This study has looked into the feasibility of operating a floating methanol plant in a North Sea environment. The plant was fed with associated gas from an oil field.
Both the technical and economical results are promising. This indicates that such projects might promising. This indicates that such projects might be an alternative solution for otherwise reinjected gas; however, more work needs to be done to evaluate their attractiveness.
By now the floating production facility approach is a well recognized concept. Its major advantages are savings in capital investments, shorter development time, and increased flexibility because parts of the facility can be easily relocated.
So far the interest has focused mostly on floating gas processing plants; however, to the author's knowledge none is planned yet for the North Sea.
The purpose of this study was to do a technical/ economical feasibility study of gas-to-methanol conversion aboard a converted oil tanker in the North Sea.
The methanol plant would be of Imperial Chemical Industries (ICI) design. Close contacts were established with their contractors in order to find what is critical when operating a plant under such adverse conditions.
With few exceptions the contractors outlined the same points as critical. Based on this information and knowledge about the limitations on other parts of the facility, it was possible to arrive at parts of the facility, it was possible to arrive at an expected "on time" plant availability.
The methanol producer was treated as a separate company, buying associated gas from the field operators.
A computer model was written to perform the economic evaluations. Both a base case calculation and a sensitivity analysis were treated in this model.
Fig. 1 shows a principle view of the thought facility. The associated gas arrives at the SALM base, rises through it, and feeds into flexible lines to the plant. The 1000 M.T./day methanol plant is ICI's L.P. (low pressure) design.
In the plant the gas is first desulphurized. It is then combined with superheated steam (prepared from seawater) and fed to a reformer. There, synthesis gas, comprising hydrogen and carbon oxides, is formed. This mixture is further compressed and fed to the reactor where the methanol reaction takes place. This methanol is thereafter distilled and place. This methanol is thereafter distilled and stored in the tanker.
The processing tanker, together with the shuttle tanker when loading occurs, is free to weathervane 360 degrees around the SALM. The shuttle tanker then brings the methanol to a shore base for further distillation into grade AA before being stored.
The methanol facility is self-sufficient with energy and has an overall thermodynamic efficiency of approximately 60%. As a rule of thumb, it can be said the production of 1 M.T. of methanol requires approximately 31 MMSCF of natural gas.
The mooring unit is of Exxon's SALM type. It is able to permanently moor a 50–60000 DWT tanker in a northern North Sea environment, and should therefore not represent operating limitations.
The Exxon SALM is built in modules for rapid connections/disconnections when maintenance or repairs are performed at the field site.
