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Lime Recovery Kiln Model

Kilns are used to uniformly heat the material that is fed into it, so that it will be chemically transformed (burned) into a product substance. Kilns are generally about 300 feet long and 10 feet in diameter and rotate at 1-2 RPM. The kiln burner must provide proper flame shaping (a long, narrow flame) to ensure uniform product consistency and to minimize damage to the kiln walls. The burners can be either gas or oil-fired, and often waste gases are injected into the kiln for incineration.

Coen uses Computational Fluid Dynamics (CFD) as a design tool to optimize the design of its Dual Air Zone (DAZ) kiln burners. Prior to the availability of CFD, physical models using water or air provided designers with limited design information, but could not accurately predict the heat transfer mechanism or flame shape characteristics within the kiln.

The model shown below represents a lime recovery kiln, which is used in the paper industry to process lime (CaO) from calcium carbonate (CaCO3). These materials are used as part of the Kraft pulping cycle. The model is a 3D representation of the first 100 feet of the kiln. The actual kiln is over 300 feet long. The kiln burner itself fires No. 6 oil and turpentine at a rate of 65 MBtu/hr. There is also an auxiliary gun used to dispose of stripper-off gas (SOG) and other non-condensable gases (NCG). The goal of the model was to identify the most favorable positions of the kiln burner and waste-gas gun.

Flame Shape
Temperature and estimated flame shape.		 Temperature Cross-Sections
Temperature at various cross-sections.
Temperature Distribution
Temperature distribution at vertical slice through kiln centerline.
Carbon Monoxide Distribution
CO distribution at vertical slice through kiln centerline.

CFD Features Used in This Model:

  • A 3D structured grid (hex mesh).
  • The standard k-e turbulence model.
  • Variable properties (viscosity, thermal conductivity, and specific heat are functions of temperature.
  • The buoyancy model.
  • The P-1 radiation model.
  • The mixture-fraction/PDF combustion model.
  • The discrete phase model for oil droplet injection and combustion.

 

 

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