EP0013081B1 - Method of and apparatus for drying products with a closed gas stream and a desiccant liquid; and products prepared thereby - Google Patents

Method of and apparatus for drying products with a closed gas stream and a desiccant liquid; and products prepared thereby Download PDF

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Publication number
EP0013081B1
EP0013081B1 EP79302699A EP79302699A EP0013081B1 EP 0013081 B1 EP0013081 B1 EP 0013081B1 EP 79302699 A EP79302699 A EP 79302699A EP 79302699 A EP79302699 A EP 79302699A EP 0013081 B1 EP0013081 B1 EP 0013081B1
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EP
European Patent Office
Prior art keywords
liquid
desiccant
drying
gas stream
product
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired
Application number
EP79302699A
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German (de)
English (en)
French (fr)
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EP0013081A3 (en
EP0013081A2 (en
Inventor
Lászlo Szücs
András Horváth
Emöd Sigmond
György Waermer
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Energiagazdalkodasi Intezet
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Energiagazdalkodasi Intezet
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Publication of EP0013081A2 publication Critical patent/EP0013081A2/en
Publication of EP0013081A3 publication Critical patent/EP0013081A3/xx
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F26—DRYING
    • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
    • F26B21/00—Arrangements or duct systems, e.g. in combination with pallet boxes, for supplying and controlling air or gases for drying solid materials or objects
    • F26B21/06—Controlling, e.g. regulating, parameters of gas supply
    • F26B21/08—Humidity
    • F26B21/083—Humidity by using sorbent or hygroscopic materials, e.g. chemical substances, molecular sieves
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24F—AIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
    • F24F3/00—Air-conditioning systems in which conditioned primary air is supplied from one or more central stations to distributing units in the rooms or spaces where it may receive secondary treatment; Apparatus specially designed for such systems
    • F24F3/12—Air-conditioning systems in which conditioned primary air is supplied from one or more central stations to distributing units in the rooms or spaces where it may receive secondary treatment; Apparatus specially designed for such systems characterised by the treatment of the air otherwise than by heating and cooling
    • F24F3/14—Air-conditioning systems in which conditioned primary air is supplied from one or more central stations to distributing units in the rooms or spaces where it may receive secondary treatment; Apparatus specially designed for such systems characterised by the treatment of the air otherwise than by heating and cooling by humidification; by dehumidification
    • F24F3/1411—Air-conditioning systems in which conditioned primary air is supplied from one or more central stations to distributing units in the rooms or spaces where it may receive secondary treatment; Apparatus specially designed for such systems characterised by the treatment of the air otherwise than by heating and cooling by humidification; by dehumidification by absorbing or adsorbing water, e.g. using an hygroscopic desiccant
    • F24F3/1417—Air-conditioning systems in which conditioned primary air is supplied from one or more central stations to distributing units in the rooms or spaces where it may receive secondary treatment; Apparatus specially designed for such systems characterised by the treatment of the air otherwise than by heating and cooling by humidification; by dehumidification by absorbing or adsorbing water, e.g. using an hygroscopic desiccant with liquid hygroscopic desiccants
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F26—DRYING
    • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
    • F26B21/00—Arrangements or duct systems, e.g. in combination with pallet boxes, for supplying and controlling air or gases for drying solid materials or objects
    • F26B21/02—Circulating air or gases in closed cycles, e.g. wholly within the drying enclosure
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24F—AIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
    • F24F3/00—Air-conditioning systems in which conditioned primary air is supplied from one or more central stations to distributing units in the rooms or spaces where it may receive secondary treatment; Apparatus specially designed for such systems
    • F24F3/12—Air-conditioning systems in which conditioned primary air is supplied from one or more central stations to distributing units in the rooms or spaces where it may receive secondary treatment; Apparatus specially designed for such systems characterised by the treatment of the air otherwise than by heating and cooling
    • F24F3/14—Air-conditioning systems in which conditioned primary air is supplied from one or more central stations to distributing units in the rooms or spaces where it may receive secondary treatment; Apparatus specially designed for such systems characterised by the treatment of the air otherwise than by heating and cooling by humidification; by dehumidification
    • F24F2003/144—Air-conditioning systems in which conditioned primary air is supplied from one or more central stations to distributing units in the rooms or spaces where it may receive secondary treatment; Apparatus specially designed for such systems characterised by the treatment of the air otherwise than by heating and cooling by humidification; by dehumidification by dehumidification only

Definitions

  • This invention relates to a method of and an apparatus for drying products with a closed gas stream and with a desiccant (sorption) liquid which reduces the moisture content of the gas stream; and to products prepared by said method or apparatus.
  • the present invention comprises a method of drying products, comprising introducing the product to be dried into a drying compartment; continuously circulating a drying gas stream in a substantially closed path so as to cause it to pass past the product to be dried; contacting the drying gas stream with at least one layer of a desiccant liquid to remove moisture from the gas; regenerating the desiccant liquid by circulating at least a part of it through regenerating means to remove moisture therefrom, and disposing said at least one layer of desiccant liquid substantially perpendicularly to the direction of flow of the drying gas stream.
  • the essence of this method consists in that the said at least one layer of the desiccant liquid is established within or substantially within the drying compartment.
  • the application of the method according to the invention is advantageous in several respects. Firstly, it renders unnecessary the drip separator applied in the known systems, while effectively preventing pollution of the gas stream by the liquid-drops, and thus it diminishes the loss of the desiccant liquid also. Secondly, the coefficient of the mass transfer between the liquid and the gas is more favourable in this instance than with liquid particles; this allows a compact structure to be employed, which factor is accompanied by a smaller pressure drop in the gas stream. Thirdly, it does not demand a gas-desiccant contact area separated from the drying compartment; the liquid layer can be established quite close to the product to be dried.
  • Another advantage is that providing a liquid layer is a less delicate operation than spraying known from most of the previous proposals, because the danger of a blockage is much reduced, as is the need for maintenance. This latter factor is of particular significance as the gas stream often transports dust and other pollutants, besides moisture, into the desiccant liquid which tend to block the spray nozzle apertures.
  • An advantageous embodiment of the method according to the invention lies in the production of a substantially horizontal desiccant liquid layer, and in bubbling the drying gas stream through said horizontal liquid layer.
  • Another extremely advantageous embodiment of the method of the invention provides an arrangement wherein at least one desiccant liquid layer is produced by causing the desiccant liquid to flow on liquid film-conducting elements arranged in a plurality of vertical planes substantially within or within the drying compartment, and said contacting is performed by causing said drying gas stream to pass past and between said liquid film-conducting elements.
  • the liquid film-conducting elements can be applied to form a curtain like arrangement which may, for example, by disposed at the boundary of the drying compartment.
  • Another preferred embodiment of the invention provides a method characterised by moving the product to be dried into, and out of the drying compartment during the drying process; and bringing about a continuous heat transfer between the desiccant liquid circulated through the regenerating means and the product to be dried so that the heat is transmitted by the drying gas stream between the desiccant liquid and the product to be dried.
  • This preferred method provides for the possibility of diminishing the quantity and velocity of the gas to be circulated because at a higher temperature the quantity of moisture extractable per unit weight of air increases, and allows an efficient recuperation of the heat of evaporation of the steam from the disiccant liquid. during the regeneration into the desiccant liquid to be regenerated.
  • a further advantage is the omission of cooling applied in the previous gas liquid contactors; this results in a simpler construction of the gas-liquid contacting device.
  • the desiccant liquid is a desiccant solution; said regenerating is performed by evaporating the desiccant solution; and the steam evaporated from the desiccant solution is at least partly condensed by the desiccant solution to be regenerated.
  • This permits highly economic regeneration during which the energy requirement of regeneration can be reduced to a great extent by applying multi-effect boiling or multi-stage flash evaporation.
  • the heat of evaporation of the evaporated steam is used for heating the air which is to pre-dry the product it is an advantage that condensation of steam with a liquid requires a smaller and cheaper device than that working with air.
  • the energy requirements can be reduced by concentrating the desiccant solution by multi-effect boiling and using the incoming solution to be evaporated for at least partly condensing the steam evaporated during the first, or during the last, boiling process of the regeneration.
  • Regeneration may be effected by heating the desiccant solution to be regenerated without causing it to boil, with the steam evaporated from the solution.
  • the desiccant solution is cooled before regeneration in dependence on the cooling down of the desiccant solution during contacting so that the desiccant solution to be regenerated is of a predetermined temperature.
  • the cooling suggested here is important for the control of the cycle of the desiccant solution and is meant to complement the cooling down which occurs in the desiccant solution on contact with the drying gas stream.
  • the degree of cooling must be varied, for instance according to the season.
  • the cooling is preferably done during regeneration.
  • the continuous circulation of the drying gas stream is performed by conducting the drying gas stream in a path section within the drying compartment between the product to be dried and the desiccant liquid so that in said path section the ratio of the maximum and minimum velocity of the drying gas stream is smaller than five to one and the alteration of the direction of the drying gas stream is less than 30 degrees.
  • This measure results in a relatively small demand for fan power; this is an important feature in the economy of the whole drying procedure.
  • the fan power may be further diminished if the drying gas stream is conducted within the drying compartment between the product to be dried and the desiccant liquid substantially without any alteration of velocity and direction.
  • Air may be used as the drying gas and an aqeuous solution of calcium chloride may be used as the desiccant solution.
  • the calcium chloride solution is particularly favourable owing to its cheapness.
  • the method according to the invention is applicable not only for eliminating water vapour but also for drying materials which contain different vapour types by using an appropriate desiccant liquid. It is possible, for instance, to apply the present method for drying materials containing alcoholic moisture using a closed air stream and petrol as the desiccant liquid.
  • the drying gas stream consists of at least two parallel partial gas streams; the product to be dried is moved across said partial gas streams; and each of said partial gas streams is contacted with a desiccant liquid of specific concentration and temperature.
  • the drying program for the product to be dried may be extensively varied.
  • each of said partial gas streams is contacted with a more concentrated desiccant liquid than the desiccant liquid contacting the previous partial gas stream, with respect to the direction of movement of the product to be dried. This results in a counter-current between the product to be dried and the desiccant liquid.
  • the method according to the invention may also be implemented by producing at least two separated groups of desiccant liquid films of different concentration; placing said groups of desiccant liquid films side by side in the path of said partial gas streams so that each of said gas streams is contacted with its own at least one group of desiccant liquid films.
  • a further embodiment provides that each of said groups of desiccant liquid films is provided with its own liquid circulating device; the liquid circulating device of the last group with respect to the direction of movement of the product to be dried is fed with the regenerated desiccant liquid coming from said regenerating means; the circulating device of each preceding group is fed with the overflow of the circulating device of the subsequent group, respectively; and the overflow of the circulating device of the first group is conducted into said regenerating means. In this way counter-current is attained between the desiccant liquid and the product to be dried.
  • a further aspect of the invention provides apparatus for drying products comprising at least'one drying compartment for the product to be dried; at least one contacting device including means for producing at least one layer of a desiccant liquid for contact with a drying gas stream to remove moisture from the gas; gas conducting means for conducting the drying gas stream in a substantially closed path through the or each contacting device and said drying compartment, the or each said desiccant liquid layer being disposed perpendicularly to the direction of flow of the drying gas stream; gas circulating means to cause the drying gas stream to circulate along said closed path; regenerating means for removing moisture from the desiccant liquid; and liquid circulating means for circulating at least a part of the desiccant liquid through said regenerating means and the or each contacting device.
  • the apparatus is characterised in that the or each said contacting device is within, or substantially within, said drying compartment.
  • the contacting device comprises a vessel for producing a substantially horizontal desiccant liquid layer, said vessel having on its wall bubbling caps for bubbling the drying gas stream through said liquid layer, said vessel being connected to said liquid circulating means so as to cause the desiccant liquid to flow long said vessel and said drying compartment being located above or below said vessel.
  • the drying compartment comprises a device for transporting the product to be dried through said drying compartment, said transporting device having openings for letting through the drying gas stream but not letting the product to be dried fall therethrough.
  • the transporting device is an endless belt conveyor, and said gas circulating means are fans or blowers placed side by side along said belt conveyor.
  • the contacting device comprises liquid film-conducting elements disposed in a plurality of vertical planes which are substantially perpendicular to the direction of flow of the drying gas stream.
  • the contacting device further comprises a receptacle for receiving and holding the incoming desiccant liquid, at least one weir to guide the liquid out of said receptacle in film form, liquid distributing means having at least one distributing surface connected to said at least one weir and facing downwardly and liquid outlet means and that said film conducting elements are connected between said liquid distributing surface and said liquid outlet means so that in use they conduct liquid films from said surface into said outlet means.
  • This embodiment is not very sensitive to the pollution which might get into the desiccant liquid from the drying gas stream.
  • the strips of fibres can be made of a metal resistant to the desiccant liquid or of a plastics material which tolerates the highest possible temperature of the desiccant liquid.
  • a specific further embodiment of the drying apparatus according to the invention is applicable for products such as wood.
  • This embodiment comprises a floor, a shell roof, and a false roof provided with openings for letting through the drying gas stream and located between said floor and said shell-roof, with the drying compartment being located between said floor and said false roof; said gas circulating means are blowers placed between said false roof and said shell roof, the or each said contacting device being placed within or substantially within said drying compartment so that said substantially vertical planes formed by said liquid film conducting elements extend between said floor and said false roof.
  • the liquid film gas contacting device is placed at a boundary surface of the drying compartment, said surface being substantially perpendicular to the direction of the gas stream. This arrangement ensures only a small pressure drop for the gas stream which results in a low fan energy consumption.
  • a very advantageous embodiment of the apparatus according to the invention provides an arrangement wherein the contacting device comprises at least two liquid film modules placed side by side each liquid film module having its own liquid film conducting elements and own liquid circulating device producing a liquid flow circuit to form the liquid films on said own conducting elements, and wherein said liquid film modules are provided with a common liquid channel interconnecting said liquid circulating devices, said common liquid channel being connected to said liquid circulating means and said gas circulating means being adapted for circulating at least two parallel partial gas streams so that each of said partial gas streams passes its own at least one liquid film module.
  • the ratio of any two flow sections of said gas conducting means in said drying compartment between said product to be dried and said contacting device is between 0.2 and 5; and the or each said contacting device is located within or substantially within said drying compartment so that in use the drying gas stream flows between the product to be dried and said contacting device with a directional change of less than 30 degrees. It is very advantageous if said flow cross-section ratio is between 0.5 and 2, and said directional change is substantially zero degree, and the distance in said drying compartment between said product to be dried and said contacting device is less than the hydraulic diameter of said gas-conducting means between them.
  • hydraulic diameter is meant the diameter of a notional duct of equivalent capacity and friction.
  • the desiccant solution regenerating means comprise a multi-effect evaporator or a multi-stage flash evaporator. It is the latter which is more expedient, because of its simple operation. This embodiment guarantees very economical regeneration also from the point of view of energy consumption.
  • a further aspect of this invention consists in, as an article of manufacture, the product prepared according to the present method.
  • a casing 42 of a drying apparatus is shown schematically.
  • a gas stream e.g. an air stream
  • product 50 e.g. bulk goods as shown in the Figure
  • Circulation is forced by a fan 66 which is in use driven by an electric motor 46 placed above a false roof 54, shown schematically without its holding means in the Figure.
  • the false roof 54 has openings 47 in it through which the air stream can pass.
  • the product 50 is situated in a drying compartment 40 under the false roof 54. After flowing through or past the product 50 the now wet air stream contacts a contacting device 43 disposed within the casing 42.
  • the air stream comes into contact with liquid films 41 of a desiccant liquid.
  • the desiccant liquid is forced by a pump 141 into a regenerator 150.
  • the active and hot desiccant liquid comes into the contacting device 43 from a pipeline 44 above, it passes into a pot-shaped receptacle 55 and from there over a weir 56 to a downwardly- facing liquid distributing surface 57. From the liquid distributing surface 57, the desiccant liquid passes to downwardly directed liquid film-conducting elements 58, e.g. fibres. These elements then conduct the desiccant liquid to an outlet channel 62, from whence it departs through a pipeline 45.
  • the desiccant liquid diluted and cooled by the contact with the wet air stream then passes into the regenerator 150 through the pipeline 45.
  • the regenerator 150 shown in Figure 1 contains an multi-stage flash evaporator 151, the liquid circulating pump 141, a pump 142 for removing the distillate of the multi-stage flash evaporator 151 through a pipe junction 149, and a heat- exchanger 143 which is fed with cooling water through pipe junction 144. Cooling in the heat- exchanger 143 is essential for the proper operation of the multi-stage flash evaporator 151.
  • the active liquid leaving the regenerator 150 is passed to a condenser 145 and is heated up while going through it. Then the liquid is returned to the contacting device 43 via pipeline 44.
  • the condenser 145 receives heating steam through a pipe 146, and the condensate is carried away by a pump 147 through a pipe 148.
  • Elements of the regenerator 150 and the heating means after the regeneration are well-known in themselves, so their detailed description is unnecessary; reference may be had e.g. to US-A-2 557 204.
  • the embodiment according to Figure 1 is particularly advantageous when drying products of high heat resistance, e.g. bricks, as in this arrangement the temperature of the desiccant liquid which has returned from the contacting device 43 and has been "cooled” there is still sufficient to eliminate the moisture during the flashing process.
  • the application of the multi-stage flash evaporator 151 shown in Figure 1 is particularly advantageous in the apparatus according to the invention because from the points of view of control, operation and reliability it is more favourable than other multi-effect evaporators of the same efficiency.
  • the evaporation does not take place along heat transfer surfaces so it is less sensitive to en- crustation and corrosion and its construction does not become complicated even if efficiency is improved.
  • an evaporator of a different arrangement of per se known construction may equally be applied for the regeneration step.
  • the drying compartment can be constructed and the product 50 to be dried can be placed in many ways, e.g. by suspension, fluidised-bed, geyser, chamber, tunnel.
  • the product can be moved during the drying process and the drying gas may also be caused to flow past the products in counter-, cross- or direct current flow.
  • FIGS 2, 3 and 4 show an embodiment of the drying apparatus according to the invention which operates with a substantially horizontal moving liquid layer 1 and with a horizontally moving product 2 above the liquid layer.
  • the product 2 e.g. soybean
  • the belt 4 has air transmitting openings 5 in it which lets the air through but retains the product 2.
  • the belt 4 is entrained around two sprockets 6 which are constructed so as to be capable of stretching and driving the belt 4, for this purpose they may e.g. be imperforated or rubberised.
  • One of the sprockets 6 is driven by electric motor 8 through a driving gear 7.
  • the loaded belt 4 of the belt conveyor transports the product 2 from the throat 3 through a drying compartment 25 which is situated in a casing 9 of the drying apparatus and then through a gate 10 to a collector 11 from where the dried product is transported to a place of storage or utilisation by a belt conveyor or a pulley, not shown in the figure.
  • the empty run of the belt conveyor passes under the casing 9.
  • blowers 17A, 17B, 17C and 17D driven in use by electric motors 23A, 23B, 23C and 23D, rkespectively, suck air from the upper air collecting space 16 through respective suction ports 22A, 22B, 22C and 22D, and force it through pressure tubes 18A, 18B, 18C and 18D and through openings 19A, 19B, 19C and 19D to the lower air collecting space 12 respectively.
  • the four blowers 17A, 17B, 17C and 17D bring about four closed circulation partial air streams.
  • the first partial air stream passes through the suction port 22D and meets the arriving wet product 2.
  • the second partial air stream passes through the suction port 22C, the third one through the suction port 22B and the fourth one through the suction port 22A, and this last one extracts from product 2 the last part of moisture to be extracted.
  • the desiccant liquid flows into the liquid vessel 13 through a pipe coupling 26 and departs through a pipe coupling 27.
  • the arriving hot and active liquid is contacted with the air of the last partial air stream, and the departing, cooled and diluted liquid is bubbled through by the first partial air stream.
  • the liquid vessel 13 is placed above the loaded run of the belt conveyor. This is advantageous when the product 2 contains particles small enough to fall into the liquid vessel 13 through openings 5 of the belt 4, and so to pollute the desiccant liquid to an unfavourable degree.
  • the air stream entering through openings 19A, 19B, 19C and 19D would first go through the product 2, then through the liquid layer 1.
  • particles of the product 2 fallen through openings 5 of the belt 4 can be collected at the bottom of the casing 9 and from there can be transported away as dried product either from time to time or continuously.
  • liquid drops which might have been carried away from the liquid layer 1 by the air stream do not reach the product 2 but, having gone through the blowers 17A, 17B, 17C and 17D, can be collected in pots or in channels formed in the bottom of tubes 18A, 18B, 18C and 18D, and from there can be fed back to the liquid circuit.
  • the pollutants which passed into the liquid layer 1, e.g. from the product 2 through openings 5, can be eliminated with the help of a separating tank, well-known in itself, which is included into the desiccant liquid circuit, preferably after the pipe coupling 27 in such a way, for example, that the liquid pouring into the separating tank can only depart through openings placed at half-way to the full height of the liquid level in the tank.
  • the tank must be cleaned appropriately, the fluid must be skimmed and deposits must be removed.
  • the diluted desiccant liquid passes to the regenerator, in the case of the embodiment shown in Figs. 3 and 4, into a solution-condenser, which consists of a liquid circulating pump 28, a vapour condenser 29 which is cooled by the arriving diluted solution, a pump 30 for removing the distillate, a steam-heated evaporator 31 and a pump 36.
  • the pump 28 pumps the diluted solution through the condenser 29 as a cooling medium and from there the solution reaches the evaporator 31 through the pipeline 32.
  • the evaporator 31 is heated by steam introduced through a pipe coupling 33 and the condensate of the heating steam departs through a pipe coupling 34.
  • the steam evaporated from the solution passes to the condenser 29 from the evaporator 31 through a pipeline 35, there it is condensed and the distillate is removed by the pump 30.
  • the pump 30 is capable of removing the non-condensable gases together with the distillate.
  • From the evaporator 31 the condensed, active solution is pumped by a pump 36 through a pipeline 24 to the pipe coupling 26 through which it returns to the liquid vessel 13.
  • This desiccant solution regenerator is also shown by way of a circuit diagram on Figure 7, for the sake of better understanding.
  • Figures 2 to 4 show the simplest possible evaporator, which uses only the arriving solution to be regenerated as the cooling medium for condensing the steam evaporated from the solution during the regeneration.
  • a multi-effect evaporator the efficiency of which is higher, for example as shown in Figures 8 or 9, or a multi-stage flash evaporator for example as shown in Figures 1 or 10.
  • the product 2 can be taken through the drying compartment 25 not only horizontally but also obliquely.
  • the cross-section of the liquid vessel 13 is much bigger than that of pipe-couplings 26 and 27; for this reason it is practical for ensuring uniform flow conditions to let the desiccant solution stream in and out of the liquid vessel 13 not only through a respective single incoming and outgoing pipe coupling but through many couplings along the width of the vessel 13.
  • Figures 5 and 6 show another embodiment which works with a horizontally moving product 50 and a contacting device 43 placed beside the product 50, bringing about a vertical liquid film 41 of a desiccant liquid.
  • the product 50 sawn wood in this embodiment, is put in carriages 51 with wheels supported in bearings on axles 52 and moves very slowly forward on a floor 49 in the direction of arrow 53. Above the top of the product 50 the drying compartment 40 is closed by a false roof 54.
  • the whole drying apparatus is closed from above by a shell-roof 65 to which the false roof 54 is connected by suspending columns 65A.
  • the shell-roof 65 is closed on two sides by walls 37 and 38 respectively; the walls have gates 39 in them for the product 50.
  • the air stream circulates in the direction of arrows 64 under the effect of blowers 66 and 66' driven by electric motors 46 and 46' respectively built into a separation wall 69.
  • the air stream proceeds between the shell-roof 65 and the false roof 54, then through an opening 47 of the false roof 54 it passes into the drying compartment 40 between the floor 49 and the false roof 54; from there it contacts liquid films 41 of the contacting device 43, then through another opening 47A between the shell-roof 65 and the false roof 54 the air flows back to the blowers 66 and 66'.
  • two blowers 66 and 66' two parallel partial air streams come about.
  • the contacting device 43 in this embodiment consists of three liquid film modules 48A, 48B and 48C placed directly side by side. Each module has its own individual liquid flow circuit and all modules have a common lower liquid outlet channel 62 through which they are connected to a regenerator, not shown here, via pipe-couplings 67 and 68.
  • the active hot desiccant liquid coming from the regenerator enters through the pipe-coupling 67, then gets more and more diluted by circulation in liquid film modules 48A, 48B and 48C as it passes along the channel 62 in the direction of arrow 63 and then via the pipe coupling 68 it passes into the regenerator.
  • the regenerator may be like the ones shown in Figure 1 or Figure 4 but multi-effect evaporators shown in Figures 8 and 9 are also suitable, and so is a multi-stage flash evaporator such as is shown in Figure 10.
  • the liquid film modules 48A, 48B and 48C are similarly constructed; for this reason, we describe the liquid film module 48A only.
  • An upper receptacle 55A is placed under the false roof 54 and is bounded by a weir 56A.
  • a downwardly directed liquid distributing surface 57A is connected to the weir 56A .
  • From the liquid distributing surface 57A there are downwardly directed liquid film conducting elements 58A, e.g. fibres as shown in drawing.
  • All the elements 58A belonging to the liquid film module 48A together make up a liquid film group the characteristic feature of which is that all the elements in the group conduct desiccant liquid of the same concentration.
  • the elements 58A reach down to the lower collecting channel 62 placed beneath.
  • a suction pipe 59A connected to the bottom of the channel 62 thus conducts the desiccant liquid to a liquid circulating pump 60A.
  • the pump 60A circulates the liquid through a tube 61A into the upper receptacle 55A, from there through the weir 56A it reaches the liquid distributing surface 57A, and then along the elements 58A into the lower collecting channel 62.
  • the upper receptacle 55A is separated from the upper receptacle of the neighbouring liquid film module 48B, but the common lower channel 62 makes it possible for the liquid circulating circuits belonging to tubes 61 A, 61 B and 61 C to pass liquid to one another.
  • Sections of lower channel 62 which belong to liquid film modules 48A, 48B and 48C respectively, are separated from one another by separating elements 162 provided with openings, so that the liquid stream is always flowing in the direction of arrow 63, without a counterflow.
  • the first liquid circulating circuit belong to the first film module 48C receives hot and active liquid from the regenerator. This is diluted by the air stream coming from the drying compartment 40, so that the liquid delivered to the second liquid circulating circuit belonging to the liquid film module 48B in the form of overflow of the first liquid circulating circle is somewhat diluted. It is the overflow of the last - in Figure 5 the third - liquid circulating circuit which is returned as diluted cold desiccant liquid to the regenerator, said liquid containing all the moisture which has been extracted from the product 50 by the air stream.
  • the two blowers 66 and 66' bring about two parallel partial air streams.
  • the velocity of each of the partial air streams should be of a value such that the liquid films along the conducting elements 58A, 58B and 58C are not disturbed by the air stream, i.e. the air stream does not carry off liquid particles from the film.
  • a velocity of 1 to 5 m/sec is suitable.
  • the embodiment shown in Figs. 5 and 6 - similarly to that shown in Figs. 2 to 4 - carries out counter-current drying, as the product 50 moving slowly in the direction of arrow 53 while going through the drying compartment 40 meets air streams which had been contacted with more and more active desiccant liquid.
  • a prerequisite of said counter-current drying here, too, is to have at least two partial air streams. It is expedient to have one partial air stream belonging to each liquid film module 48A, 48B and 48C that is, the number of blowers should be equal to that of the liquid film modules.
  • the concentration of the desiccant liquids circulated in the liquid film modules 48A, 48B and 48C can be increased in a sequence different from that of the modules in space.
  • the sequence can be arranged as seems best with appropriate joining of individual sections of the channel 62 belonging to individual modules.
  • the desiccant liquid can be directly connected to section belonging to liquid film module 48A instead of the one belonging to liquid film module 48B through the separating element 162, and from there into the section belonging to liquid film module 48B.
  • the apparatus according to the invention can be programmed with regard to the drying requirements of the product 50 going through the drying compartment 40.
  • the contacting device 43 borders the drying compartment 40 on the left-hand side, forming, as it were, "liquid curtain".
  • the contacting device 43 can also be placed on the right-hand side of the drying compartment 40; moreover it can be placed in such a way that it divides the drying compartment 40 into two parts, e.g. between the two stacks of wood shown in Fig. 5.
  • the only important thing is that the closed- circuit air stream should go through the contacting device 43 during recirculation and the contacting device 43 and the drying compartment 40 are arranged and placed in such a way that the air stream suffers the least possible alteration of velocity and direction shown going from one to the other. It is obvious that these conditions are fulfilled in all the embodiments mentioned.
  • the type of the contacting device 43 shown in Figure 5 is the same as that shown in Figure 1, but it can also be made in a different way.
  • Several contacting devices usable with the apparatus according to the invention are described, e.g. in US-A-3 857 911 and US-A-4 009 229, HU ⁇ A ⁇ 168 451 and GB-A-1 363 523.
  • regenerator In Figures 5 and 6 we do not show a regenerator, since it can be the same as that in any of Figures 1,4, 8, 9 and 10. With the appropriate selection of regenerator it is also possible to ensure that the active solution arriving through the pipe coupling 67 is as hot as is needed so that it can heat the air stream and through it the product 50. With the help of liquid film modules 48A, 48B and 48C it is possible to set a temperature program for the product 50 geoing through the drying compartment 40.
  • FIGs 7, 8 and 9 and 10 show various embodiments for the regenerator.
  • the regenerator is an interconnection of different devices known per se, so the various regenerators which may be applied in the invention are shown in Figures 7, 8, 9 and 10 only by means of circuit diagrams.
  • circuit diagrams For the sake of clarity each operation is marked with a separate schematic sign in the circuit diagrams but the invention can be realised also in such a way that, for instance, more than one device is placed into one casing.
  • Figure 7 represents the circuit diagram of the regenerator shown in Figures 2 to 4 and described in relation to these Figures in detail.
  • Figure 8 represents a regenerator which uses the steam evaporated from the desiccant liquid to boil the liquid to be regenerated and thus the steam emanating from the departing active liquid heats the incoming diluted liquid.
  • This regenerator is a multi-effect evaporator.
  • the diluted liquid is pumped by a pump 70 into a condenser 71, there it serves as cooling medium for the condenser 71, thereafter while cooling the liquid evaporating in heat exchangers 72 and 73 it gets warmed further, and finally it passes into an evaporator 75 through a pipeline 74.
  • This evaporator 75 is heated from the outside with heat taken in. For instance, according to the embodiment shown, steam is taken in through a pipe 76, this gets condensed and the condensate departs through a pipeline 77.
  • flue gas, radiant heat, solar energy or something else can also be used for heating. From here the desiccant passes through a heat exchanger 73 and a throttle 78.
  • the liquid then passes into an evaporator 79, where it is further boiled by the steam produced in the evaporator 75.
  • a pump 83 pumps the liquid through the heat exchanger 72 to a pipe coupling 80 which is connected to a pipe-coupling conducting the active liquid in the dryer body itself, e.g. to the pipe coupling 67 in Figure 6.
  • the steam produced in the evaporator 79 through a pipeline 84 and the condensate of the steam heating the evaporator 79 through a throttle 81 pass into the condenser 71 and both heat the diluted, incoming desiccant liquid.
  • the condensed distillate and the non-condensable gases are removed by a pump 82.
  • Figure 9 shows the circuit diagram of an embodiment of the regenerator which is also a multi-effect evaporator and uses the steam evaporated from the diluted liquid for heating the incoming diluted liquid to be regenerated.
  • the diluted liquid is pumped to a condenser 91 by a pump 90 as a cooling medium, there it warms up and is then used to cool the department already condensed liquid in the heat exchanger 92, where it warms further and passes into an evaporator 93.
  • a pump 94 takes it through a heat exchanger 95, where by cooling the active liquid it gets warmed and thence passes to an evaporator 96.
  • it is evaporated with heat taken in from outside for example with steam taken in through a pipe coupling 97.
  • the condensate of the steam departs through a pipe coupling 98.
  • the steam raised in the evaporator 96 boils the diluted liquid in the evaporator 93.
  • the condensed, active liquid then passes through a pipeline 99 to the heat exchanger 95, then into the heat exchanger 92, and departs through a pipe coupling 100, towards the dryer body e.g. to the pipe coupling 67 in Figure 6.
  • the steam produced in the evaporator 93 reaches the condenser 91 through a pipeline 101 and the condensate of the steam heating the evaporator 93 reaches the same place through a throttle 102; there it heats the diluted liquid and then the distillate produced by condensation and the non-condensable gases are carried away by a pump 103.
  • FIG. 10 shows the circuit diagram of a further embodiment of the regenerator in which the heat released during condensing the steam evaporated from the liquid by flash only warms the liquid to be regenerated but does not evaporate it.
  • This regenerator is a multi-stage flash evaporator.
  • the diluted liquid is driven through condenser 112, 113, and 114 by a pump 111.
  • the liquid goes through a throttle 115.
  • the pump 111 and the throttle 115 are arranged in such a way that the pressure of the liquid when going through condenser 112, 113 and 114 is greater than the saturation pressure all the way through, so vaporisation does not occur anywhere.
  • the temperature of the diluted liquid serving as cooling liquid in condensers 112, 113 and 114 of course increases.
  • After the throttle 115 in an evaporator 116 steam is released from the liquid without heat transfer. This steam is condensed in the condenser 113.
  • the liquid goes on to an evaporator 117 where more steam is released from it which gets condensed in the condenser 112.
  • the condensed active liquid that is left is carried back to the drying body by a pump 118 e.g. in Figure 6 to the pipe coupling 67.
  • the distillate condensed in the condenser 113 reaches the condenser 112 through a pipeline 119, where it flashes.
  • the distillate and the non-condensable gases are pumped away by a pump 120.
  • the diluted liquid to be regenerated should be heated by heat taken in from outside, for example with steam taken in through a pipe coupling 121, the condensate of the steam departs through a pipe-coupling 122.
  • Figure 10 shows that when the surplus heat produced by the regenerator cannot be utilised in the drying body or when the heat loss of the drying body is low, (e.g. in the summer) the desiccant liquid regenerating system should be balanced.
  • the condenser 112 is provided with cooling medium from the outside, e.g. cooling water and a coolable sub- sidary surface e.g. a coiled pipe. This latter can be placed in a separate casing, in which case the steam spaces must be connected with pipelines. Cooling water may, for example, enter the heat exchanger through a pipe-coupling 123 and leave it through a pipe-coupling 124.
  • the diluted liquid entering the condenser 112 is pre-cooled in a heat exchanger 127 which is cooled by a medium e.g. water entering through a pipe-coupling 125 and leaving through a pipe-coupling 126.
  • a medium e.g. water entering through a pipe-coupling 125 and leaving through a pipe-coupling 126.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • General Chemical & Material Sciences (AREA)
  • Drying Of Solid Materials (AREA)
  • Drying Of Gases (AREA)
  • Physical Or Chemical Processes And Apparatus (AREA)
EP79302699A 1978-11-28 1979-11-27 Method of and apparatus for drying products with a closed gas stream and a desiccant liquid; and products prepared thereby Expired EP0013081B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
HUEE002605 1978-11-28
HU78EE2605A HU179156B (en) 1978-11-28 1978-11-28 Process and apparatus for desiccating ware with closed gas stream and sorptive liquide

Publications (3)

Publication Number Publication Date
EP0013081A2 EP0013081A2 (en) 1980-07-09
EP0013081A3 EP0013081A3 (en) 1980-07-23
EP0013081B1 true EP0013081B1 (en) 1983-07-27

Family

ID=10995803

Family Applications (1)

Application Number Title Priority Date Filing Date
EP79302699A Expired EP0013081B1 (en) 1978-11-28 1979-11-27 Method of and apparatus for drying products with a closed gas stream and a desiccant liquid; and products prepared thereby

Country Status (23)

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EP (1) EP0013081B1 (el)
AR (1) AR222673A1 (el)
AT (1) ATE4348T1 (el)
AU (1) AU533601B2 (el)
BR (1) BR7907718A (el)
CA (1) CA1131903A (el)
CS (1) CS261204B2 (el)
DD (1) DD147402A5 (el)
DE (1) DE2966006D1 (el)
DK (1) DK157769C (el)
ES (2) ES486405A0 (el)
FI (1) FI67758C (el)
GR (1) GR72249B (el)
HU (1) HU179156B (el)
IL (1) IL58809A (el)
IN (1) IN152091B (el)
MX (1) MX153067A (el)
NO (1) NO151304C (el)
PL (1) PL127670B1 (el)
PT (1) PT70511A (el)
RO (1) RO84961B (el)
SU (1) SU1209043A3 (el)
YU (1) YU42317B (el)

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
HU179162B (en) * 1979-09-13 1982-08-28 Energiagazdalkodasi Intezet Method and apparatus for drying products particularly corn or lumpy goods
US6154979A (en) * 1998-01-09 2000-12-05 Asj Holding Aps Method and apparatus for the removal of liquid from particulate material
US9308491B2 (en) 2013-03-15 2016-04-12 Carrier Corporation Membrane contactor for dehumidification systems
US9273876B2 (en) 2013-03-20 2016-03-01 Carrier Corporation Membrane contactor for dehumidification systems

Family Cites Families (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2017027A (en) * 1931-08-19 1935-10-08 Henry O Forrest Method of air conditioning
US2249625A (en) * 1939-07-26 1941-07-15 Dow Chemical Co Apparatus for drying
FR939336A (fr) * 1943-06-08 1948-11-10 Cie Belge Des Freins Westingho Procédé et installation de séchage adiabatique
US2557204A (en) * 1947-06-17 1951-06-19 Allan S Richardson Concentrating hygroscopic solution
US3094574A (en) * 1958-10-20 1963-06-18 Nat Tank Co Gas dehydrator
GB1024835A (en) * 1961-10-11 1966-04-06 Andre Gabriel Margittai A process and apparatus for low-temperature dehydration
US3348601A (en) * 1964-12-21 1967-10-24 Combustion Eng Means for reconcentrating liquid absorbent
BE767730R (fr) * 1970-11-06 1971-10-18 Fabelta Sa Procede et appareillage pour la mise en contact de fluides et le transfert de matiere et de chaleur entre
CH558925A (de) * 1974-01-17 1975-02-14 Energiagazdalkodasi Intezet Vorrichtung zur waerme- und stoffuebertragung zwischen fluessigkeiten und gasen.
DE2402181C3 (de) * 1974-01-17 1979-03-29 Energiagazdalkodasi Intezet, Budapest Vorrichtung zur Wärme- und Stoffübertragung zwischen Flüssigkeiten und Gasen

Also Published As

Publication number Publication date
MX153067A (es) 1986-07-25
AU5325279A (en) 1980-05-29
ATE4348T1 (de) 1983-08-15
IL58809A0 (el) 1980-02-29
AR222673A1 (es) 1981-06-15
RO84961B (ro) 1984-09-30
YU292779A (en) 1984-08-31
DK157769C (da) 1990-07-16
IL58809A (en) 1982-12-31
HU179156B (en) 1982-08-28
SU1209043A3 (ru) 1986-01-30
ES493430A0 (es) 1981-05-16
IN152091B (el) 1983-10-15
DD147402A5 (de) 1981-04-01
NO151304C (no) 1985-03-13
EP0013081A3 (en) 1980-07-23
GR72249B (el) 1983-10-05
BR7907718A (pt) 1980-07-22
FI67758B (fi) 1985-01-31
AU533601B2 (en) 1983-12-01
ES8101256A1 (es) 1980-12-01
EP0013081A2 (en) 1980-07-09
DK503579A (da) 1980-05-29
ES486405A0 (es) 1980-12-01
PL127670B1 (en) 1983-11-30
FI793735A (fi) 1980-05-29
NO793856L (no) 1980-05-29
CS261204B2 (en) 1989-01-12
DK157769B (da) 1990-02-12
DE2966006D1 (en) 1983-09-01
RO84961A (ro) 1984-08-17
CA1131903A (en) 1982-09-21
PL219953A1 (el) 1980-08-25
NO151304B (no) 1984-12-03
FI67758C (fi) 1985-05-10
YU42317B (en) 1988-08-31
ES8105466A1 (es) 1981-05-16
PT70511A (en) 1979-12-01

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