TEXAS REFORMER DESIGNED FOR TWO-STEP EXPANSION

Alphonse Hennico Larry Mank Christophe Mansuy D.H. Smith
Institut Francais du Petrole
Rueil Malmaison, France

Diamond Shamrock Inc. is operating an IFP-licensed continuous catalyst regeneration reformer at its Three Rivers, Tex., refinery.

Because of the company's particular requirements, the unit has demonstrated important features of the Octanizing process, including:

Great suitability for stepwise implementation and tight construction schedule.
Highly flexible operation that, even at less than 50% of capacity, achieves high yield in good quality products.
Safety and ease of operation with a newly designed regenerator perfectly adapted to very large turn-downs.

The continuous catalyst regeneration reforming process is among the most advanced available to the refining industry. It continues to satisfy changing gasoline pool requirements.

Major improvements, as compared to previous designs, are the development of catalysts of increased activity, selectivity, and hydrothermal stability, along with more efficient technology, which has resulted in some noteworthy achievements:

Lower pressure operation, hence increased yields in liquid products and hydrogen production
Reduction in H2 recycle rate and therefore energy savings
Higher reformate octane yields
More efficient catalyst regeneration, leading to in creased reliability and ease of operation
Longer catalyst life.

As a consequence, the Octanizing process features high on stream efficiency, flexibility, and reliability.

Besides these general characteristics of a high-performance process, an important consideration not specifically addressed in this article, but worth mentioning, is that the overall cost of this particular project, despite all the advanced technology, compared very favorably with other similar projects.

BACKGROUND

Seventeen years before the Diamond Shamrock unit went on stream, the first IFP catalytic reformer with continuous catalyst regeneration started up in Italy. The differences between the old and the new units are as great as the distance separating them.

The earlier reformer was assembled largely with old equipment, much of which came from an old U.S. reformer. The Diamond Shamrock unit brings together the newest technology and equipment, thereby obtaining the best cost/quality relationship.

To illustrate the continuing evolution of IFP catalytic reforming, the history of two important process parameters, the hydrogen-to-hydrocarbon ratio and the reactor pressure, is shown in Fig. 1.

The only real similarity between the oldest IFP continuous regeneration reformer and the newest Octanizer is that they both worked.

Time was of the essence. The contract was awarded in March 1990, and the process design began immediately with top priority given to issuing the specification sheets for all critical equipment. The compressor was ordered even before the process design was completed.

Close cooperation among all parties during all phases of engineering and construction led to a smooth and fast construction schedule. The unit was mechanically completed in September 1991, only 18 months from the start.

Special attention was given to training the operators and, with the assistance of a full team of IFP advisors on site, the start-up went smoothly.

The unit was brought to its design specifications in October 1991, and a successful test run followed in mid-November.

Before discussing the unit further, here is a brief description of the process.

OCTANIZING

The Octanizing process reflects the results of several decades of research and development effort to adapt its performance to a present day, more demanding refining industry.

Significant performance improvements have led to today's high yield, high octane, low pressure operation, with continuous catalyst regeneration.

THE CR SERIES CATALYST

The bimetallic CR-series catalyst is particularly well suited for continuous regeneration operation. Its main advantages are the much higher yields of hydrogen and C5+ reformate, compared with those obtained with the conventional catalysts used in semiregenerative reforming.

Since cycle length is not the essential criterion for selecting a catalyst in regenerative technology, the CR series catalyst can be used at very low pressures and H2-to-hydrocarbon ratios to obtain enhanced selectivity and excellent regenerability.

In addition, the high attrition resistance of the catalyst's spherical support material leads to extremely low catalyst consumption.

THE PROCESS

A general flowsheet showing the Octanizing process is given in Fig. 2. This flow-scheme is similar in principle to any reforming process.

The feed is mixed with recycle hydrogen and heated to a specified reaction temperature prior to entering the first of several moving bed catalytic reactors.

In the reactor, the endothermic conversion to high-octane products causes the fluid temperature to decrease as it traverses the bed.

Heat is therefore added between reactors to restore the temperature and obtain the required degree of conversion.

The effluent from the last reactor is cooled and sent to the separation and stabilization sections (not shown).

Fresh catalyst enters the first bed and flows slowly to the bottom and out of the reactor. It is then transferred to the top of the next reactor. As the catalyst moves down through the reactors, it picks up a small percentage of coke, which is removed in the regeneration system.

The heart of the Octanizing technology lies in its original catalyst circulation system and the continuous catalyst regeneration system, described in more detail later.

Some specific comments will explain the basic considerations involved in the development of the process as it stands today. Reducing energy consumption has been a major goal, seemingly in contradiction to other objectives.

For example, the desired lower operating pressures and higher octane requirements would normally lead to an increase in the size and energy consumption of the recycle compressor, an increase in the heat requirements, and losses of reformate in the hydrogen-rich gas.

In order to counteract these effects, IFP has designed a very low pressure drop reaction section, improved the heat recovery on the heat exchange between the reactor effluent and feed, and optimized the recovery of the C5+ fractions from the hydrogen-rich gas under economical conditions.

This has been achieved by some equipment developments:

The specification of low pressure drop box-type heaters.
The utilization of new welded sheet feed/effluent heat exchangers, which allow both substantial improvement in the thermal approach (i.e., difference between the temperatures at the outlet of the last reactor and the inlet of the first heater), and very small pressure drop.
The optimization of the design of the radial reactors in order to reduce the pressure drop while maintaining a satisfactory distribution of the hydrocarbons on the catalyst.
The optimum separation of reformate from hydrogen offgas through the use of efficient yet inexpensive refrigeration systems.

IFP TECHNOLOGY

IFP regenerative technology has been improved to allow faster circulation of the catalyst, and as a consequence, increased regeneration frequency as required by the more severe operating conditions. It is characterized by the unique features, listed below.

Side-by-side arrangement of the reactors, which leads to a number of advantages:
It is inexpensive and pro,ides each reactor with its own integrity; thus, it is safe and easy to maintain (easy access to any reactor). It eliminates problems of thermal stresses. It is very well adapted to high severities, which require increased reactor heights. No problems occur when using four reactors because there are no height limitations.
Accurate control of catalyst regeneration and reduction:
Very accurate control of operating parameters during the various phases of catalyst regeneration and reduction ensures complete coke burning, good adjustment of the chloride level, and utilization of nonpurified hydrogen for reduction.
Absence of valves operating on circulating catalyst:
The patented lift system permits catalyst circulation without using valves, and thus considerable simplifies maintenance. As one of the key process features, it allows even control of the catalyst velocity in the lift lines. Irregular flows or pulsations of catalyst are avoided and, as a consequence, attrition is very low.

The regenerative technology is distinguished by truly continuous catalyst regeneration, which maintains the catalyst at an optimum level of activity and selectivity.

A small amount of catalyst is continuously regenerated outside the reaction section, which allows for uninterrupted operation of the reformer.

This technology permits the operation of the unit at very high severity (low pressure, low H2-to-hydrocarbon ratio).

A gas lift system transports the catalyst from the bottom of each reactor to the top of the next one. The catalyst then flows by gravity from the top of each reactor to the bottom.

A small portion of the produced hydrogen is used as lift gas to ensure catalyst circulation in the reaction section and-to reduce the fresh catalyst. A nitrogen stream is used for catalyst circulation between the last reactor and the regeneration section and to reintroduce the fresh catalyst into the reaction section.

This arrangement, as well as the special lock hopper design, provides a very high level of safety. On-line detection systems for oxygen and hydrogen in the nitrogen circuit reveal leaks immediately and isolate the two sections automatically (Fig. 3).

At the top of each reactor is an upper hopper which ensures that the reactors are full of catalyst. The upper hoppers are equipped with a gamma ray-type level controller, acting directly on the catalyst control valve.

The catalyst circulation system is designed to allow for its maintenance without shutting down the reformer. Gas-tight valves for isolation of the life system are specially designed to avoid catalyst damage.

The catalyst lift pot serves a very important function in the flow control of the catalyst circulation (Fig. 4).

To assure smooth catalyst flow, the gas feed to the lift pot is divided into two streams. The primary gas controls the lift operations and the secondary gas governs the catalyst flow.

Within the proper operating range, the rate of catalyst flow is proportional to the secondary lift gas flowrate. When this secondary gas flow is stopped, no catalyst can move in the lift.

The spent catalyst is withdrawn from the last reactor and lifted to the regeneration section by a flow of nitrogen gas. The catalyst is stored in an upper hopper and transferred by gravity to the lock hopper and regeneration tower.

The catalyst flows through the regenerator's first zone, where most of the coke is burned; then through a second zone, where a final, more complete coke burning takes place. Finally, the catalyst flows through the bottom section of the regenerator, where the oxychlorination and calcination steps are carried out (Fig. 5).

All the regeneration parameters (temperature, oxygen, chemicals, etc.) are controlled independently to ensure a constant and reproducible, high-quality regenerated catalyst. The inert gas in the regeneration loop is circulated by means of a single recycle compressor operating at ambient temperature.

Catalyst circulation is continuous in the reaction section and also through the regenerator. This arrangement allows for a minimum quantity of catalyst outside of the reaction. Moreover, the two-step coke burning system avoids any risk of runaway in the regenerator.

SAFETY FEATURES

Safe operation has been, and will continue to be, top priority. This is exemplified by the design of the regenerative system, which is oriented toward safety as well as efficiency and reliability.

The following features highlight some of the safety considerations:

Catalyst circulation equipped with two-stage nitrogen seals and emergency shutdown valve interlock
Regenerative loop with high-temperature, high-oxygen emergency shutdown system and automatic control, automatic start-up and shutdown, as well as software interlocks with hardware back-up.

THREE RIVERS PROJECT

To satisfy its future requirements in reforming additional naphtha from a refinery expansion, the management of the Diamond Shamrock Three Rivers refinery had to implement an expansion program.

The program called for a rapid debottlenecking and upgrading of its existing catalytic reforming capacity from 7,000 to 14,000 b/sd, followed in the relatively near future by an additional capacity increase to 26,000 b/sd.

To achieve this goal, several options were evaluated:

Revamp the existing high-pressure semiregenerative reformer to 14,000 b/sd as a short-term solution and then start all over with a new 20,000 b/sd unit at a later date.
Install a new 20,000 b/sd continuous catalyst regenerative reformer from the beginning.
Adopt a stepwise expansion strategy where the new continuous catalyst regenerative reformer is designed in Phase 1 for 10,000 b/sd and then expanded in Phase 2 to 20,000 b/sd.

OCTANIZER

The third option minimized the initial investment required for Phase 1 of the project, while ultimately providing a modern, state-of-the-art catalytic reformer of the desired capacity. This gained the favor of management, and IFP's Octanizing process, with its side-by-side reactor/regenerator arrangement, provided the necessary flexibility to implement this stepwise approach.

Because the unit was planned to run initially at 10,000 b/sd at 100 RON, and ultimately at 20,000 b/sd at 102 RON, certain equipment decisions were made early in the design stage to arrive at optimized capital spending for the overall project. Fig. 6 illustrates the Phase 1 configuration.

The following major items were directly involved in this optimized design:

Reactor section (including reactors and furnaces). Phase 1 employs three reactors (R1, R2, R3) and three furnace coils (F1, F3, F4). Capacity is doubled for Phase 2 by adding a fourth reactor (R4) and a fourth furnace coil (F2).
Both items, R4 and F2, are the largest of their individual services, and their deferred installation avoids spending unnecessary capital at the beginning of the project. Process piping is rerouted for Phase 2 to replace the heater in the proper sequence.
Catalyst regenerator. The regenerator is designed initially for the ultimate capacity of 20,000 b/sd; however, auxiliary equipment, such as pumps and compressors, were not spared for Phase 1. As the regenerator is greatly over-designed for Phase 1 operation, a brief shutdown for maintenance of these machines does not influence the continuous operation of the rest of the plant.
Recycle compressor. The recycle compressor frame was specified for the 20,000 b/sd case with two impeller assemblies -one for operation at 10,000 b/sd and one for operation at 20,000 b/sd.
Booster compressor for hydrogen production. For Phase 1, no booster compressor was installed because the produced hydrogen was not needed by the refinery and was sent to the fuel gas system. A small chiller was installed in order to achieve good C5+ reformate recovery.
Heat exchangers. Only one of two vertical countercurrent heat exchangers was installed during Phase 1. The same philosophy is used for the air cooler, trim cooler, and other heat exchangers in the hydrogen recontacting system.
Pumps. The pumps were sized initially for Phase 1 (10,000 b/sd), each with a 100% spare. For Phase 2, two pumps will operate in parallel, with a third to be added for use as a spare.
Piping. The unit piping was specified for the 20,000 b/sd case, because the incremental piping cost could not justify replacement of the first-stage piping at a later date.

Approximately one third of the total investment was deferred to a later date by choosing these initial design options. Fig. 7 shows the Phase 2 installation, high-lighting the additions and modifications of equipment with respect to Phase 1.

When Phase 2 is completed, the unit will operate at 20,000 b/sd and 102 RONC, with an average reactor pressure of 50 psig. This ensures high C5+ yields, with hydrogen production in excess of 1,800 scf/bbl supplying the needs of the expanded refinery.

PHASE 1 CONSTRUCTION

The unusually short construction time had been achieved through exceptionally good cooperation between the three parties. Tight coordination of the different steps allowed simultaneous advancement of certain operations and hence led to an optimized construction schedule of the whole project.

While IFP was finishing the process design for the unit, Diamond Shamrock and Howe-Baker Engineers Inc. were already evaluating the proposals from equipment suppliers based on IFP's equipment specifications. Consequently, equipment was ordered in time to escape long delivery delays.

As erected equipment was ready for field inspection, IFP was on site, thus facilitating the construction schedule. The unit was brought to design rating in October 1991, and the test run was conducted in November.

UNIT START-UP

Start-up of the Diamond Shamrock Octanizing unit involved the following major steps:

Drying of the unit and tightness tests
Catalyst loading, instrument calibration, and testing around the reactor section
Catalyst drying, followed by catalyst circulation tests
Catalyst reduction
Oil-in, followed by gradual increase of the unit temperature
Regeneration loop start-up
Bringing the unit to design capacity and severity
Test run.

During the precommissioning activities, which included unit inspection, washout of equipment and lines, and equipment testing, Diamond Shamrock organized training sessions under IFP's supervision. Commissioning, normal operation, emergency procedures, and shutdown operations were reviewed carefully during these sessions.

Catalyst loading steps went quickly, followed by calibration of the catalyst level instruments at the top of each reactor. Catalyst dryout and reduction were carried out while lining out catalyst circulation.

After oil was introduced into the unit, severity was brought up very gradually as residual moisture in the unit dissipated. As such, it took some time before there was sufficient coke on the catalyst to put the continuous Regeneration system on line.

At the same time, severity was gradually increased to test run conditions, as allowed by the moisture level in the recycle gas. An unexpected delay was encountered because of water buildup in the regeneration loop, which had caused some corrosion problems