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.     

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.     

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.     

无霜空气源热泵系统夏季运行性能初步实验

通过对比现有的空气源热泵空调系统的优缺点,提出了一种新型无霜空气源热泵空调系统。该热泵系统不仅冬季可以无霜高效运行,夏季性能也有所提升。搭建该系统实验平台,研究了室外空气干球温度、相对湿度、冷冻水、冷却水流量、室外空气流量对夏季工况系统性能的影响。该空气源热泵空调系统在湿度低、冷却水流速大、冷冻水流速大时系统性能有较大提升,COP最大可提升0.23,提高室外空气流量对系统性能影响不大可提升0.06,且在室外空气干球温度35℃相对湿度45%时,系统COP超过了该型压缩机额定COP,充分证明了该系统在夏季工况下能稳定高效运行。     

合成氨装置离心压缩机改造经验

介绍日产千吨合成氨装置增产50％的技改项目中,工艺空气压缩机和合成气压缩机的改造经验。并联一台电动多轴式离心式空压机,改造工作量小、风险小、投资省,比改造现有机组可节省数百万元人民币。合成气压缩机改内件或更换新的高低压缸,宜由两家制造厂报价确定,不宜由原制造厂独家承担,否则费用居高不下;压缩机效率提高,并改进合成工艺后,原汽轮机功率足够,不必改造。     

25000 t LNG燃料动力化学品船能量利用系统的设计及优化分析

以25000 t LNG燃料动力化学品船为研究对象,在分析及评估原船废气余热利用系统以及高温冷却水系统用能水平基础上,针对船舶发电、海水淡化、冷库及空调等需求,综合考虑原船余热资源及未加以利用的LNG冷能,以加装废气动力涡轮、LNG冷能ORC发电、冷冻法海水淡化及设置高低温冷库与空调系统等方式组合提出了五种能量系统梯级利用方案。通过HYSYS软件模拟计算和对比分析,从（火用）效率及经济性两个方面对各方案进行了评估。结果表明,诸方案中以低温冷库+高温冷库+空调系统经济性最好,所形成的新设计系统经优化后（火用）效率可提高至62.87%,每年经济收益可达1227.85万元。     

复合型蒸发冷却器在常减压电脱盐系统的应用

介绍了常减压装置电脱盐系统含盐污水冷后温度过高的现状,分析了空冷器失效的原因,确定用复合型蒸发冷却器代替空冷器的改造方案并加以实施,并对复合型蒸发冷却器投用后的运行效果进行分析。复合型蒸发冷却器投用后可满足冷后温度需要,根据实际情况,将含盐污水水冷器E1052AB切除,每小时可以节约循环水180t,而复合型蒸发冷却器每小时消耗除盐水3t。     

燃气轮机功率影响因素分析及对策

从叶片结垢、入口空气温度、内件老化、漏气、修复件等方面分析影响燃气轮机功率的原因,提出具体解决对策.通过增加空气冷却系统和采取措施降低燃气轮机的功率损失后,保证机组按100%负荷稳定、长周期运行.     

进气温度对燃气-蒸汽联合循环机组性能的影响

选取某200MW级燃气-蒸汽联合循环（GSCC）机组为研究对象,在环境温度与联合循环满负荷和部分负荷工况性能变化规律分析的基础上,本文提出了燃机进气温度控制技术。通过建模仿真和试验等方法研究了燃机进气温度变化对联合循环全工况性能的影响。结果表明,对于联合循环满负荷工况,通过进气冷却技术将燃机进气温度由32℃降低至12℃时,可增加联合循环功率14.2MW,同时提高热耗率2.3%;对联合循环80MW、120MW和160MW部分负荷工况,通过进气加热技术将燃机进气温度由12.5℃升高到40℃时,联合循环燃气耗量逐渐降低,联合循环效率分别提升0.86%、1.26%和1.11%。燃机进气温度控制技术建立了联合循环中底循环与顶循环间的耦合,在一定负荷和进气温度范围内调节燃机进气温度可有效改善联合循环性能,具有较高的研究和应用价值。     

一种低位热驱动除湿冷却空调系统的热性能分析

溶液除湿蒸发冷却空调系统（LDECS）结合了溶液除湿与蒸发冷却技术的优势,是一种具有广阔发展前景的非压缩式空调系统。提出了一种低品位热能驱动的LDECS,该系统由处理全部湿负荷的溶液除湿系统和承担显热负荷的再生式间接蒸发冷却器构成。建立了系统各主要部件的数学模型,研究了再生器进口溶液温度T_s,reg,in、液-液热交换器效率ε_SSHX、室外空气温度和相对湿度对该系统用作全新风机组时稳态热力性能的影响。结果表明,在南京夏季典型工况下,该系统送风参数为17.9℃、9.2 g·kg,热力系数TCOP可达0.56。T_s,reg,in在70℃左右时可以满足送风参数的要求同时保持较高的TCOP。自循环比越小,ε_SSHX对TCOP以及溶液加热器和冷却器负荷的影响越大。此外,该系统适合应用在夏季高温高湿地区。     

Technical and economic analysis for the integration of small reverse osmosis desalination plants into MAST gas turbine cycles for power generation

A technical and economic analysis concerning the integration of small reverse osmosis (RO) desalination plants into mixed air steam turbine (MAST) technologies for power generation was carried out. The simulation tool used is the computer aid reverse osmosis calculations optimization algorithm. This user-friendly software takes into account the capital cost, fuel cost and operation and maintenance requirements of each candidate RO desalination plan scheme and calculates the least-cost configuration. The results indicate that the integration of a RO desalination plant into MAST gas turbines has a minor effect on the final operating cost of the power plant.     

发动机尾气余热驱动的吸附式空调系统仿真与测试

针对在高太阳辐射地区,柴油车驾驶室内使用车载空调会增加车辆发动机的耗油量、降低柴油车经济效益的问题,搭建了一套由发动机尾气余热驱动的吸附式车载空调系统。系统由填充有氯化钙/氯化锰/硫化膨胀石墨复合吸附剂的吸附床、蒸发器、冷凝器、储液罐和阀门组成,使用氨作为制冷剂,利用车辆在行驶时接触到的自然风为吸附床冷却,在发动机尾气余热的驱动下,为驾驶室内提供连续的制冷效果。结合仿真和实验测试,对所设计系统的制冷性能进行了分析,仿真结果表明,系统最优循环时间为45 min,系统的理论平均制冷功率可达3.5 kW以上,系统COP处于0.2~0.25之间。实验结果表明,在230℃的尾气温度条件下,系统能产生3 kW的平均制冷量。在40℃环境温度条件下,系统在蒸发器进出口处的平均温差为6.5℃,平均制冷量为3.2 kW。     

Syngas and a separate nitrogen/argon stream via chemical looping reforming - A 140 kW pilot plant study

A dual circulating fluidized bed pilot plant was operated in chemical looping reforming conditions at a scale of 140 kW fuel power with natural gas as fuel. A nickel-based oxygen carrier was used as bed material. The pilot plant is equipped with an adjustable cooling system. Three experimental campaigns have been carried out at 747 °C (1020 K), 798 °C (1071 K) and 903 °C (1176 K), respectively. In each campaign, the global stoichiometric air/fuel ratio was varied step-wise between 1.1 and the minimum value possible to keep the desired operating temperature when the cooling is finally switched off. The results show that the fuel reactor exhaust gas approaches thermodynamic equilibrium. The residual amount of methane left decreases with increasing fuel reactor temperature. Further, the oxygen in the air reactor can be completely absorbed by the solids as soon as the air reactor operating temperature is higher than 900 °C (1173 K). Even though no steam was added to the natural gas feed no carbon formation was found for global excess air ratios larger than 0.4.     

探析室外气象条件对全空气蒸发冷却空调设备制冷量的影响

节能减排对蒸发冷却空调技术的发展提供了契机,体现出与时代相一致的绿色、节能、环保、高能效比的优势特点,然而该技术受到气象条件的影响不容忽视。以蒸发冷却空调设备的制冷量参数为着眼点,基于蒸发冷却空调设备的特点及制冷原理,把握和分析室外气象条件相关参数的变化条件,如:干球温度、湿球温度、相对温度、含湿量、大气压力等,探讨了室外气象条件对全空气蒸发冷却空调设备的制冷量影响。     

生物质两段式富氧气化-燃气轮机燃烧集成发电系统模拟研究

为实现生物质能量的高效清洁利用,本研究基于两段式富氧气化系统改进燃气品质,并将获得的洁净高热值可燃气用于燃气轮机燃烧.通过Aspen Plus模拟研究分析了氧体积分数、气化温度对气化特性、燃机运行特性的影响,研究结果证实了生物质气化燃气在燃气轮机应用的可行性,并发现氧体积分数提高对改善生物质气化燃气品质及系统发电效率具...     

Optimal design and integration of an air separation unit (ASU) for an integrated gasification combined cycle (IGCC) power plant with CO2 capture

The air separation unit (ASU) plays a key role in improving the efficiency, availability, and operability of an oxygen-fed integrated gasification combined cycle (IGCC) power plant. An optimal integration between the ASU and the balance of the plant, especially the gasifier and the gas turbine (GT), has significant potential for enhancing the overall plant efficiency. Considering the higher operating pressure of the GT, an elevated-pressure air separation unit (EP-ASU) is usually favored instead of the conventional low-pressure air separation units (LP-ASU). In addition, a pumped liquid oxygen (PLOX) cycle is usually chosen if the operating pressure of the gasifier is high. A PLOX cycle helps to improve plant safety and availability and to decrease the capital cost by reducing the size of the oxygen compressor or by eliminating it completely. However, the refrigeration lost in withdrawn liquid oxygen must be efficiently recovered. This paper considers five different configurations of an ASU with PLOX cycle and compares their power consumptions with an EP-ASU with a traditional gaseous oxygen (GOX) cycle. The study shows that an optimally designed EP-ASU with a PLOX cycle can have similar power consumption to that of an EP-ASU with GOX cycle in the case of 100% nitrogen integration. In the case of an IGCC with pre-combustion CO₂ capture, the lower heating value (LHV) of the shifted syngas, both on a mass and volumetric basis, is in between the LHV of the unshifted syngas from an IGCC plant and the LHV of natural gas, for which the GTs are generally designed. The optimal air integration in the case of a shifted syngas is found to be much lower than that of an unshifted syngas. This paper concurs with the existing literature that the optimal integration occurs when air extracted from the GT can be replaced with the nitrogen from the ASU without exceeding mass/volumetric flow limitations of the GT. Considering nitrogen and air integration between the ASU and the GT, this paper compares the power savings in an LP-ASU with a PLOX cycle to the power savings in an EP-ASU with GOX cycle and EP-ASU with PLOX cycle. The results show that an LP-ASU with a PLOX cycle has less power consumption if the nitrogen integration levels are less than 50-60%. In addition, a study is carried out by varying the concentration of nitrogen and steam in the fuel diluents to the GT while the NOx level was maintained constant. The study shows that when the nitrogen injection rate exceeds 50%, an EP-ASU with a PLOX cycle is a better option than an LP-ASU with a PLOX cycle. This paper shows that an optimal design and integration of an ASU with the balance of the plant can help to increase the net power generation from an IGCC plant with CO₂ capture.     

使用NH3-LiNO3工质对的增压型回热吸收循环性能分析

近年来,日益增长的暖通空调系统能耗已接近50%的建筑能源消费量。吸收式循环可使用太阳能热能、工业废热等低品位能源产生制冷效果,进而降低夏季制冷负荷对高品味电能的大量需求。当前常用于吸收制冷循环的LiBr-H₂O工质对虽然COP较高,但由于物性限制了其蒸发温度范围以及存在较高的结晶风险,使得系统小型风冷设计存在限制。氨水工质对具有较宽的制冷温区,但由于需要精馏以提高氨气浓度造成COP较低。NH₃-LiNO₃工质对无须增设精馏器,结晶温度远高于LiBr-H₂O,且氨气压力较高适合在耦合压缩机循环以提升循环性能,扩宽运行温区。因此,本研究提出压缩机辅助的增压型回热吸收循环使用NH₃-LiNO₃工质对,并对其进行热力分析,研究压缩机的引入对循环性能的改进作用。结果显示,压缩机辅助作用下循环驱动温度下降至34℃,蒸发温度亦可降低至-34℃,且循环倍率降低了52.16%,更适于小型风冷设计。     

Desalinated water production at LNG-terminals

A process has been worked out to apply the laws of thermodynamics to sea water desalination making use of LNG.Ambient temperature heat is applied to LNG which evaporates and generates power.This power is employed to extract heat from sea water; part of the sea water is frozen and the heat is discharged to environment.The ice produced is melted at ambient temperature and desalted water is obtained.Detailed technical calculations have been developed by Nuovo Pignone in the past and cost estimations made for both investment and production costs. At present this is probably the cheapest method of producing desalted water.Conventional technology is used for every component of the resulting plant.This kind of plant may produce quite a substantial amount of desalted water, up to 30.2 tons of water per ton of LNG. Therefore a terminal capacity of 5.10⁹ Nm3/yr of natural gas may produce 10,000 t/d of water, equivalent to the needs of a town of 40,000 inhabitants.     

Shell煤气化装置激冷流程综述

阐述Shell煤气化工艺中粗煤气激冷流程,激冷气的作用,激冷气流程主要设备激冷气压缩机及启动步骤进行简介,Shell气化炉运行过程中实际遇到问题的浅析。