PELLETS About 60 percent of the feedstock for the new pellet plant consists of pulpwood and fuel wood grade logs for which there is no alternative market. The logs are sorted by species in the logyard. The bark and reject wood is used to fuel the furnace that provides the heat for a Maquin triple pass rotary drum dryer. A secondary belt-dryer is planned with a combined heat and power (CHP) plant. Bioenergy Internat ional No 78, 2-2015 37 words not much happened in forestry. Since 1990, all three Baltic countries have had a period of restitution of private forestland to its former owners, a process that is still ongoing today. – A result is that the average private forest holding is quite small, in Lithuania for example it is around 5 ha, making it a challenge to manage as essential forest operations are fragmentised, said Kirjanen. He pointed out that the group has its own wood procurement and full forestry operations subsidiary that services forest owners, third party wood processing industries as well as its Estonian pellet plants. Tech cues from PB industry With its seventh facility it is reasonable to assume that Graanul Invest have learnt a thing or two about building plants and producing pellets. – We design the plants ourselves, adapted to the specifics of each site tapping into our experiences of what works, what does not and why. At the same time we work closely with technology suppliers keeping abreast of developments, said Kirjanen. One striking feature is the use of technologies normally found in the wood-based panel industry such as the particle board (PB) industry. Logs coming into the logyard are sorted according to species as there is a ”pellet receipe”. Sawdust and shavings are stockpiled close to the dryer area. Log debarking is done using a stationary rotary debarking unit supplied by Hekotek/Bruks. Used in the board industries as well as pellet plants it effectively debarks logs in all seasons. The machine rotors constantly turning in one direction rotate the logs and push them up and down. Bark removal is based on a combination of mechanical contact with abraders (rotor teeth) and log against log friction. The loose rebark falls through slots onto a bark conveyor under the debarker and is used to fuel the dryer furnace. Debarking quality is regulated by the amount of logs fed into the debarker and the “rolling around” time. Debarked logs drop over a shield and are conveyed to a Maier chipper. Depending on the season, debarking quality can be regulated by adjusting the angle of the debarking machine position. – It is an effective debarking solution in particular during winter as we do not need to thaw frozen logs. The amount of remaining bark is well within the limit for industrial grade pellets which we are producing here, commented Göran Westerlund, sales manager, Graanul Invest. Sliced not hammered Another example from the PB industry is that prior to drying the chips are put through one of three Maier high-speed knife ring flakers that slices chips into flakes or fine particles. It is a technology that Graanul Invest has installed at all its pellet plants. In the flaking chamber the pre-cleaned woodchips are guided to the knives of the fixed knife ring by a rotating rotor and cut into flat uniform flakes. The fixed and exact centred knife ring in combination with a precise rotor bearing system form a narrow gap between the rotor and the knife ring. This enables exceptional high precision slicing even with high rotor speed resulting in consistent flake quality and a reduced specific energy consumption of the machine. – This is a high-performance machine for the production of high quality flakes from woodchips commonly used in the particleboard industry. Together with Maier we tweaked it to get a flake with a pre-determined size and thickness to suit our pellet production. We believe we get better, more consistent drying as a result, said Westerlund. Looking ahead After flaking the material is joined with the sawdust in-feed system to the dryer, a Maguin triple pass drum heated by an own designed furnace fuelled with bark and reject wood. – A belt-dryer will also be installed once a decision about a biomass combined heat and power (CHP) plant is made later this year, said Kirjanen. Once dried the material is allowed to rest in a homogenising silo before milled in one of four Champion hammer mills. The milled material is transferred to the pelleting house and pelletised by one of ten Promill presses each with a capacity of 3.5-4 tonnes per hour. After cooling the pellets are transferred to one of three storage silos from where direct loading into pellet trucks takes place. Construction of a pellet bagging and palletising facility is underway for ENplus grade pellets. – We opted to start the plant on industrial pellet quality mode while building the bagging facility as it makes sense from both a commissioning and cashflow perspective, ended Raul Kirjanen. Text & photos: Alan Sherrard BI78/4769/AS The woodchips are passed through specifically “tweaked” Maier highspeed knife ring flakers that slice the chips into flakes prior to drying. A total of ten pellet presses supplied by Promill, each with a 3.5-4 tonne per hour capacity. Under commissioning, the reddish tinge reveals that a there is percentage of alder in the actual pellet “receipe” being tried.
Bioenergy no 2 - March 2015
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