Gas Sweetening: Welded Plate Heat Exchanger Bloc type vs. Kettle reboiler BKU in Amine process

Amine gas treatment process is conventionally used in refineries, petrochemical plants, onshore/offshore natural gas processing plants and other industries. The process is also known as acid aqueous solutions of various alkylamines (commonly called amines). Selecting the right heat exchangers for diverse heat transfer duties has a significant impact on the effectiveness and the economy of the amine plant. Amine gas treatment is a very energy intensive process, as the amines absorb a mixture of gases at low temperatures and high pressure and then releases the gas components at high temperatures and low pressures.

The process
Amine gas treatment process is critical to remove carbon dioxide and hydrogen sulfide, (generically termed: acid gas) that may be present in gas streams either in natural gas production or as a result of refining operations during gas production. If these two components are not controlled, corrosion rates become far too extreme to manage.

In a shell-and-tube installation, the tube bundle always has to be pulled out axially. This means that considerable extra space is needed – space that should be kept free of all other equipment. In practice, this is rarely the case. Everyone who has undertaken such service work will testify that it is an awkward and unpleasant task involving a lot of time, effort and manpower, as well as causing significant disruption in any production environment.

Numerous crude oil processes in refineries result in the production of sulfur-containing compounds, including H2S and organics like carbon disulfide and carbonyls. Environmental norms dictate that acid gases cannot be discharged into the atmosphere without treatment. Solvent absorption/ desorption systems are employed to treat these gases.

Energy is recovered in the amine recovery section, where rich amine is preheated before the regenerator by means of lean amine, leaving the regenerator. The more energy recovered in this service, the less energy needs to be provided to the regenerator reboiler in terms of steam.

WPHE Bloc type heat exchangers can be designed with a temperature approach of as little as 5°C. This maximizes energy recovery, thereby minimizing steam consumption in the reboiler.

The regenerator reboiler is often designed as a kettle type reboiler.

These typically require a large temperature difference between the boiling media and the steam. This means that a higher pressure steam is required to run the reboiler.

The stripper reboiler is designed either with forced circulation or natural circulation. The latter is called a thermosyphon reboiler, which is an energy efficient system as it contains no pumps to drive the reboiler. Natural circulation due to gravity drives the reboiler with condensing steam on one side and evaporating process fluids on the other. Circulation is established through the reboiler by the difference between the static head of the liquid in the stripper column and the two phase mixture inside the reboiler. When the liquid level in the stripper column increases relative to the reboiler, it creates a difference in hydrostatic head and thus increases the flow rate at which the fluid to be vaporised flows through the reboiler.

When WPHE Bloc type heat exchangers are used as rising film thermosiphon reboilers for the amine regenerator column, a temperature difference of less than 10°C is possible to initiate boiling and create natural circulation through the reboiler. This often means that it is possible to use more readily available low-pressure steam instead of medium-pressure steam.

WPHE Bloc type  heat exchangers are used in the process, the hold-up volume of the exchangers is minimized, reducing the complete amine inventory by up to 20%. In addition, due to the short hold-up time of amine in the unit rising film thermosiphon reboiler, the degradation of amine is limited and less makeup amine is required.

                                                         Kettle Reboiler BKU

Trend in Gas Sweetening market is moving from Kettle Reboiler to Welded Bloc type Heat Exchanger due to reduced dimensions (crucial for system builders on  Skid mounted units), reduced amine consumption, improved corrosion resistance and better energy efficiency in amine gas treating processes

Therefore next time you have to design a reboiler on amine sweetening process consider option of Welded Plate Heat Exchanger Bloc type as well!