ABSTRACT

Desalination plants that convert seawater into drinkable water have become essential infrastructure in the struggle against global water shortage. Using temperature differences in ocean waters, Ocean Thermal Energy Conversion (OTEC) technology provides a possible approach to sustainable desalination in coastal areas. Warm surface water and cold deep seawater temperature difference generate power using a heat engine, which is the basic principle by which OTEC system works. Flash chamber, a type of pressure vessel, is used to convert water into steam, thus making it a critical component. The design process incorporates calculations and considerations from ASME Boiler and Pressure Vessel Code (BPVC) Section VIII, Divisions 1 and 2, with ASME Section VIII, Division 1 forming the basis for initial design and Division 2 refining the design through finite element analysis (FEA) techniques. ASME Section VIII, Division 1 includes the determination of design pressure, minimum thickness calculations, and nozzle sizing for inlet and outlet connections. In line with ASME Section VIII, Division 2, FEA enables a deeper analysis of stress distribution and fatigue life, giving optimized results. The modifications include iterative design refinements to minimize material usage and weight, without compromising structural integrity or operational effectiveness. After getting an initial design of the flash chamber from ASME Section VIII, Division 1, it was subjected to internal and external pressure, vacuum loads, hydrostatic forces, and geometric constraints to simulate realistic working conditions. The paper outlines designing a flash chamber as per Division VIII of the ASME BPVC. The paper also covers the optimization of flash chamber for several load conditions using ANSYS Workbench, to check for structural integrity.

INTRODUCTION

Desalination plants, crucial in combating global water scarcity, transform seawater into potable water. OTEC (Ocean Thermal Energy Conversion) technology provides a possible approach to sustainable desalination in coastal areas. D’Arsonval first conceptualized OTEC in 1888.(D’Arsonval 1881) Suggested closed-cycle OTEC system that harnesses a thermal gradient to produce power, using ammonia as the working fluid. Later in 1926 George Claude student of D’Arsonval Proposed and demonstrated an open-cycle OTEC system that uses steam evaporated directly from seawater to drive a turbine and generate electricity (Claude 1930). NIOT Chennai has been working on setting up Low Temperature Thermal Desalination (LTTD) plants to provide drinking quality water at Lakshadweep Island from 2004.The works done in NIOT (Sistla et al. 2009) stated that LTTD process takes advantage of the temperature difference between two water bodies to evaporate warmer seawater at low pressures. The vapor produced is then condensed using the colder seawater, resulting in high-quality fresh water.(Venkatesan 2014) Stated that compared to reverse osmosis, LTTD process of sea water desalination is environmental friendly, ecological as well as economical. At present, all the LTTD plants are powered using diesel generators. OTEC resembles the LTTD process in that it generates both fresh water and electricity. The electricity is produced by harnessing the energy from warm seawater vapor as it passes through a turbine. The intent is to use this available energy to run the plant components, making it a self-sustaining plant. The plant cycle may be a closed-cycle (CC) or an open-cycle (OC) system.

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