Roots vacuum pump dewatering process in pulp and paper application

Roots vacuum pump, as efficient and reliable positive displacement vacuum devices, play a crucial role in the pulp and paper industry due to their unique structure and performance advantages. The following section, starting with the core characteristics of Roots vacuum pumps and combining them with the needs of papermaking processes, elaborates on their specific applications and value in the industry.

1. Core Characteristics and Advantages of Roots Vacuum Pumps Roots vacuum pumps utilize one or more pairs of synchronously counter-rotating figure-eight rotors (usually three-lobe or two-lobe) to achieve gas intake, compression, and discharge through the minute gaps between the rotors. Its core advantages can be summarized as follows: High pumping speed and large exhaust volume: The rotor rotates at high speed (typically 1500-3000 rpm), delivering a large amount of gas per unit time, suitable for scenarios requiring rapid vacuum establishment; Oil-free cleaning characteristics: Most Roots pumps adopt a dry design (no lubrication oil seal required), avoiding oil mist contamination and meeting the stringent cleanliness requirements of the paper industry; Strong resistance to water vapor: Large rotor clearance (compared to rotary vane pumps) and good corrosion resistance of materials (such as cast iron or stainless steel) allow for direct handling of gases containing saturated water vapor; Flexible series synergy: Often combined with liquid ring pumps, screw pumps, srl., to form a “backing pump + Roots pump” unit, balancing pumping capacity under low vacuum and ultimate vacuum under high vacuum, improving system efficiency; Stable and reliable operation: The rotor has no contact friction (relying on clearance sealing), resulting in low wear and vibration, suitable for the 24-hour continuous operation requirements of paper production lines.
2. Key Applications of Roots Vacuum Pump in the Pulp and Paper Industry: The papermaking process involves multiple stages, including pulping, papermaking, and post-processing. Among these, dewatering, forming, and paper transport all require a stable vacuum environment. Roots vacuum pumps, leveraging these advantages, are widely used in the following scenarios:
3. Paper Machine Wire Dewatering – Vacuum Support for a Core Process The wire section (forming section) of a paper machine is a critical area for wet paper sheet formation: pulp is evenly sprayed onto a metal (or plastic) wire from the headbox, and vacuum dewatering is required to remove approximately 80% of the water (increasing the concentration from 0.5%~1% to 15%~25%). At this stage, the vacuum box/vacuum couch roll is a key piece of equipment, relying on a vacuum pump to provide a stable negative pressure (-30~-60 kPa). The advantages of Roots vacuum pump in this area: High pumping speed allows for rapid response to changes in wire section dehydration (such as during speed increases), maintaining stable vacuum levels; Moisture resistance adapts to saturated water vapor (approximately 40-60℃) discharged from the wire section, preventing condensation or corrosion within the pump; Oil-free design prevents oil mist contamination of wet paper sheets (especially high-grade cultural paper and specialty paper), ensuring paper strength and appearance.
4. Press Section Dehydration – A Key Step in Improving Paper Dryness The press section further dehydrates the paper through mechanical extrusion (increasing wet paper dryness from 25% to 45%-50%), commonly using vacuum press rolls or shoe press technology. Vacuum press rolls have multiple vacuum chambers distributed on their surface, using negative pressure to adsorb the paper sheet and peel off the felt, preventing paper breaks; shoe presses require even higher vacuum levels (-70~-90kPa) to enhance dehydration efficiency.

The functions of a Roots vacuum pump: A wide pressure range (extending from coarse to medium vacuum) matches the vacuum requirements of different stages in the press section; When used in series with a liquid ring pump (the liquid ring pump acts as a pre-treatment stage for moisture, while the Roots pump increases the vacuum level), it can reduce system energy consumption (saving 20%~30% energy compared to a single liquid ring pump); Stable vacuum output reduces the risk of paper crushing (vacuum fluctuations easily lead to uneven paper thickness).

3. Vacuum paper feeding and paper transport – a guarantee of precise control. In the papermaking process, paper sheets need to be transferred between equipment such as the drying section, calender, and winding machine. Vacuum paper feeding devices (such as vacuum suction rollers and vacuum nozzles) use localized negative pressure to adsorb the paper sheet, ensuring smooth transfer at high speeds (1000~2000m/min) and avoiding paper breaks or wrinkles.

Advantages of Roots vacuum pump High instantaneous pumping speed (low rotor inertia), enabling rapid establishment of local vacuum (millisecond-level response), adapting to sudden demands during high-speed roll changes; Low noise and low vibration characteristics reduce interference with precision papers (such as thin sheets and capacitor paper); Modular design facilitates integration into compact paper feeding systems (such as small vacuum units).

4. Blanket Cleaning and Drying – Key to Extending Consumable Life Papermaking blankets (used to support wet paper sheets and transmit dehydration pressure) require regular cleaning to remove fiber and filler residues. Vacuum suction boxes are commonly used to assist in rinsing with water or compressed air drying. A vacuum environment accelerates the evaporation of moisture within the blanket pores, improving drying efficiency.

Application value of Roots vacuum pumps: Moisture resistance adapts to the humid and hot gases (containing detergent vapor) during cleaning processes, preventing pump blockage; Low maintenance costs (no rotor contact wear) make them suitable for cleaning conditions with frequent start-stop cycles; Can be connected in series with a blower to adjust vacuum and airflow, balancing cleaning effectiveness and energy consumption.

Specification of Roots Vacuum Pump:

5. Rewinding and Slitting – Auxiliary Functions for High-Precision Processing Rewinders slit large paper rolls into smaller rolls or trim paper edges. Vacuum rollers use negative pressure to fix the paper edges and prevent misalignment. The vacuum adsorption platform on the slitting machine is used to flatten the cut paper.

The Contribution of Roots Vacuum Pumps:

Stable vacuum level (within ±2kPa) ensures paper positioning accuracy (error <1mm), improving yield; Oil-free operation avoids oil spots on the paper surface (especially affecting printability); Compact design facilitates installation next to rewinders with limited space.

III. Roots Vacuum Pumps Drive Efficiency and Cleanliness in the Paper Industry

Roots vacuum pumps, with their advantages of high pumping speed, wide pressure adaptability, oil-free cleaning, and resistance to moisture, are deeply integrated into the core processes of papermaking (dewatering, forming, and transfer), solving the pain points of traditional vacuum pumps (such as rotary vane pumps which are prone to contamination, and liquid ring pumps which have high energy consumption). As the paper industry moves towards higher speeds (vehicle speed > 2000m/min), higher grades (increased proportion of specialty paper), and greener practices, Roots vacuum pumps, through integration with new technologies such as screw pumps and magnetic levitation fans (e.g., variable frequency speed control, intelligent monitoring), will further optimize system energy efficiency and help paper companies achieve cost reduction, efficiency improvement, and sustainable development.