If you missed the third episode of the FlexSNG webinar series, or you would like to watch it again, the full recording is available here: https://youtu.be/T6boiOYQaqw?si=fm4sOBTzbW_Kwh1_
The webinar welcomed more than 80 guests online and received many questions from an active audience.
A recap of all the questions and answers can be found here:
- What are the feedstock (biomass)’s size and moisture content fed into the gasifier?
At VTT gasifiers we use pellets which are around 8-10 mm diameter (length 2-3cm); moisture well below 15 %, e.g. 8%
Specifications mentioned by Minna are for VTT´s pilot tests. In industrial scale typically maximum particle size for CFB gasifier is ~40-50mm (in each direction) and maximum amount of fines is limited to ~20 %
- How much energy in the biomass used to maintain gasification temperature?
In the gasifier around 80 % biomass energy is converted to heating value of gas and the rest to entalphy..
- Thanks for your excellent presentation. The energy efficiency of the whole process (from biomass to the final products) seems to be very high. I think the H2 injection has not been considered in calculating the energy efficiency of the whole process?
Detailed evaluation of the process concept is still ongoing and there will be separate webinar related to these studies. Target of the efficiency into SNG is ~70% without H2 boosting (energy basis)
- My question is that for industrial applications, high pressure gasification seems more suitable considering the capacity and downstream application. What is your opinion about it?
High pressure operation is quite challenging for heterogenous feedstocks as biomasses and wasted. Entrained flow gasifiers need heavy pre processing (pyrolysis, torrefaction). On paper high pressure is beneficial but robustness and availability is different topic.
- Question to Ilkka Hiltunen: Temperature range of filtration? Temperature of reforming reactor?
Filtration temperature is 550-650C and reformer temperature at outlet is ~880-920C depending on sulphur content of the gas.
- What is the recommended operating pressure?
In this project we have focused to near atmospheric pressure operation (1,5-2 bar). Mostly due to feeding of fluffy feedstocks without densification. For fluffy feedstocks recommended gasification pressure is near atmospheric and for more dense feedstocks around 4 bar.
- What is the gas conversion efficiency?
In maximised operation mode, the cold gas efficiency of the gasification+reforming process is 75-80%.
- What was gas compostion? H2, CO, CO2, CH4 etc.
An example of the dry gas composition (after catalytic reforming) obtained in pilot runs with forest residue pellets (gasification temp ~880 °C): 36 vol-% H2, 21 vol-% CO, 33 vol-% CO2, 1 vol-% CH4 and the rest purge N2.
- What method are you employing for monitoring tars and benzene?
Tars and benzene were measured according to the Tar protocol with isopropanol as the solvent (extractive sampling) and the samples were analysed with a GC afterwards.
- Did you observe any agglomeration in the VTT gasifier when feeding straw?
In atmospheric pressure tests, straw was successfully gasified at up to 830 °C with no signs of agglomeration in the gasifier. One additional test was carried out at pressurised conditions where agglomeration behaviour was detected at a gasification temperature of 850-860°C.
- How to get plastic with syngas?
Gasification process can be tuned to yield olefins.
- Have you any rough idea of possible costs for the Biocahr obtained with thsi process?
The techno-economic assessments are ongoing that will generate the productions costs for SNG and biochar. The results will become available at the end of the project.
- Is there any enegy balance avialable?
Energy balance calculations and techno-economic assessments are underway and will become available towards the end of the project. The target efficiency from biomass to SGN is around 70% (in maximised operation mode).
- (Question to Sanna) Technical Solution for Biochar removal from bottom of BCFB reactor (how to handle condensing steam and escaping oxygen reacting with the biochar at the removal point?)
Biochar is removed using the standard bottom ash removal equipment where nitrogen purging is used.
- (Question to Sanna) Do you do in-bed fuel feeding or on-bed feeding in the BCFB rector?
The fuel was fed inside the dense bubbling fluidised-bed. - What is primary energy source considered?
The primary source of energy in the gasification process is biomass (biomass residues: woody, agrobiomass) or waste (biogenic waste fractions). Hybrid plants where electrolysis of water is coupled with the gasification process will also consume electricity to split the water into hydrogen (that is used to boost the syngas and tailor the H2/CO ratio suitable for methanation) and oxygen.
- What is the methanation process pressure?
The methanation process employed in the FlexSNG concept is the VESTA methanation by Wood. The pressure level has not been disclosed by Wood but it is presumably in the range 15-20 bar.
- Do you observe any phenols and naphthalene as part of tar components? If so, are they completely converted?
Both phenols and naphthalene are present in the raw gasification gas. In optimal reforming conditions, all tars are converted and only minor amounts of benzene remains in the gas. If tar conversion is not complete in reforming, also some minor amounts of naphthalene can be detected at the reformer outlet.
- Were both sand and dolomite used in separate runs?
Typically a mixture of sand and dolomite was used as bed material – in some tests sand was used alone.
