Lessons Learned on Design & Operation of Sulfer Plant at Oil Field

In near future, it is anticipated that emission regulations for oil production facilities will be reinforced as much as same limit in the refining industries by government. Presently, several sulfur plants are under operation or commissioning in north Kuwait oil field. The following schematic drawing shows typical oil & gas production facility, which include a sulfur plant with upstream amine treating unit.

To meet design SO2 emission limit from these units, there are many considerations in view of operation as well as design. These are also required for stable operation and reliability of these units.

Required considerations are as follows.  

(1)    Environmental Aspect & Capacity Issues

• Accurate analysis of feed compositions & adopting representative wells for sampling
• Selection of optimum amine type
• Revamping existing plant with oxygen enrichment
• Emission reduction at Incinerator Stack by recirculation of sulfur degassing pit vapor
• Optimization of utility design at oil field

(2)    Process Reliability Aspect

• Corrosion control for BFW quality & preventing from acid corrosion
• Advantage of steam-heated indirect reheaters against fuel gas inline burners
• Application of new heat tracing type(contro trace) to liquid sulfur piping
• Proper design & pre-commissioning to avoid plugging in the piping during operation
• Product sulfur type selection
• Prevention of Claus Burner thermal damage from overheating

For instance, we will see one example of required considerations in details.

[The Example: Accurate Estimation of Feed Components and Feed Rates]

Accurate estimation is not simple at production facilities of oil field. Because many new wells are still under developing and some wells are closed. That means feed components can be dramatically changed as well as feed rates. Furthermore, the same wells' characteristics tend to be modified with the passage of time. Therefore, the following actions are very important.

• Adopt representative wells for sampling considering long-term production plan and well developing plan.
• Check downstream samples at test separators and other separators for gas/liquid flowrates, gas-oil ratio, water cut, each stream compositions and properties and so on.
• Review analysis method and select qualified vendors for sampling and analysis.

Based on the above analysis results, perform simulations for inflow performance relationship (the relationship between flowrate and reservoir pressure drawdown) and reservoir decline with time.

One example to prove the importance of this estimation is described as follows.

The amine treating units and sulfur plants at oil field were originally design for 2% H₂S of sour gas. However, after running, the actual H₂S content was 4.0%. Presently the units are suffering lack of capacity and the company is seriously considering its revamping. Inaccurate assessment can cause considerable capital loss to companies.

To reflect all the above considerations on design, owner companies should make their experienced and qualified engineers involved from the beginning of licensor design for amine & sulfur plants. Plant design margin considering feed variations and alternative operation case design such as turndown are also critical points.

Most important thing is to build KOC database including all lessons learned, improvements and any other change with regard to process design, construction, pre-commissioning, commissioning and initial start-up.
Through this, we can avoid to possible troubles and achieve one-time start-up and stabilization for the sulfur plants.

Present operation status and commissioning plan for the sulfur plants in KOC are shown in the following table.