GB2558616A

GB2558616A - Biomass boiler cleaning method and apparatus

Info

Publication number: GB2558616A
Application number: GB1700405.2A
Authority: GB
Inventors: Anthony Reynolds Clive; Lister Cockin Mark
Original assignee: Cape Industrial Service Group Ltd; Cape Environmental Services Onshore Ltd
Current assignee: Cape Industrial Service Group Ltd; Cape Environmental Services Onshore Ltd
Priority date: 2017-01-10
Filing date: 2017-01-10
Publication date: 2018-07-18
Also published as: GB201700405D0; GB2558616A8

Abstract

Method and apparatus for cleaning interior surfaces of a boiler 110 configured for the conversion of fuel into heat energy. The method comprises providing a high pressure fluid source 204 and a fluid jetting arrangement 300, directing at least one high pressure jet of fluid to rotate about first and second non-parallel axes, when driven by the high pressure fluid source. The fluid jetting arrangement being inserted through one of plural apertures 401 into the boiler. The fluid jetting arrangement preferably being a head 300 having a nozzle turret arrangement (320, fig 3) attached thereto, the turret arranged such that when high pressure fluid is passed through the nozzles 321, 322 on the turret it rotates about two non-parallel axes (X and Y in fig 3) due to the pressure of the fluid.

Description

(54) Title of the Invention: Biomass boiler cleaning method and apparatus Abstract Title: Industrial boiler cleaning method and apparatus (57) Method and apparatus for cleaning interior surfaces of a boiler 110 configured for the conversion of fuel into heat energy. The method comprises providing a high pressure fluid source 204 and a fluid jetting arrangement 300, directing at least one high pressure jet of fluid to rotate about first and second non-parallel axes, when driven by the high pressure fluid source. The fluid jetting arrangement being inserted through one of plural apertures 401 into the boiler. The fluid jetting arrangement preferably being a head 300 having a nozzle turret arrangement (320, fig 3) attached thereto, the turret arranged such that when high pressure fluid is passed through the nozzles 321,322 on the turret it rotates about two non-parallel axes (X and Y in fig 3) due to the pressure of the fluid.

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Biomass Boiler Cleaning Method and Apparatus

FIELD OF THE INVENTION

The present invention relates to boilers used in industrial power generation such as, for example, those used for converting combustible, preferably biomass, fuel into heat energy for either power generation, or combined heat and power generation. In particular, the invention relates to a method of cleaning such a boiler.

BACKGROUND TO THE INVENTION

Increasing numbers of previously coal-fired power generation facilities are now being converted for use with biomass materials. Biomass is generally defined as organic material used for firing power generation plants and excludes fossil fuels. An environmental benefit of the use of biomass as a fuel in place of fossil fuels is that it avoids the burning of fossil fuels and so avoids the resultant release of carbon from those fossil fuels, which carbon has otherwise been stored in fossilised form for many millions of years. Biomass is considered to be more environmentally friendly in view of the fact that it only releases carbon into the atmosphere from more recently-grown organic material, which will be again re-grown to replenish fuel stocks and so will resequester the CO2 emitted more quickly. Although these views are contested in some quarters, the growth of the conversion of coal-fired power stations to biomass is real and poses new technical problems in the maintenance and operation of those converted boilers.

These new problems arise because, historically, coal-fired boilers used for industrial scale power generation needed relatively low frequency maintenance. This is because the burning of coal in those boilers generated some soot, but relatively little compared to Biomass fuels. Shut-downs for boiler cleaning of coal fired boilers were therefore relatively irregular. The conventional methods of cleaning these boilers involve human operatives being lowered into the heart of the boiler on ropes and/or supported on scaffolds, and those operatives mechanically chipping and/or scraping away buildup from the interior of the boiler, such as internal surfaces, tubes and heat exchangers, to manually remove the build-up. These techniques are of limited speed, and require full boiler shut-downs, for extended periods of time and so their cost in mere shutdown time of the plant is significant. Further, the risk to personnel from exposure to dust and debris and working at height is non-optimal. Industrial scale biomass boilers are often several tens of meters tall and so the operatives are working internally, sometimes in poor lighting conditions, at great height. Other methods which exist involve the use of explosive charges to shock material from the internal surfaces using the airborne shockwaves created by explosions. The explosion-based methods can be effective to a degree, but do not guarantee that all deposits are removed, while the level of cleanliness achieved by the manual knocking and scraping methods can be variable based upon visibility, training and other human-based factors.

There is therefore a need for improved methods for cleaning biomass boilers used in power generation.

SUMMARY OF THE INVENTION

The present invention seeks to provide an alternative to the known methods used for cleaning industrial and utility scale boilers, in particular biomass boilers. The method involves providing a fluid jetting head inside a boiler and providing a number of jets of water out or the jetting head. The jets preferably rotate about one or preferably two substantially perpendicular axes to provide full coverage of substantially all of a sphere around the jetting head. The high pressure jets remove deposits from surfaces internal to the boiler and especially to outside surfaces of fluid conduits provided in the boiler.

In addressing the drawbacks of known methods of cleaning industrial-scale boilers, there is provided a method of cleaning interior surfaces of an industrial utility scale boiler configured for the conversion of combustible fuel into heat energy, the method comprising the steps of:

providing a high pressure fluid source;

providing a fluid jetting arrangement connected to the high pressure fluid source and configured to direct at least one high pressure jet of fluid to rotate about first and second non-parallel axes, when driven by the high pressure water source;

providing the fluid jetting arrangement to the interior of the boiler though a first one of one or more openings provided in the boiler;

activating the high pressure water source to drive the jetting arrangement while the jetting arrangement is suspended inside the boiler via the first opening, to clean internal surfaces of the boiler with the at least one high pressure jet of fluid.

The method may further comprise providing the jetting arrangement to the interior of the boiler though a second opening of the one or more openings; and activating the high pressure water source to drive the fluid jetting arrangement 10 while the fluid jetting arrangement is suspended inside the boiler via the second opening, to clean further internal surfaces of the boiler with the at least one high pressure jet of fluid.

The openings may be provided in a top surface of the boiler and wherein the fluid jetting arrangement is suspended in position inside the boiler from the top surface during the cleaning.

At least one of the openings may be configured to allow the passage of the fluid jetting arrangement, but to prevent passage of an average sized adult human through the opening.

At least a majority of the openings may be configured to allow the passage of the fluid 20 jetting arrangement, but to prevent passage of an average sized adult through the opening.

One or more of the openings may be configured to prevent the passage of an average human adult has a greatest diametric dimension of between around 10cm and 50cm.

The high pressure fluid source may be configured to deliver a flow of water at over 2 25 x 10² litres per minute, preferably over 2.5 x 10² litres per minute.

The high pressure fluid source may be configured to deliver a flow of water at over 8 x 10² bar operating pressure, preferably around 1 x 10³ bar operating pressure.

The jetted fluid is preferably a liquid, preferably comprising water or at least a majority water, for example more than half, 3/4 or 8/10 water, with optional further cleaning agents of compositions.

The jetting arrangement may be a jetting head comprising a body and a rotatable turret 5 carrying one or more nozzles configured to direct the at least one high pressure jet of fluid to rotate, relative to an attachment point of the body, about first and second nonparallel axes, when driven by the high pressure water source.

The jetting arrangement may be suspended inside the boiler and left in a first location for a predetermined time without human intervention.

In the method the jetting arrangement may be:

suspended and activated with the high pressure fluid source for a predetermined time at a first height in the boiler;

de-activated;

moved to a second height in the boiler; and then reactivated and left in the second location at the second height while being activated with the high pressure fluid source to clean further internal surfaces of the boiler.

Any of the above described steps may be repeated after removing the jetting arrangement from the boiler and re-inserting the jetting arrangement through a further opening in the boiler.

Any of the above steps may be repeated for each of a plurality of openings, the openings being arranged in an array corresponding to a plurality of fluid conduits of the boiler to be cleaned.

The jetting arrangement may be attached to a hose for delivering the high pressure fluid via a first fluid connection, and via a secondary tether, to retain the jetting arrangement attached to the hose in the event of failure of the first fluid connection.

The boiler may be a biomass boiler adapted to bum biomass fuel to generate heat energy.

The boiler may be sized and configured for an energy output capacity of around 4MW, preferably 10MW, more preferably 25MW or more.

The internal surfaces cleaned by the method preferably include external surfaces of fluid conduits passing through the internal space of the boiler.

An apparatus for carrying out the method of any of the preceding claims, comprising: a high pressure fluid source;

fluid jetting arrangement connected to the high pressure fluid source by a flexible hose and configured to direct at least one high pressure jet of fluid to rotate about first and second non-parallel axes, when driven by the high pressure water source.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described with reference to the accompanying drawings, in which:

Figure 1 shows a schematic representation of a biomass boiler to which the method of the invention can be applied;

Figure 2 shows a schematic representation of a system suitable for carrying out methods of the invention;

Figure 3 shows a fluid jetting arrangement suitable for use in methods of the 20 invention; and

Figure 4 illustrates a layout of opening relative to pipework of the boiler of Figure 1 in its upper surface.

DETAILED DESCRIPTION OF EMBODIMENT(S)

Figure 1 shows a schematic representation of a cross-section through a biomass boiler used in a utility scale power generation plant. Utility scale in the present context is regarded as power generation in the Mega-Watt range (i.e. over one Mega-watt / MW), usually in excess of at least 4 Mega-watts (MW), and generally for power distribution over national distribution networks to power either a large facility such as a factory, or a large residential or domestic community. In some contexts utility scale can also be defined as over 10MW or over 20MW or 25MW and the skilled person working on utility-scale power generation facilities will be familiar with these definitions of utility-scale power. An industrial utility scale boiler is generally part of a power plant connected to deliver electrical energy directly to a distribution network such as the national grid, and is not generally connected, for example, directly to a domestic property or a single commercial or industrial site. Where a power generation facility is configured to output electrical power at a particular capacity, conversion efficiency of stages after the boiler, such as a turbine and its connected generator, may need to be taken into account and the skilled person in this area will be familiar with the usual levels of efficiency of conversion in such stages. For example a 10MW output plant may require a boiler configured to convert 16MW of heat output, to account for conversion losses in later stages. A utility scale boiler will therefore usually be configured to output at least the above figures, or more, in heat energy.

The boiler of Figure 1 comprises a boiler enclosure 110. In the enclosure 110, fuel is burnt to create a heat source in a combustion area 120. The combustion is fuelled by a fuel such as biomass material, which is provided to the combustion area 120 via one or more inlets 121 to 129, for example. The construction of such boilers will be familiar to the person skilled in the art of power station boilers and their construction and maintenance. Therefore, these details of the boiler are not described here in great detail, since the operation of the boiler is not critical to the invention. As a skilled person will be aware, a number of routes are provided within the boiler for water to pass around and above the combustion zone 120, in order to heat water passing through the pathways. For example, one or more flow paths 101, 102, 103, 104, 105 may be provided to allow water to be circulated around combustion zone 120. In certain types of boiler, further routes for water and/or steam to be returned to the boiler can be provided in the form of a platen superheater 130, a final super heat stage

131 and a final reheat stage 132. In a further zone 140, commonly referred to as the rear pass, further pipe systems may be provided in the form of a primary super heater 141 and/or a primary reheater 142. These components will be provided with different fluid connections in the form of pipework (not shown in the interests of clarity of the illustration) to deliver fluid flows through and around these fluid paths and in and out of the boiler to surrounding connected equipment such as tanks, pressure vessels and to power conversion means such as a turbine connected to a rotary generator, for converting the heat generated in the boiler to electricity and/or to a heat distribution system for distributing heat to locally placed facilities. As will be appreciated, as combustion occurs, combustion gases and/or exhaust gases are present in all areas of the enclosure around these platens and general heat exchange units 130132 and 141/142, and their connected pipework in the enclosure 110. The pipework providing these fluid paths is generally suspended from some form of upper surface 150 in the form of a cover or roof of the boiler, which surface is generally closed during operation to retain heat within the boiler enclosure 110.

In utility scale power plants, the scale of the arrangements of the kind illustrated in Figure 1 is as follows. A height H of the overall arrangement may be in the region of 60 metres or more. The length LI of the platen superheater may be in the order of 20 metres, plus or minus 5 to 10 metres. The height of the final superheater 131 may be of the order of 2/3 to 4/5 of that height LI of the platen superheater, and the height of the final reheater 132 may be in the region of, 4/10 to 6/10 of the height of the platen superheater 130. This gives an illustration of the scale of the boilers and the extent of the work required to clean internal surfaces of such a boiler. Manual cleaning of such enclosures is clearly a long and labour-intensive operation.

As has been described above, conventional methods of cleaning the internal surfaces of these boilers, to remove deposits formed on the internal surfaces during operation of the boiler, has been to have manual access to the interior region 110 of the boiler by human operatives. The human operatives have traditionally been either suspended in the enclosure 110 on ropes and/or scaffolding constructions. The work of cleaning the internal surfaces would then require manual removal by knocking the deposits off with hammers or other tools. Further, human entry into the boiler creates a risk related with working at height and the risk of falling debris posing a risk to the human operatives inside the boiler enclosure 110.

Persons skilled in the cleaning of utility scale boilers such as that illustrated in Figure 1 have therefore to date only been generally skilled in human access-based methods of cleaning, with their main skill set residing in providing human access to the internal enclosure 110 of the boiler using the ropes and scaffolding-based methods described above.

In devising the novel method of cleaning internal surfaces of the boiler 100 described herein, the inventors have realised the benefits of alternative cleaning methods by working against a prejudice, in utility-scale boiler maintenance, towards human access to the interior spaces. In recent years, many previously coal-fired boilers of the kind illustrated in Figure 1 have been converted for use with biomass fuels. The maintenance methods used by the persons skilled in this area have therefore generally been suited to such coal-fired power stations. Such power stations required relatively little and irregular cleaning, since the firing of coal created relatively few deposits within the boiler enclosure 110 when compared to biomass fuel. Shut downs for cleaning occurred on a relatively infrequent cycle, for example, perhaps every few years, leaving cleaning intervals of perhaps three to five years. Therefore, shutting down the boiler for an extended period of time to allow human access and manual cleaning of the interior surfaces, although expensive in terms of shut down costs and manual labour, was spread over several years of otherwise relatively continuous operation and so did not represent an excessive maintenance cost.

However, the inventors have realised that a new problem arises with the conversion of such boilers to biomass fuel, due to the greater degree of deposits being created. Although biomass fuels are considered cleaner for the environment when burnt, the practical implication has been found to be that greater material build up is found in the internal spaces and surfaces of boilers such as boiler 100. Cleaning of the boilers must therefore be carried out more frequently. A common frequency of cleaning may now be as regularly as once or more per year for biomass boilers. With such regular service intervals, the costs to the operator of the power generation plant becomes very significant. Regular shutdowns result in a cost in lost revenues, and the intense manual labour required, incurred or a more regular basis becomes a more significant maintenance cost. Further, it is now even more critical that cleaning is more comprehensive, to maximise the time before further cleaning is required.

For these reasons, the inventors have sought a different approach to the cleaning of utility scale biomass fuelled boilers of the kind illustrated in Figure 1.

A system suitable for implementing the new method is illustrated in Figure 2.

The system 200 and the related method is primarily based upon using a pressurised jet of water to clean the internal surfaces of the boiler. However, the particular configuration of the system and its method of use allows near-zero human entry into the boiler enclosure 110 to be necessary. The method is enabled by a fluid jetting arrangement which may include a fluid jetting head 300.

The fluid jetting head 300 will be described in greater detail in relation to Figure 3.

The system 200 comprises a pressurised fluid source 204. This may include, for example, a prime mover 201, such as a combustion engine, turbine, electric motor, or other source of motive power. The prime mover 201 may be connected by a shaft 202 to a high pressure water pump 203.

High pressure in the present context is intended to signify that the operating pressures of the fluid delivered are in excess of around 250 bar. However, preferred operating pressures are over 500 bar, preferably over 800 bar, and more preferably in the region of 1000 bar, or more broadly lx 10³ bar. Further, preferred flow rates deliverable by the pressurised fluid source are in the region of around 60 to 800 litres per minute, depending upon the application. More preferred flow rates are in the region of 100 to 300 litres per minute, more preferably over 200 litres per minute, and even more preferably over around 250 or 2.5 x 10² litres per minute.

To locate the fluid jetting head 300 in an appropriate position within the boiler enclosure 110, the fluid jetting head 300 can be suspended in the enclosure 110 from a point above the enclosure 110. In preferred examples of the methods of the invention, the fluid jetting head 300 is suspended on a length of hose 210 through an opening

401 in an upper surface 150 of the boiler enclosure 110. However, the jetting head may comprise an attachment point 301 which allows it to be suspended by alternative means. The opening or openings 401 need not necessarily be provided in the upper surface 150 of the boiler 100. For example, the jetting head 300 could alternatively be suspended after entry via a side opening or bottom opening in the enclosure 110, either via hose 210 or by its attachment point 301 or some other suspension means.

The jetting head 300 is suspended in such a manner that it may rotate about one or more axes, as will be described in more detail in relation to Figure 3.

In doing so, the jetting head 300 delivers one or more jets 330 and 340 of pressurised fluid, preferably water, from jetting nozzle 321 and 322. With sufficient power and flow rate in or around the ranges and values described above, this water jetting can clean a consistent and large amount of, and preferably substantially all, deposits from the internal surfaces of the boiler 100 in the vicinity, or in line of sight, of the jetting head 300.

In such a large boiler as the utility scale power plant boiler 100 shown in Figure 1, it can be advantageous to allow the jetting head 300 to clean the internal surfaces in a plurality of different locations in the interior of the boiler. The jetting head 300 may be suspended at a plurality of different heights and allowed to operate in static position for a chosen duration of time, before being moved to a different height, and/or being suspended at a different horizontal location in the boiler. Schemes for carrying out such changes in location of the jetting head 300 with in the boiler will be discussed further in relation to Figure 4.

As will be appreciated when considering the present disclosure, a roll of hose 211 can be used to wind the hose 210 in and out to adjust a height of the jetting head 300 when suspended in the boiler enclosure 110.

Figure 3 shows the jetting head 300 in greater detail. The jetting head 300 has a main body 310 and a rotatable turret 320. The body 310 comprises an inlet port 311. The inlet port 311 is configured for attaching the inlet hose 210, which is attached to the system 200 illustrated in Figure 2 to deliver pressurised fluid to the head 300. The inlet port 311 is configured to be rotatable relative to the body 310 whilst high pressure fluid is being delivered via hose 210. The high pressure fluid is delivered via the body 310 to the rotatable turret 320. From there it is delivered to the one or more nozzles 321 and/or 322 to deliver a jet of high pressure fluid from the one or more nozzles 321/322. More nozzles may be provided, for example, 3, 4, 5, or up to around 10 if necessary, but two is normally sufficient and preferred in most implementations. The nozzles are preferably arranged in opposing pairs so that no net force on the head is created by the thrust coming from the jets emanating from the nozzles - being opposed, or arranged at equal angular intervals around the turret, the lateral thrust forces of the nozzles forces cancel out. In the preferred mode of operation, the head 300 is configured such that the jets provided from the one or more nozzles 321/322 are rotated about at least one, and preferably two, axes, X, Y, which are preferably non-parallel axes. In the preferred illustrated example, axis X and axis Y are substantially perpendicular to one another. The turret 320 is driven in rotation about axis Y in operation. This rotation may be provided by the rotational force generated by the offset of the jetting axes of either or both of the nozzles 321/322 relative to the centre of rotation 323 of the turret 320 about axis Y. In this manner, the reactive force generated by the jets of fluid exiting the nozzle or nozzles 321/322 can provide rotational power to rotate the turret 320 about axis Y. The head 300 may be provided with internal gearing to provide that the rotation of the turret 320 is mechanically linked to the rotation of the body 310 about axis X. In this manner, in operation, the turret 320 can rotate about axis Y, while the body 310 rotates the turret 320 (and thus the axis of rotation of the turret 320, Y) about axis X. Axes X and Y are preferably substantially perpendicular. A suitable gearing ratio and a suitable length of time of operation, can therefore provide that substantially all areas of a theoretical sphere surrounding the head 300 are covered by fluid being jetted from the nozzles 321/322 of the head 300. Therefore, all surfaces in the vicinity and in line-of-sight of the jetting head 300 can be covered by the pressurised fluid jet or jets delivered by the head 300. As illustrated, rotation of the turret 320 may be in the direction of arrow 324, while rotation of the body 310 may be in the direction of arrow 315, or in the opposite respective directions in any combination.

As described in relation to Figure 2, an attachment portion 301 may be provided. In the illustrated example, this is provided in the form of a hoop or ring 301. This is connected to a mounting portion 302, which may also be configured to rotate synchronously with the turret 320 as the inlet port 311 can be. In this way, if the body 310 is mounted or hung via the engagement portion 301, then the rotation of the body 310 around axis X can be maintained regardless of whether the head is mounted by the engagement portion 301 or the hose 210, or both.

Returning to Figure 3, a tether 360 may be provided to tether the head 300 to the hose 210. This prevents the head 300 from being lost or causing damage when falling inside the boiler 100, in the unlikely event that it should accidentally become detached from the hose via its inlet port 311. This improves safety of the system and reduces downtime resulting from any malfunction of that hose connection.

In carrying out the novel methods described herein, it will therefore be appreciated that the head 300 can be suspended at a plurality of different locations within the boiler enclosure 110 of Figure 1, in order to provide cleaning of substantially all internal surfaces of the boiler via the jets 330 and 340. The inventors have found that by locating the jetting head 300 at carefully chosen locations in the boiler enclosure 110, a more comprehensive cleaning operation can be carried out. The high pressure water jets can provide a substantially uniform level of cleaning to the internal surfaces, and can do so with almost zero requirement for human entry into the boiler enclosure 110. By providing a line-of-sight path from the head 300 to all surfaces to be cleaned in the boiler at predetermined points in the cleaning procedure, even and sufficient cleaning of all relevant surfaces can be achieved. The method can therefore include determining an array of points in the boiler at which the head can be suspended to have a line-of-site path to the surfaces to be cleaned. The head is preferably left in each of the predetermined locations until a predetermined time or until such time as the surfaces in line of sight of the head in that area are sufficiently clean. This can be done without human interaction with the system, and so labour costs are vastly reduced during the cleaning operation. Once each area is sufficiently cleaned, then the height and/or lateral location of the head can be changed to clean a new part of the boiler, such as those parts which are not in line of sight of the first location, or otherwise out of reach of the fluid jets.

The system 200 may be provided on a vehicle which carried all elements of the system for ease of deployment at the location of the boiler 100.

Figure 4 illustrates a schematic view of a top section of a boiler such as that illustrated in Figure 1. As will be appreciated, the arrangements of various pipes in the boiler of

Figure 1 is three dimensional and so several rows of the items such as the final superheater 131 and the final reheater 132 may be located in front and behind one another as seen in Figure 1. When viewed from above, in schematic form, the first pair of fluid conduits 410a and 410b may represent the first final reheater 132 of Figure 1, passing through the upper surface 150 of the boiler 100. Further, final reheater fluid conduits 411a and 411Bb 412a and 412b, and 413a and 413b may also be provided.

Further pairs of fluid conduits for, for example, the primary superheater 141 may also be provided as illustrated by flow openings 420a and 420b to 427a and 427b.

In order to enable proper access of the jetting head 300 to all necessary parts of the 15 pipework in the chamber 110, it may be necessary to provide one or more arrays of openings in the form of some or all of the openings illustrated in Figure 4. For example, when considering platen superheater 410a and 410b, it may be desirable to provide access for the jetting head 300 at a plurality of locations around the platen superheater 410. For example, one or more cleaning locations 430a to 434a may be provided at locations substantially between axes of the conduits 410a, 410b forming the superheater platen or platens. A second cleaning location, or array of cleaning locations 430b to 434b may be provided to a first lateral side of the platen superheater. A further opening 430c, or array of openings 430c to 434c may also be provided at an opposite side to openings 430b to 434b. In this manner, as can be seen, the different arrays can allow substantially all surfaces of the platens 410a, 410b to 413a, 413b to be cleaned by the jetting head 300 when it is suspended through any of those openings.

Similar corresponding arrays of openings can be seen provided around the primary superheater conduits 420a and 420b, to 427a and 427b.

As can therefore be seen in Figure 4, where an array of fluid conduits is provided in the internal space 110 of the boiler 100, one or more corresponding arrays of openings may be provided to permit access of the cleaning head 300 around the internal pipework of the boiler. For example, where an array of conduits extends in an X direction, a corresponding array of openings extending in the same X direction may be provided, and may be offset from the fluid conduits in a Y direction perpendicular to the X direction. Similarly, one or more arrays of conduits may extend in a Y direction, and one or more arrays of openings may be provided offset in teh X direction from the array extending in the Y direction, so as to allow cleaning access to all sides of the array of fluid conduits in the boiler. The method may comprise sequentially passing the jetting head 300 through one or more or each of the openings and supporting the head 300 at a range of different heights in the boiler through one or more of, or through each of, the openings. This can allow the full height of the boiler and its internal fluid conduits or pipes to be cleaned from all angles. Therefore fluid jetting head 300 may be inserted through one or more of the openings, sequentially, one after the other. Further, the head 300 may be suspended at a first height in the boiler for a first time duration, may then be moved to a second height within the boiler and operated for a second time duration and may be further operated at third or further heights in the boiler to clean a sufficient amount of the surfaces in the boiler. This may be repeated through one or more of any of the arrays of openings illustrated in, for example, Figure 4. The intervention of a human operative can be entirely carried out from outside of the boiler and is only necessary to move the head 300 from one location to another. During the cleaning and rotations of the jets 330/340 by the head in situ, the operative can be attending to movement of another head at a different location, for example, making efficient use of human effort. The openings provided in the boiler may therefore be smaller than is required to allow passage of a human operative, which can further improve safety of the methods. The openings are preferably large enough to allow the jetting arrangement to pass through, so that separate human intervention is not required to attach the jetting arrangement to the hose inside the boiler enclosure 110.

As will be appreciated, the benefits of the novel cleaning method described herein are that the need for human access into the boiler is vastly reduced or eliminated, reducing risks to human operatives and also reducing the labour costs of the overall cleaning operation. Further, the use of the system and methods described herein has been found to reduce the overall shutdown time required for a full cleaning operation. This reduces the downtime of the power generation plant which is run from the boiler 100 and so reduces the impact of the increased amount of cleaning which is required in biomass fired boilers as compared to their previous use in coal fired power generation.

Although the invention has been described above with reference to one or more preferred embodiments, it will be appreciated that various changes or modifications may be made without departing from the scope of the invention as defined in the appended claims.

Claims

Claims

1. A method of cleaning interior surfaces of an industrial utility scale boiler configured for the conversion of combustible fuel into heat energy, the method comprising the steps of:

5 providing a high pressure fluid source;

providing a fluid jetting arrangement connected to the high pressure fluid source and configured to direct at least one high pressure jet of fluid to rotate about first and second non-parallel axes, when driven by the high pressure water source;

10 providing the fluid jetting arrangement to the interior of the boiler though a first one of one or more openings provided in the boiler;

activating the high pressure water source to drive the jetting arrangement while the jetting arrangement is suspended inside the boiler via the first opening, to clean internal surfaces of the boiler with the at least one

15 high pressure j et of fluid.
2. A method according to claim 1, further comprising providing the jetting arrangement to the interior of the boiler though a second opening of the one or more openings; and activating the high pressure water source to drive the fluid jetting 20 arrangement while the fluid jetting arrangement is suspended inside the boiler via the second opening, to clean further internal surfaces of the boiler with the at least one high pressure jet of fluid.
3. A method according to claim 1 or claim 2, wherein the openings are provided in a top surface of the boiler and wherein the fluid jetting arrangement is

25 suspended in position inside the boiler from the top surface during the cleaning.
4. A method according to any of claims 1 to 3, wherein at least one of the openings is configured to allow the passage of the fluid jetting arrangement, but to prevent passage of an average sized adult human through the opening.
5. A method according to claim 4, wherein at least a majority of the openings are configured to allow the passage of the fluid jetting arrangement, but to prevent passage of an average sized adult through the opening.
6. A method according to claim 5, wherein one or more of the openings

5 configured to prevent the passage of an average human adult has a greatest diametric dimension of between around 10cm and 50cm.
7. A method according to any preceding claim, wherein the high pressure fluid source is configured to deliver a flow of water at over 2 x 10² litres per minute, preferably over 2.5 x 10² litres per minute.

10
8. A method according to any preceding claim, wherein the high pressure fluid source is configured to deliver a flow of water at over 8 x 10² bar operating pressure, preferably around 1 x 10³ bar operating pressure.
9. A method according to any preceding claim, wherein the jetted fluid is a liquid, preferably water.

15 10. A method according to any preceding claim, wherein the j etting arrangement is a jetting head comprising a body and a rotatable turret carrying one or more nozzles configured to direct the at least one high pressure jet of fluid to rotate, relative to an attachment point of the body, about first and second non-parallel axes, when driven by the high pressure water source.

20 11. A method according to any preceding claim, wherein the jetting arrangement is suspended inside the boiler and left in a first location for a predetermined time without human intervention.

12. A method according to claim 11, wherein the jetting arrangement is:

suspended and activated with the high pressure fluid source for a

25 predetermined time at a first height in the boiler;

is de-activated;

is moved to a second height in the boiler; and is then reactivated and left in the second location at the second height while being activated with the high pressure fluid source to clean further internal surfaces of the boiler.

13. A method according to claim 11 or claim 12, wherein the steps of claim 11 or

5 claim 12 are repeated after removing the jetting arrangement from the boiler and re-inserting the jetting arrangement through a further opening in the boiler.

14. A method according to claim 13, wherein the steps of claim 11 and/or claim 12 and repeated for each of a plurality of openings, the openings being arranged in an array corresponding to a plurality of fluid conduits of the boiler to be
10 cleaned.
15. A method according to any preceding claim, wherein the jetting arrangement is attached to a hose for delivering the high pressure fluid via a first fluid connection, and via a secondary tether, to retain the jetting arrangement attached to the hose in the event of failure of the first fluid connection.

15
16. A method according to any of the preceding claims, wherein the boiler is a biomass boiler adapted to burn biomass fuel to generate heat energy.
17. A method according to any of the preceding claims, wherein the boiler is sized and configured for an energy output capacity of around 4MW, preferably 10MW, more preferably 25MW or more.

20
18. A method according to any of the preceding claims, wherein the internal surfaces cleaned by the method include external surfaces of fluid conduits passing through the internal space of the boiler.
19. An apparatus for carrying out the method of any of the preceding claims, comprising:

25 a high pressure fluid source;

fluid jetting arrangement connected to the high pressure fluid source by a flexible hose and configured to direct at least one high pressure jet of fluid to rotate about first and second non-parallel axes, when driven by the high pressure water source.

Intellectual

Property

Office

Application No: GB1700405.2 Examiner: Mr Colin Walker