EP1190141A1

EP1190141A1 - Wet process production of thick boards using inorganic fibers

Info

Publication number: EP1190141A1
Application number: EP00930767A
Authority: EP
Inventors: Neil A. Carter; William L. Ullman; David Rhind; Gordon Hart; Gordon Pinsky
Original assignee: Eftec Inc
Current assignee: Eftec Inc
Priority date: 1999-05-18
Filing date: 2000-05-17
Publication date: 2002-03-27
Also published as: AU4852900A; CA2373357A1; WO2000070147A1; WO2000070147B1; MXPA01011596A

Abstract

A method and system provide for the production of mineral fiber boards using at least 25 % (preferably at least about 90 %) inorganic fibers having enhanced uniformity, compressive strength, and dimensional stability. The source of fibers may be pre and/or post consumer recycled fiberglass. A liquid slurry of solids, including at least 25 % inorganic fibers having an average length of at least about one-half inch, with a solids consistency of about 0.4-8 % is formed. A pack at least about one inch thick is formed from the slurry using a foraminous element, and water is extracted. The pack is dried, and binder may be added and cured, to produce a product at least about one inch thick. Exhaust gases from the drier may be filtered by passage through the pack prior to drying, while also facilitating dewatering of the pack.

Description

WET PROCESS PRODUCTION OF THICK BOARDS USING INORGANIC FIBERS

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based upon provisional applications Serial No. 60/134,614 and 60/141 ,246, filed May 18, 1999 and June 30, 1999, respectively.

BACKGROUND AND SUMMARY OF THE INVENTION

In the production of virgin fiberglass and other types of inorganic mineral fiber products there is a large amount of waste generated. While small amounts of this waste have been incorporated with cellulose fibers (typically on the order of a few percent of the weight of the cellulose fibers) in the making of primarily cellulose fiber board products, and a few other minor uses have been envisioned, the majority of the waste is land filled, resulting in a significant depletion of resources. It is estimated that in 1998 over 250 million pounds of non-biodegradable fiberglass was deposited into land fills across the United States, and this does not even include the fiberglass products that were post-consumer waste, or from fabricators. In the conventional process of making board or blanket products from virgin fiberglass, immediately after spinning of the fiberglass it is transported by air onto a conveyor to form a non-woven web or pack of fiberglass, such as shown in U.S. patent 4,734,996. This requires that the majority of the steps of the final product production process take place at the same place. Also, with the air laid process, the fiber distribution is inherently laminar, forming layers, with the fibers primarily being oriented in a horizontal direction. Therefore board made using conventional processes have a non-uniform appearance and lower compressive strength.

A basic process that attempts to overcome the problems associated with fiber waste in the fiberglass industry, and to produce better board products, primarily for acoustical and thermal insulation uses, is a wet process originally developed by Owens Corning and run as a pilot facility for several years by EFTEC, Inc. of Newark, Ohio. According to this process recycled fiberglass in shredded form has been added to water in a hydropulper or slurry mixer (with optional refining using a Bauer mill or other similar refiner after the hydropulper or slurry mixer), to produce a slurry having a consistency of about 0.4% or less. The slurry is then fed into a headbox having an inclined Fourdrinier wire screen. The pack is formed on the wire screen beneath the level of liquid in the head box, and as the wire screen moves along, the water is drained from the slurry and thereby forming the wet pack. Additionally water is removed from the fiberglass pack, first by gravity and then by a number of suction boxes connected to a blower, with a liquid/air separator between the suction box and the blower. Binder solution is then applied by flooding using a conventional weir configuration, and then the binder solution is extracted in suction boxes by a fan, again with a gas/liquid separator between the suction boxes and the fan, with the dilute binder solution being recycled to binder reconstitution. The pack is then subjected to a heated air updraft, and a down draft, in which a small amount (less than 5.0%) of the water in the pack is removed, then the pack is fed to a dryer/oven where higher pressure convective flow of hot air (produced by the combustion of natural gas with combustion air) is blown through the pack while the pack is transported by porous conveyor belts at the top and the bottom thereof to define a predetermined amount of compression of the pack, and thereby determine the thickness of the pack.

Utilizing the above-described technique it is possible to produce mineral fiber boards, using fiberglass, mineral fibers, rock wool or other inorganic fibers as the input fibers, having enhanced uniformity and compressive strength compared to boards produced utilizing the conventional air laid process, and to turn a land fill product into a valuable resource. The boards produced by the EFTEC process have superior compressive strength and dimensional stability and dimensional tolerances compared to like boards produced by the air laid process, and the EFTEC process readily produces boards more than an inch thick (typically up to about two inches thick) that are suitable for use as acoustical boards and thermal insulation boards. While the prior art EFTEC process has been shown to be capable of producing, and has produced, commercially acceptable products, the products produced thereby still do not have the optimum uniformity or compressive strength, and cannot be produced at relatively high speeds. Also the energy penalty in production is higher than desired for optimum environmental and energy conservation purposes, and while the prior art EFTEC process is basically a low pollution process, there is the possibility that minor amounts of particles or VOCs (volatile organic compounds) may be discharged into the environment.

According to the present invention a method and apparatus are provided for producing a variety of highly desirable products in a manner that significantly enhances the EFTEC process, equipment, and products. According to the present invention the basic aspects of the EFTEC process are improved so as to be able to produce highly uniform, high compressive strength, products quickly and economically, in a highly energy efficient manner, and with essentially no pollution, to produce a wider variety of products and in a commercially feasible manner.

The method and apparatus according to the present invention are presently contemplated to be most useful for the manufacture of medium density to heavy density (e.g. approximately 3 to 12 pounds per cubic foot) fiberglass and other mineral fiber board products from about one to four inches thick, typically up to 60 inches in width, and that are highly suitable for use as acoustical wall panels, acoustical ceiling boards, mechanical thermal insulation boards, roof deck thermal insulation boards, and for a wide variety of other products. However the method and apparatus of the invention are not limited to such boards, and also can be used to manufacture boards or mats that include a wide variety of other fibers including aramid, thermoplastic, and cellulose fibers. While preferably more than 90% of the fibers are inorganic mineral fibers (such as fiberglass, mineral wool, rock wool and/or ceramic) having an average length of at least about one-half inch (typically about one-half inch to three inches), the invention is applicable to the manufacture of products having a wide variety of other fibers but at least about 25% (by weight) inorganic mineral fibers. The products produced according to the invention can be made without binder, although in most circumstances a binder will be provided, such as a conventional phenolic resin binder used in the present EFTEC process.

While the process according to the present invention is presently best suited for use with recycled fiber (typically, for ease of supply, from fiberglass manufacturers, but also any that can be collected from fabricators, or even post-consumer collected fibers), the invention is also suitable for use with virgin fibers, or mixtures of virgin fiberglass fibers with recycled fiberglass fibers, and optionally with fibers of other types (e.g. aramid, such as Nomex®, thermoplastic, thermoplastic sheath, cellulose, etc.). The invention allows the fiberglass production facility to be remote from the product manufacturing facility. Thus compressed fiberglass could be shipped to locations close to where insulation markets are the largest, and custom products could be made at a geographically proximate location for supply to an insulation contractor. Also, the invention allows quick job changes to be made because the product formation is decoupled from the fiber production, something that is not possible in conventional air laid processes where the products are produced immediately after fiber formation. Thus the invention provides a much more efficient and economical system and method compared to conventional systems and methods.

According to one aspect of the invention there is provided a method of making a board or mat (preferably having dimensional stability) comprising: (a) Forming a liquid slurry having a solids consistency of about 0.4% to 8.0%, at least 25% by weight of the solids of the slurry comprising inorganic fibers having an average length of at least about one-half inch, (b) Forming a pack from the slurry on at least one moving foraminous element, the pack at least about one inch thick, (c) Extracting water from the pack. And (d) passing elevated temperature air through the pack to effect drying of the pack to produce a product (preferably with dimensional stability) at least about one inch thick. The method according to the invention alternatively or inclusively (that is containing any one or more or all of the following procedures) includes the following novel aspects: (e) Wherein (a) is practiced in a batch process using a predetermined volume of liquid and a mass measured quantity of solids mixed to produce a slurry of substantially precisely known consistency. And/or (f) Wherein (a) is practiced to form a slurry having a solids consistency of about ¹/2%-3%. And/or further comprising (g) refining the slurry from (a) substantially immediately before (b). And/or wherein elevated temperature exhaust gases are produced during the practice of (d) and wherein (h) the elevated temperature exhaust gases are passed in counter-current indirect heat exchange relationship with ambient air to heat the ambient air and cool the exhaust gas. And/or wherein (i) the heated ambient air from (h) at a temperature of between about 150-220°F is used in a first part of (d). However, a heat exchanger is not used if the drying process used will not produce an exhaust with high enough temperature to make heat recovery practical.

Also, the exhaust gases from the dryer, and perhaps exhaust gas from the first part of (d), may be scrubbed and filtered by passage through the pack substantially during (c) prior to discharge of the exhaust gases. And/or the method may further comprise (k) applying binder to the pack between (c) and (d), and preferably withdrawing and reusing excess binder. And/or the method may further comprise in addition to (k), (I) practicing (d) so that in a second part thereof gas at a temperature of at least 250°F is passed through the pack, and so that in a third part of (d) air of a temperature to effect at least the majority of cure of the binder is passed through the pack; and wherein exhaust gas from the second part of (d) is used in (h), and wherein the exhaust gas from the third part of (d) at a temperature greater than 250°F is recycled to pass through the pack in the second part of (d). And/or the method may comprise, in addition to (I), practicing (I) and (d) so that about 15-40% of the drying of the pack takes place in the first part of (d), about 50-80% of the drying takes place in the second part of (d), and about 1-10% of the drying takes place in the third part of (d). Alternatively, (I) and (d) may be practiced so that about 80-90% of the drying of the pack takes place in the first part of (d), about 10-20% in the second part, and less than about 5% in the third part, wherein different drying equipment is used.

In addition to (I), the average drying air velocity in the second part of (d) may be at least 5% higher than in the first part of (d), and the average drying air velocity is the third part of (d) is at least 5% higher than in the second part of (d). Also, in addition to (I) the drying gas for the second and third parts of (d) may come from combustion of a fuel and combustion air; also the combustion air may be at least in part heated ambient air from (i). In the preferred practice of the invention a conventional binder solution is applied to the pack after water extraction. Then, before drying, excess binder solution is extracted and recycled for binder reconstitution. The invention is most suitable for products having an inorganic fiber content of between about 50-100%. Products produced according to the invention are typically trimmed in the conventional manner, and may be specially finished such as by sanding, bisecting, and/or application of a covering material thereto. The final products produced are highly uniform, have a high compressive strength, are dimensionally stable, and have excellent dimensional tolerances.

According to another aspect of the present invention there is provided a method of making a board or mat comprising: (a) Forming a liquid slurry having a solids consistency of at least about .4%, and at least 10% inorganic fibers, (b) Forming a pack from the slurry on at least one moving foraminous element, the pack at least about one inch thick, (c) Extracting water from the pack, (d) Drying the pack, and producing exhaust gases during drying, to product a product. And (e) passing at least about 10% of the exhaust gases from (d) through the pack substantially during (c) and prior to discharge of the exhaust gases. The method may further comprise reducing or increasing the density of the pack between (b) and (d) by about 2-50%. Other details of this aspect of the method may be as described above. In practicing the method one gets a fiber-containing matter board at least about one inch thick and having at least 25% (and typically at least about 90%) by weight inorganic fibers (such as primarily pre or post consumer waste recycled fiberglass fibers), and one that is dimensionally stable, typically including binder. A board according to the invention can be made from substantially 100% post-consumer waste recycled fiberglass, desirably with binder.

The invention also relates to apparatus for practicing a method as described above. The apparatus according to the invention handles a wide variety of different types of materials in a quick and efficient manner, has essentially no discharges of liquid, and the only discharges gasses are virtually pollution free (i.e., are free or VOCs and particulate). The apparatus produces a final desirable product with optimum energy utilization.

According to another aspect of the present invention there is provided a board or mat producing system comprising: A slurry forming device which slurries fibers in a liquid. A foraminous element which forms a pack from the fiber slurry. A device which dewaters the pack. A drier having an exhaust for exhaust gases. And means for circulating at least part of the exhaust gas from the drier to the pack to pass through the pack. For example, the dewatering device may comprise a liquid pervious conveyor supporting the pack, a hood covering at least part of the conveyor, but open along edges of the conveyor to allow ambient air to flow into the hood past the conveyor edges to flow through the pack on the conveyor; and a suction source located below the conveyor for drawing liquid from the pouch through the conveyor. Typically, there is also provided a gas/liquid separator connected to the suction source. The circulating means may circulate exhaust gas to the hood flow with ambient air through the pack to the suction source. A valve or damper may be provided for controlling the flow of exhaust gases into the hood.

The system typically further comprises a binder addition device for applying binder to the pack prior to the drier, and curing the binder at and subsequent to the drier. The drier may comprise a plurality of in-series sections, alternating sections having alternating flow directions of drying air. Also, the recirculating means may comprise a hood over the pack, a conduit from the drier to the hood, and a fan for blowing or sucking exhaust gas from the conduit through the hood and pack.

According to another aspect of the present invention there is provided a pack treating apparatus comprising: An air pervious support for a pack. A suction source below the air pervious support. A hood covering the support. And a gas inlet to the hood for introducing gas that flows through the support to the suction source.

In the preferred embodiment the hood is spaced from side edges of the support to allow ambient air to flow into the hood under the influence of the suction box. The system may further comprise means for reducing or increasing the density of the pack by at least 2% (e.g. 2-50%) prior to the drier. Other details of the apparatus are as set forth above.

It is the primary object of the present invention to provide for the efficient and effective production of a wide variety of mineral or related fiber mats and boards having dimensional stability. This and other objects of the invention will become clear form the detailed description of the invention and from the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGURES 1A and 1 B are a schematic box diagram illustrating an exemplary entire process according to the present invention, including many novel individual aspects of the process, and equipment for the practice thereof;

FIGURE 2 is a schematic view, with the tank component thereof illustrated in cross-section, of exemplary slurry batch mixing equipment that may be used in the process of FIGURE 1A;

FIGURE 3 is a side schematic view, partly in cross-section and partly in elevation, of exemplary pack formation equipment that may be utilized in the practice of the method of FIGURE 1A;

FIGURE 4 is a schematic end view, partly in cross-section and partly in elevation, of an exemplary water extraction/pollution reduction stage of the method of FIGURE 1A; FIGURE 5 is a side schematic view of an exemplary drying and curing oven and associated gas and liquid handling apparatus for the drying and curing process steps of FIGURE 1 B;

FIGURE 6 is a graphical representation showing two exemplary desired velocity profiles that may be used in the drying and curing oven of FIGURE 5; FIGURES 7A-7D are more detailed schematics of an exemplary embodiment of the apparatus and method according to the present invention than are provided in FIGURES 1 A and 1 B; FIGURE 8 is a schematic side view of a system for making lower density wet pack, and such a lower density wet pack is illustrated therein; and

FIGURE 9 is a schematic like that of FIGURE 8, only for increasing the bulk density of a wet pack.

DETAILED DESCRIPTION OF THE DRAWINGS

An exemplary method according to the present invention, utilizing exemplary apparatus according to the present invention, is illustrated schematically in FIGURES 1 A and 1 B. The invention will be described with respect to the drawings primarily by reference to scrap fiberglass as the raw material. However it is to be understood that virgin mineral fibers, such as fiberglass, rock wool fibers, ceramic fibers, and the like, may also be utilized, and may be mixed with each other or with other fibers. Typically a goal of the invention is to use at least 25% by weight inorganic fiber to produce a dimensionally stable board or mat having a thickness between about one to four inches, and utilizing fibers having an average length of at least about one-half inch, and typically between about one-half and three inches.

The first stage, 10, in the practice of the method is the receipt of the raw material, which may be any of the raw materials described above, into which other fibers (such as cellulose, aramid, thermoplastic, etc.) fibers may be added at a number of different points during the process. The fibers are preferably separated by type as indicated at 11 ; for example fiberglass fibers having a first diameter will be separated at one place, those having a second diameter and perhaps a different average length in another place, those being mineral fibers in a third place, etc. As indicated at 12 the raw input fibers may be stored. For the primary inorganic mineral fibers that are elastic in bulk, such as, they may be compressed for storage. For example they may be compressed by a hydraulic ram in a container that fits on a truck, or they may be baled and banded. Typically the compression is to about 20 to 25% of the natural bulk volume. While compressions less than that may be provided if space allows, compressions more than that may damage the fibers.

Once it is desired to start making product, fiber pre-processing is practiced as indicated at stage 13 in FIGURE 1 A. This includes stripping of any facing that is on the fiberglass, shredding it to a desired size for batch mixing, and other steps that are necessary or desirable to allow entry of the fibers in proper form to the batch mixer in the mixing stage 14. If shredding is necessary, a conventional industrial paper shredder can be used, for example to shred the fiberglass or mineral wool fiber into cubes or blocks or other shapes having each of their three dimensions between about one and three inches, or otherwise separate fibers in bulk form into a size that can be effectively used for further processing. For most applications it is desired that the inorganic mineral fibers have an average length of between about one-half to three inches, and that any other fibers used also not have a length of more than three inches. While the process allows production of products which can retain particles smaller than half inch fibers, it is desired that at least about 25%, and preferably more than 90%, of the material be fibers that have an average length of at least about one-half inch, with few or none more than four inches in length.

The details of one exemplary (only) embodiment for the slurry batch mixing stage 14 is illustrated in FIGURE 2. The equipment schematically illustrated at 14 in FIGURE 2 includes a tank 15, typically having at least a primarily open top, into which water 16, such as from recycled water source 17 (see FIGURE 1 A) is introduced so that it reaches a level 18 in the vessel 15. The level 18 is controlled or monitored by the conventional level controller 19 and once the desired level 18 has been reached so that the virtually exact amount of liquid in the tank 15 is known, the supply of water 16 is shut off. Suitable chemicals (depending upon the particular products being produced) may be added as indicated at 20. The fibers from the fiber pre-processing 13 are then weighed (as illustrated only schematically in FIGURE 2) on a scale 21 , load cell, or the like, and then dumped into, or otherwise fed to, the tank 15 where they are evenly distributed in the liquid by a conventional mixer 22. The slurry so produced will then have a precisely known solids consistency. In the desired practice of the invention that solids consistency is between about .4-8%, but preferably is between about 1-3%. The slurry (e.g. having a consistency of about 1 %) is then discharged from the tank 15 in any conventional manner, for example through conduit 23 having a valve 24 therein, by opening the valve 24.

While batch formation is preferred (for simplicity and accuracy), the slurry mixing may alternatively be done continuously.

As schematically illustrated in FIGURE 1A the conduit 23 preferably leads to a refining stage 25. It has been found according to the invention that refining is best practiced immediately before pack formation and after slurry batch mixing, not before the slurry mixing as in the known EFTEC process. Refining at 25 may be practiced using any conventional refining equipment, such as a refining mill. From the refining stage 25 the slurry is discharged, as indicated at 26 in FIGURE 1 A, to the pack formation stage 27.

In the pack formation stage 27, the pack is formed on a foraminous element (such as a Fourdrinier wire screen) by a wet laid process. A moving inclined wire screen, double wire screen, or any other suitable type of wet laid process non-woven web formation piece of equipment may be utilized to start the web formation as long as it is capable of forming a web/pack at least about an inch thick. One form that the equipment in the pack formation stage 27 may take is illustrated schematically in FIGURE 3, although any suitable conventional equipment can be utilized.

In the FIGURE 3 exemplary embodiment a conventional Fourdrinier wire screen (metal or plastic grid/belt) 28 having a surface 29 on which the pack 30 is formed is utilized. As illustrated in FIGURE 3 the slurry in line 26, preferably at a consistency of at least about 1 % fiber to water weight ratio, is added to the rear portion of the open top of the head box 31 which has a slurry level 32 therein. The level 32 may provide a head, e.g. on the order of about 15 inches of water pressure. Preferably the head box 31 has curved surfaces 33, 34 thereof leading to a substantially horizontal flow to the Fourdrinier wire screen 28.

Utilizing the head box 31 as illustrated in FIGURE 3, with a relatively high consistency slurry, and with immediate discharge at 35 onto the top 29 of the wire screen 28, and with immediate gravity and/or vacuum extraction as illustrated schematically at 36 (resulting in a water flow 37), one gets a uniform and non-layered distribution of fibers, with more fibers oriented in the vertical direction, providing a more isotropic density and compressive strength. The product produced from the pack 30 can thus have a more uniform appearance, higher compressive strength, and greater dimensional stability and tolerances certainly than in the conventional air laid process, and even compared to the prior art EFTEC process described above.

FIGURE 1 A illustrates the water in line 37 withdrawn during pack formation at 27 being recirculated to the recycled water located 17. Note that in FIGURE 1A the standard flow of the fiber and/or slurry is indicated by the vertical arrows, while essentially completely liquid flows are indicated by iines that have circles at spaced points thereon, and while essentially completely gaseous flows are indicated by lines that have spaced "xs" therein. After pack formation at 27 the pack 30 passes to the water extraction stage 38. One particularly advantageous manner in which the water extraction stage 38 may be practiced is illustrated schematically in FIGURE 4.

FIGURE 4 is a schematic end view, partially in cross-section and partially in elevation, of the wire screen 28 as it is moving (in a direction perpendicular to the paper containing FIGURE 4) with the pack 30 thereon. At this stage the wet, uncured pack 30 will be at least about 10% thicker than the final product to be produced; the pack 30 is shown only schematically in FIGURE 4 for clarity of illustration, and would typically have a greater thickness relative to the other components illustrated. At the water extraction stage 38 the wire 28 passes over a plurality of suction boxes 39 of conventional construction, and the water and gas pulled through the suction box 39 passes in line 40 first to a gas/liquid separator 41 of any conventional construction (such as a centrifugal separator with a vertical axis). The gas continues to flow in line 42 to a fan or blower 43 from which it is discharged in line 44 ultimately to a stack/gas discharge 45 (see FIGURE 1 A). The discharged gas at this stage does not have enough energy content to have any "chimney" affect and needs to be discharged solely by the motive force provided by the fan 43, or an ancillary fan (if necessary). The water separated by the separator 41 is separated in line 46, which also leads to the recycled water station 17 as illustrated in FIGURE 1 A. Pursuant to a novel feature according to the invention, the water extraction stage

38 includes a hood 48 which covers the foraminous element 28 and the pack 30, although it does not make a side seal therewith. Ambient air, as illustrated schematically at 49 in FIGURE 4, may seep through the area between the moving foraminous element 28 and the stationary hood 48 along both edges thereof. The ambient air that passes through the open space 49 is ultimately sucked into the suction boxes 39.

Preferably at a central location 50 of the hood 48 (although a number of different locations can be provided) a conduit introduces gas from subsequent processing stages, past a damper 51 , under the influence of a blower 52, from the line 53. The nature of the gas in line 53 will be described subsequently, but it typically contains some particulates and some VOCs. The damper 51 is automatically or manually adjusted to ensure the proper relative pressure, and other, conditions within hood 48. The gas from line 53, which originates from the heat exchanger 54 to be hereinafter described, passes through the wet, fibrous pack 30 while it is being pulled into the suction boxes 39 (a negative pressure preferably being maintained under the hood 48). The gas from line 53 is thus scrubbed and filtered by the pack 30, thereby removing most particulates and VOCs so that the gas discharged in line 44 and stack 45 is almost pollution free, and thereby helps the plant meet state and Federal environmental standards.

The next stage 58 illustrated in FIGURE 1 A is the binder application stage. This is an optional stage, but will be utilized in the vast majority of circumstances. For example for a typical acoustical or thermal board produced of substantially 100% scrap fiberglass, a phenolic resin binder is added at a rate of about 6% by weight of the pack 30 (although the percentage by weight of additional binder could be as low as 4% or as high as 12%).

In the practice of the binder application stage 58, binder, such as conventional phenolic resin solution, is provided from supply 59 to a conventional mixing tank 60 with a conventional mechanical mixer therein, then it is fed to the binder reconstitution stage 61. Water from source 62 is supplied to the binder mixing stage 60, while the dilute binder solution recirculated at 63 is provided typically directly to the binder reconstitution stage 61. The water from source 62 is the same source 62 providing make-up water to the line 16, if desired. Primarily the liquid for the binder reconstitution stage 61 is provided from the recycle line 63. Ultimately the reconstituted binder solution may be stored as indicated by binder storage tank 64, and then applied to the pack 30 at the binder solution application stage 58. Any suitable conventional structure, such as a weir based system, spray heads, or the like, may be used to apply the binder to the pack 30 at stage 58.

After binder application in stage 58, the pack 30 passes to a binder solution extraction stage 66 wherein dilute binder solution is pulled from the pack utilizing conventional suction boxes or the like. The dilute binder solution pulled from the pack 30 is what is recirculated in line 63 to the binder reconstitution stage 61. The pack 30, now provided with an appropriate amount of uncured binder, then passes as indicated by line 67 to a drying/curing oven 68 (see FIGURE 1 B). In the drying/curing oven 68, it is preferred that three different operations be carried out, which are referred to as a slow dry stage 69, a fast dry stage 70 in which some significant amount of curing of the binder takes place, and a cure and final dry stage 71 , as indicated in FIGURES 1 B and 5. While it is preferred that all of the stages 69-71 take place within the same external casing, they could take place in individual structures.

The heat to effect the drying and curing provided in the oven 68 is ultimately provided from a combustion source 72 (e.g. burner or furnace) which is fed with fuel 73 and combustion air. The fuel 73 may be any suitable fuel source, but preferably is methane, propane, or other gaseous fuel. Ultimately the combustion air is supplied by the supply air source 74 which may take air outside of the plant containing the equipment of FIGURES 1A and 1 B, and/or inside the plant, depending upon the ambient circumstances, the heating and cooling system within the plant, etc. For example on a hot summer day supply air 74 would definitely be taken from the outside especially if attempts were being made to cool the plant, whereas on a cold winter day if the plant had an efficient heating system supply air 74 may be taken exclusively from inside the plant.

Depending upon the equipment utilized, the level of production, and other factors, the supply air, before used in the combustion stage 72, may be preheated in the heat exchanger 54. The heat exchanger 54 may be of any suitable conventional type, but preferably is a counter-current flow indirect air/air heat exchanger, such as a fin and tube type heat exchanger as one example. In the heat exchanger 54 the combustion air, which is discharged in line 75, is heated to a moderately high temperature, typically from ambient to between about 150-220°F, and most desirably around 200-210°F. For example about 210°F temperature air in line 75 is broken into two branches, the first branch 76 which leads to the slow dry stage 69, and a second branch 77 which supplies combustion air directly to the combustion stage 72. The air in conduit 76 is introduced through a plurality of nozzles, pipes, or any other suitable introducing structures (shown schematically at 76' in FIGURE 5) that fairly uniformly introduce the drying air beneath the resin impregnated pack 30 traveling in a substantially linear horizontal direction through the oven 68.

In a similar manner, under some circumstances, the hot combustion air in line 78 (which typically is at a temperature of over 250°F, and typically a temperature that will effectively cure the binder, e.g. about 350°F or more) is introduced through the introducing structures 79, 80 which also may comprise any suitable array of plenums, pipes, nozzles, orifices, etc. for substantially uniformly introducing the hot drying/curing air into the fast dry stage 70 and the cure/final dry stage 71 , seen most clearly in FIGURE 5. Preferably, however, the temperature of the air used in this stage is controlled to 250°F. At this temperature the binder is not likely to cure but the wet pack will be substantially dried. Ambient air will be heated by heaters dedicated to the dryer. The exhaust from the curing oven will be part of the makeup air for the dryer. The drying/curing air is introduced at 76', 79, 80 in such a way as to pass through the pack 30 (which is air pervious), but so as not to move the pack 30 off of its conveying surface, so that uniform transport through the oven 68 is ensured. Typically the pack 30 is transported through the oven 68 either by conventional perforated chain conveyors, or by utilizing perforated metal plate sections conventionally referred to as "flights" attached to a conveyor roller chain at the sides of the oven. As the flights or chains (not shown) move through the oven 68 the perforations allow heated air to be forced through the pack 30. Typically flights or chains are provided both at the top and the bottom of the pack 30, but according to one aspect of the present invention, the top flights or chains (or even stationary air pervious structures) in one or both of the stages 69, 70 are placed in a position only preventing the pack 30 from moving off the bottom flights or chains as a result of the air being supplied at 76', 79, and no compression of the pack takes place. However, in the stage 71 the top flights or chains are positioned to effect compression of the pack 30 to the final desired thickness of the board (87) being produced. Conventional drying/curing oven flights or chains are shown, for example, in U.S. patents 4,734,996 and 4,263,007. By providing a simplified construction of the conveying system through the oven 68, that is by providing flights or chains only in the stage 71 , the cost of the oven 68 may be reduced while the drying efficiency in the stages 69, 70 is increased because the pack 30 is not under significant compression therein.

While not shown in FIGURES 1 B and 5 for clarity of illustration, typically the air supplied by supply structures 76', 79, 80 is powered by fans. The design of the fans, and the provision of the nozzles, orifices, plenums, conduits, or other structures used to introduce the drying/curing air at 76', 79, 80, are provided so that the air velocity is highest in the section 71 , slightly lower in the section 70, and lowest in the section 69, with a differential of the average velocity of at least 5% from each consecutive stage to the next.

The drying air in the slow dry stage 69 is captured by a conventional hood and like structures at the stage 69, and returned in conduit 81 to the cool air conduit 53 extending from the heat exchanger 54, which ultimately leads - as illustrated in FIGURE 1 A - to the water extraction stage 38 and is treated as illustrated in FIGURE 4 and described above. The input air to the heat exchanger 54 which heats the supply air from 74 and which is cooled to the discharge 53 is provided from line 82 which withdraws drying gas that has passed through the pack 30 in the fast dry stage 70. From the conduit 82 the still warm air (for example typically at about 210-220°F, such as about 212°F) passes in line 83 to the heat exchanger 54. This air is moist, and condensate will form in heat exchanger 54, which condensate (via line 84) is fed to the recycled water supply 17 illustrated in FIGURE 1 A.

From the final dry/cure stage 71 the gas that is withdrawn in conduit 85 is recirculated to the conduit 78 from the combustion chamber 72. The gas in conduit 85 typically is still at high temperature, e.g. about 300°F, and when combined with the gas in line 78 from the combustion chamber 72 forms a common line which is supplied to the introduction structures 79, 80 at a temperature sufficient to cure the binder in the pack 30 in a reasonable period of time, e.g. a temperature of at least about 350°F. If desired, treatment can be provided for the gas in line 85 as illustrated schematically at 86 in FIGURE 5; however, typically that would not be necessary since the gas will ultimately, at some point in time, be introduced into the structure 79, but will be withdrawn in the conduit 82, passing through heat exchanger 54, and then passing into line 53 to be treated at the water extraction stage 38 as illustrated in FIGURE 4. Where no binder curing is necessary, the drying temperature of the air in stages 70, 71 may be reduced.

The final stage 71 in the oven 68 is at least a stage where compression, schematically illustrated at 91 in FIGURE 5, is applied so that the final board 87 produced has the desired thickness. For example if the pack 30 is normally at two inches and the final thickness desired is an inch and a half, in the compression section 91 the top and bottom flights (or the like) will be set so that the compressive forces applied reduce to the thickness of the pack 30 to one and a half inch, and that will be the thickness of the final board 87 produced. The board 87 produced according to the invention has excellent uniformity and excellent dimensional stability, and it can be produced with accurate dimensional tolerances. In the utilization of the various stages 69, 70, 71 in the preferred embodiment illustrated in FIGURES 1 B and 5, in a typical manner of operation about 15-40% of the ultimately total moisture of the pack 30 (provided initially and produced during curing) is removed in stage 69, e.g. preferably about 30%. Slightly more than the amount of the initial volume of water within the pack 30 will ultimately be removed since some moisture is generated during the curing that takes place in the stage 70, and primarily in the stage 71.

In the stage 70 approximately 50-80% of the total moisture is removed, e.g. preferably about 65%. In the final dry stage 71 , which is primarily a curing stage, typically only about 1-10% of the total moisture will be removed, e.g. preferably about 5%.

While in FIGURE 5 the drying/curing gas is shown introduced at the bottom and withdrawn from the top in each stage 69-71 , it is to be understood that the gas flow may be substantially up and/or down in each of the stages 69-71. As described earlier, it is desirable to provide different velocities of the drying/curing air in the stages 69, 70, 71. At each successive point in the oven 68 it may be less difficult to force air through the pack 30, and therefore a higher velocity can be achieved; while at the same time it is not desired, when the pack 30 binder has not been at least somewhat cured, to force air at too high a velocity through the pack 30 which could disrupt the uniformity of the pack 30. Two of many different possible velocity gradients in the stages 69-71 are illustrated schematically in FIGURE 6.

FIGURE 6 shows the drying air velocity on the y axis, and the position of pack 30/board 87 within the oven 68 on the x axis. The various stages 69-71 are plotted along the x axis. According to one aspect of the invention, the air velocity in the stage 68 could be a substantially uniform relatively low value as indicated by line 88, and step up (at least 5%) to the value 89 in the stage 70, and step up (again at least 5%) to the value indicated by line 90 in the stage 71. Alternatively the air velocity could increase substantially linearly from the entrance to the exit as indicated by the line 92 in FIGURE 6. Any other variation could be utilized which provides a relatively low air velocity in the stage 69, a higher velocity in the stage 70, and the highest velocity in the stage 71. The exact magnitude of velocity will be controlled by controlling the fans that supply the air to the structures 76', 79, 80, and/or by providing dampers, orifices, or like air flow control mechanisms; and the absolute magnitude will also be determined depending upon the particular constituents, thickness, etc. of the pack 30. After the final board 87 is produced, as illustrated schematically in FIGURE 1 B, the board 87 may be subjected to other treatments. For example typically the board 87 will be trimmed as illustrated schematically at 93 in FIGURE 1 B using conventional trimming/milling blades which cut off the side edges so that the board 87 has the desired width. The portions cut off are then reintroduced into the supply stream at stages 10, 12, and/or 13.

Also, the board 87 may have a special finish applied, or special finishing steps practiced, as indicated at stage 94 in FIGURE 1 B. For example the board 87 may be bisected with a horizontal band saw, e.g. cutting a board three inches thick into two one and one half inch thickness boards, etc. Alternatively or in addition the board 87 may be sanded as is conventional for at least acoustical end uses, and/or have a cloth covering applied, and/or have any other special finish applied depending upon the particular use to which the final product -- illustrated schematically at 95 in FIGURE 1 B - - is to be put.

While a wide variety of products 95 can be produced according to the invention, particularly suitable uses are acoustical board wall panels which typically have a density of about four-six pounds per cubic foot; acoustical ceiling boards to which a decorative surface finish of paint, vinyl, or fabric is typically applied; mechanical insulation board, again typically having a density of about four to six pounds per cubic foot, and which provides thermal insulation for commercial and industrial applications up to about 450°F; and roof deck thermal insulation boards, which typically have a density of about six-twelve pounds per cubic foot and which provide thermal insulation as part of a "built up roof" system which also includes a facing of asphalt and reinforcing mat and paper. However as indicated above, many other uses are provided depending upon whether mineral fiber, fiberglass, or other fibers are the majority of the fibers used in the production of the pack 30 and board 87.

The invention produces products in a highly energy efficient and cost effective manner which optimizes heat recovery, in which there are no liquid discharges from the entire production facility, and in which the air discharges are virtually pollution free, being substantially devoid of particulates and also being substantially devoid of volatile organic compounds.

Where suitable, by effectively utilizing the heat exchanger 54, and associated conduits, the latent heat of vaporization of the liquid is recovered as a heat input, adding to the high efficiency of the process. Some make-up water is necessary because water vapor will be discharged in the stack 45.

While a conventional phenolic resin binder has been described in the binder embodiment above, it is to be understood that other binders could be used in place of or in addition to such a system. For example thermoplastic fibers could be added in the fiber batch mixing stage 14 illustrated in FIGURES 1 and 2, which at least partly thermoplastic fibers would melt and act as a binder instead of, or supplementing, the phenolic resin, in the stage 71. The temperature of the drying/curing air added in the stages 70 and 71 would then be adjusted to be suitable to melt the thermoplastic fibers without destroying them.

FIGURES 7A-7D illustrate, though still schematically, in more detail the various equipment that may be utilized for the practice of the method of the present invention, as illustrated in FIGURES 1A and 1 B. In FIGURES 7A-7D components that are substantially the same as those in FIGURES 1 A-5 are shown by the same reference numeral only preceded by a "1 ".

In the fiber preprocessing area 113 illustrated in FIGURE 7A, various types of input fibers and materials from sources 201 are input into the system. For example, the representations 201 illustrate various forms of conventional post consumer waste recycled fiberglass such as "pipe trim", "unfaced", and "faced", as well as pre-consumer waste recycle fiberglass as indicated as "uncured". For example, the pipe trim and unfaced fiber sources are fed by a cross conveyor 202 in the direction of the arrow indicated in FIGURE 7A for further processing, and fibers in a line 203 from a centrifugal separator 204 in an exhaust air line powered by the extraction blower 205 are also added to the fibers flowing on the cross conveyor 202. The fibers flow from the cross conveyor 202 to an incline belt scale conveyor 206, typically past a metal detector 207 which will detect and/or remove metals. From the belt scale 206 the fibers go to a slitter/chopper and then pass through a conduit 209 to an incline conveyor 210 having a hood 21 1 with an exhaust flow 212 therefrom. The line 212 is connected up to line 213, and in turn connected to the centrifugal separator 204 where fibers are removed and the gas is discharged by blower 205.

For the bottom half of FIGURE 7A in the input fiber area 113, a scissors lift 21 1 and uncured roll stand 212 may be provided, with a second cross conveyor 213, associated with the metal detector 207', incline belt scale 206', slitter/chopper 208', and transport device 209', comparable to those in the upper half of FIGURE 7A. Ultimately the fibers from the sources 201 , after slitting/chopping by the devices

208, 208' are fed to the conventional reversing conveyor 214 and ultimately deposited onto the weigh conveyor 215 where the fibers are weighed typically in a batch process, and then dumped onto the incline conveyor 216 for transport to a diverter chute 217 having two outputs, connected to two different tanks 122. There may be a conventional baffle or other diverting structure (not shown) within the diverter chute 217 to direct one batch of fibers to one of the tanks 122, and then another (the next) batch to the other tank. Makeup water and recycled water are supplied to the white water surge tank 218 which is used to supply water to the tanks 122 of the slurry batch mixing system 114. The discharge from the system 114 is a fiber slurry with a known amount of fibers per unit volume, in line 123, which moves for further processing.

The fiber slurry in line 123 can pass through a Bauer mill 220 of conventional design so as to have the fibers therein acted upon further, and then go to a slurry storage tank 221 which is operatively connected to the inlet of a slurry supply pump 222. The pump 222 supplies slurry to the pack formation system 127 (details of which are illustrated in FIGURE 3) for forming the pack 130. Liquid in line 137 from the gravity or vacuum extraction of the pack formation apparatus 127 flows into the former seal tank 223 and white water from the tank 223 is recycled by the white water recycle pump 225 back to the white water surge tank 218, and stock is recycled to the pack formation system 127 using the stock recycle pump 224.

The pack 130 then passes to a water extraction stage 138 where withdrawn liquid from the suction box 139 passes to the gas/liquid separators 141 , with the withdrawn gas is exhausted or recycled utilizing the blowers 143, and the separated water flows in pipes 146 to the former seal tank 223. Some of the removed gas is recycled in line 228, while the gas that is exhausted is exhausted (e.g. to a stack) in line 144.

FIGURE 7B also indicates the binder providing equipment, such as the binder chemical supplies 159 and the binder mixing 160. Typically, where binder is utilized, ammonia is provided in tank 229, and urea is provided in tank 240, with a metering pump 241 being connected to the ammonia supply 229 and the discharge pump 242 being connected to the urea tank 240. Resin storage is preferably provided in tank 243, and a chiller 244, heater exchanger 245, and pump 246 are preferably provided to keep the resin in the tank 243 cool and fluid.

During mixing, the pump 247 discharges resin from the tank 243 while the pumps 241 , 242 supply ammonia and urea where utilized, to the binder mixing 160. As illustrated in FIGURE 7B two mixing tanks may be provided at the binder mixing stage 160, with a binder transfer pump transferring binder slurry from the first tank to the second. A metering pump 249 meters the binder in line 250 to the conventional binder application apparatus 251 above the water-extracted pack 130, while fumes from the hoods for the tanks at the mixing stage 160 may be moved in line 230 to a conventional destruction or exhaust device.

After binder application (where utilized) binder is extracted as illustrated schematically at 252, including using a suction box 253 or similar equipment, and with binder/air separators 255 connected via lines 254 to the suction device 253. The separated binder passes in conduits 256 to the binder recycle tank 257 with the binder recycle pump pumping binder in line 163 back to the application device 251. All of the application equipment 251 in FIGURE 7 is for the binder application 158 and binder extraction 166 stages. Line 258 indicates the addition of makeup water to the binder reconstitution tank

257. The gas separated by the separators 255 passes in line 259 to the pump 260 for recirculation in line 261 into the hood 252 to facilitate binder extraction, and some of the separated gas is exhausted to a stack by binder extraction exhaust blower 263 in line 264. Where makeup air is required for both the water extraction 138 and binder extraction 166 stages the line 262 may be provided connected to conduit 272 and blower 271 in FIGURE 7C.

FIGURE 7C illustrates the majority of the drying and initial curing stages 169, 170, whereas the final cure and dry stage 171 is seen primarily in FIGURE 7D. FIGURES 7C and 7D illustrate an exemplary form of the invention where a six zone drier oven is provided, and a four zone curing oven. However, some curing may take place during drying, at least the latter stages thereof, and further drying takes place during curing.

The pack 130 from the forming stage 127 passes to the up flow drier 169, 170 zones 266, alternated with the down flow drier zones 267. It is desirable to have alternating up flow and down flow zones for the drier (which preferably comprises at least three zones but may have more than six zones) so as to insure effective and substantially uniform drying. The blower 268 preferably feeds makeup air to a burner 270, which is supplied by fuel (preferably natural gas) via line 273, for the first down flow zone 267. The air from that first down flow zone 267 is recycled by the recycle blower 269 to the first up flow zone 266. Similar makeup air blowers 260 and burners 270, and recycle blowers 269, are provided for the other four zones of the drier. Part of the air recycled by the blowers 269 may be withdrawn by the makeup air blower 271 which is supplied by a line 272 to the line 262 illustrated in FIGURE 7B. The first two zones of the curing oven which also provide some drying, are illustrated at 274, 275 in FIGURE 7C, in this case the first zone 274 being an up flow zone and the second zone 275 a down flow zone. Although the zones 274, 275 are supplied with recycled air from recycle blowers 276, while fuel gas in line 273 is supplied to burners 277 to provide the heat for the curing gas that is introduced into the curing oven zones 274, 275.

The next section of the curing oven, 171 , illustrated in FIGURE 7D also has up flow and down flow zones 274, 275, with associated recycle blowers 276, and associated burners 277. Exhaust gas from the entire end of dry/cure portions 170, 171 may be withdrawn by the blowers 278 and led back to the makeup air blower 268. This exhaust gas passes in line 283 which is illustrated in both FIGURES 7C and 7D.

Downstream of the last curing zone 275 may be a cooling conveyor 280, or like cooling structure, for cooling the final board or mat product produced. The exhaust from a hood over the cooling conveyor 280 is connected by a line 281 to the cool zone blower (which may have an exhaust gas temperature as low as 100°F) 282 and passed into the line 283. The blowers 278 are also connected to the line 283.

Further operations, as desired depending upon the particular board or mat produced, may be provided downstream of the cooling conveyor 280. Exemplary equipment illustrated in FIGURE 7D for finishing comprises an inspection conveyor 285 for manual or automatic inspection of the final board or mat product produced, an edge trim and split saw assembly 286 from which fibers and other dust are ultimately passed to the dust collector/air/solid separator 204 via the lines 287 and 288 and 289, a chop saw feed conveyor 290, a conventional chop saw 291 , a conventional take-away conveyor 292, and a packing table 293. Horizontal saw 294 and a belt sander 295 may also be provided, both having hoods connected up to the line 289, and the components 294, 295 comprising off-line processing equipment for the final board or mat produced. Various facing, coloring, spray, or other materials may be provided off-line too.

In order to use the processing equipment described above to make lower density products, as illustrated in FIGURE 8 after the wet pack 30 (or 130) comes out of the forming section 27 it may pass over a roller 300 and then be directed to a section (such as, although not necessarily, a substantially horizontal section) where the pack is made fluffier -- that is its bulk density is lowered. This is preferably accomplished by blowing a fluid into the pack to fluff it up. The pack may be on a perforated conveyor (not shown) at the time, or may be substantially unsupported at the area where the fluffing takes place. As schematically illustrated in FIGURE 8 a plurality of substantially in-line (generally perpendicular to the direction of pack movement) air jets 301 may be provided connected up to a source of air under pressure (but not high enough pressure to harm the pack 30). The air (from source 303) enters the pack 30 and causes an increase in the void volume between the fibers and other components, resulting in the thicker, lower density, fluffier pack 302 illustrated on the right hand side of FIGURE 1. The pack 302 then subsequently goes to the oven 68, or other processing.

In order to make higher density products, the system/process schematically illustrated in FIGURE 9 may be utilized, in which the wet pack 30 from the forming section 27 passes between a plurality (e.g. two, four, or more) of rollers 305 which apply a pressure which compresses the pack 30. There may be rollers 305 of various spacings so as to taper the thickness of the pack down gradually (and thereby increase the density gradually), or it can be done in one stage, to produce the compressed, higher density pack 306. The rollers 305 illustrated in FIGURE 9 may be any conventional rollers for that purpose, and preferably have an adjustable spacing. One or both (or all if more than two) of the rollers may be driven, or one roller driven and connected by a chain, gear, or other mechanism to the other so that driving of one drives the other in a complimentary manner. A construction as illustrated in FIGURE 9 reduces the load that the oven (65) need apply, lowering the capital investment in the oven. That is the capital investment in the oven can be significantly reduced because less rigid flights can be used, a significant cost savings.

Utilizing the aspect of the invention of FIGURES 8 and 9 it would be possible to increase or decrease the density of the pads 30, and/or final product 87, by anywhere from 2-50% (and all narrower ranges within that broad range). In all of the descriptions above where a particular range is provided it is to be understood that according to the invention all narrower ranges within a particular broad range are specifically included. For example for a range of inorganic mineral fibers of between 25-100% all narrower ranges within that broad range are also specifically provided, such as 35-85%, 90-99%, 50-78%, etc. Many other modifications are also possible within the scope of the invention, which is to be accorded the broadest interpretation possible consistent with the prior art.

Claims

WHAT IS CLAIMED IS:

1. A method of making a board or mat, comprising:

(a) forming a liquid slurry having a solids consistency of about .4-8%, at least 25% by weight of the solids of the slurry comprising inorganic fibers having an average length of at least about one-half inch;

(b) forming a pack from the slurry on at least one moving foraminous element, the pack at least about one inch thick;

(c) extracting water from the pack; and

(d) passing elevated temperature air through the pack to effect drying of the pack to produce a product at least about one inch thick.

2. A method as recited in claim 1 wherein (a)-(d) are practiced so as to produce a product with dimensional stability.

3. A method as recited in claim 2 wherein (a) is practiced in a batch process using a predetermined volume of liquid and a mass measured quantity of solids mixed to produce a slurry of substantially precisely known consistency.

4. A method as recited in claim 3 wherein (a) is practiced to form a slurry having a solids consistency of about 1-3%.

5. A method as recited in claim 2 further comprising (e) refining the slurry from (a) substantially immediately before (b).

6. A method as recited in claim 2 wherein elevated temperature exhaust gases are produced during the practice of (d) and further comprising (f) the elevated temperature exhaust gases are passed in counter-current indirect heat exchange relationship with ambient air to heat the ambient air and cool the exhaust gas.

7. A method as recited in claim 6 further comprising (g) the heated ambient air from (f) at a temperature of between about 150-220°F is used in a first part of (d).

8. A method as recited in claim 2 wherein exhaust gas is produced during the practice of (d); and further comprising scrubbing and filtering the exhaust gases by passage through the pack substantially during (c) prior to discharge of the exhaust gases.

9. A method as recited in claim 2 further comprising (i) applying binder to the pack between (c) and (d), and withdrawing and reusing excess binder.

10. A method as recited in claim 2 wherein (d) is practiced so that in a second part thereof gas at a temperature of at least 250°F is passed through the pack, and so that in a third part of (d) air of a temperature to effect at least the majority of cure of the binder is passed through the pack; and wherein the exhaust gas from the third part of (d) at a temperature greater than 250°F is recycled to pass through the pack in the second part of (d).

11. A method as recited in claim 10 wherein (d) is practiced so that about 80- 90% of the drying of the pack takes place in the first part of (d), about 10-20% of the drying takes place in the second part of (d), and less than about 5% of the drying takes place in the third part of (d).

12. A method as recited in claim 10 wherein (d) is practiced so that the average drying air velocity in the second part of (d) is at least 5% higher than in the first part of (d), and the average drying air velocity is the third part of (d) is at least 5% higher than in the second part of (d).

13. A method as recited in claim 10 wherein (d) is practiced so that the drying gas for the second and third parts of (d) comes from combustion of a fuel and combustion air, and wherein the combustion air is at least in part used to heat ambient air.

14. A method as recited in claim 1 wherein (a)-(d) are practiced using at least 90% inorganic fibers, and to produce a product having a thickness of between about 1 - 4 inches.

15. A method as recited in claim 2 wherein (a)-(d) are practiced using at least 90% inorganic fibers, and to produce a product having a thickness of between about 1 - 4 inches.

16. A method as recited in claim 8 wherein exhaust gas is produced during the practice of (d); and further comprising scrubbing and filtering the exhaust gases by passage through the pack substantially during (c) prior to discharge of the exhaust gases.

17. A method as recited in claim 1 wherein exhaust gas is produced during the practice of (d); and further comprising scrubbing and filtering the exhaust gases by passage through the pack substantially during (c) prior to discharge of the exhaust gases.

18. A method as recited in claim 1 wherein (a) is practiced to form a slurry having a solids consistency of about 1 -3% with at least about 50% by weight of the solids of the slurry comprising inorganic fibers.

19. A method as recited in claim 1 further comprising (e) applying binder to the pack between (c) and (d), and withdrawing and reusing excess binder.

20. A method as recited in claim 1 further comprising finishing the product from (d) by cutting, smoothing, and providing a decorative surface.

21. A method of making a board or mat comprising:

(a) forming a liquid slurry having a solids consistency of at least about .4%, and at least 10% inorganic fibers;

(c) extracting water from the pack;

(d) drying the pack, and producing exhaust gases during drying, to produce a product; and

(e) passing at least about 10% of the exhaust gases from (d) through the pack substantially during (c) and prior to discharge of the exhaust gases.

22. A method as recited in claim 11 wherein (a)-(d) are practiced so as to produce a product with dimensional stability.

23. A method as recited in claim 22 further comprising (e) applying binder to the pack between (c) and (d), and withdrawing and reusing excess binder.

24. A method of making a board or mat comprising:

(c) extracting water from the pack; and

(e) increasing or decreasing the density of the pack between (b) and (d) by 2- 50%

25. A method as recited in claim 24 wherein (a) is practiced to form a slurry having a solids consistency of about 1 -3%.

26. A method as recited in claim 1 further comprising reducing the density of the pack between (b) and (d) by about 2-50%.

27. A method as recited in claim 1 further comprising increasing the density of the pack between (b) and (d) by about 2-50%.

28. A fiber-containing mat or board at least about one inch thick and having at least 25% by weight inorganic fibers, and produced by the method of claim 1.

29. A dimensionally stable fiber-containing mat or board at least about one inch thick and having at least 25% by weight inorganic fibers, and produced by the method of claim 2.

30. A dimensionally stable fiber-containing mat or board at least about one inch thick and having at least 25% by weight inorganic fibers, and produced by the method of claim 19.

31. A method as recited in claim 1 wherein (a) is practiced so that at least 25% of the solids of the slurry is post-consumer waste recycled fiberglass.

32. A board or mat producing system comprising: a slurry forming device which slurries fibers in a liquid; a foraminous element which forms a pack from the fiber slurry; a device which dewaters the pack; a drier having an exhaust for exhaust gases; and means for circulating at least part of the exhaust gas from the drier to the pack to pass through the pack.

33. A system as recited in claim 32 wherein said dewatering device comprises a liquid pervious conveyor supporting the pack, a hood covering at least part of the conveyor, but open along edges of the conveyor to allow ambient air to flow into the hood past the conveyor edges to flow through the pack on the conveyor; and a suction source located below the conveyor for drawing liquid from the pouch through the conveyor.

34. A system as recited in claim 33 further comprising a gas/liquid separator connected to said suction source.

35. A system as recited in claim 33 wherein said circulating means circulates exhaust gases to said hood to flow with ambient air through said pack to said suction source.

36. A system as recited in claim 35 further comprising a valve or damper for controlling the flow of exhaust gases into the hood.

37. A system as recited in claim 33 further comprising a binder addition device for applying binder to the pack prior to the drier, and curing the binder at and subsequent to the drier.

38. A system as recited in claim 32 wherein said recirculating means comprises a hood over the pack, a conduit from the drier to the hood, and a fan for blowing or sucking exhaust gas from the conduit through the hood and pack.

39. A system as recited in claim 32 wherein said drier comprises a plurality of in-series sections, alternating sections having alternating flow directions of drying air.

40. A pack treating apparatus comprising: an air pervious support for a pack; a suction source below said air pervious support; a hood covering said support; and a gas inlet to said hood for introducing gas that flows through said support to said suction source.

41. Apparatus as recited in claim 40 wherein said hood is spaced from side edges of said support to allow ambient air to flow into said hood under the influence of said suction box.

42. Apparatus as recited in claim 41 further comprising a valve or damper for controlling the flow of exhaust gases into the hood.

43. Apparatus as recited in claim 41 further comprising a gas/liquid separator connected to said suction source.

44. Apparatus as recited in claim 32 further comprising means for reducing the density of the pack by at least 2% prior to said drier.

45. Apparatus as recited in claim 32 further comprising means for increasing the density of the pack by at least 2% prior to said drier.

46. A method, apparatus and product substantially as shown and described.