Chemistry: fertilizers – Processes and products – Inorganic material
Reexamination Certificate
1999-07-13
2002-03-12
Langel, Wayne (Department: 1754)
Chemistry: fertilizers
Processes and products
Inorganic material
C071S054000, C204S157300, C204S157460, C204S157490
Reexamination Certificate
active
06355084
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method of producing a fertilizer, and more particularly to a method and an apparatus for producing a fertilizer by injecting ammonia into gas containing sulfur oxides and applying electron beam to the gas.
BACKGROUND ART
There has been developed a process of producing a fertilizer by introducing gas containing sulfur oxides, such as flue gas generated when fossil fuel is combusted (hereinafter referred to as “fossil fuel combustion flue gas”), into a process vessel, injecting ammonia into and applying electron beam to the gas in the process vessel to thereby produce a product that primarily comprises ammonium sulfate, which is a typical nitrogenous fertilizer, and collecting the product with a collector such as an electrostatic precipitator. According to the process of injecting ammonia into and applying electron beam to gas containing sulfur oxides such as fossil fuel combustion flue gas, an appreciable amount of ammonium sulfamate (NH
4
SO
3
NH
2
) which is harmful to the growth of plant, is produced together with ammonium sulfate. In order to use the above product as a fertilizer, it has been necessary to remove ammonium sulfamate from the product which contains ammonium sulfamate, or to take a suitable measure to suppress the production of ammonium sulfamate.
One known process of removing ammonium sulfamate which is by-product is to heat the product. It is also known to suppress the production of ammonium sulfamate by mixing ammonia and water and spraying a mixture of ammonia and water into the process vessel.
The former process of heating the product needs an apparatus and a heat source for heating the product after the product has been collected. The latter process of spraying a mixture of ammonia and water into the process vessel is problematic in that it is impossible to suppress the production of ammonium sulfamate under all gas conditions and operating conditions to a level low enough to allow the product to be used as a fertilizer.
DISCLOSURE OF INVENTION
It is an object of the present invention to solve the problems in the conventional method and to provide a method and an apparatus for producing a fertilizer from gas containing sulfur oxides such as fossil fuel combustion flue gas, while suppressing production of ammonium sulfamate to a level low enough to use the product as a fertilizer, with a simple means without the use of an additional apparatus and a heat source, in a very wide range of gas conditions and operating conditions.
In order to achieve the above object, the inventors have studied in detail the mechanism by which ammonium sulfamate is produced in a process of injecting ammonia into and applying electron beam to gas containing sulfur oxides, as follows:
SO
2
, which is a primary component of sulfur oxides contained in fossil fuel combustion flue gas or the like, is oxidized very quickly into SO
3
by active components including O radials, OH radicals and the like generated from oxygen molecules or water molecules in the gas when irradiated with the electron beam. This SO
3
reacts with ammonia to produce sulfamic acid according to the following formula (1):
SO
3
+NH
3
→HSO
3
NH
2
(1)
The fossil fuel combustion flue gas originally contains a small amount of SO
3
as well as SO
2
. This SO
3
changes into sulfamic acid according to the formula (1), without being irradiated with the electron beam.
SO
3
also reacts with water contained in the gas and changes into sulfuric acid according to the following formula (2):
SO
3
+H
2
O→H
2
SO
4
(2)
The ratio R
1
of the proportion of the sulfur oxides, contained in the fossil fuel combustion flue gas or the like, which have changed into sulfamic acid to the proportion of the sulfur oxides which have changed into sulfuric acid is determined by the ratio (=[NH
3
]in/[H
2
O]in) of the concentration of ammonia ([NH
3
]in) to the concentration of water ([H
2
O]in) in the gas prior to irradiation of the electron beam. As the ratio [NH
3
]in/[H
2
O]in is smaller, the proportion of the sulfur oxides which change into sulfamic acid is smaller. This is because the reaction rate v
1
of the formula (1)and the reaction rate v
2
of the formula (2) are calculated from respective chemical reaction rate constants k
1
, k
2
, the concentration of SO
3
([SO
3
]) in the gas immediately after SO
2
changes into SO
3
by irradiation of the electron beam, the concentration of ammonia ([NH
3
]in) and the concentration of water ([H
2
O]in) in the gas prior to the start of the reactions represented by the formulas (1), (2), according to the following formulas (A1), (A2), because the concentrations prior to the start of the reaction represented by the formulas (1), (2) are equal to the concentrations prior to irradiation of the electron beam:
v
1
=k
1
×[SO
3
]·[NH
3
]in (A1)
v
2
=k
2
×[SO
3
]·[H
2
O]in (A2)
A portion of the sulfamic acid generated according to the formula (1) reacts again with ammonia according to the following formula (3) to produce ammonium sulfamate, and a portion of the sulfamic acid reacts with water contained in the gas according to the following formula (4) and is hydrolyzed into sulfuric acid and ammonia:
HSO
3
NH
2
+NH
3
→NH
4
SO
3
NH
2
(3)
HSO
3
NH
2
+H
2
O →H
2
SO
4
+NH
3
(4)
The sulfuric acid generated according to the formulas (2), (4) reacts with the ammonia in the gas or the ammonia generated according to the formula (4), according to the following formula (5), and is neutralized into ammonium sulfate:
H
2
SO
4
+2NH
3
→(NH
4
)
2
SO
4
(5)
The successive reactions represented by the formulas (1) through (5) are illustrated in FIG.
7
.
The generation of SO
3
by irradiation of the electron beam, and the subsequent reactions according to the formulas (1), (2) proceed very quickly, and are completed in less than 1 second after irradiation of the electron beam. On the other hand, the reactions according to the formulas (3), (4) which involve sulfamic acid are relatively slow, and are completed within a time of an order ranging from several seconds to several tens of seconds. Therefore, these reactions proceed primarily after the reactions according to the formulas (1), (2) are completed by irradiation of the electron beam until the product is collected by a collector such as an electrostatic precipitator and the gas is discharged out of the system. Therefore, the ratio R
2
of the proportion of the sulfamic acid, produced immediately after irradiation of the electron beam according to the formula (1), which has changed into the ammonium sulfamate according to the formula (3), to the proportion of the sulfamic acid which has changed into the ammonium sulfate according to the formulas (4), (5) is determined by the ratio (=[NH
3
]out/[H
2
O]out) of the concentration of ammonia ([NH
3
]out) to the concentration of water ([H
2
O]out) in the gas after irradiation of the electron beam. As the ratio [NH
3
]out/[H
2
O]out is smaller, the proportion of the sulfamic acid which changes into ammonium sulfamate is smaller. This is because the reaction rate v
3
of the formula (3) and the reaction rate v
4
of the formula (4) are calculated from respective chemical reaction rate constants k
3
, k
4
, the concentration of sulfamic acid ([HSO
3
NH
2
]), the concentration of ammonia ([NH
3
]out) and the concentration of water ([H
2
O]out) in the gas immediately after irradiation of the electron beam and the completion of the reactions represented by the formulas (1), (2), according to the following formulas (A3), (A4):
v
3
=k
3
×[HSO
3
NH
2
]·[NH
3
]out (A3)
v
4
=k
4
×[HSO
3
NH
2
]·[H
2
O]out (A4)
Iizuka Yoshitaka
Izutsu Masahiro
Suzuki Ryoji
Yokoyama Akiko
Ebara Corporation
Langel Wayne
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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