US3599343A

US3599343A - Drying apparatus, particularly for drying green crops intended to be made into briquettes

Info

Publication number: US3599343A
Application number: US840754A
Authority: US
Inventors: Alfred Thygesen Nielsen
Original assignee: Unidry Eng & Dev
Current assignee: Unidry Eng & Dev; UNIDRY K/S ENGINEERING AND DEVELOPMENT GROUP
Priority date: 1968-07-12
Filing date: 1969-07-10
Publication date: 1971-08-17
Anticipated expiration: 1988-08-17
Also published as: FR2012857A1; NL6910643A; GB1244569A; BE735927A; ES369357A1; DE1934202A1; DE6926663U; DK119956B

Abstract

In a drying apparatus, primarily for drying green crops, a rotary drying drum receives the raw material at one end at which also a flow of heated drying air is admitted to the drum for flowing therethrough in substantially axial direction. Two temperature feelers are placed respectively at the inlet and outlet ends of the drum, and a mixture of pulses or signals from these feelers is utilized to control the supply of raw material to the drum in such a way that a balance is ensured between the constant heat production and the heat consumption.

Description

United States Patent Inventor Appli N 0. Filed Patented Assignee Priority Alfred Thygesen Nielsen Holte, Denmark 840,754

July 10, 1969 Aug. 17, 197 1 Unldry K/S Engineering and Development Group Copenhagen, Denmark July 12, 1968 Denmark DRYING APPARATUS, PARTICULARLY FOR DRYING GREEN CROPS INTENDED TO BE MADE INTO BRIQUETTES 7 Claims, 1 Drawing Fig.

US. Cl 34/52, 263/33 R Int. Cl F26b 13/10 Field of Search 34/52, 32; 263/33 [56] References Cited UNITED STATES PATENTS 3,102,794 9/1963 Arnold 34/52 X 3,396,476 8/1968 Eaves 34/52 X 3,400,468 9/1968 Matthews 7. 34/52 Primary Examiner-Carroll B. Dority, Jr. Attorney-Sughrue, Rothwell, Mion, Zinn & Macpeak ABSTRACT: In a drying apparatus, primarily for drying green crops, a rotary drying drum receives the raw material at one end at which also a flow of heated drying air is admitted to the drum for flowing therethrough in substantially axial direction. Two temperature feelers are placed respectively at the inlet and outlet ends of the drum, and a mixture of pulses or signals from these feelers is utilized to control the supply of raw material to the drum in such a way that a balance is ensured between the constant heat production and the heat consumption.

PATENTED AUG] 71971 SIGNHL- pPOCESSl/VG d/ECU/ T5 INVENTOR ATTORNEY DRYING APPARATUS, PARTICULARLY FOR DRYING GREEN CROPS INTENDED TO BE MADE INTO BRIQUETTES The present invention relates to a drying apparatus, particularly for drying green crops intended to be made into briquettes. comprising a substantially horizontal rotary drying drum having at one end a feeder that is adjustable with a view to varying the amount of raw material fed into the drum, and a heat source, such as an oil burner, to supply, under a substantially constant heat production, a hot drying airflow through the drum which at its other end comprises an outlet for the dried goods and a temperature feeler for supplying adjustment pulses to the feeder.

The drying effect in such an apparatus depends mainly on the fact that while passing from the inlet end of the rotary drum to its outlet end the goods to be dried or the raw material will repeatedly fall down through the hot airflow, the particles of the material between each fall being carried upwardly by the rotating drum wall. During their fall the individual particles will to a greater or minor degree, depending on their weight and their surface area, be carried along in the axial direction by the drying airflow, and the drying process is partly self-adjusting in the sense that particles, such as stalks, that require a rather long stay in the drying drum are to a lesser degree carried along by the airflow than are particles which more rapidly obtain the desired low-moisture content. It may be mentioned that the axial velocity of the goods through the drum can be changed generally by varying the slope of the drum axis. This makes it possible to control the moisture content of the finally dried material.

The progress of the drying process depends upon a number of factors, such as the type and condition of the raw material and especially its content of inherent and free moisture, as well as the ambient temperature and moisture conditions, and at least some of these factors will normally vary within fairly wide limits during the normal operation of the apparatus. Furthermore, the goods to be dried cannot usually, without damage or risk of fire, be heated above a certain temperature but should, on the other hand, be heated as near as possible to this temperature limit for achieving the optimum drying economy. These facts necessitate a constant control and adjustment of the drying process and for the purpose it is known, as mentioned above, to use a temperature feeler at the outlet end of the drying drum. If the temperature at this point should become too high, the feeler, by yielding adjustment pulses to the feeder, may cause the supply of raw material to be increased and in the opposite case, i.e. when the temperature at the outlet end of the drum falls below a given limit, the temperature feeler can cause a temporary decrease or a stop in the supply of material. In practice, however, such a control has in many cases proved to be insufficient, mainly due to a considerable slowness in the whole system resulting from the amount of raw material that at any moment is present in the drying drum. The result will be a more or less marked wave effect which in extreme cases can cause the drying drum either to be completely blocked up by the goods being dried or to be blown completely empty, unless either the supply of raw material or the heat production, when possible, is controlled or adjusted in time by manual operation.

It is intended through the invention to make possible such a balance in the drying process that at any moment the substantially constant heat production is at least approximately equal to the amount of heat required for the drying effect so that the wave formation referred to above can be avoided without further regulation.

With regard to this the drying apparatus according to the invention is unique in that in the drum and adjacent to the feeder a further temperature feeler is provided, the pulses of which, after having been mixed in a predetermined proportion with those from the temperature feeler at the outlet end of the drum, are utilized to adjust the feeder.

' and it becomes possible to ensure automatic control of the supply of raw material when the real temperatures within the drum differ by a certain amount, for example :10" C., from the ideal value. At the same time the liability of wave formation as explained in the foregoing will to a high degree be opposed because oppositely foregoing control pulses from the two temperature feelers will wholly or partly balance each other so that adjustment of the supply of raw material will only occur in cases when there is a general need for such adjustment.

The drying apparatus according to the invention will therefore by changes in the factors influencing the progress of the drying process constantly counteract the influence of such changes and, by doing so, ensure that the drying is carried out under the best possible conditions.

When the feeder for the raw material, as known, comprises an endless conveyor belt that may be operated with at least three different speeds, viz. a normal speed, at least one higher speed and at least one lower speed, and is associated with a levelling roller that is adjustable towards and away from the conveyor belt for regulation of the thickness of the fed layer of raw material, the different speeds of the conveyor belt may, in a suitable embodiment of the invention be determined by the mixed pulses from the two temperature feelers, whereas the levelling roller is adjustable by means of a motor that is controlled for retarded automatic starting when the speed of the conveyor belt differs from the normal speed. In practice the lower speed level can suitably be chosen as being nil, and the normal speed can then be half of the higher speed level. Hereby is achieved that adjustment pulses from the two temperature feelers will result in a quick and powerful response in the way of an increased or reduced supply of raw material so that usually the feeder will rapidly settle down at its normal speed. Only when the need for such an increase or reduction remains for a certain period of time, for instance of the magnitude of 20 seconds, it will be necessary to adjust the thickness of the layer of raw material on the conveyor belt to ensure that the belt may again run almost constantly at its normal speed.

An embodiment of the drying apparatus according to the invention is shown diagrammatically on the drawing and more fully described in the following. I

On the drawing, 1 indicates -a cylindrical horizontal drying drum that is rotatably supported on a plurality of carrying rollers 2. This drum can be rotated by means of a driving mechanism, not shown. The drum comprises a heat source consisting of a furnace chamber 3 with an oil burner 4 and a blower 5 for generating a flow of hot drying air that will pass substantially axially through the drum.

The raw material 6 which is to be dried is supplied by means of an endless conveyor belt 7 which, in the direction indicated by the arrow 8, runs over an upper driving roller 9 and a lower roller, not shown. The driving roller 9 is driven by a motor, not shown, which also drives a levelling roller 10, placed above the roller 9, in the direction indicated by the arrow 11, and the worm 12- of a screw conveyor that receives the material from the conveyor belt 7 and discharges the material to the drum through a tubular chute l3.

The levelling roller 10 is used for controlling the thickness of the layer of material 6 that is delivered to the screw conveyor, and for this purpose the levelling roller 10 is adjustable towards and away from the conveyor belt 7 which on the drawing is illustrated in the way that the levelling roller is carried by a vertical screw-threaded shaft 14 with a fixed crown wheel 15 meshing with a corresponding conical pinion 16 carried by the shaft of a driving motor 17.

The finally dried material leaves the drum 1 through an outlet 18, in the vicinity of which a temperature feeler 19 is placed. A similar temperature feeler 20 is placed in the drum 1 at the inlet end thereof, i.e. close to the discharge end of the tubular chute 13 lying inside the drum.

During the normal operation of the apparatus the furnace 3 comprising the burner 4 and the blower 5 supply a substantially constant hot drying air flow to the drum 1, and the conveyor belt 7 together with the levelling roller 10 and the worm 12 are driven at half speed, i.e. half of their maximum speed. The temperature feelers l9 and can be set for temperatures of the order of 100 C. and 800 C., respectively, and the distance of the levelling roller 10 from the conveyor belt 7 will be adjusted to result in such a supply of raw material to the drum 1 that inside this drum balance will exist between the produced amount of heat and the heat consumption caused by the evaporation and losses. Any deviations from this condition of balance will cause deviations from the temperatures that are supposed to prevail at the feelers l9 and 20, and if these deviations exceed a certain limit, for instance to 10 C., the temperature feelers, as explained in the foregoing, will send signals to adjustment mechanisms, known per se and not illustrated but of a conventional form such as in the Us. Pat. No. 3,396,476, granted Aug. 13, 1968 to R. O. Eaves, which will immediately affect the speed of the conveyor belt 7, the levelling roller 10 and the worm 12. If this condition lasts over a certain period of time that as mentioned before may be e.g.

20 seconds, the motor 17 will be started, likewise by means of ordinary equipment known per se, thus causing the levelling roller 10 to be raised or lowered to increase or reduce the thickness of the layer of material 6 and thus the amount of material fed to the drum 1, so as to restore the heat balance.

Means 22 can be utilized for changing the slope of the drum axis to vary the axial velocity of the crops as it moves through the drop.

During the operation of the drying apparatus certain conditions may arise which cause the temperature feelers 19 and 20 to yield oppositely directed signals or adjustment pulses. If such opposed signals are equal they will cancel out each other and normally the balance within the drum 1 will be quickly restored without any adjustment of the supply of raw material. If, on the other hand, the adjustment pulse from one feeler is considerably stronger than the oppositely directed pulse from the other feeler, the first pulse will predominate and cause a change in the supply of raw material, although to a lesser degree than in case the temperature feeler in question had been the only decisive factor in the adjustment.

1 claim:

1. A drying apparatus for drying green crops comprising; a substantially horizontal drying drum having an inlet and outlet; means for rotatably supporting the drum; means for adjustably feeding the crops at the inlet end of the drum; a heat source adjacent to the inlet'end of the drum and operative to produce a substantially constant amount of heat per unit time; means for admitting gas to the heat source and generating a flow of heated drying gas from the inlet end to the outlet end of the drum; means at the outlet end for discharging the dried crops from the drum; temperature sensor means for signalling temperatures in the drum including at least two temperature sensors positioned in the drum, the first adjacent the inlet end of the drum and the second adjacent the outlet end and means connecting the temperature signals to the means adjustably feeding the crops whereby the rate of feeding the crops is varied to maintain a constant uniform drying of the crops.

2. A drying apparatus as in claim 1 where the means for rotatably supporting the drum permits an adjustment of the slope of the drum to help regulate the flow of crops through the drum.

3. A drying apparatus as in claim 1 where the means for adjustably feeding the crops includes an endless conveyor, a worm screw conveyor and an adjustable leveling roller.

4. A drying apparatus as in claim 1 where the means for generating a flow of heated drying gas through the drum is the on]; meansfor moving the crops throu h the drum.

. A drying apparatus as in claim where the adjustable leveling roller rotates contra to the direction of crop feed on the endless conveyor and is adjustable relative to the endless conveyor.

6. A drying apparatus for drying green crops comprising, a substantially horizontal drying drum having an inlet and outlet; means for rotatably supporting the drum; means for adjustable feeding the crops at the inlet end of the drum, including an endless conveyor belt having at least three speeds which include a normal operating speed and a higher and lower speed, and a leveling roller; means for adjusting the leveling roller relative to the conveyor belt; a heat source adjacent to the inlet end of the drum and operative to produce a substantially constant amount of heat per unit time; means for forcing a gas heated by the heat source through the drum; only two temperature sensor means both located in the drum for producing temperature signals, the first temperature sensor means located adjacent the inlet and the second temperature sensor means located adjacent the outlet of the drum; means at the outlet of the drum for discharging the crops; means for receiving the temperature signals from the first and second temperature sensor means and controlling the means for adjusting the feeding of the crops including setting an appropriate speed for the endless conveyor and positioning the leveling roller whereby the desired dryness is imparted to the crops.

7. A drying apparatus as in claim 6 where the means for forcing the gas is the only means for moving the crops relative to the drum.

Claims

1. A drying apparatus for drying green crops comprising; a substantially horizontal drying drum having an inlet and outlet; means for rotatably supporting the drum; means for adjustably feeding the crops at the inlet end of the drum; a heat source adjacent to the inlet end of the drum and operative to produce a substantially constant amount of heat per unit time; means for admitting gas to the heat source and generating a flow of heated drying gas from the inlet end to the outlet end of the drum; means at the outlet end for discharging the dried crops from the drum; temperature sensor means for signalling temperatures in the drum including at least two temperature sensors positioned in the drum, the first adjacent the inlet end of the drum and the second adjacent the outlet end and means connecting the temperature signals to the means adjustably feeding the crops whereby the rate of feeding the crops is varied to maintain a constant uniform drying of the crops.

4. A drying apparatus as in claim 1 where the means for generating a flow of heated drying gas through the drum is the only means for moving the crops through the drum.

5. A drying apparatus as in claim 3 where the adjustable leveling roller rotates contra to the direction of crop feed on the endless conveyor and is adjustable relative to the endless conveyor.