Improvement of process design for turbine energy recovery device under variable salinity conditions and its application: a case study

ABSTRACT

In order to promote energy efficiency, reverse osmosis (RO) systems are equipped with energy recovery devices (ERDs), which mostly work under stable inflow conditions. However, the inlet salinity in estuarine area fluctuates with seasons and river discharge. Traditional processes choose to add the number of high-pressure (HP) pumps to fit this situation, which brings problems of high capital cost, complex operation, and low device utilization. To overcome these drawbacks, an improved design of turbine ERD was proposed in this paper through real-time monitoring of salinity and automatic regulation of bypass valve. By controlling the opening, the ERD booster pressure could be adjusted, thereby obtaining corresponding pressures before the membrane for changeable salinities. A comparison of effective energy conversion efficiency (EECE), specific energy consumption (SEC), capital cost, and water production cost was conducted between conventional and optimized processes. Sanjiao Island RO plant operation indicated that the improvement could adapt to the fluctuation of inlet salinity. Compared to traditional process, it saved 55.7% of capital cost and 21.7% of water production cost, with EECE of 76.62–80.68% and SEC of 1.58–2.57 kWh/m³. When inflow salinity changed from 12,379 to 28,874 mg/L, the salt rejection of the primary reverse osmosis system (PROS) remained over 99.4%.

Highlights

• An optimized design of turbine is proposed for Sanjiao Island desalination plant under unstable inflow salinity conditions.

• The improvement is embodied in real-time monitoring of salinity and automatic self-regulation of bypass valves.

• Simulation is carried out before equipment operation, and the results are validated by practical running data.

• The long-term operation results confirm its reliability.

KEYWORDS:

• Reverse osmosis
• energy recovery device
• variable salinity
• real-time monitoring of salinity
• adjustment of bypass valve

Disclosure statement

No potential conflict of interest was reported by the author(s).

CRediT authorship contribution statement

Xiaoli Wang: Data Curation, Investigation, Writing-Original Draft, Writing – review & editing; Shenghui Wang: Funding acquisition, Supervision; Chengpeng Wang: Methodology, Supervision; Pengfei Huang: Supervision, Project administration; Daiwang Song: Methodology, Supervision; Yin Zhang: Editing; Lidong Jiang: Methodology; Shixian Ma: Data Curation.

Additional information

Funding

The National Key R&D Program of Shandong [No. 2019TSLH0304], the Special Fund for Basic Scientific Research Business of Central Public Research Institutes (No. K-JBYWF-2019-ZT01, K-JBYWF-2019-ZD01, R-JBYWF-2021-T02, and KJBYWF-2021-T07, K-JBYWF-2021-QR04), the Key Research and Development Project of Hainan Province [ZDYF2021SHFZ057], the Natural Science Foundation of Tianjin [No.20JCZDJC00460] is deeply appreciated.

Notes on contributors

Xiaoli Wang

Xiaoli Wang born in 1986, graduated from Tianjin University with a master’s degree. Her research interests include seawater desalination, design of water treatment process, and energy recovery technology.

Shenghui Wang

Shenghui Wang born in 1979, graduated from Tsinghua University with a master’s degree, mainly engaged in the research and development of unconventional water resources utilization technology and equipment, such as seawater desalination and industrial water treatment.

Chengpeng Wang

Chengpeng Wang born in 1982, graduated from Northwestern University with a doctoral degree. He is interested in the development of high-pressure pumps and energy recovery devices.

Pengfei Huang

Pengfei Huang born in 1982, graduated from Dalian University of Technology with a master’s degree. His research direction is engineering management.

Daiwang Song

Daiwang Song born in 1988, graduated from Tianjin University with a doctoral degree. His research interest is the development of energy recovery devices.

Yin Zhang

Yin Zhang born in 1988, graduated from Tianjin University with a doctoral degree. His research direction is the development of high-pressure pumps and energy recovery devices

Lidong Jiang

Lidong Jiang born in 1966, graduated from Tianjin University with a bachelor’s degree. He mainly engaged in seawater and brackish water desalination process design and engineering construction

Shixian Ma

Shixian Ma born in 1996, graduated from Nanjing Technology University of with a bachelor’s degree. His research interests include water treatment instrumentation and control.