Professor Joseph W. McCutchan, 1918-1982

The paper compares the energy requirements of single and dual purpose MSF distillation with seawater reverse osmosis plant. Energy consumptions are given both as heat and power consumptions for distillation and as power consumption for R.O. To enable a true comparison to be made these inputs are referred back to the heat inputs from fuel needed at the boiler plant or appropriate thermal power plant.Energy recovery is also considered for reverse osmosis and it is shown that the energy input can be expected to decrease by some 35% for a typical example.Although the prime energy input needed for reverse osmosis is shown to be substantially lower than for dual purpose distillation, the overall costs taking account Of capital charges, energy, replacements and other operating costs, are found to be in a band width of about 5% for plants in the range of 5000 to 15000 m³/day. Reverse osmosis plant water costs are significantly less than distillation if membrane life increases from 3 years to 5 years, particularly with small plant capacities.     

Desalting seawater and brackish water: a cost update

This report is a second update of costs, originally presented in ORNL/TM-5070, which gave cost estimates for desalting seawater and brackish water based upon first quarter 1975 costs. The first update was based upon 1977 costs. The specific input to the report includes two earlier U.S. Department of Energy reports, recent work sponsored by the U.S. Office of Water Research & Technology, and new equipment and operating cost input from major equipment suppliers and users.

Cost estimates are given for desalting seawater by distillation and reverse osmosis, and for desalting brackish water by reverse osmosis and electrodialysis. The report includes the cost of generating steam and electrical energy on site using coal-fired boilers as well as oil-fired boilers, and dual purpose nuclear/electric seawater distillation plants. The energy costs for both reverse osmosis and electrodialysis are based upon the availability of electricity at a fixed rate. Cost data were computed as a function of plant size, and include both capital costs and construction costs which are considered as typical. These assumptions are used to develop the reference cases of total water cost. The manner of presentation is such, however, that the costs can be easily adjusted to reflect local conditions.     

Energy advantages of reverse osmosis in seawater desalination

The very rapid increase in energy costs during the past three years is causing a change in the preferred process technology for seawater desalination. The phase changes, evaporation, and condensation, required in the distillation processes make them more energy intensive than the ambient temperature liquid separation that occurs in the reverse osmosis (RO) process. This paper describes the RO process and how to calculate its energy consultation.The RO process requires only 5–7 KWh/m³ of product water compared to 15–16 KWh/m³ required by the most efficient distillation process. The productivity of a large dual purpose electricity/RO water plant is compared to the productivity of a commercially purchased state-of-the-art dual purpose electric/distillation water plant that is currently under construction. The RO potable water productivity is about 2X the distillate flow at the same fuel rate     

Membrane processes for water supply and reuse - a question of energy consumption and cost

This paper is limited primarily to reverse osmosis which is the dominating membrane process in commercial plants. Desalination of brackish water and seawater with reverse osmosis, with special emphasis on costs and energy consumption, is the primary subject discussed in the paper. Some aspects of and development trends in industrial and domestic applications of membrane processes are also taken up, particularly with regard to by-product recovery and water reuse in connection with advanced wastewater treatment.The first RO plant to be brought into operation in Riyadh, Saudi Arabia, is located at Salbukh. The investment and total operation costs for this plant have been calculated in the paper. The water cost is at least twice as high as in a continental U.S. location. The main reason for this is the very high cost of civil and local works in Saudi Arabia. A similar calculation has been made for RO seawater desalination.Increased energy costs during the last decade have directed research and development work for all desalination methods towards reducing energy consumption. It is shown in the paper that energy recovery in connection with RO seawater desalination is particularly feasible. Different methods for energy recovery have been investigated and reported, the preferred methods depending on the size of the RO plant. A large underground RO plant for energy recovery, based on utilization of the static pressure instead of high pressure pumps, has also been studied.Another possible energy-saving, but also water quality improving method has been proposed, viz . a combined MSF-RO dual purpose plant. Excess power for reverse osmosis seems to be more and more available in Saudi Arabia due to the high power/water ratio in MSF dual purpose plants compared to the real demand for power and water.     

An evaluation of the energy requirements of desalination processes on the basis of the fuel-use performance ratio

The fuel-use performance ratio is defined as the quantity of water produced, in kg, per 1000 kJ of the heat content of the fuel used for supplying thermal, mechanical and/or electrical energy to the desalination plant. The concept is used to evaluate the energy requirements of the major sea water conversion processes - reverse osmosis, multistage flash, multiple effect boiling (as exemplified in the vertical tube foam evaporation process), vapor compression and hybrids of the thermal processes - for three types of plants: (a) single-purpose (water only), (b) dual-purpose (power/water) involving “power loss” and (c) dual-purpose (power/water) utilizing waste heat. It is concluded that only distillation systems based on waste heat can compete with the low energy requirements of reverse osmosis.     

Dual purpose power/water plants utilizing both distillation and reverse osmosis

The energy consumption of several alternate dual purpose plants are compared for application in the range of 10–50MW with 1 to 20 MGD water production. This shows that the combined gas turbine-steam turbine system is considerably more energy efficient than a steam only system. Single stage R.O., used in conjunction with this combined cycle offers the minimum overall energy consumption but has the disadvantage of producing product water with high TDS. By utilizing both R.O. and distillation, energy consumption lower than with distillation alone is achieved and product water purity is acceptable. p]A specific design of a combined dual purpose plant is presented. This plant would have a net electrical output of 29,050 kw and 3.25 MGD of 440 ppm TDS, requiring 297.1 BTU/hr. The total capital costs of this combined plant is estimated at $41,150,000 and annual operating costs at $15,087,000. The unit production costs with fuel at $2.50/MM BTU would be 4.08¢/kw-hr and $2.44 per 1000 gal. This represents an annual savings of $1,961,000 over single purpose production or 44.5% reduction in water production costs with the same electrical production costs. p]It is concluded that the combined dual purpose plant presented is the most efficient, economical and flexible method of producing power and water in the range of 10 to 50 MW and 1 to 20 MGD.     

Systems analysis of dual-purpose nuclear power and desalting plants Part I. Optimization

The optimal process design of a dual purpose plant for producing power and water is investigated. A nuclear reactor and steam turbine power generator for steam and power production is coupled with two water plants, a multi-stage flash plant and a reverse osmosis plant. The total system cost for producing given levels of power and water is minimized. Optimal designs are presented for several combinations of water and external power demands ranging from 25 mgd to 150 mgd and from 50 MWe to 200 MWe.     

Integrating hybrid systems with existing thermal desalinationplants

In Gulf countries, most power plants are co-generation power desalting plants (CPDP) that generate electric energy and also produce fresh water through the desalination of seawater. This paper provides detailed technical and economical analyses to evaluate a new generation of dual purpose technology that includes the integration of reverse osmosis (RO) processes with existing thermal desalination processes and power generation (triple hybrid system) at Layyah plant, Sharjah, UAE. Hybridization of sweater reverse osmosis (SWRO) and the multi-stage flash (MSF) technology was considered to improve the performance of latter and reduce the cost of the produced water. Moreover, “idle” power in winter (seasonal surplus of unused power) was mainly utilized by RO to further reduce the cost of the hybrid system for six months of the year. Spinning reserve was also used to further reduce the cost of the proposed hybrid system. Integration ofthe three processes of MSF, MED, and RO desalination technologies could be made at different levels through which the resulting of water cost will depend on the selected configuration and the cost of materials of construction, equipment, membrane, energy, etc. Thus, the capital and annual operating costs were calculated for all potential alternatives for various plant capacities. It was found that for all plant capacities, integrated hybrid systems resulted in most cost effective solution. For example, at a capacity of 50 MIGD, the present worth of the cost was calculated to be 588.7, 443.2, and 380 million US$ for MSF, MED, and hybrid RO systems, respectively.     

An exergetic analysis of a membrane desalination system

In this paper, the exergetic analysis of a seawater membrane-based desalination plant has been carried out. The desalination plant has been described in detail, then the exergy of the various saline water streams has been determined and a comprehensive analysis towards the exergy distribution of the major process components has been conducted. The examination of the exergy losses throughout the plant revealed that exergy destruction was mainly due to pressure drops in the membrane modules, valves and brine lines. Moreover, 12.9% of the exergy input to the system was supplied by the heater. Therefore, the most reasonable way to reduce power input to the plant, thus improving its performance and cost, has been shown (i) to be replacing the valves on the reverse osmosis brine stream by an energy recovery system, and (ii) to have thermal energy available in the plant. With the identified technical changes, energy consumption decreased from 18.3 to 2.05 kWh/m³, resulting in an annual saving of 0.17$/m³.     

Analysis of water desalination and power generation expansion plans for the Emirate of Abu Dhabi — a preliminary study

This paper contains a comparative economic study of a number of different expansion schedules for power and desalination plants required to meet a forecasted demand in electricity and water for the Emirate of Abu Dhabi. For power generation, steam turbine and gas turbine plants were considered and for desalination both multistage flash distillation and reverse osmosis processes were investigated. Nine combinations of power and desalination plants were selected and a present worth economic analysis was conducted. Capital and operating cost figures used are those typical of the local conditions at Abu Dhabi. Based on the assumptions used in this study the plant combination using steam turbine power plant connected to a reverse osmosis unit seems to represent the most economic alternative.     

Hydraulic turbine energy recovery - R.O. System

In reverse osmosis desalination plants large flow rates of concentrated brine are discharged at high pressure from the membrane modules. Currently this pressure energy is wasted. This paper reviews the impact of soaring energy costs on the technical alternative of hydraulic turbine energy recovery. The capital costs, operating costs, and economics in electrical energy are evaluated for both sea-water and brackish water systems. Schemes of hydraulic turbine coupled with electric generator, tied to the electric power supply are considered for various plant sizes from 1 to 10 mgd. The analysis, in parametric form, presents the interrelationships between the cost of money, cost of electrical energy, and recovery factors for the different plant sizes and for sea-water and brackish water systems. The results will serve as a guide to determine when such a power recovery system should be seriously considered and evaluated in greater details for specific applications.     

Jeddah seawater reverse osmosis installation

The world's largest reverse osmosis system for seawater desalination was placed on-line in January 1979 to supply 12,000 cubic meters of desalted Red Sea water per day to the drinking water supplies of Jeddah, Saudi Arabia. This system is based on the newly developed spiral-wound TFC membrane elements. These elements exhibit the high water permeability, low salt permeability, thermal stability, resistance to micro-organisms, and chemical stability required for economic desalination of seawater.

The system consists of power generation, a seawater intake, dual media filtration, nine first-stage reverse osmosis units, three second-stage reverse osmosis units and product stabilization. Since each unit can be brought on or off line in a matter of minutes, the system is extremely flexible. Simplicity of installation and operation is a major advantage of reverse osmosis.

Cost data accrued to date has verified that reverse osmosis is more economical than multistage flash distillaion, both in terms of capital and operating costs. The short lead time from bid to operation, as compared to MSF is demonstrated by the fact that the plant was designed, constructed, and accepted within eighteen months of acceptance of bid.     

Membrane‐assisted vapor stripping: energy efficient hybrid distillation–vapor permeation process for alcohol–water separation

BACKGROUND: Energy efficient alternatives to distillation for alcohol recovery from dilute solution are needed to improve biofuel sustainability. A process integrating steam stripping with a vapor compression step and a vapor permeation membrane separation step is proposed. The objective of this work is to estimate the energy and process costs required to make a fuel grade ethanol (0.5 wt% water) from 1 and 5 wt% ethanol aqueous streams using the proposed process. RESULTS: Using process simulation and spreadsheeting software, the proposed membrane‐assisted vapor stripping process was estimated to require as little as 8.9 MJ of fuel‐equivalent energy per kg of fuel grade ethanol recovered from a 1 wt% ethanol feed stream, 2.5 MJ kg^?1 for a 5 wt% ethanol solution. This represents an energy saving of at least 43% relative to standard distillation producing azeotropic ethanol (6 wt% water). Process costs were also found to be lower than for distillation at the 3.0 × 10⁶ kg‐ethanol year^?1 scale modeled. CONCLUSION: In this hybrid system, the stripping column provides high ethanol recoveries and low effluent concentrations while the vapor compression‐membrane component enables the efficient recovery of latent and sensible heat from both the retentate and permeate streams from the membrane system. Published in 2008 by John Wiley & Sons, Ltd.     

Economical study of a small-scale direct contact humidification-dehumidification desalination plant

Economical study of humidification-dehumidification desalination (HDD) pilot plant was made in order to estimate the economic benefits of the process in comparison with a small-scale reverse osmosis (RO) system. The energy recovery of the unit was investigated to be 75%. Some theoretical modifications were made to the HDD system in order to reduce the energy costs of the unit. Exact and clear economic analysis results were obtained using COMFAR ΙΙΙ software including fixed investment costs, production costs, internal rate of return on investment, operating costs, energy costs and some other economical parameters. Based on the energy prices in Iran, the total fresh water production cost was calculated to be $ 6.4/m³ that was nearly the same as produced by an imported RO plant. Finally some points were recommended whether to choose HDD or RO plant in different cases and capacities.     

太阳能海水淡化新技术综述

依据太阳能的光效应和热效应对传统的海水淡化进行分类,列举了太阳能与传统蒸馏法与渗析法的结合形式,指出了传统蒸馏法效率不高的原因,重点介绍利用冷凝潜热和提升换热效率的新型高效海水淡化技术以及反渗透的能量回收装置,认为将太阳能与传统海水淡化技术有机结合起来前景广阔,并简述了太阳能收集器的研究现状及先进技术,为太阳能海水淡化技术的进一步研究和发展提供了参考与依据.     

Conceptual design of a novel hybrid fuel cell/desalination system

A novel concept for integrating fuel cells with desalination systems is proposed and investigated in this work. Two unique case studies are discussed — the first involving a hybrid system with a reverse osmosis (RO) unit and the second — integrating with a thermal desalination process such as multi-stage flash (MSF). The underlying motivation for this system integration is that the exhaust gas from a hybrid power plant (fuel cell/turbine system) contains considerable amount of thermal energy, which may be utilized for desalination units. This exhaust heat can be suitably used for preheating the feed in desalination processes such as reverse osmosis which not only increases the potable water production, but also decreases the relative energy consumption by approximately 8% when there is an increase of just 8°C rise in temperature. Additionally, an attractive hybrid system application which combines power generation at 70%+ system efficiency with efficient waste heat utilization is thermal desalination. In this work, it is shown that the system efficiency can be raised appreciably when a high-temperature fuel cell co-generates DC power in-situ with waste heat suitable for MSF. Results indicate that such hybrid system could show a 5.6% increase in global efficiency. Such combined hybrid systems have overall system efficiencies (second-law base) exceeding those of either fuel-cell power plants or traditional desalination plants.     

Waste heat powered reverse osmosis plants

The purchased power required for operation of reverse osmosis systems can be greatly reduced or sometimes eliminated by reclaiming waste heat from diesel engines, gas turbines, flare gases, etc. This can be accomplished by using a Biphase turbine to convert low level waste heat to shaft horsepower.The system can be designed to use waste heat from existing installations or to reduce the size of the generating equipment in new supplies.The Biphase conservation turbine is driven by a two phase stream generated by flashing a superheated liquid through a nozzle to the turbine. The turbine can be directly coupled to a pump shaft, to an electrical generator or to a combination of the two. Performance of the turbine is discussed. The waste heat recovery turbine and a hydraulic turbine to recover energy from the high pressure concentrated brine can be combined into one system.This paper describes the design of a seawater reverse osmosis system using waste heat from an existing diesel generating unit. The SeaRO system is designed to produce 750 cmd of 400 ppm water at an energy consumption of approximately 2.5 KWH of purchased power per cubic meter.A discussion of available desalination capacity at various quantities and temperature levels of the waste heat source is presented. A comparison of water costs obtained using this system and a conventional electrical drive is presented.     

Investigation of different operational strategies for the variable operation of a simple reverse osmosis unit

Recent studies and projects showed that a combination of a reverse osmosis desalination plant with a wind power supply is technologically feasible if the reverse osmosis plant is operated with fluctuating and intermittent loads and thus follow the energy supply characteristic of the wind turbine. On this background the goal of this paper is to simulate the system behaviour of a simple reverse osmosis plant under changing process parameters (e.g. feed pressure, recovery or feed flow). These variations are systematized within so-called operational strategies. Therefore, four different operational strategies are analysed in detail with regard to given restrictions e.g. by the membrane system. For each of these strategies the specific energy consumption over the total usable load range is computed with the simulated hydraulic characteristics of each operational strategy. The analysis of the gathered data shows that a membrane system should be operated with constant permeate recovery under fluctuating wind power. This operational strategy provides low specific energy consumption over a broad load range.     

反渗透和压力延迟渗透耦合脱盐系统的能效优化研究

针对开环和闭环两类结构的反渗透-压力延迟渗透耦合脱盐系统进行了模型构建与系统优化分析。首先，以标准化比能耗为目标函数，构建了开环结构和闭环结构耦合系统的非线性约束优化模型。在优化模型中，引入包括半透膜性能、操作状态及设计变量的无量纲参数组，建立反渗透和压力延迟渗透单元过程的特征方程以简化模型。同时，为了保证比较的公平性，开环结构的总体能耗中额外包含了预处理和后处理能耗。通过求解上述优化模型，系统地比较和分析了无量纲半透膜总面积和水回收率同时变化导致的最优标准化比能耗、膜面积分配和操作压力的变化规律。结果表明，在水回收率处于正常水平(≤ 0.55)且系统总面积充足(≥0.9)时，闭环结构在节能及减少预处理费用方面比开环结构具有更明显优势。