Fuel sulfur compounds

In the context of fossil fuels, sulfur compounds and their interaction with metals at high temperatures are important and this is termed sulfidation. The details of sulfidation attack are discussed in the literature31. The alloys which perform well in these atmospheres have already been cited (see Table 1.12). 

In gas turbine fuel, sulfur compounds (ASTM D-2880 notably hydrogen sulfide, elemental sulfur, and polysulfides) can be corrosive (ASTM D-130, IP 30) in the fuel handling systems and mercaptans can attack any elastomers present. Thus mercaptan sulfur content (ASTM D-235, ASTM D-3227, IP 30, IP 104) is limited to low levels because of objectionable odor, adverse effects on certain fuel system elastomers, and corrosiveness toward fuel system metals. 

In diesel fuels, sulfur compounds can be present as mercaptans, sulfides, disulfides, and heterocyclic compounds, such as thiophenes. Their combustion by-products can cause wear in diesel engines and increase the amount of deposits in the combustion chamber and on the pistons. Some typical sulfur concentrations reported in diesel fuels are given in Table 2. 

Another gliding arc reformer was presented by Czemichowski et al. [541]. It was operated with natural gas, cyclohexane, heptane, toluene, gasoline, JP-8 and diesel fuel. Sulfur compounds were converted into hydrogen sulfide in the system and up to 4wt.% of sulfur did no affect the operability of the device. Only 2% of the fuel cell energy output was required for the plasma generation. Figure 7.28 shows a GlidArc reformer, which had a power equivalent of 7 kW and volume of 0.6 L. The plasma was... 

At low-temperature conditions, the fuel sulfur compounds are not sufficiently decomposed and increased concentrations of mercaptans (0.06 vol%) and CS2 (0.01 vol%) are present in the syn gas whereas thiophenes occur as traces. Of course, the dominating sulfur species remains H2S [29]. 

Control of SO is intrinsic to the MHD process because of the strong chemical affinity of the potassium seed in the flow for the sulfur in the gas. Although the system is operated fuel-rich from the primary combustor to the secondary combustor, the predominant sulfur compound in the gas is sulfur... 

Catalysis by Metal Sulfides. Metal sulfides such as M0S2, WS2, and many others catalyze numerous reactions that are catalyzed by metals (98). The metal sulfides are typically several orders of magnitude less active than the metals, but they have the unique advantage of not being poisoned by sulfur compounds. They are thus good catalysts for appHcations with sulfur-containing feeds, including many fossil fuels. 

Lead compounds were not found on the surrounding activated coating layer, rather only associated with the precious metal. The Pt sites are less poisoned by lead than are Pd or Rh sites because the Pt sites are protected by the sulfur in the fuel. Fuel sulfur is converted to SO2 in the combustion process, and Pt easily oxidizes SO2 to SO on the catalyst site. The SO reacts with the lead compounds to form PbSO, which then moves off the catalyst site so that lead sulfate is not a severe catalyst poison. Neither Pd nor Rh is as active for the SO2 to SO reaction, and therefore do not enjoy the same protection as Pt. 

Fuel sulfur is also responsible for a phenomena known as storage and release of sulfur compounds. Sulfur oxides (S02,S02) easily react with ceria, an oxygen storage compound incorporated into most TWC catalysts, and also with alumina. When the air/fuel mixture temporarily goes rich and the catalyst temperature is in a certain range, the stored sulfur is released as H2S yielding a rotten egg odor to the exhaust. A small amount of nickel oxide incorporated into the TWC removes the H2S and releases it later as SO2 (75—79). 

Contaminants in fuels, especially alkali-metal ions, vanadium, and sulfur compounds, tend to react in the combustion zone to form molten fluxes which dissolve the protective oxide film on stainless steels, allowing oxidation to proceed at a rapid rate. This problem is becoming more common as the high cost and short supply of natural gas and distillate fuel oils force increased usage of residual fuel oils and coal. 

The use of high-sulfur-content fuels could enhance undesirable carbon-forming tendencies in the engine combustion chamber as well as result in higher amounts of corrosive sulfur oxides in the combustion gases. Mercaptans (a type of sulfur compound) cause odor problems and can attack some fuel system elastomers. Both the concentration of total sulfur compounds as well as the concentration of mercaptan sulfur compounds arc controlled in... 

The gas plant products, namely fuel gas, Cfs, 4, and gasoline, contain sulfur compounds that require treatment. Impurities in the gas plant products are acidic in nature. Examples include hydrogen sulfide (HjS), carbon dioxide (COj), mercaptan (R-SH), phenol (ArOH), and naphthenic acids (R-COOH). Carbonyl and elemental sulfur may also be present in the above streams. These compounds are acidic. 

Products from the reactor are recovered in the main fractionator a J the gas plant. The main fractionator recovers the heaviest produc, such as light cycle and decanted oil, from the gasoline and ligh r products. The gas plant separates the main fractionator overhead vap< s into gasoline, Cj s, C4 s and fuel gas. The products contain sulfur compounds and need to be treated prior to being used. A combination of amine and caustic solutions are employed to sweeten these products... 

The presence of asphaltenes, originating in the fuel, acts as a trap for vanadium, nickel, and sodium (which promote slagging and sulfur corrosion)-, these asphalthenes often contain sulfur compounds, which simply add to the contaminant load. Additionally, asphaltenes act as precursors to spherical stack solids (cenospheres), which are exhausted with the flue gases as stack emissions. 

NOTE Consider a boiler burning a 1% sulfur, 500 ppm vanadium, 50 ppm sodium, heavy fuel oil at the rate of25,000 gallons per day. The contaminants produced during combustion include 2,000 lb (900 kg) of sulfur compounds, 100 lb (45 kg) of vanadium, and 20 lb (9 kg) of sodium compounds. 

Where the fuel contains sulfur compounds, sulfuric acid is ultimately formed, causing acid smutting and both hot-end (high temperature zone) and cold-end (low temperature zone) acid corrosion and fouling, and adds to the total volume of unwanted furnace area deposits. 

The demand for environment-friendly fuels requires the removal of organosulfur compounds present in crade-oil fractions. SO2 or SO3 contribute to the formation of acid rain and have an effect on pollution control devices [9]. Very stringent environmental regulations will limit the sulfur levels in diesel fuels in EU to less than 10 ppm by the end of 2010 [10]. The conventional sulfur-compound... 

It is well established that sulfur compounds even in low parts per million concentrations in fuel gas are detrimental to MCFCs. The principal sulfur compound that has an adverse effect on cell performance is H2S. A nickel anode at anodic potentials reacts with H2S to form nickel sulfide. Chemisorption on Ni surfaces occurs, which can block active electrochemical sites. The tolerance of MCFCs to sulfur compounds is strongly dependent on temperature, pressure, gas composition, cell components, and system operation (i.e., recycle, venting, and gas cleanup). Nickel anode at anodic potentials reacts with H2S to form nickel sulfide. Moreover, oxidation of H2S in a combustion reaction, when recycling system is used, causes subsequent reaction with carbonate ions in the electrolyte [1]. Some researchers have tried to overcome this problem with additional device such as sulfur removal reactor. If the anode itself has a high tolerance to sulfur, the additional device is not required, hence, cutting the capital cost for MCFC plant. To enhance the anode performance on sulfur tolerance, ceria coating on anode is proposed. The main reason is that ceria can react with H2S [2,3] to protect Ni anode. 

Sulfur in cmde oil is mainly present in organic compounds such as mercaptans (R-SH), sulfides (R-S-R ) and disulfides (R-S-S-R ), which are all relatively easy to desulfurize, and thiophene and its derivatives (Fig. 9.2). The latter require more severe conditions for desulfurization, particularly the substituted dibenzothiophenes, such as that shown in Fig. 9.2. Sulfur cannot be tolerated because it produces sulfuric add upon combustion, and it also poisons reforming catalysts in the refinery and automotive exhaust converters (particularly those for diesel-fueled cars). Moreover, sulfur compounds in fuels cause corrosion and have an unpleasant smell. 

Poisoning of deNOx catalysts by SO2 could also be a problem since diesel fuels contain small amounts of sulfur compounds. Only a few studies deal with this subject [11-13]. It appears from the literature that for Cu catalysts the use of MFI as a support reduces the inhibition by SO2. Support effects also appear in the case of Co since Co/MFI is much less sensitive to SO2 than Co/ferrierite [13]. Since this support effect may be related to acidity, it becomes important, to investigate the influence of SO2 on the properties of Cu catalysts supported on Si02, AI2O3, MFI, BEA and unpromoted or sulfate promot Ti02 and Zr02- These latter have been reported active for deNOx [14]. 

Similarly, SO2 and SO3 (SOJ compounds are produced in combustion by the oxidation of sulfur compounds within the fuel source. SO , emitted into the atmosphere can be incorporated into aerosol particles and wet-deposited as corrosive sulfuric acid. Both NO , and SO , emissions contribute to acid rain content from wet deposition, due to their participation in the formation of nitric and sulfuric acid, respectively. 

SFC-FID is widely used for the analysis of (nonvolatile) textile finish components. An application of SFC in fuel product analysis is the determination of lubricating oil additives, which consist of complex mixtures of compounds such as zinc dialkylthiophosphates, organic sulfur compounds (e.g. nonylphenyl sulfides), hindered phenols (e.g. 2,6-di-f-butyl-4-methylphenol), hindered amines (e.g. dioctyldiphenylamines) and surfactants (sulfonic acid salts). Classical TLC, SEC and LC analysis are not satisfactory here because of the complexity of such mixtures of compounds, while their lability precludes GC determination. Both cSFC and pSFC enable analysis of most of these chemical classes [305]. Rather few examples have been reported of thermally unstable compounds analysed by SFC an example of thermally labile polymer additives are fire retardants [360]. pSFC has been used for the separation of a mixture of methylvinylsilicones and peroxides (thermally labile analytes) [361]. 

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