Produced natural gas must be treated to ensure high efficiency removal of sulfurous contaminants before it can be processed into liquefied natural gas (LNG).The selection of processes for removal of H2S may be a straightforward decision with extensive supporting data available. However, when the produced natural gas feedstock contains significant mercaptan, COS or other sour components, the process selection and design may become extremely complex. Several issues including process selectivity, energy requirements, total sulfur recovery, hydrocarbon coabsorption, and impact on downstream facilities will be weighed in this poster.
When technologies are being evaluated for use in pretreatment of gas for LNG production for the first time, the extremely high reliability and strict specifications of the LNG process must be taken into consideration. Often the processes under consideration are provided by licensors, and evaluation of data from historical applications should be undertaken cooperatively by the licensor and the operator to ensure that all facets of the operation are well understood. This is particularly challenging since it is rare to encounter exactly the same compositions and conditions more than once in the midstream.
LNG facilities operating in Qatar have installed multiple processes to maximize sulfur recovery at minimum cost. Based on the operating data from these units, ExxonMobil in cooperation with RasGas Company Limited (RasGas) has developed dynamic models and modified processes to optimize the operation of the existing facilities and the design of future ones. This work is aimed at high reliability, high efficiency, environmentally sound process units that support maximum LNG production at the lowest supply cost.
RasGas has extensive experience in operating gas sweetening and sulfur recovery units. In addition to moderate concentrations of H2S and CO2 that must be removed from the produced gas, a variety of mercaptans and other sulfur containing species compose up to 400 ppm of the gas. In RasGas Trains 1 and 2, Sulfinol-D was chosen as the gas sweetening process, and the acid gas stream was directed to an Acid Gas Enrichment unit before entering the Sulfur Recovery Unit. This system has worked effectively to achieve the very low levels of total sulfur (< 14 ppm) required for the liquefied product.