Once-through burners and their arrangement
The direct-flow burner is composed of a group of circular or rectangular nozzles, and the primary and secondary air are sprayed into the furnace from the respective nozzles in the form of direct-flow jets.
Aerodynamic characteristics of straight jets:
Direct-flow jet process: The airflow ejected from a single nozzle of a direct-flow burner is the simplest circular or plane turbulent direct-flow jet. The pulverized coal airflow is injected into the large-sized furnace space with a high initial velocity (Re>105) and a certain concentration. The furnace is filled with high-temperature static flue gas, and the concentration of pulverized coal in the furnace is zero. In addition to the overall movement along the axial direction of the free turbulent jet, the fluid microgroup also has turbulent pulsation, which exchanges matter, momentum, and heat with the surrounding medium, entrains the surrounding high-temperature static smoke into the jet, and The jets move together.
Along the jet flow direction: the cross section of the jet continues to expand, the flow Q increases, the pulverized coal concentration C decreases, the temperature T increases, the axial velocity W slows down, and finally the energy of the jet completely disappears in the space medium
Jet core area: the center of the jet has not been mixed in by the surrounding gas, and the initial velocity w area is maintained
Turbulent boundary layer: The boundary where the core area maintains the initial velocity W is called the inner boundary, and the boundary between the jet and the surrounding gas is called the outer boundary. The area between the inner and outer boundaries is a turbulent boundary layer, and the inner part is the fluid of the jet itself and the entrained surrounding gas. Spreading angle: the intersection point of the outer boundary line of the jet is called the source point, and the intersection angle is the spreading angle
main body
Turning section: the section where the core area disappears only at a certain point where the jet axis maintains the initial velocity w. The jet section before the turning section is called the initial section, and the jet section after the turning section is called the basic section.