Antero Moilanen

Calcium addition in straw gasification

Abstract The present work focuses on the influence of calcium addition in gasification. The inorganic–organic element interaction as well as the detailed inorganic–inorganic elements interaction has been studied. The effect of calcium addition as calcium sugar/molasses solutions to straw significantly affected the ash chemistry and the ash sintering tendency but much less the char reactivity. Thermo balance test are made and high-temperature X-ray diffraction measurements are performed, the experimental results indicate that with calcium addition major inorganic–inorganic reactions take place very late in the char conversion process. Comprehensive global equilibrium calculations predicted important characteristics of the inorganic ash residue. Equilibrium calculations predict the formation of liquid salt if sufficient amounts of Ca are added and according to experiments as well as calculations calcium binds silicon primarily as calcium silicates and less as potassium calcium silicates.

Characterization of gasification reactivity of peat char in pressurized conditions: Effect of product gas inhibition and inorganic material

Abstract The characteristic effects of the main operating parameters in pressurized fluidized bed gasification, such as pressure and product gas composition, and of inorganic material on peat char gasification reactivity were studied. The measurements were carried out isothermally in a pressurized thermobalance at temperatures between 1023 and 1233 K and pressures up to 1.5 MPa. Steam and carbon dioxide, both pure and mixed with the product gases H2 and CO, were used as reaction agents. The reactivity was expressed in the form of instantaneous gasification rate vs. char burnoff. The steam gasification rate of peat char was only slightly higher than the CO2 gasification rate, and the gasification rates decreased at increasing pressure in both steam and carbon dioxide. The steam gasification rate of the peat char increased to a maximum before decreasing with increasing char burnoff. In carbon dioxide, the main trend was that the gasification rate slightly increased with the burnoff. Demineralization of the peat decreased the reactivity and also removed the negative burnoff behaviour observed in steam gasification. The presence of the product gases H2 and CO inhibited the gasification of the peat char almost entirely.

Ash Behaviour in Biomass Fluidised-Bed Gasification

In biomass combustion, ash deposit formation is a common problem and has been studied by a number of researchers [Miles et al., 1995; Baxter and DeSollar, 1995; Nordin et al., 1995; Bryers, 1996; Miles et al., 1996; Moilanen et al., 1996]. There are also some observations about operational problems in fluidised-bed gasification processes, caused by ash. In pressurised steam-oxygen gasification of peat, ash deposits have been formed in the upper part of the gasifier and in the cyclones [Moilanen, 1993]. Furthermore, straw ash has been found to cause both bed sintering and deposit formation in air-blown gasification [Kurkela et al., 1996], These problems were difficult to overcome in strawalone gasification. In fact, the gasification temperature had to be reduced to below 800–850°C, which resulted in poor carbon conversion and high tar concentrations. On the other hand, co-gasification of coal and straw (up to 50wt% straw) could be carried out without any signs of ash problems in spite of high operation temperatures of the order of 950–980°C [Kurkela et al., 1996]. One variable of significance that was observed to prevent the detrimental behaviour of ash in the gasification process was carbon conversion and measures to achieve this [Kurkela et al., 1996; Skrifvars et al., 1995]. The completeness of fuel carbon conversion is dependent on the reactivity of residual char and the operating conditions. If the reactivity is high, ash is formed rapidly and, consequently, deposits are also formed rapidly. The gasification reactivity of the biomasses has been observed to vary within wide limits [Moilanen and Kurkela, 1995; Moilanen and Saviharju, 1997]. Ash and its composition can be regarded essential in this respect and they vary significantly in different biomasses [Wilen et al., 1996]. The ash components, mainly alkaline metal, contribute catalytically to the rate of gasification, which may increase or decrease as a function of conversion depending of the behaviour of catalytically active substances. However, it is rather unknown, in detail, how these substances react during the gasification of biomass chars.

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)