Safety Tips for Wood Pellet Plant to Prevent Fire&Explosion

Why Is the Prevention of Fire&Explosion Important in Wood Pellet Plant?
The growing high demand of wood pellets makes the production of wood pellet under pressure constantly, wood pellet plant automation and pellet machine speeds are increased, and so the explosion risk caused by accumulated dust is increased too. In the wood pellet production process-- woody materials are ground by wood hammer mill to reduce size, and dried in the sawdust drying machine into its most combustible form, and then densified in the wood pellet making machine into pellets.--dust will accumulates. If the dust can not be controlled and managed properly, it will be the potential hazard. Dust explosion in the wood pellet plant is not uncommon nowadays.
EHSToday reported on Mar 5, 2014--A combustible-dust explosion and fire at the plant injured one worker and partially destroyed the building. The ignition of wood dust in the plant's production room migrated to a retention bin, resulting in an explosion that spread through the building, according to OSHA.
BURNS LAKE, B.C. reported on October 9, 2014-- Three mill workers were injured Thursday in a fire and explosion at a northern British Columbia wood pellet plant, which was the site of a less serious explosion two years ago and was recently fined for "repeated" safety violations.
Dust explosion and fire cause serious injuries, damage to property, and interruption of production. However, there are strategies that can be implemented to reduce the risk of fire and dust explosion.

Several Possible Zones Where Fires or Explosion Can Occur in Pelleting Process

pelleting process of wood pellet machine

In wood pellets production plant the most common ignition source generators are places where friction generates overheated materials, such as wood grinding machine, sawdust dryer, dryer cyclones, intermediate storage, pellet mill, wood pellet cooler, pellet silo, and so on.
♦ Foreign metallic materials in the production process can cause sparks resulting in a fire. For example, when high speed wood grinding machine and wood chippers are used to process biomass materials, it can generate a lot of dust if the wood is dry; if a piece of metal or even a stone falls into the equipment, sparks can be produced, which can ignite the airborne dust.
♦ Bearing problems at one of the rollers of wood pellet machine can create friction and the friction can cause the overheated pellets. When overheated pellets exit the die of pellet machine, they maybe cause the fire or dust explosion.
♦ The accumulation of combustible wood dust in the pellet production process. The production of pellets from various woody materials can produce fines. When the concentration of wood dust reaches the limit, the fire or explosion will occur.

Safety Tips on Pellet Making Machinery to Prevent Fire or Explosion
♦ Remove foreign metallic materials in the raw materials by using Permanent Magnetic Drum or other magnets and this magnetic equipment should be located in duct just after the drying machine, prior to the wood hammer mill, prior to the wood pellet machine and inside the feed ductwork to all storage silos.
♦ Check the easy wearing parts of pellet machine such as roller shell, die, bearings and so on regularly in order to avoid the overheat caused by friction between worn parts.
♦ Pellets temperature should be automatically monitored with a high temperature warning at the discharge gate of wood pellet machines.
♦ Dust collection systems should be located through the whole pellet production line to reduce the dust accumulation. Horizontal and vertical surfaces should be cleaned of the accumulation of dust buildup on a scheduled basis. Surfaces should be cleaned in a manner that minimizes the potential generation of a dust cloud.
♦ Remove all elements that can cause fire or explosion.

remove elements that can cause fire or explosion in biomass pellet plant


Explosibility Characteristics of Dust from White Pellets and Bark Pellets

Explosibility Characteristics of Dust from White Pellets and Bark Pellets

Test Mode

 Test Parameter(dust <63μm)

Measure

White Dust

Bark Dust

Coal Dust

Lycopodium Spores

Testing Standards

Dust Cloud

Auto-ignition Temp(Godbert-Greenwald)

Tc

450

450

585

430

ASTM E1491

Min Ignition Energy

MIE

mJoule

17

17

110

17

ASTM E2019

Max Explosion Pressure

Pmax

bar

8.1

8.4

7.3

7.4

ASTM E1226

Max Explosion Pressure Rate

dP/dtmax

bar/sec

537

595

426

511

ASTM E1226

Deflagration Index

KSt

bar.m/sec

146

162

124

139

ASTM E1226

Min Explosible Concentration

MEC

g/m3

70

70

65

30

ASTM E1515

Limiting Oxygen Concentration

LOC

%

10.5

10.5

12.5

14

ASTM E1515 mod

Dust Layer

Hot Surface Ignition Temp(5 mm)

Ts

300

310

 
 

ASTM E2021

Hot Surface Ignition Temp(19 mm)

Ts

260

250

 
 

ASTM E2021

Auto-ignition Temp

TL

225

215

 
 

USBM (Bureau of Mines) RI 5624

 

Dust Class(>0 to 200 bar.m/sec)

St 1

St 1

St 1

St 1

ASTM E1226

 

Dust Class (Explosion Severity: ES>0.5

Class II

Class II

 
 

OSHA CPL 03-00-06