Study On System Energy Analysis And Optimization Design Of SWRO

Developing seawater desalination technology is an important approach of solving the problem of scarcity of water. Seawater reverse osmosis (SWRO) desalination technology has an rapid development in recent ten years, and it will become the primary desalination technology in the future because of its many advantages, such as less equipment investment, lower energy consumption and shorter construction period than other desalination methods. Theoretically, it is the most energy-saving seawater desalination method. However, at present the technical economical indicators of SWRO don't reach the public expected value, and the cost of desalination is on the hign side. And system energy consumption cost is the main component of the total cost, therefore, excessive energy consumption has become the most important factor of constraining the making water cost. It shows that the current SWRO system can be improved in some aspects, such as the SWRO technology, the engineering design, and the system operation etc. For this reason, the dessertation has an analysis of operating parameters to the system's impact on energy consumption. And it carries out optimal design to the RO membrane system with cutting the system energy consumption as the goal.This paper uses Hydranautics company's RO system design software IMSdesign inspected the change characteristics of system energy consumption with the operating parameters, such as feed water temperature, system recovery, feed water salinity, energy recovery efficiency etc. There is a rule that system energy consumption will decline continuously with the rising of feed water temperature, will show a negative exponent of decline with the rising of system recovery, will show a linear decline in the proportion with the rising of energy recovery efficiency, will show a linear increase in the proportion with the rising of feed water salinity.This paper has a conversion of traditional optimization method of making system cost model, and it creates a mathematical model whose objective function is to realise the minimum of the energy consumption of unit product water. The model find its constraints from the membrane characteristic equation and system characteristic equation, together with numerical constraints as the requirements of membrane manufacturers'technical manual, which make up system's complete constraints. With membrane species, membrane numbers, membrane sequence as optimal variables, the model is a Mixed Integer Nonlinear Programming(MINLP).Linking to project example, the optimal solution of the model is obtained with Matlab'optimization toolbox to realise process optimization and operating parameters optimization. Linking with the actual design patterns closely, this paper uses the DOW company's RO system design software ROSA6.1 to verify the optimal results and the error is in an acceptable range. We choose the same membrane species and different membrane sequence for the one-stage one-pass process and one-stage two-pass process. After comparing with the two processes, we find that the project example's system energy consumption of unit product water can be achieved 2.97 kWh/m3, which is lower than the 3.31 kWh/m3 reported in literature. Clearly, using the method in this paper to choose process and parameters has a better result.