JP2018537649A - Electronic control module and method for controlling operation and safety of at least one radiant tube burner - Google Patents

Abstract

The present invention is a control module for at least one radiant tube burner, the burner comprising a fuel supply valve, an oxidant supply valve and a combustion flue gas exhaust duct, the control module comprising at least one A combustion quality measuring device, a fuel flow measuring device, an oxidant flow measuring device, an oxidant supply valve and a fuel supply of the at least one burner installed in the combustion flue gas exhaust duct of one burner And means for adjusting the ratio of oxidizer flow / fuel flow rate based on information acting on the valve opening ratio and provided by the combustion quality measuring means. [Selection] Figure 3

Description

  The present invention relates to an electronic control module and method for optimally controlling the combustion and safety of at least one industrial radiant tube burner equipped in a horizontal or vertical line for continuous heat treatment of metal strips.

  Referring to FIG. 1 of the drawings, an outline of a partial example of a vertical line according to the prior art for continuous heat treatment of a metal strip is shown. The line includes, for example, a zone Z1 for preheating the strip 2 with a hot jet, a zone Z2 for heating the strip with a radiant tube burner, and a zone Z3 for maintaining the strip temperature with a radiant tube burner, and a zone Z4, As well as other treatments of the strip, for example, zones not shown in detail following which are used for its cooling.

  The line consists of an insulating enclosure 1, in which the strip 2 enters on various rollers 3, which guide it through a number of vertical passages. At the top of each vertical passage, there are arranged radiation tubes 4, 5 schematically represented by squares. In recent annealing lines, the number of installed radiation tubes, ie burners, is between 200 and 400. Each of these burners is individually controlled and, for example, operates in an on / off mode with the radiation tube operating in a push-pull mode.

  In FIG. 1, the radiant tube 4 with the burner turned off is shown in white, and the radiant tube 5 with the burner is shown in black.

The maximum heating power P _max produced by the heating zone Z2 corresponds to when all the radiation tubes are switched on simultaneously.

In the prior art, when the _required heating power P _required for zone Z2 is lower than P _max , for example 60% of P _max , each burner of the radiant tube of the heating zone is typically 1 Or ignite for 60% of the cycle time set to 2 minutes.

It will be appreciated that the _required thermal power P _required can be obtained in any case by adjusting the operating time of each radiant tube burner during a portion of the cycle time equal to the ratio P _required / P _max .

  FIG. 2 shows a vertical row of radiant tubes 4, 5 arranged on one side of a strip 2 moving on a roller 3. The supply and exhaust of each of the radiation tubes 4 and 5 in this vertical row is shown in the figure. The supply of oxidant, for example combustion air, is diagrammatically represented by 6, the supply of liquid or gaseous fuel, for example natural gas by 7, and the exhaust of flue gas by 8. It is understood that depending on the position of the fluid connection of the radiant tube to the supply and exhaust duct, the pressure of the air supply, gas supply, or flue gas exhaust will be different for each radiant tube.

  Next, to simplify the description of the present invention, the term “gas” is used to represent the fuel (of any nature) supplied to the burner and represents the oxidant (regardless of its oxygen content). The term “air” is used for this purpose.

  The change in operating speed in the furnace as a function of the production of the strip format or the temperature it needs to reach results in a change in the number of burners in operation, which is the pressure variation of the air, gas or flue gas in the burner To trigger.

  On the other hand, ignition and extinguishing of the burner can induce pressure fluctuations to the burner duct located in the vicinity of the furnace or in the same zone.

  In addition, increasing the temperature of the radiant tube reduces excess air.

  In addition, in the production department where the heat treatment line is installed, the nature or composition of the gas can sometimes vary at a significant rate, for example, with a variation in the calorific value of +/− 10% compared to the average value. The facility can also be supplied with several types of gas, such as natural gas and coke oven gas, which have very different characteristics in terms of density or calorific value. The operating conditions of the burner include the pressure of the air or gas supply or flue gas exhaust, the characteristics of the gas used, the operating temperature of the radiant tube, the ignition and extinguishing of the adjacent burner in the row, zone or fluid circuit. It can be seen that it can be very diverse depending on the effects of.

  These variations may be fast, resulting in a total burner ignition and extinguishing cycle rate in on / off mode, for example, 30 or 60 ignition and extinguishing cycles per hour. This can cause significant interference to the operation of a single burner and to the operation of all burners in a row, in a zone, or in a fluid circuit.

  All these variations can greatly vary the air-gas ratio as compared to the desired theoretical value and / or significant production of contaminants such as CO (carbon monoxide) or NOx (nitrogen oxide).

  To solve this problem, with respect to the stoichiometric value, an excess air value of + 10% to + 20% is selected so that combustion is carried out whatever the supply conditions and characteristics of the air and gas. It has become customary. This additional portion of the combustion air does not participate in the combustion. Conversely, the energy required to heat it is lost energy at the expense of equipment efficiency.

  Prior art equipment is effective for flame quality in response to fluctuations in gas characteristics or its supply, and in the flame ignition and extinguishing stages that often occur in equipment containing a large number of burners operating in on / off mode. Cannot be controlled.

  The air-to-gas ratio at each instant of the burner ignition, operation, and extinguishing stages is the ratio of air and gas valve openings, air and gas pressures in the supply duct, and theoretical settings at each instant. It can be seen that this is the result of the actual heating value of the gas against the value. These differences are related to the opening and closing characteristics of the valve, its actual sealing, wear of the sealing device, fluctuations in the characteristics of the air and gas supply or gas heat value (eg pressure fluctuations due to clogging of pipes) Particularly important in the ignition and extinguishing stages of

The approximate phase of control over the quality of the combustion, ie the air and gas flow rate and / or the ratio of air to gas flow rate (air / gas ratio), has a set of results.
Increased production of pollutants, especially nitrogen oxides (NOx). Its release rate is limited and sometimes taxed.
・ Possibility of producing unburned by-products (unburned fuel), especially CO. The by-products reduce the efficiency of the equipment and create explosion risks in the ducts, plenums, and final flue gas exhaust circuits that threaten the safety of equipment and people.
• Production of oxidizing or reducing uncontrolled combustion atmospheres. This reduces the useful life of equipment exposed to this atmosphere, such as radiant tubes, and all equipment made of heat-resistant steel that is typically operated at high temperatures and exposed to burner combustion gases.

  Prior control equipment installed in accordance with current standards, eg, EN746-2 and EN298, controls the presence of a flame without checking the flame quality. This means that these control facilities are in an open loop mode of operation that does not optimize combustion.

  It can be seen that all the disadvantages of the prior art always result in a defective combustion control of each burner. Affects various aspects of the equipment, especially reduced combustion efficiency, decomposition of released pollutant levels, resistance of materials in contact with combustion gases, ducts, plenums, and final flue gas exhaust circuits Affects the risk of a gas explosion or, more generally, the occurrence of risks to nearby equipment or employees.

  These combustion control deficiencies are associated with high speed operation with respect to the degree of the burner operating cycle or the number of opening and closing of the gas and / or air supply valves. Insufficient control over the combustion and safety of this short time burner operation is a rapid controller, preferably a local controller as close to the burner as possible to control, and a quick control of the reaction time closure. Need to work in a loop.

  Some commercial installations are equipped with sensors located in the air and gas supply or flue gas to change the burner opening. However, none of them can optimize each operation stage of the on / off cycle and compensate for fluctuations in the heat value of the supply gas.

  In addition, prior art equipment cannot quickly detect whether a failure of the radiant tube is an elemental defect or a degraded mode of operation.

  The electronic control module and method according to the present invention optimizes the combustion of the radiant tube burner, reduces the amount of pollutants emitted, compensates for fluctuations in the thermal power of the feed gas, and reduces the excess air required As a result, it is possible to improve the combustion efficiency by ensuring the proper operation of the burner, and to quickly detect the malfunction of the radiation tube.

The present invention is a control module for at least one radiant tube burner, the burner comprising a fuel supply valve, an oxidant supply valve and a combustion flue gas exhaust duct, the control module comprising:
A combustion quality measuring device installed in the combustion flue gas exhaust duct of at least one burner;
・ Fuel flow measuring device,
・ Oxidant flow rate measuring device,
Means for controlling the at least one burner, acting on an opening ratio of the oxidant supply valve and the fuel supply valve of the at least one burner;
A control module comprising means for adjusting the oxidant flow rate / the fuel flow rate based on information provided by the combustion quality measuring device.

  Advantageously, the control module is means for calculating the fuel combustion power Va using data provided by the combustion quality measuring device, the fuel flow measuring device and the oxidant flow measuring device. The Va value calculated by the calculating means is compared with a theoretical value to detect a deviation exceeding a predetermined threshold value.

  The combustion quality measuring device may be a residual oxygen sensor.

  Further advantageously, the module is capable of controlling two radiant tube burners, and the combustion power Va of the fuel for each burner and the data provided by the oxidant flow measuring device and the fuel flow measuring device. By comparing the two Va values calculated from the information provided by the combustion quality control device and obtained for the two burners, a deviation exceeding a prescribed threshold can be detected.

The present invention is also a method for controlling at least one radiant tube burner, the burner comprising a fuel supply valve, an oxidant supply valve, and a combustion flue gas exhaust duct, the method comprising:
The operation of at least one burner is adjusted in the opening ratio of the oxidant supply valve and fuel supply valve of the at least one burner and is installed in the combustion flue gas exhaust duct of the at least one burner Controlling according to the desired oxidant / fuel ratio based on information provided by the combustion quality measuring means;
In particular, from the data provided by the oxidant flow measuring device and the fuel flow measuring device and the information provided by the combustion quality measuring device of at least one burner, the combustion power value of the fuel supplied to at least one burner Calculating Va, comparing the combustion force value Va with a theoretical value, and detecting a deviation exceeding a specified threshold value.

Advantageously, the control method comprises:
Controlling two radiation tube burners;
In particular, the combustion power value Va for each burner is calculated from the data provided by the oxidant flow measuring device and the fuel flow measuring device and the information provided by the combustion quality measuring device of the burner, and the 2 By comparing the two Va values obtained for one burner, a deviation exceeding a prescribed threshold value can be detected.

  Accordingly, the present invention provides a quick and efficient system for managing the operation of multiple radiant tube burners installed in an industrial furnace. It optimizes combustion and reduces the amount of pollutants produced while ensuring safe operation of the burner. The present invention maintains the required air / gas ratio for each burner even when the feed gas has various characteristics (heat value or feed fuel pressure) A solution for controlling the burner is provided by controlling the amount of gas in response.

It is a figure which shows the outline of the one part example of the vertical line of the continuous heat processing of the metal strip in a prior art. In the prior art, it is a partial schematic diagram representing the elevation of the fluid distribution duct to the burner. 1 is a schematic view of a radiation tube assembly according to an exemplary embodiment of the present invention.

  In the following, the present invention will be described in detail on the basis of an embodiment with reference to FIGS.

  As shown in FIGS. 2 and 3, the radiant tube burner is supplied by an air duct 6 and a gas duct 7. The air supply section of the burner is equipped with a flow rate measuring device, for example, a diaphragm 13 and a differential pressure sensor 12 and, optionally, an opening position feedback signal type electric control valve or a pneumatic control valve opening 14.

  The combustion air is heated by the flue gas in the heat exchanger diagrammed at 10 and hot air is supplied to the burner 20.

  The gas supply of the burner performs a dual seal function according to a flow measuring device, for example, the diaphragm 16 and differential pressure sensor 15, and EN 746-2, and optionally at least one provides feedback of the opening position (see FIG. The valve 18) comprises two electrically controlled or pneumatically controlled valves 17, 18 and a pressure switch between the valves 17 and 18. Thus, gas and air are supplied to the burner.

  The control valves 14, 17, 18 may also be equipped with sensors or limit switches to check the position of the valve when fully open or fully closed.

  The burner 20 is equipped with a flame detection device 21, for example, an ultraviolet type optical cell, and an ignition device 22, for example, an ignition electrode.

  The radiant tube includes a temperature sensor, for example, at least one thermocouple 25 for measuring the surface temperature of the radiant tube, and a wet flue gas exhaust 8 of the radiant tube 4 to control the quality of combustion. A sensor 24 to be arranged, for example a residual oxygen sensor, is equipped.

  The combustion system is equipped with an electronic control module 23 which is arranged in the vicinity of the burner, which comprises an output signal part 23a and an input signal part 23b. The illustrated input signal unit includes control valves 14, 18, flame detector 21, air and gas flow rate measuring units 12, 15, residual oxygen in wet flue gas measured by sensor 24, and thermocouple 25. Corresponds to the temperature measured by. The output signal unit is the control of the valves 14, 17, 18 and the ignition control unit 22.

  Ultimately, the digital link allows information to be transmitted and received between the central control / command system and the electronic control module 23 and / or between the electronic control module 23.

  This electronic control module is a safety function associated with all functions handled by the burner control system on the market, in accordance with the prior art and as specified in the standard, in particular the ignition work sequence, the burner extinguishing, and the operating phases. Provides sexual function. It also provides combustion control and fault control as described in detail below.

  In the on / off mode, the proposed system regulates the amount of air, which reflects the instantaneous power delivered by the burner at various stages of operation and uses a valve 14. The differential pressure sensor 12 is connected to an electronic control module 23, which calculates the instantaneous flow rate of air sent to the burner.

  A sensor 24 for measuring the residual oxygen in the flue gas is connected to the electronic control module 23, which is used in the wet flue gas in various operating stages of the burner, for example ignition, stable operation and extinguishing. The amount of gas required to meet the required oxygen concentration is determined and it regulates this flow rate by controlling the valve 18.

  Similarly for the gas circuit, the differential pressure sensor 15 is connected to the control module 23, which calculates the instantaneous flow rate of the gas sent to the burner.

  Air and gas flow rates are calculated using the standard specified in ISO 5167-2 and communicated to the electronic control module 23. The standard describes the geometric properties of the basic measuring elements 13, 16, parameters related to the properties of the fluid, and operations that are, for example, common dynamic data or individual measured data, atmospheric pressure, pressure, temperature, density. It is a combination of conditions.

  Combustion parameter Va (theoretical air volume or flue gas combustion power corresponding to the volume of air necessary and sufficient to ensure complete combustion in volume units of gas), the required air expressed in n From the ratio (or airflow), and the air / gas ratio represented by R (R = n × Va) and other parameters specific to each fluid, the electronic control module 23 is expected in the wet flue gas. The residual oxygen amount is calculated and the gas flow rate is adjusted to maintain the required oxygen concentration in the wet flue gas. Thus, the present invention maintains the quality of combustion whatever the fluctuations in the gas and air supply pressures.

  The present invention also provides other performance such as a gas valve tightness test sequencer controlled by pressure switch 26 and a guard in case the maximum operating temperature controlled by thermocouple 25 is exceeded.

  A sensor 25 for measuring the temperature of the radiation tube 4 is connected to the electronic control module 23. Thus, the module 23 can control the stop of the burner when the radiant tube exceeds the maximum safe temperature.

  We understand the benefits of the present invention for furnace end users. The reason is not only the improvement of the manufacturing process, but also the cost of fuel consumed in the facility and the tax required depending on the amount of pollutants released.

  Another essential feature of the present invention is that the electronic control module 23 quickly detects a failure of the radiant tube to which it is connected and places the tube in a safe position when the failure is deemed significant. Is to be able to put on.

  According to the characteristics of the received signal indicating that it is faulty, and in particular according to the factors involved, the electronic control module maintains it in use or puts it in a safe position by placing it in a safe position. Alerts local and / or central control / command system while stopping.

  As has been seen above, the electronic control module 23 includes devices 12, 13, 14 for measuring and controlling the air flow and devices 15, 17, 18, 26 for measuring and controlling the gas flow, and the residual Information is exchanged with the oxygen sensor 24 and the temperature sensor 25. Thus, the electronic control module 23 can detect the difference between the information provided by one of these elements or sensors, the information provided by other elements or sensors, and the theoretical prediction value.

For example, the difference is as follows.
The difference between the measured flow rate for air or gas and the opening of the control valve that regulates the flow rate.The difference between the measured value of residual oxygen and the predicted value for measuring the flow rate of air and gas.・ Difference between the measured temperature of the radiant tube and the predicted value

  From the data obtained by the device for measuring the oxidant and fuel flow rate and the data obtained by the sensor for measuring the residual oxygen in the burner flue gas, the electronic control module 23 calculates the fuel Va and uses it as the fuel theory. Compare with the value Va. This theoretical value Va is preferably supplied to the module by a central control / command system. The operator can also input it directly into the module. If there is a difference between the calculated value Va and the theoretical value of fuel, the electronic control module 23 issues a warning when a certain discrimination threshold is exceeded. When this difference reaches the second high threshold, the radiant tube is stopped to ensure safety. The first threshold is a deviation of 10%, for example, and the second threshold is a deviation of 15%, for example.

The theoretical value Va of the fuel can be calculated according to the gas composition by the following equation, for example. In this formula, the chemical composition of the gas is replaced with gas amount in fuel represented by gas m ³ per fuel m ^3.
Va = H ₂ x2.36 + COx2.38 + CH ₄ x9.54 + C ₂ H ₄ x14.4 + C ₂ H ₆ x16.84 +
C ₃ H ₆ x21.84 + C ₃ H ₈ x24.37 + C ₄ H ₈ x 29.64 + C ₄ H ₁₀ X32.41 +
C ₅ H ₁₂ x40.87 _ O ₂ x4.77

  In the present invention, the electronic control module 23 is advantageously located in the immediate vicinity of the radiation tube it controls. Thereby, it becomes possible to speed up information exchange between the electronic control module and the elements arranged in the radiation tube by shortening the length of the cable. This method makes it possible to control the radiation tube assembly and ensure safety faster than through a central control / command system. Also, the close proximity of the electronic control module and the radiation tube connected thereto facilitates operator intervention in the commissioning and maintenance of the equipment.

  In the present invention, the electronic control module 23 is advantageously connected to two radiation tubes that are close to each other. It can detect different movements of the two radiating tubes that clearly indicate that one of the two is faulty.

  This method is particularly advantageous because it makes it possible to eliminate disturbances associated with fluctuations in gas and / or air properties, which are common to the two radiating tubes.

  For example, if the electronic control module 23 detects a deviation between the amount of residual oxygen indicated by the sensor 24 of one radiant tube and the flow rate measured in the air and gas of the radiant tube, this deviation will be related to the fuel composition. It can be interpreted that it is related to the change in Va. In this situation, the electronic control module 23 of the present invention checks whether the second radiation tube has the same deviation. If so, it is a change in the properties of one fluid. If not, it is a failure of the first radiant tube element and a warning is given by the electronic control module. This analysis also shows that if the radiant tube is operated in push-pull mode (the pressure inside the tube is lower than outside the tube), the furnace atmosphere will enter the radiant tube and therefore be measured in the flue gas. Allows detection of radiant tube perforations, which will reduce the residual oxygen content.

As has been seen so far, the electronic control module of the present invention comprises the following in a preferred embodiment.
• Imposing prior art safety features and existing standards.
Control over the operation of one or two burners with closed loop adjustment of the air and gas supply valve openings. The loop is at the desired oxygen level in the wet flue gas at all points of the operating cycle (ignition, stable operation, fire extinguishing), whether the burner operates in on-off mode or proportional mode. Operates with a corresponding air / gas ratio.
• Review data on air and gas characteristics, especially composition, temperature, supply pressure, and fuel heat value to control the air to gas ratio in burner operation.
Control of the air to gas ratio in the operation of the burner carried out in a closed loop, from the measurement of residual O ₂ in the flue gas as confirmed by the flow rate calculation.
A system for calculating the Va of the gas to confirm that it matches the Va provided by the central control / command system and to issue a warning when there is a deviation that exceeds a specified threshold.
Control of the combined opening and closing stages of the air and gas valves in real time at each point of the air and gas valve opening or closing process to maintain the desired air / gas ratio.
・ Regarding the safety of the burner, periodically check the tightness of the gas valve when the effectiveness of the test has not been confirmed.

Claims (6)

A control module for at least one radiant tube burner (4, 5) comprising a fuel supply valve (7), an oxidant supply valve (6), a combustion flue gas exhaust duct (8), A fuel flow measuring device, an oxidant flow measuring device, and a combustion quality measuring device installed in the combustion flue gas exhaust duct (8) of at least one burner, the control module comprising:
Means for controlling the at least one burner, acting on an opening ratio of the oxidant supply valve (6) and the fuel supply valve (7) of the at least one burner, and the combustion quality measuring means Means for adjusting the ratio of oxidant flow / fuel flow based on the information provided by
Means for calculating a fuel combustion power Va using data provided by the combustion quality measuring device, the fuel flow measuring device and the oxidant flow measuring device, wherein the fuel burning power Va is calculated by the calculating means. Means for comparing the Va value with a theoretical value and detecting a deviation exceeding a predetermined threshold;
A control module comprising:   2. Control module according to claim 1, characterized in that the combustion quality control means is a residual oxygen sensor (24).   The module is capable of controlling two radiant tube burners, the fuel combustion power Va for each burner the data provided by the oxidant flow measuring device and the fuel flow measuring device, and the combustion quality control. Comparing two Va values calculated from the information provided by a device and obtained for the two burners, detecting deviations exceeding a prescribed threshold, according to claim 1 or 2 The described control module.   A fuel supply valve, an oxidant supply valve, a flue gas exhaust duct, a fuel flow measuring device, an oxidant flow measuring device, and a combustion quality measuring means installed in the combustion flue of at least one burner. A radiant tube burner comprising the control module according to claim 1, wherein the radiant tube burner is provided. A method for controlling at least one radiant tube burner, the burner comprising a fuel supply valve, an oxidant supply valve, and a flue gas exhaust duct, the method comprising:
Combustion installed in the combustion flue gas exhaust duct of the at least one burner by adjusting the opening ratio of the oxidant supply valve and fuel supply valve of the at least one burner with the operation of at least one burner Controlling according to the desired oxidant / fuel ratio based on the information provided by the quality measurement means
In particular, from the data provided by the oxidant flow measuring device and the fuel flow measuring device and the information provided by the combustion quality measuring means of at least one burner, the fuel combustion power value Va supplied to the at least one burner. And comparing the combustion force value Va with a theoretical value to detect a deviation exceeding a prescribed threshold value;
A method characterized by comprising: Controlling two radiation tube burners;
In particular, the combustion power value Va for each burner is calculated from the data provided by the oxidant flow measuring device and the fuel flow measuring device and the information provided by the burner combustion quality measuring means, and the two burners are calculated. Comparing the two Va values obtained for, and detecting a deviation exceeding a prescribed threshold;
The control method according to claim 5, comprising:

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