Coal Grains Research Articles

Comparative Analysis of Combustion of Qualified Composite Fuel for the Transitional Period in the Household and Communal Sector in Poland

Abstract The article presents the results of laboratory combustion tests of the microbriquette obtained from useless coal (grain class of < 5 mm) generated in the production of “eco-pea” (eko-groszek) coal. The briquettes of 1.5 and 2.5 cm3 were made in a roller press of crushed coal granulation down to 2 mm, mixed with a binder and/or catalytic additives and sorbents, then dried to final moisture of about 7%. The tests were carried out on a specially designed stand enabling to determine the differential curve of the weight loss of samples heated to the ignition temperature and then burnt with laminar airflow by natural chimney draft. Comparative tests were carried out with ecopea coal from the “ZG Sobieski” mine. The results indicate that composite fuels, in the form of microbriquette, ignite faster, burn at a higher temperature and leave less ash when burned than lump coal. The greater reactivity of the briquette concerning the lump coal allows for minimizing the air rate by about 10%, which also reduces the exhaust gas volume by the same amount and the stack losses. It reduces the velocity of dust lifting, which leads to the reduction of their emission.

Assessment and Effect of Mining Subsidence on Farmland in Coal–Crop Overlapped Areas: A Case of Shandong Province, China

Farmland protection and food security is highly focused on in China. However, coal mining has caused negative consequences to cropland in coal–crop overlapped areas (COA), especially in eastern China. Thus, revealing the spatiotemporal impact of coal mining on farmland on a large scale is crucial for coordinating coal mining and grainland protection. In this study, Shandong Province, a representative coal–grain composite area, was selected as a research case to evaluate the damage of mining subsidence on farmland. Firstly, the field investigation and mining subsidence prediction revealed the current situation and trend of farmland damage caused by mining in 2021 and 2030. Then, we evaluated the impact of cropland damage on grain yield. Finally, farmland landscape patterns, ecological environment, and social stability due to mining subsidence were discussed. The results show that: (1) the damaged cropland in 2021 was 6.40 × 104 ha, of which 1.40 × 104 ha was non-yield. By 2030, the accumulative area of damaged cropland is estimated to reach 7.52 × 104 ha. (2) By 2025 and 2030, the farmland yield will be reduced by 16.44 × 104 t and 18.45 × 104 t in overlapped areas of Shandong. (3) The subsidence led to cropland fragmentation, and the terrestrial ecosystem became an aquatic ecosystem, further intensifying the contradiction between more people and less land. This study provides a reference for coordinating coal and grain production and formulating cropland protection strategies in similar regions. Meanwhile, it also provides a scientific basis for the government to formulate land reclamation indicators, technology, management, and acceptance standards and establish and implement the reclamation reward and punishment system.

Measurement of the coefficient of seepage characteristics in pore-crushed coal bodies around gas extraction boreholes

Gas extraction is a form of energy extraction. The seepage and transport of gas during extraction is complex. The accurate determination of its permeation parameters is an important technical parameter. A tri-axial permeation test of the crushed grain media was designed to determine the permeation pattern of gas fuels within the crushed coal around the borehole. The resistance to gas fuel seepage was explored. The results show that: the pore structure formed by the crushed coal grains will be compressed and closed again under three-dimensional stress. The process of deformation and destruction of crushed coal grains can be divided into three stages: when the grains are subjected to a force of 1.2 kN–1.4 kN, the grains may compress each other to form a colloid. The coefficient of resistance is dependent on the permeability of the crushed coal sample, and the non-Darcian phenomenon caused by inertial loss during permeation can be characterized by the distribution of Re values f = 149.1/Re + 1.5. The two coefficients of the quadratic term in the Forchheimer equation change dynamically as the flow regime changes. This result can provide a theoretical basis for the efficient extraction of gas resources.

Mechanism of Coking Pressure Generation in the Light of the Results of Laboratory Tests

The phenomenon of coking pressure is crucial for cokemaking both in respect of a safe coke oven battery operation and a proper quality of the produced coke. In spite of that, the mechanism of this phenomenon has not been clearly explained yet. The aim of the presented research was to clarify which of the phenomena most commonly mentioned in the literature on the subject, i.e., the reduced gas permeability of the plastic layer or the swelling of plasticized coal grains, is responsible for generating internal coking pressure. To that end, laboratory equipment was developed which enabled examining the pressure generated by the bed of plasticized coal grains under conditions of a varying possibility of its expansion. The results of the examinations suggest that the swelling phenomenon of plasticized coal grains is the direct cause of coking pressure, and the coking pressure strongly depends on the possibility of plastic layer expansion. The results confirm also the migration phenomenon of plasticized coal matter, especially towards the cool part of the charge as well as the possibility of compression of this part of coal charge. As a result of both these phenomena, it becomes possible for the plastic layer to expand, which results in a reduction of generated coking pressure.

The influence of closed pores and stacked coal grains on gas transport in CO2 injection enhanced CH4 recovery process

CO2 injection enhanced coalbed methane (CH4) recovery technology can achieve the enhancement of CH4 production and the effective geological storage of carbon dioxide in coal seams. A coal seam is composed of matrix and fractures. Matrix has open pores and closed pores and fractures may have stacked coal grains. However, the influences of closed pores in matrix and stacked coal grains in fractures on CO2 injection enhanced CH4 recovery have rarely been studied. This paper develops a numerical simulation model to explore the hydraulic-mechanical coupling responses in CO2 injection enhanced coalbed methane (CO2-ECBM) recovery process. This model considers the binary gas displacement and transport in ternary pores, the deformation of coal with different porosity, and fractal stacked coal grains in fractures. After verification with the data available from literature, this model is used to simulate a field trial in the Qinshui Basin. The simulation results show that the contribution of gas in closed pores to the total CH4 production enhanced by CO2 injection is more than 60% in high-rank coal and is proportional to the volume fraction of closed pores. The stacked coal grains in fractures affect the effective roughness and can be expressed by three structural parameters. Higher effective roughness induces lower cumulative CO2 injection and lower cumulative CH4 production and the conical bottom diameter of cone-like element has the largest influence. These findings can promote our understanding for the influence of closed pores and stacked coal grains on gas transport in coalbed gas reservoirs from a multi-scale perspective.

Investigating the effects of effective stress on pore-dependent permeability measurements of crushed coal.

The accurate determination of permeability is one of the parameters essential for the study of fluid flow and transport state. However, a large number of fractured coal bodies are faced during the production of coal mines. The study of permeability of these special media composed of grains of a certain size, whose structure is different from that of raw coal, has been in the exploratory stage. In this paper, inspired by the calculation method of median particle size and the calculation principle of KC’s equation, we calculate the permeability parameters of broken coal particles. It is considered that its permeability is closely related to the compaction and re-crushing process of skeletal grains. The lateral limit compression test of the crushed coal body was designed, and the pore-dominated permeability calculation method was given to reveal the mechanism of the action of the effective stress. The dependence relationship between the effective stress and the pore-correlation permeability is obtained by data analysis, and the force and deformation process of the crushed coal grain media is described. In contrast to the conventional Darcy series of permeability discussions, our approach excludes the influence of fluid factors on the permeability of porous media. The permeability of porous media is considered to be determined only by its own pore structure.

Experimental Investigation of Early-Warning Critical Energy for Strainbursts

This research aimed to establish an early-warning critical energy for coal instability based on the energy theory and acoustic emission characteristics of coal under triaxial compression. To obtain an early-warning critical strain energy indicating the increase in the risk of coal instability, conventional triaxial compression and acoustic emission (AE) tests were carried out on coal specimens taken from a 980-m-deep mine with initial confining pressures of 10, 15, 20, 25, 30 and 35 MPa. Stress–strain relations, AE features, and energy evolution characteristics during triaxial compression were analyzed. It was found that the energy evolution and AE event count changes across different loading stages. With increasing axial stress, most of the input energy stored in the coal specimens was in the form of elastic strain energy and the AE event count was close to zero, indicating that the coal grains reach a state of balance. After the elastic deformation stage, a portion of the input energy was consumed by inelastic deformation. Once the stress level exceeded the volumetric compressibility–dilatancy transition stress, the AE event entered a period of relative quiet, and the rate of energy dissipation abruptly accelerated, indicating that the coal grains achieved another state of balance before THE instability or failure. The balance of the rock grains is broken again (AE event count and the rate of energy dissipation both increased dramatically), coal achieved the peak strength and instability soon. The point at which the dissipated energy ratio α increased rapidly or the starting point of a quiet period, indicates an increase in the risk of coal instability. The corresponding elastic strain energy accumulated within the coal can be regarded as a precursor to instability or strainburst. Accordingly, a fitting formula is presented to predict the early-warning critical energy for brittle coal subject to different minimum principal stress. The analysis results in this paper can be helpful in the assessment of coal instability risk.

High-strength nanocrystalline intermetallics with room temperature deformability enabled by nanometer thick grain boundaries.

Although intermetallics are attractive for their high strength, many of them are often brittle at room temperature, thereby severely limiting their potential as structural materials. Here, we report on a previously unidentified deformable nanocrystalline CoAl intermetallics with Co-rich thick grain boundaries (GBs). In situ micropillar compression studies show that nanocrystalline CoAl with thick GBs exhibits ultrahigh yield strength, exceeding 4.5 gigapascals. Unexpectedly, nanocrystalline CoAl intermetallics also show prominent work hardening to a flow stress of 5.7 gigapascals up to 20% compressive strain. Transmission electron microscopy studies show that deformation induces abundant dislocations inside CoAl grains with thick GBs, which accommodate plastic deformation. Molecular dynamics simulations reveal that the Co-rich thick GBs play a vital role in promoting nucleation of dislocations at the Co/CoAl interfaces, thereby enhancing the plasticity of the intermetallics. This study provides a perspective to promoting the plasticity of intermetallics via the introduction of thick GBs.

Nonlinear and Linear Equation of Gas Diffusion in Coal—Theory and Applications

The authors derived the analytical solution to diffusion equations. The solution requires linearization of diffusion equations, as well as developing the obtained expression into a series. In particular, the result of the first procedure is highly deviated from the exact solution. The authors conducted a sorption experiment and then, in relation to the registered kinetics of the diffusion of CO2 inside hard coal grains, approximated the linear solution and the numerical nonlinear solution by means of the least squares method. As confirmed by the lower value of the sum of deviation squares, it can be clearly demonstrated that the nonlinear equation represents the actual measurement more accurately.

Dynamic in situ imaging of methane hydrate formation in coal media

Fast 3D X-ray imaging has proved to provide crucial insights into multi-phase dynamic processes in various geo-materials. In particular, many in situ imaging experiments have been made to study gas-hydrate formation in porous sandy samples. Such imaging is challenging for the methane gas-hydrate formation in coal samples because of the coal micro-porosity structure and lower X-ray contrast. Here we present results of the first dynamic in situ micro-computed tomography experiment of methane-hydrate formation in coal samples. Synchrotron phase-contrast tomography techniques allowed to achieve necessary contrast levels to separate all the materials of interest (gas, water, coal, and gas hydrate) in reconstructed images with high spatial and temporal resolution. The imaging results are compared to the ones from a similar tomographic experiment with sand samples. Methane-hydrate formation is accompanied by the water movements caused by cryogenic water suction that happens in sequences of short fast movements with longer equilibrium states in between. Only one type of the hydrate formation was observed in coal (growth as shells on grain boundaries) as opposed to three types in sand (shells, growth into gas pockets, and inside water volumes). In particular, this leads to a slower hydrate-formation speed in coal. For the coal sample, we also observed water extraction from grains, and interpreted it as competitive sorption of methane. We visualized the dynamic behavior of this water extraction via micro-channels inside the coal grains, and performed nano-tomography imaging of these channels for a better understanding of this phenomenon.

Maximizing recovery, grade and throughput in a single stage Reflux Flotation Cell

The Reflux Flotation Cell (RFC) utilises the Boycott Effect to decouple the overflow water flux from the gas flux, permitting in principle high product grade and recovery at a vastly higher volumetric feed flux. This study investigated this relationship between concentrate grade, recovery, and volumetric feed throughput using a single flotation stage and feed fluxes spanning 1–9 cm/s, well beyond that used in conventional flotation. Coal flotation tailings and hydrocyclone overflow provided convenient representations of “binary” feeds for the experiments, constituting liberated hydrophobic and hydrophilic particles. The results demonstrated robust recoveries through the preservation of the gas to feed flux ratio with increasing feed flux, while minimising the gas flux strengthened the capacity to maintain high product grade using inverted fluidization water as the wash water. Remarkably, a high product grade (low product ash%) was maintained over the extreme feed flux range by ensuring a net downwards flux of wash water delivered through the upper fluidized bed of bubbles. Coal Grain Analysis (CGA), an optical imaging technique, identified the maceral composition of the feed particles and validated, with close agreement, the RFC steady state separation performance. Indeed, under continuous operation the RFC data demonstrated an overall positive shift in performance relative to that of the standard tree flotation curve. The findings showed strong preservation of product grade and recovery using a single RFC stage, over a seven-fold increase in the feed flux relative to conventional flotation systems.

Enhancing potential of hydrofracturing in mylonitic coal by biocementation

AbstractMylonite coal is a representative of tectonically deformed coal and is a result of crushing original coal into fine coal grains under strong shear or long‐low tectonic stress. Because of its granular nature and the resultant inferior mechanical property, it is difficult to initiate fluid‐driven fractures within mylonitic coal reservoirs for enhancing coalbed methane recovery. The following explores a biomineralization method of microbially mediated calcium carbonate precipitation (MICP) to enhance the structural integrity and mechanical strength of mylonitic coal, enabling potential success for hydrofracturing. The experimental results indicate that the mechanical properties of mylonite coal are significantly enhanced after a short period of MICP treatment with ten cycles of treatments yielding a maximum uniaxial compressive strength (UCS) of 8.7 MPa and a maximum brittleness index of 0.218 approaching that of the hard coal. The increments in UCS and brittleness of biocemented mylonite coal show a positive correlation with the generated calcium carbonate content. Scanning electron microscopy (SEM) imaging indicates that the generated calcium carbonate precipitates first randomly occur on the particle surfaces, and then occupies the interstitial space until particle‐particle bonds are developed. The irregular morphology of coal particles results in two contact relations between particles, point contact and planar contact, causing a significant difference in biocementation effectiveness. Two microfailure patterns of biocemented coal with uniaxial compression are observed. One is that the coal particles are crushed, and the other occurs at the biocemented interface between the coal particles and calcium carbonate crystals.

ВПЛИВ ВОЛОГОСТІ ВУГІЛЬНОЇ ШИХТИ НА ЇЇ НАСИПНУ ГУСТИНУ

The necessity of determining the bulk density of the coal charge for calculating the operation of coke ovens is argued, since this indicator affects the physicochemical properties of coke and the productivity of coke ovens. The diagram of the apparatus is provided and the method for determining the bulk density of the coal charge is presented. Each value obtained is the average of five parallel determinations. There has been presented the study of the dependence of the bulk density on moisture content for two research coal blends of different grades, compiled with the participation of domestic and imported grades of coal. For charge No. 1, it was concluded that the bulk density of the coal charge significantly depends on its working moisture. The minimum bulk density (798 kg/m3 ) is achieved at a working moisture of about 7 %. With a decrease in the value of the working moisture to 4 % or its growth to 12 %, the value of the bulk density of the coal charge increases to 820 and 871 kg/m3 , respectively. The minimum value of the bulk density of charge No. 2 (779 kg/m3 ) is noted at a working moisture of 7-8%. With a decrease in the value of the working moisture to 4.5 % or its increase to 12 %, the value of the bulk density of the coal charge increases to 845 and 892 kg/m3 , respectively. Based on the generalization of the results obtained, mathematical and graphic dependencies have been developed. They describe the effect of an increase in the moisture content of coal charges on the content of a class less than 0.5 mm in them, as well as the values of the average diameter of coal grains and bulk density. It was found that coal charges are characterized by a minimum bulk density at a moisture content of 7.2 %. With an increase in the moisture content of coal charges to 12 %, there is a sharp decrease in the content of the class less than 0.5 mm. This is due to the pelletization of small coal grains, which is reflected in an increase in their average diameter. Keywords: coal charge, bulk density, moisture content, particle size distribution, mathematical relationships. Corresponding author N.A. Desna, e-mail: desnana@ukr.net

КРАЙОВИЙ КУТ ЗМОЧУВАННЯ КАМ’ЯНОГО ВУГІЛЛЯ ВОДОЮ

It is known that in the process of coking a compacted coal charge during its ramming in an industrial ramming-loading-pushing machine, the moisture of the charge plays the role of a compaction agent. On the basis of this, the authors put forward a reasonable assumption that the higher the ability of coal grains to hydration, the stronger the contact between them and, accordingly, the greater the density of the formed rammed coal cake. Therefore, the determination of the ability to hydrate the surface of coal used in the charge for ramming is of both theoretical and practical importance. For the numerical determination of this indicator, the authors have chosen the contact angle of wetting, determined by the method of "sessile drop" of water on a carbon substrate. The article presents the results of a study of the ability of various brands of coal to hydrate. The article describes the characteristics of the studied grades of coal and their contact angle of wetting with water (Ɵ) after 1, 2 and 3 minutes of keeping the drop on a polished surface. Since according to the literature data, the organic mass of coal is hydrophobic, and mineral impurities, as a rule, are hydrophilic, the authors investigated the degree of influence of the "ash content of coal" (Аd ) indicator on the value of Ɵ. To determine the influence of the wetting angle and the internal moisture content of coal after 14 hours of moisture saturation in water (Wins) on the strength (ϭss) of the rammed sample, the corresponding graphical dependence was determined. The data obtained indicate that any significant relationship between Аd and Ɵ is absent, the correlation coefficient is insignificant (r = 0.28). Thus, the predominant factor in the hydration of cleaned coal is the properties of its organic matter. The correlation between Ɵ and the yield of volatile substances Vdaf and the content of vitrinite Vt is also insignificant – the correlation coefficient is up to 0,43 and 0,50 respectively. A close relationship of the contact angle was found with the reflection coefficient of vitrinite Ro (r = 0.72), the internal moisture content of coal after 14 hours of saturation in water, Wins (r = 0,65), and the shear strength of the rammed coal sample ϭss (r = 0,68). Keywords: coal, ability to hydration, contact angle of wetting, organic mass of coal, mineral impurities, density, strength. Corresponding author V.M. Kuznichenko, e-mail: : ko@ukhin.org.ua

Experimental study on the spontaneous imbibition characteristics of accumulated coal grains

Disaster prevention effect of hydraulic techniques in mines depends on the migration range of water and the wetting degree of coal body. Therefore, it is of great significance to study the interaction among accumulated coal grains and water during migration and flow. First, this paper simulates the migration and wetting process of water and coal grains with an inverse spontaneous imbibition experiment. Then, theoretical and experimental results are compared to determine the optimal determination method of grain diameter as a key parameter in model. The research shows that the lower the metamorphic grade is, the more obvious the imbibition, and the grain diameter of approximately 100–297 μm produces the greatest imbibition effect. At the same time, after realizing that large grains have a dominant influence on formation of imbibition channels, the traditional mathematical model of imbibition height is improved and thus provides a theoretical guiding significance for improving hydraulic techniques.

Effect of Coal Gangue Grain Size on Strength of Foam Concrete

This work shows that the grain size of coal gangue has affects on the strength of foam concrete with coal gangue. Coal gangue was crushed and separated into three grades sand according to the size which were 0.16-0.6mm, 0.6-2.5mm and 2.5-5mm. Then these coal gangue sand was used to manufacture foam concrete with a density of about 850kg/m3. The compressive, flexural strength, water absorption and softening coefficient of coal gangue foam concrete were tested. The results show that compressive strength of foam concrete exhibits a monotonic decreasing while coal gangue content increases and the decreasing rate would accelerate with the increasing of grain size. And the water absorption increased with the coal gangue content and grain size increasing. Small size coal gangue could improve the water absorption resistance. The coal gangue foam concrete is a water-resistant material and the softening coefficient is above 00.85, when the diameter of coal gangue fine aggregate is below 2.5 mm.

Assessment of Heating and Cooling of a Spontaneous Fire Source in Coal Deposits—Effect of Coal Grain Size

Fire hazard assessment in coal mines is performed on the basis of concentrations of particular gases emitted from the heating coal deposit, but more precise criteria and indicators are needed to assess fire hazard properly—both during the temperature rise phase and in the coal bed cooling phase. In the paper the impact of coal grinding on hazard assessment of spontaneous fire development in the coal deposit during heating and cooling the fire source was analyzed. The intensity of desorption of ethane, ethylene, propane, propylene, acetylene, carbon monoxide and hydrogen is the resultant of temperature and grinding of coal samples. The results proved that the ratio of concentrations emitted by standard versus coarsely crushed coal for each of the gases, changed both in the growth phase as well as in the temperature drop phase. It was found that as the temperature rose, the effect of coal grinding on the release of ethane, ethylene, propane, propylene and carbon monoxide decreased. The greatest effect of coal grinding was observed in the case of ethane and propane, while the lowest in the case of hydrogen and carbon monoxide.

Recovery of Fine Coal Grains from Post-Mining Wastes with Use of Autogenous Suspending Bed Technology

Abstract In addition to rock waste post-mining waste dump sites also contain coal grains justifying treating the dump sites as secondary mineral deposits. The article presents the results of laboratory tests aimed at determining the possibility of using suspending bed technology to separate a combustible substance from post-mining waste of a 4-0 mm grain size. The test results showed the possibility of obtaining good quality coal concentrates from coal waste of a grain size of 4-1 mm. The need for desludging and densifying the feed for the classifier with an autogenic suspending bed in the case of coal waste beneficiation in a wide 4-0 mm grain size justifies the use of a two-chamber device or two separate classifiers for narrower grain size classes. Concepts of systems for the recovery of fine coal grains providing the use of the classifier with autogenous suspending bed for the density distribution of feeds with high ash content are presented. The concepts were developed for beneficiation of the material in a 4-0 mm grain class.

Pore Size Distribution Characteristics of High Rank Coal with Various Grain Sizes.

Particle void filling effects (Pf) under low pressure and coal matrix compressibility effects (Pc) at high pressure should not be ignored when using mercury intrusion porosimetry (MIP) to study the pore size distribution of coal. In this study, two coal samples (FX and HF) collected from western Guizhou were crushed into three different grain sizes; then, the subsamples were analyzed by MIP and low-pressure nitrogen adsorption to study the pore size distribution characteristics. The micro- and transition pore volumes contribute to the total pore volume of the FX and HF subsamples. With decreasing subsample grain sizes, the macropore volume of FX subsamples tends to increase, while mesopore volume decreases; the volumes of micropores and transition pores first increase and then decrease. In regard to the HF subsamples, the volumes of macropores and mesopores do not reveal any distinctive changes, while the 40–60 mesh subsample contains the greatest volume of micropores and transition pores. Fractal theory was introduced to determine Pf and Pc. Pf barely changed as grain size decreased; it ranged from 0.1 to 0.15 MPa. However, Pc increased with reduced coal grain sizes. The coal matrix compressibility coefficients of the subsamples were calculated from the cumulative mercury volume curve, and the true pore volume was also modified. The modified volume of macropores does not change markedly, while the volumes of mesopores and transition pores decrease significantly, clearly indicating the coal matrix compressibility under high mercury injection pressure. The modified pore volume shows that the pore (<10,000 nm) still harbors fractal characteristics.

Recovery and cleaning of fine hydrophobic particles using the Reflux™ Flotation Cell

The Reflux Flotation Cell (RFC) consists of a vertical vessel located above a series of parallel inclined channels. This novel system, which is the inverse of an existing gravity separation system known as the Reflux Classifier, provides a powerful mechanism for enhancing bubble-liquid segregation. The usual link between the imposed gas flux and water recovery in the froth product is decoupled through this mechanism, resulting in the establishment of a concentrated bubbly zone throughout the upper section of the cell, and no froth zone. A downwards fluidization arrangement promotes strong washing of the flotation product, to remove the hydrophilic slimes from the hydrophobic concentrate. The mechanism also provides for strong control of the bias flux, allowing a significant positive bias flux to be established. A feed suspension of fine coal tailings containing hydrophobic coal and hydrophilic mineral matter was subjected to the novel flotation, providing an ideal basis for studying the interplay between the hydrophobic particle recovery, inferred by the combustible recovery, and the product grade, inferred by the mineral matter content of the product, expressed by the ash %. The feed ash % was about 43 wt%. The product cleaning was compared to firstly, the results from the tree flotation method, and secondly, a newer method known as Coal Grain Analysis (CGA). The RFC results were found to lie to the left of the tree curve, converging to the limit described by the CGA analysis. This work suggests the RFC and CGA provide a form of mutual validation on the limits of cleaning, though more work will be needed to confirm this finding. The RFC was operated with a volumetric feed flux of the order 1 cm/s, a rate comparable to that of conventional flotation systems, with the bias flux ranging from 0.0 cm/s to 1.9 cm/s. For a fixed gas flux of 1.1 cm/s, increases in the liquid bias flux from 0.0 cm/s to 1.0 cm/s resulted in a decrease in product ash from 18.2% to 7.8%, and a reduction in combustible recovery from the order 87% to 75.6%. Operating at the lowest gas flux of 0.6 cm/s, and the strongest bias flux of 1.9 cm/s yielded a low product ash of 6.7% at the reduced combustible recovery of 64%.