CONTROL OF DETONATIVE CLEANING APPARATUS
BACKGROUND
[0001] The disclosure relates to industrial equipment. More particularly, the disclosure
relates to the detonative cleaning of industrial equipment.
[0002] 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, and minerals, 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 downtime associated
with cleaning. A variety of technologies have been proposed.
[0003] An exemplary detonative cleaning apparatus includes a conduit into which fuel and
oxidizer are introduces and then ignited. The ignition causes a shock wave to be discharged
from the conduit to impact the surfaces to be cleaned. By way of example, U.S. patent
application publication 20050199743, the disclosure of which is incorporated herein by
reference in its entirety as if set forth at length, discloses a detonative cleaning apparatus
control system and has a specific illustration relative to a segmented conduit assembly.
Alternative apparatus are of the retractable lance-type. Such systems are often identified as
"soot blowers" after the key application for the technology.
SUMMARY
[0004] One aspect of the disclosure involves an apparatus for cleaning one or more
surfaces within a vessel having a vessel wall separating a vessel exterior from a vessel interior
and having a wall aperture. The apparatus has at least one elongate conduit having an
upstream first end and a downstream second end and positioned to direct a shockwave from
the second end into the vessel interior. A source of fuel and oxidizer is coupled to the conduit
to deliver the fuel and oxidizer to the conduit An initiator is positioned to initiate a reaction of
the fuel and oxidizer to produce the shockwave. At least one sensor coupled to the conduit to
detect motion characteristic of a detonation. A control system coupled to the initiator, the
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source, and the sensor for receiving input from the sensor and controlling operation of the
initiator and source responsive to said input.
[0005] The details of one or more embodiments of are set forth in the accompanying
drawings and the description below. Other features, objects, and advantages will be apparent
from the description and drawings, and from the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] FIG. 1 is a view of an industrial furnace associated with several soot blowers
positioned to clean a level of the furnace.
[0007] FIG. 2 is a side view of one of the blowers of FIG. 1.
[0008] FIG. 3 is a schematic view of a control system for multiple cleaning apparatus.
[0009] Like reference numbers and designations in the various drawings indicate like
elements.
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DETAILED DESCRIPTION
[0010] FIG. 1 shows a furnace 20 having an exemplary three associated soot blowers 22.
In the illustrated embodiment, the furnace vessel is formed as a right parallelepiped and the
soot blowers are all associated with a single common wall 24 of the vessel and are positioned
at like height along the wall. Other configurations are possible (e.g., a single soot blower, one
or more soot blowers on each of multiple levels, and the like).
[0011] Each soot blower 22 includes an elongate combustion conduit 26 extending from
an upstream (e.g., distal/inlet) end 28 away from the furnace wall 24 to a downstream (e.g.,
proximal/outlet) 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. The
detonation wave is expelled from the downstream end as a Shockwave along with associated
combustion gases for cleaning surfaces within the interior volume of the furnace.
[0012] 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 liquified 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 (discussed below).
[0013] FIG. 2 shows further details of an exemplary soot blower 22. The exemplary
detonation conduit 26 is formed with a main body portion formed by a series of doubly
flanged conduit sections or segments 60 arrayed from upstream to downstream and a
downstream nozzle conduit section or segment 62 having a downstream portion 64 extending
through an aperture 66 in the wall and ending in the downstream end or outlet 30 exposed to
the furnace interior 68. The term nozzle is used broadly and does not require the presence of
any aerodynamic contraction, expansion, or combination thereof. Exemplary conduit segment
material is metallic (e.g., stainless steel). The outlet 30 may be located further within the
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furnace if appropriate support and cooling are provided. FIG. 2 further shows furnace interior
tube bundles 70, the exterior surfaces of which are subject to fouling.
[0014] An overall length L between ends 28 and 30 may be 1-15 m, more narrowly, 5-15
m. 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. FIG. 2 shows conduit configured for distinct introduction of two distinct
fuel/oxidizer combinations: a predetonator combination; and a main combination. In the
exemplar)' embodiment, at an upstream first location, one or more predetonator fuel injection
conduits 90 are coupled to one or more ports 92 in the conduit to define fuel injection ports.
Similarly, one or more predetonator oxidizer conduits 94 may be coupled to oxidizer inlet
ports 96. A purge gas conduit 98 may be similarly connected to a purge gas port 100 yet
further upstream., An igniter/initiator 106 (e.g., a spark plug) may be located near the
upstream end of the combustion conduit.
[0015] In the exemplary embodiment, a main fuel is carried by a number of main fuel
conduits 112 and a main oxidizer is carried by one or more main oxidizer conduits 110. 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.
[0016] 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 to fill an upstream section (e.g., just beyond
the main fuel/oxidizer ports). The predetonator fuel and oxidizer flows may then be 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
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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.
[0017] 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.
[0018] 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
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applications including oil-fired furnaces, black liquor recovery boilers, biomass boilers, waste
reclamation burners (trash burners), and the like.
[0019] A variety of systems may be provided for monitoring and/or controlling operation
of the detonative cleaning apparatus. The implementation of any particular control and
monitoring system may be influenced by the physical environment including the nature and
configuration of the vessel and its surfaces and the arrangement of the combustion conduit(s).
FIG. 3 schematically shows one of a number of levels of a vessel 200. At this level, a number
of combustion conduits 202A-D are positioned. In the exemplary embodiment, downstream
outlets of the conduits are positioned in the interior of the vessel and upstream ends are
external to the vessel. Although shown straight, the conduits may have non-straight
configurations to discharge Shockwaves in desired locations with desired directions. Each
conduit is closely associated with an interface module 204A-D which may provide local
control of various operational parameters (e.g., including fuel and oxidizer introduction,
purge and cooling gas introduction, initiation, and the like). Further details of an exemplary
interface module are discussed below. The given vessel level may also include sensors 206,
207, and 208. However, the sensors need not be level-specific. Similarly, the conduits could
be other than level-specific and other than oriented to discharge in parallel planes. The
sensors may be conduit-specific (e.g., close to the outlet of a specific associated conduit or to
the furnace surface cleaned by such conduit) or may be more generally located. The sensors
may detect one or more of thermal conditions, pressures, flows, chemical conditions, and/or
visual conditions. Exemplary sensor operation is discussed in further detail below.
[0020] For signal communication, the modules and sensors are coupled via
communication lines 209 to a hub (e.g., ethernet) 210. In the exemplary embodiment, the
sensors are coupled to the hub via the modules (e.g., coupled to the modules by
communication or signal lines). For physical input (e.g., fuel, oxidizer, purge gas, coolant,
power, and the like), the modules are coupled to a central supply unit 212 via fluid and power
lines 213. The hub and supply unit may be level-specific, common, or some combination. The
hub is coupled for signal communication (e.g., via network lines 215 such as a fiber optic
line, Ethernet line, or the like) to a control and monitoring system 214 of the facility (e.g., a
general purpose computer running control/monitoring software) which may be specific to the
vessel or central to a group of vessels at a site (e.g., a given facility). The supply unit may
similarly be coupled to the system 214 via the hub 210 or may exist independently. The
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system 214 is in communication with a remote control and monitoring system 216. The
system 216 may be in secure communication with a number of systems 214 at a number of
different sites. In such a situation, however, the system 216 may be colocated with one or
more of those systems 214 and off-site of the others. The exemplary communication between
the system 216 and systems 214 is via a wide area network 217 such as the internet.
Alternative public and private networks or other communication systems may be used. The
supply unit 212 may, itself, be fed from a remotely located tank farm 218 (e.g., a central tank
farm of the facility) via lines 219 for supply of non-air gases and other fluids and from
appropriate shop air and power sources (not shown) which may also be central sources of the
facility). The system 214 may communicate with several central systems. For example, the
system 216 may be a central system of a facility owner/operator communicating with systems
214 at various facilities of that owner/operator. A central system 223 may be a central system
of a service vendor communicating with systems 214 of various facilities of various
owners/operators either directly or via the systems 216. Based ultimately upon data provided
by the sensors 206 and 208, the systems 214 may inform the system 223 that service or
routine maintenance is necessary or otherwise appropriate (the decision being made at any of
the systems 214, 216, or 223).
[0021] In the exemplary embodiment, an emergency control panel 220 is in close
proximity to the system 214. The exemplary emergency control panel includes one or more
status lights and one or more switches (e.g., red/green status lights and emergency kill
switches for each conduit plus a master kill switch for all conduits). These are coupled by
lines 222 extending to the individual interface modules. In the event of a control system
failure which might prevent control (namely safing) of the conduits via the system 214 and
hub 210, the kill switches may be tripped by a technician to safe the conduits (e.g., shut the
fuel and oxidizer valves, disable the ignition, and the like, to safely shut down and/or disable
the associated conduits). The interface modules themselves may be set up in a failsafe mode
whereby a break in the associated line(s) 215 or 222 causes a module to transition to a safe
mode.
[0022] The sensors 206 and/or 207 may also represent motion sensors used to sense
conduit motion responsive to the combustive event. In particular, the sensors may be used to
verify detonation, generally, and the magnitude/sufficiency of the detonation, in particular.
An exemplary motion sensor is an accelerometer. An exemplary accelerometer is a
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piezoelectric sensor such as a ceramic shear accelerometer. Another exemplary sensor is a
vibration sensor. An exemplary vibration sensor is a mercury-free mechanical vibration
switch. Another exemplary sensor is a strain gauge. Such sensors do not need direct exposure
to the conduit interior or vessel interior (although the microphone in particular may also be
amenable to interior exposure for more direct measurement). Such sensors may be mounted
on the conduit exterior without an associated aperture to the conduit interior. This can save
complexity, sensor robustness, etc. Advantageous sensor positioning may be outside the
vessel to limit sensor exposure to severe environments.
[0023] Exemplary sensor coupling is a series coupling of the sensors (or back end signal
processing circuit) for a plurality (e.g., all) of the conduits. The series circuit may be normally
closed. In the event of a detonation on any conduit, the sensor will toggle and the circuit will
open. The signal processing circuit may be configured to hold the open circuit open long
enough (e.g., greater than a second) for the controller to read. At this point, if a particular
conduit was commanded to fire and the circuit doesn't open, the controller knows which
conduit failed to detonate. After a pre-defined number of failures of a given conduit to
successfully fire, the control system may alert the operator and takes that particular conduit
offline (e.g., while allowing for continued operation of the remaining conduits).
[0024] Another option for the sensors 206 and/or 207 is a pressure switch (as
distinguished from a continuous pressure sensor). The switch threshold may be selected in
view of its positioning to correspond to a desired threshold for the pressure associated with
detonation. Triggering of the switch would thus indicate a successful detonation, while a
failure to trigger would indicate an unsucccessful or sub-threshold event. An exemplary
positioning is in an upstream half of a length of the conduit.
[0025] Such sensing of the detonation (or lack thereof) may be combined with further
control aspects and inputs such as are identified in the above-mentioned U.S. patent
application publication 20050199743.
[0026] One or more embodiments have been described. Nevertheless, it will be understood
that various modifications may be made. For example, the invention may be adapted for use
with a variety of industrial equipment and with variety of soot blower technologies. For
example, the principles may be adapted to various existing or yet-developed detonative
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cleaning apparatus, including fixed and extensible/retractable units. 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.
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CLAIMS
What is claimed is:
1. An apparatus for cleaning one or more surfaces within a vessel having a vessel wall
separating a vessel exterior from a vessel interior and having a wall aperture, the apparatus
comprising:
at least one elongate conduit having an upstream first end and a downstream second
end and positioned to direct a shockwave from the second end into the vessel interior; and
a source of fuel and oxidizer coupled to the conduit to deliver the fuel and oxidizer to
the conduit;
an initiator positioned to initiate a reaction of the fuel and oxidizer to produce the
shockwave;
at least one sensor coupled to the conduit to detect motion indicative of a detonation;
and
a control system coupled to the initiator, the source, and the sensor for receiving input
from the sensor and controlling operation of the initiator and source responsive to said input.
2. The apparatus of claim 1 wherein:
the sensor is a piezoelectric sensor.
3. The apparatus of claim 1 wherein:
the sensor is a contact accelerometer.
4. The apparatus of claim 1 wherein:
the sensor is a contact vibration sensor.
5. The apparatus of claim 1 wherein:
the sensor is in contact with an exterior of the conduit without an associated aperture
to the interior of the conduit.
6. The apparatus of claim 1 wherein:
there are a plurality of such conduits and such initiators, each of the conduits
associated with an associated one or more of the initiators; and
the sensors are series coupled to the control system.
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7. The apparatus of claim 6 wherein:
the control system is programmed to generate maintenance or service requests
responsive to the input.
8. The apparatus of claim 6 wherein:
the control system is programmed to determine detonation failures of the conduits
individually.
9. The apparatus of claim 8 wherein:
the control system is programmed to individually adjust operational parameters of the
conduits responsive to the determined failures.
10. The apparatus of claim 1 wherein:
the control system communicates with a remote monitoring system.
11. The apparatus of claim 1 wherein:
the control system is programmed to determine a detonation success or failure status.
12. The apparatus of claim 1 wherein:
the control system is programmed with a plurality of different cleaning processes and
to execute the processes responsive to corresponding sensed conditions.
13. A method for cleaning a surface within a vessel, the method comprising:
introducing fuel and oxidizer to at least one elongate conduit having an upstream first
end and a downstream second end and positioned to direct a Shockwave from the second end
into the vessel interior;
initiating a reaction of the fuel and oxidizer;
detecting a motion of the conduit;
responsive to the detecting, determining a characteristic of the reaction; and
responsive to the determined characteristic, adjusting at least one parameter of the
introducing and initiating so as to provide feedback control of the characteristic.
14. The method of claim 13 wherein:
the detecting comprises detecting an acceleration.
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15. The method of claim 13 wherein:
the detecting comprises detecting a vibration parameter.
16. The method of claim 13 wherein:
the determining comprises determining a sufficiency of a detonation.
17. The method of claim 13 further comprising:
responsive to the determined characteristic, generating an automated maintenance or
service request.
18. An apparatus for cleaning one or more surfaces within a vessel having a vessel wall
separating a vessel exterior from a vessel interior and having a wall aperture, the apparatus
comprising:
at least one elongate coauuit naving an upstream iirst end and a downstream seconu
end and positioned to direct a Shockwave from the second end into the vessel interior; and
a source of fuel and oxidizer coupled to the conduit to deliver the fuel and oxidizer to
the conduit;
an initiator positioned to initiate a reaction of the fuel and oxidizer to produce the
Shockwave;
a pressure switch coupled to the conduit to be exposed to pressure associated with the
reaction; and
a control system coupled to the initiator, the source, and the pressure switch for
receiving input from the pressure switch and controlling operation of the initiator and source
responsive to said input.
19. The apparatus of claim 18 wherein the pressure switch is a binary switch, with an
open condition associated with pressure below a threshold and a closed condition associated
with pressure above the threshold.
20. The apparatus of claim 18 wherein the pressure switch is along an upstream half of a
length of the conduit.


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An apparatus is provided for cleaning one or more surfaces within a vessel having a vessel
wall separating a vessel exterior from a vessel interior and having a wall aperture. The
apparatus has at least one elongate conduit having an upstream first end and a downstream
second end and positioned to direct a Shockwave from the second end into the vessel interior.
A source of fuel and oxidizer is coupled to the conduit to deliver the fuel and oxidizer to the
conduit An initiator is positioned to initiate a reaction of the fuel and oxidizer to produce the
shockwave. At least one sensor coupled to the conduit to detect motion indicative of a
detonation. A control system coupled to the initiator, the source, and the sensor for receiving input from the sensor and controlling operation of the initiator and source responsive to said input.