Technoeconomic evaluation of peat/water/oil mixture as a liquid fuel

Results of bench-scale tests on the rheological and calorific properties of peat/water/No. 4 fuel-oil mixtures indicated that a peat/water/oil (PWOM) slurry with rheological characteristics and calorific properties suitable for combustion in conventional boilers can be prepared using 40% (by weight) peat, of – 246.4 μm particle size and 40–45% natural moisture content, in the presence of 1% Cab-O-Sil PTG as a stabilizing additive. This low cost liquid fuel has a calorific value about 80% of, and a flow rate about 1.2 times the corresponding values for fuel oil No. 4. An economic feasibility study was conducted based on a PWOM cost to the consumer 10% below the cost of No. 4 fuel oil, and no ‘rent’ cost to the PWOM producer for the peat resource. The study shows that a project to harvest 112,000 tonnes of peat per year and to produce 282,000 tonnes of PWOM fuel is profitable for a range of assumed cost factors.     

The properties of Chinese typical brown coal water slurries

Eight typical Chinese brown coals were evaluated for their potential as coal water slurries (CWSs). The solid ratios and stability of brown coal water slurries were studied and compared with bituminous coal slurries. Results showed the amounts of oxygen functional groups in brown coals are much higher than that in bituminous. Thus, solid ratios at fixed viscosity for brown coal slurries are about 46–55%wt, much lower than those for the bituminous samples that are about 65%wt. Most slurries of brown coals exhibit good stability. Moreover, additives never universally improve slurry ability and stability simultaneously.     

Hydrothermal preparation of low-rank coal-water fuel slurries

Lignite and sub-bituminous coals are by nature high in inherent moisture and oxygen content and low in calorific heating value. As-mined low-rank coals when mixed with water generally produce slurries with low solids content and with heating values generally less than 11.6 MJ/kg. These same slurries are usually unstable and form hard-pack sediments quickly, unless chemical additives or constant agitation are added. The low heating value and poor storage and flow characteristics of these coal-water mixtures discourage the use of raw lignite and subbituminous coals for preparation of slurries for fuel purposes.Hydrothermal conditioning, in a water slurry at temperatures above 230 °C and pressures above 552 MPa, is one method that can significantly aid in the preparation of low-rank coal-water fuels. High-pressure hot-water thermal conditioning of lignites and sub-bituminous coals has been found not only to change both the chemical and physical characteristics of the coal but also to alter the coal slurry's rheological properties. These changes are controlled by process variables (i.e. temperature, residence time, particle size, and mode of processing) and result because of decarboxylation, mild pyrolysis, extraction, dehydration, and surface modification; all of which occur during hydrothermal treatment. Using the hydrothermal process, concentrated low-rank coal-water slurries with heating values approaching or exceeding the heating value of the as-mined coal have been achieved with pseudoplastic flow behavior and stability towards settling, without the use of additives.Pilot-scale studies using a 90-kg/hr process development unit (PDU) are currently under way to produce hydrothermally treated low-rank coal fuel slurries for combustion tests in a pilot-scale, slurry-fed test furnace.     

Promising components of waste-derived slurry fuels

The paper presents the results of experimental studies of energy (calorific value, ignition delay times and threshold ignition temperatures, duration and temperature of combustion) and environmental (CO₂, NO_x and SO_x emission) characteristics of fuel slurries based on pulverized wood (sawdust), agricultural (straw), and household (cardboard) waste. Wastewater from a sewage treatment plant served as a liquid medium for fuels. Petrochemical waste and heavy oil were additives to slurries. The focus is on obtaining the maximum efficiency ratio of slurry fuel, calculated taking into account environmental, cost, energy and fire safety parameters. All slurry fuels were compared with typical coal-water slurry for all the parameters studied. A comparison was also made between slurries and traditional boiler fuels (coal, fuel oil). The relative efficiency indicator for waste-based mixtures was varied in the range of 0.93–10.92. The lowest ignition costs can be expected when burning a mixture based on straw, cardboard and oil additive (ignition temperature is about 330 °C). The volumes of potential energy generated with the active involvement of industrial waste instead of traditional coal and oil combustion are forecasted. It is predicted that with the widespread use of waste-derived slurries, about 43% of coal and oil can be saved.     

Novel microreactors of polyacrylamide (PAM)CdS microgels for admirable photocatalytic H2 production under visible light

Cadmium sulfide, with its narrow band gap, can be used as a photocatalyst in the visible light region for the splitting of water, but its limited number of active sites and tendency to agglomerate are problematic for producing high yields of hydrogen. Therefore, an inverse emulsion polymerization method was used to fabricate polyacrylamide (PAM) microgels as a substrate to immobilize CdS nanoparticles (PAM-CdS). The PAM microgels not only immobilized the CdS nanoparticles, but also prevented aggregation. NCd bonds in the PAM-CdS microgels facilitated electron transfer from the PAM to the CdS resulting in more electrons participating in the H₂ production process. The electrostatic interactions between the PAM and CdS also hindered the recombination of electron-hole pairs. These PAM-CdS microgels exhibit admirable photocatalytic H₂ production performance with a H₂ production rate of up to 5.21 mmol h⁻¹ g⁻¹.     

Developing coal-combustion technologies

Improved and new methods for direct coal utilization are reviewed, including the following: direct burning of pulverized coals, clean-fuel-combined-cycle systems, atmospheric pressure fluidized-bed combustion, advanced and pressurized fluidized-bed combustion, slagging combustors, coal-oil mixtures, coal-water mixtures, other coal slurries, etc. The emphasis is on research needs identified by the DOE/Coal Combustion and Applications Working Group (CCAWG) and relating to such processes as coal cleaning, slagging and fouling, environmental control systems, on-line diagnostics, and modeling.     

Developing coal-combustion technologies

Improved and new methods for direct coal utilization are reviewed, including the following: direct burning of pulverized coals, clean-fuel-combined-cycle systems, atmospheric pressure fluidized-bed combustion, advanced and pressurized fluidized-bed combustion, slagging combustors, coal-oil mixtures, coal-water mixtures, other coal slurries, etc. The emphasis is on research needs identified by the DOE/Coal Combustion and Applications Working Group (CCAWG) and relating to such processes as coal cleaning, slagging and fouling, environmental control systems, on-line diagnostics, and modeling.     

Enhancement in proton conductivity by blending poly(polyoxometalate)-b-poly(hexanoic acid) block copolymers with sulfonated polysulfone

Designing polymer chains which contain building blocks with well-defined dimension is an efficient method to induce microphase separation and regulate the ionic channels of polymer electrolyte membranes (PEMs). In this study, a Wells-Dawson-type polyoxometalate (POM) is synthesized and chemically bonded to a norbornene derivative to prepare poly (POM) blocks. Then the block copolymer poly (POM)₁₀-b-poly (COOH)₃₀₀ is fabricated using poly (POM) and poly (COOH) blocks. Finally, the block copolymer is blended with sulfonated polysulfone (SPS). The electrostatic interactions between the block copolymer and SPS confer the blend membrane with enhanced mechanical and dimensional stabilities. Due to the homogenous distribution of POM clusters and the hydrophilic-hydrophobic interactions between POMs and polymer backbones, the adjacent hydrophilic domains are connected and continuous proton-transfer channels are induced. As a result, the blend membrane displays proton conductivity of 0.053 S cm⁻¹ (25 °C, 100% RH) and 1.5 × 10⁻² S cm⁻¹ (80 °C, 40% RH), which are 2.52 and 6.25 times higher than those of the plain SPS membrane. Furthermore, SPS/POM-BC-30 shows a maximum power density of 164.9 mW cm⁻², which is 54.7% higher than SPS.     

Lignites from the Plains region of Alberta,Canada—Part 1: Petrography and depositional environment

The petrography of two coal seams in Alberta was determined using reflected light microscopy. Random reflectance is 0.36%, indicating a lignite rank. Huminite is dominant over liptinite and inertinite. Maceral assemblage suggests a wet forest moor depositional paleoenvironment. The predominance of telohuminite and gelohuminite over detrohuminite and inertodetrinite reveals peat formation in a rather reducing environment and a rapid burial of the peat, which prevented any significant oxidation. A few intervals with high levels of oxyfusinite reveal periodic drops of the water table. Results coincide with the interpretation based on the Na/K ratio, which is used as an indicator of the rate of sedimentation.     

Hydrothermal liquefaction of Miscanthus × Giganteus: Preparation of the ideal feedstock

Hydrothermal Liquefaction (HTL) is a versatile thermochemical pathway that converts wet or moist biomass into a bio-oil with promising properties as a future replacement of fossil oil. Lignocellulosic biomasses are of particular interest as they are representative of almost all terrestrial plant material. The fibrous nature of lignocellulosic biomass may however induce clogging and damage in continuous HTL reactors systems. This study investigates the pretreatment of Miscanthus × Giganteus (a perennial grass) in order to achieve stable feedstock slurries. To this end, the stabilizing effects of homogeneous catalysts are studied as well as the use of carboxymethyl cellulose as additive to prevent sedimentation. Finally, the impact of the applied pretreatment methodologies on the HTL process was evaluated with particular emphasis on product distribution and carbon balances.     

An examination of physical and chemical properties of urban biochar for use as growing media substrate

The purpose of this study was to evaluate the suitability and optimum rate of addition of Urban Biochar (UB) as an alternative to standard coir peat in plant growing media. UB was prepared through pyrolysis of 2:1 ratio of biosolids to greenwaste on a dry mass basis. Two incubation experiments are reported both with five different growing media mixtures which were subjected to periodic wetting and drying. Media mixtures consisted of different rates of UB (100%, 60%, 40%, 20%) mixed with composted pine bark on a volume basis and compared to an industry standard media with 0% UB. The physical and chemical properties of the mixtures were compared pre and post incubation. Substituting coir peat with UB increased media pH, C:N mass ratio, nutrient content, air filled porosity and bulk density. Furthermore, addition of UB to media also increased the proportion of particles in the desirable range for growing media (0.25–2 mm). UB amended mixes were found to be most stable in terms of both bulk density and resistance to particle breakdown. Fourier transform infrared spectroscopy analysis suggested that periodic wetting and drying enhanced surface oxidation. We found that UB amended substrates, up to 60% biochar on a volume basis, could deliver similar physical and chemical benefits to those of coir peat based industry standard media.     

Pipeline hydraulic transport of biomass materials: A review of experimental programs,empirical correlations,and economic assessments

Pipeline hydro-transport, an economically viable means of delivering large volumes of biomass, can replace conventional modes of transport – road, rail, and river - to improve the economy of pulp and paper mills, as well as bio-based energy facilities. This paper is a review of experimental and theoretical studies conducted by various sectors on the transport of wood and non-wood biomass-water mixtures (slurries) in pipes. The aims were to collect technical challenges, governing mechanical equations, and associated economic issues, as well as to identify the gaps in knowledge in the area. There have been several experiments conducted on pipeline hydro-transport of wood chips over a wide range of pipeline materials, lengths, and diameters. However, pipeline transport of non-wood agricultural residue slurries, as well as the performance of the centrifugal slurry pump handling such mixtures, has recently been investigated in a single lab-scale pipeline facility. Several researchers have proposed empirical correlations to estimate friction loss in wood chip slurries flowing in pipes and also recommended technically and economically optimum pumping velocities. Those correlations, however, are reported to come with noticeable deviations from one another and from experimental measurements. One empirical correlation has been also proposed to predict, with an uncertainty of less than 10%, the longitudinal pressure gradients in pipeline hydro-transport of agricultural residue biomass. All the experimental measurements and empirical correlations based some studies on the economic feasibility of pipelining wood chip-water mixtures. These studies proved the concept of economy of scale to be highly applicable to biomass pipeline systems.     

The intensity evaluation of the hydrothermal sedimentation and the relationship with the formation of organic-rich source rocks in the Lower Cambrian Niutitang Formation in Guizhou Province,China

A synthetical study was carried out on the relationship between the hydrothermal sedimentation and the formation of organic-rich source rocks in the Lower Cambrian Niutitang Formation in Guizhou Province, China. Analysis of the high trace elemental contents showed that the V/Sc-V/Cr diagram can be used to distinguish the hydrothermal sediments from normal marine sediments. Cr/Sc ratios can quantitatively evaluate the intensity of hydrothermal sedimentation on account of the positive correlation between the ratios with enrichment factors (EFs) for As, Sb and others. The relationship between Cr/Sc ratios and TOC content illustrated that (1) there was a positive linear correlation between them under the low intensity of hydrothermal activities (Cr/Sc<20), and the enrichment and preservation of organic matters were obviously dominated and potentiated by the hydrothermal sedimentation; (2) The hydrothermal sedimentation was one of the most essential factors influencing the enrichment and preservation of organic matters amidst the medium condition (20< Cr/Sc <300); (3) in the high condition (Cr/Sc > 300), the higher the hydrothermal intensity, the less the enrichment and preservation of organic matters, in other words, it is not conducive to the formation of organic-rich source rocks.     

Pelleted biochar: Chemical and physical properties show potential use as a substrate in container nurseries

We found that peat moss, amended with various ratios of pellets comprised of equal proportions of biochar and wood flour, generally had chemical and physical properties suitable for service as a substrate during nursery production of plants. High ratios of pellets to peat (>50%) may be less desirable because of high C:N, high bulk density, swelling associated with water absorption, and low volumetric water content, whereas a mixture of 75% peat and 25% pellets had enhanced hydraulic conductivity and greater water availability at lower (<−10 kPa) matric potentials. Adding pellets to substrates used to grow plants in nurseries has potential to add value to biochar and thereby improve economic viability of pyrolysis. Moreover, biochar-amended substrates offer opportunity to sequester carbon as part of the normal outplanting process.     

A comparison of coal-water slurry pipeline systems

Coal-water slurry pipeline systems are in various stages of development and exhibit many similarities, but they also have several unique characteristics. Existing and proposed systems range from conventional coarse- and fine-coal slurry pipeline media to the stabilized flow and coal-water mixture slurries that are under development. The roles planned for the coal being burned and the coal slurry pipeline, combined with the advantages and disadvantages of the alternative systems, tend to determine which system is most applicable for a particular use. Principal selection criteria include transport distance, water requirements, cost, and end use. Conventional coarse-coal slurries are best suited to very short-distance applications, where low water use is possible through closed-loop operation. Conventional fine-coal slurries generally require greater preparation and dewatering costs but can be transported great distances. These two systems offer excellent opportunities for rapid implementation because they have been tested on a full-scale basis. Use of the stabilized-flow system offers opportunities for domestic combustion and export because it is cheaper than coal-water mixtures. Coal-water mixtures provide the unique capability to displace oil use in oil-fired boilers. The coal-water pipeline systems for stabilized-flow and coal-water mixtures have not yet been tested on a large-scale basis.     

Laminar burning velocity and Markstein length of nitrogen diluted natural gas/hydrogen/air mixtures at normal,reduced and elevated pressures

Flame propagation of premixed nitrogen diluted natural gas/hydrogen/air mixtures was studied in a constant volume combustion bomb under various initial pressures. Laminar burning velocities and Markstein lengths were obtained for the diluted stoichiometric fuel/air mixtures with different hydrogen fractions and diluent ratios under various initial pressures. The results showed that both unstretched flame speed and unstretched burning velocity are reduced with the increase in initial pressure (except when the hydrogen fraction is 80%) as well as diluent ratio. The velocity reduction rate due to diluent addition is determined mainly by hydrogen fraction and diluent ratio, and the effect of initial pressure is negligible. Flame stability was studied by analyzing Markstein length. It was found that the increase of initial pressure and hydrogen fraction decreases flame stability and the flame tends to be more stable with the addition of diluent gas. Generally speaking, Markstein length of a fuel with low hydrogen fraction is more sensitive to the change of initial pressure than that of a one with high hydrogen fraction.     

Effects of synthetic gas constituents on combustion and emission behavior of premixed H2/CO/CO2/CNG mixture flames

In this study, effects of synthetic gas constituents on combustion and emission behavior of premixed H₂/CO/CO₂/CNG blending synthetic gas flames were experimentally investigated in a swirl stabilized laboratory scale combustor. Effects of these constituents on flashback and blowout equivalence ratios of respective mixtures were also determined. Firstly, mixtures of CNG/H₂/CO with varying H₂/CO ratios were tested and then each mixture was diluted with the same amount of CO₂ (20% by volume) to better represent synthetic gas. H₂/CO ratios of tested gas mixtures were so adjusted that heating value of each gas mixture was low, moderate or high. Combustion behavior of such mixtures was evaluated with respect to measured axial and radial temperature values. Moreover, emission behavior was analyzed by means of emitted CO, CO₂ and NO_x levels. Flame temperature measurements were conducted with B and K type thermocouples. Emission measurements were performed with a flue gas analyzer, which was equipped with a ceramic coated probe, as well. Results of this study revealed the great impact of gas composition on combustion and emission behavior of studied flames. Two main findings are: H₂/CO ratio slightly alters temperature distribution throughout combustor, while hydrogen reaction kinetics play the most significant role in synthetic gas combustion (1), CO₂ addition tremendously increases emissions of CO (2).     

Mathematical Modeling of Heat and Mass Transfer during Convective Dehydration of an Anisotropic Cylindrical Foodstuff

Two‐dimensional, unsteady‐state mass transfer was studied for air drying of an anisotropic finite cylindrical body. A mathematical model was developed for predicting the temperature of the drying sample at any time and moisture in any position in the drying sample at any time. The anisotropic nature of the drying material was considered in the mathematical model by taking into account the different moisture diffusivities in the axial and radial directions. A cut fresh green bean was used as an anisotropic material and a pilot‐scaled dryer was set up to investigate the drying behavior of this foodstuff. Several length‐to‐diameter ratios of fresh green beans were considered and the mathematical model was validated by comparison of the predicted values of average moisture content with the experimental data. The model was used to predict the moisture distributions inside the drying samples. Different moisture content distributions in the axial and radial directions during drying confirms the anisotropic nature of cut green bean samples. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.21119     

A study on the combustibility of torrefied wood oil/water mixture droplets

This paper presents the results of an experimental study on the combustion characteristics of torrefied wood (TW) slurries using suspended droplets. The main factors that were investigated in this study are the initial diameter of the slurry droplets, the ambient temperature, the composition of the slurries including the solid content and the percentage content of a second liquid added to the parent slurry. The results show a linear relationship between the square of the initial diameter of the droplet and total combustion time for all kinds of TW-based slurries that were studied here but the slope of the line depends on the composition of the slurries and the ambient temperature. Also, the combustibility of TW-based slurries was better than charcoal-based slurries due to the better combustibility of TW. By adding a certain amount of a second liquid, especially water, to a TW-oil mixture, the combustibility of the resulting slurry was improved.     

Experimental and modeling study of laminar burning velocity of biomass derived gases/air mixtures

Laminar burning velocities of four biomass derived gases have been measured at atmospheric pressure over a range of equivalence ratios and hydrogen contents, using the heat flux method on a perforated flat flame burner. The studied gas mixtures include an air-blown gasification gas from an industrial gasification plant, a model gasification gas studied in the literature, and an upgraded landfill gas (bio-methane). In addition, co-firing of the industrial gasification gas (80% on volume basis) with methane (20% on volume basis) is studied. Model simulations using GRI mechanisms and detailed transport properties are carried out to compare with the measured laminar burning velocities. The results of the bio-methane flame are generally in good agreement with data in the literature and the prediction using GRI-Mech 3.0. The measured laminar burning velocity of the industrial gasification gas is generally higher than the predictions from GRI-Mech 3.0 mechanism but agree rather well with the predictions from GRI-Mech 2.11 for lean and moderate rich mixtures. For rich mixtures, the GRI mechanisms under-predict the laminar burning velocities. For the model gasification gas, the measured laminar burning velocity is higher than the data reported in the literature. The peak burning velocities of the gasification gases/air and the co-firing gases/air mixtures are in richer mixtures than the bio-methane/air mixtures due to the presence of hydrogen and CO in the gasification gases. The GRI mechanisms could well predict the rich shift of the peak burning velocity for the gasification gases but yield large discrepancy for the very rich gasification gas mixtures. The laminar burning velocities for the bio-methane/air mixtures at elevated initial temperatures are measured and compared with the literature data.