Questions&Answers

Fan is based on the input of mechanical energy, improve the gas pressure and send gas side by side of the machine, it is a driven fluid machinery. Fan in the usual sense includes ventilator, blower and wind generator. Fans are widely used in mines, tunnels, cooling towers, vehicles, ships and other places, especially in boilers and supporting burners. The problems of high fan failure rate and low reliability have been plaguing boiler operators. Today, we will briefly introduce the common faults of burner fans.

1.Excessive fan noise

Vibration can be caused by problems in the dynamic balance of the fan or damage to the blade of the fan during operation. When the fan is started, the water in the dust collector will boil violently and interact with the fan to produce a large amplitude. Vibrations are bound to cause loud noises. In addition, the fan is a centrifugal fan, which makes a huge roar and noise during operation.

Auxiliary dust removal measures can be appropriately added to solve the problem of excessive dust. The fan outlet pipe is connected to the wet dust collector through a long metal pipe. The dust collector first removes large particles of dust, and then enters the dust removal and sound insulation chamber. The technical measures combined with the expansion tube and the expansion chamber can reduce the gas flow, so that the small particles of dust with the condensation of water vapor in the flue gas fall naturally, and play a role of resistance and noise reduction. When the low flow gas enters the noise reduction chamber for further expansion, the noise is reduced through the resistance material absorption, and the resistant muffler at the bottom of the chimney is introduced through the pipe, and the flue gas is discharged into the atmosphere through the expansion pipe at the top of the chimney. Boiler drum and induced draft fan can be arranged in the same sound insulation air room. The blower draws in the air inside the room while taking away the drum. Induced draft fans and smoke pipes dissipate heat in the room, and the cold air replenished in the room enters the room through the intake muffler. The boiler exhaust pipe is fitted with silencer. Generally, the small hole muffler or multi-layer hole plate throttling and small hole injection compound muffler is used. In addition, can use low speed fan, increase the induced draft fan impeller, reduce the fan speed, fan pressure coefficient remains unchanged, the fan runs normally, to reduce the purpose of noise, but also use the hermetic cooling flue to increase the distance between the induced draft fan and residential buildings, reduce the impact of the boiler fan on residents.

2.Severe blade wear

The reasons for the wear of the boiler fan blade are various, including: there is no design condition in the operation of the boiler fan, the arc cutting line of the blade inlet is different from the inlet direction of the impeller, resulting in the inlet flushing Angle; Dust particles wear and wash the inlet position of the blade; The air inlet of the fan is set with cyclone dust removal equipment, which has good dust removal effect. But if the dust removal equipment is not cleaned in time, the fan is easy to enter the dust accumulation. The air flow generated by the boiler fan will drive the dust particles to the vicinity of the blade, which has the same function as the file blade and improves the degree of blade wear. In addition, the welding or composition material of the fan blade does not reach a certain hardness, and once the dust enters a higher hardness, it will accelerate the speed of blade wear and scouring.

For blade wear fault, the solutions are as follows: first, strengthen the dust cleaning in the dust removal equipment, reduce the amount of dust; Starting from the operation of boilers and coal, dust accumulation of dust removal equipment should be carried out at least once every 2 hours, which can effectively reduce the wear degree of dust particles. Second, the exhaust resistance is reduced to keep the arc cutting line at the blade inlet consistent with the blade airflow direction. Third, the boiler fan to strengthen the transformation of the impeller, improve the service life of the impeller. After modification, bending blade of veneer can increase motor load to a certain extent, but can effectively avoid the balance damage of equipment dust and prolong the service life of impeller. Fourth, high hardness materials can be used to effectively improve the wear resistance of boiler fan blades.

The calorific value of a cubic meter of natural gas is equivalent to that of 10 kilowatts of electricity.

One degree calorific value =3.6MJ/KWH, one cubic gas calorific value =36MJ/m.

36MJ/3.6MJ=10, that is, the calorific value of combustion per cubic meter is equivalent to the calorific value generated by 10 degrees of electricity.

Calorific value of natural gas refers to the heat released by complete combustion of natural gas per unit quantity. The heat of evaporation applied to water is called heat of evaporation (or latent heat of evaporation). The calorific value calculated for the heat of evaporation is called total calorific value (high calorific value), and the calorific value not calculated for the heat of evaporation is called net calorific value (low calorific value).

1. Calorific value of natural gas per cubic meter is 8000-10000 kcal.

2. Calorific value of gas per cubic meter is 3000-4000 kcal.

3. The calorific value of combustion of liquefied gas (propane) per kilogram is 11,000 kcal. The specific gravity of gaseous liquefied gas is 2.5 kg/m3. The calorific value of combustion per cubic meter of liquefied gas is 25200 kcal.

4. Each bottle of LPG weighs 14.5 kg and has a total calorific value of 159,500 kcal, equivalent to the calorific value of 20 cubic meters of natural gas.

Use and maintenance

1.Connect the peripheral circuit, to achieve automatic control of boiler temperature, pressure, water level, please wire according to the control system wiring diagram.

2.Suction pipe should not be close to the bottom of the tank, should keep a distance of 80-120mm.

3.The burner should be turned off before filling the tank, and the fuel can be injected into the tank after filtration. It can be restarted after 20 minutes of filling.

4.Oil system shall not leak oil and air.

5.Check whether the fuel tank is sufficient before starting the burner.

6.The size of the damper should match the nozzle specifications. When the burner is used, due to the inconsistency between the boiler and the burner, it is generally necessary to adjust the damper properly, and sometimes it is necessary to replace the nozzle with appropriate specifications and injection Angle.

7.The ambient temperature of the burner shall not exceed 70℃, otherwise cooling and heat insulation measures shall be taken. When used in cold areas, appropriate thermal insulation measures should be taken to prevent the oil storage device and the supply and return pipeline system from being blocked by freezing. At the same time, the control circuit part of the burner shall not be affected by moisture or high temperature.

8.Please turn off the burner when cleaning the chimney.

9.Motor and ignition transformer should pay attention to moistureproof, avoid using in wet environment.

10.The combustion machine should be balanced when installed, should be horizontal or vertical use, avoid inclined use.

11.When it is not convenient to operate the combustion directly, external control switch and electrical protection device should be connected.

12.Often check whether the connection of the combustion machine and various parts is firm, loose, there is no change in position.

13.When the burner is started, prevent the sudden flame from wounding and destroying objects.

Regular maintenance

1.Foreign bodies are strictly prohibited from entering the air duct.

2.The use of combustion machine site should be far away from flammable and explosive products, and equipped with fire extinguishing equipment.

3.Adjust the oil pressure appropriately according to the oil pressure representation value.

4.Regularly check the combustion cylinder, impeller, flame detector and ignition electrode, remove oil and carbon. In particular, the flame detector should be kept clean and not stained with water.

5.Be sure to cut off the power supply when maintaining the burner.

Performance characteristics

Asphalt smoke is characterized by easy adhesion and easy combustion above a certain temperature. In the process of asphalt smoke collection, transportation and smoke elimination, it is easy to stick to the surface of pipeline equipment to form liquid to solid asphalt, which is difficult to remove after consolidation, and affects the normal operation of the system. In addition, the main components of asphalt smoke are aromatic and heterocyclic compounds, which will cause serious pollution to the environment.

The properties of asphalt and asphalt smoke are as follows: asphalt spontaneous ignition point 610℃, lower limit of explosion 35g/m³, maximum ignition energy 40mJ, maximum explosion pressure 0.32mpa, average pressure rise speed 2.5mpa /s, critical oxygen content of 16% to prevent floating dust from being triggered by electric spark.

Key points of system design

According to the data, the system designed the electric top high pressure spray fire prevention device and explosion-proof device. According to the relevant data and asphalt smoke characteristics, the design points are as follows:

1. the best temperature of asphalt smoke trap is 60℃-80℃, below 50℃, asphalt is easy to bond, more than 100℃ than high resistance is not easy to capture, but also does not meet the process requirements of asphalt smoke trap.

2. prevent the flue attached to the asphalt burning, open fire, dark fire into the asphalt smoke trap.

3. as far as possible to reduce the coal dust in the flue gas, improve the fluidity of the coal tar asphalt of the asphalt smoke catcher.

4. asphalt smoke catcher with explosion-proof device.

5.In order to solve the problem of large diameter of electric capture equipment and easy deflection of airflow, an advanced diversion air distribution system should be installed at the bottom of the equipment.

1.Structural characteristics

The structure of scroll vacuum pump is simple, mainly composed of five parts: (1) dynamic scroll disc and base; (2) the crankshaft; ③ seals; (4) anti-rotation mechanism; Motor vortex vacuum pump structure.

The main moving parts of scroll vacuum pump are only moving scroll, simple power transfer, small radius of motion under the same size, so it has the characteristics of simple and compact structure, smooth operation, almost no wear, small power consumption, which is not available in other types of dry vacuum pump.

2.the scope of application

Scroll vacuum pump pumping speed is small, and is not suitable for toxic, flammable and explosive gases, corrosive gases and drugs, solvents, powder and other medium conditions. Therefore, vortex vacuum pump is more used in analytical instruments, semiconductor chip production line, LIQUID crystal display production line and scientific research equipment. Because it can be started directly at atmospheric pressure, it is often used as a precursor of molecular pumps and small cryogenic pumps.

Asphalt smoke is characterized by easy adhesion, easy to ignite above a certain temperature. In the process of the collection, transportation and smoke elimination of asphalt smoke, it is easy to stick to the surface of pipelines and equipment to form liquid to solid asphalt. After consolidation, asphalt is difficult to remove, often resulting in pipeline blockage, equipment damage, so that the system can not run normally.

In addition, the components of bitumen flue gas are very complex and vary with the source of bitumen. There are not only solid and liquid particles condensed from volatile components of asphalt, but also organic matter in vapor state. Some organic matter is polymer polymer, which will cause serious pollution to the environment. Flue gas contains a variety of organic compounds, including carbon cyclic hydrocarbons, cyclic hydrocarbon derivatives and other compounds, many of which are harmful to human health. Asphalt smoke contains benzo pyrene, benzanthracene, carbazole and other polycyclic aromatic hydrocarbons, and most of them are carcinogenic and strong carcinogens, the main way of harm to human health is attached to the dust below 8 um, through the respiratory tract is inhaled into the body. Therefore, it is very necessary to purify the asphalt fume and make the emission meet the standard of atmospheric environment.

The combustion reaction belongs to the chain reaction, and each activation of the intermediate active product or activation center involved in the reaction can cause the basic reaction to produce more chain carriers, so that the reaction selectivity increases rapidly and continues until the reactants are exhausted, which is the ignition and combustion of fuel.

In combustion equipment, the ignition of combustible gas must rely on forced ignition. The ignition conditions are related to the temperature and concentration of the gas, and the concentration is determined by the pressure of the combustion system and the composition of the gas.

At a certain pressure or temperature, not any concentration of gas can ignite, but there is a certain concentration range, known as the "ignition concentration limit". When the pressure or temperature drops beyond a certain point, the mixture of any concentration cannot ignite. The local atmospheric pressure in Xining is only 76.3% of the standard atmospheric pressure, and the ignition range of gas is greatly reduced accordingly. Improper control of the proportion of gas and air may cause the ignition difficulty of the burner, thus directly affecting the ignition and normal combustion operation.

Electric spark ignition is commonly used in engineering. When the two electrodes placed in the combustible mixture are energized to generate a spark, the local combustible molecules ionize, causing a rapid chain reaction and raising the local temperature of the spark zone. The spark zone becomes the ignition source, forming the center of the initial flame, and propagating steadily toward the unignited mixture for combustion.

Therefore, according to the principle of spark ignition, the problem of gas ignition under the condition of low pressure on the plateau is solved. High energy ignition devices must be used; Expand the spark zone, form a thicker ignition flame, improve the local ignition temperature, to ensure the normal ignition operation of the burner.

After the transformation of the low nitrogen burner, the nozzle of the low nitrogen burner is about 1m lower than the original. During the analysis, with the bottom burner as the benchmark, the height of the remaining burner moves downward, causing the flame center to drop simultaneously, reducing the heat absorbed by all heated surfaces, thereby lowering the outlet smoke temperature. The modified low nitrogen burner has a great influence on the temperature of reheating steam. Due to the slow coordination of boiler unit and the incoordination of pressure tracking and adjustment, it is easy to cause the problem of excessive adjustment, which will also lead to the instability of steam temperature.

In addition, due to the low oxygen combustion should be paid attention to in the primary and secondary air ratio process, so the steam temperature adjustment will be limited, the whole adjustment time can not be shortened, the unit operation efficiency can not be improved. In order to ensure that the outlet temperature is within the standard range, the upper powder manufacturing system can be used in the low load stage, and the height of the nozzle can be appropriately raised, but this adjustment can make the low nitrogen steam into the standard range, which has become an important issue in the transformation of the low nitrogen burner.

In the process of transformation can be appropriate to adjust burnt out the nozzle of the wind, if adjust the nozzle of the burning wind be upward swing, reheat steam temperature would rise in the state, if adjust the nozzle of the burning wind become downward swing, reheat steam temperature will reduce until in standard range, therefore, Through this principle, the low nitrogen burner can be adjusted appropriately in the process of boiler operation.

Oxygen and fuel mix into the combustion chamber for combustion, the generated flue gas into the recirculation flue gas channel, again into the combustion chamber for combustion, cycle many times, so that the fuel is fully burned, improve the combustion efficiency, reduce the emission of NOx and soot in the combustion products, to achieve clean combustion and efficient combustion.

Because thermal NOx and fast NOx are derived from nitrogen in the air, oxygen is used as oxidant, so that the generated NOx is mainly from the N in the fuel, that is, fuel NOx, so it will greatly reduce the total emissions of NOx.

Oxygen-coal flameless combustion technology is generally divided into three zones: diffusion zone, diffusion dynamic zone and chemical reaction dynamic zone. The combustion process of diffusion zone and diffusion dynamic zone is determined by material diffusion or partial material diffusion, which is manifested as the occurrence of flame, such as oxygen and coal flame combustion technology. Oxygen-coal flameless combustion technology works in chemical reaction power zone.

Oxygen coal combustion technology of pure oxygen by liquid oxygen gasification, high pressure liquid oxygen can easily get close to the speed of sound of oxygen jet, flameless combustion technology of flue gas oxygen coal outside loop is used to dry pulverized coal and conveying pulverized coal, the flow rate is needed for combustion oxygen flow rate of 1 times or so, around 200 m/s in the hearth of the secondary air oxygen jet pulverized coal jet, the entrainment CO2 a wind At the same time, due to the large slip speed between pulverized coal and flue gas, the full premix of pulverized coal and oxygen can be achieved instantly.

Many provinces in the western region are located in the plateau, low atmospheric pressure, relatively thin air, so the fuel combustion process and burner selection methods compared to the plains have their own special characteristics. Compare the technical requirements of boiler gas burner, except for the structure, the rest are directly related to the low air pressure, as follows

1.low air pressure affects the density of the gas mixture, so that the range of the gas jet changes, which in turn affects the flame shape and size and the matching problem of the furnace chamber structure.

2.the air density in the Xining area is 1/4-1/3 lower than the standard state, which generally exceeds the adjustment range of the burner air-fuel ratio, and the combustion conditions are unstable.

3.due to the instability of the combustion road conditions, directly affecting the rated output of the burner.

4.incomplete combustion under the conditions of oxygen deficiency, so that the harmful components in the flue gas increased.

There is no very clear international specification for the definition of the flameless combustion state, and the one that is more recognized is the study of Wunning and Sons, who obtained the relationship between the internal circulation rate Kv and the temperature of the flue gas under the diffusion combustion mode of methane, where the mixing and combustion are carried out simultaneously, through a large number of experiments.

The axial evolution and radial diffusion of the fuel jet MF and the oxidizer jet MA induce a coiling effect of the surrounding air ME, so that the central zone of the jet is gradually diluted by combustion products (CO2 and H20) and non-reacting gases (N2) to achieve "low oxygen" combustion conditions.

Kv is the ratio of the circulating flue gases (CO2, H2O and N2) sucked by the combustion jet to the mass flow rate of the incoming jet (fuel and air).

KV=ME/ (MF+MA)= (MJ-MF-MA) / (MF+MA)

In addition, there are some other methods of determining this. For example, the temperature rise is used to determine whether the combustion is in a flameless combustion state, and Kumar et al. concluded that the combustion can be defined as flameless combustion if the temperature rise in the reactor is normalized to a spatial temperature change of about 15%. The inlet temperature is higher than the self-ignition temperature and the temperature rise is higher than the inlet temperature, which is called high temperature combustion.

1.The burner can reach the rated output under the rated gas pressure.

2.The shape and size of the flame should match the size of the furnace chamber structure, and there should be good flame fullness.

3.Has good regulation characteristics, in the boiler from the lowest load to the highest load operation, the combustion conditions should be stable, that is, there is a large regulation ratio, regulation ratio = 1:5.

4.High combustion efficiency, combustion pollutant emissions standards.

5.Compact structure, easy to install and operate, flexible adjustment, low noise.