I. Overview
The so-called low calorific value gas refers to the low calorific value per unit volume of gas, which generally refers to the calorific value below 3000×4.18KJ/m3, such as water gas (calorific value is about 2400×4.18KJ/m3) and producer gas (calorific value is about 1250×4.18KJ/m3). 4.18KJ/m3), blast furnace gas (calorific value is about 800×4.18KJ/m3). The main reason for low calorific value coal gas is that the gas contains more inactive components such as CO2 and N2. Therefore, the volume of fuel gas required to supply the same amount of heat becomes large. In addition, gas containing a large amount of inert gas has poor ignition properties and poor flame stability.
Long-term practice has made us know that difficulty in ignition and unstable flame will lead to backfire, flameout, etc. during the combustion process, and even dangerous accidents. However, under the current situation in our country, low calorific value gas is very common in many places and the cost is very low. Making good use of these low calorific value gas is very consistent with the actual situation. Therefore, this prompts us to break through the combustion application of low calorific value gas through research on compatible and efficient combustion technology, so as to achieve safe and efficient use of low calorific value gas. Through our research and practice in the past two years, we have initially realized the safe application of low calorific value gas in the food industry, metal casting and other fields. Here is a summary of our preliminary experience in practice, hoping to be helpful to relevant colleagues, and we also hope to receive criticism and correction of shortcomings.
2. Application in food industry
Since the reform and opening up, all walks of life in the country have developed rapidly, especially the food industry. After the country has sufficient food and people's lives have reached subsistence level, the requirements for food variety and quality have been constantly updated and improved, providing the basis for the great development of the food industry. Huge and broad market space.
(1) Heat use methods in the food industry
We learned that the process heat method in the food industry mainly involves heating, baking and sterilizing semi-finished products during the food production process. There are two aspects here: one is to change the food from raw to cooked, and the other is to meet the standard requirements of sanitation and disinfection.
From the perspective of heat source, there are two main ways: 1. Using electricity to obtain heat source. The production cost of this method is high, and my country's electricity supply is still in the development stage. In the past and for a long time in the future, electricity prices will continue to increase, and its popularization and application will be greatly restricted; 2. Use gas supply hot. This method has lower costs, relatively stable prices, and a lot of low calorific value gas can be used. More importantly, gas has been a rapidly developing and popular project in my country in the past one or two years. With the West-East Gas Transmission Project put into use, it will be very Suitable for mass popularization and application. It is foreseeable that gas will become the main source of heat in many industries, including the food industry.
(2) Combination transformation of low calorific value gas and gas infrared radiation technology
1. Principle of gas infrared radiation combustion
The gas source generally used in gas infrared radiation technology is petroleum liquefied gas with a calorific value higher than 20000×4.18KJ/m3. Liquefied gas is characterized by very good ignition properties and flame stability. Low calorific value gas does not have these two aspects. How to use low calorific value gas and gas infrared radiation technology must be improved from both the combustion and control methods of this combustion technology. First, let’s analyze the combustion method of gas infrared radiation technology:
The gas enters the inlet of the ejector from the nozzle through a certain pressure, and at the same time sucks in a certain amount of combustion-supporting air. It is fully mixed in the ejector and enters the baffle and the inner cavity of the housing. Finally, it passes through the curved surface (made by accurate calculation and experiment) In the combustion radiation zone of porous ceramics, when encountering a strong external fire source, it ignites and burns. The flame quickly spreads throughout the entire surface. After a few minutes, the combustion moves to the flame channel 2mm close to the outer surface. At this time, the light blue flame disappears, the surface is hot, the color is red, and stable combustion is achieved. At this moment, the surface temperature reaches 800-1400°C, and the radiation wavelength is mainly short and medium-wave infrared rays of 2-6mm. The waves in this interval have the characteristics of concentrated energy and significant thermal effects. When the heated food is exposed to infrared radiation, its molecular vibration frequency is equal to the infrared frequency, absorbing the infrared radiation energy, causing strong resonance of molecules and atoms, so that the heated food can be heated to meet the process requirements.
Gas infrared radiation burner has the following characteristics during the combustion process:
(1) The specified proportion of gas and air is mixed;
(2) The volume heat of the combustion flame channel is very high, causing the mixed gas to burn out instantly after reaching the combustion zone;
(3) The flame is very short and the flame cannot even be seen;
(4) Infrared radiation heating does not require intermediate media and does not come into contact with the heated food;
(5) The thermal efficiency is very high; there will be no secondary (contact) pollution.
2. Application of low calorific value coal gas combined with gas infrared radiation technology
Combining the characteristics of gas infrared radiation technology and low calorific value gas, we have taken the following technical measures:
(1) Accurately determine the mixing ratio of gas and air;
(2) Reduce the hole diameter of the ceramic plate and increase the number of spaces per unit area;
(3) Powerful ignition and real-time detection.
From the perspective of combustion principles, the amount of air intake should be reduced, the amount of gas fed should be increased, and the content of combustible components should be relatively increased;
From the perspective of combustion method, in order to overcome the poor ignition characteristics of low calorific value gas, one must reduce the ventilation volume of a single hole, and two, it must use powerful ignition and use automatic high-voltage electrode spark ignition. On the other hand, in order to solve the shortcoming of low calorific value gas that is prone to flameout, we should start from the control point of view. The flame must be detected in real time. If the flameout occurs, the gas source must be cut off immediately to ensure safety. The combination of these aspects can effectively ensure the safety and stability of low calorific value gas combustion. Therefore, we believe that the safe and effective use of low calorific value gas must be combined with intelligent combustion control technology to maximize its effectiveness safely and efficiently.
I. Overview
The so-called low calorific value gas refers to the low calorific value per unit volume of gas, which generally refers to the calorific value below 3000×4.18KJ/m3, such as water gas (calorific value is about 2400×4.18KJ/m3) and producer gas (calorific value is about 1250×4.18KJ/m3). 4.18KJ/m3), blast furnace gas (calorific value is about 800×4.18KJ/m3). The main reason for low calorific value coal gas is that the gas contains more inactive components such as CO2 and N2. Therefore, the volume of fuel gas required to supply the same amount of heat becomes large. In addition, gas containing a large amount of inert gas has poor ignition properties and poor flame stability.
Long-term practice has made us know that difficulty in ignition and unstable flame will lead to backfire, flameout, etc. during the combustion process, and even dangerous accidents. However, under the current situation in our country, low calorific value gas is very common in many places and the cost is very low. Making good use of these low calorific value gas is very consistent with the actual situation. Therefore, this prompts us to break through the combustion application of low calorific value gas through research on compatible and efficient combustion technology, so as to achieve safe and efficient use of low calorific value gas. Through our research and practice in the past two years, we have initially realized the safe application of low calorific value gas in the food industry, metal casting and other fields. Here is a summary of our preliminary experience in practice, hoping to be helpful to relevant colleagues, and we also hope to receive criticism and correction of shortcomings.
2. Application in food industry
Since the reform and opening up, all walks of life in the country have developed rapidly, especially the food industry. After the country has sufficient food and people's lives have reached subsistence level, the requirements for food variety and quality have been constantly updated and improved, providing the basis for the great development of the food industry. Huge and broad market space.
(1) Heat use methods in the food industry
We learned that the process heat method in the food industry mainly involves heating, baking and sterilizing semi-finished products during the food production process. There are two aspects here: one is to change the food from raw to cooked, and the other is to meet the standard requirements of sanitation and disinfection.
From the perspective of heat source, there are two main ways: 1. Using electricity to obtain heat source. The production cost of this method is high, and my country's electricity supply is still in the development stage. In the past and for a long time in the future, electricity prices will continue to increase, and its popularization and application will be greatly restricted; 2. Use gas supply hot. This method has lower costs, relatively stable prices, and a lot of low calorific value gas can be used. More importantly, gas has been a rapidly developing and popular project in my country in the past one or two years. With the West-East Gas Transmission Project put into use, it will be very Suitable for mass popularization and application. It is foreseeable that gas will become the main source of heat in many industries, including the food industry.
(2) Combination transformation of low calorific value gas and gas infrared radiation technology
1. Principle of gas infrared radiation combustion
The gas source generally used in gas infrared radiation technology is petroleum liquefied gas with a calorific value higher than 20000×4.18KJ/m3. Liquefied gas is characterized by very good ignition properties and flame stability. Low calorific value gas does not have these two aspects. How to use low calorific value gas and gas infrared radiation technology must be improved from both the combustion and control methods of this combustion technology. First, let’s analyze the combustion method of gas infrared radiation technology:
The gas enters the inlet of the ejector from the nozzle through a certain pressure, and at the same time sucks in a certain amount of combustion-supporting air. It is fully mixed in the ejector and enters the baffle and the inner cavity of the housing. Finally, it passes through the curved surface (made by accurate calculation and experiment) In the combustion radiation zone of porous ceramics, when encountering a strong external fire source, it ignites and burns. The flame quickly spreads throughout the entire surface. After a few minutes, the combustion moves to the flame channel 2mm close to the outer surface. At this time, the light blue flame disappears, the surface is hot, the color is red, and stable combustion is achieved. At this moment, the surface temperature reaches 800-1400°C, and the radiation wavelength is mainly short and medium-wave infrared rays of 2-6mm. The waves in this interval have the characteristics of concentrated energy and significant thermal effects. When the heated food is exposed to infrared radiation, its molecular vibration frequency is equal to the infrared frequency, absorbing the infrared radiation energy, causing strong resonance of molecules and atoms, so that the heated food can be heated to meet the process requirements.
Gas infrared radiation burner has the following characteristics during the combustion process:
(1) The specified proportion of gas and air is mixed;
(2) The volume heat of the combustion flame channel is very high, causing the mixed gas to burn out instantly after reaching the combustion zone;
(3) The flame is very short and the flame cannot even be seen;
(4) Infrared radiation heating does not require intermediate media and does not come into contact with the heated food;
(5) The thermal efficiency is very high; there will be no secondary (contact) pollution.
2. Application of low calorific value coal gas combined with gas infrared radiation technology
Combining the characteristics of gas infrared radiation technology and low calorific value gas, we have taken the following technical measures:
(1) Accurately determine the mixing ratio of gas and air;
(2) Reduce the hole diameter of the ceramic plate and increase the number of spaces per unit area;
(3) Powerful ignition and real-time detection.
From the perspective of combustion principles, the amount of air intake should be reduced, the amount of gas fed should be increased, and the content of combustible components should be relatively increased;
From the perspective of combustion method, in order to overcome the poor ignition characteristics of low calorific value gas, one must reduce the ventilation volume of a single hole, and two, it must use powerful ignition and use automatic high-voltage electrode spark ignition. On the other hand, in order to solve the shortcoming of low calorific value gas that is prone to flameout, we should start from the control point of view. The flame must be detected in real time. If the flameout occurs, the gas source must be cut off immediately to ensure safety. The combination of these aspects can effectively ensure the safety and stability of low calorific value gas combustion. Therefore, we believe that the safe and effective use of low calorific value gas must be combined with intelligent combustion control technology to maximize its effectiveness safely and efficiently.