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.     

Towards sustainable seawater desalting in the Gulf area

Gulf countries experienced rapid growth in the last four decades from oil production and its price increase. Natural water resources are very limited to meet this growth, and as result, desalted seawater in Kuwait became the main source of potable water, about 93% in 2002. The electric power and desalted water, produced in co-generation power desalting plants (CPDP), consumptions are continuously increasing, almost doubled every 10 years, due to population and standard of living increases. This led to the consumption of huge amounts of fuel, draining the country main fuel (and income) resource, and negatively affecting the environment. One tenth of Kuwait’s oil production was consumed by the CPDP in 2003. If the trend of almost doubling the consumption every 10 years prevails, the total oil production may not be sufficient to desalt seawater for people to drink, and to produce power to run space air conditioning units (a necessity for Kuwaiti harsh weather). It is essential therefore to look for energy efficient ways to produce power and desalted water so as to save the nation’s income of these non-renewable fuel resources, to save the environment and indeed life itself in Kuwait, and this is the objective of this paper. It reviews the presently used desalting methods and their energy demand, and the correctness of fuel allocation formulas for CPDP, to determine the most efficient methods to apply and the less efficient ones to avoid. Fourteen desalting cases are analyzed by using the current practice, with and without combination with power generation plants (using steam or gas or combined gas/steam turbines cycles). The specific fuel energy consumed and the emitted CO₂, SO_x, and NO_x per m³ desalted water were calculated for each case. The results show that operating thermally driven desalting systems by steam directly supplied from fuel-fired boilers is the most inefficient practice, and should be avoided. The use of the gas/steam turbine combined cycle, which is also the most efficient powergeneration cycle, to drive seawater reverse osmosis (SWRO) desalination plants is the most efficient combination. Also, all conservation measures in utilization of both water and power should be applied. Reclamation of waste water, at least for non-potable water needs must be promoted, because it consumes less energy and at cost much lower than those of desalting seawater.     

工业水处理中浅除盐技术的应用

介绍了工业水处理浅除盐新技术 ,运用该技术可使锅炉给水由软化水提质为浅除盐水 ,减少排污 ,降低生产费用 ,提高蒸汽品质。     

工业水处理中浅除盐技术的应用

介绍了工业水处理浅除盐新技术,运用该技术可使锅炉给水由软化水提质为浅除盐水,减少排污,降低生产费用,提高蒸汽品质。     

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.     

FLOX® Steam Reforming for PEM Fuel Cell Systems

Primary energy savings and CO₂ reduction is one of the key motivations for the use of fuel cell systems in the energy sector. A benchmark of domestic cogeneration by PEMFC with existing large scale power production systems such as combined steam‐gas turbine cycle, clearly reveals that only fuel cell systems optimising overall energy efficiency (> 85%) and electrical efficiencies (> 35%) show significant primary energy savings, about 10%, compared with the best competing technology. In this context, fuel processing technology plays a dominant role. A comparison of autothermal and steam reforming concepts in a PEMFC system shows inherent advantages in terms of efficiency at low complexity for the latter. The main reason for this is that steam reforming allows for the straightforward and effective use of the anode‐off gas energy in the reformer burner. Consequently, practical electrical system efficiencies over 40% seem to be achievable, most likely by steam reformers. FLOX®‐steam reforming technology has reached a high state of maturity, offering diverse advantages including: compact design, stable anode off‐gas usage, high efficiency, as well as simple control behaviour. Scaling of the concept is straightforward and offers an opportunity for efficient adaptation to smaller (1 kW) and larger (50 kW) units.     

钢铁企业煤气-蒸汽-电力系统耦合优化及应用

煤气、蒸汽和电力是钢铁联合企业能源系统的重要组成部分,其消耗占钢铁企业总能耗的60%左右。合理地制定能源系统的生产以及燃料消耗、电力采购计划,对企业降低成本、减少环境污染有着非常重要的意义。针对煤气-蒸汽-电力系统的燃料结构、设备类型、工况变化等特点,以经济运行成本和环境成本最小为目标函数,建立了针对该系统的耦合优化模型。该模型综合考虑了富余煤气的波动、蒸汽和电力的动态需求、多燃料结构、分时电价等影响因素,并使用GAMS进行优化求解。将模型应用到某大型钢铁联合企业,结果表明该模型能够为钢铁企业煤气-蒸汽-电力系统提供合理的生产计划方案,实现了富余煤气的合理分配以及能源的高效利用,降低了能源系统运行成本,提高了企业的经济效益和环境效益。     

300MW机组发电煤耗影响因素分析

结合国电太原第一热电厂有限责任公司300 MW抽气凝汽式机组相关运行参数进行耗差分析,明确发电煤耗的主要影响因子,并提出合理化降耗建议。其方法是:第一步,假定管道效率在定值条件下,用图表直观描述汽机效率、锅炉效率对该机组发电煤耗的影响程度;第二步,与设计值相比,将汽机效率、锅炉效率的影响因子进行定量化分析,测算出该机组可控损失造成发电煤耗的增量,明确其发电煤耗主要影响因子为:主蒸汽压力、凝汽器真空度、最终给水温度、排烟含氧量、排烟温度,并有针对性地提出合理化降耗措施。     

A new look at dual purpose, water and power, plants - economy and design features

In light of rapidly rising equipment and fuel costs, recent studies have shown some important results in the economy and optimum designs for dual purpose power/desalting complexes. The desalination cycle chosen for- detailed comparisons in this study is the well known multistage flash (MSF) evaporator, which uses brine recirculation and polyphosphate scale prevention. The multi- stage flash evaporator has found wide spread application in large plants throughout the world. Single units of up to 1400 m3/hr (9.5 MGD), acid dosing, have been built and are now in operation. In general due to corrosion problems, polyphosphate plants are now preferred over the acid one.

A number of schemes for the combined production of power and. water were chosen, mainly a combination of MSF Unit with each of the following power cycle:

• 1- Automatic extraction steam turbine

• 2- Simple gas turbine with waste heat boiler

• 3- Back pressure steam turbineThis paper presents a study of the economic aspects, thermodynamic features and optimization analysis of each of these combined power and water production plants.

The optimum value of the performance ratio and its effect on reducing the cost of water in each of the above mentioned schemes would be discussed in this paper.     

A reverse osmosis desalting plant operated by gas turbines

Power plants in Kuwait use gas turbines (GT) only for a few hours to produce power at peak load times. Peak loadoccurs in the summer due to the air-conditioning load. As an example, the average number of operating hours for six gas turbines in the Doha East power plant was 16 in the summer of 2001. There is little concern about efficiency of these GT since they work for a very short time during the year. However, a recent increase in desalted seawater demand suggests the use of these GT to operate reverse osmosis (RO) desalting systems all year around. The summer outside design temperature in Kuwait for air-conditioning calculations is 48°C dry bulb temperature (DBT), and 28°C wet bulb temperature (WBT); but the ambient temperature can easily reach 60°C. Gas turbine power output and efficiency are drastically reduced by the increase in temperature of intake air to the gas turbine's compressor, especially during harsh Kuwaiti summer conditions. Thus, it is essential to investigate cooling of air intake to the GT compressor. The performance of a typical GT unit and its ability to produce desalted waterby a RO desalting system at different ambient temperatures are presented. Calculation of needed capacities for the cooling of intake air to the GT compressor was performed for evaporative cooling, single and multiple mechanical vapor compression cycles, and combined indirect evaporation cooling with the refrigeration system. The improvements of power output and efficiency due to the cooling of air intake of the GT and the resulting increase in desalted water are also presented.     

加氢裂化装置的能耗分析及节能措施

影响加氢裂化装置能耗的主要因素是燃料气、电、蒸汽等消耗,本文依据过程系统用能分析的三环节模型进行加氢裂化装置的能耗分析,阐明在能量转换和传输、能量利用、能量回收环节,通过采取提高加热炉热效率、液力透平、HydroCOM气量调节控制系统、夹点技术等措施,有效降低加氢裂化装置的瓦斯、电、蒸汽等主要项目的消耗,达到降低装置能耗的目的。同时,文章指出了在建的云南石化210万吨/年蜡油加氢裂化装置的一些节能措施,为其他新建加氢裂化装置提供参考。     

交直流三级电脱盐技术在炼油工业上的应用

采用先进的交直流三级电脱盐装置,改造炼油厂前原油的脱盐工艺,实现了原油的深度脱盐,原油含盐由脱前〉２００ｍｇ／Ｌ降到脱后的〈３．２ｍｇ／Ｌ以下,从而延长了常减压装置的开工周期,减少了催化裂化装置催化剂的耗量。     

低温省煤器对凝汽器真空及机组热经济性影响

为解决国内某电厂600MW直接空冷机组5^#锅炉排烟温度过高的问题,在锅炉尾部烟道加装低温省煤器,利用烟气余热加热机组凝结水。抽汽被排挤回汽轮机继续膨胀做功,增加汽轮机发电功率,降低汽轮机热耗和机组发电煤耗;同时汽轮机排汽量增加,凝汽器真空下降,机组热经济性变差。本文以TRL工况为例,对该电厂加装低温省煤器后进行了计算,得出凝汽器真空下降1.617kPa。利用热平衡法与等效焓降法,对加装低温省煤器后机组热经济性进行计算。最终结果为:热平衡法得到加装低温省煤器后汽轮机热耗下降25.711kJ/(kW·h),机组发电煤耗降低0.959g/(kW·h);等效焓降法得到,加装低温省煤器后汽轮机热耗下降26.832kJ/(kW·h),机组发电煤耗降低1.001g/(kW·h)。说明加装低温省煤器具有良好的节能效果,同时也证明了等效焓降法与常规热平衡法的一致性。     

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%).     

A comparative simulation study of power generation plants involving chemical looping combustion systems

This work presents a simulation study on both energy and economics of power generation plants with inherent CO₂ capture based on chemical looping combustion technologies. Combustion systems considered include a conventional chemical looping system and two extended three-reactor alternatives (exCLC and CLC3) for simultaneous hydrogen production. The power generation cycles include a combined cycle with steam injected gas turbines, a humid air turbine cycle and a simple steam cycle. Two oxygen carriers are considered in our study, iron and nickel. We further analyze the effect of the pressure reaction and the turbine inlet temperature on the plant efficiency. Results show that plant efficiencies as high as 54% are achieved by the chemical looping based systems with competitive costs. That value is well above the efficiency of 46% obtained by a conventional natural gas combined cycle system under the same conditions and simulation assumptions.     

The Curacao KAE-LT-MED and auxiliary steam turbine project: A model for dual purpose MSF plants replacement

KAE, the water and power company of Curacao, has contracted to replace its older and less efficient MSF plants with a 10,000 m³/day Low Temperature, Horizontal Tube, Falling Film, Multi Effect Distillation (LT-MED) plant.The plant operates at a top brine temperature of 70 degrees C and requires steam at only 0.34 bar a.However, motive steam is available, as extraction from the power station's turbines, at 2.55 bar a, 155 °C, as required by the higher temperature MSF plant. This excess pressure potential is used to generate 3.1 MW of power in an auxiliary low pressure steam turbo-generator, thereby improving overall economy and lowering desalted water cost to a level unequalled by any other system. The paper describes the power station turbine, auxiliary low pressure turbo generator and LT-MED plant combined scheme, its operational features and economics.     

火电机组余热梯级供热技术的综合分析

针对传统供热技术平均?效率低的问题,提出了乏汽余热梯级供热技术。该技术有效地利用了机组乏汽余热,并减少了汽轮机的冷源损失,避免了中排抽汽参数过高造成的能量损失,提高了机组供热经济性。以某电厂为例,本文基于热力学定律与单耗分析理论,建立了乏汽余热梯级供热系统的单耗分析模型,应用该模型对其进行了?分析和附加燃料单耗分析,为节能降耗提供了理论依据。分析结果表明,发电煤耗率由改造前的249.69g/(kW·h)降低到149.9g/(kW·h),降低了99.79g/(kW·h),机组供热负荷较由改造前的788.4MW增加到1673.9MW,增加了885.5MW;改造后传热温差在非严寒期只有7℃、严寒期为26.94℃,比改造前大幅降低;在非严寒期和严寒期,加热器蒸汽入口平均比?比改造前分别降低了524.73kJ/kg、418.2kJ/kg,供热系统的平均?效率比改造前分别提高了51.35%、32.58%,供热系统的平均附加燃料单耗分别为3.11g/(kW·h)、7.98g/(kW·h)。可见通过“乏汽余热梯级供热技术”改造后,节能效果显著,该技术具有广阔的推广应用前景。     

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.     

反渗透技术应用总结

结合辽宁华锦通达化工股份有限公司除盐水系统流程,介绍反渗透装置的主要技术参数、运行控制要点、装置消耗情况及出现的问题.通过采用反渗透技术取代石灰软化技术用于除盐水处理的应用实践,说明在除盐工艺中应用反渗透技术将取得节水、降耗的双重效益.     

石油化工企业储运系统节能分析和研究

石油化工企业油品储运系统正常生产运行时需要消耗大量的能源和公用工程资源。能源主要是指电能,公用工程资源主要是指蒸汽、生产水、低温热水、净化压缩空气、氮气等,其中蒸汽的消耗量比较大。随着国家节能减排的规划要求及石化企业效益的最大化,石油化工企业储运系统的节能优化显得尤为重要。本文就石油化工企业储运系统能源消耗进行分析和研究,并就节能做进一步的阐述和说明。