COMPARISON OF DIFFERENT METHODS ENVISAGED

These projects gather together all of the possibilities for the installation of a energy harnessing station. From reading these reports one can extract three really distinct options : the on-shore variation (on the lake shore), the semi-off-shore variation (extraction system on barge and treatment on-shore) and the off-shore variation.

Off-shore (extraction and treatment on barge)

Separator under the lake surface

Advantages	Disadvantages
Open choice of site on the lake. Maximum reduction in all piping. Number of extraction installations a priori unlimited. Mobility of harnessing stations. Preservation of extraction columns due to the lack of friction on lake bottom. Less loss of capacity and less risk of blocking because of the vertical nature of the columns. Increased yield due to the separator being at depth	Added investment for the design and manufacture of the barge. Transport of workers and maintenance material by boat. Presence of a purified gas pipeline under the lake surface. (*) Note : in the hypothesis that the separator is on the barge the yield will be equivalent to the on-shore solution and the main advantage of the off-shore solution would be lost.

Semi-off-shore (extraction system on barge and treatment on shore)

Separator under the lake surface

Advantages

Disadvantages

Preservation of extraction columns due to the lack of friction on lake bottom.
Less loss of capacity and less risk of blocking because of the vertical nature of the columns
Increased yield due to the separator being at depth.

Presence of an unrefined gas pipeline under the lake surface
Separation of the station into two distinct units resulting in the doubling of security, service and maintenance personnel. Choice of lake site dependent on where treatment plant could be established on the shore. (*) Note : in the hypothesis that the separator is on the barge the yield will be equivalent to the on-shore solution and the main advantage of the off-shore solution would be lost

On-shore (extraction and treatment system on the lake shore)

Seperator below lake surface

Advantages	Disadvantages
Pressure equivalent to immersed solution	Prohibitive cost of the trench protecting the entire installation. Scarcity of sites likely to comply with the requirement of such a solution

Separator above the lake surface

Advantages	Disadvantages
	low pressure in the separator a large amount of gas to be processed proliferation of machinery/equipment Energy cost of the extra maintenance Note : taken together, the inconveniences of this solution mean that, unless one accepts a backward step, one cannot rationally consider an entirely on-shore solution for the installation, (as is currently the case at Cape Rubona).

Advantages and disadvantages common to the 2 positions of the on-shore separator:

Advantages	Disadvantages
Ease of access for subsequent work Ease of access for personnel No sunken cables	Lengthening of the harnessing and suppression columns Serious charge loss due to the profile of lake bed Scarcity of sites with sufficiently sloping sides

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