Plunger pumps directly pressurize the medium through the reciprocating movement of plungers in the cylinder. The pressure output has low correlation with the viscosity and concentration of the medium, and the rated pressure generally reaches 10-50MPa, which fully meets the high-pressure working condition requirements of paper mills. In addition, the fluctuation range of their pressure output can be controlled within ±0.05MPa, achieving nearly no attenuation. Taking the high-pressure pressing of papermaking pulp as an example, when the set output pressure of a plunger pump is 20MPa, the actual pressure is stably maintained between 19.95MPa and 20.05MPa. This ensures uniform force on the press rolls, improves the pulp dewatering efficiency by 8%-12%, and stably controls the moisture content of filter cakes within 18%-20%, which is far better than the fluctuation performance of traditional pumps.
When the papermaking process requires pressure adjustment (e.g., pressure differences in the pressing of different pulps), traditional pumps mostly rely on "outlet valve throttling" for regulation—reducing the actual output pressure indirectly by closing the valve slightly to increase pipeline resistance. In this way, the pump still operates at full load, and the excess energy is wasted as heat energy through valve throttling, increasing energy consumption by 20%-30%. For example, in the pulping process, to reduce the pressure from 15MPa to 10MPa, a traditional pump needs to close the valve to 70% of its opening (i.e., reduce the opening by 30%). As a result, the motor energy consumption not only fails to decrease but also increases by 8%-10% due to the increased pipeline resistance.
Plunger pumps can achieve excellent pressure regulation by "adjusting the plunger stroke length" or "controlling the reciprocating frequency via frequency conversion", without relying on valve throttling. When the pressure demand decreases, the movement amplitude or frequency of the plunger decreases simultaneously, and the motor power reduces proportionally with the pressure drop, realizing "energy supply on demand". For example, during the transfer of different batches of pulp in a paper mill, when the pressure of the plunger pump decreases from 25MPa to 15MPa, the motor power drops from 110kW to 66kW, and the energy consumption decreases by 40% accordingly—completely avoiding the "energy consumption via throttling" problem of traditional pumps.
The media conveyed in paper mills (such as wood pulp, waste paper pulp, and black liquor) often contain a large amount of fibers and impurities, with a solid content of up to 15%-40%, which are typical "high-concentration viscous media". Such media are prone to cause scouring and wear on the pump's flow-through components, and fibers are easy to entangle and block the flow channel. Traditional pumps have prominent problems of "short service life and easy clogging" under such working conditions, while plunger pumps achieve "long-term stable operation" through structural optimization.
The flow-through surfaces of the impeller and volute of centrifugal pumps are curved structures. Fibers and impurities in high-concentration media will continuously scour the surfaces, resulting in an impeller wear loss of 0.5-1mm per month. On average, the impeller needs to be replaced every 3-6 months, leading to high maintenance costs. Moreover, after the impeller is worn, the flow rate and pressure will further decrease, forming a vicious cycle of "wear → efficiency reduction → more severe wear".
The gear meshing clearance of gear pumps is easily stuck by hard impurities in the medium, causing wear on the gear tooth surface and a decline in sealing performance. On average, the gear set needs to be replaced every 2-4 months, and the shutdown maintenance time can reach 8-12 hours per month, which seriously affects the continuous production of paper mills.
Plunger pumps adopt a "plunger-cylinder block" hard sealing structure, and the flow-through components are made of high-hardness wear-resistant materials (such as ceramic plungers and bimetallic alloy cylinder blocks), with a hardness of over HRC85—1.5-2 times that of traditional pump impeller materials (HRC50-60). In addition, the flow-through channel is designed as a straight large-diameter structure (with a diameter of 10-50mm), so fibers and impurities in the medium are not easy to stay, and the scouring effect is concentrated on the surface of wear-resistant components. The wear loss can be controlled within 0.05-0.1mm per month.
Taking the transportation of high-concentration wood pulp in a paper mill as an example, the service life of the flow-through components of the plunger pump can reach 2-3 years, which is 4-8 times that of the traditional centrifugal pump (3-6 months). It can reduce 4-6 shutdown maintenance times per year, lower the maintenance cost by more than 70%, and increase the equipment operation rate to over 95%.
The impeller blades and pump casing flow channels of centrifugal pumps have curved dead angles. Fibers in high-concentration pulp are prone to entanglement on the impeller, forming "fiber clumps" and causing flow channel clogging. In mild cases, the flow rate decreases by 30%-50%; in severe cases, the motor trips due to overload. For example, in the transportation of waste paper pulp, traditional centrifugal pumps need to be shut down, disassembled, and cleaned of impeller fibers every 2-3 days on average. Each cleaning takes 2-3 hours, which seriously hinders production efficiency.
The gaps at the oil inlet and gear meshing part of gear pumps are small (0.1-0.3mm). Fibers are easy to get stuck in these gaps, which not only causes clogging but also aggravates gear wear, leading to the problem of "clogging → wear → more severe clogging".
The flow-through channels of plunger pumps are designed as a "straight-in and straight-out" structure with no dead angles, and the channel diameter is much larger than that of traditional pumps (e.g., the inlet/outlet diameter of plunger pumps is mostly 50-100mm, while that of centrifugal pumps is mostly 25-50mm). Fibers and impurities can pass through smoothly without easy entanglement or retention. Some plunger pumps are also equipped with a "fiber cutting device" at the inlet end, which can cut long fibers into pieces shorter than 5mm, further reducing the risk of clogging.
In practical applications, when plunger pumps are used for transporting high-concentration pulp in paper mills, the average clogging cycle can be extended to 3-6 months. Moreover, there is no need to disassemble the pump body for cleaning; the cleaning can be completed only through the cleaning port at the inlet end, and each cleaning takes less than 30 minutes. The continuous operation capacity of the equipment is far superior to that of traditional pumps.
Compared with traditional pumps, the advantages of plunger pumps under high-pressure and high-concentration working conditions in paper mills essentially lie in the "in-depth matching between structural design and working condition requirements":
To meet the high-pressure demand, plunger pumps replace the "kinetic energy conversion pressurization" of traditional pumps with "positive displacement pressurization", achieving stable, controllable, and non-attenuating pressure output;
To meet the high-concentration demand, plunger pumps replace the "soft sealing + complex flow channels" of traditional pumps with "hard sealing + large-diameter flow channels", solving the problems of wear resistance and anti-clogging.
For paper mills, choosing a plunger pump is not just "replacing a transfer device", but providing a "stable, efficient, and low-maintenance" solution for high-severity working conditions. It can reduce the production capacity loss caused by frequent shutdowns of traditional pumps, lower the pulp loss due to insufficient pressure and clogging, and at the same time reduce operating costs through its energy-saving characteristics. Against the backdrop of the papermaking industry's pursuit of "cost reduction, efficiency improvement, and green production", the advantages of plunger pumps under high-pressure and high-concentration working conditions make them the preferred equipment that far outperforms traditional pumps.
