U.S. patent application number 12/946615 was filed with the patent office on 2012-05-03 for burner control systems and methods of operating a burner.
This patent application is currently assigned to Autoflame Engineering Limited. Invention is credited to Brendan KEMP.
Application Number | 20120107753 12/946615 |
Document ID | / |
Family ID | 43365628 |
Filed Date | 2012-05-03 |
United States Patent
Application |
20120107753 |
Kind Code |
A1 |
KEMP; Brendan |
May 3, 2012 |
BURNER CONTROL SYSTEMS AND METHODS OF OPERATING A BURNER
Abstract
Burner control systems and methods of operating a burner are for
a large boiler such as might be used in hospitals, hotels, offices
or other large commercial or domestic premises.
Inventors: |
KEMP; Brendan; (Sevenoaks,
GB) |
Assignee: |
Autoflame Engineering
Limited
Biggin Hill
GB
|
Family ID: |
43365628 |
Appl. No.: |
12/946615 |
Filed: |
November 15, 2010 |
Current U.S.
Class: |
431/12 ; 110/188;
110/189; 110/190; 431/76 |
Current CPC
Class: |
F23N 5/184 20130101;
F23N 5/18 20130101; F23N 2225/06 20200101; F23N 5/242 20130101;
F23N 2005/185 20130101; F23N 2235/06 20200101; F23N 2231/18
20200101; F23N 2235/12 20200101; F23N 1/022 20130101; F23N 2005/181
20130101; F23N 2231/26 20200101; F23N 2225/14 20200101; F23N
2223/54 20200101; F23N 2231/00 20200101; F23N 5/003 20130101 |
Class at
Publication: |
431/12 ; 110/188;
110/189; 110/190; 431/76 |
International
Class: |
F23N 3/04 20060101
F23N003/04; F23N 5/00 20060101 F23N005/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 28, 2010 |
GB |
1018178.2 |
Claims
1. A burner control system for controlling operation of a burner,
the system comprising a regulator system for controlling the
proportion of air to fuel fed to the burner, wherein the control
system is arranged to receive an input signal relating to
measurement of at least one ambient variable selected from the
group consisting of the ambient air pressure and the ambient air
temperature, and the signal is used to trim the proportion of air
to fuel fed to the burner.
2. A burner control system according to claim 1, wherein the
control system is arranged to provide an output signal for
adjusting an air valve to alter the airflow to the burner by
trimming the setting of the air valve according to the ambient air
pressure and/or the ambient air temperature.
3. A burner control system according to claim 1, further including
a system for analysing exhaust gases emitted by the burner and
trimming the proportion of air to fuel according to the
analysis.
4. A burner control system according to claim 1, wherein the system
further includes a store for storing pairs of values of air and
fuel valve settings for varying firing rates of the burner.
5. A burner control system according to claim 4, wherein for each
pair of values of air and fuel valve settings a respective value of
air pressure of the airflow to the burner is arranged to be
stored.
6. A burner control system according to claim 4, wherein for each
pair of values of air and fuel valve settings a respective value of
fuel pressure of the fuel flow to the burner is arranged to be
stored.
7. A burner control system for controlling operation of a burner,
wherein pairs of values of air and fuel valve settings are stored
for varying firing rates of the burner, and in which for each pair
of values of air and fuel valve settings at least one respective
value selected from the group consisting of the respective value of
the air pressure of the airflow to the burner and the respective
value of the fuel pressure of the fuel flow to the burner, is
arranged to be stored.
8. A burner control system according to claim 7, wherein the
control system is arranged to monitor the air pressure and/or the
fuel pressure at a given firing rate and compare the monitored air
pressure and/or fuel pressure with the stored air and/or fuel
pressure value corresponding to that firing rate, or to an
interpolated value if the firing rate is between those to which
stored air and fuel valve settings relate, and to emit an output
signal for shutting down the burner in the event that the compared
values differ by more than a predetermined amount.
9. A burner control system according to claim 7, further including
a system for analysing exhaust gases emitted by the burner and
trimming the proportion of air to fuel according to the
analysis.
10. A burner control system according to claim 1, further including
a burner which is arranged to be controlled by the control system,
a fuel valve for adjusting the flow of fuel to the burner and an
air valve for adjusting the flow of air to the burner.
11. A burner control system according to claim 10, further
including a sensor for sensing ambient air pressure and/or a sensor
for sensing ambient air temperature.
12. A burner control system according to claim 10, further
including a sensor for sensing the pressure in the airflow to the
burner and/or a sensor for sensing the pressure in the fuel flow to
the burner.
13. A method of operating a burner in which a regulator system
controls the proportion of air to fuel fed to the burner,
comprising measuring at least one ambient variable selected from
the group consisting of the ambient air pressure and the ambient
air temperature, and the measurement is used to trim the proportion
of air to fuel fed to the burner.
14. A method according to claim 13, wherein an air valve is
adjusted to alter the airflow to the burner and the setting of the
air valve is trimmed according to at least one ambient variable
selected from the group consisting of the ambient air pressure and
the ambient air temperature.
15. A method according to claim 13, in which exhaust gases emitted
by the burner are analysed and the proportion of air to fuel
trimmed according to the analysis.
16. A method of operating a burner, comprising: controlling flows
of air and fuel are controlled by air and fuel valves respectively;
storing pairs of values of air and fuel valve settings are stored
for varying firing rates of the burner; and storing for each pair
of values of air and fuel valve settings at least one respective
value selected from the group consisting of a respective value of
air pressure of the airflow and a respective value of fuel pressure
of the fuel flow.
17. A burner control system according to claim 7, further including
a burner arranged to be controlled by the control system, a fuel
valve for adjusting the flow of fuel to the burner and an air valve
for adjusting the flow of air to the burner.
Description
[0001] This application claims priority to United Kingdom
application serial no. 1018178.2 filed on Oct. 28, 2010, and which
application is incorporated herein by reference. To the extent
appropriate, a claim of priority is made to the above disclosed
application.
TECHNICAL FIELD
[0002] This invention relates generally to burner control systems
and to methods of operating a burner. The invention relates in
particular, but not exclusively, to a burner for a large boiler
such as might be used in hospitals, hotels, offices or other large
commercial or domestic premises.
BACKGROUND OF THE INVENTION
[0003] A known burner control system is described in GB 2169726A
which also refers to GB 2138610A. The disclosure of both those
specifications is incorporated herein by reference. In that control
system the flows of air and fuel are controlled by air and fuel
valves respectively, and pairs of values of air and fuel valve
settings are stored for varying firing rates of the burner. Those
air and fuel valve settings are stored during a commissioning
procedure by a commissioning engineer who is able to adjust the
valve positions to obtain ideal combustion conditions for a given
firing rate.
[0004] In accordance with the teaching in GB 2169726, an exhaust
gas analysis system is provided. That makes it possible to analyse
the exhaust gases from the burner during operation and trim the
setting of the air valve from the commissioned setting to a
slightly different setting to obtain improved combustion in the
burner. Such a closed loop control or feedback system enables good
combustion conditions to be maintained, even when conditions change
from those that applied during commissioning, since it enables the
air to fuel ratio to be finely tuned.
[0005] As is recognised in GB 2169726A, there is a significant time
delay between the air for combustion passing through the air valve
and the analysis of the combustion products from combustion of that
air. The total length of that delay depends upon the firing rate of
the burner: at relatively low firing rates, which are common during
normal use of a burner, the delay is lengthened and may often be
more than 60 seconds or even three times that. It is possible to
allow for that time delay in designing the control system so that
the results of analysis are associated with the correct, earlier,
settings of the air and fuel valves. Even so, there is inevitably a
significant period of time before the feedback from the exhaust gas
analyser can be used to correct the setting of the air valve and,
until the correction is made, the incorrect setting is maintained.
That is disadvantageous both in respect of relatively small
deviations that may be due to relatively common minor variations in
conditions or in respect of less common and much bigger deviations,
for example, arising from a major drop in airflow caused by a
plastic bag being sucked into the air inlet of the burner and
obstructing it.
[0006] It is an object of the invention to provide an improved
burner control system and an improved method of operating a
burner.
SUMMARY OF THE INVENTION
[0007] According to a first aspect of the invention there is
provided a burner control system for controlling operation of a
burner, the system including a regulator system for controlling the
proportion of air to fuel fed to the burner, wherein the control
system is arranged to receive an input signal relating to
measurement of the ambient air pressure and/or the ambient air
temperature and the signal is used to trim the proportion of air to
fuel fed to the burner.
[0008] It should be understood from the reference to measurement of
"the ambient air pressure and/or the ambient air temperature" that
there are three possibilities that are being referred to: firstly
the ambient air pressure and the ambient air temperature may be
measured; secondly, the ambient air pressure, but not the ambient
air temperature, may be measured; and thirdly, the ambient air
temperature, but not the ambient air pressure, may be measured. It
is however preferred that both the ambient pressure and the ambient
temperature are measured(the first possibility referred to
above).
[0009] The invention according to the first aspect firstly
recognises that variations in ambient temperature and/or pressure
can significantly affect the airflow rate (in terms of mass per
unit time) for a given volume airflow rate and consequently lead to
a need to trim the air to fuel volumetric flow ratio. Secondly, the
invention uses the measurement of ambient conditions to trim the
proportion of air to fuel fed to the burner. That trimming can be
done pre-emptively, without having to wait for any feedback from an
exhaust gas analyser. In that case, if there is some feedback
control, for example from an exhaust gas analyser, it can still
advantageously be employed but the amount of correction likely to
be required is reduced because variation in ambient conditions have
already been taken into account.
[0010] It is possible for the proportion of air to fuel that is fed
to the burner to be adjusted by adjusting a fuel valve, but it is
generally preferred that an air valve is adjusted to alter the
airflow to the burner. Thus it is preferred that the control system
is arranged to provide an output signal for adjusting an air valve
to alter the airflow to the burner by trimming the setting of the
air valve according to the ambient air pressure and/or the ambient
air temperature.
[0011] As already indicated, preferably the control system further
includes a system for analysing exhaust gases emitted by the burner
and trimming the proportion of air to fuel according to the
analysis. It should be understood, however, that the invention is
applicable also to control systems that do not include any exhaust
gas analysis, since it can still be advantageous to trim the
proportion of air to fuel according to ambient conditions.
[0012] The flows of air and fuel may be controlled by air and fuel
valves respectively. The burner control system may further include
a store for storing pairs of values of air and fuel valve settings
for varying firing rates of the burner. Such a system provides a
simple way of accurately controlling air and fuel flows at
different firing rates of the burner. For firing rates between the
stored settings, values of air and fuel valve settings can be
interpolated.
[0013] In an especially preferred control system, for each pair of
values of air and fuel valve settings, a respective value of air
pressure of the airflow to the burner is arranged to be stored. The
control system may further include an air pressure sensor for
sensing the respective value of air pressure of the airflow. The
control system may then be arranged to monitor the air pressure at
a given firing rate and compare the monitored air pressure with the
stored air pressure value corresponding to that firing rate, or to
an interpolated value if the firing rate is between those to which
stored air and fuel valve settings relate. Similarly, for each pair
of values of air and fuel valve settings a respective value of fuel
pressure of the fuel flow to the burner may be arranged to be
stored. This may be as an alternative to storing a respective value
of air pressure but is preferably in addition to that. The control
system may further include a fuel pressure sensor for sensing the
respective value of pressure of the fuel flow. The control system
may then be arranged to monitor the fuel pressure at a given firing
rate and compare the monitored fuel pressure with the stored fuel
pressure value corresponding to that firing rate, or to an
interpolated value if the firing rate is between those to which
stored air and fuel valve settings relate. With either of the
arrangements described in this paragraph, it becomes possible to
provide a control system which is able to react almost instantly to
a sudden change in air or fuel pressure, rather than waiting for a
feedback system such as an exhaust gas analyser to detect such a
problem. That can improve the safety of the control system
considerably. For example, the control system may be designed to
shut down the burner in the event that the air or fuel pressure
departs by more than, say, 10 percent from the stored value, or an
interpolated value of the stored value.
[0014] The storage of a fuel pressure and/or an air pressure for
each pair of air and fuel valve settings is itself a special
feature of the invention and may be used without the feature of the
first aspect of the invention of measuring ambient air temperature
and/or pressure. Accordingly, in a second aspect of the invention
there is provided a burner control system for controlling operation
of a burner, in which pairs of values of air and fuel valve
settings are stored for varying firing rates of the burner, and in
which for each pair of values of air and fuel valve settings a
respective value of air pressure of the airflow and/or a respective
value of fuel pressure of the fuel flow is arranged to be
stored.
[0015] It should be understood from the reference to "a respective
value of air pressure of the airflow and/or a respective value of
fuel pressure of the fuel flow" being stored that there are three
possibilities that are being referred to: firstly both a respective
value of air pressure of the airflow and a respective value of fuel
pressure of the fuel flow may be stored; secondly, a respective
value of air pressure of the airflow, but not a respective value of
fuel pressure of the fuel flow may be stored; and thirdly, a
respective value of fuel pressure of the fuel flow, but not a
respective value of air pressure of the airflow, may be stored. It
is however preferred that both a respective value of air pressure
of the airflow and a respective value of fuel pressure of the fuel
flow are stored (the first possibility referred to above).
[0016] Preferably, the control system is arranged to monitor the
air pressure and/or the fuel pressure at a given firing rate and
compare the monitored air pressure and/or fuel pressure with the
stored air and/or fuel pressure value corresponding to that firing
rate, or to an interpolated value if the firing rate is between
those to which stored air and fuel valve settings relate, and to
emit an output signal for shutting down the burner in the event
that the compared values differ by more than a predetermined
amount
[0017] In a preferred embodiment of the second aspect of the
invention, the system further includes a system for analysing
exhaust gases emitted by the burner and trimming the proportion of
air to fuel according to the analysis.
[0018] In either the first or second aspects of the invention, once
installed, the burner control system includes a burner. Also there
may be a fuel valve for adjusting the flow of fuel to the burner
and an air valve for adjusting the flow of air to the burner. There
may be a sensor for sensing ambient air pressure and/or a sensor
for sensing ambient air temperature. Similarly, there may be a
sensor for sensing the pressure in the airflow to the burner and/or
a sensor for sensing the pressure in the fuel flow to the burner.
These components may therefore all be part of the burner control
system according to the first or second aspects of the
invention.
[0019] Commonly, the burner control system is employed in a boiler
installation. Accordingly, the invention further provides a boiler
installation including a burner control system according to the
first or second aspects of the invention.
[0020] According to the first aspect of the invention, there is
also provided a method of operating a fuel burner in which a
regulator system controls the proportion of air to fuel fed to the
burner, wherein the ambient air pressure and/or the ambient air
temperature are measured and the measurement is used to trim the
proportion of air to fuel fed to the burner.
[0021] Preferably an air valve is adjusted to alter the airflow to
the burner and the setting of the air valve is trimmed according to
the ambient air pressure and/or the ambient air temperature.
[0022] Exhaust gases emitted by the burner are preferably analysed
and the proportion of air to fuel trimmed according to the
analysis.
[0023] Also according to the second aspect of the invention, there
is provided a method of operating a burner, in which the flows of
air and fuel are controlled by air and fuel valves respectively,
and pairs of values of air and fuel valve settings are stored for
varying firing rates of the burner, and in which for each pair of
values of air and fuel valve settings a respective value of air
pressure of the airflow and/or a respective value of fuel pressure
of the fuel flow is stored.
[0024] It will be appreciated that the burner control systems of
the various aspects of the invention are closely related to each
other and to the various aspects of the methods of the invention
and that therefore essential or preferred features of one may,
unless indicated otherwise or clearly inappropriate, be
incorporated into the other. For example, features described above
in respect of the control system of the invention may be
incorporated into the method of the invention and vice versa.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] By way of example an embodiment of the invention will now be
described with reference to the accompanying schematic drawing, of
which:
[0026] FIG. 1 is a block diagram of a burner control system.
DETAILED DESCRIPTION OF EMBODIMENTS
[0027] Referring to FIG. 1, a burner control system comprises a
fuel burner 1 which in this case is a gas burner and to which gas
is fed along a duct 2 via a fan 3 and a butterfly valve 4 and to
which air is fed along a duct 5 via a fan 6 and a butterfly valve
7. In the burner 1, the gas and air are mixed and combustion takes
place. The products of combustion pass from the burner 1 along a
duct 8 where an exhaust gas analysis system 9 is placed for
analysing the products of combustion. A control unit 10 is provided
to control the operation of the burner 1, by controlling the valves
4 and 7 via servomotors 4A and 7A to adjust the gas and air flow
rates. The operation of the fans 3 and 6 by motors 3A and 6A is
also controlled by the control unit 10.
[0028] The arrangement described above may be essentially as shown
and described in GB 2138610A with the exhaust gas analysis system 9
being essentially as shown and described in GB 2169726A. As already
indicated, the disclosures of both GB 2138610A and GB 2169726A are
incorporated herein by reference. Furthermore the arrangement
described above is commercially available from Autoflame
Engineering Ltd, for example as the Mk 7 Evolution MM control unit
and the Mk 7 Exhaust Gas Analyser. Such a burner control system is
suitable for use as part of a boiler installation which may for
example be employed in the heating system of large premises, for
example a factory, offices, a hotel or hospital.
[0029] In the arrangement described above the control unit 10
includes a store in which pairs of air and fuel valve settings are
stored for different firing rates of the burner. Those settings are
generated by a commissioning engineer when the control system for
the burner is first set up. In the embodiment of the present
invention, there are two other values stored for each firing rate:
a reading from a gas pressure sensor 11 mounted in the duct 2
downstream of the gas valve 4; and a reading from an air pressure
sensor 12 in the duct 5 downstream of the air valve 7. In the
expanded part of FIG. 1, a store 13 is shown with the left hand
column, A, showing the numbered rows for different sets of values.
There are then four further columns: the first two of those, B and
C, store the settings of the gas and air valves as in GB 2138610A;
in addition there is a further column, D, that stores a respective
gas pressure reading from the sensor 11 for each pair of gas and
air valve settings; in further addition there is a still further
column, E, that stores a respective air pressure reading from the
sensor 12 for each pair of gas and air valve settings.
[0030] The control unit 10 is connected to receive a feedback
signal from the exhaust gas analysis system 9 and that signal is
used to trim the air valve setting from the stored value to a
slightly different value, as described in GB 2169726A. In the
embodiment of the invention described herein, there is in addition
a temperature sensor 14 that is arranged to sense ambient air
temperature and a pressure sensor 15 that is arranged to sense
ambient air pressure. The control unit 10 is connected to receive
signals from the sensors 14 and 15.
[0031] When the control system of FIG. 1 is commissioned, the
ambient temperature and pressure are recorded. Consequently, during
subsequent operation of the burner 1, the control unit is able to
trim the setting of the air valve according to a comparison of the
ambient pressure and temperature during operation as compared to
the ambient temperature and pressure during commissioning. For
example, if the ambient temperature is higher during operation than
during commissioning, then to obtain the same mass flow rate of air
as was obtained during commissioning, it is necessary to have a
slightly higher volume flow rate of air and the control unit
therefore calculates a trimmed setting of the air valve 7 which is
slightly more open. Thus, without having to wait for a feedback
signal from the exhaust gas analysis system 9, the setting of the
air valve 7 can be trimmed to provide an air to fuel ratio that is
closer to the commissioned value. As will be understood, the
ambient air pressure measurement is processed in a similar manner
to the temperature measurement and used to generate the appropriate
trim of the setting of the air valve 7.
[0032] The storing of gas and air pressure values in the ducts 2
and 5 enables a further safety feature to be incorporated in the
control system: during operation of the burner, the control unit 10
can compare the stored values for the gas and air pressures in the
store 13, with actual measured pressures. If the measured pressures
are within a predefined range (say not more than 10% away) of the
stored values, then no action is taken. If, on the other hand, one
of the measured pressures is outside the predefined range, then
that is taken as an indication of some fault, for example failure
of a fan, jamming of a valve or blockage of a duct, and the burner
is shut down immediately. Without the additional pressure values
stored against the different firing rates of the burner, the
control unit 10 would not detect any such failure until a reading
from the exhaust gas analysis system was obtained. Especially at
relatively low firing rates of the burner, the delay in waiting for
a reading from the exhaust gas analysis equipment can be as much as
a few minutes. It will be seen that the extra controls provided by
the control unit 10 enable errors and failures in the burner to be
detected sooner and appropriate action taken.
[0033] Where in the foregoing description, integers or elements are
mentioned which have known, obvious or foreseeable equivalents,
then such equivalents are herein incorporated as if individually
set forth. Reference should be made to the claims for determining
the true scope of the present invention, which should be construed
so as to encompass any such equivalents. It will also be
appreciated by the reader that integers or features of the
invention that are described as preferable, advantageous,
convenient or the like are optional and do not limit the scope of
the independent claims.
* * * * *