Patent Publication Number: US-2007119350-A1

Title: Method of cooling coal fired furnace walls

Description:
CROSS REFERENCES  
      The invention relates to my copending application Coal Flue Gas Scrubber, Ser. No. 11/075,218 filed Mar. 09, 2005 relative to the collection and processing of carbon dioxide emissions from coal-fired furnaces. 
    
    
     BACKGROUND OF THE INVENTION  
      The invention disclosure describes an improved method of heat transfer that will become necessary to satisfy the additional cooling requirements of environmentally compatible coal-fired furnaces. In most coal-fired furnace designs combustion temperature, depending on fire-box pressure variations, range between 4000° F. and 5000° F. The exposed surfaces of the fire-box wall comprised of refractory ceramic coatings or ceramic tile coatings are used to protect the thermal integrity of the refractory brick internal structural support and lining. Most refractories are compounded for high temperature strength and are poor thermal insulators and require structural backside air cooling passages or water screens to lower the heat transfer rate from the 2000° F. to 2800° F. hot gas wall temperature necessary to assure a practical working gradient across the furnace wall of the heat transferred to the outer steel enclosure and support structure. The invention proposes the use of carbon dioxide as a coolant gas passing through high temperature cooling tubes fixedly attached to the internal exposed surfaces of the refractory brick structure. The coolant carbon dioxide will be obtained from sequestered flue-gas emissions in a gas scrubber described in the cross-reference. The high temperature of the carbon dioxide coolant circulating in vertically spaced cooling tubes lining the fire-box walls exits the furnace at an elevated thermal condition which is maintained in a thermally insulated manifolding facilitating cost efficient low temperature catalytic conversion into a synthetic by-product.  
      Coal-fired steam generating boilers and furnace refractories have been developed to a very high degree of durability and efficiency since the inception of the electrical generating plant at the turn of the 20th. century. However, with the dwindling supply of cheap natural gas and heavy fuel oils, many of these early types of steam generating boiler systems are being converted to coal-fired systems which produce much higher quantities of carbon dioxide (CO 2 ) and other harmful emissions such as mercury (Hg), sulfur dioxide (SO 2 ) and nitrogen oxides (NOx). This difficulty chronicles in a lesser degree, the greater future concern of the planned increased construction of new coal-fired environmentally friendly systems necessary to keep up with the increasing world demand for electrical power both in the United States and abroad.  
      The combustion of 1 ton of coal produces 3 tons of CO 2  which at the anticipated increase will have a detrimental impact on the world&#39;s environment to the extent that it now raises concern of the possibility of creating climate change.  
      The present invention relates to the cooling of furnace walls and provides the necessary means of conditioning and converting large quantities of CO 2  in the production of synthetic gas or other useful products.  
     SUMMARY OF THE INVENTION  
      The invention is a method of cooling gas-fired or coal-fired furnace fire-box walls using gaseous carbon dioxide sequestered from the furnace stack combustion products as described in the cross-reference.  
      It is the primary purpose of this invention to provide a novel manner of cooling furnace fire-box walls using gaseous carbon dioxide sequestered from the furnace stack combustion products during a preceding process scrubber operation as described in the cross-reference.  
      It is another object of the invention to provide a means of facilitating the disposal of carbon dioxide by enhancing the means of its high temperature conversion to synthetic gas.  
      It is yet another object of the invention to decrease carbon dioxide emissions of coal-fired furnaces into the atmosphere. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a top-view cross-section of a portion of a furnace wall illustrating the use of carbon dioxide cooling tubes mounted on the interior hot gas surface.  
       FIG. 2  is a top-view cross-section of a portion of a furnace wall similar to that shown in  FIG. 1  showing a different method of cooling using alternate water and carbon dioxide cooling tubes.  
       FIG. 3  is a side-view cross-section of a vertical portion of a furnace wall, also showing the associated burner equipment and employing a slightly different method of attachment of the said carbon dioxide and said water cooling tubes of  FIG. 2  to the furnace refractory brick structure. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Gaseous carbon dioxide is circulated through a tubular circuit lining the refractory brick surface of a furnace fire box. Carbon dioxide passing through the tubular structure convectively absorbs heat passing through the tube walls thereby maintaining the fire-box wall refractory brick structure at a safe operating temperature.  
       FIG. 1  is a top view of a portion of a furnace fire-box wall shown in cross-section. The said fire-box comprises a heavy sheet metal enclosure  1  and supporting steel beam structure  2 . The said metal enclosure  1  is loosely held away from the interior refractory brick structure  3  by hangers  4  and provides an insulating air-space  5  between metal enclosure  1  and elevated back surface temperatures of the refractory brick structure  3 . The refractory brick  3  heat input interface surface x-x  6  lined with a series of overlapping metal plates  7  which are loosely in contact with the refractory brick structure  3  on one side and slidably attached to ceramic pieces  8  on the opposite side. Ceramic pieces  8  provide spacing and support for cooling tubes  9  in communication with the combustion flame and hot gases. While the method of construction of the wall components shown in  FIG. 1  for this particular application are unique and most generally known to those skilled-in-the-art, the novelty most apparent in the design is the use of carbon dioxide  10  from stack emissions as a fire-box regenerative cooling fluid in cooling tubes  9 .  
      Because carbon dioxide  10  is not as efficient as water as a coolant media, the cooling tubes  9  must operate at a higher temperature and therefore are of seamless construction using materials having high temperature properties such as low-carbon steels, or from steel alloys of molybdenum, chromium, nickel, columbium, or titanium.  
      Turning now to  FIG. 2  which comprise the same outer structural elements as  FIG. 1  and therefore are similarly numbered as metal enclosure  1 , steel beam structure  2 , refractory brick structure  3 , hangers  4 , insulating air-space S, refractory interface x-x, and metal plates  7 .  FIG. 2  differs from  FIG. 1  in the method of cooling which uses both water and carbon dioxide as cooling mediums. In  FIG. 2 , water cooling tubes  11  are supported by a plurality of ceramic pieces  12  which are in slidable contact with metal plates  7 . Ceramic pieces  12  also provide spacing and support for carbon dioxide cooling tube  13 .  
      Referring now to  FIG. 3  which is a portion of a vertical side-view of the furnace fire-box shown in cross-section. The metal enclosure  1 , beam structure  2  refracting brick structure  3 , hangers  4 , and air-space  5  are the same, as those shown in  FIG. 1  and  FIG. 2  and serve the same purpose. The method of mounting the said water coolant tube  11  and said carbon dioxide tube  13  of  FIG. 2  is different in  FIG. 3 . In  FIG. 3  water coolant tubes  14  and carbon dioxide coolant tubes  17  are mounted at their lower ends in lower ceramic mounting  22  and at their upper ends by upper ceramic mounting  24 . Coolant water is supplied to water cooling tube  14  at inlet  15  and passes along the interior wall surface of refractory brick structure  3  and exits the water coolant system at outlet  16 . Carbon dioxide  10  coolant enters cooling tube  17  at inlet  18  and passes along the interior wall surfaces of refractory brick structure  3  and is spaced in alternate manner between water tubes  14  and exits the furnace at outlet  19 . Carbon dioxide  10  outlet  19  is in communication with insulated hot gas manifold  20 . Hot gas manifold  20  is thermally insulated by thermal covering  21  as an energy efficiency measure for further downstream treatment which does not comprise a feature of this disclosure.  
     Numbered Elements  
     
         
           1 . metal enclosure  17 . CO 2  cooling tube  
           2 . beam structure  18 . CO 2  inlet  
           3 . refractory brick  19 . CO 2  outlet  
           4 . hangers  20 . manifold  
           5 . air-space  21 . thermal covering  
           6 . x-x interface  22 . lower ceramic mounting  
           7 . metal plates  23 . metering valve  
           8 . ceramic pieces  24 . upper ceramic mounting  
           9 . cooling tubes  25 . primary air duct  
           10 . carbon dioxide  26 . secondary air duct manifold  
           11 . water cooling tubes  27 . secondary air duct  
           12 . ceramic pieces  28 . secondary air duct inlet  
           13 . CO 2  cooling tubes  29 . secondary air duct  
           14 . water cooling tube  30 . ceramic valve housing  
           15 . water inlet  31 . facility foundation  
           16 . water outlet