Online moisture measurement for wood chips

On-line Moisture Measurement for Wood Chips
Using the LB 356 Micro-Moist Microwave Moisture analyser

The problem is measuring the moisture of the wood chips, a necessary prerequisite for process optimization of water into the digester.

On-line measurement of the moisture on the belt conveyor provides an immediate indication to the plant operator to enable him to optimize the addition of white liquor to the digester.

Control results in improvements in pulp yield and quality as well as reduction of kappa number variations.

The Berthold Micro-Moist analyser measures the total volume of material on the conveyor compared to the other technologies, which only measure the surface moisture.

Having a Berthold on-line moisture analyser with dynamic information displayed in the control room is clearly of benefit to the process.

Features & Benefits

Plausibility control. Reliable average.
Contactless sensors installed below & above the belt. No sampler needed, whole layer thickness is measured.
Microwave Principle. Unaffected by colour & capacitance variations. Whole arrangement mounted on a single frame. Easy to install & no moving parts.
Microwaves and radiometrics are non intruding sensors. Wear of probes reducing maintenance.
Accurate measurement and long term stability. No need for frequent recalibration.
Measures continuously and instantaneously. Real time information enables process control right at the time.
Selective to water. No influence of chemically bound hydrogen.
Area weight compensation. Unaffected by change in layer thickness & bulk density.

Berthold On-line Moisture analyser

Berthold installs its Analyser providing on-line and real time measurement.
The monitor is installed on the conveyor to the digester.
The On-line Moisture analyser develops multiple microwaves in a wide frequency range. These microwaves are transmitted via horn antenna through the wood chips and received by the other antenna at the opposite side. The signal is then sent back to the amplifier for evaluation.
A radiometric area mass unit compensates for variations in layer thickness and bulk density, providing a % of mass expressed moisture indication.

Components provided by Berthold include:

Micro-Moist electronic evaluation unit.
A pair of horn antennas.
Accessories for installation.
Scintillation counter.
Small shielding with radiometric source.

Typical installation on a conveyor belt

Guages installed on the conveyor belt before the digester Evaluation unit is mounted close to the guages (2 m cables).
For the sampling representativity as well as for a representative measurement (a correct profile of the wood chips is required).
Horn antennas, perpendicular to the belt conveyor.
Scintillation counter and small shielded radiometric source, also perpendicular to the belt conveyor.
Distance between the horn antennaes max. 600 mm.
Distance between the source and scintillator max. 600 mm.
Wood chips bed depth is between 100 mm/200 mm, obtained by adjusting the belt speed.

Calibration

The initial procedure consists of performing a zero measurement. Theoretical coefficients are entered into the microprocessor (essentially a slope and offset), putting the instrument in operation.
Thereafter the Analyser is fine-tuned by taking samples from the conveyor belt every few hours, and the averaged laboratory results are compared with the Analyser readings taken at the time of sampling.
The comparative laboratory values versus the moisture readings are plotted. The linear coefficients are determined by means of a linear regression. Thus, the calibration coefficients obtained during the start-up procedure are fine-tuned.

Some rules to observe for all on-line Analysers

Ensuring the required amount of wood chips.
Correct profile of the belt loading.
Representative sampling for the calibration.
Accurate moisture determination of the samples in the laboratory.
Depending on the sampling representativity and the laboratory accuracy, a typical measuring accuracy of +/- 1,25% (1 sigma) in a range of e.g. 30% to 55% moisture can be achieved.

Are you interested in a measuring dry matter throughput?

The Berthold LB 330-1 C Radiometric belt weigher includes a moisture input, for the moisture signal delivered by MICRO-MOIST! Click here for more information on Berthold belt weighers.

for more information, email

SE Asia and Australasia: industrial@berthold.com.au

North America: usinfo@berthold.com.au

Europe: euroinfo@berthold.com.au

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On-line Moisture Measurement for Wood Chips Using the LB 356 Micro-Moist Microwave Moisture analyser