Desalination - Team E

Group E Corporation

Authors: Hassan Ali, Woo Soo Choe, Brett Sleyster, Jake Stolley

Instructors: Fengqi You, David Wegerer

March 11, 2016

Executive Summary

Outlined in this report is the project model report for the proposed desalination plant in Los Angeles, California which will provide drinking water to local citizens using reverse osmosis process. This location was chosen due to the region’s propensity for droughts in recent years. The fresh water resources in California have plummeted as water prices have risen 3-4% each year. This is only expected to continue. Other companies have worked deals with the Californian government to create desalination plants that provide a new fresh water drinking source. This suggests that there is a strong market here with potential growth.

The plant will have an output of 15 million gallons per day, which is about medium size relative to other plants. Thus the build time will be about one year. The plant will run for 30 years, with 350 days per year of use. Shutdown time will be used for cleaning and maintenance of equipment. The plant will be built on Long Beach, 500 meters from the coast nearby the Long Beach Water Reclamation Plant (LBWP). The input will withdraw 70.5 million gallons per day of seawater that will be used for reverse osmosis and dilution of brine.

Reverse osmosis was chosen as the desalination method for its low energy cost and flexibility. We designed a process that will pretreat the seawater to remove waste, colloids, bacteria, and membrane-damaging scalants. Once this seawater is treated is pumped to heavy pressures through a reverse osmosis system. After doing process optimization under various system parameter changes, we found a continuous, single stage, five element reverse osmosis process to be best. It produces a near 30% recovery. We reduce energy costs by including a pressure exchanger between our concentrate outlet and adjusted feed into the reverse osmosis system.

After performing mass and energy balances, we were able to size equipment and find our permeate composition. It turns out our process will meet L.A. standards for drinking water quality. However, post treatment will be done by the local LBWP to make the water taste better and be non-caustic to pipes. This will reduce “in-house” costs. Many environmental considerations were made, to meet our environmental standards. We meet EPA salinity requirements for our brine waste by diluting it. We also don’t use a lot of energy and thus reduce our fossil fuel consumption and CO2 generation. To be safe, we work well under max pressure limits for our equipment. We make sure we are ethical and meet all standards that our local county requires of us.

After an economic evaluation at a conservative well-water price of $700 per acre-foot, we realize that our revenue is way too low to cover our costs. Capital costs are especially large with regards to our large water tanks. We find that we reach a 10 year NPV breakpoint of $2104 per acre-foot after performing a sensitivity analysis. The Carlsbad Plant in San Diego worked out a deal for $2257 per acre-foot.

As we have met all design constraints for this project, we hope to convince policymakers to adopt our project at least $2104 per acre-foot water. If this deal is reached, we recommend that this project and design be funded. There is future work to be done to improve costs such as performing pump optimization. However, this work is minimal and won’t harm our bottom line if we reach our proposed price points.

Introduction

Due to a combination of various factors--including rising human population, climate change, increased energy consumption, and land erosion--the availability of fresh water as a resource for human consumption has been dwindling. This has had a negative impact on the world, but this impact has been especially felt in areas with natural shortages in fresh water. Desert regions, such as Saudi Arabia, have resorted to desalinating seawater at the coast and transporting up to their cities. This encompasses their entire freshwater system as very few natural water sources remain. In the United States there is a region which has shown increasing signs of following in the footsteps of Saudi Arabia and becoming fully reliant on desalination: Los Angeles, California.

Location and Market Analysis

In this project, Los Angeles was chosen as the location our plant, because the area has been subject to a severe drought for the last four years, as shown in Figure 1. The rapid decrease in the available water has caused permanent damages to the ground, decreased the amount of water in the reservoir from 45% to 25%, and reduced the amount of hydroelectric power produced in the state. Such deficiency in usable water has increased the water prices in Los Angeles by 6-7% annually for the last decade and is expected to rise by 3.4% annually for typical customers for the next five years. For customers who use more than 20000 gallons a year, the bill is expected to increase by 34% by 2021. This price increase is occurring because of both drought and maintenance.

As of March 2015 the Metropolitan Water District of Southern California was willing to pay as much as $700 per acre-foot of water to farmers in the Sacramento Valley, so we assume this will be the target price of the water produced by the this desalination plant.

Currently, there is a plant in Carlsbad which supplies drinking water to the San Diego area. The plant can produce up to 50 million gallons per day and is the nation's largest water desalination plant. The water from this plant costs $2257 per acre-foot for the first 48000 acre-feet and about $2000 for any additional acre-foot. The county signed a contract with this plant to purchase the first 48000 acre-feet of water for the next 30 years. Also, there is another desalination plant in Tampa that produces about 25 million gallons of water per day, and over 2000 other public and industrial plants with production capacity of over 300000 gallons per day. When conducting the economic analysis our plant, such numbers presented by other plants must be considered, so our project can yield positive profit.

The profitability of the project is naturally heavily dependent on the price of water in California. If the drought ends, water supply will increase and the water price will drop significantly, but if the drought continues, the price of water in California could rise even more rapidly and allow desalination plants to be more profitable. It may be difficult to make this plant profitable without a guaranteed purchase or other subsidy from the local governments because the presence of pre-existing plants maintains the water price relatively low. However, external sources of profit such as guaranteed purchase or subsidy are expected because the ramifications of not having desalination plant or other sources of water may be significantly more expensive than the subsidizing a desalination plant assuming the drought continues.

Design Basis and Technical Approach

Considering the number of pre-existing desalination plant and the potential risk of the drought ending, our plant will be tentatively designed to produce 15 million gallons of drinkable water per day to homes and businesses in the Los Angeles county area. With a recovery rate of near 30%, and a requirement for diluting any brine, the input feed flowrate will be 70.5 million gallons per day. Following the similarly built Carlsbad plant, we expect the plant to last 30 years. The project building timeline is one year based on our relatively small plant size. We will run for 350 days a year while shutting down for cleaning and maintenance once every 3 months (based on DOW standards). The plant will be built 500 meters from the coastline on Long Beach. A borehole will be drilled 10 meters into the ground. At this depth there should be seawater aquifers below the coast that regularly recharges itself with seawater from the ocean. A vertical well containing intake holes will be put into the borehole. The intake holes will be equipped with large size filters that can easily be replaced. At the surface, the well will be connected to a large-scale pump in a well pump house. From there, the seawater will be horizontally pumped into a seawater tank in the desalination plant. This will be considered the start of our process. The process ends after pretreatment, desalination, post treatment, and brine treatment are completed. Appendix 1 shows more details on the Design Basis.

The feed composition is assumed to be the standard seawater “average” based on the DOW Chemical ROSA 9.0 Technical Manual in Table 1. However, in reality the seawater composition at the plant site will have to be chemically tested. The final product will be based on L.A. standards for drinking water quality (Table 1). The specifications in the table are upper limits that we cannot exceed. We will aim to reach the salt level standards but any remineralization and pH treatment will be exported and paid for due to the added complexity and cost in making such a system in-house.

Due to the acidity of the desalinated water coming out of the reverse osmosis (RO) system (pH ~ 6), the pumps and pipes carrying the desalinated water for post treatment will likely corrode over time. We have decided to place the desalination plant by the Long Beach Water Reclamation Plant (about 50 meters away) to prevent pipe corrosion.