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Paper Industry
Large quantities of fibre waste are produced during paper production. These are dried and burned and the energy released during combustion is used as process heat or to generate electricity. The ash is stored in high silos to be later used as an additive in the building materials industry. When the ash silo is filled, a great amount of noise and dust is generated and the material forms large angles of repose and overhangs. Filling, emptying and transportation logistics are controlled through the level measurement system.
Paper Industry
The press rolls are cleaned during product changes or shutdowns of the paper machine and then treated with a special coating agent. This protects them from adhesions and deposits that could cause the paper web to tear or split in the machine. The coating agent is mixed with hot water in a batching tank at a temperature of 50 °C, and pumped to various points in the machine. To maintain automatic operation, the level in the batching tank must be measured and the filter status monitored continuously.
Paper Industry
In order to achieve the desired degree of whiteness, the pulp must be bleached. For this it is filled into the 25 meter high bleaching tower. The bleaching process runs continuously at temperatures up to 95 °C, with using chemicals such as oxygen, ozone or peroxide. The bleached pulp is discharged via screw conveyors. Due to its size, the bleaching tower is never emptied. Continuous level measurement enables a smooth process flow.
Paper Industry
Cleaners remove contaminating materials that are specifically heavier than fibres. In waste paper processing, these contaminants are, for example, sand, glass, stones or staples. The feed through the inlet is tangential in order to set the flow of material in rotation. The heavier particles migrate outwards due to the centrifugal forces and are precipitated downwards, while the lighter fibres in the middle of the vortex rise upwards and are passed on as accepted material. Pressure measurements in the inlet, outlet and overflow are required to regulate the process and ensure that it stays at the optimal operating point.
Paper Industry
The approach flow system connects the stock preparation facility with the paper machine. Here, the pulp for the paper machine is diluted to the required consistency. Additionally, the approach flow system ensures a smooth flow of stock. A particularly important element is the stock deaerator upstream of the headbox. It removes any entrained air under vacuum to ensure a constant, smoothly running process. For effective performance, the stock deaerator always has to be filled to a predefined, millimetre-exact level.
Paper Industry
In the digester, the action of chemical dissolution removes the lignin binder, thereby exposing and freeing the cellulose fibres. During the cooking process according to the alkaline sulphate method, the fibres are fed into the digester by means of steam pressure. To enable fully automatic operation of the digester, a point level detection of the filling is required. The vessel pressure also needs to be carefully monitored throughout this process.
Paper Industry
The residual moisture content of the paper web is removed by steam-heated cylinders in the drying section of the paper machine. The drying process removes heat from the steam, which then forms a thin layer of condensate on the inner walls of the cylinder. This layer influences the transfer of heat to the paper and has to be skimmed off continuously by siphoning. The correct level of heat transfer from the drying cylinder to the paper is monitored by pressure measurements both at the inlet and at the outlet.
Paper Industry
The fibre suspension created in the pulper is first drawn off into a dump chest. There it is temporarily stored for the further stages of the stock preparation process. Typical process challenges in the dump chest are fast filling from above and high stock densities. A slow-running lateral agitator ensures a homogeneous, pumpable consistency of the fibres in suspension. Level measurement in the dump chest determines when it is filled to capacity and ready for emptying and the next process step. The measurement is carried out hydrostatically via a side-mounted pressure transmitter with a ball valve fitting. This allows removal for maintenance or cleaning purposes, even when the dump chest is full.
Paper Industry
The paper suspension is pumped into the headbox of the paper machine. Via the hydraulically pressurized headbox it passes through a tapered cross-flow distributor and manifold, through the rectangular discharge opening, or slice, onto the screen. The outflow speed of the suspension is adjusted to match the speed of the screen by adjusting the pressure of the headbox feed pump. This means an accurate pressure measurement, with minimal turbulence created in the headbox is vital at this part of the process.
Paper Industry
In the press section of a paper machine, very high pressures are needed for dewatering the stock. Hydraulic oil stations provide the supply to the various parts of the machine as well as filtering and cooling the recirculating lubrication system. Integrated pumps provide oil to the required locations and to enable fully automatic operation of the station, the flow rate and the level in the supply tanks must be measured.
Paper Industry
Various chemicals are used in paper manufacturing to achieve the desired properties in the end product. The media are supplied directly to the production areas in IBC containers and added to the paper suspension via metering pumps. Level measurement ensures the supply for the ongoing processes. The stocks are continuously monitored, which allows a dwindling level to automatically trigger an order for replenishment from the chemicals distributor.
Paper Industry
The black liquor resulting from pulp cooking is regenerated and fed back into the digester. Liquor regeneration comprises several process steps. The processes take place at high temperatures and pressures; the media are aggressive and sometimes abrasive. Density measurement of the liquor in the pipelines is required for eco-friendly and energy-efficient process control.
Paper Industry
Pressure screens are used to filter out impurities and separate fibres in stock preparation. A rotating screen basket inside the filter does the actual filtering. Pressure screens have an inlet for the suspension, an outlet for accepted stock and a discharge for rejected stock and contaminants. The process conditions are characterized by pressure surges as well as abrasion and contaminants in the stock. Efficient screening requires a controlled pressure difference between inlet and outlet, which therefore requires continuous, reliable measurement.
Paper Industry
Waste paper or pulp bales are transported on a conveyor belt to the pulper, where they are broken down by adding process water. A stirrer speeds up to separate fibers. Difficult process conditions exist in the pulper: falling bales cause severe pressure shocks, the stirrer creates vortexes. Besides that, foreign substances like wire, glass or sand enter the process along with the waste paper and have an extremely abrasive effect on the interior of the vessel. To ensure an automatic process flow, the level measuring system must establish the ratio of waste paper/pulp to process water. In addition, a possible jamming of the bales on the conveyor belt must be detected.
Paper Industry
Wet strength agents are polymeric additives that enhance water resistance properties, especially in sanitary and specialty papers. They are applied in the paper machine via a size press or spraying device. Because of their high pH value, these substances are stored in double-walled GRP (glass reinforced plastic) tanks. The high viscosity of the medium requires the use of a pneumatic conveyor system and special eccentric pumps for filling and emptying. With these pump types, dry run protection and pressure monitoring is a necessity.
Paper Industry
Quicklime is an important substance for the recovery of lye in pulp production. It is produced in the lime kiln through the combustion of lime sludge from causticisation. The quicklime is conveyed via a bucket elevator into the quicklime silo, where it is temporarily stored, and then discharged via screw conveyors into the lime dosing feeder for the causticising process. Continuous level measurement in the quicklime silo is required to ensure a reliable supply is readily available.
Paper Industry
Refiners are used in paper production to grind up pulp. The main objective of the process is to impart certain properties to the pulp. Every refiner has a grinding set consisting of both fixed and rotating parts. The pressures at the input and output have to be measured for monitoring the loading and release of the grinding set as well as for display of performance.
Paper Industry
Starch is an important additive to increase the strength of the paper. The raw starch is stored in tall, narrow silos. Filling is carried out pneumatically, generating large amounts of dust. They are discharged into the starch slurry production system beneath the silo and the resulting slurry is pumped into the starch cookers by eccentric pumps. For optimal control of the silo filling process, a reliable level measurement is required. To prevent the eccentric pump from running dry, an in-line switch is needed upstream of the pump.
Paper Industry
Steam is needed in the drying section of the paper machine. There it is used to heat the drying cylinders for drying the paper web. The steam is usually generated in the company's own power plant and fed in via an insulated supply line. To ensure optimal consumption and demand planning, the flow rate is continuously measured via an orifice plate with a built-in differential pressure transmitter.
Paper Industry
Wet strength agents are polymeric additives that increase the water resistance particularly of hygienic and specialty papers. These are applied in the paper machine via a size press or spraying device. Because of their high pH value, these substances are stored in double-walled GRP (glass reinforced plastic) tanks. For safety and operational reasons, multiple level measurements are needed in these tanks.
Paper Industry
The targeted addition of chemicals and auxiliary substances influences the properties and quality of the paper. Common additives are hydrogen peroxide as well as alkalis, acids and fillers. These chemicals and additives are sometimes aggressive, produce vapours and are at temperatures of up to 95 °C. This means they are often stored in stainless steel or glass fibre reinforced plastic containers. Level and pressure measurements are essential for the safe filling and emptying of the storage tanks and for dry run protection of pumps.
Paper Industry
Large quantities of prepared stock are needed to keep a paper mill running continuously. This material is stored in high storage towers. They are characterised by their large material throughput and agitators that ensure the homogeneity of the stock. Inside, the warm stock generates lots of steam and the pumping and stirring processes make the surface very turbulent. Reliable level measurement ensures a continuous supply of stock and prevents the agitator from running dry.
Paper Industry
A vacuum system is used to perform dewatering on the high-speed paper machines. The required high vacuum is generated by a single or multi-stage centrifugal blower. The strength of the vacuum is regulated by the rotational speed of the electric drives. For this purpose, the vacuum must be continuously measured. It is also necessary to monitor the bearing lubrication system to ensure reliable operation of the vacuum blower itself. To achieve this, the pressure in the lubricating lines and the level in the lube oil supply tank need to be measured.
Paper Industry
The paper web is dewatered in the press and wire section of the paper machine. As the resulting water is removed via vacuum pipelines which are monitored by pressure transmitters to control the vacuum pump. It is also very important to prevent water from getting into the vacuum pump. To achieve this, water separators are built into the feed lines and the separated water is drawn off by a water pump. A continuous level measurement is used to control the level and the pump.
Paper Industry
The wood chips are transferred via conveyor belts to storage silos up to 25 m high and stored there temporarily for further processing. The silos are filled and emptied in batches. During the process, large amounts of dust are generated, material cones and bridges form, which collapse during emptying. Reliable level measurement is needed here to ensure supplies for downstream processes and facilitate logistics planning.
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