WO2011144946A1 - Boiler cleaning apparatus and method - Google Patents

Abstract

Cleaning apparatus for boiler tube end plates in a fire- tube boiler comprises a pair of rotatable shafts (34) located in generally; central fire tubes (32), The shafts pass from the exhaust end to the inlet end, At the exhaust end the shafts (34) are mounted on bearings (36) on an exterior wail of the boiler where motors (38) are arranged to rotate the shafts (34) in an oscillatory fashion back and forth through substantially 180° each. At end (34fc) 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 rotatable shaft (34) onto the tube end plate (32a) via a plurality of nozzles. Between the pair of spray heads (40) they cover approximately the entire circular surface of the tube end plates (32a) in their respective oscillatory motions.- As an alternative the spray heads, or a single spray head, may rotate substantially continuously through 360 degrees.

Description

Boiler cleaning apparatus and method

The present invention relates to a boiler cleaning apparatus and a method of cleaning a boiler and is particularly concerned with a cleaning apparatus and method for cleaning a tube end-plate in a fire tube boiler.

Fire tube boilers typically comprise a generally cylindrical body for holding water to be heated, within which are arranged a plurality of parallel fire tubes through which hot combustion gases are made to pass so as to heat the surrounding water. Water thus heated may then be used as steam to drive a turbine which can then drive a generator for generating electricity.

The fire tubes are held at their ends by tube end-plates. Hot gases from a combustion device are introduced into the tubes at a first end and exit the tube at a second end where they are exhausted, usually via a filter.

Keeping such a boiler clean can be a challenge. When oil or gas is the combustion fuel the problem is minimal. For uniform solid fuels such as coal, where ash melting characteristics are known and combustion can be controlled to minimise the build up of ash sintering products on boiler tube end plates and tubes, conventional steam soot blowers can be used effectively to clean the surfaces of the components. This approach can help to prevent the build up of deposits which could otherwise impair the performance of the boiler. However, on very stubborn deposits as are found with fuels derived from waste wood and refuse the sheer variety of products in the fuel mix make it impossible to predict, or cater for, every combustion characteristic. It is thus inevitable when burning these fuels at relatively high temperatures in order to comply with current waste incineration directives/legislation and clean burning techniques, that fouling of the super-heater and boiler can become severe.

In such cases a steam soot blower might require so much steam that the downstream steam turbine might have to be taken off-line during a cleaning operation.

Retractable water lances and water cannons can be used to considerable effect in these applications but these tend to be complicated and expensive. Typically in order to obtain the required angular coverage within the confines of the boiler a lance will need to be spaced from the tube end plate by several metres. Thus, in order to obtain the necessary pressure for blasting the deposits an expensive pumping system must be provided. A further disadvantage with such an apparatus is that the use of cold water in the lance or water cannon can lead to thermal shocking of the components to be cleaned, which can reduce the effective service lifetime of the components. Another problem is the need to control precisely the surfaces which are exposed to the cleaning blast, since otherwise some areas, such as the insulation around the boiler, could become damaged.

It has been observed by the inventors that the majority of boiler tube fouling first starts with build-up on the boiler tube face plate around the boiler tubes. This is sometimes referred to as "birds nesting". When the deposits become sufficient to insulate the boiler face and to allow the ash and salts to remain in a serai -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 to transfer heat effectively, or becomes so blocked that design mass gas flow is no longer possible, or both. So, the inventors have appreciated that cleaning of the deposits of the boiler face as they form is the key to keeping a clean and efficient boiler.

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

According to one aspect of the present invention there 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 longitudi.nal axis 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 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 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 plate by the spray head.

Preferably the fluid is arranged to be conveyed within the rotatable shaft. Alternatively 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 arrangement the fluid is supplied in phases with at least one phase comprising steam only and another phase comprising water. The steam may be supplied at different pressures.

In 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, ana 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 180° 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 spray head preferably comprises a plurality of nozzles which may be arranged substantially in a line.

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

The or each spray head may comprise a bow-shaped or loop- 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 of cleaning a boiler component in a boiler, the method comprising supplying cleaning fluid from a first, proximal 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 component through the at least one spray head and rotating the shaft.

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

The fluid may comprise water and is preferably heated water and/or steam. In a particularly preferred arrangement the fluid is supplied in phases with at least one phase comprising steam only and another phase comprising water. The steam may be supplied at different pressures. 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. The invention also includes apparatus for injecting an additive into a hot gas stream entering 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 axis 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 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 arranged 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 head. The additive may comprise urea. The invention also includes a method 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 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, introducing the additive through the at least one spray head and rotating the shaft.

The method may comprise a method of injecting urea.

A preferred embodiment in the present invention will now be described by way of example only with reference to the accompanying diagrammatic 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 sectional 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 5 shows a further sectional view of part of the apparatus of Figures 2-4, Figure 6 shows an alternative embodiment of spray head, and

Figure 7 is a further view of the spray head of Figure 6. Turning to Figure 1, this shows in schematic form a heat and power generation plant comprising a walking floor fuel feed area 1C, a fuel feed hopper 12, two thermal treatment units in the form of combustors 14a and 14b, residence chambers 16a and 16b, a steam boiler 16, a turbine generator 20, a condenser 22, a cooling unit 24, a filter 26 and a stack 28.

There follows a brief description of the operation of the heat and power plant schematically represented in Figure 1.

Fuel, which may be in the form of waste, wood or refuse for example, is presented to the walking floor 10 where it is conveyed and transferred 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 chambers 16a and 16b respectively before being directed to the steam boiler 18. In the boiler 18, the hot gases are used to heat water to produce steam which then passes through the turbine which turns the generator 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 the turbine back into water and this is then recycled to the boiler through line 22a, 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 can be found in close proximity to the site. Meanwhile, the flue gases leaving the boiler 18 pass through two filters 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 schematically 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 hollow fire tubes 32 through which superheated combustion gases are arranged to pass. The tubes are held at their distal and proximal ends by tube end plates respectively 32a and 32b. When the hot gas has passed through the fire tubes 32 the water surrounding the tube becomes heated by conduction so as to generate steara 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 B 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 fire tubes 32 and pass from the exhaust end to the inlet end. At the exhaust end the shafts 34 are mounted on bearings 36 on an exterior wall of the boiler where motors 38 are 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 rotatabie shaft 34 onto the tube end plate 32a via a plurality of nozzles (described in more detail below) .

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

Figure 3 is a part-sectional view of the inlet end of the boiler 18 showing the ends of the tubes 32 and the tube end plate 32a. Both of the rotatabie shafts 34 and spray heads 40 can be seen.

Figure 4 shows the spray heads 40, each of which has a plurality of nozzles 40a which are arranged to direct a closely focussed spray onto the surface of the tube end plate .

Figure 5 shows in more detail one of the spray heads 40 with 3pray nozzles 40a.

Heat shield 42 in the form of V-section plate, extends over all of the nozzles to protect them from the super-heated combustion gases which may contain particulates that would otherwise clog the nozzles.

The most effective water jet angle has been found to be approximately 90° to the boiler face and at relatively close range (50mm-100mm} to reduce the necessity for extreme water jet pressures and high volumes which would otherwise be required to maintain effective cleaning if distances were significantly greater.

Conventional systems are unable to achieve this. The number of iances required would not be practical and such a system would be costly and difficult to operate. Water cannons can achieve a required water angle but only from a greater distance and because of this they require very high water pressures and precise tracking systems in order to ensure complete coverage.

A preferred arrangement is to supply some steam to the spray head substantially continuously at a first, low level, or pressure, and to introduce increased steam ie at an increased level, or pressure, and/or water periodically.

Figures 6 and 7 show an alternative embodiment of spray head, generally at 50.

Spray head 50 comprises a generally bow-shaped or loop- shaped hollow pipe 52, comprising a distal limb 52a and a proximal limb 52b fluidically connected so that cleaning fluid from the shaft 34 enters the distal limb 52a and then flows into the proximal limb 52b before being expelled through nozzles (not shown) which direct the fluid onto the tube end plate 32a. The spray head 50 preferably operates as a single head, rotating substan ially continuously 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 52a and 52b. Furthermore, the bow-shape has greater resistance to bending which might otherwise be caused by the extreme heat in the gas flow.

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

In fact in many cases it is envisaged thac the existing boiler feed water pumps already fitted to a plant will be adequate to deliver the required water pressure, volume, temperature and water quality.

As well as providing a cost effective and efficient cleaning apparatus, the apparatus and method described above can also be used to introduce urea into the flow of combustion gases. The introduction of urea in solution can help to reduce the pressure 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 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, and/or shown in the drawings, whether or not particular emphasis has been placed thereon.

Claims

Claims

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 axis 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 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 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 plate by the spray head.

Cleaning apparatus according to Claim 1 wherein the fluid is arranged to be conveyed within the rotatable shaft .

Cleaning apparatus according to Claim 1 wherein the fluid is conveyed through a separate conduit.

Cleaning apparatus according to any of Claims 1 to 3 wherein the fluid comprises heated water and/or steam. Cleaning apparatus according to any of the preceding claims wherein the fluid is supplied in phases with at least one phase comprising steam only and another phase comprising water.

Cleaning apparatus according to any of the preceding claims wherein the rotation of the shaft is substantially continuous during operation. Cleaning apparatus according to any of the preceding claims wherein the spray head comprises a plurality of nozzles arranged substantially in a line. Cleaning apparatus according to any of the preceding claims wherein the or each spray head comprises a bow- shaped or loop-shaped pipe through which cleaning fluid is arranged to pass.

Cleaning apparatus according to any of the preceding claims wherein at least one motor is provided for driving the motion of the shaft.

Cleaning apparatus according to Claim 9 wherein the or each motor is located at the proximal end of the boiler. . A method of cleaning a boiler component in a boiler, the method comprising supplying cleaning fluid from a first, proximal 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 component through the at least one spray head and rotating the shaft.

A method according to Claim 11 wherein the supply of cleaning fluid to the spray head is through the at least one shaft or through a separate conduit adjacent the or each shaft. A method according to Claim 11 or 12 wherein the fluid comprises heated water and/or steam. A method according to any of Claims 11 to 13 wherein the fluid is supplied in phases with at least one phase comprising steam only and another phase comprising water. A method according to any of Claims 11 tc 14 wherein 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. . A method according to any of Claims 11 to 14, the method comprising a method of cleaning a boiler tube end plate. . Apparatus for injecting an additive into a hot gas stream entering 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 substan ially adjacent a longitudinal axis 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 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 arranged 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 head . Apparatus according to Claim 17 wherein the additive comprises urea. A method 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 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, introducing the additive through the at least one spray head and rotating the shaft. A method according to Claim 19, the method comprising a method of injecting urea.