Development of four - channel rotary kiln burnerDate: 2019-07-18 Views:
1. Theoretical basis of four-channel burner
According to the technical parameters of the cold and hot experimental bases, the four channel burners are developed on the basis of the three channels pulverized coal burners at home and abroad.Using the latest modern combustion technology - large speed difference and strong swirl theory, so that the internal range of the flame fuel accumulation;By reducing the consumption of primary air, the oxygen content in the flame root range and temperature peak are reduced.Optimize burner nozzle system by adjusting nozzle geometry to change the primary air volume.
1.1 primary air volume and axial injection velocity
The burner's primary function is to ensure the length of the flame.The flame length mainly depends on the mixing rate of pulverized coal and combustion air, which is mainly determined by the burner's unit thrust (namely, the momentum of primary air and the flow rate of air transported per unit time).If the thrust is large and the flame is short, the latent heat of coal will be released in a small volume, so the flame temperature becomes very high;If the thrust is reduced and the flame length is prolonged, the flame temperature will decrease.
The flame is formed by jet stream, and the amount of jet stream is determined as momentum (M).
M = A * V
M-- momentum, % M /s;
A-- percent volume of primary air, %;
V -- axial wind velocity, m/s.
For the same coal, the momentum required for complete combustion is constant.For the same type of burner, the momentum has a certain range, so the lower the percentage of primary air consumption, the higher the axial injection rate.Different types of burners have different momentum range, so their spray speed is not the same, but all kinds of burners are consistent with the above law.In the early stage, the axial jet speed of burners was about 100m/s-150/s. With the decrease of the primary air volume, the current designs are all above 200m/s.The increase of axial velocity increases the flame length and decreases the peak temperature, which is beneficial to the service life of kiln skin and firebrick.
When the fuel is burned in the kiln, the air used for combustion is the low temperature primary air sprayed into the kiln by the burner, and the high temperature secondary air from the grate cooler.In the combustion process, the proportion of primary air quantity decreases, and the proportion of secondary air quantity increases.It is estimated that when the secondary air temperature is 900℃, the fuel heat consumption can be reduced by 13.5kj/kg for each 1% reduction in the primary air volume.Early three-way burners had primary air volume of 12-15% or more.After optimization, the primary air volume of the four-channel burner has been reduced to less than 7%, greatly saving energy.
1.2 cyclone intensity and volatile content of fuel
In addition to the flame length, the burner should keep the flame with a suitable gas flow field.The combustion process in the rotary kiln is controlled by diffusion. It is very important that the gas flow in the flame is smooth when the ignition temperature is high.The easiest way to ensure that the fuel burns properly and stably is to remix the hot combustion product back into the burner end with a cooler primary wind and fuel.Therefore, the flow field of the burner outlet should be fully considered in design, and the structure of large speed difference and stable combustion chamber can be adopted.For coal and anthracite with low volatile content, the ignition point is high, the temperature is low and the maximum heat area is in the back.In order to rapidly volatilize the volatile components, increase the combustion temperature, accelerate the combustion of carbon particles, increase the flame temperature, and shorten the maximum heat flux from the kiln head, it is necessary to have a strong swirl intensity.Therefore, an adjustable swirl device should be set up to form a swirl wind.
1.3 flame shape and kiln skin stability
In the process of rotary kiln production, the flame must be kept stable to avoid steep peak temperature, and a long fire can form a stable kiln skin, so as to protect the service life of burned refractory brick.The following measures can be taken:
(1) transfer swirling air from the inner pipe for conveying pulverized coal and air to the pipe.Swirl air inside the pulverized coal tube will cause local swirl, resulting in steep peak temperature, while the flame outside the pulverized coal tube in a longer distance to form a swirl, its intensity is more balanced, fuel volatile volatile is more balanced, the corresponding peak temperature is more balanced.
(2) increase the axial flow wind speed, and set a closed flame cover at the front of the axial flow nozzle.When the wind speeds up, the flames lengthen.The front end is set with a closed flame cover, which can appropriately reduce the horizontal diffusion degree of flame and equalize the corresponding flame.
(3) adjust the swirl Angle, swirl jet speed and axial jet speed to adjust the shape of flame.
(4) in the center of the burner design, with parallel round nozzle jet air, the outermost layer of the axial air with annular jet or parallel round nozzle jet, the two jet can generate flow back, so in the middle of the flame, forming a backflow, outside the flame also form a big return, these two kinds of reflux is advantageous to the volatile matter in coal balance volatilization, slow down the steep peak temperature, the stability of the flame.
1.4 NOx emissions
The yield of nitride increases with temperature, and the higher the oxygen content, the higher the NOx produced in combustion.By taking measures to reduce the peak temperature of the flame and promote combustion in a local reducing atmosphere, NOx emission can be reduced.
The multi-channel rotary kiln pulverized coal burner can be used not only in the cement clinker production line of new dry cement pre-decomposition kiln, but also in other traditional cement production lines.