Bleached softwood kraft pulp with chemical recovery (1000 ADt/d market pulp, concept)

Softwood chips to bleached kraft market pulp: continuous digester, brown stock washing, O2 delignification, ECF bleaching outline, drying machine, black liquor evaporation, recovery boiler, recausticizing and lime kiln, with the turbine generator; biogenic and fossil CO2 kept apart. Concept stage, assumed basis.

Calculation maturity: not assessedDesign maturity: Concept (research)Not independently reviewedBio based chemicalsReport a problem with this process
Research outputNot engineering advice and not an approved design: do not use it for construction, operation or safety decisions. What this means

Chips are cooked with white liquor (NaOH and Na2S) in a continuous digester; the brown stock is washed counter-currently with the O2-stage filtrate, delignified with oxygen, bleached in a D0-EOP-D1 sequence (outline) and dried to 90 % dry market pulp. The weak black liquor is evaporated to 80 % solids and burnt in the recovery boiler: the organics raise HP steam for an extraction back-pressure turbine with a condensing tail, and the smelt (Na2CO3, Na2S) is dissolved to green liquor, causticized with lime to white liquor and returned to the digester. The lime mud is reburned in a natural gas fired kiln. Sodium and sulfur losses are made up with NaOH and saltcake, calcium losses with purchased lime.

All flows are concept estimates of an independent balance (scripts/kraft_balance.py) on lumped model components for wood and black liquor, with sourced ranges (JRC pulp and paper BREF 2015, Tran and Vakkilainen) and assumed design parameters. No wood, black liquor or electrolyte thermodynamics is calculated. See DESIGN.md for every assumption and gated step.

Capacity
1000 ADt/d bleached softwood kraft market pulp (ASSUMED normalisation basis)
Operation
8,400 h/a
Location
generic (not chosen)
Engineering gates
Concept and feasibility (no results yet)
Maintainers
Artur Schweidtmann
Design basis and assumptions (8)
  • ASSUMED wood: 41/28/27/3.5/0.5 % cellulose/hemicellulose/lignin/extractives/ash, 50 % moisture (D-003).
  • ASSUMED yields on dry wood: 47.0 % after cooking (kappa ~28), 45.6 % after O2 (kappa ~15), 44.0 % bleached (D-004).
  • ASSUMED washing: 3 % of dissolved solids carried out of brown stock washing, 6 % out of post-O2 washing; wash presses discharge at 25 % consistency (D-006).
  • ASSUMED black liquor 15 % solids weak, 80 % strong; evaporator economy 6.0 (D-007).
  • ASSUMED recovery boiler: air ratio 1.15; 3.5 kg steam per kg BLDS (Tran and Vakkilainen); SO2 0.1 kg S, NOx 1.2 kg, dust 0.3 kg per ADt inside BREF Table 3.13 (D-010).
  • ASSUMED recausticizing and kiln: grits 5, mud purge 10 kg/ADt; calcination 0.95; mud 80 % solids; kiln 1.5 GJ/ADt natural gas (D-009).
  • ASSUMED heat and power by consumer (D-011): 11.6 GJ/ADt process heat and 650 kWh/ADt, inside BREF 2015 sec. 3.2.2.3 ranges.
  • No wood or electrolyte thermodynamics: wood, liquors and smelt are lumped model components (materials.yaml, D-007).

From process/design-basis.yaml.

Engineering model

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Drawing of the process (preview)Open the engineering model

The interactive model (drawings, streams, 3D) is made for larger screens.

Snapshot of c3ab348, cheme-as-code 1.6.0.

What goes in and out

In

  • Wood chipsFeedstockfeed:CHIPS: softwood chips, screened, 50 % moisture, 4.09 kg/kg pulp
  • Sodium hydroxideFeedstockfeed:NAOH: sodium hydroxide 50 wt% make-up, counted by mass of the solution
  • Chlorine dioxideFeedstockfeed:CLO2: chlorine dioxide water, 10 g ClO2 per kg, generated outside the boundary, counted by mass of the solution
  • Hydrogen peroxideFeedstockfeed:H2O2: hydrogen peroxide 50 wt%, counted by mass of the solution
  • Sulfuric acidFeedstockfeed:H2SO4: sulfuric acid 93 wt%
  • Sodium sulfateFeedstockfeed:SALT: sodium sulfate (saltcake make-up)
  • Calcium oxideFeedstockfeed:CAO: purchased burnt lime (Ca make-up)
  • OxygenFeedstockO2 delignification and EOP stage; asu-1 makes it
  • WaterFeedstockProcess water to the bleach plant and post-O2 washing
  • AirFeedstockRecovery boiler and kiln combustion air
  • MethaneFeedstockNatural gas (as methane) to the lime kiln

Out

  • Bleached kraft pulpMain productBleached softwood kraft market pulp, 90 % dry (bales)
  • ElectricityCo-productNet export, 263 kWh/ADt (D-014)
  • WastewaterWasteBleach plant effluent, 18 m3/ADt to biological treatment
  • Carbon dioxideEmissionMostly biogenic (black liquor, lime mud); fossil from kiln natural gas

Utilities: Cooling water (25/35 C (ASSUMED))

Show in the process graph

Reactions

IdAs writtenReactionOther processes
BL_CLO25 LIG + 2 ClO2 + 2 NaOH → 5 OXL + 2 NaCl + H2O · Lignin oxidation by chlorine dioxide (5 electrons per ClO2)5LIG+2ClO2+2NaOH5OXL+2NaCl+H2O
BL_H2O2LIG + H2O2 → OXL + H2O · Lignin oxidation by hydrogen peroxideLIG+H2O2OXL+H2O
BURN_EXT2 NaEXT + 53 O2 → Na2CO3 + 39 CO2B + 29 H2O · Combustion of resin soap2NaEXT+53O2Na2CO3+39CO2+29H2O
BURN_ISA2 NaISA + 12 O2 → Na2CO3 + 11 CO2B + 11 H2O · Combustion of sodium isosaccharinate2NaISA+12O2Na2CO3+11CO2+11H2O
BURN_LIG2 NaLIG + 23 O2 → Na2CO3 + 19 CO2B + 11 H2O · Combustion of sodium lignate2NaLIG+23O2Na2CO3+19CO2+11H2O
BURN_OXL2 NaOXL + 22 O2 → Na2CO3 + 19 CO2B + 11 H2O · Combustion of oxidised sodium lignate2NaOXL+22O2Na2CO3+19CO2+11H2O
CALCCaCO3 → CaO + CO2B · Lime mud calcination (biogenic carbonate carbon)CaCO3CaO+CO21 other process
CARB_OX5 CELL + 24 ClO2 + 24 NaOH → 30 CO2B + 24 NaCl + 37 H2O · Oxidation of carbohydrate by the ClO2 not used on lignin (yield loss)5CELL+24ClO2+24NaOH30CO2+24NaCl+37H2O
CARBON2 NaOH + CO2B → Na2CO3 + H2O · Carbonation of residual alkali in the furnaceCO2+2NaOHNa2CO3+H2O1 other process
CAUSTNa2CO3 + Ca(OH)2 → CaCO3 + 2 NaOH · CausticizingNa2CO3+CaH2O2CaCO3+2NaOH
COMB_NGCH4 + 2 O2 → CO2 + 2 H2O · Natural gas combustion (fossil)CH4+2O2CO2+2H2O9 other processes
COOK_LIGLIG + NaOH → NaLIG + H2O · Lignin dissolution as sodium lignateLIG+NaOHNaLIG+H2O
NEUTH2SO4 + 2 NaOH → Na2SO4 + 2 H2O · Neutralisation (pH control with sulfuric acid)H2SO4+2NaOHNa2SO4+2H2O2 other processes
NOXN2 + 2 O2 → 2 NO2 · NOx formation (fuel and thermal, as NO2)N2+2O22NO2
OXD_LIG2 LIG + 2 NaOH + O2 → 2 NaOXL + 2 H2O · Oxidative lignin dissolution in the O2 stage2LIG+2NaOH+O22NaOXL+2H2O
PEEL_CCELL + NaOH → NaISA · Alkaline peeling of cellulose to isosaccharinateCELL+NaOHNaISA
PEEL_HHEMI + NaOH → NaISA · Alkaline dissolution and peeling of hemicelluloseHEMI+NaOHNaISA
PER_DEC2 H2O2 → 2 H2O + O2 · Peroxide decomposition2H2O22H2O+O21 other process
REDUCNa2SO4 → Na2S + 2 O2 · Sulfate reduction in the char bed (formal net reaction; the reductant is the char carbon of the combustion reactions)Na2SO4Na2S+2O2
SAPONEXTR + NaOH → NaEXT + H2O · Saponification of extractives to resin soapEXTR+NaOHNaEXT+H2O
SLAKECaO + H2O → Ca(OH)2 · Lime slakingCaO+H2OCaH2O22 other processes
SO2_REL2 Na2S + 2 CO2B + 3 O2 → 2 Na2CO3 + 2 SO2 · Sulfur release as SO2 to the flue gas2Na2S+2CO2+3O22Na2CO3+2SO2
SULF_OXNa2S + 2 O2 → Na2SO4 · Oxidation of the sulfide of the white liquor alkali to sulfateNa2S+2O2Na2SO4

Each reaction's page has the conversion, heat of reaction, catalyst and sources this process states, next to those of other processes with the same reaction. All reactions

Life cycle assessment

Footprint not publishedThe process changed since the LCA was last run; its values return once it is run again. Method, functional unit and inventory are below.
Method and data
Goal
Preliminary foreground (gate-to-gate) life cycle inventory of bleached softwood kraft market pulp at the concept stage: which wood, chemicals, utilities, emissions (biogenic and fossil CO2 apart) and wastes the balanced flowsheet implies per kg of air-dry pulp, ready to be linked to background datasets later. Flows are concept estimates on sourced ranges and assumed design parameters (DESIGN.md D-003 to D-011).
Functional unit
1 kg Bleached softwood kraft market pulp, 90 % dry (bales) (1 kg bleached kraft pulp)
Boundary
cradle-to-gate
Allocation
shares
Characterisation
Factors kept with the process · GWP100
Data quality
Published factors
Result
partial screening carbon footprint · 13 data gaps

Inventory per 1 kg Bleached softwood kraft market pulp, 90 % dry (bales) (26 flows)

FlowPhaseDirectionQuantityUnitProvenance
Softwood chips, screened (50 % moisture)operationinput4.091kgassumed
Sodium hydroxide 50 wt% (make-up to the O2 stage, bleaching alkali)operationinput0.04188kgassumed
Oxygen (O2 delignification and EOP stage)operationinput0.026kgassumed
Chlorine dioxide water, 10 g/kg (generated outside the boundary)operationinput1kgassumed
Hydrogen peroxide 50 wt%operationinput0.006kgassumed
Sulfuric acid 93 wt%operationinput0.004301kgassumed
Sodium sulfate (saltcake make-up)operationinput0.003276kgassumed
Purchased burnt lime (Ca make-up)operationinput0.008393kgassumed
Natural gas (lime kiln fuel)operationinput0.03kgassumed
Combustion airoperationinput9.859kgassumed
Process water (fresh, treated)operationinput16.42kgassumed
Bleached softwood kraft market pulp, 90 % dry (bales)operationoutput1kgassumed
Electricity export to the grid (turbine generation less mill use)operationoutput0.2627kWhassumed
Bleach plant effluent to the biological treatment plantoperationoutput18kgassumed
Flue gases (recovery boiler after ESP, lime kiln) to stackoperationoutput11.54kgassumed
Vents to atmosphere (O2 stage, bleach plant, pulp dryer exhaust)operationoutput0.9127kgassumed
Solid wastes to landfill (dregs, grits, lime mud purge)operationoutput0.03789kgassumed
Cooling water returnoperationoutput1.266kWhassumed
CO2 to the environmentoperationoutput0.0823kgassumed
CO2B to the environmentoperationoutput2.305kgassumed
H2O to the environmentoperationoutput2.166kgassumed
N2 to the environmentoperationoutput7.577kgassumed
NO2 to the environmentoperationoutput0.001605kgassumed
Na2SO4 to the environmentoperationoutput0.0002986kgassumed
O2 to the environmentoperationoutput0.3165kgassumed
SO2 to the environmentoperationoutput0.0002026kgassumed

Computed by ChemE-as-Code from lca/README.md, lca/dataset.yaml, lca/factors.yaml, lca/gaps.csv, lca/inventory.csv, lca/lca.yaml, lca/mappings.yaml, lca/results.csv, lca/results.md, lca/uncertainty.csv.

In the open LCI database (cheme-as-code-atlas-preview-c3ab348) as Bleached kraft pulp, Bleached softwood kraft market pulp, 90 % dry (bales) Preliminary.

Download it for Brightway, openLCA and other tools.

In the LCI database: system model, datasets and KPIs against the benchmarks

In the LCI database

Status
Preliminary 4 unmapped exchanges. Some exchanges have no background mapping yet: they are exported unlinked and count no burden, so the inventory is incomplete.
System model
attributional, cut-off (methodology 1.1.0)
Allocation
shares (deviation, from study) · product:EEXP 0 %, product:PULP 100 %
Allocation findings
none
Change report
Not available: this build has no change report against an earlier release.
Dataset pages
Bleached kraft pulp, Bleached softwood kraft market pulp, 90 % dry (bales) Preliminary

KPI benchmark positions: not available (no benchmarked KPI for this process's datasets).

Maturity and review

Design maturity Concept (claimed): An idea or first flowsheet; numbers are rough. Concept BFD/PFD with closed mass, component and element balances (cheme validate, cheme process streams: 10 blocks, 17 steps, reactive steps balanced by extents of lumped bookkeeping reactions). Flows and compositions are specified values of an independent balance (scripts/kraft_balance.py) whose element residuals are below 1e-6 kmol/h. Wood and black liquor are lumped model components (not molecular identities), no electrolyte speciation and no property package covers the streams, so the energy balance is not evaluable in core: duties are sourced specific consumptions split by consumer (ASSUMED). Calculation maturity: none (`cheme maturity`), because no feed flow or composition is `given` with a source: every value is an ASSUMED design parameter or a sourced range, and `concept` is the lowest level the manifest allows. The gate-to-gate LCI is preliminary, every background unmapped. Per kg pulp: fossil CO2 0.0823 kg (kiln natural gas), biogenic CO2 2.30 kg. The climate result keeps each CO2 flow's declared origin (trace_emissions false). The PCF line "fossil carbon content of the product" (0.0084 kg C) is a core limitation; the pulp's carbon is all biogenic (lca/README.md, DESIGN.md D-012). Independent agent review 2026-10-28 (reviews/), findings answered in PROGRESS.md.

Calculation maturity, from the checked evidenceNot assessed

The process has no maturity report (cheme maturity, checks/maturity.json), so no calculation maturity is established.

No level shownThe design maturity (Concept) is the manifest's claim, not evidence. A level appears here once the process's repository holds a current report from cheme maturity --write.

Artifact completeness

Which deliverables exist. They never raise a calculation maturity level: a drawing from unchecked numbers is still unchecked.

Not reported without a maturity report.

Independent review

Not independently reviewed

No independent engineering review yet. Automated checks passing is not a review.

Set by people only. Reaching a calculation maturity level or passing automated checks is not an independent review or an approval.

Where the evidence comes from
Report
processes/kraft-pulp-1/checks/maturity.json (not in the library)
Design basis
process/design-basis.yaml
Method
How ChemE-as-Code checks the levels (requirement by requirement)

Open items

0 open items · 0 closed

New action itemNew engineering holdNew technical queryNew design changeAll issues

Sources

Engineering project
Kraft pulp and chemical recovery · cheme-as-code>=0.8
Library version
c3ab348 (process last changed in c3ab348)
Drawings rendered by
cheme 1.6.0 (pyDEXPI 2.1.0)
Data
Catalog record (JSON) · CC-BY-4.0
Files
View the files on GitHub · change history and authors

References

How to cite

For the data, cite the Process Atlas paper; for the platform that builds and checks it, the ChemE-as-Code paper.

Schweidtmann, A. M. & Weber, J. M. (2026, in preparation). Process Atlas: an open, git-native, reproducible library and life cycle inventory of chemical processes (working title).

For this process: "Bleached softwood kraft pulp with chemical recovery (1000 ADt/d market pulp, concept)", ChemE-as-Code process library, version c3ab348.

BibTeX
@unpublished{schweidtmann_process_atlas,
  author = {Schweidtmann, Artur M. and Weber, Jana M.},
  title = {{Process Atlas: an open, git-native, reproducible library and life cycle inventory of chemical processes (working title)}},
  year = {2026},
  url = {https://atlas.cheme-as-code.org},
  note = {in preparation}
}

Schweidtmann, A. M. (2026, in preparation). ChemE-as-Code: An Open-Source Platform for AI-Accelerated Chemical Process Engineering (working title).

BibTeX
@unpublished{schweidtmann_cheme_as_code,
  author = {Schweidtmann, Artur M.},
  title = {{ChemE-as-Code: An Open-Source Platform for AI-Accelerated Chemical Process Engineering (working title)}},
  year = {2026},
  url = {https://cheme-as-code.org},
  note = {in preparation}
}