Introduction
Chemistry
Technology
Process description
Status of the technology
Economics
Reference projects
Links
Leaflet
Contact
Introduction
Fast pyrolysis is a process in which organic materials are rapidly
heated to 450 - 600 oC in absence of air. Under these conditions,
organic vapours, pyrolysis gases and charcoal are produced. The vapours
are condensed to bio-oil. Typically, 70-75 wt.% of the feedstock is converted
into oil
Pyrolysis offers the possibility of de-coupling (time, place and scale), easy handling of the liquids and a more consistent quality compared to any solid biomass. With fast pyrolysis a clean liquid is produced as an intermediate for a wide variety of applications.
Chemistry
In the fast pyrolysis process, biomass is rapidly heated to a temperature
of 450 - 600 oC. Due to heavy vibrations at this temperature
the atoms vibrate apart at random positions. The figure given below shows
that fragmentation of a complex structure like wood at random positions
results in a wide variety of products.
Pyrolysis characterized
When biomass decomposes at elevated temperatures, three primary products are formed: gas, bio-oil and char. At high temperatures the bio-oil vapours are decomposed in secundary products like gas and polymetric tar (Fuel Proc. Techn., 291, (1993)).
Yields of the primary pyrolysis products are temperature dependent. It can be observed that a maximum oil yield of 79 wt.% is obtained at 500 oC. For the temperature range studied, the char yield decreases and the gas yield increases with temperature.
Technology
The rotating cone reactor
BTG's fast pyrolysis technology is based on the rotating cone reactor. It is a proven gas-solid contactor which has been developed at the University of Twente (Chem.Eng. Sci., 5109, (1994)). A schematic representation of the reactor is presented in the figure on the right hand side. Biomass particles at room temperature and hot sand particles are introduced near the bottom of the cone where the solids are mixed and transported upwards by the rotating action of the cone. In this type of reactor, rapid heating and a short gas phase residence time can be realized.
Fast heating of biomass will prevent char forming reactions. In this mode, 75 wt.% bio-oil and only 15 wt.% char and gas are produced as primary products. Rapid removal of the pyrolysis vapours from the hot reactor enclosure ensures that less than 10 wt.% bio-oil is lost due to cracking reactions. Since no "inert" carrier gas is needed (unlike fluidized bed pyrolysis), the pyrolysis products are undiluted. This undiluted and hence small vapour flow results in downstream equipment of minimum size. Consequently, the capital costs of the complete unit are minimal.
In mechanical terms, the reactor technology is remarkably simple and robust. The rotational speed of the cone is only 300 rpm and after more than 1000 hours of operation in the current 250 kg/h pilot plant signs of abrasion or wear are absent
Scaling up of the rotating cone reactor is possible by increasing its diameter. For capacities which require a cone diameter larger than 2 meters, stacking of multiply cones on a single axis leads to the lowest investment costs. This conventional approach is also encountered in centrifugal disk separators or rotating disks contactors. With these options all pilot plant capacities between 2 and 100 ton/hr can be served.
Feedstock requirements
Before processing organic materials in a fast pyrolysis plant, the feedstock
must have the following requirements:
- particle size < 6 mm,
- moisture content < 10 wt.%
Process description
A process flow diagram of BTG's fast pyrolysis process is given below.
Biomass particles are fed near the bottom of the pyrolysis reactor together with an excess flow of hot heat carrier material such as sand, where it is being pyrolysed. The produced vapours pass through several cyclones (not shown) before entering the condenser, in which the vapours are quenched by re-circulated oil. The pyrolysis reactor is integrated in a circulating sand system composed of a riser, a fluidized bed char combustor, the pyrolysis reactor, and a down-comer. In this concept, char is burned with air to provide the heat required for the pyrolysis process. In this case the plant is self sustaining. Oil is the main product; non-condensable pyrolysis gases are currently flared-off, but application in a gas engine is foreseen. Excess heat can be used for drying the feedstock.
For details on the oil properties and its applications see bio oil applications
Status of the technology
BTG has demonstrated the rotating cone pyrolysis technology on the
scale of 250 kg per hour based on wood residues. The figure below shows
a picture of the 250 kg/h pilot plant.
A number of organic materials has successfully been processed in the current pilot plant, such as bagasse, palm residues, rice husks, straw, automotive scredder residues, dried sludges, pine wood, olive husks, beech wood, oak wood, switch grass and poplar.
The 250 kg/h pilot plant has processed in total 50 tonnes of oil for a number of clients
Currently BTG is involved in the engineering of a 50 ton/day fast pyrolysis plant for clean wood residues. This plant will be constructed and commissioned in 2003
On request, it is possible for clients to test their waste materials in the 250 kg/h fast pyrolysis pilot plant. Also bio-oil is available on request.
Economics
Due to the small number and limited scale of existing
pyrolysis oil production units, the economics of a commercial scale unit
can only be estimated. Costs of bio-oil production depend i.a. on feedstock
(pre-treatment) costs, plant scale, type of technology etc. Studies indicate
that pyrolysis oils can be produced for between 75 and 300 € per ton oil (4 to 18 €/GJ),
assuming feedstock costs between 0 and 100 €/t (0 to 1.9 €/GJ)
(Bridgwater A.V., 1999, An introduction to fast pyrolysis of biomass
for fuels and chemicals, in: Fast Pyrolysis of Biomass: a Handbook (edited
by Bridgwater et al.), CPL Press, UK, 1-13).
For its envisaged 2 t/hr unit BTG calculated a bio-oil production cost of less than 85 €/t (approx. € 5,-/GJ, which is close to the crude oil price) assuming feedstock costs of 25 €/t (BTG, 2000).
At these levels, the cost of bio-oil
is already competitive with industrial light fuel oil, which costs up
to 6.64 €/GJ excluding
taxes, in certain European markets (e.g. Norway, Denmark, Greece, Italy
and Portugal, Figures 1998). The same holds for bio-oil as a substitute
in diesel engines. Diesel prices without tax have increase rapidly in recent
months and reached levels of up to 10 €/GJ.
Reference
projects
A selection of BTG's projects concerned with pyrolysis is given below:
- The rotating cone flash pyrolysis pilot, 1994-1995, Project partner: Royal Schelde, Supported by FAO, project DP/CPR/88053-001/AGO-1
- Design and operation of a bench scale bio-oil production reactor, 1997-1999, NOVEM EWAB 355297/6030
- Scaling-up of the rotating cone reactor to 200 kg biomass per hour, 1997-2000, Project partners: KARA (NL), CIEMAT (SP), University of Rostock (GE), EC FAIR97-3203
- Development of advanced fast pyrolysis processes for power and heat, 1998-2001, Project partners: Aston University (UK), BHF-IWCT (GE), Wellman (UK), KARA (NL), Ormrod Diesels (UK), EC Joule JOR3-CT-97-0197
- Demonstration of a flash pyrolysis plant, 2000-2003, Project partners: Ansaldo (IT), ASM Brescia (IT), KARA (NL), ARI (EST), EC NNE5/2000/233
Links
www.pyne.co.uk
Leaflet
Leaflet
Fast Pyrolysis
Folder Pyrolysis
Contact
Dr. Ir. L. van de Beld
Tel +31 53 486 2288