CFD Modeling of Industrial Burners

Introduction to Industrial Burners

• Wall-fired premix burner mounted on the fired heater wall is shown below

 

• High-pressure fuel is injected in the Centre of the venturi cone to entrain more air for combustion

• The mixture of air and fuel is ignited to form a flame. The following figure shows an example of venturi burner.

 

• The mounting of the gas-fired burner on the fired heater is shown below

 Coal Fired Burner

• In power generation, most of the power is generated by coal-fired thermal power plant
• Coals are easily available at low cost in many countries
• The combustion process of a coal-fired boiler is more complex compared to gas-fired boiler due to turbulence, multiphase flow, ash handling, and pollution
• To understand such complex combustion and waste heat absorption, CFD modeling can be used to design and select the best configurations of burner and boiler furnace

• The pulverized coal-fired boiler is shown below. Burners can be wall-fired or corner-fired.

 

 

Schematic of Coal-fired Burner

• In a coal burner, coal particles are spread in the Centre of of burner surrounded by air

• Air staging carried out for low NOx
• The air-jet type low NOx burner of Babcock Wilcox is shown below. Air staging is carreid out to control combustion.

Cement Kiln Burner

• Cement kilns are used for the pyro-processing stage of the manufacture of Portland and other types of hydraulic cement, in which calcium carbonate reacts with silica-bearing minerals to form a mixture of calcium
• A burner is used to heat the cement mixture. Different types of burners have been used in cement industries
• Due to the high-temperature gradient across the cement kiln, thermal stress results in the failure of the shell of the cement kiln
• Major issues is the selection of low NOx burners and overheating of cement kiln
• CFD modeling will help to design a low NO burner and configuration of air cooling

• A typical Cement kiln Burner is shown below. It can be gas-fired or coal fired.

 

Oil burner

• Oil burners are also used in some cases when fuel gas is not available
• Oil burners need the mechanics of fuel automation for spreading liquid droplets, evaporation  and mixing with air

• CFD modeling of the oil burner is presented in the previous post

Scope of CFD Simulation

• Objective: CFD simulation is carried out for industrial burners to understand the following results:
  1. Velocity contours
  2. Mixing Flow Pattern of fuel and air
  3. Flame Pattern
  4. NOx
• The following three industrial burners are considered for CFD modeling
  1. Premix (Inspiration Mix) burner
     • Type pf fuel: Natural Gas
     • Firing rate: 0.3 MM Btu/hr
     • A simple heater model considered to check burner design
  2. Coal-Fired Burners in Boiler
     • Type pf fuel: Coal
     • Firing rate: 800 MW
     • waste recovery units like super heater, economizers,s and air pre-heater
  3. Cement Kiln burners :
     • Type pf fuel: Natural Gas
     • Firing rate: 3.7 MM Btu/hr
     • Air jets used for cooling of heated cement kiln

• Pre-mix burners have been mounted vertically in the fired heater
• The maximum capacity of the Venturi  burner is up to 2 MM Btu/hr
• We have to select the best suitable burner configuration based on CFD results

CFD Modelings of Premix Venturi Burner

Computational Domain

• The computational domain is created in ANSYS space claim
• Hight of the furnace is sufficiently taken high

Geometry of Burner

• The computational domain for the Venturi- type burner is shown below
• The opening of the air inlet is fixed for the present simulation
• The 3D model was created in ANSYS space claim
• The details of combustion modeling is discussed in the previous post

• Details of the Burner are shown below
• To retain the stability of the flame, a large number of mixture holes are created at the outlet of the mixing tube. The size of the hole is 0.2 inches. These holes plays the role of  flame arrester.
• The mass flux across each hole should not exceed 6 lb/ft2-s for stable flame

Boundary Conditions for Premix Burner

• Fuel Firing Rate: 0.25 MM Btu/hr
• Type of Fuel : Natural Gas
• Burner Air Inlet
  • The mass flow rate of air: 230 lbm/hr
  • Inlet temperature: 90 °F
• Burner Fuel Air inlet
  • A mass flow rate of air: 11.7 lbm/hr
  • Inlet temperature: 80 °F
• Ambient Condition
• Air inlet temperature: 80­­­° F

CFD Results

Velocity Contours

• High-velocity fuel induct the surrounding air via the venturi effect. It does need external means to supply air.
• Inducted air and fuel are mixed in the mixing chamber. After that its velocity decreases.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Temperature contours

 

 

 

 

 

CFD Modelings of Coal-Fired Burners in Boiler

Computational Domain 

 

 

CFD Results for Coal-Fired Boiler

 

CFD Modeling of Cement kiln with Burner

 

 

Computational Domain