Coal-water Mixture Research Articles

湿式ボールミルによる高濃度石炭‐水スラリー用微粉粒群の調整

A fuel of coal water mixture, called CWM, is required to be highly concen-trated with coal for the purpose of combustion without previous dehydration. In the production of CWM it is necessary to prepare a coal fraction with wide size distribution in which the portion of very fine particles is considerable.In this study an wet grinding test was carried out to investigate the productivity of fine particle fraction using a small laboratory ball mill depending on mill filling, slurry concentration, ball size and mill speed, from which an optimum condition for the best grinding effect proved to be found with regard to feed slurry concentration and mill filling.

高濃度石炭水スラリー（ＣＷＭ）の流動性に及ぼす溶出灰分の影響

Highly concentrated coal water mixtures (CWM' s) were found to display various flow properties when prepared and stored at different pH values, eventhough they con-sist of the same coal, having the same particle size distribution, and the same anionic dispersing agent. It was found that, at low pH values, much mineral matter dissolves into the dispersing medium (water), and that the resultant multi-valent cations affected the CWM rheology by changing inter-particle interactions, decreasing the degree of dispersion.The pH adjustment to higher values restored the CWM flow properties, however not completely. It was attributed to Ca2+ and/or Mg2+ ions which have higher solubility at pH values of about 8.Cation masking reagents were examined to prevent the adverse effects of the cations. Sodium silicate was shown to be effective in masking Ca2+ ion. The reagent may be used to control the rheological properties of CWM' s using coals with higher water-dissolvable mineral matter content.

Effect of stabilizing additives on the stability of coal-water mixtures.

Effect of stabilizing additives on the stability of coal-water mixtures.

A study on the twin-fluid atomization of a highly concentrated coal-water mixture. (1st report Basic disintegration mechanism and spray characteristics)

Consecutive studies has been carried out for the purpose of clarifying spray performances of highly concentrated CWM and for obtaining a guide for the design of practical twin-fluid atomizers. Disintegration mechanisms and spray characteristics were investigated using plain-jet type of CWM atomization, and compared with those of single phase liquids. Furthermore, those disintegration phenomena and spray characteristics were considered in the proposed disintegration model. In the disintegration of a CWM jet by high speed air, atomization phenomena become similar to those of low viscosity liquids. Spray is generated basically by the tearing off of irregularly shaped small drops from the jet surface and splitting up of the unstably fluctuating jet into spherical drops. The change in Sauter's mean diameter of spray for air velocity changes its tendency at a certain velocity.

Assessment of dispersibility of coal particles by the sedimentation method using hydrometer.

The dispersion effect consequent upon the addition of surfactants to coal particles in water was examined by means of the sedimentation method using a hydrometer to obtain fundamental information on preparation of a highly loaded coal-water mixture. This method was found to be useful for assessing the settling characteristics of coal particles in a dilute suspension.

A study on the twin-fluid atomization of a highly concentrated coal-water mixture.

A study has been carried out for the purpose of clarifying spray performances of highly concentrated coal-water mixtures (CWM) and obtaining a guide for the design of practical twin-fluid atomizers. Disintegration mechanisms and spray characteristics were investigated on the simple twin-fluid atomization of CWM, and compared with those of single-phase liquids. Furthermore, these disintegration model. In the disintegration of a CWM jet by high-speed air, atomization phenomena are similar to those of low-viscosity liquids. Spray is generated basically by the tearing-off of irregularly shaped small drops from the jet surface and by the splitting-up of the unstably fluctuating jet into spherical drops. With the increase of air velocity, Sauter's mean diameter of spray decreases steeply, but its manner depends on the disintegration mechanism.

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.

U.S./India co-operative coal conversion program

In India, coal has come to occupy a pivotal position in sustaining the country's rising energy consumption and speeding economic growth. The U.S. Agency for International Development (USAID), in joint collaboration with the Government of India (GOI), is supporting research and development programs aimed at increasing the utilization of coal feedstocks with advanced technologies. The four areas selected for collaboration are: 1. (1) fluidized-bed combustion, 2. (2) coal-water mixture, 3. (3) coal cleaning and preparation, and 4. (4) gas clean-up and separation. This paper presents both the rationale behind the selection of these areas and an overview of the coal technologies being implemented under the USAID/GOI program.

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.

Burning of suspended coal-water slurry droplet with oil as combustion additive

Coal-water slurries have been regarded as a potential substitute for heavy fuel oil. Various demonstrations of coal-water slurry combustion have been performed; however, a fundamental understanding of how the combustion process of a slurry fuel is enhanced is still not adequate. The combustion of coal-water mixture droplets suspended on microthermocouples has been investigated. It was found that droplets of lignite coal (which is a noncaking coal) burn effectively; however, droplets of bituminous coal (which is a caking coal) are relatively difficult to burn. During the heat-up of bituminous coal-water slurry droplets may turn to ''popcorn'' and show significant agglomeration. The incomplete combustion of coal-water slurry droplets in furnaces has been reported, and this is a drawback of this process. The objective of the present study is to explore the possibility of enhancing the combustion of coal-water slurry droplets with the use of a combustible emulsified oil.

The effect of particle size and pH on the removal of pyrite from coal by conditioning with bacteria followed by oil agglomeration

The removal of 90% of the pyrite from coal by bacterial conditioning followed by oil agglomeration is attainable in Minto coal only if it is ball milled in the laboratory to an average particle size of about 5 μm. In grinding to industrially practical sizes of about 8 to 10 μm, the maximum amount of pyrite removed was about 50%. The contribution of the bacterial conditioning step was highly dependent on the pH of the feed slurry. A positive effect of bacterial conditioning was greatest at pH 2. At pH 10, the presence of bacteria was detrimental to desulfurization by oil agglomeration. Bacterial conditioning does not involve pyrite oxidation by Thiobacillus ferrooxidane because the pH of a coal—water mixture was normally above pH 5 for best pyrite depression where these bacteria are physiologically inactive, and because conditioning was achieved equally well with cells of Thiobacillus acidophilus and Escherichia coli.

Properties of Highly Loaded Coal-Water Mixture (CWM) Produced by Continuous Process

To use CWM as a fuel in large quantity, the feasibility of this must first be demonstrated by a larger scale experiment. For this purpose, the properties of CWM containing a nonionic dispersant [N-poly (oxyalkylene) polyethylenimine, abbreviated as POA-PEI] or anionic dispersant (sodium salt of formalin condensate of naphthalenesulfonic acid, NSF-Na) were examined by continuous production and storage tests.The findings warranting attention are as follows : 1) CWM produced by the large-scale continuous and small-scale batch processes showed essentially the same properties. CWM produced by the batch process made it possible to examine the physical properties of that produced by the large scale continuous process.2) CWM was obtained with a coal concentration and viscosity that was higher and lower, respectively, than that containing NSF-Na, using POA-PEI, regardless of the scale of production.3) Older, or more carbonized coal could be made into CWM loaded to a greater extent. Analytical values (O/C and H/C values) of coal made possible estimation of the loading level of CWM.4) POA-PEI showed higher pulverizing efficiency in CWM production than NSF-Na.5) The viscosity of CWM using POA-PEI could be owered more effectively by stirring than using NSF-Na. The CWM showed storage stability exceeding a period of one month.

石炭スラリーの物性および流動と伝熱

The recent increase in interests on the coal utilization technology has brought about the various research of coal slurry preparation, transportation and combustion. In this article, the recent developments for the measurements of physical properties of Coal-Water mixture (CWM) will be reviewed. The physical properties means viscosity, thermal conductivity, specific heat, density and zeta potential of CWM. Stability of coal slurries will be discussed comparing with the thixotropic characteristics.It is necessary to predict relationships between pressure drop and CWM flow rate in the design of pipeline transportation systems based on the experimental results in a laboratory. Flow characteristic data obtained from pilot-plant experiments are compared with the rheometrical data. The comparison indicates that laboratory rheometry data enable us to design pipeline transportation. The correlation of heat transfer data for CWM in a laminar tube flow will be also discussed.

浮遊選鉱法による石炭の脱灰特性に関する速度論的検討

The objective of this research is to develop a new froth flotation method to be employed in CWM (Coal Water Mixture) preparation. The froth flotation method is famous for practical coal cleaning, but it has some problems relating to CWM preparation. In conventional flotation method, deashed coals tend to coagulate because much oil used as a collector is included in them. Therefore, it seems to be difficult to disperse the deashed coals into water in preparing CWM. Accordingly, its important to increase the carbon recovery rate by making use of the small amount of oil.In this report, the kinetic study of carbon recovery was made using coals with wide size distribution which is suitable for CWM preparation. The flotation method used here is different from the conventional one at the point that collector is fed in the form of gas.Carbon recovery rates for various coals were found to obey the first order kinetics with respect to carbon concentration in the suspension. The rate constants were found to correlate well with the O/C atomic ratio of the coals. Coal concentration of the feed suspension had no effect on the recovery rate when it was smaller than 10%. But at higher concentration, a large decrease of carbon recovery was observed.

石炭スラリー化技術の現状

Coal slurry technology has been developed in order to dissolve the demerit of bulk handling and promote the utilization of coal since the Oil Crisis. Recently, this technology has been watched with much interests as an alternate fuel. Especially, CWM (highly Loaded Coal Water Mixture) is considered as one of the promising coal slurry technologies in future, because it is economical and easy to utilize.Electric Power Development Company (EPDC) has started the development of CWM technology since 1980. After the fundamental test, 1.5t/h CWM preparation pilot plant test was started in 1983.The following techniques have been developed by EPDC.1. Save the pulverizing energy by two stage preparation system.2. Estimation of coal slurriability.3. Effect of dispersant to slurry.4. Stabilization method of CWM and estimation of CWM stability.In U.S.A. and Sweden, the development has been started earlier than us. Now the big projects are going on in Canada, USSR and Italy.These projects are explained briefly.

特許にみられる石炭スラリー技術の動向

The Japanes e patents on coal slurry fuel were investigated for the trend of coal slurry technology.The number of patents was 106 for coal oil mixture, 354 for coal water mixture, 27 for system and elemental technology on coal slurry.The mainly patents on coal slurry were coal water mixture, Which were involved 262 patents on surface active agents and 225 patents on preparation technology of slurry.

高炉における石炭の利用技術

This paper describes the present status of coal utilization in ironmaking.The two main processes of coal injection into blast furnace have been developed to save expensive metallurgical coke;1) The colloidal fuel mixture injection2) The pulverized coal injection (PCI)The development of the former process, that is coal oil mixture (COM) and coal tar mixture (CTM) injection into blast furnace, was completed by Sumitomo Metal Industries and other Japanese steel works in 1982.As for the latter one, the first PCI equipment in Japan has been operated in Oita No.1 BF of Nippon Steel Corporation since 1981. It was successfully completed by modifing the ARMCO system. The number of blast furnace with PCI system operation has come up to sixteen in Japan, which implies remarkable development of the system.The present technology of coal utilization in iron and steel industry is focused on the development of both coal water mixture (CWM) injection into blast furnace and coal addition into steelmaking vessels.

Thixotropy of Highly Loaded Coal-Water Mixtures

The shear stress-shear rate behavior of a thixotropic coal-water mixture(CWM) was studied in a coaxial rotating cylinder rheometer under a wide variety of rest and shear rate history. The transient stress data were used to construct equilibrium and constant-structure flow curves. These transient stress data, i. e. the stress relaxation data and the stress recovery data, were also used to evaluate the breakdown and buildup processes of the internal structure. A phenomenological thixotropy model, which had the structural stress as a thixotropic structural parameter, was proposed. Dependence of thixotropic parameters on pH values of CWM was experimentally determined. Strong dependence of the time constant for buildup of structural stress on pH values was observed, and this phenomenon corresponded to the rapid coagulation of coal particles at lower pH values. However, coagulation and dispersion of coal particles could not be explained by the simple hetero-coagulation theory with measured zeta-potential values.

高濃度石炭水スラリー（ＣＷＭ）の流動性に及ぼす石炭性状の影響

Highly concentrated coal water mixtures (CWM's) were prepared using eight different coals and an anionic dispersant. Viscosity of the CWM's was investigated in relation to the coal properties. It was found that coals with lower water-holding capacity (WHC) would make more highly concentrated CWM's. Their viscosity was correlated well with the solid volume fraction and maximum packing density using Krieger-Dougherty equation. For these coals, the particle size distribution was found to influence the CWM viscosity only through the values of maximum packing density.CWM's made from coals with high WHC exhibited higher viscosity. This was attributed to the lower degree of dispersion of the coal particles. CWM's with coals having low WHC displayed similar viscosity-solid concentration relationship when electrolyte was added.

Laboratory-scale combustion of coal-water mixtures

A detailed study of the combustion of coal-water mixtures (70–73% coal, 22–30% water) and formation of nitrogen-containing pollutants has been performed in a vertical, laboratory-scale combustor. Space-resolved, local measurements of solid and gaseous combustion products were made with a stainless steel, water-quenched probe to determine the percentage of coal burnout and local gaseous composition at various locations within the reactor. Rapid mixing of the gas and particle streams eliminated fuel-rich regions within the reactor. Carbon monoxide was found only near the inlet region of the reactor with the highest concentration being 0.8%. Particle residence time in the reactor was estimated to be about 100 ms, with coal burnout (daf) ranging from 82 to 98% as secondary air swirl number and stoichiometric ratio were varied. The only nitrogen-containing pollutant found was nitrogen oxide, with the exit concentrations ranging from 180 to 750 ppm.