Pulp and Paper Edition

Yokogawa's role

Supporting the efficient and environmentally friendly production of paper that has the required quality characteristics

Many different kinds of paper are produced for a variety of purposes, and each has differing characteristics and quality criteria. Pulp is produced from wood and non-wood materials such as wastepaper, each of which varies in quality. Even the same raw materials can vary in quality . Yokogawa provides a quality control system (QCS) that measures and controls the final quality of the paper on the production line. By accurately identifying key management points in the manufacturing process, coordinating between different manufacturing units, and optimizing entire plants, we help to keep operations running stably and efficiently while reducing production costs. We also support efforts to reduce their environmental impact by recovering and reusing waste generated in the manufacturing process.

How paper is made

At pulp and paper plants, wood chips and wastepaper are treated under high temperature and pressure to extract pulp fibers. In the papermaking process, rollers are used to flatten the pulp. There are measurement instruments and control systems for each stage of this process. A QCS measures paper weight, water content, thickness, and other variables to determine whether they are within standard values and, if not, adjustments are made by a control system to produce paper that has the required quality characteristics and is suitable for shipment.

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Measurement and control in pulp and paper plants

Pulp production process

With the production of pulp from wood chips, chemicals are used to extract cellulose fibers from the wood chips. As lignin tightly binds together the cells in these fibers, the wood chips are immersed in a white liquor solution inside an impregnator and then transferred to a digester unit to extract the cellulose fibers by dissolving the lignin at high temperature and pressure. Then, the fibers pass through washing, thickening, delignification, and bleaching processes. When pulp is made from wastepaper, the paper is dissolved to remove ink, dust, and other foreign substances, then bleached and pulped again.

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In the pulp production process, equipment is controlled based on the measurement of various kinds of data from flowmeters, level meters, pressure transmitters, pH analyzers, fiber optic temperature sensors, and other instruments. In particular, the process of handling wood chips, the raw material for pulp, always has the risk of fire and requires careful attention. Surveillance cameras and thermal cameras constantly monitor the chip yard, and fiber optic temperature sensors detect temperature rises in conveyor belts. A Yokogawa monitoring system is installed to keep track of site conditions and ensure appropriate responses.

Refining process

The pulp is then sent to the refining process. Inside a refiner, the pulp fibers are hammered and crushed, and the operation of this machinery is adjusted depending on the type of paper that is being produced and its desired strength. The pulp is then transferred to a tank into which a blend of chemicals is added that match the quality and function of the paper. A Yokogawa control system controls these processes, including the management of the ingredient and chemical content ratio, additive amount, and blending condition.

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Papermaking process

The papermaking process involves using a machine to make paper from pulp. The pulp is spread evenly on a net (wire) to form a thin sheet of paper, which is then sandwiched between cloths, and pressed and dehydrated using rollers. The sheet of paper is then pressed against heated metal cylinders, dried, and wound onto a reel using rollers. This completes the papermaking process. Yokogawa measurement devices such as temperature sensors and pressure transmitters as well as a Yokogawa QCS that measures paper weight, water content, thickness, and other variables are used in this process. The paper quality is accurately measured online, and if not within the specified range, the information is sent to a control system, which then makes the necessary adjustments. To ensure high-quality paper manufacturing, the QCS and the control system play an essential role in monitoring and managing the papermaking process.

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Coating process

The coating process involves the application of a pigment mixture to the surface of the finished paper and the smoothing and drying of the paper surface. The QCS is also used in this process. Chemicals are added to the pigment to create a glossy finish. Depending on the type of paper that is to be produced, different chemicals and contents are applied. After drying with hot air or infrared light, the paper proceeds to the finishing process.

Finishing process

After the finished paper is wound onto a reel, defective portions are identified using measurements from the QCS and other instruments, and these defects are removed as the paper is rewound onto the roll. The paper is then cut into the required shapes. Yokogawa’s compact controllers provide high-speed control for these operations.

Transportation and warehouse management

The finished product is transported and stored in the warehouse and then shipped.

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Environmental initiatives at pulp and paper plants

Pulp and paper plants consume large amounts of water and energy. Efforts are made to protect the environment by recycling and reusing resources, and a Yokogawa control system plays an active role in this.

Recovery process

Pulp and paper plants generate wood, paper, plastic, and other forms of waste. In addition, waste liquid called black liquor is also generated when cellulose fibers are extracted in the digester. The water in the black liquor is evaporated to produce a biomass fuel that is incinerated to generate steam in a recovery boiler. This steam can be used in papermaking and other processes, and can also drive turbines for power production.

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Additionally, residual materials from the recovery boiler are reacted with quicklime to regenerate white liquor, which is reused in the impregnator to facilitate the cooking of wood chips.

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To reduce costs, a Yokogawa control system optimizes the operation of recovery boilers and monitors power flow and plant power supply and demand. It also monitors the hazardous substances generated in the manufacturing processes.

Effluent treatment process

Effluents containing fibers, waste, and chemicals are collected in a clarifier for treatment using advanced technologies, and then reused. The sludge generated during the effluent treatment process is incinerated and the residual materials are used as ingredients in cement and other civil engineering materials. A Yokogawa control system controls the amount of effluent and the addition of chemicals to neutralize water quality.

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