High consistency (HC) refining of hardwood kraft pulps is emerging as an effective solution even in tissue paper production. Operating at high pulp concentrations, this process favors internal fibrillation and fiber flexibility, preserving fiber length and increasing sheet bulk. The results show a good balance between mechanical strength and sensory properties, allowing a reduction in the use of long fibers and overall production costs
High consistency refining of hardwood kraft pulps represents a significant evolution in pulp preparation strategies for various paper grades. In recent years, new developments have extended its application to the tissue sector. Andreas Gorton-Hülgerth, Global Technology Director, Fiber at Andritz addressed this topic – also presented at Miac 2025 – analyzing the pros and cons of this type of refining applied to sanitary and hygiene paper production.
Refining: LC vs. HC
Traditionally, explains Gorton-Hülgerth, the paper industry has relied heavily on low consistency (LC) refining – a well-known and established process operating at pulp concentrations generally between 3% and 5%. In these conditions, the refining gap between plates is extremely small – usually in the range of 0.1–0.2 mm – and the mechanical action is dominated by shear forces that act mainly on the fiber surfaces.
This type of refining is associated with increased external fibrillation, fiber separation, and improved strength properties, particularly tensile strength and sheet density. However, these benefits are often accompanied by greater fiber shortening, higher production of fines, and a negative impact on some sensory properties – elements that, the director emphasizes, are highly relevant in high-performance tissue production.
In the case of high consistency (HC) refining, the operating principle is radically different. The process works at much higher pulp consistencies, typically between 25% and 35%, and with a refining gap ranging from 0.4 to 2 mm. In this context, Gorton-Hülgerth notes, “high consistency refining does not act by cutting fibers, but by working on their internal structure, mainly using friction and compression.” The predominant forces are therefore not abrasive in nature but result from fiber-to-fiber friction, promoting deep internal fibrillation.
The difference in fibrillation
A direct comparison between LC and HC refining clearly highlights the difference in mechanisms at play. In the HC process, as mentioned, internal fibrillation becomes the dominant factor. “This characteristic leads to increased fiber flexibility without compromising structural integrity,” a particularly important aspect for tissue applications, where balancing mechanical strength and sensory properties is essential.
“Another distinctive effect of high consistency refining is the generation of pronounced fiber curling and actual entanglements, even with sharp curves.” To these phenomena, “oriented micro-compressions, resulting from fiber compression inside the refiner, are added.” All these factors contribute to increasing sheet bulk – i.e., its specific volume – a key parameter for the perception of softness and plushness in the final tissue product. This combination of effects thus gives the pulp unique morphological properties, which translate into different behavior during sheet formation and in final use. As Gorton-Hülgerth observes, “it is precisely the combination of curling and micro-compression that makes high consistency refining so interesting for applications where bulk is a decisive factor.”
In recent years, based on these theoretical considerations, Andritz has defined a new refining strategy specifically oriented toward tissue paper preparation, particularly in Asian production facilities. The high availability of short eucalyptus fibers and the economic context of China and Southeast Asia provided an ideal environment for large-scale implementation of this technology.
HC Refining: effects on tissue
Andritz’s interest in applying high consistency refining to tissue production stems from several challenges faced by producers. One of the main challenges, emphasizes the director, is reducing the content of long fibers in the pulp. These are generally used to ensure adequate mechanical strength. In many areas of Southeast Asia and China, long-fiber pulp is abundant, but its cost remains significantly higher than short fibers. At the same time, the market demands tissue products that are increasingly lightweight, bulky, and soft, without compromising mechanical performance.
The goal of the process development was therefore to maintain strength properties at the same level – or even improve them – while reducing the use of long fibers. “We sought a strategy that would fully exploit the strength potential of eucalyptus while keeping key tissue parameters such as bulk, softness, and tactile feel unchanged,” states Gorton-Hülgerth.
The solution identified was high consistency refining applied specifically to short fibers. By increasing internal fibrillation and the flexibility of eucalyptus fibers, their contribution to sheet strength could be enhanced, compensating for the reduced proportion of long fibers. At the same time, the increase in bulk improved the product’s sensory characteristics, positively impacting the user’s perception.
From a plant perspective, a typical system involves an initial pressing phase via a screw press, where “the pulp enters at about 5% consistency and exits at approximately 26%. The pulp is then fed via a screw to a high consistency refiner specifically designed for eucalyptus.” A reference installation in China, Gorton-Hülgerth notes, “operates with a production capacity of up to 350 tons per day, a working consistency between 26% and 28%, and a specific energy consumption up to 90 kWh/ton. The process takes place at approximately 40 °C and allows a typical refining increase of 6–8 °SR, thanks to plates specifically developed for HC refining.”
Advantages
Field results show several significant benefits. “The tensile strength of tissue produced with high consistency refining is comparable to that obtained with low consistency refining, but with a clearly better sensory profile,” continues the director. The fibers, made more flexible by internal fibrillation, contribute to a more open and bulky sheet structure, improving softness and tactile feel.
Another benefit concerns the reduction of fines and dust generation. “Since the process involves less fiber cutting, the amount of fines is lower, positively affecting both machine cleanliness and final product quality. In this context, the lifetime of refining plates is also significantly longer, reaching up to one year of operation.”
Industrial applications confirm the economic impact of the technology. In one case, the long fiber content in the pulp was reduced from 21% to less than 11% – almost halved, emphasizes Gorton-Hülgerth – without significant changes in tensile strength, either in machine or cross direction. The main difference translated into savings of about €26/ton in fiber costs. Despite the higher energy consumption of the HC refiner, the overall balance remains positive, with a net saving of around €22/ton and an estimated annual benefit of over €1.2 million, considering high energy prices.
Similar results were observed on lines producing facial tissue, where savings per ton can reach €26, with an annual economic return of about €1.16 million. As the Andritz expert specifies, “the calculation must always be adapted to local conditions, particularly energy costs, but the potential savings from reduced long fiber use is evident.”
HC Refining: a technological strategy
Experience gained by Andritz demonstrates that high consistency refining of hardwood kraft pulps can be successfully introduced in tissue production. From 2023 to 2025, over thirty installations of this type were implemented in China and Southeast Asia, reflecting growing interest among paper producers. The main driver for adoption, recalls Gorton-Hülgerth, remains cost savings, achieved through significant reduction of long fiber usage in the pulp, without compromising product performance.
Quality parameters achieved are high, the tissue’s tactile feel meets market expectations, and lower fines production contributes to greater process stability. In conclusion, high consistency refining emerges as a mature and reliable technological strategy, capable of meeting the economic and quality requirements of the tissue industry, offering a concrete alternative to conventional refining systems.