Liquid purification or separation – With means to add treating material – Directly applied to separator
Reexamination Certificate
1999-08-04
2001-07-03
Simmons, David A. (Department: 1724)
Liquid purification or separation
With means to add treating material
Directly applied to separator
C210S221200, C209S168000, C209S170000, C423S461000
Reexamination Certificate
active
06254771
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a technique for separating and removing fine particles of unburned carbon and other materials present in a desulfurization absorbing fluid after gas-liquid contact in a wet flue gas desulfurizer for removing sulfur oxides from the combustion exhaust gas of a boiler or the like.
2. Description of the Related Art
In a wet flue gas desulfurizer, exhaust gas is cleaned by gas-liquid contact with an absorbing fluid containing lime or the like, so that sulfur oxides (SO
x
) and fine particles of unburned carbon and other materials are removed therefrom. The fine particles of unburned carbon and other materials which have passed from the exhaust gas to the absorbing fluid remain in the by-product (e.g., gypsum) separated and recovered from the absorbing fluid and cause a reduction in purity and a reduction in quality due to discoloration.
Conventionally, in order to reduce the content of impurities (i.e., fine particles of unburned carbon and other materials) in gypsum obtained as a by-product to less than a specified level, it has been common practice to concentrate the gypsum present in the absorbing fluid having sulfur oxides (SO
x
) absorbed therein by means of a liquid cyclone and thereby reduce the content of unburned carbon on a relative basis. However, since unburned carbon behaves in substantially the same manner as the absorbing fluid, there is a limit in reducing the content of unburned carbon by concentrating the gypsum by means of a liquid cyclone. For example, even if the requirements for the purity of gypsum are met, a reduction in quality due to a deterioration of appearance by discoloration may be unavoidable.
Thus, gypsum obtained as a by-product in wet flue gas desulfurization involves problems such as reduced prices and limited uses due to discoloration caused by impurities comprising fine particles of unburned carbon and other materials.
An object of the present invention is to provide a method and apparatus for the treatment of a desulfurization absorbing fluid which enables fine particles of unburned carbon and other materials to be efficiently removed from the desulfurization absorbing fluid prior to the separation of a by-product so that a by-product (e.g., gypsum) having a low impurity content and showing little discoloration may be separated and recovered from the desulfurization absorbing fluid.
SUMMARY OF THE INVENTION
According to the present invention, there Is provided a method for the treatment of a desulfurization absorbing fluid after gas-liquid contact with combustion exhaust gas containing fine particles of unburned carbon and other materials, which comprises the steps of feeding a gas into the absorbing fluid containing the fine particles and thereby producing gas bubbles so as to cause the fine particles to adhere to the surfaces of the gas bubbles and create a foam phase consisting of the gas bubbles; and breaking the foam phase to obtain a liquid containing the fine particles. Preferably, the gas is fed into the absorbing fluid at a flow rate of 50 to 300 m
3
N/h·m
2
per unit cross-sectional area of the absorbing fluid.
According to the present invention, there is also provided an apparatus for the treatment of a desulfurization absorbing fluid after gas-liquid contact with combustion exhaust gas containing fine particles of unburned carbon and other materials, which comprises a treating tank for storing the absorbing fluid containing the fine particles, the treating tank having an absorbing fluid feed port for feeding the absorbing fluid into the treating tank, and a gas feed port for feeding a gas into the absorbing fluid stored in the treating tank and thereby producing gas bubbles to create a foam phase consisting of the gas bubbles in the treating tank; a foam breaking tank adjoining the treating tank; a foam inlet pipe for connecting the treating tank with the foam breaking tank in fluid communication relationship; and foam breaker means disposed in the foam breaking tank for breaking the foam phase having passed through the foam inlet pipe to obtain a liquid containing the fine particles.
A plurality of apparatus for the treatment of a desulfurization absorbing fluid as described above may be installed in successive stages, and these apparatus may be connected by feeding means for delivering the fine particle-containing liquid obtained in the apparatus at the preceding stage to the absorbing fluid feed port of the apparatus at the succeeding stage.
In the aforesaid apparatus for the treatment of a desulfurization absorbing fluid, the treating tank may have an outlet port for withdrawing the absorbing fluid stored in the treating tank, and the aforesaid apparatus may be equipped with means for returning a portion of the absorbing fluid withdrawn from the outlet port, together with the gas, to the treating tank through the gas feed port.
A plurality of apparatus for the treatment of a desulfurization absorbing fluid as described above may be installed in successive stages, and these apparatus may be connected by feeding means for delivering the absorbing fluid withdrawn from the outlet port of the treating tank of the apparatus at the preceding stage, except the portion returned to the treating tank, to the absorbing fluid feed port of the apparatus at the succeeding stage.
According to the method of the present invention, fine particles of unburned carbon and other materials are efficiently removed from a desulfurization absorbing fluid containing such fine particles as a result of gas-liquid contact with combustion exhaust gas, so that the by-product (e.g., gypsum) obtained by solid-liquid separation of the desulfurization absorbing fluid has high purity and shows little discoloration.
Moreover, when the treating apparatus of the present invention is employed, highly pure gypsum having high whiteness can be recovered even if the electrostatic precipitator is omitted.
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Hino Masao
Inoue Kenji
Iwashita Koichiro
Onizuka Masakazu
Shinoda Takeo
Mitsubishi Heavy Industries Ltd.
Myers Bigel Sibley & Sajovec P.A.
Prince Fred
Simmons David A.
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