Gases refinery

Refinery gas process gas) is the noncondensable gas that is obtained during distillation of crude oil or treatment (cracking, thermal decomposition) of petroleum (Gary and Handwerk 1975 Austin, 1984 Speight, 1999 Robinson and Faulkner, 2000 Speight and Ozum, 2002). There are also components of the gaseous products that must be removed prior to release of the gases to the atmosphere or prior to use of the gas in another part of the refinery (i.e., as a fuel gas or as a process feedstock). 

Petroleum refining also produces substantial amounts of carbon dioxide, which with hydrogen sulfide, corrode refining equipment, harm catalysts, pollute the atmosphere, and prevent the use of hydrocarbon components in petrochemical manufacture. When the amount of hydrogen sulfide is high, it may be removed from a gas stream and converted to sulfur or sulfuric acid. Some natural gases contain sufficient carbon dioxide to warrant recovery as dry ice. 

In summary, refinery process gas, in addition to hydrocarbons, may contain other contaminants, such as carbon oxides (CO , where x = 1 and/or 2) and sulfur oxides (SO, where x = 2 and/or 3) as well as ammonia (NH3), mercaptans (R-SH), and carbonyl sulfide (COS). 

Residual refinery gases, usually in more than one stream, which allows a degree of quality control, are treated for hydrogen sulfide removal, and gas sales are usually on a thermal content (calorific value, heating value) basis, with some adjustment for variation in the calorific value and hydrocarbon type (Rawlinson and Ward, 1973 McKetta, 1993 Speight, 1993 Johansen, 1998 Cranmore and Stanton, 2000). For fuel uses, gas as specified above presents little difficulty used 

In all cases, it is the composition of the gas in terms of hydrocarbon type that is more important in the context of the application. For example, in petrochemical appUcations, the presence of propylene and butylene above 10% v/v can have an adverse effect on hydrodesulfurization before steam reforming. On the other hand, petrochemical processes, such as in the production of iso-octane from iso-butane and butylene, can require the exclusion of the saturated hydrocarbons. 

Refinery gas specifications will vary according to the gas quality available and the end use (Rawlinson and Ward, 1973 Johansen, 1998). For fuel uses, gas as specified above presents little difficulty when used as supplied. Alternatively, a gas of constant Wobbe index, say for gas turbine use, could readily be produced by the user. Part of the combustion air would be diverted into the gas stream by a Wobbe index controller. This would be set to supply gas at the lowest Wobbe index of the undiluted gas. 

One of the more critical aspects for the analysis of low-boiling hydrocarbons is the question of volumetric measurement (ASTM D-1071) and sampling (ASTM D-1145, ASTM D-1247, ASTM D-1265). However, sampling liquefied petroleum gas from a liquid storage system is complicated by existence of two phases (gas and liquid), and the composition of the supernatant vapor phase will, most probably, differ from the composition of the liquid phase. Furthermore, the compositions of both phases will vary as a sample (or sample) is removed from one or both phases. An accurate check of composition can only be made if samples are taken during filling of the tank or from a fuUy charged tank. 

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It is clear that these gases have widely varying compositions according to the processes used, but refinery gas is distinguished from natural gases by the presence of hydrogen, mono- and diolefins, and even acetylenes. 

The average error of this simplified method is about 3°C and can reach 5°C. Table 4.22 shows an application of this method calculating the temperature of hydrate formation of a refinery gas at 14 bar. Table 4.23 gives an example applied to natural gas at 80 bar. Note that the presence of H2S increases the hydrate formation temperature. 

One of the principal aspects of refinery gas cleanup is the removal of acid gas constituents, ie, carbon dioxide, CO2, and hydrogen sulfide, H2S. Treatment of natural gas to remove the acid gas constituents is most often accompHshed by contacting the natural gas with an alkaline solution. The most commonly used treating solutions are aqueous solutions of the ethanolamines or alkah carbonates. There are several hydrogen sulfide removal processes (29), most of which are followed by a Claus plant that produces elemental sulfur from the hydrogen sulfide. 

Sulfur, another inorganic petrochemical, is obtained by the oxidation of hydrogen sulfide 2H2S + O2 — 2H2 0 + 2S. Hydrogen sulfide is a constituent of natural gas and also of the majority of refinery gas streams, especially those off-gases from hydrodesulfurization processes. A majority of the sulfur is converted to sulfuric acid for the manufacture of fertilizers and other chemicals. Other uses for sulfur include the production of carbon disulfide, refined sulfur, and pulp and paper industry chemicals. 

The hydrocarbon gas feedstock and Hquid sulfur are separately preheated in an externally fired tubular heater. When the gas reaches 480—650°C, it joins the vaporized sulfur. A special venturi nozzle can be used for mixing the two streams (81). The mixed stream flows through a radiantly-heated pipe cod, where some reaction takes place, before entering an adiabatic catalytic reactor. In the adiabatic reactor, the reaction goes to over 90% completion at a temperature of 580—635°C and a pressure of approximately 250—500 kPa (2.5—5.0 atm). Heater tubes are constmcted from high alloy stainless steel and reportedly must be replaced every 2—3 years (79,82—84). Furnaces are generally fired with natural gas or refinery gas, and heat transfer to the tube coil occurs primarily by radiation with no direct contact of the flames on the tubes. Design of the furnace is critical to achieve uniform heat around the tubes to avoid rapid corrosion at "hot spots."... 

Citric acid is used to chelate vanadium catalyst in a process for removing hydrogen sulfide from natural and refinery gas and forming elemental sulfur, a valuable product (133). 

Liquefied Petroleum Gas The term liquefied petroleum gas (LPG) is applied to certain specific hydrocarbons which can be liquefied under moderate pressure at normal temperatures but are gaseous under normal atmospheric conditions. The chief constituents of LPG are propane, propylene, butane, butylene, and isobutane. LPG produced in the separation of heavier hydrocarbons from natural gas is mainly of the paraffinic (saturated) series. LPG derived from oil-refinery gas may contain varying low amounts of olefinic (unsaturated) hydrocamons. 

Cryogenic processes using turboexpanders facilitate high levels of ethylene recovery from refinery gas while producing byproducts of hydrogen- and methane-rich gas. In a cryogenic process, most of the ethylene and almost all of the heavier components are liquified and ethylene is separated from this liquid. 

Refinery gas is the collective noun used for a range of off-gases originating from the various oil processes. A detailed knowledge of the composition of these gases is needed for three reasons, as follows ... 

Refinery gas (High Paraffin) - Has a greater mol. percent of saturated hydrocarbons (example C2H5)... 

However, a strong caustic solution is used to remove mercaptans from gas and liquid streams. In the Merox Process, for example, a caustic solvent containing a catalyst such as cobalt, which is capable of converting mercaptans (RSH) to caustic insoluble disulfides (RSSR), is used for streams rich in mercaptans after removal of H2S. Air is used to oxidize the mercaptans to disulfides. The caustic solution is then recycled for regeneration. The Merox process (Fig. 1-3) is mainly used for treatment of refinery gas streams. ... 

Propane is a more reactive paraffin than ethane and methane. This is due to the presence of two secondary hydrogens that could be easily substituted (Chapter 6). Propane is obtained from natural gas liquids or from refinery gas streams. Liquefied petroleum gas (LPG) is a mixture of propane and butane and is mainly used as a fuel. The heating value of propane is 2,300 Btu/ft. LPG is currently an important feedstock for the production of olefins for petrochemical use. 

Like propane, butanes are obtained from natural gas liquids and from refinery gas streams. The C4 acyclic paraffin consists of two isomers n-butane and isobutane (2-methylpropane). The physical as well as the chemical properties of the two isomers are quite different due to structural differences, for example, the vapor pressure (Reid method) for n-butane is 52 Ib/in., while it is 71 Ib/in. for isobutane. This makes the former a more favorable gasoline additive to adjust its vapor pressure. However, this use is declining in the United States due to new regulations that reduce the volatility of gasolines to 9 psi, primarily by removing butane. ... 

Like ethylene, propylene (propene) is a reactive alkene that can be obtained from refinery gas streams, especially those from cracking processes. The main source of propylene, however, is steam cracking of hydrocarbons, where it is coproduced with ethylene. There is no special process for propylene production except the dehydrogenation of propane. 

Sulfur is a reactive, nonmetallic element naturally found in nature in a free or combined state. Large deposits of elemental sulfur are found in various parts of the world, with some of the largest being along the coastal plains of Louisiana. In its combined form, sulfur is naturally present in sulfide ores of metals such as iron, zinc, copper, and lead. It is also a constituent of natural gas and refinery gas streams in the form of hydrogen sulfide. Different processes have been developed for obtaining sulfur and sulfuric acid from these three sources. 

The Ce-Cg aromatic hydrocarbons—though present in crude oil—are generally so low in concentration that it is not technically or economically feasible to separate them. However, an aromatic-rich mixture can be obtained from catalytic reforming and cracking processes, which can be further extracted to obtain the required aromatics for petrochemical use. Liquefied petroleum gases (C3-C4) from natural gas and refinery gas streams can also be catalytically converted into a liquid hydrocarbon mixture rich in C6-C8 aromatics. 

Carbon monoxide, refinery gas, petroleum coke (petroleum industry)... 

Gaseous Natural gas Producer gas coal gas water gas oil gas blast furnace gas coke oven gas oil refinery gas... 

As one more common example of liquid fuels present reference may be drawn to liquified petroleum gas (LPG) or bottled gas or refinery gas. This fuel is obtained as a by-product during the cracking of heavy oils or from natural gas. It is dehydrated, desulfurized and traces of odours organic sulfides (mercaptans) are added in order to identify whether a gas leak has occurred. Supply of LPG is carried out under pressure in containers under different trade names. It consists of hydrocarbons of great volatility such that they can occur in the gaseous state under atmospheric pressure, but are readily liquifiable under high pressures. The principal constituents of LPG are n-butane, iso-butane, butylene and propane,... 

MAWR [Mobil alkanolamine waste recovery] A process which reduces the quantity of waste generated by alkanolamine processes, which remove acid gases from oil refinery gas streams. Developed by Mobil Oil, Germany, and used commercially there since 1979. 

Hydrocarbon feedstocks for steam reformers include natural gas, refinery gas, propane, LPG and butane. Naphtha feedstocks with boiling points up to about 430°F can also be used. The ideal fuels for steam reformers are light hydrocarbons such as natural gas and refinery gas, although distillate fuels are also used. Residual fuels are not used since they contain metals that can damage reformer tubes. 

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