Patent Application
20050126512
(1) Field of the Invention
The invention relates to industrial equipment. More particularly, the invention relates to the detonative cleaning of industrial equipment.
(2) Description of the Related Art
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 technologies have been proposed. By way of example, various technologies have been proposed in U.S. Pat. Nos. 5,494,004 and 6,438,191 and U.S. patent application publication 2002/0112638. Additional technology is disclosed in Huque, Z. Experimental Investigation of Slag Removal Using Pulse Detonation Wave Technique, DOE/HBCU/OMI Annual Symposium, Miami, Fla., Mar. 16-18, 1999. Particular blast wave techniques are described by Hanjalić and Smajević in their publications: Hanjalić, K. and Smajević, I., Further Experience Using Detonation Waves for Cleaning Boiler Heating Surfaces, International Journal of Energy Research Vol. 17, 583-595 (1993) and Hanjalić, K. and Smajević, I., Detonation-Wave Technique for On-load Deposit Removal from Surfaces Exposed to Fouling: Parts I and II, Journal of Engineering for Gas Turbines and Power, Transactions of the ASME, Vol. 1, 116 223-236, January 1994. Such systems are also discussed in Yugoslav patent publications P 1756/88 and P 1728/88. Such systems are often identified as “soot blowers” after an exemplary application for the technology.
Nevertheless, there remain opportunities for further improvement in the field.
Accordingly, one aspect of the invention involves an apparatus for cleaning a surface within a vessel. A vessel wall separates a vessel exterior from a vessel interior and has a wall aperture. The apparatus includes an elongate conduit having an upstream first and a downstream second end and positioned to direct a shockwave from the second end into the vessel interior. A pressure probe includes a body held in an operative position within the vessel so as to be exposed to the shockwave after the shockwave exits the conduit second end. The body has an exterior surface with a convergent nose portion. There is a first port in the body. A passageway extends between the first port and a pressure sensor. A support member holds the body in the operative position.
In various implementations, the probe may further include a cooling fluid circuit at least partially through the support member and body. The support member may include a cooling liquid-carrying conduit joining the body from above. The cooling liquid-carrying conduit may extend through the vessel wall. A source of fuel and oxidizer may be coupled to the conduit to deliver the fuel and oxidizer to the conduit. An initiator may be positioned to initiate a reaction of the fuel and oxidizer to produce the shockwave.
Another aspect of the invention involves a pressure probe apparatus with a body having an exterior surface with a forwardly-convergent nose portion. A passageway extends between a first port in the body and a pressure sensor. A support member holds the body in an operative position. A cooling fluid circuit extends at least partially through the support member and body.
In various implementations, the cooling circuit may extend around a periphery of a conduit defining the passageway. The body may have an aft surface with a second port and the cooling circuit may extend through the second port. The first port may be on a flat. The aft surface may have a third port and the cooling circuit may bifurcate so as to extend through the second and third ports. The apparatus may be combined with a cooling liquid flow in the cooling circuit. The support may carry a signal communication line from the pressure sensor. The nose may extend for at least 50% of a body length. Along at least 50% of a nose length, the nose may essentially converge forwardly with a half angle between 5° and 15°. The cooling circuit may span, within the body, at least 50% of the body length. An exemplary body length is between 2 cm and 20 cm and an exemplary maximum transverse dimension is no more than 4 cm. The apparatus may be used in combination with a detonative cleaning apparatus.
Another aspect of the invention involves a method for cleaning a surface within a vessel. Fuel and oxidizer are introduced to a conduit. A reaction of the fuel and oxidizer is initiated so as to cause a shockwave to impinge upon the surface. A pressure probe is used within the vessel to measure a pressure magnitude of the shockwave.
In various implementations, the method may be performed in a repeated sequential way. The reaction may include a deflagration-to-detonation transition. A cooling fluid may be passed through the pressure probe. The pressure probe may be repositioned by acting upon a support portion of a probe support member outside of the vessel.
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 an elongate combustion conduit 26 extending from an upstream distal end 28 away from the furnace wall 24 to a downstream proximal end 30 closely associated with the wall 24. Optionally, however, the end 30 may be well within the furnace. In operation of each soot blower, combustion of a fuel/oxidizer mixture within the conduit 26 is initiated proximate the upstream end (e.g., within an upstreammost 10% of a conduit length) to produce a detonation wave which is expelled from the downstream end as a shockwave along with associated combustion gases for cleaning surfaces within the interior volume of the furnace. Each soot blower may be associated with a fuel/oxidizer source 32. Such source or one or more components thereof may be shared amongst the various soot blowers. An exemplary source includes a liquefied or compressed gaseous fuel cylinder 34 and an oxygen cylinder 36 in respective containment structures 38 and 40. In the exemplary embodiment, the oxidizer is a first oxidizer such as essentially pure oxygen. A second oxidizer may be in the form of shop air delivered from a central air source 42. In the exemplary embodiment, air is stored in an air accumulator 44. Fuel, expanded from that in the cylinder 34 is generally stored in a fuel accumulator 46. Each exemplary source 32 is coupled to the associated conduit 26 by appropriate plumbing below. Similarly, each soot blower includes a spark box 50 for initiating combustion of the fuel oxidizer mixture and which, along with the source 32, is controlled by a control and monitoring system (not shown).
Extending downstream from the upstream end 28 is a predetonator conduit section/segment 84 which also may be doubly flanged and has a length L3. The predetonator conduit segment 84 has a characteristic internal cross-sectional area (transverse to an axis/centerline 500 of the conduit) which is smaller than a characteristic internal cross-sectional area (e.g., mean, median, mode, or the like) of the downstream portion (60, 62) of the combustion conduit. In an exemplary embodiment involving circular sectioned conduit segments, the predetonator cross-sectional area is a characterized by a diameter of between 8 cm and 12 cm whereas the downstream portion is characterized by a diameter of between 20 cm and 40 cm. Accordingly, exemplary cross-sectional area ratios of the downstream portion to the predetonator segment are between 1:1 and 10:1, more narrowly, 2:1 and 10:1. An overall length L between ends 28 and 30 may be 1-15 m, more narrowly, 5-15 m. In the exemplary embodiment, a transition conduit segment 86 extends between the predetonator segment 84 and the upstreammost segment 60. The segment 86 has upstream and downstream flanges sized to mate with the respective flanges of the segments 84 and 60 has an interior surface which provides a smooth transition between the internal cross-sections thereof. The exemplary segment 86 has a length L4. An exemplary half angle of divergence of the interior surface of segment 86 is ≦12°, more narrowly 5-10°.
A fuel/oxidizer charge may be introduced to the detonation conduit interior in a variety of ways. There may be one or more distinct fuel/oxidizer mixtures. Such mixture(s) may be premixed external to the detonation conduit, or may be mixed at or subsequent to introduction to the conduit.
In the exemplary embodiment, the main fuel and oxidizer are introduced to the segment 86. In the illustrated embodiment, main fuel is carried by a number of main fuel conduits 112 and main oxidizer is carried by a number of main oxidizer conduits 110, each of which has terminal portions concentrically surrounding an associated one of the fuel conduits 112 so as to mix the main fuel and oxidizer at an associated inlet 114. In exemplary embodiments, the fuels are hydrocarbons. In particular exemplary embodiments, both fuels are the same, drawn from a single fuel source but mixed with distinct oxidizers: essentially pure oxygen for the predetonator mixture; and air for the main mixture. Exemplary fuels useful in such a situation are propane, MAPP gas, or mixtures thereof. Other fuels are possible, including ethylene and liquid fuels (e.g., diesel, kerosene, and jet aviation fuels). The oxidizers can include mixtures such as air/oxygen mixtures of appropriate ratios to achieve desired main and/or predetonator charge chemistries. Further, monopropellant fuels having molecularly combined fuel and oxidizer components may be options.
In operation, at the beginning of a use cycle, the combustion conduit is initially empty except for the presence of air (or other purge gas). The predetonator fuel and oxidizer are then introduced through the associated ports filling the segment 84 and extending partially into the segment 86 (e.g., to near the midpoint) and advantageously just beyond the main fuel/oxidizer ports. The predetonator fuel and oxidizer flows are then shut off. An exemplary volume filled the predetonator fuel and oxidizer is 1-40%, more narrowly 1-20% of the combustion conduit volume. The main fuel and oxidizer are then introduced, to substantially fill some fraction (e.g., 20-100%) of the remaining volume of the combustor conduit. The main fuel and oxidizer flows are then shut off. The prior introduction of predetonator fuel and oxidizer past the main fuel/oxidizer ports largely eliminates the risk of the formation of an air or other non-combustible slug between the predetonator and main charges. Such a slug could prevent migration of the combustion front between the two charges.
With the charges introduced, the spark box is triggered to provide a spark discharge of the initiator igniting the predetonator charge. The predetonator charge being selected for very fast combustion chemistry, the initial deflagration quickly transitions to a detonation within the segment 84 and producing a detonation wave. Once such a detonation wave occurs, it is effective to pass through the main charge 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 30 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 30 and further completing the cleaning process (e.g., removing the loosened material). After or overlapping such venting of combustion products, a purge gas (e.g., air from the same source providing the main oxidizer and/or nitrogen) is introduced through the purge port 100 to drive the final combustion products out and leave the detonation conduit 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)). Optionally, a baseline flow of the purge gas 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.
In various implementations, internal surface enhancements may substantially increase internal surface area beyond that provided by the nominally cylindrical and frustoconical segment interior surfaces. The enhancement may be effective to assist in the deflagration-to-detonation transition or in the maintenance of the detonation wave.
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 signal communication line 162 (e.g., coaxial cable). The line 162 may be connected to a control/monitoring system (not shown). As the length of the flowpath 210 may affect measured pressure values relative to the inlet 212, the control/monitoring subsystem may be programmed to correct for this (e.g., ID pressure magnitude attenuation and phase corrections).
An annular or interrupted annular space 216 between the fixture 204 and conduit 200 accommodates the downstream flow of fluid from the fluid line 164 along fluid flowpaths 218. In the exemplary embodiment, the probe body interior 194 has a series of progressively smaller cross-section areas, one ahead of the other within the nose, to permit the pathway to pass therewithin to cool the nose. In the exemplary embodiment, the endplate 186 has a pair of apertures 220 (
In operation, the shockwave passes downstream over the nose, and along the body aft portion 178. When the shockwave reaches the port 212, its effects can pass along the path 210 to the pressure transducer that in turn provides an output signal indicative of the pressure magnitude of the shockwave. The probe assembly is initially positioned so that the probe unit is at a predetermined location relative to the combustion tube outlet. This may be performed while the outlet is disengaged from the furnace. Thereafter, the outlet may be inserted into the furnace, and the reaction strap or other restraints installed. The firing process may then be initiated.
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.
