Chemistry of inorganic compounds – Modifying or removing component of normally gaseous mixture – Nitrogen or nitrogenous component
Patent
1997-06-20
1999-05-25
Straub, Gary P.
Chemistry of inorganic compounds
Modifying or removing component of normally gaseous mixture
Nitrogen or nitrogenous component
423235, 4232391, 423351, C01B 112
Patent
active
059068035
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for removing, by selective oxidation in the presence of a solid catalyst, ammonia from gasification gas obtained from fuel.
In the gasification of a fuel, such as carbon, peat or fuel oil, the fuel and an oxygen-containing gas, such as air or oxygen, form a gasification gas the principal components of which are, depending on the conditions, carbon monoxide, carbon dioxide, hydrogen, methane, water, and nitrogen. In addition, the gasification gas contains ammonia formed from the nitrogen present in the fuel. In the subsequent combustion step the ammonia of the gasification gas burns to oxides of nitrogen, such as nitrogen monoxide NO or nitrogen dioxide NO.sub.2. To avoid environmental problems, the emission of these acidifying gases into the atmosphere is to be prevented, and this can be done by the use of a specific combustion technique by which the burning of ammonia to nitrogen oxides is prevented, or by removing ammonia from the gasification gas before the combustion step The present invention concerns the latter solution model.
It is a previously known method to remove ammonia from gasification gas by scrubbing the gas before the combustion step. This method has the disadvantage that the scrubbing will cool the gas radically, thereby reducing the efficiency ratio of the process. According to another known method, the ammonia is removed by selective oxidation of the gasification gas. FI lay-open print 83393 describes a technique in which oxygen and nitrogen oxides, in particular nitrogen monoxide NO, are fed into the midst of the gasification gas in order to cause a reaction in which gaseous nitrogen and water are formed. According to the publication, the reaction can be accelerated by means of a selective catalyst, such as dolomite or zeolite. FI lay-open print 89810 describes a catalyst suitable, for example, for the said ammonia removal reaction, the catalyst being made up mainly of an oxide of iron or nickel, mixed with a carbonate or oxide of an alkali metal or an earth alkali metal By using such a catalyst, 75-90% of the ammonia present in gasification gas has been decomposed at a reaction temperature of 900.degree. C.
The object of the present invention is to make more effective the oxidation of the ammonia present in gasification gas by using a new catalyst, which oxidizes ammonia selectively, i.e. without substantially affecting hydrogen, methane or other oxidizing components of the gasification gas, and by means of which the ammonia can be decomposed more completely and/or at a substantially lower temperature than by means of previously used catalysts. The invention is characterized in that the catalyst used is made up of aluminum oxide Al.sub.2 O.sub.3.
According to preliminary experiments, when the catalyst consists of a substantially pure aluminum oxide Al.sub.2 O.sub.3, 90-98% of the ammonia present in gasification gas can be caused to react to form nitrogen at a reaction temperature of 400-600.degree. C. The oxidant used was a mixture of oxygen and nitrogen monoxide NO.
On the basis of the experiments it seems-that the most advantageous application of the invention is the oxidation of ammonia by means of oxygen and nitrogen monoxide by using aluminum oxide as a catalyst, at a reaction temperature of approx. 400-500.degree. C. Thereby a maximal conversion of ammonia to nitrogen is achieved within a temperature range which corresponds to the temperature to which the temperature of the gasification gas in many combustion plants is even otherwise adjusted between the gasification and the combustion.
The contact between the reacting gas mixture and the catalyst can be achieved advantageously in a solid or fluidized bed made up of small catalyst particles, most preferably less than 1 mm in size. Such a catalyst bed may be located in a separate oxidation reactor which is equipped with heat controls and in which the reacting gas mixture is caused to flow through the bed, the oxidation reactor being located at a point subsequent to the gasification react
REFERENCES:
patent: 3467491 (1969-09-01), Hardison
patent: 3914390 (1975-10-01), Kudo et al.
patent: 4080426 (1978-03-01), Kittrell et al.
patent: 4093707 (1978-06-01), Merkl
patent: 4096096 (1978-06-01), Nishkawa et al.
patent: 4179407 (1979-12-01), Iiyama et al.
patent: 4220632 (1980-09-01), Pence et al.
patent: 4258020 (1981-03-01), Ginger
patent: 4368057 (1983-01-01), Matthews
patent: 4609539 (1986-09-01), Horecky et al.
patent: 4692318 (1987-09-01), Tozpin et al.
patent: 4778665 (1988-10-01), Kishnamurthy et al.
Straub Gary P.
Valton Teknillinen Tutkismuskeskus
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