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Off-gassing of VOCs and permanent gases during storage of torrefied and steam exploded wood
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik. Umeå University Industrial Doctoral School for Research and Innovation. (Thermochemical Energy Conversion Laboratory (TEC-Lab))
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
Vise andre og tillknytning
2017 (engelsk)Inngår i: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 31, nr 10, s. 10954-10965Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

Thermal treatment for upgrading of low-value feedstocks to improve fuel properties has gained large industrial interest in recent years. From a storage and transport perspective, hazardous off-gassing could be expected to decrease through the degradation of reactive biomass components. However, thermal treatment could also shift chemical compositions of volatile organic components, VOCs. While technologies are approaching commercialization, off-gassing behavior of the products, especially in terms of VOCs, is still unknown. In the present study, we measured off-gassing of VOCs together with CO, CO2, CH4, and O2 depletion from torrefied and steam exploded softwood during closed storage. The storage temperature, head space gas (air and N2), and storage time were varied. VOCs were monitored with a newly developed protocol based on active sampling with Tenax TA absorbent analyzed by thermal desorption-GC/MS. High VOC levels were found for both untreated and steam exploded softwood, but with a complete shift in composition from terpenes dominating the storage gas for untreated wood samples to an abundance of furfural in the headspace of steam exploded wood. Torrefied material emitted low levels of VOCs. By using multivariate statistics, it was shown that for both treatment methods and within the ranges tested, VOC off-gassing was affected first by the storage temperature and second by increasing treatment severity. Both steam exploded and torrefied biomass formed lower levels of CO than the reference biomass, but steam explosion caused a more severe O2 depletion.

sted, utgiver, år, opplag, sider
Washington: American Chemical Society (ACS), 2017. Vol. 31, nr 10, s. 10954-10965
Emneord [en]
volatile organic compounds, carbon monoxide, physicochemical characteristics, thermal degradation, physical properties, pellet types, solid wood, emissions, biomass, explosion
HSV kategori
Identifikatorer
URN: urn:nbn:se:umu:diva-141086DOI: 10.1021/acs.energyfuels.7b01959ISI: 000413710300066OAI: oai:DiVA.org:umu-141086DiVA, id: diva2:1152427
Prosjekter
Bio4EnergyTilgjengelig fra: 2017-10-24 Laget: 2017-10-24 Sist oppdatert: 2019-09-02bibliografisk kontrollert
Inngår i avhandling
1. Off-gassing from thermally treated lignocellulosic biomass
Åpne denne publikasjonen i ny fane eller vindu >>Off-gassing from thermally treated lignocellulosic biomass
2017 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
Abstract [en]

Off-gassing of hazardous compounds is, together with self-heating and dust explosions, the main safety hazards within large-scale biomass storage and handling. Formation of CO, CO2, and VOCs with concurrent O2 depletion can occur to hazardous levels in enclosed stored forest products. Several incidents of CO poisoning and suffocation of oxygen depletion have resulted in fatalities and injuries during cargo vessel discharge of forest products and in conjunction with wood pellet storage rooms and silos. Technologies for torrefaction and steam explosion for thermal treatment of biomass are under development and approaching commercialization, but their off-gassing behavior is essentially unknown.

The overall objective of this thesis was to provide answers to one main question: “What is the off-gassing behaviour of thermally treated lignocellulosic biomass during storage?”. This was achieved by experimental studies and detailed analysis of off-gassing compounds sampled under realistic conditions, with special emphasis on the VOCs.

Presented results show that off-gassing behavior is influenced by numerous factors, in the following ways. CO, CO2 and CH4 off-gassing levels from torrefied and stream-exploded biomass and pellets, and accompanying O2 depletion, are comparable to or lower than corresponding from untreated biomass. The treatments also cause major compositional shifts in VOCs; emissions of terpenes and native aldehydes decline, but levels of volatile cell wall degradation products (notably furans and aromatics) increase. The severity of the thermal treatment is also important; increases in torrefaction severity increase CO off-gassing from torrefied pine to levels comparable to emissions from conventional pellets, and increase O2 depletion for both torrefied chips and pellets. Both treatment temperature and duration also influence degradation rates and VOC composition. The product cooling technique is influential too; water spraying in addition to heat exchange increased CO2 and VOCs off-gassing from torrefied pine chips, as well as O2 depletion. Moreover, the composition of emitted gases co-varied with pellets’ moisture content; pellets of more severely treated material retained less moisture, regardless of their pre-conditioning moisture content. However, no co-variance was found between off-gassing and pelletization settings, the resulting pellet quality, or storage time of torrefied chips before pelletization. Pelletization of steam-exploded bark increased subsequent VOC off-gassing, and induced compositional shifts relative to emissions from unpelletized steam-exploded material. In addition, CO, CO2 and CH4 off-gassing, and O2 depletion, were positively correlated with the storage temperature of torrefied softwood. Similarly, CO and CH4 emissions from steam-exploded softwood increased with increases in storage temperature, and VOC off-gassing from both torrefied and steam-exploded softwood was more affected by storage temperature than by treatment severity. Levels of CO, CO2 and CH4 increased, while levels of O2 and most VOCs decreased, during storage of both torrefied and steam-exploded softwood.CO, CO2 and O2 levels were more affected by storage time than by treatment severity. Levels of VOCs were not significantly decreased or altered by nitrogen purging of storage spaces of steam-exploded or torrefied softwood, or controlled headspace gas exchange (intermittent ventilation) during storage of steam-exploded bark.

In conclusion, rates of off-gassing of CO and CO2 from thermally treated biomass, and associated O2 depletion, are comparable to or lower than corresponding rates for untreated biomass. Thermal treatment induces shifts in both concentrations and profiles of VOCs. It is believed that the knowledge and insights gained provide refined foundations for future research and safe implementation of thermally treated fuels as energy carriers in renewable energy process chains.

sted, utgiver, år, opplag, sider
Umeå: Umeå universitet, 2017. s. 94
Emneord
Torrefaction, steam explosion, enclosed storage, CO, CO2, O2 depletion, VOCs, Tenax-TA, SPME, process settings, storage temperature, storage time
HSV kategori
Identifikatorer
urn:nbn:se:umu:diva-141921 (URN)978-91-7601-809-5 (ISBN)
Disputas
2017-12-08, KB.E3.01, KBC-huset, Umeå, 09:00 (engelsk)
Opponent
Veileder
Forskningsfinansiär
Bio4EnergyJ. Gust. Richert stiftelseSwedish Energy Agency
Tilgjengelig fra: 2017-11-17 Laget: 2017-11-16 Sist oppdatert: 2018-06-09bibliografisk kontrollert

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