Membrane distillation: Solar and waste heat driven demonstration plants for desalination

The development of small to medium size, autonomous and robust desalination units is needed to establish an independent water supply in remote areas. This is the motivation for research on alternative desalination processes. Membrane distillation (MD) seems to meet the specific requirements very well. This work is focused on experimental studies on full scale demonstration systems, utilizing a parallel multi MD-module setup. Three different plant concepts are introduced, one of them is waste heat driven and two of them are powered by solar thermal collectors. Design parameters and system design are presented. After the analysis of plant operation a comparison among the plants as well as a comparison with laboratory experiments is carried out and discussed. Impact of different feed flow rates, salinities, operating hours and process temperatures are taken into consideration and put into relation. GOR values and specific thermal heat demand are derived and compared. Energy balances of all three plants are given, uncovering heat losses and identifying room for improvemen

Economic Benefits of Waste Pickling Solution Valorization

An integrated hybrid membrane process, composed of a diffusion dialysis (DD), a membrane distillation (MD) and a reactive precipitation unit (CSTR), is proposed as a promising solution for the valorization and onsite recycling of pickling waste streams. An economic analysis was performed aiming to demonstrate the feasibility of the developed process with a NPV of about EUR 40,000 and a DPBP of 4 years. The investment and operating costs, as well as the avoided costs and the benefits for the company operating the plant, were analyzed with an extensive cost tracking exercise and through face-to-face contact with manufacturers and sector leaders. A mathematical model was implemented using the gPROMS modelling platform. It is able to simulate steady state operations and run optimization analysis of the process performance. The impact of key operating and design parameters, such as the set-point bath concentration and the DD and MD membrane areas, respectively, was investigated and the optimal arrangement was identified. Finally, operating variables and design parameters were optimized simultaneously in a nonlinear framework as a tradeoff between profitability and environmental impact. We show how the integration of new technologies into the traditional pickling industry could provide a significant benefit for the issues of process sustainability, which are currently pressing

Brines from industrial water recycling: New ways to resource recovery

Stricter environmental regulation policies and freshwater as an increasingly valuable resource have led to global growth of zero liquid discharge (ZLD) processes in recent years. During this development, in addition to water, the recovery of recyclable materials, e.g. salts, from industrial wastewater and brines is considered more frequently. Within the framework of the HighCon research project, the subject of this study, a new ZLD process with the goal of pure single-salt recovery from industrial wastewater has been developed and investigated in a demonstrational setup at an industrial site. With regard to pure salts recovery, separating organic components is of great importance during the treatment of the concentrate arising from used water recycling. The removal of COD and of ions responsible for scaling worked very well using nanofiltration. The nanofiltration permeate containing the monovalent ions was pre-concentrated using electrodialysis and membrane distillation before selective crystallization for single-salt recovery was performed. An example economic case study for the newly developed ZLD process - based on demonstration results and considering optimization measures for a full-scale design - indicates that the costs are equal to those of a conventional ZLD process, which, however, does not provide inter alia the aforementioned benefit of single-salt recovery

An integrated approach for HCl and metals recovery from waste pickling solutions: pilot plant design and operations

Continuous regeneration of industrial pickling solutions and recovery of valuable materials are implemented in a pilot-scale plant including diffusion dialysis, membrane distillation and reactive precipitation units. The main results of the preliminary assessment of on site operation are presented. Different hydrochloric acid concentration and metals composition were investigated and the performance of the system were analysed in terms of quality of recovered compounds, energy efficiency and environmental footprint

Methodical design and operation of membrane distillation plants for desalination

The operation of pre-industrial membrane distillation (MD) units is of great importance in order to implement this new technology. The systematic development from module to plant design for MD is conducted in an industrial research-cooperation. The consequent up-scaling from a lab plant at Hamburg University of Technology (TUHH) for MD module evaluation to a pre-industrial plant is presented. Permeate gap MD (PGMD) and Direct Contact MD (DCMD) spiral wound modules with different channel lengths have been used in this study to evaluate the most suitable module configuration and design. It has been decided to go along with DCMD modules with a relatively short channel length. A pilot plant for on land testing has been built and operated for 9 months before constructing the pre-industrial unit. In the pre-industrial plant waste heat was used and a heat recovery and recycle concept was implemented and tested successfully. It has been proven that long-term operation with real seawater is possible without significant performance decline. Besides operational data also MD plant design specifics will be discussed. The importance of ambient pressure conditions for the MD modules was determined. In addition, the possibility of piping system deaeration is discussed

Experimental parametric study of membrane distillation unit using solar energy

Solar distillation is a promising method for the supply of freshwater to rural communities because water is a vital factor for the survival of humans. Therefore potable water demand is increasing continuously because of the industrial, population and, fast agricultural applications. Nowadays, different techniques for water purification have been created to provide freshwater from salty and polluted water such as solar distillation method to distill brackish/saline water. This work presents an experimental study of the solar membrane distillation unit which is coupled with direct contact membrane (DCMD) which located at Kairouan University. The system is installed as part of a cooperation project research and development between Tunisian Electromechanical Systems Laboratory and German Institute for Solar Energy Systems entitled: Solar driven membrane distillation for resource efficient desalination in remote areas. For the heating of the hot feed water stream, a heat exchanger is included which can be operated with any external heat supply between 60 and 80 °C. For the cooling of the cold feed water stream, no heat exchanger is included. The cooling can be provided over the intake of cold feed water. The effect of solar irradiation and all temperature on the journal productivity of the unit has been presented

Autonomous solar powered membrane distillation systems: State of the art

Being a basic element for the every existence of any form of life on earth, water is one of the most abundant resources on earth, covering three-fourth of the planet’s surface. However, there is a shortage of freshwater in many areas worldwide. Desalination seems to be the most suitable solution. Major conventional desalination processes, such as distillation and reverse osmosis, consume a large amount of energy derived from oil and natural gas as heat and electricity, which is responsible for harmful CO2 emission. Solar desalination has emerged as a promising renewable energy-powered technology for producing freshwater. Solar membrane distillation (MD) is the best option in decentralized regions with scattered population and lack of infrastructures jointly with hard climate conditions make it difficult or at least not cost-effective to scale down bigger desalination technologies, such as RO or MSF, designed for very big water productions. Moreover, MD compared to conventional thermal desalination is less demanding regarding vapor space and building material’s quality leading to potential lower construction costs. The aim of this paper is to present the state-of-the-art review of developments in solar MD technology. In this review, membrane configurations, module design, and recent applications of this technology were discussed in detail