Abstract:
The apparatus herein comprises a kettle for calcining particulate material and a surrounding furnace having a porous wall to pass heat of combustion into the kettle at one side and to permit evacuation of the products of combustion from an opposite side, and a control system to cycle the combustion and the evacuation of products of combustion between the opposite sides so that the side being evacuated becomes a heat sink to return the heat so retained therein upon the combustion cycle whereby the furnace structure is kept to a desirable level of temperature while the material in the kettle is at a significant higher temperature.

Description:
BACKGROUND OF THE INVENTION 
     1. The Field of the Invention 
     This invention is directed to apparatus for reclaiming heat of combustion associated with calcining kettle means. 
     2. Description of the Prior Art 
     It is known that a mixture of gas and air can be passed through a porous wall so that combustion takes place over a large area of the wall on the side opposite to the side first impinged by the gas and air. Reference is directed to Holden U.S. Pat. No. 2,828,813 of Apr. 1, 1958, and the safety construction for a luminous wall furnace patent of Holden U.S. Pat. No. 3,008,513 of Nov. 14, 1961. 
     The examples of prior art show a concern for too much heat build-up in the furnace wall so that there is a danger of a back-fire or explosion. Another problem is found that operation of a furnace at a high temperature level can lead to progressive cracking and deterioration of the mortar between bricks, as well as flash back into the plenum chamber that can result in an explosion. 
     SUMMARY OF THE INVENTION 
     The invention is directed to apparatus for processing gypsum particulate material in which a porous wall surrounding a gypsum kettle is divided into portions so that one portion can present a luminous heat wall to the kettle and another portion of the porous wall becomes a heat sink for conservation of the heat delivery to the kettle. 
     It is an important feature of the invention to cycle the portions of the porous wall so that each can be used as a luminous wall part of the time and a heat sink part of the time; thereby keeping the porous wall at a desirable temperature level while the kettle is operated at a significant higher temperature suitable for calcining. 
     Another important feature of the invention is to provide a control system that cycles the effect of firing and heat sink accumulation so that the problems of the prior apparatus is avoided. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The practice of the invention can be carried out with apparatus wherein: 
     FIG. 1 is a vertical section through a calcining kettle provided with a porous wall and a surrounding plenum chamber constituting the apparatus; 
     FIG. 2 is a transverse section of the apparatus taken along line 2--2 in FIG. 1; 
     FIG. 3 is a schematic view of a control system for the apparatus of FIGS. 1 and 2; and 
     FIG. 4 is a schematic view of a modified apparatus and control for multiple plenum chambers. 
    
    
     DETAILED DESCRIPTION 
     Referring to FIGS. 1 and 2, one form of apparatus includes a kettle 10 having a top wall 11, a bottom wall 12 and side wall 13. The top wall is provided with an inlet 14 for the particulate material to be calcined, while there is an outlet 15 for the product. The particulate material during the calcining process is agitated by motor 16 operating through a gear box 17 to actuate drive shafts 18, 19 and 20 for the agitator blades 21. The shafts are stabilized adjacent the lower ends by arms 22 associated with a sweep scraper 23. The vapor driven off the particulate material escapes through a top vent 24. 
     The kettle 10 is enclosed in a furnace comprising an outer wall 25 forming a plenum chamber 26 which surrounds a porous means 27 presenting an inner face 28 to the kettle 10, which face is spaced from the kettle side wall 13. The outer side of the porous wall means is enclosed by a fire check perforated screen 29 which is exposed in the plenum chamber 26. 
     It is seen in FIG. 2 that the plenum chamber 26 is divided by stop wall means 30 into a first chamber portion 26A and a second chamber portion 26B. The stop wall means 30 also intersects the porous wall means 27 so as to divide that wall into parts 28A and 28B. The plenum chamber portion 26A is provided with a port 31A and the opposite plenum chamber portion 26B is provided with a port 31B. 
     Referring again to FIG. 1, the structure of the furnace chamber 25 is supported on a suitable base 32 having a space 33 to accommodate the product outlet 15. The plenum chamber has a top wall 34 which serves to suspend the kettle 10 within the porous wall means. Any suitable load carrying provision can be employed to support the kettle 10, and to support the drive motor 16 and the gear box 17, and the bottom wall 12 can be supported in the base 32 to the extent necessary. 
     Turning now to FIG. 3 there is shown schematically the control means for the apparatus of FIGS. 1 and 2 having the ports 31A and 31B. The control means includes a system of conduits, valves and fans in the following arrangement. A fan 35 has its outlet conduit 36 connected into a divider conduit having a branch 37A and a branch 37B. Branch 37A is connected into a conduit 38A extending from a conduit 39A at port 31A to a junction 40. Conduit 39A is connected into a source of gaseous fuel 41A. Branch conduit 37B is connected into a conduit 38B extending from a conduit 39B at port 31B to the aforesaid junction 40. Conduit 39B is connected into a source of gaseous fuel 41B. Also, the junction 40 which is common to conduits 38A and 38B is connected by conduit 42 to an exhaust fan 43. 
     The conduit system set forth above is under the control of a central console 44 which is connected to a group of respective motorized valves 45A, 46A and 47A, and motorized valves 45B, 46B and 47B. There is a common air supply fan 35, the operation of which is controlled by the console 44. The console 44 is provided with sequencing means which establishes a repetitive program, as follows: 
     a first program for opening valves 46A, 45A, operating fans 35 and 43, and closing valves 45B, 46B and 47A. 
     a second program for opening valves 46B, 45B and closing valves 45A, 46A and 47B, while allowing fans 35 and 43 to continue operating. 
     a third program for alternating the period of operation of the first and second programs. 
     It is intended that the alternating periods of admitting gas and air at ports 31A and 31B shall be of the order of 20-60 seconds so that the temperature of the products of combustion can be kept to a range of from about 250° to 400° F., while maintaining the temperature in the kettle 10 in the range of from 1600° to 2500° F. 
     A modified arrangement of apparatus is seen in FIG. 4 where the kettle 50 has a side wall 51 enclosed by a furnace assembly having a porous wall means 52 spaced from the kettle side wall 51. The porous wall 52 is surrounded on its exterior surface with a perforated fire check screen 53, and the screen 53 is enclosed by an outer wall 54 which is spaced therefrom to define a perimeter plenum chamber or space divided by stop wall means 55 to separate that space into four plenum chambers 56A, 56B, 56C and 56D. The chamber 56A has an external port 57A, chamber 57B has an external port 57B, chamber 56C has an external port 57C, and finally chamber 56D has an external port 57D. Though not shown, the kettle 50 has a top material inlet and a bottom product outlet substantially like the construction seen in FIG. 1. 
     Plenum chambers 56A and 56B are operably related so that gas and air admitted at port 57A is translated into a host of small flames all over the inner face of the adjacent porous wall 52, while the products of combustion are evacuated at port 57B from chamber 56B. 
     In like manner, the admission of gas and air at port 57C to chamber 56C is translated into a host of small flames all over the inner face of the porous wall 52, while the products of combustion are evacuated at port 57D. As explained above, the admission of gas and air at any inlet port, and the evacuation at any outlet port of the products of combustion can be reversed, preferably on a programmed basis, so the heat of combustion and its evacuation can be cyclically controlled as desired. 
     It is shown in FIG. 4 a control system governed by suitable operating provisions in the control console 58 which can be related by air admission valve 59 from a fan 60, the directing of that air by conduit 61 to a junction 62 to flow through either open valve of the valve 63 and valve 64. If valve 63 is open, valve 64 must be closed, thereby feeding air through conduit 64A to join with gaseous fuel from open valve 65A to enter the open port 57A. The products of combustion created in the inner space at the kettle side wall 51 are evacuated by action of an exhaust fan 65 connected by conduit 66 in junction 67 to a conduit 68 with an open valve 69B to extend to port 57B. At this time the gaseous fuel supply valve 65B is closed, as is valve 64. Upon switching the operation, air is conducted by conduit branch 64B on opening valve 64 while closing valves 63. At the same time, gas valve 65A must be closed, and valve 69A is opened to allow the fan 65 to evacuate the products of combustion through port 57A. 
     While the foregoing heating and evacuation is carried on at ports 57A and 57B, the other ports 57C and 57D are alternately used to accomplish the same sequence. Combustion air is supplied by fan 60B and conduit 61B with valve 59B open to junction 67B, and from there, the air flows in conduit 70 through open valve 63B to join with gaseous fuel from open valve 65B to feed port 57C to create combustion at the inner face of the porous wall means 52. The products of combustion are evacuated from that space through porous wall means and out through port 57D, past closed valve 65D and closed valve 63D, through open valve 71A, and past closed valves 71B, and is evacuated to atmosphere by fan 72. Here again the function of heating by supplying gas and air at port 57C, while evacuating the products of combustion at port 57D is understood to be cycled so port 57D can receive gas and air while the valve system is set to effect evacuation of products of combustion at port 57C. The setting of the various valves associated with ports 57C and 57D is effected by control means in console 58A. Whichever is the case selected, the porous wall means 52 can function as a heat sink when connected up on the evacuation cycle for the products of combustion.