Numerical simulation and analysis of a patented desalination and power co-generation cycle

A patented cycle for water desalination and power generation was evaluated with regard to thermal efficiency and water production. The inventor of the patent claimed that the patented cycle provides a thermal efficiency of 41%, which is higher than current combined water and power generation steam plants. A simulation program was developed to evaluate the thermal efficiency and water productivity of this cycle. Simulation parameters were selected from data provided by the patent as well as data generally used in the design of combined power and desalination plants. Results of the simulation were compared with a simulation of the Jubail-II combined plant. The simulation proved that the patented cycle is far inferior to current dual-purpose MSF desalination plants in terms of water production. In addition, the patent was found to have a much lower efficiency than what was claimed by the inventor.

The main objective of the patented cycle as stated by the inventor [2,3] is to overcome the temperature limitations imposed by scale formation on direct contact heating equipment used in conventional desalination plants. Another claim of the invention is that it increases the thermal efficiency of the power plant over conventional power plants. Our analysis shows that the objective of overcoming the temperature limitations has not been accomplished because direct contact heating is used only in the power generation cycle and not in the desalination part of the process. The only temperature limitation of conventional power plants is construction materials, and temperatures up to 600°C have been used in power plants. The temperature limitation of MSF desalination (which is around 120°C to prevent scale formation) was not addressed by the patent. The simulated thermal efficiency of the patented cycle corresponds with the efficiency reported by the inventor when corrected for major equipment efficiencies. This efficiency is below the thermal efficiencies of conventional power cycles (36–38%) when calculated using the appropriate turbine, generator and heater efficiencies. As a result, no advantages are offered by the patented cycle over other conventional power plants. The main disadvantage of the patented cycle, however, is the very low water output compared to conventional dual-purpose power–MSF plants. This disadvantage discourages the use of the patented cycle in situations where pure water is the main product and electricity is the by-product of the cogeneration process. Other aspects of the process such as efficiency of direct contact heating, scale formation, corrosion, component sizing, and selective precipitation of salts need to be explored because of the unconventional nature of using seawater as a power cycle fluid.