Combustion – Process of combustion or burner operation – Controlling or proportioning feed
Reexamination Certificate
2001-02-26
2003-05-06
Clarke, Sara (Department: 3743)
Combustion
Process of combustion or burner operation
Controlling or proportioning feed
C431S089000, C432S019000
Reexamination Certificate
active
06558155
ABSTRACT:
The invention relates to a process for regulating the water vapor content in a very high temperature furnace, and particularly in a furnace for baking ceramics and carbonaceous products.
It is known that in the production of technical ceramics and carbonaceous products at temperatures of 1300 to 1800° C. in furnaces with burners, that the presence of water vapor resulting from the combustion of the hydrocarbon combustibles from the burners has undesirable consequences as to the quality of the ceramics and the carbonaceous products obtained.
At lower temperatures, this drawback is overcome by using electric furnaces or furnaces with radiant burners, in which furnaces no water vapor is produced. But it is technically and economically difficult to achieve temperatures of 1300 to 1800° C. with such furnaces and the furnaces burning combustibles are required.
As the invention thus provides a process for adjusting the water vapor content in a very high temperature furnace, which consists in using as the essential combustible, carbon monoxide and as the combustion supporter, oxygen or air enriched in oxygen.
Carbon monoxide can be used alone or combined with a small quantity of hydrocarbon combustible (natural gas for example), small quantity being calculated to give a predetermined quantity of water vapor in the furnace.
The equations prevailing in the combustion are as follows:
2CO+O
2
+(xN
2
)→2CO
2
+(xN
2
) 1)
CH
4
+20
2
+(yN
2
)→CO
2
+2H
2
O+(yN
2
) 2)
(equations similar to 2) are written for diverse hydrocarbons C
n
H
2n-2
other than methane).
In the case of equation 1), there is no production of water; whilst in equation 2), corresponding schematically to the use of natural gas as combustible, the formation of a large quantity of water is shown.
On the contrary, if there is introduced a small flow rate of natural gas into the burner, the quantity of water present in the furnace can be predetermined and adjusted.
Moreover, the use of CO has other advantages relative to the use of natural gas and permits limiting the volume of the fumes and also improving the thermal output.
It is seen that according to equations 1 and 2, with stoichiometric combustion, the volume ratio of the combustion supporter to the combustible favors carbon monoxide relative to methane (natural gas) when using pure oxygen or air as the combustion supporter.
volume
O
2
volume
CO
=
0.5
volume
air
volume
CH
4
=
2.38
whilst
volume
O
2
volume
CH
4
=
2
volume
air
volume
CH
4
=
9.53
The same advantageous ratio obtains for the production of fumes:
volume of fumes (air)
volume CO
=
2.89
volume of fumes (air)
volume
CH
4
=
10.56
Moreover, the energy released by the combustion of a cubic meter of CO (with air at 20° C.) is 12 MJ/m
3
and gives a theoretical adiabatic temperature of 2468° C. (apart from the energy of dissociation) or 1958° C. (with the energy of dissociation).
This temperature is thus sufficient for the furnace and the product to be heated to reach a temperature of 1800° C.
The energy released by the combustion of a cubic meter of CH
4
under the same conditions being 33.9 MJ/m
3
“net heating value”, the quantity of fumes released by MJ is also favorable for the combustion of CO
volume of fumes (air)
MJ
CO
=
0.24
volume of fumes (air)
MJ
CO
4
=
0.31
It will be noted that the thermal output for the combustion of pure CO is further improved by the absence of the formation of water, because the energy of vaporizing this water is saved.
Carbon monoxide is more expensive combustible than natural gas or the other conventional combustibles, but the advantages that it gives and the very great technical difficulty to obtain temperatures of 1800° C. with electric furnaces or radiant burners on an industrial scale, compensate this drawback.
The combustion supporters constituted by air which can be dried if it is desired to obtain an atmosphere free from water or by air enriched in oxygen up to the point of being pure oxygen.
REFERENCES:
patent: 3363993 (1968-01-01), Campbell
patent: 4050877 (1977-09-01), Craig et al.
patent: 4309168 (1982-01-01), Prill et al.
patent: 4462792 (1984-07-01), Roth et al.
patent: 4927348 (1990-05-01), Avidan
patent: 5569312 (1996-10-01), Quirk et al.
patent: 6289694 (2001-09-01), Pieper
patent: 2179532 (1973-11-01), None
Ceric
Clarke Sara
Young & Thompson
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