FOR EFFICIENT FIRING OF PULVERISED COAL MINIMIZING NITROGEN OXIDES FORMATION IN TANGENTIALLY-FIRED BOILERS
The technology is based on the common, widely used by EVT, Combustion Engineering, Alstom and Russian boiler manufacturers - Podolsk and BKZ tangential firing with jet burners. The key advantage of the tangentially fired system is the single rotating flame ball in the centre of the furnace, which gives out heat uniformly independent of the fuel-air proportion in the different burners.
ТОТЕМА’s contribution is in:
• staged feeding of pulverized coal into the combustion chamber with a decreasing concentration gradient at an appropriate continuously growing outflow velocity of the pulverized coal/gas mixture along the height of the burner.
• uniform distribution of combustion air along all the burners independent of whether they are in operation or not;
• staged feeding of combustion air so that temperatures in the combustion area remain constant and relatively low to ensure combustion with low emissions of nitrogen oxides.
• selection of an appropriate, high-enough outflow velocity of the secondary air in order to maintain the optimum aerodynamics in the furnace.
To ensure the required distribution, the pulverized coal should be of adequate particle size – much coarser than the usually fed. It is achieved by using fan mills for grinding with flue gas for drying and transportation and inertial classifiers, regulating the size or degree of fineness of the finished product. After the classifier the coal/gas-mixture is fed to a centrifugal (swirl) pulverized coal concentrator. The concentration and the size of the fuel particles decrease from the periphery to the center of the cylinder after the swirl concentrator. Feeding the pulverized fuel-gas mixture from the outward annulus to the lowest finger of the burner, from the next annulus to the second finger and further to the third, fourth etc, a reverse gradient of grading pulverized coal along the furnace height is received. Implementing rising gradient of outlet velocities of the pf-gas mixture along the burner height, equal conditions are provided for coal particles of different size to reach the center of the furnace. Meanwhile, despite the coarser particles are fed to the bottom fingers, which are “responsible” for the stable combustion, there are enough amount of fine particles among them introduced at the bottom of the furnace at relatively low velocity, initiating by their rapid ignition enough heat for further ignition and combustion along the height of the furnace.
The rising gradient of jet velocity and the reverse gradient of pulverized coal concentration counteract the tendency towards progressive jet deformation upwards in the furnace, as a result of the change in the flame viscosity and in the vertical component of the gas velocity. That prevents the expansion of the isotherms along the furnace height and staged the combustion to provide for constant, relatively low temperatures avoiding fouling and slagging of the heating surfaces above the top burner finger including those, around drying gas of-takes.
ТОТЕМА’s technology is at the basis of the three-dimensional modelling of the furnace processes for a 650 t/h boiler and a 260 t/h boiler made by the Thermal Power department of the Technical University of Sofia with TOTEMA’s participation.
TOТЕМА has applied its technology in developing coal firing systems for the following projects:
• 150 MW units at Maritza East 2 TPP were reconstructed for burning low grade local lignite coal without pre-drying
• 210 MW units at Bobov Dol TPP where pulverized coal combustion was optimised and furnace water walls slagging was eliminated;
• 110 MW units at Kraiova TPP and 220 MW units at Rovinari TPP in Rumania were reconstructed for stable and efficient combustion of local lignite coal without supporting fuel;
• 850 t/h boilers at Hagenwerder TPP in Germany were reconstructed for increasing boiler output and improving their technical and efficiency parameters;
• 110 MW units at Novaki TPP in Slovakia for eliminating furnace water walls slagging;
• 350 MW units at Puentes TPP in Spain for eliminating slagging of heat-exchange surfaces;
• 350 MW units at Puentes TPP in Spain for conversion to new fuel mixture;
• 210 MW units at Maritza East 2 TPP for eliminating furnace water walls slagging;
• 150 MW units at Maritza East 2 TPP for increasing their heat production;
• 160 t/h boiler at Deven TPP for lowering NOx emissions and ensuring stable and efficient combustion;
• 220 t/h boiler and 125 t/h boiler at Republica TPP for lowering NOx emissions and ensuring stable and efficient co
The technology is based on the common, widely used by EVT, Combustion Engineering, Alstom and Russian boiler manufacturers - Podolsk and BKZ tangential firing with jet burners. The key advantage of the tangentially fired system is the single rotating flame ball in the centre of the furnace, which gives out heat uniformly independent of the fuel-air proportion in the different burners.
ТОТЕМА’s contribution is in:
• staged feeding of pulverized coal into the combustion chamber with a decreasing concentration gradient at an appropriate continuously growing outflow velocity of the pulverized coal/gas mixture along the height of the burner.
• uniform distribution of combustion air along all the burners independent of whether they are in operation or not;
• staged feeding of combustion air so that temperatures in the combustion area remain constant and relatively low to ensure combustion with low emissions of nitrogen oxides.
• selection of an appropriate, high-enough outflow velocity of the secondary air in order to maintain the optimum aerodynamics in the furnace.
To ensure the required distribution, the pulverized coal should be of adequate particle size – much coarser than the usually fed. It is achieved by using fan mills for grinding with flue gas for drying and transportation and inertial classifiers, regulating the size or degree of fineness of the finished product. After the classifier the coal/gas-mixture is fed to a centrifugal (swirl) pulverized coal concentrator. The concentration and the size of the fuel particles decrease from the periphery to the center of the cylinder after the swirl concentrator. Feeding the pulverized fuel-gas mixture from the outward annulus to the lowest finger of the burner, from the next annulus to the second finger and further to the third, fourth etc, a reverse gradient of grading pulverized coal along the furnace height is received. Implementing rising gradient of outlet velocities of the pf-gas mixture along the burner height, equal conditions are provided for coal particles of different size to reach the center of the furnace. Meanwhile, despite the coarser particles are fed to the bottom fingers, which are “responsible” for the stable combustion, there are enough amount of fine particles among them introduced at the bottom of the furnace at relatively low velocity, initiating by their rapid ignition enough heat for further ignition and combustion along the height of the furnace.
The rising gradient of jet velocity and the reverse gradient of pulverized coal concentration counteract the tendency towards progressive jet deformation upwards in the furnace, as a result of the change in the flame viscosity and in the vertical component of the gas velocity. That prevents the expansion of the isotherms along the furnace height and staged the combustion to provide for constant, relatively low temperatures avoiding fouling and slagging of the heating surfaces above the top burner finger including those, around drying gas of-takes.
ТОТЕМА’s technology is at the basis of the three-dimensional modelling of the furnace processes for a 650 t/h boiler and a 260 t/h boiler made by the Thermal Power department of the Technical University of Sofia with TOTEMA’s participation.
TOТЕМА has applied its technology in developing coal firing systems for the following projects:
• 150 MW units at Maritza East 2 TPP were reconstructed for burning low grade local lignite coal without pre-drying
• 210 MW units at Bobov Dol TPP where pulverized coal combustion was optimised and furnace water walls slagging was eliminated;
• 110 MW units at Kraiova TPP and 220 MW units at Rovinari TPP in Rumania were reconstructed for stable and efficient combustion of local lignite coal without supporting fuel;
• 850 t/h boilers at Hagenwerder TPP in Germany were reconstructed for increasing boiler output and improving their technical and efficiency parameters;
• 110 MW units at Novaki TPP in Slovakia for eliminating furnace water walls slagging;
• 350 MW units at Puentes TPP in Spain for eliminating slagging of heat-exchange surfaces;
• 350 MW units at Puentes TPP in Spain for conversion to new fuel mixture;
• 210 MW units at Maritza East 2 TPP for eliminating furnace water walls slagging;
• 150 MW units at Maritza East 2 TPP for increasing their heat production;
• 160 t/h boiler at Deven TPP for lowering NOx emissions and ensuring stable and efficient combustion;
• 220 t/h boiler and 125 t/h boiler at Republica TPP for lowering NOx emissions and ensuring stable and efficient co