Hybrid membrane systems process flow

Figure 3.42 A typical boiler water treatment hybrid membrane system process flow schematic.

The pretreatments, described above, that deliver a particulate-free stream at 38 °C to the amine system provide a ready-made feed for processing via membrane modules. This feed can be used with simple and efficient membranes, new structured sorbents, membrane + structured sorbent hybrid systems or more advanced super H2 selective membranes. These membrane systems can simplify and condense the flow sheet in Figure 7.10, thereby enabling a more compact plant with less piping and associated maintenance concerns. 

For the model validation and the analysis of the heat integration in the hybrid pervaporation distillation process, a laboratory plant has been built at the TU -Berlin and prepared for the connection with the distillation column (see fig. 3). With this plant experiments with a flat PVA-based (Polyvinylalcohol from GKSS) hydrophilic membrane have been done. A heat exchanger has been built within the pervaporation module. The temperature in the heat exchanger has been necessary to avoid the temperature drop between feed and retentate streams in the pervaporation process. In the process a 2-Propanol/ Water mixture has been separated. The concentration of 2-Propanol in the feed is between 80 and 90 % in weight and the temperature range in the experiments was between 70 and 90°C. The feed flow is turbulent and the system fully insulated to avoid heat looses. The pressure in the permeate side has been kept at 30 mbar and the feed pressure at 1.5 bar. 

A NF/IX water treatment system is very effective in removing virtually aU nitrates from drinking water [6]. In the NF/IX hybrid system, pre-filtered water flows through a NF membrane system, which removes all the multivalent ions and some of the monovalent nitrate ions. The NF permeate is then polished in an anion IX column where the nitrates are exchanged with chloride ions. NF pre-treatment increases the efficiency of the IX process since it removes dissolved organic carbon and divalent ions such as sulphate ions. 

For the study of the process, a set of partial differential model equations for a flat sheet pervaporation membrane with an integrated heat exchanger (see fig.2) has been developed. The temperature dependence of the permeability coefficient is defined like an Arrhenius function [S. Sommer, 2003] and our new developed model of the pervaporation process is based on the model proposed by [Wijmans and Baker, 1993] (see equation 1). With this model the effect of the heat integration can be studied under different operating conditions and module geometry and material using a turbulent flow in the feed. The model has been developed in gPROMS and coupled with the model of the distillation column described by [J.-U Repke, 2006], for the study of the whole hybrid system pervaporation distillation. 

A schematic diagram of the PMR utilizing DCMD is shown in Fig. 21,16. The hybrid system was applied for removal of different dyes from water. The experimental setup was a typical installation for DCMD. The only modification was the incorporation of a UV-A lamp above the feed tank. Thus, the feed tank fulfilled also a role as a photoreactor, in which the photocata-lytic degradation took place. The process was conducted in batch mode. The suspension of a photocatalyst in the treated water was pumped from the feed tank (volume of 3 dm ) using a peristaltic pump through the heater to the capillary PP membrane module. At the same time distillate was pumped through the cooler to the membrane module. The warm feed flowed inside the capillaries, whereas the cold distillate flowed outside the capillaries. Water vapor and volatile compounds present in the warm feed were transferred through the pores of the MD membrane and then condensed/... 

Membranes can also be used to purify a mixmre and attain composition beyond the azeotropic composition. The pervaporation process features a liquid feed, a liquid retentate, and a vapor permeate. While gas-phase membrane processes are essentially isothermal, the phase change in the pervaporation process produces a temperature decrease as the retentate flows through the unit. Since flux rates decrease with decreasing temperature, the conventional pervaporation unit consists of several membrane modules in series with interstage heating. The vapor permeate must be condensed for recovery and recycle, and refrigeration is usually required. Hybrid systems of distillation columns and pervaporation units are frequently used in situations where distillation alone is impossible or very expensive. An important application is the removal of water from the ethanol-water azeotrope. Chapter 14 will discuss the details of design and control of such processes. 

Curdo, S., Calabro, V., lorio, G., Reduction and control of flux decline in cross-flow membrane processes modeled by artifidal neural networks and hybrid systems. Desalination, 2009,236(1-3), 234-243. 

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