The pulp and paper industry is one of the most important industrial sectors in the world - not only because of its market volume of around 905 billion US dollars (2023), but also because of its enormous innovation and market dynamics. Forecasts show: The global production volume is set to rise to almost one trillion US dollars by 2028. The main drivers are packaging papers, which are gaining in importance as a result of e-commerce and growing sustainability awareness.
At POWTECH TECHNOPHARM 2025, the central industry meeting place for mechanical process engineering in Nuremberg in September, visitors will be able to experience live how modern processes and measurement technology make pulp production more efficient, sustainable and competitive - from raw material preparation to reliable paper production.
Pulp production: an overview of processes
Pulp production is the starting point for paper and cardboard production. The aim is to extract the cellulose fibres from plant material - predominantly from wood, but increasingly also from alternative sources. The pulping process can be carried out chemically, mechanically or in combination, and there are basically three methods available: chemical, mechanical and semi-chemical processing.
In the predominant sulphate process, the wood is digested with an alkaline cooking liquor. In a large digester, wood is boiled at high temperatures and pressures with an alkaline solution of sodium sulphide and caustic soda. The chemical reaction dissolves the lignin from the wood, while the cellulose fibres remain intact. The resulting black liquor is then burnt, recovering valuable energy - an important aspect for the energy efficiency of the process.
The advantage of the sulphate process, also known as the "kraft process", lies in the high strength of the pulp and the broad raw material base - even resistant types of wood can be processed with it. Precise pressure measurement is essential throughout the entire cooking process in order to keep the process parameters stable and avoid safety risks. The fill levels in the liquor and pulp tanks must also be permanently monitored to ensure a consistent supply and optimum chemical recovery.
The sulphite process, a somewhat older technology that plays a lesser role today, relies on acidic or neutral cooking chemicals. Although it provides better bleachable pulp, it is now used less frequently due to its lower raw material flexibility and higher chemical input. Here, measurement technology is used primarily for the precise dosing of cooking chemicals and the monitoring of pressure and fill levels in the cooking towers.
In addition to these chemical processes, pulp can also be obtained mechanically: In this process, the wood is pulped purely mechanically in a refiner with the addition of water and heat. Processes such as mechanical pulping or thermomechanical pulping (TMP) require significantly more energy, but deliver a higher fibre yield: mechanical pulps contain all the lignin, which reduces the ageing resistance of the paper, but makes them ideal for applications such as newspaper printing or cardboard. The disadvantage of mechanical processes is their extremely high energy requirement. In mechanical processes, pressure sensors in the pipe systems and pump controls are essential, while level sensors monitor the material flow in the fibre towers and buffer tanks. Precise level and pressure control is crucial here in order to protect the systems from overloading and to ensure the desired fibre consistency.
In the somewhat more exotic semi-chemical pulp production process, the wood chips are first mildly chemically pre-treated and then mechanically pulped. This combination reduces the energy requirement compared to purely mechanical processing and at the same time retains some of the strength properties of chemical pulps. Here too, level measuring devices monitor the material flows between the process stages, while pressure measuring devices keep the process parameters stable in the preparation stages.
Following pulping, the pulp is cleaned in several stages and bleached in several stages depending on the desired end product. Chemicals such as oxygen, hydrogen peroxide or chlorine dioxide are used in the process. Level measuring devices in the chemical stores and pressure sensors in the dosing lines ensure precise and safe dosing of these often aggressive substances.
Alternative raw materials: Hemp, bamboo & co. require adapted technology
In view of rising wood prices, increasing environmental regulations and the search for sustainable solutions, alternative plant fibres are gaining in importance. Raw materials such as hemp, bamboo, reed or grass offer convincing ecological advantages: lower water and chemical requirements, faster growth and often easier processing.
Hemp, for example, provides particularly long and stable fibres that are easy to recycle and hardly need to be bleached. Grass paper scores highly due to its low energy consumption, while bamboo is particularly sustainable due to its rapid growth. From a process engineering point of view, the pulping of these materials differs from that of wood primarily due to the lower amount of lignin - as a result, the processes are often gentler, but also less standardised.
The challenge: processing alternative fibres often requires adapted machines and entails higher costs. There is great potential for innovation here - especially for mechanical process engineering companies that are working on solutions for more flexible, cross-commodity processes.
