Chemical apparatus and process disinfecting – deodorizing – preser – Chemical reactor – Waste gas purifier
Patent
1992-06-22
1994-09-13
McMahon, Timothy M.
Chemical apparatus and process disinfecting, deodorizing, preser
Chemical reactor
Waste gas purifier
34 74, 34 75, 34 80, 62 17, 62544, 423210, B01D 5302
Patent
active
053466748
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a process and apparatus for removing impurities from flue gases and, more particularly, relates to a process and apparatus for removing gaseous and solid pollutants in flue gases such as emissions from thermochemical and the like reactions.
BACKGROUND OF THE INVENTION
Gaseous emissions from many thermochemical processes involve the emission of a number of pollutants ranging from heavy metal vapours (Hg, Cd, Pb and Zn), salt vapours (NaCl, KCl, KF, and NaF), acid gases (HF,HCl and SO.sub.2), organic compounds (dioxins, furans, hydrocarbons and solvents) as well as submicron particle emissions. The imposition of increasingly stringent environmental regulations to control these emissions has resulted in air pollution control devices becoming an integral component of thermochemical processes.
Typical attempts at reducing these pollutants include dry, wet and semi-dry scrubbing systems followed by particle removal in a baghouse or electrostatic precipitator. Wet scrubbing, by water spraying alone, is usually sufficient for control of HCl and HF emissions. For effective removal of SO.sub.2, sorbents are used. U.S. Pat. No. 4,704,972 discloses a method and apparatus for removing dust and water-soluble acid pollutants contained in smoke from the incineration of garbage wherein dust is removed from the smoke and the smoke is cooled by a heat exchanger below the dew point of gases therein whereby condensed water vapour traps acid pollutants for neutralization. The lowering of the temperature of saturated flue gas to below the dew point of acid pollutants does permit substantial condensation of said gases. However, low temperature emission control systems control systems suffer from a number of operational difficulties such as build up of insoluble salts on the walls of the vessel (scaling), corrosion and fouling of the vessel internals, difficulties in sedimentation of the produced salts, and clarification and recycling of vessel residue.
U.S. Pat. No. 4,281,518 (De-A-2902391) discloses the separation of certain components of a gas mixture therefrom by cooling the gas mixture by the addition of a liquid or cold inert gas to cause those components to go into a liquid or solid state. The condensed or precipitated components are collected and heated to form a liquid suitable for removal. This reference does not disclose contacting the gases with a powdered sorbent during cooling and adding an alkali metal to the sorbent to adjust the pH to about 9 to 11 for pH control.
It will be understood that the term "heavy metals" used in the specification and claims will include the metals, cadmium, lead, zinc, arsenic, antimony and selenium.
SUMMARY OF THE INVENTION
It has been found that the cooling of flue gases by the introduction of a liquified gas into direct contact with the flue gases for cooling of the flue gases to a temperature in the range of 60.degree. C. to -20.degree. C., the concurrent introduction of a powdered sorbent into said gases for nucleation and for the condensation or precipitation of heavy metals, salts, acids and hydrocarbons thereon, and the concurrent formation of a porous and permeable filter bed of said sorbents in which the pH of the sorbents is maintained in the range of about 9 to 11 for absorption and adsorption of said condensed or precipitated heavy metals, salts, acids, hydrocarbons and solid pollutants thereon as the flue gases are drawn therethrough, effectively removes impurities from the gases.
Measurement of the pressure drop of gases passing through the filter bed and scraping of the filter bed to reduce its thickness as the pressure drop exceeds a predetermined value, with recycle of sorbent until it is saturated with impurities, allows maintenance of an effective porous and permeable filter bed.
In its broad aspect, the process of the invention relates to the removal of at least one gaseous impurity selected from heavy metals, alkali salts, acids, hydrocarbons and submicron particle emissions contained in gases such as flue gase
REFERENCES:
patent: 4281518 (1981-08-01), Muller et al.
patent: 4424680 (1984-01-01), Rothchild
patent: 4668489 (1987-05-01), Alexander et al.
patent: 4744964 (1988-05-01), Kuhl
patent: 4982512 (1991-01-01), McClenny
patent: 5100643 (1992-03-01), Brna et al.
patent: 5118480 (1992-06-01), Cook et al.
Weinwurm Paul S.
Weinwurm Peter
Agglo Recovery
McMahon Timothy M.
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