Scale Deposits In Liquid Ring Vacuum Pump In Paper Industry
SCALE DEPOSITS IN THE PAPER INDUSTRY
Scale formation is a process, which counts as one of the most notorious problems in modern paper and pulp mills. The deposits commonly known as insoluble scales (mostly CaCO3) require a complicated removal procedure, usually acid or high-pressure washing. The soluble deposits are usually composed of double salts of Na-CO3-SO4 type or of sodium oxalate. Although easier to wash out, they may form in such large amounts that their sheer volume may effectively block the entire evaporation unit. In both cases, the scales may greatly reduce the heat transfer, increase the energy consumption and worsen the steam economy, leading eventually to expensive shutdowns. It is therefore important to understand how a deposit is formed and thus find a way to avoid it. Formation of various precipitates that disturbs the process is common in the pulp and paper industry and can result in large losses of production. It has a unique competence and experimental equipment for investigating causes and solutions to these problems.
Liquid ring vacuum pumps are the ideal vacuum source for pulp & paper applications. The vacuum pumps provide maximum efficiency at varying vacuum levels with rugged reliability and exclusive performance features. With the increasing cost of power, energy cost is a concern for papermakers. The scale deposits can cause a number of operational problems such as plugging of equipment, inefficient usage of chemicals, increased utility costs, lost production due to downtime, and downgraded products from increased dirt counts.
WORKING PROCESS OF LIQUID RING VACUUM PUMP
The working process of vacuum pump, compressor and steam-water separator is as follows: the gas enters the vacuum pump or compressor through the pipeline through the valve, then it is discharged into the steam water separator through the air guide elbow, and then it is discharged through the steam-water separator exhaust pipe. When used as a compressor, the steam-water mixture discharged from the compressor is separated in the steam water separator, and the gas is delivered to the system of the gas to be compressed through the valve, while the water is left in the steam water separator, and the water level in the steam water separator is adjusted by the automatic overflow switch. When the water level is higher than the required water level, the overflow switch is opened, and the water overflows from the overflow pipe; when the water level is low and the required water level is reached, the overflow switch is closed, and the water level in the steam water separator rises to reach the required water level. The working liquid in the vacuum pump or compressor is supplied by the steam-water separator (or tap water). The size of the water supply is adjusted by the valve on the water supply pipe. The difference between gas suction and pressure delivery system is only that the internal structure of the steam-water separator is different.
THE LIQUID RING VACUUM PUMP PROCESS INVOLVES TWO SECTIONS
FORMING SECTION
Removing as much water as possible early in the papermaking process allows the formation of a stronger, more consistent sheet while reducing web breaks and water removal costs in the press and drying sections. Low vacuum fan efficiency aids water removal at the foils. As the sheet moves down the wire, the alignment of the web fibres makes it more difficult to remove water from the sheet. This requires flat boxes to operate at a slightly higher vacuum level and the use of liquid ring vacuum pumps to help remove water. When the sheet reaches the couch, the liquid ring vacuum pump provides the high vacuum dewatering needed for proper sheet consistency entering the press section. Its unique design allows our pumps to operate at varying vacuum levels, and handle liquid carryover while providing the rugged, reliable performance that you’ve always expected.
PRESS SECTION
Felt conditioning, which is critical to sheet dryness and paper machine run ability, requires a vacuum source at each box that can effectively track felt performance and respond to changes in vacuum level over the life of the felt. As the felt ages, it becomes less permeable and is more resistant to water removal. This requires an increasing vacuum level to remove water. For more effective felt conditioning, recommends that each felt be serviced by an independent vacuum source. The inherent operating characteristics of liquid ring vacuum pumps applied to each box service automatically adjust the operating vacuum levels to provide optimum water removal over the life of the felt. The water removed during the felt conditioning process contains felt hairs, paper fibres, and chemical contaminants that can cause premature wear of the vacuum pump internal components if not removed before the pump inlet. Air-water separators (with either barometric drop legs or low water removal pumps) prevent process water from entering the seal water systems and extend the operating life of the vacuum pump.
CAUSES OF SCALING DEPOSITS IN WATER RING VACUUM PUMP
The heat transfer environment in the circulating water ring vacuum pump is gradually destroyed, the heat exchange frequency will be lower and lower, and the scaling speed will be faster and faster. The causes of scale are as follows,
THERMAL DECOMPOSITION
After the circulating water with hardness component enters the vacuum pump, it forms a water ring in the pump body with the rotation of the pump to do work and heat, which makes the bicarbonate dissolved in the water decompose gradually, and precipitates the precipitation which is difficult to dissolve in the water to form scale.
SOLUBILITY REDUCTION
The salts such as ca-so4, CaSiO3 and CaCO3 with negative solubility temperature coefficient decrease the solubility with the increase of circulating water temperature and precipitate to form scale.
INTERACTION
During the operation of the vacuum pump, the salts with high solubility in circulating water react with other salts to form insoluble substances and scale.
EVAPORATION AND CONCENTRATION
Due to the continuous work and heating of circulating water, evaporation and concentration are inevitable, which makes the concentration of dissolved salt in water increase continuously, and precipitates and forms scale when it reaches saturation.
CLOSED-LOOP VACUUM PUMP APPLICATIONS
When the vacuum pump seal water is reused and the heat of compression must be removed, or in once-through applications, the temperature of the water must be reduced for environmental concerns. The compact/modular design of the closed-loop vacuum pump allows it to be used by both indoors and outdoors and its unique fill design reduces the clogging in most dirty water applications.
CONCLUSION
The paper demand increases every day as a result of the developed population and industrialisation. A major goal is to decrease damage to the environment through waste minimization, reuse and recycling. Using the best available techniques and innovative methods is becoming more compatible.
For more information about scale deposits in the paper industry or to learn more about how our technology can best serve your pulp & paper application needs contact us through our mail at maa.dewborn@gmail.com