The Modified Claus Process is widely used to recover sulphur in the natural gas processing industry1. It consists of two defined conversion stages: thermal and catalytic. The non-converted acid gas is sent, along with the tail gas, to the incineration furnace. This is a typical arrangement to prevent the release of toxic gases.
Qatar Petroleum operates an NGL complex with a Sulphur Recovery Unit (SRU) that uses the Modified Claus Process. In July 2011, a leak developed in an expandable pipe segment that allowed toxic gas to be released.
The incineration furnace's flue gas stack is designed to cause negative pressure at the incineration furnace. This is made possible by having it open to atmosphere through its effluent stack. Negative pressure is always met at reduced throughput. Thus, reducing the SRU throughput would prevent toxic gas leakage. The downside of the throughput reduction is that the excess acid gas would be flared.
Gas Operations, in a unique approach, utilized the inherited selectivity characteristics of MDEA solution, to optimize the overall operation. The optimization was done in a way that would affect the quantity and composition of the acid gas. This meant that we could operate the SRU in a safe manner with no environmental impact.
A detailed description of what we did to minimize Acid Gas flaring, without violating the AGRU product specs and without further deterioration of the leaking expansion bellow, are covered below. We also describe the benefits realized.