Refining Overview – Part 3 Processing Chapter 27 Simple and Complex Refineries

CHAPTER 27 SIMPLE AND COMPLEX REFINERIES About This Chapter This chapter discusses the complexity of a refinery. Each additional processing unit adds complexity, which indicates the contribution of each processing unit on a cost-weighted basis. This chapter will illustrate the concept of complexity by comparing a simple refinery to a more complex refinery. This example is for illustration only and is not indicative of any operating refinery. The costs and throughputs are based on generalizations with no attempt to construct material balances and costs for any processes. The Market for Products is the Determining Factor for the Complexity of a Refinery The complexity of a refinery is determined by the market it serves. The biggest factor is the demand for gasoline. Three indicators of gasoline demand are: „ Production of gasoline as a percentage of crude charge. „ The cracking ratio which is the combined capacity of catalytic cracking and hydrocracking as a percentage of crude capacity. „ The upgrade ratio which is the combined capacity of reforming and alkylation as a percentage of crude capacity. Gasoline production in the U.S. averages about half of the crude charge. The crack ratio approaches 50% of crude capacity. The upgrade ratio averages about 30% of crude capacity. Europe and Asia do not have nearly the gasoline demand of the U.S. in of percentage of crude charged. The cracking ratio is barely 20% of crude capacity. In Europe that combination of gasoline upgrading amounts to something less than 20% of crude capacity. The ratio is lower in Asia but it is increasing more rapidly as a percentage than Europe. Flow Sheets of Two Refineries of Different Complexities Simple Refinery – The Hydroskimmer (European / Asian) Refinery In general, if gasoline demand can be supplied by the naphtha content of crudes, a refinery can be quite simple. A refinery typical in Europe or Asia is a hydroskimmer or topping refinery. A hydroskimmer refinery consists of atmospheric distillation, hydrotreating of naphtha, kerosene, and diesel, and naphtha catalytic reforming. It does not have processes for residue upgrading including vacuum distillation. The products from this refinery are LPG, gasoline, jet fuel, diesel, gas oil and large quantities of fuel oils. The hydroskimmer refinery is relatively simple since it is not necessary to satisfy a demand for gasoline. It should be noted this is changing. Gasoline demand is such in Europe that catalytic cracking capacity is being installed and in time the refineries of both Europe and Asia will become gasoline producers of a higher complexity. Complex Refinery – The Gasoline (United States) Refinery A refinery typical in the United States is a gasoline refinery. This may also be described as a catalytic cracking refinery. In addition to the units for a hydroskimmer refinery, processes are added for fluid catalytic cracking, Page 27-1

Refining Overview – Part 3 Processing Chapter 27 Simple and Complex Refineries

alkylation, vacuum distillation, and visbreaking. This refinery makes much more gasoline but it is still oriented to production of fuel oil since processes for residue upgrading are limited. In particular, gas oil for the catalytic cracker is fed from the crude and vacuum units. The visbreaker is used to increase gas oil availability for charge to catalytic cracking and to reduce viscosity of residual fuel oil. Although typical, this refinery is still simple compared to a hydrocracker refinery. Economics of Refineries and the Introduction of the Complexity Factor The economics of a refinery depend on the sales revenues minus the costs of production. The costs depend on the complexity of the refinery. Preliminary costs can be evaluated using the concept of a Complexity Factor. This procedure has been used for years and is still a good tool for preliminary evaluation. The Complexity Factor is defined as the “the cost per barrel of crude feed divided by the barrel cost of the atmospheric distillation unit for the refinery”. But besides used for obtaining the cost of a refinery, it can also be used to compare the relative costs of each process unit in the refinery. To obtain the full cost of a refinery, the following adjustments are made. „ An estimate of the cost of the atmospheric unit is made and the complexity factor applied. „ An exponential coefficient is used to adjust investment costs to some other desired capacity. „ A cost index to adjust investment costs to some desired date. Nelson began to publish his Nelson Cost Index in Oil & Gas Journal in July 1946. At that time, the capital cost index of refining facilities was defined as 100. The index is now known as the Nelson-Farrar index. In September 1998, the cost was reported to be 1484. Calculation of the Complexity Factor for Two Refineries Simple Refinery – The Hydroskimmer (European / Asian) Refinery The calculation basically follows the following procedure. A material balance is established to determine the feed to each unit and the ratio of the size of each unit compared to the crude unit. This is the Throughput Ratio. Then the cost of each unit at that material balance on a per barrel cost is developed. This is the Cost Ratio. The product of the Cost Ratio and the Throughput Ratio is the Complexity Factor for each unit and the sum is the complexity factor for the refinery. The Complexity Factor is defined as the “the cost per barrel of crude feed divided by the barrel cost of the atmospheric distillation unit for the refinery”. That calculation can be summarized as follows.

Unit Distillation Gas Plant Gasoline/Naphtha Splitter Naphtha Hydrotreater Naphtha Catalytic Reformer Gasoline Clay Treater Light Distillate (Kerosene) Hydrotreater Heavy Distillate (Diesel) Hydrotreater Total Complexity

Simple Hydroskimmer Refinery Cost Ratio Throughput Ratio 1.0 1.00 0.5 0.50 0.3 0.30 2.0 0.15 4.0 0.15 2.0 0.15 2.0 0.15 2.0 0.20

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Complexity 1.00 0.25 0.09 0.30 0.60 0.30 0.30 0.40 3.24

Refining Overview – Part 3 Processing Chapter 27 Simple and Complex Refineries

SIMPLE REFINERY Light Ends

Sulfur

Gas Plant

Fuel Gas

Gasoline Naphtha -Gasoline Splitter Atmospheric Column

Naphtha

Light Distillate

Heavy Distillate

Naphtha Hydrotreating

Naphtha Reforming

Gasoline

Light Distillate Hydrotreating

Kerosene & Jet Fuels

Heavy Distillate Hydrotreating

Diesel & Heating Oil

Gas Oil & Resid

Heavy Fuel Oil #6

The complexity of this hydroskimmer is 3.2, which seems low even for so simple a refinery. Part of the explanation for the low complexity is the crude which is quite light. It is assumed that the processes on distillate streams amounting to 65% of the crude charge and the light ends are ignored. Thus the long resid from bottoms of the atmospheric tower to the vacuum tower is 35%. No provision is made for hydrogen sulfide removal, tail gas cleanup, or sulfur production. Including these may raise the complexity of the hydroskimmer to something closer to 4. The foregoing example illustrates the variability of the complexity calculation method. The estimated costs for units are subject to wide variability and the unit cost ($/barrel of feed) may not reflect a total cost for a unit of that size. Nonetheless the concept is useful for analysis. Complex Refinery – The Gasoline (United States) Refinery The more complex gasoline refinery is typical of a refinery in the United States and probably what a European refinery might resemble when gasoline demands increase. But Europe not only has a high ratio of fuel oil to gasoline, its volume of fuel oil on an absolute basis is large. In order to analyze the complex refinery, it is necessary to compute throughputs and establish unit costs for the catalytic cracker, alkylation plant, vacuum unit and a visbreaker. To do this all percentages are expressed in of crude charge to the atmospheric unit. Assume that the same crude as charged to the hydroskimmer is charged to the more complex refinery. Naphtha side stream is 30%, the light distillate side stream is 15%, heavy distillate side stream is 15%, atmospheric gas oil is 15%, and long resid to the vacuum column is 25%. From the vacuum column, 15% is vacuum gas oil and 10% is resid. The naphtha-gasoline splitter will split half 15% to the isomerization unit and 15% to naphtha hydrotreating and reforming. Both the light distillate hydrotreater and heavy distillate hydrotreater will process 15%. The atmospheric gas oil will be added to the vacuum gas oil and charged to the catalytic cracker, which is thus processing 30% of feed. The catalytic cracker will route 10% to the alkylation unit, which will produce 5% Page 27-3

Refining Overview – Part 3 Processing Chapter 27 Simple and Complex Refineries

light ends and 5% gasoline. Also from the catalytic cracker, 10% will go to diesel and 10% to heavy fuel oil. The resid will charge to the visbreaker where half 5% goes to gasoline and 5% goes to heavy fuel oil. The products are light ends at 5%, gasoline at 40%, kerosene / jet fuel at 15%, diesel at 25%, and heavy fuel oil at 15%. The summary is as follows. Complex Gasoline Refinery Unit Cost Ratio Throughput Ratio Distillation 1.0 1.00 Gas Plant 0.5 0.50 Gasoline/Naphtha Splitter 0.3 0.30 Naphtha Hydrotreater 2.0 0.15 Reformer 4.0 0.15 Gasoline Clay Treater 2.0 0.15 Light Distillate (Kerosene) Hydrotreater 2.0 0.15 Heavy Distillate (Diesel) Hydrotreater 2.0 0.15 Fluid Catalytic Cracker 5.0 0.30 Alkylation Unit 5.0 0.10 Vacuum Unit 1.0 0.25 Visbreaker 4.0 0.10 Total Complexity

Complexity 1.00 0.25 0.09 0.30 0.60 0.30 0.30 0.30 1.50 0.50 0.25 0.40 5.79

COMPEX GASOLINE REFINERY Sulfur

Light Ends

Gas Plant Fuel Gas Gasoline

Naphtha -Gasoline Splitter Atmospheric Column

Naphtha

Isomerization Naphtha Hydrotreating

Light Distillate

Gasoline Naphtha Reforming Light Distillate Hydrotreating

Kerosene & Jet Fuel

Heavy Distillate Hydrotreating

Diesel & Heating Oil

Heavy Distillate Atmospheric Gas Oil

Olefins Vacuum Gas Oil

Vacuum Column Resid

Catalytic Cracking

Visbreaking

Alkylation

Heavy Fuel Oil #6

The complexity calculated for this combination of units and the assumed material balance is of the order of 6+ if allowance is made for sulfur processing. That is a probably low but the crude being charged very light for a refinery today. Most refineries in the U.S. would have a vacuum unit that is twice as big. This refinery balance calls for lifting 75% of the crude to distillate side streams and overhead in the atmospheric crude tower. Page 27-4

Refining Overview – Part 3 Processing Chapter 27 Simple and Complex Refineries

Evaluation of the Complexity Factor for Two Refineries Complexity Factors The complexity of 6 for the complex refinery may be compared with typical values around the world. These complexity factors are typical of those published in the literature over the last decade. Note that increasingly, as refineries respond to the increasing demands for clean fuel and safe operation, the factors are expected to change. Summary of World Complexity Factors Refinery Complexity Factor Hydroskimmers 3.5 to 5 Europe 6 Russia 4 Canada 7 United States 10 The world average complexity is about 6. In the United States, although the average for complex refineries is 10 there are refineries with complexities of 15+. Lubes can add to complexity as can other specialties and aromatic compounds such as benzene extraction and xylene isomers. In addition, refineries with cryogenic units for recovering ethylene and hydrogen have a higher complexity that must be assessed in some non-standard way. Finally, propylene purification, butadiene separation and other petrochemicals production processes can increase complexity. Cost Ratios Cost ratios are the per barrel cost of a reasonably sized unit for a refinery, divided by the per barrel cost of the crude unit. They are the key to complexity calculations. A table of possible values follows. These complexity factors are typical of those published in the literature over the last decade. Note that increasingly, as refineries respond to the increasing demands for clean fuel and safe operation, the factors are expected to change. Cost Ratios for Processing Units Processing Unit Cost Ratio Atmospheric Distillation 1 Vacuum Distillation 1 to 2 Hydrotreating 2 Catalytic cracking 4 to 5 Hydrocracking 6 Alkylation 5 Lubes (several units) 10 Mild catalytic cracking 3 Coking, severe cracking 5t6 The cost ratio must be carefully defined for certain units. In particular, the alkylation plant capacity is expressed here based on total feed rate to be consistent since the Complexity Factor is normally based on feed as a percent of crude capacity. However, alkylation plant capacity is often expressed as barrels of gasoline product, which is equivalent to about a value of 10. Alkylation plants cost is also influenced by the extent to which it has its own light ends fractionators. Further, allowance must be made for the complexity associated with process units, such as sulfur plants. Page 27-5

Refining Overview – Part 3 Processing Chapter 27 Simple and Complex Refineries

Total Costs For many processes it is useful to have a size and cost of the process related to some crude unit size and then develop a ratio to the operation under study. This applies to sulfur treating, hydrogen manufacture, etc., but basis must be carefully defined. Total costs are quite variable, mostly a function of a differing basis and scope, which is not clearly documented. All costs must be adjusted to a common consistent basis. For a given year it is best to use the mid-year published value or an average of early and late values in the year. One way to compensate for lack of overall definition is through consistency in estimate quality and standards of what is included.

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