Rajshree Group is one of India's leading turnkey suppliers of Pulp Washing Systems for kraft and chemical pulp mills. The washing stage — also known as Brown Stock Washing — is one of the most critical steps in the pulp manufacturing process.
Product Overview
It separates the spent cooking liquor (black liquor) from the cellulose fibres after the digester, recovering valuable chemicals for reuse and preparing clean pulp for the bleaching stage.
Efficient washing directly impacts chemical recovery efficiency, bleaching chemical consumption, and overall mill profitability. Rajshree's washing systems are engineered for maximum black liquor extraction, minimum dilution factor, and consistent pulp quality — using proven drum washer, diffusion washer, and press washer technologies suited to every mill size and pulp grade.
Key Features
- ✓Multi-stage drum washer configuration for maximum black liquor extraction
- ✓Diffusion washer option for energy-efficient continuous washing
- ✓Twin-roll press washers for high-consistency outlet (30–35% DS)
- ✓Counter-current washing for minimum fresh water consumption
- ✓Sealed hood design to capture non-condensable gases (NCG)
- ✓Stainless steel 316L construction for high corrosion resistance
- ✓Automatic shower system with controlled water distribution
- ✓DCS/PLC-based automated consistency and flow control
- ✓Integrated black liquor storage tank and transfer pump system
- ✓Low soda loss — less than 8 kg Na₂SO₄ equivalent per tonne of pulp
Types of Washing Systems We Supply
Drum Washer
Rotary vacuum drum washer with multi-stage counter-current configuration. Ideal for medium to large capacity mills. Proven technology with consistent performance.
Diffusion Washer
Atmospheric or pressurized diffusion washer for continuous, energy-efficient washing. Suitable for all pulp types with minimum fibre damage and low energy consumption.
Press Washer (Twin Roll)
High-pressure twin-roll press washers delivering 30–35% outlet consistency. Excellent black liquor extraction with compact footprint. Ideal for retrofit and space-constrained mills.
Belt Washer
Horizontal belt washers for agro-based pulps (bagasse, straw). Gentle handling of short fibres with excellent washing efficiency and low maintenance requirements.
How the Washing Process Works
Hot pulp slurry from the digester blow tank enters the first washing stage at 10–15% consistency, carrying black liquor with dissolved lignin and spent chemicals.
Clean wash water enters at the last stage and flows counter to the pulp direction through 3–4 stages. Each stage displaces progressively more black liquor from the fibre mat.
Strong black liquor (15–18% dry solids) is extracted from the first stage and sent to the evaporation plant for concentration before being fired in the recovery boiler.
Washed pulp exits the final stage at 10–35% consistency (depending on washer type) with soda loss below 8 kg/tonne — ready for oxygen delignification or bleaching.
Applications
- Kraft pulp mills — softwood and hardwood
- Agro-based pulp mills — bagasse, rice straw, wheat straw
- Bleached and unbleached kraft pulp production
- Dissolving pulp and specialty pulp mills
- Waste paper recycled fibre washing and cleaning
- Upgrade and retrofit of existing washing lines
Our Turnkey Project Process
We evaluate your pulp grade, capacity, and existing layout to recommend the best washing technology for your mill.
Complete process design, P&IDs, civil foundation drawings, electrical layouts and equipment datasheets prepared by our experienced team.
Equipment manufactured in our shop or sourced from trusted vendors, quality-inspected, and dispatched with installation drawings.
Our field engineers supervise erection, pipework, instrumentation, and commission the washing system to guaranteed performance parameters.
Full operator and maintenance training, performance guarantee trial run, and ongoing technical support and spare parts supply.
Get a Free Quote
Tell us your pulp capacity and raw material — we'll send a detailed technical and commercial proposal within 48 hours.
Request a Quote →Contact Our Experts
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Why Choose Rajshree?
- ✅20+ years specialised experience in pulp & paper
- ✅22+ successful projects across India, Africa & Middle East
- ✅Complete turnkey — single point of responsibility
- ✅All washer types — drum, diffusion, press, belt
- ✅Compatible with wood, bagasse and straw pulp mills
- ✅After-sales support, spare parts & AMC available
- ✅Competitive pricing with flexible payment terms
Brown Stock Washing: Efficiency in Chemical Recovery and Pulp Purity
After cooking in the digester, the pulp leaving the blow tank contains dissolved lignin, cooking chemicals, and organic compounds suspended in the cooking liquor — collectively known as black liquor. Brown stock washing removes this black liquor from the pulp fibres before bleaching, serving two critical purposes: recovering valuable cooking chemicals for recycling through the chemical recovery system, and producing clean pulp with low residual chemical carryover that would otherwise consume excess bleaching chemicals.
Washing efficiency is measured by two parameters: Dilution Factor (DF, the litres of wash water added per tonne of oven-dry pulp) and Washing Losses (kg of NaOH equivalent lost to the pulp per tonne of pulp). Lower DF means less water to evaporate in the evaporators (reducing steam consumption); lower washing losses mean more chemicals returned to recovery and less chemical carryover to bleaching. Rajshree's counter-current washing systems optimise both simultaneously.
Rajshree supplies drum washers, pressure diffusion washers, and horizontal belt washers depending on mill capacity, fibre type, and target washing efficiency. For agro-based pulps (bagasse, rice straw) where fibre drainage rates are slower than wood pulp, Rajshree's drum washer designs use extended vat residence time and modified wire fabric porosity to achieve washing efficiencies comparable to wood pulp systems.
Rajshree's brown stock washers use counter-current washing — where clean wash water enters at the last washing stage and flows backward through the system to emerge as strong black liquor at the first stage. This minimises total wash water consumption (low dilution factor of 2.5–3.5 m³/tonne) while achieving washing losses below 15 kg NaOH/tonne — both superior to conventional single-stage washing.