Combustion Processes in the Forest Products Industry
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- Lee Randall
- 5 years ago
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1 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
2 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
3 Pulp and Paper
4 Weyerhaeuser energy data 2003 (acquired from
5 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)
6 Production Rates yr yr
7 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
8 Kraft (or Chemical) Pulping In chemical pulping, the objective is to separate the wood fibers by dissolving the lignin with chemicals and heat. )
9 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
10 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
11 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
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13 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%
14 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
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16 Black liquor combustion model
17 Typical Fiber Sourcing 40% Other 1% Recycled 59% Virgin Fiber
18 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
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20 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
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23 Lime Kiln Zones Calcination Preheat Drying Temperature ( F) Gas Solids Solids Surface Bulk Solids 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
24 Wood Products
25 Weyerhaeuser energy data 2003 (acquired from
26 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
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41 Comparison with other WeyCo sites
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49 Approximate illustration of current fuel distribution
50 Desired fuel distribution
51 Example of tramp air source
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