Optimization of Energy and Exergy Consumption in MEG Regeneration Processes

Abstract

Monoethylene glycol (MEG) is commonly used for hydrate inhibition in fields that require continuous injection. Traditional processes for regeneration and reclamation of MEG require significant amounts of heat. Reclamation (salt removal) is usually done by complete evaporation of salty MEG in a flash separator under partial vacuum. Regeneration (water removal) is done by distillation. Heat integration in current processes is limited. The oil and gas industry is heading towards energy systems based on electricity from dedicated power plants or from the grid, in an effort to reduce greenhouse gas emissions related to petroleum production. Current energy systems, at least offshore, are often based on gas turbines which produce electricity and drive large pumps and compressors. Heat is recovered from the exhaust gases, and sufficient supply of process heat is normally not a problem. However, in future scenarios, there may be little or no available source of low quality energy to produce process heat. Hence, efficient utilization of energy becomes even more important than today.Three process layouts for MEG regeneration and reclamation processes with vapor recompression of the steam from the distillation column were simulated in HYSYS. The simulations were based on a typical feed flow rate of rich MEG for a recovery plant. A compressor raises the saturation temperature of the steam in order to allow it to condense in the process heat exchangers. Thus, the external heat demand of the process can be reduced. Another advantage of vapor recompression is reduced cooling requirements, since heat which is normally rejected, is used internally in the process. Increased complexity and capital costs are the major disadvantages.Exergy analyses were performed on the proposed process layout. The analyses showed that the net reduction in exergy consumption for slip-stream reclamation is too low to be of practical importance. However, up to 30 % reductions in exergy consumption were observed when then the steam is condensed in the reboiler of the water removal unit.The tradeoff between heat transfer area and steam saturation temperature is subject to further optimization. Future activities should focus on the technological challenges of steam compression at relatively high temperatures. An economical optimization of the compressor discharge pressure and different compressor solutions should also be considered in order to further evaluate the feasibility and profitability of vapor recompression in MEG recovery units.