Refinery economics

C. A. Cabrera, C. L. Hebner, and S. P. Davis, "Improve Refinery Economics via Enhanced ECC Operations," presented at Katalistiks 8thMnnual FCC Symposium, Budapest, Hungary, June 1987. 

The arrangement of light ends separation facilities is an important factor in overall refinery economics. The development of the optimum scheme for a particular application often involves postulation of a number of alternatives and comparison of the economics for each. 

Consider, as an example, the logic of a policy decision to build and locate an electric generating plant or oil refinery. Economic considerations such as the availability of ample and inexpensive land, and social considerations such as zoning regulations and political influence, would play a major role m such a decision. In practice, this makes it more likely that plants and refineries, as well as waste sites and other locally undesirable land uses, will be located in poorer communities whose population is often largely people of color. 

The cat cracker s operational philosophy is dictated by refinery-economics. Economics of a refinery are divided into internal and external economics. 

For consequence analysis, we have developed a dynamic simulation model of the refinery SC, called Integrated Refinery In-Silico (IRIS) (Pitty et al., 2007). It is implemented in Matlab/Simulink (MathWorks, 1996). Four types of entities are incorporated in the model external SC entities (e.g. suppliers), refinery functional departments (e.g. procurement), refinery units (e.g. crude distillation), and refinery economics. Some of these entities, such as the refinery units, operate continuously while others embody discrete events such as arrival of a VLCC, delivery of products, etc. Both are considered here using a unified discrete-time model. The model explicitly considers the various SC activities such as crude oil supply and transportation, along with intra-refinery SC activities such as procurement planning, scheduling, and operations management. Stochastic variations in transportation, yields, prices, and operational problems are considered. The economics of the refinery SC includes consideration of different crude slates, product prices, operation costs, transportation, etc. The impact of any disruptions or risks such as demand uncertainties on the profit and customer satisfaction level of the refinery can be simulated through IRIS. 

Two important measures of refinery economics are (1) refinery complexity, which is reflected largely in the capital investment and required capital charges to cover depreciation, return on investment, and taxes on that investment and (2) the financial burden imposed on premium product margins as a result of degradation of raw materials to a low fuel value. 

Refiners have typically solved this problem by using linear programming (LP) methods, which have been used extensively in refineries since 1950. Gary et al. [7] state that "a site-wide model of the refinery is therefore usually required to in order to properly determine refinery economics". 

Since refinery economics reqnire operating at minimum coke formation, the new... 

Hybrid Crystallization/Adsorption Process. In 1994, IFP and Chevron announced the development of a hybrid process that reportedly combines the best features of adsorption and crystallization (59,99). In this option of the Eluxyl process, the adsorbent bed is used to initially produce PX of 90—95% purity. The PX product from the adsorption section is then further purified in a small single-stage crystallizer and the filtrate is recycled back to the adsorption section. It is reported that ultrahigh (99.9+%) purity PX can be produced easily and economically with this scheme for both retrofits of existing crystallization units as well as grass-roots units. A demonstration plant was built at Chevron s Pascagoula refinery in 1994. 

M. E. Frank and B. K. Schmid, "Economic Evaluation and Process Design of a Coal—Oil—Gas (COG) Refinery," paper presented at Symposium on Conceptual Plantsfor the Production of Synthetic Fuels From Coal, AIChE 65th Annual Meeting, New York, Nov. 26, 1972. 

Each refiner has the flexibiUty to choose the specific formulation to produce based on the economics of the individual refineries. REG meeting the statutory requirements must be sold in the nine areas of the country which have the worst ozone (qv) problem. In addition, all other areas of the country which exceed the ozone NAAQS may elect the REG regulations, and EPA has estimated that 40% of the nation s gasoline should be subject to REG rules (66). 

Location Reserve base Economic Total reserves Ore-grade fraction, % Mine capacity Refinery and smelter capacity Mine production... 

Propylene has many commercial and potential uses. The actual utilisation of a particular propylene supply depends not only on the relative economics of the petrochemicals and the value of propylene in various uses, but also on the location of the supply and the form in which the propylene is available. Eor example, economics dictate that recovery of high purity propylene for polymerisation from a smaH-volume, dilute off-gas stream is not feasible, whereas polymer-grade propylene is routinely recovered from large refineries and olefins steam crackers. A synthetic fuels project located in the western United States might use propylene as fuel rather than recover it for petrochemical use a plant on the Gulf Coast would recover it (see Euels, synthetic). 

Fuel. Propylene has a net heating value of 45.8 MJ/kg (19,700 Btu/lb) and is often contained in refinery fuel-gas streams. However, propylene is diverted from streams for refinery fuel use in large quantities only when economics for other uses are unfavorable, or equipment for propylene recovery does not exist or is limited in capacity. Propylene is also contained in Hquid petroleum gas (LPG), but is limited to a maximum concentration of 5 vol % in certain grades (83) (see Liquefied PETROLEUM gas). 

The ethylene feedstock used in most plants is of high purity and contains 200—2000 ppm of ethane as the only significant impurity. Ethane is inert in the reactor and is rejected from the plant in the vent gas for use as fuel. Dilute gas streams, such as treated fluid-catalytic cracking (FCC) off-gas from refineries with ethylene concentrations as low as 10%, have also been used as the ethylene feedstock. The refinery FCC off-gas, which is otherwise used as fuel, can be an attractive source of ethylene even with the added costs of the treatments needed to remove undesirable impurities such as acetylene and higher olefins. Its use for ethylbenzene production, however, is limited by the quantity available. Only large refineries are capable of deUvering sufficient FCC off-gas to support an ethylbenzene—styrene plant of an economical scale. 

Economic Aspects. Most hydrogen sulfide is made and used captively or sold by pipeline at prices which are highly variable, depending on locahty. Production ia the United States exceeds 1.1 X 10 t/yr-It has been estimated that 2.4 x 10 t/yr of sulfur are recovered from H2S-containing refinery streams and 1.8 x 10 t/yr of sulfur are recovered from H S-containing natural gas (120). 

The exacting Hst of specification requirements for aviation gas turbine fuels and the constraints imposed by deUvering clean fuel safely from refinery to aircraft are the factors that affect the economics. Compared with other distillates such as diesel and burner fuels, kerosene jet fuels are narrow-cut specialized products, and usually command a premium price over other distillates. The prices charged for jet fuels tend to escalate with the basic price of cmde, a factor which seriously underrnined airline profits during the Persian Gulf war as cmde prices increased sharply. 

Production Controls The nature of the produc tion control logic differs greatly between continuous and batch plants. A good example of produc tion control in a continuous process is refineiy optimization. From the assay of the incoming crude oil, the values of the various possible refined products, the contractual commitments to dehver certain products, the performance measures of the various units within a refinery, and the hke, it is possible to determine the mix of produc ts that optimizes the economic return from processing this crude. The solution of this problem involves many relationships and constraints and is solved with techniques such as linear programming. 

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