Abstract:
A batch type pyrolysis furnace is described for the removal of organic contaminants from various metal parts with superior heating efficiency. The described pyrolysis furnace employs a modified gas burner construction providing combined radiant and convection heating to carry out the pyrolysis cycle in shorter heat-up and cool-down time periods accompanied by fuel savings. A novel furnace apparatus and method for its operation to achieve these benefits is disclosed.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to the manner of operation of a pyrolysis type furnace for removal of various organic contaminants from metal parts and more particularly to a novel manner for said furnace operation which provides superior heating efficiency. 
     In our earlier issued U.S. Pat. No. 4,970,969 there is described a novel batch type pyrolysis furnace for volatilizing and burning organic material from a metal part to which said organic material is bonded. This furnace apparatus employs a main combustion chamber operating at negative chamber pressure which is heated with an adjustable heating rate burner to directly heat air ducted into said main combustion chamber by convection heat transfer. A supplemental combustion chamber in open communication with said main combustion chamber and vented to the atmosphere contains an auxiliary burner to complete combustion of the volatilized organic contaminants being transported from the main combustion chamber. A single temperature sensing means is disposed within said main combustion chamber together with water spray means responsive to said temperature sensing means for operative cooperation with said adjustable heating rate burner to regulate operating temperatures within said main combustion chamber in accordance with a preselected heating schedule. Control of the furnace operation includes programmable temperature control means to maintain continuous operation of said adjustable heating rate burner with (i) a normal full supply of fuel necessary to maintain full combustion in the presence of excess oxygen during a major portion of the pyrolysis cycle, said excess oxygen being relative to the amount required to burn the fuel in said burner, and (ii) a diminished supply of fuel sufficient to maintain fuel-starved combustion during the final portion of the pyrolysis cycle, also in the presence of excess oxygen. The entire contents of my earlier issued patent are hereby specifically incorporated into the present application since the present invention provides a superior manner of operating this same type pyrolysis furnace. 
     Said prior art method of heating air solely by convection in this type furnace is subject to serious drawbacks including a relatively low rate of heat transfer as well as an inherent requirement for air movement. These heating characteristics result in longer startup and cool down periods for the pyrolysis cycle. Understandably, such extended furnace operation to complete the pyrolysis cycle further increases both fuel and still other operating costs. Heating solely with convection heating means can also increase furnace equipment costs by utilization of recirculating fans to improve air movement during the pyrolysis cycle. Having the present pyrolysis cycle being carried out entirely with convection heating results in still further drawbacks attributable to uneven heating taking place in the main combustion chamber. The contaminated metal parts in the main combustion chamber are heated non-uniformly resulting in damaged products while uneven heating also produces cold spots in the furnace enclosure with stratification of warm air at roof level further wasting fuel efficiency. 
     It is an important object of the present invention, therefore, to provide a more effective means to remove organic contaminants from metal parts in a pyrolysis furnace. 
     It is another important object of the present invention to provide novel heating means in a pyrolysis furnace exhibiting superior heating efficiency. 
     Still another important object of the present is to provide novel heating means in a batch type pyrolysis furnace for energy savings and shorter time cycles. 
     Still another important object of the present invention is to provide a novel method for heating in a pyrolysis furnace. 
     These and still further objects of the present invention will become more apparent upon considering the following more detailed description of the present invention. 
     SUMMARY OF THE INVENTION 
     It has been discovered, surprisingly, that removal of organic contaminants from metal parts in a pyrolysis furnace can be carried out more effectively with combined radiant and convection heating in a particular manner during the pyrolysis cycle. More particularly, the processing procedure of the present invention employs a pyrolysis furnace having a main combustion chamber employing an adjustable heating rate burner adapted to supply both convection and radiant heating energy to directly heat air ducted into said main combustion chamber for passage of the volatilized organic contaminants into a supplemental combustion chamber in open communication with said main combustion chamber and vented to the atmosphere which further contains an auxiliary burner. In said operating procedure, the main combustion chamber is operated with a single temperature sensing means in combination with control means including programmable temperature control means to maintain continuous operation of said adjustable heating rate burner with (i) a normal fuel supply necessary to maintain full combustion of said organic contaminants in the presence of excess oxygen during a major portion of the pyrolysis cycle, said excess oxygen being relative to the amount required to burn the fuel in said burner, and (ii) a diminished supply of fuel sufficient to maintain fuel-starved combustion during the final portion of the pyrolysis cycle, also in the presence of excess oxygen, while further activating a water spray within said main combustion chamber responsive to said temperature sensing means for operative cooperation with said adjustable heating rate burner to regulate operating temperature within said combustion chamber in accordance with a preselected heating schedule, and employing said auxiliary burner to complete the combustion of the volatilized organic contaminants being transported from the main combustion chamber within said supplemental combustion chamber. A suitable adjustable heating rate burner enabling the desired purpose can simply feature a radiant tube extension protruding from the front end of said burner which further includes multiple openings along the tube length. Said modified burner assembly can be easily positioned beneath the cart member containing the contaminated metal parts being processed within the main combustion chamber. Employing such heating means enables the modified gas burner to fire directly into the length of the radiant tube extension for its rapid heating as the radiant energy source while simultaneously supplying convection heating with flames emerging evenly out the tube openings. The illustrated burner construction has been found to enable a 50% improvement for the present operating procedure in rapid heat-up and cool-down during shortened cycle times accompanied by a 20% fuel savings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a front elevational view of a representative pyrolysis furnace according to the present invention which is controlled by a single temperature sensing means in accordance with a preselected heating schedule. 
     FIG. 2 is a side elevational view depicting the FIG. 1 furnace construction together with the control means being employed to regulate operating temperatures during the pyrolysis process. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings, FIGS. 1-2 depicts schematically a representative pyrolysis furnace construction which can be employed to completely remove organic contaminants from various metal parts in a far more effective manner. More particularly, novel radiant heating means are now combined with convection heating means in the illustrated furnace embodiment to enable a more rapid pyrolysis of the organic contaminants with lesser fuel expenditure. Said furnace  10  is typically a large enclosed physical structure which can be shaped as a rectangular parallelepiped having a main combustion chamber  12 . The floor  13  of said main combustion chambers holds a cart member  14  which can be admitted thru furnace door  15 . Said cart member contain a batch  16  of the contaminated metal parts being pyrolized while the depicted furnace enclosure includes a rear wall  17 , a right side wall  18  and a left side wall  19 . Said main combustion chamber  12  is also suitably insulated with ceramic fiber. An adjustable heating rate gas burner  20  having a closed end radiant tube extension  21  is provided in said main combustion chamber to volatilize the organic contaminants in accordance with the presently improved procedure. The gas burner being employed operates either with a normal or “full burner” fuel supply or with a diminished or “fuel-starved” fuel supply during the pyrolysis cycle in a controlled manner to be more fully explained hereinafter. The type of adjustable heating rate burner being selected generally depends upon the batch size and composition of the organic contaminants as well as physical size of the main combustion chamber. For example, in a representative size chamber having a width of 4 feet, a length of 4 feet and a height of 4 feet within which a batch charge of about 500 lbs of motor mounts contaminated with 25% rubber insulation is to be processed, a Midco Incinomite burner having a rated output of 100,000 BTu/hr can be used. The selected burner is desirably adjusted to operate with an excess of oxygen wile further providing flame to the far end of the radiant tube extension  21  including emergence from openings  22  in the tube walls. Such mode of operation for directly heating air ducted into said main combustion chamber  12  results in a negative chamber pressure which is maintained throughout the pyrolysis cycle. A suitable radiant tube extension  21  can be fabricated with various heat resistant materials, such as stainless steel, to desirably project the entire length of said main combustion chamber and be physically placed beneath the cart member  14  containing the contaminated metal parts. In said manner, the heated tube directs the radiant energy upward in a relatively uniform pattern over an extended area. An 8 inch diameter stainless steel tube was selected for the radiant tube extension member being depicted having 2 inch diameter holes provided on each side of the tube walls. 
     There is also provided in the present furnace embodiment a supplemental combustion chamber  26  in open communication with said main combustion chamber via throat  24  and which includes an auxiliary burner  30  to complete the combustion of the volatilized organic contaminants being transported from said main combustion chamber. Said auxiliary combustion chamber includes openings  32  vented to the atmosphere for air introduction to supply oxygen for complete combustion of the volatilized organic contaminants as well as an exhaust stack  34 . 
     Control means for operation of said presently illustrated furnace embodiment includes programmable temperature control means to maintain continuous operation of said adjustable heating rate burner throughout the entire pyrolysis cycle with (i) a normal full supply of fuel necessary to maintain full combustion in the presence of excess oxygen during a major portion of the pyrolysis cycle, said excess of oxygen being relative to the amount required to burn the fuel in said burner, and (ii) a diminished supply of fuel sufficient to maintain fuel-starved combustion during the final portion of the pyrolysis cycle, also in the presence of excess oxygen. Said present control procedure employs a single thermocouple  29  disposed in the main combustion chamber for transmission of the control signals to said temperature control means  37  mounted on electrical panel  33  in the furnace apparatus. A manometer M (shown in FIG. 2) is also mounted on said control panel to insure negative pressure conditions being maintained in said main combustion chamber. Operation of said programmable temperature control means proceeds in the same general manner more fully explained in our aforementioned previously issued United States Patent. Operating temperatures in the main combustion chamber are thereby raised in preestablished incremental stages. In further accordance therewith, water spray means  40  disposed in the main combustion chamber responds to the temperature sensing means for operative cooperation with said adjustable heating rate burner to regulate operating temperatures within said main combustion chamber pursuant to said preselected heating schedule. Combustion efficiency reaches approximately 90% for the herein illustrated embodiment when carried out in the above described manner. 
     It will be apparent from the foregoing description that a broadly useful and novel means to remove organic contaminants from various metal parts has been provided. It is also contemplated that already known modifications can be made in the disclosed furnace apparatus and method for its operation than herein specifically recited without departing from the present invention. For example, the employment of additional burners in the main or supplemental combustion chambers can be permitted although complicating the control procedure associated with multiple heat sources. Likewise, multiple temperature sensing means in the disclosed apparatus to further monitor the pyrolysis cycle in certain other respects can also complicate the present control procedure. Consequently, it is intended to cover all variations of the present improvements which may be devised by persons skilled in the art as falling within the true spirit and scope of the herein claimed invention.