AGGIE CHALLENGE Nuclear Powered Water Desalination Plant Executive Summary Theoretical calculations were performed around a turbine, multistage jet ejector and multi effect evaporator to describe the optimal nuclear powered water desalination plant. The calculations were tabulated in Microsoft Excel, with X steam version 2.6 being used for the steam tables where the jet ejector data and calculations were based on the dissertation CFD OPTIMIZATION STUDY OF HIGH-EFFICIENCY JET EJECTORS, by Somsak Watanawanavet. This system proved to be the most efficient and productive thus far, but future research and calculations must be done to optimize the dimensions and type of nuclear reactor and the number and sizes of the jet ejectors and multi effect evaporators. AggiE Challenge Team Fall 2013 gtsteiger@tamu.edu
Table of Contents Project Statement ………………………………………………………………………………………………………………………2 Project Overview ……………………………………………………………………………………………………………………….3 Economics .…………………………………………………………………………………………………………………………………3 Nuclear Reactor …………………………………………………………………………………………………………………………4 Desalination System .………………………………………………………………………………………………………………….7 Calculations ……………………………………………………………………………………………………………………………….9 Multi-Stage Jet Ejector …………………………………………………………………………………………………16 Multi-Effect Evaporator ……………………………………………………………………………………………….17 Conclusions ……………………………………………………………………………………………………………………………..1 9 References ……………………………………………………………………………………………………………………………… 20 Appendix A ………………………………………………………………………………………………………………………………2 1 1
Project Statement Design a water desalination plant Conditions: 1. Energy will be provided by a nuclear plant 2. Plant will utilize thermal vapor-compression desalination (jet ejector technologies) 3. Plant must be able to supply fresh water to a large city (10 to 12 million people) Questions: 1. What size, design and type of nuclear reactor will be the most effective? 2. What is the most efficient scheme of water desalination? i.e. number of jet ejectors, additional collection means, etc. 3. Is it cost effective to produce electricity in addition to water? 2
Project overview Fresh water is vital to life. In areas of the world where fresh water is not easily accessible or even accessible at all, it is necessary to desalinate salt water. The concept of desalination is simple; evaporate salt water to separate the water from the salt, but this can be more complicated on a scale large enough to supply a city or small country with fresh water. One of the most common large scale means of desalination is distillation, which usually involves an enormous assortment of moving parts, pumps, turbines, et cetera accompanied by vast maintenance and capital costs. In order to optimize and simplify the process, we opted to convert the system to be motivated by a jet ejector. A jet ejector is a low maintenance device requiring no moving parts and can be easily replaced. It is driven by an enthalpy difference between the inlet and outlet of the nozzle of the jet ejector and uses a fast moving “motive” stream of steam to evaporate fresh water out of a supply of salt water. The efficiency of the jet ejector system is magnified when multiple jet ejectors are used in stages to progressively increase the concentration of the waste brine. The exit steam can then be fed into a series of multi effect evaporators to further increase the amount of fresh water produced. The jet ejector requires high pressure and high temperature steam to comprise the motive stream. The optimal source to provide the energy to vaporize the water, creating this high enthalpy steam, is with a nuclear reactor. This system can be adapted to produce electricity, in addition to fresh water, by inserting a turbine between the steam coming off the nuclear reactor and jet ejector. This would also include adding a separator and a line returning to the nuclear reactor to superheat the steam, between the turbine and the jet ejector, to produce a sufficient enthalpy difference in the jet ejector to drive the production of fresh water. While this adds complexity to the system, it also greatly increases the markets that can be catered to, and subsequently the potential profits, of the desalination plant. Economics When choosing a location for the desalination plant, the wholesale price of water and electricity, the region’s necessity for clean water, and the region’s opinion towards nuclear energy were all assessed. We determined that Los Angeles matched our desires very well. Los Angeles is in desperate need for clean water since the growing population has depleted much of its water from the Colorado River. Additionally, it is close to the coast, so an ample supply of salt water is not an issue. There are no major adversities to the use of nuclear power, and California has even started looking into the utilization of desalination technology. Therefore, the implementation of a desalination plant powered by nuclear energy should not face much opposition. When doing an economic analysis of the costs and profits associated with implementing this desalination process, the wholesale prices of water and electricity in Los Angeles had to be investigated. The wholesale price of water in the region is $0.0235/ft 3 (U.S. Energy Information Administration), and the wholesale price of electricity is $39.09/MWh (Olivenhain Municipal Water District). These prices were examined graphically so that the optimum ratio of electricity and water production could be determined. Before we are able to specify a solid cut off for the discharge pressure from the turbine, we need to account for local demand for each water and electricity, full capabilities of the plant, 3
potential profit for each and the production costs for each. Our preliminary analysis indicates an all electric plant would be more profitable, however fresh water production is the main objective of this project. Potential Profits 7000 6000 5000 Sales ($/h) Total Sales 4000 3000 Water Sales 2000 1000 0 0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 Turbine Discharge Pressure (psia) Figure 1: Potential profits for data based on single jet ejector system, with 50 degrees F of superheat, not including water produced by the multi effect evaporator. Nuclear Reactor The nuclear team objectives were to recommend a reactor type, size and design the steam and/or power production side of the plant. Throughout our decision-making process, we sought to recommend this new technology with optimal feasibility. Reactor Recommendation For the Los Angeles, CA case study, the nuclear team recommended the Diablo Canyon Nuclear Power Plant. We chose this site because of the proximity to LA as well as direct contact with ocean water. The plant contains two PWRs (Pressurized Water Reactors), which are a preferred choice of reactor type because it is commonly used and therefore easier to accept by the client than other, lesser known reactors. Table 1 shows more details about Diablo Canyon’s two units. Using the general rule of thumb conversion (Equation 1) between the thermal (steam) power and electrical power produced in such a plant, we determined that Unit 1 can produce 3,366 MW(th) and Unit 2 can produce 3,354 MW(th). 4
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