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Optimization of NCG System Lineups

By Matthew Fishman, POWER Engineers, Inc. and William Harvey, Reykjavik University


The composition of the available steam resource for a geothermal flash plant strongly influences its design. A high non-condensable gas (NCG) concentration in the steam will require a large NCG removal system in order to maintain condenser vacuum. Unlike conventional thermal plants, which rely on a more consistent quality fuel source, the nature of the geothermal resource means the NCG load in a geothermal plant may vary from the design point—potentially both at initial operations and also over the life of the plant. Inadequate NCG system capacity reduces plant output, while excess capacity may result in excess use of ejector steam. This study presents a model of a geothermal plant and its associated NCG system, which allowed examination of variable NCG system lineups in order to determine preferred economical lineups and the potential savings. The model considers annual variations in wet bulb temperature which influence the achievable condenser pressure. The methodology presented here would be a tool used by engineers to consider appropriate configuration of the NCG system in the initial design as well as by plant staff to consider appropriate operating lineups throughout the life of the plant.

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