NL9500202A - Method and apparatus for treating a medium - Google Patents

Abstract

Method for treating a medium, said medium being passed successively through a first duct in a first heat exchanger, through a second heat exchanger and then through a second duct in the said first heat exchanger, the said first and second ducts of the first heat exchanger being separated from one another and being in a heat-exchanging relationship with one another, care being taken to ensure that one or more constituents from the medium escape selectively through the respective duct wall from the first or second duct, to be collected in a third duct in said first heat exchanger, said third duct being separated from said first and second duct.

Description

Method and device for treating a medium.

The invention relates to a treatment of a medium, such as a gas or a liquid, with the aid of heat exchangers, heat supply and separating membrane technology. In particular, the invention relates to the preparation of drinking water, for example from sea water, other because water, or other contaminated water, is unsuitable for humans, animals or plants, due to too high a content of minerals dissolved therein and other components. However, the invention is not exclusive to drinking water preparation. By the term "membrane separation technology" is meant herein any way that allows one or more components from a medium flow through the channel wall to escape from that medium flow. Furthermore, the invention is, however not exclusively, aimed at the direct use of solar energy (solar heat) in the treatment of the medium.

By Elle and Ripperger in "Transmembrane destination (TMD), Experimental result in different fields of application", Conf. Engineering of Membrane Processes II; Environmental Applications, April 26-28, 1994, Lucca, Italy, describes the use of direct heat solar membrane distillation to concentrate sugar palm juice and thereby produce distilled water. A solar panel has been proposed for heating the sugar palm juice and river water is used for cooling. A transmembrane distillation TMD (module) has been described with a gap between the flat membrane and a heat exchanger, in which the distillate is discharged through the condenser either by a vacuum pump or by air passing along the membrane. The energy consumption is not optimized.

In "Solar heated membrane distillation", G.L. Morrison et al., Sch. Mech. Manufact. Eng., Univ. New South Wales, Sydney, Australia Sol. World Congr., Proc. Bienn. Congr. Int. Sol. Energy Soc. (1992), Meeting Date 1991, Volume 2, Issue Pt. 2, 2329-34, Pergamon, Oxford, UK., Biz. 2329 to 2333, desalination equipment using solar heat directly is described. Seawater heated in a solar collector is passed through a bundle of hollow fibers with which the membrane distillation is carried out. This bundle of hollow fibers acts as a non-selective, porous membrane. The choice of material for the membrane is such that the pores of the membrane are not wetted by the seawater, but are filled with air and / or vapor. By evaporating, the water can escape from the seawater flow through the fiber wall. Cooler (drinking) water is allowed to flow on the outside of the hollow fibers from the bundle, so that the water evaporated from the hollow fibers condenses on the outside of the hollow fibers and is carried along with the (drinking) water flowing past.

The present invention contemplates, a medium treatment which, from the viewpoint of energy management (e.g. heat loss), simplicity of construction of the installation to be used, speed of start-up of the installation (in particular with direct use of solar energy which is only available during the day) and simple possibility of balancing the product flows depending on the medium to be treated.

According to the invention, a method according to the combination of measures included in claim 1 is proposed for this purpose, and a device according to the combination of measures according to claim 6.

With the present invention, the medium to be treated itself, flowing through the first channel in the first heat exchanger, functions as a condenser. At the same time, the medium flowing through the first channel in the first heat exchanger is preheated. After final heating in the second heat exchanger to the temperature desired for the "membrane distillation", the medium is led through the second channel again through the first heat exchanger, with the excretion of one or more components which heat using the first channel as a condenser in the first heat exchanger. and with a third channel outside the first and second channels through the first heat exchanger and passed therefrom.

The invention can be applied, for example, by means of parallel or substantially parallel first, second and third channels in the first heat exchanger. For example, said first, second and third channels may be so arranged that they surround one another, the inner channel being the second channel, the outer channel being the first channel and the third channel therebetween.

According to an advantageous embodiment of the invention, the first and second channels in the first heat exchanger comprise a first hollow fiber assembly and a second hollow fiber assembly, respectively. The hollow fibers of the first assembly define the "heat exchanger portion" or "condenser portion" of the first heat exchanger. The fibers of the second assembly form the "membrane distillation portion" of the first heat exchanger. The ratio of the number of fibers of the first assembly to the number of fibers of the second assembly can be adjusted depending on the desired degree of heat exchange and membrane separation. Wall thicknesses, diameters and material types for the fibers can also be adapted to the intended use and intended setting. The fibers can be made of, for example, plastics such as polypropylene or Teflon, but also of metal (in particular the fibers for the first assembly). It is possible, for example, to let air or another gas flow through the third channel, for instance in a closed circuit, and the condensate droplets formed on the (condenser) fibers of the first assembly obtained from the fibers of the (membrane distillate) of the second assembly entrains evading constituents. In this way it is possible to keep the heat losses as small as possible while a very short heating time can be achieved.

As is more particularly apparent from the figure description below of advantageous embodiments, the installation requires a particularly simple and uncomplicated construction. In connection with desalination of sea water to drinking water, the installation can therefore be designed, for example, as a floating installation, to set up floating off-shore. The pipes for the transport of seawater can thus be kept as short as possible, so that the lowest possible pump capacity can be selected. The desalinated (drinking) water produced on site by the floating installation can be pumped to land via a pipeline system. Compared to pumping seawater to land, to desalinate it on land and then return the residue to the sea, the proposed method requires considerably less pumping energy.

The sun can be used as a heat source for the second heat exchanger, for which purpose the second heat exchanger is designed as a solar collector.

Further advantages and features of the invention are apparent from the subclaims as well as from the following description of advantageous embodiments of the invention, with reference to the appended drawing. Hereby shows:

Figure 1 schematically shows a side view of a first embodiment according to the present invention; and

Figure 2 schematically in perspective a second embodiment according to the invention.

Figure 1 shows a first heat exchanger 1 and a second heat exchanger 2. The first heat exchanger 1 is composed of heat exchanger modules 3, 4. The basic embodiment for each module 3, 4 is described, for example, in the European patent application 919022830 in the name of the applicant, in particular figure 1. Each module 3, 4 consists of a cross section, preferably symmetrical (square, round, polygonal) tube part. The tube wall defines separate collection chambers for the medium. Two diametrically opposed chambers are in medium communication with each other via hollow fibers. Those hollow fibers bridge the tube cavity. A further chamber is provided separate from the hollow fibers and the aforementioned chambers. Thus, each module 3, 4 is capable of conducting three medium flows; one medium flow through the hollow fibers and the two chambers communicated therewith, a second medium flow through the further chamber and a third medium flow through the tube cavity to rinse the hollow fibers. In Figure 1, the modules 3, 4 are arranged one after the other in alternation such that the medium flow B at each module 3 flows through the hollow fibers in each case, in order to flow at each module 4 exclusively through the further chamber on the pipe wall. The reverse applies to the medium flow C. The medium flow A always flows through the tube cavity and washes the fibers.

The operation of the installation shown in figure 1 is as follows: sea water is first guided through the first heat exchanger 1 according to the course of medium flow B. This relatively cold sea water flows through the fibers of the modules 3, which fibers determine the first channels of the first heat exchanger 1. This sea water then flows through the second heat exchanger 2, which is designed as a solar collector. The construction of a solar collector for heating water or other liquids or gases is generally known to the skilled person and requires no further explanation. The sea water heated in the solar collector 2 then flows again as the medium flow C through the first heat exchanger 1. Thereby this warm sea water C flows through the fibers of the modules 4, which determine the second channels of the first heat exchanger 1. Water evaporates through the fiber walls of the fibers of the modules 4. The water vapor is entrained with the gas stream A, flowing through the tube cavity which defines the third channel of the first heat exchanger 1, and condenses on the relatively cold fibers of the modules 3, through which relatively cold sea water flows according to the medium flow B. This condensate is then conducted in the form of droplets or flowing along the wall from the first heat exchanger 1 to, for example, a collecting device (not shown). Because the water vapor condenses on the fibers of the modules 3, the relatively cool seawater thereby preheated is at the same time. In this way, as little heat as possible collected with the solar collector 2 is lost. The gas flow λ can optionally be replaced by a liquid flow, for instance a flow of condensate led in recirculation. However, the use of a gas stream, in particular an air stream, is preferable from the viewpoint of heat management. Said gas flow A is further preferably guided in a closed cycle, so that any heat from the relatively warm fibers of the modules 4, which may be absorbed by the gas flow A, benefits as much as possible to the preheating of the seawater which is passed through the hollow fibers of the modules 3. flows. Optionally, the gas flow λ can be replaced by stationary gas, in particular air, whereby internal temperature differences in the third channel may lead to free convection flows of the gas, or the air.

Figure 2 shows a variant for the first heat exchanger 1. As shown, this first heat exchanger 1 is designed as a pipe with a circular diameter. A first supply chamber 5 and a second supply chamber 6 are formed in the pipe wall. Diametrically opposite the first supply chamber 5 is a first discharge chamber 7. Diametrically opposite the second supply chamber 6 is a second discharge chamber 8 in the pipe wall. First hollow fibers 9 medium communicate the first feed chamber 5 with the first discharge chamber 7. Second hollow fibers 10 medium communicate the second feed chamber 6 with the second discharge chamber 8. The first fibers 9 and the second fibers 10 are alternately layered behind as shown. viewed in the longitudinal direction of the first heat exchanger 1. Sea water is introduced into the first heat exchanger 1 via the first supply chamber 5 according to arrow B. This sea water is then evenly distributed over the first fibers 11 to the first discharge chamber 7. The seawater flows from said first discharge chamber 7, in a manner not shown in detail, to the second heat exchanger 2 (see figure 1). Coming from the second heat exchanger 2, the heated sea water flows into the second supply chamber 6. Subsequently, this warm seawater, evenly distributed over the second hollow fibers 10, flows into the second discharge chamber 8, from which it is discharged as a residue according to the arrow C, for instance for discharge into the sea. The gas flow according to the arrow A flows through both the first fibers 9 and the second fibers 10 and transfers the water vapor formed at the second fibers 10 to the first fibers 9 for condensation.

Of course, the first heat exchanger 1 shown in Figure 2 is provided at its end ends with suitable connecting pieces and seals for the chambers 5, 6, 7 and 8 and the tube cavity 11, which are however omitted in the drawing.

Naturally, other variants for the first heat exchanger 1 are also possible. For instance, in deviation from the embodiments shown in figures 1 and 2, an embodiment can be chosen in which the flow direction of the medium flow through the first heat exchanger 1, prior to passage of the second heat exchanger 2, is aligned with that of the medium flow through the first heat exchanger 1 after passage of the second heat exchanger 2. In addition, instead of hollow fibers 9, 10 oriented transversely of the longitudinal direction of the tube cavity 11, it is possible to opt for, for example, three tube parts which are spaced apart (concentrically). The hollow fibers of the first and / or second channel can also run parallel or substantially parallel to the third channel.

In a preferred embodiment, it is important that a medium flow is first passed through a first heat exchanger, then it is heated to the desired process temperature in a second heat exchanger, then it is again passed through the first heat exchanger such that in that first heat exchanger dust is discharged from the one medium flow to the other medium flow occurs as well as heat exchange in the same sense.

Claims (10)

A method for treating a medium, wherein said medium is passed successively through a first channel in a first heat exchanger, through a second heat exchanger and then through a second channel in the said first heat exchanger, with the said first and second channels of the first heat exchanger separated from each other and in heat exchanging relationship with each other, and one or more constituents from the medium are selectively escaped from the first or second channel through the respective channel wall, to be collected in a third channel in that first heat exchanger, which third channel is separated from the intended first and second channel. The method of claim 1, wherein said first and second channels pass through said third channel. The method of claim 2, wherein said first and second channels comprise respective first and second hollow fiber assemblies, and the hollow fibers of said first and second assemblies run transverse to the longitudinal direction of said third channel. A method according to any one of the preceding claims, wherein the second heat exchanger is a solar collector. A method according to any one of the preceding claims, wherein the medium is sea water which is heated sufficiently in the second heat exchanger so that the second channel through its channel wall is able to discharge water vapor which subsequently condenses on the outside of the first channel and desalinates (drinking) water in the third channel is collected and removed for further use. 6. Medium treatment device provided with a first and a second heat exchanger, which first heat exchanger has first and second channels for passing the medium through it, which first and second channels are in medium communication with the inlet and outlet of the second heat exchanger and which first and second channels in the first heat exchanger are separated from each other and are in heat-exchanging relationship, such that medium flowing through the first channel enters the second channel via the second heat exchanger, and the first and second channels are designed such that one or more components from the medium to be passed through said first and second channels can selectively pass through the channel wall of said first or second channel, for which purpose said channel wall is designed as a membrane filter, and which first heat exchanger further has a third channel, separated from the first and second channel and suitable for passing through the channel wall from the first or tw the channel to catch escaped components. The device of claim 6, wherein said first and second channels pass through the third channel. The device of claim 7, wherein said first and second channels are formed by respective first and second hollow fiber assemblies which pass transverse to the longitudinal direction of the third channel and terminate with their respective ends in respective Collection Chambers for delivery to the first supplying or removing the heat exchanger and distributing the medium flow over the respective hollow fiber assembly, which collection chambers are arranged to separate the medium flow through the first channel from the medium flow through the second channel in the first heat exchanger. The device of claim 8, wherein the collection chambers are arranged to the side of the third channel. Device as claimed in any of the foregoing claims 6-9, wherein the second heat exchanger is a solar collector.