Coal-water Mixture Research Articles

Development and Industrialization of Sodium Polystyrenesulfonate (PSS) as an Additive for a Highly Concentrated Coal Water Mixture (CWM)

Sodium polystyrenesulfonate (PSS) was shown to be suitable as an additive for a highly concentrated coal water mixture (CWM) used by electric power plants. By combining PSS with an appropriate auxiliary CWM was able to be produced with various coals.Using colloid vibration potential (CVP) technique by which the ζ-potential of particles in a concentrated colloidal dispersion can be measured, we have developed a novel technique to measure the ζ-potential of coal particles in CWM. By means of this technique the dispersion mechanism of CWM was estimated.A technique for PSS production, in which styrene is polymerized by cationic polymerization and the resultant oligostyrene is sulfonated successively, was also developed.This new technique make possible the manufacture of PSS at low cost.

Fossil Energy. Effects of Weathering of Coal on the Properties of a Highly Loaded Coal Water Mixture.

石炭の風化が高濃度石炭水スラリー (CWM : Coal Water Mixture) の性状に及ほす影響について検討した.風化炭は風化期間の増加にともないCWMの粘度 (1 Pa・S) を基準とした到達濃度が低下し, またCWMを2週間静置した際に生じる沈降物量が増加した.風化によるスラリー化性の低下の原因について検討した結果, 風化期間の増加にともない石炭中の硫化鉄の酸化によって生じる硫酸塩が増加し, CWMが酸性化することが明らかになった.また風化により石炭表面の親水基が増加し, 石炭表面に吸着される水分量が増加する結果, CWMの流動化に寄与する “自由水” の割合が減少することが示唆された.以上のことからCWMの酸性化と石炭表面の親水基の増加が原料石炭の風化に伴うスラリー化性の低下の主な原因と考えられた.

Yield stress of coal-water mixtures

The yield stresses of coal-water mixtures as functions of solids volume fraction, suspended particle size, and suspension pH were measured using the vane method. The suspension yield stress-solids volume fraction data were used to estimate the asymptotic values of solids concentration in the limit of infinite yield stress. The limiting solids volume fractions, obtained by such an extrapolation, were found to be approximately the same as those estimated independently from the irreducible sediment volumes obtained by centrifugation. The yield stress-concentration dependence was found to depend on particle size as well as pH, or the corresponding zeta potential which was also measured. However, for a given particle size mix the yield stress-concentration plots for different pH appeared to converge, as the yield stress became large, and to approach a common asymptotic value of solids concentration in the limit of infinite yield stress. A number of different extrapolation procedures were tested to establish the type of plot capable of providing a consistent, unambiguous value of these limiting concentrations. The procedures for estimating the maximum packing solids concentrations from centrifugal sedimentation were also tested by varying the speed and the duration of centrifugation. The solids concentration dependence of the yield stress of CWM was found to be described by two-parameter non-linear relationships based upon the mean interparticle spacing, and incorporating the maximum packing volume of solids. Furthermore, it is established that the yield stress is proportional to the reciprocal of the mean particle size.

An evaporation model for coal-water mixture droplets at elevated temperatures

A model of the evaporation of coal-water mixture droplets was developed, based on the concept of variable mass and using the moisture content as the scalar parameter. The model treats the droplet as a heterogeneous mixture of pulverized coal and water. Previous work using liquid droplet description is shown not to be suitable for coal-water mixture.

Rheological studies on the pipeline transportation of coal slurries and oil

Drag reduction caused by the injection of polymer solution into a turbulent pipe flow was investigated by means of a flow visualization technique. Turbulent fluctuating velocity in a drag‐reducing flow was determined by a tracer method. It became evident from the experimental results that the defect of Reynolds stress existed over the wide range of the radial position in a polymer drag‐reducing pipe flow. The optimum preparation method of coal water mixtures (CMW) has been developed. The present study contributed to the successful production of highly loaded CMW with lower viscosity. An evaluation method of the dynamic stability during the transportation of CWM was proposed. This method was based on a thixotropy model for slurries, and it was successfully used for the estimation of dynamic stability of CWM with a laboratory stability test.

Mechanism of microbial flotation using Thiobacillus ferrooxidans for pyrite suppression

Microbial desulfurization might be developed as a new process for the removal of pyrite sulfur from coal sluries such as coal-water mixture (CWM). An application of iron-oxidizing bacterium Thiobacillus ferrooxidans to flotation would shorten the periods of the microbial removal of pyrite from some weeks by leaching methods to a few minutes. The floatability of pyrite in flotation was mainly reduced by T. ferrooxidans itself rather than by other microbial substances in bacterial culture as additive of flotation liquor. Floatability was suppressed within a few seconds by bacterial contact. The suppression was proportional to increasing the number of cells observed between bacterial adhesion and the suppression of floatability. If 25% of the total pyrite surface area covered with the bacteria, pyrite floatability would be completely depressed. Bacteria that lost their iron-oxidizing activities by sodium cyanide treatment were also able to adhere to pyrite and reduced pyrite floatability as much as normal bacteria did. Thiobacillus ferrooxidans ATCC 23270, T-1, 9, and 11, which had different iron-oxidizing abilities, suppressed floatability to similar-levels. The oxidizing ability of bacteria did not influence the suppressing effect. These results showed the mechanism of the suppression of pyrite floatability by bacteria. Quick bacterial adhesion to pyrite induced floatability suppression by changing the surface property from hydrophobic. The quick adhesion of the bacterium was the novel function which worked to change the surface property of pyrite to remove it from coal.

Drag reducing effects of polymer additives on Coal-Water Mixture in rotating disk system

Using a rotating disk apparatus, the concept of drag reduction produced by polymer additives is applied to Coal-Water Mixture(CWM) transport. Experiments were undertaken for a wide range of polymer concentrations of poly(ethylene oxide: PEO), poly(acrylamide: PAAM), coal concentrations and rotating disk speeds. Drag reduction decreased with higher coal concentrations, and increased with higher polymer concentrations up to 150 wppm for PEO. Further increases in the PEO concentration led to lower drag reduction. Howere, PAAM produced higher drag reduction which remained almost constant over a wide range of concentrations. The effect of polymer degradation was also investigated and it was found that PAAM is a better drag reducer than PEO when applied to long time transportation of CWM.

Synthesis of poly(4-methylstyrene)- graft-poly(ethylene oxide)s and application as polymeric dispersant in coal-water mixture

Poly(4-methylstyrene)-graft-poly(ethylene oxide)s were prepared via polymerisation of ethylene oxide on to poly(4-methylstyrene)s function alised with hydroxyl groups. In this way, many «comb-like» polymers having different hydrophobic backbone length, hydrophilic branch length and frequency of branches were synthesised. These polymers were tested as dispersants in coal-water mixtures in order to correlate the dispersing properties of this class of polymers with the investigated parameters

Combustion Behavior and Simulation of a Small Amount of Spray with Coal-Water Mixture.

The ignition and combustion behavior of a small amount of spray with coal-water mixture (CWM) and that of emulsitied CWM were observed in an electric furnace in order to obtain fundamental data in prediction of practical furnace combustion. The experiments were carried out in the furnace temperature range of 973 K to 1273 K under nozzle pressure of 0.168 MPa to 0.294 MPa. They showed reasonable results such as that the time lag and the location of ignition tend to become shorter at higher furnace temperature under constant nozzle pressure. The data of experimental time lag and the location of ignition were compared with the simulation predictions for each size of CWM droplet under several experimental conditions of both the furnace temperature and the nozzle pressure. The predictions are in rough agreement with the experimental data for the time lag and the location of ignition.

Coagulation and dispersion characteristics of coal water mixtures in higher temperature range.

The present investigation is aimed at finding the reason for the anomalous increase in viscosity of coal water mixtures (CWMs) in the higher temperature range (>150°C). The ζ-potential of coal particles in the higher temperature range was measured with the addition of six kinds of surfactants. The experimental results showed that the ζ-potential of Wallarah coal with anionic surfactants still show negatively higher values in the higher temperature range; thus it was expected that no significant desorption of anionic surfactants occurs. Furthermore, from considerations based on the DLVO theory it was concluded that the temperature dependence of the dielectric constant of water affects the coagulation of coal particles.

Isolation of coal-solubilizing microorganisms and utilization of the solubilized product

Twenty-eight strains of microorganisms able to solubilize pretreated subbituminous coal were isolated. One fungal strain was selected as the most effective isolate, because it produced black liquid rapidly from coal. The black liquid contained about 2% (w/v) of a coal-derived material that had a high molecular weight and gave precipitate in an acidic condition. Characteristics of the precipitate that were investigated and compared with the original coals were elemental composition and IR spectrum. Coal-water mixture containing 64% (w/v) of bituminous coal and 0.7% (w/v) of the material had a viscosity of 0.31 Pa·s. It might be possible to use the microbial product as an additive for coal-water mixture.

Effect of swirling flow on unburned ratio and nitrogen oxide concentration in a spray combustion system

The effect of swirling flow on the unburned ratio and NO concentration in exhausted gas was studied for slurry [coal-water mixture (CWM)] spray combustion with variations of swirl numbers. A numerical analysis for CWM combustion was performed for axisymmetric flow in a cylindrical geometry. First, to check the performance of three previous k- ϵ turbulence models modified with swirling flow, velocity components of isothermal swirling jets were measured by laser-Doppler anemometry (LDA) and compared with predicted results. The two modified models gave more reliable results than the conventional one. Next, as the swirl number could not be estimated by the angular momentum derived from the vane angle of the circular swirler, the reduction rate of the tangential momentum flux through the tube of the circular swirler was measured and calculated. Both measured and predicted results showed that when the swirl number S′ given by the vane angle was 2.0, the effective swirl number S eff decreased by about 60% to S′. To take the results mentioned above into consideration, effects of swirl number on both the exhausted NO concentration and unburned ratio were investigated. The predicted unburned ratio showed good agreement with the experimental results. Both experimental and calculated results showed that the optimum operating conditions controlling the exhausted NO concentration and unburned ratio in this spray combustion system were obtained when the swirl number S eff was about 0.5.

Two-Stage Slagging Combustor Design for a Coal-Fueled Industrial Gas Turbine

A full-size combustor for a coal-fueled industrial gas turbine engine has been designed and fabricated. The design is based on extensive work completed through one-tenth scale combustion tests. Testing of the combustion hardware will be completed with a high pressure air supply in a combustion test facility before the components are integrated with the gas turbine engine. The combustor is a two-staged, rich-lean design. Fuel and air are introduced in the primary combustion zone where the combustion process is initiated. The primary zone operates in a slagging mode inertially removing coal ash from the gas stream. Four injectors designed for coal water mixture (CWM) atomization are used to introduce the fuel and primary air. In the secondary combustion zone, additional air is injected to complete the combustion process at fuel lean conditions. The secondary zone also serves to reduce the gas temperatures exiting the combustor. Between the primary and secondary zones is a Particulate Rejection Impact Separator (PRIS). In this device much of the coal ash that passes from the primary zone is inertially separated from the gas stream. The two-staged combustor along with the PRIS have been designated as the combustor island. All of the combustor island components are refractory-lined to minimize heat loss. Fabrication of the combustor has been completed. The PRIS is still under construction. The combustor hardware is being installed at the Caterpillar Technical Center for high pressure test evaluation. The design, test installation, and test plan of the full-size combustor island are discussed.

Experimental Evaluation of Sorbents for Sulfur Control in a Coal-Fueled Gas Turbine Slagging Combustor

A slagging combustor has been used to evaluate three calcium-based sorbents for sulfur capture efficiency in order to assess their applicability for use in a coal-fueled gas turbine. Testing is completed in a bench-scale combustor with one-tenth the heat input needed for the full-scale gas turbine. The bench-scale rig is a two-stage combustor featuring a fuel-rich primary zone and a fuel-lean secondary zone. The combustor is operated at 6.5 bars with inlet air preheated to 600 K. Gas temperatures of 1840 K are generated in the primary zone and 1280 K in the secondary zone. Sorbents are either fed into the secondary zone or mixed with the coal-water mixture and fed into the primary zone. Dry powdered sorbents are fed into the secondary zone by an auger into one of six secondary air inlet ports. The three sorbents tested in the secondary zone include dolomite, pressure-hydrated dolomitic lime, and hydrated lime. Sorbents have been tested while burning coal-water mixtures with coal sulfur loadings of 0.56 to 3.13 weight percent sulfur. Sorbents are injected into the secondary zone at varying flow rates such that the calcium/sulfur ratio varies from 0.5 to 10.0. Hydrated lime exhibits the highest sulfur dioxide reductions in the exhaust of 90 percent. Pressure-hydrated dolomitic lime and dolomite reduce SO2 concentrations by 82 and 55 percent, respectively. Coal sulfur loading is found to have a small influence on sorbent sulfur capture efficiency. Pressure-hydrated dolomitic lime ground with the coal during coal-water mixture preparation and injected into the primary zone is found to lower the sulfur dioxide concentration by an insignificant amount.

The Combustion Mechanism and Combustion Promotion of Coal-Water Mixture Fuel.

The combustion behavior of coal-water mixture (CWM) droplets was observed in the electric furnace, where the measurement of droplet temperature, video recording and high-speed photography were carried out at sequential steps of the combustion process. The effects of furnace temperature, slurry concentration and oxygen concentration were examined in order to elucidate the combustion mechanism of CWM droplets. The results indicate that they are influenced considerably at each step of the combustion process such as vaporization, ignition, visible envelope flame combustion and char combustion. The effects of the addition of C-heavy oil, A-heavy oil, methanol and kerosene were examined in order to elucidate the feasibility and the mechanism of microexplosion of CWM droplets. The results show that the explosion makes fairly short both ignition delay time and total combustion time in the fuel of C-heavy oil in addition to the CWM.

Interfacial Electrokinetic Phenomena of Aqueous Concentrated Coal Dispersion Systems in the Presence of Polyelectrolyte. II.

The correlation between electrokinetic behavior and rheological phenomena of a highly concentrated coal water mixture (CWM) in the presence of a polyelectrolyte (sodium polystyrene sulfonate; PSS-Na) was studied by usual electrophoretic method and colloid vibration potential (CVP) technique. ζ-Potential determined by usual electrophoretic method was found not to be closely correlated to the viscosity of the CWM slurry. The structure of the electrical double layer around coal particles changes by dilution due to variation in the concentration of free polymer and eluted ions from the coal is the reason for this.ζ-potential determined by the colloid vibration potential technique was shown to have goodcorrelation with the viscosity of the slurry over a wide range of volume fraction of coal particles, when the conductivity of dispersed medium was maintained constant after dilution. At a constant volume fraction (φ=0.24), a certain value of PSS-Na additive maximized the ζ-potential of each sample. This was because the additive functioned as a counter ion for the surface charge of particles following saturated adsorption and thereby reducing the ζ-potential of the particles.

Rheological Studies on the Pipeline Transportation of Coal Slurries and Oil

Drag reduction caused by the injection of polymer solution into a turbulent pipe flow was investigated by means of a flow visualization technique. Turbulent fluctuating velocity in a drag‐reducing flow was determined by a tracer method. It became evident from the experimental results that the defect of Reynolds stress existed over the wide range of the radial position in a polymer drag‐reducing pipe flow. The optimum preparation method of coal water mixtures (CMW) has been developed. The present study contributed to the successful production of highly loaded CMW with lower viscosity. An evaluation method of the dynamic stability during the transportation of CWM was proposed. This method was based on a thixotropy model for slurries, and it was successfully used for the estimation of dynamic stability of CWM with a laboratory stability test.

Interfacial Electrokinetic Phenomena of Aqueous Concentrated Coal Dispersion Systems in the Presence of Polyelectrolytes. I.

The correlation between electrokinetic behavior and rheological phenomena of a highly concentrated coal water mixture (CWM) in the presence of a polyelectrolyte (sodium polystyrene sulfonate; PSS-Na) was studied by usual electrophoretic method and colloid vibration potential (CVP) technique. ζ-Potential determined by usual electrophoretic method was found not to be closely correlated to the viscosity of the CWM slurry. The structure of the electrical double layer around coal particles changes by dilution due to variation in the concentration of free polymer and eluted ions from the coal is the reason for this.ζ-potential determined by the colloid vibration potential technique was shown to have goodcorrelation with the viscosity of the slurry over a wide range of volume fraction of coal particles, when the conductivity of dispersed medium was maintained constant after dilution. At a constant volume fraction (φ=0.24), a certain value of PSS-Na additive maximized the ζ-potential of each sample. This was because the additive functioned as a counter ion for the surface charge of particles following saturated adsorption and thereby reducing the ζ-potential of the particles.

Thermal conductivity of granular coals, coal-water mixtures and multi-solid/liquid suspensions

The thermal conductivities of suspensions of particulate coals in water, in fuel oil and in other liquids, and of mixtures of different particulate solids in liquids were measured. The binary suspension data were used to determine the solid thermal conductivities of the particulate inclusions by various extrapolations, and to test the different extrapolation schemes. A general, second-order, effective conductivity formula for binary mixtures, valid for small differences between the conductivities of dispersed and continuous phases, was derived. For suspensions containing a mixture of N different solids, of solid to liquid conductivity ratios β t = k i k 0 and volume fractions φ i , the formulae ( k ∗ k 0 ) = β 1 φ1β 2 φ2 … β N φN and ( k ∗ k 0 ) = [1 + ∑(β i 1 3 − 1)φ i] 3 were derived for the suspension thermal conductivity k ∗ . The former was found to do a good job of prediction for binary and multi-solid suspensions. As the volume fraction weighted geometric mean of the constituent conductivities, this formula is known to lie between the harmonic and arithmetic means as lower and upper bounds, respectively. Furthermore, over the range of conductivity ratios β i where it works well, it either lies between tighter bounds based on variational principles, or when it falls outside it differs indistinguishably from these bounds, which in this case turn out to be quite close.

Reduction of coal‐water mixture consistency with soda ash and lime

AbstractThe addition of soda ash and lime to improve the Theological properties of a 60 wt % bituminous coal‐water mixture (CWM) was investigated. Soda ash and lime were used to precipitate calcium and magnesium cations naturally present in the aqueous phase of the CWM. Addition of the required amounts of soda ash and lime alone, based on analyses of the total Ca2+ and Mg2+ burdens in the CWM, using standard water softening technology as well as addition of soda ash and lime along with an ionic dispersant were studied. Significant reduction in consistency was measured following soda ash and lime addition alone, and marked reduction in consistency resulted when both soda ash and lime and dispersant were used. Additive costs to obtain a given degree of consistency reduction were lowered by factors ranging from 3 to 15 with soda ash and lime, either alone or in concert with an anionic dispersant, relative to the use of anionic dispersant alone.