Offset Rising Energy and Raw Material Cost by Eliminating Instability and Downtime
Offset Rising Energy and Raw Material Cost by Eliminating Instability and Downtime
Plant-wide optimisation partnership
Anssum is engaged in a multi year partnership to transform the operations of a mill spanning the recovery circuit, fibre line, environmental performance, safety & health, and mill profitability.
Instead of relying on new equipment, the work extracted more performance from existing assets using first-principles analysis and targeted control improvements embedded in the existing DCS — no black boxes, no shutdowns, and no new instrumentation — then scaled what worked across circuits.
0.9 Mt/year dissolving wood-pulp mill
Operating for more than six decades, this flagship mill turns sustainably managed hardwood plantations into high-quality material, targeting 900,000 tonnes of pulp annually. Its output supports diversified industrial markets across the Asia-Pacific, Europe, and the Americas.
Several constraints were eroding stable operating days and driving avoidable cost:
- Recovery boiler soot-fouling forced six-monthly water washes and reduced annual pulp days.
- Evaporator scaling and off-design energy distribution increased shutdown frequency and steam demand.
- Sulphur losses and SO₂/odour peaks drove complaints, unsafe working areas, and higher make-up chemical spend.
- Winter fresh-water constraints threatened planned production rates.
Find the constraint, implement on existing equipment, then scale
Anssum used a repeatable method: align on outcomes, isolate the real constraint using first principles and plant data, then implement targeted control and operating improvements directly inside the DCS to make performance stable and repeatable.
Changes were implemented with formal risk assessment and joint governance, with value verified through steering committees and sustained through documentation and training.
Implementation Process
How we work:
- Align on outcomes: Start with board-level targets (throughput, emissions, water, cost/tonne) and agree the few that matter now.
- Find the real constraint: Use first principles and plant data to separate causes from symptoms.
- Get more from what you have: Improve control strategies and operating practice inside the DCS so existing assets deliver more — avoiding equipment modifications and downtime.
- Prove in production, then scale: Implement in-line, measure against agreed KPIs, and replicate across similar units.
- Joint governance and risk: Run formal risk assessments before implementation; verify value at steering committees; document and train so gains stick.
What we did - Highlights:
Recovery boiler: Keep it clean, keep it running
Problem: Soot‑fouling forced six‑monthly water washes and cut annual pulp‑days.
What we changed: Built an intelligent soot‑blowing regime requiring no boiler modifications; tuned to improve heat‑transfer without wasting steam.
Impact: 12 months continuous run; steam-to-black-liquor +4%; soot‑blow steam −7%; coal −US$500k p.a.
Evaporators: More tonnes per tonne of steam
Problem: Rapid scaling drove frequent shutdowns; energy distribution across effects was off design.
What we changed: Augmented control to track per-effect efficiency, predict optimal online cleaning windows, and set correct wash durations.
Impact: Efficiency +5%; steam −7 t/h; higher, more stable throughput.
Stop fouling at the source
Problem: Lamella banks fouled because liquor filters passed fibres that burned onto surfaces.
What we changed: Automated filter control (drum speed, deposition, levels) to cut fibre carry-over.
Impact: Fibre passage −25%; recovery stabilised with minimal energy penalty.
Sulphur & emissions: Cut cost, improve safety, reduce impact
Problem: Sulphur losses washed out with effluent and escaped as SO₂/odour, driving complaints, unsafe working areas, and higher chemical spend.
What we changed: Re-designed the high-pressure gas release to control volume(not just pressure) for stronger absorption in strengthening tanks; stabilised flash-tank discharges with enhanced feed-forward + feedback control. Prior stabilisation in the venturi FGR enabled quick wins.
Impact: Raw MgO −7.5 t/h (lower purchased chemical); stack SO₂−35 ppm; SO₂ absorption +500%; flash-tank variability −38%with SO₂ recovery +40%; mono-sulphites −50% in the venturi FGR. Fewer odour complaints and a safer working envelope from lower gas peaks and variability.
Fibre line: Throughput and stability without rebuilds
Problem: Beltwasher and blowtank instability drove variability and poor washing.
What we changed: Stabilised discharge consistency and optimised vacuum profile; upgraded an ageing controller to a modern, maintainable design.
Impact: Pulp consistency stability +74%; washing efficiency +32%; belt‑washer throughput +40%; water −32%; thin‑liquor density +50%(no overflows) and more TDS recovered.
Water-use programme: More pulp with less water
Problem: Winter river levels restricted fresh-water intake, leaving insufficient water to run at planned rates. The mill needed to produce more pulp per cubic metre and protect winter production.
What we changed: Recovered heat-exchanger condensate; stabilised scrubber condenser control; optimised liquor coolers; improved LP-gas release.
Impact: Condensate recovery +20%; scrubber fresh-water −50m³/h; liquor cooler −60 m³/h; LP‑gas release change −200 m³/h. Achieved with controls and operating practice, not new kit.
Continuous recovery operation for 12 months & verified KPI shifts across recovery, steam, emissions and water.
Selected KPI Shifts (before → after)
- Steam‑to‑black‑liquor ratio: +4%
- Soot‑blow steam use: −7%
- Coal cost: −US$500k p.a.
- Evaporator efficiency: +5%
- Evaporator steam draw: −7 t/h
- Fibre carry‑over through liquor filters: −25%
- Mono‑sulphites (venturi FGR): −50%
- Raw MgO dose: −7.5 t/h
- Stack SO₂: −35 ppm
- SO₂ absorption: +500%
- Flash‑tank liquor variability: −38%
- SO₂ recovery: +40%
- Pulp discharge consistency stability: +74%
- Washing efficiency: +32%
- Belt‑washer throughput: +40%
- Water use (belt‑washer): −32%
- Thin‑liquor density: +50%
- Condensate recovery: +20%
- Scrubber fresh-water: −50 m³/h
- Liquor cooler fresh-water: −60 m³/h
- LP‑gas release related fresh-water: −200 m³/h
Key Takeaways
- Partner, not vendor. We integrate with your team and stay until the gains are stable.
- Use what you have. Existing sensors and historians are enough to start.
- Control beats heroics. Multivariable decisions belong in control, not on an operator’s shoulders.
- First‑principles + evidence. Physics narrows the search; data proves the move.
- No black boxes. Logic is open, maintainable, and handed over.
- No shutdowns; changes engineered with safeguards. We protect uptime and de-risk change.
- Scale what’s proven. Once a pattern works, we replicate across similar assets.
