Simulation Studies of Process Improvement of Three-Tower Low-Temperature Distillation Process to Minimize Energy Consumption for Separation of Produced Gas of CO2-Enhanced Oil Recovery (EOR)

摘要

High concentrations of carbon dioxide (CO2) obtained from the associated gas of CO2-based Enhanced Oil Recovery (EOR) process need to be recovered and re-injected into the oilfield in order to improve the amount of extracted crude oil and reduce total operational cost. A three-tower low-temperature distillation process is one of the effective technologies for the CO2 recovery process. However, its high energy consumption is a major drawback. In this work, an improved three-tower low-temperature distillation process which adds two intermediate reboilers in the stripping section of the CO2 recovery column and uses the overhead vapour of the demethanizer to pre-cool the feed gas is proposed, in order to reduce the total energy consumption compared with the conventional process. The simulation was performed using ProMax3.2 software. Sensitivity analyses were carried out to evaluate the effects of key parameters (e.g. solvent flow rate, feed inlet stage, solvent inlet stage, reboiler inlet stage, and intermediate reboiler flow ratio) on the energy requirement. The simulation results showed that for a CO2 product purity of 96%, the methane gas aligned with the GB17820-2012 natural gas II requirements, and no solid CO2 existed. The reboiler heat duty of the CO2 recovery column of the improved process was reduced by 66.6% compared with the conventional process. The total equivalent work of the improved process was 1.066 GJ/tCO(2),13.4% lower than the 1.231 GJ/tCO(2) of the conventional process.