1 Introduction
As the country attaches increasing importance to environmental protection, cities have imposed strict restrictions on the discharge of waste gas and waste water. The smoke and dust from coal-fired boilers is one of the main factors causing urban air pollution. In order to realize the beautiful ideal of "giving us a blue sky", many large and medium-sized cities have now banned the operation of coal-fired boilers and replaced them with oil and gas boilers. In oil and gas boilers, the most important component is the burner, and the high-pressure ignition device is one of the key electronic components in the burner. Since the information attached to the imported burner does not provide the principle circuit, performance and parameter description of the high-voltage ignition device, but only provides an extremely simple one-page description of the external dimensions, external wiring, etc., this gives our country's burner agents , brings considerable inconvenience to users, and also makes the design and complete sets of domestic burners more difficult. In the past ten years, the author has selected and debugged a variety of imported burners and their high-pressure ignition devices, and has successively collected some relevant information. I provide it here to everyone, hoping to be helpful to those in the industry.
At present, there are dozens of burners from eight countries on the Chinese market. Common ones include Germany's Weisaupt, SAACHE, MAN, and ElcoKlockner, France's CUENOD, Guillot, SICMA, and RADIANT, the United States' Johnson, Power Flame, and the United Kingdom's NUWAY, Italy's FBR, Baltur, UNIGAS, Riello, ECOFLAM, the Netherlands' Purlpher, Sweden's Bentone and South Korea's ABC, Sookook, etc. Although there are many types of burners, there are only a limited number of high-pressure ignition devices. Except for a few burners equipped with locally produced high-pressure ignition devices, the high-pressure ignition devices of the other dozen burners are basically products from several well-known international companies, such as BRAHAMA of Italy, Danfoss of Sweden, France Landis and Honeywell of the United States, etc.
2 Introduction to the principles of high-pressure ignition and its devices
2.1 Principle of high-pressure ignition
High-voltage ignition, also known as spark ignition, is a widely used ignition method. When an electric spark passes through gas or atomized fuel, the fuel quickly changes from a good insulator to a good conductor. As the voltage between the two poles increases, the electric field gradually strengthens, the charged objects in the fuel are accelerated by the electric field, and the moving charged particles and molecules undergo inelastic collisions. When the collision is severe enough, the molecules are ionized and become charged particles. The concentration of charged particles increases exponentially, and the initial tiny current is amplified millions of times, producing a large current. The time required for this process depends on the ratio of applied voltage to breakdown voltage. The breakdown voltage depends on the fuel composition, electrode shape, inter-electrode distance, and the temperature and pressure conditions of the fuel. The breakdown voltage can be approximately calculated by the following formula [1]:
Ub=2.7+1.4Lwhere: Ub——breakdown voltage (KV); L——distance between poles (Mm).
When the electrode spacing is greater than the critical distance, the minimum ignition energy has nothing to do with the electrode spacing; when the electrode spacing is less than the critical distance, the minimum ignition energy increases with the decrease of the electrode spacing due to the heat absorption of the electrodes themselves. Figure 1 shows the relationship between the minimum ignition energy and the electrode spacing and electrode size. The fuel is 11% methane air mixture.
The shape of the discharge electrode also has a certain impact on the minimum ignition energy. As shown in Figure 2, under the same electrode spacing and electrode size conditions, the sharper the discharge point, the less heat it absorbs, and the required minimum ignition is The energy is also smaller.
2.2 Introduction to the principle of high-voltage ignition device
The high-pressure ignition device is one of the core electronic components of the burner. Although its price only accounts for a small part of the total price of the burner, it is responsible for the important work of fuel ignition. The failure of the high-pressure ignition device may cause the burner to fail to work and affect production; or may cause the boiler to explode. Especially when the high-pressure ignition device has not completely failed, a large amount of fuel has been injected into the furnace, and the flameout protection device has not yet been activated. At this time, the high-pressure ignition device suddenly ignites, which will cause very serious consequences. This shows the importance of high-voltage ignition device.
High-voltage ignition devices generally consist of a rectifier circuit, an oscillation circuit, a boost component and a discharge electrode. The rectifier circuit rectifies and filters the 220 V/50 Hz alternating current and converts it into direct current; the function of the oscillation circuit is to oscillate the direct current into alternating current according to the discharge frequency; the boost component boosts the oscillated alternating current to achieve the desired voltage. The high voltage of ionized air is used to form a high-voltage pulse current using a high-voltage silicon stack; the discharge electrode is made of special materials and placed at the fuel outlet. The output waveforms of each component are shown in Figure 3 [2].
Figure 4 is a schematic diagram of the schematic circuit of the ignition device. The AC 220 V/50 Hz power supply becomes a lower voltage power supply after passing through the power transformer T1, and then passes through the rectifier bridge B to change the AC power supply into a DC pulse power supply. After filtering by the capacitor C1, the DC power supply is obtained. This part That is the rectifier circuit. The oscillation circuit is composed of resistor R1, transistor BG and the primary of step-up transformer T2. After oscillation, the step-up transformer T2 performs a boost, and then is rectified by a high-voltage diode or high-voltage silicon stack D to obtain high-voltage direct current. This direct current charges capacitor C2 through resistor R2, and at the same time stores energy on large capacitor C3. When C2 is charged to a certain voltage, the bidirectional diode D2 turns on, triggering the triac SCR to conduct. At this time, the capacitor C3 has reserved considerable energy. This energy passes through the loop capacitor C3, the triac SCR and the secondary riser. The primary release of the voltage transformer T3, at this time, a high voltage is generated on the secondary of the secondary step-up transformer. The high voltage is discharged after the discharge electrode breaks down a certain thickness of air, thus completing the primary discharge ignition of pulse ignition. Capacitor C3 is charged again after being discharged, thus performing a series of charging and discharging processes. A series of discharge sparks are generated between the electrodes, completing an ignition process.
3 Comparison of high-voltage ignition devices
3.1 Parameters of several typical high-voltage ignition devices
Honeywell is a high-voltage ignition device produced in the United States. The commonly used Satronic series electronic igniters are designed based on solid-state relays. Different from traditional iron-core transformers, it generates high-frequency and high-voltage sparks in the secondary through an internal ignition circuit. The working parameters of this series of electronic igniters are given in Table 1.
Danfoss is a high-pressure ignition device produced in Sweden. The EBI series electronic igniter is commonly used for ignition of oil and gas burners. It works on the principle of electronic frequency conversion to generate high voltage, and is suitable for intermittent ignition. Within 3 minutes, the ignition rate is 33% under the conditions of 35℃; the ignition rate is 20% under the conditions of 60℃. Table 2 shows Operating parameters of this series of electronic ignition.
BRAHAMA is a high-voltage ignition device produced in Italy. It is divided into three series: E, G and S. They all use high-performance ignition transformers to boost the voltage. Table 3, Table 4 and Table 5 give their working parameters respectively.
3.2 Comparison of high-pressure ignition devices
The comparison of high-voltage ignition devices includes a comparison of solid-state relay electronic igniters and ignition transformer electronic igniters; a comparison of unipolar, bipolar, and intermediate grounded bipolar electronic igniters; a comparison of different fuel burner electrode arrangements and different Comparison of the advantages and disadvantages of discharge locations.
Compared with electronic igniters using ignition transformers, electronic igniters using solid-state relays use more advanced solid-state relay voltage boosting technology and have the advantages of small size, light weight, low heat generation and reliable operation. However, due to the use of a relatively expensive solid-state relay, the cost of the entire electronic igniter increases, and the price is much higher than that of an electronic igniter using an ignition transformer. For the above-mentioned well-known brands of ignition transformer electronic igniters, after decades of on-site use, it has been proven that their working reliability and lifespan are no worse than solid-state relay electronic igniters, and are much better than electric heating wire igniters. The latter is an ignition device for oil and gas burners that was used in the early days (and is still used in China). Although this ignition device is reliable in ignition, it has slow ignition speed, short ignition wire life, and requires a large power. Currently, it is used in Foreign countries have been eliminated.
The output of the electronic ignition is divided into unipolar type, bipolar type and bipolar type with grounding in the middle to adapt to different burner designs. The so-called unipolar type has only one electrode in its output, and the other electrode is grounded inside or outside the igniter (that is, connected to the burner shell). During operation, the electrode discharges to the ground, generating sparks and igniting the fuel gas. Its characteristics are that it is relatively safe, reliable and easy to use. It only needs to lead out an electrode for insulation. It should be noted that for externally grounded unipolar electronic igniters, remember not to reverse the two poles, otherwise it may cause damage to the electronic igniter and even the entire control equipment. The so-called bipolar type is basically the same internally as the unipolar type, except that the other electrode is not grounded. When working, the fuel gas is ignited by discharge between the two poles. It is characterized by flexible use, but is not as safe as the unipolar type, and the two lead electrodes need to be insulated. Indirect
The bipolar version of the ground is achieved using an ignition transformer with a center tap or using two solid state relays. When working, it can use the discharge between the two poles to ignite the fuel gas, or it can use the two poles to discharge to the ground to ignite the fuel gas (not often). At this time, a higher output voltage is required. The characteristic of using discharge between two poles is that the arrangement is flexible and can be placed at the ideal ignition position without being affected by the position of the nozzle. It is suitable for fuels with strict ignition position requirements. Compared with the unipolar type, the voltage of each electrode to the ground is only half of the unipolar type, which is beneficial to the insulation of the electrode leads and is relatively safer.
In terms of the discharge ignition method and the arrangement of the electrodes, there are two types of discharge to the ground and discharge between the two poles. Due to the flammable and explosive nature of fuel gas, all gas burners use a safer discharge method to the ground. Due to the different compositions of the gases, their flame propagation speeds are also quite different. For fuels with low flame propagation speeds, premixed combustion is used. The ignition method is that the electrode discharges against the flame stabilizing plate or side wall, as shown in Figure 5. . For fuels with high flame propagation speed, post-mixed combustion is used, and the ignition method is electrode discharge to the nozzle, as shown in Figure 6. Some fuel burners use discharge to the ground, while others use discharge between two electrodes. Discharge to the ground can be divided into several ways, one is a single electrode discharges to the nozzle, the other is a single electrode discharges to the flame stabilizing disk, and the other is a double electrode discharges to the nozzle. The discharge between two electrodes can be divided into one electric
There are two methods of false two-electrode discharge at the pole contact and real discharge between two electrodes. The so-called false two-electrode discharge means that one of the electrodes is actually grounded. Unipolar discharge emphasizes its electrical safety because one electrode is grounded and there is no floating electrode; while bipolar discharge emphasizes the success rate of ignition because the two poles can be placed at the best position in the ignition zone. Figure 7 shows a schematic diagram of the electrode position for discharge ignition between a single electrode and a nozzle. Figure 8 shows the electrode position for discharge ignition between double electrodes or false two electrodes and two single electrodes (connected in parallel to the same igniter output pole). Schematic diagram of the electrode locations for discharge ignition of the nozzle.
4 Conclusion
Through the above analysis and comparison, it can be concluded that although electronic igniters using different boost components have different working principles and different prices, they can all meet the needs of igniting fuel. Different output forms (unipolar, bipolar and bipolar with grounding in the middle) each have their own advantages and disadvantages, some focus on safety, while others focus on flexibility. Burners that use different fuels must choose corresponding electronic igniters and different electrode arrangements. Otherwise, safety may not be guaranteed or the fuel may not be ignited. For burners whose fuel is gas, single-electrode ignition must be used due to safety considerations; for oil burners, in order to obtain a better ignition position and higher ignition rate, it is recommended to use a bipolar ignition method. .
1 Introduction
As the country attaches increasing importance to environmental protection, cities have imposed strict restrictions on the discharge of waste gas and waste water. The smoke and dust from coal-fired boilers is one of the main factors causing urban air pollution. In order to realize the beautiful ideal of "giving us a blue sky", many large and medium-sized cities have now banned the operation of coal-fired boilers and replaced them with oil and gas boilers. In oil and gas boilers, the most important component is the burner, and the high-pressure ignition device is one of the key electronic components in the burner. Since the information attached to the imported burner does not provide the principle circuit, performance and parameter description of the high-voltage ignition device, but only provides an extremely simple one-page description of the external dimensions, external wiring, etc., this gives our country's burner agents , brings considerable inconvenience to users, and also makes the design and complete sets of domestic burners more difficult. In the past ten years, the author has selected and debugged a variety of imported burners and their high-pressure ignition devices, and has successively collected some relevant information. I provide it here to everyone, hoping to be helpful to those in the industry.
At present, there are dozens of burners from eight countries on the Chinese market. Common ones include Germany's Weisaupt, SAACHE, MAN, and ElcoKlockner, France's CUENOD, Guillot, SICMA, and RADIANT, the United States' Johnson, Power Flame, and the United Kingdom's NUWAY, Italy's FBR, Baltur, UNIGAS, Riello, ECOFLAM, the Netherlands' Purlpher, Sweden's Bentone and South Korea's ABC, Sookook, etc. Although there are many types of burners, there are only a limited number of high-pressure ignition devices. Except for a few burners equipped with locally produced high-pressure ignition devices, the high-pressure ignition devices of the other dozen burners are basically products from several well-known international companies, such as BRAHAMA of Italy, Danfoss of Sweden, France Landis and Honeywell of the United States, etc.
2 Introduction to the principles of high-pressure ignition and its devices
2.1 Principle of high-pressure ignition
High-voltage ignition, also known as spark ignition, is a widely used ignition method. When an electric spark passes through gas or atomized fuel, the fuel quickly changes from a good insulator to a good conductor. As the voltage between the two poles increases, the electric field gradually strengthens, the charged objects in the fuel are accelerated by the electric field, and the moving charged particles and molecules undergo inelastic collisions. When the collision is severe enough, the molecules are ionized and become charged particles. The concentration of charged particles increases exponentially, and the initial tiny current is amplified millions of times, producing a large current. The time required for this process depends on the ratio of applied voltage to breakdown voltage. The breakdown voltage depends on the fuel composition, electrode shape, inter-electrode distance, and the temperature and pressure conditions of the fuel. The breakdown voltage can be approximately calculated by the following formula [1]:
Ub=2.7+1.4Lwhere: Ub——breakdown voltage (KV); L——distance between poles (Mm).
When the electrode spacing is greater than the critical distance, the minimum ignition energy has nothing to do with the electrode spacing; when the electrode spacing is less than the critical distance, the minimum ignition energy increases with the decrease of the electrode spacing due to the heat absorption of the electrodes themselves. Figure 1 shows the relationship between the minimum ignition energy and the electrode spacing and electrode size. The fuel is 11% methane air mixture.
The shape of the discharge electrode also has a certain impact on the minimum ignition energy. As shown in Figure 2, under the same electrode spacing and electrode size conditions, the sharper the discharge point, the less heat it absorbs, and the required minimum ignition is The energy is also smaller.
2.2 Introduction to the principle of high-voltage ignition device
The high-pressure ignition device is one of the core electronic components of the burner. Although its price only accounts for a small part of the total price of the burner, it is responsible for the important work of fuel ignition. The failure of the high-pressure ignition device may cause the burner to fail to work and affect production; or may cause the boiler to explode. Especially when the high-pressure ignition device has not completely failed, a large amount of fuel has been injected into the furnace, and the flameout protection device has not yet been activated. At this time, the high-pressure ignition device suddenly ignites, which will cause very serious consequences. This shows the importance of high-voltage ignition device.
High-voltage ignition devices generally consist of a rectifier circuit, an oscillation circuit, a boost component and a discharge electrode. The rectifier circuit rectifies and filters the 220 V/50 Hz alternating current and converts it into direct current; the function of the oscillation circuit is to oscillate the direct current into alternating current according to the discharge frequency; the boost component boosts the oscillated alternating current to achieve the desired voltage. The high voltage of ionized air is used to form a high-voltage pulse current using a high-voltage silicon stack; the discharge electrode is made of special materials and placed at the fuel outlet. The output waveforms of each component are shown in Figure 3 [2].
Figure 4 is a schematic diagram of the schematic circuit of the ignition device. The AC 220 V/50 Hz power supply becomes a lower voltage power supply after passing through the power transformer T1, and then passes through the rectifier bridge B to change the AC power supply into a DC pulse power supply. After filtering by the capacitor C1, the DC power supply is obtained. This part That is the rectifier circuit. The oscillation circuit is composed of resistor R1, transistor BG and the primary of step-up transformer T2. After oscillation, the step-up transformer T2 performs a boost, and then is rectified by a high-voltage diode or high-voltage silicon stack D to obtain high-voltage direct current. This direct current charges capacitor C2 through resistor R2, and at the same time stores energy on large capacitor C3. When C2 is charged to a certain voltage, the bidirectional diode D2 turns on, triggering the triac SCR to conduct. At this time, the capacitor C3 has reserved considerable energy. This energy passes through the loop capacitor C3, the triac SCR and the secondary riser. The primary release of the voltage transformer T3, at this time, a high voltage is generated on the secondary of the secondary step-up transformer. The high voltage is discharged after the discharge electrode breaks down a certain thickness of air, thus completing the primary discharge ignition of pulse ignition. Capacitor C3 is charged again after being discharged, thus performing a series of charging and discharging processes. A series of discharge sparks are generated between the electrodes, completing an ignition process.
3 Comparison of high-voltage ignition devices
3.1 Parameters of several typical high-voltage ignition devices
Honeywell is a high-voltage ignition device produced in the United States. The commonly used Satronic series electronic igniters are designed based on solid-state relays. Different from traditional iron-core transformers, it generates high-frequency and high-voltage sparks in the secondary through an internal ignition circuit. The working parameters of this series of electronic igniters are given in Table 1.
Danfoss is a high-pressure ignition device produced in Sweden. The EBI series electronic igniter is commonly used for ignition of oil and gas burners. It works on the principle of electronic frequency conversion to generate high voltage, and is suitable for intermittent ignition. Within 3 minutes, the ignition rate is 33% under the conditions of 35℃; the ignition rate is 20% under the conditions of 60℃. Table 2 shows Operating parameters of this series of electronic ignition.
BRAHAMA is a high-voltage ignition device produced in Italy. It is divided into three series: E, G and S. They all use high-performance ignition transformers to boost the voltage. Table 3, Table 4 and Table 5 give their working parameters respectively.
3.2 Comparison of high-pressure ignition devices
The comparison of high-voltage ignition devices includes a comparison of solid-state relay electronic igniters and ignition transformer electronic igniters; a comparison of unipolar, bipolar, and intermediate grounded bipolar electronic igniters; a comparison of different fuel burner electrode arrangements and different Comparison of the advantages and disadvantages of discharge locations.
Compared with electronic igniters using ignition transformers, electronic igniters using solid-state relays use more advanced solid-state relay voltage boosting technology and have the advantages of small size, light weight, low heat generation and reliable operation. However, due to the use of a relatively expensive solid-state relay, the cost of the entire electronic igniter increases, and the price is much higher than that of an electronic igniter using an ignition transformer. For the above-mentioned well-known brands of ignition transformer electronic igniters, after decades of on-site use, it has been proven that their working reliability and lifespan are no worse than solid-state relay electronic igniters, and are much better than electric heating wire igniters. The latter is an ignition device for oil and gas burners that was used in the early days (and is still used in China). Although this ignition device is reliable in ignition, it has slow ignition speed, short ignition wire life, and requires a large power. Currently, it is used in Foreign countries have been eliminated.
The output of the electronic ignition is divided into unipolar type, bipolar type and bipolar type with grounding in the middle to adapt to different burner designs. The so-called unipolar type has only one electrode in its output, and the other electrode is grounded inside or outside the igniter (that is, connected to the burner shell). During operation, the electrode discharges to the ground, generating sparks and igniting the fuel gas. Its characteristics are that it is relatively safe, reliable and easy to use. It only needs to lead out an electrode for insulation. It should be noted that for externally grounded unipolar electronic igniters, remember not to reverse the two poles, otherwise it may cause damage to the electronic igniter and even the entire control equipment. The so-called bipolar type is basically the same internally as the unipolar type, except that the other electrode is not grounded. When working, the fuel gas is ignited by discharge between the two poles. It is characterized by flexible use, but is not as safe as the unipolar type, and the two lead electrodes need to be insulated. Indirect
The bipolar version of the ground is achieved using an ignition transformer with a center tap or using two solid state relays. When working, it can use the discharge between the two poles to ignite the fuel gas, or it can use the two poles to discharge to the ground to ignite the fuel gas (not often). At this time, a higher output voltage is required. The characteristic of using discharge between two poles is that the arrangement is flexible and can be placed at the ideal ignition position without being affected by the position of the nozzle. It is suitable for fuels with strict ignition position requirements. Compared with the unipolar type, the voltage of each electrode to the ground is only half of the unipolar type, which is beneficial to the insulation of the electrode leads and is relatively safer.
In terms of the discharge ignition method and the arrangement of the electrodes, there are two types of discharge to the ground and discharge between the two poles. Due to the flammable and explosive nature of fuel gas, all gas burners use a safer discharge method to the ground. Due to the different compositions of the gases, their flame propagation speeds are also quite different. For fuels with low flame propagation speeds, premixed combustion is used. The ignition method is that the electrode discharges against the flame stabilizing plate or side wall, as shown in Figure 5. . For fuels with high flame propagation speed, post-mixed combustion is used, and the ignition method is electrode discharge to the nozzle, as shown in Figure 6. Some fuel burners use discharge to the ground, while others use discharge between two electrodes. Discharge to the ground can be divided into several ways, one is a single electrode discharges to the nozzle, the other is a single electrode discharges to the flame stabilizing disk, and the other is a double electrode discharges to the nozzle. The discharge between two electrodes can be divided into one electric
There are two methods of false two-electrode discharge at the pole contact and real discharge between two electrodes. The so-called false two-electrode discharge means that one of the electrodes is actually grounded. Unipolar discharge emphasizes its electrical safety because one electrode is grounded and there is no floating electrode; while bipolar discharge emphasizes the success rate of ignition because the two poles can be placed at the best position in the ignition zone. Figure 7 shows a schematic diagram of the electrode position for discharge ignition between a single electrode and a nozzle. Figure 8 shows the electrode position for discharge ignition between double electrodes or false two electrodes and two single electrodes (connected in parallel to the same igniter output pole). Schematic diagram of the electrode locations for discharge ignition of the nozzle.
4 Conclusion
Through the above analysis and comparison, it can be concluded that although electronic igniters using different boost components have different working principles and different prices, they can all meet the needs of igniting fuel. Different output forms (unipolar, bipolar and bipolar with grounding in the middle) each have their own advantages and disadvantages, some focus on safety, while others focus on flexibility. Burners that use different fuels must choose corresponding electronic igniters and different electrode arrangements. Otherwise, safety may not be guaranteed or the fuel may not be ignited. For burners whose fuel is gas, single-electrode ignition must be used due to safety considerations; for oil burners, in order to obtain a better ignition position and higher ignition rate, it is recommended to use a bipolar ignition method. .