No abstract

Pullulan is a well-known extracellular polysaccharide produced by the aerobically growing yeast-like fungus Aureobasidium pullulans (A pullulans). Pullulan has a wide range of commercial and industrial applications, eg it is used in adhesives, in laminates or nylon-like fibres and fabrics, and in various foods as a low calorie ingredient. Pullulan itself is produced and deposited on the outside of the fungal cells, and because of the low oxygen permeability of the pullulan, this layer acts as a barrier for the transfer of oxygen from the medium to the fungus. This could be detrimental to the survival of the cells and, in turn, restrict the cultivation of the pullulan. In pullulan fermentation it is therefore desirable to break up and remove this layer of pullulan adherent to the cells. The conventional impeller-driven vessels often exhibit a gradient in mixing capabilities, with high intensities at and near the impeller but low intensities in peripheral regions. Such gradients increase significantly with the scale. The existence of the mixing gradient in a given vessel can potentially inhibit the process of pullulan generation in regions distant from the impeller, leading to reduced productivity. The oscillatory baffled bioreactor (OBB) offers enhanced and uniform mixing at very low shear rate compared with conventional mixing vessels; this would provide better control over the cultivation of pullulan. In this paper, the production of pullulan in the OBB is reported and compared with the fermentation process carried out in a conventional stirred tank fermenter.

For most of the Early Oil Production (EOP) facilities in early days of the field life, higher oil production is expected due high reservoir pressure. In this specific case study, oil production has hit the FPSO topsides design limit of 100 kbopd with only 5 wells connected. Most of these wells were choked to 30-50% to limit to oil production within installed name plate capacity of the FPSO. Therefore to take advantage of low GOR and high dry oil production during early field, Client has requested SBM to undertake the study to identify the maximum oil production without compromising Process safety and major modifications.The main bottlenecks to increase the crude production above the design capacity are identified as -increased crude temperature results in non-stabilized crude entering into the cargo tank mainly due to limitation on utility systems. To further increase production separator capacity is a bottleneck.Increased Temperature Non-Stabilized Crude: Based on the oil composition, stabilization of the crude before leaving the topsides is an issue. With increase in the production and limitation on utility system, enough heat is not available to flash-off light components and/or cool the crude down before entering cargo tank to prevent any further flashing in cargo tank. These flashed off gases will be vented through the cargo vent system along with displaced gases (which is significantly higher than flash gases). The cargo vent system is designed for vent-load during cargo terminal loading and therefore crude flash rates will not be anywhere near the design capacity of the vent system. Limitation of Utility Systems: As expected, all utilities systems are designed for 100 kbpd liquid production and any increase in production will have impact on the utility balance. To cater additional flow, either modifications are required in the existing system (e.g. additional duty, exchanger modifications, etc) or the optimization of the existing system is required.Separators Capacity: As long as water cut is negligible and small quantity of the water can be allowed to settle in the cargo tank, current crude oil production can potentially be increased with separator operating as two phase separators.

The actual field trial did match with the study results, and production was increased to greater than the design capacity without many process-stability issues. Therefore, this type of study provides a quick but thorough method of investigating the way forward to improve production without compromising safety limits, allowing the operator to take full advantage of favorable reservoir performance to optimize field economics. Study AssumptionsThe following assumptions were determined for the study, to simplify the results and to achieve better clarity:1. The composition of the production fluid does not vary considerably, and the carbon dioxide (CO 2 ) or hydrogen sulfide (H 2 S) levels are within the existing design limit. 2. Water production is negligible (less than 5%). 3. The maximum gas production is within the nameplate capacity of the existing facility (i.e., the GOR is below the design value); therefore, the study is to be focused on debottlenecking of the oil-processing side only. 4. There is no change in the crude-oil export specifications [i.e., the Reids vapor pressure=10 psia (0.69 bara) at 37.8°C and the crude-oil export temperature ranges from 35 to 55°C].Hemraj Gaidhani is currently working as a senior principal process engineer at SBM Offshore, Houston. He has more than 15 years of experience, mainly in the upstream side of the oil and gas industry, with the added experience of leading projects from the conceptual phase through commissioning/operations, including front-end engineering design and the detailed engineering phase. Previously, Gaidhani worked with major companies in the oil and gas industry, including KBR, CB&I, AMEC/BP EMS, and L&T, covering various areas of process engineering and operations support. He has published more than six international papers on the basis of his research and industrial experience. Gaidhani holds a PhD degree in chemical engineering from Heriot-Watt University, along with the prestigious James Watt Scholarship. He is keen to share his offshore-engineering experience and background in operations to improve the productivity and debottlenecking of existing assets.