Assessing the Feasibility of a Progressive Distillation Scheme

1. Assessing the Feasibility of a Progressive Distillation Scheme Presented by: Brian Howard Submitted: April 30, 2009

2. Topics for Discussion • Background of crude oil refining • Conventional method of crude distillation • Direct sequence vs. indirect sequence • Progressive crude distillation • Current applications of progressive distillation

3. Crude Oil Refining - Basics • Crude oil is a complex mixture of hydrocarbons • Compounds in crude oil contain anywhere from one carbon to chains in excess of fifty carbons • In general, the higher the molecular weight of a component, the higher the normal boiling point • The purpose of refining is to separate and manipulate (i.e. via chemical reactions) these compounds to produce usable products

4. Crude Oil Refining – Box Flow Diagram Focus of the Project

5. Crude Oil Refining – Process Overview • Atmospheric distillation is the primary separation process • Downstream processes convert distillation effluents into more useful products • Reforming – converts naphtha to gasoline • Cracking – produces more gasoline from gas oil • Coking – produces more gasoline from residue and petroleum coke

6. Distillation – Basic Theory • Definition: a separation process which separates components in a mixture on the basis of differing volatilities • Volatility of a component is expressed by its vapor-liquid equilibrium ratio, K • An “at first glance” approximation of the ease with which two components can be separated is given by the relative volatility, a • The larger the value of a, the more readily the components may be separated

7. Distillation – Apparatus • Trays provide the medium for liquid vapor contact and mass transfer • As vapor rises through the column, it becomes enriched in the more volatile components • As liquid falls through the column, it becomes enriched in the less volatile components Temperature Trays

8. Topics for Discussion • Background of crude oil refining • Conventional method of crude distillation • Direct sequence vs. indirect sequence • Progressive crude distillation • Current applications of progressive distillation

9. “Unconventional” Distillation Failed Capstone Student

10. Conventional Crude Distillation – Process Flow Diagram Steam fed side strippers strip lighter components from side draws improving sharpness of cuts Pumparounds remove excess heat from the column and use it to pre-heat the feed stream Furnace preheats crude to temperature of feed tray

11. Conventional Crude Distillation – Product Streams • Products of distillation are not pure components • Contain a range of molecular weights and normal boiling points • 5 major product streams • Naphtha –critical component of gasoline • Kerosene – heating fuel, jet fuel • Diesel – transportation fuel • Gas oil – transportation fuel • Residue –further refined to produce more useful products Molecular Weight Volatility

12. Defining Product Streams – ASTM D86 • The ASTM D86 distillation test measures the boiling point ranges of distillation products • The D86 criteria were used to define the products of distillation

13. Indirect Distillation Sequence • Conventional distillation is an indirect sequence • Least volatile (heavier) components are removed first • More volatile (lighter) components proceed to next column in the sequence • Process is repeated until desired degree of separation achieved Molecular Weight

14. Conventional Crude Distillation –Envisioning the Indirect Sequence How is this… • …related to this?

15. Conventional Crude Distillation –Envisioning the Indirect Sequence Answer: Each side stripper and the corresponding rectifying section of the main column can be treated as an independent column in an indirect sequence. Pumparounds serve as condensers.

16. Direct Distillation Sequence • Reversal of the indirect sequence • More volatile (lighter) components are removed first • Less volatile (heavier) components proceed to next column in the sequence • No industrial applications of a purely direct sequence Molecular Weight

17. Topics for Discussion • Background of crude oil refining • Conventional method of crude distillation • Direct sequence vs. indirect sequence • Progressive crude distillation • Current applications of progressive distillation

18. Direct vs. Indirect – So What? • Up to this point, the distinction between a direct and indirect sequence has been purely academic • Two important questions: • Can the differences between the two sequences increase revenues or decrease expenses? • If a direct sequence can produce savings, how can it be applied?

19. Direct vs. Indirect – Question of Savings • Distillation is one of the most energy intensive aspects of processing. • Over 2% of the energy content in a crude stream is used in distillation. • Distillation accounts for about 40% of energy use in a refinery. 641.6 TeraBTU!!!

20. Direct vs. Indirect – Energy Savings • In June of 2008, Natural Gas was trading at $10.82/MMBTU • As energy becomes an increasingly important factor in the operational costs of process plants, so does energy efficiency • Where does the direct sequence provide potential energy savings when compared to an indirect sequence?

21. Direct vs. Indirect – Energy Savings • In conventional distillation, the furnace must preheat crude to the feed tray temperature • This heats lighter components to higher temperatures than necessary to vaporize them • The furnace wastes energy superheating light end components in an indirect sequence

22. Direct vs. Indirect – Energy Savings • Because the direct sequence separates the most volatile (lightest) components first, superheating of lightends is avoided • Consequently, the opportunity for energy savings exists • How can the indirect sequence be applied?

23. Topics for Discussion • Background of crude oil refining • Conventional method of crude distillation • Direct sequence vs. indirect sequence • Progressive crude distillation • Current applications of progressive distillation

24. Progressive Distillation • Definition: “The process consists in successively separating increasingly heavy petroleum cuts at the head of a plurality of columns…of a first series of columns which feed individually each column of the second series.” Naphtha Kerosene Diesel Steam Gas Oil Residue

25. Progressive Distillation – A Direct Sequence? • Not a purely direct sequence • Separations are not sharp • Separations occur in series

26. Progressive Distillation – Justification • Progressive distillation is not truly a direct sequence – why bother? • Best approximation of a direct sequence provided the limitations of a complex hydrocarbon mixture • Patent claims energy savings of up to 16% • Progressive scheme has been implemented at a refinery in Germany

27. Topics for Discussion • Background of crude oil refining • Conventional method of crude distillation • Direct sequence vs. indirect sequence • Progressive crude distillation • Comparison of conventional and progressive distillation

28. Conventional vs. Progressive – Comparing Apples to Apples • To enable comparison between the two distillation schemes, the following factors were fixed between both models: • Crude composition profile • D86 95% points • Product gaps

29. Crude Composition Profile • Light Crude Composition is weighted more heavily towards the lower normal boiling point components

30. Crude Composition Profile • Heavy Crude Composition is weighted more heavily towards the higher normal boiling point components

31. D86 95% Points and Product Gaps Temperature at which 5% of heavier component will boil

32. Conventional vs. Progressive – Comparing the Simulations Conventional Progressive

33. Conventional vs. Progressive – Determining Utility Usage • In-program “Pinch” calculator determines utility consumption from inputs in the process simulator. • Additionally, Excel calculator is available but requires user input of the same process parameters • Cross-checking outputs from both calculators verifies results

34. Conventional vs. Progressive – Utility for a Light Crude 5% increase in hot utility consumption for progressive model $9 million increase in operational costs for progressive model 125% increase in cool utility consumption for progressive model

35. Conventional vs. Progressive – Utility for a Heavy Crude 7% decrease in hot utility consumption for progressive model $11 million decrease operational costs for utility consumption 224% increase in hot utility consumption for progressive model

36. Conventional vs. Progressive - Results • Results are mixed for hot utility • Heavy Crude: 7% reduction • Light Crude: 6% increase • Does the hot utility savings produced in processing a heavy crude justify implementing a progressive scheme? Analyze the cost of an increased cold utility and capital costs of new columns

37. Conventional vs. Progressive – Costs of Cold Utility • Dramatic increase in cold utility requires cooling water capacity increase • Capital Costs for expansion • Piping • Cooling Tower • Heat Exchanger Area • Cost: $1.35 million

38. Conventional vs. Progressive – Capital Costs of Installing Column Network • Implementing the progressive scheme would require the addition of 6 columns • Estimated capital cost: $3.65 million

39. Conventional vs. Progressive – Pay Out Time Pay out time is slightly over 5 months, indicating an excellent return on investment and sustained energetic savings.

40. Conventional vs. Progressive – Hold on a Minute… • A progressive scheme that has produced energy savings of up to 16% is already working in Germany

41. Conventional vs. Progressive – Implemented Progressive Scheme Progressive Scheme in Germany is drastically different. Involves a pre-flash unit placed before the furnace, which knocks off lightest components before the main column.

42. Conventional vs. Progressive – Conclusions • The progressive distillation scheme studied in this report showed mixed results with respect to reducing utility consumption. For a heavy crude, a progressive scheme would ultimately produce annual savings of $11 million after a payout time of 5 months. For a lighter crude, no such savings were observed

43. References Bagajewicz M. and S. Ji. “On the Energy Efficiency of Stripping-Type Crude Distillation.” Ind. Eng. Chem. Res. 2002, 41, 12, 3003‐3011. Bagajewicz, Miguel and Ji, Shuncheng. “Rigorous Procedure for the Design of Conventional Atmospheric Crude Fractionation Units. Part I: Targeting.” Ind. Eng. Chem. Res. 2001, 40, 617-626. Bagajewicz M. and S. Ji. “Rigorous Targeting Procedure for the Design of Crude Fractionation Units with Pre‐Flashing or Pre‐Fractionation.” Ind. Eng. Chem. Res. 2002, 41, 12, 3003‐3011. Devos et al. United States Patent No. 4,664,785. May 12, 2987. Dobesh, Dan et al. “Evaluation of the Energy Savings Claims of Progressive Distillation.” Unpublished. 2008. Perry, Robert H. et al. Perry’s Chemical Engineers’ Handbook. 7th ed. McGraw Hill, New York: 1997.

44. Thank you for listening. Any questions?