column are calculated,and 350 Y metal corrugated packing column with diameter of 0.5 m and height of6.64 m is selected for the pilot test study.Then,FLUENT was used to conduct fluid simulation on the tower kettle,and it was determined that the cone structure was adopted at the bottom of the tower kettle,which could effectively avoid the deposition of salt at the bottom of the tower kettle.Finally,the pilot test data is analyzed,which is consistent with the pilot test data and meets the technological requirements.The improved distillation column was designed through simulation calculation,and then compared with the original process to verify the feasibility and economy of the improved process.Then the feasibility of the design and the stability of the experiment are verified through the study of small scale and pilot scale experiments.Finally,the one-step dehydration and desalination process can not only reduce the footprint,but also reduce the operating cost,which is the best choice for MEG regeneration and recovery of offshore platforms.