Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F28—HEAT EXCHANGE IN GENERAL
  • F28G—CLEANING OF INTERNAL OR EXTERNAL SURFACES OF HEAT-EXCHANGE OR HEAT-TRANSFER CONDUITS, e.g. WATER TUBES OR BOILERS
  • F28G1/00—Non-rotary, e.g. reciprocated, appliances
  • F28G1/16—Non-rotary, e.g. reciprocated, appliances using jets of fluid for removing debris
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B24—GRINDING; POLISHING
  • B24C—ABRASIVE OR RELATED BLASTING WITH PARTICULATE MATERIAL
  • B24C1/00—Methods for use of abrasive blasting for producing particular effects; Use of auxiliary equipment in connection with such methods
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B24—GRINDING; POLISHING
  • B24C—ABRASIVE OR RELATED BLASTING WITH PARTICULATE MATERIAL
  • B24C11/00—Selection of abrasive materials or additives for abrasive blasts
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23J—REMOVAL OR TREATMENT OF COMBUSTION PRODUCTS OR COMBUSTION RESIDUES; FLUES 
  • F23J3/00—Removing solid residues from passages or chambers beyond the fire, e.g. from flues by soot blowers
  • F23J3/02—Cleaning furnace tubes; Cleaning flues or chimneys
  • F23J3/023—Cleaning furnace tubes; Cleaning flues or chimneys cleaning the fireside of watertubes in boilers
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F28—HEAT EXCHANGE IN GENERAL
  • F28G—CLEANING OF INTERNAL OR EXTERNAL SURFACES OF HEAT-EXCHANGE OR HEAT-TRANSFER CONDUITS, e.g. WATER TUBES OR BOILERS
  • F28G1/00—Non-rotary, e.g. reciprocated, appliances
  • F28G1/12—Fluid-propelled scrapers, bullets, or like solid bodies
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F28—HEAT EXCHANGE IN GENERAL
  • F28G—CLEANING OF INTERNAL OR EXTERNAL SURFACES OF HEAT-EXCHANGE OR HEAT-TRANSFER CONDUITS, e.g. WATER TUBES OR BOILERS
  • F28G1/00—Non-rotary, e.g. reciprocated, appliances
  • F28G1/16—Non-rotary, e.g. reciprocated, appliances using jets of fluid for removing debris
  • F28G1/166—Non-rotary, e.g. reciprocated, appliances using jets of fluid for removing debris from external surfaces of heat exchange conduits
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F22—STEAM GENERATION
  • F22B—METHODS OF STEAM GENERATION; STEAM BOILERS
  • F22B37/00—Component parts or details of steam boilers
  • F22B37/02—Component parts or details of steam boilers applicable to more than one kind or type of steam boiler

Definitions

• the present invention relates to a method according to the preamble of claim 1 of cleaning the heat-transfer surface which is in connection to the masonry structure of a combustion boiler. Such a method is disclosed in DE 197 23 389 .
• the surface is cleaned by blasting solid particles onto it.
• the heat-transfer surfaces of power plants are typically cleaned by using sandblasting.
• sand typically screened sand
• water is used to bind the fines, in order to prevent dusting caused by the sand particles.
• This wet blasting method has proven to be problematic in several respects.
• the masonries absorb moisture.
• the heating phase of the start-up stage is extended because the masonries must be "dried". In such cases, it is quite possible that the masonries will fail.
• Such materials include steel grains and steel sand, copper slag, glass beads, metal pellets, dry ice, corundum and even ground coconut shells and corn grains.
• Patent Application Publication No. 102313288 describes a solution in which heat-transfer surfaces are cleaned using smooth-surface particles.
• the particles described in the publication are metal or non-metal particles or composite particles having a density of 2-8 g/cm 3 .
• JP Patent Application Publication No. 2002098323 describes the use of granulated slag grains to remove, by using blast cleaning, the metal residues which are adhered to the exhaust pipe of an electric furnace.
• the metal is generated when melting, in an electric furnace, the burning residues which are generated from burning of municipal waste.
• alkali metal carbonates provide efficient cleaning of surfaces, without formation of dust or damaging the surfaces.
• Suitable materials mentioned in the publication are in particular natural carbonates, such as calcium carbonate and dolomite. These may be used, for example, to remove paint, foodstuff and drug residues from the inner
• the heat-transfer surface of the combustion boiler is cleaned by blasting onto it, in water-free conditions, metal slag particles having a particle size of approximately 0.3 - 2.5 mm, and by using a blasting pressure of 8-12 bar.
• the present invention also comprises the use of nickel slag particles for cleaning of the heat-transfer surface which is in connection to a masonry structure, by using blasting treatment.
• the method according to the present invention is mainly characterised by what is stated in the preamble of Claim 1.
• the slag particles which represent the waste fraction, and which otherwise cannot be used in any significant application, form an economically and technically advantageous material which, if needed, can be ground and graded in order to achieve a fraction of a desired fineness.
• the nickel slag particles are particularly well suited for the cleaning of steel heat-transfer surfaces, because the nickel slag do not comprise significant amounts of ferrite compounds. This, in turn, means that when cleaning steel surfaces with nickel slag, no corrosion problems appear, which is not the case when blasting with metal slags that comprise ferrite compounds, or when blasting with for example steel particles that also comprise ferrite compounds.
• heat-transfer surfaces of a power plant in dry conditions, are cleaned using a fine fraction of a waste product generated in a metallurgical process.
• the surface to be cleaned comprises sulphur or silicate-bearing compounds which are generated when burning wood or fossil fuels or mixtures thereof, and possibly ash, coke or slag which comprise organic compounds (such as tar-like compounds).
• deposits and similar dirt layers which are generated during the combustion process are removed from the metal surfaces without substantially damaging these.
• the operation is carried out in essentially "water-free conditions".
• water or aqueous solutions are not fed, either together with or separately from the blasted particles, onto the object to be cleaned.
• no water or aqueous solutions at all are fed.
• operating in water-free conditions means that, due to the effect of particle blasting, condensed water does not flow from the surface to be cleaned into the adjacent structure, which, for example, is masonry.
• the surface to be cleaned is a heat-transfer surface.
• the method can also be used to clean other surfaces of a power plant boiler structure, which surfaces comprise impurities, including ash, coke and/or slag deposits which are generated from the combustion.
• the structure to be cleaned is part of a power boiler, such as a heat boiler, or part of a recovery boiler, such as a kiln for reburning lime sludge or a soda recovery unit.
• a power boiler such as a heat boiler
• a recovery boiler such as a kiln for reburning lime sludge or a soda recovery unit.
• the heat-transfer surface is a metal surface, typically it is a steel surface.
• the steel may be, for example, a ferritic or an austenitic steel alloy which meets ASTM standards A213 or A213M, respectively. It is also possible to use other types of metal alloys.
• the surfaces may be of a material other than metal, for example a ceramic.
• Examples of surfaces to be cleaned are, in particular, the heat-transfer surface which forms part of a heat boiler, such as the eco- and the superheater packages of grate-fired boilers or fluidised bed boilers.
• the surface to be cleaned a metal surface, typically a steel surface, forms at least part of a superheater or at least part of an Economizer or a Luvo unit.
• the surface to be cleaned is in the vicinity of the masonry or at least partly on top of it.
• the distance to the nearest masonry i.e. the masonry surface, is at maximum approximately 250 cm, usually at maximum approximately 150 cm, especially at maximum approximately 100 cm, for example at maximum 50 cm.
• the masonry surface may be in direct contact with the surface to be cleaned.
• the blasting is carried out with nickel slag, which is in particle form, in which case the particle size of the nickel slag is approximately 0.3-2.5 mm.
• nickel slag means the by-product which is generated in the production or cleaning of the metal in question, i.e. in general "material", which typically is primarily silicate-based.
• the silicate material is, nickel silicate, and it comprises, besides the main component, also for example metals which are derived from the metal raw material, and alkaline earth metals, and their compounds, such as oxides, sulphates, sulphides and silicates.
• nickel slag is used which is essentially free of ferritic compounds.
• nickel slag is used, the particles of which are non-spherical shaped.
• nickel slag is used. This is a waste product which is generated in association with the recovering of nickel.
• the particle material of the nickel slag used must have, besides a particle size which is suitable for the blasting, also a sufficient hardness and weight.
• the hardness of the nickel slag particles must be greater than approximately 6°, most suitably even approximately 8°, on the Mohs scale of hardness, and the density must be greater than approximately 3.0 g/cm 3 , for example approximately 3.1-4.2 g/cm 3 , most suitably approximately 3.3-3.9 g/cm 3 , or 3.5-3.8 g/cm 3 .
• the hardness can be over 8° on the Mohs scale, but usually a hardness of approximately 8° ( ⁇ 0.5°) is sufficient to carry out the cleaning.
• the particles must have a suitable shape.
• the bulk density is greater than 1.8 g/cm 3 , especially 1.85 g/cm 3 or greater.
• the hardness, shape, and weight of the material used are within the ranges described above, the dirt can be removed from the object to be cleaned. With excessively light or chip-like slag, the result will not be as desired.
• the particle size of the slag is within a pre-selected range.
• the present particles may be individual particles or agglomerates (granules) which are formed of several particles.
• the average particle size of the nickel slag is within the range of 0.3-2.5 mm, for example 0.5-2.2 mm. Typically, this means that the maximum dimension of least 90 % of the particles, most suitably at least approximately 95 % (by weight) is within the said range.
• the particle size typically means the screened particle size (that is, grain-size).
• the nickel slag particles are not spherical, but they have an irregular shape. This also means that, when the blasted nickel slag particles hit the surface, both the surface pressure generated and the interaction between the particles and the surface are different from the case where spherical particles are used. The width of the contact area of individual slag particles varies depending on which part of the particle hits the surface. Thus, by using slag particles, the ash layer remaining on the surface can be loosened more efficiently than with steel balls, without damaging the steel surface.
• the blast nozzle used can be either small or large.
• the nozzle diameter may be, for example, 0.5-25 mm, usually approximately 1-15 mm, typically approximately 12 mm. These nozzle sizes are particularly suitable for the application described above, in which the nickel slag particles have a narrow distribution of particle size.
• the blasting is carried out by using a blasting pressure of 8-12 bar. More preferably, the pressure used is 9-11 bar. At this pressure, an efficient cleaning of the dirt layers is achieved and, at the same time, damage to the surface is avoided.
• the consumption of air varies with the nozzle size, but is generally approximately 50-2500 1/min, most suitably approximately 70-1500 1/min, for example approximately 150-1000 1/min.
• the blasting can be carried out by using a nozzle which is straight, curved or bent at 45 degrees.
• the shape of the nozzle is selected according to the object to be cleaned.
• the surface does not corrode as easily as after treatment in which sand is used.
• the surface is not prone to become dirty.
• nickel slag forms a chromium oxide compound on the metal surface, which compound protects the metal from corrosion, and which, on the other hand, also slows down the adhesion of new dirt to the metal surface.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Combustion & Propulsion (AREA)
• Cleaning In General (AREA)
• Polishing Bodies And Polishing Tools (AREA)
• Curing Cements, Concrete, And Artificial Stone (AREA)
• Cleaning By Liquid Or Steam (AREA)
• Application Of Or Painting With Fluid Materials (AREA)

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