Patent Application
20090277479
The disclosure relates to industrial equipment. More particularly, the disclosure relates to the detonative cleaning of industrial equipment.
Surface fouling is a major problem in industrial equipment. Such equipment includes furnaces (coal, oil, waste, etc.), boilers, gasifiers, reactors, heat exchangers, and the like. Typically the equipment involves a vessel containing internal heat transfer surfaces that are subjected to fouling by accumulating particulate such as soot, ash, minerals and other products and byproducts of combustion, more integrated buildup such as slag and/or fouling, and the like. Such particulate build-up may progressively interfere with plant operation, reducing efficiency and throughput and potentially causing damage. Cleaning of the equipment is therefore highly desirable and is attended by a number of relevant considerations. Often direct access to the fouled surfaces is difficult. Additionally, to maintain revenue it is desirable to minimize industrial equipment downtime and related costs associated with cleaning. A variety of cleaning technologies have been proposed. Such systems are often identified as “soot blowers” after an exemplary application for the technology.
A basic soot blower configuration is the steam lance soot blower. Additionally, combustion soot blower technologies have been proposed. Recent examples include those of U.S. Pat. No. 7,011,047 and US Patent Publication Nos. 2005/0126594, 2005/0130084, 2005/0125931, and 2005/0199743 the disclosures of which are incorporated by reference in their entireties herein as if set forth at length.
One aspect of the disclosure involves an apparatus for cleaning a surface within a vessel. The apparatus has a combustion conduit having an outlet. The outlet is positioned to direct a shockwave toward the surface. The apparatus includes a source of fuel and oxidizer coupled to the conduit to deliver the fuel and oxidizer to the conduit. The apparatus includes an initiator coupled to the conduit and positioned to initiate combustion of the delivered fuel and oxidizer to form the shockwave. A buffer chamber is positioned between the conduit and the source and may provide means for preventing a flame propagation upstream from the conduit back to the source. In various implementations, there may be a fixed restriction between the conduit and the buffer chamber. The buffer chamber may have a volume of at least 5,000 cubic centimeters and a peak transverse cross-sectional area of at least 50 cm2. The fuel and oxidizer may be delivered to the conduit as a fuel/oxidizer mixture (i.e., contrasted with separate delivery and formation of the mixture only in the conduit).
The apparatus may be operated by introducing the fuel/oxidizer mixture to the conduit through the buffer chamber and introducing a buffer gas to the buffer chamber. A reaction of the fuel/oxidizer mixture is initiated so as to, in turn, cause a detonation of the fuel/oxidizer mixture so as to cause the shockwave to impinge upon the surface. The reaction may comprise a deflagration-to-detonation transition.
In various implementations, the buffer gas may be different from the fuel/oxidizer mixture and from the fuel and oxidizer separately. The buffer gas may be a portion of a purge gas used to purge the conduit of combustion products of the fuel/oxidizer mixture. To complete the purge, a further portion of the purge gas may be introduced after the detonation. The further portion may drive the buffer gas into the combustion conduit as part of the purge.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.
Like reference numbers and designations in the various drawings indicate like elements.
Each soot blower 22 includes a combustor 34 having an elongate combustion conduit 36 extending from a first (e.g., an upstream/distal/inlet end) 38 away from the boiler wall 24 to a second (e.g., downstream/proximal/outlet) end 40 closely associated with the wall 24. Optionally, however, the end 40 may be well within the boiler. In operation of each soot blower 22, combustion of a fuel/oxidizer mixture within the conduit 36 is initiated proximate the upstream end 38 (e.g., within an upstreammost 10% of a conduit length) to produce a detonation wave which is expelled from the downstream end 40 as a shockwave along with associated combustion gases for cleaning surfaces within the interior volume of the furnace.
Each soot blower 22 may be associated with a fuel/oxidizer source 42. Such source or one or more components thereof may be shared amongst the various soot blowers. In the illustrated example, a single source 42 is part of a single gas delivery system 43 shared by the various conduits 22. The exemplary source 42 includes a fuel source 44 and an oxidizer source 46 separate from the fuel source. An exemplary source 42 includes a liquified or compressed gaseous fuel cylinder 44 and an oxygen cylinder 46. As is discussed below,
In one example, there is a single fuel (e.g., propane) and a single oxidizer (e.g., pure oxygen). In a second example, the oxidizer is a first oxidizer such as essentially pure oxygen. A second oxidizer may be in the form of air delivered from the air source 48. The first and second oxidizers may be used to deliver a two-stage charge: a high detonable charge including the pure oxygen; and a less detonable charge containing the air (the highly detonable charge being used to detonate the less detonable charge). The source 42 may be controlled and monitored by a control and monitoring system 50 (controller). An exemplary controller 50 may include a computer or microcontroller appropriately programmed via one or both of hardware and software.
The sources 42 (44, 46) and 48 are coupled to the various conduits by appropriate plumbing. In the illustrated example, the sources 44, 46, and 48 are coupled via upstream root branches 54, 56, and 58 joining in a mixing line 60. In each of the roots 54, 56, and 58, there is a selector valve 62, 64, 66 upstream and a one-way check valve 68, 70, 72 downstream (oriented to prevent upstream flow). The selector valves 62, 64, 66 may be coupled via appropriate power and/or signal lines to the controller 50 to be selectively opened and closed by the controller 50. A distribution manifold 74 is at a downstream end of the mixing line 60. The distribution manifold 74 divides flow into separate branches 76 (distribution lines) for individual combustors or individual groups of combustors. In the illustrated example, a selector valve 78 and a one-way check valve 80 (oriented to prevent upstream flow) are positioned in each distribution line 76. The selector valves 78 are also coupled to the controller 50. In the illustrated example, a pressure sensor 82 is positioned along the mixing line 60 and coupled to the controller 50.
There are also means for igniting or initiating combustion. In the illustrated example, the means for initiating or igniting includes an initiator/igniter 90 for each combustor. In the example, each igniter 90 is connected to an associated spark box 92 which is in turn coupled to the controller 50. There may be one or more separate power sources (not shown) for powering the spark boxes, selector valves, and other components.
Means are provided for isolating the gas delivery system (or at least upstream components thereof which might otherwise be subject to damage) from the combustor and its combustion and detonation. The exemplary means for isolating includes one or more buffer chambers. In the
In operation, at the beginning of a use cycle of a given combustor 34, the combustion conduit 36 is initially empty except for the presence of air (or other purge gas or flue gas or other residual gas as discussed below). The controller 50 controls the selector valves 62 and 64 to deliver fuel and oxidizer to the mixing tube 60 where they mix to form a fuel/oxidizer charge. The appropriate selector valve(s) 78 are opened by the controller to deliver the charge through the appropriate delivery line(s) 76 to the appropriate conduit(s). The fuel/oxidizer mixture passes into the buffer chamber through the inlet 124, filling the buffer chamber(s) 20 and then passing through the injector 128 into the conduit 36. During this passage, the fuel/oxidizer mixture may drive the residual gas ahead of the fuel/oxidizer mixture, there being an interface (a first interface) between the residual gas and the fuel/oxidizer mixture.
When an appropriate amount of fuel and oxidizer have been supplied by the fuel and oxidizer sources, the respective source selector valves 62 and 64 are closed by the controller 50 and the air source selector valve 66 is opened, introducing air to the mixing line 60. This will form an interface (a second interface) between the air and the fuel/oxidizer mixture. The flow of air will drive this second interface downstream through the distribution manifold 74, and delivery line(s) 76 and into the buffer chamber. This will drive more of the fuel/oxidizer mixture into the conduit through the injector.
Eventually, a desired ignition/firing condition will be achieved. This is achieved when sufficient air has reached the buffer chamber to provide the buffer function (discussed below) yet the fuel/air mixture in the conduit 36 is sufficient to properly ignite and, in turn, detonate.
Prior to firing, the air source selector valve 66 and the appropriate selector valve(s) 78 are closed. Although the closing may be simultaneous, it may be advantageous to close the valve 66 slightly before the valve(s) 78 to minimize pressure in the mixing line 60. With the selector valve(s) 78 of the about-to-fire combustor(s) closed, the controller may trigger the associated spark box 92 to provide a spark discharge of the initiator 90 igniting charge (or the predetonator charge in a multi-charge example). The initial deflagration of the charge quickly transitions to a detonation, producing a detonation wave. Once such a detonation wave occurs, it is effective to pass through the rest of the charge (or the main charge (in a multi-charge example) which might, otherwise, have sufficiently slow chemistry to not detonate within the conduit of its own accord). The wave passes longitudinally downstream and emerges from the downstream end 40 as a shockwave within the furnace interior, impinging upon the surfaces to be cleaned and thermally and mechanically shocking to typically at least loosen the contamination. The wave will be followed by the expulsion of pressurized combustion products from the detonation conduit, the expelled products emerging as a jet from the downstream end 40 and further completing the cleaning process (e.g., removing the loosened material).
Upon initiation/firing, the gas contained in the buffer chamber 120 advantageously has appropriate composition and distribution to prevent a detonation wave from passing upstream through the buffer chamber and into the delivery line 76 (thus avoiding damaging upstream components including avoiding igniting fuel at the fuel source). It is expected that, at initiation/firing, there will be some fuel and oxidizer in the buffer chamber, particularly toward the downstream end near the outlet 126. This is because the second interface will tend to smear, locally diluting the fuel/oxidizer mixture with air. However, the conduit 36 must have sufficient fuel and oxidizer at the initiator 90 to initiate combustion. Accordingly, it may be necessary that most of the smeared second interface be contained within the buffer chamber. The buffer chamber has sufficient volume and length to sufficiently dilute the overall content of fuel and oxidizer in the buffer chamber and sufficiently isolate the fuel and oxidizer toward the downstream end. The restriction provided by the injector 128 is also effective to limit/control backpressure or backflow from the detonation to within tolerable margins. The result is that the delivery line 76 and upstream components will experience only a tolerable pressure pulse and temperature increase.
The air selector valve 66 may be reopened, pressurizing the mixing tube 60 with air. This pressurization may be detected by the pressure sensor 82. An exemplary sensor 82 is a simple pressure switch with a threshold corresponding to a predetermined sufficient air pressure. If sufficient pressure is not determined, the controller 50 may determine an error condition and cease further operation of the combustors and signal for assistance/maintenance.
If, however, sufficient pressure is determined, the controller 50 may then reclose the air valve 66. The controller 50 may then reopen the appropriate valve(s) 78. The opening of the valve(s) 78 bleeds pressurized air from the mixing tube into the delivery line(s) and buffer chamber(s). Sufficient completion of this bleed may be measured by the pressure sensor 82. When the bleed has occurred, the fuel and oxidizer source selector valves 62 and 64 may be reopened as the start of the next cycle.
As a variation, after or overlapping the venting of combustion products, a purge gas (e.g., air from the source 48) may be introduced through the buffer chamber 120 to drive the final combustion products out and leave the buffer chamber 120 and conduit 36 filled with purge gas ready to repeat the cycle (either immediately or at a subsequent regular interval or at a subsequent irregular interval (which may be manually or automatically determined by the control and monitoring system)). As another variation, a baseline flow of the air may be maintained between charge/discharge cycles so as to prevent gas and particulate from the furnace interior from infiltrating upstream and to assist in cooling of the detonation conduit. Thus, in various combinations, the purge gas, residual combustion product and/or flue gas may provide the residual gas which is driven out by the fuel/oxidizer mix of the next firing cycle.
Various means may be provided for monitoring combustor performance. Monitored or determined (e.g., calculated) parameters may include verification of detonation and sufficiency of power on the one hand and safety margin on the other hand.
After firing, sufficiency of the output of the motion sensor 150 may be used by the controller 50 to confirm detonation and confirm sufficiency of associated combustor shockwave power. The temperature sensor 152 may be used to verify non-excessive temperature. For example, the temperature sensor 152 may be positioned near the buffer chamber inlet 124. An excessive temperature measured near the buffer chamber inlet 124 may indicate that there was too much fuel (or fuel/oxidizer mixture) in the buffer chamber, generally, or at least in the upstream end near the inlet. Responsive to an excessive temperature, the controller 50 may alter timing or other parameters for the next shot/firing. For example, the controller 50 might cause the next shot of the combustor to occur only after more air has been introduced to drive the second interface further downstream. However, if temperature is within the acceptable range, and a failure of detonation or insufficiency of detonation power is detected (via the motion sensor 152), less air could be introduced for the next shot/firing to increase the likely detonation power. More complex control variations and/or systems are possible. For example, other sensors and control variations are disclosed in commonly owned U.S. patent application Ser. No. 11/740,413, filed Apr. 26, 2007.
The apparatus may be used in a wide variety of applications. By way of example, just within a typical coal-fired furnace, the apparatus may be applied to: the pendants or secondary superheaters, the convective pass (primary superheaters and the economizer bundles); air preheaters; selective catalyst removers (SCR) scrubbers; the baghouse or electrostatic precipitator; economizer hoppers; ash or other heat/accumulations whether on heat transfer surfaces or elsewhere, and the like. Similar possibilities exist within other applications including oil-fired furnaces, black liquor recovery boilers, biomass boilers, waste reclamation burners (trash burners), and the like.
The buffer chamber 120 includes a domed cap 220 having a rim 222 welded to an upstream rim 224 of the tube 204. The buffer chamber inlet 124 is formed at a boss 226 which mates with the associated delivery line 76. The exemplary cap 220 includes a central aperture 230 accommodating the temperature sensor 152. The exemplary motion sensor 150 is mounted to the exterior surface 232 of the cap 220. The exemplary buffer chamber has an overall internal length LB and an internal diameter DB. A flowpath length from the inlet 124 to the outlet 126 may be close to LB (e.g., at least 75%).
Exemplary combustor materials include stainless steel. An exemplary tube 204 is formed of 6″ outer diameter (OD) stock having an inner diameter (ID) of 5.136″ (13.05 cm) and a length LT of 36″ (91 cm). The exemplary cap 220 adds less than 10% to the associated tube volume of 746 inch3 (12,222 cm3). More broadly, the exemplary buffer chamber may have a volume of at least 5,000 cm3 (e.g., 5,000-20,000) or greater than 10,000 cm3 (e.g., 10,000-15,000). The exemplary peak cross-sectional area is 20.7 in2 (134 cm2). More broadly, exemplary cross-sectional area is at least 50 cm2 (e.g., 50-200) or at least 100 (e.g., 100-150). An exemplary flowpath length from the inlet 124 to the outlet 126 is at least 50 cm (e.g., 50-200 cm).
By contrast, the characteristic cross-sectional area of the restriction (injector) may be much smaller than that of the buffer chamber and the characteristic cross-sectional area of the combustor may be much larger. The exemplary injector ID BI is 1.0″ (2.54 cm) for a cross-sectional area of 0.785 in2 (10.44 cm2). Exemplary injector outlet diameters DIO are 0.375″ (0.95 cm) for an individual cross-sectional area of 0.11 in2 (0.713 cm2) and an overall cross-sectional area of 8.55 cm2. The effective fluidic restriction of the outlets is equivalent to a single circular hole having less than that total cross-sectional area. Exemplary total cross-sectional area is less than 10% that of the buffer chamber.
One or more embodiments of the present invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. For example, the invention may be adapted for use with a variety of industrial equipment and with variety of soot blower technologies. Aspects of the existing equipment and technologies may influence aspects of any particular implementation. Accordingly, other embodiments are within the scope of the following claims.
