Patent Application
20140051029
This application claims benefit of Ser. No. 1214740.1, filed 17 Aug. 2012 in United Kingdom and which application is incorporated herein by reference. To the extent appropriate, a claim of priority is made to the above disclosed application.
This invention relates generally to burner installations, to control systems for use in such installations and to methods of commissioning and operating burner installations. The invention relates in particular, but not exclusively, to a burner installation for a large boiler such as might be used in hospitals, hotels, offices or other industrial, commercial or domestic premises.
A known burner control system is described in GB2138610A, the disclosure of which 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. A control system of this kind has been used for many years in the United Kingdom, the United States and elsewhere, being commercially available from Autoflame Engineering Ltd, for example as the Mk 7 Evolution MM control unit, and has proved very successful.
Burner installations typically incorporate a stack, through which the products of combustion are discharged. Usually the stack is vertical and a back flue extends from the burner to the stack to transfer the products of combustion from the burner to the stack. Sometimes more than one burner will be associated with the same stack. The conditions in the stack can affect the combustion at the burner. It has previously been proposed to include a regulator valve in the flow of combustion products and to control the position of the regulator valve with a servo motor in order to try to maintain a constant draught. Such a control arrangement is unable to take account of a wide variety of parameters that may affect the desired draught. For example, different firing rates of a burner may desirably require different draughts to achieve optimum combustion conditions and even at a given firing rate, other factors, for example ambient temperature, may still affect the most desirable position of a stack regulator valve.
It is an object of the invention to provide an improved burner installation and improved methods of commissioning and operating a burner installation.
According to the invention there is provided a burner installation comprising a stack and a burner upstream of the stack for burning fuel in air to produce combustion products which are passed into the stack, a fuel valve for adjusting the flow of fuel to the burner, an air valve for adjusting the flow of air to the burner, a control device including a store arranged to store pairs of values of air and fuel valve settings at various firing rates of the burner and for controlling the air and fuel valve settings in dependence upon the stored air and fuel valve settings, wherein the installation further comprises a stack flow regulator for adjusting the flow of combustion products through the stack, and a pressure sensing arrangement for monitoring the pressure of combustion products downstream of the burner, wherein the store is further arranged for storing respective pairs of values of the setting of the stack flow regulator and a measured value from the pressure sensing arrangement for the pairs of values of air and fuel valve settings, and wherein the control device is arranged to receive a feedback signal from the pressure sensing arrangement for comparing an actual pressure value with a stored pressure value and to trim the setting of the stack flow regulator to cause the actual pressure value from the pressure sensing arrangement to move closer to the stored pressure value.
A burner installation of this kind is able to set different stack flow regulator settings at different firing rates of the burner. Furthermore, that setting can be further trimmed according to an actual pressure value measured in the flow of the combustion products to bring that pressure value closer to a stored value for that firing rate of the burner. In this way the effect of varying stack conditions on the combustion in the burner can be very much reduced across a range of firing rates of the burner.
The stored values are preferably obtained during commissioning of the burner by a commissioning engineer who is able to select optimum settings for the air and fuel valves, and the stack flow regulator at a particular firing rate of the burner and also store a pressure value from the pressure sensing arrangement, and repeat the exercise at other firing rates. The commissioning engineer is free to take any factor he chooses into account when selecting the values to store.
The fuel may be oil or gas and the fuel control valve may take any suitable form. Similarly the air control valve may take any suitable form. As will be understood the purpose of the fuel and air valves is to control the flow rates of fuel and air to the burner and any arrangement which achieves that and can be controlled may be adopted. For example the airflow may be controlled partly by adjusting an impeller. In a particular example of the invention described below the burner is able to be supplied with either oil or gas. The fuel and air valves are vaned valves for example butterfly valves whose angular positions are controlled by servo motors.
The invention is able to be applied to a wide variety of flue and stack arrangements and in a variety of ways. In one example, the burner installation may further comprise a flue for conveying combustion products from the burner to the stack. The stack flow regulator may be disposed in various positions; in particular it may be disposed in the flue. Of course, since the flue leads to the stack, the adjustment of the flow through the flue adjusts the flow through the stack. The flue may extend between the burner and the stack. The stack may extend approximately vertically upwardly. The flue may include a vertical portion and/or an upwardly inclined portion. There may be more than one burner, and therefore more than one flue, connected to the same stack.
The stack flow regulator may be of any suitable form for regulating the flow through the stack. The stack flow regulator may comprise a valve having one or more vanes. For example, in a relatively small installation it may be a butterfly valve and in a larger installation it may have two or more vanes which may be pivotally mounted. A servo motor may be provided for operating the valve.
The pressure sensing arrangement may sense one or more pressures in the flow of combustion products downstream of the burner. The pressure sensing arrangement may comprise a pressure sensor upstream of the stack flow regulator. A variety of pressure sensing arrangements may be adopted, but in an embodiment of the invention described below, the pressure sensing arrangement is a differential pressure sensing arrangement and is arranged to measure the pressure difference between the pressure sensor upstream of the stack flow regulator and ambient pressure. In this embodiment, the pressure sensing arrangement is connected to the control device to provide a pressure value representing the difference in pressure measured between the pressure sensor upstream of the stack flow regulator and ambient pressure.
According to the invention there is also provided a method of operating a burner installation, including the following steps:
providing a burner installation comprising a stack and a burner upstream of the stack for burning fuel in air to produce combustion products which are passed into the stack, a fuel valve for adjusting the flow of fuel to the burner, an air valve for adjusting the flow of air to the burner, a control device including a store, a stack flow regulator for adjusting the flow of combustion products through the stack, and a pressure sensing arrangement for monitoring the pressure of combustion products downstream of the burner,
storing, at various firing rates of the burner, pairs of values of air and fuel valve settings and associated pairs of values of a setting of the stack flow regulator and a measured value from the pressure sensing arrangement,
operating the burner and controlling the air and fuel valve settings and the stack flow regulator valve setting in dependence upon the stored air and fuel valve settings and the associated stack flow regulator setting,
receiving at the control device a feedback signal of the actual pressure value from the pressure sensing arrangement,
comparing the actual pressure value from the feedback signal with a stored pressure value, and
trimming the setting of the stack flow regulator to cause the actual pressure value from the pressure sensing arrangement to move closer to the stored value.
The pressure sensing arrangement may measure the pressure difference between a pressure sensor upstream of the stack flow regulator and ambient pressure, and the pressure difference may be the pressure value fed back as a signal to the control device.
If it is desired to operate the burner at a firing rate between the stored settings, stored values can be interpolated. The control device can arrive at values for settings of the valves and the pressure value by interpolating between stored values associated with a higher firing rate and a lower firing rate. Such operation in which interpolated values are employed is within the scope of the invention.
According to the invention there is further provided a method of commissioning a burner installation, including the following steps:
(i) providing a burner installation comprising a stack and a burner upstream of the stack for burning fuel in air to produce combustion products which are passed into the stack, a fuel valve for adjusting the flow of fuel to the burner, an air valve for adjusting the flow of air to the burner, a control device including a store, a stack flow regulator for adjusting the flow of combustion products through the stack, and a pressure sensing arrangement for monitoring the pressure of combustion products downstream of the burner,
(ii) adjusting the air and fuel valve settings to positions where desired combustion conditions are obtained for that, first, firing rate of the burner,
(iii) storing the pair of values of air and fuel valve settings that provide those combustion conditions,
(iv) adjusting the setting of the stack flow regulator to a position where, for the first firing rate of the burner, the desired stack flow of combustion products is obtained,
(v) storing a value of the setting of the stack flow regulator and the pressure value from the pressure sensing arrangement with the values of the air and fuel valve settings, and
(vi) repeating steps (ii) to (v) above at other firing rates of the burner.
It should be understood that steps (ii) to (v) above are not necessarily carried out in the same order in which they are listed.
The pressure sensing arrangement may measure the pressure difference between a pressure sensor upstream of the stack flow regulator and ambient pressure, and the pressure difference may be the pressure value stored.
As will be understood, the commissioning of the burner will be followed by operation of the burner. Commissioning will take place prior to any operation of the burner and may also take place at any desired time after a period of operation, for example as a result of some modification to the burner installation or merely for routine maintenance purposes. The commissioning method may thus include the following subsequent steps:
operating the burner, controlling the air and fuel valve settings in dependence upon the stored air and fuel valve settings, and setting the stack flow regulator according to the value stored in association with the air and fuel valve settings,
receiving at the control device a feedback signal of the actual pressure value from the pressure sensing arrangement,
comparing the actual pressure value from the feedback signal with the stored pressure value associated with the stack flow regulator setting value, and
trimming the setting of the stack flow regulator to cause the actual pressure value from the pressure sensing arrangement to move closer to the stored value.
Whilst it is within the scope of the invention for the trimming of the setting of the stack flow regulator to cause the actual pressure value from the pressure sensing arrangement merely to move partway towards the stored value, it is usually preferred that the setting of the stack flow regulator is trimmed until the actual pressure value from the pressure sensing arrangement is the stored value.
It will be appreciated that the burner installation and the methods of operating and commissioning the burner installation are closely related to each other and that features described in respect of the installation may be adopted in either of the methods, and that features described in respect of one of the methods may be adopted in the other method or in the installation.
By way of example an embodiment of the invention will now be described with reference to the accompanying schematic drawing, of which:
Referring to
In the burner 1, the fuel and air are mixed and combustion takes place. The products of combustion pass from the burner 1 through a heat exchanger 11 of a boiler 12 into the flue 14. The combustion products pass up the flue 14 through a stack flow regulator 15, which comprises a damper valve, through an inclined portion 14A of the flue and into a vertical stack 16. In
A control device 20 is provided to control the operation of the burner installation. The control device receives many inputs and controls the operation of many parts of the installation in a conventional manner; in the interests of clarity, it is only the control aspects of relevance to the present invention that will now be described and that are shown in
The control unit 20 includes a store 30 which is also shown in
In operation, when the control system of
Once the burner has been fully commissioned, it is ready for operation. When the burner is set to a given firing rate, the control device looks up in the store 30 the settings of the servo motors 21, 22, 23 and 24 for that firing rate and adjusts them accordingly. The control device also looks up the stored differential pressure value corresponding to the servo motor settings and receives a signal from the differential pressure setting arrangement 26 of the actual differential pressure value. In the event that there is a difference between those two differential pressure values, the control device trims the setting of the servo motor of the differential pressure setting arrangement 26 to reduce or eliminate the difference.
The boiler installation described above may for example be employed in the heating system of large premises, for example a factory, offices, a hotel or hospital.
It is also possible for other values to be stored alongside the four values just referred to. For example in WO2012/056228A2, the contents of which are incorporated herein by reference, a modified version of the control arrangement of GB2138610A is described in which respective values of fuel pressure and air pressure upstream of the burner are stored in the store 30 for each pair of fuel and air valve settings. Such values could be stored in a modified version of this invention in addition to the other values already mentioned.
In GB 2169726A, the contents of which are incorporated herein by reference, the control device 20 is connected to receive a feedback signal from an exhaust gas analysis system and that signal is used to trim the air valve setting from the stored value to a slightly different value. That arrangement, with or without the modifications and developments described in WO2012/056228A2, may be employed in embodiments of the present invention.
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1214740.1 | Aug 2012 | GB | national |
