View source for Amine Reboilers(HT-1103A/B)

=Purpose=

The Amine Reboilers are kettle-type shell/tube heat exchangers. In each reboiler, a tubeside flow of saturated 65# steam heats the shellside lean amine. The heat transfer is important because heating vapourizes some of the water in the amine solution to produce the stripping steam used in the regenerator. The stripping steam:
*provides the heat needed to regenerate rich amine to lean amine
*carries the removed acid gas upward and out the top of the regenerator


=Operation=

Lean amine gathers on the regenerator’s chimney tray and drains via separate flowlines to the two reboilers.

Inside the reboiler, a shellside weir keeps the tube bundle submerged in lean amine (Figure 6). Heat is transferred from the tube bundle to the lean amine:
*the 65# steam tubeside flow serves as the reboiler’s heat medium. The 65# steam gives up the heat that warms the shellside lean amine to 260°F to boil off some of the water as stripping steam.
*the stripping steam rises into the reboiler shell’s large vapour space. The large vapour space allows amine liquid droplets to disengage from the stripping steam. The stripping steam leaves the reboiler’s shell through a top vapour outlet line. The stripping steam then enters the Regenerator below the chimney tray.

In each reboiler, lean amine spills over the weir into the reboiler’s drawoff section. Lean amine flows from each reboiler’s drawoff section into the bottom surge area of the regenerator.

<u>'''Note:'''</u> The regenerator and its reboilers are configured such that the level in the bottom of the still is the same as the drawoff section level in the Reboilers.

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


=LP Heating Controls and Instrumentation=

The reboilers each receive desuperheated 65# heating steam. The 65# steam supply to each reboiler is identical; the LP steam from the low pressure steam header.
*flows through a flowmeter and flow control valve (FV-1812A/B) used for the reboiler’s steam flow control
*enters the reboiler’s tube bundle. Near the end of the tubeside flow, the LP steam condenses. The steam condensate then drains from the reboiler to the Amine reboiler’s steam condensate pot


=Heating Steam Flow Control=
The Reboilers each have steam flow controls:
*a flow transmitter relays the flowrate of 65# steam to a DCS-based flow controller
*the controller modulates the steam flow control valve to maintain the setpoint flowrate.

For each reboiler, the 65# steam flowrate’s setpoint is entered by the CRO to ensure that the reboiler will generate sufficient stripping steam. (Higher amine circulation requires more stripping steam from the reboilers). With sufficient stripping steam, the still will successfully regenerate the amine:
*If the 65# steam setpoint is too high, the reboiler will generate too much stripping steam. Supplying too much stripping steam to the still results in excessive amine regeneration (known as overstripping). Overstripping:
:-wastes LP steam
:-may cause thermal degradation and corrosion in lean amine piping
:-overloads the reflux system because the system must condense the excessive stripping steam leaving the regenerator
*If the LP steam setpoint is too low, the reboiler will not generate enough stripping steam. Supplying too little stripping steam to the still results in insufficient amine regeneration (known as understripping). With understripping:
:-too much H2S remains entrained in the lean amine solution leaving the Regenerator and risks souring out the train (i.e., failing to sweeten raw gas to sales specifications)
:-amine regeneration can occur in the wrong section of the Regenerator (or even within the reboilers) and thereby lead to serious corrosion/erosion