Title of Invention

"METHOD AND SYSTEM OF AUTOMATIC COMBUSTION CONTROL IN FURNACE"

Abstract

Method of automatic combustion control in furnace involves the decreasing of defined concentration of free oxygen until exceeding defined concentration of carbon oxide in waste gases. Then, the defined concentration of free oxygen is increased, which after decreasing the concentration of carbon oxide again lowers the defined concent-ration of free oxygen. The system contains a controller (4) containing a programme for changing the defined concentration of free oxygen in waste gases, depending on the ratio of carbon oxide concentration and defines concentration of carbon oxide.

Full Text

The present invention refers to the method and system of automatic combustion control in furnace on the ground of measured free oxygen concentration and carbon monoxide concentration1 in waste gases, with defined free oxygen concentration in waste gases established on the ground of measured and allowed defined carbon monoxide concentration and compensation of disturbances caused by fuel stream variations. The method and system are destined for industrial furnaces, especially in power plants, supplied with a fuel air mixture, especially with coal ground in a coal mill and fed to the furnace in a stream of air. A method of automatic combustion control, described in the Polish patent application No 118 383, involves a correction of the combustion process on the ground of measured amount of free oxygen in waste gases. This method assume a constant free oxygen concentration in waste gases, and when the measured free oxygen concentration differs from the assumed value, fuel to air ratio in the mixture fed to the furnace is changed to equal the free oxygen concentration to the assumed value. A method is also known, in which the assumed concentration of free oxygen in waste gases is automatically corrected, on the ground of the object power variations, it means variations in the size of the fuel stream fed to the furnace or on the ground of the lower heating value (l.h.v.) of the fuel. With ideal course of combustion only carbon dioxide is present in waste gases with no carbon monoxide added, and there is no free oxygen in the waste gases. The amount of air fed to the combustion is in this case as high as results from the stoichiometric calculation by combining carbon with oxygen. In practice it is impossible to obtain and carbon monoxide is present in waste gases. The excess air is fed to the furnace to minimising the amount of carbon monoxide in waste gases. However, more air means moire chimney losses, because of increase in waste gases volume, and increase in the amount of heat carried through the chimney to the atmosphere. Therefore, in practice, a compromise must be reached, regarding the composition and amount of waste gases. It means, the presence of a certain limited amount of carbon monoxide must be allowed, and the excess air must be used so the amount of carbon monoxide in waste gases is -not too high, but the excess air must be as low as possibly. The amount of excess air is defined by measure of free oxygen concentration in waste gases. In known methods of combustion control, a limiting minimum of free oxygen concentration in waste gases and a limiting maximum of carbon monoxide concentration are assumed, selected experimentally for the given object. The limiting maximum of carbon monoxide concentration is defined not only with reference to the loss caused by incomplete combustion, but also with regard to the harmfulness of carbon monoxide to the environment. For this reason, even if the amount of carbon monoxide emitted into the atmosphere may be higher for economical running of the object, it is limited for ecological effects of such emissions. The limiting minimum of free oxygen concentration in waste gases is defined on the ground of the loss caused by incomplete combustion and thermal energy chimney loss, and also on the ground of the oxygen and . nitrogen compounds content in waste gases. These compounds are specially dangerous to the environment and therefore the amount of emission is limited. The amount of oxygen supplied for combustion should be limited to reduce formation of nitric oxide, and to lower the amount of free oxygen in waste gases, even if it is accomplished at the cost of rising of the carbon monoxide concentration. Known from the Polish patent No 156 836, system of automatic optimisation of the combustion process in a thermal object, is provided with sensors of free oxygen concentration in waste gases, connected to controller input, the output of which is connected to the fan of secondary air fed to the furnace. The purpose of the invention is to deliver the method and system, which optimises the combustion process, so that, with an average concentration of carbon monoxide in waste gases, not exceeding the limiting defined concentration, the excess air fed to the furnace is minimised, thereby decreasing chimney losses and facilitating decrease of nitric oxides amount emitted to the atmosphere in waste gases. This purpose is achieved in that the defined free oxygen concentration in waste gases is automatically decreased until the measured carbon monoxide concentration in waste gases is equal to the allowed defined carbon monoxide concentration. At the instant of attaining this state the defined free oxygen concentration increase jump-wise by static and dynamic values of defined free oxygen concentration. Then, in the first predetermined period, after defined time, the defined free oxygen concentration is decreased by the dynamic value of defined free oxygen concentration and the defined free oxygen concentration is maintained till the end of the predetermined period. The predetermined period starts at the instant when the carbon monoxide concentration in waste gases equals to the allowed defined carbon monoxide concentration. If, after second predetermined period of time, the carbon monoxide concentration in waste gases is lower than the allowed defined carbon monoxide concentration, the defined free oxygen concentration in waste gases is automatically lowered until allowed defined carbon monoxide concentration in waste gases is reached again. If, after second determined period of time, carbon monoxide concentration in waste gases is higher than allowed defined carbon monoxide concentration, the actual defined free oxygen concentration in waste gases is increased by static value of defined free oxygen concentration and the value of defined free oxygen concentration is maintained during the next predetermined period of time and then the defined free oxygen concentration is automatically lowered, if carbon monoxide concentration in waste gases is not greater then allowed defined carbon monoxide concentration. Each next predetermined period of time is identical with first predetermined period of time. The lowering of defined free oxygen concentration in waste gases is linear or exponential depending on design of the system. Defined free oxygen concentration, changed jump-wise by static and dynamic value of defined free oxygen concentration, is maintained during the defined time and then is lowered by dynamic value of defined free oxygen concentration. Owing to fact, that the method of this invention comprises programmed time evaluation of free oxygen concentration, the invention may be' used not only in combustion systems working .in very homogeneous conditions, but also in- the systems with large load variations. In the system of the invention, signal path of variable value of defined free oxygen concentration is connected by means of switching unit to the signal path of the defined free oxygen concentration in waste gases. The signal path of variable value of defined free oxygen concentration in waste gases includes a controller, which has two inputs and one output. The controller output is connected to the -input of the switching unit, its one input is connected to the carbon monoxide sensor in waste gases, the other input is connected to the setting station for defined carbon monoxide concentration. The said controller is executing a programme implementing the method of automatic combustion control. Accordingly, there is provided, a method of automatic combustion control in furnace on the ground of measured free oxygen and carbon monoxide concentration in waste gases and defined free oxygen concentration in waste gases, established on the ground of the measured and allowed limiting defined carbon monoxide concentration, characterized in that the defined free oxygen concentration (02z) in waste gases is automatically decreased until the carbon monoxide concentration in waste gases is equal to the allowed limiting defined carbon monoxide concentration (COZ) , and at this instant the defined free oxygen concentration (O2z) in waste gases is increased jump-wise by dynamic and static value of defined free oxygen concentration, ( ΔO2zd + ΔO2zs) / which in turn, in a first defined period (T) , is decreased by dynamic value (ΔO2zd) of free oxygen concentration and resulted defined free oxygen concentration (O2z) is maintained until the end of the predetermined period (T), started when carbon monoxide concentration (CO) in waste gases equals to the allowed limiting defined concentration of carbon monoxide (COZ) , and if, after the second predetermined period (T) , the carbon monoxide concentration (CO) in waste gases is lower than the allowed defined concentration (O2z) in waste gases is automatically decreased until the allowed defined concentration of carbon monoxide (CO2) is attained, and if, after the second predetermined period (T), the carbon monoxide concentration (CO)in waste gases in higher than the allowed defined concentration (COZ) , then the defined free oxygen concentration (O2z) in waste gases is increased by static value of oxygen concentration (ΔO2zS) which results in maintaing an excess free oxygen concentration (O2) for the following predetermined period (T) , and after its termination, the defined free oxygen concentration (O2z) is lowered unless the carbon monoxide concentration (CO) in waste gases is not higher than allowed defined carbon monoxide concentration (CO2) , wherein every next predetermined period (T) is as long as the first predetermined period (T). Accordingly, there is also provided the system of automatic combustion control in furnace on the ground of the measured free oxygen and carbon monoxide concentrations in waste gases and defined free oxygen concentration, comprises an adder for coal feeders rotation sensors signals, free oxygen concentration in waste gases sensors signals and carbon monoxide concentration in waste gases sensors signals, characterized in that path (D22) of defined free oxygen concentration (O2z) in waste gases is connected to the path (D222) of the signal of variable value of defined concentration of free oxygen (O2Z) in waste gases, by means of the switching unit (6) , whereas path (D222) of the signal of variable value of defined free oxtgen concentration value (O2z) comprises controller (4) , which has two inputs and one output, said output of controller (4_) is connected to the input of the switching unit (6] , one of said controller (4) inputs is connected to carbon monoxide concentration in waste gases sensor (2) , and the other input is connected to the switch (B] for setting of defined carbon monoxide concentration (CO2) . The innovation is explained on example of embodiment referring to the drawings, in which fig. 1 shows schematically performance of the embodiment, and fig. 2 shows block diagram of the system of this invention. Example for implementing the method For a selected object, an experimental minimum defined free oxygen concentration in waste gases 0^ = 1.8% by volume has been established, with maximum experimental defined carbon monoxide concentration in waste gases COz = 24 mg/m3. It was found, that with the defined carbon monoxide concentration COz = 24 mg/m3 the content of nitric oxides does not exceeds the allowed level of 460 mg/m3 in the whole control area of object work. The predetermined time, was assumed T = 260 s. Moreover, experimentally were established the dynamic value of the defined free oxygen concentration AO2zd = 0.2% and the static value of the defined free oxygen concentration AO^g = 0.23% by volume. It was assumed, that the linear decrease of the defined .free oxygen concentration C^z runs with a velocity of dO^/dt = 0.25% 02/hour. Referring to fig. 1, curve 15 of carbon monoxide concentration CO in waste gases versus time and curve 16 of defined free oxygen concentration of O2z in free oxygen concentration controller ROZ 12 versus time are shown. In the instant _0 on the fig. 1, carbon monoxide concentration CO in waste gases is much lower than defined carbon monoxide concentration COz. Defined free oxygen concentration 02z in waste gases decreases linearly with a velocity d02z /dt = 0.25% O2/hour, thereby the concentration of carbon monoxide CO in waste gases is increased and at the instant 1 it is equal to the defined carbon monoxide concentration COZ. At this instant the defined free .oxygen concentration increases from the value at instant 1 by the dynamic and static value of free oxygen concentration ΔO2zd + ΔO2zs = (0.23+0.2)% by volume. Owing to object inertia, the carbon monoxide concentration CO in waste gases still increases. During a determined time TD the defined free oxygen concentration 02z is maintained constant, and after time TD this value is decreased to the value at instant I_ increased by the static value of defined free oxygen concentration ΔO2zd = 0.23% by volume, and is maintained without any changes until instant II, that is until the predetermined period T is elapsed. However, if at instant II carbon monoxide concentration CO in waste gases is still higher than the defined carbon monoxide concentration COz, the defined free oxygen concentration o2z in waste gases is increased by an extra A02zs = 0.23% by volume and the predetermined period T is started. After time T, at instant III , the carbon monoxide concentration CO is lower than the defined concentration COz . Thus, linear decrease of the defined free oxygen concentration O is started. If the carbon monoxide concentration CO is at the instant III not lower than the defined concentration COz, the defined free oxygen concentration O2z at the instant III is increased by additional static value ΔO2zd = 0.23% by volume. As it is shown in the example, when carbon monoxide concentration CO is lower than the defined concentration the defined free oxygen concentration O^z is decreased until instant IV, at which the carbon monoxide concentration CO again reaches the value of defined carbon monoxide concentration COz • Thus an identical activity occurs as between instant !_ and II . However, after time T, at instant V, the carbon monoxide concentration CO is lower than the defined carbon monoxide concentration COz and still shows a decreasing tendency. Thus linear decrease of the defined free oxygen concentration O2z in waste gases is started. The course of combustion, according to the method, causes specific wavy variations of the carbon monoxide concentration CO in waste gases, around the allowed defined concentration COz . However, the assumed parameters for the given object are selected in such a way, that the average carbon monoxide concentration CO is not higher than the allowed defined concentration COz in a longer period of time. However, the amount of air fed to the furnace during this time is lower than by maintaining the defined free oxygen concentration O2z in waste gases constant, adjusted to the allowed defined carbon monoxide concentration COZ . As mentioned, in practice, the nitric oxides concentration in waste gases was maintained at a level not exceeding 460 mg/m3 . Referring to fig. 2, the system of automatic combustion control in furnace comprises a path D for signal of air complete amount change, the said path D is connected to air fan output control systems, not shown in Fig. 2. Path D is connected to output of an adder 14, one input of which is connected to an adder 3_ of all mills feeders MP rotation sensors signals, also not shown in the figure. The second input of adder 14 is connected to path D2 of the signal of air complete amount changes, depended on the concentration of free oxygen and carbon monoxide in waste gases. Path D2 is connected to output of superior free oxygen control Ro2 12. One of the inputs of superior free oxygen control Ro2 12 is connected to path D22 of the signal of free oxygen concentration 02 in waste gases, the said path 021 is connected by means of switching unit 13 to sensors 11 of free oxygen concentration O2 in waste gases, located in the stream of waste gases. The second input of superior free oxygen control Ro2 12 is connected to path D22 of the signal of defined free oxygen concentration O2z in waste gases. Path D22 is connected to output of system 7 of minimum defined free oxygen concentration O2min in waste gases. The input of the system 7 is connected to the output of the switching unit 6_ provided with a switch 5. One input of the switching unit 6 is connected by means of a path D22i to a switch I for establishing a constant defined free oxygen concentration O2z in waste gases. The second input of the switching unit _6 is connected by means of the' path D222 to output of controller 4 which comprises . two inputs and is executing a programme for changing the defined free oxygen concentration 02z in waste gases depending on the carbon monoxide concentration CO in waste gases versus the defined carbon monoxide concentration COz. One of the inputs of controller 4_ is connected to a sensor 2 of carbon monoxide concentration CO in waste gases, the other input is connected to a switch 9 for the defined carbon monoxide concentration COZ. For example, the switch 1 for defined free oxygen concentration 02z in waste gases is set to 02z = 1.8% by volume. The signal from the switch 1_, by means of the switching unit 6 reaches system 7 of minimum free oxygen concentration O2min in waste gases. If the signal from the switch 1 represents a free oxygen concentration O2 lower than the minimum free oxygen concentration 02min, system 1_ directs signal representing minimum free oxygen concentration 02min by path D22 to the superior free oxygen concentration control Ro2 12. If the defined free oxygen concentration 02z exceeds the minimum free oxygen concentration 02min, then this signal will be transferred in its full value to superior free oxygen concentration control Ro2 12 . Signals from paths D21 and D22 are compared in the superior free oxygen concentration control Ro2 12. If the signal from sensors 11 represents a free oxygen concentration o2 in waste gases lower than the defined free oxygen concentration 02z the superior free oxygen concentration control R02 12 transfers to the adder 14 and further to the fans the signal to increase the air-complete amount, fed to the furnace, to the value at which the signals will equalise. If the signal from sensors 11 represents the free oxygen concentration 02 in waste gases higher than the defined free oxygen concentration 02z the superior free oxygen concentration control Ro2 12 passes to the fans a signal to decrease the amount of fed air to an amount at which the signals will equalise, it means the free oxygen concentration 02 in waste gases is decreased. The signal from superior free oxygen concentration control Ro2 12 is added in the adder 14 to the signal passed along path D1 from the adder 3 of coal feeders MP rotation sensors 8, which represents size of the stream of fuel fed to the furnace. When the size of the fuel stream is changed, the signal of changing the amount of the supplied complete air will be passed to the fan. Using the switch _5 one can switch unit 6_ to connect the path D22 to controller 4 or to the switch for manual setting of defined free oxygen concentration O2z. Controller 4 changes the defined free oxygen concentration O2z according to the programme implementing the method of automatic control according to the invention. The signal from the controller 4_ is compared in the superior free . oxygen concentration control Ro2 12 with the signal from sensors 11. The superior free oxygen concentration control Ro2 12 and adder 14 work as described with reference to connecting switch 1, it means with constant defined free oxygen concentration 02z in waste gases. Adder 14 enables control of the ratio of air complete amount to the size of fuel stream fed to the furnace with superior free oxygen concentration control Ro2 12 switched to manual control, for example when free oxygen concentration sensors 11 fail. WE CLAIM; 1. Method of automatic combustion control in furnace with reference to the measured content of free oxygen and carbon monoxide concentration in waste gases with defined free oxygen concentration in waste gases, defined on the basis of the measured and defined limiting allowed carbon monoxide concentration, characterized in that the defined value of free oxygen concentration (O2z) in waste gases is automatically decreased until attaining the carbon monoxide concentration in waste gases equal to the defined limiting allowed carbon monoxide concentration (COz), and at this instant the defined value of free oxygen concentration (O2z) in waste gases changes jump-wise by a dynamic and static value of defined free oxygen concentration, (ΔO2zd + ΔO2zs). which in turn, after a first defined period (T), is decreased to dynamic value (ΔO2zd) of free oxygen concentration and this defined free oxygen concentration (O2z) is maintained until the end of the predetermined period (T), starting at the instant of reaching carbon monoxide concentration (CO) in waste gases equal to the allowed limiting defined concentration of carbon monoxide (COz), and if, after the second predetermined period (T), the carbon monoxide concentration (CO) in waste gases is lower than the allowed defined concentration (O2z) in waste gases is automatically decreased until the allowed defined concentration of carbon monoxide (COZ) is attained, and if, after the second predetermined period (T), the carbon monoxide concentration (CO) in waste gases in higher than the allowed defined concentration (COz), then the defined free oxygen concentration (Oaz) in waste gases is increased by static value of oxygen concentration (ΔO2zs) which results in maintaing an excess free oxygen concentration (O2) for the following predetermined period (T), and after its termination, the defined free oxygen concentration (O2z) is lowered unless the carbon monoxide concentration (CO) in waste gases is not higher than allowed defined carbon monoxide concentration (COz), wherein every next predetermined period (T) is as long as the first predetermined period (T). 2. Method as claimed in claim 1, wherein automatic decrease of defined free oxygen concentration (O2z) in waste gases is performed linearly. 3. Method as claimed in claim 1, wherein automatic decrease of defined free oxygen concentration (O2z) in waste gases is performed exponentially. 4. Method as claimed in claim 1, wherein the defined free oxygen concentration (O2z) jump-wise changed by static (ΔO2zs) and dynamic (ΔO2zd) values, is maintained by selected time (TD), and after this time it is decreased by dynamic value of free oxygen concentration (ΔO2zd) 5. The system of automatic combustion control in furnace with reference to the measured content of free oxygen and carbon monoxide concentrations in waste gases with defined free oxygen concentration, comprising an adder for coal feeders rotation sensors signals, free oxygen concentration in waste gases sensors signals and carbon monoxide concentration in waste gases sensors signals, characterized in that path (D22) of defined free oxygen concentration (O2z) in waste gases is connected to the path (D 222) of the signal of variable value of defined concentration of free oxygen (O2z) in waste gases, by means of the switching unit (6), whereas path (D222) of the signal of variable value of defined free oxtgen concentration value (O2z] comprises controller (4), which has two inputs and one output, said output of controller (4) is connected to the input of the switching unit (6), one of said controller (4) inputs is connected to carbon monoxide concentration in waste gases sensor (2), and the other input is connected to the switch (9) for setting of defined carbon monoxide concentration (COZ). 6. Method of automatic combustion control in furnace substantially as herein described with reference to the accompanying drawings and description. 7. System of automatic combustion control in furnace substantially as herein described with reference to the accompanying drawings and description.

Documents:

950-del-1997-abstract.pdf

950-del-1997-claims.pdf

950-del-1997-correspondence-others.pdf

950-del-1997-correspondence-po.pdf

950-del-1997-description (complete).pdf

950-del-1997-drawings.pdf

950-del-1997-form-1.pdf

950-del-1997-form-13.pdf

950-del-1997-form-19.pdf

950-del-1997-form-2.pdf

950-del-1997-form-29.pdf

950-del-1997-form-3.pdf

950-del-1997-form-4.pdf

950-del-1997-gpa.pdf

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