MXPA06009638A - High efficiency refractoryless kettle - Google Patents

Abstract

An apparatus for calcining gypsum including a housing having a bottom wall, opentop, and a plurality of side walls extending therebetween. A fixture is located adjacent the open top for receiving gypsum from a source and transferring the gypsum into the housing. At least one burner is connected to the housing and operable for combusting an air-fuel mixture to heat the gypsum. At least one serpentine burner conduit extends from the burner through the housing and terminates through a support floor of the apparatus. The exhaust flow is then directed through a fluidization pad and into the gypsum to further heat the gypsum product. An agitation mechanism is operable to mix the gypsum adjacent the fluidization pad to prevent pockets of gypsum from coagulating and preventing fluidization of the gypsum.

Description

BOILER WITHOUT REFRACTORY. HIGH EFFICIENCY The present invention relates to a highly efficient method and apparatus for calcining gypsum and / or drying gypsum. BACKGROUND OF THE INVENTION Calcining gypsum comprises converting calcium sulfate dihydrate by heating it in calcium sulfate hemihydrate, better known as stucco. Calcination apparatuses and previous methods have taken various forms. Traditionally, calcination of gypsum has occurred in a large kettle or kettle, which has a thickened dome-shaped bottom, against which a gas flame is directed, with the boiler and burner flame enclosed in a convenient refractory structure. There is usually an associated hot pit on which the calcined material is fed. The boiler must withstand temperatures in the range of 1093 - 1316 degrees C (2,000-2,400 degrees F), hence requiring an expensive combustion chamber steel plate in its dome bottom, which is typically 4,445 cm (1 3 / 4 inches) thick. The U.S. Patent No. 3,236,509 characterizes this type of construction. This approach had numerous disadvantages, such as the extreme waste of hot gases from the burner, and the associated refractory brick enclosure which, when repairs or shutdown of the boiler are required, first requires a prolonged cooling period. Other calcination boilers, of the general type described above, have included supplementary submerged combustion designs where the exhaust gases from the gas burners were discharged directly to the contents of the boiler. Here, the gas flare that directly hits the material that. it was calcined, and there was an increased possibility of creating the so-called "thoroughly calcined" material, that is, insoluble anhydrite. The Patents of the U.S.A.

Nos. 4,176,157 and 4,238,238 typify this type of approach. In addition, other calcination boilers of the prior art, of the general type described above, include a series of transverse burner tubes that pass in general completely horizontally through the boiler, allowing the hot gases inside the refractory structure and surrounding the boiler they are directed additionally by the tubes, and thus, by the contents of the boiler to heat it more. The Patents of the U.S.A. Nos. 3,307,915 and 4,163,390 characterize this type of boiler construction. There have also been rotating calcining structures horizontally aligned; the U.S. Patent No. 3,871, 829 characterizes this type of approach. In addition to the previous boiler constructions that normally require an expensive refractory structure, there are also non-refractory boilers that use the principle of submerged combustion, even those that have the auxiliary suction tube structure that covers the main burner tube, to reduce formation of insoluble anhydride calcined thoroughly. The U.S. Patent No. 4,626,199 characterizes this type of construction. In addition, there are so-called non-refractory conical boilers with several types of submerged combustion heating systems, again with the attendant risk of creating non-uniform stucco and thoroughly calcined material. The Patents of the U.S.A. Nos. 4,629,419 and 4,744,961 typify these constructions of conical boilers.

More recent calcination boiler modifications have included so-called "booster" burner constructions, including electric heating booster resistors, see U.S. Pat. No. 4,744,963, and gas-operated booster burner designs, both added as supplementary heaters to traditional refractory-type boiler constructions. The Patents of the U.S.A. Nos. 5,743,954 and 5,927,968, discloses a method and apparatus for continuous calcination of the gypsum material in an unrefined boiler preferably heated by a series of multiple separate dip tube coils, each coil works within a specific calcination zone inside the boiler. SUMMARY OF THE INVENTION The present invention provides an apparatus for calcining gypsum, having a housing with a bottom wall, an open lid, and a plurality of side walls extending between the bottom wall and the open lid. An accessory is connected to the housing to receive the raw plaster from a source and transfer the plaster to the housing. The apparatus also includes at least one burner connected to the housing and operable to burn a mixture of air and fuel to heat the plaster. At least one serpentine burner conduit extends from the burner through the housing and terminates through a top surface of an operable support floor for holding the plaster in the housing. The gypsum is first heated by the transfer of heat from the burner conduit and is further heated by the exhaust gas that enters the gypsum from the bottom of the apparatus. The exhaust gas fluidizes the gypsum as part of the calcination process. The apparatus may include an operable stirring mechanism to ensure good fluidization of the sprayed gypsum. The apparatus is operable to avoid channeling exhaust gas through the plaster, avoiding dead zones in the plaster, and to prevent the plaster from being collected along the surface of the plaster support floor. The stirring mechanism includes a stirring frame and a plurality of stirring members connected thereto. The stirring mechanism is operable to agitate the gypsum adjacent to the support floor when the agitation frame is moved reciprocally from a first position to a second position. The stirring frame has at least one pivoting support arm rotatably connected to the calcination apparatus at one end and the frame at the other end such that the frame will swing on a pivot axis when the movement is imparted to the frame. An actuator arm extends on the side of the housing to provide a mechanical connection between an actuator and the agitator frame. A method for calcining gypsum includes providing gypsum to a calcining apparatus. The gypsum is first heated by conduction with a serpentine burner duct that extends from an external burner through the gypsum and terminates through a gypsum support floor surface. The exhaust gas is directed by a fluidization structure to fluidize and further heat the gypsum by convection as the exhaust gas flows through the gypsum and exits at the top of the apparatus. Other applications of the present invention will become apparent to those skilled in the art when reading the following description of the best mode contemplated for practicing the invention along with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a perspective view of a high efficiency calcining apparatus; Figure 2 is an enlarged perspective view of a fluidization bed in partial section to show the layers of a fluidization structure; Figure 3 is a perspective view of a stirring mechanism; Figure 4 is the apparatus of Figure 1 with the burner duct in a non-installed position; Figure 5 is the apparatus of Figure 1 showing a plurality of additionally connected access panels; Figure 6 is a perspective view of the calcination apparatus of Figure 1 showing the route of exhaust gas flow with arrows. DETAILED DESCRIPTION OF THE INVENTION With respect to Figure 1, there is shown an apparatus 10 for calcining gypsum. A housing 12 includes a bottom wall 14, an open lid 16, and a plurality of side walls 18 extending between the bottom wall 14 and the open lid 16. An inlet fitting 20 is located in the housing 12 for receiving crushed or synthetic raw gypsum from a source (not shown) and for transferring the gypsum into the housing 12. At least one burner 22 is connected to the housing 12. The burner 22 is operable to burn a mixture of air and fuel supplied by a forced air duct 24 and a fuel conduit 26. Burner 22 may be any type known to those skilled in the art, but will typically burn a hydrocarbon-based fuel. The hot combustion gases from the burner 22 will flow through at least one serpentine burner duct 28 which extends through a gypsum support floor 23 adjacent to the bottom wall 14 of the housing 12. The flow of hot exhaust gases from the Burner 22 is used to heat gypsum material to approximately 149 degrees C (300 degrees F). In a known manner, the heating process converts the gypsum into calcium sulfate hemihydrate, or stucco. Alternatively, the heating process can simply heat the wet synthetic plaster to a desired temperature, typically below 149 degrees C (300 degrees F) in order to dry excess moisture from the wet synthetic plaster for subsequent calcination in a separate process. Alternatively, the heating process can perform the drying and calcination processes in the same container. The burner conduit 28 advantageously includes an elongated linear portion 30 extending away from the burner 22. The linear portion increases the service life of the burner conduit 28. That is, if the flames of the burner 22 were to directly strike the burner conduit. burner 28 along a curved or angled portion, the flames will reheat the side wall of the conduit which causes high stress which shortens the life of conduit 28. However, due to the presence of initial elongate burner section 30 (which can extending approximately 4.6 to 6.09 m (fifteen to twenty feet) in a commercial installation), the burner flames do not directly affect the burner duct, and this is because the flames have become, throughout section 30, in hot exhaust gases, importantly, the burner conduit 28 includes a plurality of curved sections 32 for connecting the linear portions 30, 31, and 33, provide the serpentine shape. The burner conduit 28 may include the at least one section 34 of reduced diameter to provide the increased exhaust gas flow rate to thereby enhance the heat transfer efficiency of the conduit 28. The temperature of the combustion gases is proportionally cooled at a distance away from the burner 22, therefore the speed can be increased to maintain a convenient heat transfer rate. The burner conduit 28 may also include a multiple conduit portion 36, wherein a plurality of relatively smaller diameter conduits 38 is formed to be in fluid communication with relatively larger single conduit portions 32. The diameter conduits more small 38 provide more surface area for a given effective flow area and thus increase heat transfer relative to the larger conduit 32. The multiple conduit parts 36 can be connected to the single conduit portions 32 through various means known by those with skill in the specialty such as brazing, welding, and snap fit, mechanical welding machines, etc. The burner conduit 28 can be connected to the burner 22 by means of a flange 40 with a plurality of threaded fasteners 42. The burner conduit 28 can likewise be connected at the discharge end 44 to an outlet conduit 46 extending across the supporting floor 23. The burner conduit 28 can be connected to the outlet conduit 46 by a flange 48 with a plurality of threaded fasteners 50. A fluidization base 52, shown in Figures 1, 2, 4, and 6 (best seen in FIG. Figure 2) can be placed in a lower portion of the housing 12 to receive the exhaust gas flow from the burner conduit 28. The fluidization base 52 has the plurality of side walls 53 extending upwardly from a bottom 55. fluidization base 52 may have a fluidization structure 54 placed on top of the bottom 55 of the fluidization base 52. The fluidization structure 54 forms at least a part of the support floor 23 of the housing. 12. The fluidization structure 54 is operable to contain the gypsum product on the lower portions of the housing 12, and to regularly distribute the flow of exhaust gases as it passes from the fluidization base 52 directly into the gypsum. The fluidization base 52 supplies the aeration, the agitation ensures good fluidization especially of cohesive powders that will not otherwise fluidize. The fluidizing structure 54 includes first and second outer perforated plates 56, 58. The plates 56, 58 include a plurality of through openings 57 that allow passage to the flow of combustion gases. A bore 59 is formed in the fluidization structure 54 to provide through access to the conduit 46 (see Figure 1) and supply the flow of exhaust gases to the fluidization base 52. At least one intermediate porous layer 60, formed from a mat of porous fibers or woven stainless steel medium, is placed between the outer plates 56, 58. The intermediate layer 60 of the medium can be made of compressed silica fibers, woven stainless steel mesh or similar materials suitable for fluidization as is known by those with skill in the specialty to withstand high exhaust gas temperatures. The perforated plates 56, 58 are more preferably made of a metal such as stainless steel or the like. The fluidization structure 54 functions by allowing diffused exhaust gases to bubble through the generally regularly spaced openings 57 of the perforated plate 56. An advantage to the use of woven stainless steel means 60 is that the perforated plates 56, 58 are not they require except to provide the support and protection for the means against perforations. A stirring mechanism 62, shown in Figures 1, 3, 4, and 6 (best seen in Figure 3), can be placed just above the fluidizing structure 54. The stirring mechanism 62 includes a stirring frame 64. having a pair of side beams 65. The agitating frame 64 has a plurality of agitating members 66 connected to the agitating frame 64, to agitate the plaster product adjacent the fluidizing structure 54 along the supporting floor 23 In one embodiment, the agitating members 66 may take the form of a crossbar pattern. The stirring mechanism 62 locally agitates the heated plaster product when the stirring frame 64 is set in motion. At least one rotating support arm 68 rotatably connects the agitation frame 64 to the housing 12 (shown in Figure 1). The connection to the housing 12 can be formed with an angled plate 70 fixed to the housing 12 in a convenient manner such as by welding or mechanical connection, etc. The support arm 68 can be secured to the angle plate 70 by a threaded fastener 72 or the like. The pivoting support arm 68 is more preferably a cable or similar structure to further facilitate an oscillating or rocking movement by the agitating frame 64 relative to a common pivot axis., when the movement is imparted to the stirring frame 64. Alternate motion patterns by the stirring frame 64 are contemplated by the present invention. For example, a person skilled in the art will readily understand how to impart movement to the agitating frame 64 in a vertical, horizontal, or arched pattern, or any combination thereof. A drive power source, such as an air cylinder, an electric motor 74, may be connected to the agitating frame 64 by an actuator arm 76. An expandable seal 78 is connected to the actuator arm 76 and the housing 12 (not shown in Figure 2) to prevent the plaster product from escaping from the housing 12 relative to the actuator arm. The seal 78 expands and contracts as the actuator arm 76 moves between first and second positions as the agitating frame 64 oscillates. Alternatively, the actuator arm 76 may be connected with mechanically levered joints (not shown) that may extend from the drive power source (not shown) positioned in the upper part of the housing 12 to the stirring frame 64 as known to those skilled in the art. The seal 78 can be made of any suitable material that can withstand temperatures greater than 149 degrees C (300 degrees F) and pressures up to 68.9 kPa man. (10 psig (pounds per square inch man.) Again with reference to Figure 1, a spill tube 80 is fluidly connected to the housing 12 to allow the processed plaster to exit the housing 12 to the overflow tube 80. A Spill valve 82 is associated with the spill tube 80 to prevent the plaster from leaving the housing 12 before being heated to a predetermined condition A discharge gate 84 includes the discharge valve 86 allowing selective draining of the contents in the housing 12. Valves 82, 86 may be of any type known to those skilled in the art, but are more preferably electrically or pneumatically operated Referring now to Figure 4, a conduit support 88 is slidably connected to housing 12. to support the burner conduit 28 during installation The support 88 is operable to slide between an outer position at least partially external to the Locking 12 (shown in Figure 4) and the position installed inside the housing 12. The conduit support 88 maintains the conduit during installation and removal of the housing 12. The support 88 includes a pair of side rails 90, 92 slidably connected with elements slides 91 formed in parallel walls 18 of the housing 12. A plurality of crossbars 94 extend between the side rails 90, 92 to provide support surfaces for the burner conduit 28 to be supported therein. The housing 12 includes a side panel 96 operable to open when the burner conduit 28 is installed. A plurality of tie rods 97 structurally connect the side walls 18 of the housing 12 together to prevent warping out of the walls 18, when the housing 12 It is filled with plaster. The straps 97 can be welded or otherwise fixed by any conventional means. Referring now to Figure 5, the apparatus 10 includes access panels 98 located on the side of the housing 12 to allow service of the internal components, such as the burner 22 and the duct 28, etc. A release chamber 100 is placed on the open cover 16 of the housing 12 and is constructed to allow access to service the internal components of the housing 12. A dust collector 102 can be placed on top of the release chamber 100 to collect Gypsum powder particles and recycle the particles to the housing 12 for calcination. The dust collector 102 may include a plurality of replaceable filters 104. The filters 104 can be of any desired type such as round cartridge filters, bag filters, or the like. The filters 104 may be cleaned periodically by intermittently injecting air from an opposite side of where the powder is collected or by agitation as is known to those skilled in the art. A stack of flue gases 106 allows the combustion gases to be removed from the apparatus 10 after the gypsum powder particles have been removed from the filters 104. In operation, the plaster powder is fed to an inlet fitting 20. to fill the housing 12. The air and fuel are supplied by the conduits 24,26 respectively, to the burner 22. The burner 22 burns the mixture of air and fuel and provides hot exhaust gases which flow in the direction of the arrows shown in FIG. Figure 6. The combustion gases flow through the serpentine burner conduit 28 to the fluidization base 52. From the fluidization base 52, the combustion gases flow horizontally and then upwards through the fluidization structure 54 placed on top. from the base 52. The fluidization structure 54 distributes the exhaust gases by the gypsum product in such a way that the hot exhaust gases are evenly distributed. The external surface of the burner duct 28 provides heat to the plaster by conduction heat transfer. Thus, the gypsum product is heated both when the exhaust gas flows through the burner duct 28 and the gypsum after traversing the fluidization structure 54. The present invention provides the increased fuel efficiency versus the prior art due because the dual heating method removes the maximum amount of heat from the combustion gases and transfers it to the gypsum. The exhaust gas continues to flow up through the release chamber 100 allowing some of the gypsum particles to separate from the flow of the combustion gases and fall back into the housing 12. The dust collector 102 cleans the gypsum particles transported by the exhaust gas air before the exhaust gas leaves the flue gas chimney 106. The gypsum particles can be periodically shaken from the collector filter cartridges (or bags) back to the gypsum bed . Advantageously, a stirring mechanism 62 is provided to ensure good fluidization to prevent the combustion gases from being channeled directly by the gypsum powder. Natural gypsum typically includes a fine powder that may be too cohesive to achieve good fluidization without agitation. The stirring mechanism 62 is operated by oscillating between first and second positions to locally mix the gypsum and detach it from the fluidized structure 54. The calcining apparatus 10 has a high efficiency because substantially all the heat produced by the burner 22 is used to heat the plaster and is not lost through the process of exhaust gases or combustion. The temperature of the exhaust gas leaving the gypsum product is approximately 149 degrees C (300 degrees F), which is the approximate temperature required for the gypsum to be processed in stucco. Synthetic gypsum that is manufactured with a standard particle size may not require agitation to ensure good fluidization. While the preceding text establishes a detailed description of numerous different embodiments of the invention, it will be understood that the legal scope of the invention is defined by the wording of the claims set forth at the end of this patent. The detailed description should be interpreted as exemplary only and does not describe any possible mode of the invention since any description of each possible mode would be impractical, if not impossible. Numerous alternate modalities can be implemented, either using current technology or technology developed after the date of presentation of this patent, which would still fall within the scope of the claims defining the invention.

Claims (70)

1. CLAIMS 1. An apparatus for calcining gypsum, characterized in that it comprises: a housing having an open lid, a bottom wall, and a plurality of side walls extending between them; an accessory located in the housing to receive raw gypsum from a source and transfer the gypsum to the housing; a support floor located next to the back wall to hold the plaster in the housing; at least one burner connected to the housing and operable to burn an air / fuel mixture to heat the plaster; and at least one serpentine burner duct extending through the housing from at least one burner and ending through the support floor. The apparatus of claim 1, characterized in that the burner conduit includes an initial linear section extending from the burner. The apparatus of claim 1, characterized in that the burner conduit includes at least a section of reduced diameter, to provide the increased flow velocity and improved heat transfer efficiency. The apparatus of claim 1, characterized in that the burner conduit further comprises: a plurality of relatively smaller diameter conduits forming at least a portion of multiple conduits of the burner conduit, the multiple conduit portion being constructed at least to be in fluid communication with the relatively larger diameter duct. The apparatus of claim 1, characterized in that the support floor comprises: a fluidization base for receiving the flow of the combustion gases from the burner conduit. 6. The apparatus of claim 5, characterized in that it further comprises: a fluidization structure located on the basis of fluidization, the fluidization structure at least partially forming the support floor to support the gypsum and which is operable to control and distribute the flow of leakage of fluidization base in the plaster. The apparatus of claim 6, characterized in that the fluidization structure comprises: first and second outer perforated plates; and at least one intermediate layer of material located between the outer plates. The apparatus of claim 7, characterized in that the intermediate layer of the material is a porous medium made from compressed silica fibers and woven stainless steel mesh. The apparatus of claim 7, characterized in that the perforated plates are made of metal. 10. The apparatus of claim 6, characterized in that the fluidization structure comprises: a porous medium material. The apparatus of claim 10, characterized in that the porous medium produces compressed silica fibers and a woven stainless steel mesh. 12. The apparatus of claim 1, characterized in that it further comprises: an operable stirring mechanism to prevent channeling of fluid and prevent dead plaster cavities from forming adjacent to the support floor. The apparatus of claim 12, characterized in that the stirring mechanism includes a stirring frame. The apparatus of claim 13, characterized in that the agitating mechanism includes a plurality of agitation members connected to the agitator frame, to agitate the plaster adjacent to the support floor when the agitator frame is moved. 15. The apparatus of claim 13, characterized in that the stirring mechanism includes at least one pivoting support arm for rotatably connecting the agitator frame to the apparatus. The apparatus of claim 15, characterized in that at least one pivoting support arm is a cable connected rotating with the roasting apparatus at one end and the stirring frame at the other end, wherein the agitator frame will oscillate about an axis pivot when you are imparted movement. 17. The apparatus of claim 13, characterized in that the agitator mechanism includes a source of powder for moving the agitator frame. 18. The apparatus of claim 17, characterized in that the power source includes one of an electric motor and a pneumatic actuator. The apparatus of claim 18, characterized in that it further comprises: an actuator arm extending through the housing to provide a connection between the motor and the agitator frame. The apparatus of claim 19, characterized in that the agitating mechanism further comprises: an expandable seal coupled with the actuator arm and the housing, to prevent the plaster from leaking out of the housing. The apparatus of claim 20, characterized in that the seal expands and contracts as the actuator arm moves between the first and second portions. 22. The apparatus of claim 13, characterized in that the agitator frame is moved in one of: a vertical horizontal pattern, and an arcuate one. 23. The apparatus of claim 1, characterized in that it further comprises: a spill tube in fluid communication with the apparatus to allow the processed plaster to exit the apparatus. 24. The apparatus of claim 23, characterized in that it further comprises: a spill valve associated with the spill tube, to prevent the plaster from leaving the apparatus before it is heated to a predetermined condition. 25. The apparatus of claim 1, characterized in that it further comprises: a discharge gate having a discharge valve to allow selective draining of the housing. 26. The apparatus of claim 1, characterized in that it further comprises: an exhaust chimney connected to the apparatus to exhaust the combustion gases of the apparatus. The apparatus of claim 1, characterized in that it further comprises: a duct support slidably connected to the apparatus for supporting the burner duct during installed and not installed positions, the duct support is movable between a first portion internal to the housing and a second portion at least partially external to the housing, to hold the conduit during installation and remove it from the housing. The apparatus of claim 27, characterized in that the conduit support comprises: a pair of beams slidably connected with parallel walls of the apparatus; and a plurality of transverse rods extending between the beams that engage the burner conduit. 29. The apparatus of claim 1, characterized in that it further comprises: at least one access panel located in the housing to service its internal components. 30. The apparatus of claim 1, characterized in that it further comprises: a detachment chamber located adjacent to the open cover of the housing, the detachment chamber has at least one door to allow access. 31. The apparatus of claim 1, characterized in that it further comprises: a dust collector for collecting dust and gypsum particles and recycling the particles to the housing. 32. The apparatus of claim 31, characterized in that the dust collector includes a plurality of filters. 33. The apparatus of claim 32, characterized in that the filters are cleaned by intermittently injecting air through an opposite side from where the powder is collected. 34. The apparatus of claim 1, characterized in that the burner conduit includes a section having at least one through opening to allow exhaust flow to exit therefrom directly to the plaster. 35. An apparatus for calcining gypsum, characterized in that it comprises: a housing having an open lid, a bottom wall, and a plurality of side walls extending therebetween; an accessory connected to the housing to receive raw plaster from a source and transfer the plaster to the apparatus; at least one burner connected to a side wall and operable to burn an air / fuel mixture to heat the plaster; at least one burner duct extending from the burner as a minimum, the duct passes in heat exchange relationship with the plaster and discharges the exhaust flow to the plaster, causing it to fluidize; and an operable stirring mechanism to prevent channeling of fluid and dead plaster cavities adjacent to the bottom wall. 36. The apparatus of claim 35, characterized in that the burner conduit includes a substantially straight section extending from the burner. 37. The apparatus of claim 35, characterized in that the burner conduit includes a! less a reduced diameter section to provide increased flow rate and improved heat transfer efficiency. 38. The apparatus of claim 35, characterized in that the burner conduit further comprises: a plurality of relatively smaller diameter conduits., which form at least a portion of multiple ducts of the burner duct, the at least multiple duct portion is constructed to be in fluid communication with the duct of relatively larger diameter. 39. The apparatus of claim 35, characterized in that it further comprises: a fluidization base for receiving the exhaust flow from the burner conduit. 40. The apparatus of claim 39, characterized in that it further comprises: a fluidization structure located on the basis of fluidization, the fluidization structure forms a floor to support the plaster and is operable to control and distribute the exhaust flow in the plaster . 41. The apparatus of claim 40, characterized in that the fluidization structure comprises: first and second outer perforated plates; and at least one intermediate layer of material located between the outer plates. 42. The apparatus of claim 41, characterized in that the intermediate layer of the material is a porous medium made from compressed silica fibers. 43. The apparatus of claim 41, characterized in that the perforated plates are made of metal. 44. The apparatus of claim 35, characterized in that the stirring mechanism includes a stirring frame. 45. The apparatus of claim 44, characterized in that the agitating mechanism includes a plurality of agitation members connected to the agitator frame, to agitate the plaster adjacent to the bottom wall, when the agitator frame is moved. 46. The apparatus of claim 44, characterized in that the stirring mechanism includes at least one pivoting support arm, for rotatably connecting the agitator frame with the apparatus. 47. The apparatus of claim 46, characterized in that the pivoting support arm is at least one cable rotatably connected to the calcination apparatus at one end and to the agitator frame at the other end, wherein the frame will oscillate about an axis pivot, when you impart movement. 48. The apparatus of claim 35, characterized in that the agitation mechanism includes a power source for moving the agitator frame. 49. The apparatus of claim 48, characterized in that the power source includes one of an electric r and a pneumatic actuator. 50. The apparatus of claim 48, characterized in that it further comprises: an actuator arm extending through the housing, to provide a connection between the power source and the agitator frame. 51. The apparatus of claim 50, characterized in that the agitating mechanism further comprises: an expandable seal coupled with the actuator arm and the housing, to prevent the plaster from leaking from the housing. 52. The apparatus of claim 51, characterized in that the seal expands and contracts as the actuator arm moves between first and second positions. 53. The apparatus of claim 35, characterized in that it further comprises: a spill tube in fluid communication with the apparatus, to allow processed plaster to exit the apparatus. 54. The apparatus of claim 53, characterized in that it further comprises: a spill valve associated with the spill tube, to prevent the plaster from leaving the apparatus before heating to a predetermined condition. 55. The apparatus of claim 35, characterized in that it further comprises: a discharge gate having a discharge valve to allow selective draining of the housing. 56. The apparatus of claim 35, characterized in that it further comprises: an exhaust chimney connected to the apparatus, for discharging combustion gas from the apparatus. 57. The apparatus of claim 35, characterized in that it further comprises: a conduit support having a pair of lateral rails slidably connected with parallel walls of the apparatus; and a plurality of transverse bars extending between the side rails that engage with the burner conduit to support the burner conduit during the installed and not installed positions, the support is movable between a first position internal to the housing and a second position at least partially external to the housing, to support the conduit during installation and removal of the housing. 58. The apparatus of claim 35, characterized in that it further comprises: at least one access panel located in the housing to service its internal components. 59. The apparatus of claim 35, characterized in that it further comprises: a detachment chamber located adjacent the open cover of the housing, the detachment chamber has at least one door to allow access. 60. The apparatus of claim 35, characterized in that it further comprises: a dust collector for collecting gypsum powder particles and recycling the particles to the apparatus. 61. The apparatus of claim 60, characterized in that the dust collector includes a plurality of filters. 62. The apparatus of claim 61, characterized in that the filters are cleaned by intermittently injecting air through an opposite side from where the powder is collected. 63. The apparatus of claim 35, characterized in that the burner conduit includes a section having at least one through opening, to allow the exhaust flow to exit directly to the plaster. 64. The apparatus of claim 35, characterized in that the burner conduit is formed in a generally serpentine structure. 65. The apparatus of claim 35, characterized in that the housing includes a generally rectangular cross section. 66. The apparatus of claim 65, characterized in that a section of cross section is approximately 4.88 m (16 feet). 67. The apparatus of claim 35, characterized in that the burner conduit includes a plurality of conduits located adjacent to each other, the number of conduits being proportional to the width of the housing. 68. A method for calcining gypsum, characterized in that it comprises the steps of: providing gypsum to a roasting apparatus; heating the gypsum with a serpentine burner by transferring combustion heat with a duct extending from an external burner through the plaster and ending in the bottom wall of the apparatus; flowing the exhaust gas through a structure of fiuidization; and fluidizing and further heating the gypsum by convective heat transfer to substantially flow all of the exhaust gas through the gypsum. 69. The method according to claim 68, characterized in that it further comprises: opening a spill valve to allow the fluidized gypsum to pass through, when the plaster reaches approximately 149 degrees C (300 degrees F). 70. The method according to claim 68, characterized in that it further comprises: removing and agitating stagnant portions of gypsum adjacent to the bottom wall, with a stirring mechanism.