RU2838110C1 - Device for complete premixing of natural gas and air - Google Patents

Abstract

FIELD: heat power engineering.

SUBSTANCE: invention relates to the field of heat engineering, in particular to the low-pressure natural gas combustion device in the furnaces of hot water boilers. Device for complete premixing of natural gas and air contains in-series connected shutoff device, supply gas nozzle with low pressure gas volumetric flow sensor, throttle with damper and swirler, located on suction nozzle of centrifugal fan in gas vacuum area, wherein the outlet of the centrifugal fan is connected to the gas-air mixture supply pipe to the burner pipe, which is equipped with a gas-air mixture volumetric flow sensor, wherein the shutoff device, the throttle with a damper with a drive and a swirler, as well as sensors of volumetric flow rate of gas and gas-air mixture are connected to an electronic control unit made with possibility of regulating and maintaining gas-air ratio. A throttle with a damper, a swirler, a shutoff device and a gas supply nozzle are installed on a bearing plate fixed on a centrifugal fan.

EFFECT: improving the quality of natural gas combustion by supplying the burner pipe with a prepared combustible gas-air mixture in a rational gas-to-air ratio.

6 cl, 6 dwg

Description

The invention relates to the field of thermal power engineering, in particular to a device for burning low-pressure natural gas in the furnaces of hot water boilers, and is intended for complete preliminary mixing of natural gas with air before feeding it to the burner tube of the hot water boiler for subsequent combustion, as well as regulating and maintaining a constant gas-air ratio in a wide range of modulation of the boiler's thermal power.

A device for mixing combustible gas and air is known (RU Patent No. 2693538, published on July 3, 2019), comprising an air duct for supplying combustion air, a gas duct for supplying combustible gas, which is equipped with an external control valve, while the volumetric flow sensors are located only on the first and second measuring pipelines supplying gas.

The disadvantages of such a device are the absence of a measuring sensor after the fan, i.e. after mixing natural gas with air and forming a gas-air mixture for feeding to the burner pipe, which provides less accuracy in measuring the volumetric flow rate of the medium pumped into the combustion chamber. At the same time, the mixing device is equipped with such additional elements as an external valve operating as a gas mass flow regulator located on the supply gas pipeline, as well as additional measuring pipelines, which significantly complicates the overall design of the device.

A device for mixing combustible gas and air is known (RU Patent No. 2511783, published on 10.04.2014), accepted as the closest analogue to the claimed solution, containing a cylindrical body, a stabilizer, a gas swirler, while the cylindrical body is equipped with an adjustable damper for air supply. The device also contains a flame radiation sensor, which converts radiation into an electrical signal and compares the value of this signal with the required value for the optimal mode. As a result, a signal is generated for adjusting the air flow using an electric motor moving the damper flap, in accordance with the thermal load of the device.

The disadvantage of the considered solution is the inaccuracy of the gas supply regulation at the device input due to the analysis of only the thermal energy of the gas-air mixture at its output, as well as the inaccuracy of the chemical composition of the gas-air mixture in a wide range of thermal power modulation.

The technical objective of the invention is to create a device for complete preliminary mixing of natural gas and air, ensuring complete combustion of fuel with excess air in a wide range of capacities with low emissions of harmful emissions, as well as increasing the reliability and simplifying the design of the device in comparison with existing analogues.

The technical result of the invention is an increase in the quality of combustion of natural gas by supplying a prepared combustible gas-air mixture to the burner pipe in a rational gas-air ratio due to the design features of the solution.

The technical result is achieved by using a device for complete preliminary mixing of natural gas and air, comprising a series-connected shut-off device, a gas supply pipe with a low-pressure gas volumetric flow sensor, a throttle with a damper and a swirler, located on the suction pipe of a centrifugal fan in the gas vacuum region, wherein the outlet of the centrifugal fan is connected to a pipe for supplying a gas-air mixture to a burner pipe, equipped with a sensor for the volumetric flow of the gas-air mixture, wherein the shut-off device, the throttle with a damper with a drive and a swirler, as well as the sensors for the volumetric flow of gas and the gas-air mixture are connected to an electronic control unit, designed with the possibility of regulating and maintaining the gas-air ratio.

In a particular case, the throttle with a damper, a swirl valve, a shut-off device and a gas supply pipe are installed on a support plate fixed to a centrifugal fan.

In a particular case, the damper is made in the form of a toothed wheel or in the form of a sector with a circular groove of variable cross-section, equipped with a toothed sector.

In a particular case, on one side of the swirler there is a Venturi nozzle with a coaxial pipe built into it, through which gas is supplied to the swirler, and on the other side there is an opening for supplying the gas-air mixture to the centrifugal fan.

In a particular case, the electronic unit is designed with the ability to control a stepper motor that controls the throttle valve.

In a particular case, the electronic control unit is designed with the ability to regulate and maintain a constant gas-to-air ratio in a wide range of modulation of the thermal power of the hot water boiler.

The presence of an electronic control unit and a throttle valve drive allows you to accurately set and maintain a specified value of the gas-air ratio. In this case, control is carried out based on the readings of the volumetric gas flow and gas-air mixture sensors. The drive strives to set the throttle valve so that the difference between the current gas flow value and the theoretically required one is minimal or tends to zero.

The installation of a throttle with a damper with a drive and a swirler on the suction branch of a centrifugal fan allows the swirler of the gas-air mixture to be positioned opposite the suction branch of the fan, which ensures that the entire incoming flow of gas and air is directed strictly through the fan with subsequent readings of the gas-air mixture by a volumetric flow sensor located at the outlet of the centrifugal fan, which makes it possible to obtain more accurate data on the gas-air mixture that has passed through the fan for more accurate regulation of the supplied portion of gas.

Installing the throttle in the gas vacuum area allows the operation of the claimed device to be implemented as a whole. In this area, natural gas, exiting the gas supply pipe under excess pressure, and air from the room are mixed. Getting into the vacuum area on the fan suction pipe, they are guaranteed to mix and are strictly directed to the burner pipe. In this case, the fan, like a vortex pump, creates an increase in pressure due to the centrifugal force that occurs when the fan blades rotate and acts on the gas-air mixture, while the gas-air flow moves from the vacuum area to the fan (on the suction pipe, where the throttle is installed) to the high-pressure area (on the discharge pipe for supplying the gas-air mixture). This ensures that the gas-air mixture is pumped from the low-pressure area to the area where the fan creates higher pressure due to mechanical work.

Maintaining the gas-to-air ratio involves maintaining the required proportion of gas and air. The claimed device allows modulating the thermal power of the burner (i.e. increasing or decreasing the amount of gas burned), while the gas combustion process must be maintained throughout the entire operating range at a given and constant gas-to-air ratio for:

- completeness of fuel combustion;

- correct and safe operation of the boiler and burner pipe, which are designed to operate under strictly defined combustion parameters, depending on the ratio of gas and air, the temperature at the burner, the excess air coefficient, the carbon dioxide content, etc.;

- ensuring a minimum amount of harmful emissions throughout the entire operating range.

As a result, the considered design features of the claimed solution ensure constant monitoring and regulation of the gas-air ratio for a complete and high-quality gas combustion process.

Fig. 1 shows the design of the claimed device.

Fig. 2 shows the design of a damper with restrictive elements in the form of a circular guide groove.

Fig. 3a shows the design of the damper with restrictive elements in the form of an external guide, Fig. 3b shows the front view of the swirler design.

Fig. 4a shows a front view of the swirler design, and Fig. 4b shows a side view of the swirler design.

The claimed device contains a shut-off device 1 at the inlet, which is an electromagnetic valve, which is controlled by an electronic control unit 2 of a centrifugal fan 3.

The device also contains a supporting plate 4, on one side of which an electromagnetic valve 1 and a gas supply pipe 5 are fixed, and on the other side - a throttle 6 with a damper 7 and a swirler 8.

The supporting plate 4 serves to create an annular channel for air intake by the swirler 8 formed between the supporting plate 4 and the centrifugal fan 3.

The supply gas pipe 5 with the volumetric gas flow sensor 9 is located at the input of the throttle 6. In this case, the gas pipe 5 has a constant and known cross-section for further calculation in the control algorithm. The volumetric gas flow sensor 9 of the supply gas pipe 5 is a thermal anemometer equipped with a thermal correction element to ensure correct readings at different temperatures of the supplied natural gas.

The centrifugal fan 3 is connected to the gas-air mixture supply pipe 10 to the burner pipe 11, equipped with a sensor for the volumetric flow rate of the gas-air mixture 12. The sensor 12 is a thermal anemometer equipped with a temperature correction element to ensure correct readings at different temperatures of the supplied air and the gas-air mixture.

The electronic control unit 2 receives signals from the gas volume flow sensor 9 of the gas supply pipe 5 and the gas-air mixture volume flow sensor 12 of the gas-air mixture supply pipe 10 to the burner pipe 11, and also controls the stepper motor (not shown).

The centrifugal fan 3 provides an increase in pressure for the operation of the claimed device, controlled by an external controller of the hot water boiler. The process of regulating the gas-air ratio of the claimed device is adjusted to the operating mode of this external boiler controller.

The throttle 6 (Fig. 2) is a plate with a through hole 13 made in the center, on which the gas flow rate is regulated. In the recess of the throttle 6, grooves are made: a circular groove 14 of variable cross-section with circular guides for installing the damper 7, a groove with spiral channels 15 for discharging gas from the throttle 6 into the swirler 8, a groove 16 for the toothed sector of the damper 7. The throttle 6 is also equipped with an axis 17 for rotating the damper 7 inside it.

The damper 7 is a plate in the form of a toothed wheel (Fig. 3a) or in the form of a sector with a circular groove of variable cross-section (Fig. 3b) for smooth regulation of the flow through the throttle 6, equipped with a toothed sector 18 for obtaining rotational movement from the gear of the stepper motor. In the damper 7, an opening 19 is made, on which the rotational movement of the damper 7 inside the throttle 6 is carried out.

In this case, the shutter 7 contains limiting elements in the form of a guide circular groove 20 (Fig. 3a) or an external guide (Fig. 3b) to limit the angle of rotation.

The swirler 8 is an impeller with radial curved blades 21 (Fig. 4a) and a cover 22 (Fig. 4b). On one side of the swirler 8 there is a Venturi nozzle 23 with a coaxial branch pipe 24 built into it, through which the gas enters the swirler 8, and on the other side there is an opening 25 for feeding the gas-air mixture into the centrifugal fan 3.

The built-in coaxial branch pipe 24 is made in the form of coaxial channels: the main channel 26, through which gas enters the swirler 8 from the throttle 6, and auxiliary channels 27, through which gas reflected from the damper 7 of the throttle 6 enters the swirler 8.

The claimed device operates as follows.

After the centrifugal fan 3 is switched on, the swirler 8, throttle 6 and damper 7 are in the vacuum region on the suction pipe of the fan 3, while the gas-air mixture flow sensor 12 records the air flow after the fan 3.

Air enters the swirler 8 along the radial curved blades 21, and the Venturi nozzle 23 with coaxial channels 26 and 27 is thus located opposite the suction branch of the fan 3.

Based on the current signal from the gas-air mixture volume flow sensor 12, the electronic control unit 2 calculates the theoretically required signal from the gas volume flow sensor 9 of the gas supply pipe 5.

The electronic control unit 2 is equipped with a setting function for adjusting the gas-air ratio, as well as a temperature correction function.

The adjustment coefficient is a function of the gas-air mixture flow rate:

Setting the gas-air ratio consists of constructing the function of the coefficient k _p from the current gas-air mixture flow rate in such a way as to correct the theoretical value of the required gas flow rate signal over the entire range of thermal power. That is, to set the gas-air ratio, the canonical equation of a straight line on a plane is taken as a basis.

In the electronic control unit 2, the correction of the readings of the volumetric gas flow sensors 9 and the gas-air mixture 12 is carried out as follows: the head of such sensors is equipped with a correction thermistor or an external sensor for reading the temperature of the measured medium.

The function for correcting the value of the signal from the sensor of the volumetric flow of gas 9 and the gas-air mixture 12 takes the following form:

Where

k is the arithmetic mean of the differences between the values of the volumetric flow sensor signals for each degree;

- the value of the signal from the correction thermistor at room temperature;

t' - current value of the signal from the correction thermometer.

The arithmetic mean of the differences between the values of the signals of the gas volume flow sensor 9 and the gas-air mixture 12 for each degree k is determined as follows:

The damper 7 is set to the position corresponding to ignition. On the damper 7, a toothed sector 18 is made (or the damper as a whole is a toothed wheel), in engagement with which is the gear of the stepper motor, when turning which the rotation is transmitted to the damper 7, accordingly, the cross-section of the throttle 6 changes.

Next, the electromagnetic valve 1, which is a shut-off device, opens. The volumetric gas flow sensor 9 registers the gas flow through the gas supply pipe 5 to the throttle 6.

Entering the throttle 6, the gas flow is directed into a narrowed section formed by the circular groove of the valve and the opening 19 for rotating the valve 7 in the throttle 6. In this way, the required volumetric gas flow rate is established.

When throttling the gas on valve 7, the main part of the gas is divided into three parts:

1) part of the gas passes through the section of the throttle 6 and enters the internal branch pipe 24 in the Venturi nozzle 23 of the swirler 8;

2) part of the gas reflected from the valve 7 enters the coaxial channel tube 24 into the vacuum region of the Venturi nozzle 23;

3) part of the gas flows through the spiral channels 15 of the throttle 6 to the beginning of the radial blades 21 of the swirler 8, where it is captured by the air flow and enters the swirler 8, thereby ensuring the tightness of the device.

The stepper motor tends to set the valve 7 of the throttle 6 in such a way that the difference between the current value of the signal of the volumetric gas flow sensor 9 and the theoretically required value is minimal or tends to zero.

The objective function for regulating the volumetric gas flow rate is as follows:

The theoretically required value of the signal from the volumetric gas flow sensor 9 is determined by the following expression:

Where

- theoretically required signal of the gas volume flow sensor 9 by value;

- current value of the gas-air mixture flow rate (signal from the gas-air mixture volume flow rate sensor 12 behind fan 3);

- current value of gas flow rate at the inlet to the burner unit (signal from volumetric gas flow sensor 9);

n is the zero value of the signal from the volumetric gas flow sensor 9 at rest, in the absence of flow, at room temperature;

S _c - cross-sectional area of the control section in which the sensor of the volumetric flow of the gas-air mixture 12 is located, mm ² ;

S _g is the cross-sectional area of the control section in which the gas flow sensor 9 is located, ^mm2 ;

k _p is the tuning coefficient according to expression (1).

The operating algorithm of the claimed device has the following order of action during operation:

1) definition of meaning according to the current value of the gas-air mixture volume flow sensor 12;

2) determination of control coefficients;

3) checking the condition and generating the control action P (0 - opening of damper 7, 1 - closing of damper 7).

If the required gas flow rate and the current gas flow rate deviate, the electronic control unit 2 gives a command to open or close the valve 7 until the difference between the target and current values is zero. In this way, a constant gas-air ratio is maintained.

In this case, the gas-air ratio is taken into account each time when determining the theoretical signal of the gas volume flow sensor 9 and the current value of the signal of the gas-air mixture volume flow sensor 12, which allows not only to maintain the gas-air ratio, but also to ensure this ratio when the thermal power (modulation) changes.

The claimed device, with its simplified design, ensures high-quality preparation of a combustible gas-air mixture in a rational gas-air ratio for complete combustion of fuel with excess air in a wide range of capacities with low emissions of harmful emissions, which distinguishes it favorably from its analogues.

Claims (6)

1. A device for complete preliminary mixing of natural gas and air, characterized in that it contains a series-connected shut-off device, a gas supply pipe with a low-pressure gas volumetric flow sensor, a throttle with a damper and a swirler, located on the suction pipe of a centrifugal fan in the gas vacuum region, wherein the outlet of the centrifugal fan is connected to the pipe for supplying the gas-air mixture to the burner pipe, equipped with a sensor for the volumetric flow of the gas-air mixture, wherein the shut-off device, the throttle with a damper with a drive and a swirler, as well as the sensors for the volumetric flow of gas and the gas-air mixture are connected to an electronic control unit designed with the possibility of regulating and maintaining the gas-air ratio. 2. The device according to item 1, characterized in that the throttle with the damper, the swirler, the shut-off device and the gas supply pipe are installed on a support plate secured to the centrifugal fan. 3. The device according to item 1, characterized in that the damper is made in the form of a toothed wheel or in the form of a sector with a circular groove of variable cross-section, equipped with a toothed sector. 4. The device according to item 1, characterized in that on one side of the swirler there is a Venturi nozzle with a coaxial branch pipe built into it, through which gas is supplied to the swirler, and on the other side there is an opening for supplying a gas-air mixture to a centrifugal fan. 5. The device according to item 1, characterized in that the electronic unit is designed with the ability to control a stepper motor that controls the throttle valve. 6. The device according to item 1, characterized in that the electronic control unit is designed with the ability to regulate and maintain a constant gas-to-air ratio in a wide range of modulation of the thermal power of the hot water boiler.

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