Magnetic Desulfurization Research Articles

A novel high-sulfur fine coal clean desulfurization pretreatment：Microwave magnetic separation, high-gradient effect and magnetic strengthen

A new type of fine coal dry separation technology was investigated. Microwave energy was used to improve the magnetic properties of fine coal with a high sulfur content collected from different regions, and a magnetic medium was added to enhance the microwave energy absorption. The enhancement of magnetic desulfurization of −0.5 mm coal using microwave energy was studied, and the gradient effect of secondary magnetic separation of magnetic particle chain on the enhancement mechanism of desulfurization efficiency was evaluated. Microwave energy was used to strengthen the magnetic properties of coal pyrite, leading to high-gradient magnetic separation. In the X axis, demagnetizing field and background magnetic field of particles with different sizes interact near magnetic particles, producing a low magnetic field in the internal region of particles. Further, the change in the internal magnetic field of the entire particle is consistent with the background magnetic field in the positive direction along the X axis. The optimum sulfur content of clean coal in the two types of high-sulfur coal was obtained when 5% magnetic medium was added under a pretreatment time of 180 s, and the sulfur contents of clean coal were 3.12% and 2.08%, respectively. The clean coal yield of the two types of high-sulfur coal decreased by increasing the desulfurization rate, and the optimum media content used for the desulfurization of the two types of high-sulfur coal by rare-earth magnetic separator was 5%. A high-intensity magnetic separator was used for the separation of fine coal, and an effective way to achieve the clean utilization of pulverized coal before its combustion was investigated.

Fine coal desulfurization and modeling based on high-gradient magnetic separation by microwave energy

Fine coal separation is one of the research focuses in the field of clean coal technology. A new type of fine coal dry separation technology was studied. Microwave energy was used to strengthen the magnetic properties of coal pyrite, leading to high- gradient magnetic separation. A high-intensity magnetic separator was used for the separation of fine coal, and an effective way to achieve the clean utilization of pulverized coal before its combustion was investigated. The R2 and corrected R2 values of the two-order model according to the sulfur content of clean coal were small. This shows that the recommended model has a higher fitting degree of response surface. Microwave pretreatment time T has a higher sensitivity to the sulfur content of clean coal than MC in a given range. The response surface has an optimal value, i.e., the highest desulfurization rate. With the increase in magnetic particle size, the desulfurization rate increased continuously. The evaluation index of the clean coal sulfur content of fine coal microwave-enhanced magnetic desulfurization test was optimized by a better two-order fitting model. The constraint conditions of the main influencing factors and the optimization indexes after the response were obtained. The sulfur content of clean coal was in the range of [1.98, 3.35].

96/04659 Dry magnetic desulfurization of pulverized coal

96/04659 Dry magnetic desulfurization of pulverized coal

Dry superconducting magnetic cleaning of pulverized coal

There are wet and dry methods of cleaning pulverized coal for thermal power stations. However, it may be desirable to use a dry process because dewatering finely pulverized coal is difficult and expensive, and burning wet coal reduces the thermal efficiency of the combustion process. It has been shown that high gradient magnetic filters can be constructed which will extract micron-sized paramagnetic particles from a pulverized coal-air stream passing through the filter. Conventional magnetic separators are generally restricted to separating strongly magnetic materials, such as iron and magnetite. High gradient magnetic filters are capable of separating weakly paramagnetic particles, the magnetic force being proportional to the product of field strength and gradient. Only superconducting magnets are currently economic to generate sufficiently large background magnetic fields of, say, more than 2 Tesla, over the volumes required for the desulfurization of coal. These experimental tests indicated that the dry magnetic desulfurization process was able to remove up to 69% of the pyritic sulfur and 33% of the ash content from a typical pulverized coal in a vertically upward airstream rig, and the heating value recovery is 97%. Increasing magnetic fields increases the percentage of reductions of pyritic sulfur, total sulfur, and ash.more » The penalty for the improved sulfur removals was the reduced heating value recoveries.« less

Enhanced Magnetic Desulfurization of Coal

An oxidative alkaline pressure leach is shown to increase the magnetic susceptibility of coal-pyrite particles. The leach was successfully exploited as a pretreatment in the magnetic desulfurization of an eastern Canadian coal. Greater than 50% total sulfur (65% pyritic sulfur) rejection at 85% clean coal yield was achieved using a high-gradient magnetic separator (HGMS) at 1.3 T and 53 mm/s (2 in. per sec) flow rate, after pretreatment at 0.5 mol NaOH, 85°C (185°F), 930 kPa (135 psi) air pressure, 15 minutes retention time, and 20% solids by weight (w/w). Without pretreatment, sulfur rejection at these HGMS settings was less than 5%.

Tracking pyritic sulfur in the microwave desulfurization of coal

Magnetic desulfurization is an attractive physical method of coal cleaning which has been studied for a quarter century. High-frequency selective heating of coal to convert nonmagnetic pyrite to moderately magnetic pyrrhotite has been suggested to enhance separation. Despite predicted feasibility, some successes have only recently been attained. We report on the use of Mössbauer spectroscopy and magnetization to follow indirectly the amounts of inorganic sulfur in coal. We observe significant conversion (≳10%) to pyrrhotite by microwave treatment of coarse coal granules at 915 MHz and 2.45 GHz at power levels of a few kW for about 1 min. Analysis of phase distribution allows independent calculation of the inorganic desulfurization resulting from microwave treatment and magnetic separation.

Magnetic desulfurization of liquefied coals: Conceptual process design and cost estimation

Estimates of magnetic separation characteristics, conceptual process requirements, and capital costs for magnetic separation of mineral sulfur from liquid coal produced in a solvent refining process have been determined from preliminary empirical data obtained by Hydrocarbon Research, Incorporated, in a laboratory program sponsored by EPRI. The magnetic separator has been scaled to remove weakly magnetic sulfurous minerals from the process stream of a solvent refining plant fed by 9,072 metric tons (10,000 short tons) of raw coal per day whose product (moisture and ash-free solvent refined coal plus distillates plus undissolved carbon plus ash) meets point source sulfur emission standards for new installations burning coal. The conceptual installation, employing four batch type high-field high-gradient magnetic separators, each with 3.1 M <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> magnetized volume, packed to 94% void volume with fine stainless steel wool, and energized by a 2 T magnetic field, processes a stream of 315 liters/sec (5,000 gal/minute) reactor liquid effluent. The flow velocity through each unit is 1.8 cm/sec (27 GPM/ft <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) with a 74% on line factor. The installation processes 3.31 million tons per year of raw coal, or 2.9 million tons per year of desulfurized product. Cost of installed magnets is estimated at $18 million and the add on processing costs associated with magnetic separation (including O&M) are estimated at $1.01 per ton of coal feed, $1.16 per ton of low sulfur product (4 cents per million Btu), and 33 cents per 1,000 liters of reactor effluent filtered ($1.27 per 1,000 gallons).

Organization of magnetic desulfurization of coal symposium

Organization of magnetic desulfurization of coal symposium

Magnetic desulfurization of coal

This work is probably the first systematic attempt at using high gradient magnetic separation techniques in coal slurries. The rationale for magnetic desulfurization of coal resides in the paramagnetism of pyrites and their liberation from the coal substance. Principles of magnetic separation are discussed. A model based on the balance of forces acting on a particle in the vicinity of a magnetized strand is developed. The experimental separator consisted of a laboratory column, packed with either steel wool or screens, inserted in the bore of a solenoid magnet. Experimental results, confirmed the effects of coal particle size and slurry velocity as predicted by the model. Evidence of magnetic action was obtained from the magnetization curves of the coal minerals in the products of separation. Preliminary economic analysis shows promise for the commercial application of the process. Directions for future research are indicated.