Refinery operations

The function of the refinery is to convert crude oil into the finished products required by the market in the most efficient, and hence most profitable manner. 

The methods employed neeessarily vary widely from one refinery to another, depending on the crude processed, the nature and location of the market, the type of equipment available, and many other factors. However, for simplifieation, it may be considered that all refining processes fall into one of four basic categories. 

The fourth basic category is blending of the finished cuts into commercially saleable products such as motor gasoline, kerosene, lubricating oils, and bunker fuel oil, according to their specifications. 

It is the ultimate objective of a refinery to transform the fractions from the distillation towers into streams (intermediate components) that eventually become finished products. This also is where a refinery makes money, because only through conversion can most low-value fractions become gasoline. The most widely used conversion method is called cracking because it uses heat and pressure to crack  

Raw petroleum (crude oil) is extracted from underground around the globe in a variety of ways and refined for tens of thousands of applications in our everyday lives. Crude oil is refined into usable petroleum products through several unique processes. Fractional distillation is the process used to efficiently extract or distill products that are a mixture of chemicals such as gasoline, diesel fuel, and kerosene or may selectively extract pure chemical compounds or petrochemicals such as 

Natural Gas The lightest, most volatile petroleum fractions, such as propane, pentane, etc. 

Gasolines Higher distillates used for automotive fuel. 

Middle Distillates Lower volatility distillates including diesel fuel, kerosene, jet fuels, and lighter fuel oils. 

The terms cracking and reforming are often used without qualification to describe a variety of refinery and primary petrochemical operations. It is hoped 

Fluid residues (from light crudes) Semi-solid residues 

Feedstocks for motor spirit, also known as straight-run gasoline (US). 

Vaporizing oil, jet fuel Diesel fuel, light fuel oil 

Feedstocks for lubricants and waxes, or heavy fuel oils. 

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We believe to have shown here that the RVP of gasoline is a primary characteristic for quality resulting from a delicate compromise between the demands for vehicle performance, optimization of refinery operations and environmental protection. 

Butanes are naturally occurring alkane hydrocarbons that are produced primarily in association with natural gas processing and certain refinery operations such as catalytic cracking and catalytic reforming. The term butanes includes the two stmctural isomers, / -butane [106-97-8] CH2CH2CH2CH2, and isobutane [79-28-9], (CH2)2CHCH2 (2-methylpropane). 

Butanes are recovered from raw natural gas and from petroleum refinery streams that result from catalytic cracking, catalytic reforming, and other refinery operations. The most common separation techniques are based on a vapor—Hquid, two-phase system by which Hquid butane is recovered from the feed gas. 

This by-product hydrogen can be used as fuel or purified and used in other chemical or refinery operations. 

Historically, about two-thirds of the LPG produced in the United States came from natural gas processing and one-third was produced from refinery operations (2). In 1991, this ratio was 61% from natural gas processing and 39% from refinery operations. Total production of LPG in 1991 was 76.85 X 10 m (294.19 x 10 bbl) from natural gas processing and 30.08 x 10 m (189.23 x 10 bbl) produced from refinery operations. 

Fig. 1. General refinery operations (a) light petroleum refining section (b) heavy feedstock refining section.

Naphthalene (qv) from coal tar continued to be the feedstock of choice ia both the United States and Germany until the late 1950s, when a shortage of naphthalene coupled with the availabihty of xylenes from a burgeoning petrochemical industry forced many companies to use o-xylene [95-47-6] (8). Air oxidation of 90% pure o-xylene to phthaUc anhydride was commercialized ia 1946 (9,10). An advantage of o-xylene is the theoretical yield to phthaUc anhydride of 1.395 kg/kg. With naphthalene, two of the ten carbon atoms are lost to carbon oxide formation and at most a 1.157-kg/kg yield is possible. Although both are suitable feedstocks, o-xylene is overwhelmingly favored. Coal-tar naphthalene is used ia some cases, eg, where it is readily available from coke operations ia steel mills (see Steel). Naphthalene can be produced by hydrodealkylation of substituted naphthalenes from refinery operations (8), but no refinery-produced napthalene is used as feedstock. Alkyl naphthalenes can be converted directiy to phthaUc anhydride, but at low yields (11,12). 

The hydrocarbon cracking operations that generate feed olefins generally do not produce sufficient isobutane to satisfy the reaction requirements. Additional isobutane must be recovered from cmde oil or natural gas Hquids or generated by other refinery operations. A growing quantity of isobutane is produced by the isomerization of / -butane [106-97-8]. 

Worldwide propylene production and capacity utilization for 1992 are given in Table 6 (74). The world capacity to produce propylene reached 41.5 X 10 t in 1992 the demand for propylene amounted to 32.3 x 10 t. About 80% of propylene produced worldwide was derived from steam crackers the balance came from refinery operations and propylene dehydrogenation. The manufacture of polypropylene, a thermoplastic resin, accounted for about 45% of the total demand. Demand for other uses included manufacture of acrylonitrile (qv), oxochemicals, propylene oxide (qv), cumene (qv), isopropyl alcohol (see Propyl alcohols), and polygas chemicals. Each of these markets accounted for about 5—15% of the propylene demand in 1992 (Table 7). 

The term tar sands is a misnomer tar is a product of coal processing. Oil sands is also a misnomer but equivalent to usage of "oil shale." Bituminous sands is more correct bitumen is a naturally occurring asphalt. Asphalt is a product of a refinery operation, usually made from a residuum. Residuum is the nonvolatile portion of petroleum and often further defined as atmospheric (bp > 350° C) or vacuum (bp > 565° C). For convenience, the terms "asphalt" and "bitumen" will be used interchangeably in this article. 

The majority of refineries operated by petroleum companies in different parts of the world to make local products, such as gasoline and burner fuels, also produce jet fuels. Even a small refinery with simple equipment can make suitable jet fuel if it has access to the right cmde. However, the principal supply of both civil and military jet fuels is produced in large refineries. Many are located near major cities and airports and are frequentiy connected by pipeline directiy to the airport. Modem airports have extensive storage and handling faciUties operated by local authorities, petroleum companies or consortia, or the airlines themselves. 

Many important refinery operations are not directly involved in the production of hydrocarbon fuels but serve in a supporting role. Some of the major supporting processes are described below. 

Table 6 lists typical air emissions from petroleum refining operations. Where possible, typical quantities and concentrations of pollutants are reported. These should be considered very approximate figures since no two refinery operations are identical. However, they do provide a general idea of the quantities, flows, and levels of different types of priority pollutants handled by refinery operations. 

As you continue to read, scan over the sidebar discussions. These provide a summary of the toxicity and fate data for the principal hazardous chemicals released by petroleum refinery operations. The sidebar discussions also provide descriptions of the most common routes by which these pollutants enter the environment as a result of common refinery practices and operations. 

A refinery operation produces about 500,000 barrels of crude per year. There are approximately 1500 gate valves used in the operation. Develop an estimate of the potential hydrocarbon emissions resulting from valve leakage. What is this worth in terms of lost revenues to the facility You can find some information on typical valve leakage rates from searching on w w w. google. com. 

With the above as an elementary baekground to the subjeet of distillation, we will turn our attention to refinery operations and the equipment typieally used. Before doing so, a diseussion of the properties of hydrocarbons is provided. 

Fluid catalytic cracking and hydrocracking are two additional processes that are often encountered. There are many other processes used in refineries not mentioned here. The list above is intended only to emphasize the wide diversity of processing which is common to petroleum refinuig and to introduce in a very general way some of the more important of these processes. Also it must be emphasized that only fundamental principles of refinery operations have been discussed and modern manufacturing techniques vary widely from company to company. 

The following section provides general information on the major products and processes used to manufacture them from crude oil. The basic refinery operations have already been described. Emphasis is now given to the downstream processes which are used in transforming distillates into a multitude of consumer products. Not all products and processes are discussed, and indeed, only highlights are provided on those discussed. 

Spirits manufacturing is a sophisticated technology, but in general process operations are less complex and demanding as in the case of oil refinery operations. Often the technology may be described as being closer to an art as opposed to an exact science, but clearly engineering principles for distillation, filtration and batchwise type operations are meticulously employed. 

Mixing Valve This type of mixing device is normally a manually operated globe valve operated at 20 to 350 kPa pressure drop. Common use of this device in refinery operations is for water and crude oil mixing before a desalter and in caustic scrubbing operations. 

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