Operating experience of the Dhekelia seawater desalination plant using an innovative energy recovery system

Dhekelia Desalination Plant in Cyprus has been in operation for 7 years. It includes eight 5,000 m³/d seawaterreverse osmosis trains operating with Mediterranean seawater with a TDS content of 41,800 ppm, with water temperature ranging from 17°C to 32°C. The energy recovery system originally installed at the plant is the Francis turbine, which, at the time, was considered one of the most efficient and economical devices on the market. Since then, however, market forces to reduce operational costs, by cutting down energy consumption, led to the advent of new energy recovery systems. Today several systems are in operation which reduce the RO energy consumption. Apart from the versions of the Francis turbine and Pelton wheel they include the hydraulic turbocharger, work exchanger and pressure exchanger, all harnessing the pressure energy of the brine. In our effort to be competitive for the years to come we decided to convert our existing energy recovery system from Francis turbines to the pressure exchanger. This paper outlines how it was decided to go ahead with the pressure exchangers, and gives comparisons with other energy recovery methods, and describes our operating experience with the pressure exchangers.     

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.     

超临界水氧化能量回收系统的设计优化

超临界水氧化（SCWO）工艺非常适用于高浓度废液的处理。针对目前SCWO处理系统能耗大、能量回用方式单一的问题,介绍了传统工艺流程的能量回收方式,分析了系统能量利用效率,创新性地采用透平和有机朗肯循环（ORC）串联的方式分别对压力能和热能进行回收。利用Aspen Plus建立SCWO系统能量回收模型,研究不同工艺流程对系统能效、(火用)效及输出功率的影响,在此基础上探讨透平的入口温度和出口压力、ORC的蒸发温度对系统性能的影响。结果表明：对反应产物依次进行压力能和热能回收为系统最佳能量回收方式;提高透平的入口温度和出口压力均可提高系统的性能,并同时提高透平输出功率的稳定性;降低ORC的蒸发温度会提高系统蒸汽产量,但同时也减少了可直接利用电能的产生量。     

Energy and water in Kuwait: A sustainability viewpoint, Part II

In Kuwait, the daily consumption per capita of electric power is 14,000 kWh, and of desalted water is 600 L. These are among the highest in the world, and the total consumption of each is almost doubled every 10 years. The cogeneration power desalting plants CPDP producing these two commodities consumed about 54% of the total 150 millions barrels of fuel consumed in the year 2005. If these consumption and production patterns prevail, the fuel oil produced in the country can be fully consumed locally in 30 years, with nothing left for export, the main source of income. The picture can be changed if better desalted water and power production methods are used. These include changing the desalting method from multistage flash MSF known by its high energy consumption to the more energy efficient seawater reverse osmosis SWRO; and power production method of steam or gas turbine cycles to combined gas/steam turbine combined cycle known of its high efficiency. The energy consumed by the air conditioning AC systems should be reduced by using better codes of building insulation and more efficient AC systems. Other conservation methods to reduce water consumption and the energy consumed by transportation are outlined in this paper.     

压力交换式能量回收器在反渗透海水淡化技术中的应用

在反渗透海水淡化系统中，高压系统中采用压力交换式能量回收器，大大地降低海水淡化的能耗。压力交换式能量回收器的能量回收效率达到95％以上，本文从其工作原理和反渗透海水淡化设计上阐述其应用的优点。     

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.     

Sea water desalination by reverse osmosis in chigasaki laboratory

For the purpose of constructing a reverse osmosis [RO) sea water desalination plant of 800 m³/day capacity, a series of tests on the following themes have been carried out in the Chigasaki Laboratory:

1. Performance and durability of 8B modules made in Japan

2. Simplification of pretreatment system

3. Establishment of energy recovery system.

Domestic modules showed good and stable performance during long term operation, and water recovery ratio of these modules have been raised to 40%.

In-line coagulation and filtration system has been established for the pretreatment of feed sea water, instead of coagulation, sedimentation and filtration system.

The energy recovery equipment is consisted of a high-pressure pump, a motor and a hydraulic turbine on a common base. Recovered energy from pressurized brine is used for the auxiliary motive power of the high-pressure pump. The experimental data show that about 20% of required power for the pump was recovered.     

Fresh water,energy, and food from the sea and the sun

Surface waters of tropic and sub-tropic seas hold most of the solar energy retained by the earth; but the heat therein may be increased even more by heat which can be added by intensive solar heaters. The sea water so heated naturally or additionally by the sun, when flash evaporated, gives vapors which may be passed through a heat engine to give power, then condensed at a lower pressure to give fresh water, which may be much more valuable than the power produced. Heat of condensation is removed by circulating cold sea water from a depth of a few thousand feet. This water from the deep also has considerable nutrients for sea plants and animals coming from the degradation of former sea life; and these nutrients may be used in well studied mariculture systems to grow commercial food fish in ponds adjacent the land-based plant. Various arrangements of flows of the several liquid streams are presented to illustrate variations to the process which will produce fresh water and/or electric power, also food fish. These modifications may be optimized with various component systems, some of which are well known and evaluated in this usage, including the use of a second thermodynamic fluid, conventional multistage flash evaporation, also two of its variations: Controlled Flash Evaporation and Vapor Reheat. Calculations indicate that even without the use of intensive solar heaters, a profitable desalination and mariculture operation may be expected which would pay for its substantial cost in two or three years of profits; however, the incorporation of certain intensive solar heaters may increase the profitability significantly.     

Gas Turbine Direct Integration in the Context of Pinch Technology

Gas‐turbine‐based cogeneration systems have been widely used in different applications in recent years. Although the most common method of using gas turbine exhaust energy is through the generation of steam in a heat recovery boiler, there are some applications where the exhaust energy has been directly used for drying or process fluid heating. In this work, direct integration of a gas turbine with a process was fully investigated in the context of pinch technology. This investigation includes simple gas turbine and gas turbines equipped with recuperator and afterburner. It was found that the best thermodynamic efficiency in a direct gas turbine system is achieved when two conditions are met: first, turbine inlet temperature is maximized, second, optimum pressure ratio is that which yields the maximum specific network. Two total cost optimization methods were also introduced. The first method is based on the assumption that power produced equates to power demand. In the second approach the power export opportunity was also considered. Finally, illustrative examples have been presented to show how approaches can be applied in practice.     

Optimisation of vertical axis wind turbine: CFD simulations and experimental measurements

A system for the conversion of kinetic energy of wind into thermal energy has been developed which can replace relatively expensive electro‐mechanical equipment. The system consists of a vertical axis wind turbine (VAWT) which is coupled with the shaft of a stirred vessel. In the present work, computational fluid dynamic (CFD) simulations have been performed for the flow generated in a stirred tank with disc turbine (DT). The predicted values of the mean axial, radial and tangential velocities along with the turbulent kinetic energy have been compared with those measured by laser Doppler anemometry (LDA). Good agreement was found between the CFD simulations and experimental results. Such a validated model was employed for the optimisation of drag‐based VAWT. An attempt has been made to increase the efficiency of turbine by optimising the shape and the number of blades. For this purpose, the combination of CFD and experiments has been used. The flows generated in a stirred tank and that generated by a wind turbine were simulated using commercial CFD software Fluent 6.2. A comparison has been made between the different configurations of wind turbines. Results show that a provision in blade twist enhances the efficiency of wind turbine. Also, a wind turbine with two blades has higher efficiency than the turbine with three blades. Based on the detailed CFD simulations, it is proposed that two bladed turbine with 30° twist shows maximum efficiency. © 2011 Canadian Society for Chemical Engineering     

汽动给水泵在我公司节能生产中的应用

利用除氧加热蒸汽先驱动给水泵汽轮机做功,给水泵汽轮机的排汽再供除氧器加热脱盐水,可以减少调节阀的节流损失,实现能源梯级利用,减少用电量,提高热电厂的经济效益。给水泵汽轮机采用变速调节,提高了其与给水泵之间的能量转换效率,同时也使锅炉给水系统运行更安全可靠。     

基于夹点技术的烟气处理系统的优化与评价

二氧化碳捕集系统节能技术受到了人们的广泛关注,但基本上集中在系统本身,鲜见有关烟气余热回收利用方面的研究报道,缺少具体的应用方案。然而,要进一步提高二氧化碳捕集系统的效率,就必须对烟气余热进行有效利用。为此,本文以某发电厂与660MW热电联产装置相配套的烟气处理系统为研究对象,首先采用问题表法确定了换热网络的夹点温度,然后通过冷、热物流间的“新”匹配对原换热网络进行改造,得出3种改造方案：烟气余热回收一级换热网络是高温烟气与胺补液之间进行匹配;烟气余热直接回收二级换热网络是高温烟气依次与富液、胺补液之间进行匹配;而烟气余热间接回收二级换热网络包括高温烟气与富液之间的间接换热。通过对以上3种改造方案投资费用的比较,发现烟气余热回收一级换热网络的投资成本最低,是最优改造方案。     

Considerations of energy consumption in desalination by reverse osmosis

The primary factors affecting the energy consumption of a reverse osmosis plant are considered. These are the osmotic pressure of the feedwater, the feedwater temperature, the water recovery, and the relationship between the water flux and salt flux characteristics of the membrane. In addition, the required permeate quality may have several indirect effects on the energy consumption. Permeate quality standards may impose minimum operating pressures, limit the recovery, and/or require treatment with a full or partial second stage. As a general rule, the energy required increases with increasing feed salinity and increasing permeate quality.For any given recovery, a single stage system will require less energy than a partial two stage system. However, for a specified permeate quality, a partial two stage system can operate at a higher overall recovery and a lower energy consumption than a single stage systemEnergy recovery systems can recover between 50 and 90 percent of the available energy in a reverse osmosis unit, thus significantly lowering the energy consumption. Studies have shown that with an energy recovery system, the minimum energy consumption occurs at a first stage recovery of 30 to 35 percent. Currently, very few energy recovery systems are in use due to their high capital cost, but as energy recovery systems become more available and reliable, they will greatly increase the energy efficiency of reverse osmosis plants.     

Ro, MSF and VTE/VC desalination: a comparative evaluation

The two main processes currently in vogue, for sea -water desalination 3?-- multistage flash. (MSF) and reverse osmosis (R.O.) -- are compared, on the basis of cost economics. Cost data are reported for unit sizes up to 10 million (U.S.) gallons per day. Both single-pass and double-pass systems are considered for the R. 0. unit, while the cost of water from MSF plants is calculated for different performance ratios. Controlling factors such. as fuel prices, pretreatment costs, membrane life, energy recovery and terms of financing, are discussed.On the basis of present technology, notwithstanding new developments, it is concluded that R. 0. is the more economical of the two for small unit sizes and regions of high fuel costs. There is a break-even point, depending on these two parameters, beyond which the MSF process yields lower water costs.Attention is focussed on a third process —- Vertical Tube Evaporation/Vapor Compression (VTE/VC), a self-contained, low-energy consuming system which is particularly suitable for barge-mounted or land-based single- purpose (water only) installations. The process, -which, is in an advanced stage of development under Envirogenics Systems Company's R and D program, is potentially competitive with R.O , even for small unit sizes. Future improvements and operational experience could make this the process of choice for single-purpose sea water desalination plants.     

余压能量回收装置在湿法脱碳工艺中的应用

介绍了能量回收透平、涡轮增压器、功交换器等余压能量回收装置的基本流程;简述了余压能量回收装置在我国湿法脱碳工艺中的应用情况;对比分析了上述3种余压能量回收装置的优缺点。结果表明,涡轮增压器具有占地面积小、易于安装、运行周期长、能量回收效率高（达80%以上）等优势,若将其应用于现有脱碳系统的改造及低温甲醇洗工艺,将会产生良好的节能效果和经济效益。     

Performance analysis of integrated biomass gasification fuel cell (BGFC) and biomass gasification combined cycle (BGCC) systems

Biomass gasification processes are more commonly integrated to gas turbine based combined heat and power (CHP) generation systems. However, efficiency can be greatly enhanced by the use of more advanced power generation technology such as solid oxide fuel cells (SOFC). The key objective of this work is to develop systematic site-wide process integration strategies, based on detailed process simulation in Aspen Plus, in view to improve heat recovery including waste heat, energy efficiency and cleaner operation, of biomass gasification fuel cell (BGFC) systems. The BGFC system considers integration of the exhaust gas as a source of steam and unreacted fuel from the SOFC to the steam gasifier, utilising biomass volatilised gases and tars, which is separately carried out from the combustion of the remaining char of the biomass in the presence of depleted air from the SOFC. The high grade process heat is utilised into direct heating of the process streams, e.g. heating of the syngas feed to the SOFC after cooling, condensation and ultra-cleaning with the Rectisol^® process, using the hot product gas from the steam gasifier and heating of air to the SOFC using exhaust gas from the char combustor. The medium to low grade process heat is extracted into excess steam and hot water generation from the BGFC site. This study presents a comprehensive comparison of energetic and emission performances between BGFC and biomass gasification combined cycle (BGCC) systems, based on a 4th generation biomass waste resource, straws. The former integrated system provides as much as twice the power, than the latter. Furthermore, the performance of the integrated BGFC system is thoroughly analysed for a range of power generations, ～100–997 kW. Increasing power generation from a BGFC system decreases its power generation efficiency (69–63%), while increasing CHP generation efficiency (80–85%).     

有机朗肯循环热电联供系统的实验研究

有机朗肯循环低温热力循环性能优越,易于小型化和自动运行,非常适合于分布式热电联供系统。依托已有的ORC-CHP实验平台,对热源温度101℃,膨胀机乏汽余热利用温度21.6～48.7℃时系统的热力性能进行了实验研究。在该温度范围内,ORC-CHP系统的综合能量效率96%～97%,其中热功转换效率4.4%～5.1%,乏汽余热利用效率91%～92%;从可用能角度出发,系统综合可用能效率50.0%～75.3%,其中热功可用能效率24.4%～19.2%,乏汽余热可用能效率25.7%～56.2%。实验表明该系统可以高效利用膨胀机乏汽余热,明显提高了有机朗肯循环的综合利用效率。     

CFD analysis of performance improvement of the Savonius water turbine by using an impinging jet duct design

The majority of research on water turbines focuses on design improvement of large-scale hydrokinetic turbines for power generation, which may have delayed the utilization of kinetic energy contained in rivers and canals. The aim of this paper is to improve the efficiency of a two bladed Savonius type cross-flow hydrokinetic turbine, which can be used as an energy converter to harness free-stream kinetic energy of water. An impinging jet duct design is presented for improving performance of the Savonius turbine in wind application as seen from literature. The performance of the modified turbine is evaluated using CFD software Fluent, and is compared with that of a simple two bladed Savonius water turbine and some of the prominent literature designs of the Savonius turbine. It is shown that the present design exhibits improved performance compared to the selected designs of the Savonius turbine.Further an insight of the improved performance of the modified turbine is also obtained from flow physics study.     

Energy analysis of a lignite predrying power generation system with an efficient waste heat recovery system

Lignite has been extensively used for electricity generation in many regions worldwide. However, its high water content has obviously negative effect on plant thermal efficiency. Performance of lignite-fired power plant can be improved by predrying the lignite before combustion. In addition, recovery of waste heat from the dryer and the power generation system will enhance the plant thermal efficiency further. In the present study, a new lignite predrying power generation system integrated with an efficient waste heat recovery system was proposed. Both dryer exhaust waste heat and steam turbine exhaust latent heat were recovered to heat boiler feed water. Energy analysis indicates that system performance is improved significantly. The plant thermal efficiency increases linearly with drying degree and then increases at a lower rate. The generation of unused dryer exhaust changes the variation tendency of system performance with drying degree.     

Modeling and Optimization of Jet Milling

The energy efficiencies of the acceleration nozzles of ejector and pneumatic jet mills are compared. Mathematical models are proposed for the acceleration of a two-phase mixture in the nozzle and the jet, and a procedure is put forward for optimizing subsonic nozzles and open-loop jet mills. The gas-dynamic perfection of the nozzles of pneumatic jet mills is assessed, and the initial particle-size range where the mill efficiency is highest is determined.