Resource Limitations Water

Another regulatory concern is access to a key resource that substantially influences the efficiency of the underlying power process as well as any added post-combustion emission controls. This other is with water consumption and its use as a thermal reservoir for heat rejection. Water is not only used as the primary working fluid in the vapor power cycle, but it is also used as the heat sink that helps fix the lower end of the thermodynamic boundary for efficiency. In essence, it sets the value of Tlow in Carnot expression:

For power plants located near a cold ocean, efficiencies are usually better than those located inland. In desert climates where water is unavailable or inaccessible, the minimum temperature for condenser discharge could be 30°C or higher during the day (a time when power demands are likely to be greatest). To compensate for the lack of cooling water, air cooled condenser technology may be the only likely alternative. This approach erodes plant efficiency since the lowest air is a poor quality thermal sink in comparison to water. The power demands to operate fans for cooling can add tens of megawatts of additional parasitic load to a utility scale generator. In turn, this will demand even greater fuel consumption to meet specific load requirements. Finally, the large heat exchanger requirement adds millions to the overall plant costs, which is recovered in the cost of the electricity.

In a post-combustion carbon capture plant, water is also required to cool the chemical solutions after regeneration (or in some cases, perhaps the coolant for the exhaust gases). And extraction of steam from the turbine cycle that is not returned will require an increase in the size of the water treatment facility for the unit for the make-up water. High purity water is also critical for any power plant, placing additional water requirements on a project. Even with a separate steam system for the CO2 process, water treatment for the make up water will be required. Facilities that have difficulties gaining access to water now would find the problems compounded by these additional water requirements.

Another challenge associated with water is not the lack of water, but rather the elimination of water from where it could cause serious operational problems— namely in a CO2 pipeline. Water, combined with CO2, forms a corrosive acid, which can attack the pipeline from the inside. High corrosion rates of up to 1-2 mm per week are possible. The source of the water is likely to be the loss of dehydration at the carbon capture plant prior to pipeline injection, possibly a more likely event during transients such as startup, shutdown, or trips (that might occur for various reasons). Preventing and forecasting such process failures represents enormous uncertainty and increased risk.

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