Fouling tendency of ash resulting from burning mixtures of biofuels. Part 2: Deposit chemistry

Mixtures of peat with bark and peat with straw were burned in a lab-scale entrained flow reactor under controlled conditions, and deposits were collected on an air-cooled probe at a temperature of 550 °C. The fuel and deposit compositions were compared using chemical fractionation analysis and SEM/EDX. Chemical fractionation analysis was capable of explaining the relative fouling tendency of peat, bark, and straw. The composition of deposits obtained from firing peat, bark, and straw individually resembled the composition of their ashes. When firing peat–bark and peat–straw mixtures, it was found that the deposition rate only started to increase when the Cl/S molar ratio in the feed ash exceeded 0.15. The composition of the ensuing deposits resembled the deposits obtained from burning either bark or straw individually. For peat–bark mixtures it was concluded that the presence of S in the feed suppresses deposition by sulfating chloride compounds, leading to deposits that contain less Cl and have less molten phase. For peat–straw mixtures it was concluded that the deposition behaviour is governed by other mechanisms than the interaction of Cl and S.     

Deposition behaviour of model biofuel ash in mixtures with quartz sand. Part 1: Experimental data

Model biofuel ash of well-defined size and melting properties was fed into an entrained flow reactor (EFR) to simulate the deposition behaviour of commercially applied biofuel mixtures in large-scale boilers. The aim was to obtain consistent experimental data that can be used for validation of computational fluid dynamics (CFD)-based deposition models. The results showed that while up to 80 wt% of the feed was lost to the EFR wall, the composition of the model ash particles collected at the reactor exit did not change. When model ashes were fed into the reactor individually, the ash particles were found to be sticky when they contained more than 15 wt% molten phase. When model ashes were fed in mixtures with silica sand, it was found that only a small amount of sand particles was captured in the deposits; the majority rebounded upon impact. The presence of sand in the feed mixture reduced the deposit buildup by more than could be expected from linear interpolation between the model ash and the sand. The results suggested that sand addition to model ash may prevent deposit buildup through erosion.     

Hydrothermal liquefaction of wheat straw in hot compressed water and subcritical water–alcohol mixtures

Hydrothermal liquefaction of lignocellulosic biomass (wheat straw) into bio-oil has been investigated under subcritical conditions (temperature up to 350 °C, pressure up to 200 bar) in water and water–alcohol mixtures using ethanol and isopropanol in a continuously operated tubular reactor. The effect of different reaction parameters such as temperature, pressure and water–alcohol ratio on the biomass conversion, cracking products yield and the higher heating value (HHV) of the received bio-oil was studied. The water–ethanol mixture was found to be a very reactive medium showing a complete biomass conversion and >30 wt% yield of high caloric oil (HCO). A maximum HHV of 28 MJ/kg for HCO was achieved. In addition, Ru (5 wt%) on H-Beta support was used as catalyst in a run with hydrogen in the feed showing deeper deoxygenation of reaction intermediates and highest HHV of the product oil (30 MJ/kg). This work demonstrated the usability of water–ethanol mixtures for an effective depolymerization of lignocellulosic biomass to bio-oils under subcritical reaction conditions with more than doubled HHV compared to the feedstock, in particular using a catalyst and the presence of hydrogen for further deoxygenation.     

Fouling tendency of ash resulting from burning mixtures of biofuels. Part 3. Influence of probe surface temperature

Mixtures of peat with bark and peat with straw were burned in a large lab-scale entrained flow reactor under controlled conditions, and deposits were collected on an air-cooled probe controlled at four to six different probe surface temperatures between 475 and 625 °C. The results show that the probe surface temperature has no effect on the deposition rate when peat is burned. When burning bark, either alone or in mixtures with peat, the deposition rate decreases with increasing probe surface temperature. When burning straw, either alone or in mixtures with peat, the deposition rate increases with increasing probe surface temperature up to 550 °C and remains constant at higher temperatures. The Cl content in the deposits decreases with increasing probe surface temperature, regardless of the mixture composition. In deposits obtained from burning peat–bark mixtures, K appears as K₂SO₄ when the deposition rate is low and as KCl when the deposition rate is high. In deposits obtained from burning peat–straw mixtures, no clear relationship is found between the deposition rate and the contents of Cl, S and K in the deposits.     

The effect of gamma irradiation on mechanical,thermal and morphological properties of glass fiber reinforced polyethylene waste/reclaim rubber composites

Composites of waste polyethylene (WPE), collected from municipal solid waste/recycled waste rubber powder (RWRP) reactive compatibilizing agent, maleic anhydride (MA) and glass fiber (GF) up to 20 wt%, prepared by melting and irradiated with gamma-rays up to 150 kGy have been studied. Tensile strength (T_S), elongation at break (E_b), elastic modulus, hardness, thermal and morphological parameters of the irradiated composites were investigated. The examined mechanical properties have been found to improve largely with filler content. Interesting E_b behavior has been detected for the irradiated composites loaded up to ∼10 wt% GF and has been basically discussed in view of matrix crystallinity and morphology. TGA thermograms of unirradiated composites revealed enhanced thermal stability than that reported for the blend whereas comparatively slight improvement has been demonstrated by irradiation. Whereby insignificant alteration in T_m values was observed by loading or irradiation, yet ΔH_m maximum of 3.41 J/g, indicated for the 5 wt% GF irradiated composite with an integral dose of 75 kGy, emphasizes the influence of the relatively moderate load and dose levels on matrix stability. The phenomenon has been confirmed by the respective SEM micrographs.     

Optimization of the technological properties of porcelain tile bodies containing rice straw ash using the design of experiments methodology

This study examines the effects of replacing fluxing and filler materials with rice straw ash (RSA) in manufacturing porcelain stoneware tile, using the design of experiments (DOE) methodology. The results of the characterization were used to obtain statistically significant, valid regression equations, relating the technological properties of the dried and fired test pieces to the raw materials content in the unfired mixtures. The regression models were analysed in relation to the X-ray diffraction and scanning electron microscopy results and used to determine the most appropriate combinations of traditional raw materials and RSA to produce porcelain stoneware tiles with specific technological properties. The studied range of tile body compositions: clay (40 wt%), feldspar (20–50 wt%), feldspathic sand (5–20 wt%), and RSA (0–25 wt%) was shown to be appropriate for porcelain stoneware tile manufacture.     

A study of the thermal and mechanical properties of electron beam irradiated HDPE/EPDM blends in the presence of triallyl cyanurate

The enhancing effects of cross-linking by the addition of 1, 3, and 5 wt% of triallyl cyanurate (TAC) to blends containing 80 wt% of high-density polyethylene (HDPE) and 20 wt% of ethylene–propylene diene monomer (EPDM) during electron beam irradiation were investigated. More specifically, the thermal and mechanical properties were studied as a function of the electron beam irradiation dose and an amount of the cross-linking agent, such as triallyl cyanurate (TAC). The results showed that the values of the gel content, thermal stability, tensile properties, impact strength, and rheology increased with increasing irradiation dose up to 150 kGy. For higher doses, the values decreased. Addition of the cross-linking agent to the HDPE/EPDM blends showed an enhanced cross-linking effect of various properties during electron beam irradiation. The addition of 3 wt% of TAC led to the highest thermal and mechanical properties. An irradiation dose of 150 kGy with the addition of 3 wt% TAC was the optimal condition to obtain blends with the best properties.     

Influence of SiC particle addition on the nucleation density and adhesion strength of MPCVD diamond coatings on Si3N4 substrates

It is generally accepted that SiC layers are often involved in the adhesion efficiency of chemical vapour deposition (CVD) diamond films on Si-containing substrates. Si₃N₄–SiC composite substrates with different amounts of SiC particles (0–50 wt%) were then used for diamond deposition. Samples were produced by pressureless sintering (1750°C, N₂ atmosphere, 2–4 h). The diamond films were grown on a commercial MPCVD reactor using H₂/CH₄ mixtures. Despite there being no special substrate pre-treatment, the films were densely nucleated when SiC was added (N_d≈1×10¹⁰ cm⁻²) with primary nanosized (∼100 nm) particles, followed by a less dense (N_d≈1×10⁶ cm⁻²) secondary nucleation. Indentation experiments with a Brale tip of up to 588 N applied load corroborated the benefit of SiC inclusion for a strong adhesion. The low thermal expansion coefficient mismatch between Si₃N₄ and diamond resulted in very low compressive stresses in the film, as proved by micro-Raman spectroscopy.     

Investigating the effect of SPRM on mechanical strength and thermal conductivity of highly porous alumina ceramics

For recycling waste refractory materials in metallurgical industry, porous alumina ceramics were prepared via pore forming agent method from α-Al₂O₃ powder and slide plate renewable material. Effects of slide plate renewable material (SPRM) on densification, mechanical strength, thermal conductivity, phase composition and microstructure of the porous alumina ceramics were investigated. The results showed that SPRM effectively affected physical and thermal properties of the porous ceramics. With the increase of SPRM, apparent porosity of the ceramic materials firstly increased and then decreased, which brought an opposite change for the bulk density and thermal conductivity values, whereas the bending strength didn’t decrease obviously. The optimum sample A2 with 50 wt% SPRM introducing sintered at 1500 °C obtained the best properties. The water absorption, apparent porosity, bulk density, bending strength and thermal conductivity of the sample were 31.7%, 62.8%, 1.71 g/cm³, 47.1 ± 3.7 MPa and 1.73 W/m K, respectively. XRD analysis indicated that a small quantity of silicon carbide and graphite in SPRM have been oxidized to SiO₂ during the firing process, resulting in rising the porous microstructures. SEM micrographs illustrated that rod-like mullite grains combined with plate-like corundum grains to endow the samples with high bending strength. This study was intended to confirm the preparation of porous alumina ceramics with high porosity, good mechanical properties and low thermal conductivity by using SPRM as pore forming additive.     

Extraction of jojoba oil with liquid CO2 + propane solvent mixtures

In this work liquid CO₂/propane mixtures were used to extract jojoba oil from oilseeds. First, experiments at 313 K and pressures of 70 bar and 200 bars were carried out on jojoba oil deposited on glass spheres, using different solvent concentrations (30 wt%, 50 wt% and 70 wt% CO₂), to assess the influence of the solvent composition and phase behavior on the extraction rate. Then, jojoba oil was extracted from the milled seeds under homogeneous liquid conditions, using solvent mixtures containing 30 wt% and 50 wt% CO₂ at 70 bar and 313 K. A solvent mixture with 30 wt% CO₂ exhibited good solvent power. Oil extraction yields of 98% were obtained using a minimum solvent to oilseed mass ratio of 5 g solvent/g oilseed and operating the extractor at 313 K and 70 bar.     

Recycling in ceramic glazes of zirconia overspray from thermal barrier coatings manufacturing

Glazed ceramic tiles are the most common building material for floor and wall covering. Glazes are produced from frits. The aim of this work is to make a total or partial replacement of a raw material, zircon, widely used in ceramic tiles manufacturing, with a waste material, in order to prepare ceramic frits. The waste material used in this work, is the overspray zirconia, which is produced during the deposition process by atmospheric plasma spraying (APS) of thermal barrier coatings (TBC) on turbine blades. In particular, a replacement of 100 wt%, 1 wt% and 0.2 wt% of zirconium silicate with zirconia has been studied. Ceramic glazes prepared mixing frits and other raw materials are applied on a single-fired tile. The glazes obtained were characterized with different analytical techniques. This study has revealed that the substitution of zircon with waste zirconia is possible in small percentages due to the presence of small amount of chromophore ions in the overspray zirconia, which tend to colour the glaze.     

Structural study of mullite based ceramics derived from a mica-rich kaolin waste

Mullite-based ceramics have been synthesized by reactive sintering of a mixture containing kaolin and a mica-rich kaolin waste. Samples fired in the temperature range from 1300 to 1500 °C were characterized by X-ray diffraction (XRD). The quantitative phase analysis and unit cell parameters of the mullite were determined by Rietveld refinement analysis of the XRD data. Mullite-based ceramics with 1.2 wt% quartz, 56.3 wt% glass (amorphous phase), 2.64 g/cm³ of apparent density, and 35±1.2 MPa of flexural strength were obtained after firing at 1500 °C. A liquid phase sintering mechanism activated by a total mica content of 13.3 wt% allowed to increase the mullite content to 47.6 wt% (2.3 wt% quartz and 50.1 wt% glass phase) and improve the flexural strength (70±3.9 MPa) after firing at 1400 °C.     

Aluminum titanate based ceramics from aluminum sludge waste

This work aims at obtaining aluminum titanate-based ceramics (Al₂TiO₅: AT) composites from industrial wastes. Al-sludge waste and rutile ore were used as rich sources of alumina and titania instead of pure materials. Sludge-(0–40 wt%) rutile mixtures were mixed, formed and fired at 1350 °C for various times. Phase composition, microstructure, densification, mechanical and thermal behaviors of the obtained AT composites have been investigated. Complete conversion of the starting materials to AT with bulk density of 3.199 g/cm³, compressive strength and modulus of rupture of 326.425 MPa and 30.84 MPa, respectively and very low CTE (−0.927*10⁻⁶ K⁻¹) were achieved by firing the sludge-(30 wt%) rutile at 1350 °C for 4 h. These results suggest that the obtained AT-ceramics from Al-sludge waste-rutile ore are a promising and an ecofriendly route.     

The influence of lignosulphonate on the properties of single and mixed Si3N4 and ZrO2 suspensions

Lignosulphonate (LS), was evaluated as a dispersing agent for single and mixed powder slips, containing Si₃N₄ and ZrO₂ powders, respectively. The surface charge was investigated by measuring the electrophoretic mobility in dilute powder dispersions. The slip stability was determined by visual observations of the settling of the powder and the fluidity of the slip was monitored by measuring the viscosity. It was evident that the different powder dispersions were most successfully stabilized by a high charge induced at high pH-values. However, in order to produce a sufficient fluidity of the slip, a dispersing agent had to be introduced. The optimal concentration range of LS at pH = 10 was found to be 0·2 wt%. The stabilizing mechanism in alkaline dispersions seems to be electrostatic depletion stabilization. The flow properties were finally tested by recording the viscosity for a mixed (composite) powder containing 68·4 wt% Si₃N₄ and 31·6 wt% ZrO₂ at a total solids content of 29–37 vol%.     

Direct-utilization of sewage sludge to prepare split tiles

As a type of solid waste with large quantities of pollutants, municipal sewage sludge (MSS) itself and its reclamation are becoming a growing concern of governments. In this paper, the direct-utilization of MSS to prepare split tiles is proposed and tested. Without any pretreatments such as thermokinetic drying, the crude MSS from domestic wastewater treatment plant is directly incorporated into the batch mixtures, and then wet ball-milled, filter-pressed, pug-milled, extrusion-formed, dried and fired to obtain split tiles. A series of formulation experiments and physical and chemical characterizations were carried out; the results show that the feasible maximum content of the crude MSS is as high as 60 wt%, and corresponding bending strength and water absorption of split tile samples fired at 1210 °C are 25.5 MPa and 1.14 wt% respectively. TCLP test reveals that the samples are environmentally compatible. The prospective industrial application of MSS to produce split tile will help to significantly reduce its environmental impacts.     

Preparation of spherical foamed body with function of media for waste water treatment by using waste LCD glass

Using waste LCD glass as a base material helped developed the manufacturing process of the spherical foamed body and its varied functionality. Also, the manufactured spherical foamed body showed great performance as a water treatment media. By mixing 90 wt% of waste LCD glass, 100 parts by weight of glass mixture that has 10 wt% kaolinite as a shaping agent, 1.0 part by weight of carbon foaming agent, and mixture of each 1.5 parts by weight of Na₂CO₃, CaCO₃ and Na₂SO₄ as foaming agents and the MgO as a parting agent for 10 min of foaming calcination in the rotary kiln at 970–1000 °C, the spherical foamed body can be manufactured effectively. The manufactured spherical foamed body performed as a great water treatment media by showing 70.5% of SS removal efficiency, 56.1% of BOD removal efficiency, 57.5% of COD removal efficiency, 28.6% of denitrification and 49.8% of phosphorous removal.     

Fast pyrolysis of chicken litter and turkey litter in a fluidized bed reactor

Disposal of poultry litter such as chicken litter and turkey litter is becoming a major problem in the USA poultry industry because of environmental pressures and health concerns. Poultry litters form wood chips, chicken litter (flock 1, flock 2 and broiler) and turkey litter were converted into bio-oil, gas and char in a fluidized bed reactor at the temperature ranges of 450–550 °C. The bio-oil yield of poultry litter was relatively low (15–30 wt%) compared to wood derived bio-oil (34–42 wt%). The gas yield was increased from 32 to 61 wt% with increasing reaction temperature, and char yield was between 22 and 45 wt% depending on age and reaction conditions. The higher heating value (HHV) of the poultry litter bio-oil were between 26 and 29 MJ/kg, whereas that of the bedding material (wood chips) was 24 MJ/kg. The dynamic viscosities of bio-oil were varied from 0.01 to 27.9 Pa s at 60 °C, and those of values were decreased with increasing shear rate.     

Preparation and characterization of the one-piece wall ceramic board by using solid wastes

For the purpose of building energy-saving, a novel one-piece wall ceramic board was prepared by using fly ash and ceramic waste as the main raw materials for its matrix part and foam part, respectively. The effects of raw material composition, sintering temperature on the macro and micro properties were systematically investigated. The optimum parameter for the matrix part was obtained at 1220 °C with 70 wt% fly ash and 4 wt% quartz, while that for the foam part was 1220 °C with 97 wt% ceramic waste and 3 wt% silicon carbide. For the matrix sample, the highest rupture modulus reaches 53.97 MPa, and the corresponding water absorption capacity and thermal conductivity are 1.08% and 0.54396 W/(m K), respectively. For the foam part, the best bulk density and thermal conductivity are 443 kg/m³ and 0.10528 W/(m K), respectively. Subsequently, the optimal matrix and foam samples were introduced into the co-fired process (1220 °C), and the results show that the new method for the preparation of one-piece wall ceramic board was fully acceptable. Furthermore, the simulated results indicate that the proposed one-piece wall ceramic board can efficiently reduce the thermal bridges and exerts excellent energy conservation effect.     

Compressive strength and microstructure of alkali-activated mortars with high ceramic waste content

The present work investigated alkali-activated mortars with high ceramic waste contents. Tile ceramic waste (TCW) was used as both a recycled aggregate (TCWA) and a precursor (TCWP) to obtain a binding matrix by the alkali-activation process. Mortars with natural siliceous (quartz) and calcareous (limestone) aggregates, and with other ceramic waste materials (red clay brick RCB and ceramic sanitaryware CSW waste), were also prepared for comparison purposes. Given the lower density and higher water absorption values of the ceramic aggregates, compared to the natural ones, it was necessary to adapt the preparation process of the recycled mortars by presaturating the aggregate with water before mixing with the TCWP alkali-activated paste. Aggregate type considerably determined the mechanical behaviour of the samples cured at 65 °C for 3 days. The mortars prepared with the siliceous aggregate presented poor mechanical properties, even when cured at 65 °C. The behaviour of the limestone aggregate mortars depended heavily on the applied curing temperature and, although they presented the best mechanical properties of all those cured at room temperature, their compressive strength reached a maximum when cured at 65 °C, and then decreased. The mechanical properties of the mortars prepared with TCWA progressively increased with curing time (53 MPa at 65 °C for 28 days). An optimum 50 wt% proportion was observed for the limestone/TCWA mortars (≈43 MPa, 3 days at 65 °C), whereas the mechanical properties of that prepared with siliceous particles (10 MPa) progressively increased with the TCWA content, up to 100 wt% substitution (23 MPa). Limestone particles interacted with the binding matrix, and played an interesting beneficial role at the 20 °C curing temperature, with a slight reduction when cured long term (28 days) at 65 °C. The results demonstrated a potential added value for these ceramic waste materials.     

Development of a plate-to-plate MPCVD reactor configuration for diamond synthesis

The design and performance of a microwave plasma chemical vapor deposition (MPCVD) reactor based on compressed microwave waveguides and plate-to-plate substrate holders are described. This reactor can be operated at pressures from 10 to 40 kPa with microwave power of 0.4–1.2 kW, and a high plasma power density up to 500 W/cm³ can be obtained. The single-crystal diamond (lower substrate holder) and polycrystalline diamond (upper substrate holder) have been grown by the plate-to-plate MPCVD reactor using high pressure CH₄-H₂ mixture gases. Experimental results show that high quality single-crystal diamond and polycrystalline diamond were simultaneously synthesized at a growth rate of 25 μm/h and 12 μm/h, respectively. The results indicate that our MPCVD reactor is unique for the synthesis of diamond with high efficiency.