The object of this invention is the fluid distributor of a membrane distiller, comprised of a batten at the upper end of a bag-like distilling element made of membrane material, the batten comprising parallel feeding channels for distributing vaporizable liquid transversally on the outer surface of the element.

The membrane distiller is a device comprised of flat bag-like elements placed against each other and made of thin membrane material such as plastic membrane. The heat transfer is carried out inside the elements from condensing steam through the membrane to the vaporizable liquid running along the outer surfaces of the elements. The heating steam is steam which is generated on the outer surfaces of the elements and fed inside the elements through a compressor to be condensed into the distillate obtained as the end product of the process.

A typical use of a membrane distiller has been the production of fresh water from sea water. In addition, it has been recently applied to evaporation treatments of suspensions containing solid matter.

Publication print Fl 86961 discloses a distillation element of a membrane distiller comprising a honeycomb-structured end batten at its upper end, the feeding of vaporizable liquid to the outer surfaces of the element being carried out from the end batten. The batten is provided with parallel inclined feeding channels starting from one end thereof, the feeding channels being in contact with a fluid container on the side of the elements and distributing the vaporizable liquid along the whole width of the element surface. In addition to these fluid feeding channels, the battens also contain steam channels for the steam pressurized by the compressor and entering the elements.

In parallel fluid feeding channels of the batten formed of

honeycomb board according to the above-mentioned known solution which are of the same width but of different lengths wit respect to each other, pressure loss is increased with th length of the channels when moving from the side of the elemen on the side of said fluid container towards the opposite side o the element. This results in that the distributing of liquid i the transversal direction of the element is uneven while th first-mentioned side, where the liquid channels are shorter receives more liquid than the opposite side of the element, th liquid channels leading to the opposite side being longer. I addition, it has been proven that when evaporating liqui suspensions containing solids, parallel feeding channel starting from the container are blocked very easily.

The purpose of this invention is to form a batten-like liqui distributor of a membrane distiller, containing parallel feedin channels, in which said drawbacks of known solutions ar avoided. The invention is characterized in that the batte situated at the upper end of the distillation element contain the transversal main channel of the element, the paralle feeding channels leading to the surface of the element branchin from the main channel.

In the solution according to the invention the main channel ca be formed essentially wider than the feeding channels o approximately the same length branching from it, whereby th main channel distributes liquid evenly to the feeding channels, the liquid spreading out on the surface of the element as a essentially even transversal front. It has been further notice that a turbulence generated in the main channel can be used t prevent blocking of the feeding channels, making the solutio especially suitable for the evaporation treatment of liqui suspensions containing solid particles.

According to a particularly advantageous embodiment of th invention, the main channel is led through the batten so that i distributes part of the liquid flow to the feeding channel while the rest exits through the outlet of the main channel. When treating liquid suspensions containing solids, th

turbulence generated by the liquid flow of the main channel ha been proven to keep the solid particles mainly in the flow o the main channel where they end up in the outlet of the channe without getting to the membrane surfaces of the distillatio elements through the feeding channels. Mainly only the liqui phase is separated in the feeding channels and on the surfaces of the elements. Another advantage in addition to the feedin channels remaining unblocked is that the need to clean th elements is decreased.

It furthers the above if the main channel is essentially evenly wide and slighty inclined downwards and the feeding channels are branched diagonally backwards from the main channel.

Regarding the even distribution of the vaporizable liquid, it is preferred to construct the batten forming the liquid distributor so that it comprises two main channels situating in different halves of the element, and that the feeding channels branching from each main channel are orientated towards the vertical centre line of the element. Thus the inlets and outlets of the main channels can be situated in the opposite ends of the batten, while each main channel is deflected by a bend of about 180° near the centre line of the element, whereby the feeding channels are branched from the main channel in the portion between said bend and the outlet of the main channel. The flow in the main channel can effectively cause turbulence effectively with the aid of the bend situated in the main channel before the branching points of the feeding channels. The purpose of the orientation of the feeding channels is to ensure that no dead space without liquid remains in the middle of the element.

It is preferable to connect the liquid distributor according to the invention to the bag-like distillation element as an integral end batten. The batten can also comprise, in a manner known per se, steam channels leading inside the element. On the other hand, it is possible for the batten-like liquid distributor according to the invention to form, in the membrane distiller, an element separate of the bag-like distillation elements.

Another object of the invention is the use of the membrane distiller provided with the above-described liquid distributors according to the invention in evaporation treatment of liquid suspensions containing solid particles, especially fiber suspensions such as the waste liquor from pulping. We refer to Claims 9 and 10 with respect to these applications of use.

The invention is described in the following in more detail with the aid of an example with reference to the appended drawing in which:

Fig. 1 shows the upper end of the bag-like distillation element of the membrane distiller with its batten serving as the liquid distributor, as viewed from the front, and

Fig. 2 shows the upper ends of two adjacent distillation elements with their liquid distributing battens, as section II-

II of Fig. 1.

Distillation elements 1 according to the drawing are included in the membrane distiller which can comprise a large number of mutually similar elements placed against one another according to Fig. 2. Each element 1 comprises a bag formed by two membrane layers 4 joined to each other using spot welds 3 or the like and joined together by edges 2 thereof, and end batten 5 transversal to the element and situated at the upper end of the element, serving as the liquid distributor. Batten 5 is intended to feed, onto membrane surface 4 forming the outer surface of the element, the liquid which is evaporated by the effect of the heat transfer from the condensing steam fed inside the element between the membrane layers. The steam formed on membrane surfaces 4 of the elements is used as heating steam and recycled inside the elements through a compressor (not shown).

End batten 5 of the element serving as the liquid distributor contains sets of channels in the left and right halves of the element which are mirror-images of each other according to Fig. 1. Each set of channels comprises wider main channel 6 whose inlet and outlet 7, 8 are situated at the end 9 of the batten, the main channel being deflected by bend 10 of about 180° in the vicinity of the vertical centre line (dashed line 11 in Fig. 1)

of the element. Main channel 6 is evenly wide and slightl downwards inclined between bend 10 and outlet 8, and in thi span a number of feeding channels 12 leading to membrane surfac 4 of the element are branched from it in a comb-like manner, th feeding channels being of the same mutual length and orientate diagonally backwards from the main channel towards said centr line 11 of the element. Fig. 1 shows the flowing of vaporizabl fiber suspension 13 in the left-hand channels, while the right hand channels are only provided with arrows illustrating th flowing.

In practice, the same liquid suspension is naturally fed to th membrane surface of the element from both sets of channels.

The purpose of liquid distributor 5 shown in the drawing is t provide as even as possible distribution of vaporizable liqui on membrane surface 4 of the element. Another purpose is t enable the evaporation treatment of liquid suspensions such a fiber suspension 13 containing solid particles, utilizing th turbulence caused by the streams in main channels 6, preventin the blocking of feeding channels 12 branching from the mai channel, in accordance with observations.

The illustrated batten-like liquid distributor 5 can be manufactured from plastics, for instance, by tying formed pieces 14 limiting main channels 6 and feeding channels 12 between two opposite plastic sheets 15 (cf. Fig. 2). It is also possible to connect the steam channels leading inside elements 1 to batten¬ like liquid distributor 5, the steam channels not being shown in the drawing being unessential to the invention. It is further possible to include, in the liquid distributor, common or separate sets of liquid channels which feed liquid to both membrane surfaces 4 of the same element l. In the solution according to Fig. 2 each liquid distributor 5 feeds liquid to opposite membrane surfaces 4 of two adjacent elements 1. Liquid distributors 5 of adjacent elements are drawn at a small distance from each other in Fig. 2 for the sake of clarity, but in practice they are pressed against one another during the operation of the distiller.

It is clear to those skilled in the art that differe applications of the invention are not limited to the abov described example but can vary within the appended Claims.