Solar power plants using parabolic trough solar collectors, operating Rankine steam cycles, are well proven and the most widely used type of solar power plant (SPP) worldwide. These plants have a low power cycle efficiency (30%) due to low throttling conditions of 350-375°C and 100 bar. Conventional steam power plants have high throttling conditions (535-560°C and 140-160 bar) and high efficiency (38-40%). An SPP was suggested for generating electric power and desalted seawater; i.e. a cogeneration power desalting plant (CPDP) in Qatar. Qatar has large natural gas (NG) resources and Qatar's power plants use NG-fueled gas turbines. However, NG resources are finite and NG consumption is rising. As in many countries, SPPs contribute to electric power and desalted seawater production. This prolongs the life of the NG resources, and maintains an export revenue stream. This also limits the emission of greenhouse gases and air polluting gases due to NG combustion, which badly affect the environment. While NG is used in SPP to compensate the intermittent nature of solar energy, and keeps the operation during non-sunshine hours, its main purpose is to raise the SPP throttling temperature, and thus increases the steam cycle efficiency, even during full sunshine. It also lowers the cost of using expensive land where the SPP is planned. This paper studies the feasibility of utilizing NG to superheat the steam leaving the SPP solar collector field, and to heat the feed water to the collector. This drastically increases both power output and efficiency. Modifications of SPP power cycle to become a CPDP are presented.


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