Patent Publication Number: US-2012031350-A1

Title: Ice blast cleaning systems and methods

Description:
TECHNICAL FIELD 
     The present application relates generally to ice blast cleaning systems and methods and more particularly relates to high pressure ice blast cleaning systems and methods to clean slag and the like from industrial boiler tubes via mechanical impact and thermal stress. 
     BACKGROUND OF THE INVENTION 
     Generally described, industrial boilers operate by using a heat source to create steam from water or another type of a working fluid. The steam may be used to drive a turbine or another type of load. The heat source may be a combustor that burns a fuel-air mixture therein. Heat may be transferred to the working fluid from the combustor via a heat exchanger. Burning the fuel-air mixture, however, may generate residue on the surface of the combustor, the heat exchanger, and the like. Such deposits of soot, ash, slag, dust, and/or other types of residues on the heat exchanger surfaces may inhibit the efficient transfer of heat to the working fluid. This reduction in efficiency may be reflected by an increase in exhaust gas temperatures from the backend of the process as well as an increase in the fuel burn rate required to maintain steady steam production and energy output. 
     Periodic removal of these deposits thus may help maintain the efficiency of such a boiler system. Typically, the complete removal of the deposits generally requires the boiler to be shutdown while the cleaning process is performed. Such cleaning processes thus may be relatively time consuming and costly at least in terms of boiler downtime. 
     Pressurized steam, water jets, acoustic waves, abrasive ash, mechanical hammering, detonative combustion devices, and other types of cleaning processes have been used to remove these internal deposits. The use of pressurized steam and/or water may blow the accumulated ash off of the tube banks but generally will not eliminate a hard layer of slag. Moreover, the abrasive particle methods may add more hard particles of materials into the boiler, which also may cause a blockage. Other types of cleaning processes may be known. 
     There is thus a desire for improved boiler cleaning system and methods that are able to operate quickly to remove internal slag deposits and the like so as to minimize overall downtime of the boiler and similar types of devices. Moreover, such cleaning systems and methods should not interfere with the overall operation and use of the boiler. 
     SUMMARY OF THE INVENTION 
     The present application thus provides an ice blast cleaning method for a layer of slag on a surface. The ice blast cleaning method may include the steps of maintaining the surface with the layer of slag thereon at an elevated temperature, shooting a number of ice pellets at the layer of slag on the surface, and loosening the layer of slag on the surface via a mechanical impact of the ice pellets on the layer of slag and a thermal shock caused by a temperature differential between the ice pellets and the layer of slag. 
     The present application further provides a heat exchanger system. The heat exchanger system may include a heat exchanger positioned within a combustion stream such that the combustion stream creates a layer of slag on the heat exchanger. The heat exchanger system further includes an ice blast system positioned about the heat exchanger. The ice blast system shoots a stream of ice pellets at the layer of slag so as to loosen the layer of slag via a mechanical impact of the stream of ice pellets on the layer of slag and a thermal shock caused by a temperature differential between the stream of ice pellets and the layer of slag. 
     The present application further provides a boiler system. The boiler system may include a boiler with a number of boiler tubes therein. The boiler tubes may include a layer of slag thereon. The boiler system also may include an ice blast system positioned about the boiler. The ice blast system shoots a stream of ice pellets at the layer of slag so as to loosen the layer of slag via a mechanical impact of the stream of ice pellets on the layer of slag and a thermal shock caused by a temperature differential between the stream of ice pellets and the layer of slag. 
     These and other features and improvements of the present application will become apparent to one of ordinary skill in the art upon review of the following detailed description when taken in conjunction with the several drawings and the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of an ice blast cleaning system as may be described herein for use with a boiler system or other type of heat exchanger system and the like. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to the drawings, in which like numbers refer to like elements throughout the view,  FIG. 1  shows a heat exchanger system  10  such as a boiler  15  as may be known in the art. The boiler  15  may include a number of boiler tubes  20  or other types of heat exchanger surfaces positioned therein. Heat is transferred to a medium flowing within the boiler tubes  20  via a combustion stream  25  or other types of heat sources. As described above, the combustion stream  25  tends to build a layer of slag  30  onto the boiler tubes  20  or other types of internal surfaces  40  such as boiler chamber water walls  45 . By the term “slag”, we refer to slag, soot, ash, slug, dust, and/or any type of unwanted residue thereon. This layer of slag  30  may interfere with the efficiency of the overall boiler  15 . Other types of heat exchangers  10  or boiler  15  configurations also may be used herein. Generally described, any surface  40  with a buildup of the layer of slag  30  or the like may be used herein. 
       FIG. 1  further shows an ice blast cleaning system  100  as may be described herein that may be used with the heat exchanger  10  or the boiler  15 . Generally described, the ice blast cleaning system  100  may shoot a stream of ice pellets  110  at the layer of slag  30  of the boiler tubes  20  or other type of surface  40 . The ice pellets  110  may be made out of any type of fluid such as water and the like. The ice pellets  110  also may be dry ice pellets. The ice pellets  110  may have any desired size, shape, temperature, velocity, and/or other characteristics and combinations thereof. Any number of the ice pellets  110  may be used herein. 
     The ice blast cleaning system  100  may include an ice hopper  120  for making and/or storing the ice pellets  110 . In turn, the ice hopper  120  may be in communication with a mixer  130  or other type of staging device. The mixer  130  also may be in communication with a compressed air source  140 . Any type of compressed air source  140  or other type of pressurized medium may be used herein. Likewise, any type of drive force may be used as a drive mechanism herein. The mixer  130  may forward a stream of the ice pellets  110  with the aid of the compressed air source  140  or other type of drive mechanism. 
     The ice blast cleaning system also may use a tube  150  with a lance or a nozzle  160 . The tube  150  and the nozzle  160  may deliver the ice pellets  110  to the surface  40  of the desired target. The tube  150  may be of conventional design and may be flexible or stiff. The tube  150  and the nozzle  160  may be retractable and may be positioned in any desired location. The nozzle  160  may have one or multiple apertures thereon. Other types of delivery systems may be used herein. 
     The ice blast cleaning system  100  as a whole may have any desired size, shape, or configuration. Specifically, any device for shooting ice pellets  110  at a sufficient rate, velocity, and/or other characteristics with respect to the boiler tubes  20  or other surface  40  may be used herein. 
     In use, the ice blast cleaning system  100  may be used while the boiler  15  is still in operation or at least still heated. The nozzle  160  or other type of delivery device of the ice blast cleaning system  100  may be positioned about the boiler tubes  20  or other surface  40  and blast the ice pellets  110  under pressure towards the layer of slag  30 . The combination of the impact of the ice pellets  110  and the thermal shock of the high temperature layer of the slag  30  combines to loosen and remove the layer of slag  30  thereon. Specifically, the mechanical impact of the ice pellets  110  on the layer of slag  30  combines with the thermal shock caused by the temperature differential between the cold ice pellets  110  and the hot layer of slag  30 . 
     Modifications may be made as to the size of the ice pellets  110 , the initial temperature of the ice pellets  110 , and other variables. Moreover, the initial velocity of the ice pellets  110  also may vary. Calculations based upon the size, temperature, and velocity of the ice pellets  110  may ensure the desired mechanical and thermal impact of the ice pellets  110  on the layer of slag  30  or otherwise. As described above, dry ice also may be used herein and has the advantage of a colder initial temperature. Other types of frozen mediums also may be used herein. Likewise, combinations of different types of ice pellets  110  also may be used herein. 
     The ice blast cleaning system  100  thus provides the advantage of the steam, water, or abrasive cleaning systems and methods described above but without the associated detriments of each, i.e., thicker layers of slag  30  may be removed as compared to steam or water system but without the potential for blockage that may be caused by the use of abrasive particles. The combination of the high pressure impact of the ice pellets  110  along with the associated thermal shock to the high temperature layer of the slag  30  thus provide the improved cleaning methods and benefits herein without the downtime normally associated with such cleaning methods. 
     It should be apparent that the foregoing relates only to certain embodiments of the present application and that numerous changes and modifications may be made herein by one of ordinary skill in the art without departing from the general spirit and scope of the invention as defined by the following claims and the equivalents thereof.