Refinery gases separation

Table 4 summarizes commercial and precommercial gas separation appHcations (86,87). The first large-scale commercial appHcation of gas separation was the separation of hydrogen from nitrogen ia ammonia purge gas streams. This process, launched ia 1980 by Monsanto, was followed by a number of similar appHcations, such as hydrogen—methane separation ia refinery off-gases and hydrogen—carbon monoxide adjustment ia oxo-chemical synthetic plants. 

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."... 

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 product separation falls into a number of common classes namely Main fractionators gas plants classical distillation, extraction (liquid-liquid), precipitation (solvent deasphalting), solid facilitated (Parex(TM), PSA), and Membrane (PRSIM(TM)). This list has been ordered from most common to least common. Main fractionators are required in every refinery. Nearly every refinery has some type of gas plant. Most refineries have classical distillation columns. Liquid-liquid extraction is in a few places. Precipitation, solid facilitated and membrane separations are used in specific applications. 

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. 

The optimal routing of a two-phase flow pipeline was investigated by Shamir (SI). Such pipelines are commonly used to convey both oil and gas from producing wells to collecting facilities and plants. They obviate the necessity for oil-gas separation facilities at the well head, which are sometimes uneconomical or impractical. In this context it is reasonable to assume that the pipeline will operate under the pressure differential naturally available between the source (well) and the point of delivery (refinery) and that the desired flow rate is specified. Hence one constraint on the optimal route is given by... 

From a commercial point of view, inorganic membranes will become increasingly interesting. In 1989, the inorganic membrane market was estimated to be 31 million, of which 28 million was in ultra- and microfiltration (Egan 1989). By 1999 the total is projected to reach 432 million, of which 80 million will be in gas separation, primarily in refineries (Crull 1989). 

In the incessant scramble to reduce capital and operating costs, chemical engineers adapted a related technique for removing benzene from benzene concentrate. For years, absorption, a gas/liquid extraction process, has been used for separations in refinery gas plants and natural gas plants. It only took a technique for using the special absorbents, the same ones used in solvent extraction, to reduce the complexity of the equipment and the processing costs. See Figure 2-5)... 

HYPERSORPTION. Process in w-hiclt activated car lion selectively absorbs the less-volatile components from a gaseous mix. while the more-volatile components pass on unaffected. Particularly applicable to separations of low-boiling mixtures such as hydrogen and methane, ethane from natural gas, ethylene from refinery gas, etc. 

Absorption plant a plant for recovering the condensable portion of natural or refinery gas, by absorbing the higher boiling hydrocarbons in an absorption oil, followed by separation and fractionation of the absorbed material. Absorption tower a tower or column which promotes contact between a rising gas and a falling liquid so that part of the gas may be dissolved in the liquid. 

Girbotol process a continuous, regenerative process to separate hydrogen sulfide, carbon dioxide, and other acid impurities from natural gas, refinery gas, etc., using mono-, di-, or triethanolamine as the reagent. 

Review team members or consultants retained to support a review should be chosen that are intimately familiar with the hydrocarbon or chemical processes under examination. For example a crude separation operator should not be chosen to support a review of a refinery gas plant, however he could serve as a reviewer for another crude separation unit. The typical review team should also have a balanced number of individuals from different organizations such as company employees, consultants, equipment fabricators, etc. Hopefully one group s self interest should not be able to outweigh and unduly sway the entire groups outlook. 

A demethanizer tower is used in a refinery to separate natural gas firom a light hydrocarbon gas mixture stream (1) having the composition listed below. However, initial calculations show that there is a considerable energy wastage in the process. A proposed improved stem is outlined in Fig. P5.34. Calculate the temperature (°F), pressure (psig), and composition (lb mol/hr) of all the process streams in the proposed system. 

The temperature profile inside the catalyst bed was monitored by three thermocouples and controlled by five-zone furnace. The performance activity tests were carried out for 48 hours after the steady state had been reached. The liquid product stream from the reactor was condensed at 10°C in a gas-liquid separator, and was immediately stripped of dissolved hydrogen sulfide by extraction with acidified cadmium chloride solution prior to analysis. The gaseous products were analyzed periodically by refinery gas analyzer. The experiments were designed to investigate the effects of temperature (220-350°C), space velocity (10 and 13 h ), hydrogen gas rate (67 and 80 NmVm ) with two feedstock types on the performance of the catalysts. 

Oil shale (33 gal/ton by Fischer assay) from the Piceance Rasin (Green River Formation, Colony mine) in Colorado was crushed and sieved to -16/+60 mesh. Retorting was carried out in a fixed bed reactor at a pressure of 2.6 MPa (380 psig) with a slow (6°C/min.) heat up to 600°C followed by 10 min. at 600°C. Short gas residence times were used to minimize secondary oil degradation reactions. Gases were analyzed by GC using a Carle 157A refinery gas analyzer. Liquids were collected in a cyclone, and the water was separated from the oil by distillation. 

Gas separation membrane technologies are extensively used in industry. Typical applications include carbon dioxide separation from various gas streams, production of oxygen enriched air, hydrogen recovery from a variety of refinery and petrochemical streams, olefin separation such as ethylene-ethane or propylene-propane mixtures. However, membrane separation methods often do not allow reaching needed levels of performance and selectivity. Polymeric membrane materials with relatively high selectivities used so far show generally low permeabilities, which is referred to as trade-off or upper bound relationship for specific gas pairs [1]. 

In California (US), a 385 MW cogeneration facility comprising four gas turbine combined cycle trains is in operation [137]. Separate fuels such as natural gas, butane, and refinery fuel gas may be used. The refinery gas contains 800 ppm (by volume) sulfur. Sulfur was removed from the fuel before it was burnt in the gas turbine. The gas cleanup system includes a CO oxidation catalyst and downstream from this catalyst a SCR system. 

Within a relatively short period after their commercialization, membranes for gas separation have been utilized in a wide variety of applications. Among these applications are recovery of hydrogen from purge streams such as encountered in ammonia plants, retrofit chemical plants and from hydroprocessors in refineries. Membrane systems have been introduced into oil fields for C02 recovery from well-head gas in enhanced oil recovery, and they have been used to separate oxygen from nitrogen in air. Also, they have been utilized in combination with other recovery systems, such as cryogenic and adsorption, to both reduce cost and increase efficiency. 

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