Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F28—HEAT EXCHANGE IN GENERAL
  • F28D—HEAT-EXCHANGE APPARATUS, NOT PROVIDED FOR IN ANOTHER SUBCLASS, IN WHICH THE HEAT-EXCHANGE MEDIA DO NOT COME INTO DIRECT CONTACT
  • F28D21/00—Heat-exchange apparatus not covered by any of the groups F28D1/00 - F28D20/00
  • F28D21/0001—Recuperative heat exchangers
  • F28D21/0003—Recuperative heat exchangers the heat being recuperated from exhaust gases
  • F28D21/0005—Recuperative heat exchangers the heat being recuperated from exhaust gases for domestic or space-heating systems
  • F28D21/0007—Water heaters
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F28—HEAT EXCHANGE IN GENERAL
  • F28D—HEAT-EXCHANGE APPARATUS, NOT PROVIDED FOR IN ANOTHER SUBCLASS, IN WHICH THE HEAT-EXCHANGE MEDIA DO NOT COME INTO DIRECT CONTACT
  • F28D15/00—Heat-exchange apparatus with the intermediate heat-transfer medium in closed tubes passing into or through the conduit walls ; Heat-exchange apparatus employing intermediate heat-transfer medium or bodies
  • F28D15/02—Heat-exchange apparatus with the intermediate heat-transfer medium in closed tubes passing into or through the conduit walls ; Heat-exchange apparatus employing intermediate heat-transfer medium or bodies in which the medium condenses and evaporates, e.g. heat pipes
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F28—HEAT EXCHANGE IN GENERAL
  • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
  • F28F19/00—Preventing the formation of deposits or corrosion, e.g. by using filters or scrapers
  • F28F19/02—Preventing the formation of deposits or corrosion, e.g. by using filters or scrapers by using coatings, e.g. vitreous or enamel coatings

Definitions

• the present invention relates to flue gas ducts and recuperative heat exchangers for flue gases which operate in the area at risk of dew point.
• these fluorinated hydrocarbon polymers have a relatively poor thermal conductivity and, due to their microporosity, still have a certain permeability for the small acid molecules. Too thin layers of these polymers are therefore not suitable for completely protecting the underlying metal layers from acid attack.
• Regenerative heat exchangers in which the heat is absorbed, stored and released again by the mass used and around which the gases flow, work with certain leaks and thus always have a certain slip between the gases to be heated and cooled. In the case of regenerative heat exchangers in flue gas desulfurization systems, this means that a certain amount of unpurified flue gas is always added to the already cleaned clean gas. These regenerative heat exchangers can therefore only be used where the emission requirements are not too high and, on top of that, the acidity is relatively low. These regenerative heat exchangers consist of very large and very thin deformed and pressed sheets, which can be enamelled particularly acid-proof on the cold side. The sheet thickness is generally only 0.5 to 1.0 mm, since there are no strong mechanical stresses. The heat exchange is primarily a function of the mass on the one hand and the exchange surface on the other.
• the wall thickness of flue gas ducts is therefore generally at least 5 mm and more.
• Such strong metal sheets can no longer be enamelled in accordance with DIN 1623, since this DIN applies only up to and including 3 mm thick and only exceptional thicknesses up to 4 mm are permitted for enamelling after agreement with the manufacturer.
• Pipes for tubular heat exchangers can be produced from such thin sheets, but the tubes are very bulky due to their length. The same applies to the dimensioning of sheets for flue gas ducts that has been used up to now.
• the flue gas ducts according to the invention thus preferably consist of structural elements, such as smooth or curved, rectangular, trapezoidal or triangular sheets, which have stiffeners on the rear.
• stiffened components are mechanically stable to absorb pressure fluctuations in the flue gas duct of more than -60 mbar without causing damage to the enamel layer.
• These stiffened components are sealed to one another and to other components using fixed seals made of fluorocarbon polymers or else using commercially available acid-resistant sealing compounds.
• the individual components are carried by an externally attached support frame, which is not only able to support the weight of these components, but also to absorb the mechanical stresses caused by pressure fluctuations.
• the recuperative heat exchangers according to the invention preferably consist of seam-welded steel pipes according to DIN 1623, which are subsequently enamelled on the outside.
• the enamel can be applied in the form of a slip or electrostatically and burned in with the help of an annular heating unit through which the pipes are pulled through or which migrates over the pipes.
• This heating unit can in particular also be heated inductively, since such inductive heaters can be easily controlled.
• other ring-shaped ovens can also be used to bake the enamel.
• the enamelled tubes are then used as components of recuperative heat exchangers, for example by ending at both ends in boxes which are charged with the heating medium or coolant.
• the bottom plate of such boxes facing the flue gas can optionally also be enamelled beforehand.
• these base plates With boreholes through which the enamelled tubes can be inserted and then to coat the plate with a sufficiently thick film of fluorocarbon polymers. At the same time, these layers also act as a seal between the enameled tube and the borehole wall of the base plate.
• recuperative tube heat exchangers are stable enough to be charged with water at a pressure of approximately 25 bar, so that they can also be charged with water as a cooling or heating medium in the temperature range above 100 ° C.
• the advantage of such recuperative tube heat exchangers is that in the worst case, if the enamelled tube is damaged by corrosion, water can enter the flue gas from the tube, limiting the amount of leakage and causing no greater damage. Such a damaged pipe can also be shut down without having to repair the heat exchanger as a whole. Any corrosion damage due to damage to the enamel layer then becomes noticeable through loss of water and / or pressure in the cooling or heating water used. However, this does not yet result in a slippage between the unpurified flue gas and the clean gas as in the case of the regenerative heat exchangers.
• the components used according to the invention are enamelled with the already known highly acid-resistant enamels, which have already proven themselves in regenerative heat exchangers. Due to the higher mechanical load due to pressure or pressure fluctuations, care must be taken to ensure that the enamel is applied and burned in without bubbles or pores. In the event of any damage to the enamel layer, the corrosion on the exposed steel then progresses very rapidly, so that such damage can soon be found. However, the repair is facilitated and simplified in that only relatively small components need to be replaced, which are relatively easy to handle in terms of size and weight.
• heat pipes can also be used as recuperative heat exchangers, which, as is known, can only transport the heat in one direction, namely from the evaporable liquid collected to the point of recondensation of the vapors. As soon as the point of recondensation is warmer than the collection point for the liquid, the heat transport is interrupted.
• These are practically maintenance-free closed systems which, according to the invention, consist of steel, at least externally enamelled, in accordance with DIN 1623.
• the filling of the heat pipes should have a boiling point below 60 ° C, at least below 80 * C, so that they can be used for flue gases in the area where the dew point is at risk.
• enamel is an optimally suitable corrosion protection in itself, since enamel both against sulfuric acid and against hydrochloric acid with increasing concentrations ⁇ tration of these acids becomes more constant, while the corrosion of materials such as tantalum, titanium, chromium-nickel steel and nickel-based alloys such as Hastelloy ⁇ 'increases with increasing acid concentrations additional mechanical stress is not possible to build flue gas ducts and recuperative heat exchangers for flue gases in the dew point-prone area from acid-resistant enamelled steel, but according to the invention it has now become possible and at the same time considerable costs compared to the only material that can be used hitherto, namely fluorinated hydrocarbon polymers n save and even achieve better heat transfer and thus higher efficiency.
• Typical components for flue gas ducts have dimensions between 80 and 160 cm edge length.
• Typical pipes for recuperative heat exchangers have a diameter of 2 to 8 cm.

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• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Life Sciences & Earth Sciences (AREA)
• Sustainable Development (AREA)
• Heat-Exchange Devices With Radiators And Conduit Assemblies (AREA)
• Chimneys And Flues (AREA)

Applications Claiming Priority (3)

Publications (1)

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Family Applications (1)

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• 1993
  • 1993-03-26 DE DE4309844A patent/DE4309844C2/de not_active Expired - Fee Related
• 1994
  • 1994-03-18 JP JP6521612A patent/JPH08511860A/ja active Pending
  • 1994-03-18 EP EP94911920A patent/EP0689660A1/de not_active Withdrawn
  • 1994-03-18 WO PCT/EP1994/000858 patent/WO1994023260A1/de not_active Ceased
  • 1994-03-26 TW TW83102675A patent/TW233335B/zh active

Non-Patent Citations (1)

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