Dryer, particularly for the chemical industry
BACKGROUND OF THE INVENTION 
     The invention relates to a dryer and more particularly to a dryer for the chemical industry which functions to allow both fresh air operation and return air operation. 
     One prior art dryer is disclosed in European Pat. No. 60,212. The prior art dryer has a very complicated structure and is difficult to use. In the prior art arrangement, a fan basket in the ceiling part of the housing extends directly into the drying chamber and draws off the flow of gas from the chamber. On the exhaust side, the fan basket in the ceiling part directs the flow of gas as a main flow along the back wall of the drying chamber, where a heating device is located, and down past the division plate to the back side of a loading car that is located in the drying chamber. The main flow of gas then passes through the loading car in the longitudinal direction. The ceiling part of the chamber on the exhaust side has a control device which directs a secondary flow along the side walls and into the drying chamber where condensers are located. The secondary flow is suctioned back by a fan on the suction side of the chamber. Since the secondary flow of gas is led directly to the condensers, heat is lost through the fan rather than being absorbed by the material to be dried. 
     SUMMARY OF THE INVENTION 
     The above and other disadvantages of the prior art dryers are overcome by providing a dryer which is versatile and energy efficient. 
     A flow of heated gas is led past material to be dried in a generally laminar flow, without sharp turns, thus efficiently extracting thermal energy from the gas to dry the material. This means a reduction in the amount of energy required for cooling and condensing purposes. Chambers are located on both the exhaust and the inlet or suction sides of the dryer as well as in a housing structure located adjacent to the housing to dampen the flow of gas. Additionally, filters are provided to eliminate particles, such as dust, that may be carried along in the gas flow. A ventilator produces an air flow at the inlet side of the dryer and a lower pressure or vacuum on the suction side of the dryer thus allowing the gas inlets and/or outlets to be located in the inlet and outlet housing structures. 
     Since the loading car is kept free of baffles, it can be of a very simple construction. It is, preferably, constructed as a framework that is open on all sides. The dryer of the present invention can be utilized with either a closed circuit operation or a fresh air gas fed operation. Controlled amounts of fresh air can be added as required and/or a portion of the flow of gas can be drawn off as exhaust. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagrammatic side view of a dryer embodying the present invention; 
     FIG. 2 is a diagrammatic section along the line II--II of FIG. 1 and in the direction indicated generally; and 
     FIG. 3 is a diagrammatic top plan view of the dryer of FIG. 1. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, a dryer which embodies the present invention is designated by the numeral 1. The dryer 1 has a housing 2 with an approximately square cross-section which encloses an approximately square drying chamber 3. The drying chamber 3 is defined by side walls 4 and 5, a rear wall 6 and a door 7 (best seen in FIG. 3), a floor 8 and a cover 9. 
     A loading car 10 is loaded into the square drying chamber 3 through the door 7. The car 10 has tiers 11 which are supported by a frame (not shown) between which racks (not shown) containing the products to be dried thereon can be pushed. The dimensions, or at least the side dimensions, of the car 10, shown equipped with rollers 12, are adapted to fit within the drying chamber 3. The car 10 is open at the sides and, preferably, the front and the back are open as well. The drying chamber 3 can be constructed so that it will receive several loading cars 10 wherein the cars can be positioned either one next to the other or one behind the other. 
     The side walls 4 and 5 of the drying chamber 3 are made of perforated sheets which are attached so that they can swing inward into the drying chamber for cleaning purposes. Perforations 13 are arranged in rows across the width of the side walls 4 and 5 with the rows extending above the height of the loading car 10. The perforations 13 are dimensioned to allow the partial flows of gas, indicated by the arrows I, to pass approximately equally through the loading car 10 in the cross direction. 
     The side walls 4 and 5 as well as housing sides 14 and 15 form delivery and exhaust chambers 16 and 17. Openings 16a and 17a, in the chambers 16 and 17, can be fitted with filters 18 and 19, respectively. A plate, perforated plate, or other closure that will cause a laminar flow of gas can be substituted for the filters 18 and 19. The chambers 16 and 17 are closed at the bottom by panels 20 and 21. 
     The side chambers 16 and 17 (formed by the sides 14 and 15, the side walls 4 and 5, the filters 18 and 19 and the panels 20 and 21) can be constructed as separate modular units or in combination with the drying chamber modules as uniform modules. 
     A housing cover 22 is fixed on the housing 2. The housing cover 22 is generally formed coextensive with the housing 2. The housing cover 22 has an outlet housing structure 23 that overlaps the filter 19 and the cover 9. The housing structure 23 is divided into a main chamber 25 and a secondary chamber 26 by a horizontal baffle 24. The main chamber 25 is equipped with an adjustable valve 27, located near the opening 17a, through which gas flows in the direction of arrow 27a. A similar valve can be provided for the secondary chamber 26. In addition, there is an adjustable valve 28 at the exit of the secondary chamber 26. 
     A condenser 29 is located in a horizontal position in the secondary chamber 26. The condenser 29 has a tubular register through which a coolant can flow. A collecting reservoir 30 is located below the condenser 29 to collect any condensate that forms on the condenser 29. 
     A gas outlet 31, having a control valve 32, is positioned between the opening 17a and the valve 27. When the valves 27 and 28 are in the closed position, the entire flow of gas can be diverted to the outside of the dryer 1 through the outlet 31. An outlet filter 33 can be provided to capture any particles that might be exhausted through the outlet 31. 
     A gas inlet valve 34 can be equipped with a filter 35 and a control valve 36 to open into the main chamber 25. Fresh air, for &#34;fresh-air operation&#34;, can be supplied through the valve 34. The chambers 25 and 26 are associated, on the suction side, with a ventilator formed by a fan basket 37 and a motor 38 to draw gas through an intake 39 in the direction indicated by the arrow 39a thus creating a lower pressure in the chambers 25 and 26. The intake of fresh air through the inlet valve 34, in the direction of arrow 34a, is adjusted by means of the motor 38. 
     An inlet housing structure 40, which partly covers the outlet housing structure 23, encloses the fan basket 37 and supports the motor 38. The housing structure 40 is adjacent a pressure chamber (not shown) which expands in relation to the intake 39. The pressure chamber has a heating device (not shown) which is constructed as a tubular register that can be heated by an external source, such as steam. The housing structure 40 has an upward directed gas outlet valve 42 to release gas in the direction indicated by the arrow 42a. The structure 40 is further equipped with a control valve 43 and, if desired, with an outlet filter 44. 
     The dryer 1 can be utilized in a closed circuit operation as well as for an operation that is exclusively fresh air or partial amounts of fresh air. Further, the dryer can utilize inert gases, such as nitrogen, so that the danger of explosion during the drying of, for example, products containing solvents is reduced. 
     The flow of heated gas passes into the large gas chamber 16 as a laminar flow and is therein divided as it flows through the side wall 4, of perforated sheet metal, to reach the tiers 11 and dry the material placed thereon with an evenly distributed flow of gas. The temperature of the gas flow is reduced as the gas passes over the tiers 11 due to evaporation during the drying process. Further, the filter 19 captures particles, such as dust, that may be carried along with the flow of gas. The filter is constructed to be easily removable so that it can be cleaned or replaced. 
     Depending on the amount of moisture that has been removed from the material, a secondary flow of gas must be led to the condenser 29. The condensation output is adjusted by means of the control valves 27 and 28. Preferably, the condenser 29 is supplied with a cooling liquid to obtain a preliminary lowering of the gas temperature. The amount of heat generated by the rotation of the fan basket 37 must be taken into account when the heating device is set to a desired temperature. A totally fresh-air operation can be obtained by completely replacing the recirculated air with fresh air through the outlet 31 and the inlet valve 34. 
     Modification and variations of the present invention are possible in light of the above teachings. The housing 2 and the drying chamber 3 can have a shape other than square, for example rectangular, so long as the herein disclosed flow of gas through the dryer 1 is not unnecessarily restricted. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.