PILOT PERFORMANCE

In 1999 Fortum Oil &Gas (presently Neste Oil), Fortum Power & Heat and Vapo entered into an agreement where they would jointly develop a proprietary pyrolysis process and related production technologies. The result was the Forestera™ process realized in the pilot plant located at the Technology Centre of the Fortum Oil Porvoo Refinery (Finland).
This is a fast pyrolysis process which is a fast cracking or thermal degradation of biomass in an oxygen free atmosphere producing a combination of condensable vapours, solids and gases.
The Forestera™ cracking process uses circulating fluid bed pyrolyzer with the special feature of solid separation using multi-inlet cyclones where highly efficient solids removal (solid content less than 0.1 % weight in the product) can be achieved with a minimal pressure drop. Another important feature is the unique combination of reactor heating by the bed material, the reactor walls and the fluidizing gas.

The construction of the plant took about one year an was ready in the spring of 2002. The nominal size of the plant was 500 kg dried feed input per hour. This maximum capacity was not reached due to temperature limitations of materials chosen in the char combustion side (800°C) in order to reduce problems with ash melting. The consequence was a reduced capacity of the plant down to 300 kg/hr.

During plant commissioning in 2002, several modifications were made to the plant subsystems, especially in the area of the feedstock pre-treatment. Tests of different feedstocks such as sawdust, wood shavings, wood chips and forestry residues having different moisture contents were carried out. The best feedstock was white wood chips since this gave the highest yield and best product quality and was thus chosen for the majority of the pilot runs.

The goal for the Forestera™ pilot plant was to produce sufficiently good quality products for application development.
Two main criteria were used for determining the product quality: solids and water content. Also of interest were viscosity and stability. The type of solids in the liquid was characterised as these were found to have a significant effect on the combustion equipment life and level of emissions.

The main factors influencing the products quality were feedstock characteristics, condenser temperatures, efficiency of cyclones and alcohol addition. Temperatures and residence times were chosen to give maximum liquid yield and were similar to those in the literature.

Another goal was to improve the availability of the plant and to test the influence of operating conditions.

From the combustion field tests and from pump rig trials it was decided to reduce the solid content target from the initial value of 0.1 % weight to 0.05% in order to reduce erosion and corrosion problems. The main solids constituents are: char, ash and sand. Inorganics, mainly silicates, either from the feedstock or from the bed material, lead to erosion in burner nozzles and pumps (striations in pump are shown in the picture on the left).

A combination of cyclones, on-line liquid filtering and centrifuges were used to reduce the solids to the desired level. The cyclones were able to remove down the solids to 0.1% with a good quality feedstock, but solids in the fuel were seen to increase to as much as 0.3% when the cyclones became partially blocked with char and tar deposits or when the feedstock contained a larger portion of very fine material.

Other problems that were encountered during the initial stages of production was the deposits of aerosols in the piping after the gas compressor. This could be reduced by improving the efficiency in the demisters and modifications in the secondary condenser.

During 2003 more than 30 m3 (36 tonnes) of pyrolysis oil was produced. In most of the runs the feedstock was white wood chips, crushed and dried to the required moisture content of less than 8% (weight). As mentioned above the solid content in the liquid was reduced to less than 0.05% and the water content was in the range 23-25%. Forestry residues were also processed, but due to quality that was available locally, there was a high concentration of inorganics and fine materials which caused problems in feeding and solids separation. This product, due to its high concentration of extractives, formed a two phases oil and a lower overall yield than with feedstock without bark.

The typical properties of Forestera™ product are summarized in the table below:

 

	Typical value
Lower heating value (MJ/kg)	15
Lower heating value (MJ/l)	19
Viscosity  (cSt) at 0 Cº	500
Viscosity  (cSt) at 30 Cº	20
Viscosity  (cSt) at 50 Cº	10
Viscosity  (cSt) at 80 Cº	4
Sulfur content (ppm)	300
Flash point (closed cup, Cº)	45-65
Water content (wt-%)	23-28
Solids content (wt%)	0,01-0,05
Density  (kg/l)	1,2

The experimental stage in the pilot plant in Porvoo has been completed (Click here for more information)


Conclusions from the test runs:

• The reaction conditions were very stable with small reaction temperature variations;
• Process could be run on a continuous basis for 4-5 days;
• Depending on the feedstock processed the main reason for coming off-line was coking of some transfer piping or agglomeration of char in cyclones;
• Runs were carried out both with multiple cyclones and with cyclones and on-line centrifuging. The use of centrifuges gave a liquid product with very low solids <0.05 wt %;
• Nominal capacity of 500 kg/hr feed could not be reached due to high temperatures in the char combustor;
• The  liquid yield was lower than  the expected value of  70-72 wt % and was measured for white feedstocks to be approximately 65±2%. This was attributed to the larger mean average particle size of the fed fuel than in other pyrolysis processes;
• The process requires further development work in order to permit very long duration runs, to achieve maximum capacity and to process wet feedstock.

This consortium of companies have concluded that commercialization of this technology is currently not sufficiently profitable to warrant the required investments in Finland.

This was due to:

• an increase in feedstock costs of forestry residues brought by the Kyoto agreement which has increased the demand;
• a cost of the combustion system higher than expected;
• higher shipping cost than for conventional heating oils.

Due to these reasons the pilot plant has been dismantled.