Impregnation
Unlock superior fiber quality with Valmet impregnation technology
Impregnation is a vital step in the CTMP (Chemi-ThermoMechanical Pulping) process, where wood chips are chemically and thermally treated to enhance fiber separation. Valmet’s PREX technology ensures uniform impregnation, reduced energy consumption, and superior pulp quality – setting the foundation for high-performance mechanical pulping.
What is impregnation in mechanical pulping and why is it critical?
Impregnation prepares wood chips for refining by softening and saturating them with chemicals. Valmet’s PREX™ method uses pressure expansion to maximize chemical uptake while preserving chip integrity. This leads to stronger fibers, fewer fines, and a more efficient refining process.
The process of impregnation
- Pre-steaming: Chips are softened with steam to replace air and prepare for chemical absorption.
- Compression & Structure Opening: A plug screw feeder compresses chips, removing air and pitch while opening the structure.
- Impregnation & Expansion: Chips expand rapidly in the impregnator, absorbing chemicals deeply and evenly.
- Reaction: Where the chips rest in an atmospheric bin.
Valmet’s impregnation process
Valmet offers two advanced impregnation solutions tailored to different production needs: the PREX impregnation system and the HT-CTMP (High-Temperature Chemi-ThermoMechanical Pulping) concept. Both are designed to maximize fiber quality, energy efficiency, and process reliability.
PREX Impregnation uses a pressure-expansion method that enables deep and uniform chemical penetration with minimal mechanical stress. This preserves chip integrity, reduces fines, and ensures consistent pulp quality. The system operates at atmospheric pressure and is ideal for softwood and general-purpose CTMP applications.
HT-CTMP Impregnation, on the other hand, adds a second control parameter, temperature, to the process. Operating at elevated temperatures (up to 170 °C), it softens lignin more effectively, allowing easier fiber separation during refining. This makes it especially suitable for hardwoods and low-moisture raw materials that are difficult to impregnate under atmospheric conditions. The result is a cleaner pulp with higher bulk, fewer shives, and significantly lower refining energy consumption.
Together, these technologies offer unmatched flexibility and performance, allowing producers to tailor pulp properties while minimizing operational costs.
Presteaming Bin
Softens chips for optimal chemical absorption
The Presteaming Bin gently heats wood chips with steam, replacing air and preparing them for efficient impregnation. This step ensures better chemical uptake and reduces energy use in refining.
- Enhances chip softening for deeper impregnation
- Eliminates air pockets for uniform treatment
- Improves refining efficiency
- Reduces energy consumption
- Stable and reliable operation
Plug Screw Feeder
Compresses chips for high liquor uptake
Valmet’s ADI Plug Screw Feeder compresses and dewaters chips, opening their structure for optimal chemical absorption. It ensures consistent feeding and supports high-quality pulp production. Read more about our feeding technology
- High and uniform liquor uptake
- Gentle chip handling preserves fiber integrity
- Low wear and maintenance costs
- Low energy consumption
- Flexible operation across raw material types
Impregnator
Delivers deep and even chemical penetration
The Impregnator uses Valmet’s PREX pressure-expansion method to rapidly expand compressed chips, enabling instant and uniform chemical absorption for superior pulp quality.
- Uniform impregnation with minimal fiber damage
- Efficient chemical usage
- High availability and reliability
- Proven performance with over 100 installations worldwide
Retention Bin
Ensures consistent chip conditioning before refining
The Retention Bin holds impregnated chips under controlled conditions, allowing for uniform chemical reaction and stable feeding to the refiner.
- Controlled retention time for consistent treatment
- Smooth transition to refining
- Supports high pulp quality
- Reliable and low-maintenance design
Preheater
Elevated temperature for enhanced fiber separation
The Preheater applies heat and agitation to impregnated chips, softening lignin and improving fiber separation. It’s a key component in Valmet’s HT-CTMP system for high-quality pulp.
- Improves fiber separation with thermal softening
- Enables lower refining energy
- Enhances bulk and strength properties
- Reduces chemical consumption
- Compact design for efficient layout
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