Industrial Gas Treating

In the previous two sections, we showed how mass transfer can be accelerated by a chemical reaction. We showed that for a first-order irreversible reaction, the mass transfer 

I want to go beyond this point because I believe there is still a large step between these idealized models and what actually happens in industrial gas treatment. In doing so, I am trying to avoid the usual chemical reaction of 

Gas mixtures like these occur widely. They occur in hydrogen manufacture, petroleum desulfurization and coal liquifaction. They occur in the manufacture of ammonia. 

They occur frequently in natural-gas purification, both in the upgrading of pipeline gas and in the purification of liquid natural gas (LNG). Gas streams like these occur in the manufacture of such commodity organic chemicals like ethylene and ethyl acetate. 

The current treatment of these materials depends on the concentration of the undesired gas to be removed in the mixed feed. When this undesired gas concentration is high, above perhaps 20%, the gas to be removed can often be absorbed in nonreactive liquids. Such nonreactive liquids are called physical solvents. When the concentration in the feed is smaller, the free energy required for any separation will be larger. In this case, the solubility in nonreactive hquids is frequently insufficient to achieve the desired separation in reasonably sized equipment. Instead, we must absorb the target species in reactive liquids, which are called chemical solvents.  

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Volume-based solubilities are crucial data used in engineering and economic models in the design of industrial gas treating processes [1]. The amount of solvent required or solvent flow rate (e.g., L/min, etc.) is often the first consideration for projecting process capital and operating expenses, as the size of the process will be directly proportional to the flow rate of solvent [1]. Thus, one consideration of determining whether ILs can be competitive with organic solvents for H S removal is the relative solubihty of H S as it will directly impact the process scale and economics. 

While Fig. 6.6a-c indicates the potential process conditions where ILs might find applicability as physical solvents for H S removal, these ranges represent only a fraction of the conditions that must be addressed by industrial gas treating processes [1-4]. In view of the unique physical and thermodynamic properties of ILs and the... 

The overhead gas product from the regeneration unit of an industrial gas treating process contains a large amount of the gaseous components removed from the gas stream to be treated and the practical problem of its disposal needs to be considered. The most important example is the one where the components to be removed are carbon dioxide and hydrogen sulfide. 

Fluidized-Bed Combustion The principles of gas-solid fluidization and their application to the chemical process industry are treated in Sec tion 17. Their general application to combustion is reviewed briefly here, and their more specific application to fluidized-bed boilers is discussed later in this section. 

Fluor Solvent A process for removing carbon dioxide from natural gas and various industrial gas streams by dissolution in propylene carbonate. Carbon dioxide is much more soluble than other common gases in this solvent at low temperatures. The process cannot be used when hydrogen sulfide is present. The process was invented in 1958 by A. L. Kohl and F. E. Miller at the Fluor Corporation, Los Angeles. It is now licensed by Fluor Daniel. The first plant was built for the Terrell County Treating plant, El Paso, TX in 1960 by 1985, 13 plants were operating. 

X-ray fluorescence can be used to analyse all types of samples. Its applications are numerous, whether in research and development or in quality control of production. Initially, X-ray fluorescence was used in industries that treat metals of primary fusion or alloys and, more generally, in the mineral industry (for use one ceramics, cements, steel, glass, etc.). Because of the ease of use of common X-ray fluorescence instruments, its scope of application has expanded into other areas the photographic industry and semi-conductors (for impurity control in silicon chips), the petroleum industry, geology, paper mills, gas analyses (such as nitrogen), toxicology and environmental applications (dust, fumes from combustion, heavy metals, and dangerous materials in waste such as Pb, As, Cr, Cd, etc.). 

Indirect cost normally ranges from 20 to 35% of material plus labor of the modular major equipment cost. In most cost analysis of complete processing units, the indirect cost is very significant. Indirect cost factors should therefore always be a part of the summary sheet s total cost analysis and never overlooked. For most refinery, chemical plant, and oil- and gas-treating facilities, a 25% indirect cost factor is a well-accepted number in the industry, worldwide. The 25% factor of the material plus labor is therefore advised and is used in this chapter. 

Capture of C02from Flue Gas 511 Table 22.2 Design of an industrial plant treating 300000 m3/h of flue gas. 

Process conditions have been optimized in order to obtain the best possible efficiency and cost. It has been shown that membrane contactors can be advantageously used to capture C02 from flue gases containing about 25% by volume of C02 and to obtain in the decarbonated gas maximum 3% of C02 mole (i.e. 88% capture of C02). It has been proven that the contactors can capture up to 6 m3/h of C02 per m2 of membrane. In Table 22.2 results of a design of a potential industrial plant treating 300 000 m3/h of flue gas are reported. 

For convenience, the discussion of materials for these various processes is divided into five chapters. Crude units and utilities are discussed in this chapter. FCCs, fluid cokers, delayed cokers, sour water strippers, and sulfur plants are covered in Chapter Two. Desulfurizers, reformers, hydrocrackers, and flue gas are discussed in Chapter Three. Hydrogen plants, methanol plants, ammonia plants, and gas treating are discussed in Chapter Four. Underground piping, pipelines, production equipment, and tankage associated with the refinery industry are covered in Chapter Five. Discussed throughout these chapters are many common environments and equipment (e.g., sour or foul water, distillation, etc.) that appear in the various types of refinery process plants. 

Since the early 1960s there have been developed some excellent laboratory experimental techniques, which unfortunately have largely been ignored by the industry. A noteworthy exception was described by Ouwerkerk Hydrocarbon Process., April 1978, pp. 89-94), in which it was revealed that both laboratory and small-scale pilot-plant data were employed as the basis for the design of an 8.5-m- (28-ft-) diameter commercial Shell Claus off-gas treating (SCOT) plate-type absorber. It is claimed that the cost of developing comprehensive design procedures can be kept to a minimum, especially in the development of a new process, by the use of these modern techniques. 

Specialized texts have been published on some of the more important bulk industrial chemicals, such as that by Miller (1969) on ethylene and its derivatives these are too numerous to list but should be available in the larger reference libraries and can be found by reference to the library catalogue. Meyers (2003) gives a good introduction to the processes used in oil refining. Kohl and Nielsen (1997) provide an excellent overview of the processes used for gas treating and sulfur recovery. 

Sulfur recovery can be achieved using the industrially proven Claus and SCOT (Shell Claus Off-gas Treating process) processes where the absorbed H2S is recovered as elemental sulfur via the following reactions ... 

Physical sorbents for carbon dioxide separation and removal were extensively studied by industrial gas companies. Zeolite 13X, activated alumina, and their improved versions are typically used for removing carbon dioxide and moisture from air in either a TSA or a PSA process. The sorption temperatures for these applications are usually close to ambient temperature. There are a few studies on adsorption of carbon dioxide at high temperatures. The carbon dioxide adsorption isotherms on two commercial sorbents hydrotalcite-like compounds, EXM911 and activated alumina made by LaRoche Industries, are displayed in Fig. 8.F23,i24] shown in Fig. 8, LaRoche activated alumina has a higher carbon dioxide capacity than the EXM911 at 300° C. However, the adsorption capacities on both sorbents are too low for any practical applications in carbon dioxide sorption at high temperature. Conventional physical sorbents are basically not effective for carbon dioxide capture at flue gas temperature (> 400°C). There is a need to develop effective sorbents that can adsorb carbon dioxide at flue gas temperature to significantly reduce the gas volume to be treated for carbon sequestration. 

In the industrial practice of gas treating, removal of one or more components of a gas stream by means of a chemically rea tive liquid is almost always accompanied by a process which r generates the rich liquid solution by stripping out the absorbed gas. The only important exception is flue gas desulfurization, where, often the product of the reaction (usually calcium sulfite and sulfate) is simply disposed of as waste however, also for flue gas desulfurization processes where a regeneration step is inclu ed, such as the Wellman-Lord process, are in common industrial use. 

Many different developments are currently in the technology maturation for gas treating. In the following a few technologies are desciihed, which are in or at the end of the testing in the demonstration scale and which should see their introduction to industry within the next five years. 

In a multiphase stratified flow, the interfaces between immiscible fluids have several characteristics. Firstly, the specific interfacial area can be very large just as droplet-based flow. It can for example be about 10,000 m in a microchannel compared with only 100 m for conventional reactors used in chemical processes. Secondly, the mass transfer coefficient can be very high because of the small transfer distance and high specific interfacial area. It is more than 100 times larger than that achieved in typical industrial gas-liquid reactors. Thirdly, the interfaces of a stratified microchannel flow can be treated as nano-spaces. Simulation results show that the width of the interfaces of a stratified flow is in nanometers, and that diffusion-based mixing occurs at the interface. The interface width can be experimentally adjusted by adding surfactants. Finally, reactants only contact and react with each other at the interface. Therefore, the interfaces supply us with mediums to study interfacial phenomena, diffusion-controlled interfacial reactions and extraction. 

Final Recovery—Tail-Gas Treating. Given that Claus plants achieve only about 98% sulfur recovery, and given the stringent sulfur emissions in the oil and natural gas industries, numerous processes have been developed to recover sulfur from the tail-gas of Claus plants. Table 2-5 lists the prominent tail-gas treating processes and licensors. 

There are a number of cases of industrial gas cleanups where two (A and B) or more gases are being simultaneously absorbed in the Uquid. The nature of mass transport, and therefore separation, will depend on how ficist each species reacts with the nonvolatile reactive species C (often the species C has some volatility, e.g. monoetha-nolamine). Each of gas species A and B can either react slowly or have a fast or instantaneous reaction with C. Thus, there can be a number of combinations, many of which are treated in Astarita et al. (1983). We consider here a particular case of considerable industrial importance, namely simultaneous absorption of H2S and CO2 into a reactive aqueous solution containing, say, methyldiethanolamine (MDEA). We want to show how the different rates of absorption lead to a high selectivity of H2S over CO2. The specific reactions are (Haimour et al, 1987)... 

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