Key Roles of Pressure Transmitters in Different Stages of the Pulp and Paper Industry

The pulp and paper industry is a typical process industry, involving the entire production chain from raw material preparation to finished paper rolls. Every stage demands precise measurement of pressure, flow, and level. Pressure transmitters, especially electromagnetic flow-pressure composite instruments, serve as the core sensing elements throughout the production line. Their selection directly affects pulp consistency, chemical dosing stability, equipment safety, and final paper quality consistency.

As the domestic paper industry shifts toward high-grade, cultural, and specialty papers, requirements for instrument corrosion resistance, high-temperature tolerance, response speed, and long-term stability continue to increase. Nexisense, with years of experience in industrial process control, offers a series of pressure transmitters featuring PTFE, PFA, and other high-performance fluoropolymer linings with various corrosion-resistant electrode materials. These are especially suitable for complex conditions with high temperature, high corrosion, and solid-laden pulps. This article analyzes the specific roles and selection criteria of pressure transmitters in key paper production stages.

Stock Preparation and Pulping: High Temperature and Strong Alkaline Challenges

Pulping is the starting point of papermaking. Stock preparation involves mechanical grinding of wood or straw and chemical cooking. After mechanical pulping, pulp temperatures typically reach around 80°C. Chemical cooking, especially alkaline pulping, uses high-temperature, high-pressure NaOH solutions, with medium temperatures reaching 140–160°C and very high pH, placing extreme demands on instrument linings and electrodes.

In this stage, pressure transmitters measure instantaneous and cumulative flow of cooking liquids, pulping water, and chemicals, monitor inlet and outlet pressures of digesters and refiners, ensure stable process parameters, and control steam, black liquor, and other auxiliary media pressures.

Nexisense recommends PFA or high-temperature PTFE full-lining structures for these conditions, with electrode materials like Hastelloy C, tantalum, or platinum-iridium alloys to ensure long-term leak-free, scaling-free operation under high temperature and strong alkaline environments. Remote or split installation helps sensors stay away from high-temperature media, effectively extending service life.

Screening and Bleaching: Multiple Pulp Types and Wide Temperature Ranges

Pulp entering the paper machine from the stock preparation workshop includes various types: chemical pulp, deinked pulp, CTMP, mechanical pulp, and loss pulps. Mechanical and CTMP pulps usually range from 50–80°C and contain fibers, fillers, and chemical residues, which can easily clog ordinary instruments or damage linings.

Pressure transmitters at this stage precisely measure instantaneous and cumulative flow entering stock pipes, monitor pressure differences across screens and bleaching towers, ensuring equipment operates at optimal conditions and providing reliable flow data for subsequent stock mixing control.

Given the diversity of pulp types and temperature ranges, Nexisense offers linings of PFA, PTFE, polyurethane, etc., allowing flexible selection based on pulp type and temperature. Built-in self-diagnostics monitor electrode contamination and lining integrity, significantly reducing measurement drift caused by scaling.

Stock Mixing and Paper Machine: Accuracy, Repeatability, and Response Speed Determine Paper Quality

Stock mixing is crucial for paper quality. Different paper grades require precise pulp ratios, concentration, and ash content. Any deviation can cause entire batches to be scrapped, resulting in significant losses.

In this stage, pressure transmitters perform fine measurements: high-precision transmitters monitor each stock line for instantaneous and total flow; combined with online concentration meters and control valves, they form closed-loop systems that adjust flow according to set ratios; pressures in headboxes and flow boxes are monitored to ensure uniform stock distribution.

Key requirements: high accuracy (typically better than ±0.5%), excellent repeatability, and fast dynamic response. Nexisense high-end models use digital signal processing and multi-point temperature compensation to maintain measurement consistency under varying concentration, temperature, and flow conditions. HART protocol support enables DCS or PLC integration for remote configuration and diagnostics.

Installation and Selection Considerations Affecting Measurement Accuracy

Even with high-quality transmitters, improper installation or process conditions can significantly increase measurement errors. Common factors in papermaking include non-full pipe operation, air bubbles in pulp, insufficient straight pipe lengths (recommended 10D upstream, 5D downstream), eccentric mounting in small diameters causing lining deformation or electrode damage, pulsation and vibration requiring damping or anti-vibration supports, and scaling or cavitation.

Nexisense provides on-site installation guidance and offers special models with self-cleaning and anti-scaling coatings to minimize installation errors.

Trends: Intelligent and Digital Transformation

By 2026, the paper industry is accelerating towards smart manufacturing and low-carbon production. Pressure transmitters are no longer simple measuring devices but important nodes in the Industrial Internet sensing layer. Future trends include support for Industrial Ethernet, PROFINET, Modbus TCP for seamless cloud data integration; edge computing for flow anomaly alerts and predictive maintenance; multi-parameter modules combining online concentration meters, pH meters, and solids content analyzers; and ceramic or full-ceramic sensors to address high-wear pulp measurement challenges.

Nexisense continues R&D investment, providing next-generation products with these capabilities to support transparent processes, traceable quality, and energy optimization in paper mills.

FAQ: Common Questions on Pressure Transmitters in Papermaking

Why choose PTFE or PFA linings in papermaking?
PTFE and PFA offer excellent resistance to acids, alkalis, high temperature, and corrosion, with smooth surfaces that resist scaling, ideal for strong alkaline cooking liquors, acidic bleaching solutions, and various pulps.

How to select electrode material?
Electrode selection depends on medium acidity, alkalinity, and redox properties: strong alkaline environments use Hastelloy C or tantalum; highly oxidative bleaching liquors use platinum-iridium; typical pulps use 316L stainless steel.

Accuracy requirements for stock mixing?
Typically better than ±0.5%, with high repeatability and response<1s, ensuring ratio deviations within 0.1% and preventing product quality fluctuations.

How to handle non-full pipe operation?
Install on vertical rising sections to ensure full pipe, or use U-shaped bottom installation; add vent valves or intelligent instruments with bubble suppression if needed.

Conclusion

From stock preparation and cooking to mixing and paper forming, pressure transmitters span the entire papermaking process, ensuring stable operation, precise ratios, and consistent product quality. Selection must consider medium properties, temperature, corrosion, solids content, and installation conditions. Nexisense transmitters, with high reliability, corrosion resistance, fast response, and intelligent features, serve major domestic and international paper groups, enhancing process control, reducing scrap, and optimizing energy consumption.

In the era of smart manufacturing and green papermaking, choosing suppliers with deep industry experience and continuous innovation is crucial. Pressure transmitters will evolve from “measurement tools” to “intelligent nodes,” deeply integrated with digital platforms, providing solid support for high-quality development in the papermaking industry. Accurate sensing ensures quality from the start.