1. HDS-1 Low Sulfur Gasoline Project
General Overview

2. Introduction
The purpose of FCCU Gasoline Hydrodesulfurization (HDS-1), as part of the Low Sulfur Gasoline Project, is to reduce the sulfur content of the FCCU Naphtha to a combined sulfur content of 30 ppmw.
FCCU gasoline makes up over 50% of the gasoline pool at Convent and currently contains ~1200 ppmw sulfur .

3. Introduction (cont.)
HDS-1 will enable Convent Refinery’s gasoline pool to meet the Federally mandated Tier II sulfur specification for gasoline sold at the pumps.
In 2004, the maximum sulfur allowed in any gasoline blend will be 300 ppmw, and Motiva must meet a Corporate average of <120 ppmw.
In 2006, the maximum sulfur allowed in any gasoline blend will be 80 ppmw, and Motiva must meet a Refinery average of <30 ppmw.

4. Background The Low Sulfur Gasoline (LSG) Project began in 1999.
CDTech Catalytic Distillation Technology was chosen for the project.
The Motiva Convent design is part of a centrally managed project to provide Port Arthur, Convent, Puget Sound, Norco, and Deer Park with processing facilities to produce low sulfur gasoline.
Bechtel was chosen to provide FEL and detailed engineering for ISBL. Bechtel was also chosen to provide CM for ISBL & OSBL
Jacobs Engineering was chosen to provide FEL and detailed engineering for OSBL (including CWT#4).

5. HDS-1 Feed Debutanizer bottoms from the FCCU (Full range naphtha)
Cold Feed from Tankage (offspec tank will be 20D-5)

6. Modes of Operation
The HDS-1 unit is designed for two modes of operation:
Case 2 describes the base case where HTU-3 is running in gas oil hydrotreating mode. In Case 2, HDS-1 feed is expected to contain 1000 –1300 ppmw Sulfur.
Case 3 describes the case where HTU3 is down, or not operating in gas oil mode, and is designed for an HDS-1 feedstock with a higher sulfur content (up to 1732 ppmw by design).
The unit design for both cases will desulfurize FCCU naphtha feed with high purity hydrogen to meet the 30 ppmw sulfur spec in the combined products.

7. Charge Rates
HDS-1 is designed to charge up to 57,000 BPSD of full range FCCU naphtha.
This charge rate includes up to 9,000 BPSD of cold feed from tankage (20D-5).
HDS-1 does not have a charge heater, so the heat balance of the unit dictates the amount of cold charge that can be fed (~15% cold feed).
Design turndown of the unit is 50% of the design charge or 28,500 BPSD. This turndown limit will be tested after start-up.

8. Hydrogen
Hydrogen is utilized to remove the sulfur in the FCCU naphtha feed.
Fresh make-up hydrogen from the hydrogen pipeline is introduced through several injection points to the unit.
In Case 2, Hydrogen usage is estimated to be MMSCFD.
In Case 3, Hydrogen usage is estimated to be MMSCFD.

9. Hydrogen (cont.)
A hydrogen purge operation is also employed to maintain hydrogen partial pressure required for the treating process.
The unit produces a low-pressure and a high-pressure purge gas stream from the amine scrubbers, as well as a low-pressure purge stream from the CDHydro Reflux Drum.
Combined, the streams are >70% hydrogen and ~150 MSCFH and will be routed to the refinery East-side fuel gas system.
Alternate line-ups include the flare.

10. Other Inputs 600# Steam for three column reboilers
Fuel Gas and Natural Gas for the Fired Reboiler
Lean Amine for the two Amine Absorbers (one high pressure and one low pressure)
DMDS (located in a storage vessel on the unit) for injection when the Recycle Gas Compressor is not operating.

11. Other Effluent Streams
Rich Amine routed to ARU2/3/4 for Regeneration
Sour Water collected from various drums in the unit and routed to the Sour Water Strippers.

12. HDS-1 Products
Light Cat Naphtha (LCN) – a side draw product from the CDHydro Naphtha Splitter tower
Stabilized Naphtha – bottom product from the Naphtha Stabilizer tower.
The LCN will be “sponged” with Stabilized Naphtha, as needed for RVP control, as final product leaving the unit.

13. Some Affected Areas of HDS-1
The FCCU will decommission equipment downstream of the Debutanizer and have a new gum inhibitor injection skid.
The TAME Depentanizer will receive LCN from HDS-1 as feed instead of LFC from the FCCU.
HTU-1 will supply catalyst preparation material in the form of hydrotreated naphtha and low sulfur avjet.
Several tanks in PUL have been taken over by HDS-1, for products and offspec material (Tanks 20D-26/66/25/65 and 5).
HDS-1 is tied to Flare 4.
Purge Gas from HDS-1 will be routed to the East Side Refinery Fuel Gas Drum.

14. HDS-1 Low Sulfur Gasoline Project
Process Description

15. Basic Operation
The function of the HDS-1 unit is to desulfurize the FCCU Naphtha while minimizing the amount of olefin saturation, using CDTech Technology.

16. CDHydro Naphtha Splitter
The CDHydro Column:
Receives ppmw sulfur feed from the FCCU and tankage.
Processes FCCU gasoline to produce and overhead C6 and lighter stream (LCN) that contains ~35 ppmw sulfur and a bottoms stream that contains ppmw sulfur.
Uses Pipeline hydrogen to enhance reaction rates.

17. CDHydro Design
The CDHydro Column consists of 32 valve trays, 3 chimney trays, and 2 sections of catalyst packing (a Nickel bed and a Palladium bed).
The CDHydro Column is a 143’ tall, 15’6” diameter reaction-distillation column. This column has a skirt of ~50’, which brings the total height to almost 200’.

18. CDHydro Split
The feed with high olefins content flashes up the column, via a temperature controller that controls heat input into the column.
On the way up the tower, these lighter products interact with hydrogen injected into the tower to cause 3 chemical reactions.

19. CDHydro Reactions
Thioetherification: where mercaptans and olefins react to form disulfides (a stable heavy sulfur compound) which distills into the bottoms.
Diene hydrogenation: where diolefins react with hydrogen to form olefins. This reaction creates the reactants for the next step.
Hydroisomerization: where the double bonds in olefin molecules move to a different location in the same molecule, causing an octane boost.

20. CDHydro Products
The LCN product (a C6 and lighter stream) is drawn from Tray 6, the chimney tray above the catalyst packing, and contains ~35 ppmw sulfur by design (<5 ppm mercaptans).
The LCN product is cooled, then mixed with Stabilized Naphtha product to reduce vapor pressure, before it is sent OSBL to the TAME Depentanizer for further processing or to product tankage (Tanks 20D-26/66).
The CDHydro bottoms ( ppmw sulfur at this point) are further treated in the CDHDS and Polishing Reactor systems.

21. CDHDS Column The CDHDS Column: Receives the CDHydro bottoms as feed.
Processes the CDHydro bottoms to produce a C7 and heavier heavy naphtha stream that contains ppmw sulfur.
Uses recycle hydrogen provided by the Recycle Gas Compressor as well as pipeline hydrogen injected into the catalyst beds and reboiler inlet to achieve proper reaction rates and reduce heater fouling.

22. CDHDS Design
The CDHDS Column consists of five individually supported catalyst beds (all Cobalt-Molybdenum), a section of structured packing and a liquid distributor above the top catalyst bed, a liquid distributor and chimney tray above each of the remaining four catalyst beds, and a chimney-liquid collector tray below the bottom bed.
The CDHDS Column is a 133’ tall, 15’6” diameter reaction-distillation column.

23. CDHDS Split
The feed enters the column as ~40% vapor. Using a temperature controller that controls heat input into the column, 80% of the feed is taken overhead and the remaining 20% exits the column as bottoms.
This 80:20 overhead to bottom ratio splits the sulfur evenly between the upper and lower catalyst beds and concentrates the heaviest sulfur in the bottoms beds to be exposed to the highest reaction temperatures.

24. CDHDS Reactions
Hydro-Desulfurization (HDS): where sulfur is removed from hydrocarbon molecules by converting it to H2S. This is a desired reaction in the CDHDS column and Polishing Reactor in order to produce a low sulfur heavy gasoline stream.
Olefin Saturation: where the double bond in a hydrocarbon molecule is converted to a single bond by the addition of hydrogen. This is an undesired reaction in the CDHDS column and Polishing Reactor.

25. Recycle Hydrogen
Vapors from the CDHDS Overhead system are treated in the Recycle Gas Amine Absorber.
They are then routed to the Recycle Gas Compressor Knock Out Drum where it is recycled back to the CDHDS column reboiler inlet via the Recycle Gas Compressor.

26. Reboiler Furnace
The Reboiler for the CDHDS column is a Fired Heater, the only one on the unit.
The Reboiler has 4 parallel passes, and 8 fired burners.
The boil-up, regulated by the flow of fuel gas, is controlled by a temperature controller on the CDHDS column.

27. CDHDS Products
The CDHDS Column overhead stream is condensed, cooled, and collected in a series of overhead drums and coolers.
Some of the liquid collected from the overhead is fed back to the column as reflux, and the rest is fed to the H2S Stripper.
The CDHDS Column bottoms stream can be routed to the Reboiler Furnace, to the Polishing Reactor, to the Polishing Reactor Feed Heater, or to the Naphtha Stabilizer (Pol. Rx. Bypass).

28. H2S Stripper Design
In the H2S Stripper, 26 valve trays remove dissolved Hydrogen, light hydrocarbons, and H2S from the desulfurized CDHDS overhead.
The Stripper is designed to strip H2S in the CDHDS overhead to less than 5 ppmw prior to entering the Polishing Reactor.
Vapors from the H2S Stripper and Naphtha Stabilizer Reflux Drums are routed to the Vent Gas Amine Absorber for treatment prior to entering the refinery fuel gas system.

29. H2S Stripper – Preparing the Polishing Reactor Feed
The H2S Stripper is an essential element in preparing the CDHDS overhead liquid for further reaction in the Polishing Reactor as this stream makes up 80% of Polishing Reactor feed.
Since olefins are present in the Polishing Reactor feed, free H2S in the feed could combine with the olefins to form mercaptans through Mercaptan Recombination.
Olefins that react with H2S in the Polishing Reactor are removed from the gasoline product with an associated loss of octane.

30. Polishing Reactor Design
The Polishing Reactor is a 19’6” tall fixed bed reactor with a 10’ diameter.
The Polishing Reactor receives feed from the H2S Stripper and the CDHDS Column bottoms.
Hydrogen is injected into the feed upstream of the Polishing Reactor feed/effluent exchangers.

31. Polishing Reactor
The feed passes through the Polishing Reactor’s single Cobalt-Molybdenum fixed catalyst bed, to reduce the sulfur content from ppmw down to ~28 ppmw by design.
The Polishing Reactor bottoms are routed through the Polishing Reactor Hot/Cold Separator System, where a recycle Hydrogen stream is produced and routed to the CDHDS Column feed stream.
The liquids collected in the Hot and Cold Separators are routed to the Naphtha Stabilizer.

32. Naphtha Stabilizer The Naphtha Stabilizer :
Receives feed from the Polishing Reactor Hot and Cold Separators.
Uses a 600# steam reboiler to strip dissolved hydrogen, H2S, and light hydrocarbon from the heavy gasoline product.
Naphtha Stabilizer bottoms are cooled and used to sponge the LCN product for vapor pressure control, before being sent to product tankage (Tanks 20D-25/65) as Stabilized Naphtha Product.

33. LSG Project Fast Facts
ISBL has about 108 pieces of mechanical equipment
OSBL has about 29 pieces of mechanical equipment including the CWT
Total cubic yards of concrete = 2,590 cu yds
Total tons of steel = 1,180 tons
Total linear feet of pipe = 127,000 ft (24.1 miles)
Total linear feet of cable tray = 5,490 ft (1.0 miles)
Total linear feet of cable = 283,500 ft (53.7 miles)