U.S. patent application number 13/512207 was filed with the patent office on 2012-11-22 for method for correcting the combustion settings of a set of combustion chambers and apparatus implementing the method.
This patent application is currently assigned to Five Stein. Invention is credited to Patrick Giraud.
Application Number | 20120291679 13/512207 |
Document ID | / |
Family ID | 42312642 |
Filed Date | 2012-11-22 |
United States Patent
Application |
20120291679 |
Kind Code |
A1 |
Giraud; Patrick |
November 22, 2012 |
METHOD FOR CORRECTING THE COMBUSTION SETTINGS OF A SET OF
COMBUSTION CHAMBERS AND APPARATUS IMPLEMENTING THE METHOD
Abstract
The invention relates to a method for real-time, continuous
adjustment of a set of thermal combustion chambers (2, 2i) having
similar characteristics supplied by the same combustive agent (8)
and fuel (9) networks, according to which one of the chambers (2i)
is used as a reference chamber, combustion parameters are measured
(7) in the fumes output from the reference chamber, and the control
parameters of all the chambers (2) are adjusted according to the
combustion parameters measured at the output of the reference
chamber (2i), in particular according to the ratio of combustive
agent to fuel and/or the composition of the combustive agent and/or
fuel.
Inventors: |
Giraud; Patrick; (Maisons
Alfort, FR) |
Assignee: |
Five Stein
Maisons-Alfort
FR
|
Family ID: |
42312642 |
Appl. No.: |
13/512207 |
Filed: |
November 26, 2010 |
PCT Filed: |
November 26, 2010 |
PCT NO: |
PCT/IB10/55454 |
371 Date: |
July 30, 2012 |
Current U.S.
Class: |
110/186 ;
431/12 |
Current CPC
Class: |
F23C 2202/30 20130101;
F23C 2201/20 20130101; F23N 3/00 20130101; F23N 5/003 20130101;
F23N 5/006 20130101; F23C 2202/20 20130101; F23D 2203/002 20130101;
F23N 2237/02 20200101; F23N 1/00 20130101; F23C 6/02 20130101 |
Class at
Publication: |
110/186 ;
431/12 |
International
Class: |
F23N 1/02 20060101
F23N001/02; F23C 6/00 20060101 F23C006/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 30, 2009 |
FR |
0905752 |
Claims
1-12. (canceled)
13. A method for real-time and continuous control of a set of
thermal combustion chambers (2, 2r, 2i) having similar
characteristics, supplied by the same combustion agent (8) and fuel
(9) networks, the method comprising: using one of the chambers (2,
2r, 2i) as a reference chamber; measuring combustion parameters (7)
in the fumes at an outlet of the reference chamber; and adjusting
control parameters of all the chambers according to the combustion
parameters measured at the outlet of the reference chamber, in
particular according to the ratio of combustion agent to fuel
and/or the composition of combustion agent and/or fuel.
14. The method as claimed in claim 13, wherein the combustion
parameters measured in the fumes at the outlet of the reference
chamber include at least a concentration of oxygen and/or a
concentration of carbon dioxide and/or a concentration of carbon
monoxide and/or a concentration of hydrogen and/or a rate of
unburnt residues and/or a concentration of nitrogen oxides.
15. The method as claimed in claim 14, wherein the level of excess
air is determined according to the concentration of oxygen or
carbon dioxide in the fumes at the outlet of the reference
chamber.
16. The method as claimed in claim 14, wherein the lack of air is
determined by the concentration of carbon monoxide or hydrogen or
unburnt residues in the fumes at the outlet of the reference
chamber.
17. The method as claimed in claim 13, wherein the control
parameters of all the chambers are adjusted so as to obtain the
desired level of excess air and/or rate of unburnt residues.
18. The method as claimed in claim 16, wherein the control
parameters of all the chambers are adjusted so as to obtain a
desired lack of air.
19. The method as claimed in claim 14, wherein the concentration of
nitrogen oxides is regulated by adjusting the composition of the
combustion agent and/or fuel, in particular by diluting with
combustion products.
20. The method as claimed in claim 13, wherein the thermal chambers
comprise radiant tubes, one of the radiant tubes being a reference
tube, and the other radiant tubes being supplied with proportions
of gas which are different from those of the reference tube.
21. An apparatus for implementing a method as claimed in claim 13,
comprising a set of thermal combustion chambers (2, 2r, 2i) having
similar characteristics, supplied by the same combustion agent (8)
and fuel (9) networks, wherein: one of the chambers (2, 2r, 2i) is
used as a reference chamber, means for measuring (7) the combustion
parameters are installed at the outlet of the reference chamber to
measure said combustion parameters in the fumes at the outlet,
control means (FCVc, FCVf) are provided to adjust the control
parameters of the set of chambers according to the measures
implemented at the outlet of the reference chamber, in particular
according to the ratio of combustion agent to fuel and/or the
composition of combustion agent and/or fuel.
22. The apparatus as claimed in claim 21, wherein the thermal
chambers comprise radiant tubes, wherein a reference tube (2r) is
supplied together with the other tubes, the control members (FCVc,
FCVf) being placed on supply circuits (8, 9) common to all the
tubes.
23. The apparatus as claimed in claim 21, wherein the thermal
chambers comprise radiant tubes, wherein one of the radiant tubes
is a reference tube (2i), and wherein the other radiant tubes are
supplied separately from the reference tube (2i) and have different
control members (FCVc, FCVf) from those (FCVci, FCVfi) of the
reference tube (2i), on different supply circuits (8, 9, 8i, 9i),
the control members (FCVc, FCVf) of the tubes (2) being controlled
such that said tubes (2) are supplied with the same proportions of
gas as the reference tube (2i).
24. The apparatus as claimed in claim 23, wherein the control
members (FCVc, FCVf) of the radiant tubes (2) are controlled such
that said tubes are supplied with proportions of gas which are
different from those of the reference tube (2i), in particular with
a different level of excess air.
Description
[0001] The present invention relates to a method for the adjustment
of devices for supplying a set of combustion chambers supplied with
a combustion agent and a fuel, the properties thereof being
variable. The invention enables possible fluctuations of said
properties to be taken into account so as to maintain the desired
quality of combustion.
[0002] Numerous industrial heating devices consist of a set of
separate combustion chambers supplied by a common device for
supplying combustion agent and fuel. For example, in the iron and
steel industry the devices are furnaces for continuous processing
lines for metal strips, provided with radiant tubes.
[0003] In many cases, the combustion agents or fuels used have
properties which may vary over time. For example, when using
enriched air or depleted air, or even when using fuels co-produced
on site such as coke oven gas, steel furnace gas, a mixture of
gases or even alternative fuels such as biogas or generator
gas.
[0004] Numerous methods exist for correcting the regulation of a
furnace according to the properties of the fuel. Said methods make
it possible to correct the fluctuation of one of the principal
parameters of the fuel, for example the calorific power PCI, the
combustive power, the combustion index or Wobbe index.
[0005] Said methods do not permit the properties of the fuel and
the combustion agent to be taken properly into account as, in the
majority of cases, the sampling process modifies the properties of
the fuel and the combustion agent. Said methods also have the
drawback of having a relatively long response time and require
devices for measuring in protected areas to be put in place.
[0006] A specific method is proposed by FR2712961. According to
this method, a burner is controlled by removing a given quantity of
fuel, said fuel being combusted in a dedicated chamber with a
quantity of air resulting in combustion in excess air, and a
variable reflecting the deviation from stoechiometry is measured in
the fumes from the complete combustion of the fuel. This variable
is then used for determining the representative value of the
coefficient for regulating the quantity of combustion air from the
burner. Said device for measuring the combustion consists of a
combustion tunnel, a burner and appropriate measuring means.
[0007] Said system has the drawback of using a specifically
constructed mini-furnace in which an air/fuel mixture is combusted
in proportions which are controlled in order to provide an excess
level of air. Said mini-furnace consumes fuel and has to operate
with an excess level of air. The combustion is carried out in said
mini-furnace at an operating point which may be very different from
that of the apparatus to be regulated, for example in terms of the
power of the burner, the air/gas ratio, the temperature of the
furnace and the containment of the flame. The processing of the
results thus requires the use of mathematical correction
formulae.
[0008] Said system also has the drawback of being exclusively
dedicated to taking into account variations in the properties of
the fuel. It does not take into account variations in the
properties of the combustion agent nor the combustion parameters
appropriate for the monitored apparatus, namely the proportion of
unburnt residues or even the proportion of nitrogen oxide NOx
emissions.
[0009] The object of the invention is primarily to improve the
control of the combustion of a set of combustion chambers involved
in a manufacturing process; in particular, the invention aims to
improve the control of a set of radiant tubes for a continuous
processing line for metal strips.
[0010] Said combustion chambers are of the same type. The power of
each of said combustion chambers may be variable but the
technologies implemented are similar. The potential differences
between said combustion chambers do not influence the combustion
parameters which are desired to be monitored.
[0011] In order to ensure the control of the combustion of the set
of radiant tubes, one of said tubes installed in the furnace shell
is used as a reference tube. Said reference tube takes part in the
heating of the strip, as do all the other tubes. Said radiant tube
has a similar construction to that of the other tubes and is acted
upon in a manner representative of the operation of the other tubes
which take part in the heating process.
[0012] The combustion products at the outlet of the radiant tube
are cooled by taking part in the process of heating the furnace. A
measurement device is installed at the outlet of said reference
tube, said measurement device providing information about the
status of the combustion products downstream of the tube.
Generally, said device is a gas analyzer which permits information,
for example about the excess air and/or unburnt residues, to be
obtained, in particular.
[0013] Thus, according to the invention, the method for real-time
and continuous control of a set of thermal combustion chambers
having similar characteristics, supplied by the same combustion
agent and fuel networks, is characterized in that: [0014] one of
the chambers is used as reference chamber, [0015] combustion
parameters are measured in the fumes at the outlet of the reference
chamber, [0016] the control parameters of all the chambers are
adjusted according to the combustion parameters measured at the
outlet of the reference chamber, in particular according to the
ratio of combustion agent to fuel and/or the composition of the
combustion agent and/or fuel.
[0017] The combustion parameters measured in the fumes at the
outlet of the reference chamber may consist at least of the
concentration of oxygen and/or the concentration of carbon dioxide
and/or the concentration of hydrogen and/or the concentration of
nitrogen oxides and/or the rate of unburnt residues.
[0018] The level of excess air may be determined according to the
concentration of oxygen or carbon dioxide in the fumes at the
outlet of the reference chamber. The lack of air may be determined
by the concentration of carbon monoxide or hydrogen or unburnt
residues in the fumes at the outlet of the reference chamber.
[0019] Advantageously, the control parameters for all the chambers
are adjusted so as to obtain the desired level of excess air and/or
rate of unburnt residues. It is possible to adjust the control
parameters for all the chambers so as to obtain the desired lack of
air and/or the rate of unburnt residues.
[0020] The concentration of nitrogen oxides may be regulated by
adjusting the composition of the combustion agent and/or fuel, in
particular by diluting with combustion products.
[0021] The thermal chambers may consist of radiant tubes supplied
with proportions of gas which are different from those of the
reference tube.
[0022] The invention also relates to an apparatus for implementing
a method as defined above, comprising a set of thermal combustion
chambers having similar characteristics, supplied by the same
combustion agent and fuel networks, characterized in that: [0023]
one of the chambers is used as a reference chamber, [0024] means
for measuring the combustion parameters are installed at the outlet
of the reference chamber to measure said combustion parameters in
the fumes at the outlet, [0025] control means are provided to
adjust the control parameters of the set of chambers according to
the measures implemented at the outlet of the reference chamber, in
particular according to the ratio of combustion agent to fuel
and/or the composition of combustion agent and/or fuel.
[0026] The thermal chambers may consist of radiant tubes and a
reference tube may be supplied together with the other tubes, the
control members being placed on supply circuits common to all the
tubes.
[0027] According to a further possibility, the radiant tubes are
supplied separately from the reference tube and have different
control members from those of the reference tube, on different
supply circuits, the control members of the tubes being controlled
such that said tubes are supplied with the same proportions of gas
as the reference tube. According to a further possibility, the
control members of the radiant tubes may be controlled such that
said tubes are supplied with proportions of gas which are different
from those of the reference tube, in particular with a different
level of excess air.
[0028] Relative to the equipment used in the prior art, according
to the invention a standard device is used as the combustion
chamber, said device being similar to the others and being used in
the method, and the control thereof being entirely representative
of the operation of all the devices. In particular, it permits the
parameters which depend on the mode of operation of the entire
apparatus to be controlled.
[0029] Generally, the main parameter is the level of excess air
measured by the concentration of oxygen. However, it may be
necessary to monitor other parameters, for example the unburnt
residues when the furnace is cold or even the nitrogen oxide
emissions which may be regulated, for example according to
variations in the properties of the combustion agent and/or
fuel.
[0030] The method according to the invention also enables devices
functioning in the absence of air to be regulated. In this case,
the monitored parameter may be a component representing one of the
gases representative of this combustion mode, present in a high
proportion in the fumes. This gas may, for example, be carbon
monoxide CO.
[0031] The reference tube is supplied by circuits supplying
combustion agent and fuel provided with control members enabling
the proportion thereof to be adjusted. Said reference tube may also
be supplied by additional circuits, for example for combustion
fumes or oxygen.
[0032] The analyses carried out on the combustion products at the
outlet of the reference tube are taken into account to control the
control members of the supply circuits so as to obtain the desired
quality of combustion.
[0033] When the reference tube is supplied together with the other
tubes, i.e. when the control members are placed on supply circuits
common to all the tubes, including the reference tube, the other
tubes benefit from this same control.
[0034] When the radiant tubes are supplied separately from the
reference tube, i.e. they have control members on the different
supply circuits, said control members are controlled such that said
tubes are supplied with the same proportions of gas as the
reference tube, or with a different proportion.
[0035] If the two sets of radiant tubes are designed to have
identical controlled parameters, for example an identical supply
pressure for a different operating power, whilst maintaining the
same proportion of gas, the controlled parameters of the reference
tube are reproduced for the members of the supply circuits of the
second set of tubes.
[0036] If the two sets of radiant tubes are designed to have
different controlled parameters, for example a different supply
pressure, whilst maintaining the same proportion of gas, the
controlled parameters of the reference tube are corrected for the
members of the supply circuits of the second set of tubes. Said
correction depends on the law of physics of the measured value, for
example the variation in the flow rate according to the variation
using the square of the differential pressure.
[0037] According to the invention, when the radiant tubes are
supplied separately from the reference tube, their control members
may be controlled such that said tubes are supplied with different
proportions of gas from those of the reference tube, for example
with a different level of excess air.
[0038] The control of the calorific requirement of the reference
tube may be implemented by altering the flow rate or altering the
duration. The control may be associated with that of other radiant
tubes or it may be separate.
[0039] Apart from the arrangements set forth above, the invention
consists of a certain number of other arrangements which will be
referred to in more detail hereinafter with reference to
embodiments, disclosed with reference to the accompanying drawings,
but which are in no way limiting. In the drawings:
[0040] FIG. 1 is a schematic view of a continuous treatment line
for metal strips,
[0041] FIG. 2 is a schematic view of a radiant tube,
[0042] FIG. 3 shows an example for supplying a pair of radiant
tubes,
[0043] and FIG. 4 is a second example for supplying a set of
radiant tubes.
[0044] With reference to FIG. 1 of the drawings it is possible to
see a furnace 1, shown schematically, provided with radiant tubes 2
providing the heating of a metal strip 3, passing along rollers,
not shown. The heating is carried out in a protective atmosphere,
generally composed of a mixture of nitrogen oxide and hydrogen. In
each radiant tube, the combustion is ensured in a confined
combustion chamber, separated from the furnace shell by the tube.
Thus indirect heating takes place.
[0045] With reference to FIG. 2 of the drawings, it is possible to
see a U-shaped radiant tube 2, shown schematically. The radiant
tubes may have other shapes, for example they may be I-shaped,
P-shaped, double P-shaped or W-shaped. A burner 4 is located at one
end of the tube 2. The flame 5 is propagated in the tube and
releases its energy toward the walls of the tube which heats the
shell and the strip. As they pass into the tube, the fumes
thermally dissipate on the walls of the tube. A heat recovery
system, not shown, enabling the combustion air to be preheated is
generally positioned at the end of the tube opposing the burner. At
the outlet of the tube, the partially dissipated fumes are
evacuated toward a collector 6 connected to a flue. An analyzer 7
positioned downstream of the outlet of the tube, permits the
analysis of the combustion products.
[0046] With reference to FIG. 3 of the drawings, it is possible to
see an embodiment of the circuit for supplying combustion agent and
fuel to a set of U-shaped radiant tubes, including a reference tube
2r, shown schematically. The burners 4 are supplied by a system for
supplying combustion agent 8, with a control valve FCVc and a
system for supplying fuel 9 with a control valve FCVf. The
automatic control of the valves may be ensured by an automatic
system (not shown) which receives at the inlet information about
the combustion parameters measured by the analyzer 7 at the outlet
of the reference tube 2r. The automated system provides, at the
outlets connected to the controls of the valves, specific
instructions for control as a function of the input data.
[0047] In this embodiment, the furnace zone is provided with
radiant tubes 2, the burners 4 thereof being supplied in parallel
by common combustion agent and fuel networks. The variation in the
calorific requirement is controlled by the operating times of the
burners, i.e. for each burner the proportion of the duration of
opening of its combustion agent valve FCVc and its fuel valve FCVf
during a given time.
[0048] Each of the burners has been previously controlled during
commissioning for a known operating point by means of manual flow
limiters 10. For a given operating point, for example at 100%
power, each of the burners has been previously controlled by an
individual flow limiter device. In these conditions, for a given
general operation of the furnace zone, the operation of a tube
selected as a reference tube generally illustrates the operation of
the set of burners connected to the same supply systems. By
modifying the settings of the system for supplying the reference
tube, i.e. the valves FCVc and FCVf, to take into account the
change in the characteristics of the fuel or combustion agent, the
control of all the radiant tubes is modified.
[0049] The control of the valves FCVc and FCVf causes a variation
in the pressure of the combustion agent Pc or the pressure of the
fuel Pf, enabling the proportion of the gases to be adjusted to be
identical with all the tubes.
[0050] The measurements carried out by the analyzer 7 placed at the
outlet of the reference tube may, for example, be limited to two
parameters: the oxygen content which represents the level of excess
combustion agent and the proportion of unburnt residues, the
quantity thereof resulting in corrections to the level of excess
air, in particular at low temperatures.
[0051] With reference to FIG. 4 of the drawings, it is possible to
see a furnace provided with U-shaped radiant tubes, shown
schematically.
[0052] In this apparatus, a set of four radiant tubes 2 is supplied
by combustion agent 8 and fuel 9 networks common to the set of four
tubes by means of the control valves FCVc and FCVf. In this
apparatus, a reference radiant tube 2i is supplied separately by
its own system for supplying combustion agent 8i regulated by a
valve FCVci and fuel 9i regulated by a valve FCVfi.
[0053] According to a preferred embodiment of the invention, the
transmitters used on the reference tube 2i and the set of tubes 2
to be regulated, make use of the same laws of physics. For example,
it is possible to use a differential pressure transmitter to
measure the flow rate.
[0054] At a given operating point, for example at 100% power, each
of the burners, including that of the reference tube, has been
previously controlled during commissioning by a separate flow
limiter device 10, in particular by manual control, so as to obtain
the same ratio of combustion agent/fuel at each burner. This
control is carried out in the same conditions for all the tubes,
i.e. with the same quality of combustion agent and fuel.
[0055] It should be noted that each of the tubes may have a nominal
power and/or different dimensions. The tubes may also be of
different shapes, for example they may be U-shaped or W-shaped.
[0056] In control mode, the flows of combustion agent and fuel from
the reference tube are adjusted so as to have the correct rate of
oxygen in the fumes according to variations in the properties of
the fuel and/or the combustion agent. The analyzer 7 enables the
valves FCVci and FCVfi to be controlled so as to obtain the desired
combustion quality in the reference tube. The corresponding
operating point measured by the pressures Pci and Pfi defines the
control variables Pc and Pf used to control the valves FCVc and
FCVf.
[0057] As the settings of the reference tube 2i are representative
of the desired combustion at all the tubes, the values measured at
its supply system are used to govern the regulation of the set of
tubes 2.
[0058] For example, the fuel valve FCVf will be controlled
according to the calorific requirement and the combustion agent
valve FCVc will be controlled so that the value Iva of the
measurement signal which is representative of the flow of
combustion agent at the set of tubes to be regulated is defined
according to the following relation:
Iva/Ivf=K.times.Ivai/Ivfi
[0059] In this relation, K is a constant value, Ivai expresses the
measurement signal which is representative of the combustion agent
at the reference tube 2i, Ivfi expresses the signal of the
measurement which is representative of the fuel at the reference
tube 2i and Ivf expresses the measurement signal which is
representative of the fuel at the set of tubes 2 to be
regulated.
[0060] The advantage of this system is that it enables corrections
to be easily made to the regulation of a heating system. The
response time is thus very short and the control parameters are
entirely representative of the desired control.
[0061] An extension of this application is to control an apparatus
of which the composition of the combustion agent is variable. This
variation may be unintentional, for example the composition of the
air is dependent on the humidity content.
[0062] This variation may be intentional, for example by modifying
the rate of oxygen of the combustion agent. Thus, oxygen enrichment
may be carried out to increase the output of a furnace, reduce the
consumption of fuel or reduce CO2 emissions. Oxygen depletion may
be implemented in order to modify the thermal transfer, for example
by extending the flame, or to reduce the NOx emissions. In this
application, the measurement of NOx in the fumes of the reference
tube serves to regulate the rate of dilution of the combustion
agent.
[0063] The invention makes it possible to adjust the settings which
may be different from those of the reference burner. According to
the invention, the flame develops in a reference chamber which is
similar to the other chambers, but not in the open air.
[0064] The combustion in a chamber is significantly influenced by
the geometry thereof. Said geometry dictates the containment of the
flame, the nature of the flow of gas, the recirculation of part of
the fumes and the temperature cartography in the chamber. All these
parameters influence the combustion, in particular the temperature
of the flame.
[0065] The results of the combustion measured at the outlet of the
reference chamber are thus directly representative of the
combustion as produced in the other chambers.
* * * * *