US2376612A

US2376612A - Method of and apparatus for drying moving material

Info

Publication number: US2376612A
Application number: US251064A
Authority: US
Inventors: Carl G Muench; George H Burt
Original assignee: Celotex Corp
Current assignee: Celotex Corp
Priority date: 1939-01-16
Filing date: 1939-01-16
Publication date: 1945-05-22
Anticipated expiration: 1962-05-22

Description

May 22, 1945- f c. G. MuENcH ETAL METHOD OF AND APPARATUS FOR DRYING MOVING MATERIAL 2 sheets-snaai 2 Filed Jan. 16, 1939 Patented May 22, 1945 Ms'rnon or Ann APPARATUS Foa Danno Movmc Marsman t Carl G. Muencli, New Orleans, and George Ej Burt, Metairie, La., assignors to The Celotex Corporation, Chicago, Ill., a corporation of Delv Application January 16, 1939, Serial No.251,064

13 Claims. (Cl. 263-540) This invention relates to a method of and apparatus for dryingsheets of articial heat insulating lumber, preferably formed by the felting Vof bagasse ber along ,with other materials necessary to m-ake a satisfactory structural ber board. This invention notionly relates to the drying of the sheets, but in particularrelates to the thermal economy of a drying system. Y

'I'he principal object of the invention is to prol vide a drying system particularly for drying of ber insulating board and the like.

, Another object of the invention is to provide Another feature of the invention is to provide the novel heat exchanger with a mixing chamber so that the hot due gases are tempered by the waste gases from the airheat'er.

for rapid drying by high temperature water vapor,

particularly super-heated water vapor, so that the drying can be carried on at a high temperature.

Another object of the invention is to combine a steam plant with a novel drying system s o that the thermal efficiency of both systems is in'- creased.

Another object of the invention is to provide a novel heat exchanger or air and water vapor mixture heater wherein the iiue gasses for heating the heat exchanger are tempered by the waste gases therefrom. In describing this invention, from time to time the heat exchanger o r air and water vapor mixture heater will be referred t0 merely as 'an air heater or the air heater, and the atmosphere of super-heated steam, which, as hereinafter explained, normally includes a content of air,'is hereinafter from timeto time generally referred .to merely as air or the air, since this terminology, by merely thinking 'of the circulation of the drying medium as that ofa simple sas, simplifies the terminology used in eilciency of a heating system comprising a steam plant and a drying system.

Another object of jthe invention is to provide a novel method of controllingthe temperature within a drying system wherein combustion products at a temperature of substantially 3300 F. are tempered to 1200 F. by recirculating a per tion of the waste gases from the air heater at a temperature ofV substantially '700 F. By this method, the resulting hot air or super-heated water vapor is discharged from the air heater for the drier at a temperature of substantially 700 F., and it is reducedwithin the -drier from' substantially 700"l F. to substantially 350 F. by the material which is conveyed through the drier to I the drying 'system throughan i i 00 Another feature of the invention is to provide a drier whereinthe hot drier gasesy preferably super-heated water-vapor are circulated in a substantially closedl system, the super-heated water-vapor being heated in the air heater and 'I discharged in the direction ofvtravel of the iber Y board which is being dried;v and, as the drier system is a closed systm, the expansion due to the evaporation of water fromV the board is suitstack at the end of ably relieved by a vapor vent the drier. y v y 4With these and other objects in View, the invention consists' of the novell steps and combination of steps constituting the process and inthe novel parts and combination of parts constituting the apparatus, all of which will be more fully hereinafter disclosed and particularly pointed out in the claims.

Referring to the accompanying drawings forming a part of the specification in which like nucombined therewith;

Figure 2 is an elevation along line l2---742 of Figure 1 looking in the direction of the arrows and particularly. showing the mixing chamber in detail;

y Figure 3 is a side elevationlof a steam plant comprising the economizer looking along line 3-3 of Figure l in the direction of the arrows;

Figure 'l is a`partial sectional view along the line t-t of Figure `1 looking in the direction of the arrows and illustrating the return air .duct

. from the drier together with a section through mths drier; and,

In order that the invention may be better understood, it is said; this invention is especially adapted for drying the wet sheets of heat vinsulating artificial lumber such as .thosethat are now made from bagasse ber and mixed with fibers derived. from wood and known to the trade as Celotex brand cane ber insulation.

The mixture of bers arerst passed over a sheet forming machine (not shown) which forms them into a sheet of a width of about ten or twelve feet. The sheet is then Apassed through y the drier of this invention in continuous lengths;

.and, it is preferable, however, that the sheets fromthe sheet forming machines are cut into suitable lengths so that the length of a drier will not be as longas in priordriers of this type, such as disclosed in the U. S. Patent to 'l'. B. Munroe 1,598,980, granted September 7,- y 1926. The thickness of the finished sheet "from the drier is about one-half inch; and, after being dried, it is cut up into boards of any desired dimensions. In practice, it is found that if the heat insulating artificial lumber or Celotex ber sheets are made up from bagasse bers alone, the said sheets are apt to dry unevenly, to warp, and to require a relatively long drying period for a desired product, thus reducing the output of the mill. If it is attempted, o n the other hand, to

speed up thev commercial production of these sheets, as byincreasing the temperature of the air employed in the drier, it is found that before any substantial practical results can be obtained, the air will have to be so hot as will unavoidably scorch theouter surfaces of the drying sheets, so that the latterwlllY be injured, and the drying will also be found to be still/unevenandstoggive rise to an/objectionablefwarping of the nish sheets. l

In addition to this, the felted ber sheets are highly insulating in their properties and are provided with greater or less quantities of water repellent or waterproofing materials usually in the forni Voian aluminumv resinate or other well known water resisting compound or repellent,

and when air is employed as the drying medium or uid, it is found that' heat insulating water resisting layers are readily formed, at the outer surfaces of the sheets in the drier whllethe interior portion of the sheets have a relatively large percentage of theiroriginal water still present. In fact, these layers retard the heat in reaching the inter-iemand retard the water there present in reaching the exterior Vofthe sheets.

on the other hand; it is reime met i: the

original bagasse bers are admixed with a percentage of other bers derived from wood, such for example as the. waste wood'bers from a paper mill, or ifdisintegrated or groimd up paper asvaeia becausev of the steam dry substantially uniform throughout. In order, however, to employ super-heated steam eillciently, it is preferable that the air should be substantially excluded from contact with the sheets, for at the temperatures mentioned any free oxygen present is liable to produce an objectionable scorching of the sheets and sometimes a re in the drier which is impossible when steam is used.

Accordingly, in `carrying out this invention, Y

we provide a drier construction which is substantially air and steam tight, except at its ends where the ber sheets enter and leavethe drier.

It is obvious that the drier may be several hun-4 dred or a thousand feet longer longer if necessary to satisfactorily dry the sheets within the drier. In this particular drier, however, the length of the drier is only about one hundred .fifty feet.

`the general arrangements of parts yand their cooperation'v with each other. In a plant for the manufacture of insulating board of this type, it

stock, is admixed with the bagasse bers, the 'Y drying action itself becomes more even and satisfactory. So long as air is used as a drying medium, even if at a temperature-above 250vF., or is heated up to a temperature of about 300 F., 350 F. or higher, which it is very Vdesirable to do, if a'high speed of drying is to be attained,

is necessary that there be had a great deal of steam and hot water for processing. Therefore. a novel steam plant is provided with the additional heat saving device employed with a plant. By so using an economiser, the thermal v emciency'of the steam plantis very much increased. To further increase the thermal emciency of our combined steam plant and novel drying system of our invention, our novel dry'-` ing system is also adapted to be connected to the economiser.

The novel vheating or drying system of our Yinvention comprises a furnace for supplying the of combustion" are then discharged into a niix-l the surfaces of the cane ber sheets will stillV have the objectionable heat' insulatingand water resisting layers, and will still bescorched to an objectionable extent, although the drying action may be free from warping.

It is` found that ifA the above oi? bagasse bers and bers derived from wood is provided in the rst place and if the formedvl cane Vber insulating sheets are subjected tol steam at temperatures of lsay from 215" F. to

350 F. or higher. the sheets are found to dry' very rapidly without scorchingor warping and a very satisfactoryvquality and quantity of the product is produced. We are unable to satisfactorily explain the marked advantages of steam over air as a drying medium for these sheets, but have observed that steam especially at high temperatures does not produce the above water resisting layers on the surfaces of the sheets, but seems to penetrate throughout the interiors thereof, and to efficiently remove thewater present by, vevaporating it. Apparently the sheets `do notdry from the surfaces, and

ing chamber where they are tempered to a temperature of substantially 1200 F. The tempered' gases are then led through a suitable heat exchange means where they heat the air or super-heated steam, for drying, to a temperature of 700 F. The waste flue gases are ther tempering the gases. et

then partially discharged through the economizer and the remaining portions are discharged into the mixing chamber where they are used to temper the incoming hot products be by-passed into the mixing chamber for fur- As the waste ue gases from the air heater are discharged into the economiser or water heater,y it is evident that the combined thermal eiciency -of the steam plant and the drying system is materiallyincreased.

The heated air at a temperature of F. is then discharged into the novel drier at one end thereof and preferably in the direction of travel of the sheets'to be dried. Although the conveying means have not been shown in detailfor 7s conveying the sheet through the drier, it is `We prefer, however, to use the type of convey- A ing apparatus as disclosed in the U. S. Patent 1,598,980 granted to T. B. Munroe, September 7, 1926,'adapt/ed for a multiple. deck drier. Since the temperature of air is '700` F. coming from form a suitable water-heater, and the water withthe air heater, it is obvious that the water within the sheet is rapidly dried therefrom, with the result that the air within the drier becomes substantially saturated water-vapor and superheated: and, as the process is a continuous one it is obvious that theresultant drying of a sheet .is effected by the use of super-heated watervapor or super-heated steam, so that the sheets being dried within this drier are dried evenly and`without warping. As the tiers of sheets being dried travel down through the drier, it is evident that the temperature within the drier is substantially reduced; and, at the end where the sheets leave the drier, the temperature ofthe steam within the drier is reduced to a temperature of 350 F. As our novel drying system is of the type known as a closed system, the expansion due to the evaporation of the water from the board must be released, and this is accomplished by a vapor vent stack at the end of `the drier from which the sheets which are dried leave. Y

The super-.heated steam now reduced at the end of the drier to a temperature of 350 F. is then divided and returned alongside on each side of the center drying duct counter to the direction of travel of the board. 'I'he steam and air at a temperature of 350 F. is then preferably dis-f charged into the air heater where it is reheated to a temperature of 700 F. to be recirculated through the drier.

The gas or super-heated steam that does the drying does not come in contact with the combustion gases within the air heater at any time. Su-

per-heated steam is recirculated from the air heater to the drier and back again at a predetermined rate so that the incoming sheets to the drier when they leave the drier are thoroughly dried. The air or gaseous medium. within the drying system after the starting period quickly progresses from air to water-vapor and to superheated steam and theoretically would -be water vapor only for drier operation. Since this drier system is operating at subsi'antiallyy atmospheric pressure, it, is evident that the water vapor within the drying'system would be 'highly super-heated.

An emergency damper is provided at the outlet of the hot gas chamber to protect the air heater and other equipment in case the fans should stop.

The damper is suitably controlled by thermostatically operated devices placed in strategic points within the drier and air heater.

In the drawings, Figure 1 shows the essential elements of our novel drying system and steam plant. The novel steam plant of our drying sysin this water heater is heated to a temperature of preferably 180 F.

As best illustrated in Figures 1 and 3. the hot products of combustion as they-leave the water heater I1 are discharged downwardly into a flue. I8. Depending upon whether the temperature-of the discharged gases is suitable to provide a natural draft, the gases are then discharged into the stack 2| directly. If thenatural draft is not sufficient, an induced draft is produced by an induced draft fan 20; and, a damper I 9 is set in duct I8, as illustrated in Figure 3, to cause the combustion products to discharge through

bypass flues

22 and 23 into the stack 2l. The fan 20 is adapted to be driven by a suitable motor 24. In order to have the steam plant operate at its maximum efllclency, it is preferable that the complant or separately therefrom. Similarly, the

steam plant is also adapted to operate conjointly with the heating or drying system or separably therefrom. Referring to Figures 1 and 2, furnaces 30 are suitably fired from coal bunkers 8| by stokers 32. The hot products of combustion from the furnaces 30, as best illustrated in Figure 5, are discharged into a hot gas or combustion chamber 33. and are preferably at a temperature of 3300 F. The combustion products at a temperature of 3300 F. are discharged into a mixing chamber 30 which may be controlled by a damper 35. The combustion chamber 03 is also adapted to discharge to the atmosphere through a suitable by-pass chimney 30 which is also controlled by a damper 3l. The by-pass chimney is only used .in case of emergency or when it is not desired to operate the drier or to control the amount of hot gases discharged into the mixing chamber 0d. 'With the damper 3l, as indicated in Figure 5, substantially closing the by-pass chimney 3B, the hot combustion products discharge into the mixing chamber when the damper 35 is lopen. The damper 35. is an emergency damper and is open at all times exceptwhen the temperature within the air heater and drier becomes excessive. Then, the damper which is thermostatically operated is adapted to close so that the hot products oi' combustion are bypassed through the by-pass chimney 3B as the damper `'l is simultaneously opened. Generally, the temperature within the air heater and drier becomes excessive when the fans. which are to be described later, stop.

is fired from bunker .I2 by suitable stokers lndl- Y cated at I3.

The combustion gases `from the boiler l0 pass to a boiler ue I4, and the gasesk are preferably discharged. at a temperature .of 800 F. The

combustion gases enter .an economizer chamber l5 and are deflected by a barde I8 acrossan econ- The hot products of combustion at the temperature o f 3300 F. are tempered within the mixing chamber 34, i. e., reduced in temperature from 3300 F. to 1200 F. lby admitting wastepr'oducts of combustion or fresh air to the mixing chamber 34. The cool combustion gases for tempering the hot combustion gases are admitted into the mixing chamber through cool combustionigas inlets 3B. Referring to Figures 1, 2 and 5, the I inlets 38 are connected to a flue 39 which is suit- .ably connected to the heat exchanger or air heater I0 so that a portion or 'all of the hot waste gases from the heat exchanger or air heater are adapted to be returned to the mixing chamber. As the products of .combustion which have been tempered by the waste gases from the air heater I0 to a temperature of 1200 F. pass down across the means for heating the air within the air heater,

the hot gases are reduced from 1200 F. to substantially 700 F. as they enter the Waste gas flue 4 I. The air heater is so constructed that the gas. air or super-heated steam that is circulated for drying does not come in contact with the combustion gases at any time. The air or water vapo as it leaves the air heater is super-heated to a temperature of 700 F. and is recirculated from the heater to the drier and back again.

The waste gas iiue 4| is adapted to be connected from the heatv exchanger 40 or air heater,

to the economizer or water heater I1 of the steam plant, and is also adapted to be connected by the flue 4I to the mixing chamber 34 so that a portion of the waste ue gases may be used to temper the hot combustion products from the hot gas chamber, A cool combustion gas return flue 42 is adapted to be connected to the waste gas flue 4I and is provided with a cold air inlet 43 having a damper 44 for suitably controlling the cold air inlet or means for supplying cold air 43. 'Ihe function of the cold air inlet 43 is to provide cold air, if required, in suicient amounts to additionally temper the waste iiue gases from the air heater 40 before they enter the mixing chamber 34.

In order to temper the hot products of combustion from the hot gas chamber 33 as they enter the mixing chamber 34, it is within the scope of our invention that we may temper these hot gases either solely by the waste flue gases vfrom the air heater 40, or by combining the waste fiue gases with cold air or by cold air alone. A fan 45 circulates the gases for tempering the hot products of combustion from the waste gas ue 4I through the flue 42 to where it is connected to V the duct 86 and from there into the mixing `3300" F. to 12007 F. in the mixing chamber 34..

We accomplish this by returning a portion of the waste flue gases from the air heater at a temperature of 100 F. to the mixing chamber 34. The proportion of hot gases at 3300 F. and waste flue gases at '700 F. are such that the resultant temperature of the gases leaving the mixing chamber 34 is reduced to 1200 F. Itis also Within the scope of our invention that the temperature of the gases may be tempered in the mixing chamber solely by the use of cold air or by the mixture of cold air and waste flue gases. The

remainder of the ue gases from the air heater.

40 which are not used to temper the gases in the mixing chamber 34 are led by the duct 4I to the economizer chamber I5 where they are then distributed through the economizer or water heater I1. v

These waste flue gases from the air heater 40 are discharged into the economizer chamber I5 at a' temperature of.700 F. and the amount of gases passing through the flue 4I are suitably controlled by a damper 41. By utilizing these waste flue gases from the air heater 40 by passing them through the economizer I1, it is obvious that the thermal efficiency of the drier system is materially increased. Similarly, the overall tlermal eiiiciency of the steam plant and the drier system is also increased. Since the Waste gas ilue 4I of the air heater and the Waste gas 2| and 35, it is also obvious that both of these systems may be used together or independently.

The air or super-heated steam within the closed system of our drier is rapidly circulated by a fan 48 driven from an electric motor 49. The fan 48 is connected at its discharge end with an air duct 50 which discharges into a header 5I connected to the air heater 40 composed ofl a plurality of horizontal ues. As best illustrated in Figures l, 2 and 5, the air or super-heated steam to be heated to a drying temperature of '100 F. is passed through the air heater 40 and from there into a hot air header 52 which is in turn connected to a hot air distributing duct 53. The duct 53 serves to connect the header 52 with a drier header 54.

The novel drier 56 of our invention is adapted to be connected to the header 54 at one end of the drier, and this is preferably the incoming end for the sheets to be dried. -Our drier has many important features, one oi.' which is dividing the drier 56 into three separate chambers. An inner or drying chamber is formed as best illustrated in Figures 1 and 4, by dividing the drier with the -inner drying chamber in the center and side air passages on each side of the inner drying chamber. The outer walls 51 and 58 of the drier 56 serve to provide the outer walls for the side air passages, and the walls 59 and 60 of the inner drying chamber serve to provide the inner walls of the side air passages. Partitions 8l at each end of the side air passages where the side air passages are adjacent to the drier header 54 serve to separate the side air return passages from the drier header 54. The drier header 54 discharges the hot airor super-heated steam for drying the sheets into the inner drying chamber.

The side air passages formed respectively by the walls 51 and 59, and similarly 60'and 58, discharge into an outlet flue 62, as best illustrated in Figures 1 and 4. The air return duct 62 is suitably connected to the intake of the circulating fan 48 for the closed system of our novel drier system.

The inner drying chamber to which the ytiers of sheets to be dried are suitably conveyed on a conveyor for each of its respective tiers, has at its end adjacent to Where the sheets enter the conveyor at the drier header 54 a. plurality of bales 63 corresponding to the upper and lower side of each tier of the conveyor. The ends of the baffle 63 are suitably rounded as at 54 so that the hot air or super-heated steam entering flue I4 of the steam plant are connected and.-

into the inner drying chamber may circulate around the edges of the sheets which are being dried to thus thoroughly and evenly dry the sheets all over. A large baflle 65 serves to support the upper side ofthel drying chamber and also serves to discharge the super-heated steam\ or air across the top of the drying chamber adjacent to the upper sheet or tier of material being conveyed through the drying chamber. Conveyors 66, as illustrated in Figures 4 and 5 diagrammatically, are adapted to convey each tier of material which is being dried between the bafiles 63 at the entering end of the drier 55. The bailies 63 on each side of the sheet as it enters the drier 55 serve to distribute the hot air or super-heated steam uniformly across the surfaces of the sheet but also serve to seal the drier from the outside atmosphere and are additionally provided with canvas iaps (not shown) to complete the sealing. Although any type of conveyor, as disclosed in the prior art, may be satishowever, to use the type of conveyor as disclosed in the U. S. patent to T. B. Munroe No. 1,598,980, granted September 7, 1926. It is also preferred to use a .type of conveyor wherein the conveyor is entirely within the drying chamber so that no heat is lost by returning the. conveyor from outside 'where the ltemperature is lower, thus causing a material heat loss. We also provide a large baille B1 over the top of the inner drying chamber adjacent to the return air duct 82 so that the return air or super-heated steam is caused to flow along the side airpassages formed adjacent to the inner drying chamber and also to now across the top thereof in order to transfer as much heat as possible to dry the material as it is passed through the inner drying chamber. As our drier system is a closed system, the expansion due to the evaporation of the water from the board must be released, and this is accomplished by a vapor vent stack 69 at the end of the drier, and this stack is suitably controlled by a' damper 10.

In the operation of our drier, the sheets from the sheet forming apparatus where they are ielted from a water suspension of ber and the like are formed ina continuous sheet and fed to the drier where they are cut into suitable lengths.

and elevated by a tipple to the various tiers of the drier.v We prefer to cut the sheet as it comes from the sheet forming machine into lengths of from 150 to 250 ft. long `and feed them into the drier in 8 tiers. It is also within the scope of our invention that the sheets may be cut into smallerv sizes and placed on suitable racks, the racks then being suitably conveyed or pushed through the drying chamber of our drier. The movement of these sheets is comparatively slow, or saylabout as fast as one would walk at a slow gait. The actual speed, however, depends of course upon the temperature of the drying medium, the quantity of moisture to be evaporated and lthe drying eillciency of the medium.'

As these sheets travel slowly and uniformly through the inner chamber oi our drier, suitable hot air or preferably super-heated steam is fed into the drying chamber in the direction of travel of these sheets. The fluid Afor drying is forced through the air heater and heated to a temperature of substantially 700 F. whereupon it is discharged into the header and from there into inner drying chamber through the side air passages and from there to the fan l0. 'I'he superheated steam which has` .now reached a temperature of 350 F. because of the reduction in temperature due to the evaporation oi the water within thesheet is reheated `by means of the air heater. and is thus used'over and over again being recirculated by the fan 49.

Owing to the presence oi? a water repellent on the fibers, the water derived from the forming machine is held more tenaclously by the sheets when the air is used as the drying medium than' when steam is used and therefore, an air drying process does not seem to satisfactorily reach` the interior of a sheetv and dislodge the water retained therein as does a steam drying process, as disclosed in ourl novel invention. Further, by the substantial exclusion of air from the drier,

and by keeping the whole interior ofthe drying chamber filled with steam as above disclosed, it is found that the water 'is readily evaporated from the sheet. in an expeditious, uniform and satisfactory manner not attainable bythe use of air,

so that the output of the mill is greatly increased.

The air heater 40 readily resupplies any heat that may be extracted from the-super-heated combustion gases at any time.

the drying chamber. Asthe fluid, and especially V drying steam when the water is thus evaporated from the interiorA of the sheets, and the 'air or super-heated steam' heater also aids in maintaining. a high temperature inside the drying chamber which varies from an inlet temperature of substantially '100 F. to an .outlet temperature of 350 F.

It is obviousto those skilled in the art that we have disclosed anovel heating or drying system in combination with a steam plant so that the combined thermal emciency of the steam plant' and drying or heating system is ,materially increased.

It is also apparent from our disclosure that we have disclosed a novel vair heater wherein hot products oi combustion are tempered and reduced in temperature by passing waste ilue gases into a mixing chamber before they enter the heat exchange means to heat the gas that does the drying without coming in contact with the It is also obvious that we have disclosed a novel method oi controlling the thermal emciency oi' a heating system comprising a steam plant having .an economiser and a drying system having a vsource of combustion products, and an air heater,

which comprises passing the iiue gases of the steam plant through an economizer, passing a lportion of the liuc gases from the air heater `for the drying system through the economiser,

and tempering the combustion products to the air heater with the remainingV portion ci the flue by these sheets may amount to as much as several hundred tons daily, so it is important that thel heat remaining within the evaporated water shall be utilized as much as possible. For this reason the super-heated steam is recirculated over and over, and the excess water vapor evaand which reduces in temperature to substan-j" tlally 350"v F. as vthe boardsleave the` drier, is

divided and circulated along .the outside of the or super-heated steam whichis heated by the' tempered products of combustion is heated to a temperature of '700 F. andthen recirculated from the temperature of 350 F. to bel reheated to 700 F. The temperature within the drier having A heated steam or air at a temperature oi.'- substantially 350 F. to the air heater to be reheated and recirculated. Whenever airis used in the claims, it is to be understood that it is usedl generically and to broadly cover any suitable drying fluid or medium, such as super-heated water vapor or super-heated steam. Also, the specific temperatures recited are given by way of example only, ar approximate, and will vary according to conditions of individual usage and are to be taken as indicative only.

It is obvious that those skilled in the art may vary the details of construction, the arrangement oi parts and the mode of operation, without departing from the spirit of this invention, and therefore it is not desired to be limited to the foregoing disclosure except as may be required by the claims.

What is claimed is:

1` In a heating system forming a drying medium heating, water heating, and drying system, the combination of a drying system for drying moist fibrous insulation board and comprising a drier, an air and water vapor mixture heater comprising a mixing chamber and means generating hot gases for heating/the air and water vapor mixture heater; a steam plant comprising a furnace, a boiler, and an economizer for heating processing water; means for circulating through the economizer the ue gases from the boiler. means for circulating through the economizer a Y portion of thefiue gases from the means for heating the air and water vapor mixture heater whereby the overall thermal efficiency of the heating system is increased, means for .tempering the hot gases from the means for heating the air and water vapor mixture heater. whereby the temperature of the hot gases entering the air and water vapor mixture heater is reduced, and means for circulating heated air and water vapor mixture from the air and water vapor mixture heater through the drier in a closed circuit, whereby the moist fibrous insulating board is dried in an atmosphere of super-heated water vapor. 2. In a drying system for drying moisture carry ing fabricated fiber board in an atmosphere of super-heated water vapor, the combination of a drier through which fabricated iiber board may be passed, an airand water vapor mixture heater comprising means for circulating a drying medium horizontally therethrough, means generating hot gases for heating the'air and water vapor mixture heater, the air and water vapor mixture heater comprising means for circulating the hot gases downwardly through the air and water vapor mixture heater and transversely with respect to the drying medium, means comprising a closed system for circulating the drying medium comprising an atmosphere of super-heated water vapor through the drier and returning it to the air and water vapor mixture heater, and means for tempering the hot gases from the means for heating the air and Water vapormixture `heater,

' whereby the gases entering the air and water vapor mixture heater are reduced in temperature. 3. In a hot air drying moisture carrying system.

for drying fabricated ber board in an atmosphere oi super-heated water vapor, the combination of a closed drying system comprising means through which moisture carrying fabricated fiber board may be passed,` an airv and water vapor mixture heater comprising means for circulating a drying atmosphere horizontally therethrough, and means for circulating the such drying atmosphere of super-heated water vapor through the drier and returning it to the air and water vapor mixture aavaoia' comprising means for circulating the hot gases downwardly through the air and water vapor mixture heater and transversely with respect to the drying medium, and means fortempering the flue gases from the furnace whereby the flue gases entering the air and water vapor mixture lheater are reduced in temperature.

. water vapor mixture heater through the drier and through the air and water vapor mixture heater for re-heating and recirculation, the air and water vapor mixture heater comprising means 1 gases entering the air and water vapor mixture heater, a furnace adapted for supplying ue gases for heating the air and water vapor mixture heater, the air and water vapor mixture heater heater are reduced in temperature.

5. The combination with a means for supplying flue gases at a substantially high temperature. of an air heater comprising means for circulating an atmosphere of super-heated water vapor horizontally therethrough in heat transfer relation with respect to the flue gases, means for tempering the flue gases comprising a mixing chamber intermediate the means for supplying the flue gases and the air and water vapor mixture heater,

the air and water vapor mixture heater comprising means for circulating the tempered flue gases downwardly lthrough the air and water vapor mixture heater and transversely with respect to the ow therethrough of the drying medium, a drier for drying fabricated fiber board in an atmosphere of super-heated water vapor, means for circulating the atmosphere of the super-heated water vapor from the air and water vapor mixture heater through the drier, and 'means for circulating a portion of the flue gases from the air and water vapor mixture heater into the mixing chamber whereby the flue gases entering the air and water vapor mixture heater from the means -or supplying flue gases are reduced in temperaure.

6. An air and water vapor mixture heater for a heating system comprising a mixing chamber, means operatively connecting the mixing chamber to a supplyof combustion products, means for super-heating an atmosphere of water vapor connected to the mixing chamber comprising means fox` circulating the atmosphere of water vaporhorizontally through the air and water vapor mixture heater and underneath the mixing chamber and means for circulating the combustion products from the mixing chamber down through the air heater and transverse with respect to the atmosphere oi' water vapor but in heat transfer relation, means for circulating the atmosphere of water vapor to be super-heated through the heater, and means for re-circulating a portion of the waste combustion products from chamber and connected to the mixing chamber and adapted to vcirculate the combustion productsl and water vapor mixture heater and in 4heat transfer relation with respect to the air and water vapor mixture to be heated and -transverselywith respectthereto, means for circulattrolled damper means between the hot'gas chamber and the air and water vapor mixture heater lor the drier and located in the aforesaid passv age and actuated by the change in temperature of the atmosphere within the drier, whereby the material within the drier is protected from excessive temperature rises.

l1. In a drying system, the combination of a source of combustion products, a hot gas chamdown from the mixing chamber through the air 10 ing air ,and water vapor mixture to be heated l5 water vapoimixture heater to the mixing chamber. and means for supplying cold air to the last mentioned means, whereby the combustion products supplied to the mixing chamber are -tempered.

8. In a heating system comprising a closed circuit drier system, the combination of a furnace.

a hot gas chamber connectedto the furnace, anV

air and water vapor mixture heater supplying drying medium to a connected closed circuit dryer ber connected to the source of combustion products, an air and water vapor mixture heater operativelv connected to the hot gas chamber by a damper controlled passage, a drier connected tothe air and water vapor mixture heater, and thermostatically controlled damper means between the source of hot combustion products andV the air and water vapor mixture heater for the drier and located in the aforesaid passage, where- 'by the material within the drier is protected from excessive temperature rises.

12. 'I'he combination with a source of combustion products and a drier, of an air' and water vapor mixture heater comprising a heat exchange means operatively ,connected to the drier and means for circulating the atmosphere of the drier to be' heated through the heat exchange means',

and comprising a mixing chamber operatively A connected to the hot gas chamber, damper'controlled means for discharging the hot gases from the hot gas chamber to 'the atmosphere, and thermostatically controlled ,damper means between the hot gas chamber and the mixing cham- :is

ber and actuated by the change-in temperature of the connected atmosphre within the closed circuit drier system, whereby the air and water vapor mixture heater is protected from excessive temperature rises.

9. In a heating system comprisingv a closed drier system, the combination of a dryer, a'. iurnace, a hot gas chamber connected to the furnace for supplying hot gases, anv air and water vapor mixture heater comprising a mixing chamber operatively connected to the hot `gas-cham-- ber, the air heater also comprising means for the circulation of the atmosphere of the drier system horizontally therethrough, means for discharging a portion of the .waste gases from the air heater to the mixing chamber whereby the hot gases from the hot gas chamber are tempered, the air heater comprising means for circulating the loA ' tion products and a drier, of an air and water said air and water vapor mixture heater comprising a mixing chamber connected to .the heat exchange means and saidA source of combustion products, means for circulating a portion o f the waste combustion products from the heat ex` change means to the mixing chamber, whereby the combustion products entering the mixing chamber are tempered, and the air and water vapor mixture heater comprising means for the circulation of the atmosphere of the drier hori-4 zontally therethrough and means for circulating the tempered combustion products downwardly therethrough and in heat transfer relation with respect to the drier atmosphere.

13. 'I'he combination with a source of combusexchange means comprising horizontal passageways and means lincluding passages for circula- Y tion of air and water vapor mixture to be heated through the heat-exchange means whereby the airand water vapor mixture to be heated is tempered hot gases downwardly through the air 'and water vapor mixture heater and transversely with respect to the atmosphere of they drier syste'm circulated therethrough, means for discharging the remainder of the waste -gases from the air and water vapor mixture heater to the atmos` phere, and means for circulating, the. atmosphere of the drier system through the air and water; vapor mixture heater to be heated.

I0. In a heating system, the combination of a furnace, a hot gas chamber connected to the furforced horizontally through the passages of the heat exchange means, said air and water vapor mixture heater comprising a mixing chamber operatively connected to the heat exchange means and said source of combustion products by a damper controlled passage and mounted over the heat exchange means, means for circulating a Y portionv of the waste combustion products from the heat exchange means to the mixing chamber whereby the combustion products entering the nace for` supplying hot gases., an air and water vapor mixture heater comprising a mixing chamber operatively connected to the hot gas chainber by a damper controlled passage, a drier operatively connected to the air and watervapor mixture heater, damper controlled means for dis- .0

charging the hot gases from the hot gas chamber to the atmosphere. and; thermostatically conc" mixing chamber .are tempered and are caused to pass through the mixingchamber downwardly across the heat exchange means, and thermostatically controlled damper means between the source of combustion products and the air and water vapor mixture heater for 'the drier and located in the aforesaid damper controlled passage and actuated bythe change in temperature of the atmosphere circulated through the drier. whereby the air and water vapor mixture heater is protected from excessivev temperature rises.

CARL G. MUENCH. GEORGE H. BURT.