Kett KJT130 can simplify pulp, paper moisture measurement

In the pulp and paper industry, measuring and controlling moisture content can affect product quality, production throughput, processing efficiency and the purchase price of wood chips, pulp and converted paper products, not to mention shipping costs.

Pulp or paper product quality, drying efficiency and transactions based on weight, can be adversely affected by improper moisture content. As well, strict international specifications can influence a mill or converter to measure moisture content.

Until recently, frequent moisture-content tests through a process or in the field have been difficult because sophisticated moisture measurement devices must be operated by trained personnel who can properly calibrate the equipment. Many tests also require meticulous sample preparation and disposal.

Fortunately, handheld devices are now available that allow even less-skilled personnel to take lab-quality moisture measurements. These “point-and-measure” options allow moisture readings to be quickly taken at any stage of the process, as well as at loading docks, on trucks, at suppliers, or in bins, vats or vessels.

By simplifying the process, pulp and paper producers and converters can increase the quality of their products from wood chip receipt and pulping to endproduct conversion and distribution.

The benefits of moisture readings

Although the reasons for measuring the moisture content of pulp and paper products can vary, the primary motivation is to improve quality and the bottom line. As such, monitoring and controlling moisture content at all stages of production ensure the most efficient processing and resource use while increasing customer satisfaction.

In terms of quality control, there are strict international specifications required for pulp by the paper industry. Failing to meet required standards can result in rejected product or even fines by customers and clients.

To optimize quality and processing, it is also important to analyze continuous paper webs for wet streaks and uneven drying. This is crucial, because all of a paper product’s physical properties such as curl, porosity, permeability, opacity, smoothness, roughness, stiffness, breaking strength, compression strength and tear resistance also depend on measuring and controlling moisture content. Calendering and printing also depend on working with the materials at specified levels of moisture.

While drying has been reported to account for 12- 20% of industrial energy consumption, drying processes can be particularly energy-intensive in the pulp and paper processing. As such, measuring moisture content in batch or continuous drying processes can help to optimize the process and significantly reduce energy costs.

Finally, since moisture content contributes significantly to the weight of pulp and paper, properly drying a product to acceptable limits before it is transported can significantly reduce shipping costs.

Simplifying moisture measurement

Although traditional laboratory and on-line moisture measurement techniques are useful in the right settings, they have lacked the simplicity and flexibility required for frequent spot checks.

One common test is Loss on Drying which measures the total material weight change after drying. Such tests typically require a sample to be prepared and taken to the lab. It can take from 15 minutes to several hours to do the test which is too slow when more immediate measurements are required. It also requires the sample to be altered or destroyed.

The other common test is a Karl Fischer (KF) test. This procedure calls for chemical reagents to be added to the sample to separate the water from the remaining product and is normally used on liquid samples. The water removed is then compared with the initial mass or volume. Samples are generally small, making the assumption that a large batch is homogeneous. Also, since chemical reagents need to be used, skilled personnel are required to determine the initial parameters, confirm that the system is properly calibrated and maintained and, at times, required to actually do the tests. Disposal of the reagents and waste can be subject to substantial documentation and costly handling.

As a result, secondary test methods have typically been used to deliver faster results. This type of test uses an indirect method and a single conversion to achieve accurate results. Secondary measurement techniques are routinely accepted as equal to the gold standard method. Examples are speedometers, common infrared and liquid thermometers and most pressure gauges. If there is a disadvantage, it is that the instrument must first be calibrated to ensure accurate results. In some cases, calibration can only be done by trained staff familiar with the equipment.

In response, industry innovators have developed a simplified, portable approach that allows even lesstrained personnel to take instant moisture reading spot checks of pulp and paper industry inputs, in-process conditions or finished products as needed. This can be used for measuring wood chips and incoming fiber before the “value-add” of the mill begins. It can include checking pulp sheets before pulp mill processing, analyzing the web for wet streaks and uneven drying before or after dryer cans, inspecting incoming roll stock before conversion and end-product quality checks.

The approach involves moisture meters that utilize near-infrared (NIR) light, a highly accurate, non-contact, secondary measurement method that can deliver immediate, laboratory-quality moisture readings.

“NIR moisture meters allow very accurate instant measurement of solids, pastes, slurries and liquids without contact or sample preparation, so there is no contamination in hand-held and on-line models,” says John Bogart, managing director of Kett USA, a manufacturer of a full range of moisture and organic composition analyzers. “Once the meter has been calibrated against the lab or production standard, the calibration is stored in the device so no calibration is required in the field. Measurements are fully traceable to the original measurement method.”

In addition, because the process is nondestructive, samples remain unaltered so they can be used for additional tests or put back into the product stream.

“NIR moisture meters follow the principle that water absorbs certain wavelengths of light,” says Bogart. “The meter reflects light off the sample, measures how much light has been absorbed and the result is automatically converted into a moisture content reading.”

Unlike complex laboratory equipment, portable NIR equipment is designed for ease of use. For example, with Kett’s KJT130 hand-held portable instant moisture meter, the user simply points the instrument at the product and the moisture content is instantly displayed digitally with results accurate to 0.01% in a 0-100% measurement range.

Because no direct contact or sample alteration is required, particle size variation and unusual textures are not an issue. This can be important when used with a range of inputs, processes or end-products in different settings.

For ease of use, the unit is operated via user-friendly menu commands. The unit, which is the size of a camcorder, is designed for frequent spot checks wherever necessary, on both stationary and moving (process line) products. Moisture measurement data may be stored in the instrument, downloaded continuously or manually recorded.

“The goal is for any staff member to be able to successfully use the moisture meter wherever it is needed, with minimal required training,” says Bogart. “This allows pulp and paper industry processors and converters to have the certainty that what they are producing is of the highest quality.”

The same technology is also available for on-line/in-line systems that allow instant moisture measurement on pulp and paper production lines. Such continuous monitoring can help to eliminate batch waste and provide superior data to optimize the process. Instant desk-top options are available as well for settings where producers want to remove a sample, test it and then replace it.

Kett USA, www.kett.com

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