Distillation and reverse osmosis energy consumption and costs

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.     

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.     

Analysis of water production costs of a nuclear desalination plant with a nuclear heating reactor coupled with MED processes

A nuclear heating reactor (NHR) was designed with the required inherent safety and simplified design features. Power capacity of the NHR-200 (200 MW(th), with steam production of 380 t/h) is compatible with reasonably sized desalination plants. Thermal-hydraulic parameters of the produced steam (2.4 bar and 124°C) are suitable for coupling with distillation processes. Economic competitiveness of the NHR desalination plant is the key point to which the public and decision-makers are paying good deal of attention. Coupling of the NHR with selected MED processes and design parameters of an integrated desalination plant are described. Results of analyses of water production costs are presented as well. Based on the economic evaluation, the average energy cost of the nuclear plant may reach 5.44 $/t of steam, and the provided water production cost may reach 0.72 $/m³ and 0.76 $/m³ for coupling with HT–VTE–MED and LT–HTE–MED processes, respectively.     

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     

Application of the multi-effect process at high temperature for large seawater desalination plants

A large sea water desalination plant, using the multi-effect process at high temperature has been described and a comparison is given with the other distillation processes.The multi-effect plant is easily adaptable in a wide range of operating conditions. It has a low total energy consumption (8.75 KWh per m3 produced (expressed as electrical energy). A high GOR is obtained (12.4). Compared with a MSF of the same production capacity, the investment costs are smaller. This leads to a substantial decrease in cost of the produced water. The technology of horizontal sprayed tubes is a proven one and has been executed more than a hundred times on small and medium units.     

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.     

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.     

热泵耦合甲醇多效精馏节能新工艺

粗甲醇精馏的能耗是影响甲醇生产成本的关键因素之一。虽然五塔多效精馏可以降低精馏过程能耗,但仍存在相当的低品位余热未利用,为进一步降低五塔多效精馏工艺的能耗,本研究引入机械蒸汽再压缩式（MVR）热泵,在常压塔提馏段增设辅助再沸器,形成热泵耦合多效甲醇精馏新工艺。基于新工艺的全流程模拟数据,文章利用夹点技术对热泵设置的合理性进行分析,采用能耗、效能系数（COP）和年总成本（TAC）等指标对新工艺过程进行评价。结果表明：热泵耦合多效甲醇精馏新工艺中热泵设置合理,冷负荷为24.7MW,再沸器总热负荷为22.25MW,COP为22.5,相比五塔多效精馏工艺,冷负荷、热负荷以及TAC分别降低33.76%、32.64%和26.97%。热泵耦合多效甲醇精馏新工艺节能效果显著。     

用混相催化精馏和超精密精馏技术生产1-丁烯及其改进

介绍了用混相催化精馏和超精密精馏技术生产1－丁烯装置的生产工艺特点，总结了生产中以循环水代替过滤水作为泵的冷却水，将系统低压 蒸汽操作压力由0.2MPa提高到0.42MPa，将两段保护反应器工艺流程由串联改为并联，改进塔压控制系统等优化工艺，降低产品能耗物等技术改进措施。     

Pilot investigation on the treatment of fertilizer manufacturing process effluent using lime and electrodialysis reversal

The treatment of a fertilizer company's effluent was evaluated using lime and electrodialysis reversal (EDR) for phosphate removal, water and chemical recovery, and effluent volume reduction. Phosphate could be reduced from 3 800 to less than 50 mg/1 at pH 8.5 with lime; however, phosphate removal from the lime treated effluent using EDR was poor (75% removal). The EDR product water complied with the requirements for cooling tower make-up except for TDS and phosphates. However, the required specifications should be met using 10 stage EDR.

In addition, plant nutrients (NH₄⁺ NO₃⁻) may be recovered from the brine, which comprised 20% of the initial effluent volume. Membrane scaling was virtually absent. A full scale EDR plant should run well with electrical adjustments and/or frequent acid cleaning. Electrical energy consumption for EDR treatment was found to be 4.5 kWh/m³ feed (pumping costs excluded). The capital cost for a 30 m³/h EDR plant and clariflocculator (PO₄ removal) was estimated at US $750 000.     

Ocean thermal energy and desalination

In 1881, the French physicist d'Arsonval was the first to suggest the harnessing of the temperature difference between the warm surface layers and cold deep layers of tropical oceans. Since then, several attempts have been made to convert this undepletable supply of thermal potential energy into mechanical energy and, later, into electricity. In recent years, various countries including France have launched thermal energy conversion (OTEC) programmes. Tropical regions with useful temperature differences often lack both conventional energy resources and potable water. In such regions, OTEC plants could be used with advantage for the simultaneous production of power and desalinated seawater.An original seawater distillation scheme using surface water and the cold reject stream from an OTEC cycle is discussed. Power not required for distillation may be exported outside the plant. The combined distillation and OTEC scheme is compared with conventional desalination plant producing both potable water and electricity. The OTEC scheme appears highly flexible and shows considerable economic promise.     

Status of reverse osmosis desalination technology

Reverse osmosis (RO), a relatively new technology, is gradually becoming an established and economical method for demineralization of saline waters. Over 50 commercial plants ranging in size from 50,000 gpd to 2 million gpd (2 mgd) are producing fresh quality water for municipal and industrial uses from brackish water sources. The U.S. Congress has authorized construction of a 100 mgd plant in Yuma, Arizona to demineralize otherwise unusable high salinity irrigation return flows as part of the Colorado River Salinity Control. Engineering design and operation details together with cost information on some commercial plants and the planned 100 mgd plant will be presented.A review of the plant operation data indicates that is imperative for the plant owners and equipment suppliers to place due emphasis on providing adequate feed water pretreatment facilities and trained plant operation personnel to ensure trouble-free operation and to achieve furthur economy in desalting costs.Significant advances have been made in the development of RO process for sea water desalination. Soaring energy costs are providing incentive for plant owners to prefer RO plants (up to 100,000 gpd) over vapor compression distillation hardware. Results of the Federal Government Desalting R & D Programs clearly indicate that RO desalting costs will be at least 20–30% lower than distillation.     

最大限度降低生产成本是电石法生产PVC企业的唯一出路

分析了影响电石法PVC树脂成本的因素 ,指出电石法生产PVC树脂的企业降低生产成本的出路是降低电石、氯化氢和能源的消耗 ,并详细介绍了降低这三项消耗要采取的相应措施。实施改进措施后可使PVC生产成本降低约 2 1 2元 /t,这样可节约资金 4 2 4万元 /a(以产能为 2万t/aPVC计 ) ,经济效益显著     

On the reduction of desalting energy and its cost in Kuwait

All seawater desalting processes, multi-stage flash (MSF), multi-effect boiling (MEB), mechanical vapor compression (MVC) and seawater reverse osmosis (SWRO) consume significant amounts of energy. The recent increase of fuel oil cost raises the cost of energy consumed for desalting water and the final water cost, and creates more interest in using more energy efficient desalting systems.

The most used desalting systems by distillation (MSF and MEB) are usually combined with power plants in what is called co-generation power desalting plants, CPDP. Fuel is supplied to the CPDP to produce both desalted water D and power W, and the fuel cost is shared between D and W. Exergy analysis and equivalent work are among the methods used to determine the fuel energy charged to each product. When desalting systems, such as SWRO and MVC, are not combined with a power plant, the fuel energy can be directly determined from its electrical power consumption.

In this paper, the fuel energy cost charged to desalting seawater in the presently used CPDP in Kuwait is calculated based on exergy analysis. The MSF, known by its high energy consumption, is the only desalting method used in Kuwait. The MSF units consume 258 kJ/kg thermal energy by steam supplied to the brine heater BH, 16 kJ/kg by steam supplied to steam ejectors, and 4 kWh/m3 mechanical energy for pumping. These MSF units are operated either by:

(1) Steam extracted from extraction/condensing steam turbines EC/ST as in as in Doha West, Azzour, and Sabbiya CPDP. This practice is used in most Gulf area.

(2) Steam supplied directly from boilers as occurred in single purpose desalting plants as Al Shuwaikh plant; or in winter time when no steam turbines are in operation in the CPDP to supply steam to the desalting units.

The CPDP have limited water to power production ratio. While they can cope with the increase of power demand, it cannot satisfy the water demand, which is increasing with higher pace than the power demand.

The case of steam CPDP used in Kuwait is presented in this paper as a reference plant to evaluate the amount of fuel energy consumed to desalt water in MJ/m3, its cost in $/m3. The resulted high fuel cost calls for some modifications in the reference CPDP to lower the energy cost, and to increase its water to power ratio. The modifications include the use of an auxiliary back-pressure steam turbine ABPST supplied with the steam presently extracted to the MSF units. The power output of the ABPST operates MVC or SWRO desalting units; while the ABPST discharged steam operates LT-MEB desalting unit. The desalting fuel energy costs when applying these modifications are also calculated by the exergy analysis and compared with that present situation.

It is also suggested to increase desalted water output by using separate SWRO desalting units operated by the existing power plants of typical η_c = 0.388, or by new combined gas/steam turbines power cycle GT/ST-CC of typical η_c = 0.54 under construction. The SWRO with energy recovery is assumed to consume typical 5.2 kWh/m³ electric energy.     

Solutions for coupling a mechanical vapour compression distiller with a multi-stage-flash evaporator

The paper discusses various familiar and new process combinations of multi-stage-flash (MSF) and mechanical vapour compression (MVC) distillation. Coupling of an MVC distiller to an MSF unit considerably reduces the consumption of energy and chemicals as well as feed water requirements. The plant is extremely flexible with respect to partial load operation and adaption to varying availabilities of thermal and electrical energy. An existing MSF distiller with a capacity of up to 2000 m³/d can be extended by coupling it with a simplified MVC module. Investment and operation costs are notably lower than with the installation of additional MSF units.     

Die Praxis der Fettsäure-Geradeausdestillation in moderner Sicht

The Practice of Fatty-Acid Straight-Run Distillation in Modern View Due to world-wide increasing of plant running costs a new process for fatty-acid straight-run distillation has to be developed which also fulfill the stricter environmental laws. The production plant results with this new process shows lower energy consumption, lower environmental laod and distinguished product datas for odour, colour and heat stability. The process principle is a combination of a two stage main distillation with a two stage pre-system. The falling film type main distillation is operating under high vacuum. The pre-system for degasing, dehydration and precut distillation is operating by a head pressure of 133–266 mbar.     

Methyl esters directly from acidulated cottonseed soapstock. Preliminary cost study

A product containing from 80 to 95% of the methyl esters of cottonseed, soybean, and corn oil is produced commercially in the United States directly from the respective acidulated soapstocks of these oils, using a process developed at the Southern Utilization Research and Development Division. The product is marketed as a high-energy additive for poultry and livestock feed, and its ready acceptance indicates that it has nutritional and handling advantages over other by-product fats for this purpose, which, in 1958, represented a ready and expanding market for almost 600 million pounds of animal and vegetable fats and oils. A flow sheet for the process is given, and hypothetical plants with capacities of 15,000 and 60,000 lbs. of acidulated foots per 24 hrs. are described for the continuous production of up to 21 million pounds of methylated foots product annually. The lowest manufacturing costs are realized for each plant when operating 24 hrs. a day, 250 days annually, averaging five days per week. For these optimum operations the estimated capital investment for the small plant is $223,000, and for the large plant $410,000. Manufacturing costs range from a high of 11.2￠ per pound of product at an annual production of 11/4 million pounds to 6.5￠ at an annual production of 15.3 million pounds. The cost of the raw materials, although only 3.4￠ per pound of product and chiefly the cost of foots, is the largest single item of unit cost in producing methyl esters; and, for the higher productions covered by this study, raw material costs account for more than one-half of total unit manufacturing cost. Surplus cottonseed foots can be economically converted into a low-cost feed additive with improved nutritional and handling properties. The process is already a commercial success. Presented at the 51st Annual Meeting of the American Oil Chemists' Society, Dallas, Tex., April 4–6, 1960. Development Division, Agricultural Research Service, U. S. Department of Agriculture.     

Solar distillation : the solar-driven case

This paper considers distillation systems where all the plant's thermal energy requirements are provided by solar energy. Fairly small capacity plants are considered operating in remote arid regions. Such systems consist of solar collectors and thermal storage coupled to a distillation plant.Each of these aspects is considered as well as the type of control strategy to be used. Using a dynamic computer simulation model, two solar-driven systems are considered: one using flat-plate collectors and a 76°C MEE desalination plant, the other using evacuated tubular collectors and a 95°C MEE plant. Various combinations of collector area and thermal storage volume are considered, and optimal values determined for each case. For the particular example chosen (lOOm³/day, located at 23$\text{1}\text{2}$°S) the flat-plate collector system was superior at current prices, giving an overall water cost of $5.82/m³ versus $7.34 for the second system. Both these costs are considerably less than water costs from conventional solar stills.     

Desalination and water recycling by air gap membrane distillation

Membrane distillation (MD) is an emerging technology for desalination. Membrane distillation differs from other membrane technologies in that the driving force for desalination is the difference in vapour pressure of water across the membrane, rather than total pressure. The membranes for MD are hydrophobic, which allows water vapour (but not liquid water) to pass. The vapour pressure gradient is created by heating the source water, thereby elevating its vapour pressure. The major energy requirement is for low-grade thermal energy. It is expected that the total costs for drinking water with membrane distillation will be lower than $0.50/m³, even as low as $0.26/m³, depending on the source of the thermal energy required for the evaporation of water through the membrane.     

基于MVR热泵精馏的混合醇热集成分离工艺

机械蒸汽再压缩(MVR)热泵技术是把低品位的蒸汽通过压缩转变为高品位的蒸汽,循环用于热源的供热以减少能耗。而热集成技术则是合理的匹配冷热物流的换热,以提高物流的有效能利用率。鉴于精馏过程的高能耗和低热力学效率,本文以四元混合醇的分离为研究对象,把基于MVR热泵技术的热集成精馏工艺应用于该体系的分离,提出并研究了该体系带热集成与不带热集成各种MVR精馏工艺;以能耗和年总费用(TAC)为评价指标,采用Aspen Plus 软件对各分离工艺进行模拟与优化,确定各分离工艺的操作参数与设备参数。研究结果表明,与常规顺序分离工艺相比,MVR精馏工艺节约能耗50%以上,节约年总费用约61%。带热集成MVR精馏工艺与不带热集成MVR精馏工艺相比,在能耗和年总费用方面,优势相当,但前者热力学效率提高了约9.5%。