Biofuels: Is black liquor the key to a brighter future for the pulp industry?

It is a long way from a pulp mill to a Volvo truck, but if all goes according to plan, by early 2010 a small fleet of Volvo trucks will be running in Sweden powered by a biofuel called BioDME.

The source of the fuel: Black liquor, a by-product of the pulping process. Black liquor is said to be the largest, readily available, concentrated form of biomass on Earth. Through more efficient extraction of the hydrocarbon value of black liquor, pulp mills can be converted to bio-refineries that can make both papermaking fibers as well as syngas for fuels. A massive BioDME project financed heavily by both the Swedish Energy Agency and the EU is underway in Sweden to do just that.


Hugh O’Brian

This is not a normal story about the tissue business. In fact, in some ways it is hardly related to the tissue making process at all. On the other hand, it has everything to do with issues that are today vitally important for all tissue companies: Fiber Supply, Energy Sources, Greenhouse Gas Emissions, and last but certainly not least, Improved Economic Payback. In fact, there are so many exciting aspects to this story that it is hard to know what to start with.

A recent visit to a very interesting project site in northern Sweden got me extremely enthused about the subject of black liquor gasification for production of transportation fuels. I realize that it is a mouthful for many people, even some of the highly technical people that read this magazine on a regular basis, but it isn’t really too complicated. Black liquor gasification (BLG) for production of transportation fuels is a process that offers so many advantages that it should be of enormous interest not only to the technical experts but also to the executives and finance guys in the pulp and paper industry who are looking for new, larger revenue streams from their pulp mill operations. How many pulp and paper CEOs and CFOs know what black liquor gasification is? Not many I would guess. A key player in the BLG area is a Swedish company called Chemrec, which holds more than a hundred patents in the area of gasification, gas cleaning and pulp mill integration aspects. The company and its predecessor companies have been working with black liquor gasification for more than 20 years. Recent new advances in the process technology, as well as steep increases in fossil-based energy costs, combined with a global concern about CO2 emissions, have led to vastly increased interest in the technology today. Poor profitability for much of the pulp and paper industry over a long period time has also been part of the equation. “The main point we want to get across,” says Jonas Rudberg, CEO at Chemrec, “is that a pulp mill can increase its cash flow by 30 to 50% by producing fuels from black liquor. That can increase the return on capital from a typical 5% in a pulp mill to perhaps 15% in the new biorefinery, with a payback time of less than four years. So it can turn a marginally profitable pulp mill today, which may be fighting for its survival, into a viable, efficient biorefinery making fibers and high-value fuels from renewable raw materials with a very low carbon footprint.” (fig. 1).


A SHORT LESSON IN WOOD AND PULPING CHEMISTRY. Before we go further, it might be worthwhile to talk a bit about the chemistry involved. Very basically, wood is made up of white cellulosic fibers, hemi-cellulose (complex sugars) and black lignin, which acts as the glue holding those fibers together. This combination of white and black materials gives wood the familiar brown or tan color that we all recognize, (fig. 2). Pulping is a separation process in which a highly alkaline chemical solution, called white liquor, is cooked with wood chips at high temperature in a high-pressure digester. This causes the black glue-like lignin to break up and dissolve. The white liquor thus becomes black liquor, which is a solution of water, lignin, hemi-cellulose and the pulping chemicals. Lignin, as defined on Wikipedia, is a complex chemical compound most commonly derived from wood and an integral part of the secondary cell walls of plants. The term comes from the Latin word lignum, meaning wood. Lignin is one of the most abundant organic polymers on Earth, superseded only by cellulose, employing 30% of non-fossil organic carbon and constituting from a quarter to a third of the dry mass of wood. As a biopolymer, lignin is unusual because of its heterogeneity and lack of a defined primary structure. Thus lignin is actually not one compound but many. In their natural unprocessed form, they are so complex that none of them has ever been completely defined chemically. All lignins are intricate, amorphous, three-dimensional polymers that have in common a phenylpropane structure, that is, a benzene ring with a tail of three carbons. It is thought that they may have molecular weights that may reach 15,000 or more, a sign of their complexity. Since the chemical pulping process was invented in the 1800s, lignin has usually been seen as a pulping by-product for which no real valuable use has been discovered. That perception might be about to change.


LOOKING FOR HIGHER EFFICIENCY. Therefore, there are two main process streams coming out of the pulp mill: cellulose fibers and black liquor. The black liquor, which is mainly lignin and hemi-cellulose, is a thick, viscous, oil-like material with high hydrocarbon content that has traditionally been burned in a recovery boiler to generate heat and electricity to power the pulp mill. The recovery boiler is actually a low-efficiency operation, from an energy point of view, which has been used more for convenience and for recycling of cooking chemicals rather than for efficient extraction of heat value. However, even though the efficiency is low, the resulting heat is still a highly valued energy stream, producing power and heat for the pulp and paper mills, making many of them self-sufficient in energy. Excess mill heat is also often used to heat homes and buildings in local surrounding communities, (fig. 3). In black liquor gasification (fig. 4 ), black liquor is injected in an atomized form into a high pressure, high temperature reactor with either oxygen or air as the combustion medium. The organic materials are gasified into raw synthetic gas (syngas) while the inorganic solids such as sodium and potassium fall to the bottom to be returned to the pulp mill, recycled as cooking chemicals.


BLACK LIQUOR IS IDEAL. Black liquor has many inherent advantages that make it an excellent biofuel source, says Patrik Lownertz, VP of Marketing at Chemrec. “Black liquor is liquid biomass with properties that make it uniquely suitable for gasification. As a liquid it is easy to feed to a pressurized gasifier and it can be atomized to fine droplets for rapid gasification rates. In addition, the sodium and potassium content of black liquor make it highly reactive, speeding up the process.” “The resulting gasification in an entrained flow, high-temperature mode can then give full carbon conversion with no tar formation and low methane formation. BLG is quite simply the most efficient route from biomass to automotive fuel. In addition, for pulp mills that are limited in production due to the recovery boiler, BLG can kill two birds with one stone: allow production of valuable renewable fuels and increase pulping chemical recovery capacity.”

(See the separate boxed item about the BLG system at Weyerhaeuser’s New Bern, North Carolina, USA pulp mill where a BLG system has been used to give added recovery capacity.)


FOUR-YEAR 28 MILLION EURO PROJECT IN PITEA. To bring the Volvo truck and the pulp mill fuel closer together, a real live biofuels plant is now being constructed in Piteå, Sweden, alongside the Smurfit Kappa Kraftliner (SKK) mill there, as shown in Figure 5. The BioDME project, supported by the EU’s 7th framework programme (FP7) and The Swedish Energy Agency, has as its overall project objective to “demonstrate production of environmentally optimized synthetic biofuel from lignocellulosic biomass on an industrial scale.” The final output of this demonstration is dimethylether (DME) produced from black liquor through the production of clean synthesis gas and a final fuel synthesis step. In order to check technical standards, commercial possibilities and engine compatibilities, the BioDME will be tested in a fleet consisting of 14 Volvo trucks. Research, development and demonstration will be made of improved fuel production systems and conversion technologies for the sustainable production and supply chains of DME from biomass. The planned timeframe for the BioDME project is 2008 until 2012, at which time an evaluation will be made as to whether to go further.


PILOT PLANT RUNNING FULL TIME MAKING SYNGAS. Chemrec has been running an oxygen-blown high pressure gasifier development plant, called DP1, at the mill since 2005. In late 2007 it started running the DP1 line on a 24-hour-a-day, 365-days-a-year basis to prove that the equipment and technology can work on a continuous basis.

The raw material input is black liquor from Smurfit Kappa, amounting to about 1% of the mill’s total black liquor or 20 tons per day of dry solids. It is important to note that, today, this line is only making raw syngas that now is simply burned in a flare above the plant. There are two major steps in the process chain, the first being from black liquor to syngas, and the second being from syngas to DME. To turn this raw syngas into DME that can be used to fuel vehicles, a synthesizing plant must be built. That will be done by Chemrec and a Danish company called Haldor Topsøe as part of the BioDME project.


PULP INDUSTRY IN A UNIQUE POSITION. Speaking in Piteå last September at the kickoff of the BioDME project, Smurfit Kappa CEO Gary McGann described the unique position that the pulp industry has in the question of energy from renewable materials. “The pulp and paper industry has many advantages here,” said McGann. “We know the chemistry and properties of the feedstock, black liquor, very well. We already control the supply to our large industrial infrastructure sites near the forests and the pulp mills are very efficient at separating the lignin from the cellulose. In addition, we also have important operations such as steam and power generation, chemical preparation and effluent treatment onsite. Finally we have the rail, road, sea transport routes close by. Our mills already use some of the by-products, and can today produce fuels from the likes of tall oil.” “If we go a step further down the biorefinery road, we can envisage transforming wood into fuels, chemicals and other substances that also currently come from oil. As it stands today we can make this change via modular and flexible developments, meaning we don’t have to do it in one big step. We consider this to be a very real and exciting possibility to transform our mills into integrated forest biomass conversion plants making energy, chemicals and transportation fuel as well as paper.”


COORDINATED BY VOLVO. The Volvo Group is the coordinator for the BioDME project, with the project partners representing all the various industrial sectors necessary to introduce a new fuel. In addition to Volvo and Chemrec, other partners are Delphi, ETC, Haldor Topsøe, Preem and Total. As far as the tasks, Chemrec and Haldor Topsøe will construct the DME plant, gasoline company Preem will implement the DME distribution and build filling stations, while Volvo will demonstrate DME technology for heavy vehicles in a field test. ETC will evaluate performance characteristics in the pilot plant, Delphi is to deliver fuel injection equipment for the truck engines and Total will work on fuel and lube oil specifications. Volvo’s Per Salomonsson is the overall project coordinator. The objective, he explains, is to demonstrate the entire technology chain, from biomass to trucks powered by DME fuel, including fuel distribution and filling stations. At this point, he says he is optimistic about BioDME. “Our analysis shows that BioDME from black liquor is the best fuel when you look at it on an overall ‘well-to-wheel’ basis, (fig. 6). Black liquor is a very concentrated, available biomass source which can be gasified very efficiently. There are other alternative sources of biomass but black liquor is ahead of the alternatives. In addition, BioDME produces no soot during combustion, which is also an advantage.”

Support for the BioDME project comes from the top of Volvo. “Already more than a year ago,” says Volvo Group CEO Leif Johansson, “Volvo presented seven trucks that could all be operated carbon-dioxide neutral. The BioDME project is an example of what the next step could look like and illustrates the possibilities of producing renewable fuel on a major scale.” “From the holistic viewpoint, we see DME as one of the most efficient renewable fuels, an alternative with extremely low exhaust emissions. If the fuel is produced from biomass such as black liquor from the pulp industry, DME is carbon dioxide-neutral. With modest changes, a diesel engine can run on DME.” According to Volvo’s estimates, BioDME has excellent potential as road transport fuel, with the possibility to replace up to 25% of the transport fuel presently used in Sweden. In Finland, a country that has many pulp mills but a small population, the figure is an amazing 50%. In addition, CO2 emissions by BioDME are much lower than the first generation biofuels such as ethanol and bio-diesel (Fig. 7). No wonder the energy-poor, environmentally-conscious EU is giving a strong backing to the BioDME pilot plant project in Piteå.


NEXT STEP WOULD BE A BIG SCALE-UP. So that is where the BioDME project is today. A little more than a year from now, by early 2010, the pilot plant should be up and running, making DME which is then handled and distributed in a way similar to LPG and used by Volvo trucks at various points throughout Sweden. But the Piteå technical demonstration plant and project is really only the beginning. The next steps will come as pulp mills scale up to full scale biorefineries. This will of course require large capital expenditures in the order of USD 400 million but the economics look very positive, depending certainly on the price of oil. By extracting the hydrocarbon value of lignin and hemicelluoses, it is estimated that the pulp industry has the potential to replace 225 million barrels of oil a year. The driving forces are very strong, considering the energy shortage facing the world, as well as the environmental threat of increasing CO2 emissions. We will continue following this BioDME story and keep you informed as it progresses. •


What is DME?


DME, Di-methyl-ether, has the potential to become a highly competitive renewable alternative to today’s fossil fuels. It is a simple chemical compound (fig. 8) with a short carbon chain, which leads to very low particulate emissions during combustion. This fuel also produces low emissions of nitrogen oxides. DME can be produced from fossil sources, such as natural gas, and also from various types of biomass, which makes the fuel carbon dioxide-neutral. DME is classified as less dangerous to health and the environment than today’s diesel and petrol. It is a non-toxic chemical that is already used today as propellant gas in spray cans.


DME: Di-Methyl-Ether Properties

• Oxygenate, no C-C bonds, high H/C ratio, high cetane number

• Non-toxic

• Non-carcinogenic

• Rapid degradation in ambient air

• Very low exhaust emissions (soot free)

• Non-Greenhouse Gas, no impact on ozone layer

• Handles like LPG (liquid at 5 bars)

• High well-to-wheel efficiency

• Used as propellant in spray cans

• Available for diesel engines and fuel cells


New Bern gasifier running well

Chemrec’s first commercial installation of the gasification technology is at Weyerhaeuser’s New Bern, North Carolina, pulp mill in the USA. The New Bern Booster gasifier, which is not meant to make DME but only adds to the recovery capacity at the mill, has now had more than 50,000 hours of full-scale operation. It is a commercial atmospheric, air-blown gasifier that is able to boost recovery capacity by about 300 tons of black liquor solids per day, or about 15% of total mill recovery capacity. It is seen as having served a very important role in the development of refractory systems and other components. Originally installed in 1996, the equipment required several modifications, especially for the ceramic refractory materials surrounding the containment vessel where the gasification reaction takes place. This, says Jonas Rudberg, is part of the development process. “This is a very harsh process, taking place at temperatures of around 1,000°C, at high pressures and a very alkaline pH of 13. So it is naturally very tough on the materials.

However, we worked to find the right ceramics to make it function well and now we are pleased that it has been very efficient. In New Bern we have now been running at greater than 94% uptime for the past 12 months with no problems.”

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