Combustion – Process of combustion or burner operation – In a porous body or bed – e.g. – surface combustion – etc.
Patent
1986-02-18
1988-05-03
Yeung, James C.
Combustion
Process of combustion or burner operation
In a porous body or bed, e.g., surface combustion, etc.
431170, 122 4D, 110245, 110345, F23D 340
Patent
active
047416904
DESCRIPTION:
BRIEF SUMMARY
The rate of a combustion reaction is very sensitive to temperature and the rate increases strongly with increasing temperature. In a combustion process it is necessary that the temperature of the flame or combustion zone is high enough to make the reaction proceed with reasonable speed.
In an ordinary flame this is accomplished by the fact that heat from reacted gas heats not yet reacted gas. For a flame to survive it is then necessary that the heat generated in a gas volume during the reaction is enough both to cover losses to the environment and to heat adjacent not yet reacted gas to a temperature sufficiently high to make the combustion process proceed there.
Even for good fuels like hydrogen and hydrocarbons the case may be that generated heat is not sufficient. The flame then dies. This is the case when the concentration of burnables in an air mixture is too low (or so high that the oxygen concentration is too low). When judging the danger for a possible explosion a common concept is lower (or upper) explosion limit.
In many cases there are emissions of inherently energy rich and easily combusted substances where, however, their concentrations are so low that they cannot support an ordinary combustion. This is the case for instance with evacuated air from many paint and printing shops.
To purify such air by combustion of the solvents there are two conventional ways:
1. The administration of heat to the air for instance by means of support flames so that the whole gas mixture is heated to a temperature high enough. This method is simple and usually works well, but when the original concentration is low it demands much energy for the heating, which makes this method expensive.
2. The use of catalysts. By using catalysts it is possible to make a combustion process proceed at a comparatively low temperature. This is done by making the gas pass over the catalyst which has the capability to make a combustion process proceed although both temperature and concentrations of burnables are low. Hereby much energy is saved compared to method 1 above. However, the method has some drawbacks, for instance:
(a) Catalysts are expensive.
(b) Catalysts are easily destroyed by certain impurities in the gas even if their concentration is low (catalyst poisons).
(c) Catalysts usually are sensitive to temperature and destroyed at too high temperatures. Consequently, gas mixtures with too high concentrations of burnables cannot be treated and the whole process is sensitive to variations of concentration of burnables.
The present invention relates to a process for the establishment of combustion and/or decomposition of pollutants in the form of gas or particles carried by air or other gas.
The main object of this invention is to bring about a process of the above mentioned kind which makes possible an effective and reliable combustion and/or decomposition of pollutants for instance obtained in industry such as air evacuated from paint spraying booths or nitrogen oxides and thereby prevent harmful gases and particles from entering the environment.
This object is attained by a process according to the present invention of which the main characteristics are that the pollutants are fed into an apparatus in which the pollutants are heated to self combustion and/or decomposition temperature while warmer treated gas flowing through the bed in direction towards the exhaust part of the combustion device is allowed to heat inflowing gas and/or by air or other gas carried particles by means of regenerative countercurrent heat exchange.
A second object of the invention is to present an apparatus by means of which the above mentioned process can be practised.
Said second object is accomplished by an apparatus according to the present invention characterized by said apparatus incorporating a bed filled with sand, stone or the like having the ability to store heat and exchange heat and having means for heating of the inner portion of said bed to self decomposition temperature and/or self combustion temperature for instance by means of an e
REFERENCES:
patent: 2795054 (1957-06-01), Bowen
patent: 3769922 (1973-11-01), Furlong et al.
patent: 3888193 (1975-06-01), Kishigami et al.
patent: 3942264 (1976-03-01), Zenker
patent: 4310020 (1982-01-01), Jespersen
patent: 4475884 (1984-10-01), Shang et al.
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