Glass manufacturing – Processes – With measuring – sensing – inspecting – indicating – or testing
Reexamination Certificate
1999-08-30
2001-05-29
Silverman, Stanley S. (Department: 1731)
Glass manufacturing
Processes
With measuring, sensing, inspecting, indicating, or testing
C065S029110, C065S029130, C065S134600, C065S157000, C065S158000, C065S160000, C065SDIG001, C095S008000, C095S025000, C095S232000, C096S244000, C423S235000, C423S239100, C422S119000, C422S105000, C422S120000, C422S900000
Reexamination Certificate
active
06237368
ABSTRACT:
This invention relates to a method of regulating or controlling the content of NO
x
in exhaust gases produced during the operation of glass-melting furnaces with several burners which are operated in alternation.
BACKGROUND OF THE INVENTION
Methods of reducing nitrogen oxides in exhaust gases are known. The DE-OS-3615021 describes a method for the selective catalytic reduction of nitrogen oxides from exhaust gases of internal combustion engines by adding ammonia in a reactor. In accordance with this method the addition of ammonia is effected in dependence on the NO
x
-concentration in the exhaust gas, and the NO
x
-concentration is determined indirectly by measuring operating parameters of the internal combustion engine and subsequently calculating the concentration of nitrogen monoxide and nitrogen dioxide in dependence on at least one selected operating parameter on the internal combustion engine in consideration of families of characteristics.
In Römpps Chemie-Lexikon, 8th edition, pp. 1484 to 1490 the operation of glass-melting furnaces is described in detail. Glass-melting furnaces mostly are tank furnaces having a plurality of laterally disposed burners which are operated in alternation. The actual heating of the glass-melting furnaces is mostly effected by means of long-distance gas, heating oil or natural gas. The exhaust gases produced contain nitrogen oxides, due to fuels, high temperatures or additives. During the denitrification of exhaust gases, the NO
x
-content of the pure gas must, for legal reasons, always be monitored in connection with the O
2
-content of the pure gas, which leads to the fact that in practice the setpoint of the NO
x
-content, NO
x
set, is transformed into a standardized setpoint NO
x
set n. In general, the following relation is used for the standardization:
NO
x
set
n
=
NO
x
set
·
(
21
-
O
2
act
)
(
21
-
8
)
However, this standardization is disadvantageous when the glass-melting furnaces comprise several burners which are operated in alternation. If one burner is switched off during a combustion break, the NO
x
-content of the exhaust gas drops to a relatively large extent. When regulating the content of NO
x
in the exhaust gases by means of a simple regulator circuit, the introduced amount of NH
3
, which reacts with the nitrogen oxides in a known manner, is dependent on the deviation xd, wherein:
xd=
NO
x
set
n−
NO
x
′
With decreasing NO
x
-content of the exhaust gases both the value NO
x
set n and the value NO
x
′ are decreased, which leads to the fact that the deviation xd does not or only insignificantly change. Since with a reduction of the content of NO
x
in the exhaust gases the deviation xd changes only insignificantly, the amount of NH
3
to be supplied likewise remains almost constant in the denitrating plant, which leads to the fact that more NH
3
is introduced than can be reacted with the nitrogen oxides. This in turn leads to the fact that the content of NH
3
in the pure gas generally exceeds the admissible limit values. A further disadvantage of this conventional known regulation lies in the fact that the denitrating plant is generally not arranged in direct vicinity of the glass-melting furnaces. Thus, the exhaust gas requires some time to flow from the glass-melting furnace to the pure-gas port of the denitrating plant, in which port the pure gas values are measured in general. When the operation of a burner is interrupted, a NO
x
-content is measured in the denitrating plant which requires a higher amount of NH
3
than this is actually necessary with the real values in the glass-melting furnace. Thus, a certain time must elapse before a regulation by means of a simple regulator circuit can be performed to react on the individual combustion breaks of the burners in the glass-melting furnaces.
SUMMARY OF THE INVENTION
The object underlying the invention is to provide a method of regulating or controlling the content of NO
x
in exhaust gases produced during the operation of glass-melting furnaces with several burners which are operated in alternation, where the known standardization of the setpoint NO
x
set need not be omitted. By means of this method a relatively quick reaction to fluctuating NO
x
-contents during combustion breaks of individual burners in the glass-melting furnace should furthermore be possible.
DETAILED DESCRIPTION
The object underlying the invention is solved by a method of regulating or controlling the content of NO
x
in exhaust gases produced during the operation of glass-melting furnaces with several burners which are operated in alternation, where the setpoint of the NO
x
-content, NO
x
set, is supplied to a multiplier, at the same time the content of O
2
in the pure gas, O
2
act, is measured continuously, and the content of O
2
detected in a first transducer, O
2
act′, is likewise supplied to the multiplier, and in the multiplier a standardization of the setpoint NO
x
set into a standardized setpoint NO
x
set n is effected, where the following applies for the standardization:
NO
x
set
n
=
NO
x
set
·
(
21
-
O
2
act
)
(
21
-
8
)
and where the standardized setpoint NO
x
set n is compared with the content of NO
x
in the pure gas, NO
x
′, which has been detected by a second transducer, the deviation xd resulting from such comparison is supplied to a regulator, which adapts the amount of NH
3
to be supplied to the denitrating plant as a correcting variable y for regulating the NO
x
-content as a regulating variable, and where both the beginning of a combustion break FP
+
and the end of a combustion break FP
−
are each supplied as a signal to a binary signal generator, which supplies the signals with a time delay as time-delayed beginning of a combustion break FP
z
+
or as time-delayed end of a combustion break FP
z
−
to the regulator, which interrupts the regulation upon receipt of the signal FP
z
+
and adjusts the amount of NH
3
to a lower constant fixed value F
1
by means of a control, the content of NO
x
in the pure gas, NO
x
′, detected by the second transducer is supplied to a memory element, where it is transformed into a higher constant fixed value F
2
as amount of NH
3
, which is likewise supplied to the regulator, and where, as soon as the regulator has received the signal FP
z
−
, the fixed value F
1
is adjusted to the fixed value F
2
via a control, and directly subsequent thereto the regulation is continued. As glass-melting furnaces there are generally used pot furnaces or tank furnaces, which operate continuously or discontinuously and comprise several burners. The term“burner” not only includes the heatings with long-distance gas, heating oil or natural gas, but also heating electrodes. The term “combustion break” refers to the interruption of the operation of at least one burner. The signal for the beginning of a combustion break FP
+
is immediately generated whenever the burner is switched off. The signal for the end of a combustion break FP
−
is immediately generated whenever the burner is switched on again. The signal for the time-delayed beginning of a combustion break FP
z
+
is generated by the binary signal generator a certain period after the burner has been switched off. The signal for the time-delayed end of a combustion break FP
z
−
is generated by the binary signal generator a certain period after the burner has been switched on again. In the definition of this time delay &Dgr;t, which in both cases is the same, two definitions are required for technical reasons. When the temperature of the exhaust gases lies between 750 and 1100° C., the denitrification can be effected by addition of NH
3
without a catalyst being present. In this case, &Dgr;t is the time required by the exhaust gas to flow from the glass-melting furnace to the point where NH
3
is introduced into the denitrating plant. When the temper
Beisswenger Hans
Hasselwander Klaus
Herden Hansjörg
Ludwig Peter
Mayer-Schwinning Gernot
Colaianni Michael P.
Metallgesellschaft Aktiengesellschaft
Norris & McLaughlin & Marcus
Silverman Stanley S.
LandOfFree
Process for the regulating or controlling the NOx content of... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for the regulating or controlling the NOx content of..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for the regulating or controlling the NOx content of... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2472430