US 3783527 A
An improved dryer for bulk material of the type employing a feed apron, a pin elevator and an endless, foraminous belt moved through a series of air drying zones, the improvement comprising (A) a humidity transducer in the air exhaust stack arranged to regulate flow of steam to a sparger under the belt in a zone and (B) a power level transducer attached to the pin elevator drive motor, a temperature transducer located under the belt in the final zone, each transducer connected through a separate controller to a booster relay arranged to select the lower of the two control signals and apply this to regulate feed apron drive motor speed.
Description (OCR text may contain errors)
United States Patent 1191 Driscoll et al.
 3,783,527 Jan. 8, 1974 DRYING APPARATUS WITH FEED AND HUMIDITY CONTROL  Assignee: E.I. du Pont de Nemours and Company, Wilmington, Del.
22 Filed: Dec. 13, 1972 211 App]. No.: 314,603
 US. Cl 34/56, 34/54, 34/52,
- 34/44  Int. Cl. F26d 13/12, F26b 21/08  Field of Search ..34/56, 52, 54, 50, 34/44, 45, 51
 References Cited UNITED STATES PATENTS 3,186,102 6/1965 Brociner et a1. 34/56 X 3,259,995 7/1966 Powischill 34/54 X 3,396,476 7/1 968 Eves 34/52 X 3,599,343 8/1971 Nielson 34/52 T0 CUTTER STA 1011s COMPUTING RELAY CUTTERS CONTROLLER TO BELT MOTOR Arnold ..l 3.4/51 x FOREIGN PATENTS OR APPLICATIONS 480,355 1 1952 Canada .l .L ..34 44 Primary Examiner--William F. ODea Assistant Examiner-Paul Devinsky Attorney-Howard P. West, Jr.
 ABSTRACT An improved dryer for bulk material of the type employing a feed apron, a pin elevator and an endless,
foraminous belt moved through a series of air drying zones, the improvement comprising (A) a humidity transducer in the air exhaust stack arranged to regulate flow of steam to a sparger under the belt in a zone and (B) a power level transducer attached to the pin elevator drive motor, a temperature transducer located under the belt in the final zone, each transducer connected through a separate controller to a booster relay arranged to select the lower of the. two control signals and apply this to regulate feed apron drive motor speed,
2 Claims, 1' Drawing Figure 111011 515114 SUPPLY DRYING APPARATUS WITH FEED AND HUMIDITY CONTROL BACKGROUND OF THE INVENTION This invention concerns apparatus for improved drying of loose bulky material such as textile staple fibers in bulk. More specifically, it relates to auxiliary control apparatus appended to a continuous dryer which employs an enclosed endless foraminous belt and circulating air.
Uniform rate of drying and final level of moisture content are important to product quality. Color, dyeability and openness of synthetic fiber staple products are often adversely affected by variable or poorly regulated drying conditions.
A significant improvement in controlling dryers of this type has been realized by the apparatus of Powischill in U.S. Pat. No. 3,259,995. However, further improvement was required for certain drying systems such as, for example, a system where the dryer is supplied from a hopper that has an intermittent input. A case in point is a dryer of the type for textile staple wherein the feed hopper is supplied from tow cutters, one or more of which must be interrupted for splices, knife change, etc. In these cases, the hopper fill level may vary sharply and the rate of feeding of staple to the dryer as well as dryer conditions require special regulation.
SUMMARY OF THE INVENTION This invention provides apparatus attached to an enclosed endless belt dryer chamber that is supplied with bulk material in a hopper by a feed apron in the bottom of the hopper and a pin elevator extending from the apron to deposit material on the belt. Both the apron and the pin elevator are independently driven by variable speed motors. Improved regulation of the extent of drying is provided by the novel auxiliary control apparatuses of this invention. These comprise in combination wet and dry bulb temperature transducers in the exhaust duct. These transducers are connected to a computing relay. The resulting difference Signal is fed to a controller arranged'to regulate the flow of steam to a steam sparger located under the belt at a position along the belt which is near the latter stages of drying. The belt enclosure is separated into three zones along its length by transverse partitions. Circulating fans bring air in from the room outside the enclosure and pass it over control conditioning elements, then through the belt from above to below and finally exhaust through a duct.
In addition to sparger control effects, further improvement is provided by a temperature transducer located under the belt in the last zone of drying. This transducer is connected to a first of two companion controllers. A power level transducer is attached to the motor of the pin elevator and the output signal of this transducer is connected to the second controller. The outputs of these controllers are connected to a booster relay which selects the lower signal. The output of this relay is connected to the speed controller of feed apron motor of the supply hopper. Thus, the speed of the feed apron is regulated in response to either pin elevator power drop below set point or below belt temperature dropping too low.
These improvements may be used in conjunction with or as a replacement for one or more of the known arrangements, e.g., those of Powischill. These known methods include: (A) control of the dryer belt speed; (B) control of fan motors; (C) control of an exhaust damper; (D) adjustment of a unit to humidify incoming air; and (E) regulation of steam supply to heaters employed in conditioning the air used for drying, all in response to the below belt temperature measurement.
BRIEF DESCRIPTION OF THE DRAWING The Drawing is a schematic plan view of an endless belt enclosed dryer and acircuit diagram showing the novel control features of this invention attached thereto.
DESCRIPTION OF THE PREFERRED EMBODIMENT An understanding of the apparatus of this invention can best be achieved by reference to the attached drawing. The preferred apparatus is described in connection with the drying of synthetic textile staple fibers in bulk which are received from textile tow cutters, not shown, and which after drying are transported to staple balers also not shown. The novelty of the invention lies in the control apparatus appended to a substantially conventional dryer.
The dryer as shown in the drawing comprises an endless foraminous belt 10 extending around drive sprockets l2, l4. Sprocket 14 is driven through chain 16 by gear motor assembly 18. Optionally, motor 18 has a speed control component 20 which is responsive to a thermocouple 22 located underneath the belt 10 near the exit end of the belt. The upper horizontal leg of belt 10 extends from the input end underneath a shoe 24 which is designed to push the material being dried down onto the belt. In some cases, this shoe is provided with a steam supply and perforations for applying steam to the incoming bulk material. The belt extends into a drying enclosure 26 which is divided into three drying zones 27, 28, 29. Each zone is substantially the same size and has a configuration essentially the same as that shown by Powischill in U.S. Pat. No. 3,259,995.
rator 42 from which it drops into feed hopper 44. The
bottom of hopper 44 comprises a feed apron 46 which is driven through chain 48 by variable speed motor 50, such as a Reeves drive with Airtrol unit attached. At the exit end of apron 46, there is provided a pin elevator arrangement 52 which is driven through chain 54 by variable speed motor 56. A withdrawing roll 58 and a scrapping bar 60 are arranged as shown and driven through chain 64 by variable speed motor 62. Two photoelectric staple level detectors 66, 68 are located in the sides of hopper 44 at locations as shown. The upper detector 66 is arranged to send a signal to the staple cutters when the level of staple to be dried becomes excessive within hopper 44. Detector 68, on the other hand, sends signals to stop the belt 'motor 18 when the level passes below a critical limit and restarts motor 18 when the level rises again above detector 68. Time delay circuits are provided in connection with the outputs of these detectors to avoid reaction to very transient over or under supply.
The novel control features of this invention comprise I first a wet and dry bulb temperature transducer 70 located within the stack 40. Transducer 70 has attached thereto a conventional fluid-to-air transducer so that pneumatic signals are transmitted over lines 71, 71 to a computing relay 72.
The dry and wet bulb temperature signals are algebraically combined in the computing relay 72 to provide an output signal to controller 74 proportional to the difference between the dry bulb and wet bulb temperatures and consequently related to the relative humidity of the air in stack 40. Thus, pneumatic controller 74 (typically a Moore Syncro Station) provides signals for adjusting valve 76 to control the flow of steam through pipe 78 to sparger 80 and out through nozzles 81. In this way, the quantity of steam forced upward through fan 31 and down through the sample being dried is based on the relative humidity of the air exhausting from the dryer. This forms the first part of the added control system.
The second part of the novel control system comprises a duel input selective control in which a power level transducer 84 (Halltiplyer WT 31K5) is con-.
nected through cable 85 to pin elevator motor 56. The signal from transducer 84 is passed to a first controller 86 over cable 87 through a conventional voltage-to-air pressure transducer not shown. The output of pneumatic controller 86, which in the preferred embodiment is Moore Syncro Station, is passed first over line 89, to a Mercoid switch 90 and then to the start-stop mechanism of motor 50 over line 93. A second output from controller 86 is transmitted over line 91 to a first input terminal of a booster relay 94 (Moore Products C0., Model 61). A temperature transducer 96 is located under the dryer belt near the exit end of the drying stages and arranged to provide a signal over line 97 to another (Moore Syncro Station) controller 98-. Output from controller 98 is transmitted over line 99 to a second input terminal of booster relay 94. The output signal from relay 94 is connected over lines 101 and 103, respectively, to the speed control unit (Airtrol unit) of feed apron drive motor 50. This signal also goes to recorder 104 (Rustrack Recorder)and thence to a system of readout devices located at the low cutter stations. Relay 94 is designed to select the lower of the two input control signals and transmit its output control signal based on this selection.
This invention provides two important means for the regulation of the moisture content in materials being dried on an endless belt. The relative humidity of the air exhausted through stack 40 is employed to regulate the opening of the valve which controls the amount of steam blown down through the material being dried, thus evening out humidity in the drying air and therefore, reducing potential wet spots in the material. In addition, one signal based on the amount of power being drawn by the pin elevator motor, which is related to the drying load level being imposed on the dryer, is used to provide one possible signal for regulating the rate of supply of material by adjusting the speed of the feed apron 46. An alternate signal is provided by a readout of the temperature of the air underneath the dryer belt near the dry end of the drying zones. These two signals are employed by respective controllers 86, 98 to provide two signals to a booster relay which selects the lower of the two signals (power level or underbed temperature) to provide the regulating signal for the speed of apron motor 50.
The utility of this invention lies in the attainment of more uniform product which is desirable. In actual tests, a comparison was made between operation of a I trol system of this invention was put into operation on the same dryer, the number of moisture stops per day was reduced to a very low level of only two and this had the corollary effect of increasing possible dryer throughput by about 4 percent. Furthermore, it was found that manual control was able to maintain a dryer rate variation at no better than i 20 lb. per min. whereas the new system controlled the rate of variation in dryer throughput to a level of i 10 lb. per min. This obviously provides improved fiber heat treatment uniformity and consequent improvement in dyeability uniformity and uniformity in color of the production.
Although this invention has been described in terms of the present preferred embodiment wherein synthetic textile staple is dried, the novel structure and function of this invention is applicable to the drying of other bulk materials which may be fed by means of a feed apron and pin elevator onto an endless forarninous belt and dried with circulating air. In addition, the invention is described in terms of pneumatic controller devices. Obviously electronic controllers could be substituted and other variations would be apparent to those skilled in the art without departing from the spirit of the present invention. 7
What is claimed is: g
1. In an apparatus for continuously drying material including an endless belt dryer chamber supplied with material by a pin elevator driven by a motor and a feed apron driven by a variable speed motor the improvement comprising: a power level transducer connected to the pin elevator motor for detecting the power consumed by the pin elevator motor and for generating first signals proportional to the power consumed by the pin elevator motor; a temperature transducer located in said dryer chamber for detecting the temperature therein and for generating second signals proportional to the temperature detected; means for comparing said first and second signals and for selecting the lower of said signals; and a controller connected to said feed apron motor for regulating the speed of said feed apron motor, said controller being actuated by the lower of said first and second signals.
2. The apparatus as defined in claim 1, said dryer chamber having an exhaust duct connected thereto and a steam sparger located therein'for admitting steam into said chamber and further including means for detecting relative humidity in said exhaust stack and generating third signals proportional thereto; a controller connected to said steam sparger for regulating the steam flow therethrough, said controller being actuated by said third signals.