The bubble atomization nozzle technology uses bubbles as the driving force for atomization, and uses the generation, movement, deformation of bubbles until the outlet bursts to produce very fine liquid mist. Different from the atomization principle of the “Y” type oil gun, the purpose of atomization is not achieved by overcoming the surface tension of the liquid. Due to the wide adjustable output range of the oil gun and the good atomization effect, the powder can be fed in advance during the start-up of the unit, and the coal is used to carry the oil and save the oil used for the start of the unit.
At present, the most widely used power plant boiler oil guns are mechanical atomization technology and pneumatic atomization technology. The mechanical atomization technology mainly relies on the pressure of the liquid itself as kinetic energy to atomize the fuel. It is characterized by simple structure and low operating cost. The ability is poor, the adjustability of the atomization cone angle is poor, and as the viscosity of the fuel increases, the average size of the liquid mist increases rapidly. At the same time, when designing a small flow burner, it is easy to block and coke because the outlet aperture is too small. Although the atomization performance of pneumatic atomization is better than that of pressure atomization, the air consumption of atomization is too large, and the flame length and cone angle cannot be designed, nor can it be used as a large-flow fuel nozzle, otherwise the combustion efficiency will be very low.
1 The principle and characteristics of bubble atomization
Uniform size distribution (size distribution index Nmµd40 bubble atomization nozzle technology is to use air bubbles as the driving force of atomization, and use the generation, movement, deformation of air bubbles until the outlet bursts to produce very fine liquid mist. It is the same as the mist described above. The atomization principle is different, and the purpose of atomization is not achieved by overcoming the surface tension of the liquid. For liquid fuels, such as light diesel oil, heavy diesel oil, heavy oil, residual oil, etc., the viscosity is very different, but the surface tension is in the same order of magnitude. Therefore, The bubble atomizing nozzle is not sensitive to the change of viscosity. The advantages are: (1) The particle size of the liquid mist is small (Sotel average diameter SMD>2); (2) The atomization effect is basically not affected by the viscosity of the fuel, and the viscosity can be used in the range (3) Complete combustion without black smoke, the combustion efficiency is over 99.5%, and the pollutants in the combustion products are lower than the indicators stipulated by the State Environmental Protection Agency; ( 4) Flame length, flame cone angle, flame shape and fuel injection volume can be designed according to user requirements; (5) The burner is not coked or blocked; (6) The flame is rigid and the injection speed is high; (7) The atomization effect does not follow The flow rate is affected, and the flow adjustment ratio is large, up to 1:5.
2 Application of bubble atomization oil gun in power plant
No. 1-4 boiler oil guns in the power plant were originally “Y” type steam atomizing oil guns. During operation, the atomization effect was poor, the combustion was insufficient, the efficiency was low, and the phenomenon of black smoke on ignition was serious. At the same time, the atomized steam If the drainage is insufficient, it will be difficult to ignite, which not only increases the start-up cost of the unit, but also pollutes the environment. At the same time, the reliability is poor, which seriously affects the economy and safety of the unit operation.
2.1 Transformation plan
a. Replace the original “Y” type oil gun with the WDH-DL type bubble atomizing oil gun, the propulsion device and ignition device remain unchanged.
b. Retain the original oil pipeline and steam pipeline, but change the original steam pipeline to the compressed air pipeline network.
c. Remove the three-way valve of the crude oil gun, and install an electric ball valve in the oil pipeline and the gas pipeline for independent control.
d. After modification, relocate the oil gun and igniter.
2.2 Powder feeding in advance during unit startup
2.2.1 Brief introduction of milling system
The boilers in our factory are tangentially fired at four corners, and the pulverizing method adopts the positive pressure direct blowing type. Each boiler is equipped with 5 sets of RP923 medium-speed bowl-type coal mills. There are four pulverized coal nozzles in each layer; each group of burners is arranged with 5 primary air nozzles, and the primary and secondary air nozzles are arranged at intervals.
Before the transformation of the oil gun, the traditional starting and ignition method is: the oil is injected until the generator is connected to the grid, and the pulverizing system is started to inject powder after the load is 50MW. After the modification of the oil gun, on the basis of enabling the large bypass of the steam turbine, when the temperature of the hot air reaches the milling requirements, the milling system starts to feed powder.
2.2.2 Powder feeding measures
a. Boiler ignition (4 corners of AB layer oil gun), oil pressure 0.5 ~ 0.6MPa, furnace smoke temperature detector gun is put in (at least 60% inward).
b. When the temperature of the hot secondary air reaches about 100℃, start two primary fans, maintain the wind pressure of the hot primary air main pipe at 6.5KPa, and put the steam turbine bypass.
c. In order to start the first coal mill, the two conditions of the steam drum pressure>3.5MPa and the hot secondary air temperature>177℃ in the start-up conditions of the first coal mill should be temporarily lifted.
d. Start the B coal mill or the A coal mill to warm up.
e. During the warm-grinding period, turn on the lead and blower on the other side.
f. When the temperature of the mill outlet is above 55℃, start the coal feeder, and keep the air volume of the coal mill at 60-65t/h.
g. In order to prevent the steam pressure and steam temperature from rising too fast after the coal mill discharges powder, after the coal feeder bites the coal, reduce the oil pressure to about 0.35MPa (not lower than 0.3MPa to prevent the oil gun from falling off the angle).
h. Pay attention to monitoring the change of coal fire monitoring after feeding powder. In the initial stage of feeding powder, check the fire situation of coal powder on the spot. When it is found that the coal powder is not on fire, the pulverizing system should be stopped immediately.
i. Gradually increase the amount of coal according to the rate of temperature increase and pressure increase, and gradually increase the outlet temperature of the coal mill to 77°C.
j. Stop the steam turbine bypass before the steam turbine is running, and reduce the coal amount to the minimum. As long as the flue gas temperature at the furnace outlet does not exceed 548℃, the coal feeder can be kept non-stop.
k. When the coal volume is at a minimum (10T/H), if the coal mill vibrates greatly, the coal volume can be appropriately increased and the air volume can be reduced (but not lower than 60t/h).
l. During the ignition and oil injection of the boiler, the air preheater is continuously blown soot (auxiliary steam).
m. During the operation of the one-layer oil-one-layer pulverizing system, it must be ensured that at least 3 corner oil guns are put into operation, otherwise, the boiler MFT will be caused when the pulverizing system trips or stops the coal feeder.
After the oil gun is transformed with a bubble atomizing nozzle, the atomization effect is good, the combustion is sufficient, the flame is wheat white gold, and the combustion is stable without black smoke. The flow rate of the “Y” type steam atomizing oil gun originally used in our factory is 2T/H. After replacing the bubble atomizing oil gun, the flow rate is 0.8~1.5T/H. In the early stage of startup, the powder is injected in advance, and the coal is used to bring oil. The starting oil in the cold state (the steam engine does not need to be warmed up at a medium speed) is about 15 tons, and the starting oil in the cold state (the steam engine needs to be warmed up at a medium speed) is about 40 tons, which saves 50% of fuel compared with the previous one, and greatly improves the economy of the unit.