Economic evaluation of reverse osmosis desalination system coupled with tidal energy

A reverse osmosis (RO) desalination system coupled with tidal energy is proposed. The mechanical energy produced by the tidal energy through hydraulic turbine is directly used to drive the RO unit. The system performances and the water cost of the conventional and tidal energy RO systems are compared. It is found that the proposed tidal energy RO system can save water cost in the range of 31.0%-41.7% in comparison with the conventional RO system. There is an optimum feed pressure that leads to the lowest water cost. The tidal RO system can save more costs at a high feed pressure or a high water recovery rate. The optimum feed pressure of the tidal energy RO system is higher than that of the conventional RO system. The longer lifetime of the tidal energy RO system can save even more water cost. When the site development cost rate is lower than 40%, the water cost of the tidal energy RO system will be lower than that of the conventional RO system. The proposed technology will be an effective alternative desalination method in the future.     

Proposal and analysis of a dual-purpose system integrating a chemically recuperated gas turbine cycle with thermal seawater desalination

A novel cogeneration system is proposed for power generation and seawater desalination. It combines the CRGT (chemically recuperated gas turbine) with the MED-TVC (multi-effect thermal vapor compression desalination) system. The CRGT contains a MSR (methane-steam reformer). The produced syngas includes plenty of steam and hydrogen, so the working medium flow increases and NO_x emissions can achieve 1 ppm low. However, the water consumption is large, ∼23 t/d water per MW power output. To solve this problem and produce water for sale, MED-TVC is introduced, driven by exhaust heat. Such a dual-purpose plant was analyzed to investigate its performance and parameter selection, and compared with four conventional cogeneration systems with the same methane input. Some main results are following: In the base case of the CRGT with a TIT of 1308 °C and a compression ratio of 15, the MED-TVC with 9 effects, the specific work output, performance ratio and CRGT-consumed water ratio are 491.5 kJ/kg, 11.3 and 18.2%, respectively. Compared with the backpressure ST (steam turbine)/CC (combined cycle) plus MED/MSF (multistage flash), the CRGT + MED has better thermal performance, lower product cost and shorter payback period, which indicates the CRGT + MED dual-purpose system is a feasible and attractive choice for power and water cogeneration.     

Internalisation of external cost in the power generation sector: Analysis with Global Multi-regional MARKAL model

The Global MARKAL-Model (GMM), a multi-regional “bottom-up” partial equilibrium model of the global energy system with endogenous technological learning, is used to address impacts of internalisation of external costs from power production. This modelling approach imposes additional charges on electricity generation, which reflect the costs of environmental and health damages from local pollutants (SO₂, NO_x) and climate change, wastes, occupational health, risk of accidents, noise and other burdens. Technologies allowing abatement of pollutants emitted from power plants are rapidly introduced into the energy system, for example, desulphurisation, NO_x removal, and CO₂ scrubbers. The modelling results indicate substantial changes in the electricity production system in favour of natural gas combined cycle, nuclear power and renewables induced by internalisation of external costs and also efficiency loss due to the use of scrubbers. Structural changes and fuel switching in the electricity sector result in significant reduction of emissions of both local pollution and CO₂ over the modelled time period. Strong decarbonisation impact of internalising local externalities suggests that ancillary benefits can be expected from policies directly addressing other issues then CO₂ mitigation. Finally, the detailed analysis of the total generation cost of different technologies points out that inclusion of external cost in the price of electricity increases competitiveness of non-fossil generation sources and fossil power plants with emission control.