Abstract
As the leading thermal desalination method, multistage flash (MSF) desalination plays an important role in obtaining freshwater. Its dynamic modeling and dynamic performance prediction are quite important for the optimal control, real-time optimal operation, maintenance, and fault diagnosis of MSF plants. In this study, a detailed mathematical model of the MSF system, based on the first principle and its treatment strategy, was established to obtain transient performance change quickly. Firstly, the whole MSF system was divided into four parts, which are brine heat exchanger, flashing stage room, mixed and split modulate, and physical parameter modulate. Secondly, based on mass, energy, and momentum conservation laws, the dynamic correlation equations were formulated and then put together for a simultaneous solution. Next, with the established model, the performance of a brine-recirculation (BR)-MSF plant with 16-stage flash chambers was simulated and compared for validation. Finally, with the validated model and the simultaneous solution method, dynamic simulation and analysis were carried out to respond to the dynamic change of feed seawater temperature, feed seawater concentration, recycle stream mass flow rate, and steam temperature. The dynamic response curves of TBT (top brine temperature), BBT (bottom brine temperature), the temperature of flashing brine at previous stages, and distillate mass flow rate at previous stages were obtained, which specifically reflect the dynamic characteristics of the system. The presented dynamic model and its treatment can provide better analysis for the real-time optimal operation and control of the MSF system to achieve lower operational cost and more stable freshwater quality.
Highlights
With the development of society, the shortage of freshwater resources has gotten worse, and seawater desalination is an important way to solve it [1,2]
Among the many seawater desalination methods, multistage flash (MSF) desalination leads the way in the desalination industry because of its high reliability, large capacity of single units, and good water quality [3,4,5,6]
Multistage flash is one of the most widely used desalination methods, and its dynamic performance is very important for optimal operation, design, maintenance, and fault diagnosis
Summary
With the development of society, the shortage of freshwater resources has gotten worse, and seawater desalination is an important way to solve it [1,2]. Mazzotti [16] et al established a dynamic model considering the geometric characteristics of the flash chamber and the variation of physical parameters of water, steam, and brine with temperature and concentration, but the work content of dynamic response was not rich enough. Alsadaie and Mujtaba [20] considered the effect of noncondensable gases and established the dynamic model of the system on the gPROMS platform; in the main, the influence of noncondensable gases on the steady-state of the system was analyzed and their work provides a good foundation for dynamic analysis and real-time operation. This paper considers the compensation effect of the recycled brine flow rate on the seawater temperature and establishes a relatively complete and realistic dynamic mechanism model. ΡV j ρBj ρD j where ρVj is the density of steam at Stage j, kg·m−1; ρBj is the density of flashing brine at Stage j, kg·m−1; ρDj is the density of distillate at Stage j, kg·m−1; VTUBE is the volume of the condenser tube, m3; NTUBE is the number of condenser tubes
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