GB2480750A - Apparatus for cleaning or injecting an additive into a boiler - Google Patents

Abstract

A cleaning apparatus, for cleaning a boiler component in a boiler 18, comprises at least one rotatable shaft 34 with a spray head 40 mounted on it. The shaft is mounted in the boiler along, or substantially adjacent, a longitudinal axis of the boiler from a proximal to a distal end of the boiler. The shaft projects beyond a tube end plate 32a of the boiler at the distal end of the boiler. The spray head is mounted on the shaft at the distal end and is arranged to face the tube end plate. Cleaning fluid is conveyed through the boiler, within or alongside the shaft, and the cleaning fluid is directed onto the boiler tube end plate by the spray head. Preferably, the cleaning fluid comprises heated water and/or steam. At least one motor 38 may be provided for driving the motion of the shaft. In a further aspect, apparatus for injecting an additive into a hot gas stream entering a boiler is disclosed.

Description

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$4: çpfl, whacs asZi iIt.itq: 4A çpowa aS cqnbqath,n cn. bs tsnts�itS 2 t *tIiis build u iDt as% .stfttarSng 4dU'JtS fl bOSifl tube Vfl* flatte aM UW�1 4ñifltp1bi flfla spq howns an bt ue: * tjij. M. t1. rnt the $t:*: fl$ *pPZQaó 4n: Jisip W pflVtrit US 5b44:tjp *> tPOMtt tith tolild otknwae. S pet**naance at the bod3t. Ho\.bvf1 bil npy flhfb)ora pust'S a an trca aa waS tWttfbW é. * 4sty 4am th' EL 4Ss make it impossible to oredict or cater fcr every combustion cbs recterist Ic itt s thus inevitable when burning these fuels at. relatively high temperatures in order to comoly with current waste incineratIon direotives/leqislat ion and clean ourning techniques, that foul log ci the suner-heerer and holier can become severe tO such c5ses a steam soot blower might toquire so much steam that the dc; tream. steam turbine mioht ave to be RI tasenoff-flne during a cleaning operattoru v\eLractc.bre water lances and water cannons can be used to consrderable effect in these anpilcations but; these renal to be complicated and extensive. Tvpica liv in order to obtain 15..hsreau.reo angular coverace within the. confin.ea oft he boiler a lance will need to be spaced from the tube end plate by several metres. Thus, in order to obtain the necessary pressure icr blastin the deposits an expensive pumping system must be provided. A further. disadvantage with such an apparatus is that the use cf cold water in the lance orwat cx cannon can lead to thermal shocking of the ococonents to be cleane& which can reduce the effective service lifetime of the components. ?r.other problem is the need t*o control precisely the surfaces, which are exposed to the cleaning blast, since otherwise some areas such as the insu.lation around the boiler, could become daqed it has been observed by the inventors that the majority cf boiler tube fculin first starts with huildup on the boiler tube face. plate around the boiler tubes. This is sometimes referred to as birds nest ing". When the ceposit:s bec:ome sufficient h insulate the boiler face and to allow the nix and salts to remain in a. semi-molten state, the fouling then starts to migrate down the boiler tubes. This process of congealing, insulating and further migration continues until either the boiler becomes unable S to transfer heat effectively, or becomes so blocked that design mass gas flow is no longer possible, or both. So, the inventors haste appreciated that cleaning of the deposits of the boiler tace as they form is the key to keeping a clean and eff±cient boiler. I0

The present invention was made with the above problems in mind.

According to one aspect of the present invention there is IS provided cleaning apparatus for cleaning a boiler component in a boiler, the apparatus comprising at least one rotatable shaft and a spray head mounted thereon, the at least one shaft being mounted in the boiler along or substantially adjacent a longitudinal axLs of the boiler from a proximal end of the boiler to a distal end of the boiler, and projecting beyond a tube end plate of the boirer it Said distal end, wherein mounted on the shaft at said distal end is a spray head which is arranged to face the tube end plate, and wherein cleaning fluid is arranged to be conveyed through the boiler within or alongside the shaft, said cleaning fluid being directed onto the boiler tube end plte by the spray head.

Preferably the fluid is arranged to be conveyed within the rotatable shaft. Alternatinty the fluid may be conveyed through a separate conduit, The fluid may comprise water and is preferably heated water and/or steam In a particularly preferred arrengemeitt the fluid is supplied in phases with at least one phase cowprising steam only and another phase comprising water. The steam may be supplied at different pSssures..

S

tn a preferred arrangement the rotation of the rotatable shaft is arranged to oscillate So as to allow the spray head to cover a substantially circular or semicircular area of the boiler tube end plate during each cycle.

Alternatively, the rotation of the shaft may be substantIally continuous during operation, and may rotate through substantially 360 degrees.

There may be two, three, four Or more spray heads arranged to rotate 360 degrees or a fraction thereof. In one arrangement there may be N spray heads, each of which covers 360/N degrees of rotation. There are preferably as many shafts as spray heads.

In a preferred arrangement here are two shafts and two heads, each shaft beinG arranged to oscillate through substantially 120' so as to allow the respective spray heads to cover areas which are substantially semicircular.

Single or multiple spray heads could be used, depending upon the configuration.

In a preferred arrangement hot water is supplied as the cleaning fluid from a hot well of water itself supplied from a condenser of a steam turbine.

The or each sptay head preferably comprises a plurality of nottles which may be arranged substantially in a Line.

The or each spray head preferably comprises a heat shield arranged to protect the nozzles trait exposure to hostile gases being supplied to the boiler.

The or each spray head itay comprise a bow-shaped or iOO shaped pipe through which cleaning fluid is arranged to pass.

In a preferred arrangement at least one motor is provided for driving the motion of the or each shaft. The or each motor is preferably located at the proximal end of the boiler.

The invention also includes a method or cleaning a boiler component in a boiler, the method comprising supplying cleaning fluid from a first. pro*imal end of a boiler through the boiler along or substantially adjacent a longitudinal axis of the boiler to at least one spray head located at a second, distal end of the boiler and mounted on a rotatable shaft, directing the cleaning fluid onto the boiler cothponent through the at least OFtS spray head and 2$ rotating the shaft.

Preferably the supply of cleaning fluid to the spray head is through the at least one shaft or through a separate coadgit adjacent the or each shaft.

The fluid may comprise water end is preferably heated water and/or steam. In a particularly prefecred arrangement the fluid i supplied in phases with at least one phase comprising steam only and another phase comprising water.

The steam may be supptisd at different pressures.

S in a preferred arrangement the method comprises turning the shaft at the first, proximal end, so that the or each spray head located at the second, distal end moves in either a substantially continuous rotation or an oscillatory motion to cover a substantially circular or substantially semicircular area.

The method may comprise a method of cleaning a boiler tube end plate.

IS The invention also includes apparatus foe injecting an additive into a hot gas strewn entering a boiler, the apparatus comprising: at least one rotatable shaft and a spray head mounted therêon, the at least one shaft being mounted in the boiler aLong or substantially adjacent a longitudinal axis of the boiler front a proximal end of the boiler to a distal end of the boiler, and projecting beyond a tube end plate of the boiler at said distal end, wherein mounted on the shaft at said distal end is a spray head which is arranged to face the tube end plate, and wherein an additive is Srranged to be conveyed through the boiler within or alongside the shaft, said additive being introduced in the region of the boiler tube end plate by the spray heads The additive may compx tee urea a The invention also includes a m*thod for injecting an additive into a hot gas flow entering a boiler, the method comprising: supplying an additive from a first, proximal end of a boiler through the boiler along or substantially adjacent a lo'tgitudinal axis of the boiler to at least one *prey head located at a second, distal end of the baLlet and mounted on a rotatable shaft, introducing the additive through the at least one spray head and rotating the shaft. I0

The method may comprise a method of injecting urea.

A preferred embodiment Sn the present invention will now be described by way of exaple only with reference to the IS accompanying diaqranwtatic drawings, in which: Figure 1 is a schematic representation of a heat and power generation plant incorporating a boiler cleaning apparatus of the present invention, Figure 2 shows schematically a boiler cleaning apparatus according to an embodiment of the present invention, Figure 3 shows in part sect ionel view a portion of the boiler cleaning apparatus of Figure 3, Figure 4 shows the boiler cleaning apparatus of Figures 2 and 3 in another view, Figure $ shows a further sectional view of part of the apparatas of Figures 2-4, Figure 6 shows an alternative embodiment of spray head, and Figure 7 is a further flew of the spray head of Figiate 6.

$ Turning to Figure 1, this sh'nts in schematic form a heat and power generation plant comprising a walking floor fuel feed area 10, a fuel teed hopper 12, two thermal treatment units in the form of combustors 14a and 14b, residence chambers 16a and 1Gb, a steam boiler 16, a turbine gstserator 20, g condenser 22, a cooling unit 24, a tiltek 26 and a stack 28 There follows a brief description of the operation of the heat and power plant schematically represented in Figure l 1$ Fuel, which may be in the form of waste, wood or refuse for example, is presented t* the walking floor 10 where iS is conveyed and tranflerred to the feed hopper 12. The feed hopper 12 feeds the fuel into two parallel thermal treatment units 14a and 14b where combustion of the fuel takes place Hot combustion gases exiting the thermal treatment units 14a and 14b are oxidised in thambers lEa and 1Gb respectively before being directed to the steam boiler 13. In the boiler 38, the hot gases are used to heat water to produce stnm which then passes through the turbine which turns the gerterator 20 to produce electrical power which may be output at 20a for example to the national grid. The condenser 22 condenses the steam passing through tim turbine back into water and this is then recycled to the boiler through line 22*, de-aerator "hot well" 22b and feed water pumps 22c. Low grade "waste" heat is available for the cooling unit 24 if a suitable use tan be found in close proximity to the site. Meanwhile the flue gases leaving the boiler IS pass through two CUters at 26 to remove particulates and unwanted emissions, prior to being released to the atmosphere $ through the stack 28, where the emissions are continuously monitored.

Figure 2 shows schen,aticafly a portIon of the boiler 18.

The boiler 18 comprises a generally cyLindricaL body 30 for containing water to be heated. Within the body 30 are a plurality of hollo4i tire tubes 32 through which super-heated combustion gases are arranged to pass. The tubes ace held at thsir distal and proximal ends by tube end plates respectively 32a and 32b. When the hot gas has IS passed through the tire tubes 32 the water surrounding the tube becomes heated by conduction so as to generate steam for the turbine. The gases enter the tubes 32 from a super-heater chamber 34 in the direction of arrow A and impinge upon the tube 32 and the tube end plate 32a. After passing through the tube the gases are exhausted to the filter 26 in the direction of arrows S and ultimately to the stack 28.

A pair of rotatable shafts 34 (only one of which can be seen in Figure 2) are located in generally central Lire tubes 32 and pass from the exhaust end to the inlet end.

At the exhaust end the shatt 34 are mounted on bearings 36 on an exterior wall at the boiler where motors 38 axe arranged to rotate the shafts 34 in an oscillatory fashion back and forth through substantially 180 each. At end 34b of the shaft the shaft is coupled to a supply of hot water from a hot well reservoir 22b supplied independently from the condenser 22. At the inlet end 34a of the shaft a spray head 40 is mounted on each shaft so as to direct water (or steam or a combination thereof) supplied through the roeflaifle shalt 34 onto the tube eoi plate 32. via a plurality of nozzles (described in more detail below).

Between the pair of spray heads 40 they cover approxtmateiy the entire circular surface of the tube end plates 32a in their respective oscillatory motions. As an alternative the tO spray heads, or single spray head, may rotate substantially continuously through 360 degrees.

Figure 3 is a part'sectional view of the inlet end of the boiler IS showIng the ends of the tubes 32 and the tube end plate 32a Both of the rotatable shafts 34 end sp'ay heads can be seen.

flgure 4 shows the spr*y heads 40, each of which has a plurality of nozzles 40a which are arranged to direct a closely Zocusse,d spray onto the surface of the tube end plate.

Figure 5 shows in more detail, one of the spray heads 40 with spray nozzles 40a.

Heat shieLd 42 in the form of V-sectto plate, extends over all of the nozzles to protect them from the super-heated combustion gases which may contain particulates that would ot!teni clog the nozzles.

The most effecftivs water jet angle has been found to be approximately 900 to the boiler face and at relatively close rancrc Omo-lOOmm) to reduce the necessity for extreme water let pressures and high volumes which would otherwise be recuired to maintain effective cleanin if distances were significantly teaser.

Conventional austere are unable to achi eve this The number of lances reguired would not be practical and such a system would be costly and diffIcult to operate. Water c»=annons can achieve a required water angle but: only.f±om a greater distance. and because of this they require very high water pressures and precise tracking systems zn order to ensdre complete ccveraqe P. oreferreo arrangement is to supply sorre steam to the spray head substantially continuously at. a first low level., or pressure, and to rntroduoe. increased steam ie at an increased le vele or pressure, and/or water peniodically Fiures $ and 7 show an alternative embodiment of spray head, generally at SO.

Foray head SO comorises a cenerally hew-shaped or loon--shaped hollow pipe Olç comprising a distal limb Ole and a proxrmal. Limb SIb fluictica liv connected so that cleaning fluid from the shaft 34 enters the: distal limb SIc ano' then flows into the oroximal limb 52b before being expelled throuqh nozzles ihtot shown) which direct the fluid onto the tube end plate SIc, The spray head SO preferably operates as a single head, rotating substantially ocmtinuousiy through 360 degrees, this configuration allows the water and/or steam from the shaft 34 to cool the spray head as it flows around the limbs SZa and 52b. Furthermore, the bow-shape has greater resistance to bending which might otherwise be caused by S the extreme heat in the gas flow.

Accotdingly the present invention is able to deliver a water/steam spray precisely as required to a boiler Lace with many hundreds of boiler tubes, without compromising tO angle or water pressurt, at low cost and wsth relative simplicity.

tn fact in many cases it is envisaged that the existing boiler teed water pumps already fitted to a plant Will be IS adequate to deliver the required water pressure, volume, temperature and water quality1 As well as providing a vest effective and efficient cleaning apparatus, the Ipparatus and method described above can also be issed to introduce urea into the flow of combustion gases. The introduction of urea in solution can help to reduce the pressute of NoX emissions in the flue gases and in the apparatus and method described above urea solution can replace or mix with cleaning fluid to achieve 2$ this additional function.

Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance, it should be understood that the applicant claims protection in respect of any patentable feature or combination of features referred to herein, scwn *n the c1.r':w:) whether cr rct particular emphasis has been placed therecn