The objective of this paper is to show five innovative options of operating the hydrate inhibition system which aims to eliminate future wet natural gas production limitations and optimize capital and operation expenses during a 25-year life cycle period.
Mono-Ethylene Glycol (MEG) is injected in wet natural gas trunk lines from an offshore gas field, as a means of hydrate inhibition during the winter season. The used MEG is supposed to be recovered in MEG Regeneration Unit (MRU) at onshore gas plant, where the wet natural gas is further processed. The MRU often faces challenges in producing to achieve specified MEG purity, which consequently results in injecting a diluted solution of MEG into the offshore systems, and thereby lowering the maximum allowable production capacity of wet natural gas.
This paper describes the study in five different options. Option 1 represents the current operating scenario of maintaining the existing system with MRU in service, while option 2 explores shutting down MRU at onshore gas plant, and pumping fresh MEG during winter days from the gas plant to the offshore platforms. Option 3 explores shutting down MRU at the gas plant and pumping fresh MEG during winter days, but from a Beach Valve Station (BVS) at an onshore location. Option 4 explores maintaining the existing system with MRU in service and upgrade the storage tanks to address the unsteady state nature of rich MEG flow. Option 5 explores pumping lean MEG during winter days from the gas plant, storing rich MEG in tanks for MEG regeneration and reclaiming MEG through the existing system during the summer including storing lean MEG in tanks for winter usage.
The evaluation has shown that options 2 and 3 can easily meet the required hydrate depression specification during winter period, at far lower MEG injection rates and at a substantially lower life cycle cost (LCC) compared to option 1. The evaluation also showed that options 4 and 5 will ensure MRU operation not interrupted due to low-low levels in MEG storage tanks and will maintain high purity MEG in the trunk lines, which is different from option 1. In conclusion, option 5 has the lowest LCC which is the most economically attractive option.