For natural gas processing plants, amine scrubbing is a common unit process that relies heavily on filtration and separation technology. It is well documented that solid contaminants in the amine stream contribute to process challenges such as corrosion, erosion, fouling, and foaming. Therefore, the operational stability of gas ‘sweetening’ plants is largely dependent on the mitigation of contaminants.
Operators understand the high cost of inefficient filtration. They recognise that low efficiency filtration units and undersized filtration systems can both lead to issues including frequent and prolonged process upsets, downtime due to equipment fouling, repeated filter change-outs, and higher process-related operating costs. Additionally, frequent filter change-outs result in higher direct consumable costs as well as indirect costs related to safety, labour, inventory, and disposal.
It is important to review the process and discuss the primary sources of contamination during the amine sweetening process.
Natural gas processing facilities and refineries use treatment solvents to remove acid gas components from gas streams. Amines such as MDEA, DEA, MEA, and specially designed formulations absorb hydrogen sulfide (H2S) and carbon dioxide (CO2) to ‘sweeten’ the gas stream.
In the operation of a typical gas-sweetening unit, the inlet gas first passes into the bottom of the contactor, also referred to as an absorber, and flows upward through a series of trays, counter-current to the aqueous amine solution which absorbs the acid gas components. The ‘rich’ amine solution, which has absorbed CO2 and H2S molecules, flows from the bottom of the contactor through a heat exchanger where its temperature is elevated to minimise the additional heat required for regeneration. The rich amine is then sent to the upper section of the stripper, also known as the regenerator column, where it flows downward under low pressure, contacting the hot vapours from the reboiler. The contact with the hot vapour strips the acid gas molecules from the amine solution. This acid gas flows out the top of the stripper to a condenser, referred to as a reflux accumulator, where liquid vapour is recovered and recycled back to the system. The hot ‘lean’ amine solution, which no longer contains acid gas, flows from the reboiler back through the lean/rich heat exchanger and is cooled before being pumped back to the contactor for reuse. Prior to being sent to the contactor, a 15 – 30% slipstream of lean amine is sent to a carbon bed to remove dissolved hydrocarbons...
Written by Chris Wallace, FTC, USA.
This article was originally published in the April 2020 issue of Hydrocarbon Engineering. To read the full article, and other great technical articles in this issue, view the full issue here. You can also register to receive a free regular copy of the magazine here.
Read the article online at: https://www.hydrocarbonengineering.com/special-reports/29042020/amine-scrubbing-optimisation/