Structural and chemical developments of biochar used in horticultural trials for various periods of time

There is a growing interest in peat alternatives for the preparation of horticultural potting soils. Pot trials have shown that Biochar can play an important role in decreasing the peat fraction and the associated GHG emissions. Biochar is very stable (no decay) and completely free of diseases. Despite some first successes up to 35% Biochar in the mixture, further application will require more knowledge to increase the share of biochar as well as the yield in horticultural production. Pot trials in greenhouses provide a unique opportunity to follow the structural and chemical development of biochar over time, as the ingredients of the potting mix are known and all nutrient and water streams are recorded. Biochar grains can be retrieved from the pots at intervals during the trials. Precise pore size distributions at the start (t=0) were made (Hg-porosimetry and N2 adsorption) and followed over time using Scanning electron microscopy (SEM). Also the chemical composition and adsorption of compound on the biochar were measured over time for a number of pot trails. It was concluded that for the greenhouse application, clay-free mixtures might be better in order to avoid blocking of the internal pore structure of biochar and thereby maintaining the water holding capacity. For soil applications this may provide information on the formation of micro-aggregates. A first attempt was made to include bacillus and Trichoderma in different pot trails on the biochar. Crop results on biochar as carrier for resilience enhancing Bacillus subtilis were not improved, although the bacillus could be found in samples after the trial under the SEM. The use of Trichoderma in biochar/peat pot trails is currently in progress. A number of sampling moment from the pots allows for a structural development screening of the biochar under well-known conditions in the greenhouse. The results will be presented. Tracing bacillus and Trichoderma in samples with the SEM is very difficult as very few previous examples are available. This presentation aims to add also to the knowledge base on following “life” under the low-pressure electron microscope

Biochar as potting soil constituent and as carrier of Bacillus in the cultivation of Cyclamen

There is a growing interest in peat alternatives for the preparation of horticultural potting soils. There is also a growing interest in preparing potting soil mixes with added micro-organisms to increase the resilience of the potting soil – plant combination against diseases. Our goal was to use biochar to partly replace peat as well as to carry a commercial Bacillus subtilis into peat based potting soils. Peat based rooting media were prepared with an increasing volume fraction of biochar (0, 20, 20, 35 and 50%-v/v). Two extra treatments based on 0 and 20%-v/v biochar were inoculated with Bacillus subtilis in a concentration of 10^7 c.f.u./g dry rooting medium. Cyclamen persicum Halios® Blush were planted and cultivated during 4 months. The water content of the pot was monitored and the irrigation schedule was set to maintain a minimum volume of 32%-v/v of water. At the end of the cultivation period the fresh and dry biomass of the leaves, flowers and tubers was measured. Results showed an optimum Cyclamen growth in the treatment with 20%-v/v biochar. However the reduced biomass production at higher levels of biochar were caused by a lack of nutrients added and not by the biochar itself, as indicated by EC levels and levels of individual elements. The inoculated Bacillus population first decreased and finally stabilized in the rooting media. Bacillus inoculation had a negative effect on biomass production. In conclusion the use of biochar as peat alternative is possible if additional attention is paid to irrigation settings and nutrient levels. The use of biochar as carrier for resilience enhancing Bacillus subtilis was unsuccessful

Study on ash deposition under oxyfuel combustion of coal/biomass blends

Combustion in an O₂/CO₂mixture (oxyfuel) has been recognized as a promising technology for CO₂capture as it produces a high CO₂concentration flue gas. Furthermore, biofuels in general contribute to CO₂reduction in comparison with fossil fuels as they are considered CO₂neutral. Ash formation and deposition (surface fouling) behavior of coal/biomass blends under O₂/CO₂combustion conditions is still not extensively studied. Aim of this work is the comparative study of ash formation and deposition of selected coal/biomass blends under oxyfuel and air conditions in a lab scale pulverized coal combustor (drop tube). The fuels used were Russian and South African coals and their blends with Shea meal (cocoa). A horizontal deposition probe, equipped with thermocouples and heat transfer sensors for on line data acquisition, was placed at a fixed distance from the burner in order to simulate the ash deposition on heat transfer surfaces (e.g. water or steam tubes). Furthermore, a cascade impactor (staged filter) was used to obtain size distributed ash samples including the submicron range at the reactor exit. The deposition ratio and propensity measured for the various experimental conditions were higher in all oxyfuel cases. The SEM/EDS and ICP analyses of the deposit and cascade impactor ash samples indicate K interactions with the alumina silicates and to a smaller extend with Cl, which was all released in the gas phase, in both the oxyfuel and air combustion samples. Sulfur was depleted in both the air or oxyfuel ash deposits. S and K enrichment was detected in the fine ash stages, slightly increased under air combustion conditions. Chemical equilibrium calculations were carried out to facilitate the interpretation of the measured data; the results indicate that temperature dependence and fuels/blends ash composition are the major factors affecting gaseous compounds and ash composition rather than the combustion environment, which seems to affect the fine ash (submicron) ash composition, and the ash deposition mechanismsThe research work reported in this paper was partly carried out with the financial support from the RFCS contract number RFCRCT- 2006-00010. The very fine work done by Peter Heere in carrying out the experiments is highly acknowledgedPublicad

Study of ash deposition during coal combustion under oxyfuel conditions

This paper presents a comparative study on ash deposition of two selected coals, Russian coal and lignite, under oxyfuel (O₂/CO₂) and air combustion conditions. The comparison is based on experimental results and subsequent evaluation of the data and observed trends. Deposited as well as remaining filter ash (fine ash) samples were subjected to XRD and ICP analyses in order to study the chemical composition and mineral transformations undergone in the ash under the combustion conditions. The experimental results show higher deposition propensities under oxyfuel conditions; the possible reasons for this are investigated by analyzing the parameters affecting the ash deposition phenomena. Particle size seems to be larger for the Russian coal oxy-fired ash, leading to increased impaction on the deposition surfaces. The chemical and mineralogical compositions do not seem to differ significantly between air and oxyfuel conditions. The differences in the physical properties of the flue gas between air combustion and oxyfuel combustion, e.g. density, viscosity, molar heat capacity, lead to changes in the flow field (velocities, particle trajectory and temperature) that together with the ash particle size shift seem to play a role in the observed ash deposition phenomenaThe work presented was financially supported by the RFCS projects BOFCOM and ECOSCRUB, the Dutch National project CATO2, and the Dutch National program EOS-LT, Consortium Biomass Co-firing. The fine work of Peter Heere in operating the reactor is highly acknowledgedPublicad

Poultry Litter Gasification in a Fluidized Bed Reactor: Effects of Gasifying Agent and Limestone Addition

Air and air-steam gasification of poultry litter was experimentally studied in a laboratory scale bubbling fluidized bed gasifier at atmospheric pressure using silica sand as the bed material. The effects of equivalence ratio (ER), gasifier temperature, steam-to-biomass ratio (SBR), and addition of limestone blended with the poultry litter, on product gas species yields and process efficiency, are discussed. The optimum conditions (maximum carbon conversion, gas yield, heating value, and cold gas efficiency) were achieved at an ER 0.25 and 800 °C, using air (SBR = 0) and poultry litter blended with 8% w/w limestone, yielding a product gas with a lower heating value (LHV) of 4.52 MJ/Nm 3 and an average product gas composition (dry basis) of H 2 : 10.78%, CO: 9.38%, CH 4 : 2.61, and CO 2 : 13.13. Under these optimum processing conditions, the cold gas efficiency, carbon conversion efficiency, and hydrogen conversion efficiency were 89, 73, and 43% respectively. The reported NH 3 measurement at an ER of 0.28 and 750 °C is 2.7% (equivalent to 19,300 mg/Nm 3 ) with 14.7 mg/Nm 3 of HCl observed as the dry product gas. High temperature and steam injection favor production of CO and H 2 , while their effect on CH 4 was almost negligible. It is demonstrated that poultry litter can be gasified by blending with limestone, making it possible to overcome the fluidization problems caused by the mineral composition of poultry litter ash (high K and P content), yielding a gas with a similar heating value compared to gasifying without limestone addition, but with a significantly lower tar content