Chemistry: electrical and wave energy – Processes and products – Processes of treating materials by wave energy
Reexamination Certificate
1999-01-20
2001-01-30
Gorgos, Kathryn (Department: 1741)
Chemistry: electrical and wave energy
Processes and products
Processes of treating materials by wave energy
C204S157440, C204S157460, C204S157490, C204S158200, C422S186000, C250S492300
Reexamination Certificate
active
06179968
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and an apparatus for treating gas such as flue gas by irradiation of electron beam, and more particularly to a method and an apparatus for treating gas containing sulfur oxides and/or nitrogen oxides by injection of ammonia and irradiation of electron beam to thereby remove sulfur oxides and/or nitrogen oxides therefrom.
2. Discussion of the Background
As economy develops, more and more energy is demanded. Amidst the continuous growth of energy demand, energy source is still dependent on fossil fuels such as coal and petroleum. However, the harmful products or pollutants generated by burning of fossil fuels are responsible for global pollution. To prevent the release of pollutants into the atmosphere and to stop the pollution of global environment, development work is being carried out at an accelerated pace to create a flue gas treatment system for installation in fuel combustion plant such as thermal power plants. There are still many areas of improvement to meet problems such as the complicated configuration of the equipment requiring a large number of control variables and the need for large-scale waste water treatment systems requiring sophisticated treatment technology.
In an effort to solve these problems, a flue gas treatment system in which flue gas discharged from the fuel combustion facility such as a boiler is treated by irradiation of electron beam has been developed.
In this system, ammonia is injected into gas containing sulfur oxides and/or nitrogen oxides, and the mixed gas is irradiated with electron beam to remove the sulfur oxides and/or the nitrogen oxides therefrom in the form of reaction by-product (hereinafter referred to as by-product). However, this by-product mainly composed of ammonium sulfate and/or ammonium nitrate tends to be deposited on a passage for allowing the treated gas to pass therethrough. There have been made various attempts to prevent deposition of by-product mainly composed of ammonium sulfate and/or ammonium nitrate in such an electron-beam process.
According to one of the attempts, the speed of a gas flow after irradiation of electron beam is set to 10 m/s or less, preferably 5 m/s or less, as disclosed in Japanese patent publication No. 3-65211. According to another attempt, the temperature of a gas-contacting portion from an electron-beam irradiation area to a by-product collecting area is kept in a range of 80 to 150° C., preferably 100 to 150° C., as disclosed in Japanese laid-open patent publication No. 7-31844.
The former attempt is disadvantageous in that an apparatus downstream of irradiation area of electron beam and/or a cross-sectional area of a duct need to be large, resulting in a large-sized facility. The latter attempt is problematic as it requires a heat source for raising the temperature of the gas-contacting portion. Further, both attempts fail to completely prevent the deposition of by-product, but allow by-product to be deposited at an accelerated rate once it starts being deposited.
It has been proposed in International application No. PCT/JP97/00772 to surround a passage having inlet and outlet openings with a shielding wall and place partition plates and/or inner partition walls in the shielded passage in order to shield X-rays that are generated by irradiation of electron beam. If the proposed structure is applied to a duct extending from a process vessel to a by-product collector in the flue gas treatment system, then a portion of the duct is constructed as the shielded passage and the partition plates and/or inner partition walls are provided in the shielded passage. Generally, it is known that the by-product tends to be deposited in locations where the gas flow is turbulent. Consequently, in the proposed structure, since the gas flow is caused to be turbulent by the partition plate and/or the inner partition wall in the shielded passage, the by-product will be deposited at a greater rate on the partition plate and/or the inner partition wall or thereabouts.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a method and an apparatus for treating gas containing sulfur oxides and/or nitrogen oxides by injection of ammonia and irradiation of electron beam to thereby remove sulfur oxides and/or nitrogen oxides therefrom, while preventing an apparatus and/or a duct from a process vessel to a by-product collector from being clogged with by-product that would mainly be composed of ammonium sulfate and/or ammonium nitrate.
According to one aspect of the present invention, there is provided a method of treating gas by irradiation of electron beam, comprising the steps of: adding ammonia to gas containing sulfur oxides and/or nitrogen oxides in a process vessel; irradiating gas with electron beam in the process vessel to remove the sulfur oxides and/or the nitrogen oxides from the gas; collecting by-product produced by reaction in the process vessel by a collector; and cooling at least a part of a gas-contacting portion extending from the process vessel to the collector to a dew point of the gas or below.
In the present invention, reaction is carried out under the atmospheric pressure. The dew point of the gas is mainly affected by the concentration of water vapor in the gas although it is slightly affected by the composition of the gas. The relationship between the concentration (%) of water vapor and the dew point (°C.) is given in Table shown below.
Water vapor concentration (%)
Dew point (° C.)
2
18
4
29
6
36
8
42
10
46
12
50
14
53
16
56
18
58
20
60
25
65
30
69
When the gas-contacting portion extending from the process vessel to the collector is cooled, either wholly or partly, to a dew point of the gas or below, the water vapor contained in the gas is condensed in the gas-contacting portion, and by-product which contacts the gas-contacting portion or adheres to the gas-contacting portion is dissolved and washed away by the condensed water. Therefore, the by-product is prevented from being deposited on or adhering to the gas-contacting portion. The gas-containing portion may be cooled only in a region where by-product tends to be deposited due to gas flow turbulences, or only in an upper region thereof whereas a lower region thereof may be washed by the condensed water flowing down from the upper region.
The method may further comprises the step of spraying condensed water, produced in the gas-contacting portion, into the gas either before or after irradiation of electron beam.
According to another aspect of the present invention, there is provided an apparatus for treating gas by irradiation of electron beam, comprising: a process vessel for being supplied with gas containing sulfur oxides and/or nitrogen oxides; a supply device for supplying ammonia to the gas in the process vessel; an electron accelerator for irradiating the gas with electron beam in the process vessel; a collector for collecting by-product produced by reaction; a duct extending from the process vessel to the collector for allowing the gas to pass therethrough; and a cooling structure for cooling at least a part of a gas-contacting portion extending from the process vessel to the collector to a dew point of the gas or below.
The apparatus further comprises a plurality of spaced partition plates or walls disposed in the duct, and the gas-contacting portion comprises outer surfaces of the partition plates or walls with a cooling structure for cooling at least a part of a gas-contacting portion.
The cooling structure may comprise a cooling jacket provided on the duct, or a cooling water pipe at a gas-contacting portion or gas-noncontacting portion to cool gas-contacting portion. The cooling structure may comprise a cooling water passage provided in the partition plate or wall.
Particularly, in the case where the partition plates and/or the partition walls are provided in the duct, a division duct may be provided between the partition plates. The division duct may be provided with a cooling jacket thereon or a cool
Hayashi Kazuaki
Iizuka Yoshitaka
Izutsu Masahiro
Ebara Corporation
Gorgos Kathryn
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Wong Edna
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