ANDRITZ GROUP
PULP & PAPER products
Pulp production
Pre-hydrolysis continuous cooking

ANDRITZ pre-hydrolysis continuous cooking

The most advanced way to produce dissolving pulps

The key to successful dissolving pulp production is efficient removal of the hemicelluloses in the fiber source without damaging the actual cellulose. The Pre-Hydrolysis Vessel (PHV) designed and delivered by ANDRITZ is state-of-the-art technology to produce high-quality dissolving pulp and other valuable by-products at the lowest cost.

Continous Lo-Solids cooking with pre-hydrolysis vessel. Shandong Sun Honghe Paper, China.

Older methods for pre-hydrolysis of kraft pulp were less than ideal

There are significant challenges in the removal of hemicelluloses when producing dissolving pulp with a continuous cooking system. Achieving stable production and avoiding the precipitation of by-products from the cooking reaction were common difficulties in older systems that led to operational and quality issues.

The PHV: advanced and effective cooking for dissolving pulps

ANDRITZ took a fresh look at the process and re-designed its cooking system to make the removal of hemicellulose much more effective. The foundation for modifying the process and producing new equipment components is based on years of experience in producing pulps for paper grades. The ANDRITZ Pre-Hydrolysis Vessel (PHV) has gained rapid acceptance and has been delivered to several mills in Asia where viscose fiber growth is the highest.

The PHV utilizes autohydrolysis for efficient hemicellulose removal. This allows the recovery of the hydrolysate, which contains dissolved hemicellulose, in a water solution. The process is simplified and costs are reduced since autohydrolysis does not require additional chemicals in order to start the hydrolysis reaction.

The ANDRITZ Pre-Hydrolysis Vessel (PHV) can be retrofitted to existing continuous cooking installations. Installation and operational costs are likely to be much lower than traditional cooking systems for dissolving pulps. Fiber yields are expected to be several percentage points higher than batch technologies due to excellent selectivity of the principle reactions and controlled, sustainable recovery of by-products.

Current practice for handling the hydrolysate is to neutralize it and combust it with the bulk black liquor. However, in the future, this valuable stream could be processed for energy production or as a building block in other added-value products, further improving the economics of the overall pulping process.