Description
BACKGROUND OF THE INVENTION
The invention relates to blanks made from zeolite which adsorb
and desorb an adsorbed substance and a process for making the
same.
Zeolite crystals adsorb liquid and gaseous adsorbed substances
under heat development. The released reaction heat must be
dissipated from the zeolite material during the adsorption and
must again be fed thereto during the desorption (separation of
both substances). The reaction kinetic of the adsorption and
desorption process is limited by a low heat conductivity of
zeolite mass and by high pressure drops of the adsorbed
substance which either flows thereto or therefrom.
The diameter of synthetic zeolite crystals is limited to a few
micrometer. Powder fillings are not suitable for technical
absorbing processes, since the fine zeolite crystals are
subjected to turbulence and are carried out from the reaction
spaces by the flow of the adsorbed substances. A further
processing of the powderlike zeolite products in specific but
expensive granulating processes by adding of binders in
granulate, for example, small balls or cylinder permits the use
of zeolite in drying processes. In these processes moist gases
flow through the granulate fillers and emit the moisture to the
granulate fillers. In this manner the dry gases absorb the
generated reaction heat and cool the granulate. Hot and dry
gases are fed in the subsequent process step for desorption of
the granulate fillers. They transmit the reaction heat to the
granulate and absorb the released moisture. In these so-called
open processes the gases flow around each granulate body. The
total surface of the granulate body is available for the heat
exchange.
Zeolite granulates for the adsorption of steam in adsorption
heat pumps and air conditioners are suggested in a plurality of
patent applications. There the zeolite crystals adsorb steam in
a closed process. Gas flows which could transmit the reaction
heat are not available. The heat must be fed and dissipated from
the outside by specific heat exchangers. The heat can only be
transmitted via the contact faces of the granulate fillers.
Therefore, the heat transmission is not dependent on the
granulate surface but from the number of contact locations of
the granulates among each other and with respect to the heat
exchanger. Hence, the heat conductivity is therefore lower with
fillers than with homogenic substances. The flow resistance is
higher than in comparable flow conduits with smooth surfaces.
The DE No. 3 207 656 A1 suggests zeolite blanks which are
adapted to the heat exchanger surfaces and which are provided
with flow conduits that are most favorably designed for the
adsorbed substance. After only a few desorption cycles the
zeolite blanks detach from the heat exchanger surfaces. Thin
slots are created which limit the heat transfer even more
severely than with granulate fillers. Severely fluctuating
temperature and load gradients generate cracks and slots within
the blanks which additionally lower the heat conductivity.
Broken-off zeolite parts block the flow conduits and prevent the
access of the adsorbed substance to the zeolite.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to increase the
inner heat conductivity and the heat transfer to an adjacent
heat exchanger in blanks made of zeolite and to assure it even
under severely fluctuating temperature and load conditions.
Simultaneously, the flow resistance for the given adsorbed
substances is to be reduced to a minimum.
The object of the invention is solved in that the zeolite mass
is imbedded into a fine meshed metal texture. The metal texture
prevents a bursting and a breaking down of the zeolite blanks
and simultaneously increases the heat conductivity. The low heat
conductivity of the zeolite substance is considerably improved
by the good heat conductivity of the metal structures.
Particularly high adsorption speed can be obtained by a dense
metal texture made from gold, silver, copper, aluminum, etc.,
and by a flat method of construction of the blanks.
In order to assure an unobstructed access for the adsorbed
substances to the zeolite crystals, certain areas within the
blank are not filled with zeolite mass. It is particularly
advantageous when the outer zones of the metal texture are not
covered with zeolite. Thus, a breaking off of small zeolite
pieces and a blocking of the flow conduits can be effectively
prevented.
Particularly fine meshed metal textures retain zeolite powder
which is not solidified with a binder or only solidified to a
lesser degree. Low amounts of binder components are advantageous
for high heat conditions. In one form the binder content is
lower in the inner area of the blank than in the edge zones. The
outer areas which are more exposed to erosion will receive a
higher portion of binder than the less stressed inner areas.
Fine meshed metal structures, like steel wool, metal textures,
metal shavings and metal fleeces are suitable as metal textures.
Particularly advantageous are metallic filter materials, like
RETIMET.RTM. or BEKIPOR.RTM.. These commercial products have
very good heat conductivity and retaining characteristics due to
the dense interlacing structure of these products.
It is contemplated that a breaking off of the blanks from the
heat exchanger surfaces can be prevented by having the metal
texture adhere permanently to the heat exchanger surfaces.
Different heat expansions between the metal texture and the
zeolite crystals are compensated for by the elasticity of the
metal structure.
For making the connections the following techniques are very
useful, sintering, welding, galvanizing and tinning, soldering,
among others. With the assistance of these connecting techniques
one does not only achieve a permanent and good heat conductive
coupling of the metal structure to the heat exchanger surfaces,
but also to the inner interlacing metal structure at the
crossing points of the texture.
A flowable zeolite mixture consisting of zeolite powder, water
and, if need be, binders are fed to the metal texture or the
metal texture is immersed therein for making the blanks.
Encapsulated hollow spaces can be filled by high frequency
shaking on the metal texture. During a careful drying at
temperatures of below 100.degree. C. the superfluous water is
evaporated from the zeolite mixture. The remaining zeolite
crystals connect with the metal texture and the admixed binders
into solid, stable blanks.
The outer areas of the metal structure which are not to be
filled with zeolite mixture are advantageously filled with water
which is subsequently frozen.
The ice melts during the drying process and the water
evaporates. Thus flow conduits are generated for the adsorbed
substances. Since the conduits are filled with metal texture, no
zeolite particles can break off and block the conduits. Flow
conduits within the blanks may be kept free from zeolite in that
the metal texture is removed or displaced from the flow conduits
in a first operating step and that the flow conduits are filled
with adaptable ice pieces which are frozen into the metal
textures in a further processing step. The metal structure which
had been prepared in this manner can be subsequently filled with
the zeolite mixture. After the melting of the ice pieces, the
flow conduits are free for the flow of the adsorptive substance.
Flow conduits are generated in a further process in that the
metal structure is deformed after filling with flowable zeolite
mixture. For this purpose, pressing or roller tools are
advantageously suitable which press the flow conduits into the
still soft blank. Compressions are generated in the metal
structure with this process in the transition zones from the
blank to the flow conduits. The wall of the flow conduits become
so strong that an additional subsequent lining of the flow
conduits with a metal texture may be partially eliminated. The
pressing tool remains in the blank until the blank is partially
solidified, so that the conduits cannot fill with the zeolite
mixture any longer. The solidification process can be
accelerated by heating the pressing tool. The water in the
zeolite mixture evaporates when contacted by the hot pressing
tool. A thin layer of solidified zeolite is generated. A
penetration of still flowable zeolite mixture is prevented after
removal of the pressing tool.
BRIEF DESCRIPTION OF THE DRAWING
One exemplified embodiment of the invention is illustrated in
the drawing and is described in the following in more detail. In
the drawings:
FIG. 1 shows a heat exchanger with blanks made of
zeolite (1) between the heat exchanger plates (2); and
FIG. 2 shows a blank made of zeolite (1) on a heat
exchanger plate (2) with impressed flow conduits.
DETAILED DESCRIPTION OF THE DRAWING
A section of a laminated heat exchanger is illustrated in FIG.
1. The blanks of zeolite 1 are mounted between the heat
exchanger plates 2. The metal textures 3 are connected in a good
heat conducting manner with the heat exchanger plates 2 by means
of a resistance welding process. The blanks 1 have areas which
are not filled with zeolite. These flow conduits 4 permit the
adsorbed substances a rapid access to the zeolite crystals.
An exemplified embodiment of a blank made from zeolite 1 is
illustrated in FIG. 2 being mounted on a heat exchanger plate 2.
The outer areas of the metal structure 4 are kept free from
zeolite by a lining with ice. The flow conduits 5 on the upper
side of the blank were produced by the pressing tools. The
conduits are lined with a metal texture.
Thus, the several aforementioned objects and advantages are
most effectively attained. Although several somewhat preferred
embodiments have been disclosed and described in detail herein,
it should be understood that this invention is in no sense
limited thereby and its scope is to be determined by that of the
appended claims.
