GB2169726A - Fuel burner controller - Google Patents

Abstract

A fuel burner controller arranged to respond to signals representative of the relative amounts of a plurality of the combustion products providing an unambiguous indication of the condition in a fuel burner and to maintain those fuel burner conditions which provide a set of selected values of the combustion products.

Description

1 GB2169726A 1

SPECIFICATION

Fuel burner controller The present invention relates to a fuel burner .gptroller.

The control of a fuel burner involves supplying matched quantities of fuel and air to the burner in order to achieve complete combus- tion of the fuel, that is, to release as much of the energy available in the fuel, while avoiding as far as is possible, the supplying of excess air. Heat absorbed by excess air leaves with the flue gases and represents heat wasted.

Fuel burner control systems are usually arranged to supply fuel at a rate corresponding to the heat demanded from the burner and to supply air at such a rate as to provide for full combustion of the fuel with the minimum of air in excess of that required for full combustion of the fuel.

It is known, for example, to employ a computer system for deciding on the fuel and air valve settings of a fuel burner, and to include an oxygen sensor to signal the flue gas oxygen concentration to the computer system in order to permit fine adjustment of the air valve, by the computer system, to maintain minimum excess oxygen conditions, that is, minimum excess air conditions at the burner.

The known system, referred to above, suffers from several deficiencies. First of all, the condition of minimum excess oxygen may represent combustion conditions generating significant quantities of products such as carbon monoxide and unburnt fuel, both of which are undesirable combustion products, and seeondly, the computer system is usually unable to return the burner to a state at which the combustion products do not include excessive carbon monoxide or unburnt fuel.

The present invention recognises that the sensing of oxygen alone does not provide an unambiguous indication of conditions in a fuel burner, and envisages the provision of a fuel burner controller arranged to respond to signals representative of the actual relative amounts of a plurality of the combustion products of a fuel burner to provide a substan- tially unambiguous indication of the conditions in the fuel burner and, as a result, to maintain or correct those actual fuel burner conditions if those conditions are the same as or different from desired fuel burner conditions.

The present invention provides a fuel burner controller including a memory storing information relating to relative concentrations of combustion products for a range of desired air/fuel settings providing optimum combustion characteristics of the fuel burner, the information comprising a plurality of sets of information each set having constituents representative of the relative concentrations corresponding to a respective desired air/fuel setting and to deviations from that setting, wherein, in use, the system is capable of receiving input information, relating to actual relative concentrations, of recognising a match between the input information and a constituent of a given set of stored information and, in response to that recognition, of providing an output for maintaining or correcting the actual air/fuel setting. The procedure for recognising a match between input and stored information may include comparing input and stored information.

The present invention also provides a fuel burner controller including input means for receiving input signals representative of the ac- tual relative amounts of a plurality of the combustion products of a fuel burner, memory means for storing, for a range of air/fuel settings at respective energy output levels, representative values of the relative amounts of the combustion products incorporating error values including zero error values, and output means providing output signals corresponding to the representative values for maintaining or correcting the air/fuel setting of the fuel burners.

Preferably, the fuel burner controller is arranged to respond to signals representative of the relative amounts of three of the combustion products of a fuel burner. The three signals may be obtained from independent sensors, for example, separate oxygen, carbon monoxide, and carbon dioxide sensors.

The fuel burner controller, in accordance with the present invention, responsive to a plurality of signals has the advantages over known systems that each combustion condition is unique, the result being that the controller may be set to provide a balance be tween excess air and significant amounts of carbon monoxide, and is able not only to determine when the fuel burner conditions are unsatisfactory but also, if they are unsatisfactory what correction is needed.

The present invention further provides a fuel burner controller including means for storing a plurality of values representative of desired proportions of combustion products representative of respective fuel valve settings with zero error, means arranged so to control a setting valve controller as to cause the setting of a supply valve at each, in turn, of a plurality of shifted positions representing predetermined errors of valve setting about the zero error position, means for recording, for each shifted position, a plurality of values repre- senting actual proportions of conbustion products and the corresponding error of valve setting, and means for delivering the appropriate value representing error of valve setting as output in response to each input combination representing recognised proportions of cornbustion products.

Preferably, the fuel burner controller is arranged to store values representative of the percentages of oxygen, carbon dioxide and carbon monoxide in the flue gases under corn- 2 GB2169726A 2 missioned conditions, that is, desired condi- tions, against the corresponding supply valve settings representing zero error position of the valves, to effect predetermined shifted settings of a supply valve at each of a plurality of positions about the zero error position, to note the shifted setting and the flue gas percentage values at each of the plurality of positions, and to provide the appropriate valve er- ror values as output in response to an input recognisable as representative of percentages of oxygen, carbon dioxide and carbon monoxide.

In accordance with the second aspect of the present invention, the fuel burner controller, in combination with a supply valve controller, is capable of building up a look-up table of sets of combustion product values and corresponding supply valve error values, after being sup- plied with the zero error values, and is arranged to apply the appropriate error value when, during operation, it is supplied with a recognisable set of combustion product values.

Preferably, the fuel burner controller includes a combustion products analysing system for sensing and indicating the relative proportions of a plurality of the products of combustion. Preferably, the combustion products analysing system is arranged to operate both in a commissioning phase and during the subsequent operation of the burner controller.

Preferably, the fuel burner controller includes means for sensing the relative concentrations of combustion products providing electrical output signals corresponding to the combustion products, and means for removing moisture from combustion product samples in advance of the sensing means, to avoid mois- ture contamination of the sensing means.

Preferably, the sensing means is an absorption sensing means, and, preferably means are included for chilling the combustion product samples to remove moisture from them.

Fuel burner control systems embodying the various aspects of the present invention will now be described by way of example only and with reference to the accompanying drawings in which:- Figure 1 is a schematic representation of a burner control system embodying various aspects of the present invention, including flue gas sampling and analysis apparatus, a fuel burner controller connected to the flue gas sampling and analysis apparatus, and a supply valve controller connected to the fuel burner controller.

Figure 2 is a diagrammatic representation of air valve settings against combustion products in flue gas samples for a commissioned air valve setting and fuel-rich and fuel-lean air valve settings slightly away from the commissioned value, Figure 3 is a diagrammatic representation of the corresponding fuel valve range, air valve range, and load level range, Figure 4 is a diagrammatic representation of the angular displacement required of the air valve in order to provide volumetric input oxy- gen alterations of.5%, 1%, 1.5% and 2% at each setting over the setting range of the air valve, Figure 5 is a diagrammatic representation of the positions, relative to the commissioned positions, assumed by an air valve under the control of a fuel burner controller, in accordance with one aspect of the present invention, in building up data relating combustion products to supply valve error, Figure 6 is a mixed graphical and table representation of the relationships between the valve settings at commissioning and the amounts of air valve trim required, in the vicinity of each commissioned fuel valve setting, to return the system to the commissioned state, Figure 7 is a plan view representation of a control panel forming part of a fuel burner controller embodying various aspects of the present invention, and, Figure 8 is an exploded view representation of a flue gas chiller unit forming part of a fuel burner control system embodying various as pects of the present invention, Figure 9 is a plan view representation of a second control panel providing facilities for controlling a fuel burner controller in accor dance with the present invention and as con troller as described in British Patent Specifica tion No. 2138610A.

Referring now to Fig. 1, a fuel burner con trol system includes a fuel burner supply valve controller 1 (which may, for example, be of the type described and illustrated in British Pa tent Specification No. 2138610A to which at tention is directed for full details), a fuel bur ner controller 2 connected to the supply valve controller 1 by way of a data link, gas ana lyser cells 3 connected to the fuel burner con- troller 2, a gas pump 4 connected to, and controlled by, the fuel burner controller 2, and a gas chilling unit. The gas chilling unit includes a length of heat exchanger tube 5, a Peltier cell 6 in contact with the heat ex- changer tube 5 and controlled by the fuel burner controller 2, and a fan 7 controlled by the fuel burner controller 2. The heat exchanger tube 5 is provided with a drain tap.

As described in GB 2138610A, the fuel burner supply valve controller 1 is such as to be capable of controlling fuel and air supply valves operated by motors arranged to provide positional feedback information to the supply valve controller 1. The supply valve controller 1 includes a memory in which are stored corresponding air valve and fuel valve settings required to yield, as far as is practically ideal, combustion conditions for each of a plurality of heat output levels from a fuel burner, the corresponding air and fuel valve 3 GB2169726A 3 settings having been selected, for the particu lar installation, by a skilled operator using gas analysis equipment to check the quality of combustion and select the settings accord ingly. The manner in which the supply valve settings are stored and used depends on the number of supply valves required for the parti cular installation. For example, a system with a single air valve would be provided with one set of air valve data, whereas a system with more than one air valve may, with advantage, be provided with separate data for each air valve. The supply valves and motors are not shown in Fig. 1.

Referring still to Fig. 1, the fuel burner con- 80 troller 2 includes a memory in which are stored corresponding values of oxygen, car bon dioxide and carbon monoxide concentra tions, each group of three values being related to an air valve error. The values of oxygen, carbon dioxide and carbon monoxide concen trations for zero air valve error are included, the zero air valve error values for flue gas oxygen, carbon dioxide, and carbon monoxide being determined by a skilled operator using flue gas analysis equipment, and being stored by the fuel burner controller 2, at the operato r's command, during a commissioning phase of the controller 2.

During the commissioning phase of the fuel 95 burner controller 2, a skilled operator will se lect, in turn, fuel valve settings representing the maximum opening, minimum opening, and a plurality of intermediate openings, and for each setting will adjust the air valve setting to 100 provide a compromise involving the minimum oxygen and the minimum carbon monoxide concentrations, and the maximum carbon dioxide concentrations, in the flue gases. The operator-determined fuel and air valve settings are memorised by the supply valve controller 1 and the operator-determined oxygen carbon monoxide and carbon dioxide concentration values are memorised by the fuel burner controller 2, as representing the zero error air valve setting.

The fuel burner controller 2 then takes control of the supply valve controller 1 to effect settings of the air valve on each side of the operator-determined setting to give theoretical air inputs (based on the air valve geometry) with 1 %, and 2% input oxygen deviations from the operator-determined input settings and the corresponding flue gas oxygen, carbon dioxide and carbon monoxide concentrations are read and stored alongside the corresponding deviation of the air valve setting. The stored value of air valve deviation is an error value of valve setting corresponding to the respective flue gas compositions accompanying the theoretical 1 % and 2% input oxygen level deviations. The operator-determined values of exhaust gas constituents are entered for fuel valve settings at 5' intervals from 0' to 90' and the controller 2 builds up a table of flue gas components against air valve error values around each of the operator-determined data. The operator-determined data is identified in storage as zero error valve conditions. The angular deviations need not, of course, be restricted to values corresponding to theoretical 1 % and 2 % excess oxygen.

As is shown in Fig. 1, the fuel burner con- troller 2 is able to sense the relative concentrations of the flue gas components by means of three gas sensing cells 3 which sense oxygen, carbon monoxide, and carbon dioxide, respectively, and supply the fuel burner controller 2 with electrical signals representing the respective concentrations.

Although it is not so shown in Fig. 1, the fuel burner controller 2 is equipped with display means arranged to display the values of oxygen, carbon dioxide, and carbon monoxide concentrations, as determined by the gassensing cells 3. The provision of the gassensing cells 3 and display means in the fuel burner controller 2 facilitates the use of the controller 2 for indicating combustion conditions during the commissioning phase, referred to above, since the fuel burner controller 2 and the gas-sensing cells 3 function, during the commissioning phase, as gas-analysis instrumentation by means of which a skilled operator is able to determine combustion conditions, to assess the effects of supply valve adjustments, and to select the compromise flue gas conditions to which the fuel burner is subsequently set to operate.

Referring still to Fig. 1, gas samples are drawn from a burner flue or stack, by means of the pump 4, and pass through a length of heat exchanger tube 5 and three gas-sensitive cells 3 before being vented. The length of heat exchanger tube 5 is cooled by a Peltier cell 6 attached to the tube 5. A fan 7 moves air past the Peltier cell 6. The heat exchanger tube 5 includes a drain tap for removing con- densate. The pump 4, the Peltier cell 6, and the fan 7, are controlled by the burner controller 2. The gas samples are taken on a sampled data basis, that is, gas samples are taken at specified intervals, rather than contin- uously, and the pump 4 is operated for just long enough to obtain steady- state signals from the gas sensors 3. Such intermittent operation of the sampling sub-system maximises both the operational life of the pump 4 and the intervals at which the system needs to be drained of condensate.

It will be appreciated, from Fig. 1, that there will be a measurable time lag between a change in burner settings and a corresponding change in the flue gas conditions detectable by the gas sensors 3 because of the time taken for gases to flow from the burner to the gas sensors 3. The time lag, referred to, may be determined for any installation by changing one supply valve setting, activating the sampl- 4 GB2169726A 4 ing sub-system immediately, and measuring the time that passes before a new and stable of readings is provided by the burner control ler 2. In addition, a second time lag, corre sponding to the time required for the sampling 70 subsystem to draw a sample and to provide a stable set of readings, may be obtained by changing the burner conditions, activating the sampling sub-system after a delay which ex ceeds the first time lag, referred to, and then 75 measuring the time that passes before a new and stable set of readings is obtained. From the two time lags, referred to, there may be obtained a measure of the time it takes for gases to travel from the burner to the gas sampling region in the flue or stack, at a plu rality of heat output values, and this time de lay information is included among data stored in the burner controller 2. The time delay data available to the burner controller 2 ensures that the sampling sub-system is activated only while the flue gases are representative of the current burner settings and that the time re quired, following a change in burner setting, to obtain stable burner readings is only as long as is necessary.

In the operation of the sampling sub-sys tem, referred to above with reference to Fig.

1, burner controller 2 activates the sampling system periodically during burner operation at a fixed heat output, and makes fine adjust ments to the air valve setting, as necessary, in response to the results of sampling, and the burner controller 2 activates the sampling system whenever there is a change in heat output from the burner, after a delay as dis cussed above, and makes fine adjustments ti the air valve setting, as necessary, in re sponse to the results of sampling.

The arrangement, represented by Fig. 1, including the heat exchanger tube 5 and the Peltier cell 6 for chilling the heat exchanger tube 5, effects the removal of moisture from the gas samples applied to the gas sensors 3.

The gas sensors 3 are of a type which would be rendered inoperative if exposed to moist gases, and the technique of moisture extraction from the flue gas samples therefore permits the use of simple sensors previously con- sidered unusable as flue gas sensors. The operational life of the sensors 3, and also that of the fan 7, is maximised by the intermittent operation of the sampling system.

Referring to Fig. 2, a diagrammatic represen- tation of the data held in store by the burner controller 2 shows that triad values for oxygen, carbon dioxide, and carbon monoxide concentrations are related to air supply value trim angle requirements. The values include supply valve zero trim angle requirements and are placed symmetrically about the supply valve zero trim-angle requirements. The triad values for oxygen, carbon dioxide, and carbon monoxide are represented for supply valve trim angles of 1 to 4 degrees away from the zero trim angle position at 1 degree intervals, and, therefore, for any of the triad values, the burner controller 2 is in a position to obtain a corresponding trim angle requirement, including a zero trim angle requirement, required to obtain combustion conditions comparable to those selected by the skilled operator during commissioning, for implementation by the fuel valve supply controller 1.

Fig. 3 is a diagrammatic representation of the arrangement of air and fuel valve setting data, with heat output requirement, as triad values, in store in the fuel valve supply controller 1. The fuel valve range is 90 degrees, which corresponds to a more limited air valve range (about 650), to provide the full range of heat output values.

Referring to Fig. 4 a graphical representation of the angular deviation against air valve set- tings, over the full range of 0-90 degrees, required to provide oxygen input deviations of 2, 1, 4, 1 and.5 per cent, respectively, by volume, (based on valve geometry) reveals that the angular deviation is not directly re- lated to the valve setting, that is, the constant excess oxygen line is not a straight line. Also, the angular deviation is not directly related to change in excess oxygen at fixed air valve setting, that is, the constant excess oxygen lines are not evenly spaced and become less evenly spaced at higher valve settings.

The burner controller 2, of the present invention, is arranged to use the theoretical relationships, represented by Fig. 4, between an- gular deviation and valve setting at constant excess input oxygen and between angular deviation and change in excess input oxygen at fixed air valve setting (fuel valve alteration).

On referring to Fig. 5 which illustrates the air valve angular settings effected by the burner controller 2 and the valve controller 1 in building up the storage arrangement, represented partly by Fig. 2, it will be noted that air valve settings at 10 degree intervals are represented over the range 0-90 degrees, and for each air valve setting, there are represented angular displacements giving rise to theoretical input oxygen deviations of .5, t 1, t 1.5, and t 2 per cent from the com- missioned value. The commissioned value settings represent zero displacement or zero trim.

The burner controller 2, of the present invention, not only effects the operation represented by Fig. 5 and records the results in a data store, but also, in operation, interpolates between adjacent groups of data to provide trim values for settings not actually investigated during the commissioning phase.

The result of the controller establishing an air valve trim value for each commissionedvalue setting results in trim value data which may be represented by the graphical part of Fig. 6.

In building up its trim value data, the con- troller applies the information represented by GB2169726A 5 Fig. 4 to move the air valve away from its commissioned settings by angles such as to provide input oxygen deviations represented by the.5% 0, volume curve, say, starting with the minimum air valve setting (20', say as shown in Fig. 6) and continuing up to the maximum air valve setting (65', say, as shown in Fig. 6). For each air valve setting away from the commissioned position, the proportions of exhaust oxygen, carbon diox ide, and carbon monoxide are noted, and there is built up a set of data relating to air valve angle, deviation from that air valve angle to give a set input oxygen deviation (as deter mined from Fig. 4), and exhaust gas constitu- 80 ents, for input oxygen deviations of.5%, 1%, 1.5% and 2% (as determined from Fig. 4).

The trim data, as represented by Fig. 6, includes proportions of carbon monoxide, car bon dioxide, and oxygen for air valve angular settings of 25', 35', 41', 47', 55', and 650 located at the points of intersection of the air valve setting valves with the respective angu Jar trim values. The central vertical line A, jo ins points corresponding to commissioned set tings.

Referring to Fig. 6, the angular deviation of the air valve from its commisioned setting is dir ctly linked to the exhaust gas composition and using the information represented by Fig.

6 makes it possible to determine in one oper ation what amount of trim is required to move from non-commissioned conditions to commis sioned conditions.

For example, it is observed that values of 250 ppm carbon monoxide, 10.7% carbon dioxide, and 2.5% oxygen are indicated at the intersection of the curve A, and the 25' AIR VALVE POSITION LINE, establishing that, with the air valve set at 25', exhaust gas readings of 250 ppm CO, 10.7% CO, and 2.5% 0, will be brought to the commissioned values (140 PPM Col 10% C02, 3.5% 0, on the line AJ by opening the air valve a further. 6'. As a further example, with the air valve at its 65' position, exhaust gas readings of 250 ppm CO, 12%C02 and 0.5%02 on the curve A2 may be brought to the commissioned-values of 50 ppm CO, 11.5% CO, and'% 02 on the A,) line by opening the air valve a further 1.7'.

During its operation, therefore, the fuel burner is able to apply a specific correction to the air valve in order to restore commissioned conditions, by examining the exhaust gas constituents and finding the corresponding correction from the data represented by Fig. 6. The correction may, of course by a zero correction, where operation is taking place under commissioned conditions. The controller is able also to deal with conditions lying off the curves A, to A, and B, to B, of Fig. 6 by interpolating. The proportions of exhaust gas constituents given in Fig. 6 apply to natural gas as the fuel. The exhaust gas composition and/or constituents for other fuels (oil for example) will, of course, not necessarily be the same.

in addition where combustion conditions are such that the values representing actual exhaust gas constituent proportions will not match stored values representing exhaust gas constituent proportions, the controller will investigate the angular trim required to correct for each exhaust gas constituent and trim by the mean of the respective trim valves so long as the valves are close together. Where one of the valves representing an exhaust gas constituent proportion would require an angular trim widely different from the trims required for dealing with other exhaust gas constituent proportions, the widely different trim valve will be excluded and the mean valve derived from the other valves. The action of ignoring one valve is based on the expection that one exhaust gas sensor is malfunctioning and accordingly a sensor malfunction is indicated.

In Fig. 6, and in the remainder of the description, carbon monoxide is referred to on the basis that it is representative of unburnt combustibles and references to carbon monoxide are intended to indicate unburnt cornbustibles generally.

Referring to Fig. 7, an operator's panel for the burner controller 2 includes display means 100, 101 and 102 for displaying the results of flue gas analysis in terms of the oxygen, carbon dioxide, and carbon monoxide concentrations, and push button controls 103 to 108 for altering the supply valve settings, during commissioning, to yield desired flue gas conditions. The panel includes push button controls 109, 110 for entering commands to effect the display of commissioned and actual flue gas component values, a reset control 111, controls 112 to 117 for entering respective commands to effect discontinuing trim control. displaying a set oxygen limit, display ing a set carbon dioxide limit, displaying a set carbon monoxide limit, displaying exhaust gas temperature and displaying boiler efficiency. An additional display device 118 is included for displaying the exhaust gas temperature and the boiler efficiency, and display devices 119 and 120 indicate whether the system is in its controlling or commissioning mode and the type of fuel in use.

It will be evident from the form of the operator's panel represented by Fig. 7, that the burner controller 2 includes facilities for measuring the exhaust gas temperature. An assessment of the efficiency of the burner sys tem is effected by comparing the measured exhaust gas temperature with the measured combination gas percentage saturation by volume.

Referring to Fig. 8, a heat exchanger/chiller unit, for removing water vapour from flue gas samples, includes an aluminium block 200 with two cylindrical bores 201, 202 each of 6 GB2169726A 6 which accommodates a helically grooved core one of which is illustrated as 203. The alumi nium block 200 is attached to a Peltier ther mal transducer (not shown) towhich is at tached a heat sink (not shown). The block 70 includes a drain 204.

In the operation of the heat exchanger/chil ler unit, a gas sample is taken through the helical passages between the helically grooved cores 203 and the bores 201, 202 which, with the block 200, are maintained at a temperature of 2 degrees Centigrade. The cooling is effected by the Peltier thermal transducer which transfers heat from the block to the heat sink, the heat sink being cooled by means of air blown over it by a fan. Water collected in the block is removed via the drain 204 as necessary. The drain 204 serves a second purpose which acts as an air inlet port and to provide ambient air, chilled to the same temperature as flue gas are, for effecting calibration of the gas sensors included in the remainder of the system.

After commissioning of the control system as previously described and illustrated, the system is ready to operate in its "run" mode and to effect control of a fuel burner. During the "run" mode signals from the cells 3 are received by the controller 2, those signals representing the actual relative concentrations of the combustion products. The controller 2 is capable of recognising a match between that input information and the stored information and, as a result, produces an output sig- nal for effecting control of the controller 1.

For example, if the input information is matched with stored information for combus tion product concentrations reflecting a devia tion in the optimum fuel/air valve setting (pre viously set by the controller 1) the controller 2 105 will provide an output signal, instructing the controller 1 appropriately to correct that set ting. In practice, for example, the deviation may be corrected by angular displacement of the or one one of the air valves. If, however, the input information is matched with the stored information for combustion product concentrations reflecting optimum fuel/air valve setting the controller 2 will provide an output signal instructing the controller 1 to 115 maintain that setting.

It will be evident from the foregoing description that the burner controller or gas exhaust analysis (EGA) optimiser is a trim system which considers the three main parameters of combustion, 02, C02 and CO (unburnt combustibles) and, by comparing these measured values with the originally commissioned values of 02, C02 and CO for any given point in the load input range, produces a trim value in degrees angular rotation from data acquired during the auto commissioning phase of operation (as distinct from the manual commissioning phase). This trim value data is expressed in degrees angular rotation and is transferred di- gitally via a serial link RS422 from the EGA unit to the unit which implements the trim correction value on the air damper positioning data.

The gas sample for the EGA optimiser is taken from the flue gas duct at the point where the flue gases exit from the boiler and is passed through a chilling unit which removes water from the sample by condensa- tion. it is then taken through a pump and from the outlet of the pump it is passed across the three chemical analysis cells (02, CO & C02). Each cell quantifies the volume concentration of the particular gas with which it is dealing as an electrical signal, which is passed into the input ports of the EGA unit. The EGA unit compares measured data with stored commissioned data and in the context of the particular fuel which is being burnt and if there is any deviation from the comissioned data the air damper position is then modified using the 'Error Line' stored data table, and from this is derived the actual amount of degrees angular correction that is necessary to return the com- bustion system to originally commissioned values.

The EGA unit, when coupled to the micromodulation (MM) valve control unit, can store data for any two types of fuel.

The EGA unit has a further facility in that it measures exhaust gas temperature and by comparing this with the measured combustion gas percentage saturation by volume can calculate an efficiency for the boiler/burner unit.

Displayed on the facia of the EGA are C02, 02 and CO/unburnt combustibles, exhaust temperature in degrees C and boiler/burner unit efficiency. By pressing various membrane switches on the keypad front facia, the stored commissioned values for C02, 02 and CO may be displayed for comparison purposes and for use by the operator to demonstrate how effectively the trim system is working. There is a facility also for setting limit values for each of the three main combustion parameters and in the event of any of these being exceeded during normal operation an audible alarm can be made to operate or the trim system will switch off and leave the combustion system under the control of the Micro Modulation unit only or the EGA system will turn off the combustion system totally but will indicate via the displays in the keypad front facia at which point in the load input range the limits were exceeded.

During commissioning, the data commissioning points will be entered in increments of 5 degrees angular at a time. The EGA in the manual commissioning mode operates as in- strumentation which the commissioning engineer can use as the basis for his assessment of the air fuel relationship at any given point, and at the time that he is satisfied with the relationship of air to fuel he will press the 'Enter Memory' key and this will be stored 7 GB2169726A 7 together with a C02, 02 and CO value. This method of operation will apply to the 'High Position', each 'Inter Position' and the 'Start Position'. At each point of the entered set of values the EGA/MM system will go into an auto commissioning routine and will run the air damper fuel rich by the equivalent of 1% vol ume 02 and by 2% volume 02 over the com missioned value and will record the data at each of these positions for the C02, 02 and CO. It will also then run the air damper air rich by 1% volume and 2% volume 02 by refer encing the information, as detailed in the graphs and drawings previously referred to.

The information created at each commissioned value point will form the basis for the 'Error Line' data which relates deviation from origi nally commissioned value to a degrees angular correction value. This described operation will be performed at each 'Inter Position' and for High Position' and 'Start Position'. When all the data referred to is established the system will be put into a run mode and will work automatically.

Another line of data that is stored for each commissioned value is residence time. This is the time, from moving the air damper, that it takes the sampling cells to register a change of value. The time that it takes the gases to travel down the sampling tube through the chiller, through the pump and into the various chemical cells and to power these up to a stable reading is a known time. If, therefore, this known time is subtracted from the total system residence time, the result is a known residence time for the gases going through the boiler at any load input. This information is useful as it makes possible an arrangement for running the sampling pump for the length of time necessary to take the sample from the exit of the boiler, power up the cells, and make a comparison reading with the commis sioned data for any given load input position.

By running the sampling system only when necessary, the problems of wear on the sampling pump and also the amount of water collected from the sample gas by the chilling/ filter system is reduced.

The chiller system that is used for removing water vapour from the sample gas operates 115 and is configured in the following way. The sample gas is taken through an aluminium block which has two cylindrical cores. Around each of the cylindrical cores a helical groove is cut and the sample gas is taken down and 120 around one helical core and up and around the other. The whole aluminium unit including cores is maintained at a temperature of 2 deg.

C. The cooling is caused by a Peltier thermal transducer which transfers heat from the block into a heat sink which is then cooled by a fan blowing ambient air across it. The water col lected during the cooling process is taken out through the bottom of the block via a drain which is periodically emptied. This drain con- nection serves a second purpose which is as a source of reference air which is chilled until it reaches the same relative humidity as the sample gas. This chilled reference air is per- iodically passed across the cells to recalibrate them.

Claims (13)

1. A fuel burner controller arranged to respond to signals representative of the actual relative amounts of a plurality of the combustion products providing a substantially unambiguous indication of the conditions in a fuel burner and as a result to maintain or correct those actual fuel burner conditions if those conditions are the same as or different from desired fuel burner conditions

2. A fuel burner controller including a memory storing information relating to relative concentrations of combustion products for a range of desired air/fuel settings providing optimum combustion characteristics of the fuel burner the information comprising a plurality of sets of information each set having constituents representative of the relative concentrations corresponding to a respective desired air/fuel setting and to deviations from that setting wherein in use the system is capable of receiving input information relating to actual relative concentrations of recognising a match between the input information and a constituent of a given set of stored information and, in response to that recognition of providing an output for maintaining or correcting the actual 100 air/fuel setting.

3. A fuel burner controller as claimed in claim 2, wherein the controller includes means for comparing input and stored information and, as a result, to recognise a match be105 tween that information.

4. A fuel burner controller including input means for receiving input signals representative of the actual relative amounts of a plurality of the combustion products of a fuel bur- ner, memory means for storing, for a range of air/fuel settings of the fuel burner at respective energy output levels, data representative of desired values of the relative amounts of the combustion products, the data incorporating error values including zero error values, and output means for providing output signals corresponding to the desired values for maintaining or correcting the air/fuel setting of the fuel burner.

5. A fuel burner controller, as claimed in any one of claims 1 to 4 and arranged to respond to signals representative of the relative amounts of three of the combustion products of a fuel burner.

6. A fuel burner controller including input means for receiving input signals representative of the actual proportions of combustion products of the fuel burner, means for storing a plurality of values representative of desired proportions of combustion products represen- 8 GB2169726A 8 tative of respective burner supply valve settings with zero error, means arranged so to control a setting valve controller as to cause the setting of a supply valve at each, in turn, of a plurality of shifted positions representing predetermined errors of valve settings about the zero error position, means for recording, for each shifted position, a plurality of values representing actual proportions of combustion products and the corresponding error of valve setting, and means for delivering the appropriate value representing error of valve setting as an output signal in response to an input signal recognisable as representing the proportions of combustion products for that value.

7. A fuel burner controller as claimed in claim 6, and arranged to store values representative of the percentages of oxygen, carbon dioxide and carbon monoxide in the flue gases under commissioned conditions, that is, desired conditions, against the corresponding supply valve settings representing zero error position of the valves, to effect predetermined shifted settings of a supply valve at each of a plurality of positions about the zero error position, to note the shifted setting and the flue gas percentage values at each of the plurality of positions, and to provide the appropriate valve error values as output in response to an input recognisable as representative of percen tages of oxygen, carbon dioxide and carbon monoxide for those error values.

8. A fuel burner controller as claimed in any one of claims 1 to 7, including a combus- tion products analysing system for sensing and indicating the relative proportion of a plurality of the products of combustion.

9. A fuel burner controller, as claimed in claim 8, wherein the combustion products an- alysing system is arranged to operate both in the commissioning phase and during the subsequent operation of the burner controller.

10. A fuel burner controller, as claimed in claim 8 or claim 9, including means for sens- ing the relative concentrations of combustion products providing electrical output signals corresponding to the combustion products, and r- neans for removing moisture from combustion product samples in advance of the sensing means, to avoid moisture contamina- tion of the sensing means.

11. A fuel burner controller as claimed in claim 10, wherein the sensing means is an absorption sensing means. 55

12. A fuel burner controller as claimed in any one of claims 8 to 11, including means for chilling the combustion product samples to remove moisture from them.

13. A fuel burner controller substantially as herein described with reference to, and as illustrated by, Figs. 1 to 6, or Figs. 1 to 8, of the accompanying drawings.

Printed in the United Kingdom for Her Majesty's Stationery Office, Dd 8818935, 1986, 4235. Published at The Patent Office, 25 Southampton Buildings, London, WC2A l AY, from which copies may be obtained.