Nueces Desalination Center: Production of Drinking Water by Multi-Stage Flash Distillation

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Team F: Rankine 672 Final Report

Authors: Kedric Daly, Ben Granger, Evan Rosati, Kathleen Zhou

Instructors: Fengqi You, David Wegerer

March 11, 2016

Executive Summary

Desalination of seawater to drinking water is a technology of ever-increasing importance given trends of increasingly widespread water shortages around the world. Even in the United States, water shortages are becoming increasingly common in dry, highly-populated such as California and certain areas of the Gulf Coast. Our design team, Rankine 672, was tasked with evaluating the need for and designing a desalination plant to provide purified water in a place of need. Investigation revealed that the city of Corpus Christi, Texas, is a strategic location for development of a desalination facility, as surrounding region is in need of new drinking water sources and the city has expressed serious interest in contracting the development of a large-scale desalination plant. Our proposed solution is a multi-stage flash distillation desalination facility capable of producing 20,000,000 gallons (75,708 m3) of purified drinking water for the city and surrounding region per operating day.

In this design, drinking water is produced from seawater feedstock through a 21-stage flash distillation process. By strategically locating the facility next to an existing natural gas power plant, the Nueces Bay Energy Center, pre-heated feed water can be taken directly from the outbound cooling systems of the power plant, allowing energy savings for our desalination plant. The process is designed for 16 hour-per-day operation, requires a seawater feed of 8250 m3/hr, and produces 4758 m3/hr of purified drinking water alongside a waste stream of 3485 m3/hr of concentrated brine. The waste stream is isolated from a recycle stream through a 9.0% purge; this results in an overall product yield of 57.7% on a volume basis. The process requires an additional pretreatment stream of 16.5 kg/hr Belgard EV 2030, which serves as an antiscalant, as well as 9.5 kg/hr chlorine, 352.1 kg/hr lime, and 418.7 kg/hr CO2 for post-treatment purposes.

The overall capital cost of the plant is expected to be $345MM, with a total operating cost of $103MM/yr, $59MM/yr of which comes from utilities. Due to the low price at which the product water can be sold, the 30-year net present value of the plant, assuming a 6% discount rate, is $-1,035MM. It is thus imperative this plant be constructed with public funds because it cannot return a profit to any private investor. The growing need for water however could justify the cost, because it is important that the residents of the greater Corpus Christi area have access to drinkable water.

Introduction