Dust problems

Fines content (percentage of particles with the size below 3,15mm) should not be over 4% at loading port and mechanical durability should be over 97%.This level of mechanical durability and fines content should guarantee that pellets will not create dust problems at loading or unloading.

Mechanical durability of the pellets (MD)  is checked in  accordance with  CEN/TS 12210-1. Pellets are placed for a certain time period  into  rotating container  of special construction with the certain number of revolutions per min. After rotation  the  mass percentage of crushed pellets coming through the sieve of 3,15 mm  is counted. According the I2 Pellets Specification the amount of crushed pellets should not be bigger than 3,0%.It means that minimum 97,0% of the pellets  have to stay uncrushed. For I 1 pellets this number is 97,5%, for I 3 – it is 96,5%.Mechanical durability is a very sensitive parameter. Pellets with MD even slightly below 97%,for example 95-96% may already  have a tendency to be dusty at loading and unloading  and give a bigger amount of  fines (particles below 3,15mm). MD 99% is typical for EN Plus pellets used for private market. Bulk density (BD) also has  a certain influence on the dust formation, but connection between the bulk density and fine content  is much less than between the dust content and mechanical durability.BD of the pellets has to be more than 600 kg/m3.It is importance  when deciding the tonnage of the pellets which can be lifted by a vessel with the certain volume of the holds. The higher bulk density, the bigger tonnage may be loaded on board. Every handling of pellets will create an increase of the percentage of dust. That is why it is always  better to decrease the  number of re-loadings of  the pellets. During the loading  of the pellets  so called “soft loading” procedure have to be used. It is not allowed to throw the pellets into the hold from bigger height, to squeeze them and to trim. Unloading of the pellets also have to be soft.

Problems with a lot of dust may arise  at the loading and unloading ports in a case the  port is situated close to the residential area. Dust may be also dangerous for the other goods which are at the moment staying near the  vessel with wood pellets ( grains ,sugar etc).

         

One big industrial   Scandinavian  power concern  is very sensitive to dust.Big   amounts   of fines - and related dust,   create huge problem in their   port   which receive every year 200 cargoes of wood pellets on top of the cargoes of coal and oil. They say   if the crew at the port   would   not be   regularly  cleaning  they  would have there  a mountain of dust. They have suggested to check not only the amount of particles below 3,15 mm, but  also  the quantity of the particles below 0,5 mm  which is most likely the fraction making the dust. According this company particles below 0,5 mm   may  vary from 0,86 to 2,21%. But   of course   nothing about particles below 0,5 mm is  yet   mentioned  in the International Classification.