Fast pyrolysis as a biomass-to-liquid (BtL) conversion technology has been generating keen interest for some time with numerous lab, pilot, and demonstration initiatives. The allure is almost any kind of biomass can be converted into an energy-dense, transportable and storable bio-oil. In practice, commercial plants are few and far between. This may change as Empyro, Europe’s first-of-a-kind commercial poly-generation flash pyrolysis plant, hot commissions.
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Located in an industrial park in Hengelo, the Netherlands the 25 MWth Empyro BV fast pyrolysis plant is a snug and inconspicuous building sited next door to the much larger Akzo Nobel salt factory. There is a reason for that apart from the high cost of land development in the Netherlands.
Post EU project
The plant is the end result of an EU-co-funded collaborative research project called EMPYRO which ran from 2009 to 2013 under the 7th Framework Programme. The main objective of the project was to build and demonstrate a commercial-scale poly-generation pyrolysis plant to produce electricity, and process steam and bio-oil from woody biomass.
– The EU project itself was the merger of the long-term strategies of the two main initiators: the pyrolysis technology developer Biomass Technology Group BV (BTG), and the chemical industry giant Akzo Nobel Industrial Chemicals B.V, reveals Gerhard Muggen, Managing Director, BTG BioLiquids BV and Empyro BV during the visit.
The eight-partner consortium was set up to gather all the complementary expertise required to reach the objectives of the project. Bruins & Kwast Recycling, BTG, BTG BioLiquids, Stork Thermeq, HoSt and Amandus Kahl supplied the process technology, Jan Rusaas has modelled and optimised pyrolysis oil combustion. Akzo Nobel is the industrial end-user of the process steam from the Empyro plant. Future plans include the usage of extracted organic acids such as acetic acid from the pyrolysis oil for which other research at BTG is ongoing. Finally, another BTG BioLiquids BV subsidiary Empyro BV is in charge of the post-project plant operation and exploitation.
Modular design
– The entire pyrolysis plant consists of modules or skids that are transported like standard shipping containers. These are constructed, assembled and tested in the workshop of our manufacturing partner Zeton and then disassembled for transportation to the plant site, said Muggen.
All that is needed is the onsite foundation on which the skids are reassembled to form a freestanding structure. According to Muggen this modular approach enables rapid onsite construction and gives the client an opportunity to see the plant and make any amendments or adjustments before it is built on-site. Indeed onsite video footage from the Empyro construction site suggests about 8 days from when the first skid arrived to the concrete foundation and the last skid was added.
– Getting it right and vetted by the client before it is built at the client site is just so much more time and cost-beneficial for all parties. Zeton is just 2 km from our office and R&D facilities remarked Muggen.
Feedstock preparation
A fast pyrolysis process typically includes drying a feedstock to around 6 percent moisture content and grinding it to 2-6 mm in length and 1-3 mm thick particles before it is fed into the reactor. This is necessary to ensure a rapid pyrolysis reaction and minimise the amount of water in the final bio-oil product. In the case of Empyro the feedstock is wood residues that are delivered by truck, ready-milled and dried to around 10 percent moisture content. Empyro has a 10-year supply contract and the biomass itself is sourced locally.
On arrival, the biomass is transferred to one of two 200 m3 storage silos. From here it goes to a low-temperature belt dryer. On exiting the dryer the moisture content is under 6 percent and the material is transferred to a reactor feed bin inside the main building.
– Sufficient excess heat is normally available from the pyrolysis plant to dry biomass from 40–50 percent moisture content to below 6 percent. Here we have a 12-year agreement with AkzoNobel to supply low-pressure high temperature steam for its process, said Muggen.
Proprietary rotary cone reactor
The heart of the Empyro process is the BTG-BTL proprietary flash pyrolysis-modified rotary cone reactor (RCR). Originally researched as a concept with mechanical mixing some 20 years ago at the University of Twente, it was then further developed by BTG who built a pilot plant in 1998 at its R&D facilities in Enschede, the Netherlands. In 2005 BTG built the first commercial 50-tonne per day plant in Malaysia using empty fruit bunches (EFB) as feedstock. In 2007 BTG formed a subsidiary BTG BioLiquids to commercialise its modified RCRpyrolysis technology.
Unlike other fluidised bed reactor concepts, no inert gases are needed in the RCR to enable the intensive mixing of biomass particles with the hot sand bed. Biomass particles are fed near the bottom of the pyrolysis reactor together with an excess flow of 500o C sand, which acts as the circulating heat carrier material. The biomass and sand are mixed within the pyrolysis reactor and converted into pyrolysis oil vapours, gas and char.
– The residence time for the reaction is 2 seconds, thereof flash rather than fast, explained Muggen.
The produced vapours and gasses pass through several cyclones that separate out the solids, char and sand particles, from the vapours and gases, before these enter the condenser. Here the vapours are condensed by re-circulated bio-oil. The sand and char are transferred to a specially designed fluidised bed combustor, where the air is added to combust the char and reheat the sand. The hot sand is then transported back to the reactor to close the loop. The combustor flue gas passes cyclones and bag filter for particle removal before being mixed with uncondensed vapours from the condenser and burnt in an afterburner. A heat recovery steam generator and afterburner provide high-temperature steam for a Siemens steam turbine with the post-turbine steam supplied to Akzo Nobel as well as the belt dryer.
Defining commercial scale
A continuous process the Empyro plant has a design capacity to convert 5 tonnes per hour of woody biomass into 3.3 tonnes of pyrolysis oil, 4.5 MW of steam and 435 kW of electricity with self-consumption of heat and power taken into account. This is deliberately the commercial scale.
– It is technically possible to build larger units, the compact design of our modified RCR makes scaling up to larger capacities straightforward. A 10-tonne-per-hour plant design is just a matter of duplicating the units. If larger outputs are required then additional plants can be set up in cascade keeping CAPEX low and revenue coming in once the first unit is running, commented Muggen adding that it is much better to transport the bio-oil over longer distances than the raw biomass feedstock.
In theory, different units could run on different feedstock and it would seem to be relatively easy to dismantle a unit again should a plant need to be decommissioned or moved to make it a more liquid asset.
According to Muggen due to the simplicity of the rotating cone process, investment costs can be considerably lower in comparison to other pyrolysis technologies that require larger downstream equipment and in some cases ATEX compliance.
– Depending on local conditions energy efficiencies of 85–90 percent can be achieved based on biomass in and oil, heat, electricity out, Muggen said.
Valorising bio-oil
FrieslandCampina, a major global dairy producer, has agreed to a 12-year off-take deal for 80-100 percent of pyrolysis oil allowing Empyro to supply test volumes to other third parties. The bio-oil is being co-fired with fossil gas in a Stork Thermeq steam boiler.
– Using this high-quality single-phase bio-oil as a fuel is the first step. BTG is looking at other downstream processing such as organic acid extraction and further refining into renewable fuels and chemicals, ended Gerhard Muggen.
