Optimization of coal water slurry properties through fine coal particle addition

The project proposal was approved for only the phase I period. The goal for this Phase I project was to develop an industrial model that can perform continuous and efficient dewatering of fine coal slurries of the previous flotation process to fine coal cake of {approx}15% water content from 50-70%. The feasibility of this model should be demonstrated experimentally using a lab scale setup. The Phase I project was originally for one year, from May 2005 to May 2006. With DOE approval, the project was extended to Dec. 2006 without additional cost from DOE to accomplish the work. Water has been used in mining for a number of purposes such as a carrier, washing liquid, dust-catching media, fire-retardation media, temperature-control media, and solvent. When coal is cleaned in wet-processing circuits, waste streams containing water, fine coal, and noncombustible particles (ash-forming minerals) are produced. In many coal preparation plants, the fine waste stream is fed into a series of selection processes where fine coal particles are recovered from the mixture to form diluted coal fine slurries. A dewatering process is then needed to reduce the water content to about 15%-20% so that the product is marketable. However, in the dewatering processmore » currently used in coal preparation plants, coal fines smaller than 45 micrometers are lost, and in many other plants, coal fines up to 100 micrometers are also wasted. These not-recovered coal fines are mixed with water and mineral particles of the similar particle size range and discharged to impoundment. The wasted water from coal preparation plants containing unrecoverable coal fine and mineral particles are called tailings. With time the amount of wastewater accumulates occupying vast land space while it appears as threat to the environment. This project developed a special extruder and demonstrated its application in solid-liquid separation of coal slurry, tailings containing coal fines mostly less than 50 micron. The extruder is special because all of its auger surface and the internal barrier surface are covered with the membranes allowing water to drain and solid particles retained. It is believed that there are four mechanisms working together in the dewatering process. They are hydrophilic diffusion flow, pressure flow, agitation and air purging. Hydrophilic diffusion flow is effective with hydrophilic membrane. Pressure flow is due to the difference of hydraulic pressure between the two sides of the membrane. Agitation is provided by the rotation of the auger. Purging is achieved with the air blow from the near bottom of the extruder, which is in vertical direction.« less

This study examined the incompatibility of high-intensity conditioning (HIC) conditions required for fine and coarse coal particles. The effects of speed and time of stirring on the recovery of coarse and fine particles were investigated by using three different flotation processes. The results showed that the coarse particle recovery of surface cleaning (SC) flotation reached the maximum value of 69.71% at the stirring condition combination of ‘1400 rpm +2 min.’ However, the coarse particle recovery reached the maximum value of ~69.37% at a stirring condition combination of ‘1600 rpm +3 min’ or ‘2000 rpm +2 min’ in HIC flotation. Achieving the same coarse particle recovery, SC flotation consumes less energy than HIC flotation. The maximum recovery of fine particle 65.37% was achieved at a stirring condition combination of ‘1600 rpm +2 min’ in HIC flotation. SC failed to promote the recovery of fine particles and even produced some negative effects in some cases. Fine particles consume less energy than coarse particles with respect to their maximum recovery. In addition, the optimum stirring speed and time for SC were 1400 rpm and 2 min, respectively, while 2000 rpm and 3 min for HIC, respectively. The optimum energy requirements involving stirring speed and time for SC do not match that for reagent dispersion and particle-reagent collision. The best flotation result achieved by HIC is a compromise of the above three aspects. It is suggested that SC, reagent dispersion, and particle-reagent collision should be carried out separately.

Performance and mechanism of polyacrylamide stabilizers in coal water slurry

Characteristics of Coal Water Slurry (CWS) sprays generated by an effervescent atomizer are measured using a PDPA system. Coal particles of sizes 75 & 250 µm are considered. Measurements of both CWS and water only along axial and radial coordinates are carried out over the range of air to liquid ratio (ALR) of 0.02 – 0.1 and atomizing air pressure of 2 – 4 bar. The results show the increase of Sauter Mean Diameter (SMD) and the decrease in droplet velocity with the increase of the radial distance away from the centerline. A decrease in SMD with the increase of ALR is observed up to a value of 0.4. Above this value, the ALR has a little effect. The results also show that the SMD of CWS having smaller coal particles is larger than SMD of CWS having larger coal particles. The results of CWS having larger coal particles are closer to the results of water only than CWS having smaller coal particles.

In-situ study on the heterocoagulation between fine coal particles and coarse glass beads by the particle vision and measurement (PVM) techniques

Changes of size, ash and density of coal particles on the column axis of a liquid–solid fluidized bed

Coal water slurry gasification is a main source of hydrogen in the developing hydrogen economy. Moreover, biomass and waste can be added, making gasification process greener. To expand the application of coal water slurry and gasification process, it is necessary to understand the micro-structure in this large particle suspension system. In this paper, the micro-structure in coal water slurry was studied by extended DLVO (eDLVO) theory and fractal dimension, which is used to explain the mechanism of stability in large particle suspension systems. The interaction between two coal particles was characterized from the interparticle potential and energy barrier based on the eDLVO theory. The rheology and stability between different types of coals are measured and explained by the aggregating structure and fractal dimension in coal water slurry. The results indicated that there would be an aggregating structure in high rank coals, due to the interparticle potential caused by the surface properties, but probably not in low rank coals. This aggregating structure can be described and characterized by fractal dimension. The aggregation of particles is the source of the stability for high rank coals, as the close-packed 3D network structure in large particle suspension can support coal particles from settling down. The results have demonstrated that the combination of the eDLVO theory and rheological measurement is an effective way to investigate the stability of large particle suspension systems.

The hydrophobic aggregation of fine particles in high muddied coal slurry water in the presence of four quaternary ammonium salts of 1231(dodecyl trimethyl ammonium chloride), 1431(tetradecyl trimethyl ammonium chloride), 1631(cetyl trimethyl ammonium chloride) and 1831(octadecyl trimethyl ammonium chloride) was investigated through the measurement of contact angles, zeta potentials, aggregation observation, adsorption and sedimentation. The results show that quaternary ammonium salts can enhance the hydrophobicity and reduce the electronegativity of particle surface, and thus induce a strong hydrophobic aggregation of slurry fine particles which promotes the settlement of coal slurry water. The adsorption of quaternary ammonium salts on slurry particles increases with the increase of alkyl chain length and reagent dosage, and will reach equilibrium when the dosage reaches a certain value. Weak alkaline conditions also can promote quaternary ammonium salts to be adsorbed on the coal slurry fine particles. In addition, reasonable energy input and a chemical environment of weak alkaline solution are conducive to hydrophobic aggregation settlement of high muddied coal slurry water with quaternary ammonium salts. The main mechanism of hydrophobic aggregation of coal slurry particles with quaternary ammonium salts is 'adsorption charge neutralization' and hydrophobic interaction.

Many studies have shown that the mineral cleaning by feeding directly into the froth phase is much more efficient than feeding into the pulp phase in the flotation column, especially for the coarse particles and low-hydrophobicity particles. In this research, the weathered coal particles (0.125–2 mm), which were a combination of coarse and low-hydrophobicity properties, were used to conduct the tests in a conventional flotation column. The results indicated that the froth feed flotation had a higher combustible matter recovery of 43.67% compared with that of the pulp feed flotation of 32.07%. For the +0.5 mm size fraction, the combustible matter recovery increased by 3.33%. The fine particles could improve the froth stability in the flotation system and further improve the recovery of the coarse coal particles. Froth feed flotation with the addition of fine intermediate-hydrophobicity coal particles showed that the combustible matter recovery increased by 6.27%, while the concentrate ash decreased by 0.58% in the same operating conditions. For the +0.5 mm size fraction, the combustible matter recovery increased by 2.55%. The mechanism of fine coal particles to enhance the recovery of coarse coal particles was analyzed.

Study interactions between fine particles and micron size bubbles generated by hydrodynamic cavitation

Viscometry and rheology of coal water slurry

Preparation of high concentration coal water slurry with good fluidity based on only modified fine particles under bimodal distribution using the second fluid and the second particle

ABSTRACTA novel humic acid-based polycarboxylic-type (HAP) dispersant for coal–water slurry (CWS) was successfully synthesized in aqueous solution from the copolymerization of HA, acrylic acid and maleic acid. The structure of HAP was characterized by Fourier transform infrared (FTIR), thermogravimetry (TG) and 1H NMR. With HAP as a dispersant for Linfen coal slurry, the effects of the mass ratio of HA and monomer, initiator concentration, reaction temperature and reaction time on the HAP dispersant performance were discussed by examining the apparent viscosity of CWS. The results showed that CWS prepared withHAP dispersant performed excellent dispersity and stability. When the dosage of HAP was up to 0.5 wt.%, the apparent viscosity of CWS was 505 mPa·s. Experiments on the stability of CWS containing 0.5 wt.% HAP demonstrated that the penetration ratio reached 85.45 % after 96 h, which was higher by 12.87 % than that of CWS prepared with HA. And the CWS produced with HAP had lower dewatering rate within the storage time, which was less 1.85 % than that of CWS with HA when the storage time was 72 h. Furthermore, the maximum coal content of CWS with 0.5 wt.% HAP may reached 70 wt.%. This work found a new route for utilizing humic acid and enlarged the selecting range of the dispersant for CWS. It has a positive significance for protection of environment.

The interactions between fine particles of coal and kaolinite in aqueous, insights from experiments and molecular simulations

Adsorption and dispersion performance of oxidized sulfomethylated kraft lignin in coal water slurry