Questions&Answers

Principle

When the combustible gas (city gas, natural gas, LPG) is controlled by the microcomputer control system according to the program into the combustion head of the burner, the primary air is mixed with the combustible gas, ignition and combustion, and the secondary air assists combustion to achieve full combustion. The combustion condition is detected and controlled by the flame automatic tracking system. When there is a failure in combustion (lack of oxygen in the combustion chamber, underpressure of combustible gas, cut-off of combustible gas, insufficient gas quantity, etc.), the control system issues a command and the solenoid valve of the gas supply system is quickly closed to cut off the gas power supply, and the gas burner is automatically shut down after blowing to indicate the failure.

Features

(1) high thermal efficiency: can adapt to pressure fluctuations, self-regulating primary air distribution (that is, large gas pressure, inhaling more primary air; small gas pressure, inhaling less primary air), full combustion, high thermal efficiency.

(2) High safety: The burner is equipped with small fire. When the boiler starts, the small fire is lit first, and when the small fire burns normally and steadily, the automatic control system opens the main gas valve before the fuel enters the boiler for normal combustion, which will not produce the phenomenon of deflagration.

(3) High adaptability of fuel: This burner can be applied to natural gas, LPG, gas, LPG mixture and other types of gas by only replacing a small number of parts.

1.Power system

On the commonly used burner, there should be only electric motor related to power.

2.Fuel supply system

On the burner, this is one of the more complicated systems, in fact, the mechanical products involved in this system are much more complicated than the electrical products on the control system. Including fuel pumps, nozzles, fuel heaters, oil cups, fuel lines, fuel solenoid valves gas valves (including gas solenoid valves), gas regulators, gas filters, etc.

3.The combustion system

The most technical content of the burner industry a system. In fact, no matter how cutting-edge the technology of the electrical products in charge of the control, or how sophisticated the manufacture of the oil pump is, the level of these technologies and means have nothing to do with the burner manufacturer's own ability, but the design of the combustion system is something they must do on their own. Therefore, the level of the combustion system is what determines the ability of a burner. This part of the product includes the combustion cylinder, forced air blower impeller, flame plate, oil gun, gas core tube, and built-in or external diffusion head. This is the part of the product that constitutes the air-fuel premixing device.

1.Controller

The core part of the burner control, including the process management controller called proportional regulator, the gas leak detector responsible for detecting valve leaks, etc., are responsible for collecting and triggering the signal of each action, which is equivalent to the brain of the burner.

2.Servo mechanism

All electric servo motors and mechanical drive hydraulic cylinders are classified as control system, the reason is that the former and the program controller constitute a closed-loop control system, the latter's power source from the oil pump, the instructions for the execution of the action is actually triggered by the controller, and control the opening and closing of the dampers.

3.Flame monitor

This name is the name of the industry, the more popularly known as the name of its actual function, and eventually confused with the controller category, simply through the flame signal control open and close the controller - can monitor the flame is actually only photoresistors and phototubes, as well as the detection of flame ion ion probe, if the power can be turned on and off by itself should obviously be called more appropriate controller.

4.Pressure and temperature switch

Broadly speaking, it should be called pressure or temperature sensors. Among the pressure switches in the gas switch: gas switch, mostly used for gas burner gas control, wind pressure switch for the control of air (such as no forced air supply and wind pressure, the whole power cut off). The temperature switch is mostly used for the control of heating temperature of high viscosity fuel, such as heavy oil or residual oil.

Gas (liquefied gas, natural gas, city gas, coke oven gas, converter gas, mixed gas, furnace gas, blast furnace gas, etc.) burners have the advantages of easy ignition, complete combustion, stable flame, good spreading, no tempering, no de-flaming, large adjustment range, low noise, long life, safety and reliability due to reasonable structural design. 

1.Definition

According to its working principle, a burner can be defined as a device that converts substances into heat energy by means of a chemical reaction called combustion - that is, air and fuel are mixed in the right proportion through a premixing device to make them burn fully. The burner is a kind of thermal energy device that feeds fuel and air into the furnace chamber according to the required concentration, speed, turbulence and mixing method, and enables the fuel to fire and burn stably in the furnace chamber.

2.classification

Gas burner is divided into natural gas burner, city gas burner, etc.

According to the combustion control mode of the burner is divided into: single-stage fire burner, double-stage fire burner, proportional regulation burner.

Divided by fuel atomization: mechanical atomization burner, medium atomization burner.

Divided by structure: integral burner as well as split burner.

China's natural gas and coal gas (raw materials for coal) resources are abundant and clean energy, so there are good socio-economic benefits. However, in the design of gas burner development, gas characteristics - flammable, explosive and toxic, the primary issue of safety control. The following is an introduction to the gas burner safety control requirements: according to the combustion characteristics of gas in the furnace, the content of its safety control requirements are mainly pre-blowing, automatic ignition, combustion state monitoring, protection against non-ignition, protection against flame failure, protection against flame failure, protection against high and low gas pressure limits, protection against insufficient air pressure, power failure protection, measures to prevent gas leakage accidents, etc.

1.Pre-blowing air

Burner in the ignition before, there must be a period of pre-blowing air, the furnace and flue gas in the residual blowing or dilution. Because the work of the burner furnace inevitably have residual gas, if not pre-blowing air and ignition, there is a risk of explosion. The residual gas must be blown clean or diluted to ensure that the gas concentration is not within the explosion limit.

2.Automatic ignition

Gas burners should use electric spark ignition, to facilitate the realization of automatic control. Available high-voltage ignition transformer to generate an arc ignition, the output energy required: voltage ≥ 3.5K V, current ≥ 15mA.

3.Combustion state monitoring

Combustion state must be monitored dynamically, once the flame detector detects the flame out signal, must be a very short time feedback to the burner, the burner then into the protection state, while cutting off the gas supply.

4.The protection of non-ignition

When the burner is ignited, gas is introduced and the gas catches fire and burns. Ignition action is required to occur before the gas into the first formation of the ignition temperature field, to facilitate the ignition and combustion. If the fire does not ignite, the flame detector does not sense the flame signal, the burner enters the protection state. The time from ignition to enter the protection state should be appropriate, neither too short nor too long, generally required in 2-3 seconds into the gas, the burner to the flame detector to detect the flame signal to judge, not on fire then enter the protection state, on fire to maintain combustion.

5.Flame out protection

Burner in the process of combustion, if the accidental flame out, the burner into the protection state. As the furnace chamber is hot. Gas is prone to deflagration, so it must enter the protection state in a very short time, cut off the gas supply.

6.Gas pressure high and low limit protection

 Stable combustion of gas burners have a certain range, only allow gas pressure fluctuations within a certain range. The purpose of limiting the gas high and low pressure is to ensure flame stability: no flame off, no flame out and no flame back, while limiting the output thermal power of the burner to ensure the safe and economic operation of the equipment. When the gas pressure exceeds this range, the burner should be locked to work.

7.Insufficient air pressure protection

 The gas burner is designed with high thermal intensity and its combustion method is forced by the blower. If the fan fails to cause air interruption or air shortage, immediately cut off the gas, otherwise, the chamber will be burst combustion or backfire to the fan. Therefore, while improving the quality of the fan, the gas control must be interlocked with the air pressure, when the air pressure is insufficient, the gas supply should be cut off immediately.

8.Power failure protection

Burner in the process of working suddenly power failure, must immediately cut off the natural gas supply to protect the safety of equipment. Gas control solenoid valve must be normally closed type, once the power failure, automatically shut off the gas supply.

9.Measures to prevent gas leakage accidents

Gas leakage includes two aspects, one refers to the gas leakage to the environment through the pipeline, and the other refers to the gas leakage to the furnace through the end of the solenoid valve spool. Environmental leakage may cause poisoning and explosion at the work site, which must be paid great attention to. Leakage inside the furnace may cause an explosion inside the furnace. Prevention of gas leakage measures are peripheral control, generally not included in the burner body control.

Tracing the history of the development of solenoid valves, so far, domestic and foreign solenoid valves from the principle is divided into three categories, namely: direct-acting, step-by-step direct-acting, pilot type .

First, direct-acting solenoid valve 

Principle: When energized, the solenoid coil generates electromagnetic force to lift the closing member from the valve seat, the valve opens; when disconnected, the electromagnetic force disappears and the spring force presses the closing member on the valve seat, the valve closes. 

Features: in the vacuum, negative pressure, zero pressure can work properly, but the general diameter does not exceed 25mm. 

Second, step-by-step direct-acting solenoid valve 

Principle: It is a combination of direct-acting and piloting principle, when the inlet and outlet pressure difference ≤ 0.05Mpa, when energized, the electromagnetic force directly to the pilot small valve and the main valve closure parts in turn upward lift, the valve open. When the inlet and outlet pressure difference > 0.05Mpa, when the power is applied, the electromagnetic force opens the pilot valve first, the pressure in the lower chamber of the main valve rises and the pressure in the upper chamber falls, thus using the pressure difference to push the main valve upward; when the power is off, the pilot valve and the main valve use the spring force or medium pressure to push the closing member and move downward to close the valve. 

Features: in zero differential pressure or vacuum, high pressure can also work reliably, but the power is larger, requiring vertical installation. 

Third, the pilot operated solenoid valve 

Principle: When energized, the electromagnetic force opens the pilot hole, the pressure in the upper chamber drops rapidly, forming a low pressure differential around the closing member, pushing the closing member to move upward and open the valve; when disconnected, the spring force closes the pilot hole, the inlet pressure through the bypass hole quickly into the upper chamber to form a low pressure differential around the closing member, pushing the closing member to move downward and close the valve. 

Features: the upper limit of the fluid pressure range is high, but must meet the fluid pressure differential conditions.

Fourth, the solenoid valve open and closed state

Commonly used solenoid valve is mostly diaphragm valve, its working principle is: the valve body is divided into two chambers, the middle for the diaphragm, under the same conditions of water pressure, due to the diaphragm up and down the force area is different and the pressure difference, to cut off the flow of water.

Burner solenoid valve open state: when the remote controller to give an electrical signal or manually rotate the solenoid head, drainage channel open, the upper diaphragm chamber water discharge, indoor pressure decreases, the pressure acting on the upper diaphragm becomes smaller, under the action of upstream pressure to push the diaphragm upward movement, open the pipeline channel.

Solenoid valve closed state: manually close or disconnect the solenoid head electrical signal, so that the drainage channel is closed, the upper diaphragm chamber slowly filled with water, wait until the diaphragm up and down the same pressure, due to the diaphragm on the upper side of the force area is larger, so that the diaphragm downward movement, close the pipeline channel.  

1、Preparation stage.

After the program controller gets power, start the internal program self-test, at the same time, servo motor drive dampers to the closed state, the program self-test is completed, in standby mode, when the thermostat, too high and too low gas pressure switch, steam boiler steam pressure switch and other restriction switches allowed, the program controller begins to start, enter the pre-blowing stage. If the solenoid valve set with a leak detection system, the system in the above restriction switch allows the valve leak detection first, the detection passed, before entering the pre-purge stage.

2、Pre-blowing stage.

Servo motor drive damper to the fire open state, while the fan motor start, start 13 seconds air supply to blow into the air for pre-blowing, depending on the programmable controller, about 20 ~ 40 seconds after blowing, servo motor drive damper to the ignition open state, ready to ignite. Throughout the pre-blowing stage, the air pressure switch measures the air pressure, and only if the air pressure is kept at a high enough level, the pre-blowing process can be continued. 

3、Ignition stage. 

After the servo motor drives the damper to the ignition open state, the ignition transformer cuts in and outputs high voltage to the ignition electrode to produce an ignition spark. After about 3 seconds, the programmable controller sends electricity to the safety solenoid valve and the proportional solenoid valve, the valve opens and the gas reaches the combustion head, mixes with the air supplied by the fan and is then ignited. Within 2 seconds after the valve opens, the ionization electrode should detect the presence of the flame, only then the program controller continues the program later, otherwise, the program controller locks and disconnects the solenoid valve to stop the gas supply, and at the same time the alarm.

4、Normal combustion stage.

 Ignition normal and stable combustion for a few seconds, the servo motor drives the damper to the large fire open state, (the oil pump of the fuel engine opens and starts to spray oil), at the same time, the servo motor of the proportional gas regulating valve cuts in and adjusts the gas pressure after the gas valve according to the air pressure and the back pressure of the furnace chamber to adjust the gas volume to achieve stable and efficient combustion. Thereafter, the burner automatically realizes small and large fire changeover and shutdown according to the requirements of each limit switch. In addition, the burner is monitored by ionization electrodes and air pressure switches throughout the combustion process.

1, flame monitor: Its main role is to monitor the formation of the flame condition, and generate signals to report the program controller. Flame detector mainly has three kinds: photoresistor, UV eye and ionization electrode.

(1) photo resistor: mostly used in light oil, heavy oil burner, its function and working principle: photo resistor and a flame relay with three contacts are connected, the resistance value of the photo resistor changes with the brightness of the light received by the device, when the voltage added to the two ends of the photo resistor is certain, the higher the current in the circuit, when the current reaches a certain value, the flame relay is activated, so that the burner continues to work down . When the photoresistor does not sense enough light, the flame relay does not work and the burner will stop working. The photoresistor is not applicable to gas burners.

(2) UV UV eye: generally used on oil and gas burners, the eye can only feel the ultraviolet light in the flame, the UV tube will not respond to the refractory daylight, ordinary light or furnace glow material flickering in the chamber, the life of the UV tube is about 100 hours at an ambient temperature of no more than 50 ℃, the ambient temperature is too high for its life has a great impact. If it receives a sufficient amount of UV light, it can produce current, to ensure that the burner works properly, its current must be stable and cannot be lower than the current required by the programmable controller.

(3) Ionization electrode: mostly used on gas burners. Program controller to ionization electrode power supply, if there is no flame, the power supply on the electrode will stop, if there is a flame, the gas is ionized by its own high temperature, ion current flows between the electrode, flame and combustion head, ion current is rectified into DC, and through the grounded burner shell to reach the flame relay to make it work, to ensure that the burner after-sequence work smoothly. 

2, pressure monitor: generally used for gas burners, mainly gas high-pressure, low-pressure monitoring, as well as wind pressure monitoring, if the burner is used for steam boilers, there is steam pressure monitoring.

3、Temperature monitor: monitoring and control of fuel oil (heavy oil) temperature.

The function of the ignition system is to ignite the mixture of air and fuel, and its main components are: ignition transformer, ignition electrode, and electric fire high-voltage cable.  

ignition transformer: electronic and mechanical (inductive) two, is a kind of high-voltage output conversion components, its output voltage is generally: 25KV, 26KV, 27KV, the output current is generally 15 ~ 30mA. oil machine and gas machine is the difference: oil machine is generally two heads, gas machine is generally a head.

Ignition electrode: convert high voltage electric energy into light and heat energy through the form of electric arc discharge to ignite the fuel, generally there are two types of single and split type.

electric fire high-voltage cable: its role is to transmit electrical energy, can withstand 1.5 million volts.

1.Shell: it is the main part of the installation bracket of each component of the burner and the fresh air inlet channel. From the perspective of appearance, it can be divided into box type and gun type. Most box type burners have an outer cover of injection material, and the power is generally small. Most high-power burners use split shell, generally gun type. The shell is usually made of high strength light alloy castings.

2.Fan motor: mainly provides power for the operation of fan impeller and high-pressure oil pump, and some burners use separate motor to provide power for oil pump. Some small burners use single-phase motors, which can only be rotated in a certain direction to make the burner work normally.

3.Fan impeller: through high-speed rotation to produce enough wind pressure to overcome the resistance of the furnace and the resistance of the chimney, and blow enough air into the combustion chamber to meet the needs of combustion. It is composed of cylindrical wheels loaded into a certain Angle of the blade, the composition of the material is generally high strength light alloy steel, but also injection molding products, all qualified fan impeller has good balance performance.

4.Air gun fire tube: it plays the role of guiding airflow and stabilizing wind pressure, and is also a part of the air inlet channel. Generally, there is a shell flange connected with the furnace mouth. Its composition material is generally high strength and high temperature resistant alloy steel.

5.Damper controller: it is a driving device that controls the rotation of damper through mechanical connecting rod. Generally, there are two kinds of hydraulic drive controller and servo motor controller. The former works stably and is not easy to produce faults. The latter controls accurately and the air volume changes smoothly.

6.Damper: the main role is to adjust the size of the air inlet channel to control the size of the air inlet volume. Its composition material has injection molding and alloy two kinds, injection molding baffle is generally single, double, three pieces of a variety of combination.

7.Diffusion disc (air regulator) : its special structure can produce rotating air flow, which contributes to the full mixing of air and fuel, as well as the role of regulating the secondary air volume.

The fuel system of oil burner mainly includes: oil pipe and connector, oil pump, solenoid valve, nozzle and heavy oil preheater.

1、Oil pipe and connector: used to transmit fuel.

2、Oil pump: make oil to form a certain pressure mechanism, the output oil pressure is generally above 10bar (1bar = 1Kg/cm2), to meet the requirements of atomization and oil injection volume, divided into single pipe output and double pipe output two. Some burner oil pump and fan motor coaxial connection, some have a separate oil pump motor drive.

3, solenoid valve: used to control the oil circuit on and off, mostly two-way valve and three-way valve.

4, nozzle: the main role is to atomize oil droplets. The main parameters of the nozzle are the injection angle (30 °, 45 °, 60 °, 80 °), spraying mode (solid, hollow, semi-hollow) and the amount of oil spraying. Under the same pressure, the nozzle of smaller oil spray volume, the atomization effect is better.

5, heavy oil preheater: heavy oil burner specific equipment, used to heat the heavy oil to a certain temperature, reduce viscosity, in order to increase the atomization effect of heavy oil, its temperature control device and burner control circuit chain.

The fuel system of the gas burner mainly has: filter, regulator, solenoid valve group, solenoid valve leakage detector, ignition solenoid valve group.

1, filter: its role is to prevent impurities from entering the solenoid valve group and burner.

2, regulator: the main role is to reduce the pressure stabilization, generally used in high-pressure gas supply system, the inlet pressure can not be less than 100mbar (1bar = 1Kg/CM2).

3, solenoid valve group: generally by the safety solenoid valve and the main solenoid valve composition, there are split and integrated type, integrated solenoid valve group is generally combined with a pressure regulator and filter. Safety solenoid valve is generally fast-opening and fast-closing type; the main solenoid valve is generally two-stage type, and fast-opening and fast-closing type and slow-opening and fast-closing type.

4, solenoid valve leakage detector: its role is to detect whether the closure of the solenoid valve group is tight. Generally used for power greater than 1400Kw on the burner.

5, ignition solenoid valve group: generally have a manual ball valve, pressure regulator, solenoid valve, mainly for the power of the larger burner.

Natural gas boilers are now widely used and have become the focus of energy-saving and environmentally friendly renovations in the thermal industry. Do you know how the burner of the gas boiler you are using burns? Today to talk about the combustion method of gas boiler burner.

1.Diffusion combustion

Diffusion type combustion method is not to premix, but to diffuse the gas to each other at the nozzle opening, and then burn it.

Advantage: This type of combustion is not pre-mixed, but diffuse the gas at the nozzle opening, and then burn it. The combustion method is relatively simple and the flame is relatively stable.

Disadvantages: Because of the long flame, it is easy to produce incomplete combustion phenomenon, will produce more carbon monoxide and nitrogen oxides, which is not conducive to the full use of boiler fuel, boiler thermal efficiency, and difficult to meet the boiler emission standards.

2.Full premixed combustion method

Full premixed combustion method is to pre-mix natural gas and air before combustion, the mixed gas in the burner chamber combustion.

Advantage: Pre-mixed air and gas, multiple radiant heat transfer, heat transfer intensity is increased. The advantage of using this combustion method is that the flame is clearer and the thermal efficiency is higher.

Disadvantages: combustion premixing ratio requires accurate combustion rate fast, uniform combustion full radiation heat transfer.

3.Flameless combustion

The space before combustion and gas in the gas boiler for homogeneous mixing of combustion methods. When using this method, the oxygen required by the gas in the process of combustion does not need to be obtained in the surrounding air, and only needs to reach the combustion zone with the air mixture to achieve instantaneous combustion completion.