Desulfurization effect

Reactivity of absorbent prepared from oil palm ash for flue gas desulfurization Effect of SO2 concentration and reaction temperature... 

In this study subbituminous coals were liquefied and desulfurized effectively by hydrotreating with synthesis gas at moderate operating conditions In the presence of steam and anthracene oil used as a solvent. The data were compared when the same coals were liquefied with pure hydrogen under similar experimental conditions. Pyrltlc and organic sulfur present In these coals appear to be responsible for the formation of catalytic active form of Iron sulfide that functions as an effective hydrotreating catalyst (14). The presence of... 

The main justification for diesel fuel desulfurization is related to particulate emissions which are subject to very strict rules. Part of the sulfur is transformed first into SO3, then into hydrated sulfuric acid on the filter designed to collect the particulates. Figure 5.21 gives an estimate of the variation of the particulate weights as a function of sulfur content of diesel fuel for heavy vehicles. The effect is greater when the test cycle contains more high temperature operating phases which favor the transformation of SO2 to SO3. This is particularly noticeable in the standard cycle used in Europe (ECE R49). 

Finally, sulfur has a negative effect on the performance of the catalyst itself. One sees for example in Figure 5.23 that the initiation temperature increases with the sulfur level in the diesel fuel, even between 0.01% and 0.05%. Yet, in the diesel engine, characterized by relatively low exhaust temperatures, the operation of the catalyst is a determining factor. One can thus predict an ultimate diesel fuel desulfurization to levels lower than 0.05%. 

Process Pa.ra.meters, The most notable effects ia gasifiers are those of pressure (Fig. 1) and coal character. Some initial processiag of the coal feedstock maybe requited. The type and degree of pretreatment is a function of the process and/or the type of coal (see Coal conversion processes, CLEANING AND DESULFURIZATION). 

Additionally, there are a number of useful electrochemical reactions for desulfurization processes (185). Solar—thermal effusional separation of hydrogen from H2S has been proposed (188). The use of microporous Vicor membranes has been proposed to effect the separation of H2 from H2S at 1000°C. These membrane systems function on the principle of upsetting equiUbrium, resulting in a twofold increase in yield over equiUbrium amounts. 

Emissions control systems play an important role at most coal-fired power plants. For example, PC-fired plants sited in the United States require some type of sulfur dioxide control system to meet the regulations set forth in the Clean Air Act Amendments of 1990, unless the boiler bums low sulfur coal or benefits from offsets from other highly controlled boilers within a given utiUty system. Flue-gas desulfurization (FGD) is most commonly accomphshed by the appHcation of either dry- or wet-limestone systems. Wet FGD systems, also referred to as wet scmbbers, are the most effective solution for large faciUties. Modem scmbbers can typically produce a saleable waUboard-quaUty gypsum as a by-product of the SO2 control process (see SULFURREMOVAL AND RECOVERY). 

Reaction With Sulfur. An important use of calcium carbide has developed in the iron (qv) and steel (qv) industries where the carbide has been found to be an effective desulfurizing agent for blast-furnace iron. Calcium carbide and sulfur present in the molten metal react... 

These scrubbers have had limited use as part of flue gas desulfurization (FGD) systems, but the scrubbing solution flow rate must be carefully controlled to avoid flooding. When absorption is used for VOC control, packed towers are usually more cost effective than impingement plate towers (discussed later). 

The discussion that follows will show the effects of several operating variables on product inspections. The effects of the variables are illustrated best by deep desulfurization of heavier gas oils. 

Effect of HjS, Carbon Oxides, Etc. Hydrogen sulfide in the treat gas has an inhibiting effect on the kinetics of hydrotreating. Being a product of the desulfurization reactions, HjS must diffuse from the catalyst surface into the bulk gas stream. Any HjS present beyond that formed, further slows down the rate of diffusion with a consequent decrease in the amount of desulfurization for a given amount of catalyst. Therefore, additional catalyst would be required. 

With higher boiling stocks, mild Hydrofining of kerosene effects desulfurization, color improvement, and a reduction in wick char. Hydrofining improves odor and by reducing sulfur content makes the kerosene less corrosive. 

The extent of reduction of the carbonyl group of ketones and keto acids during desulfurization depends on the kind of catalyst used and on the solvent. The W 7 catalyst was most effective in reducing... 

Raney cobalt is generally less effective than Raney nickel, but may be of use when the rupture of other bonds must be avoided. The important use of Raney nickel desulfurization for the structure determination of thiophenes and for the determination of the absolute configuration of optically active thiophene and benzene derivatives has been stressed earlier. 

Ross (R2) reported measurements of desulfurization efficiency of fixed-bed pilot and commercial units operated under trickle-flow conditions. The percentage of retained sulfur is given as a function of reciprocal space velocity, and the curve for a 2-in. diameter pilot reactor was found to lie below the curves for commercial units it is argued that this is proof of bad liquid distribution in the commercial units. The efficiency of the commercial units increased with increasing nominal liquid velocity. This may be an effect either of mass-transfer resistance or liquid distribution. 

Van Driesen and Stewart (V4) have reported temperature measurements for various locations in commercial gas-liquid fluidized reactors for the large-scale catalytic desulfurization and hydrocracking of heavy petroleum fractions (2500 barrels per day capacity). The hydrogenation was carried out in two stages the maximum and minimum temperatures measured were 774° and 778°F for the first stage and 768° and 770°F for the second. These results indicate that gas-liquid fluidized reactors are characterized by a high effective thermal conductivity. 

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