Hydrocarbon emissions from platforms and refineries are a source of atmospheric pollution, and there is a strong drive in the industry to find environment-friendly solutions. Ramboll Oil & Gas has considerable experience in this field and is currently carrying out several studies to review the feasibility of installing flare gas recovery. Recent studies include a zero flare solution for the North Sea platform, South Arne, operated by Hess Denmark.
What is there to recover?
The concept of flare gas recovery is quite simple; in fact it is difficult not to see the idea in recovering valuable products instead of discharging them into the atmosphere via a stack or to be burned in a flare. And for many companies a reduction in carbon taxes is yet another incentive for recovering flare gas.
Facts about the system
The flare gas recovery system recovers the process releases which are normally lead to the flare system and directs this gas back into the gas processing system (recovery mode). If the pressure rises or any other unforeseen event happens, the flare gas recovery will change into flaring mode, allowing emergency releases to be lead to the flare tip and burnt off safely. Emitting the gas without igniting it first, would be much more harmful to the environment.
When operating in recovery mode, a fast opening valve will close off the path to the flare stack. The recovered gas will then be lead back to the existing gas compression system and reintroduced; preferably where the process pressure is lowest. A pressure-boosting device - i.e. a compressor - may be necessary to meet the operating pressure at the tie-in point to the gas compression system.
Securing against hazardous situations
If the pressure in the gas recovery system rises due to any unforeseen event, the fast opening valve will open instantly re-establishing the path to the flare, which is ignited promptly to ensure burning of the gas. A secondary pressure protection device, for instance a burst disc, is installed in parallel to the fast opening valve to provide a positive path to the flare in case the valve should fail to open.
These safety features are considered sufficient to secure the platform against any potentially hazardous situations, where emergency flaring is fed back into the compression system. A thorough risk analysis, however, is still needed to ensure optimum safety before choosing a zero-flare solution.
Danish CVR number 35128417 