Chemical descaling of acid dosed desalination plants

The heat transfer efficiency of sea water desalters is very often impaired by the deposition of scale of various compositions on the heat transfer surfaces. Four major classifications of such scales can be recognised—corrosion products such as iron and copper oxides, alkaline scale Ca(OH)₂ and MgO, additive scales consisting of calcium and magnesium combined with additive materials that are usually soft and easily removed, and calcium sulphate.Acid cleaning techniques have been developed and successfully applied to the problem of removing in the first 3 categories of scale and these are reviewed. However for calcium sulphate scale there is as yet no widely accepted chemical cleaning process and mechanical methods are usually adopted. These also are briefly considered and shown to be inadequate to deal effectively with every instance of calcium sulphate scaling. The need therefore for chemical descaling techniques able to adequately remove calcium sulphate is shown to be clear.A number of chelating agents which can dissolve calcium sulphate and therefore are potential candidates for the formulation of a suitable reagent have been reviewed and two such reagents taken to pilot scale trials. These trials included corrosion tests on a typical range of desalter construction materials and in later work used actual scale removed from operational plants.From the data obtained an economic assessment of the use of these reagents for the descaling of a typical desalter heat input vessel was made, from which it was concluded that the once through application of either reagent could only be considered feasible for limited treatment. To overcome this economic problem, processes for the regeneration of the spent reagents have been developed to the pilot plant stage. From this data one reagent has been chosen and following continuing development, a design for a mobile chemical descaling unit has been evolved. This unit, which also has the capability of carrying out a wide range of descaling operations is described.     

Corrosion measurement and assessment in acid dosed desalination plants

An investigation of brine chemistry and corrosion behaviour of a wide range of possible construction materials has been carried out under actual service conditions in an acid dosed sea water distiller. A preliminary report on this work carried out by the UKAEA over the last five years in a multi-stage flash distiller in Jersey CI was presented at the Alghero Symposium in 1976. The programme is now complete and this paper presents a synopsis of the results.The programme has investigated the corrosion behaviour of some sixteen alloys which have been used or suggested as possible materials for the construction of sea water distillers. Test materials in the form of plain coupons, crevice and galvanic couples, weldments and stressed specimens, where applicable, were used in the assessment of material behaviour. Additionally, electrical resistance and electropotential techniques were used to assess the behaviour of some materials and to measure instantaneous corrosion rates and the change of rates under varying operating conditions, particularly during acid cleaning. The programme examined corrosion under all the conditions prevailing in the plant, that is, sea water inlet; before and after degassing; recirculating brine at various temperatures; vapour spaces and distillate.The accuracy and usefulness of the methods used are examined, together with the importance of the correct siting of probes and coupons. The methods used to determine brine chemistry parameters are also presented.It is concluded that carbon steel, aluminium brass and naval brass are adequate constructional materials for plant life of twenty years provided that strict control of brine chemistry is maintained. More expensive fall back materials are identified which are more tolerant of brine chemistry.     

Comparison of indices for the scaling and corrosion tendency of water

Three commonly used fouling indices to characterize the scaling and corrosion tendencies of water, namely the Saturation Index, the Langelier Saturation Index and the Ryznar Stability Index, have been compared and checked for consistency. While the first two indices give similar results, major deviations between the predictions of saturation and stability indices were found.     

Comparison of the dynamic behaviour of packed and plate distillation columns

The results of experimental investigations on distillation columns operating on a lab and on a production scale are presented and compared with the results obtained by simulation. There is good agreement between experiment and simulation. On the basis of these results a dynamic analysis was carried out. It compares the dynamic behaviour of packed and plate distillation columns of the same diameter and same number of theoretical plates. This reflects the influence of the different hold-ups of the two columns.     

Control of organic fouling at two seawater reverse osmosis plants

Organic fouling of seawater Reverse Osmosis (RC) membranes is a phenomenon not well understood; it can result in a loss of membrane productivity and salt rejection properties. Two seawater RO plants using DuPont B-10 hollow fiber permeators had experienced organic fouling and were studied.The two plants used different sources of feedwater; one RO plant at Culebra, Puerto Rico, used open seawater; while the other RO plant at Grand Cayman Island, British West Indies, used a sea well. Both feed water sources possessed high concentrations of soluble organics (40–80mg/1) which were mainly humic acids. In an attempt to remove these organics with in-line cationic polyelectrolyte coagulation, the plants experienced organic fouling which caused excessive loss of productivity and salt rejection; both plants initially failed their acceptance tests.It was discovered that the fouling was actually caused by interactions between the humic acids and in-line cationic, polyelectrolyte coagulants which were not removed by in-dedth and cartridge filtration. Rather than remove the humic acid material, acid addition was initiated and in-line cationic coagulants use discontinued to keep the humic acids soluble. It should be noted that with the open seawater intake ferrous sulfate was still used to remove colloidal material and reduce the SDI. Both plants subsequently have passed their 720-hour acceptance test.Culebra and Grand Cayman plants have now exceeded design specification for both productivity and salt rejection. The aramid hollow fiber permeators on acidified feed have shown 100% rejection of these organics at both 25% and 50% conversion and organic fouling has not been evident.     

氨基磺酸及其混合酸腐蚀性比较

通过对氨基磺酸及与一定量的盐酸混合酸,在投加同剂量的缓蚀剂后对铁、铜、不锈钢金属腐蚀率大小的实验比较,得出在氨基磺酸溶液中加入一定量的盐酸和缓蚀剂可以减轻其对铁、铜、不锈钢的腐蚀性,又可以增加其反应速度.     

Electrochemical behaviour and corrosion of lead in some carboxylic acid solutions

The electrochemical behaviour and corrosion of lead in various concentrations of acetic, lactic (0·01 M –1·0 M ), oxalic and tartaric (0·01 M –0·15 M ) acid solutions were studied at 25°C by a potentiodynamic method. The lead anode is readily soluble both in acetic and lactic acid solutions up to 2000 mV. In these two acid solutions, the anodic dissolution of lead increases with increases in the acid concentration and the dissolution process is under charge transfer control. Lactic acid is more corrosive than acetic acid. However, in oxalic and tartaric acid solutions, the E/i profiles depend on the acid concentration. Above a certain specific concentration, the profiles exhibit an anodic current peak associated with a dissolution of the metal and the formation of a passivating lead salt film and a cathodic peak which is related to the reduction of the film. The active dissolution of the lead increases with the acid concentration, the scan rate and stirring of the solution. The passivation of lead in these two acid solutions occurs by a dissolution–precipitation mechanism and the process is controlled by diffusion. X-ray diffraction analysis confirmed the presence of a passivating salt film (either lead oxalate or lead tartrate) on the electrode surface. © 1998 SCI     

液化天然气深冷-膜蒸馏海水淡化系统集成与分析

提出了一种PRICO天然气液化-膜蒸馏（MD）海水淡化系统集成方法,利用PRICO过程压缩机出口的余热驱动MD海水淡化。采用Aspen Plus和GAMS建立了集成系统的数学模型,综合考虑系统的结构、物流物性、设备规模、操作参数等系统设计问题,分析不同设计下系统的投资、能耗、运行费用以及MD单位产水成本。模型应用于一个处理量为1 kmol/s的PRICO天然气液化系统与MD集成的案例研究。计算结果表明,单位产水成本最小时,系统产水成本为1.98 USD/m³,淡水产量为5.78 m³/h,与反渗透等海水淡化技术相比,MD在经济性方面具有较强的竞争力。     

衣康酸介质中杂质离子对两种不锈钢腐蚀行为的影响

针对发酵法生产衣康酸过程中的腐蚀问题研究了两种不锈钢在衣康酸工况介质（发酵液）中的腐蚀行为,探讨了介质中杂质离子Ｃｌ－、Ｆｅ３＋、ＳＯ２－４等对腐蚀的影响。结果表明,随衣康酸介质中Ｃｌ－含量增加,不锈钢的腐蚀速率也增大,而其点蚀电位则随Ｃｌ－浓度的对数值增加呈线性下降;Ｆｅ３＋浓度的增大可使不锈钢／发酵液由活化体系转变成活化 钝化体系;ＳＯ２－４对不锈钢稍有缓蚀作用;在含杂质的衣康酸介质中,Ｒ１双相不锈钢的耐全面腐蚀和耐点蚀性显著优于３１６Ｌ奥氏体不锈钢。     

Mobile and floating flash distillation plants

A single mobile floating desalination plant could serve the increasing water requirements of several scattered communities such as those living on a group of islands or along an arid coastline. The use of such plants could satisfy the requirements of small communities for additional high quality water supplies where the present demand does not justify the installation and operation of several small land-based desalination plants and where the cost of transporting alternative water supplies is high. The inherent flexibility of a mobile plant would enable seasonal peak demands of certain communities to be readily met.This paper presents the results of a design study of a mobile and floating desalination plant with a fresh water production capacity of 200,000 igpd (909 m³/d). The capital cost of such a facility has been estimated to be £ 384,000. This plant could supply each of 60,000 persons in 12 isolated communities with 2.7 igpd (12 litres/pay) of fresh water at a cost of 26/-d per 1,000 Imp. gallons.     

真空膜蒸馏海水淡化过程的强化研究

采用气液两相流技术对管状炭膜真空膜蒸馏模拟海水淡化过程进行强化研究。纯水物系和NaC l水溶液的气液两相流强化实验中,相比未通气体时通量分别增加了29%~35%和16%~66%。气体流量、渗透侧真空度和膜组件放置方式对两相流膜蒸馏过程通量的影响结果表明:气液体积流量之比在(1~2)∶1时两相流强化效果最佳;通量随着渗透侧真空度的增大而增大,且气液两相流操作在较小真空度时通量增加的幅度大于较大真空度时;膜组件的放置方式对通量影响较大,相对于水平放置时,膜管竖直放置时的通量较大,最大可达水平放置时的131%左右。     

Concentration of heavy water in seawater distillation process

Distributions of deuterium in two multi-stage flash plants and a multi-effect plant were calculated by use of a numerical model. The calculated values were in good agreement with the observed ones. The maximum error was less than 1%. Product water of high deuterium concentration can be obtained from the distillation chamber at the highest temperature with a high concentration factor. The deuterium concentration in the product water was around 155 ppm.     

四元海水缓蚀剂的缓蚀性能研究

四元海水缓蚀剂由聚天冬氨酸(PASP)、葡萄糖酸钠、七水硫酸锌与2-羟基膦酰基乙酸(HPAA)复配制得.利用失重法和电化学法研究了缓蚀剂在海水中对A3碳钢的缓蚀性能.结果表明,当缓蚀剂的用量为100 mg/L时,其缓蚀率大于94％,该缓蚀剂是一种抑制阳极腐蚀为主的缓蚀剂,在海水中具有优良的缓蚀性能.     

钛在稀盐酸溶液中腐蚀行为的研究

本文用测定自腐蚀电位随时间变化关系、极化曲线、失重法和Ｘ射线光电子能谱分析等手段研究了稀盐酸浓度和温度对钛腐蚀行为的影响，测出了钛在不同温度的稀盐酸中产生腐蚀的临界浓度和不同浓度稀盐酸中产生腐蚀的临界温度。     

Solar barometric distillation for seawater desalting Part II: Analyses of one-stage and two-stage distillation technologies

The report concerns design aspects for the recently proposed solar barometric distillation technology for seawater desalting (SW–SBD) with an underground barometric layout. Two types of SW–SBD desalting plants are analysed. The first plant utilizes a single-stage distillation process with one distillation heat exchanger (operative condensation temperature 50°C). The second plant utilizes a two-stage distillation process with two distillation heat exchangers connected in series (operative condensation temperatures 40 and 60°C). Vacuum solar collectors of simple design and construction, utilizing glass or suitable glass/polymer blends as transparent material, are proposed for the SW–SBD plants. The present analyses suggest that SW–SBD desalting technology may have a promising technico-economic potential. Field research on SW–SBD prototype plants is necessary to bring SW–SBD desalting technology to its full technological development.     

膜蒸馏海水淡化研究进展及发展趋势

海水淡化是解决我国水资源短缺的重要措施之一。膜蒸馏海水淡化技术可以充分利用太阳能等低品位热源，具有成本低、设备简单、操作容易、能耗低等优点，在海水及苦咸水淡化方面应用前景广阔。     

低温多效蒸发海水淡化系统热力分析

建立了喷射器低温多效蒸发海水淡化系统的数学模型,计算分析了各种温度损失随温度的变化,并研究了顶值盐水温度、蒸发器效数和动力蒸汽等参数对系统的造水比和生产单位质量淡水所需传热面积的影响。结果表明各种温度损失在末效蒸发器内显著增加;喷射器低温多效蒸发系统的热力特性明显优于多效蒸发系统;通过增加顶值盐水温度、蒸发器效数和动力蒸汽温度,可以实现系统的优化运行。     

Crevice corrosion cathodic reactions and crevice scaling laws

A numerical model that predicts the rates of metal dissolution and electrolyte composition along the length of a metallic crevice was used to simulate the crevice corrosion of AISI 304 stainless steel. The model considers both the forward and reverse electrochemical reactions that might take place during the corrosion process. The environment exterior to the crevice, where a net cathodic current is produced, was simultaneously modeled. It was found that cathodic reactions are likely to occur towards the tip of the crevice. For the case when the hydrogen evolution reaction was considered as a possible cathodic reaction in the crevice, it is shown how the delayed instigation of this reaction may be the cause of an experimentally observed increase in pH at the crevice tip. Two critical crevice scaling laws were examined using model predictions and one scaling law fit the model predictions very well. This scaling law differentiates between crevices that will undergo active corrosion and those that will remain indefinitely passive.     

浅谈残液蒸出域的腐蚀问题

详细论述了用电石法生产氯乙烯过程中残液蒸出塔的腐蚀原因,并指明解决问题的办法,经过近年来的实践,取得了较好的效果。     

稠化酸返排液回注处理方法与腐蚀结垢性研究

针对陕北某油井稠化酸返排液具有p H值低、SS含量和含油量高、颗粒大、透光率低、Fe2+含量高、腐蚀性强等特点,采用氧化除铁-絮凝-砂滤工艺进行处理,将处理后稠化酸返排液与注入水、地层水按不同体积比掺混,对3种不同处理阶段水样的配伍性进行评价。结果表明:调节p H值至7.5左右,Na Cl O氧化除铁效果较好,适宜投加量为40 mg/L;絮凝-砂滤处理氧化后的稠化酸返排液,当PAC投加量为500 mg/L、CPAM投加量为1.5 mg/L、加药间隔时间为10 s、搅拌时间为5 min时,稠化酸返排液透光率为99.1%,SS的质量浓度为0.5 mg/L,油的质量浓度为1.2 mg/L,Fe~(2+)的质量浓度与腐蚀速率分别降为0.14 mg/L和0.026 3 mm/a,粒径中值为0.52μm,水质符合SY/T 5329—2012《碎屑岩油藏注水水质指标及分析方法》中的油田回注水标准,处理后稠化酸返排液和注入水、地层水按不同体积比混合,混合水水质稳定,配伍性良好,无结垢趋势。