Oxygen combustion

Release date:2017-12-14 Author: Click:

1.1 Definition of total oxygen combustion

      Mass production of glass melting furnaces has always used air as a combustion medium. After analyzing and studying the existing combustion system, it is believed that the use of air-assisted combustion is an important factor leading to high energy consumption, high pollution, and high cost. 21% oxygen, 78% nitrogen, and 0.93% argon and other components in the air are very small. As a result, only 21% of oxygen contributes to combustion, and 78% of nitrogen not only does not participate in combustion, but also carries a large amount of heat into the atmosphere, resulting in a great deal of waste of heat. Through long-term repeated experiments, it is believed that the use of oxygen with a purity of ≥85% as a combustion-supporting medium is very effective in saving energy and improving the environment. Therefore, a system that uses oxygen with a purity of ≥ 85% to participate in combustion is called full-oxygen combustion.

1.2 The difference between oxyfuel combustion and air combustion

    Air combustion reaction:

CH4+2O2+ 8 N2→ CO2 + 2 H2O+8 N2

 Oxygen combustion reaction:

      CH4+2O2 → CO2 + 2 H2O

  Compared with air-assisted combustion, all-oxygen combustion is mainly due to the large reduction of nitrogen. The combustion products above the glass are mainly water and carbon dioxide. The volume of flue gas after combustion is 70-80% lower than that of air-assisted flue gas, making the furnace The structure is greatly simplified. Using air or total oxygen as a combustion-supporting medium, the heat transfer process is also different. Air+Fuel Characteristics Its characteristics include radiant gas (H2O, CO2), low concentration, low gas emissivity, short gas residence time, limited hot runner port position, and good heat transfer. The key to good heat transfer is a large number of bright flames and glass melt surfaces. Cover, need to change the fire, intermittent combustion, air storage. The oxygen + fuel radiation gas concentration is high, the gas emissivity is high, the gas residence time is long, the average kiln volume is about 30s, the burner can be placed in any position where heat is needed, regardless of burner type can achieve excellent overall heat transfer, local The heat source still depends on the type and configuration of the burner, no need to change the fire, continuous combustion, and stable combustion. Conventional air-assisted combustion requires heat exchange between flue gas and combustion-supporting air through timed fire exchange to recover part of the heat energy. However, during the fire change process, the flame is lost instantaneously in the kiln, and the glass liquid will inevitably lose its heat source, causing the kiln temperature to fluctuate and being affected by the fire change process. The fluctuation of the gas pressure in the kiln is also an inevitable result.

1.3 The significance of total oxygen combustion

1. The oxy-combustion flame has a high temperature, which accelerates the glass melting process, so it can greatly improve production.

The ability is more than 25%. At the same time, due to the improved temperature system in the furnace, the controllability is improved, and the quality of glass melting can be significantly improved.

2. Because the combustion assists with pure oxygen and no nitrogen in the air, the exhaust gas emissions (nitrides) are reduced by 80-90% compared with the air-assisted combustion, which is beneficial to environmental protection, and at the same time, the large amount of heat energy loss required for heating the nitrogen gas is saved. More than 25%.

3. Due to the reduction of total exhaust gas emissions, the loss of entrained dust during exhaust gas discharge is greatly reduced. Experience has shown that dust emissions can be reduced by approximately 70%. Thereby reducing the cost of loss, and the accuracy of the glass composition can be ensured. It helps to improve the stability and environmental protection of glass components.

4. After adopting the oxy-combustion technology, the huge regenerator, small furnace, reversing system and other structures are no longer needed, which greatly reduces the one-time investment of the kiln up to l/3, and at the same time, due to the simplified structure of the kiln, the actual The upper part is a single unit of the melting part, and the floor space is greatly reduced, which is beneficial to improve the operating environment and maintenance of the kiln.

5. The structure of the furnace is simple, and the heat loss at regenerators, small furnaces, etc. is greatly reduced, which is very favorable for energy conservation.

6. Due to the superiority of the oxy-combustion technology and the scientific and reasonable controllability and stability of the kiln temperature system, the erosion of the refractory material of the dome (flame space height, ie high dome kiln), pool wall, etc. is alleviated. It is beneficial to extend the life of the kiln.

7. The oxy-combustion technology fully meets the development goals of China's energy-saving and environmentally friendly enterprises.

2.1 Oxygen gun selection mechanism

Oxygen lance (fuel burner) is one of the key equipments of oxy-fuel combustion kiln. It plays an important role in the flame conditions of humidity cloth, heat transfer effect, and the service life of kiln refractories. When selecting an oxygen spray gun, the main factors to be considered are: large flame coverage, control of carbon black formation, and Nox minimum use of oxygen (usually 0.5 atmosphere lower without boost), high adjustment ratio, no Need water cooling, low noise, small maintenance, and can use gas, liquid fuel, cheap, good durability and so on.

2.2 Classification of Oxygen Guns

Due to the difference in fuel (oil and gas) combustion in the glass melting furnace, when using oxygen combustion, the different oxygen oxygen spray guns used for the pure oxygen input to the furnace are also different. For example, when the glass melting furnace is burning natural gas or gas, the direct injection of oxygen into the spray gun will have a greater impact on the characteristics of burning. Therefore, two kinds of spray guns (type A guns and closed guns) are currently used.

1, A type spray gun (Figure 2-1)

 The nozzle of this type of spray gun has a unique design. When the oxy-combustion is ignited, the furnace can be heated evenly. It is characterized by large firepower, short flame length and high temperature.

Figure 2-1 A type spray gun

2, closed spray gun (Figure 2-2)

   This is a closed-type spray gun burner for pure oxygen fluxing. It is characterized by good sealing performance, waterless cold system and even heat distribution of the flame (produced by a company in the United States).

Figure 2-2 Closed Spray Gun

2.3 Oxygen Gun Precautions

     When the gun is inspected and maintained during operation, the used burner will be burned, removed from the burner block in the furnace, and the following inspections will be performed:

  1. Check if burner bricks have large cracks; 2. Burner bricks have no traces of ash formation and flame overheating. Burning guns should not have ash accumulation in the burning state. Only when burning guns do not burn will produce ;

  3. Overheating of the burner block may cause deformation of the gun or gun mounting plate. Failure to install or severely damage the gasket may also result in overheating of the burner block.

  4. The natural gas nozzle has carbon spots formed, and the presence of carbon spots at the bottom of the flame end of the burner brick is normal. Make sure that there is no carbon deposit on the fuel nozzle. The carbon deposit will affect the firing position (angle) of the gun;

  5. If the burning gun mounting plate is mechanically damaged or deformed due to overheating, it will cause gas leakage. In this case, it is necessary to replace the new fixing plate in time;

  6. If the gun body is mechanically damaged or leaks due to deformation, the nozzles do not overlap, the mounting surface is uneven or the combustion condition is poor. Guns should be stopped. Do not attempt to repair such guns yourself.

3.1 Preparation of oxygen

   In the air, 21% oxygen, 78% nitrogen, and 0.93% argon, and other components have very little content. Since oxygen is only needed in industry, it is necessary to remove excess gas such as nitrogen and compress oxygen to increase oxygen concentration. To meet the needs of industrial combustion. The currently used oxygen production methods are vacuum pressure swing absorption, cryogenic (cold cooling) oxygen separation, and liquid oxygen filling.

3.1.1 Vacuum Pressure Swing Absorption (VPSA) - Oxygenation

    It uses molecular sieves to selectively absorb oxygen (O2) and nitrogen (N2) components in the air, and separates O2 and N2 from the air to obtain oxygen. The process is divided into two types: single bed adsorption and multi-bed adsorption. The process device has a compact and simple structure, reliable equipment operation, simple maintenance operation, and significant energy saving effect. Oxygen can be installed directly on the production site, eliminating the need for oxygen source transportation costs. Oxygen production costs are low. Adjustable yield. It is suitable for moderate dosages (10000m3/h) and oxygen (O) purity < 95%. Compared with traditional air separation technology, it has the following advantages: simple process flow, no complicated pre-processing equipment;

Oxygen product oxygen purity of up to 93%, nitrogen content of less than 1% (generally recommended oxygen purity of not less than 93%. Of course, the purity is not the higher the better, the same if the purity of VPSA equipment to achieve more than 93% can mean The sharp increase in consumption has not been as good as comprehensive economy;)

When the oxygen production scale of tantalum is more than 10000 NM3/h, the oxygen production power consumption is lower and the investment is smaller;

 The device has a high degree of automation and is convenient and quick to open and stop.

 The device operates with strong independence and high security.

 The device is simple in operation, flexible in operation (excellent partial load, fast load conversion);

 The cost of operation and maintenance of the unit is low;

 Civil engineering costs are low and occupy less land.

    At present, the VPSA oxygen system of Kunshan Jincheng Gas Equipment Co., Ltd. has realized modular design, and the user can be more selective.

   Energy consumption index: 0.36KWh/Nm3

3.1.2 Low temperature (deep cooling) oxygen separation method - oxygen production

This method compresses the air, cools it, cools it, liquefies it, and separates the air into oxygen (O2) and nitrogen (N2) using a dedicated distillation tower. It is characterized by not only producing low-pressure oxygen (O2) with a purity of 99%, but also nitrogen (N 2 ). The equipment has low noise and good safety, but the device system is complex and difficult to maintain. It is suitable for large-scale oxygen production (usually 10,000 NM3/H or more of oxygen is produced, and currently the largest equipment can provide 60000 NM3/H). At present, the main air separation technologies in China are Hangyang, Kaikong, Chuankong, and Ha oxygen. Foreign brands such as Linde, Praxair, Air Liquide, and AP all have access. These multinational companies have reliable equipment and low unit energy consumption, but their prices are more expensive than domestic brands. Oxygen production cost: The oxygen consumption of small and medium-sized oxygen production is high, about 0.5 ~ 1.0KW/Nm3 (non-typical data, but usually get the corresponding amount of nitrogen)

3.1.3 Canned Liquid Oxygen

Liquid oxygen, which is suitable for enterprises that have difficulties in producing oxygen sources on site, such as small-scale special and light industrial daily glass plants and small glass fiber manufacturing plants. Canned liquid oxygen is up to 99.5% pure

High pressure oxygen (O2).

3.2 Oxygen use safety

  Most flammable materials burn faster under oxygen enrichment, which can easily lead to equipment damage and personal injury.

  1. When using oxygen or oxidants, their safety regulations should be followed. When the oxygen content exceeds 25%, the explosion risk to people and equipment increases significantly. Combustible substances in the air can accelerate combustion and explosion under oxygen-rich conditions.

  2. Pure oxygen system can only use oxygen components. The use of unsuitable materials increases the risk of fire in pipes and controllers. The pipe size design must meet the oxygen and oxidant fusion speed requirements. Do not replace the components and accessories of the oxygen system without considering the above risk factors.

  3. Keep the oxygen system clean. All equipment, pipes, fittings, etc. that are in contact with oxygen must be cleaned, otherwise it will increase the risk of fire.

  4. It is forbidden to open flames, smoke, and sparks around oxygen equipment. 5. Do not use oxygen instead of compressed air. Replacing compressed air with oxygen is very dangerous. An explosion occurs when oxygen substitutes for compressed air. Instrument air equipment and oxygen equipment cannot be interchanged.

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