Coal Streams Research Articles

97/01837 Removal of hydrogen chloride from hot coal gas streams

During gasification, chloride species in coal are converted to HCl, a reactive, corrosive, and toxic gas that must be removed to meet environmental regulations, to protect power generation equipment, and to minimize deterioration of hot coal gas desulfurization sorbents. Thermochemical calculations indicated that sodium-based sorbents are capable of reducing HCl vapor to less than 1 ppm in coal gas streams up to a temperature of 650 C, but they are not easily regenerable. The mineral nahcolite (NaHCO{sub 3}) was used to make inexpensive sorbents suitable for fixed- and fluidized-bed reactors. Bench-scale tests confirmed that these sorbents have >50 wt% chloride capacity. The reaction of HCl with the sorbent was rapid and followed overall first-order kinetics.

97/01133 Removal of hydrogen chloride from hot coal gas streams

97/01133 Removal of hydrogen chloride from hot coal gas streams

97/01192 Moving granular-bed filter for multi-contaminant control

In addition to the control of ash particulates, a moving granular-bed filter can control other contaminants found in high-temperature, high-pressure coal gas streams through the use of chemically-reactive filter media. Under sponsorship of the U.S. Department of Energy, a laboratory test program is underway to evaluate the following three types of chemically-reactive filter media: a clay-based filter medium for the control of alkali and heavy metals in either reducing or oxidizing environments, a sodium-based filter medium for the control of halogens and metaloids in reducing-gas environments, and a nickel catalyst for the destruction of ammonia and hydrogen cyanide in a reducing-gas environments. The test program calls for the evaluation of techniques for forming reactive clay filter media and the evaluation of the structural and chemical properties of clay media, nahcolite (NaHCO{sub 3}) media, and media composed of nickel catalysts. Initial results of the development of a clay-based filter medium are presented.

The body ion loss biomarker. 2. Field validation in coal mine-polluted streams

We performed a field validation of the body ion loss biomarker by developing a predictive model of the level of impact of coal mining on receiving streams. Hatchery brook charr (Salvelinus fontinalis ; wet mass = 1.25 to 32.2 g) were exposed in four mine-impacted streams that exhibited differing levels of acid and trace metals and in two unimpacted control streams. Net whole-body ion (Na, Ca) fluxes over a 4-h exposure were determined. Stepwise regression was used to develop predictive models of body ion flux over 4 h from measured stream water chemistry variables. The predictive power of the best model was assessed using cross validation. The best model predicting net sodium flux explained 48% of the variability in the model with six chemical variables (Mn, Zn, Mg, Al, Fe, and Na). The model of calcium flux explained 42% of the variation with eight variables (H + , Ca, Na, Mn, Al, Ni, Mg, and Zn). A multiple regression model derived from principal components analysis did not significantly improve the predictive power of these models. We conclude that whole-body net sodium flux and to a lesser extent whole-body net calcium flux are acute indicators of the level of impact of acid and trace metals in streams polluted by coal mine discharge and may be useful as biomarkers under field conditions.

96/01422 Elimination of ammonia from coal gasification streams by using a catalytic membrane reactor

96/01422 Elimination of ammonia from coal gasification streams by using a catalytic membrane reactor

Solving Mass Balance Problems in Coal Processing Using the Constrained/ Weighted Least-Squares Method

The use of the constrained/weighted least-squares method for solving the mass balance problems of separators with multi-product streams in coal preparation plants is described. An algorithm was developed to solve consistent data and to estimate relative mass flow rates of coal product streams (yields) referenced to the feed from the measured density distribution and size distribution. These consistent data can be used for the process evaluation and calculation of chemical composition distribution of the products in coal preparation. To estimate reliable and meaningful mass balance results, while conserving mass in the system, this algorithm includes additional constraints: the sum of component data must equal one hundred percent, and individual component datum must have a non-negative value. The effect of weighting factors on the mass balance solutions is presented, and the weight procedure to minimize the sum squares of errors between measured data and adjusted data, and ensure that statistically adjuste...

System Evaluation and LBTU Fuel Combustion Studies for IGCC Power Generation

The integration of gas turbines and combined cycle systems with advances in coal gasification and gas stream cleanup systems will result in economically viable IGCC systems. Optimization of IGCC systems for both emission levels and cost of electricity is critical to achieving this goal. A technical issue is the ability to use a wide range of coal and petroleum-based fuel gases in conventional gas turbine combustor hardware. In order to characterize the acceptability of these syngases for gas turbines, combustion studies were conducted with simulated coal gases using full-scale advanced gas turbine (7F) combustor components. It was found that NOx emissions could be correlated as a simple function of stoichiometric flame temperature for a wide range of heating values while CO emissions were shown to depend primarily on the H2 content of the fuel below heating values of 130 Btu/scf (5125 kJ/NM3) and for H2/CO ratios less than unity. The test program further demonstrated the capability of advanced can-annular combustion systems to burn fuels from air-blown gasifiers with fuel lower heating values as low as 90 Btu/scf (3548 kJ/NM3) at 2300°F (1260°C) firing temperature. In support of ongoing economic studies, numerous IGCC system evaluations have been conducted incorporating a majority of the commercial or near-commercial coal gasification systems coupled with “F” series gas turbine combined cycles. Both oxygen and air-blown configurations have been studied, in some cases with high and low-temperature gas cleaning systems. It has been shown that system studies must start with the characteristics and limitations of the gas turbine if output and operating economics are to be optimized throughout the range of ambient operating temperature and load variation.

Baffled-column flotation of a coal plant fine-waste stream

Coal-cleaning operations commonly produce a fine-waste stream containing a considerable amount of coal. The recovery of this coal is normally not economical because the coal is mixed with large amounts of difficult-to-remove clay slimes and is often heavily oxidized or contaminated. Conventional froth-flotation machines cannot, in a single flotation stage, produce an acceptable product from such material, and even flotation columns often have difficulty cleaning this type of feed. A new type of flotation column was designed specifically to deal with these problems, and a column of this design was installed and tested in a coal-cleaning plant in Ohio. The feed coal tested was the plant’s tailings-thickener product. The coal was 80% −176 µm and had a heating value of 8401 Btu/lb. The coal contained 39.8% ash, as fine clay, and 2.83% total sulfur. Because previous attempts at conventional flotation of this type of material had been abandoned, plant personnel believed that the coal was too heavily oxidized and contaminated for flotation to be effective. However, by using the new column it was possible to recover up to 85% of the calorific value in a product containing <11% ash, and it was possible to recover 60% of the calorific value in a product containing <8% ash. In addition, the bulk of the pyritic sulfur was also rejected from the coal.

Ignition and combustion of coal particle streams

This paper presents a model for group combustion of a cylindrical stream of coal particles and preliminary experimental data. Results are obtained for transient ignition and combustion behaviour. It is found that homogeneous ignition (ignition of volatiles) occurs for a dense cloud, while heterogeneous ignition (ignition of carbon) occurs for a dilute cloud. Once ignited, the flame moves towards the cloud, reaches the cloud surface and then bifurcates into two flames, called the inner and outer flames. The inner flame propagates into an unburnt volatile-air mixture in the cloud, while the outer diffusion flame moves away from the cloud. The inner flame propagates at the laminar burning velocity and rapidly heats the particles. There is only a diffusion flame outside the cloud after all the oxygen in the cloud is consumed. The flame moves toward the cloud as the volatiles are depleted. The cloud, with the volatiles exhausted and starved of oxygen, burns slowly, controlled by diffusion into the cloud rather than to each particle in the cloud. Qualitative comparisons are given with preliminary experimental data obtained using a digital imaging system.

High Performance Liquid Chromatography (HPLC) of Coal Liquefaction Process Streams Using Normal-Phase Separation with Diode Array Detection

A method is described for a normal-phase separation and quantification of polynuclear aromatic hydrocarbons (PAHs) using high performance liquid chromatography (HPLC) coupled with UV-diode array detection. The method employed takes advantage of the inherent capabilities of a «charge-transfer» normal-phase HPLC column (Holstein, W. Chromatographia 1981, 14, 468), the Hypersil PAH-2 column (Keystone Scientific, Inc., Bellefonte, PA), and the ability of the diode array detector to provide UV spectra for each eluting compound having chromophores in the UV range which allows for separation, identification, and quantification in the normal phase of individual PAHs. Elaborate sample preparations, which in the past have accompanied determination and separation of individual PAHs, can be avoided for the analysis of PAHs in either extracts of natural samples or complex fuel mixtures. The potential for this method was demonstrated by the separation and quantification of five well-studied coal liquefaction process stream samples. PAHs having from two rings up to nine rings, along with their isomers and alkylated derivatives, were separated and quantified using this method. Clear differences were observed among liquefaction process streams due, in large part, to differences in feed coals and process conditions

Ignition and combustion of coal particle streams

Ignition and combustion of coal particle streams

Modelling of spontaneous combustion of coal with moisture content included

A mathematical model for spontaneous combustion of coal has been developed that takes into consideration the moisture content of coal. The one-dimensional non-steady-state model consists of conservation equations for oxygen, water vapour, inherent moisture of the coal, and energy for both gaseous and solid phases. A first-order Arrhenius reaction rate for oxidation under pore diffusion and chemically controlled reaction regimes is considered. The rate of evaporation or condensation is also considered as a function of particle size, isothermal temperature of coal particles, energy of water-coal bonding and water content of coal and gas streams. The equations of the model have been solved numerically by a finite-difference technique, and the influences of gas velocity, particle size and inherent moisture content on the process of spontaneous heating have been examined parametrically.

Pulverized coal plasma gasification

A number of experiments on the plasma-vapor gasification of brown coals of three types have been carried out using an experimental plant with an electric-arc reactor of the combined type. On the basis of the material and heat balances, process parameters have been obtained: the degree of carbon gasification (ζc), the level of sulfur conversion into the gas phase (ζs), the synthesis gas concentration (CO+Hz) in the gaseous products, and the specific power consumption for the gasification process. The degree of gasification was 90.5-95.0%, the concentration of the synthesis gas amounted to 84.7–85.7%, and the level of sulfur conversion into the gas phase was 94.3–96.7%. Numerical study of the process of plasma gasification of coals was carried out using a mathematical model of motion, heating, and gasification of polydisperse coal particles in an electric-arc reactor of the combined type with an internal heat source (arc). The initial conditions for a conjugate system of nonlinear differential equations of the gas dynamics and kinetics of a pulverized coal stream interacting with the electric arc and oxidizer (water vapor) agree with the initial conditions of the experiments. The computation results satisfactorily correlate with the experimental data. The mathematical model can be used for the determination of reagent residence time and geometrical dimensions of the plasma reactor for the gasification of coals.

Appraisal and Optimisation of Dense Medium Plant Separations

An extensive plant-orientated testwork campaign was undertaken to quantify and determine the causes of significant dense medium cyclone operating inefficiencies. Comprehensive plant trials, with 20–30 people sampling up to 100 process (medium and coal) streams simultaneously for eight hour shifts permitted both magnetite media and coal processing characteristics to be simultaneously quantified. Dense medium classification and coal partition curves were principally used to show that the root cause of inefficient cyclone performance was related to incorrect magnetite particle size in the cyclone circuits. When magnetite with the correct specifications was used in the plant, the reasons for coarse magnetite in the cyclone circuits was found not to result from selective fine magnetite losses in the small coal circuits, but from a fundamental design flaw in the magnetite distribution system. The flawed system was shown to prevent correct specification magnetite entering the cyclone circuits, thereby starving t...

Low-resistivity Related ESP Performance Problems in Dry Scrubbing Applications

This paper describes the evaluation of the performance of ESPs operating downstream of spray dryers in high- and medium-sulfur coal flue gas streams. Tests were conducted at the TV A10 MW Spray Dryer/ESP Pilot Plant and the EPRI High Sulfur Test Center. The results of the analysis of particle characteristics, spray dryer operating parameters, and ESP operating variables identify the occurrence of severe particle reentrainment due to the low resistivity (108 ohm-cm and lower) of the sorbent/flyash mixtures at low approach-tosaturation temperatures. The reentrainment has a significant impact on the collection efficiency of ESPs which could represent a fundamental limitation on their ability to adequately perform in this environment. Although this program has been focused on spray dryer applications, because of the similarities of the gas and particle characteristics produced from spray drying and other dry scrubbing processes, the results also have implications to duct slurry injection, dry sorbent injection with humidification, and processes involving furnace sorbent injection with humidification. The performance characteristics of the ESPs are presented under both baseline and spray dryer conditions. The results are analyzed and the Southern Research Institute ESP Computer Model was used to evaluate the data. Special techniques for measuring particle resistivity at these conditions are described. A theoretical examination of particle reentrainment was undertaken which indicated that at low-resistivity levels the electrostatic forces reverse and tend to pull the particles off the plates with a force proportional to the square of the electric field. This repulsion of particles from the plates at spray dryer conditions was confirmed by laboratory experiments. Chloride content of the coal was found to be an important parameter effecting the performance of the ESP. Implications of the results of this evaluation relative to ESP upgrades are presented.

Theoretical aspects of parallel coal processing circuits optimization and M-curve

The problem of determining the optimum cutpoints of separation for processing different coals or different size ranges of a coal in parallel coal processing circuits which produce an overall product of maximum yield or mass flow rate at a specified ash or sulphur level is investigated. The processed products are blended with the raw coal stream. Mayer curves (M-curves) based on actual data are utilized to illustrate the results obtained.

Electrostatic separators for insulating fluids

Electrostatic separators have been used in purifying hydraulic fluids, fuels, petroleum refining and coal liquefaction streams, lubricating oils, and other insulating liquids. The designs, applications, and separation efficiencies of these separators are discussed. The separators are categorized as employing either spatially uniform or nonuniform electrical fields, or electrical fields in conjunction with other physical separation techniques. They require low inlet pressures, draw low current, and are resistant to plugging. They are rugged, allowing use in high-temperature and -pressure applications. Many designs allow continuous or semicontinuous operation. Electrostatic separators can separate particles of similar density, shape and size by differences in electrical properties. >

Rapid characterization of mutagenic aromatic amines in energy-related materials by short column liquid chromatography with electrochemical detection.

A liquid Chromatograph equipped with a short (3 cm) reverse phase column and electrochemical detector was used to characterize aromatic amines in shale oil, synthetic oil, and coal gasification streams. Five major peaks were produced from each sample mixture. The composition of the peaks was determined by high performance liquid chromatography with a long (25 cm) reverse phase column and by gas chromatography/mass spectrometry. Amines in the various peaks included aminonaphthalenes, aminobiphenyls, aminofluorenes, and aminophenanthrenes plus aminoanthracenes. The concentration of aminofluorenes, and aminophenanthrenes plus aminoanthracenes correlated with relative mutagenicity of the base fraction from the oils or tars. The levels of 2- and 3-ringed aromatic amines from shale oil and oil from the Great Plains commercial coal gasification plan were 24 and 184 μg/g tar, respectively, while the respective mutagenicities were 8 and 214 revertants/μg base fraction. This technique has the advantages of high sensitivity and rapid analysis, and could be used to screen for the presence of mutagens in synthetic fuel samples.

Method for processing coal preparation plant washings for elimination of sludge ponds

The solids concentration obtained from the aqueous suspension derived from coal beneficiation plant streams can be promptly processed in stabilized load bearing mass by passing these solids plus proportionally added portland cement powder thru a temperature controlled pug mill. The product is then delivered to a fill area for disposal. This eliminates the need for ponds and permits the immediate reuse of water in the plant. Major economies in land purchases, waste treatment, water requirements, and operating costs are effected.

Modelling of High Intensity Combustion of Pulversized Coal in a Tabular Combustor

Abstract A quasi-two-dimensional model of pulverized coal combustion under very high heating rates (about 10nK/s) and at high temperatures (2000 K or more) is described. The model considers mixing between the coal and oxidant streams, coal demoisturization, coal devolatilization, char oxidation, conductive-convective and radiative heat transfer and fragmentation of the coal/char particles. The mixing between the streams is shown to have a prominent effect on the predictions of the model, while the predictions are rather insensitive to fragmentation. Devolatilization plays an important role in coal particle burn-off, particularly because of the very low residence time (10 to 20 ms) of the particles in the combustor for the cases studied. The predictions of the model are in good agreement with the measured gas temperatures and coal burn-offs.