The present invention relates to a device and process for dehydration.

Processes of dehydration are generally employed for concentration of solutions and for evaporation of water from firm substances (drying of firm substances) .

Transition of water from liquid to vapour occurs at different tempera¬ tures, depending on the mode of boiling or evaporation.

Industrial dehydration is usually performed at the boiling point of water. Thus, in order to have evaporation the temperature of the mate- rial subjected to dehydration may be relatively high. Drawbacks with this mode of dehydration are that the process has a high power demand, that an excess pressure must be produced, that the corrosion stability of the equipment decreases and that material subjected to high tempera¬ tures may be adversely effected.

Evaporation of water at temperatures below the boiling-point is seldom used in practice, as such a process is time consuming and demands the use of extensive equipment. This process is only used when other proc¬ esses in a harmful way effects the quality of the dehydrated material.

In practice the following main methods for evaporation of water exist:

- a heat carrier (hot air superheated air, gas flow etc.) which direct¬ ly affect the material to be dehydrated; - the material to be dehydrated is placed in the vicinity of electro- heating elements (halogen lamps, resistance coils, electroheaters etc.) ;

- heat transfer through a wall between the material to be dehydrated and fluid or gas of a heat carrier or a electroheating element; - heating of a material by induced currents; and

- dielectrics heated by use of high-frequency currents.

In the traditional methods of heat transfer to an object to be hydrated the heating of the inner parts takes place by heat transfer from the outer parts. However, the heating of the outer parts often leads to the formation of a water proof layer which stops the humidity of the inner parts from reaching the surface. To overcome this effect a method is used where steam heating is alternated with cooling. It is only di¬ electrics heated by use of high frequency (0,5-100 Mhz) currents that provide heating capacities which makes it possible to dry objects from the centre and outwards. The principle of this method is that the mole- cules of the heated dielectric are polarized under the action of the electrical field (Gluhanov N.P. Fedorova, N.G. "High frequency heating of dielectrical material in mechanical engineering", Leningrad 1972 and Pushner G., "Heating by energy of superhigh frequencies", Moscow 1968).

Heating by high-frequency currents gives:

- an opportunity to achieve different heating temperatures;

- high heating rate;

- no local superheating as the material is evenly heated throughout its thickness;

- no inertial period;

- an opportunity to selectively heat separate parts of a material, which is achieved by selecting a proper frequency of the current, thus it is possible to evaporate water without substantially increas- ing the temperature of the material to be hydrated.

The drawbacks with this method are high costs for the equipment, in¬ creased power consumption, decreased efficiency of the high-frequency currents when the humidity of the material is decreasing and also the risk that the properties of the dehydrated material are changed due to effects of the electrical field.

One object of the present invention is to make it possible to actively dehydrate various organic and inorganic substances and solutions by means of thermal radiation in a narrow wavelength band affecting the humidity of the material to be dehydrated.

By using special ceramic materials according to the present invention it is possible to dehydrate a material without significantly increasing the temperature and without subjecting it to the effects of an electri¬ cal field. This is due to the fact that the materials of the invention are used as a special cover through which the heat radiation for dehy¬ dration is transferred. The materials are based on ceramics and complex compositions which include oxides of elements from groups 3 and 4 of the periodic table and stabilizing additives. The stabilizers are added to impart improved thermal, chemical and physical properties. The spe- cial cover transforms heat radiation from a source such as a halogen lamp, coil, electroheater, to radiation within a narrow, infrared range (1.8 to 54 μm) . It is the IR radiation in the lower part of the range which is most effective for dehydration. The chosen radiation range is one in which the object to be dehydrated is unaffected while water shows maximal absorption. The generated radiation sublimates the water, which is evaporated with high efficiency while the temperature of the object is substantially unaffected. This provides high efficiency of the process and high quality of the final product.

The material of the invention has been tested in processes for drying (dehydration) of various objects such as ferment, proteins, blood, hides, fabrics, foodstuff, wood, various ceramic items, such as bricks, tiles and plates, raw materials and products of the chemical industry. In these tests the power consumption is decreased 1.5 to 4 times, the properties of the dried objects are preserved, drying cycles are re¬ duced 3 to 5 times, the working costs are reduced up to 10 times and the active saprohyte microflora is declined.

The special ceramic material according to the present invention is ob- tained by preparation of one of the combinations, which are described below. The prepared combination gives a ceramic structure based on a rare earth chromium oxide or a structure containing silica which sur¬ prisingly shows improved thermal, chemical and physical properties. Furthermore, this combination makes it possible to heat the structure with high rate of heating.

The rare earth chromium oxide has the general formula RCrθ3, wherein R is anyone of lanthanum, neodymium and samarium, preferably lanthanum or neodymium, and most preferably lanthanum.

The stabilizing additives include alkaline earth spinels of the type MgAl2θ4 _j MrO:Al2θ3 or CuO:Al2θ3, and most preferably MgAl2θ4 optimal amounts of alkaline earth zirconate or alkaline earth hafniate pre¬ ferably CaZrθ3 or CaHfθ3 and alkaline earth chromate of the type MgCrθ4, SrCrθ4 or CaC θ and most preferably MgCrθ - This combination of additives may constitute 1 to 35% by weight and most preferably 15 to 26% by weight of the general ceramic structure of rare earth chro¬ mium oxide. The ceramic material may further include at least one of an oxide of zirconium or hafnium in an amount of approx. 0.5 to 5% by weight, a chromate of yttrium, scandium, ytterbium or terbium in an amount of approx. 0.5 to 5% by weight and an oxide of cerium, dyspro¬ sium, lutetium or europium in an amount of approx. 0.1 to 1% by weight. The general structure of one ceramic material according to the inven¬ tion is shown in Table 1 below.

Formulation A

Component % by weight

gAl2θ 0.5 - 10

MgCr04 1.0 - 15

CaZrθ3 up to 10

YCrθ3 up to 5

Z θ2 up to 5 eθ up to 1 aCrθ3 Balance

Table 1

The invention is further directed to silica containing structures which surprisingly also show stable thermal, chemical and physical proper-

ties. These structures include Siθ in an amount of 10 to 28% of weight and Fe2θ3 in an amount of 15 to 35% of weight, the balance being Cr2θ3- One or more of the following stabilizing additives may be included in the silica containing structure in the stated amounts: AI2O3 0.5 to 3.5% by weight, CuO 0.1 to 2% by weight, CaO 0.5 to 15% by weight and MgO 0.1 to 3% by weight. Each of AI2O3, CuO, CaO and MgO may be added in the stated amounts, preferably at least two of these additives are present in the stated amounts. The general structure of the silica con¬ taining structure is shown in table 2 below.

Formulation B

Component % by weight

S1O2 10-28

Fe2θ3 15-35

CaO up to 15

AI2O3 up to 3.5

MgO up to 3

CuO up to 2

Cr2U3 Balance

Table 2

Typically, the preparation of the formulations A and B according to the invention is done in the following way. The components are grounded in a mill using teflon balls to provide a base. The powder is melted, dried and pressed into shaped articles. These articles are then used as a base for the final product. Generally, the melting of these materials are executed under conditions which minimize the loss of oxygen from the prepared powder. It is possible to melt the prepared powder of the rare earth chromium oxide ceramic structures at a temperature of ap¬ prox. 2500°C. The silica containing ceramic structures are possible to melt at approx. 1900°C. Preferably, melting is executed in oxidizing atmospheres, most preferably air.

Sintering of the structures of rare earth chromium oxide (Formulation A) is executed in oxidizing atmospheres at a temperature up to approx. 1700°C, preferably approx. 1600°C for approx. 12 hours. The sintering of the silica containing structures (Formulation B) is also executed in oxidizing atmospheres at a temperature of up to approx. 1800°C, pre¬ ferably at approx. 1500°C for 12 hours. Furnaces suitable for sintering at these temperatures and in oxidizing atmospheres are e.g. furnaces using radiation sources covered with aCrθ3 as heating elements. After the sintering the resulting articles are heated at high temperatures, e.g. approx. 1500°C, during extended periods of time and in an oxidizing atmosphere, to give the desired thermal, natural and mechanical proper¬ ties such as compressing force. Samples are heated at approx. 1600°C for approx. 20 hours to evaluate loss of weight. Additional samples are metallized to evaluate specific reflectance.

The samples are evaluated to measure the maximal rate with which the ceramic structures of the invention may be heated. The maximal heating rate depends on the occurrence of any surface cracks or internal melt¬ ing and cracking. The evaluation of the samples show that the ceramic materials of the invention are useful in a variety of applications, in which it is important with a high heating rating and a stability of the properties of the heated material. For example, the materials of the invention may be used in applications directed to dehydration or drying at low temperatures. The improved properties of the ceramics of the present invention means that the ceramics are useful in dehydration or drying applications where these properties support optimal action. To avoid overheating or oxide formation a suitable amount IR radiation should be emitted in such a way that the product to be dehydrated is unifor ally exposed to the IR radiation.

Another aspect of the present invention concerns apparatuses for drying or dehydration of products in which apparatuses the ceramic materials according to the invention are used. The apparatuses include a source of IR radiation, such as a halogen lamp, resistance coil, electro- heater etc., a chamber for reception of the products, and one or more special ceramic materials placed between the source of radiation and the products to be dried or dehydrated. The ceramic materials absorb

the radiation emitted from the source and transforms the radiation to IR radiation within a preselected wave length range, such as 1.8 to 54 μm. The IR radiation is emitted to the products to be dried or dehy¬ drated.

For optimal results the ceramic material consists of two layers accord¬ ing to formulation A and B above (Tables 1 and 2). The two layers of ceramic material are placed adjacent each other in such a way that es¬ sentially all radiation emitted from the first layer is absorbed by the second layer. Preferably, the source of radiation is placed inside a glass pipe on which the two layers of ceramic material are coated. The first layer is the rare earth chromium oxide ceramic structure (Formulation A) described above. The second layer is the silica con¬ taining composition (Formulation B) described above.

However, it is possible to use just one of the above materials for transforming the heat radiation to IR radiation. It is also possible to use more than two materials. The type, thickness and number of materi¬ als one chooses depends inter alia of the type and thickness of the product to be dehydrated and also the physical and chemical properties of the product to be dehydrated.

The invention is described further below by means of preferred embodi¬ ments for different applications of the present invention, showed in the accompanying drawings, in which:

Fig. 1 is a perspective view of a dryer according to one embodiment of the invention;

Fig. 2 is a perspective view of a screen used in the dryer of Fig. 1;

Fig. 3 is a perspective view of a tray which may replace the screen of fig. 2;

Fig. 4 is a cross-section view of a first heating element used in the dryer of Fig. 1;

Fi g . 5 i s a schemati c cross-secti on vi ew of the dryer of

Fi g . 1 ;

fig. 6 is a plan view of the net tray of Fig. 3;

Fig. 7 is a cross-section view of a second heating element;

Figs. 8 and 9 are graphic representations showing the result of dehydration when testing different embodiments.

The drying or dehydration system 100 illustrated in Figs. 1 to 7 con¬ sists of a chamber, accessible through a door 110. The chamber and the door 110 have different shapes and sizes depending on in which context the dryer is to be used. The products to be dehydrated (dried) are placed on screens or trays 140,190 and are placed in the chamber be¬ tween plates 190 enclosing heating elements 150. The dryer further in¬ cludes suitable operators 120 and displays 130 to control and monitor the heating elements and the temperature and humidity of the chamber. The operators 120 and displays 130 are located at suitable sites on the outside of the dryer 100.

The heating elements 150, 230 include an energizable source of radia¬ tion, such as a halogen lamp or resistance coil 160, 240, placed within a pipe 170, 250 of ceramic material, quartz glass and/or metal. For effective dehydration and thus shorter dehydration time the heating elements are covered with one or more concentric layers 180,260,270 of the ceramic materials of the present invention described as Formula¬ tions A and B in tables 1 and 2 above. The layer(s) of ceramic material receives and absorbs the radiation emitted from the source of radiation 160, 240. The absorbed radiation is transformed in the ceramic material and emitted as IR radiation in a preselected wavelength range, such as 1,8 - 54 μm. The IR radiation is directed to the products placed in the chamber to be dehydrated.

As an alternative to the embodiment of Fig. 7, in which the heating element 230 has two layers 260,270 of ceramic material, heating ele-

ments having one ceramic layer (Fig. 4) are enclosed in a screen 190 made of a second ceramic material. The thickness of the layers is pre¬ ferably 0.1 - 0.5 mm, but could be more. The optimal effective range of action for the source of radiation, e.g. the heating elements 150,230, is approx. 30 cm.

As shown schematically in Fig. 5, the products 220 to be dehydrated are placed in nets or trays 210, which are slid into the chamber between plates enclosing the heating elements 150, 230.

A person skilled in the art recognizes that the exact arrangement of the chamber and the ceramic materials is adjusted depending on require¬ ments and desires on the one condition that the main portion of the IR radiation emitted through the ceramic materials may be directed to the products to be dehydrated. Thus, the ceramic materials do not have to be coated on the pipes. A person skilled in the art recognizes further that the dehydration systems may be used in continuous methods in which the heating elements are placed adjacent conveyer belts or other means of transportation supporting the products to be dehydrated.

The ceramic materials according to the present invention are suitable for use in various dehydration or drying systems. Such systems may be used for dehydration of various products such as food, plastic, cera¬ mics, wood, bricks, leather, china, containers, raw material, pharma- ceutical items, products of the chemical industry and in any other area in which there is a demand for a rapid and effective dehydration of high quality and in which the main properties of the dehydrated products are preserved.

The invention will be further described below by a number of examples, which are given to clarify the invention without limiting the inven¬ tion. The examples 2 to 7 show unexpected results due to the ceramic materials of the invention and compared to the results when prior art ceramic material is used. Examples of preferred structures of the ceramic materials according to the present invention are given in the examples below.

Exampl e 1

An example of a prior art is given in Table 3 below.

Component % by weight

LaCrθ3 98.55

MgCrθ4 0.5

YCrθ3 0.3

Zrθ2 0.3

CaZrθ3 0.3

Ceθ2 0.05

Table 3

These components were grounded and mixed in a plastic lined planet mill with Teflon balls. The resulting powder was dried, melted, re- ground and pressed into samples having the dimension 50 x 6 x 6 mm at the centre and 50 x 6 x 12 mm at the ends. Each of these samples were heated in a furnace with heating elements of LaCrθ3 to a temperature of approx. 1600°C for approx. 12 hours in air.

Example 2

The materials of the present invention were tested in a system for dry- ing wood in a periodic manner in a chamber. According to one known method (Bogdanov E.C. et al , "Managing and Technical Materials on Tech¬ nology Chamber Drying Wood" Archangel) the drying of wood is accom¬ plished in a chamber in a way which gives the fastest drying process while preserving a given assortment, durability and other natural pro- perties of the wood.

To dry wood, methods are used in which in a first step a high degree of water saturation of the drying agent is maintained at a certain given temperature. When the moisture content of the wood decreases the tem- perature is raised and the water saturation of the drying agent de¬ creases. This method, which includes changes of the parameters of the

drying agent, is controlled by the development of the internal pressure of the wood. The heat for drying the wood is provided by means of damp air at temperatures below 100°C or superheated vapour of atmospheric pressure at temperatures above 100°C.

The drying of wood is carried out at temperatures of the drying agent of 30 to 130°C at a supply rate for the drying agent of 1.5 to 2.5 m/s during from 23 up to 737 hours depending on the thickness of the timber and the desired quality of the dried wood. Thus, the first heating pe- riod alone for timber in a drying chamber reaches 8 hours. To get tim¬ ber of high quality a long drying period (2 to 7 days) at a low tem¬ perature (52 to 125°C) of the drying agent is used.

To release or decrease residual internal pressure, arising in the wood when drying according to the prescribed method, the final and interme¬ diate treatments of the wood is done in an environment of increased temperature and humidity. This treatment is named hydro-thermo process¬ ing. The hydro-thermo processing is carried out at temperatures below 100°C for 1.5 to 80 hours. At a timber thickness of for example 40 mm the time for hydro-thermo processing is 6 to 20 hours depending on sort of wood.

Different sorts of wood were placed on racks in drying chambers having periodic action. In the drying chambers use was made of built-in heat- ing elements covered with ceramic material according to the present in¬ vention, transforming radiation from a primary source to radiation in a narrow range of IR radiation, for which range water shows maximal ab¬ sorption and the wood is permeable. There is no inertial period as there is no need for heating the timber to be dried. After 1 to 2 hours of drying, the temperature of the chamber was 50 to 60°C and due to the evaporated water from the wood the relative humidity of the air in the chamber increased up to 45 to 55%. In order to equalize the moisture content in the upper and lower parts of the chamber, the damp air was circulated within the chamber by means of a fan. As the timber was dried the temperature of the chamber increased up to 70 to 90°C and the moisture content of the circulating air was held on a level of 35 to 40% in that a part of the damp air was removed from the chamber. The

damp air was completely expelled from the chamber by the fan during the final stage. By this method using the materials according to the inven¬ tion no further hydro-thermo processing of the wood was needed.

In drying tests pine wood having the length of 6250 mm, the width of 100 to 200 mm and the thickness of 20 to 75 mm was used. The results of the drying tests using a traditional method and a method based on the present invention are shown in Table 4 below.

Timber dried in a chamber using heating elements covered with the mate¬ rials of the present invention showed significantly less cracks and substantially no warping. Thus, the dried timber did not have to be put under pressure, which is a normal procedure when drying wood.

In Table 5 comparative characteristics of wood dryers are given. A tra¬ ditional method using a dryer UT-T50 from the Swedish firm UTEC is de¬ signated UTEC in Tables 4 and 5. A dryer equipped with electroheating elements covered with ceramics of the present invention is designated ALG in tables 4 and 5.

First stage

Initial heating, Temp, of drying Moist, cont. of Duration, h h agent °C drying agent %

UTEC 3.0 108 75 52

ALG not needed See Diagr. 1 See Diagr. 2

Second stage

Temperature of Moist, cont. of Duration, h Hydro-thermo drying agent °C drying agent % process at 100°C

UTEC 155 58 35 6

ALG See Diagr. 1 See Diagr. 2 not needed

Total drying Moist, cont. of Timber quality Nominal power time, h wood % consumption

UTEC 96 18.0 - 19.0 dim colour, no 1.0 def. or stress

ALG 20 - 24 15.0 - 17.0 no colour 0.36 change, def. or stress

Tabl e 4

5 hours

Diagram 1. Temperature in drying chamber

Diagram 2. Moisture content in drying chamber

Table 5

Example 3

In a test 500 g microcrystal powder-like samples of cellulose was dried from an initial humidity of 50% until constant weight was achieved. To compare the drying, tests were conducted using a traditional heating element and a heating element covered with the ceramic materials of the invention. The power supply in each case was set to 1.6 kW. As a fur¬ ther comparison the samples of cellulose was also dried using a high- frequency installation. The results of the tests are shown in Table 6 below.

Drying Power Temp, of Keratosis Clotting time, h supply, kW sample of sample of sample surface °C

Electroheater 8.5 1.6 108 present present

Elektroheater 2.0 1.6 60 absent absent having ceramics of invention

High-frequency 1.5 6.2 88 absent absent current

Tabl e 6

When using the material of the present invention the method shows all the benefits of the high-frequency installation but at a significantly reduced power consumption and reduced costs for the equipment.

Example 4

The ceramics of the invention were tested for drying different agricul¬ tural products such as fresh carrots. Tests were conducted in which the agricultural products were dried using conventional electroheaters and electroheaters covered with the ceramics of the invention.

The conducted tests showed:

All test products had high organoleptic qualities (appearance, con¬ sistency, smell, colour etc.). All dried products had insignificant smack.

In all tests the content of ascorbic acid (vitamin C) and carotene was preserved.

No changes of the concentration of nitrates.

4. The dried products showed an active atrophy saprophyte microflora. When using traditional electroheaters the seeding was reduced 5 000 times, while when using the electroheaters covered with the cera¬ mics of the invention the seeding was reduced more than 10 000 times. The result of these tests are shown in Table 7 below.

Fresh carrot Dry carrot Dry carrot sample 1 sample 2

Moisture, % 87.4 9.3 7.6

Ascorbic acid

- in lOOg of samp. ,mg 0.58 4.06 5.22

- in lOOg of dry samp.,mg 4.60 4.48 5.64

Carotene content in lOOg 68.4 66.2 68.4 of dry sample, mg

Nitrate content in moist 66.1 69.1 72.0 weight, mg/kg

Content of invert sugar

- in lOOg of samp.,mg 24.9 190.4 165.2

- in lOOg of dry samp.,mg 197.6 207.6 180.5

Saprophyte content

- KOE/g of sample 1000 < 10

- KOE/g of moist weight 500 000 106

Titer of BGKP > 1 1 < 1

B. cereys in lg of 10 none none product

Salmonella content in 25g none none none of product

Sample 1 was dried with a traditional electroheater. Sample 2 was dried with a electroheater covered with ceramic material of the invention. K0E is coloniforming units. BGKP is bacteria of Escherichia coli group.

Table 7

Exampl e 5

Samples of vegetables and fruits were dried using electroheaters cov¬ ered with the ceramic materials of the invention and installed in an experimental installation. As a comparison samples of vegetables and fruits were also dried using a steam dryer (type T4 - KCK - 45) manu¬ factured by Shebekinsk Machine-building Factory (Russia). The following advantages were attained when using the ceramics of the invention:

- Reduction of power supply per unit of final product - up to 5 times;

Reduction of time cycle for drying 3-5 times depending on type of product;

Reduction of drying temperature 10 to 55°C; - Easy operation;

Reduction of working costs up to 10 times per unit of final pro¬ duct;

Good reducibility when a made product is dehydrated.

Example 6

The ceramics of the invention were used in a method for drying varnish, paints and ground colours applied to a metal base. The layers of enamel, priming and ground colour are permeable for the generated IR radiation, therefore the major part of the radiant energy will reach the metal base. Thus, the drying process goes from the metal to the inner layers of the cover and outwards. This will provide:

1. The best adhesion of the cover on the base. 2. Reduced risk of formation of smudge.

3. Guaranteed drying of the inner layers of the cover.

The generated IR radiation influences the molecule structure of the cover in an optimal way, which reduces the temperature of polymeriza- tion and provides a complete drying of the cover at a temperature below 70°C.

In a process for hardening for example a cover of water emulsion the following considerations were made.

The formation of a film (water-soluble, film forming substance) is as- sociated with transition of a material from liquid phase to solid phase, which transition forms the cover and leads to a change of the position of the molecules and the thermodynamic properties of the sys¬ tem. The proceeding physical and chemical conversions thus determine the final structure of the formed cover. For a better understanding of the effect of the IR radiation on the formation of the cover, we will more closely consider the process for forming the film.

a. To form the cover from equilibrium and by the thermodynamic of con¬ vertible systems a transition from a film forming substance diluted with a solvent to a concentrate of the substance is made by evaporation of the solvent. At the evaporation of the solvent the surface tension increases, the volume of the film decreases and the dehydration tem¬ perature decreases.

b. For transition of a film forming substance into a firm phase within the paint industry it is not enough to only evaporate the solvent as the molecular weight is less than 2000 units and it is therefore neces¬ sary with a chemical formation of three-dimensional polymers. By the chemical formation of three-dimensional polymers the film becomes hy- drophobic after having been hydrophilic, which is very important and useful. The process of chemical hardening of the water-soluble film forming substance proceeds with interaction of functional groups and links. Favourable for this process of hardening a water soluble film forming substance by using IR radiation are the obtainable low molecu- lar weight, the large content of functional groups, especially polar groups and obtainable organic groups which are contributing to thermo¬ dynamic dissociation. Due to the IR radiation active disintegration of hydrophilic groups takes place which is accelerated by the other chemi¬ cal reactions throughout the total layer of the water-soluble film forming substance.

This further provides:

4. A reduced risk for cracking of the cover at drying and a re¬ duced risk of exfoliation for the cover or ground colours from the substrate due to low quality coating.

5. Complete hardening of all layers of the cover up to a total thickness of 10 mm.

6. That the given method may be used to dry large items such as boats, aeroplanes and cars, but also for drying items and units which contain greases or non-metallic (rubber, plastic) details which makes drying at elevated temperatures impossible.

7. Reduced drying time.

8. Substantial reduction of power consumption.

Example 7

An object to be dried was prepared in a suitable way. For instance, vegetables and fruits were washed, possible rotting parts were removed, the vegetables and fruits were cut, if necessary, and then put into a drying chamber as described above. The objects were then exposed to IR radiation, which IR radiation was produced by a primary source emitting radiation to a transforming layer of a ceramic material according to formulation B above. As the primary source the energizable elements de¬ scribed above may be used. The drying process continued until the de- crease of the weight of the product stopped. The weight decrease is due to evaporation of free water from the product. The cell mass of the product is preserved during the drying process without destruction or alteration. This allows the preservation of the most primary properties and features of the dried object, such as its nutritious properties in- eluding colour, taste, smell etc. At the same time as the object is dried it is also sterilized.

When the dried object is submerged in water it takes about 15 to 25 minutes to reabsorb lost water and to restore the original shape and condition, i.e. the volume, weight, taste, smell etc.

In order to do comparative analysis of different materials an experi¬ mental device was developed. The device consists of heating elements disposed at the bottom of a chamber and a net made of stainless steel placed 200 mm above the heating elements. The object to be dried is placed on the net.

To compare different drying equipments a carrot was sliced into 5x5x60 mm parts and exposed to a radiation energy of 3 kW/m . The drying re¬ sults when using the following elements were compared.

(1) A customary high-temperature coil of nichro e placed in a pipe of quartz glass.

(2) The element of (1) covered with a layer of mullite.

(3) The element of (1) covered with a ceramic material

(Formulation C) according to the present invention and stated in Table 8 below.

For ulation C

Component % by weiqht

Fe2θ3 28

Siθ2 17

CaO 5.5

Al ₂ 03 2.5

MgO 2

CuO 0.3

Cr ₂ 0 ₃ 44.7

Table 8

(4) The element of (1) covered with 1% by weight of a material according to formulation B (Table 2) and 99% by weight mullite (Formulation D) .

(5) The element of (1) covered with a first layer of the ceramic material according to formulation C (Table 8) and a second layer of 1% by weight of a material according to formulation B (Table 2) and 99% by weight mullite.

The various formulations having the approx. particle size 1 μm was app¬ lied as a cover on the element of (1) by means of a brush and glue made of polyvinylalcohol and/or water glass (sodium silicates).

The results of the tests are shown in Fig. 8. As is evident from fig. 8, the maximal drying speed is achieved when the heating elements are covered with two ceramic materials (the element of (5)). In that case the object to be dried approaches constant weight after approx. 40 min¬ utes. With the element of (4) drying is achieved in approx. 75 minutes. These elements have higher drying efficiency than previous systems using IR radiation for drying.

Further tests were made using the following elements.

(6) The element of (1) covered with a ceramic material (Formulation E) according to the present invention stated in

Table 9 below.

Formulation E

Component % by weiqht

Fe θ3 35

Siθ2 28

CaO 15

AI2O3 3.5

MgO 3

CuO 2

Cr ₂ 0 ₃ 13.5

Tabl e 9

(7) The element of (1) covered with a layer of mullite.

(8) The element of (1) covered with 1% by weight of the ceramic material (Formulation D) used for the element of (4) above and

99% by weight mullite (Formulation F) .

(9) The element of (1) covered with a first layer of the ceramic material according to formulation E (Table 9) and a second layer of the ceramic material (Formulation F) used for the element of (8) above.

The various formulations were applied as a cover on the element. The results of these last tests are shown in Fig. 9.

Once again the maximal drying speed is achieved when the heating ele¬ ments are covered with two layers of ceramic material. When the ele¬ ments of (9) were used the object approach constant weight after a dry¬ ing time of approx. 40 minutes. When using the elements of (8) drying was achieved in approx. 75 minutes. These elements have higher drying efficiency than previous systems using IR radiation. Furthermore, the tests for drying a carrot show that when using materials according to the present invention better organoleptic properties are achieved in¬ cluding maximal preservation of such properties of the carrot as the nutritional value and the overall appearance.