Apparatus and process for cooling and de-steaming calcined stucco

The present invention is an apparatus and process for cooling and de-steaming hot calcined stucco used in the production of gypsum boards or bagged plaster. The apparatus is a fluid bed stucco cooler and comprises a cooler housing having a plenum having a stucco inlet and stucco outlet. The stucco cooler includes a rotating disk in the plenum. The rotating disk includes nozzle for spraying fluid, and is attached to a rotable shaft extending from the side of the cooler also includes a fluidization pad and agitator to help to mix the air and the stucco powder to insure fluidization, prevent channeling, and prevent the stucco powder from building up on the various components. The air also forces steam from the hot calcined stucco out through an air outlet located at the top of the stucco cooler, thereby de-steaming the stucco. The stucco flows through the plenum and passes over the cooling coils, thereby cooling the stucco as it reaches the stucco outlet.

BACKGROUND OF THE INVENTION

The present invention relates to an improved apparatus and process for cooling and de-steaming calcined gypsum stucco (calcium sulfate hemihydrate). The cooling of gypsum stucco has been of interest in the gypsum industry for many decades. Stucco is physically and thermodynamically unstable at high temperatures. In order to maintain its quality, the stucco should be quickly aerated and cooled below the temperature of calcination (250° F.). This is especially true when the calcined stucco is to be stored over time. An example of a stucco cooler is U.S. Pat. No. 6,138,377 assigned to U.S. Gypsum Company, and that disclosure is incorporated here by reference.

Hot and steamy calcined stucco stored in containers will age over time. This aging process adversely affects many of the desirable properties of the stucco, including pouring consistency, hydration rate, set time, response to accelerator, and potential for strength development. If a storage silo does not empty its contents on a “first-in-first-out” basis, the quality of the stucco removed from storage can vary drastically. Thus, the cooling and de-steaming of calcined stucco before storage is essential to long-term age stability.

Apart from age stability during storage, a further problem is caused by mechanical energy from tube mill grinding during the processing of the stucco. The mechanical energy adds more heat to the stucco, preventing many plants from being able to meet temperature requirements for bagging the stucco. Thus, immediate cooling and de-steaming of hot calcined stucco allows for stucco to be properly bagged.

Previous coolers, such as the coil cooler described in U.S. Pat. No. 6,138,377 have a high initial capital cost. Specifically, the coils and heat transfer fluid system used in a coil cooler are expensive. Also, a much larger coil cooler is required to cool the same stucco throughput compared to the invention described herein. Further, when the stucco cooled with the apparatus described herein is used to make products such as wall board, the amount of water and additives required is reduced when compared to stucco cooled in other ways. Thus, the invention described herein enjoys an economic and performance advantage over the prior art coolers.

SUMMARY OF THE INVENTION

The present invention is an apparatus and process for cooling and de-steaming hot calcined stucco, such as that used in the production of gypsum boards or plaster products. The apparatus is a fluid bed stucco cooler, the cooler including a water spray apparatus to spray water on the stucco. Typically, hot and steamy calcined stucco is transferred to the cooler from a calcination kettle, and the stucco is then cooled and de-steamed. The cooler can be implemented in a stucco processing line where the stucco may be stored for a period of time after the cooling process, or it can also be directly implemented into a gypsum board production line where the stucco is made available for immediate use. Each cooler unit may stand alone or several may be connected in series or parallel, depending on the processing output and cooling requirements of the system.

The cooler in its basic description comprises a cooler housing having a plenum and a stucco inlet and a stucco outlet. The cooler further includes a water spray apparatus or distributor to spray and distribute fluid, preferably water, in the plenum. The cooler also includes a fluidization pad and an agitator, to move and distribute the stucco within the plenum. Further, refinements, such as the use of compressed air to prevent clogging of the water spray apparatus, are also disclosed.

Hot and steamy stucco powder enters the plenum from a calcination kettle at a temperature of in the range of 290° to 320° F. and is transported to a cooler and is fluidized by a fluidization pad positioned at the bottom of the plenum of the cooler housing. Depending upon the distance and mode of transport from the calcination kettle to the cooler, the stucco entering the cooler may be at a temperature lower than the temperature exiting the calcination kettle. The stucco may be at a temperature as low as 260 to 250° F.

The fluidization pad is a generally cylindrical chamber having a perforated top surface and a bottom surface with an air inlet. As described in U.S. Pat. No. 6,138,377, the fluidization pad can be any shape, including square or rectangular. The fluidization pad is of relatively short height as compared to the plenum height and is positioned such that the perforated top surface comprises the bottom surface of the plenum. Air supplied by a blower enters the air inlet and is diffused through the perforated top surface and introduced into the plenum of the cooler housing. In order to increase the effectiveness of the stucco fluidization, an agitator unit is used to mix the stucco powder with the air to prevent channeling of the air directly through the powder, especially with natural stucco. The agitator unit has an agitator propeller mounted on a shaft that passes thought the top of the housing and extends downward to the propeller, which is preferably positioned just above the perforated top of the fluidization pad. In an alternate embodiment, the agitator extends from the bottom of the housing, and the shaft passes through a tube in the fluidization pad such that the propeller is positioned just above the perforated top surface of the fluidization pad. Each agitator unit also has a seal unit to prevent stucco from exiting the plenum at the location of the shaft. The agitator unit is driven by a motor at an appropriate RPM to insure adequate fluidization. One skilled in the art will recognize that one or more agitators may be used and they may extend from the fluid bed, as described in U.S. Pat. No. 6,138,377.

During the cooling process, the steam from the stucco and steam mixture is forced upward and out of the plenum through the stucco outlet. In an alternate embodiment, the cooler includes an air outlet. Such an outlet is described in U.S. Pat. No. 6,138,377. In the alternate embodiment, the air outlet is located at the top of the cooler housing and is in direct fluid communication with the plenum, thus allowing the removal of steam from the plenum. A disengagement zone is provided at the top of the plenum of the housing below the air outlet. The disengagement zone is an upwardly extending portion of the plenum that provides additional plenum space to allow the stucco powder particles to fall back from the exiting air, thus reducing entrainment of the particles in the air that exits through the air outlet.

In either embodiment, a water spray apparatus is present in the plenum to spray water or other fluid, which cools the stucco. A fixed orifice or a plurality of fixed orifices can be used. In such an embodiment, a nozzle is fixed in an aperture in the plenum wall, and a source of water is connected to the aperture from the exterior of the plenum. However, experimentation revealed that the stucco collected on and around the fixed point of water distribution, causing a buildup of stucco around the fixed point or points of distribution, hampering the operation, and requiring frequent shut down and disassembly for cleaning. In the preferred embodiment, a disk or other rotating member or distributor having a plurality of orifices or nozzles is mounted on a rotatable shaft. The shaft includes a channel or conduit to provide water to the nozzles of the disk. A motor is connected to the shaft to rotate the shaft and hence the disk. The rotation causes any stucco that may try to adhere to the nozzles or area around the nozzles to be cast off, thus alleviating the collection of stucco on the nozzles and eliminating or reducing the build up of stucco around the nozzles and clogging of the cooler with set gypsum.

By operation of the fluidization pad, and water spray, the stucco is thereby cooled and de-steamed when it reaches the stucco outlet at the top of the plenum chamber. The cooled and de-steamed stucco is typically at a temperature between 250° F. and 220° F. when it exits the cooler housing, well below the calcination temperature of 250° F. The cooled and de-steamed stucco may then be stored without the risk of substantial adverse effects due to aging, or use in manufacturing processes. If cooled below 212° F., the evaporation temperature, the stucco is preferably dried and further cooled by feeding the stucco to a second fluidization bed. This second bed acts as a drier to evaporate remaining water, as well as cooling the stucco.

DETAILED DESCRIPTION OF THE INVENTION

With reference toFIGS. 1-4, a fluid bed stucco cooler apparatus20for cooling and de-steaming hot calcined stucco is shown. The stucco cooler apparatus20essentially comprises a housing21having a plenum22therein. The housing21is generally cylindrical, although other shapes may be used. In an example for processing 40 tons of stucco per hour, the plenum23is 24 inches in diameter and approximately 7.5 feet tall. The housing may have other dimensions, depending upon the application and desired throughput. As an example, a plenum designed for an 80 ton per hour throughput has a diameter of 36 inches.

The cooler housing21has a stucco inlet19and a stucco outlet29, both located near the top of the cooler housing21. A baffle23is placed in the plenum22sidewall near the stucco outlet29to control flow out of the outlet29. Both the stucco inlet19and stucco outlet29are in fluid communication with the plenum22. Both the stucco inlet19and the stucco outlet29are sized to accommodate a flow of stucco desired as the throughput. Hot and steamy stucco powder enters the plenum22of the stucco cooler20from a calcination kettle (not shown) at a temperature typically in the range of 260° F. to 320° F.

During the cooling and desteaming process, stucco flows into the plenum22thru inlet19and is cooled by the air flow from the fluidization pad30and water from the spray distributor66, and then expelled out the outlet29. The cooled stucco can then be bagged, or sent to other processing stations, such as wall board manufacturing lines.

The stucco cooler apparatus20can stand alone or be connected in series or parallel with several other coolers, depending upon the cooling requirements of the system. In a preferred embodiment, the stucco cooler apparatus20is compact and upright, thereby minimizing the plant floor area occupied. As shown inFIGS. 1 through 4, legs25are provided on the cooler housing21in order to support the stucco cooler apparatus20in an upright position. One skilled in the art will recognize other structures can be used to support the housing.

In order to fluidize the stucco powder within the plenum22, a fluidization pad30is provided at the bottom of the cooler housing21. The fluidization pad30is a generally cylindrical chamber having a perforated top surface32and a bottom surface33with an air inlet46. In the preferred embodiment, the perforated top surface32is a sandwich of silica fibers or other fluidization media compressed between two perforated plates. The plates have ⅜″ diameter holes spaced on 9/16″ staggered centers, resulting in an open area of approximately 40%. Other fluidization media known to one skilled in the art could be used, such as a stainless steel mesh. Although cylindrical in the preferred embodiment the fluidization pad30, and the plenum22, may be in any shape. The fluidization pad30is attached to the bottom of the cooler housing21. The perforated top surface32forms the bottom of the plenum22. The fluidization media diffuses the air as it enters the plenum22. Air provided by a blower (not shown) enters the fluidization pad30through the air inlet46and is diffused through the perforated top surface32and introduced into the plenum22of the cooler housing21. This air helps to fluidize the stucco powder so that it effectively flows through the plenum22. This air flow is also used to help remove the steam from the stucco powder.

In order to prevent the fluidization air from channeling directly through the stucco powder and to minimize stucco powder buildup on surfaces within the plenum22, an optional agitator34is used to mix the stucco powder with the air. If the stucco is fluidizable without agitation, the agitator34may be omitted as the cooler20will function without the agitator unit34.

The agitator34has an agitator propeller37mounted on a shaft36that passes through the top15of the housing21, such that the propeller37is positioned just above the perforated top surface32of the fluidization pad30. The propeller need not be of any particular shape. In the preferred embodiment, the propeller37is a pair of ¼″ wide by 2 inch tall stainless steel bars extending from the shaft to near the walls of the plenum22. One will recognize other mechanisms could be used to agitate the stucco, such as a swinging gate agitator. If a rectangular or other non-circular housing21is used, the propeller37is of a size that allows it to rotate without contacting the walls of a plenum22.

The agitator34also has a transmission unit38. The transmission unit38converts the horizontal rotation of the motor40into vertical rotation for the shaft36. The transmission unit38also includes a bearing to hold the shaft36in a rotably fixed position. In the preferred embodiment, the transmission unit38is a gear motor supplied by Falk having a part number 05UWFQZA71AB. One skilled in the art will recognize other mechanisms can be used to transmit power to the agitator, such as belts and pulleys, worm gears, planetary gears, and other known assemblies. In order to prevent or reduce the amount of stucco that escapes the plenum22through the aperture through which the shaft36enters the plenum22, positive air pressure or other seal is applied to the aperture. Air is provided to the seal39by a conduit from outside the transmission unit38to the seal39. The conduit is connected by hoses or piping to a plant source of compressed air119as shown inFIG. 10. In the preferred embodiment, the air is regulated to a pressure of 1 psi, or a pressure just sufficient to keep the stucco from exiting the plenum22at the aperture. In a preferred embodiment, the motor40runs at approximately 60 RPM, although other rotation speeds will work.

In an alternative embodiment shown inFIG. 9, the agitator unit34extends upward into the plenum22through the fluidization pad30. The shaft36runs through a tube170extending from the bottom of the housing21and through the perforated top surface32. Such an arrangement is described in U.S. Pat. No. 6,138,377. In other respects, the alternative embodiment of the agitator unit, extending through the fluidization pad30is similar to the agitator unit previously described.

A baffle23is provided at the stucco outlet29to reduce or prevent the stucco from traveling directly from the stucco inlet19to the stucco outlet29. The baffle23is a 10 gauge stainless steel plate attached to the wall of the housing21. The baffle23includes a main portion13approximately 8¾″ wide, flanked by two side portions14approximately 4⅞″ inches wide. The side portions14are arranged at an angle of approximately 130° to the surface of the main portion13. When the baffle23is attached to the housing21, it occupies an arc of approximately 80°. The baffle23is preferably of sufficient size so as to exceed the dimensions of the stucco outlet29.

The housing21further includes an inspection port18, The inspection port18can be fitted with a removable metal lid to allow for access in to the plenum22. The inspection port18may also be fitted with a clear lid, allowing observation of the plenum22during operation of the cooler20. In alternate embodiments, the inspection port18can be left open to the ambient air, or fitted with appropriate duct work, to provide an air outlet150, as discussed later.

In the preferred embodiment, the stucco outlet29leads to an extension tube28that extends in a generally downward direction, along the side of the housing21. Near the bottom of the plenum is a discharge outlet27, in selective fluid communication with the extension tube. The fluid communication is regulated by a valve, which is normally in the closed position. The valve is opened when the operator desires to empty the plenum22of stucco, such as after shutdown of the process line, or in the event of an overfill condition. A second discharge outlet31can be located in the housing approximately 180° from the first, to increase the rate of discharge, and to more easily completely clear the plenum22of stucco. The second discharge outlet31need not be connected to the extension tube28, although it can be in order to provide a contained path to dispose of the stucco.

The stucco cooler apparatus20achieves fluidization by a low pressure blower in connection with the fluidization pad30and agitator units34. In a preferred embodiment, a blower having a capacity of approximately 20 cfm per square foot of horizontal cross-sectional area of the plenum22and providing a pressure head of approximately 6 psi is utilized. This creates the required pressure differential to allow fluidization of the stucco powder in the stucco cooler20.

With reference toFIGS. 1-6, the water spray or distributor apparatus of the preferred embodiment includes a motor60, a shaft62having a channel64for communication of fluid there through, and a spray distributor66, including a plurality of channels92in fluid communication with channel64of the shaft62.

The motor60is preferably an electric motor capable of turning the shaft62and spray distributor66assembly at a rotation speed of 1750 RPM. The motor includes a drive shaft70and a drive pully72. A pully74is mounted on the shaft62and connected to the drive pully72by a drive belt76. One skilled in the art will recognize other arrangements can be used to transfer power from the motor to the shaft, such as a gear box or direct drive of the shaft.

In the preferred embodiment, the motor60and shaft62are mounted on a support assembly80. The support assembly80is fastened or welded to the outside of the housing21. The shaft62is mounted to the support assembly80by bearings82, which allow the shaft62to rotate about its axis. The shaft is positioned in a generally horizontal position and extends into the plenum22through an aperture in the housing21. A shaft seal81is fitted around the shaft62at the point of entry into the aperture. The shaft seal81keeps material from within the plenum23from exiting at the aperture. In the preferred embodiment, the shaft seal81includes an air channel to allow communication of compressed air from the exterior of the seal, to the interior of the seal. An example of such a seal is CinchSeal® brand seals manufactured by Damar Inc. of Cherry Hill, N.J. When CinchSeal® brand seals are used, compressed air from a plant compressed air source119, typically in the range of 80 to 100 psi, is reduced to 5-15 psi and supplied to the shaft seal81by suitable pipes or hose.

The spray distributor66, shown in detail inFIGS. 6 and 7, is a generally circular shaped disk. It need not be circular, but may be of any convenient shape. In the preferred embodiment, the spray distributor66is approximately 4″ in diameter and ¾″ thick about its disk portion95. The interior of the spray distributor66includes a plenum90. Extending from the plenum90to the perimeter of the spray distributor66are spray channels92having orifices to the atmosphere. The spray channels92allow fluid in the plenum90to be expelled from the spray distributor66. In the preferred embodiment, there are eight spray channels92. One will recognize the number can be varied to suit a desired water application rate. In the preferred embodiment, the spray channels92are approximately 1/16″ in diameter. The diameter and any other dimensions of the spray channels92may vary with the desired application rate and distribution pattern desired. Nozzles may be fitted to the spray channels92to create patterned spray, although they are not necessary to achieve the desired cooling results.

The spray distributor66includes a collar portion94to provide attachment to the shaft26. In the preferred embodiment, threads (not shown) in the collar94are used to attach the collar portion94to corresponding threads (not shown) on the shaft62. One skilled in the art will recognize that other structures can be used to attach the spray distributor66to the shaft62. Rivets, welds, adhesives, and set screws are some examples. Further, the shaft62and spray distributor66could be formed as a single piece.

In the preferred embodiment, the spray distributor66is formed of two pieces. A main body100including the collar portion94and disk portion95, and a cover102. Such a construction allows access into the plenum90when the cover102is removed, and also makes manufacture by machining possible. Such construction also permits cleaning of the spray channels92. The cover is retained by fasteners104. In the preferred embodiment, the fasteners104are screws, however other removable fasteners could be used. If interior access is not desired, the cover102could be joined to the main body100by welds or adhesive.

In an alternate embodiment, the spray distributor66can be an arrangement of conduits extending radially from the shaft62. The conduits are in fluid communication with the channel64, allowing fluid to be passed from the channel64to the conduits and expelled from the conduits at orifaces. One skilled in the art will recognize the conduit need not extend perpendicular to the axis of the shaft, but could also be placed at angles to the shaft, so long as the rotational forces created when the assembly rotates are sufficient to keep stucco from building up or adhering to the distributor66.

In another alternate embodiment, the spray distributor66can be eliminated by placing radial channels in the shaft62, allowing for communication of fluid from the channel64to the radial channels, and out into the plenum22. In such an embodiment, the shaft62extends across part or all of the diameter of the plenum22, with radial channels placed at various locations along the shaft's length within the plenum22.

In any of the embodiments, water is provided to the rotating shaft62by a fluid coupling96. An example of such a coupling is a high speed single flow rotating joint number 9177K32 supplied by McMaster-Carr. The fluid coupling96allows a fixed pipe or hose97to provide water to the channel64of the rotating shaft62. The water may be provided by any number of sources, such as city tap water, a gravity feed tank or a pump, so long as sufficient water can be delivered. In the preferred embodiment, as outlined inFIG. 10, the water is delivered from the city tap115and held in a 30 gallon head tank. Water is drawn from the tank by a water pump110capable of pumping 5 gallons per minute.

The cooling taking place in the stucco cooler can be regulated by adjusting the amount of water delivered by the spray distributor66. In the preferred embodiment, the water pump110supplies water to a 3-way valve assembly having an input for water121and an input for compressed air122from the plant compressed air source119, and an output123for providing any mixture of the two inputs, including all of air or water. The valve output is connected by suitable conduit to the fluid coupling97for delivery to the water spray distributor66by way of the channel64in the shaft62. In the preferred embodiment, either air or water is delivered from the output123. In a typical application, air is delivered at approximately 80 to 100 psi to the valve. The valve is controlled by a controller130that receives a signal from a thermocouple or other temperature sensor135placed in the plenum22. When the controller130senses a temperature of less than 212° F., it adjusts the valve assembly120so that only air is delivered to the spray distributor66. When the temperature is equal to, or above 220° F., the valve assembly120is adjusted so water is delivered to the spray distributor66. One skilled in the art will recognize that a mixture of air and water could also be delivered, the mixture varying to achieve the desired cooling rate and water usage. In operation, it is preferred that air or water is supplied to the distributor any time there is stucco in the plenum22, to prevent any stucco from entering the distributor66possibly causing clogging of the distributor66.

In an alternate embodiment shown inFIGS. 8 and 9, the steam from the stucco mixture is forced upward and out of the plenum22through an air outlet150. The air outlet150is located at or near the top of the cooler housing21, and above the level of the stucco outlet29, thus allowing the removal of steam from the plenum22. The disengagement zone160is an upwardly extending portion of the plenum22located above the stucco outlet29. As the air is removed from the plenum22through the air outlet150, the disengagement zone160provides space to allow the stucco powder particles to drop and fall back before possibly entering the air outlet150, thereby preventing entrainment of the stucco powder particles in the air that exits through the air outlet150. The air outlet150is typically in fluid communication with a dust collector (not shown), which collects and filters any stucco particle residue within the air. However, it has been found that the air outlet is not necessary, and sufficient cooling is achieved by allowing the steam to exit the plenum22through the stucco outlet29.

Performance requirements of a cooling system can also be met by using more than one cooling apparatus20, either in parallel, or in series. A similar arrangement is described in U.S. Pat. No. 6,138,377. Additionally, if further drying or cooling below 212° F., the stucco exiting the stucco outlet29can be fed to a drier, such as a fluid bed drier, familiar to one skilled in the art. Any drier that provides a flow of air without adding heat to the stucco may be considered for the drier.

While specific embodiments of the present invention have been shown here for the purposes of explaining preferred and alternate embodiments of the invention, it is to be understood that the appended claims have a wide range of equivalents and a broader scope than the embodiments disclosed.