Judit Sandquist

Gasification of Biomass to Second Generation Biofuels: A Review

ABSTRACT Biomass gasification has gained significant attention in the last couple of decades for the production of heat, power and second generation biofuels. Biomass gasification processes are highly complex due to the large number of reactions involved in the overall process as well as the high sensitivity of the process to changes in the operational conditions. This report reviews the state-of-the-art of biomass gasification by evaluating key process parameters such as gasifying agent, temperature, pressure, particle size, etc., for fluidized bed and entrained flow gasifiers. The pros and cons of each technology and the remaining bottlenecks are also addressed. INTRODUCTION Biomass, the renewable source which stores energy in molecular carbon bond structures, is bound to play an important role in the current challenging energy scenario to provide the energy required to meet the continuous increase in energy demand and to mitigate climate change [1-2]. The large flexibility of biomass as a feedstock has been widely recognized as, besides heat and power, it can be converted into chemicals and transportation fuels. Biofuels can be used in recent infrastructures more or less directly, while other technologies, such as fuel cells and batteries, require changes in infrastructure and thus are considered as long-term solutions. Second generation biofuels can be grouped into biochemically or thermo-chemically produced, either route using non-food crops, purpose-grown perennial grasses, trees or residues. Among the different available thermo-chemical processes for the conversion of biomass to biofuels, gasification is perceived as one of the most attractive routes, as it converts feedstock very efficiently to the highest density fuels, i.e. synthetic, resulting in the most economical viable system [3]. The biomass gasification process produces synthesis gas through the chemical conversion of biomass under partial oxidation of the feedstock in reducing atmosphere in the presence of air, oxygen and/or steam [4]. The synthesis gas produced can be then converted to second generation biofuels. Various types of gasification reactor designs have been developed up to now. Fluidized bed and entrained flow gasifiers are currently the two main categories of gasification technologies for biofuels production. Fluid bed gasifiers operate below the biomass ash melting point in order to avoid fluid bed agglomeration and eventual collapse. This technology is attractive for its relatively low cost, ease of operation and good scale-up potential. However, it has associated relatively low energy efficiencies and poorer gas qualities; it requires intensive additional gas cleaning after the gasifier, namely tars handling and hydrocarbon reforming and is limited to small scale operations. On the other hand, entrained flow gasifiers operate above the melting point of the biomass ashes and produce a product gas that is essentially fully converted to synthesis gas with very low contents of residual tar components, resulting in high efficiencies and higher gas quality. However, the feeding is a challenge, it has higher investment and operating costs than fluidized beds and therefore it is only suitable for high capacities. Thus, although substantial progress has been achieved over the last years, none of the two technologies have become commercially available and therefore a significant amount of work is still needed in this field to enable the deployment of second generation biofuels production.

Combustion Properties of Norwegian Biomass: Wood Chips and Forest Residues

Flue gas emissions and particle size distribution were investigated during combustion experiments of wood, forest residue and mixtures of these two. The combustion experiments were carried out in a grate fired multi-fuel reactor with and without air staging at stable operation conditions and constant temperature of 850 °C. The overall excess air ratio was held at 1.6, and the primary excess air ratio was 0.8 during air staged experiments. NOx emissions are reduced by air staging. Fly ash particle concentration of forest residues in the flue gas is lower than wood. Aerosols number increased in the staged experiments for fuel blends.

Sustainable jet fuel for aviation

The study assesses to what extent the production and use of advanced sustainable jet fuel may contribute to GHG reduction and mitigation, and identifies the commercial potential for initiating and ...

Elemental composition and phosphorus availability in hydrochars from seaweed and organic waste digestate

ABSTRACT By hydrothermal liquefaction (HTL) of organic matter, hydrochars are produced which may be applied to soil for carbon sequestration. From substrates of wild seaweed and organic waste digestate, we measured the distribution of solids (hydrochars) and liquids after HTL at 150 and 200°C, 50 bar for 1 h. The output of liquids and solids was recorded. Elemental analysis was conducted for essential plant nutrients, potentially toxic elements (PTEs) and silicon in the hydrochars. Sequential extraction of phosphorous (P) was conducted to assess the P availability for plants. About 20% of the initial dry matter dissolved during HTL of digestate, and 55% for seaweed. More dry matter was dissolved by increased temperature. Except from arsenic in seaweed chars, the concentrations of PTEs were below quality compost thresholds. About 85% of P was recovered in chars for digestate. For seaweed, the recovery was 97% at 150°C, decreasing to 84% at 200°C. The solubility of P in chars decreased by HTL, and more with higher temperature. Reduced P availability, especially by higher temperature, is negative for the immediate fertilization effect. However, for soil sequestration of carbon, reduced P availability in hydrochars may expand the area where application may occur without negative environmental effects of eutrophication of water bodies.

Biomass gasification fundamentals to support the development of BTL in forest industry

The Nordic forest industry creates new concepts and provides solutions to mitigate climate challenge. One of the most interesting concepts is the integrated production of pulp and paper products and transportation fuels. The Finnish and Swedish activities are aiming to the same objective increased profitability of pulp and paper industry by using their by-products for producing high-quality renewable fuels. The technical approaches are different. For the technologies the scientific co-operation in the R & D consortium of VTT-ETC-LTU-SINTEF created background know-how through experiments and modelling in NORDSYNGAS project realised between 2010–2014. The objective of the project was to create new scientific knowledge on fluidised-bed and entrained-flow gasification of biomass residues and black liquor in order to support the Nordic industrial development and demonstration projects. In addition, close co-operation between the Finnish, Swedish and Norwegian R&D organisations was organised. ISBN, ISSN ISBN 978-951-38-8220-4 (URL: http://www.vtt.fi/publications/index.jsp) ISSN-L 2242-1211 ISSN 2242-122X (Online)