Descripción de las zonas y políticas de manejo

It must be remembered that oil or flammable gas should never be charged into process lines or vessels indiscriminately. The unit must be purged before admitting hydrocarbons. There are many ways to purge the unit and ambient conditions may dictate the procedure to be followed: nitrogen or inert gas purging, displacement of air by liquid filling followed by gas blanketing, or steaming followed by gas blanketing.

For the remainder of the unit other than the reactor section, steam purging followed by fuel gas blanketing can be used to air free the unit. The following steps will briefly outline this method.

Potential problems or hazards could develop during the steam purge are as follows: a. Collapse due to vacuum: some of the vessels are not designed for vacuum.

This equipment must not be allowed to stand blocked in with steam since the condensation of the steam will develop a vacuum. Thus, the vessel must be vented during steaming and immediately followed up with fuel gas purge at the conclusion of the steamout.

b. Flange and gasket leaks: thermal expansion and stress during warm-up of equipment along with dirty flange faces can cause small leaks at flanges and gasket joints. These must be corrected at this time.

c. Water hammering: care must be taken to prevent “water hammering” when steam purging the unit. Severe equipment damage can result from water hammering.

uop 117115 VI-47

Block in the cooling water to all coolers and condensers.

Shut down fans on fin-fan coolers and condensers. Open high point vents and low point drains on the vessels to be steam purged.

Start introducing steam into the bottom of the columns, towers, and at low points of the various vessels. It may be necessary to make up additional steam connections to properly purge some piping which may be “dead-ended.”

Thoroughly purge all equipment and associated piping of air. Be sure to open sufficient drains to drain condensate which will accumulate in low spots and receivers.

When purging is completed, close all vents and drains. Start introducing fuel gas into all vessels and cut back the steam flow until it is stopped completely when the systems are pressured. Regulate the fuel gas flow and the reduction of steam so that a vacuum due to condensing steam is not created in any vessel or that the refinery fuel gas system pressure is not appreciably reduced.

C. INITIAL STARTUP

1. Discussion

This procedure is designed to prepare UOP Hydrobon® catalyst for service in the fastest and safest manner without sacrificing catalyst activity or cycle length. If the procedure is not followed, catalyst activity or cycle length may be diminished, or equipment may be damaged. The procedure has been prepared for a startup with fresh or freshly regenerated catalyst. It is not intended to apply to individual units and refinery situations. THE PURPOSE OF THIS PROCEDURE IS TO PROVIDE GUIDELINES FOR THE REFINER WHEN HE IS PREPARING SPECIFIC PROCEDURES FOR AN INDIVIDUAL UNIT.

uop 117115 VI-48

Fresh or freshly regenerated Hydrobon® Hydrotreating catalyst is a complex of metal and nonmetal oxides. During normal operation, the catalyst exists as a complex of nonmetal oxides and metal sulfides. Conversion of the metals from oxides to sulfides during startup must be done in a careful, prescribed manner in order to achieve optimum catalyst activity. An improper startup can result in depressed catalyst activity, reduced catalyst stability and possible temperature runaways.

The startup naphtha used to sulfide the Hydrobon® catalyst should be straight run material with a maximum end point of 205°C (400°F) and a bromine number of 1 or less. This minimizes the possibility of polymerization taking place in the reactor at lower temperatures, and avoids excessive heat of reaction due to olefin hydrogenation during sulfiding. In the event that the startup naphtha is quite low in sulfur, organic sulfur may be added to the feed to the unit in order to reduce the time required for sulfiding. Typically the sulfiding procedure should take 8 - 12 hours. If the time is too short it will be difficult to properly monitor the H2S in the

recycle gas and insure that all the metal sites were properly sulfided. Too long a sulfiding period can start to affect the catalyst and may have some impact on the metal oxide state. The objective is to conduct the sulfiding in a controlled, orderly fashion.

Sulfur compounds added to the charge for accelerated sulfiding may be any light, liquid, organic sulfur compound (e.g., dimethyl sulfide, propyl- or butylmercaptan) which will easily decompose in the system. H₂S may be used in place of a liquid sulfur compound, but the source must be examined for detrimental contaminants such as olefinic gases, sulfur oxides, carbon oxides, and ammonia, which may damage the catalyst. The total detrimental contaminants in the H₂S-rich gas should be limited to a maximum of 0.1 mol-%.

Disulfides, such as carbon disulfide, are not recommended for sulfiding, since there is a safety and handling problem. Also carbon disulfide (CS2) may not hydrogenate

completely at sulfiding temperatures, resulting in excessive coking of the catalyst. There is also evidence that a temperature runaway is more likely than when using other sulfides.

uop 117115 VI-49

The following table is a list of common sulfiding agents and their associated properties. SA-200 (UOP) DMS DMDS TNPS Sulfur, wt% 40 51 68 37 Specific Gravity @ 60°F 1.045 0.854 1.06 1.03 Thermal Decomposition Temp, °F 320 482 392 320

Since feed must be started to the unit while the system is relatively cold, the reactor charge heater flow will be two phase during the period temperatures are being increased. For units with a multiple pass charge heater, a coil could be damaged if it were blocked by a liquid pocket and the heater firing continued. To ensure that the feed to the heater becomes single phase (all vapor) at relatively low temperatures, the reactor inlet pressure is initially limited to 14 kg/cm2_{g (200 psig).}

When a Platforming Unit is the only potential source of hydrogen for startup and the Naphtha Hydrotreating Unit will be supplying charge for the Platforming Unit, a sweet, stripped, low-sulfur naphtha should be stored prior to the unit shutdown for startup purposes. It is strongly recommended that a hydrotreated naphtha be made available, but when this is not possible, straight run naphtha may be used, subject to the following limitations:

Total sulfur 100 wt ppm maximum

Total nitrogen 1 wt ppm maximum

Arsenic 5 wt ppb maximum

Lead 25 wt ppb maximum

Halides 1 wt ppm maximum

Distillation endpoint 205°C (400°F) maximum

Bromine No. 1 maximum

uop 117115 VI-50

The above stock may also be used for sulfiding the Hydrobon® catalyst if a sufficient amount is available, particularly if it is planned to sulfide using additional organic sulfur or H₂S.

The charge stock to the Platforming Unit should be as free of water as possible during the startup. The Naphtha Hydrotreating Unit fractionation or stripping section should be in service with reflux if possible, preferably at about the design rate prior to routing naphtha to the Platforming Unit.

PRECAUTION: HYDROGEN SULFIDE (H₂S) IS A POISONOUS GAS

During sulfiding of the hydrotreating catalyst, hydrogen sulfide will be released to the gas and liquid streams of the unit as sulfur-bearing compounds are decomposed. Hydrogen sulfide may also be utilized as additional sulfur in the sulfiding step. The safety procedures for handling H₂S should be reviewed with the appropriate operating personnel before starting the unit. Make certain that each person in the operating area is familiar with the dangers of H₂S, approved methods for handling it, and first aid in case of H₂S poisoning.

PRECAUTION

Organic sulfur-bearing compounds which may be used for adding sulfur to the Naphtha Hydrotreater charge are dangerous materials. Make certain that each person in the operating area is familiar with the dangers of the materials being used, approved methods for handling them and appropriate first aid procedures in case of contact with the materials.

2. Detailed Procedure – Fresh or Freshly Regenerated