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Title:
METHOD AND EQUIPMENT FOR THE ENERGY-SAVING DRYING ESPECIALLY OF HEAT-SENSITIVE AS WELL AS OF TOXIC AND/OR SMELLY GAS PRODUCING MATERIALS
Document Type and Number:
WIPO Patent Application WO/1981/003695
Kind Code:
A1
Abstract:
In course of the process air or a gaseous medium is used in an open or in a closed system, by the aid of which the moisture content of the material to be dried is extracted. The drying medium is brought into contact with the humidity absorbing solution in the absorber; between the steam having been obtained in such a manner and the drying medium heat exchange is taking place; the steam is condensed, the drying medium is heated, at last the condensate is discharged into the atmosphere, while the heated drying medium is recirculated in the drying process. In case, if sludge has to be dried and to be annihilated, the sludge - having been pre-condensed to a solid matter content of 30% - is dried to the moisture content of 1- 2% by means of the drying medium, hereafter - in a given case by using an auxiliary firing - the sludge is burnt in the combustion space of the expeller. The equipment provided with an open or closed drier operating with a heated drying medium, incorporates an absorber having been arranged in the path of the stream of the drying medium. In the absorber there is a liquid distributor introducing the humidity absorbing solution. Furthermore the equipment comprises an expeller for the removal of the humidity content of the humidity absorbing solution and the steam space of said expeller is connected to the heat exchanger arranged in the stream path of the drying medium leaving the absorber, while the liquid space is connected to the liquid distributor. When the sludge is to be dried and burnt, the equipment comprises a sludge drier, which is connected to the firing chamber of the furnace through the drying line for the dried sludge.

Inventors:
BARTA G (HU)
ASZLANYI J (HU)
RAKOLCAI L (HU)
HEGEDUES S (HU)
Application Number:
PCT/HU1981/000025
Publication Date:
December 24, 1981
Filing Date:
June 11, 1981
Export Citation:
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Assignee:
NOVEX FOREIGN TRADE CO LTD (HU)
BARTA G (HU)
ASZLANYI J (HU)
RAKOLCAI L (HU)
HEGEDUES S (HU)
International Classes:
C02F11/12; F26B21/08; F26B23/00; (IPC1-7): F26B5/16; F25B15/02; F26B21/00
Foreign References:
SU567055A11977-07-30
SU186514A
GB1305070A1973-01-31
GB1175888A1970-01-01
Other References:
SPRAVOCHNIK HOLODILSCHIKA, published 1962, Mashgiz, Moscow, see page 144, Fig. 94
See also references of EP 0054046A4
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Claims:
Claims:
1. Process for the energysaving drying especially of heatsensitive materials and of toxic, and/or smelly gas producing materials, e. g. organic substances, provisions, agricultural produces, in course of which air or a gaseous medium is used as a drying medium either in an open or in a closed system for extracting the moisture content of the material to be dried, c h a r a c t e r iz e d in that the drying medium, in general the ambient air, is brought into contact with the humidity absorbing solution in the absorber in order to reduce the moisture contained therein, subsequently the absorbing solution with the humidity is heated and evaporated in the expeller; between the steam having been obtained in such a manner and the drying medium heat exchange is taking place in . the heat exchanger and as a result the steam gets condensed, at last the condensate is discharged into the atmosphere, while the* heated drying medium is re¬ circulated* into the drying process.
2. Process as claimed in claim 1, where the, drying medium is used in an open system, c h a r a c ¬ t e r i z e d in that the drying medium is brought into contact with the humidity absorbing medium* prior to the contact with the material to be dried i. e. prior to drying and the humidity vapour having been obtained in such a manner is utilized in course of the heat exchange with the drying medium, that is to say, a part of the heat content of the vapour resulting from solar energy is also utilized.
3. Process as claimed in claim 1, where the drying medium is used in an open system, c h a r t e r i z e d in that the drying medium is brought " into contact with the humidity absorbing medium after the contact with the material to be dried, i. e. after drying, whereby partly the drying medium will be pre.
4. heated, partly a part of the energy contained in the solar energy and the fuel, respectively, will be utilizedo 4» Process as claimed in claim 1, where the drying medium is used in a closed system, c h a r a c t* e r i z e d in that, the moisture content of the dry¬ ing medium haying been extracted by the humidity absorb¬ ing solution is removed from the system,* simultaneously the heat content is recirculated into the circuit.
5. Process as claimed in claim 1, where the toxic or smelly gaseous content of the material (sludge) to be dried is to be annihilated, c h a r a c t e r i z e d in that the sludge to be dried is previously pre condensed to a solid matter content of 30 %, subsequently it is dried to a moisture content of 1 2 by means of the drying medium, at last the sludge is burnt in the combustion space of the expeller.
6. Process as claimed in claim 5, c h r c¬ t e r i z e d in tha a supplementary firing is used ' for burning .the sludge.
7. Process as claimed in claim 6, c h a r a c¬ t e r i z e d in that the intensity of the supplementary firing is controlled by the pressure of the condensed seam having been evaporated in the combus¬ tion space of the expeller, while the rate of the flow off of the water excess is regulated by means of the water level .of the steam generator.
8. Equipment for the energysaving drying especially of heatsensitive, as well as toxic smelly gas producing materials, e. g. organic provisions, agricultural produces, being provided with a drier operating in an open or closed system using a warm dry¬ ing medium, c h a r a c t e r i z e d in that in the path of the drying medium there is an absorber (2) * provided with a liquid distributor (3) for introducing the humidity absorbing solution, furtheron there is an expeller (7) for the removal of the humidity content of the humidity absorbing medium having been discharged from the absorber (2), while the steam space of said expeller is connected to the heat exchanger. (9) arrang¬ ed in the' path of the stream of the drying medium leav¬ ing the absorber (2) and the liquid space thereof is connected to the liquid distributor (3).
9. 9* Equipment as claimed in claim 8, c h a r a c t e r i z e d in that in the absorber (2) a condenser • coil (5) has been arranged.
10. Equipment as claimed in claim 8, c h a r a c t e r i z e d in that the solution exchanger (l2) is arranged in the pipeline connecting the expeller (7) with the liquid distributor (3) and the absorber (2).
11. Equipment as claimed in claim 8, c h a r a c t e r i z e d , in that the expeller (7) is arranged in the combustion equipment (δ) delivering the warm drying medium.
12. Equipment as claimed in claim 8, c h a r a c t e r i z e d in that the flue (lO) of the waste gases of the combustion equipment (δ) is connected to the mixingchamber (ll) having been' arranged in the conduit (37) of the absorber (2) delivering the drying medium.
13. Equipment as claimed in claim 8, c h a r a c t e r i z e d in that one or more pumps (4, 6) are inserted into the pipeline(s) connecting the expeller (7) with the absorber (2) and/or the liquid distributor (3).
14. Equipment as claimed in claim 8, , c h a r a c t e r i z e d in that the absorber (2) is provided with a level sensing element (l3) which is connected via the regulator (14) to the combustion equipment (δ) and/or the control valve (l5, 16) there of.
15. • 15* Equipment as claimed in claim 8, c h a r a c t e r i z e d in that it contains a closed drying circuit incorporating the combustion equipment (δ), the recipient (17) for the wet product, the heat exchanger (9), the ventilator (l) and the absorber (2) while the heat exchanger (9) is arranged in the pipeline connecting the steam space of the expeller (7) to he atmosphere.
16. Equipment for performing the process according to claim 5, containing an absorber, a furnace incorporating the expeller, a combustion equipment and a heat exchanger, c h a r a c t e r i z e d in that it is provided with the sludge drier (23.), which is connected to the combustion chamber of the furnace (33) via the dryingline (32) for the dry sludge, while the absorber (2) and the sludge drier (23) are inter¬ connected by means of the pipeline preferably led through the heat carrying space of the heat exchangers (9, 27), at the same time the sludgedrier (23) is connected preferably through the cyclone (24) to the absorber (2) via the pipelines (25).
17. Equipment as claimed in claim 16, c h a r a c t e r i z e d in that it is provided with a steam generator preferably a boiler tube register (3l) having been arranged in the firing OΓΛ chamber of the furnace (33) and with a pipeline (28) connected to said steam generator and the exother space of the heat exchangers (9, 27). • Equipment as claimed in claim 16, c h a r a c t e r i z e d in that in the outlet pipe string of the steam generator there is a mano¬ meter (36), while the combustion equipment (δ) is provided with automatical control means being in connec tion with the manometer o 1 • Equipment as claimed in claim 16, c h a r a c t e r i z e d in that it is provided with a valve (29) regulating the flowoff, being controlled from the water level of the steam generator.
Description:
Method and equipment for the energy-saving; drying especially of heat-sensitive as well a3 of toxic and/or smelly gas producing materials

Technical field

The invention relates to a method for the energy- saving drying especially of heat-sensitive materials, as e. g. provisions, agricultural produces, furtheron of toxic and/or smelly gas producing organic substances and organic sludges, in course of which air or a gaseous medium is used as a drying medium in an. open or closed system, by the aid of which the moisture of the material to be dried is extracted.

Background art

Essentially, the cycle of proceedings of equipments and processes operating with air or a gaseous drying medium is taking place in such a manner, that the drying medium is simultaneously the heat-carrying agent, i. e. it delivers the heat quantity needed for the evaporation of the moisture to be removed * The moisture leaving the material to be dried mixes with the drying medium and discharges in the atmosphere in form of a saturated or su ersaturated steam.

It goes without .saying, that by increasing the heat content and thus raising the temperature of the drying medium drying capacity may be increased. However, from the point of view of thermodynamics, this increasing is to be considered as disadvantageous, i. e. the endeavour for an increased capacity in such a manner involves the deteriorated efficiency of the process; that means that instead of the ideal re-

versibility, the process is more arid " more shifted to the irreversibility and to the disadvantageous efficiency.

The rise of the temperature with the intention of 5. increasing capacity is accompanied by detrimental consequences at certain heat-sensitive materials, since these materials become decomposed at an increas¬ ing rate, when the temperature is rising, e. g. organic substances in general, provisions and agricultural produces. Decomposition is considerably diminishing the value in use, in fact it may happen, that it is entirely annihilated.

Prom the aforesaid it becomes obvious, that if reduct¬ ion of temperature became possible with the process and equipment mentioned above, it would mean consider¬ able improvement regarding to the efficiency of the drying process as well .as to the quality of the dried product•

Disclosure of Invention

The aim of the invention is to reduce the drying tem¬ perature with a view to energy savings, simultaneously to increase the efficiency of the drying process by extracting the moisture content of the drying medium before and/or after drying, as well as by utilizing the heat content of the humidity having been abstracted in such a manner.

The invention is based on the recognition, in so far as the aim set can be achieved by absorbing the moisture content of the drying medium in a humidity absorbing medium (solution), whereby the moisture absorbing capacity of the drying medium will be increased.

In a known manner drying capacity can be further in-, creased by direct or indirect heating, however, in

case of a more dried medium the same drying, capacity may be obtained by means of a drying medium of lower temperature resulting simultaneously the elimination of damages effected by heat. If at the same time we _ provide for the utilization of the heat content of the original humidity of the drying medium or of the moisture having been extracted from the product, heat economy of the process can be improved up to the physically possible optimum. The essence of the process according to the invention lies in, that the moisture content of the enviromental drying air is reduced in an absorber by bringing it into contact with a humidity absorbing medium; the solution with the absorbed humidity is evaporated while heated in an expeller; t.he steam is condensed via the heat exchanger and it is led in a liquid state to the atmosphere, meanwhile the drying air is ' heated in the same heat exchanger. The moisture content of the drying medium is extracted by bringing it into contact with the humidity absorbing solution either before drying or after. In case, if the drying medium is used in an open system, the drying medium is brought into contact with the humidity absorbing solution prior to the drying process, i. e. before it would come into contact with the material to be dried, while the moisture absorbed in such a manner is used in course of the heat exchange with the drying medium, accordingly, a part of the heat content of the humidity resulting from solar energy may be also utilized. In case of an open system we may proceed in such a manner too, that the drying medium is brought into contact with the humidity absorbing medium after dry¬ ing; in such a manner the drying medium is pre-dried and in addition to this a part of the energy content of the heating medium may be also utilized., ,^ό ' -7 i'-i. £P< _ []

( -S7OL, 'V, 1

The automatical control of the process is to be performed by means of the fluctuation of the level of the absorbing solution contained in the absorber, and so the capacity of the heating equipment producing the warm drying medium and the dosage of the humidity ab- • ' sorbing medium are controlled **

By applying the process according to the invention, drying in a closed cycle may be also realized. In this case the warm drying medium is circulated in a closed circuit through the wet product, the humidity absorb¬ ing liquid curtain having * been produced in the absorber and the heat exchanger. Meanwhile " the humidity absorb¬ ing medium is evaporated and the- steam led through the . * heat exchanger comes in a liquid state to the atmosphere. When the drying medium is used in a closed system, we proceed in such a manner, that the moisture .content of the drying medium having been abstracted by the humidity absorbing .solution is removed from the closed system, while the heat content is recirculated into the closed circuit.

Drying in a closed circuit can be particularly advan¬ tageously used for drying smelly or toxic materials and the process may be well combined with the equip¬ ment serving for burning of the mentioned materials. Industrial waste-water - especially in the chemical-, food-, and pharmaceutical industry - as well as communal sewage are containing contaminating, toxic and smelly gas producing substances in a considerable quantity, as -consequence * , they cannot be discharged directly into the outlets. The diverse sewage treat¬ ment plants serve for the extraction, decomposition, neutralization and conversion of said " materials with the intention to render them harmless. The by-products of these materials - cont minating the enviroment

are diverse sludges, mostly containing organic substances in a significant quantity, which are generally burned, although they could be well used - due to their considerable content of organic substances - for soil amelioration. In such a manner, apart from the fact, that useful value is going to be lost, due to the high water content a considerable quantity of energy carrier, i. e. heat energy is consumed. Due to the more and more rigorous prescriptions relating to ecology all over the world, valuable energy carriers in an increasing quantity have been continuously used. It may happen, that the sludges - at ' the expense of a considerable heat energy - are dried, dege minated and by adding additives rendered suitable for soil amelioration.

However, the heat quantity being discharged with the flue gases arising from the burnt energy carrier and the ' burning air can be recuperated with inefficiency only, increasing the costs of sludge treatment. For the reasons of energy savings in several cases said process cannot be used at all. The application of the process is further complicated by the fact, that the flue gases to be discharged are to be separated from dust and to be cleaned.

Iii course of developing the process according to the invention we arrived at the recognition, in so lar as sludge treatment can be decisively improved by using the heat quantity resulting from the utiliza¬ tion of the own thermal value of the previously dried sludge for heating the expeller and it can be well used for substituting the heating energy to be used in the combustion equipment of the expeller in dependence of the combustile content and the thermal value of the sludge.

In sense of the invention, in said cases we are proceeding, in such a manner, that starting from a " state - in which the sludge is pre-condensed to a 30 % solid content - the sludge is dried to an in- significant moisture content (l - 2 ), the drying medium having been enriched with the moisture content of- the sludge is brought into contact with the humidity absorbing solution and the drying medium having been dried in such a manner is led through the drier, at least the dried sludge is burnt n the combustion space of the expeller. In case if the heatin ' value -is not sufficient for maintaining the process, supplementary firing becomes necessary.

When operating with, a supplementary firing, intensity thereof can be controlled by the pressure of the condensed steam having been evaporated in the combus¬ tion space of the expeller, while the rate of dis¬ charge of the excess water may be controlled by the water level in the steam generator.

For air-conditioning purposes the moisture content of the ambient air is adjusted to the prescribed value by bringing it into contact with the humidity absorb¬ ing solution in the absorberj the abstracted solution containing the humidity is evaporated while being heated in the expeller and the steam thus obtained is used in the heat exchanger for heating the air or heating the absorbtion cooling equipment. In case, if in the drier any other liquid (e. g. a solvent), than water is to be evaporated, the absorbing solu- tion is to be selected accordingly.

The essential feature of the equipment being suit¬ able for performing the process ' according to the invention lies in, that it comprises an absorber

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extract ng the moisture of the drying air, which is provided with a fluid distributor for charging the humidity absorbing solution, an expeller for the removal of the moisture content of the humidity ab- sorbing solution and a heating coil having been arranged in the stream of the drying air. The liquid space of the expeller, the reservoir of the absorber and the liquid distributor, as well as the vapour space and the heating coil are interconnected by means of pipelines. In the absorber there is a condenser coil arranged.

In the pipeline connecting the heated expeller with the absorber, i. e. with the liquid distributor one or more pumps as well as heat exchangers are arranged. The warm heating medium and the combustion products are mixed in the.mixing-chamber. For the automatic control of the equipment the absorber is provided with a level sensing element and a control device, while the latter one is connected to the combustion equipment and the pumps or the control valve thereof.

With an equipment operated in a closed circuit the drying system consists of the combustion equipment, the resβrvoir(s), the absorber, the heat exchanger and the ventilator. The- heat exchanger is arranged between the vapour space of the expeller and the closed drying circuit.

Brief Description of Drawings

The invention will be described in detail by means of preferred embodiments, by the aid of the accompany- ing drawings, wherein: figure 1 * is the schematical side-view of one of the preferred embodiments, figure 2 is showing the schematical side-view of

an other preferred embodiment, figure 3 is the schematical side-view of a further embodiment.

Best Mode of Carrying out the Invention ' With reference to figure 1, the ventilator 1 is press¬ ing the ambient air into the absorber 2, wherein the air is brought into contact in a counter-flow with the humidity absorbing solution, streaming through the nozzles of the liquid distributor 3 and being .delivered by the pump 4.

The humidity absorbing liquid having been sprayed through the nozzles of the liquid distributor 3 into the absorber 2 is able to reduce the moisture content of the air in a rate corresponding to the sate of equilibrium. The state of equilibrium can be determin¬ ed by means of unambiguous physical correlations from the initial weight-concentration of the solution and the temperature of absorption. The equilibrium moisture content can be considerably reduced e. g. by means of a water cooled condenser coil 5. So e. g. by using the aqueous solution lithium chloride the moisture content of the air of the temperature of 32 G and with a relative moisture content of 40 % may be reduced to a value corresponding to a dew-point of 0 C , that means, that- about 8 g/m moisture can be extracted. The quantity of the humidity extracted may be increased by increasing the concentration of the solution and/or by reducing the temperature of tha condenser coil 5. When water having been cooled in a cooling tower is used as coolant, the quantity of the humidity absorb¬ ed by the solution can be considerably increased by reducing the ambient temperature, simultaneously maintaining the value of the solution circulation.

In the absorber 2 the humidity absorbing solution is warmed up in course of absorbing the moisture content of the air. In order to be able to maintain the pre¬ scribed moisture content of the air, the heat formed is to be extracted by means of the condenser coil 5; up to a certain air temperature heat extraction may take place by the air itself in this case the so- called solution heat can be utilized or heating- the drying air and increasing the efficiency of the process.

However, in any case the air leaving the. absorber 2 is of the same ' emperature, as the ambient air or it is even warmer, but by all means it contains less moisture. The solution pump 6 delivers the solution having been enriched with water to the expeller 7. * Under the heating influence of the flue gases of the combustion equipment 8 - in our example an oil burner - the humidity haying been absorbed from the solution is discharged in form of steam, whereas the water steam is transferring the heat contained there¬ in to the dry air leaving the absorber 2 in the heat exchanger 9, resp. the condenser coil during conden¬ sation. In course of a continuous operation in the heat exchanger 9 and in the condenser coil, resp., accurately the same quantity of steam is condensed, as it has been extracted from the air in the absorber 2. The humidity quantity of 8 g/ according to our " example represents e. g. a heat quantity of 4.5 kcal, by which the air temperature can be raised by about 14 * C°.

The equipment previously described represents ' practically a thermic compressor, which,when acting as a heat pump, renders the heat content of the steam quantity corresponding to the moisture contents of

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the ambient air suitable for heating the air in such a manner, that it raises the temperature of the humidity. The temperature ' and pressure of the steam leaving the expeller 7 depend on the concentration of the solution, which again develops in the expeller 7 in dependence of. the delivery capacity of the pumps 4, β; from the heat exchanger resp. the heating coil the ' condensate is discharged into the atmosphere, the quantity of which corresponds to the quantity of the humidity having been absorbed in the absorber 2.

The capacity of the combustion equipment 8 may be selected in such a manner, that in addition to the heat requirement of the expeller 7 it β should further heat the drying air * up to the permitted temperature. In this case the flue gas . of the- combustion equipment 8 is led via the flue 10 of waste gases into the mix¬ ing-chamber 11 having been arranged in the conduit 37 of the absorber 2 delivering the drying medium, where it is mixed with the dry air leaving the absorber 2. In such a manner firing can be rendered practically free of losses. At last economicalness can be further- increased by applying the solution heat exchanger 12.'

The expeller 7 can be heated by the flue gas of any type of combustion equipment, with steam or any other heat source staying at disposal on a given place. Flue gases may be directly used for heating the air. Instead of the.solution pumps 4, 6 solely the solu¬ tion pump 4 may be used with a solution stream being divided on the delivery side between the absorber 2 and the expeller 7, or the solution pump 6 alone is used, when the pressure in the expeller 7 is such, that * spraying of the solution through the nozzles of the liquid divisor 3 becomes possible.

When we intend to apply the process according to the invention with an already existing equipment, the ventilator 1 may be connected either to the suction or to the delivery side. The expeller 7 may be built- -in into the path of the flue gas stream, while the heat exchanger 9 is to be inserted into the cold sec¬ tion before the inlet of the flue gas or in case of suction at the absorber 2, it is to be connected to the delivery side of the ventilator 1. For the continuous control of the function of the system one single pulse suffices, and this is the liquid level in the absorber 2. The increase of the moisture content of the drying medium entering into the system is accompanied by the increase of the volume of the absorbing solution. As a consequence, he level sensing element 14 arranged in the level indic.ater 13 is giving a pulse for the increase of the capacity of the combustion equipment 8 and for opening the control valves 15, 16 and thereby for the increase of the quantity of the circulated solution, as a consequence, the system comes to an equilibrium state corresponding to a higher moisture content. The same equilibrium sets in without the control valves 15 and 16, when the equipment is having suitable spaces -for receiving the increased volume of the solution.

In a contrary case, when the humidity content of the air decreases, the liquid levels in the absorber 2 and- in the leveJL indicator 13 are descending. The level sensing element 14 detects the descent of the liquid level and gives a pulse for decreasing the capacity of the combustion equipment 8 and for throttling the control valves 15, 16. As a consequence, the quantity of the circulated solution also .decreases and the system is set in a state of equilibrium,

corresponding to a lower humidity content. The state of equilibrium may be reached by the exclusive decrease of the heating intensity of the combustion equipment 8.

5. At another preferred embodiment of the drier accord¬ ing to the invention the drier is inserted into the flue- 10 of the waste gases. In this case humidity in a significant quantity is discharged.through the out¬ let of the system; the humidity consists of the origina 0 ' - moisture content of the air and the moisture having been extracted from the dried product. This humidity quantity is ' carrying a considerable amount of heat, however, due to the low temperature and the corrosive character utilization thereof would be uneconomical 5 or could not be carried out at all.

The -humidity mentioned above is absorbed in the absorber 2 having been connected after the system and converted in the ' expeller 7 into water steam of increased temperature and pressure. This water steam 0 can be expediently used either for heating the air to be introduced into the system or for pre-heating the material. In such a manner the specific fuel consump¬ tion of the drier related to the dried material can be considerably reduced, in addition to this,- due to ' 5 pre-drying, the temperature of the cylindrical drum may be kept on a lower level resulting in an improved quality of the dried organic material.

Another method may be used, when - as it is to be seen in figure . 2 - the absorber is inserted into the 0 drying system in such a manner, that the humidity is quasi "lifted out" by the solution from the closed space. The solution absorbs the moisture content coming from the wet material stored in the recipient 17 in the absorber 2. In the expeller 7 the humidity 5 is transformed in water steam, which - after havi g ξt R OM

heated the air in the heat exchanger 9 - is dis¬ charged into the atmosphere. In this case the drying process is taking place in a completely closed circuit, and enables the use of any drying medium not being air, or e. g. the drying of toxic materials.

Furthermore, the process may be well used for air- .conditioning purposes, i. e. for heating or cooling or for the control of the moisture content of the air. The absorber * 2 is adjusting the humidity of the ambient air to the prescribed value. According to necessity, the temperature of the air leaving the absorber 2 can be heated by means of the steam coming from the expeller 7 via the heat exchanger or the steam can be : used for heating an absorption cooling equipment and cooling of the air may be realized up to the rate corresponding to the humidity contents having been extracted. Simultaneousliy cooling effect can be achieved by spraying water into the dry air.

A further mode of performation of the process accord- ing to the invention and the equipment being suitable for performing the process will be described in . connection with figure 3. The const-ruction and opera¬ tion of the equipment is, as follows:

The ventilator 1 is producing a depression in the absorber 2. The air - streaming under the influence of the activity of the ventilator - comes into contact with the humidity absorbing solution arriving through the nozzles of the liquid distributor 3. The solution may be the aqueous solution of lithium chloride or lithium bromide or any other humidity absorbing solu¬ tion.

The humidity absorbing solution having been sprayed by means of the nozzles of the liquid distributor 3 into the absorber 2 reduces the humidity contents of the air in a rate corresponding to the state of --r.ττ

"equilibrium. The humidity content corresponding to the state of. equilibrium may be reduced by means of the condenser- coil 5. In the absorber 2 the humidity absorb¬ ing solution is warmed up, when the moisture is bound, the heat developed is also extracted by the condenser coil 5*

- The air leaving the absorber via the ventilator 1 has the same temperature, as the ambient air or it is even warmer, but the moisture contents is always less. The . solution pump 6 is delivering the humidity absorbing solution having been diluted with water into the expeller 7» The combustion equipment 8 - in our example an oil burner - heats the humidity absorbing solution by burn¬ ing the dry sludge in a manner to be described later, in the expeller 7 * From the humidity absorbing solution the humidity having been absorbed, is leaving in form of steam and after having passed through the heat exchanger 9, it transfers its heat content from the absorber 2 to the dry air having been exhausted by the ventilator 1. By using the solution exchanger 12 econoraicalness of the system may be increased..Spraying of the absorbing solution through the nozzles of the liquid distributor is induced by the overpressure in the expeller 7- The mechanically dehydrated and compacted sludge contain¬ ing about 30 % solid matter is transported by means of the conveyor 21 to the receiver 22. The sludge is dried in the drier 23 - in our example a fluidization drier - by means of the preheated dry air having been introduced * at the bottom through the heat exchanger 9 by means of the ventilator 1 and circulating in a closed circuit to a moisture content of 1 - 2 ' o. The fly dust having been seized by the drying air streaming through the drier 23 precipitates in the precipitator 24, wherefrom it is recirculated into the drier 23» The air containing

small quantity of dust and the moisture having been extracted in the drier 23 streams from the pre- * cipitator 24 through the pipeline 25 under the depression prevailing in the absorber 2 into said absorber and transfers its moisture content to the humidity absorbing solution. The contamination contained in the -absorbing solution is entrapped in the filter 26.

The task of the heat exchanger 27 is to replace the heat losses, when starting the operation and during the operational period. The condensate of the heat exchanger 9 and the heat exchanger 27 is discharged by the common pipeline 28. The part of the condensate, which corresponds to the moisture content of the sludge, is discharged by the valve 29 controlling the flow-off. This hot water may be utilized for the pre¬ heating of the sludge in the receiver 22 or in a y- other heat utilizing equipment .

The remaining part of the condensate is delivered by the pump 30 into the boiler tube register 31, here the condensate evaporates and transfers its heat content via the heat exchanger 27 to the air streaming into the drier 23.

The dried sludge arrives from the drier 23 via the conveyor line 32 into the furnace 33 incorporating the expeller 7 and the boiler tube register 31 * The combustible part of the- dried sludge is burnt in the combustion equipment 8, the air quantity needed for this process is obtained either from the air excess of the combustion * equipment 8 or it is delivered by the ventilator 34. The burnt sludge is leaving the furnace

33 through the discharge 35, while the flue gases of the furnace 33 are discharged into the atmosphere through the flue 10 of the waste gases. The flue 10 is to be formed in accordance with the prescriptions -^ FTEAT}' relating to eco

combined with a precipitator.

The .automatical operation of the equipment according to the invention is ensured by the components 13, 14, 15, 16 previously described, by the pressure indicator gauge 36 of the boiler tube register 31 and the valve 29, which controls the flow-off. The higher moisture content in the closed system of the drying air does not only cause the raise of the liquid level in the. absorber 2, but simultaneously it results in the increased heat demand of the heat exchanger 27 0 To satisfy both the capacity of the combustion equipment 8 has to be increased.

In compliance with prevailing circumstances the equipment . according to the invention .may be constructed in different versions; so e. g. the combustion equipment 8 can be fired with any liquid, gaseous or solid fuel instead of oil. When a solid fuel is used, it may 'be mixed with the dry sludge and to be burnt with it. The burnt hot sludge discharged from ' the discharger 35 may be well used for pre-heating the air delivered by the ventilator 34. The boiler tube register may be built-in into the path of the stream leaving the furnace 33, but the heat content * of the flue gas may be used for pre¬ heating the air. ~

The application of the process according to the inven- tion in practice will be demonstrated by means of some examples.

Example 1

When drying cereals, e. g. maize, and the aqueous solu¬ tion of lithium chloride is used in a concentration of 65 as a humidity absorbing solution in course of drying, it becomes possible to reduce the humidity content of the atmospheric drying air, which presumably

amounts to 12.5 g/kg, to 2.5 g/kg prior to drying. From the humidity absorbing solution having been enriched with water, in the absorber 10 g water steam with a pressure of 1.5 bar - related to 1 kg air - may be obtained, by the aid of which the dry air after the absorber can be warmed up by approx. 18 G°. As a con- - sequence, drying capacity of the air will be con¬ siderably increased in comparison with the atmospherical air, e. g. in case of the temperature of 18 G° it can be doubled, resulting in the increase in the same proportion at maize drying i. e. relating to the capacity of the drier.

__ Example 2

The process having been described in Example 1 is modified in so far as humidity absorption is taking place after the drying of the maize. In this pase - using the same quantity of absorbing solution - a considerably higher rate of humidity absorption may be realized,, since in the drying air the moisture of the dried material also. appears in addition to the atmospherical moisture (in our example 12.5 g/kg)-, which may totally amount to 50 g humidity/kg. ' In this case it seems to be expedient to expel the moisture at a higher pressure, e. g. 5 bar, in the expeller. With the generated saturated steam of a pressure of 5 bar the air in the drier can be pre¬ heated by 90 C° instead of 18 C°, that means, that dry¬ ing capacity may be increased to the fivefold instead of the double.

Example 3 We proceed in accordance with Example 1 or 2, but the efficiency of expelling is further improved in such a manner, that the hot flue gases of the solid or liquid fuel used for heating the expeller are directly admixed

to the drying air. In " such a manner efficiency of ex¬ pelling can be increased by about 25 , either in relation to example 1 or 2. The same effect may be indirectly realized i. e. by using a heat exchanger, In this case efficiency may be improved by 22 - 23 % •

Example 4

In course of drying limestone grist serving as a carrier for plant protectives, we intended to achieve, a remanent moisture content of 0.1 . For this purpose the carrier was dried with air of the temperature of 48 G°, circulat¬ ed in a closed circuit and with.a moisture content of 2.5 g/kg. The parameters of the air could be obtained by using the aqueous solution of lithium chloride with a concentration of 65 % as a humidity absorbing medium, while absorption took place at 12 C°. The solution was enriched to a water content of 69 % • In the expeller steam of pressure of 1.5 bar was generated, the expeller was heated with steam of. the pressure of 5 bar. The efficiency of the process can be characterized in that 110.5 kg moisture could be expelled from the closed cir¬ cuit by means of 152 kg steam, that means, that a heat quantity of 650 kcal (2530 KJ) has been used for drying 1- kg water. In course of the traditional processes often 12000 KJ are required and a process, where only 5000 KJ * are needed, is considered, as most advantageous.

Example '

For cooling and heating air-conditioning air a process has been used, in course of which the air having been exhausted from the_ rooms and partly mixed with fresh air is led through the absorbing unit of the equipment. Here about ' 12 g/kg moisture may be extracted by using the aqueous concentration of lithium chloride in a concentration of 65 % * In the expeller water steam in a quantity of 12 g/kg of a pressure of 2 bar may be

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released from the solution having been enriched in wate j by means of this steam quantity the .treated air of 25 C may be heated to about 45 C 0 ', as a consequence, in winter the thermal requirement of heating may be reduced, in summer again, the released steam may be well used for operating the absorption cooling equipment. In such a manner the air of a temperature of 36 C° having been exhausted from the rooms may be cooled to 28 0°, accordingly air-conditioning of the rooms may be ensured without requiring separate cooling energy.

Example 6

In course of drying, the mechanically dehydrated sewage sludge with a moisture contents of 60 - 70 % is deliver¬ ed itrto an absorber with a fluidization bed, where the drying air (20.000 Ηm^ , 70 G°, moisture contents . 2.5 g/kg) is circulated in a closed circuit. When leaving the drier with .the fluidiz ng bed, the moisture content of the air increases to 17.00 g/kg, simultaneously the temperature is dropping to 33 C°. The moisture being extracted from the sludge amounts to about 7 tons/day, while the solid-matter amounts to 3 tons/day. The substance floating in the drying air is separated in a ulticyclon. The moisture of the drying air having been led to the absorber is extracted by means of the lean aqueous solution of lithium chloride with a concentration of 60 % , in a quantity of 2610 kg/h, until reaching the value of 2,5 g/kg; meanwhile the solution is enriched to the water content of 64 % • * ' simultaneously the mass stream is increased to 2900 kg/h. The heat having been developed in course of absorption is extracted in the water coolero The solution having been enriched in water is pressed through the solution cooler into the expeller, where the part of the water taken up in course of absorption is

leaving in form of steam of an overpressure of 0.5 bar.

The steam is used for heating the drying * ir circulat¬ ing in a closed circuit, by means of the; heat exchanger, while the expeller is heated with the dry sewage siudge If the sewage sludge had such a high thermal value* tha it is able to release heat excess, steam may be generat ed in the boiler tube register, while the steam- thus obtained" may- be utilized for further heating the. dry¬ ing air. In case of the heating value. ' did not enable th satisfaction of the heat demand of drying, the missing ' heat quantity is to be ensured from ' the outside, y a supplementary heating, e. g. by means of ' an oil burner. In case, if the heat value exceeds 6000 KJ/kg, by burn¬ ing the dri * ed sludge demand on thermal,energy of drying may be met. Over this value the process is calorific, below it the application of a supplementary heating is needed.

The equipment and the process according :to the inventio may be expediently used for burning coal dust having be classified byflotation. The coal dust with the high moisture content can be dried with a good 'efficiency an can be directly fed into the coal mill* i. e. into the coal dust burner. Due to the fact, that the water adher ing to the coal dust can be evaporated in the vicinity of the reversibility of the cycle, the heat requirement amounts merely to 700 Kcal/kg instead of the traditiona 1000 - 1100 Kcal/kg, in addition to this, labour intens of the grinding process and accordingly, energy consump tion of the mill are reduced. It -is not necessary to lea the hot flue gas from the combustion chamber of the boiler to the grinding process for the purpose of dry¬ ing, accordingly, the heat contents thereof can be utilized on the after-heating surfaces of the boiler for the pre-heating of the feed ter and air * The expel

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7 and the boiler tube register 31 can be built-in into the draft-path of the boiler resulting in a further reduction of the energy consumption.

The main advantage of the process according to the 5 invention lies in that. by using drying air of the same temperature and in the same quantity ' , a greater quantity of moisture may be removed from the material to be dried, than in course of the traditional processes. In such a manner the temperature of any drying process may be

10. reduced, as a consequence, partly thermodynamical efficiency can be improved, partly the stability of heat sensitive materials to be dried may be ensured. When • • drying toxic and/or smelly gas producing materials, e. g. sludges, the separated burning of the dry sludge and

15 utilization of the generated heat require considerably less accessory heating energy, than burning of the we sludge, since in the case of the latter one drying and burning taking place in a common space significantly increase the losses. By utilizing the condense heat

20 having been generated in the heat 'exchangers 9, 27, thermal economy may be further improved.

A further essential advantage lies in, that whether with newly constructed equipments, whether with already exist¬ ing equipments, in addition to the reduction of drying '

25 temperature, the energetic efficiency of the process will also improve.

By using the solution according to the invention it becomes possible to pre-dry the entering drying medium, in general the ambient air, or to extract the water 30 steam from the discharged drying medium rich in humidityo In both cases the heat contents of the humidity having been extracted in form of steam, can be well used for increasing the heat content of the drying medium. With driers operating in a closed circuit, the humidity be-

ing * resent in form of steam is discharged by sorption into the atmosphere, while the heat content of the humidity vapour is recirculated into the closed system.

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