Background of the Invention Field of the Invention

The present invention relates to a heating and/or drying apparatus and components used therein. More particularly, the present invention is directed toward a heating and/or drying appara- tus well suited for heating and/or drying solid granular or particulate material, such as aggregate comprising rocks, gravel and sand used in. aking asphalt concrete, for example. The apparatus according to the present invention has a novel construction which allows for the efficient and cost effective indirect transfer of heat energy from and to various parts of the apparatus.

In general, the presently preferred use contemplated for the present invention is to heat and dry aggregate used to make asphalt concrete.

The aggregate usually contains a substantial amount of moisture. The amount of moisture within the

aggregate can be reduced from the amount contained in the aggregate to zero moisture if desired. How¬ ever, the heater and heater-condenser of the present invention may be used to heat and/or dry other materials besides the aggregate used for asphalt concrete, including other granular and/or particulate material and, with slight modi¬ fications, even liguid material.

The components of the present invention considered independently of each other, as well as considered in association with each other, represent improvements over current and prior art equipment for heating and/or drying various kinds of materials and particularly aggregate material used to make asphalt concrete. Description of the Prior Art

One such prior art system is disclosed in the inventor's U.S. patents 4,245,915 entitled "Apparatus for Making Asphalt Concrete," and RE. 32,206 entitled "Process for Making Asphalt

Concrete." These patents are directed, inter alia, to a system for heating aggregate in a storage bin indirectly using steam evolved during a subsequent

step including heating a mixture of aggregate and binder.

There are other examples of prior art systems which dry various materials, including cement and other aggregate used to make Portland cement concrete, aggregate used to make asphalt concrete, and other solid aggregate and liquid materials. However, none of such systems are believed to provide as efficient and cost effective drying as the present invention. Moreover, the operation of the present invention reεults in substantially no atmospheric pollution. The present invention makes use of the energy value of moisture or other liquid contained in the material to be dried, which is usually lost by evaporation in typical drying or heating systems. The present invention preferably uses substantially all of the heat generated by various components of the system in other components of the system, rather than wasting such heat as in prior art apparatus and processes.

Summary of the Invention One aspect of the present invention relates to an apparatus for indirectly heating material containing at least some liquid comprising a preheater-condenser for preheating the material, a heater for heating the preheated material and for generating heater generated heat transfer fluid from the material, first conduit means connecting the preheater-condenser to the heater through which the heater generated heat transfer fluid is carried from the heater to the preheater-condenser, and conveyor means for conveying preheated material from the preheater-condenser to the heater, the preheater-condenser including a housing, inlet means through which the material enters the housing, outlet means for discharging the preheated material from the housing, first hollow heat exchange means supported vertically within the housing, first distributing means connecting the first conduit means and the first hollow heat exchange means for distributing the heater generated heat transfer fluid to the first hollow heat exchange means, and condensate removal means

connected to the first hollow heat exchange means for removing from the housing condensed heater generated heat transfer fluid from the first hollow heat exchange means, the heater ^• including a receptacle and a chamber in which the material is heated, a sealable inlet means through which the preheated material to be heated enters the receptacle, but through which gases formed in the heater will not escape to the atmosphere, the chamber having outlet means through which heated material is discharged from the chamber, heating means supported in a vertical orientation within the chamber, a plurality of collecting means supported within the chamber for collecting the heater generated heat transfer fluid from the material being heated, and accumulating means for accumulating the heater generated heat transfer fluid from the plurality of collecting means, the accumulating means being in communication with the collecting means and with the first conduit means through which the heater generated heat transfer fluid flows to the preheater-condenser.

Another aspect of the present invention relates to an apparatus for making asphalt concrete comprising a preheater-condenser for indirectly heating aggregate material containing at least some liquid, a heater for heating the preheated aggregate material and for evolving vapor from the liquid contained in the aggregate material, a first conduit connecting the preheater-condenser and the heater, a first conveyor means for conveying the preheated aggregate material from the preheater- condenser to the heater, a source of binder to be mixed with the aggregate material to form asphalt concrete, a mixer to mix the binder and aggregate material, a second conduit connecting the source of binder and the mixer, a second conveyor means for conveying the heated aggregate material to the mixer, and means for discharging the asphalt concrete from the mixer, the preheater-condenser including a housing, inlet means through which the aggregate material enters the housing, outlet means through which the preheated aggregate material is discharged onto the first conveyor means, and heat exchange means associated with the housing and

connected to the first conduit for heating the aggregate material in the housing using the vapor evolved by the heater as a heat transfer fluid, the heater including a chamber in which the preheated aggregate material is heated, the chamber having an inlet in an upper portion of the chamber through which the aggregate material enters the chamber and an outlet in a lower portion of the chamber through which the preheated aggregate material is discharged from the chamber, heating means oriented vertically within the chamber for indirectly heating the aggregate material and evolving vapor from the liquid contained therein, and collecting means for collecting the vapor evolved from the liquid contained in the aggregate material, the collecting means being connected to the first conduit.

Still another aspect of the present invention relates to a heat exchange apparatus for indirectly heating material containing at least some liquid comprising a receptacle for holding the material and through which the material passes to a chamber in which the material is heated, a sealable

inlet means through which the material enters the receptacle, but through which vapor evolved from the heated material in the apparatus will not escape to the atmosphere, the chamber having outlet means through which heated material is discharged from the chamber, heating means supported by support means in a vertical orientation within the chamber, and collecting means supported within the chamber for collecting the vapor. Brief Description of the Drawings

For the purpose of illustrating the invention, there is shown in the drawings a form which is presently preferred; it being understood, however, that this invention is not limited to the precise arrangements and instrumentalities shown. Figure 1 is divided into two separate figures, Figure 1A and Figure IB. Figure 1A is a front elevation view, partially including a schematic diagram of the left-hand portion of a system for making asphalt concrete using the apparatus of the present invention. Figure IB is a front elevation view partially including a

schematic diagram of the right-hand portion of the system of Figure 1A.

Figure 2 is a right hand side elevation view, partially in vertical cross section, of a heater apparatus according to the present invention.

Figure 3 is a horizontal sectional view of the heater apparatus taken along line 3—3 of Figure 2. Figure 4 is a front elevation view, partially broken away and partially in vertical cross section, of the heater illustrated in Figure 2.

Figure 5 is a left hand side elevation view, partially broken away and partially in vertical section, of the heater of Figure 4 taken along line 5—5 of Figure 4.

Figure 6 is a right hand side elevation view of the heater of Figure 4 taken along line 6- -6 of Figure 4.

Figure 7 is a partial vertical sectional view of the heater of Figure 2 taken along line 7- -7 of Figure 2 showing a portion of an inlet for

heat transfer fluid and associated support structure.

Figure 8 is a partial vertical sectional view of the heater of Figure 2 taken along line 8- -8 of Figure 2.

Figure 9 is a partial horizontal sectional view of the portion of the heater illustrated in Figure 8 taken along line 9—9 of Figure 8. Figure 10 is a partial horizontal sectional view of the portion of the heater illustrated in Figure 8 taken along line 10—10 of Figure 8.

Figure 11 is a partial vertical sectional view of a portion of the apparatus illustrated in Figure 8 taken along line 11—11 of Figure 8.

Figure 12 is a partial vertical sectional view of a portion of the apparatus of Figure 8 taken along line 12—12 of Figure 8. Figure 13 is a vertical sectional view of the portion of the apparatus illustrated in Figure 8 taken along line 13—13 of Figure 8.

Figure 14 is a side elevation view, partly broken away and partly in vertical cross section, of a heater-condenser apparatus and associated material handling means according to the present invention.

Figure 15 is a partial vertical sectional view of a portion of the apparatus of Figure 14, partly broken away, and taken along line 15—15 of Figure 14. Figure 16 is a partial vertical sectional view of the portion of the heater-condenser of Figure 15 taken along line 16—16 of Figure 15.

Figure 17 is a partial vertical sectional view of a portion of a heat exchange plate illustrated in Figure 15 taken along line 17—17 of Figure 15.

Figure 18 is a partial bottom perspective view, partly in vertical cross section, of a vapor inlet manifold used with the heater-condenser apparatus illustrated in Figures 14 through 16.

Detailed Description of the Preferred Embodiments Referring to the drawings in detail, wherein like numerals indicate like elements

throughout the several views, there is shown in Figures 1A and IB one type of system 30 incorporating many of the components according to the present invention for the exemplary purpose of making asphalt concrete. It should be understood that the schematic arrangement illustrated in Figures 1A and IB are for purposes of illustration only, and that the apparatus of the present invention can be used for other purposes besides in an asphalt concrete system, and the components may have different orientations in the system than those set forth in the drawings. Nevertheless, so* that the detailed descriptions of the individual components of the present invention as set forth hereinafter will be more clear, an overview of the present invention will be described with respect to asphalt concrete system 30.

There are several different types of materials moving to, through and from the various components of system 30. One component is the material to be heated and/or dried, in this specific example aggregate material including small to large particles such as stone, rocks, sand,

reclaimed pieces of old asphalt concrete, and the like. Material has been "dried" according to the present invention when the material leaving the various heater components contains relatively less liquid than when the material entered the heater components. For the sake of convenience in describing the heating and/or drying components of the present invention, they will be referred to herein as a "heater," "heater-condenser" or "preheater-condenser" and such terms are to be interpreted to mean that such components may provide a drying function in addition to or in lieu of a heating function.

Other materials moving to, through and from various components of system 30 include two different types of heat transfer fluids. One heat transfer fluid referred to herein as the "primary heat transfer fluid" is preferably in liquid form, although it may be gaseous, and is heated initially by any suitable means such as that described hereinafter. The second heat transfer fluid is a vapor generated by the heater from the liquid contained in the material being heated and/or dried

by the primary heat transfer fluid. This second type of fluid is referred to herein as the "heater generated heat transfer fluid."

With reference to Figure 1A, aggregate material to be heated and/or dried, such as aggregate material, is placed within heater- condenser apparatus 32 which is used in system 30 as a preheater-condenser. The material can be transferred to preheater-condenser 32 by any suitable means, such as bucket conveyors, power shovels, wheel loaders or the like. Material in preheater-condenser 32 is heated by the heater generated heat transfer fluid, as explained hereinafter in more detail, and is discharged by conveyor means 34, such as typical conveyor belt feeder. From belt feeder 34, the initially heated and/or dried aggregate material is transferred by conveyor means 36 into heater apparatus 38. Heater apparatus 38 heats the initially heated and/or dried aggregate material by heat transfer from the primary heater transfer fluid until the aggregate material has a desired final moisture content and/or until the material reaches a predetermined

te perature, such as 148.9°C (300°F). Because of current asphalt concrete industry standards, it is preferred that the heated and/or dried material be as dry as possible, and most preferred that there be substantially no moisture or other liquid contained in the dried material.

The heated and/or dried material is discharged from heater 38 by conveyor means 40 which conveys the heated and/or dried material into an inlet of a mixer 41. Although conveyor means 40 is illustrated schematically as being a conveyor belt, it could be in the form of a pan feeder or an enclosed auger preferably sealed from the atmosphere to retain the heat of the material and to prevent any uncontrolled atmospheric emissions. Mixer 41 may include inlet and outlet means which are sealable from the atmosphere for the same purpose.

A binder, such as asphalt cement, with or without various additives known to those skilled in the art, may be contained in a source 42, such as a storage tank. The binder is pumped through conduits 43 and 45 by pump 44 into mixer 41. The

mixing is accomplished by virtue of an auger, paddles, mixing blades, or the like, within the mixer. The amounts and flow rates of the heated and/or dried aggregate, and binder material, as well as the mixing and discharge rate within mixer 41 may be monitored, adjusted and controlled by typical state-of-the-art controls.

Hot asphalt concrete is discharged from mixer 41 onto a conveyor means 46 for further storage, delivery to trucks, or the like. Having described the flow of the aggregate material with respect to Figure 1A, the flow of the heat transfer fluids will now be described initially with reference to Figure IB. Primary heat transfer fluid of a type to be described hereinafter is heated by primary heat transfer fluid heater 47. The heater may include a fossil fuel burner, such as an oil burner, a gas burner or a coal burner, or the heater may be heated electrically. The primary heat transfer fluid may also be heated by solar energy. Most typically, such heaters include fossil fuel burners.

The primary heat transfer fluid leaves heater 47 at a temperature of about 315.6°C (600°F) to about 371.l°C (700°F) , although the temperature could be adjusted to other values, if desired for any given purpose. The fluid flows through conduit 48 and past pressure control device 50. Device 50 including a pressure gauge 52 or other pressure sensor, detects the pressure within conduit 48 and compares it to the maximum pressure which can be sustained in hollow heat exchange plates within heater 38. The device is designed to open the valve associated with the device if the pressure within conduit 48 exceeds the allowable pressure designed for the system within heater 38. When the valve is opened, fluid within conduit 48 is diverted to return conduit 58 until the pressure within conduit 48 is within the desired parameters. Referring to Figure 1A, the primary heat transfer fluid then passes through a product (heated and/or dried material) temperature control device 54. Device 54 is electrically connected by wire 55 to a thermocouple or other temperature sensing device 56 to sense the temperature of the

heated and/or dried material about to be discharged from heater 38. If the temperature of the material is too low, a valve associated with temperature control device 54 is opened, allowing the hot primary heat transfer fluid to circulate through the heat exchange plates within heater 38. If the temperature exceeds the desired limit, the valve of device 54 closes. If this happens, the pressure will build in conduit 48, triggering the opening of the valve associated with pressure control device 50. Thus, the operation of pressure control device 50 and temperature control device 54 are interrelated and coordinated by suitable state-of- the-art monitoring and control equipment. The primary heat transfer fluid then exits from heater 38 through return conduit 58. The now cooler primary heat transfer, fluid passes by pressure control device 50 and then past the primary heat transfer fluid expansion tank 60. Valves 62, 64 and 66 may be opened and closed as necessary to remove moisture from the primary heat transfer fluid and to allow for primary heat transfer fluid expansion. Nitrogen or other inert

gas used to maintain a system blanket pressure in expansion tank 60 may enter through inlet 68 through suitable valves (not shown) . Primary heat transfer fluid can be added to the system by adding it to expansion tank 60 through inlet 70, preferably containing suitable valving (not shown) . The primary heat transfer fluid may be a gas, such as super-heated steam, or preferably a liquid, such as hot oil, commercially available synthetic heat transfer fluids or commercially available molten salt mixtures, such as a mixture of potassium nitrate, sodium nitrite and sodium nitrate. Selection of the appropriate primary heat transfer fluid will depend upon such factors as availability, cost, temperature ranges desired, and the like. In general, the criteria for the proper selection of an appropriate primary heat transfer fluid is well within the realm of those of ordinary skill in the art. The primary heat transfer fluid passes through strainer 72 and past pressure gauge or other sensor 74. Then it is pumped by pump 76 past another pressure gauge or sensor 78 and through

suitable valving 80. From there, the primary heat transfer fluid is heated or re-heated by heater 47, and the cycle is repeated.

At present, it may be most economical to use a fossil fuel burning heater for the primary heat transfer fluid heater 47. Particularly with fossil fuel burning heaters, substantial heat and energy value is lost through exhaust gases (generally 15-20%) . The present invention also provides for the substantial recovery of this lost heat.

In the present invention, instead of exhausting the combustion gases directly to the atmosphere, the gases, typically at a temperature of about 370°C (700°F) , are routed from heater 47 through conduit 98 (see Figure IB) to a housing surrounding at least the heating chamber portion of at least heater 38 (see Figure 1A) . The heat contained in the exhaust gases can be transferred indirectly through an inner housing wall to the material to be dried and then exhausted through an outlet in the housing.

If desired, the exhaust gas from heater 47 could be transferred in a like manner to surround preheater-condenser 32 either solely or in addition to the transfer to heater 38. Within heater 38, the aggregate material containing some moisture or other liquid is heated to the point where the liquid is evaporated to form a vapor or gas. The evolved vapor or gas becomes the heater generated heat transfer fluid described above, and exits heater 38 through conduit 82.

Conduit 82 connects to delivery conduits 84 and 85 which, in turn, connect to inlet manifolds ^' 86 and 88 associated with hollow heat exchange plates contained within preheater-condenser 32. Although conduits 82 and 84 preferably are insulated to reduce the heat loss through the walls of the conduits, some condensation may occur, which is removed through trap 90 and condensate removal conduit 92. The heat exchange plates within preheater-condenser 32 result in the heating, or preheating in this particular system, of the aggregate material. As the aggregate material is heated, much if not most of the gas within the

hollow heat transfer plates condenses within pre¬ heater-condenser 32. The condensate is collected and removed from the preheater-condenser through conduit 94. A gas vent valve 96 is provided to bleed off air entrained within the system.

System 30 can operate in a batch, semi- continuous or continuous mode. Because of the residence time of the aggregate in heater 38, and in view of the indirect heat transfer process taking place in heater 38, primary heat transfer fluid heater 47 may at times have excess capacity. To utilize the excess 'capacity, particularly when- the system is operating in a batch or semi- continuous mode, primary heat transfer fluid heater 47 may be connected by a plurality of conduits 48 and 58 to a plurality of heaters corresponding to heater 38. Appropriate sensing means and valving would direct the hot primary heat transfer fluid to the particular heater requiring the fluid at any particular time.

System 30 has been described to provide a basic understanding of the overall operation of several major components of the present invention,

and particularly preheater-condenser 32 and heater 38. With this understanding as background, the construction and operation of the various novel components of the present invention will be described in detail.

Details relating to heater 38 are illustrated in Figures 2 through 13. To have a common frame of reference, Figure 1A is considered a front view, whereby Figure 2 is a side view, partially in vertical cross section, of the right hand side of heater 38, Figure 4 primarily is a front view, Figure 5 is primarily a left side view, and Figure 6 is primarily a right side view of heater 38. Heater 38 comprises support legs 100 which are supported in a conventional manner on any suitable foundation, portable trailer equipped with jack supports, or the like. Support legs 100 are attached to a housing 102 by any suitable means, such as by welding, nuts and bolts, rivets, or other fastening means. Appropriate bracing and other framework may be used as required, and need not be described herein in detail. Housing 102 may

be of any desired shape and may include inwardly sloping lower walls as illustrated, front, rear and side walls which are substantially vertical from the top to the bottom, or any other shape as desired.

Housing 102, which preferably contains a solid, flowable material containing at least some liquid to be evaporated, may be an integral structure, but preferably comprises an upper portion 104 which is preferably welded or otherwise sealingly attached to a lower portion 106. The upper portion functions primarily as a receptacle for receiving material 103 to be dried. Lower portion 106 functions primarily as a heating chamber.

Attached to the top of receptacle 104, preferably to suitable framing members, are support members 108 which support a sealable inlet hopper 110. Hopper 110 receives aggregate from conveyor 36 and represents the only inlet into receptacle 104. Since receptacle 104 must be sealed from the atmosphere during its operation to be most effi¬ cient, hopper 110 must have appropriate sealing

eans. For operation in a continuous mode, hopper 110 may have a screw conveyor which carries sufficient material and is so dimensioned that it effectively seals the receptacle 104 from the atmosphere. Other suitable sealable inlet means useable with hopper 110 include star valve, air cylinder operated gates or the like.

Support members 112 depend from the frame structure or are supported by support members 108. Attached to support members 112 is a splitter bar 114. A plurality of adjustable diverting vanes 116 are mounted on splitter bar 114. As illustrated in Figure 2, vanes 116 are oriented to divert material toward the left hand portion of the Figure, while vanes 118 are oriented to divert material toward the right hand portion of the Figure. The vanes may be adjusted by rotating them about a horizontal axis to distribute material 103 evenly within housing 102. Referring now primarily to Figure 7, a support angle bracket 120 is illustrated as being supported on support leg 100. Angle bracket 120 includes a shelf portion 122 and a horizontal

flange portion 124. These elements are illustrated at the top of Figure 3. The support angle bracket typically is attached to lower portion 106 of housing 102. Receptacle portion 104 of housing 102 typically is attached to flange 124 by bolts and nuts extending through holes 126 formed in flange portion 124. Corresponding flange portions extend around the perimeter of portion 104 of housing 102 as identified by flanges 128, 130 and 132 having a plurality of holes 134, 136 and 138, respectively. Appropriate gasket material may be placed between the flanges of upper and lower housing portions 104 and 106, respectively, to assure a fluid tight seal. Figure 7 illustrates a portion of heater

38 and shows the relative positions, prior to final assembly, of the support structure and a preferred embodiment of the heating means used in the heater. More specifically, Figure 7 shows the interrelationship during the assembly of the heater among one of a plurality of hollow heat exchange plate assemblies 180 of the heating means, an associated inlet manifold 166 and the support

structure. During assembly, one end of the heat exchange plate assemblies 180 are supported by manifold 166 which initially rests on shelf 122 of support angle bracket 120. When the apparatus is entirely assembled, and during operation, heat exchange plate assemblies 180 are suspended from above in a manner described hereinafter such that there is a space between the bottom of manifold 166 and the top of shelf 122. A similar structure supports manifold 170 associated with the other end of heat exchange plate assemblies 180 (See Figure 3).

With reference to Figures 2 and 3, a plurality of support blocks 140, 142, 144 and 146 (Figure 3) may be supported by support angle brackets 130 and 132. Support blocks 140 and 142 are illustrated in Figure 2. Elasto eric pads 148, 150 are attached to the upper surface of support blocks 140 and 142 by a suitable means, such as by bonding with a suitable adhesive. Likewise, there are pads attached to support blocks 144 and 146, although such pads are not visible in the drawings. The pads may be made of any suitable material which

can withstand the particular environment, including high temperatures, and which can absorb shocks associated with a vibrating beam supported on the pads. Support beam 152 is supported on and bolted through pads 148 and 150. Likewise, beam 154 is supported on pads mounted to support blocks 144 and 146. A plurality of hollow heat exchange plate assemblies 180 are attached to and depend from beams 152 and 154 in a manner described hereinafter.

At least one vibrating means 156, and preferably two such means 156, are secured to each beam 152 and 154. The vibrating means may be any suitable type, such as a motor driven eccentric wheel or other conventional device. Housings 158 and 159 protect vibrators 156. Although the tops of housings 158 and 159 are illustrated as being flat in Figures 2 and 3, if desired, they could be arched, pointed or the like to aid material flow around the vibrators. Power lines and a cooling fluid, such as air, are supplied to vibrators 156 through through inlet conduit 160 and intermediate

conduits 162. The cooling fluid continues to flow through outlet conduit 164.

Hollow heat exchange plate assembly 180 will now be described briefly, with a more detailed description to follow hereinafter. Figures 2, 3 and 8 best illustrate how hollow heat exchange plate assemblies 180 are supported by support beams 152 and 154. Each heat exchange plate assembly includes a top .support bar 208 to which threaded studs 178 are welded or otherwise attached. Studs 178 pass through holes in lower flanges of support beams 152 and"154 and are retained in place by nuts 179.

An inlet manifold 166 is attached to the upper outer side wall of all heat exchange plate assemblies 180 below support bars 208 by means such as welding. Inlet manifold 166 includes a flange 168 which attaches to a flange 49 of primary heat transfer fluid supply conduit 48 by suitable fasteners in the usual manner. A sealed, sliding expansion joint accommodates the passage of manifold 166 through the wall of housing 102 while

maintaining the interior of the housing in a sealed condition.

An outlet manifold 170 is attached to the top of the opposite side wall of all of the heat ^' exchange plate assemblies 180 below support bars 208 by means, such as welding. Outlet manifold 170 has a flange 172 which is fastened in a conventional manner to flange 174 of primary heat transf r fluid return conduit 58. As described more particularly hereinafter, hot primary heat transfer fluid is delivered through conduit 48 into inlet manifold 166. From there, the hot primary heat transfer fluid flows through the hollow heat exchange plate assemblies 180. The primary heat transfer fluid then flows out of the heat exchange plate assemblies through outlet conduit 170, where it enters return conduit 58. The aggregate or other material 103 is heated indirectly by virtue of the heat transfer from the primary heat transfer fluid through the walls of plate assemblies 180. Although the preferred embodiment of the heating means used in the heater to indirectly heat the

aggregate includes the hollow heat exchange plate assemblies 180 and the associated primary heat transfer fluid delivery system as they are described herein in detail, other heating means may be used to indirectly heat the aggregate, such as electric resistance heating plates, for example.

As the aggregate is heated, water or other liquid contained therein begins to evaporate. The evolved vapor or gas, which becomes the heater generated heat'transfer fluid, flows through a number of orifices formed in the bottom surface of sparger tubes 190 aligned below at least some of the heat exchange plate assemblies 180. The sparger tubes are a part of an evolved vapor collecting assembly or means 194 which includes a generally V-shaped collection chamber (best illustrated in Figures 2, 4 and 5). Collecting means 194 includes legs 196 and 198 in fluid connection with open ends 192 of sparger tubes 190 (Figure 8) . The opposite ends of sparger tubes 190 are closed as by caps or plugs 193 (Figure 8) .

The evolved vapor collected in collecting means 194 flows through a removal conduit 199 to

conduit 82 (Figure 2) . Since some of the evolved vapor may find its way to the upper portion of receptacle 104, another vapor removal conduit is provided having one end in fluid communication with the top of receptacle 104 and the other end in fluid communication with vapor removal conduit 199 or conduit 82.

The general operation of heater 38 should be apparent from the foregoing description. In general, aggregate or other material to be heated and/or dried enters sealable inlet hopper 110. The material flows through the hopper, is diverted by vanes 116 and 118 to fill heating chamber 106 and at least partially fill receptacle 104. To aid the material flow and heat transfer, vibrators 156 are turned on, by which support beams 152 and 154, and therefore heat exchange plate assemblies 180 are vibrated. Aggregate 103 flows downwardly between heat exchange plate assemblies 180 and along the walls of heating chamber 106 to outlet portion 202. As described in more detail hereinafter, a material flow control apparatus 300 preferably is used to aid in directing the flow of the aggregate onto a

conveyor out of the open bottom 204 and preferably through a novel material discharge control apparatus 350 to be described hereinafter. The hot, dried aggregate is thereby discharged onto conveyor 40 for further processing.

As mentioned above, the present invention includes the recovery of heat generated by primary heat transfer fluid heater 47 which often is wasted. The wasted heat, which may be in the form of hot combustion gases, flows through conduit 98 to heater 38 as illustrated in Figure 1A, although conduit 98 could also direct.such hot gases to preheater-condenser 32.

For the sake of clarity, a description of how the waste heat is used at heater 38 or preheater-condenser 32 is illustrated and will be described only with respect to heater 38, particularly with reference to Figures 2 and 4 through 6. Conduit 98 is attached by welding, flanges or other suitable fastening means to a waste heat recovery housing inlet 182. Inlet 182 is attached to a waste heat recovery housing 184

which surrounds the entire heating chamber 106, including evolved vapor collecting means 194. As indicated in Figure 4, the hot combustion gases flow between waste heat recovery housing 184 which forms the outside wall, and the collection chamber of collecting means 194 and heating chamber 106, which together form the inner walls of the space through which the combustion gases flow. The hot combustion gases exit housing 184 through opening 186 which is protected from the elements by rain cover or shield 188. If desired, the walls of housing 184 could be insulated to reduce heat loss through the walls.

The details of the construction of hollow heat exchange plate assemblies 180 will now be described with reference to Figures 8 through 13.

Each hollow heat exchange plate assembly 180 includes a support bar 208 supported by beams 152 and 154 as described above. A hollow heat exchange plate 212 is attached, preferably by welding, to support bar 208. Inlet manifold 166 and outlet manifold 170 are attached to the top side wall of hollow plate 212, also as described

above. An entry orifice 210 allows for the entry of primary heat transfer fluid from inlet manifold 166 into inlet channel 213 formed between outer wall 214 and inner wall 215 of hollow plate 212. The flow of the primary heat transfer fluid is illustrated by the arrows in Figure 8, beginning with the arrow extending from inlet manifold 166 into channel 213. After the fluid flows through channel 213, it enters into a series of preferably parallel, generally horizontal serpentine channels 216 formed between interior channel walls 216A through 216L. Interior serpentine channel walls 216A, 216C, 216E, 216G, 2161 and .216K extend from , interior side wall 215, but do not extend all of the way to opposite side wall 217. Interior serpentine channel walls 216B, 216D, 216F, 216H, 216J and 216L extend from side wall 217, but do not extend all of the way to opposite side wall 215. The primary heat transfer fluid flows upwardly through serpentine channels 216 until it reaches exit channel 218. From channel 218, primary heat transfer fluid enters outlet manifold 170 through orifice 220. Exit orifice 220 has a

size defined by an opening in the interior wall of manifold 170 communicating with channel 218. So that there is a balanced pressure drop among all of the relatively shorter and relatively longer hollow heat exchange plates within the heater, the exit orifices 220 of the various heat exchange plates are adjusted to have proper dimensions. The longest central heat exchange plate communicates with manifold 170 through an exit orifice 220 having a large area. Shorter heat exchange plates, such as the heat exchange plate illustrated in Figure 8, have smaller exit orifices. As illustrated in Figures 8 and 13, an orifice plate 219 is welded or otherwise attached to the wall of manifold 170 adjacent the interior of channel 218 to restrict the size of exit orifice 220. The shorter hollow heat exchange plates have larger orifice plates corresponding to plate 219, so that they have correspondingly smaller exit orifices 220. If desired, orifice plates of the type described with respect to orifice plate 219 could be used in conjunction with the entry orifices 210, rather than with the exit orifices 220, to provide

for the balanced flow of primary heat transfer fluid throughout the several heat exchange plates.

Hollow heat exchange plate 212 includes a first or front major face 222 which is fastened, such as by welding, at the top to support bar 208, and at the bottom, after curving to form bottom wall 223, to a second or rear major face 224. Interior walls 216A through 216L are welded between major faces 222 and 224. A drain opening and removeable plug 226 are formed in a lower corner of hollow heat exchange plate 212.

Heater 38 is constructed -to enable the relatively easy removal and/or replacement of all of the hollow heat exchange plate assemblies 180 as a unit attached to support beams 152 and 154. The removal is relatively easy, since beams 152 and 154 are merely bolted through the rubber pads mounted on support blocks 140, 142, 144 and 146. Inlet and outlet manifolds 166 and 170 can have flanges of a conventional structure within housing 102 to allow for the easy removal of the hollow heat exchange plate assemblies.

While a preferred use of heater 38 is in the system 30 of the present invention as described above, heater 38 may be used with other systems either with preheater-condenser 32 or as a separate heating unit.

The construction and operation of preheater-condenser 32 will now be described in detail. Initially, it should be emphasized that, although apparatus 32 is used in system 30 as a preheater-condenser, it may be used in other systems, if desired, as a heater-condenser. Never¬ theless, for the sake of clarity, apparatus 32 will be described herein in its presently preferred use as a preheater-condenser. With reference to Figure 14, apparatus 32 includes support legs 230 for supporting the apparatus on any type of conventional foundation, directly on the ground, on a portable trailer equipped with jack supports, etc. The apparatus includes a housing 232 which may be in the form of a storage bin, silo, hopper or the like containing material 233 to be dried, heated or pre-heated. Housing 232, which may be insulated if desired,

includes an upper, generally rectangular portion 234 and a lower portion 236 generally having at least two, and preferably four, downwardly and inwardly sloping walls. The housing can have any other desired shape, including substantially vertical, nonsloping side walls. Lower portion 236 has an outlet portion 238 terminating in an open bottom 239. An optional material flow control apparatus 300 is illustrated in Figure 14 as being attached to outlet portion 238. Heated or pre¬ heated material 233 is discharged from preheater- condenser apparatus 32 by belt ^' conveyor means 34, an equivalent pan feeder, or the like, for further processing. Unlike heater 38, preheater-condenser 32 preferably has an open top and is not sealed from the atmosphere.

Preheater-condenser 32 includes a plurality of hollow heat exchange plate assemblies 240. The plate assemblies are supported by and depend from support beams 242, 243 as best illustrated in Figures 15 and 16. If desired, vibrating means, such as vibrators 156 (Figures 2

and 3) as used with heater 38, can be mounted on beams 242 and 243 of the preheater-condenser. The use of vibrators makes the aggregate or other solid particulate material flow through housing 232 more efficiently, but the use of such vibrators is not required.

Hollow heat exchange plate assemblies 240 include hollow heat exchange plates 241, each of which is attached to and in communication with a heat transfer fluid inlet header 246 as described below. Threaded studs 244 are welded or otherwise attached to the upper wall of inlet header 246. Studs 244 are then inserted through holes in the bottom flanges of beams 242 and 243 and nuts 245 are threaded onto studs 244 to support hollow heat exchange plates 241 from beams 242 and 243.

With reference to Figure 14, it is apparent that hollow heat exchange plate assemblies 240 are of varying length. The shorter hollow plate assemblies are located adjacent the side walls of housing 232 to accommodate the sloping walls of lower portion 236. The number, size and spacing of the plates within housing 232 can be

selected based on the type and size of material expected to be dried, the type of heat transfer fluid to be used, the type and shape of the preheater-condenser housing and other such considerations.

The construction of the hollow heat exchange plate 241 will now be described with particular reference to one typical hollow heat exchange assembly 24OB illustrated in Figures 15 through 17.

Hollow heat exchange plate 241 includes a first or front major face 250 having angled side and bottom margins ^" 252 which are welded to a second or rear major face 254. The upper portions of major faces 250 and 254 are welded to the outside of header 246 as best illustrated in Figure 16. Fluid communication between header 246 and the interior of hollow heat exchange plate 241 is provided through a plurality of orifices 248 formed in the bottom wall of header 246.

A plurality of internal walls 256 are welded between front and rear faces 250 and 254 to provide reinforcement. The orientation of walls

256 are for purposes of illustration only and need not be located as illustrated. The orientation illustrated should provide both reasonable flow and retention of the heat transfer fluid within heat exchange plates 241.

Heat transfer fluid, which may be the heater generated heat transfer fluid as defined above where preheater-condenser 32 is used in system 30 of Figures 1A and IB, flows through delivery conduit 85 (Figures 1A and 14) to inlet manifolds 86 and 88 (Figures 1A and 15) . From inlet manifolds 86 and 88, the heat transfer fluid flows through orifices 87 and 89, respectively, into header 246. From header 246, the fluid flows through orifices 248 into the interior of plates 241.

By virtue of the heat transfer from the heat transfer fluid through the walls of plates 241 to the material 233 being dried, preheated or heated, the heat transfer fluid, initially preferably a vapor or gas, condenses within plates 241. Accordingly, it is necessary to have a condensate collecting means preferably located

within the housing for collecting liquid condensed within the plates. In general, the heat transfer fluid will tend to be primarily gaseous in the upper portion of each plate 241, but primarily in a liquid state in a lower portion of plate 241. The lower portions of the adjacent plates 241 are interconnected by conduits 258, best illustrated in .Figures 14 and 17. Connecting conduits 258 are welded to opposite faces of adjacent plates. Thus, for example, with reference to Figure 14, connecting conduit 258A connects the lower portions of plates 241A and 24IB. Connecting conduit 258B connects the lower portions of plate 241B and 241C. The above-described connections using conduits 258 relate to interconnecting plates of different lengths so that the condensed heat transfer fluid flows downwardly by gravity. A different. condensate collection arrangement may be used with the longest plates in the central portion of housing 232. For the longest plates, connecting conduits 260 connect the lower portion of the plates to a condensate collecting manifold 260. A condensate outlet means in the form of a condensate

re oval conduit 94 (Figures 1A and 14) is connected at one end to manifold 260 and at the other end to a suitable storage tank or drain for holding or draining off the condensate as desired under the circumstances.

It should be mentioned that the heat exchange plates 241 in preheater-condenser 32, as well as the heat exchange plates 212 used in heater 38, may be made of any suitable material capable of transferring heat through the walls of the plates and capable of withstanding the wear and tear associated with movement of tons of aggregate or other similar, solid ^' articulate material through the apparatus. The presently preferred material is carbon steel. The housings for preheater-condenser 32 and heater 38 may be made of any suitable durable material, but steel is the presently preferred material.

Preheater-condenser 32 and heater 38 may be built to have any desired capacity. Typical commercial capacities for both preheater-condenser 32 and heater 38 are from about 75 to about 150

tons per hour of aggregate or other material to be heated, dried and discharged.

The present invention may be embodied in other specific forms without departing from the spirit or essential attributed thereof and, accordingly, reference should be made to the appended c" ims, rather than to the foregoing specification, as indicating the scope of the invention.