Wood Pellet Moisture Impacts Cost, Value, and BTU

Wood pellet moisture is important in all phases of manufacturing and processing. Homes and businesses throughout the world are looking at wood pellet fuel as an alternative or supplementary source for heat. Wood pellets yield high BTU?s at an economical price. Moisture measurement is important in all stages of processing. Cord wood that you might burn in a fireplace or fire pit generally has a moisture from 20 to 60 %. Cord wood is relatively inefficient in energy conversion. Wood pellets offer high BTU energy yields.

Wood pellets are processed from waste materials that are unsuitable for other uses. The waste material is typically sawdust and chips from hard and softwood used in manufacturing flooring or furniture, or other waste wood. The raw material is processed to a moisture level of 12 to 18 % and shipped and purchased on a bone dry weight basis. Moisture control is important to avoid agglomeration or clumping.

This processed sawdust is then compressed to either a standard level 10% for standard pellets, or 8% for premium pellets. Pelletizing is essentially a compression process under high pressure and temperature in which the natural wood lignin binds the wood fibers together without having to add expensive resins.

Process Sensors MCT-360WP can make all these measurements with analog outputs for control, and digital interface for data archiving.

Please click below to view our application sheet.

Wood Pellet Moisture Application Sheet

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Near Infrared Conversion Coat-weight measurement

The MCT-360 series is routinely used in various converting applications to make a moisture measurement on a continuous basis, normally over a moving web. This measurement can be converted to a coat weight measurement, if the coating is applied as a function of a water carrier.

So, a gauge located on the wet end of a process can be used to determine finished coat weight in whatever engineering units are used by the converter. The critical element in this sort of measurement scheme is that the solids/liquid ratio of the applied coating is constant.

Conversion Coatings

Chromate Conversion Coatings have traditionally been applied to electro-galvanized steel and aluminum alloy surfaces to render them corrosive resistant, and to establish an adhesive base for organic coatings in the early stages of the coil coating process. Chromium VI, hexavalent chromium has been the most predominantly used form, but its usage is being curtailed through RoSH legislation owing to its toxicity. Chromium III is safe to use, and is still being used by many aluminum manufacturers but recently, newer alternatives based upon titanium, zirconium, cerium and cerium molybdenum systems have been introduced.

Control of coat weight and coverage is important as it impacts the physical and chemical properties of the sheet metal. The surface film is formed by a chemical reaction so it effectively becomes an integral part of the metal surface. Provided the film is continuous, the metal sheet can be molded without adhesive failure of paint, lacquer or powdered coatings that are applied further down the coil coating line.

Application process and measurement location

The aqueous based coatings can be applied in a number of ways; via a roll coater, brushes or spray nozzles.

Water is an excellent absorber of NIR so measurement is made at the ?wet end? shortly after the tensioned metal sheet has left the metal roller with the water based coating applied. As coating is applied to both front and back of the metal sheet, a gauge is typically mounted either in a fixed position or on a scanning frame either side of the web, the scanning option will obviously provide a better indication of the total coverage. The MCT 360 is calibrated against the dry coat weight value and is extremely accurate providing the solids ratio remains constant; gauge readout is continuous, updating every 90ms. The data enables manual or automatic adjustment of the coater through the MCT Controller Output. This could be implemented through a change of speed and/or pressure of the rollers, or pressure in the case of the spray nozzle.

Measurement Performance
Typical measurement performance: 0.05 ? 0.1 mg m-2 over the range of 3 ? 8 mg m-2 dry coat weight.

Example: Titanium based granodine coating.
The calibration and trend plot below relate to 9 samples that were taken from production. In this example dry coat weight range was between 3.4 and 6.5 mg m-2

Pack Expo Exhibit

Process Sensors will be exhibiting at the PackExpo at McCormick Place, Chicago, IL on Oct. 31-Nov 3rd. Featured products will be the MCT360 measuring moisture, coat weight, film thickness and temperature by using on-line near infrared technology. It gives instant, continual readings as product pass beneath its light beam. Also featured will be our Automatic Scanning Frame that continuously moves the transmitter across a moving web. Proprietary PSC software can then create a cross web profile for moisture, coat weight or film thickness in real time.

Breakfast Cereal Applications

Knowledge of the moisture content at the exit of the cooker, cooker extruder and exit of the

toaster, yields important information which can be utilized to maintain the consistent form,

taste and texture of the cereal in addition to optimizing product yield, reducing scrap and

saving on energy costs. On-line measurements give instantaneous information, enabling

tighter process control than can be obtained through lab analyzed data.

Cereal Production Process

Processes vary, but one such example might contain: a Mixing stage where dry and liquid

ingredients are mixed, Cooker, Extruder or Former, Cutter, Cooler, Flaking Roll,

Dryer-Toaster, Froster-Sprayer and Dryer.

Measurement Location

Moisture measurement at the exit of the Cooker, prior to the Former, reduces the quantity

of misshapes through product sticking or disintegrating in the flaking process. Moisture

measurement post Toaster enables maximization of final moisture, this optimizes yield,

without compromising taste, texture and shelf life characteristics.

Gauge Installation

Typically the gauge is installed over a conveyor, approximately 8? from the product. It is

important to maintain sufficient product bed depth to cover the conveyor, and continuous

product flow, especially if the gauge is used in closed loop control of the toaster or dryer.

The gauge is best positioned at a location several feet from the exit of the toaster/dryer as

this gives the product a chance to reach a degree of equilibration. If possible

measurement should be made on well mixed product; an ideal location is after a short drop

from one conveyor onto another.

The Food Grade MCT300 incorporates a food grade electro less nickel enclosure and either

a kel F polymeric, or sapphire viewing window. An optional water/air cooling panel or vortec

cooler are available if the ambient temperature exceeds 55?C.

Measurement Performance

Application Notes

Moisture in Breakfast Cereals

www.processsensors.com | ?2005 Process Sensors Corp.

Measurement Location Target % Typical Accuracy %

Moisture Exit Cooker 20-30% 0.4%

Moisture Exit Toaster/Dryer 2-8% 0.15%