Combustion Processes in the Forest Products Industry UW ...faculty.washington.edu/malte/OldSite/seminar/Au04/Nichols.pdf · Weyerhaeuser Company • Pulp and paper manufacture •

Combustion Processes in the Forest Products Industry

An informal presentationby Kenneth M. Nichols, Weyerhaeuser Company

Presented to Students and Faculty of theUniversity of Washington

at the ME 523 Seminar series – Energy and EnvironmentOctober 20, 2004

Principle areas of energy use within Weyerhaeuser Company

• Pulp and paper manufacture

• Wood products manufacture

– Kraft pulp– Mechanical pulp– Containerboard– Printing papers– Other

– 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

Biomass Fuel (67%)• Recovery Boilers (spent pulping

liquor)

• Power Boilers (wood-waste, sludge, rejects)

Fossil Fuel (25%)• Power Boilers

• Lime Kilns

• NCG Incinerators

Purchased Electricity (7%)

yr

yr

Production Rates

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) PulpingIn chemical pulping, the objective is to separate the wood fibers by dissolving the lignin with chemicals and heat.

)

Chemical Pulping• 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

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

Chipper

Washers

Digester

Precipitators

Pulp

LimeLimestone

Evaporators

Smelt

Clarifier

ChemicalMixing Tank

Black Liquor Tank

Recovery Furnace Green Liquor Tank

TreesSlakerCausticizersWhite

LiquorTank

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 ProcessChemical 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

Recycled Virgin Fiber

Other1%1%

40%40%

59%59%

PULPING PROCESS

Chipper

Washers

Digester

Precipitators

Pulp

LimeLimestone

Evaporators

Smelt

Clarifier

ChemicalMixing Tank

Black Liquor Tank

Recovery Furnace Green Liquor Tank

TreesSlakerCausticizersWhite

LiquorTank

Function of Lime Kiln

• The causticizing process that produces white liquor from green liquor consumes lime (CaO) and produces lime mud (CaCO3) as a by-product.

• The function of the lime kiln is to convert CaCO3 back to CaO for reuse in the causticizing process.

CaCO3 ↔ CaO + CO2

Flame Chains Feed Spirals

Solids Flow

Gas Flow

Dam or Nose Ring

Lime Kiln Zones

PreheatCalcination Drying

Distance Along Kiln (ft)

Tem

pera

ture

(°F)

2500

3000

0 50 100 150 200 250 3000

500

1000

1500

2000

GasSolids

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.

Bulk Solids

Solids Surface

Flame Chains Feed Spirals

Solids Flow

Gas Flow

Dam or Nose Ring

Wood Products

Weyerhaeuser energy data 2003(acquired from http://www.weyerhaeuser.com/environment/sustainability)

Wood products manufacture

Biomass Fuel (53%)• Boilers (bark, sawdust, sanderdust,

board trim, rejects)

• Burners

Fossil Fuel (23%)• Boilers

• BurnersPurchased Electricity (17%)

Purchased Steam (7%)

Comparison with other WeyCosites

Approximate illustration of current fuel distribution

Desired fuel distribution

Example of tramp air source