Chemistry of inorganic compounds – Modifying or removing component of normally gaseous mixture – Nitrogen or nitrogenous component
Patent
1982-08-23
1985-12-31
Heller, Gregory A.
Chemistry of inorganic compounds
Modifying or removing component of normally gaseous mixture
Nitrogen or nitrogenous component
423242, 55 73, 55257HE, 261149, C01B 2100, C01B 1700
Patent
active
045620539
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to a process of cleaning flue gases from heating plants such as oil burners, whereby it is substantially ensured that solid particles such as fly ash are initially removed from the flue gas, whereafter nitrogen oxides and sulphur dioxide are removed from the flue gas prior to the discharging to the atmospheric air, optionally through a neutralizing device. The invention furthermore relates to a plant for carrying out the process.
BACKGROUND ART
It is known to clean flue gases both of solid particles and of nitrogen oxides and sulphur dioxide, and it is known to utilize the heat of the flue gas. The previously known plants ensure a reduction of about 90% of the amount of sulphur dioxide in the flue gas. The remaining amount of sulphur dioxide assures that the flue gas discharged into the atmospheric air is particularly aggressive, said flue gas usually being discharged at a temperature of about 60.degree.-70.degree. C.
DISCLOSURE OF INVENTION
The object of the invention is to provide a process ensuring a reduction of the amount of sulphur dioxide of 98-100% at the same time as the flue gas is cooled almost to room temperature.
The process according to the invention is characterised in that initially the flue gas cleaned of solid particles is carried through an optionally intermittent, first shower of aqueous liquid, subsequently through a heat exchanger, in which the temperature of the flue gas is reduced to about 20.degree.-30.degree. C., optionally through a film of an alkaline liquid such as milk of lime or chloride of lime, through a second shower of aqueous liquid, and finally through a sulphuric acid neutralizing liquid in a container prior to the exhaust to the atmospheric air or an additional neutralizing device.
As a result, the discharged flue is cleaned to such an extent that it is comparable with the atmospheric air as to the content of combustion gases. The content of sulphur dioxide and sulphuric acid is almost completely removed, i.e. only from 0 to 2% thereof remain. Only a small amount of nitrogen and carbon dioxide remain, and the result of the cleaning is that the expenses involved in building large chimneys are completely avoided. At the same time the heat of the flue gas can be completely utilized as low as to 20.degree.-30.degree. C. for heating purposes since a temperature of at least about 150.degree. C. to 160.degree. C. in the flue gas is no longer required during the passage of said flue gas through a chimney. This high temperature was necessary in connection with the previous plants in order to ensure that the content of sulphuric acid of the flue gas did not turn aggressive within the chimney. This effect is due to a co-operation of the various liquids and the great reduction of the temperature which the flue gas is subjected to. A reduction of the temperature of the partly cleaned flue gas after the first treatment with a shower of aqueous liquid involves an intensely accelerating effect concerning the conversion of SO.sub.2 --SO.sub.3 into H.sub.2 SO.sub.3 and H.sub.2 SO.sub.4. The film with alkaline liquid ensures a neutralization of the previously formed H.sub.2 SO.sub.4 and an oxidation of present nitrogen oxides. The later shower of aqueous liquid ensures a conversion of the remaining amounts of SO.sub.2 and SO.sub.3 into H.sub.2 SO.sub.3 and H.sub.2 SO.sub.4 being removed during the passage through the sulphuric acid neutralizing liquid in a container before the discharging into the atmospheric air. As an additional security measure, the flue gas cleaned may optionally pass through an additional neutralizing device. The low temperature of the cooled flue gas ensures an essential increase of the capacity of the sulphur dioxide of being absorbed in the amount in question of aqueous liquid. By a usual liquefaction of sulphur dioxide at 0.degree. C. with water, the dissolving or absorbing is carried out with the following ratios, viz. 1 part of water to 80 parts of SO.sub.2, and each time an increase of temperature of 20.degree. C.
REFERENCES:
patent: 3473298 (1969-10-01), Berman
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patent: 3733777 (1973-05-01), Huntington
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patent: 4038367 (1977-07-01), Atsukawa et al.
patent: 4194889 (1980-03-01), Wanner
patent: 4284609 (1981-08-01), deVries
patent: 4340572 (1982-07-01), Ben-Shmuel et al.
Desco K/S
Heller Gregory A.
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