PRENSAP a21 Pressure Vessels

CONFIDENTIAL

Process Engineering & Safeguarding Practices Manual

OG.02.30930 Rev. 0

A2.1

PRESSURE VESSELS (INCLUDING REACTORS AND COLUMNS)

A2.1.1

Representation on PEFS For arrangement sketches refer to figures: A2.1.1.1 A2.1.1.2 A2.1.1.3

Vertical vessel Horizontal Vessel Distillation column

- Symbols, identification and essential internals shall be in accordance with DEP 31.10.03.10-Gen. - The outline should be as simple as practical, but including all essentials such as sumps, domes and body flanges. - The relative size and elevation, although not to scale, should be indicated. Notes for critical elevations should be given, where necessary. - All nozzles, instrument connections, manholes etc., as specified on the relevant data/requisition sheets should be shown. Specify the nozzle size when different from the corresponding line size (1). - Skirts and support legs should be shown. Show a gap where a process line crosses the support (2).

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ALL PAPER COPIES ARE UNCONTROLLED

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RELIEF (14)

(13) TI

(9)

PROCESS

V

ALTERNATIVE RELIEF LOCATION

(12) PG

(15)

MH (11) (10)

(4)

UC

(6)

(2)

D(7)

Figure A2.1.1.1 VERTICAL VESSEL

RELIEF

(9)

(12)

(13) TI

PROCESS

PG

V

(3)

(10)

MH (11)

(5)

UC

(4)

(8)

D(7) 600 mm MIN.

Figure A2.1.1.2 HORIZONTAL VESSEL

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OG.02.30930 Rev. 0

(9) V

TI

MH

(13)

20

(12) PG

PRC 15

TI

TRC

14

DN... MH

(1)

11

(12)

2

PG

1

From reboiler

LRCA

MH (11)

(10)

LG

(10) UC

(4)

UC

(4)

(6) (2) (6) (2)

D

(7)

D

(7)

To reboiler

Figure A2.1.1.3 DISTILLATION COLUMN

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A2.1.2


CONFIDENTIAL

Engineering Requirements Process - In horizontal vessels, the vapour and liquid outlets, including a possible water sump, shall be located at the opposite side from the inlet (at a minimum distance from the tangent line). - All inlets, where liquid may enter, are preferably to be provided with a deflector, when no other device is specified for process reasons (3). - All liquid outlet nozzles shall be provided with vortex breakers (4). Internally extended vortex breakers shall be used in fouling service and for hydrocarbon liquid outlet where the liquid is separated from water or aqueous solutions to prevent water from entering the product (DEP 31.22.10.32.Gen.) (5). Piping - The number of connections on vessels, particularly below the liquid level, should be minimized. Nozzle sizes on vessels should not be smaller than DN 50 for strength reasons. - Rule out potential leak sources inside the skirt of a vessel by locating the first flanged connections outside full skirts. Piping inside the skirt up to the flange shall be an integral part of the vessel (DEP 31.22.10.32-Gen.) (6). - All vessels shall have a low point valved drain (DEP 31.38.01.11-Gen.) (7). This drain should be located on the bottom line, outside the skirt, between the vessel and the first pipeline shut-off location (valve, spade or blind flange). The drain shall be located on the bottom of the vessel when no bottom line is present, or when the bottom outlet is not flush with the lowest point of the vessel. Drain lines for pressure vessels should be sized to empty the required vessel volume by gravity flow within two hours. The minimum size of the drain shall be DN 50 and usually maximum DN 100. - For equipment and piping containing liquefied petroleum gases, including water drains on LPG vessels, operational drains shall consist of a springloaded ball valve and a manual ball valve located a minimum of 600 mm upstream of the springloaded valve to prevent freezing, and operable from the same location as the springloaded valve (8). The drain line-up to and including the manual valve shall be maximum DN 50, and the spring loaded valve and downstream piping should be DN 20. However for strength reasons, the spring loaded valve may be increased to DN 40 and the downstream piping to DN 25, for typical process vessels.

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If a level indication is available to the operator, it shall be in line of sight of the operating station for the spring loaded valve. If the drain is to atmosphere, the atmospheric drainage point shall be in line of sight of the operator while at the spring loaded valve, but not so close that the operator would be affected by any vapours escaping. - All vessels shall have a high point valved vent (DEP 31.38.01.11-Gen.) (9). It shall be ensured that the vessel can never be isolated from this vent when spading off at the process flanges. To prevent pulling vacuum in equipment not designed for vacuum, the size of the vent and drain connections shall be the same. - A valved DN 50 utility connection for steam-out and purge purposes should be installed (DEP 31.38.01.11-Gen.). The utility connection shall not be connected permanently to the utility header. If the vessel is divided into more than one compartment, for example by baffles, a utility connection per compartment should be considered (10). - Vents, drains and utility connections shall be closed with a blind flange. - An access opening shall be provided for each vessel. Manholes shall have a minimum clear inside diameter of 460 mm however, nominal pipe sizes DN 500, DN 600 and DN 750 are preferred (11). The nominal minimum diameter for inspection openings (hand holes) is DN 150 (DEP 31.22.10.32-Gen.). For the required sizes of access openings in columns with removable trays, see DEP 31.20.20.31-Gen. If a vessel is divided into compartments, for example by baffles, sufficient access openings, internal and/or external, shall be provided for safe entry into each compartment. - Spades and spectacle blinds are used for isolation prior to inspection, testing, maintenance or entry of personnel. Spectacle blinds have to be provided in the following cases: ° In lines of equipment, which can be blocked in with the unit still in operation. ° At equipment nozzles DN 250 and larger, although the operating company may choose to use spectacle blinds for smaller nozzles. ° At equipment nozzles of rigid piping (i.e. where a spade cannot be installed), regardless of pipe size. For very large vessel nozzles (e.g. DN 750 and larger) at locations which are difficult to access an alternative location of the spectacle blind can be considered. Typical examples are:

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° An overhead line ending in a more convenient condenser inlet nozzle or even dividing up into a number of smaller and more manageable condenser nozzles where the spectacle blinds can be located. ° A transfer line from a furnace to a large fractionator (CDU, HVU, TGU), where the fractionator inlet flange shall be deleted entirely (DEP 31.38.01.11-Gen), because it is prone to leak due to thermal shock during start-up and shutdown. The spectacle blinds should be located in the furnace outlets. The transfer line now becomes part of the fractionator and should be provided with an inspection manhole at the furnace end and in the top and/or bottom plate of the "schoepentoeter" inlet device. In this case it will obviously not anymore possible to pass the schoepentoeter through its own nozzle. This should then be accommodated by the nearby manhole. In either case care should be taken that no other connection exist or will be temporarily made between the vessel and the spectacle blinds that would defeat the isolation of the vessel. Spacers shall be installed instead of spectacle blinds in the following cases: ° In lines with operating temperatures below 0°C. ° In lines outside the range of drawing S 38.011. S 38.011 covers line sizes DN 15 to DN 600 for ANS classes 150 to 1500 and DN 15 to DN 300 for ANS class 2500 lbs (DEP 31.38.01.11-Gen.). - Flange connections, DN 150 and larger in hydrogen service operating above 200°C, which are not readily accessible, can have smothering steam rings with weather protection covers to extinguish a possible fire from leaking hydrogen. The steam supply line valves to the rings should be operable from a safe distance (DEP 31.38.01.11-Gen.). For flanges with a good accessibility, steam lances can be provided as an alternative. - The use of bends outside the vertical plane through the axis of the feed nozzle shall be avoided within ten pipe diameters of a two phase flow inlet nozzle in order not to generate vapour flow maldistribution (DEP 31.22.05.11-Gen.). In addition, to avoid liquid entrainment in CDU, TGU and HVU distillation columns, the transfer line should run down to the feed nozzle, without pockets. - Where no connection to flare is available for process reasons, for example from a column overheads system, a manual valve or HIC control valve should be provided for depressuring to flare at shutdown. This connection will not be required for units normally operating at subatmospheric pressure. Instrumentation

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- A pressure gauge shall be installed on every vessel (12). This PG is normally located in the vapour space. It should be clearly visible from grade or easily accessible platforms, i.e. installation on top of tall columns should be avoided. When a vessel is to be pressured or depressured manually a pressure gauge shall be installed within line of sight of the valve to assist the operator. - If a temperature indicator is required at the outlet, it should preferably be located on the top outlet line (13). - Where exotherms are possible outside the normal temperature range, wide range thermocouples shall be installed so that, should an exotherm occur, the maximum temperature can be monitored. The information is important for metallurgical reasons. These thermocouples and indicators shall be in addition to the narrow range thermocouples and indicators used for control and normal process monitoring. For example, hydrotreating, hydrocracking, isomerization, polymerization reactors, and reactors and treating beds where in situ regeneration takes place.

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A2.1.3


CONFIDENTIAL

Equipment Protection - Pressure relief valves shall be connected to the protected equipment in the vapour space above any contained liquid or to piping connected to the vapour space, downstream of the equipment blinding point (DEP 80.45.10.10-Gen.) (14). For vessels fitted with a demister, a pressure relief valve downstream the demister is allowed in case the relieving capacity is of the same order of magnitude as the normal operating flow. The relief connection shall be upstream of the demister for larger relief flows (15). It shall be established that blockage in equipment cannot occur as a result of fouling, solidification, collapse of internals etc., otherwise the relief connection shall be located upstream of the potential restriction. The inlet piping between the protected equipment and the inlet flange of the pressure relief valve should be designed so that the total pressure loss does not exceed 3 percent of the valve set pressure. The pressure loss should be calculated using the maximum rated capacity of the pressure relief valve. Excessive pressure loss will cause rapid opening and closing of the valve, or chatter. The nominal size of the inlet piping must be the same as or larger than the nominal size of the valve inlet flange. The inlet piping of the pressure relief valve shall be self-draining back into the process. - All process equipment containing under normal operating conditions at least 4 m3 of LPG (butane or more volatile liquid) shall be provided with remotely operated depressuring valves (DEP 80.45.10.10-Gen.). High-rate depressuring of plant facilities is applied during an emergency. This will for instance, serve to avoid a BLEVE in the event of a fire and can also reduce the consequences of leakage. High-rate depressuring systems shall be designed in accordance with DEP 32.45.10.10-Gen. with a preference for the normally energized (NE) mode. For the purpose of sizing depressuring systems, each unit area shall be divided in probable fire areas. Within each fire area one depressuring valve can serve a number of equipment items which are normally interconnected and can be isolated as a subsystem.

A2.1.4

Not applicable

A2.1.5

Not applicable

A2.1.6

Not applicable

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A2.1.7


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Operational Aspects and Failure Modes The following situations introduce potential risks, for which the design does not cater and reliance is made on operational procedures: Commissioning - Overfilling with water, for example for hydrotesting when the vessel or support is not designed for it, might lead to overstressing the shell or bottom head and/or overloading the supports or foundation. Start-up - Similar to water, hydrocarbons especially heavy hydrocarbons, can lead to damage if the equipment is overfilled during start-up and the design has not catered for a full vessel. More frequently equipment is designed for full water load, but the overhead vapour lines of CDU/HVU/TGU columns and transfer lines of HVUs are not. - Inadequate air removal Oxygen left in the vessel, due to insufficient purging, may lead to internal fire/explosion. - Inadequate water removal Water introduced in hot environments often causes steam explosions resulting in damage to vessel internals. - Overpressure When spades and spectacle blinds have not been removed/opened and the vessel is isolated from the pressure relief valve, purging with an inadvertently closed vent will cause pressure build up to the operating pressure of the purge fluid, which can be higher than the design pressure of the vessel. Similarly starting a reboiler before commissioning the overhead cooling system will rapidly overpressure a column. - Sub-atmospheric pressure Vacuum may be developed by: ° Inadequate venting when draining a liquid full vessel. ° Condensing steam and no gas make up provided for. Shutdown - Inadequate purging Air entering vessels, which are not inerted properly, may contact pyrophoric iron and start burning when insufficiently wetted, thus initiating a hydrocarbon fire/explosion.

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Normal operation - Ingress of air Air leaking into systems at sub-atmospheric pressures may cause internal fire/explosions. Small amounts of air may have an adverse effect on product/solvent quality. Disposal of (contaminated) air may also cause problems. - Draining water from sumps of pressurized vessels The downstream system should be able to cope with the effects of overdraining. Draining to atmosphere is generally not recommended.

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A2.1.8


OG.02.30930 Rev. 0

Equipment Design - Process - For specialized internals for different processes, refer to the relevant Process Design Guides and Specialist Groups. - For type selection and design rules of Gas/Liquid Separators, refer to DEP 31.22.05.11-Gen. - For determination of temperature and pressure levels, refer to DEP 01.00.01.30-Gen. For amendments on vessel codes of design pressures and temperatures, refer to DEP 31.22.10.32-Gen. and DEP 31.22.20.31-Gen.

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References DEP 01.00.01.30-Gen..

Definition of Temperature, Pressure and Toxicity levels

DEP 30.06.10.12-Gen.

Pressurised Bulk Storage Installations for LPG

DEP 31.10.03.10-Gen.

Symbols and Identification System - Mechanical

DEP 31.20.20.31-Gen.

Internals for Columns

DEP 31.22.05.11-Gen.

Gas/Liquid Separators - Type Selection and Design Rules

DEP 31.22.10.32-Gen.

Pressure Vessels (Amendments/supplements to PD 5500)

DEP 31.22.20.31-Gen.

Pressure Vessels (Amendments/supplements to ASME Section VIII, Division 1 and Division 2)

DEP 31.38.01.11-Gen.

Piping - General Requirements

DEP 32.45.10.10-Gen.

Instrumentation of Depressuring Systems

DEP 80.45.10.10-Gen.

Pressure Relief, Emergency Depressuring, Flare and Vent System

Standard Drawing S 38.011

Spectacle Blinds for ANS Flanges


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PRENSAP a21 Pressure Vessels

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