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FAIR-CT96-3203
Scaling-up and operation of a flash-pyrolysis system for bio-oil production and applications on basis of the rotating cone technology |
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Contract No: | FAIR-CT96-3203 |
| Date Prepared: | July 2001, February 1999, July 1998 | |
| Source: |
Final Report First Annual Progress Report Six Month Progress Report |
Source: Final Report December 2000
Consortium: The project was co-ordinated by BTG Biomass Technology Group BV, Enschede (The Netherlands) in partnership with CIEMAT, Instituto de Energias Renovables, Madrid (Spain), KARA Energy Systems B.V., Almelo (The Netherlands) and the Institute of Thermal Machines and Systems, University Rostock (Germany).
Abstract
The overall objective of the project is to scale-up novel, rotating cone technology for flash pyrolysis of biomass and examine the related bio-energy system by application of bio-oil from several feedstocks in engines and combustion chambers.
The specific objectives were to:
In addition further objectives (met by CIEMAT) have been to characterise and study the preparation of biomass to meet the necessary specifications to be used for bio-oil production in the rotating cone pyrolysis technology. This includes selection of a number of relevant biomass materials based on primary criteria such as their high availability in the EU and low production costs. However, biomass materials with certain degree of homogeneity and/or low humidity content have also been considered as well as agroindustrial and agricultural residues produced in Southern Europe. These are well suited to be utilised in the pyrolysis technology. An appraisal of the resource availability and costs has been developed in order to assess the selection of the biomass to be studied in detail within the project. As a result, twenty substrates have been selected fulfilling the required characteristics. Samples of such substrates have been fully analysed for physical, chemical and energetic characteristics. Based on their properties, a further selection reducing the number to six types of biomass, has been carried out. The following materials were selected:
A study was then carried out in order to define the most suitable pre-treatment techniques for each of them in order to obtain adequate feedstock for the rotating cone technology.. Hammermill technology has been selected as most appropriate for biomass comminution since it is robust resulting in lower maintenance costs than those associated with other mill types commonly utilised, such as knife based mills.
A pilot study has been carried out in a installation equipped with various machines currently utilised by industry to effect such operations using a hammermill based particle size reduction plant (200-400 kg/h dry biomass).
For each biomass, grinding tests have been performed with various pore sizes in the insert hammermill screens . The pore sizes investigated were 25 mm, 20 mm, 15 mm, 8 mm, 5 mm, 3 mm, 2.5 mm, 2 mm and 1.2 mm. For the last three pore sizes, two-stage grinding was applied to raw material with a mean particle size greater than 8 mm.
The pilot experiments showed that the amount of energy used for milling to obtain small particles is relatively very high. More than 80 kWh/t are required to grind coarse biomass (mean particle size greater than 10 mm) to mean particle sizes below 1 mm. This figure can be reduced by up to 50% to obtain products with mean sizes between 2 and 3 mm.
Based on the pilot plant results, a economic approach, developed for a pre-treatment installation, designed to produce 4 tones per hour of ground biomass, shows that for 8400 effective working hours per year, the costs of size reduction to produce particles under one mm of mean particle size, utilising 2 mm screen pore ranges from 7 Euro/t for rice husks to 22.2 Euro/t for short rotation poplar chips. Electricity consumption is the major cost for the comminution of wood chips (46% of the total costs for poplar chips).
This work enabled various pre-treated biomass materials to be delivered for pyrolysis tests over the duration of the project. These were sent to the nominal 200 kg/h rotating cone pyrolysis pilot plant, the development of which was the main task for KARA and BTG.
The core of the pyrolysis pilot plant is the rotating cone reactor which is a compact high intensity reactor in which biomass of ambient temperature is mixed with hot sand. Upon mixing with the hot sand at 550°C the biomass decomposes providing 70 weight percent condensable vapours, 15 weight percent non-condensable gases and 15 weight percent char.
During the project BTG and KARA have successfully designed and constructed a fully automated pyrolysis plant with a capacity of 260 kg/h. This was operated over a number of trial periods, during which the following conditions were established as those that gave the highest oil yield and produced the best quality bio-oil:
Using the pilot plant the following was achieved:
The main task of the Rostock University was to use the bio-oil for energy applications. This entailed:
Bio-oil from fast pyrolysis is in many ways different from other liquid fuels (such as rape seed oil or bio ethanol derived) from biomass like. It also differs significantly from diesel fuel in both physical properties and chemical composition. Bio-oil contains water and solids, it is acidic and has a low calorific value.
The first task therefore was to determine the chemical and physical properties of pyrolysis oil generated using this technology from different feedstock and compare them with other bio-fuels and fuels derived from mineral oil. The standard methods developed for petroleum based fuels need to be adapted to bio-oil. The results have been summarised in a characterisation report.
The results of the analysis and characterisation of bio-oil are very important for further application of bio-oil in combustion engines. Not all the oil batches received by the Rostock University could be analysed within the time frame of the project. However, it would appear that an improvement of the bio-oil quality is necessary and the focus should be on the homogeneity, low content of solids, water content less than 25%, and a sufficiently low viscosity.
A quality specification for bio-oil is urgently required. The analysis, determination and certification of the most important parameters should ideally take place at the site of production of the bio-oil.
All routes to utilising bio-oils for energy production lead through a combustion stage. A central task is to study the combustion behaviour in a special test facility equipped with extensive measuring and analysing devices and data processing. Combustion of bio-oil under continuous firing conditions has been performed and analysed. The operating conditions are similar to those in the combustion chamber of a gas turbine. It appears simpler to burn bio-oil in a gas turbine than in a reciprocating combustion engine and therefore the first practical test to produce electricity and heat were performed in a small gas turbine. Due to the properties of bio-oil from fast pyrolysis a major modification of the fuel system was necessary, in particular, a fuel pre-heat system is required to overcome the high viscosity. With a dual fuel system operation was successful but due to various technical problems in the fuel supply lines no long term duration tests were possible.
Originally, the diesel engine was thought to be the best candidate for the application of bio-oil to energy production. Assessment of this concept was also an important objective of the project. However, with standard diesel engines developed for high quality diesel fuel no successful runs could be performed. Initial tests have been started with dual fuel engines equipped with ignition aids which may prove successful but could not be included in the present project. The gas turbine appears to be better suited for energy utilisation of bio-oil from pyrolysis than the diesel engine and in agreement with the project co-ordinator the programme was altered to emphasise on combustion tests in the flame tunnel and in the combustion chamber. Accordingly, the planned duration tests in the diesel engine were deleted from the programme.
Airborne emissions are of global environmental concern. Hence, these were investigated in this project. Using the combustion test facility, detailed measurements of the emissions from the combustion of pyrolysis bio-oil were performed. The data obtained included information on levels of carbon monoxide, sulphur and nitrogen oxides as well as hydrocarbons. Measurements were carried out with a gas analyser that enabled 24 different chemical compounds to be measured continuously. In addition the content of solid particles, hydrocarbons and water was measured using an opacimeter. The emission data were compared to those from a similar operation using diesel fuel.
The various experiments demonstrated that bio-oil from fast pyrolysis of wood can successfully be applied for energy generation in boilers and gas turbines. A priority for future investigations is the optimisation of the operating parameters to the heat value, viscosity, fuel pressure and air ratio. With such optimisation it should be possible also to improve the emission characteristics which for some of the components are inferior to diesel fuel.
In order to enable safe and reliable operation of combustion engines with bio-oil more fundamental research is required, including investigation on factors affecting the quality of the bio-oils as well as on the concept of using an engine as the prime mover.
The following conclusions can be obtained from the economic analysis based on power generation scenario:
Description of work
During the first twelve months CIEMAT
has made an initial selection of the most suitable biomass materials for
application in the pyrolysis reactor on basis of availability, production
costs, particle diameter, moisture content and use of waste. The following
six types of biomass are selected:
During the second six months CIEMAT has executed a preliminary study of pretreatment techniques. Knife and hammer milling have been compared.
KARA and BTG have finished designing the main parts of the pilot plant. At present KARA and BTG are carrying out some initial tests with their pilot plant. It is expected that the pyrolysis plant will be operational by month 13.
The University of Rostock has investigated five main subjects during this period:
Achievements
Six types of biomass have been selected by
CIEMAT to pyrolyse in the rotating cone reactor. KARA and BTG have
finished designing the pyrolysis pilot plant, which will be operation in
month 13. The University of Rostock has completed the following tasks in
their work programme: construction of a combustion test facility;
pretreatment of pyrolysis oil for combustion; preliminary chemical
analysis of bio-oil.
Future actions
CIEMAT will finish the study of pretreatment
techniques and will supply BTG with feedstock suitable for pyrolysis in
the pilot plant.
KARA and BTG expect that the pyrolysis plant will be operational at a biomass capacity of 50 kg/h. The activities of the next period are aimed at optimising the pilot plant. The activities will also include characterisation of the pilot plant.
The University of Rostock will study the results obtained from GC-MS analysis. The extent to which physical (ultrasonic) pretreatment can influence the properties of the processed oil samples will be investigated. At present some experiments are running on storage conditions and the related changes in oil properties.
Further open combustion tests with different charges and qualities of pyrolysis oil and different pyrolysis oil/ethanol mixtures have to be carried out. In addition, the analysis of exhaust emissions will be prepared and gauges and devices installed.
Activities
In general the research activities are within the proposed time schedule. During the first six months CIEMAT has made an initial selection of the most suitable biomass materials for use as feedstock for the pyrolysis reactor. Analytical tests on the various types of biomass are in progress. Kara and BTG have finished designing the main parts of the pilot plant. At present Kara is concerned with construction of the pilot-plant in close co-operation with BTG. BTG is testing a cold flow model of the rotating cone reactor. The University of Rostock has investigated three main subjects during this period:
The University of Rostock will construct the combustion plant during the next six months and will modify chemical analysis methods for bio-oil.
Future actions
During the next six months the analyses of the selected types biomass will be concluded (end of May 1998). The most interesting types of biomass (6 in total) will be finally selected in order to study the availability of pre-treatment techniques. The implementation of the pre-treatment pilot plant will still take about four months (for the refining hammer mill) and 6 months (for the cyclone separator). However, drying and milling trials will be started with the present facilities.
Kara will start with construction of the rotating cone pyrolysis plant. BTG is starting to do some cold tests with the reactor. In July BTG and Kara will start-up the 200 kg/h pilot-plant at 25% design capacity, thus in a 50 kg/h mode. The University of Rostock will construct the combustion plant during the next period and will modify chemical analysis methods for bio-oil.
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