Semester

Fall

Date of Graduation

2022

Document Type

Thesis

Degree Type

MS

College

Statler College of Engineering and Mineral Resources

Department

Mechanical and Aerospace Engineering

Committee Chair

Hailin Li

Committee Co-Chair

Lian Shin Li

Committee Member

Lian Shin Li

Committee Member

Kenneth Means

Abstract

Abstract

Development of a Thermal Desalination System Using Low Quality Thermal Energy

Takudzwa Chipunza

The blowdown water from the cooling tower of the power plant and the produced water from shale gas industry cannot be disposed directly to the environment as they may contain dissolved solids that are harmful to the environment. A detailed physical and chemical process to remove the mineral and organic solids has been developed in West Virginia University. Such a process includes running the blowdown and produced water through a softening tank, activated carbon tank, and a reverse osmosis (RO) system. The RO reject contains a high concentration of total dissolved salts (TDS) and cannot be disposed to landfill.

This work develops a shell and tube heat exchanger unit to further condense the RO reject by removing the water in RO reject through evaporation. The RO reject water is treated by running it through a one pass shell and tube heat exchanger system with the thermal energy needed for the evaporation of water provided by low quality steam extracted from steam turbine. The heat exchanger is designed with two outlets: one expected to collect steam and the other residual water. Low quality steam is run through on the tube side of the heat exchanger to provide the thermal energy necessary for the evaporation of water in shell. Preliminary testing is conducted using an initial iteration of a simple thermal desalination system with 82.2g/L of brine to observe if 10lbf brine can be produced. The design of the heat exchanger involved using analytical correlations, which are further verified with simulations using ANSYS FLUENT. The heat exchanger designed has been fabricated and integrated with other components purchased into a thermal desalination system with the steam provided by a steam canner. The steam canner is equipped with a 2kW electric heater and two pressure relief valves which are activated when the pressure in canner is beyond 1.65bar. The integrated system has been tested and inspected by EHS to make sure it is safe to run at the designed operating condition, and the safety valves do activate at the pressure designed. The preliminary operation test verified that the system must be insulated due to the large heat loss from the system to ambient air. The insulated system was tested to verify its capability in evaporating the water in shell. The preliminary test concluded that such a facility is able producing fresh water at a mass flow rate of 2.5 kg/h. The thermal energy transferred from the steam in tube to liquid water in shell estimated using water produced is 1.5 kW, which is about 75% of the heat produced by the electrical heater. The rest of energy is lost from the system to ambient air. It should be noted that the current system was manually operated by adjusting the flow rate control valve at exit of steam canner and exit valve of the tubes. The temperature of cooling water is also controlled by changing the cooling water and blending the cooling water in condenser. Further insulating the system and improving the control of the system will increase the utilization of the thermal energy in evaporating water in shell and reducing the energy cost of the thermal desalination system.

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