Combustion Processes in the Forest Products Industry An informal presentation by Kenneth M. Nichols, Weyerhaeuser Company Presented to Students and Faculty of the University of Washington at the ME 523 Seminar series Energy and Environment October 20, 2004
Principle areas of energy use within Weyerhaeuser Company Pulp and paper manufacture Kraft pulp Mechanical pulp Containerboard Printing papers Other Wood products manufacture Lumber Plywood OSB (Oriented Strand Board) LSL (Laminated Strand Lumber Composites (particleboard, fiberboard) Other
Pulp and Paper
Weyerhaeuser energy data 2003 (acquired from http://www.weyerhaeuser.com/environment/sustainability)
Pulp and Paper manufacture Purchased Electricity (7%) Fossil Fuel (25%) Power Boilers Lime Kilns NCG Incinerators Biomass Fuel (67%) Recovery Boilers (spent pulping liquor) Power Boilers (wood-waste, sludge, rejects)
Production Rates yr yr
Raw Materials-Wood Fiber Whole timber or chips are delivered to the mill The logs are cut and debarked Debarked logs are chipped in preparation for pulping
Kraft (or Chemical) Pulping In chemical pulping, the objective is to separate the wood fibers by dissolving the lignin with chemicals and heat. )
In the digester, wood chips are mixed with chemicals and cooked with steam to separate the fibers in the wood. The material holding the fibers together, lignin, is dissolved in this process. (Most wood contains 18-30% lignin) Chemical Pulping
Chemical Pulping Pulping processes are chosen for yield and pulp strength. Increased lignin removal reduces yield Overly aggressive chemistry degrades the cellulose and reduces pulp quality
PULPING PROCESS Limestone Lime Chipper Trees White Liquor Tank Causticizers Slaker Digester Precipitators Recovery Furnace Green Liquor Tank Pulp Clarifier Black Liquor Tank Smelt Chemical Mixing Tank Washers Evaporators
Typical Recovery Boiler Liquor Composition: Carbon 37.2% Na 18.2% Sulfur 3.7% hydrogen 3.5% Oxygen 35.1% Inerts 0.3% Potassium 1.4% Chlorine 0.6%
The Papermaking Process Chemical Recovery Boiler Concentrated black liquor (70% solids) is sprayed into the furnace Droplets are formed, which dry, swell, pyrolyze, and burn
Black liquor combustion model
Typical Fiber Sourcing 40% Other 1% Recycled 59% Virgin Fiber
PULPING PROCESS Limestone Lime Chipper Trees White Liquor Tank Causticizers Slaker Digester Precipitators Recovery Furnace Green Liquor Tank Pulp Clarifier Black Liquor Tank Smelt Chemical Mixing Tank Washers Evaporators
Function of Lime Kiln The causticizing process that produces white liquor from green liquor consumes lime (CaO) and produces lime mud (CaCO 3 ) as a by-product. The function of the lime kiln is to convert CaCO 3 back to CaO for reuse in the causticizing process. CaCO 3 CaO + CO 2 Gas Flow Solids Flow Dam or Nose Ring Flame Chains Feed Spirals
Lime Kiln Zones Calcination Preheat Drying Temperature ( F) 3000 2500 2000 1500 1000 500 0 Gas Solids Solids Surface Bulk Solids 0 50 100 150 200 250 300 Distance Along Kiln (ft) The zones in the kiln are easy to distinguish using the bulk solids temperature profile. The drying zone is the region where the bulk solids temperature is constant, at a value of about 175 F. The bulk solids temperature in the calcining zone is constant at 1600 F, though the surface temperature of the solids can be as much as 500 F higher. The peak flame temperature is near 2800 F, with an exit gas temperature around 400 F. Gas Flow Solids Flow Dam or Nose Ring Flame Chains Feed Spirals
Wood Products
Weyerhaeuser energy data 2003 (acquired from http://www.weyerhaeuser.com/environment/sustainability)
Wood products manufacture Purchased Steam (7%) Purchased Electricity (17%) Fossil Fuel (23%) Boilers Burners Biomass Fuel (53%) Boilers (bark, sawdust, sanderdust, board trim, rejects) Burners
Comparison with other WeyCo sites
Approximate illustration of current fuel distribution
Desired fuel distribution
Example of tramp air source