High Alpha Pulp Production via Segmented Cooking and CCE Filtrate Recycling
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Solution Overview
Problem
Current high alpha and high intrinsic viscosity pulp production processes face challenges in achieving high pulp purity and viscosity due to fouling issues and reduced yield in continuous cooking systems, and non-selective bleaching processes lead to cellulose degradation and lower final product quality.
Innovation Solution
The implementation of a combined cooking and Cold Caustic Extraction (CCE) process that uses non-purified CCE filtrate in the cooking step, along with selective bleaching, and redistribution of purification work to the CCE stage, allowing for high intrinsic viscosity pulp production without extensive equipment changes, and recycling CCE filtrate as a main alkali source.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If pre-hydrolysis kraft process with cold caustic extraction is used, then pulp purity (alpha cellulose content) is improved to 96-98%, but equipment fouling occurs leading to short campaign times and cleaning requirements
Solution Approach 1:
The cooking process is divided into two separate vessels: one dedicated to pre-hydrolysis (PHKP) and another to kraft cooking (KP). This segmentation allows each vessel to be optimized for its specific function, with the PHKP vessel handling hemicellulose removal and the KP vessel handling lignin removal, thereby reducing fouling in each individual vessel while maintaining high overall pulp purity
Solution Approach 2:
The pre-hydrolysis stage is extracted and performed separately before the main kraft cooking process. This removes the hemicellulose-rich phase that causes fouling problems in continuous cookers, allowing the main cooking vessel to operate with less fouling and longer campaign times while still achieving the desired 96-98% alpha cellulose content
2Illumination intensity
If traditional bleaching processes are used, then brightness is improved, but cellulose degradation occurs leading to lower intrinsic viscosity
Solution Approach 1:
The bleaching process uses controlled parameter changes with specific sequences (e.g., D-E-D-E-D with oxygen delignification, or TCF sequences with ozone and peroxide) to achieve high brightness while minimizing cellulose degradation. The use of oxygen as a primary bleaching agent and controlled peroxide treatment preserves intrinsic viscosity above 1200 ml/g while reaching brightness levels suitable for specialty applications
3Productivity
If CCE filtrate is recycled without purification, then process simplicity and productivity are improved, but hemicellulose precipitation occurs
Solution Approach 1:
The CCE filtrate is pre-treated by adjusting pH and temperature conditions before recycling to the cooking process. This preliminary action prevents hemicellulose precipitation by maintaining the filtrate in a stable state, allowing direct recycling without complex purification systems while avoiding fouling problems
Solution Approach 2:
The pH and temperature parameters of the CCE filtrate are adjusted before recycling to prevent hemicellulose precipitation. By controlling these parameters, the filtrate can be directly reused in the cooking process without causing fouling, maintaining both productivity and process simplicity
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach results in pulp with alpha cellulose content above 94% and intrinsic viscosity above 1200 ml/g, maintaining high brightness and purity, suitable for specialty applications like cellulose ethers and high-strength regenerated cellulose, while reducing equipment scaling and fouling issues.
Implementation Method 1
The use of pre-hydrolysis kraft process (PHKP) associated to cold caustic extraction (CCE) has been described previously
Implementation Method 2
association of cooking process and CCE process has been described and presents useful industrial application for production of high purity pulps
Implementation Method 3
CCE acts by solubilizing the low molecular weight substances present in the pulp fiber. With such action not only hemicellulose and degraded cellulose molecules are removed from the fibers
Implementation Method 4
After CCE stage, pulp is washed 124 to remove residual caustic content and also lignin, hemicellulose and low degree of polymerization (dp) cellulose in CCE process
Implementation Method 5
In bleaching plant 125 pulp residual lignin is chemically removed and brightness is increased in a multi stage setup with typically 2 to 5 stages
Data Source
AI summary
The HIGH ALPHA AND HIGH INTRINSIC VISCOSITY PULP PRODUCTION APPARATUSES, METHODS AND SYSTEMS (hereinafter “HIGH-A HIGH-IV PULP PRODUCTION”) disclosed herein provide for pulp processing used in connection with Kraft Processes (KP) or Pre Hydrolysis Kraft Processes (PHKP), embodiments employing a Cold Caustic Extraction (CCE) stage and/or appropriate washing and bleaching stages, resulting in pulp with high Intrinsic Viscosity (IV) and high purity, such as may be as determined by alpha cellulose content, and adequate brightness for use downstream in applications such as high tensile regenerated cellulose and ether applications, or other applications employing high IV pulp with significant purity (e.g., alpha cellulose>92%).