Nature at its finest: part two

Read part one of this article here.

Development

After its successful introduction in the oil and gas industry in 2002, the THIOPAQ O&G technology captured its place as proven and competitive in the global market for desulfurisation. Continuous research and development efforts and design improvements based on operational experiences ensure that the technology remains cutting edge. Most frequently, such improvements involve relatively small adaptations to general hardware or measurement/control equipment. The latest improvement, however, is more far reaching.

A vital parameter in the design of a biological process is the activity of the bacteria; in the THIOPAQ O&G case, this is the maximum conversion rate of sulfide by the sulfide oxidising bacteria. In terms of process design, it is expressed as the volumetric sulfide conversion capacity. The greater the conversion capacity, the smaller the bioreactor can be.

Recent small scale laboratory experiments revealed a much higher maximum sulfide conversion capacity than is currently applied as a design rule. A dedicated demonstration plant was constructed to demonstrate the increased volumetric sulfide conversion capacity of the bacteria in a full scale setup. The demonstration plant (Figure 3) was able to convert up to 270 kg/d of H₂S and has been in operation for more than a year. These findings firmly allow an increase of a bioreactor’s volumetric conversion capacity to twice that of the existing design rules. In addition, as the minimum sulfur load remains unchanged, the turndown of a single bioreactor can be doubled as well (up to 15% of the design load). The successful completion of this demonstration phase has led to the launch of a new generation of the THIOPAQ O&G process. It is more compact, more flexible and more cost effective than the original version.

The demonstration plant.

Size of the price

Quantifying the absolute benefits of the improved design of the process is an intricate matter. The cost structure is strongly affected by the feed gas composition and by operational conditions. In addition, the Capex is influenced by project specific requirements, such as turndown and geographical location. Furthermore, different types of bioreactors, depending on the specific sulfur load, require different considerations to be taken into account. The following two examples outline case specific benefits:

Maximum sulfur loads in one single bioreactor

The capacity of a single bioreactor of maximum dimensions increases from 35 to 70 tpd of sulfur. For projects in this range of sulfur load, this means that in one complete bioreactor, an SS tank with maximum ID of approximately 11 m and internals, less is needed. This is not only a considerable cost saving, but also a significant reduction in the required plot space.

Application in a multiple bioreactor setup

A setup with multiple bioreactors can have advantages in terms of costs and operational flexibility. Even though having a greater number of bioreactors requires more piping, valves and controls, smaller reactors can be constructed of cheaper materials, such as glass fibre-reinforced plastic, and can often be shop fabricated, which saves costs in comparison with onsite construction. With regard to flexibility and turndown, the system can be operated with fewer than the maximum number of bioreactors. For example, a 10 tpd sulfur plant required six small bioreactors in such a multiple bioreactor setup, according to the previous design rules. The new design criteria prescribed only three bioreactors of the same size.

Conclusion

The improved THIOPAQ O&G process is more cost effective and flexible over the entire range of applicable sulfur loads, with a doubled specific conversion capacity of bioreactors. The effects are most pronounced for larger sulfur loads, where cost savings can be realised on stainless steel bioreactors. Since the maximum sulfur load of a bioreactor increases while the minimum sulfur load remains unchanged, the turndown of a single bioreactor is also doubled. The application of smaller bioreactors or fewer bioreactors in parallel also significantly reduces the required plot area for a given sulfur load.

Written by Gijs van Heeringen, Bob van de Genderand Jan Klok, Paqell BV, the Netherlands. This is an abridged article taken from the April 2016 issue of Hydrocarbon Engineering. Subscribers can view the issue in full by logging in.

Read the article online at: https://www.hydrocarbonengineering.com/special-reports/05042016/nature-at-its-finest-part-two-2917/