The mobile pellet plant

Bringing bulky biomass to market in an efficient way is one of the biggest logistical problems for the development of the green fuel sector. Plants growing on a plot of land act like a very low-cost solar energy collector. As they grow, crops convert sunlight and CO2 into biomass, which stores the solar energy. But crops like tall grasses or residues like hay and sawdust are rather bulky: compared to oil or coal, they take up much more space to pack a similar amount of energy.

For this reason, biomass is first converted into a fuel with a higher energy density before it is transported to market. Several concepts exist aimed at overcoming this problem: biomass can either be collected and transformed into an energy dense bio-oil (pyrolysis oil) in decentralised plants, after which the oil is transported to more centrally located "biorefineries" where it is turned into marketable products like green gasoline and diesel fuels, or building blocks for green chemistry. Another, more simple concept consists of densifying bulky biomass into pellets or fuel briquettes. Such pellets can then be used in power plants (in combination with coal or as such) as well as in household pellet stoves and small combined heat-and-power systems as an alternative to heating oil.

Over the past years, the biomass pellet market in the EU and to a lesser extent in the US has skyrocketed because the fuel is considerably less costly than heating oil. Whereas the NYMEX heating oil price this month averaged around US$1.86 per gallon (US$0.49/€0.36 per liter), a ton of pellets stood at around US$150 per ton. With a heating value equivalent to around 17MJ/kg versus 35MJ/liter for heating oil, the cost of a gallon of heating oil equivalent energy contained in pellets is around US$1.25 (US$0.33/€0.24 per liter), a considerable difference. Heating oil prices topped US$ 2.25/gallon last year.

The favorable economics have seduced several entrepreneurs to step into the opportunity. Large scale pellet mills are under construction in the US (earlier post), where producers eye exports to the EU, in South Africa (earlier post) and in the Republic of Congo, whereas the already well established European industry is booming (overview of the market for solid biofuels in the EU).

However, smaller and creative players are entering the arena too. An entrepreneurial family in Northeastern Pennsylvania , for example, has begun to experiment with an concept it thinks will make a difference: a mobile pelletiser. The machine can be brought to the field and transform grasses or agricultural residues into market-ready solid biofuels. The Reggie family grows switchgrass as the feedstock on its own land. The Reggies feel the concept will preserve farmland, create wildlife habitat and lessen America's dependence on foreign oil.

Every day, Leonard Reggie and his two sons, Bryan and Adam, work on fabricating, welding and building the machine that will transform common switchgrass into an affordable and abundant heat source. They organised their efforts in a company called BHS Energy LLC. Although the design and construction of the mobile pellet mill are complex, the concept is simple: bales of switchgrass are placed in one end, ground up and compressed into half-inch pellets that resemble rabbit feed:
bioenergy :: biofuels :: energy :: sustainability :: heating oil ::switchgrass :: pelletiser :: pellets :: biomass ::

When burned, the pellets don’t release carbon into the atmosphere and 5 tons can heat an average home for a year, Bryan said. Simply put, the Reggies believe they are onto something big, and all three have left their jobs to work full time on the endeavor. “This is totally sustainable,” Leonard said. “It can be done indefinitely into the future without harming the environment, and it’s probably the least expensive option to replace heating oil.”

Leonard came up with the idea to pelletize biomass (renewable, organic matter) and use it for heat several years ago. He was in business making cabinets when things began to slow down and he looked for something else. Shortly after Leonard conceived the plan, energy costs plummeted and he abandoned the idea. In 2005, oil prices skyrocketed and, with the encouragement of his two sons, Leonard rekindled the biomass idea.

Adam, who graduated from Penn State Harrisburg with a degree in mechanical engineering technology, left his job with Specialty Defense in Dunmore to join the family business. Bryan, an electrical engineering graduate from Penn State Erie, left his career with Lockheed Martin last summer and the trio formed BHS Energy.

Today, Leonard and his two sons spend their days on the farm, planting switchgrass or building the pellet mill in their spacious workshop. “I actually enjoy getting up and going to work for a change,” Adam said. “I always wanted to do engineering and work for myself.”

They hope to have the machine ready to go this summer, and local farmers have already expressed interest, they said. “There are a lot of farms here that haven’t been used in years, and we’re trying to lease their land to grow switchgrass,” Bryan said. “It’s a good way for people who own land to get money to pay their taxes.”

Because the pelletizer can be hauled to the farm, farmers can raise their own switchgrass and sell the pellets. Leonard said a farmer can make an annual profit of $500 per acre, more than any other crop. The pelletizer can be operated with a 65-horsepower tractor in the field, he said, so farmers don’t have to haul the bales into a barn.

Another benefit, he said, is the switchgrass, which grows 5 to 6 feet high, provides for excellent wildlife habitat and only needs to be planted once. “This is a native grass that grew in the prairies,” Leonard said. “It can produce a yield of 3 to 5 tons per acre every year, and it requires minimal fertilizer and no chemicals to control weeds.”

The Reggies don’t expect everyone to take their word on the benefits of switchgrass pellets, so they are going to practice what they preach. Adam said their barn is filled with switchgrass bales that will be used to heat their house, shop and barn this winter. They will also plant their entire 18-acre farm in switchgrass.

The estimated cost of the pelletizer will be around $60,000, and the Reggies are exploring the possibility of renting machines. They hope to have units ready to sell this July, and intend to produce two to four per month. “Our goal is to give people the ability to produce their own energy,” Bryan said. “You can’t drill for your own oil, but you can grow switchgrass.”

More information:
Times Leader: "Family sees hot promise in pellets" - April 26, 2007.

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Plants do not emit methane

A recent study [*abstract] by Keppler and collegues in Nature suggested that terrestrial plants may be a global source of the potent greenhouse gas methane (CH4), making plants substantial contributors to the annual global methane budget. This controversial finding and the resulting commotion in the scientific community triggered a consortium of Dutch scientists to re-examine this in an independent study. Reporting in New Phytologist, Tom Dueck and colleagues present their results and conclude that methane emissions from plants are negligible and do not contribute to global climate change. The findings are crucial for those striving towards the creation of a global plant-based "bioeconomy" that substitites for petroleum products.

Being a potent greenhouse gas, methane emissions are controlled by humans and international rules, but there exists a natural methane cycle, driven by methanogenic microbes that thrive in anaerobic conditions (in the absence of air), such as in the stomachs of ruminants, the soils of swamps, in landfills, rice paddies or water reservoirs. A carbon cycle, based on one-carbon compounds, is taking place in the sediments and overlaying water of such freshwater environments. The anoxic sediments harbor archaea, which produce methane as a byproduct of their energy metabolism. The methane rises from the sediment and moves into the zone above it (image, click to enlarge). The vast bulk of methane enters the atmosphere because of this type of microbial action.

Terrestrial plants grow in an aerobic environment, that is in the open air. For this reason Keppler's finding that ordinary vegetation emits methane too came as a surprise to the scientific community. The Dutch consortium of researchers decided to revisit the issue, by bringing together a unique combination of expertise and facilities enabling the design and execution of a novel experiment. Plants were grown in a facility containing atmospheric carbon dioxide almost exclusively with a heavy form of carbon (13C). This makes the carbon released from the plants relatively easy to detect. Thus, if plants are able to emit methane, it will contain the heavy carbon isotope and can be detected against the background of lighter carbon molecules in the air:

Six plant species were grown in a 13C-carbon dioxide atmosphere, saturating the plants with heavy carbon: Ocimum basilicum L. (basil), Triticum aestivum L. (wheat), Zea mays L. (maize), Salvia officinalis L. (sage), Lycopersicon esculentum Miller (tomato), and Oenothera biennis L. (common evening primrose) - the first three of which were also used by Keppler. 13C-Methane emission was measured under controlled, but natural conditions with a photo-acoustic laser technique. This technique is so sensitive that the scientists are able to measure the carbon dioxide in the breath of small insects like ants:
bioenergy :: biofuels :: energy :: sustainability :: greenhouse gas :: methane :: anaerobic :: aerobic :: vegetation :: biomass ::

Even with this state-of-the-art technique, the measured emission rates were so close to the detection limit that they did not statistically differ from zero (graph, click to enlarge). To our knowledge this is the first independent test which has been published since the controversy last year.

Conscious of the fact that a small amount of plant material might only result in small amounts of methane, the researchers sampled the ‘heavy’ methane in the air in which a large amount of plants were growing. Again, the measured methane emissions were neglible. Thus these plant specialists conclude that there is no reason to reassess the mitigation potential of plants. The researchers stress that questions still remain and that the gap in the global methane budget needs to be properly addressed.

The Dutch consortium included scientists from Plant Research International, IsoLife and Plant Dynamics in Wageningen, Utrecht University, and the Radboud University in Nijmegen.


Graph: Long-term steady-state methane emissions by vegetation. (a) Measured 13C-methane emissions (mean ± SE) by a mixture of 13C-enriched plants in the ESPAS (Experimental Soil Plant Atmosphere System) growth chamber under controlled steady-state conditions. Plant biomass increased from 289 (day 0) to 374 (day 6) g dry weight during the experiment (n = 3), and the emissions are given at the median of the time for accumulated emission. (b) Measured (solid line) and predicted (dashed lines) accumulation of methane by 13C-enriched plants in the ESPAS growth chamber. Measured methane concentrations (solid line, closed squares), and methane concentrations predicted from our continuous-flow experiment (Table 3; 21 ng g-1 h-1, dashed line, open triangles), or from Keppler et al. (2006: ‘sunlight’, 374 ng g-1 h-1, dot-dashed line, closed diamond; ‘no sun’, 119 ng g-1 h-1, dotted line, open squares). Courtesy: Nature.

More information:
Keppler F, Hamilton JT, Brass M, Rockmann T. "Methane emissions from terrestrial plants under aerobic conditions", Nature 439, 2006 Jan 12;439(7073):187-91.

Tom A. Dueck, Ries de Visser, Hendrik Poorter, Stefan Persijn, Antonie Gorissen, Willem de Visser, Ad Schapendonk, Jan Verhagen, Jan Snel, Frans J. M. Harren, Anthony K. Y. Ngai, Francel Verstappen, Harro Bouwmeester, Laurentius A. C. J. Voesenek and Adrie van der Werf, "No evidence for substantial aerobic methane emission by terrestrial plants: A 13C-labelling approach", New Phytologist. Article published online: 27-April-2007, doi:10.1111/j.1469-8137.2007.02103.x

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