Membrane distillation (MD) integrated with a district heating network (DHN) to supply the heat demand has been investigated in a bioethanol production plant (BP). The specific application considered here is ethanol recovery from fermentation off-gas (CO₂) scrubber water, where the main objective of this study was to develop an air gap MD system that is driven by heat from DHN, thereby offloading the steam-driven distillation column. Experiments conducted on an MD laboratory facility combined with data from the bioethanol industry were used to assess the technological and economic feasibility of this integrated MD-DHN-BP system. Comparisons were also made between the distillation column and MD units regarding heat demand and economic savings. Results of the study showed that MD could be a competitive technology for ethanol recovery given that low-grade heat such as from district heating network or waste heat is accessible.

Here, we presented a novel industrial application for membrane distillation (MD) in a pharmaceutical production facility’s wastewater treatment plant (WWTP). Two semi-commercial air gap MD module designs (Xzero and Elixir500) were studied for comparison, with experimental results of product yield and heat demand up-scaled for inclusion in system simulations. District heating was considered to drive the 3 m3/h capacity MD process, with heat recovery employed in various process streams and for heating purposes in offices. The selected configurations show a high degree of thermal integration with an increase of yearly district heating purchases of 2-13%. Economic assessments of the full-scale MD system indicate that unit costs of purification would be $1.3/m3 and $7/m3 for Elixier500 and Xzero MD modules respectively. Module heat losses should be considered in the future design of MD systems since the heat demand contributed to up to 77% of the specific costs.

Water purification is an important separation process that can be found in various industrial applications. Process water quality varies between applications, but the trend of increased reuse or recycling of process streams in combination with stricter emission regulations lead to additional needs for water purification in the future. Membrane technology such as reverse osmosis, ultrafiltration and nanofiltration are often employed. However even if these technologies are mature there is still a need to explore alternatives that can lead to more robust performance, lower energy consumption, reduced environmental effects, and lower costs. Membrane Distillation (MD) is such an alternative. The process is heat driven and can be paired up with district heating when a high degree of purity is desired.The purpose of this project is to develop MD’s role within a district heating perspective. The following three sub-goals have been investigated:Sub-goal

Sub-goal 1 considered a mapping of water purification in relevant industrial processes. Various possible application areas were identified, including treatment of flue gas condensate, ultrapure water, processes in the food industry, reconcentrating, desalination, and others. Three case studies with relevance to MD driven by district heating were identified for further analysis.Sub-goal 2 encompassed system analyses and optimization studies for the particular case studies:

• Wastewater treatment at Astra Zeneca in Södertälje. It is theoretically possible to place MD between the district heating network and end users in order to achieve advanced treatment for a smaller wastewater line. The district heating demand would increase by about 7-13%, and costs (excluding retrofitting) are estimated to increase by 60% compared to the available treatment method (activated carbon).• Reconcentrating of ethanol from CO2 scubber water at Agroetanol inNorrköping. The concept involves off-loading of the distillation column via introduction of MD technology. Exchange between steam (distillation column) and district heating (MD system) is roughly balanced which implies significant cost savings potential with MD.• Water purification and reconcentrating at Arla Foods, Kalmar facility. A poor thermal integration yields a high district heating demand for MD in this particular application.For sub-goal 3 experimental investigations were conducted for two MD prototypes. A newer generation of MD prototype showed a marked reduction in heat losses with increase in yield, which in turn leads to lower energy demand.

In this study, membrane distillation integrated with district heating network has been investigated for applications in a bioethanol production plant. The specific application considered was recovery of ethanol from CO2 scrubber water, where the main objective of this study was to develop an air gap membrane distillation system that is driven by heat from district heating network, to offload the distillation column. Experiments on membrane distillation lab unit along with data from the industry were used to assess the technologic and economic feasibilities of this system. Comparisons were also made between the distillation columns and membrane distillation units in terms of heat demand and economic savings. Results of the study showed that MD can be a competitive technology for ethanol concentration depending on availability of low-grade heat like district heating or waste heat. 

In this study, membrane distillation integrated with district heating network has been investigated for applications in a bioethanol production plant. The specific application considered was recovery of ethanol from CO₂ scrubber water, where the main objective of this study was to develop an air gap membrane distillation system that is driven by heat from district heating network, to offload the distillation column. Experiments on membrane distillation lab unit along with data from the industry were used to assess the technologic and economic feasibilities of this system. Comparisons were also made between the distillation columns and membrane distillation units in terms of heat demand and economic savings. Results of the study showed that MD can be a competitive technology for ethanol concentration depending on availability of low-grade heat like district heating or waste heat.

In this study, an air gap membrane distillation (AGMD) system at pilot scale is applied for purification of effluent from a municipal wastewater treatment plant. A district heating network (DHN) is considered as a heat source for the membrane distillation system. Removal performance of pharmaceutical residuals, specific heat demand, and economic assessments were analyzed on the membrane distillation plant. Almost all targeted pharmaceutical compounds were removed to a very high degree, often below the method detection limit. The heat requirement for the MD process could be sufficiently supplied by the low-temperature district heating return line. Specific heat demands for the AGMD ranges from 692 to 875 kWh/m³ without heat recovery and as low as 105 kWh/m³ when heat recovery is possible. Different approaches to integrating the MD within the DHN system were analyzed; the advantages and shortcomings of each are discussed with emphasis on the MD system’s capacity requirement and annual heat demand. The thermoeconomic analyses from this study presented the potential for energy optimization regarding heat recovery and module design improvement of the current MD equipment.

Modifications were implemented on a semi-commercial air-gap membrane distillation prototype to assess experimentally any improvement in its performance. The main changes were in the air-gap domain with focus on reducing the conductive heat transfer losses by reducing the physical support that separates the membrane from the condensation surface. Moreover, several feed channel spacers were tested as well and assessed based on their effect in increasing the mass transfer and imposed pressure drop. Results show that the modifications increased slightly the distillate mass flow rate by 9-11% and reduced the conductive heat losses by 20-24%. Spacer effect was found to be mainly in imposed pressure drop within the tested types.

Water treatment is an important auxiliary process in all thermal cogeneration plants. In this context membrane distillation (MD) is a novel technology that has potential advantages in: the ability to utilize low-grade heat instead of electricity; reduced sensitivity to fluctuations in pH or salt concentrations. This research is a continuation of a previously conducted theoretical study where the performance of MD-based water treatment was explored via laboratory testing, system simulations of thermodynamic performance, and economic evaluations. The current paper, encompassing field trials, contains details of a test rig deployed at Idbacken Cogeneration Facility (Nykoping, Sweden) with a five-module MD unit capable of producing 1-2 m(3)/day purified water. District heating supply line was employed for heating while municipal water was used for cooling; feed stocks include municipal water and flue gas condensate. A long-term performance evaluation including thorough chemical testing of product water quality is presented. (c) 2010 Elsevier B.V. All rights reserved.