Characterization of selected Nigerian biomass for combustion and pyrolysis applications

Biomass is the most utilized form of renewable energy, especially in developing nations, and is a possible replacement for fossil fuel in power generation. The most commonly used method for recovering energy from biomass is combustion. Many countries are exploring the utilization of energy crops and indigenous residues to deliver sustainable sources of biomass. For these bio-resources, detailed characterization of the fuel properties is essential in order to optimize the combustion processes. In this study, some potential energy crops and woods from Nigeria, namely Terminalia superba, Gmelina arborea, Lophira alata, Nauclea diderrichii, and also one abundant agricultural residue, palm kernel expellers (PKE), were characterized for their combustion properties. Standard characterization methods such as proximate and ultimate analyses, metals analysis, and ash fusion test were used for this purpose and the results were compared with some U.K. biomass. In addition, their thermal conversion was assessed by thermogravimetric analysis and pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS). Finally, combustion studies were conducted by suspending single biomass particles in a methane flame to obtain information on reactivities and combustion characteristics. Results indicate that the ash fractions in the Nigerian woods were low in K, Si, and Ca, resulting in low calculated alkali indices, hence these fuels are not predicted to cause severe fouling problems. Furthermore, the analysis of the evolved product during devolatilisation from Py-GC-MS suggests that the content of oil is high in Gmelina. Finally, the results from the single particle combustion experiments revealed a longer char burn out rate for Lophira and Nauclea when compared with those of Terminalia and Gmelina

Torrefied Biomass Pellets—Comparing Grindability in Different Laboratory Mills

The firing and co-firing of biomass in pulverized coal fired power plants around the world is expected to increase in the coming years. Torrefaction may prove to be a suitable way of upgrading biomass for such an application. For transport and storage purposes, the torrefied biomass will tend to be in pellet form. Whilst standard methods for the assessment of the milling characteristics of coal exist, this is not the case for torrefied materials—whether in pellet form or not. The grindability of the fuel directly impacts the overall efficiency of the combustion process and as such it is an important parameter. In the present study, the grindability of different torrefied biomass pellets was tested in three different laboratory mill types; cutting mill (CM), hammer mill (HM) and impact mill (IM). The specific grinding energy (SGE) required for a defined mass throughput of pellets in each mill was measured and results were compared to other pellet characterization methods (e.g., durability, and hardness) as well as the modified Hardgrove Index. Seven different torrefied biomass pellets including willow, pine, beech, poplar, spruce, forest residue and straw were used as feedstock. On average, the particle-size distribution width (across all feedstock) was narrowest for the IM (0.41 mm), followed by the HM (0.51 mm) and widest for the CM (0.62 mm). Regarding the SGE, the IM consumed on average 8.23 Wh/kg while CM and HM consumed 5.15 and 5.24 Wh/kg, respectively. From the three mills compared in this study, the IM seems better fit for being used in a standardized method that could be developed in the future, e.g., as an ISO standard

Experimental and theoretical methods for evaluating ash properties of pine and El Cerrejon coal used in co-firing

There has been an increase in the use of biomass for power generation by means of co-firing with coal as well as by the combustion of 100% biomass. Despite the advantages of biomass in reducing carbon emissions from the electricity sector, the co-firing of high percentages of biomass can potentially aggravate ash related problems in the boiler. In order to develop mitigation strategies for the formation of deposits, an understanding of the ash behaviour during the combustion of high percentages of biomass is required. In this work, ash samples from El Cerrejon coal and pine biomass were characterised for their inorganic composition by X-ray fluorescence and wet chemical methods. Relationships between these two methods were found. Furthermore, the melting behaviour of ashes from pure coal, pine, and their blends were studied through ash fusion tests (AFT) and via a method using a simultaneous thermal analyser coupled to mass spectrometer (STA-MS) for the evolved gas analysis. Pine ash has lower slagging potential than El Cerrejon coal ash and results show that for 20:80 and 80:20 pine:coal ash belends the characteristic ash fusion temperatures increase with increasing pine ash content. There is unusually higher slagging potential (lower ash fusion temperatures) at a 50:50 blend ratio. Viscosity models produced sensible results for coal and coal/pine blends, but further refinement is required for modelling the viscosity of pure biomass ash. Thermodynamic modelling of slag formation was undertaken using the FactSage model. This model was successful in predicting the changes of gas, solid and liquid phases during pure pine, coal and co-combustion

Solubility of strontium-substituted apatite by solid titration

Solid titration was used to explore the solubility isotherms of partially (Srx-HAp, x = 1, 5, 10, 40, 60 mol.%) and fully substituted strontium hydroxyapatite (Sr-HAp). Solubility increased with increasing strontium content. No phase other than strontium-substituted HAp, corresponding to the original titrant, was detected in the solid present at equilibrium; in particular, dicalcium hydrogen phosphate was not detected at low pH. The increase in solubility with strontium content is interpreted as a destabilization of the crystal structure by the larger strontium ion. Carbonated HAp was formed in simulated body fluid containing carbonate on seeding with Sr10-HAp, but the precipitate was strontium-substituted on seeding with Sr-HAp. Strontium-substituted HAp might be usable as a template for the growth of new bone, since nucleation appears to be facilitated. © 2008 Acta Materialia Inc.postprin

Solubility of strontium-substituted apatite by solid titration

Solid titration was used to explore the solubility isotherms of partially (Srx-HAp, x = 1, 5, 10, 40, 60 mol.%) and fully substituted strontium hydroxyapatite (Sr-HAp). Solubility increased with increasing strontium content. No phase other than strontium-substituted HAp, corresponding to the original titrant, was detected in the solid present at equilibrium; in particular, dicalcium hydrogen phosphate was not detected at low pH. The increase in solubility with strontium content is interpreted as a destabilization of the crystal structure by the larger strontium ion. Carbonated HAp was formed in simulated body fluid containing carbonate on seeding with Sr10-HAp, but the precipitate was strontium-substituted on seeding with Sr-HAp. Strontium-substituted HAp might be usable as a template for the growth of new bone, since nucleation appears to be facilitated. © 2008 Acta Materialia Inc.postprin

In vitro bioactivity and setting times of white portland cement combined with different radio pacifying agents

Commercial formulations based on 80:20 mixtures of Portland cement and bismuth oxide (a radiopacifying agent) are used in dentistry as root-filling materials. This study compares the impact of two alternative radiopacifiers, barium sulphate and zirconium oxide, with that of bismuth oxide, on the setting times and bioactivity of white Portland cement. The findings indicate that bismuth oxide prolongs both the initial and final setting times of the cement, and that barium sulphate and zirconium oxide have no effect on this parameter. Hydroxyapatite (HA) formed on the surfaces of all test samples within 7 days of exposure to simulated body fluid, indicating that they possess the potential to stimulate new hard tissue formation. Fourier transform infrared spectroscopy, the traditional technique for the identification of HA, was not appropriate for the analysis of these cement systems owing to the overlap of signals from each of the radiopacifiers with the characteristic P-O bending modes of HA in the 570 – 610 cm-1 region. In this respect, the P-O band at 965 cm-1 of HA in the Raman spectrum was found to be a suitable means of detection since it is discrete with respect to all signals arising from the radiopacifying agents and cement phases

Biomass fuel flexibility in future conventional power generation

Power generation from the combustion of solid fuels has been a conventional technology for electricity production in the UK and most of the world for many decades. While the phasing out of coal as a fuel is an important aspect of the ‘decarbonising’ the electricity sector, the respective power plant technology could still play an important role into the future by use of abundant sources of solid biomass fuels. If such resources are to be effectively utilised, it is then necessary to accommodate the wide variation in the characteristics and behaviour of biomass fuels. Some of the key challenges in this context include: control of burn-out efficiency for different fuels; predictability of ash behaviour including operational problems and emissions arising from high ash and high potassium content fuels; the fate of fuel nitrogen content and the consequent effects on NOx emissions. This article presents an overview of these issues, their significance in the context of power plant design and operation and details of some recent research seeking to address them. Results of laboratory scale experiments showing the variation in properties and behaviour of different types of biomass fuel are also presented. These include studies on the relationship between fuel particle size and burn-out duration, gas-phase potassium release from biomass materials during combustion, variability in biomass ash composition and nitrogen release patterns from fuels in high temperature combustion

The use of equilibrium thermodynamic models for the prediction of inorganic phase changes in the co-firing of wheat straw with El Cerrejon coal

The combustion of pulverised coal in power stations results in slagging and fouling in the boiler section and this can be a more severe problem when co-fired with biomass, especially straw. Prediction of the effects of different combination of biomass and coal are helpful to the plant operators. Predictive software gives information about the onset and nature of the slag formed but often the results of these calculations have to be validated. This was undertaken in this work which gave a comparison of ash behaviour for coal (El Cerrejon) and wheat straw blends studied by ash fusion test, X-ray diffraction (XRD) and by using predictive software (FactSage). Ash prepared in the laboratory was also compared with ash produced in a 250 kW pilot-scale test furnace. The FactSage model showed good agreements with XRD data for the presence of inorganic phases with temperature, although it predicted some inorganic phases which are not detected in the XRD, particularly in low temperature ashes. Nevertheless, FactSage gave insight into liquid phase formation, more so than the ash fusion test, since it predicted the beginning of slag formation below the initial deformation temperature seen in the ash fusion test. For the coal, wheat straw and their blends, FactSage always predicted that slag formation is near to completion by the flow temperature observed in the ash fusion test

E-Glass Fiber Reinforced Composites in Dental Applications

Fiber reinforced composites (FRCs) are more and more widely applied in dentistry to substitute for metallic restorations: periodontal splints, fixed partial dentures, endodontic posts, orthodontic appliances, and some other indirect restorations. In general in FRCs, the fiber reinforcement provides the composite structure with better biomechanical performance due to their superior properties in tension and flexure. Nowadays, the E-glass fiber is most frequently used because of its chemical resistance and relatively low cost. Growing interest is being paid to enhance its clinical performance. Moreover, various techniques are utilized to reinforce the adhesion between the fiber and the matrix. Oral conditions set special requirements and challenges for the clinical applications of FRCs. The biomechanical properties of dental materials are of high importance in dentistry, and given this, there is on-going scientific interest to develop E-glass fiber reinforced composite systems. FRCs are generally biocompatible and their toxicity is not a concern. © 2011 The Author(s).published_or_final_versionSpringer Open Choice, 21 Feb 201

Gas phase potassium release from a single particle of biomass during high temperature combustion

A notable characteristic of solid biomass fuels as compared to coal is their significantly higher potassium content. Potassium influences ash deposition and corrosion mechanisms in furnaces and boilers, the effects of which may differ depending on phase transformations of potassium species in the gas phase and condensed phase. An understanding of how potassium is released from biomass fuels during the combustion process is therefore useful for plant designers and operators assessing means of avoiding or mitigating these potential problems. An experimental method is used to measure release patterns from single particles of biomass fuels using flame emission spectroscopy and a single-particle combustion rig. The experimental arrangement also allowed simultaneous thermal imaging of the combusting particle in order to determine the surface temperature. A model of the single particle combustion is presented. Using experimental data on devolatilisation and burnout times for different sized particles and the measured surface temperature profiles, the thermal and kinetic sub-models are verified. A model for potassium release is described and this is integrated to the single particle combustion model to allow prediction of the temporal patterns of release of gas-phase potassium. The modelled release patterns were compared with those observed. Good agreement between modelled and measured potassium release patterns was attained confirming that the proposed mechanisms affecting potassium release are valid