Patent Publication Number: US-2015068112-A1

Title: Lignin and method and system for processing lignin

Description:
FIELD OF THE INVENTION 
     This invention relates to a method and a system for processing lignin and a lignin powder. In addition, this invention relates to a product comprising lignin and a method and a system for manufacturing product comprising lignin. 
     BACKGROUND OF THE INVENTION 
     Lignin is an organic substance found in tissues of plants. Lignin binds, for example, the cells, fibres and vessels which constitute wood or another plant and hence causes sturdy, strong cell walls. It is one of the most abundant organic polymers and the second most abundant renewable carbon source on Earth, after cellulose. Lignin is quite an unusual biopolymer due to its heterogeneity, i.e. lignins show a certain variation in their chemical composition. The definition common to all is a dendritic network polymer of phenyl propene basic units. 
     It is possible to extract the lignin for an assortment of uses when plants are processed for various industrial purposes. For example in paper manufacturing, lignin is removed from the pulp when high-quality bleached paper is manufactured. In this case, the removed lignin is often burned providing energy to run the mill, because lignin yields a great deal of energy (more than cellulose) when burned. 
     SUMMARY OF THE INVENTION 
     The present invention discloses lignin powder and a method and a system for processing lignin powder. The invention further discloses a method and a system for manufacturing a product comprising lignin. In addition, this invention discloses a product comprising lignin powder. 
     Advantageously the product comprising lignin powder is a composite, a barrier film, a briquette, a pellet, a fuel, or a brown paperboard. 
     Lignin has typically been used as a cake or a clump because lignin dust is explosive material and, hence, grinding of lignin agglomerates into small particles has been very challenging. 
     If the lignin powder comprises big agglomerates, it may be impossible to mix the lignin powder uniformly to other raw materials, especially at lignin contents of less than 2%. Thus, in this case, the lignin content of the product may be high locally and, on the other hand, there is no lignin in some locations. According to the present invention, lignin powder and products comprising lignin powder can be manufactured. 
     Aspects of the invention are characterized by what is stated in the independent claims  1 ,  10 ,  11 ,  14 ,  15  and  16 . Various embodiments of the invention are disclosed in the dependent claims. 
     Advantageously the method for processing lignin comprises the following steps:
         feeding lignin material to the system,   decreasing particle size of the lignin material in a grinding device in order to manufacture lignin powder having particle size distribution wherein at least 85 wt. % of the lignin agglomerates and particles are less than 300 microns, and   increasing dry solids content of the lignin material at least 5 percentage units, more preferably at least 10 or at least 15 percentage units and most preferably at least 20 or at least 25 percentage units while decreasing the particle size in the grinding device.       

     Preferably, at least 90% of the lignin agglomerates and particles in the lignin powder have a size of less than 200 microns, more preferably at least 95 of the lignin agglomerates and particles in the lignin powder have a size of less than 100 microns. 
     Advantageously dry matter content of the lignin material increases at least 10 percentage units during the grinding process in the grinding device. Dry solids content of the lignin material introduced to the system is preferably between 40 and 90%. Dry solids content of the manufactured powder is preferably between 80 and 100%. 
     Advantageously the grinding device is a rotor mill. The grinding device preferably comprises a rotor and temperature of a surface of the rotor during the powdering process is less than glass transition temperature of the lignin material. In an example, the grinding device is a hammer mill. 
     Advantageously the system for processing lignin comprises:
         an apparatus adapted to feed lignin material to the system, and   a grinding device that is arranged
           to decrease size of lignin agglomerates and/or particles in order to obtain lignin powder having particle size distribution wherein at least 85 wt. % of the lignin agglomerates and particles have a size of less than 300 microns, and   to increase dry solids content of the lignin material at least 5 percentage units while decreasing the particle size in the grinding device.   
               

     Advantageously lignin powder according to the present invention has particle size distribution in which at least 85 wt. % of the lignin agglomerates and particles are less than 300 microns, more preferably at least 90 wt. % of the lignin agglomerates and particles are less than 200 microns and most preferably at least 95 wt. % of the lignin agglomerates and particles are less than 100 microns. Advantageously moisture content of the manufactured lignin powder is less than 60%, more preferably less than 40% and most preferably less than 20%, i.e. most advantageously the lignin powder has dry solids content between 80 and 100%. 
     The lignin powder may be used, for example,
         as an additive, such as a binder, or   as a source of energy.       

     Advantageously a method for manufacturing a product comprising lignin powder comprises the following steps:
         feeding first raw material to a system, which raw material may comprise, for example, wood, wood dust, plastic polymer and/or animal feed,   feeding second raw material to the system, which second raw material comprises lignin powder having particle size distribution wherein at least 85 wt. % of the lignin agglomerates and particles are less than 300 microns, and   forming the product comprising the first and the second raw material, the amount of the lignin powder being at least 0.1 wt. % of dry weight of the product.       

     Advantageously a system for manufacturing a product comprises
         an apparatus adapted to feed first raw material and second raw material to the system, which second raw material comprises lignin powder having particle size distribution wherein at least 85 wt. % of the lignin agglomerates and particles are less than 300 microns,   means for mixing the first raw material with the second raw material to obtain a mixture, such as a mixer, and   an apparatus adapted to form the product from the mixture, wherein the product comprises at least 0.1 wt. % of said lignin powder.       

     The product according to the present invention comprises the lignin powder defined in the present application. Advantageously the product according to the present invention has lignin content of at least 0.1 wt. %. Preferably the product comprises lignin powder in which at least 85 wt. % of the lignin agglomerates and particles are less than 300 microns, more preferably at least 90 wt. % of the lignin agglomerates and particles are less than 100 microns and most preferably at least 95 wt. % of the lignin agglomerates and particles are less than 50 microns. Advantageously the product is
         a composite, preferably comprising the lignin powder between 0.1 and 50 wt. %,   a barrier film, preferably comprising the lignin powder between 0.1 and 30 wt. %,   a pellet, preferably comprising the lignin powder between 0.1 and 20 wt. %,   a briquette, preferably comprising the lignin powder between 0.1 and 20 wt. %   a granulate, preferably comprising the lignin powder between 0.1 and 50 wt. %   fuel, preferably comprising the lignin powder between 0.1 and 100 wt. %,   a particle board, preferably comprising the lignin powder between 0.5 and 20 wt. %, or   a brown paperboard, preferably comprising the lignin powder between 0.5 and 20 wt. %.       

     In an example, the product is a pellet or a briquette. In this case, the apparatus adapted to form the product comprises a pelleting device or a briquetting device for forming the pellet or the briquette comprising lignin powder from 0.1 to 20 wt. %. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       In the following, the invention will be illustrated by drawings in which 
         FIG. 1   a  shows an example embodiment of the powdering process in reduced schematic view, 
         FIG. 1   b  shows an example embodiment of the manufacturing process of the product comprising lignin powder in reduced schematic view, 
         FIGS. 2-14  show photos and results from experimental tests, wherein 
         FIG. 2  shows particle size distribution of hammer milled lignin cakes, 
         FIG. 3  shows some particle size distributions, 
         FIG. 4   a  shows some examples of the lignin material to be powdered, 
         FIG. 4   b  shows an example of the lignin powder, 
         FIG. 4   c  shows an example of the lignin powder comprising lumps, 
         FIG. 5   a  shows particle size distributions of the Long Gap mill processed lignin, 
         FIG. 5   b  shows an example of the rotor section of the rotor mill comprising lignin material, 
         FIG. 6  shows particle size distributions of the Ultra Rotor mill processed lignin, 
         FIG. 7  shows some particle size distributions of lignin material, 
         FIG. 8  shows some particle size distributions of lignin, potato flour and potato starch, 
         FIG. 9  shows modified particle size distribution of lignin and starch, 
         FIGS. 10   a - b  show particle sizes of wood dust, 
         FIG. 11   a  shows pellet durability as a function of additive amount, 
         FIG. 11   b  shows pellet durability vs. die temperature, 
         FIG. 12   a  shows amount of Sulphur, 
         FIG. 12   b  shows amount of Sulphur and Zinc, 
         FIG. 13   a  shows amount of Ash, 
         FIG. 13   b  shows amount of Chromium and Copper, and 
         FIG. 14  shows amounts of Potassium and Sodium. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the following disclosure, all percentages are by dry weight, if not indicated otherwise. 
     The following reference numbers are used in this application:
       11  lignin material to be powdered,     10  lignin powder, i.e. first raw material of a product,     13  second raw material(s) of the product,     14  product comprising lignin,     15  heated air,     20  supplying device for the powdering process,     22  filtering device,     27  air heater,     30  grinding device, and     40  apparatus adapted to manufacture the product comprising lignin powder.   

     Lignin is polyphenol which can form strong bindings. It is relatively hydrophobic material and the second most common biopolymer in the nature. Amount of lignin vary in plants. For example, boreal trees have typically about 20-30 percent of lignin but, for example, in coconut shell (coir), the lignin content can be over 45 percent. Lignins show a certain variation in their chemical composition. The definition common to all is a dendritic network polymer of phenyl propene basic units. 
     The lignin material can be separated from any plant material that contains lignin, i.e. any plant material that contains cellulose. The plant material may be wood. The wood can be from softwood trees such as spruce, pine, fir, larch, douglas-fir and/or hemlock, or from hardwood trees such as birch, aspen, poplar, alder, eucalyptus or acasia, or from a mixture of softwood(s) and/or hardwood(s). Nonwood material can be from agricultural residues, grasses or other plant substances such as straw, leaves, bark, seeds, hulls, flowers, vegetables or fruits from cotton, corn, wheat, oat, rye, barley, rice, flax, hemp, manila hemp, sisal hemp, jute, ramie, kenaf, bagasse, bamboo or reed, or from a mixture of nonwood material(s) and/or wood material(s). 
     Lignin can be precipitated from black liquor of a kraft pulp mill by a carbon dioxide process, after which it may be pressure filtered, dispersed, acid washed by sulphuric acid and finally pressure filtered and washed by water. After these stages lignin is in a form of filter cakes. 
     The lignin material can also be separated using a lignin separation process, such as Lignoboost or similar. Typically, the separated lignin is in a form of a lignin cake or a lignin clump. The lignin cake or the lignin clump to be powdered preferably has size between 5-150 mm, but the size may vary. 
       FIG. 1   a  describes an example of a system wherein lignin material  11  to be powdered is supplied to a powdering process. The  FIG. 1   a  shows the lignin material to be powdered  11 , lignin powder  12 , heated air  15 , a supplying device  20  for the powdering process, a filtering device  22 , an air heater  27 , and a grinding device  30 . 
     Advantageously the lignin material to be powdered is supplied to the powdering system and the grinding device  30  therein by the supplying device  20 . The air is preferably heated by an air heater  27 , such as a heat exchanger, after which the heated air  15  is led to the grinding device  30 . In an example, the heated air  15  is generated by means of a heat exchanger from waste heat of a pulp mill. After the grinding step, the powdered lignin material is preferably conveyed to the filtering device  22 , in which the lignin material is separated from the circulating air. 
     In addition, the system preferably comprises a fan, a silencer, a pipe, a pump, and/or valves, such as a rotary valve, a flap valve and an explosion barrier valve. 
     The lignin material  11  is treated mechanically using grinding technology in order to achieve lignin powder. The lignin material  11  to be powdered may be in a form of pressure filtrated lignin cakes or clumps. Preferably the lignin material that is supplied to the grinding device  30  has dry solids content (before the grinding process) between 40 and 90%, more preferably between 60 and 80%. 
     Advantageously the grinding device  30  is a rotor mill, a hammer mill, a stone mill, or an air mill. The system comprises at least one grinding device  30 , preferably one, two, three or four grinding devices  30 . If the hammer mill is used, the system preferably comprises at least two grinding devices, preferably two or four grinding devices. 
     In an advantageous embodiment, the grinding device  30  comprises small air volume inside the rotor. Therefore, the grinding device  30  according to the present invention can work well with the explosive lignin powder. 
     The grinding device  30  is preferably a rotor mill such as a long gap mill or an ultra-rotor mill. Alternatively or in addition, at least one grinding device  30  can be a hammer mill. 
     One, two, three, four or five of the following may be used to control the grinding process:
         a type of the grinding device,   speed of the rotor of the grinding device,   an air volume inside the rotor of the grinding device,   amount of oxygen inside the rotor of the grinding device, and   amount of inert gas supplied inside the rotor of the grinding device.       

     The supplying device  20  is preferably a screw. In an advantageous example, a rotor mill is used as the grinding device  30  and the lignin material is supplied directly to the rotor section of the rotor mill by the screw. 
     Moisture content of the lignin material preferably decreases significantly in the grinding device  30  during the powdering process. Preferably the moisture content of the lignin material decreases at least 5 or at least 10 percentage units, more preferably at least 15 or at least 20 percentage units, and most preferably at least 25 percentage units in the grinding device  30 . 
     In an advantageous example, dry solids content of the lignin material  11  to be powdered is between 60 and 80% when the lignin material is fed to the grinding device  30 . 
     Advantageously, dry solids content of the lignin powder coming out from the grinding device is at least 40% or at least 60, more preferably between 80 and 100% or between 85 and 99.9%, and most preferably between 90 and 95%. 
     Advantageously the lignin powder  12  according to the invention has particle size distribution wherein at least 85% or at least 90%, more preferably at least 95% or at least 97% and most preferably at least 99% or at least 100% of the lignin agglomerates and particles have a size of less than 300 microns, or less than 200 microns, more preferably less than 150 microns or less than 100 microns, and most preferably less than 70 microns or less than 50 microns. For example, if the lignin material is used as an additive, it must have small enough particles and agglomerates to be able to effectively work as a binder and to mix efficiently with other raw materials used. 
     In an example, inert gas, preferably nitrogen, is supplied to the grinding device  30  and used therein during the grinding process. Inert gas is preferably used if the grinding device  30  has large air space. Advantageously, a grinding device having small air space, such as a rotor mill, is used. In this case, the inert gas is not preferably used to avoid increased manufacturing costs. 
       FIG. 1   b  shows in reduced schematic view an example embodiment of the manufacturing process of the product comprising lignin powder. The lignin powder  12  and other raw material(s)  13  are conveyed to the system in order to manufacture a product  14  comprising lignin powder  12 . 
     Advantageously the product comprising lignin powder  12  is
         a composite,   a barrier,   a pellet,   a briquette,   fuel, or   a brown paperboard.       

     The lignin powder may be used, for example,
         as an additive, such as a binder, or   as a source of energy.       

     The lignin, especially if used as an additive, should have small enough agglomerate and particle size distributions to be able to effectively work as a binder. Advantageously the product comprises lignin powder that has particle size distribution wherein at least 85% or at least 90%, more preferably at least 95% or at least 97% and most preferably at least 99% or at least 100% of the lignin particles and agglomerates have size less than 300 microns, or less than 200 microns, more preferably less than 150 microns or less than 100 microns, and most preferably less than 70 microns or less than 50 microns. 
     For example in fuels, lignin used as an additive may bind particles together improving durability and, in addition, improve the quality of the fuel, e.g. fuel&#39;s combustion properties and heat value. 
     Advantageously the lignin powder is used as an additive in pellets or briquettes. The lignin powder may be used, for example, as an additive in such a way that the lignin powder works as a binder in the pellet or in the briquette. In addition, the lignin powder may work as a source of additional energy. 
     The briquette is preferably a wood briquette. The amount of lignin powder in the briquette is preferably between 0.1 and 20% or between 0.2 and 10%, more preferably between 0.3 and 5% or between 0.4 and 2% and most preferably between 0.5 and 1%. The amount of lignin used in the briquette typically depends on the sulphur content of the lignin. 
     A briquette according to the present invention, especially the wood briquette, is densified biofuel made with lignin powder additive in the form of cubiform or cylindrical units, produced by compressing pulverized biomass. Biofuel briquettes are advantageously manufactured in a piston press, with the total moisture content preferably being less than 15% of the mass on wet basis. 
     The pellet is preferably a feed pellet or a wood pellet. The amount of lignin powder in the pellet is preferably between 0.1 and 20% or between 0.2 and 10%, more preferably between 0.3 and 5% or between 0.4 and 2% and most preferably between 0.5 and 1%. The amount of lignin used in the pellet typically depends on the sulphur content of the lignin. Advantageously the lignin powder to be fed to the pellet processing system has a dry solids content between 60 and 100%, more preferably between 80 and 95% and most preferably between 85 and 92%. 
     A pellet according to the present invention, such as the wood pellet or the feed pellet, is typically made from pulverized biomass with lignin powder additive. The pellet is usually in a cylindrical form. The wood pellet according to the present invention is preferably densified biofuel made from pulverized woody biomass. 
     Pelleting may be implemented by means known to a man skilled in the art. Pelleting plant may comprise, for example, a cooling tower, a pelleting machine, additive feeding devices, raw material silos, and a grinding device such as a hammer mill. 
     The pellet production process advantageously comprises at least some of the below mentioned apparatuses:
         supplying device(s) for feeding the wood dust or another raw material(s), and the lignin powder,   a first mixer, for example hammer mill, to mix the supplied materials to obtain a mixture,   air flow transportation means to convey the mixture,   a separating device, such as a cyclone, to separate air from the mixture,   a second mixer to remix the mixture,   steaming and wetting means in order to achieve predetermined moisture content of the mixture,   a feeding device for the pelleting device, such as a screw, to feed the mixture to the pelleting device,   a pelleting device to obtain the product  14 ,   a cooling device, and   conveyer to convey the product  14  to a storage.       

     Advantageously the length of the pellet is between 5 mm to 50 mm, more preferably the length is less than 45 mm and most preferably the length is less than 40 mm. Typically the pellet comprises broken ends. A portion of the pellets having length more than 40 mm is preferably 1 w-% at the most. Advantageously diameter of the pellets is less than 25 mm, more preferably less than 12 mm and most preferably less than 10 mm. 
     Advantageously the amount of fines in the pellets (w-% of particles having particle size less than 3.15 mm, standard CEN/TS 15149-1, valid in 2011) is 5% at the most, more preferably 2% at the most and most preferably 1% at the most. 
     In an example, the amount of Sulphur (w-% of dry basis, standard CEN/TS 15289, valid in 2011) in the pellet or in the briquette is 0.20% at the most, more preferably 0.1% at the most and most preferably 0.08% at the most. 
     Advantageously, the amount of the Sulphur (standard EN 15289, valid in 2011) in the pellet or in the briquette is preferably 0.05 w-% dry at the most, more preferably 0.04 w-% dry at the most and most preferably 0.03 w-% dry at the most. 
     In an example, the amount of Nitrogen (w-% of dry basis, standard CEN/TS 15104, valid in 2011) in the pellet or in the briquette is preferably 3 w-% dry at the most, more preferably 2 w-% dry at the most and most preferably 1 w-% dry at the most. 
     Advantageously, the amount of Nitrogen (w-% of dry basis, standard EN 15104, valid in 2011) in the pellet or in the briquette is preferably 1 w-% dry at the most, more preferably 0.5 w-% dry at the most and most preferably 0.3 w-% dry at the most. 
     In an example, the amount of Chlorine (w-% of dry basis, standard CEN/TS 15289, valid in 2011) in the pellet or in the briquette is preferably 0.1 w-% dry at the most, more preferably 0.07 w-% dry at the most and most preferably 0.03 w-% dry at the most. 
     Advantageously, the amount of Chlorine (w-% of dry basis, standard EN 15289, valid in 2011) in the pellet or in the briquette is preferably 0.04 w-% dry at the most, more preferably 0.03 w-% dry at the most and most preferably 0.02 w-% dry at the most. 
     The amount of Arsenic (As, standard EN 15297, valid in 2011) in the pellet or in the briquette is preferably 1 mg/kg dry at the most. 
     The amount of Cadmium (Cd, standard EN 15297, valid in 2011) in the pellet or in the briquette is preferably 0.5 mg/kg dry at the most. 
     The amount of Chromium (Cr, standard EN 15297, valid in 2011) in the pellet or in the briquette is preferably 10 mg/kg dry at the most. 
     The amount of Copper (Cu, standard EN 15297, valid in 2011) in the pellet or in the briquette is preferably 10 mg/kg dry at the most. 
     The amount of the Lead (Pb, standard EN 15297, valid in 2011) in the pellet or in the briquette is preferably 10 mg/kg dry at the most. 
     The amount of the Mercury (Hg, standard EN 15297, valid in 2011) in the pellet or in the briquette is preferably 0.1 mg/kg dry at the most. 
     The amount of the Nickel (Ni, standard EN 15297, valid in 2011) in the pellet or in the briquette is preferably 10 mg/kg dry at the most. 
     The amount of the Zinc (Zn, standard EN 15297, valid in 2011) in the pellet or in the briquette is preferably 100 mg/kg dry at the most. 
     The function of the lignin powder additive in the product may be to improve technical quality of the product and to also strengthen the product towards humidity. The lignin additive may also decrease quality changes caused by heterogeneous raw material and works as a dust binder. For example in pellet production process, lignin gets elastic due to increased temperature and glues particles, such as wood particles, together to pellet. Cooling of pellet hardens the lignin again and makes pellet durable. The caloric value of lignin is high, which makes it good biofuel. 
       FIG. 2  shows example particle size distributions of hammermilled lignin cakes. The lignin cakes are hammermilled in room temperature using sieve with 5 mm aperture size. As can be seen, three times hammermilled lignin material has a smaller average particle size than lignin material that is hammermilled once or twice. Preferably the lignin material is at least twice hammermilled. However, already once hammermilled lignin material may be good enough to use for some products. 
       FIG. 3  shows an example of particle size distributions of lignin, potato starch and potato flour. The materials are treated using hot air during the grinding. As can be seen from  FIG. 3 , the powdered lignin material has typically, especially if grinded with a rotor mill, more small particles than potato starch or potato flour. 
       FIG. 4   a  shows some examples of the lignin material to be supplied to the rotor mill device. An effect of a grinding temperature on the lignin material is illustrated in  FIGS. 4   b  and  4   c .  FIG. 4   b  shows lignin powder manufactured using good process temperature, hence, the obtained material is even lignin powder. If lignin melts it typically forms, not only lignin powder, but also big hard lumps, which is shown in  FIG. 4   c . The lumps shown in  FIG. 4   c  are formed due to very high inlet air temperature (350° C.) during powdering process. 
     Advantageously the inlet temperature of the heated air during the powdering process is less than 160° C., preferably between 90 and 130° C., and more preferably between 100 and 120° C. Most preferably the inlet temperature of the heated air during the powdering process is less than glass transition temperature (Tg) of the lignin material. 
     An amount of the inlet heated air during the powdering process is preferably at least 8300 m 3 /t, for example between 8300 and 20000 m 3 /t, more preferably at least 13 000 m 3 /t, for example between 13 000 and 17 000 m 3 /t. 
     Thanks to the present invention, new lignin products with controlled particle size distribution as well as controlled dry matter content can be obtained. Some experimental tests are shown in the following examples. 
     Example 1 
     In this trial, the performance of powdered lignin as pellet additive was measured and the performance was compared with potato starch and genuine pellets without additives. 
     In the trial, a mixture of Norway spruce ( Picea abies ) 20% and Scotts pine ( Pinus sylvestris ) 80% was used. Moisture content of the raw material before pelletizing was 9-11%. Pelletizing was done by so called SPC pellet press with vertical fixed round die. Press channel was 50 mm and pellet diameter was 8 mm. 
     Pellets were cooled after pressing in cooling tower by fresh air and sampled after cooling. First test of technical durability was done about one hour after pressing. The test was repeated after 5-7 days after pressing in order to see if technical durability would develop differently with lignin additive or starch additive. 
     Technical durability was tested by a device and a procedure following the European standard of solid biofuels. Pellets were tumbled 500 rounds (50 rpm) in the box with metal blade; after that all particles smaller than 3.15 mm were sieved out and remaining mass of pellets was measured. 
     Temperature and energy consumption as well as all functional measures, like weight changes were monitored as a tailor made data control system built for research purposes in the pellet plant. Tested pellet formulas are shown in Table 1. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Additives used in the trial. 
               
            
           
           
               
               
               
            
               
                   
                 Batch 
                 Description 
               
               
                   
                   
               
               
                   
                 0-test2 
                 No additives 
               
               
                   
                 S0.5% 
                 0.5% of starch as an additive 
               
               
                   
                 L0.5%2 
                 0.5% of lignin as an additive. 
               
               
                   
                 0-test3 
                 No additives 
               
               
                   
                 0-test1 
                 No additives 
               
               
                   
                 L1% 
                 1% of lignin as an additive 
               
               
                   
                 L0.4% 
                 0.4% of lignin as an additive 
               
               
                   
                 L0.5% 
                 0.5% of lignin as an additive 
               
               
                   
                 S0.6% 
                 0.6% of starch as an additive 
               
               
                   
                 S0.9% 
                 0.9% of starch as an additive 
               
               
                   
                   
               
            
           
         
       
     
     Technical durability is presented in Table 2. All tested batches were tested twice and average of those two tests was used as a comparison value and input in further tests. CEN-test was repeated some days later in order to find differences of the later strengthening of pellets in storage. 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Durability test results of produced pellet batches. 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                   
                   
                 Sample 
                 Sample 
                   
                 Average 
                   
                 Average 
                   
               
               
                   
                   
                 mass before 
                 mass after 
                   
                 of sample 
                   
                 of sample 
                 Difference 
               
               
                 Batch 
                 Date 
                 test, g 
                 test, g 
                 CEN-% 
                 pairs 
                 CEN-% 
                 pairs 
                 %-units 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 0-test3 
                 22.9. 
                 501.06 
                 443.29 
                 88.47% 
                   
                   
                   
                   
               
               
                 0-test3 
                 22.9. 
                 503.34 
                 442.63 
                 87.94% 
                 88.20% 
               
               
                 L1% 
                 22.9. 
                 502.97 
                 481.14 
                 95.66% 
                   
                 95.61% 
               
               
                 L1% 
                 22.9. 
                 503.49 
                 480.29 
                 95.39% 
                 95.53% 
                 95.66% 
                 95.64% 
                 0.11% 
               
               
                 L0.4% 
                 22.9. 
                 503.81 
                 465.97 
                 92.49% 
                   
                 93.01% 
               
               
                 L0.4% 
                 22.9. 
                 503.78 
                 467.65 
                 92.83% 
                 92.66% 
                 93.12% 
                 93.07% 
                 0.41% 
               
               
                 L0.5% 
                 22.9. 
                 508.22 
                 473.86 
                 93.24% 
               
               
                 L0.5% 
                 22.9. 
                 508.05 
                 467.63 
                 92.04% 
                 92.64% 
               
               
                 L0.5% 
                 22.9. 
                 645.34 
                 599.17 
                 92.85% 
               
               
                 L0.5% 
                 22.9. 
                 527.42 
                 489.96 
                 92.90% 
                 92.87% 
               
               
                 S0.6% 
                 22.9. 
                 512.23 
                 485.09 
                 94.70% 
                   
                 95.14% 
               
               
                 S0.6% 
                 22.9. 
                 524.92 
                 497.55 
                 94.79% 
                 94.74% 
                 95.32% 
                 95.23% 
                 0.49% 
               
               
                 0-test1 
                 21.9. 
                 462.3 
                 394.6 
                 85.36% 
                   
                 88.68% 
               
               
                 0-test1 
                 21.9. 
                 518.5 
                 451.1 
                 87.00% 
                 86.18% 
                 87.87% 
                 88.27% 
                 2.09% 
               
               
                 S0.5%. 
                 21.9. 
                 557.3 
                 507.9 
                 91.14% 
                   
                 91.66% 
               
               
                 S0.5%. 
                 21.9. 
                 526.5 
                 477.6 
                 90.71% 
                 90.92% 
                 91.85% 
                 91.76% 
                 0.83% 
               
               
                 L0.5% 
                 21.9. 
                 597.8 
                 550.3 
                 92.05% 
                   
                 92.15% 
               
               
                 L0.5% 
                 21.9. 
                 605.0 
                 555.6 
                 91.83% 
                 91.94% 
                 92.04% 
                 92.09% 
                 0.15% 
               
               
                 0-test2 
                 21.9. 
                 616.6 
                 545.0 
                 88.39% 
               
               
                 0-test2 
                 21.9. 
                 581.8 
                 511.0 
                 87.83% 
                 88.11% 
               
               
                 S0.9% 
                 23.9. 
                 545.35 
                 524.98 
                 96.26% 
                   
                 96.21% 
               
               
                 S0.9% 
                 23.9. 
                 519.5 
                 498.96 
                 96.05% 
                 96.16% 
                 96.30% 
                 96.25% 
                 0.10% 
               
               
                   
               
            
           
         
       
     
     Pressing temperatures were followed from 11 measurement points on die and also gear oil temperature was followed. Measurement point numbers follow clock face numbers closely. Temperatures between different batches are not remarkably different. Temperature was not significant in regression analysis either. 
     Two additive percentages, 0.5 and about 1% were tested for both starch and lignin. With 0.5% the moisture resistance was about 65% but it changed when additive percentage was added. When doubling the additive amount, moisture resistance decreased with lignin and increased with starch. These results are shown in Table 3. 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Results of the moisture resistance test. 
               
            
           
           
               
               
               
               
               
            
               
                   
                   
                   
                 Mass after moisture 
                   
               
               
                   
                   
                 Original 
                 treatment and CEN- 
               
               
                   
                 Batch 
                 mass, g 
                 test, g 
                 CEN-% 
               
               
                   
                   
               
               
                   
                 L0.5% 
                 500.44 
                 322.88 
                 65% 
               
               
                   
                 S0.5% 
                 500.70 
                 321.37 
                 64% 
               
               
                   
                 S0.9% 
                 501.17 
                 333.20 
                 66% 
               
               
                   
                 L1% 
                 501.23 
                 306.38 
                 61% 
               
               
                   
                   
               
            
           
         
       
     
     According to the trial, lignin is as good pellet additive as starch. Remarkable differences cannot be found according to test run made. Technical properties of used lignin additive were somewhat different if compared with starch. Lignin powder is really fine and gets more easily in the air in the process, and it seems to get mixed with raw material better than starch. In a fresh, hot pellet, lignin does not make surface of the pellet sticky like starch does. 
     Durability of pellets improves in storage. In this test, durability improved most in pellets without additive. According to results, lignin as an additive might decrease this improvement; in other words, lignin added pellet reaches the final strength faster than normal pellets. 
     Example 2 
     During these experimental tests, different kinds of devices and process parameters were tested. The devices used during the trial were:
         Rotor mill 1: a long gap mill,   Rotor mill 2: an ultra-rotor mill, and   Rotor mill 3: a flash dryer agitated by a high-speed disintegrating rotor.       

     The wood material used was a mixture consisting 54-60% of pine and 40-46% of spruce. The raw material was processed by the hammer mill before pelletizing. 
     Pellet durability test was implemented as follows: 
     Pellets were treated first by 3.15 mm sieve. 500±10 g of pellets were put to a box and rotated in the box 10 min at speed of 50 rotations per minute. After this, pellets were sieved again and the final mass of the pellets was measured. Durability was calculated as Final mass/Original mass*100%. 
     The lignin used is shown in table 4. In addition, Finnamyl potato starch was used as a reference binder. 
     
       
         
           
               
             
               
                 TABLE 4 
               
             
            
               
                   
               
               
                 Selected lignin additive 
               
            
           
           
               
               
               
               
            
               
                 Sample 
                 Sample 
                   
                 Initial 
               
               
                 number 
                 code 
                 Weight (kg) 
                 moisture (%) 
               
               
                   
               
            
           
           
               
               
               
               
            
               
                 1 
                 G1/CH4 
                 50 
                 26 
               
               
                 2 
                 G2/CH4 
                 51 
                 26 
               
               
                 3 
                 G2/CH4 
                 47 
                 26 
               
               
                 4 
                 C3/CH1 
                 33 
                 53 
               
               
                 5 
                 G3/CH1 
                 30 
                 53 
               
               
                 6 
                 G3/CH1 
                 31.5 
                 53 
               
               
                 7 
                 G3/CH1 
                 32 
                 53 
               
               
                 8 
                 G3/CH1 
                 31.5 
                 53 
               
               
                 9 
                 G4/CH2 
                 58 
                 23 
               
               
                 10 
                 G5/CH3 
                 56.5 
                 30 
               
               
                 11 
                 G6/CH6/1 
                 37.5 
                 37 
               
               
                 12 
                 Big batch 
                 6095 
                 39 
               
               
                   
               
            
           
         
       
     
     Results of Rotor mill 3 are shown in Table 5. The lignin material could be processed well. The dry matter content of the lignin material varied between 47% and 77%. Some kind of pre-crushing was beneficial to be able to crush the biggest lumps before the feeding screw. The raw material was fed directly to the disintegrator area of the machine. 
     As can be seen from the particle size distribution in  FIG. 8  there is a fraction of bigger particles than 100 microns. The coarse material can be felt easily by fingers too. Thus, the sieving is needed to cut away the coarsest fraction of the product. 
     
       
         
           
               
             
               
                 TABLE 5 
               
             
            
               
                   
               
               
                 Resuls of Rotor mill 3 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                   
                   
                 Initial 
                 Target 
                   
                   
                   
               
               
                 Sam- 
                 Sample 
                 Weight 
                 mois- 
                 mois- 
                 mois- 
                 Dry 
                 Final 
               
               
                 ple 
                 code 
                 (kg) 
                 ture (%) 
                 ture 
                 ture 
                 weigth 
                 weight 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 1 
                 G 1/CH4 
                 50 
                 26 
                 2 
                 1.5 
                 37 
                   
               
               
                 2 
                 G 2/CH4 
                 51 
                 26 
                 2 
                 1.5 
                 37.74 
                 39 
               
               
                 3 
                 G 2/CH4 
                 47 
                 26 
                 10 
                 4.5 
                 34.78 
                 29 
               
               
                 4 
                 G 3/CH1 
                 33 
                 53 
                 10 
                 10 
                 15.51 
               
               
                 5 
                 G 3/CH1 
                 30 
                 53 
                 10 
                 10 
                 14.1 
               
               
                 6 
                 G 3/CH1 
                 31.5 
                 53 
                 10 
                 13 
                 14.81 
               
               
                 7 
                 G 3/CH1 
                 32 
                 53 
                 10 
                 13 
                 15.04 
               
               
                 8 
                 G 3/CH1 
                 31.5 
                 53 
                 10 
                 7.2 
                 14.81 
                 57 
               
               
                 9 
                 G 4/CH2 
                 58 
                 23 
                 10 
                 8 
                 44.66 
                 40 
               
               
                 10 
                 G 5/CH3 
                 56.5 
                 30 
                 2 
                 2 
                 39.55 
                 12.6 
               
               
                 11 
                 G 6/CH 
                 37.5 
                 37 
                 2 
                 2 
                 23.63 
                 11 
               
               
                   
                 6/1 
               
               
                   
               
            
           
         
       
     
     The runnability of Rotor Mill 2 was good from the beginning. The lignin material was fed by the screw directly to the rotor section of the machine. Further, the inlet air temperature was only 100-110° C. The low air temperature was compensated by the high air flow amount to reach still considerably high evaporation capacity. The final product was fine, good quality powder. Results of the Rotor Mill 2 trials are shown in Table 6. 
     
       
         
           
               
             
               
                 TABLE 6 
               
               
                   
               
               
                 Results of the Rotor Mill 2 trials. 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                   
                 Test 1 
                 Test 2 
                 Test 3 
               
               
                   
                   
               
               
                   
                 Inlet temperature, ° C. 
                 100-108 
                 96 
                 95 
               
               
                   
                 Outlet temperature, ° C. 
                 59-62 
                 42 
                 37 
               
               
                   
                 Initial moisture, % 
                 40 
                 40 
                 40 
               
               
                   
                 Residual moisture, % 
                 3.6 
                 5.8 
                 7.9 
               
               
                   
                 Capacity, kg/h 
                 150 
                 150 
                 150 
               
               
                   
                 Bulk density, kg/m3 
                 290 
                   
                 290 
               
               
                   
                   
               
               
                   
                   
                 Test 4 
                 Test 5 
                 Test 6 
               
               
                   
                   
               
               
                   
                 Inlet temperature 
                 105 
                 102-110 
                 102-110 
               
               
                   
                 Outlet temperature 
                 45 
                 45-47 
                 45-47 
               
               
                   
                 Initial moisture 
                 40 
                 40 
                 40 
               
               
                   
                 Residual moisture 
                 8 
                  5.9-6.35 
                  5.9-6.35 
               
               
                   
                 Capacity 
                 150 
                 150 
                 150 
               
               
                   
                 Bulk density 
                   
                 290 
               
               
                   
                   
               
            
           
         
       
     
     With Rotor mill 1, an effect of temperature on the lignin powdering process was tested. Results of Rotor mill 1 are shown in Table 7. The feed material was fed to the inlet air channel of the Rotor mill 1. Feeding took place by the screw first and further by the rotating dozer. 
     
       
         
           
               
             
               
                 TABLE 7 
               
             
            
               
                   
               
               
                 Results of Rotor mill 1 
               
            
           
           
               
               
               
               
               
            
               
                   
                 Test 1 
                 Test 2 
                 Test 3 
                 Test 4 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Inlet temperature 
                 350 
                 350 
                 350 
                 350 
               
               
                   
                 Outlet temperature 
                 70 
                 65 
                 60 
                 63-65 
               
               
                   
                 Initial moisture 
                 40 
                 40 
                 40 
                  40 
               
               
                   
                 Residual moisture 
                 4.6 
                 5.5 
                 8.9 
                 4.8-6.3 
               
               
                   
                 Capacity 
                 220 
                 297 
                 315 
                 315 
               
               
                   
                   
               
            
           
         
       
     
     Extremely high, 350° C., inlet temperature was used in the process in order to see the effect of the high temperature on the lignin material. At the beginning of the trial, the inlet channel was blocked by the feed material. Therefore, the feed material was pre-milled by the hammer mill. The particle sizes after milling were as follows 39.3%&lt;63 μm, 70%&lt;500 μm, 80.6%&lt;1 mm, 96.5%&lt;3.15 mm, 99.9%&lt;5 mm. No technical problems were seen in the hammer milling. 
     After that the Rotor mill 1 was still blocked after every half an hour&#39;s running. Finally the final product was reported to include big dark and hard lumps as is shown in  FIG. 5   b . Most probably the lignin has stuck onto the hot walls of the machine, melted and formed those lumps. Therefore, the lower temperature, advantageously lower than the melting point of the lignin, should be used. In addition, the material is preferably fed directly to the rotor section. Table 8 shows an effect of the temperature on lignin powder 
     
       
         
           
               
             
               
                 TABLE 8 
               
             
            
               
                   
               
               
                 Effect of the temperature on the lignin powder 
               
            
           
           
               
               
               
               
            
               
                 Property 
                 Rotor mill 2 
                 Rotor mill 1 
                 Rotor mill 3 
               
               
                   
               
               
                 Production, kg/h 
                 150 
                 300 
                 50 
               
               
                 T in, ° C. 
                 100-110 
                 350 
                 170  
               
               
                 T out, ° C. 
                 45-46 
                 60-65 
                 55-65 
               
               
                 Particle size, μm 
                 &lt;50 fine 
                 &lt;50 + lumps 
                 &lt;300  
               
               
                 Pre processing 
                 Crushing screw 
                 Hammer mill 
                 Crushing feeder 
               
               
                 Feed in 
                 To rotor section 
                 To inlet air 
                 To disintegrator 
               
               
                 Runnability 
                 Good 
                 Blocking 
                 Good 
               
               
                   
                   
                 problems, 
               
               
                   
                   
                 lumps 
               
               
                   
               
            
           
         
       
     
     Particle size distribution of lignin and starch is shown in  FIG. 8 . For the pilot scale trial, the particle size distribution of the Rotor mill 3 dried lignin was modified by 100 microns sieve. About 25% of material was rejected and milled further by a ball mill. However, the lignin tended to get stuck onto the ball mill walls. The modified particle size distribution is seen in the  FIG. 9 . Particle size distribution of Rotor mill 1 product is presented in  FIG. 5   a .  FIG. 5   b  shows an example of the rotor section of the rotor mill comprising lignin material. Particle size distribution of Rotor mill 2 product is presented in  FIG. 6 . 
     The sieved particle size distribution measured as mass fractions was as shown in  FIGS. 10   a  and  10   b , wherein wood dust tested in a pilot scale is shown in  FIG. 10   a  and wood dust tested in a production scale is shown in FIG.  10   b . In the pilot scale 6 mm sieve was used in hammer mill, while in production scale trial 10 mm sieve was used. This can be seen as a slightly finer dust in the pilot scale trial. 
     Durability tests were done just after the trials and couple of days after the trials. The pellet durability as a function of additive amount tested in pilot scale trial are shown in  FIG. 11   a  and the pellet durability vs. die temperature tested in the production scale trial is shown in  FIG. 11   b . The die temperature seems to increase durability, which was seen especially in the production scale trials. The durability increases slightly during storing. All in all, both lignin and starch are very comparable binders. 
     In the production scale trials, the A1 quality level 97.5% was reached by both lignin and starch containing pellets, while in the pilot trials, the durability of both starch and lignin containing pellet remained under the A1 quality 97.5%. The reason for this was a 30 degrees higher die temperature in the production machine than in the pilot machine. Additionally the die temperature varied a lot in the pilot machine as can be seen in the  FIG. 11   b.    
     Amount of Sulphur is shown in  FIG. 12   a , and amount of Zinc is shown in  FIG. 12   b . Ash content is shown in  FIG. 13   a  and amounts of Chromium and Copper are shown in  FIG. 13   b.    
     Potassium and Sodium contents are shown in  FIG. 14 . These elements are important for ash melting properties, which were good with both starch and lignin additives. Mixture of nitric acid, hydrogen peroxide and fluorhydric acid was used in the testing. 
     The Pellet Burning tests were also made. The pellets made at 0.5% additive level were analyzed as follows. The lignin-containing pellet had slightly better ash melting properties than starch-containing pellet. All the properties fulfilled the A1 specification. Results are shown in Tables 9 to 11. 
     
       
         
           
               
             
               
                 TABLE 9 
               
             
            
               
                   
               
               
                 Pellet analysis table 1 
               
            
           
           
               
               
               
               
            
               
                   
                 Lignin 
                 Starch 
                   
               
               
                   
                   
               
            
           
           
               
               
               
               
            
               
                 Ash content (550° C.) 
                 0.3 
                 0.3 
                 wt %, d 
               
               
                 Sulphur content 
                 &lt;0.02 
                 &lt;0.02 
                 wt %, d 
               
               
                 Gross calorific value 
                 20.50 
                 20.48 
                 MJ/kg, d 
               
               
                 Net calorific value 
                 19.15 
                 19.13 
                 MJ/kg, d 
               
               
                 Net calorific value 
                 5.319 
                 5.314 
                 MWh/t, d 
               
               
                 Oxygen bomb combustion for 
                 — 
                 — 
               
               
                 halogens 
               
               
                 Cl 
                 0.003 
                 0.003 
                 wt %, d 
               
               
                 Fusibility of ash (oxidizing atm.) 
                 — 
                 — 
               
               
                 Deformation temperature, DT 
                 1350 
                 1310 
                 ° C. 
               
               
                 Sphere temperature, ST 
                 — 
                 1350 
                 ° C. 
               
               
                 Hemisphere temperature, HT 
                 1430 
                 1360 
                 ° C. 
               
               
                 Flow temperature, FT 
                 &gt;1450 
                 1420 
                 ° C. 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 10 
               
             
            
               
                   
               
               
                 Pellet analysis table 2 
               
            
           
           
               
               
               
               
            
               
                   
                 Lignin 
                 Starch 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 Na 
                 46 
                 26 
                 mg/kg, d 
               
               
                   
                 K 
                 440 
                 440 
                 mg/kg, d 
               
               
                   
                 Ca 
                 720 
                 700 
                 mg/kg, d 
               
               
                   
                 Mg 
                 170 
                 170 
                 mg/kg, d 
               
               
                   
                 P 
                 50 
                 52 
                 mg/kg, d 
               
               
                   
                 Al 
                 70 
                 63 
                 mg/kg, d 
               
               
                   
                 Si 
                 350 
                 370 
                 mg/kg, d 
               
               
                   
                 Fe 
                 87 
                 86 
                 mg/kg, d 
               
               
                   
                 Cr 
                 0.74 
                 0.77 
                 mg/kg, d 
               
               
                   
                 Cu 
                 0.74 
                 0.78 
                 mg/kg, d 
               
               
                   
                 Mn 
                 75 
                 76 
                 mg/kg, d 
               
               
                   
                 Ni 
                 0.78 
                 &lt;0.5 
                 mg/kg, d 
               
               
                   
                 Zn 
                 12 
                 9.7 
                 mg/kg, d 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 11 
               
               
                   
               
               
                 Pellet analysis table 3 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                   
                 Trialpoint 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                   
                 4 
                 2 
                 3 
                 10 
                 6 
                 7 
               
               
                 Additive 
                 Spec 
                 0% 
                 S 0.5% 
                 L 0.5% 
                 S 0.9% 
                 L 1% 
                 L 0.4% 
               
               
                   
               
               
                 Sulphur, S, ICP % 
                 0.03 
                 0.0068 
                 0.0070 
                 0.0158 
                 0.0068 
                 0.0279 
                 0.0153 
               
               
                 Sulphur, S, ICP mg/kg 
                 300 
                 68 
                 70.2 
                 158 
                 68.3 
                 279 
                 153 
               
               
                 Potassium, K, ICP mg/kg 
                   
                 347 
                 350 
                 339 
                 343 
                 348 
                 347 
               
               
                 Sodium, Na, ICP mg/kg 
                   
                 18.9 
                 30.1 
                 29.8 
                 22.1 
                 45.2 
                 31.2 
               
               
                 Zinc, Zn, ICP mg/kg 
                 100 
                 9.1 
                 8.23 
                 8.6 
                 8.26 
                 8.66 
                 9.15 
               
               
                 Chromium, Cr, ICP mg/kg 
                 10 
                 0.58 
                 0.402 
                 0.414 
                 0.638 
                 0.457 
                 0.48 
               
               
                 Copper, Cu, ICP mg/kg 
                 10 
                 0.707 
                 0.662 
                 0.65 
                 0.68 
                 0.642 
                 0.715 
               
               
                 Arsenic, As, ICP mg/kg 
                 1 
                 &lt;0.01 
                 &lt;0.01 
                 &lt;0.01 
                 &lt;0.01 
                 &lt;0.01 
                 &lt;0.01 
               
               
                 Cadmium, Cd, ICP mg/kg 
                 0.5 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 Nickel, Ni, ICP mg/kg 
                 10 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 Lead, Pb, ICP mg/kg 
                 10 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 Ash 700° C. (black liquer) % 
                 0.7 
                 0.4 
                 0.4 
                 0.4 
                 0.3 
                 0.4 
                 0.4 
               
               
                 Total dry content 60° C. % 
                   
                 95.9 
                 96.1 
                 96.6 
                 95.8 
                 96.2 
                 96.3 
               
               
                   
               
            
           
           
               
               
               
            
               
                   
                 Trialpoint 
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                   
                 8 
                 9 
                 5 
                 1 
                 Lignin 
               
               
                   
                 Additive 
                 L 0.5% 
                 S 0.6% 
                 0% 
                 0% 
                 Lig 
               
               
                   
                   
               
               
                   
                 Sulphur, S, ICP % 
                 0.0155 
                 0.0066 
                 0.0072 
                 0.0081 
                 1.9596 
               
               
                   
                 Sulphur, S, ICP mg/kg 
                 155 
                 66.3 
                 71.7 
                 80.5 
                 19596 
               
               
                   
                 Potassium, K, ICP mg/kg 
                 346 
                 344 
                 348 
                 350 
                 373 
               
               
                   
                 Sodium, Na, ICP mg/kg 
                 32.3 
                 21.7 
                 21.1 
                 57.7 
                 1879 
               
               
                   
                 Zinc, Zn, ICP mg/kg 
                 8.64 
                 8.29 
                 8.77 
                 8.47 
                 60.4 
               
               
                   
                 Chromium, Cr, ICP mg/kg 
                 0.471 
                 0.369 
                 0.504 
                 0.517 
                 1.32 
               
               
                   
                 Copper, Cu, ICP mg/kg 
                 0.752 
                 0.667 
                 0.743 
                 0.774 
                 2.88 
               
               
                   
                 Arsenic, As, ICP mg/kg 
                 &lt;0.01 
                 &lt;0.01 
                 &lt;0.01 
                 &lt;0.01 
                 &lt;0.01 
               
               
                   
                 Cadmium, Cd, ICP mg/kg 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                   
                 Nickel, Ni, ICP mg/kg 
                 0 
                 0 
                 0 
                 0 
                 0.561 
               
               
                   
                 Lead, Pb, ICP mg/kg 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                   
                 Ash 700° C. (black liquer) % 
                 0.3 
                 0.4 
                 0.4 
                 0.4 
                 0.9 
               
               
                   
                 Total dry content 60° C. % 
                 96.5 
                 96.4 
                 95.4 
                 95.6 
                 92.7 
               
               
                   
                   
               
            
           
         
       
     
     According to the burnability analyses and pellet durability tests the lignin powder can be used as an additive. Moreover, native starch pellet additive can be replaced by lignin. Further, the production scale trial showed clearly the potential of dry lignin powder as an additive in wood pellets. By the 0.59% addition the A1 durability level 97.5% was reached. 
     One skilled in the art readily understands that the different embodiments of the invention may have applications in environments where optimization of processing lignin is desired. It is also obvious that the present invention is not limited solely to the above-presented embodiments, but it can be modified within the scope of the appended claims.