Heat exchange – Line connected conduit assemblies – In common casing
Patent
1988-08-31
1990-03-20
Schwadron, Martin P.
Heat exchange
Line connected conduit assemblies
In common casing
165111, 165162, 165163, 165 95, 122 20B, F28F 926
Patent
active
049093185
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a method and an apparatus for recovering heat and separating substances from a flue gas streaming through a heat exchange apparatus.
During combustion of oil and other fossil fuels, there are formed flue gases containing carbon oxides, sulphur oxides, nitrogen oxides, water vapour and soot particles. Other gaseous chemicals can be present in the flue gases from other types of fuels. These flue gases are normally blown out into the air via a chimney. Flue gases from combustion of fuel thus contribute to atmospheric pollution and increased acidity in lakes and rivers. Actions are taken to reduce the atmospheric pollution, e.g. reduce the sulphur content in the fuel or clean the flue gases. Almost all sulphur in the fuel is oxidized to SO.sub.2 during combustion and a small part is further oxidized to SO.sub.3. When cooling the flue gases the SO.sub.3 reacts with water vapour and form sulphuric acid. The SO.sub.2 can partly be dissolved in condensed moisture, specially in the presence of sulphuric acid, and forms sulphurous acid. Cooling of the flue gases leads to corrosion of heat exchangers and chimneys thereby reducing the possibility of recovering all the heat from the combustion of the fuel. Further, the condensed acid causes a conglomeration of oil and soot particles present in the flue gases.
A known method is to cool the flue gases in a heat exchanger whereby the sulphuric acid is condensed and separated from the flue gases. When cooling the flue gases, the heat can be recovered reducing the amount of fuel to the boiler.
According to a known apparatus (see FIG. 1) the flue gases from a combustion room are introduced to a flue gas cooler commprising a vertical heat exchanger provided with long straight tubes 10 of a material which shall resist corrosion. The flue gases stream inside the tubes at high velocity (more than 5 m/sec) partly so that the soot shall not fasten on the inner tube wall and partly that a high heat transfer shall be obtained. Between the tubes a liquid, for instance water, is heated by the flue gases inside the tubes 10.
The known apparatus, however, is impaired by a serious drawback. The design of the apparatus and the high gas velocity makes the separation degree for the sulphur low. Only 10-30% of the sulphur content in the fuel can be removed from the flue gases.
The present invention aims to recover energy from flue gases, to improve the cleaning of the flue gases, especially reducing the sulphur content in the same and to make a heat exchanger of corrosion resistant plastic material. This purpose has been solved as is apparent from the description of the invention and the attached claims.
According to the invention there is provided a method for recovering heat and separating substances from a flue gas streaming through a heat exchange apparatus comprising a casing with heat exchange elements inserted thereinto, a medium being provided for absorbing heat from the flue gas, characterized in
that the medium that shall absorb heat from the flue gas is conducted through the heat exchange elements and has a temperature which is lower than the dew point of sulphuric acid,
that the heat exchange elements are so placed inside the casing of the heat exchanger and the connections to the casing for flue gas so made that the flue gas streams essentially perpendicularly to the longitudinal axis of the heat exchange elements,
that the flue gas is given a flow velocity cross the heat exchange elements of not more than 3 118 m/sec.
that water vapour and sulphur trioxide in the flue gas form sulphuric acid when the flue gas is cooled, the sulphuric acid being condensed onto the outer walls of the heat exchange elements,
that soot in the flue gas is collected on the heat exchange elements and this soot can adsorb and/or dissolve gaseous substances, such as sulphur dioxide, and
that the soot particles, sulphuric acid and the adsorbed or dissolved SO.sub.2 on the heat exchange elements are removed from the heat exchange elements when the capcity of the soot layer to ads
REFERENCES:
patent: 2693346 (1954-11-01), Petersen
patent: 3240675 (1966-03-01), Weber
patent: 4619317 (1986-10-01), Disselbeck et al.
Alfa-Laval Thermal AB
Flanigan Allen J.
Schwadron Martin P.
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