Apr-2015

Acid gas treatment for giant LNG plant (TIA)

Prosernat, an engineering company and licensor of Total’s amine based technology portfolio, AdvAmine, has announced the successful start-up of a major integrated acid gas removal and tail gas treatment unit designed using AdvAmine MDEAmax (selective MDEA) technology.

Laurent Normand
Prosernat

Article Summary

The unit is part of Qatargas 1 and is a major debottlenecking project known as the Plateau Maintenance Project (PMP). The purpose of the project is to maintain LNG production while coping with increased levels of H2S and CO2 in the inlet feed gas streams. A new pretreatment acid gas removal unit (AGRU), upstream of the existing gas sweetening facilities, and an additional sulphur recovery unit (SRU) were selected for the debottlenecking.

The PMP project involves the construction of an additional AGRU treating, in a single train, 1100 million cu ft/day of natural gas, and an associated SRU and tail gas treatment unit (TGTU). An AGRU with integrated TGTU amine was considered the most effective solution to install a new compact plant inside the existing facilities of Qatargas 1 LNG plant at Ras Laffan, Qatar.

After an international bidding contest for the design of the process units, AdvAmine MDEAmax, licensed by Prosernat, was selected for the design of the integrated AGRU + TGTU absorber. The proposed design based on MDEA solvent offers a fully integrated unit meeting multiple process requirements with high operational flexibility.

The process includes the following steps:
•    Partial removal of H2S and CO2 from the 1100 million cu ft/day inlet gas, in a high pressure absorber, to meet required specifications to feed the downstream existing sweetening units
•    Clean up of H2S from tail gas by TGTU amine, installed downstream of the 880 tonnes of sulphur per day SRU, to meet environmental emissions specifications
•    Control of the H2S, RSH and BTX content of the 
acid gas by partial enrichment of the acid gas in a selective hot preflash column upstream the MDEA regenerator, in order to meet the inlet specifications of the SRU
•    Semi-lean solvent recycle from the TGT column to the HP absorber giving benefits in term of reduced solvent circulation and minimised solvent regeneration duty
•    A MDEA regeneration section in one single common regenerator.

The overall process scheme is shown in Figure 1.

Performance tests were performed at the beginning of 2015, and all of the guarantees associated with 
the operation of the AGRU and TGT amine section 
at design and turndown capacities have been 
demonstrated without operational issues (see 
Table 1). Operators have reported simple management of the H2S content of acid gas by the preflash 
column.

This short case study originally appeared in PTQ's Technology In Action feature - Q2 2015 issue.
For more infomation, please contact:  lnormand@prosernat.com