聚合物对离子交换膜脱盐性能的影响及其污染特性

通过自制的电渗析(ED)装置,从聚合物(部分水解型聚丙烯酰胺,HPAM)浓度、操作电压以及进水流速等方面研究了HPAM对离子交换膜脱盐性能的影响,并结合HPAM在膜上的吸附情况,分析了其污染特性.结果表明,聚合物对离子交换膜的脱盐性能有显著的影响,聚合物浓度的增加会加大HPAM的单位膜面积吸附量,加剧膜污染,降低膜脱盐效率;升高操作电压,同样会促进HPAM在膜上的吸附,但不及对溶液离子迁移的影响,脱盐效果虽得到提高,但能耗增加;提高进水流速,可以减少HPAM在膜上的吸附,减轻膜污染,同时提高离子扩散速率,增强脱盐效果,但增强幅度不如提高电压的明显,且在一定范围内对能耗的影响不显著.另外,SEM分析发现,阴膜污染相比阳膜更为严重,且FTiR分析验证了膜表面的污染物质为HPAM.     

Thermoeconomic analysis of a low-temperature multi-effect thermal desalination system coupled with an absorption heat pump

This study presents a thermal and economic performance analysis of a LT-MEE (low-temperature multi-effect evaporation) water desalination system coupled with an LiBr-H₂O ABHP (absorption heat pump). A 60-78% water production increase over a stand-alone LT-MEE run at the same heat source conditions can be obtained owing to the coupling. A detailed thermodynamic sensitivity analysis of the ABHP-MEE is performed. Although ABHP is usually considered to be more efficient than an EHP (ejector heat pump), we also compare the thermal performance of the ABHP-MEE with an integrated EHP-MEE system. The results show that the ABHP has a more favorable thermal performance than the EHP only in certain parameters ranges. The reasons and these parameters ranges are discussed. The economic analysis of the ABHP-MEE shows that the capital cost of the ABHP accounts for a very small part of the water cost, and when designing an ABHP for an existing MEE unit, the parameters selection of an ABHP for lower water cost is consistent with that for better thermal performance. The unit steam cost is an important factor in determining whether the ABHP-MEE or the EHP-MEE is economically favorable, with the influence discussed. Also, a recommended general procedure for economic comparison between ABHP-MEE and EHP-MEE is outlined.     

CDI二维浓度传质模型的建立以及实验验证

电容去离子技术(CDI)作为一种新兴的水处理脱盐技术,因其具有诸多优异性能而受到广泛关注。厘清CDI的传质机制是理论研究的焦点。通过对已有经验模型的分析,从沿流向方向和垂直流向方向两个方面,考虑了电场迁移以及传质扩散等因素,提出了一种新的CDI二维浓度传质模型,对CDI在除盐过程中的离子扩散及浓度分布规律进行模拟探究,根据实际实验结果对该模型进行实验验证及参数修正。结果表明,该二维模型可以较好地模拟CDI除盐过程。将该二维模型利用COMSOL软件进行模拟,观测CDI在除盐过程中的内部浓度变化。并针对存在问题提出合理化建议,为CDI技术的未来发展提供理论支撑。     

Incipient crystallization of sparingly soluble salts on membrane surfaces: The case of dead-end filtration with no agitation

This paper aims at contributing to development of reliable criteria for determining the onset of scaling on desalination membranes. A novel approach is proposed to investigate incipient crystallization on membranes through modeling and RO filtration experiments. The evolution of membrane surface concentration of rejected ionic species (e.g. Ca²⁺, CO₃²⁻) is theoretically determined, and coupled with a detailed kinetic model for nucleation and growth of particles on the membrane. Model results contribute to our understanding of this problem and are in general accord with experimental data on membrane surface crystal density and mean size. Experimental data and model results show that incipient crystallization on RO membrane surfaces, when the bulk supersaturation ratio is maintained near its critical value (S ~ 1), is controlled by fluid permeation, and that the “induction time” may be insignificant under typical RO conditions. This work also suggests that the ability to determine the onset of crystallization on membranes is dependent on the combined sensitivity and adequate spatial resolution of the experimental technique employed, which explains the significant uncertainty associated with the reported in literature “induction period” data of different origin. Directions for future research are discussed.     

Development of a Measuring Method for the Determination of Bisulfite and Sulfite in Seawater

In conventional reverse osmosis processes for seawater desalination, a disinfection of the process stream with chlorine compounds is carried out for antifouling. After disinfection the reduction agent Na₂S₂O₅ is used for the removal of residual chlorine in a strongly overstoichiometric way in order to protect the membranes from oxidational damages. To save chemicals a controlled dosing of Na₂S₂O₅ based on a reliable concentration measurement is desirable. Therefore, a measuring method for the determination of the sulfur(IV) components bisulfite and sulfite in seawater is developed based on the combination of UV spectroscopy and a PLS regression method. Experimental results as well as the development of the regression model for sulfur species in ultrapure and seawater is described.     

Assessment of localized corrosion in carbon steel tube-grade AISI 1045 used in output oil–gas separator vessel of desalination unit in oil refinery industry

In this research, we aimed to investigate the level of damage occurred in the steel tube material grade CK45 (AISI 1045) after a short period of service in an output desalination unit of an oil refinery industry. Visual examinations revealed that the material of the failed tube had significant thickness reduction and also localized corrosion damage. Energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction spectrum show that the corrosion products mostly consist of oxygen as the main element and slightly sulfur. Metallographic observations on the failed sample show that the observed pinholes were initiated on the inner surface of the tube sample where the surface was exposed to a possible mixed corrosive gas of H₂S, CO₂, and naphthenic acid. It is assumed that a severe thickness reduction has been initially taken place from the inner surface of the tube, and consequently the condensation of byproducts led to development of a localized corrosion and formation of pinholes due to flow stream of corrosive exhausted gases in output oil–gas separator vessel of the desalination unite. Presence of metallic elements in the EDS analysis such as calcium, magnesium, potassium, aluminum, manganese, silica, and zinc confirmed the possibility of condensation of corrosive compounds on the inner surface of the carbon steel tube grade CK45 in output oil–gas separator vessel of desalination unit. Microhardness measurements confirm that the steel tube has no hardness change in its core and outer surface. However, slight reduction in hardness is noticed near the inner surface of the tube sample which can be attributed to the presence of the pinholes. Electrochemical corrosion studies were carried out in the corrosive media filled up with a NACE ID 182 solution. Electrochemical investigations revealed that the corrosion products formed are typically porous which cannot provide a protective layer on the surface of the steel tube sample. Finally, recommendations mainly include application of protective coatings on the inner surface of the tube sample, and/or substitution of more resistive alloys with lower susceptibility to corrosive environments. Moreover, operational conditions such as temperature, water to oil ration and addition of any emulsifiers should be precisely controlled in order to decline any unpredicted fluctuations in output desalination unit’s products.     

Performance evaluation of a two-stage silica gel + water adsorption based cooling-cum-desalination system

The first objective of this paper is to show that a single-stage adsorption based cooling-cum-desalination system cannot be used if air cooled heat rejection is used under tropical conditions. This objective is achieved by operating a silica gel + water adsorption chiller first in a single-stage mode and then in a 2-stage mode with 2 beds/stage in each case. The second objective is to improve upon the simulation results obtained earlier by way of empirically describing the thermal wave phenomena during switching of operation of beds between adsorption and desorption and vice versa. Performance indicators, namely, cooling capacity, coefficient of performance and desalinated water output are extracted for various evaporator pressures and half cycle times. The improved simulation model is found to interpret experimental results more closely than the earlier one. Reasons for decline in performance indicators between theoretical and actual scenarios are appraised.     

一种新型海洋温差能海水淡化装置

水源与能源是现代社会发展必不可少的两种重要资源.地球上最充足的水资源是海水,海水淡化技术已是解决全球淡水资源危机的重要途径,而在能源日趋紧张的将来,开发利用新能源将倍加受人瞩目.介绍了海洋温差能的发展及主要海水淡化技术,提出了一种利用可再生能源——海洋温差能进行海水淡化的新型海水淡化装置,给出了海水淡化系统的系统图.     

热法海水淡化阻垢及清洗技术研究现状

换热装置的结垢是热法海水淡化技术面临和必须解决的主要问题之一.介绍了热法海水淡化过程中的主要结垢物质,阐述了结垢对于海水淡化装置的危害,总结了目前防止结垢的方法及清洗技术,提出了热法海水淡化阻垢和清洗技术研究应注意的问题.