Why tail gas incinerators burn more fuel than they should, and what a mixing checkerwall changed in one Claus SRU.
An incinerator that mixes poorly
pays for it in fuel gas and excess oxygen.
This article by Uday N. Parekh of Blasch looks at the efficiency and environmental performance of the thermal incinerator behind a sulfur recovery unit. Complete combustion of the tail gas depends on temperature, residence time and turbulence. When the incinerator mixes poorly, operators compensate with more fuel gas and more excess oxygen. A published US case shows what a mixing checkerwall changed: almost 50% less fuel gas and nearly no sulfur carryover.
Every extra unit of fuel gas and oxygen in the incinerator pays for mixing that the combustion chamber is not providing.
The incinerator oxidizes the remaining sulfur compounds in the Claus tail gas before it goes to the stack. Feed volume swings with the refinery, and at low flow a conventional checkerwall often does not create enough turbulence for complete combustion.
The result, as the case study lists it: elemental sulfur leaving the incinerator and depositing downstream, soot during upsets, higher excess oxygen, more fuel gas, and a low shell temperature that lets acid condense and corrode the casing. Brick checkerwalls in this service also fail mechanically.
A US Mid-Continent operator of Claus sulfur recovery for several refineries had both problems in one incinerator: a highly variable feed and repeated mechanical failures of the brick checkerwall. The plant already used Blasch hex head ferrules at the Claus burner and the incinerator. During the 2009 turnaround, the old wall was replaced by a VectorWall built from interlocking hex blocks with deflector tiles to increase mixing.
Results reported by the operator:
The case is described in full under VectorWall in a Claus SRU incinerator.
If you run the incinerator hot and rich in oxygen to be safe, mixing is the place to look. The VectorWall mixing checkerwall is set in the combustion chamber, and the tail gas incinerator page covers the unit as a whole.
Operators fire more fuel gas and add excess oxygen to make sure combustion is complete when the chamber itself does not mix the gas well.
In the published case, inspections showed no cracks or deterioration after five years in service.
Yes. In the case above it replaced the old checkerwall during a scheduled turnaround.
Send the incinerator dimensions, the feed range and today's fuel gas and oxygen. A Blasch engineer looks at the combustion chamber.
