Furnaces – With exhaust gas treatment means – Means contacting exhaust gas with liquid
Patent
1988-02-02
1989-08-29
Favors, Edward G.
Furnaces
With exhaust gas treatment means
Means contacting exhaust gas with liquid
55227, 55228, 110345, 422168, 422169, 261DIG9, F23J 1500
Patent
active
048606707
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a method and plant for the cleaning and desulphurization of flue gas from the combustion of sulphurous fuels, and the recovery of heat from the flue gas, whereby the flue gas is conducted from a boiler through a heat exchanger.
When burning fossil fuels such as coal and oil in boiler plants, a flue gas arises which, in accordance with the relevant environmental regulations, must maintain stipulated norms in order to be able to be discharged into the atmosphere. The flue gas also contains a certain amount of thermal energy, even from boiler plants with economizers, whereby the feed water is heated by the flue gas before it is fed to the boiler plant. For reasons of economy, it is therefore desirable to recover as great an amount of the thermal energy as possible from the flue gas.
It is known to clean the smoke and recover a part of the thermal energy existing in the flue gas, in that one leads the flue gas from the economizer to a flue gas-air heat exchanger in which one heats the combustion air, which is to be fed to the boiler's combustion chamber.
Downstream of the heat exchanger, a smoke cleaner is provided in which a scrubber fluid, e.g. lime water, is used to remove acids and particles from the smoke, after which the flue gas can be conducted to the chimney and out into the atmosphere.
These known installations have several drawbacks. The smoke is cooled down considerably by using a flue-gas-air heat exchanger after the economizer, thus reducing the temperature of the flue gas to below the dew point of the acid, so that the acid is condensed and settles in the heat exchanger. This must therefore be made of an acid-resisting material, e.g. acid-resisting steel or glass, which results in a very expensive heat exchanger. As a rule, the flue gas from fossil fuels contains a smaller amount of lime connections, the result being that the particles in the flue gas become chalky and, in connection with the acid, thus form a gypsum paste which quickly blocks the heat exchanger. The heat exchanger must therefore be frequently cleaned, which is difficult. Known systems use vigorous flushing with water in order to clean the heat exchanger, but this gives rise to acidiferous water which must be neutralized before it can be led away. During the flushing periods, which are quite frequent, the heat exchanger cannot be used, the result being that the smoke must be conducted around the heat exchanger, whereby one loses some of the heat recovery, or a change must be made between two heat ecxhangers, which considerably increases the costs of the plant.
The aim underlying the present invention essentially rsesides in providing a method and a plant for cleaning and desulfurization of flue gas from the combustion of sulfurous fuels and recovery of heat from the flue gas which avoids, by simple means, shortcomings and disadvantages encountered in the prior art.
In methods and plants for cleaning a flue gas and recovery of heat from the same, the flue gas from a boiler is lead through a heat exchanger for water, a so-called economizer, and subsequently washed with a scrubber fluid before being lead to a chimney possibly by way of means which filter out drops of liquids with the thermal energy being collected in the scrubber fluid being reused.
According to the method of the present invention, the flue gas is cooled on its way through the economizer only so much that it still has a temperature above the acid dew point when the flue gas meets the scrubber fluid, and the scrubber fluid is maintained substantially at a neutral pH value by an addition of base in the liquid form, and an additive base is produced by the use of lime through a double alkaline process between the lime and the scrubber fluid in a high speed reactor wherein the pH value is maintained in a range of 8.5-10.5 and, preferably, at approximately 9.5.
In the plant or apparatus for cleaning of the flue gas of the present invention, a means is provided for feeding the gas flue through the economizer in such a
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patent: 4019444 (1977-04-01), Kleeber et al.
patent: 4515754 (1985-05-01), Stehning
patent: 4624190 (1986-11-01), Cappi
patent: 4644877 (1987-02-01), Barton et al.
patent: 4718357 (1988-01-01), Wang etal.
Favors Edward G.
Jydsk Varmekedelfabrik A/S
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