Dynamotive begins construction of modular fast-pyrolysis plant in Ontario

Each year, the world's agriculture and forestry sectors generate vast amounts of biomass residues, worth several million barrels of oil. There are different ways to convert this biomass into liquid biofuels: either by breaking down the lignocellulose contained in it with specially designed enzymes (cellulose ethanol), or by destroying it in a fast-pyrolysis process to obtain pyrolysis oil (bio-oil). Alternatively, the biomass can also be turned into very clean, synthetic biofuels, by gasifying it and then liquefying the gas via Fischer-Tropsch synthesis.

Each of these bioconversion technologies has its advantages and drawbacks and most of them are still in an experimental phase (especially the production of cellulosic ethanol). However, Dynamotive Energy Systems and Evolution Biofuels, have partnered and are now actually building a modular, decentralised fast-pyrolysis plant that will convert wood residues into bio-oil. The 200 tonne per day plant will be located in Guelph, Ontario.

The idea behind the concept can be found in other companies and is easy to understand: make the plants modular, so you can bring the plant to the biomass source, instead of bringing the biomass to the plant (earlier post).

Biomass residues from agriculture (such as straw, stems, cobs) and forestry (wood chips, bark, sawdust) are bulky. This means you would waste a lot of energy in gathering and transporting them over long distances to a centralised plant. By making the conversion plant smaller and by locating it near the feedstock, you can densify the residues into a substance with a much higher energy density, in this case, bio-oil (pyrolysis oil). This raw fuel contains 12 times more energy than the bulky biomass, which allows you to transport it over much larger distances (to a centralised refinery).

The whole philosophy of fabrication and construction is modular to minimize on-site activities and allow for the rapid deployment of plants. We have used advanced modeling and fabrication methods to achieve this flexibility. BioOil plants will be quickly deployed given their modular nature and will have the advantage of being located right where the biomass sources are. With an energy density 12 times greater than an original wood residue, it means the BioOil can be transported economically over very large distances. Larry Herman, President of Evolution Biofuels

The modular plant consists of eight modules that are transported in and assembled on site in a relatively quick way. During this assembly phase, biomass operations are already underway at the site. It is estimated that 3,000 tonnes of clean recycled wood has been received and that about 15,000 tonnes of feedstock will be on site in readiness for the start-up early next year.

China's potential
This model and its technology - being developed by several companies (earlier post) - is attracting great attention outside the West, where biomass waste resources are abundant and where dependence on costly energy is high. Most notably in China:
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China ’s National Development and Reform Commission (‘NDRC’), a management agency under the State Council which studies and formulates policies for economic and social development, recommended after a year long review, the promotion of fast-pyrolysis of biomass residues as a means to increasing energy security and independence.

The report concluded that: “There is strong potential for using bio-oil to substitute fuel oil. Analysis shows that if one-third of China’s agricultural and forestry waste could be used to produce bio-oil, 15 million tons of fuel oil could be substituted, and half of imported fuel oil by China could be theoretically displaced.”

The process and the product
So how does the fast-pyrolysis process (also known as dry distillation) work? And what kind of products are obtained from it?

Prepared feedstock (<10% moisture and 1-2 mm particle size) is fed into a reactor (often a bubbling fluid-bed reactor), which is then heated to 450–500 °C in the absence of oxygen (some systems use higher temperatures, which decreases conversion efficiency). The feedstock instantly flashes and vaporizes (a bit like throwing droplets of water onto a hot frying pan.) The resulting gases pass into a cyclone where solid particles and char are extracted. The gases then enter a quench tower where they are quickly cooled using bio-oil already made in the process. The bio-oil condenses and falls into a product tank, while non-condensable gases are returned to the reactor to maintain process heating. The entire reaction from injection to quenching takes only two seconds. 100% of the feedstock is utilized in the process to produce bio-oil and char. As the non-condensable gases are used as energy to run the process, nothing is wasted and no waste is produced. The uncondensed, flammable gases are re-circulated to fuel approximately 75% of the energy needed by the pyrolysis process.

Three products are produced: pyrolysis oil, a heavy fuel oil known as bio-oil (60-75% by weight), char (15-20% wt.) and non-condensable gases (10-20% wt.). Yields vary depending on the feedstock composition. Bio-oil and char are commercial products and non-condensable gases are recycled and supply a major part of the energy required by the process. In the most advanced plants, no waste is produced and no external fossil energy is required to power the process.

Potential in the Global South
As we have said many times, the biomass potential in the developing world is considerable (over 650 Exajoules in Latin America and Africa alone), but the challenges to exploit it are serious too. Several analysts who have calculated the potential for export from the South and the logistical challenges that go with it, use the fast-pyrolysis technology to develop base-line scenarios in which different logistical cost chains are compared (See our previous post for a case-study on Mozambique).

From these analyses it appears that converting raw biomass (either waste or dedicated energy crops) into a fuel with a high energy density (such as pyrolysis oil) is one of the most feasible ways of tapping the biomass potential of the south. The alternative would be to export bulky biomass, which drives up costs.

The modularity of the concept as sketched above and its decentralised implementation, makes it possible to circumvent some of the infrastructural disadvantages of the South (such as a lack of railways or waterways).