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The Pellet Making Process and the Importance of Moisture Monitoring  

Moisture control is one of the major challenges for pellet plant operators. PSC offers a solution with an online sensor that provides continuous moisture measurement through out the process. Being proactive with moisture measurement offers cost savings in the manufacturing process and eliminates the chance of packaging wet or low quality product. It is Process Sensors’s goal to help the mill make a high quality pellet by providing state-of-the-art moisture measurement with NIR technology.

Waste sawdust and wood chips are delivered to the pellet plant by truck or rail car then stacked outside in large mounds. A front loader is used to take the sawdust from the different piles and load the feed system for the plant. Wet and dry sawdust is selected by the tractor operator in an attempt to keep a moisture balanced load heading into the dryer system. This green wood generally has a moisture content of 20 to 50%. If the sawdust is stored outside the moisture can be higher or lower depending on the weather. It can be a challenge for the loader operator to keep an even mix of wet and dry sawdust going into the feeder system.

A Process Sensors Corp. moisture meter is very helpful to the loader operator as a sensor is mounted on the screen infeed conveyor and a large display is mounted outside for the operator’s use.

The first step in the process is to screen the sawdust and wood chip mixture to separate the fine chips from the coarse chips. The coarse chips are ground to reduce their size for quick and even drying. They are then remixed for temporary storage.

After a second screening to separate the fines from the coarse, the coarse chips are reduced in size with the hammer mill. The hammer mill output and fines are again mixed and stored in bins by moisture content.

The sawdust is then conveyed into a large drum dryer where the moisture is reduced to less than 10%. The sawdust is then conveyed into a cyclone dryer where high speed swirling air removes additional water vapors and cools the product down.

A PSC moisture meter is typically mounted on the dryer outfeed to ensure the moisture is approximately 10%. If the moisture is higher than 10% the sawdust will be directed to a moist bin. Typically, moist bins and dry bins will be blended for the ideal moisture level going into the pellet press. Use of PSC moisture meters on each of the bin outputs can offer additional information to aid in the blending process.

One of the most important measurements is of the final mixture after blending and prior to the press. A PSC moisture meter is used to continuously measure this moisture level going into the pellet mills. The analog output signals from the sensor can be used to forward feed a PLC. The PLC can be programmed to take control of the power level and speed of the press thus creating a more consistent product. This mixture is now ready to be pressed into pellets or sent back to the dryer as fuel for the burner.

The processed sawdust is conveyed into the pellet press where the pellets are formed under very high pressure. This high pressure drives off additional water and causes the natural wood lignites to bind the sawdust into shiny hard pellets. After the pressing, the finished pellets go through one final screening to recover any leftover sawdust for recycling. The cooled and screened pellets are stored in silos while waiting to be bagged and shipped. The standard package is a 40 lb. moisture protected bag for household heating. A major market is Europe, where many homes and power plants use wood pellets as their energy source.

Application Photos
MCT460   MCT460-WP   MCT460-T   MCT466HD   MCT466SF   MCT466QC   GUARDIAN  
Moisture Transmitter
Tobacco Moisture Transmitter
Wood Products Moisture Transmitter
MCT466 QuikCheck
Rugged NIR Tester
Scanning Frame System
Process Sensors Corp.
113 Cedar Street
Milford, MA 01757 USA
Tel: (508) 473-9901
Fax: (508) 473-0715
Process Sensors Europe
Unit 4, Adelaide House
Corbygate Business Park
Corby, Northants NN17 5JG
United Kingdom
Tel: 01536-408066
Fax: 01536-407813
Process Sensors Polska
Ul. Modlinska 310/312 lokal 216
03-152 Warszawa
Tel: (48) 22 6739526
Fax: (48) 22 6739527
Gsm: (48) 509 202759
Process Sensors Asia
PT 3852 Taman Binaraya 3
Off Jalan Pasir Puteh
Limbat, 16150 Kota Bharu Kelantan, Malaysia
Tel: 00-609-765-1352
Fax: 011 60 6601 4588
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  Process Sensors Moisture Transmitters

MCT 460: Used in a wide variety of industrial processes, the MCT 460 Multi-Constituent NIR Transmitter, a True Stand-Alone Transmitter, provides off-line accuracy under on-line operating conditions. Read more about the MCT 460 moisture sensors...

MCT 460-T: The MCT 460-T measures moisture... the most critical variable in tobacco processing... providing the world's most accurate, reliable and stable moisture measurement for the tobacco industry. Read more about the MCT 460-T moisture measurement tool...

MCT 460-WP: The MCT 460-WP uses a well proven algorithm which works on a wide range of wood varieties and forms. You choose the mode of operation, stand-alone or networked. Read more about the MCT 460-WP moisture measurement tool...

MCT 466HD: The MCT466HD features a heavy duty stainless steel enclosure, is resistant to high temperatures, is sealed for wash down environments, and provides reliable, continuous moisture measurement. Read more about the MCT466HD moisture measurement tool...

MCT 466-SF: The MCT 466-SF features a food grade optical window, a robust stainless steel enclosure, and reliably operates in high temperature locations, measuring moisture, oil & product temperatures. Read more about the MCT 466-SF moisture measurement tool...

MCT 466 QuikCheck: Used for quality control in a wide variety of industrial processes, the MCT 466 QuikCheck bench top NIR Tester provides fast accurate results every time. Read more about the MCT 466 QuikCheck moisture analyzer...

GUARDIAN: The Guardian Scanning Frame System is comprised of three components: MCT-460 NIR Transmitter, the automated Scanning Frame and a PC with Automated Guardian Profile Software. Read more about the GUARDIAN Scanning Frame System...