Process Description
The Amine Treating Unit removes CO2 and H2S from sour gas and hydrocarbon streams in the Amine Contactor. The Amine (MDEA) is regenerated in the Amine Regenerator, and recycled to the Amine Contactor.
The sour gas streams enter the bottom of the Amine Contactor. The cooled lean amine is trim cooled and enters the top of the contactor column. The sour gas flows upward counter-current to the lean amine solution. An acid-gas-rich-amine solution leaves the bottom of the column at an elevated temperature, due to the exothermic absorption reaction. The sweet gas, after absorption of H2S by the amine solution, flows overhead from the Amine Contactor.
The Rich Amine Surge Drum allows separation of hydrocarbon from the amine solution. Condensed hydrocarbons flow over a weir and are pumped to the drain. The rich amine from the surge drum is pumped to the Lean/Rich Amine Exchanger.
The stripping of H2S and CO2 in the Amine Regenerator regenerates the rich amine solution. The Amine Regenerator Reboiler supplies the necessary heat to strip H2S and CO2 from the rich amine, using steam as the heating medium.
Acid gas, primarily H2S and water vapor from the regenerator is cooled in the Amine Regenerator Overhead Condenser. The mixture of gas and condensed liquid is collected in the Amine Regenerator Overhead Accumulator. The uncondensed gas is sent to Sulfur Recovery.
The Amine Regenerator Reflux Pump, pumps the condensate in the Regenerator Accumulator, mainly water, to the top tray of the Amine Regenerator A portion of the pump discharge is sent to the sour water tank.
Lean amine solution from the Amine Regenerator is cooled in the Lean/Rich Exchanger. A slipstream of rich amine solution passes through a filter to remove particulates and hydrocarbons, and is returned to the suction of the pump. The lean amine is further cooled in the Lean Amine Air Cooler, before entering the Amine Contactor.
Instrumentation
Basic Controls: Gas Stream
The sour gas stream, 752 MSCF/H, enters the bottom of the Amine Contactor at 95 DEG F and 130 PSIG. HIC-104 is used to adjust the flow rate of the sour gas. The flow rate of sour gas is indicated on FI-101, its temperature is indicated on TI-101 and the feed gas hydrogen sulfide (H2S) and carbon dioxide (CO2) concentration are indicated on AI-101 and AI-102, respectively.
The temperature of lean amine from E-101 is indicated on TI-108. The lean amine from E-101 is first air-cooled in Lean Amine Air Cooler, E-102, and its outlet temperature is indicated on TI-109. The motor of the fan of E-102 is controlled by switch HS-103. Lean amine from E-102 is trim cooled using cooling water in exchanger, E-103, and enters the top of the absorber column at 105 DEG F. The lean amine solution temperature is controlled 10 degrees higher than the feed gas to prevent any hydrocarbon condensation and foaming problems. This temperature differential is maintained by TDIC-103, which allows bypassing of lean amine around the Lean Amine Trim Cooler, E-103.
The sour gas flows upward counter-current to the lean amine solution in T-101. An acid-gas-rich-amine solution leaves the bottom of the column at an elevated temperature, 157 DEG F, due to the exothermic absorption reaction. The rich amine solution temperature is monitored by TI-105. Rich amine leaves the bottom of the column on level control LIC-101 to the Rich Amine Surge Drum, D-101.
The sweet gas, after absorption of H2S by the amine solution, flows overhead from T-101 under pressure control PIC-101, monitored by the H2S and CO2 analyzers, AI102 and AI-103. The temperature and flow rate of the gas are monitored with TI104 and FI-103.
Basic Controls: Amine Solution
The Rich Amine Surge Drum, D-101, allows the amine solution 30 minutes of residence time, which allows separation of hydrocarbon from the amine solution. The drum pressure is maintained by a backpressure controller, PIC-102, at 5.0 PSIG. Any condensed hydrocarbons flow over a weir and are pumped to the drain system using P-102. Hand controller, HIC-102, is used to regulate the opening of HV-102 on the discharge of P-102. HS-102 is used to operate the motor of P-102.
The level of rich amine in D-101 is indicated on LI-102. This level will fluctuate as amine inventories in the Amine Treating Unit (ATU) change, but over the long term the level normally settles at a constant value of around 50%. Any significant change in this level over the long term indicates an accumulation or depletion of water in the ATU due to excessive water in the sour gas feed, loss of water vapor in the sweet gas, loss of water vapor in the acid gas produced by the Regenerator and purging of water from the Regenerator’s reflux line.
The rich amine from the surge drum is pumped by P-101 to the Lean/Rich Amine Exchanger, E-101. HS-101 is used to operate the motor of P-101. The rich amine enters the tube side at 157 DEG F as indicated on TI-106, where it is heated to 236 DEG F as indicated on TI-107 by the hot lean amine solution from the regenerator bottoms. The hot lean amine solution enters the Lean/Rich Exchanger on the shell side at 275 DEG F.
Basic Controls: Regenerator
The flow of hot rich amine from E-101 to the top of the Amine Regenerator, T-201, is controlled by FIC-201. The level of regenerated lean amine in the base of T-201 is controlled by LIC-203 which adjusts the setpoint of FIC-201.
The stripping of hydrogen sulfide (H2S) and carbon dioxide (CO2) in the Amine Regenerator, T-201, regenerates the rich amine solution. The Amine Regenerator Reboiler supplies the necessary heat to strip H2S from the rich amine, using 60 PSIG steam as the heating medium. FIC-203 regulates the steam flow to the Reboiler.
Acid gas, primarily H2S, CO2 and water vapor from the regenerator is cooled to 98 DEG F in the Amine Regenerator Overhead Condenser, E-201. The temperature of the overhead gas is monitored by TI-202. The motor of the fan for E-201 is controlled by HS-203. The mixture of gas and condensed liquid is collected in the Amine Regenerator Overhead Accumulator. The pressure is maintained at 16 PSIG with PIC-201 controlling the acid gas from the Regenerator Accumulator, D-201, to Sulfur Recovery.
The condensate in the Regenerator Accumulator, D-201, mainly water, is pumped by the Amine Regenerator Reflux Pumps, P-202A/B, to the top tray of the Amine Regenerator. Switches HS-202A/B are used to control the motors of P-202A/B, respectively. The reflux flow is regulated by level controller, LIC-201, and is monitored by FI-203. A small part of the pump discharge can be sent to the sour water tank using HIC-202 to maintain the water balance in the ATU since some water is condensed from the feed sour gas by the circulating amine solution. Normally, HIC-202 is closed because the unit is water-balanced at design conditions.
Basic Controls: Lean Amine Solution
Lean amine solution from the bottom of the Amine Regenerator is pumped by Lean Amine Pumps, P-201A/B, and cooled from 275 DEG F to 184 DEG F in the Lean/Rich Exchanger, E-101. The motors of P-201A/B are controlled by switches HS-201A/B, respectively. A slipstream of rich amine solution is controlled by PDIC-202 through a filter F-201 to remove particulates and hydrocarbons, and returned to the suction of P-201A/B. The lean amine is further cooled in the Lean Amine Air Cooler, E-102, to 130 DEG F.
Fresh lean amine can be brought in from storage to the bottom of Amine Regenerator, T-201, using hand controller HIC-201. Regenerated lean amine from the bottom of T-201 can be sent to storage/disposal using switch HV-201.
Advanced Controls
The lean amine solution temperature is maintained 10 degrees higher than the feed gas to the Amine Contactor to prevent any hydrocarbon condensation and foaming. The lean amine solution temperature controller, TIC-102, allows bypassing of lean amine around the Lean Amine Trim Cooler, E-103, and is regulated by TDIC-103 to maintain this 10 degree difference.