Slurries (such as wood pulp, waste paper pulp, etc.) in paper mills are core production raw materials. For every 1% reduction in the slurry loss rate, a paper mill with an annual output of 100,000 tonnes can save hundreds of thousands of yuan in costs. Traditional pumps (e.g., centrifugal pumps, gear pumps) often cause slurry waste during conveyance due to "flow fluctuations, residual retention, and leakage overflow," while piston pumps minimize slurry loss through three key design features.
Each process in papermaking (e.g., pulping, papermaking, sizing) has high requirements for slurry flow precision. Excessively high flow can lead to slurry accumulation inside equipment, requiring the discharge of surplus slurry; excessively low flow necessitates shutdowns for refilling, and air or impurities are easily mixed in during refilling, resulting in the scrapping of the batch of slurry.
The flow of centrifugal pumps is greatly affected by medium viscosity and pipeline resistance, with a fluctuation range of up to ±10%-15%. For example, in the papermaking process, if the set flow rate is 60 m³/h, the actual flow rate of a traditional pump may fluctuate between 45.5-57.5 m³/h. When the flow rate is too high, 5-7.5 m³/h of qualified slurry must be discharged. The annual waste volume can reach 300-500 tonnes (calculated based on 8,000 operating hours per year), and at a cost of 1,500 yuan per tonne of slurry, the annual loss amounts to 450,000-750,000 yuan.
Piston pumps adopt the principle of "positive displacement conveyance," where the flow rate is only related to the piston stroke and reciprocating frequency, and is not affected by external working conditions. The flow precision can be controlled within ±1%-3%. Taking the papermaking process with a set flow rate of 60 m³/h as an example, the actual flow rate of a piston pump remains stable between 59.5-60.5 m³/h, eliminating the need for discharge or refilling. This reduces slurry waste by 300-500 tonnes annually and directly saves 450,000-750,000 yuan in raw material costs.
The flow channels of traditional pumps (such as the volute of centrifugal pumps and the meshing gap of gear pumps) have curved dead zones. After conveyance, 5%-10% of the slurry is likely to remain in the pump. If this residual slurry is not cleaned in a timely manner, it will dry and harden inside the pump. This not only requires flushing when the pump is started next time (wasting clean water and slurry) but also accelerates equipment wear.
Calculated based on 20 liters of residual slurry left in a single pump after each conveyance and 10 starts/stops per day, one pump has an average daily residue of 200 liters, with an annual residual volume of 72 cubic meters. Converted at a slurry concentration of 10%, the annual waste of dry pulp reaches 7.2 tonnes, resulting in an annual loss of 10,800 yuan (based on a dry pulp cost of 1,500 yuan per tonne). If a factory has 20 traditional pumps, the total annual waste amounts to 216,000 yuan.
Piston pumps adopt a "straight-in and straight-out" flow channel design, which has no curved dead zones. Moreover, the reciprocating movement of the piston can "push" the residual slurry, controlling the in-pump residue within 0.5%-1%. Under the same working conditions, a single piston pump has a daily residual volume of only 10-20 liters, an annual residual volume of 3.6-7.2 cubic meters, and a dry pulp waste of 0.36-0.72 tonnes. The annual loss is reduced to 540-1,080 yuan, and 20 piston pumps save 201,600-209,200 yuan annually.
If slurry leaks from the pump body's seal, it not only causes direct waste but also pollutes the workshop environment and increases cleaning costs. Traditional pumps mostly use packing seals or ordinary mechanical seals, which are prone to wear under the scouring of high-concentration slurry, resulting in short seal service life and a leakage rate of up to 0.5%-1%.
For a traditional pump with a conveying capacity of 60 m³/h, if the leakage rate is 0.8%, the hourly leakage volume is 0.4 m³, and the annual leakage volume reaches 3,200 m³. Converted to dry pulp, this is 320 tonnes, leading to an annual loss of 480,000 yuan (based on a dry pulp cost of 1,500 yuan per tonne).
Piston pumps adopt "multi-layer combined seals" (such as polyurethane + polytetrafluoroethylene seals) or "hydraulic balanced mechanical seals," combined with wear-resistant materials. Their seal service life can be 3-4 times that of traditional seals, and the leakage rate is controlled within 0.05%-0.1%. Under the same working conditions, the annual leakage volume of a piston pump is only 200-400 m³, with dry pulp waste of 20-40 tonnes. The annual loss is reduced to 30,000-60,000 yuan, saving 420,000-450,000 yuan compared with traditional pumps.
The energy consumption of pump equipment in paper mills accounts for 15%-25% of the total energy consumption of the entire plant. Traditional pumps cause a large amount of ineffective energy consumption due to "inefficient pressure regulation and increased energy consumption caused by wear". However, piston pumps achieve a significant reduction in energy consumption through three key characteristics: "excellent pressure control, low-friction operation, and working condition adaptability".
Processes in papermaking such as black liquor conveyance and slurry pressing require different pressures. Traditional pumps mostly adjust pressure through "valve throttling" – that is, the pump operates at full load, and the actual pressure is reduced by closing the valve to increase resistance. During this process, 30%-50% of the energy is wasted in the form of heat energy.
Taking a traditional pump with a power of 110kW as an example, in the black liquor conveyance process, it is necessary to reduce the pressure from 20MPa to 12MPa, which requires closing the valve to 40% of its opening. At this time, the motor still operates at full load (110kW), but the actual effective power is only 66kW. The hourly ineffective energy consumption is 44kW, and the annual ineffective energy consumption reaches 387,200 kWh (calculated based on 8,000 operating hours per year). Based on an industrial electricity price of 0.8 yuan/kWh, the annual wasted electricity cost is 309,800 yuan.
Piston pumps directly adjust the output pressure by "adjusting the piston stroke" or "frequency conversion control", without the need for valve throttling. When the pressure is reduced from 20MPa to 12MPa, the power of the piston pump is synchronously reduced from 110kW to 66kW, reducing hourly energy consumption by 44kW and saving 387,200 kWh of energy annually. This translates to an annual electricity cost saving of 309,800 yuan, achieving the goal of "pressure reduction and simultaneous energy consumption reduction".
When the flow-passing components of traditional pumps (such as centrifugal pump impellers and gear pump gears) are worn, the equipment efficiency will decrease. For every 1mm increase in wear, the efficiency drops by 5%-8%, and energy consumption rises accordingly.
For a traditional pump with an initial power of 55kW, its efficiency decreases by 6% and energy consumption increases by 6.6kW annually due to wear. This results in an additional annual energy consumption of 52,800 kWh and an extra annual electricity cost of 42,200 yuan. If used for 3 years, the cumulative additional energy consumption reaches 158,400 kWh, with an extra electricity cost of 126,700 yuan.
The flow-passing components of piston pumps are made of wear-resistant materials such as ceramics and bimetallic alloys, with a friction coefficient of only 0.01-0.03 (compared to 0.05-0.08 for traditional pumps). The annual wear is merely 0.1-0.2mm, and the efficiency drop is controlled within 0.5%-1%. The additional annual energy consumption is only 4,400-8,800 kWh, with an extra electricity cost of 3,500-7,000 yuan. A cumulative electricity cost saving of 119,700-123,200 yuan can be achieved over 3 years.
Different processes in paper mills have significant differences in flow and pressure requirements. Traditional pumps often suffer from the "oversized pump for low load" issue due to "over-sizing"—that is, the rated parameters of the pump are much higher than the actual demand. Long-term operation under low load leads to an efficiency of only 50%-60% (compared to the rated efficiency of 80%-85%), resulting in hidden energy consumption.
For a traditional pump with a rated power of 55kW and a rated flow of 60 m³/h, if the actual demand is only 50 m³/h (62.5% load), the pump efficiency drops from 85% to 55%. The actual power required is 118.18kW (theoretical power = flow × pressure / efficiency; when pressure is constant, power is proportional to flow and inversely proportional to efficiency). The hourly energy consumption is 118.18kW, the annual energy consumption is 945,400 kWh, and the electricity cost is 756,300 yuan.
Piston pumps can be equipped with "variable-flow models" according to actual needs or adjusted via frequency conversion to adapt to low-load working conditions, maintaining an efficiency of 80%-85 at all times. With the same actual demand of 80 m³/h, the actual power of the piston pump is only 22kW, with an annual energy consumption of 588,200 kWh and an electricity cost of 470,600 yuan, saving 285,700 yuan compared to traditional pumps.
Although the initial purchase cost of piston pumps is slightly higher than that of traditional pumps (approximately 30%-50% higher), the cost difference can be recovered in just 1-2 years by reducing slurry loss, lowering operating electricity costs, and cutting maintenance expenses. Over an 8-year period, piston pumps can save paper mills a total of 18 million yuan, making them a typical piece of equipment with "short-term investment and long-term high returns".
For paper mills, choosing a piston pump is not a "simple equipment replacement" but a restructuring of the cost structure through "efficient conveyance". It not only reduces the waste of raw materials (slurry) and the consumption of energy (electricity), but also cuts down on labor and capital investment in maintenance. Against the backdrop of the gradually narrowing profit margins in the papermaking industry and increasingly stringent requirements for environmental protection and energy conservation, piston pumps, by "calculating every economic account well", have become a "core driver" for paper mills to reduce costs and improve efficiency, providing solid support for long-term stable profitability.
