By Graeme Rodden, Executive Editor, Pulp & Paper International magazine
BRUSSELS,
Jan. 17, 2012
(RISI) -
In August 2007, PPI presented news about an exciting new biofuel development taking place at Wermland Paper's mill in Backhammars, Sweden, in conjunction with STFI-Packforsk. Since, Backhammars has been bought by Nordic Paper and STFI has evolved into Innventia. However, the biofuel development, LignoBoost, is going stronger than ever and in 2008, the technology was purchased by Metso. Simply stated, LignoBoost is a fuel made from lignin with a high dry solids content that is taken from a pulp mill's evaporators. LignoBoost even has its own predecessors. LignoTech began producing lignin at Backhammars in 1994 but its use then was for specialty chemicals.
The plant is now producing 1.2 tonnes/hr of LignoBoost. It uses about 10% of the mill's black liquor and from this, can take out about 70% of the lignin content. Lignin content of a tree can vary from 510 kg/tonne of pulp for spruce to 340 kg/tonne of pulp for birch and eucalyptus.
Anders Larsson, sales and marketing manager for LignoBoost Technology, says Metso purchased the technology as a "new service product". It can help mills increase capacity and save energy. It fits well with our product line across the recovery island."
Although Metso owns the patented technology, Innventia is still the owner of the Backhammars facility. The two have a long-term R&D agreement regarding LignoBoost.
Larsson explains that new installations can be a standalone unit installed in parallel with a pulp mill's evaporators. "You just need a few tie-ins (about eight). It can be built while the mill is still operating."
A typical installation would have two or three Vertical Plate Pressure Filters (VPA, the "heart" of the process, according to Larsson), precipitation equipment, process pumps and tanks, piping and valves. The VPAs are built by Metso Minerals and have been used in the mining and energy sectors. The presses at Backhammars have 24 chambers but presses can be built to hold up to 60 chambers. To handle the H2S produced in the LignoBoost plant, a scrubber using caustic is installed.
The process removes black liquor at 40% dryness. Carbon dioxide and gases from other pulp processing stages are added. The CO2 lowers the pH from 13 to about 10. Lignin starts to precipitate at that level. The slurry is then sent to a filter press where the rejects (lignin and spent black liquor) are separated and returned to the recovery process. As lignin wash water is returned to the process, the load to the evaporators is increased by about 2-3 m3/tone of lignin extracted.
The accepts (in powder form, 65% dryness) are conveyed to an acidification tank where H2SO4 is added, lowering the pH to 2-2.5. This changes the ion strength of the components making it possible to wash the lignin. The material is sent to another VPA to remove the sodium. The lignin is removed at about 70% dryness. The LignoBoost is then ready to be transported.
Lignin fuel can be used in a number of applications. When dry, as described, it can be used to fuel lime kilns. A ring dryer using the lime kiln flue gas as a fuel will be needed to further dry the LignoBoost. It can also be mixed with oil in a disperger to fuel a kiln. It can also be mixed with heavy fuel oil. Up to 40% dry weight lignin fuel can be added to oils.
Moist LignoBoost cakes can be co-combusted with biofuels or coal. Moist LignoBoost can be used as an additive in biofuel pellets. As a slurry, it can be added to fossil fuel, tall oil, tall oil pitch or glycerine.
The fuel has a high heat value, 25-26.5 MJ/kg. The fuel contains 64-66% carbon, 26-27.5% oxygen, 5.7-5.8% hydrogen, 0.1% nitrogen 1-3% sulfur (typically 2-2.5%) and 0.1-0,3% sodium.
There is an ongoing project, the LignoFuel Programme, in which lignin fuel is being evaluated in various applications. It began in 2009 and is scheduled to go through to the end of 2012. Innventia is coordinating the research with various partners such as Metso and the Swedish energy body.
The program grew out of a trial at Södra's Mönsterås mill in Sweden. Lignin fuel could replace 50-100% of oil in the lime kiln. Operation was stable and continuous using a standard burner and feed system. There were no plugging problems. Temperature levels were the same as in traditional operation and lime quality was not affected.
There were higher emissions and higher sulfur content when a high percentage of LignoBoost was used. But the sulfur came from the process, not the LignoBoost. As mentioned, this problem can be solved with a scrubber.
More added value products
As can be seen by the Mönsterås test, the first applications of LignoBoost are as a fuel but in the future there are plans to turn to more value-added products. Lignin can be used in phenols, carbon fiber, as a binder or for soil improvement.
Innventia will test various mills' black liquor samples to determine the compounds they contain. A test skid containing a small LignoBoost demonstration plant can then be sent to the mill.
What are the advantages for a mill? If it wants to increase production, the process can reduce the thermal load to the recovery boiler. If lignin corresponding to 25% of the black liquor's heat value is removed, then the mill can increase pulp production by 25%.
Payback can be very short, adds Larsson; it can depend on the price of pulp.
Black liquor viscosity will decrease with lignin extraction. There will also be a small effect on the boiling point. Evaporator capacity will be unchanged or mills may see a slight improvement. The point of crystallization (scaling) may change due to the change in inorganic composition.
A mill can also reduce its fossil fuel consumption by substituting LignoBoost. Or, it can use the lignin fuel as an extra revenue stream, selling it as fuel or to be used in other products.
There used to be a saying in the industry about being able to make anything out of lignin but money. That should be about to change.
| |
Formed to provide a link between academic research and industrial application, Innventia grew out of the Swedish pulp and paper research institution, STFI, based in Stockholm. It now focuses on implementation of R&D ideas, says Rufus Ziesig, research assistant, energy and mill systems, business area biorefining. “We deal with suppliers such as Metso, Voith, ABB and even Ericsson as well as the major pulp and paper producers.”
As well as pulp and paper, it covers such sectors as packaging, graphic media, new materials and biorefining. It is majority owned by the Scandinavian pulp and paper producers the Swedish government, the STFI association and Packforst (packaging body) also holding shares.
It now has 270 employees and in 2010, had sales 37 million euros and can serve customers worldwide. Besides the Backhammars plant, it also has facilities in Norway and the UK. |
Pulp & Paper International is FREE to qualified subscribers. Click here to find out more.
