View source for Amine Regenerator(PV-1102)

The Regenerator is a stripping tower that operates at low pressure and high temperature to regenerate the rich amine. Rich amine enters the Regenerator near the top and travels downward through a rising flow of steam that strips the acid gases from the amine.

Removing acid gases from the rich amine regenerates the amine to the lean conditions needed for raw gas sweetening to continue. Overly rich amine cannot sweeten the incoming sour gas to sales gas specifications.


=Operation=

The Regenerator has 20 valve trays:
'''Trays 1 – 4:''' Reflux from the reflux accumulator is returned at tray 1 and flows downwards through the lower 3 trays. Released gases from the amine flow upward through the trays. The cool reflux entering at the highest tray helps to knock out any amine solution vapor carried up by the gases.

'''Trays 4 – 20:''' Rich amine enters the Regenerator (see Figure 5) at tray 4 to begin its descent across the 16 lower trays. At the same time, two hot vapor flows (i.e. the stripping steam generated in the Regenerator’s two reboilers) enter below tray one to begin their way upward, through the acid gas stripping path.

At the 16 lower trays amine contacts the rising stripping steam. Stripping steam blows open the tray’s valve plates (Koch-Glitsch valves )and then bubbles through the amine liquid flowing crosswise over the tray.

Each valve tray has weirs and downcomers:
*weirs maintain the level of amine liquid on the tray
*downcomers direct amine flowing over the weir down to the tray below:
:-even-number trays have 2 downcomers; one at each end
:-odd-number trays have 1 centrally mounted downcomer
*downflowing amine liquid in the downcomer is a seal to prevent stripping steam from bypassing the tray valves through the downcomer

[[File:AmineRegen.png|center|]]

During the amine/stripping steam contact at the 16 trays, amine is progressively regenerated:
*The chemical absorption reaction (whereby amine became rich) is reversed:
:-steam heating breaks down the water soluble salt compounds (into acid gases and amine) that were formed when the amine absorbed acid gas
:-the steam then strips the acid gases from the amine
*Rich amine becomes leaner as it flows downward, while the stripping steam becomes more heavily laden with acid gases as it rises. Lean amine settles on a chimney tray below tray 1 tray 20 and then gravity drains to the Regenerator two reboilers.

The Regenerator operates with two reboilers and a reflux system:
*Reboilers—From the regenerator chimney tray, lean amine drains to the two reboilers). In each reboiler, heating the amine solution generates the steam which returns to the Regenerator to rise as stripping steam. Hot lean amine from each reboiler drains into the bottom accumulator section of the still and is then directed under level control through the Exchangers.
*Reflux system—the rising acid-gas laden stripping steam leaves the top of the Regenerator and flows to a reflux system. The reflux system:
:-cools the stripping steam/acid gas to liquefy the steam back to water
:-separates the water and acid gas:
::~water is pumped into the top of the Regenerator as reflux liquid
::~acid gas flows to the Incinerator for incineration.

<u>'''Note:'''</u> The reflux system is described in [[Amine Regenerator Overhead System]].


=Process Controls and Instrumentation=

The Regenerator has the following level controls and instrumentation:
*a Gauge glass (LG-1816) and Level Transmitter (LIT-1816) in the Regenerator’s bottom accumulator section
*a level transmitter (LIT-1843) and a level column that gives indication of the Level above the chimney tray inside the Regenerator
:-the ( LIT-1816) reading appears on DCS and is used by a DCS-based level controller. The controller modulates the Level control valve (LV-1816) to maintain setpoint in the bottom of the Regenerator
:-the regenerator’s LCV is upstream of the Exchangers. Lean amine from the Regenerator passes through the Exchangers, through the Regenerator LCV, and into the Amine Surge Tank.

<u>'''Note:'''</u> The LCV’s (LV-1816) location downstream of the exchangers ensures the exchangers stay full of lean amine and do not vapor lock. As well, the cooler lean amine downstream of the exchangers reduces the LCV’s (LV-1816) operating temperature.

The Regenerator has the following temperature and pressure instrumentation:
*a local temperature indicator (TIT-1844) shows the hot lean amine temperature leaving the regenerator’s bottom accumulator section and relays it to the DCS.
*a pressure transmitter (PIT-1845) relays Regenerator pressure of the bottom surge compartment to the DCS.
*a differential pressure transmitter (PDIT-1840) (relays the gas pressure drop across the Regenerator’s trays (i.e., between the still’s bottom accumulator section and top stripping steam/acid gas outlet) to DCS. Increasing differential pressure is an indication to CRO that the Regenerator is foaming.
*Local pressure indication (PI-1842)
*Local temperature indication (TI-1842)

The Regenerator is affected by the control actions of downstream equipment:
*the Regenerator’s pressure is determined by the backpressure control downstream in the still reflux system. Regenerator pressure must be low for the regeneration of the amine yet must be sufficient to ensure a driving force that directs lean amine from the bottom of the regenerator to the Surge Tank.
*the regenerator’s ability to regenerate amine is determined by the amount of stripping steam generated at the two reboilers. The amount of stripping steam generated depends on the flow-controlled amount of 65# steam admitted to the reboilers.


=Additional Specialty Lines and Valves=

The Regenerator has overpressure/vacuum relief valving to protect the Regenerator and its two reboilers. The relief valve is on the stripping steam line from the Regenerator’s F1 reboiler:
*one PRV (PRV-1846C) set at 50 psig relieve overpressure into a tall stack that vents to atmosphere

The Regenerator has:
*a top manual vent valve to atmosphere used during pre-startup or post-shutdown steam purging
*level column and Regenerator bottom drain valving to allow manual drainage to either:
:-the Amine Drain Vessel when draining amine
:-the FNNPF open drain system when draining condensate during steam purging
*an isolated and blinded 65# steam purge connection for pre-startup and post-shutdown steam purging


=Operations Monitoring=

At the regenerator, the Area Operator:
*checks that the Regenerator’s bottom pressure is approximately 15 psig and bottom lean amine outlet temperature is 250oF
*checks that the Regenerator’s level is at setpoint
*blows down level gauges and columns to ensure they are clean and readable (ensure to notify the CRO when blowing down equipment)

When notified by the CRO of abnormal Regenerator operation, the Area Operator works together with the CRO to rectify the problem.

The Area Operator is responsible for preventing regenerator vacuum when shutting down and isolating the train from the acid gas header. Because the regenerator cannot withstand vacuum conditions, vacuum must be prevented during shutdown when the stripping steam in the cooling regenerator begins to condense. Instead of relying on Regenerator’s vacuum breaker, the CRO radios the Area Operator to request the opening of a manual vent valve at the regenerators reflux accumulator (see [[Amine regenerator Overhead System]]).