A Novel Concept
With refineries facing not only larger demand on their sulphur recovery capacity, but more and more, face capacity problems due to the quantity of sour water they generate, Duiker introduced a novel concept. This novel concept was sprouted from the idea that ammonia should be treated separately from a sulphur recovery unit as not only it increases the hydraulic load but its’ incomplete combustion can cause problems such as corrosive salt formation.
Dynamically Controlled Staged Incineration
The staged oxidation process that was developed for this purpose was dubbed a Stoichiometry-Controlled Oxidation unit as this name clearly outlines the core concept. The process dynamically controls the air demand to prevent NOX from being formed. With this process being extremely robust and able to treat feeds containing sulphur species, it allows for a myriad of integration options. Specifically it allows for alternative process routes for the sour water.
Integrating SCO Units in the Refinery
The most dominant of these alternative processing routes are the following: First we have the option to, with the use of a two stage stripper, combust nearly pure ammonia. This generates a large thermal output which can either be recovered as steam or be used to incinerate the tail gas generated by the tail gas treating unit. For most general design conditions, this results in the thermal oxidation of the tail gases to be almost fuel gas free.
The second option is to oxidize conventional sour water stripper gas in the Stoichiometry-Controlled Oxidation unit. Through utilizing a sulphur dioxide absorption system and recycling this stream to the main reaction furnace, we can still utilize the generated heat to incinerate process gas from the sulphur recovery unit.
Finally, the third option is to utilize the sour water, with the use of a single stage stripper, to provide a process input for a sulphuric acid plant. Consequently this eliminates the need for catalytic selective reduction of nitrous oxide. Thus, the process becomes more robust and elegant and the investment from both a capital as well as an operational perspective decreases.