Experimental Study on the Influence of Flexible Control on Key Parameters in Reverse Osmosis Desalination

Shuai Chu,Xiaona Ma,Denggao Qiu,Yinxuan Li,Lei Kou,Weichun Ge,Shitan Zhang

doi:10.1109/access.2021.3140071

Abstract

Variable-frequency drive (VFD) has been widely used in reverse osmosis desalination. Our purpose is to study how the VFD and pressure regulating valve affect the key parameters of reverse osmosis desalination and their action principle through experiments. Firstly, the power frequency is controlled by VFD, and the operating pressure is controlled by pressure regulating valve (needle valve) in the experiment. The feed water passes through the multimedia filter, precision filter and permeable membrane channel in turn, and permeate water and brine enter the fresh water tank and the brine tank respectively. Secondly, through experiments on seawater and brackish water respectively, the water flow rate, product water quality, energy consumption and recovery rate under different operating pressures are obtained when the power frequency is 25, 30, 35, 40, 45, and 50 respectively. Finally, combined with the working principle and mathematical model of VFD and high-pressure pump motor, the reason for the experimental results caused by the operation change is explained theoretically. The experimental results verify that for a certain recovery rate, the specific energy consumption required for water production decreases with decreasing power frequency. This provides desalination energy savings but at the expense of permeate production speed.

Highlights

As an important natural resource, water is closely related to production and life
We have fully considered the effects of the recovery rate, brine temperature and salinity on the energy consumption (Table 6), but consideration of the power frequency is lacking
The application of the Variable-frequency drive (VFD) in RO desalination has a certain impact on the water production efficiency, power consumption and recovery rate

Summary

Introduction

As an important natural resource, water is closely related to production and life. water resources cover 70% of the Earth’s surface, 97.5% of them are too high in salt to be directly consumed by humans [1]. The shortage of fresh water has become a common global crisis [2]–[4]. According to the World Resources Association, the threat of global water shortages is expected to intensify in the 20 years due to population growth, economic growth and energy consumption. The desalination capacity is growing rapidly in China and around the world (Figure 1(a)). Tianjin and Shandong Provinces account for 26% and 24% of China’s desalination capacity, respectively (Figure 1(b)), and they are the two cities with the largest desalination capacity in China. The Middle East is starved of fresh water and has the largest desalination capacity in the world (Figure 1(c)). With the emergence of PX energy recovery devices, the SEC of RO is significantly lower than that of other desalination technologies [5], [6]. RO is currently the most popular and widely method to provide sustainable freshwater [7]–[9]

Objectives

Findings

Discussion

Conclusion