Solar cogeneration power-desalting plant with assisted fuel

Solar power plants (SPP) using parabolic trough solar collectors operating Rankine steam cycle are well proven and most widely used worldwide. These plants have 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%). Qatar is endowed with abundance of natural gas (NG) resources and production. Qatar's power plants use natural gas-operated gas turbines. However, resources are finite and domestic consumption is rising because of rapid economic and population growth. As in many countries, SPPs are considered to take share in electric power and desalted seawater productions. This elongates the life of the NG resources, and keeps the income return from its exporting. This also limits the emission of greenhouse gases and air polluting gases due to NG combustion, which badly affects the environment. While NG is used in SPP to compensate solar energy intermittent nature and keeps operation during non-sunshine hours, the main purpose of using NG here is to raise the SPP throttling temperature, and thus increasing steam cycle efficiency, even during full sun shine. It also lowers 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 feedwater to the collector. This drastically increases both power output and efficiency. Modifications of SPP power cycle to become cogeneration power desalting plants are presented.