Phase diagrams reveal acid-gas injection subtleties

Examination of phase equilibria in a binary hydrogen sulfide (H{sub 2}S) and water system explains some nuances of acid-gas injection. Also, the phase diagrams dispel some misconceptions, prevalent in literature, on hydrate formation. This article shows how hydrates can form without free water (an aqueous liquid phase) present and how hydrates can also form in the presence of a nonaqueous liquid. This first of a two-part series describes multicomponent phase diagrams. The concluding part will explain acid-gas phase changes from the amine unit to the bottom of an injection well. To replace flaring, acid-gas injection is quickly becoming an environmentally friendly alternative. Acid-gas injection also has attracted the attention of larger producers. With sulfur prices depressed, reinjection could be an economical alternative to building a Claus plant and stockpiling sulfur. It is even possible that injected H{sub 2}S could be produced at a future date if sulfur prices improve.