Precision in Pulp: The Role of Flow Meters in Paper Production

Papermaking is a continuous process where the continuity and effective control of the production line are crucial for the quality of the finished paper. Flow meters play an essential role in ensuring the stability of pulp flow during production, thereby enhancing paper quality and production efficiency.

Flow Meters in the Pulp Supply System

The pulp supply system typically involves several stages that require the cooperation of flow meters: the pulping process, the beating process, and the pulp mixing process.

1. Pulping Process:

During pulping, flow meters are used to accurately measure the pulp flow to ensure stability, which is crucial for the subsequent beating process.

2. Beating Process:

In the beating process, flow meters are integrated with control valves to form a PID control loop, ensuring stable pulp flow into the grinder. This improves the efficiency of the grinder, stabilizes the pulp consistency, and enhances the quality of the beating.

3. Pulp Mixing Process:

The pulp mixing process must meet the following conditions:

    The ratio and concentration of the pulp must be constant, with fluctuations not exceeding 2%.

    The pulp supplied to the paper machine must be stable to ensure normal supply.

    A certain amount of pulp must be reserved to adapt to changes in the paper machine's speed and variety.

Flow meters are installed at the outlet of each pulp pump to regulate the pulp flow through control valves, ensuring that each type of pulp is mixed according to the process requirements, achieving a stable and uniform pulp ratio.

Customer Requirements

A paper mill needed to monitor the flow of various liquids in the pulp supply system and consulted Sure Instrument for a configuration plan. The requirements were:

    Accurate measurement of pulp at all stages, corrosion-resistant, and stable performance;

    Easy installation and low maintenance costs;

    Instruments must meet safety production needs.

Solution

After analyzing and discussing the production process diagram with the manufacturer, Sure Instrument selected ultrasonic flow meters and remote pulp electromagnetic flow meters, equipping them with corresponding electrodes and liners according to the nature of the medium.

Ultrasonic Flow Meters:

• Selected for pulp delivery pipelines, these meters do not affect normal pulp delivery and accurately measure flow. They are installed externally on the pipeline without intruding the internal flow, making the installation process simple and quick. They do not interfere with the fluid flow within the pipeline, nor do they cause pressure loss due to installation.

• Consideration is given to the interference of ultrasonic signals by pipeline vibrations, which can lead to measurement errors. It is recommended to install ultrasonic flow meters in areas with minimal vibration and to take corresponding vibration reduction measures, such as installing vibration mounts.

Electromagnetic Flow Meters:

• Generally, after mechanical grinding, the pulp temperature reaches 80°C. When materials like wood or grass are used for pulping, a cooking process is often required. Since the cooking solution is alkaline, such as Ca(OH)2 or NaOH, electromagnetic flow meters are equipped with high-temperature-resistant PTFE liners and a split structure. The choice of electrode materials should consider strong corrosion resistance. For alkaline pulp, materials like Hastelloy C and titanium are generally used, and tantalum electrodes should not be used; for acidic pulp, if the requirements are not high, acid-resistant steel 316SS can also be chosen.

• Many companies use waste paper for pulping, which involves pulping waste paper and then washing and bleaching. Here, electromagnetic flow meters are mainly used to measure the water flow after pulping. It is understood that the raw water used by the paper mill is mostly river water from nearby areas, which is slightly treated before use, so the water quality is poor but not corrosive. Conventional rubber liners and stainless steel electrodes can be used for electromagnetic flow meters; however, careful selection of electrodes and liners is required when measuring deinking agents involved in the deinking process (common deinking agents include NaOH, Na2SiO3, Na2O2, or H2O2).

Customer Feedback

The customer used 200 electromagnetic flow meters and 60 ultrasonic flow meters provided by Sure Instrument in their new project, leading to significant improvements in the measurement system, with data being truly stable. The precise measurement data provided by the electromagnetic flow meters offered a reliable basis for production decisions, ensuring smooth production processes. This also enhanced the stability and consistency of the production process, helping the company improve product quality and production efficiency. The customer is very satisfied with the performance and solutions of Sure Instrument products and has expressed a desire to continue using Sure Instrument products in future new factory constructions.