AM-01-11

Page 1

Start-up of First CDHDS® Unit at

Motiva’s Port Arthur, Texas Refinery

By Messrs., R. S. Peninger, J. C. Demeter (Motiva Enterprises LLC),

Mr. A. Judzis, Jr. (Equilon Enterprises LLC), and

 Messrs. E. A. Schwarz, K. L. Rock (CDTECH)

Prepared for the NPRA Annual Meeting, March 18-20, 2001 in New Orleans

Introduction/Background

In 1998, Motiva Enterprises LLC’s Port Arthur Refinery approved funding to proceed with a

project to design and construct a cracked naphtha desulfurization process to desulfurize heavy

FCCU naphtha. The unit had to provide the refinery with the ability to economically produce

reformulated gasoline meeting the Phase II Complex Model requirements of the 1990 Clean

Air Act Amendments (CAAA). In particular, to meet the NOX emission standard for Port

Arthur Refinery’s RFG and to continue to meet the NOX emissions requirements for

conventional gasoline, the gasoline sulfur content had to be reduced. The technology

selected had to be consistent with future requirements to further reduce sulfur in gasoline

products. Port Arthur Refinery’s target was to drop the gasoline pool sulfur by 20-25 percent

following implementation of this project.

Although Motiva had experience with a CDTECH competitor’s technology in the same

service at Port Arthur Refinery and a related technology within its own organization, it

selected the CDHDSâ process from CDTECH due primarily to lower capital costs, superior

octane retention, and ability to operate at reduced severities without encountering high

mercaptan levels in the treated gasoline. The lower operating pressure of the CDHDS

technology when compared to conventional processes was also an attractive parameter in the

technology selection. Moreover, it was anticipated the aforementioned technology would not

provide the necessary performance to meet the more stringent sulfur levels required by the

Phase II CAAA regulations while minimizing octane loss.

The unit design was “kicked off” in the fall of 1998. Matrix Engineering, located in

Beaumont, Texas, was selected to perform detailed engineering and procurement services.
AM-01-11

Page 2

Conex International, also out of Beaumont, was the general contractor responsible for the

construction phase of the project.

The project was completed on schedule and on budget. Figure 1 summarizes the schedule of

the main project activities:

Figure 1

The unit was mechanically complete in March 2000 but start-up was delayed until May due

to an unplanned shutdown of the fluid catalytic cracking unit (FCCU). Heavy cracked

naphtha (HCN) was introduced to the unit on May 14 and since then, the plant has been

operating steadily at design rates, with the exception of two short FCCU outages, producing

on-specification desulfurized gasoline product.

Process Overview

Following is a brief description of the CDHDS processing scheme at the Port Arthur

Refinery. The unit design maximizes heat integration in order to conserve energy.

The source of the HCN feedstock is the existing Heavy Cat Naphtha Stripper off the FCCU

main fractionator. Figure 2 is a simplified flow diagram of the process. The HCN feeds the

CDHDS unit via a feed preheat train (not shown) consisting of several exchangers

maximizing heat integration within the unit. The feed enters the CDHDS column on flow

control.

ID Task

Name 1

2 CDTECH Process Design

3

4 Detailed Engineering

5

6 Procurement

7

8 Construction

9

10 Start-Up

Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun

1999 2000
AM-01-11

Page 3

Figure 2

The CDHDS column contains the hydro-desulfurization catalyst embedded in CDTECHproprietary structured packing. This arrangement facilitates simultaneous distillation and

hydrodesulfurization.

The conditions in the CDHDS column form a selective hydrodesulfurization environment in

which the sulfur compounds will react with hydrogen to form hydrogen sulfide (H2S) while

preserving olefins. The greater portion of the desulfurized naphtha leaves with the overhead

vapor.

Make-up hydrogen supplements the recycle hydrogen to provide the total hydrogen

requirement.

The CDHDS column reboiler is a fuel gas fired heater. A temperature controller, located on

the column, controls the boil-up by regulating fuel gas to the burners.

The overhead vapor from the CDHDS column is partially condensed and sent to an

accumulator that operates at moderate temperature. A portion of the liquid from this drum is

pumped back to the column as reflux while the remainder feeds the stabilizer. The vapor

containing H2S is routed to an amine contactor.

From FCC Heavy

Naphtha Stripper

CDHDSColumn

Make-up H2

Recycle Compressor

To FCC Fractionator

Overhead Condenser

Stabilizer

Contactor

Lean Amine

Purge to

Fuel Gas

Rich Amine

FCHN

Product

Cooling

and

Separation

Reboiler
AM-01-11

Page 4

The sour vapor from the cooling and separation section is contacted with lean amine to

remove H2S. The vapor leaving the contactor is recycled back to the process by a recycle

compressor on flow control. A purge is taken to fuel gas to control non-condensables in the

process.

The function of the stabilizer is to remove hydrogen, H2S and light hydrocarbons from the

desulfurized naphtha. The vent from the stabilizer is returned to the FCC Fractionator

Overhead Condenser for reprocessing. The bottom stream from the stabilizer is the HDS

naphtha product (FCHN) that is routed to offsite blending.

Process Design

The unit is designed to process HCN with the following characteristics:

ASTM (D-86), °F

IBP 124

5 % 229

10% 263

20% 297

30% 319

40% 339

50% 353

60% 368

70% 384

80% 401

90% 422

95% 437

FBP 451

Sulfur, wt% 0.52
AM-01-11

Page 5

The unit uses available pipeline hydrogen with a purity of 99 percent at a rate of 1.5

MMSCFD. The process does not require high purity hydrogen, so it is possible to use lower

purity hydrogen such as reformer hydrogen.

Operator Training

In preparation for initial start up of the CDHDS unit, Port Arthur Refinery and CDTECH

personnel worked together on training the refinery technical and operations staff. As part of

CDTECH’s basic engineering package, a supervisory operating manual was prepared. Using

this document as a guide, Motiva developed training modules that were finalized in a joint

CDTECH/Motiva review at CDTECH’s R&D facilities in Pasadena, Texas. The overall

program covered such topics as normal operation and control, commissioning and start-up,

shutdown and emergencies, safety and environmental issues, and analytical control. The

modules formed the basis for a one-week training course provided to unit operators and

engineers at site. Instructors were Motiva technical personnel, assisted by CDTECH. This

was conducted within a few months of start-up when most of the construction was complete,

allowing the trainees to spend a portion of the “class” in the actual unit.

Commissioning & Catalyst Loading

The construction contractor and Port Arthur Refinery personnel divided the plant into more

than 100 test systems to track construction progress, hydrostatic testing and flushing/blowing

of systems. CDTECH provided an experienced operations expert to assist Port Arthur

Refinery inspectors with these pre-commissioning activities. Most of the hydrostatic testing

and flushing of the unit systems was done with water. Special care was taken with lines that

were tied into the CDHDS column to protect the catalyst and distributors from extraneous

materials. The column was blinded and put under a nitrogen blanket following catalyst

loading to protect the column internals from ingress of such materials during the final stages

of construction and pre-commissioning.

The hydrodesulfurization catalyst used in the CDHDS unit is a commercially available

catalyst that is contained in a proprietary catalytic distillation structure provided by

CDTECH. Physically, the structure is very similar to other commercial structured packing
AM-01-11

Page 6

and loading it into the column is the same process. It is placed into the column in a specified

pattern to maximize catalyst loading density.

Each bed of catalyst contains multiple levels (or layers) of structure (Figure 3) arranged

according to a predetermined loading diagram onto a catalyst support grid. Special perimeter

structures are provided to fit the curvature of the tower wall. The catalyst packing is loaded

to optimize the overall vapor-liquid contact efficiency for simultaneous fractionation and

reaction.

Figure 3

There is a loading manway located at each catalyst bed on the column between the catalyst

support grid and the chimney-collector tray. The construction contractor’s personnel

provided the labor for loading the catalyst structure under the supervision of CDTECH

personnel.

Catalyst loading of the CDHDS column was completed in March and the tower was put under

a nitrogen blanket awaiting catalyst conditioning and start up.
AM-01-11

Page 7

Initial Start-Up

The CDHDS unit was ready for start-up in late March; an unplanned shutdown of the FCCU

delayed commissioning of the CDHDS unit. After repairs and startup of the FCCU the

CDHDS unit was commissioned in May.

In addition to pre-commissioning, training, and catalyst loading services, technical and

analytical support were provided around-the-clock during the commissioning and initial startup of the plant. The analytical support included on-site laboratory equipment (total

sulfur/nitrogen analyzer and bromine number/mercaptans titrator). This information was

important for detailed analysis and comparison of plant operating data against pilot plant

results.

Prior to the introduction of heavy naphtha feedstock to the CDHDS unit, the hydrodesulfurization catalyst has to be “conditioned.” The fresh catalyst as loaded is in an oxide

form that is not active for the desired hydrodesulfurization reactions. A thorough sulfiding is

needed to convert the metal oxides into active substoichiometric sulfides. The sulfiding

procedure consists of soaking the catalyst with hydrocarbons containing DMDS and sulfiding

at elevated temperatures. Prior to presulfiding, the catalyst has to be dried to remove

moisture absorbed from the atmosphere during handling and packaging. Drying is

accomplished by circulating hot hydrocarbons through the column and injecting nitrogen to

act as a sweeping gas to carry the moisture-laden vapor overhead.

The catalyst conditioning steps took four days to complete. Once finished, the column was

kept under nitrogen pressure until reactive feedstock was introduced.

HCN from the FCCU heavy naphtha stripper was introduced to the unit on May 14 at about

50 percent of design rate. A hydraulic restriction in the line from the HCN stripper to the

feed surge drum initially limited capacity to about 80 percent of design rate. The start up of

the CDHDS column is similar to the start up of conventional distillation columns with one

exception, the additional hydrogen feed (for reaction) is not started until the column reflux is

well established.
AM-01-11

Page 8

Following is a brief chronology of the key activities during the commissioning and initial

start up of the plant:

• May 10: Dry-out of HDS catalyst started with N2 injection and heat up

• May 11: Dry-out completed. Sulfiding procedure started with Injection of DMDS to

provide initial “soak” of catalyst.

• May 12: Started H2 and heat up of catalyst to first sulfiding “hold” step at 450°F. Await

H2S breakthrough at these conditions.

• May 13: Breakthrough of H2S confirmed. Heat catalyst to second “hold” step at 600°F.

Await second H2S breakthrough.

• May 14: Sulfiding of catalyst completed. Feed introduced to unit at 09:00 hrs. Unit

lined out by 14:00 hrs. Sample of product taken at 22:00 hrs. showed it meeting

desulfurization specification. Charge rate limited to 80 percent of design due to

hydraulic limitations on tie-in to HCN Stripper.

• May 15: Recycle Compressor started – ran for eight hours then tripped on high motor

amps. Unit returned to once through H2 operation.

• May 16: HDS product sent to normal rundown line as restart of compressor delayed to

modify anti-surge piping.

• May 20: Charge rate increased to design rate following modifications to remove

hydraulic restriction in piping from HCN Stripper to Feed Surge Drum.

• May 21: Started stripping steam to HCN Stripper. Water collecting regularly in Surge

Drum boot. Some water carryover noted.

• May 23: Compressor modifications completed – machine restarted. Recycle gas rate

limited by molecular weight and check valve restriction.

• May 30: Lowered HDS column pressure to reduce HDS conversion to determine unit

flexibility and to approach design severity. HDS conversion lowered to design level of

90 percent.

• September: Recycle compressor check valve has been repaired and hydrogen recycle is

at design rate.
AM-01-11

Page 9

Unit Performance Figure 4

Since initial start-up, the unit (Figure 4) has been operating steadily at design throughput

producing a product meeting desulfurization and octane retention specifications. There have

been two upsets thus far, both involving electrical trips of the recycle gas compressor. In

both cases, the operation of the unit was unaffected, with smooth transition from recycle to

once-through hydrogen operation.

The feedstock composition has changed significantly at times, e.g. sulfur levels in the HCN

feedstock have varied up to as high as 0.75 wt percent. Even so, the unit control remained

unchanged and the product continued to meet desulfurization and octane retention

specifications. The unit operation and control follows conventional distillation practices and

the reaction parameters are easily controlled within normal column operation.
AM-01-11

Page 10

The operating data over the first six months of operation is shown in Figures 5 through 7.

Figure 5

 Figure 6

The HDS conversion across the unit was high during initial operations. The HDS level was

deliberately lowered to the design HDS condition. This was accomplished by reducing the

pressure of the CDHDS column, which resulted in less severe hydrodesulfurization

conditions within the column, yielding lower HDS conversion. At the same time, the

saturation of olefins declined as shown by the reduction in octane loss.

CDHDS Sulfur Conversion, %

70

80

90

100

0 50 100 150 200

Date

Percent HDS

CD HDS Octane Loss

0

1

2

3

4

5

0 50 100 150 200

Date

Octane Loss, (R+M)/2
AM-01-11

Page 11

Figure 7

During the past few months, the HDS conversion has been maintained within the design

range over a wide range of feed sulfur levels. Average octane loss has been at or below one

number over this time period.

The mercaptan levels in Port Arthur’s CDHDS treated Heavy Cat Naphtha have been low

enough that the refinery has been able to blend and ship gasoline with no further treatment

required. The data from the fixed bed unit (see Figure 7) were gathered during a prior run on

the same Heavy Cat Naphtha feedstock. While acceptable RSH levels could be achieved on

the old unit, octane losses at the necessary operating conditions were extremely high,

typically 4-6 numbers (vs. current loss of 1 number with the CDHDS process).

The unit has been operating smoothly since start-up in May. Little operator attention is

required to control the unit and no gasoline blends have been produced off-specification for

sulfur or octane.

Mercaptan Levels

0

50

100

150

200

250

0 2 4 6 8 10

Octane Loss (R+M)/2

RSH Level, ppm

fixed bed RSH

CDHDS RSH
AM-01-11

Page 12

Additional Work

The CDHDS unit was shut down early in 2001 during a scheduled FCCU maintenance turnaround. At that time, the only work planned on the CDHDS unit was to modify the feed

surge drum to include a coalescer element to mitigate water carryover from the feed surge

drum.

Based on the successful performance and operations of the CDHDS unit Port Arthur Refinery

has authorized CDTECH to begin work on the basic engineering of a second phase, low

sulfur gasoline project. The project will provide additional facilities to treat the entire FCCU

cracked naphtha stream using CDHydro®/CDHDS technologies.

CDTECH

Tel: 713-821-5181

Fax: 713-821-3587

3010 Briarpark Drive

Houston, TX 77042