Thomas D. Wheelock

Development of an advanced calcium-based sorbent for desulfurizing hot coal gas

Abstract Modern coal power plants that employ an IGCC system provide an efficient means for power generation. However, toxic and extremely corrosive sulfurous gases produced in a coal gasifier need to be removed from the hot gas prior to combustion in gas turbines. Due to stringent environmental laws, a regenerable sorbent that can remove the unwanted gases at high temperature (e.g. 1170 K) is preferred. In this work, composite sorbents consisting of a limestone core and a cement shell were prepared by pelletizing the powdered materials. In some cases limestone was also incorporated in the shell. The sorbents were characterized by measuring their crushing strength and their adsorption capacity when exposed to H2S gas at high temperature. Several different hydraulic cements were tested including Type I, Type III, and Type IV Portland cements and CA-14 calcium aluminate cement. Other factors investigated included the shell thickness, concentration of limestone in the shell, and pelletization time. The results showed that formulations containing high concentrations of limestone in the shell had higher absorption capacities but at the expense of pellet strength. Longer pelletization times improved pellet strength. The best overall results were achieved when CA-14 cement was incorporated in the shell. While a foundation was laid for sorbents based on the core-in-shell pellet concept, further development is essential and is underway.

Behavior of Oxidized Coal During Oil Agglomeration

Abstract The surface of Upper Freeport coal was oxidized by air at 150°C for up to 144 h, and the behavior of this coal during oil agglomeration was studied at various pH values. With increased oxidation time the surface concentration of both carboxyl and hydroxyl groups was increased, and the recovery of coal with a given amount of oil was decreased. Spherical agglomeration was possible only with the unoxidized or mildly oxidized coal. The effect of oxidation on the zeta potential and three-phase contact angle was studied as well as the relation between these parameters and the agglomeration behavior. The recovery of coal was also measured as a function of pH, oil dosage, and addition of the surface-active agents sodium oleate and cetyl trimethyl ammonium bromide. The results indicate that the relative oleophilic/hydrophilic nature of the coal surface is more important to the oil agglomeration process than the electrokinetic properties of the system.

On the role of oil wetting in the cleaning of high rank coals by agglomeration

Abstract The wettability of three Spanish anthracites with a large mineral matter content was studied by measuring the oil/water/coal contact angle with heptane and with crude and refined vegetable oils. The captive drop method was used for this purpose. The contact angle was found to depend on the coal, oil, and an interaction between coal and oil. Particle agglomeration tests were conducted to determine the maximum recovery of organic matter for each combination of coal and oil. The maximum recovery was observed to correlate well with the three-phase contact angle when heptane was employed as an agglomerant for the different anthracites. When vegetable oils were employed as agglomerants, the maximum recovery was also observed to correlate well with the contact angle in half the cases. For the other half the recovery exceeded what would have been predicted by the contact angle. Therefore, for these cases the oil wettability of the coal seemed greater under dynamic conditions than under static conditions.

Effect of Calcination Temperature on Characteristics and Performance of Ni/MgO Catalyst for CO2 Reforming of Toluene

Abstract A Ni/MgO catalyst for CO 2 reforming of toluene was prepared by impregnating MgO with Ni(NO 3 ) 2 . During calcination, some of the NiO diffused into the MgO and formed a solid solution structure of NiO-MgO, which was analyzed by Raman spectroscopy. In the temperature-programmed reduction with hydrogen analysis, only a small part of the Ni species in the outermost layer was reduced to metallic Ni at 700 °C. The calcination temperature played a key role in determining the subsequent catalytic activity of Ni/MgO, consequently the catalyst calcined at 600 °C had the highest activity. This catalyst also had the highest surface concentration of reduced Ni, which probably accounted for its high activity. During the reforming tests, a small amount of coke was deposited on Ni/MgO catalyst. Polyaromatic compounds were observed by Raman spectroscopy. The coke was probably responsible for the activity loss of Ni/MgO.

Coal Desulfurization and Deashing by Oil Agglomeration

Abstract Coal organic matter was separated from its associated mineral matter by reducing the material to a fine-size, suspending the particles in water, selectively agglomerating with oil the particles which were largely organic, and screening the suspension to recover the agglomerates. Since particles of iron pyrites tended to be agglomerated with the coal, various means of preventing the agglomeration of pyrite were investigated. In some cases pyrite agglomeration was prevented by suspending the particles in an alkaline solution. In other cases it was prevented by pretreating the particles with a warm alkaline suspension through which air was bubbled to oxidize the surface of the pyrite. However, when this method of pretreatment was applied to several Pennsylvania coals, a considerable part of the pyritic sulfur was extracted through dissolution. An unexpected discovery revealed by scanning electron microscopy was the unusual stability of the coal microagglomerates which remained after the oil was extr...

Air agglomeration of hydrophobic particles

The agglomeration of hydrophobic particles in an aqueous suspension was accomplished by introducing small amounts of air into the suspension while it was agitated vigorously. The extent of aggregation was proportional both to the air to solids ratio and to the hydrophobicity of the solids. For a given air/solids ratio, the extent of aggregation of different materials increased in the following order: graphite, gilsonite, coal coated with heptane, and Teflon. The structure of agglomerates produced from coarse Teflon particles differed noticeably from the structure of bubble-particle aggregates produced from smaller, less hydrophobic particles.

Effect of Air Dosage in a Model Mixing System

Abstract In Part 1 of this series of papers, it was shown that a definite amount of air had to be present in a laboratory mixing unit which produced a moderate shear rate in order to form compact, spherical agglomerates in an aqueous suspension of moderately hydro-phobic coal using heptane or hexadecane as an agglomerant. In this paper, the effects of different amounts of air including dissolved air are discussed. The results indicate that a small amount of air will trigger the process of agglomeration, and even the air dissolved in water under equilibrium conditions at room temperature and pressure is sufficient to promote agglomeration provided it is released from solution.

Oil agglomeration of sulfurized pyrite

Abstract The surface of high-grade mineral pyrite from Huanzala, Peru, appeared to oxidize rapidly on exposure to the atmosphere and the oxidized surface was hydrophilic. When fine particles of this material were suspended in water and treated with small amounts of heptane under rigorous agitation, there was only limited tendency for the particles to agglomerate. However, if the pyrite particles, were first treated with an acidified solution of sodium sulfide, the particles became highly oleophilic and they were readily agglomerated by heptane. Compact spherical agglomerates were produced with relatively small amounts of heptane. The oleophilicity appeared due to a coating of elemental sulfur on the surface of the pyrite. The coating was fairly durable as the aggromerability of the particles declined only slightly when the material was stored as a dry powder for up to three weeks. The agglomerability of the coated pyrite declined somewhat in suspensions having a high pH. Also agglomeration of the material was suppressed by sodium sulfide, especially at high pH.

Agglomeration with heptane of coal and other materials in aqueous suspensions

Abstract Ultrafine particles of Illinois No. 6 coal, graphite, iron pyrite, kaolin, or quarts were suspended in water and agglomerated in a closed system with heptane. The coal and graphite formed bulky agglomerates which were held together by heptane bridges, whereas the other materials formed aggregates which collected around and between oil droplets. With large amounts of heptane, graphite readily formed spherical agglomerates whereas the coal exhibited much less tendency to undergo spherical agglomeration. Agglomerates produced from either coal, graphite, or pyrite were easily recovered by screening while those produced from either kaolin or quartz were too weak to withstand screening. The amount of material recovered per gram of heptane (i.e., specific recovery), achieved by agglomeration and screening, increased in the following order: kaolin or quartz

Coal Hydrophobicity and its Role in Filtration and Dewatering

Abstract Surface hydrophobicity as indicated by the three-phase contact angle can be important in fine coal filtration and dewatering. Coal hydrophobicity is generally a maximum for low- and medium-volatile bituminous coals and a minimum for lower rank coals; It is reduced by surface oxidation. Theoretical considerations and experimental evidence suggest that residual filter cake moisture content is minimised when coal hydrophobicity is maximised. Coal hydrophobicity and dewaterability can be enhanced through adsorption of a surfactant or a film of oil.