Desalination - Team D

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Team D: Final Report

Authors: Thomas Aunins, Robert Cignoni, John Dombrowski, Iris Zhao

Instructors: Fengqi You, David Wegerer

March 11, 2016

Executive Summary

Water shortage is one of the foremost and most urgent issues facing the world today, as developing and developed countries alike have struggled with depletion of natural reservoirs and severe droughts. This issue has resulted in the recent rapid development of desalination technology and the construction of desalination facilities. Since the turn of the millennium, the United State alone has increased its desalination capacity from 600 million gallons per day to 1650 million gallons per day, with much more currently being planned. California, in particular, is the focus of a large amount of the United States’ desalination efforts, as its current drought has exposed a discrepancy in water supply contingency and demonstrated a need for non-natural freshwater sources.

This project aims to design a 10 million gallon per day seawater desalination plant on the Southern California Bight--near San Diego--to fill this need. A reverse osmosis system was chosen based on the fact that it is the most rapidly developing and innovating technology in the desalination field, as well as the fact that it has a lower theoretical energy production per gallon of water than the common multi-stage flash purification methods. Our plant will pressurize seawater from subterranean wells off the coast of the bight and send it to our pre-treatment system. There, it will go through a drum screen, multimedia filter, antiscalant addition, and finally ultrafiltration to remove varying size of suspended solids and contaminants, before entering our reverse osmosis system.

The RO system itself is a 2-stage, 6 element per stage process, using Dow SW30XHR-440i membranes and operating at 50% recovery with a feed of 20 million gallons per day. This allows the process to achieve a final dissolved solids concentration of 109 mg/L, far below the California drinking water recommendation of 500 mg/L. This freshwater can then be sent to post-treatment and merged with water of the San Diego County Water Authority’s distribution system. Waste concentrate from the process is sent back into the bay through a long diffuser pipe system that will dilute the brine to necessary levels to avoid environmental damage.

An economic analysis of the process found total capital costs to be slightly more than $600 million, with yearly revenues and operating costs at $25.4 million and $6.2 million, respectively. On a 25 year time scale, this results in a final net present value for the project at -$402.5 million, causing us to conclude that as a commercial venture the project is not viable. We do note, however, that increased demand and decreased supply may cause water prices to rise and create a motivation for government investment in the project in the future. For this reason, we believe that it is possible for this project to become an economically feasible and practically necessary venture in coming years.

Contents


Introduction

Background

Problem Statement

Technical Approach

Site Location and Capacity

Feed Stream

Product Stream

Flowsheet

Process Flow Diagram, Major Technology, and Alternatives

100 - Pretreatment

200 - Reverse Osmosis

Seawater Reverse Osmosis Technology

Energy Recovery

300 - Posttreatment

400 - Brine Treatment

500 - Solids Treatment

Economic Evaluation

Equipment Sizing/Pricing

Pretreatment

RO System

Feed Intake

Concentrate Return and Dilution Pipelines

Pumps

Pretreatment Pumps

RO Pumps

Posttreatment Pumps

Chemical Storage Tanks

Product Selling Price

Operating Costs

Capital Costs

NPV Analysis

Optimization

Sensitivity Analysis

Capital Costs

Operating Costs and Revenue

Conclusion

References

Appendices

Appendix 1 - Plant Location Map

Appendix 2 - Posttreatment Water Quality Goals

Appendix 3 - Dissolved Ion Concentration of Seawater Inlet

Appendix 4 - Process Flow Diagram

Appendix 5 - Final Simulation Mass Balance and Stream Pressure

Appendix 6 - Stream Tables

Appendix 7 - Composition of Pass Streams from RO Process

Appendix 8 - Pumping Requirements

Appendix 9 - ERD Simulation

Appendix 10 - Example Diffuser System from Camp Pendleton Plant

Appendix 11 - Capital Cost

Appendix 12 - Holding Tank Costs

Appendix 13 - Utility Calculations

Appendix 14 - Yearly Cost of Chemical Additions

Appendix 15 - Economic Analysis

Appendix 16 - Optimization