INTERNALS. scope Definition Internals : Any part used to achieve the most efficient separation of liquid and gas mixture in side the column either.

INTERNALS

scope

Definition

Internals : Any part used to achieve the most efficient separation of liquid and gas mixture in side the column either in separation process or in organizing it.

-Columns include two major categories, trays and

packing.

- the following columns: Distillation Absorption Stripping Extraction

Type of internals

Trays

Packing

Packing additions

collectors

Trays

Trays force the liquid to flow back

and forth horizontally while the

vapor bubbles up through holes in

the trays.

The purpose of trays is to increase

the amount of contact area between

the liquid and vapor phases.

Type of trays

Bubble cap tray

Sieve tray

Valve tray

Bubble cap

Bubble-cap trays are one of the types of

physical devices which are used to provide

good contact between the up flowing vapor and

the down flowing liquid inside a separation

column.

A bubble cap tray has a riser or chimney fitted

over each hole, and a cap that covers the riser.

Bubble cap

Sieve tray

Sieve trays are simple metal plates

with holes in them.

Vapor passes straight upward through the

liquid on the plate.

Valve tray

In moving valve trays, holes are covered

by lift able caps. Vapor flows lift the caps,

thus self-creating a flow area for the

passage of vapor.

Tray Configuration

Vapor flows up the

column and is forced to

pass through the liquid,

via the openings on each

tray. The area allowed for

the passage of vapor on

each tray is called the

active area.

Mechanics of Trays

A weir on the tray ensures that

there is always some liquid

(holdup) on the tray and is

designed such that the holdup is

at a suitable height, e.g. such

that the bubble caps are covered

by liquid.

Types of Down comer

Types of Down comer based on the shape

Types of Down comer based on the number

packing

Packing are passive devices that are designed to increase the interfacial area for vapor-liquid contact, without causing excessive pressure drop across a packed section .

Liquids tend to wet the surface of the packing and the vapors pass across this wet surface, where mass transfer takes place.

Liquid

Vapor

Types of packing

Random packing Structural packing

Packing versus Trays

A tray column that is facing throughput problems may be de-bottlenecked by replacing a section of trays with packing. This is because: packing provide extra inter-facial area for

liquid- vapor contact efficiency of separation is increased for the

same column height packed columns are shorter than trayed

columns

Packing additions

Liquid Distributor

Bed limiter Support plate

Liquid Distributor

- If the liquid and vapor are not evenly

distributed across the superficial tower area as it

enters the packed bed, the liquid to vapor ratio

will not be correct in the packed bed and the

required separation will not be achieved. The

packing will appear not to be working properly.

Type of liquid distributor

Orifice Type

Spray Nozzle

Trough Type

Pipe Ladder

Bed Limiter

A bed-limiter is positioned inside the tower,

directly above a randomly packed bed to

confine any upward movement of packing.

- Grating type

For large packing, the bed limiter, in its simplest form, consists of a grid of flat bars welded to a ring

- Grating with Mesh type

For small packing, the bed limiter consists of grating and mesh.

Support Plate

A randomly packed bed is held on

a packing support plate, whose

essential attributes are to have

a high percentage of open area

so as not to inhibit the capacity

of the tower and to allow the

unrestricted counter-current flow

of both liquid and vapor through it. This is achieved by providing

separate passageways for the gas and the liquid.

Collector

Liquid collector's main functions are liquid collection and gas

redistribution.

Chimney trays must be installed to function as a collector device either

for feeding to a liquid distributor or for a liquid draw off.

When installed below the bottom packed bed, chimney trays perform a

useful function as a vapor distributor. This is especially important

where high vapor rates are encountered due to the low pressure drop

across most packed beds.

Chimney type

Chevron Vane

SAFETY

All the safety guidelines for the confined space entry will be followed.

In general workers shall enter the tower only verifying the proper oxygen level and confirming non-existence of any toxic gas and flammable gases and completing a confined space entry permit.

For better ventilation in the tower, all manholes at the bottom and top shall be fully

opened. Additional ventilation shall be provided if internal welding is required. Person in-

charge for tray work is required to have awareness of safety regulation.

 The temperature inside of vessels shall not be beyond 500C during installation or Inspection.

Shift safety officer and supervisor should check the working condition i.e., obstruction, scaffolding (if required), proper tools & tackles, PPE etc., prior to commence any activity.

TOOLS AND EQUIPMENTS

In general all tools and equipments should be in good working order in compliance with all safety requirements and testing requirements.

  Calibration for all special tools and instruments shall be ensured as per specification

procedure prior to start any activity. All fasteners should be kept in canvas bucket

or small boxes. The Torque value for the bolts tighten should

be according to the vendor recommendation.

MATERIAL STORAGE & HANDLING

Material receiving, handling, storage, preservation and issuance of material should be as per applicable procedures. Extra care shall be taken to prevent damage and corrosion during installation

All Wooden boxes that contains column internals materials shall be shifted to predetermined location in order to segregate the internal as per the installation sequences.

The boxes top cover shall be opened carefully and ensured no damage on internal material during removing the top cover and the tray material shall be taken out carefully.

Tray parts and hardware shall be stored in such a way that no damage or loss to occurs. Small items i.e. bolts nuts and washers should be secured properly until ready for Installation.

SEGREGATION & TRAIL ASSEMBLY

Once the boxes are opened and ensured that all the material there in good condition and the quantity are correct against packing list. The segregation of the tray shall start with seal pan tray which is coming just below the tray number 1.

Prior to installation, the entire tray shall be pre-assembled on the ground to familiarize workmen with the general layouts of the trays.

 All the dimensions that are required to meet the vessel check and the material receiving shall be carried out with the respect to the vendor drawing and the specific hardware location to be witnessed by QC and must be documented.

Each piece of tray which is marked will be arranged as per sequences.

GENERAL PRECAUTIONS AND INSTRUCTION

When any person enters the tower inside, he shall remove dust completely from his shoes, to keep a clean environment.

No food drinks and smoking allowed within the vessel.

All manholes should be open for ventilation at the time installation.

The lifting of parts into the tray should be carefully performed so that the parts or the containers do not fall or get damaged.

All bolts, nuts and washer at every tray should be checked for correct length, type and sizes.

Lighting and Ventilation

Sufficient lighting and ventilation should be provided at all working level prior to commence any activity inside the column. Sufficient air movers should be provided to cool down top level of column. 

Lighting and air mover’s connection should be positioned in such a manner that it would not cause tripping hazard.

INSTALLATION OF TRAYS

The Tray installation shall be as per tray manufactures certified drawings and installation procedure or as project specification and procedures.

All man ways opening and serration area should be covered and protected to avoid scratch/damage.

The tray assembly work shall be started from bottom stage to top stage. However, in case of small diameter tower, it may be easy to make partition platform at middle and

another group can proceed with installation from middle to top, so the work progress will be very fast.

A minimum of 1 tray for each type shall be pre-assembled on the ground to familiarize workmen with general layout of trays and the specific hardware location to be witnessed by Quality control.

 Tray support ring should be inspected for horizontal levelness and shall be accepted if the high to low point measurement are within the tolerance as per ARAMCO STANDARD. Levelness checking by manometer (Transparent PVC tube with water and steel scale.

Sign off ring levelness or review the levelness inspection report conducted at vendor shop.

Rings and walls should be cleaned prior to installation of tray. Use vacuum cleaner to clean tray prior inspection

Erect the scaffold inside column to install the bottom trays of each group.

PRIOR TO INSTALLATION

INSTALLATION OF TRAYS

Determine the correct orientation of the first layer from the vessel arrangement drawings.

It is normal to start from lower side of the tower and built upward.

The down comers shall be installed first followed by inlet panels and active panels.

The bottom tray in section can act as a platform provided adequate load spreading Metallic boards, wooden blocks are in place.

Install all the Panels as per the vendor installation drawing until top of column.

Cleaning and keeping in order shall be done for each tray stage successively and final inspection should be carried out.

The following shall be confirmed after tray assembling work Tightness of bolt is sufficient. There is no other disorder

Direction of clamp is correct. Flow direction of tray panel

The manholes should be closed immediately after final inspection

TRAY INSTALLATION

QUALITY CONTROL

At all the levels of work execution relevant project specification, drawings, vendor instruction and applicable codes and standard will be followed.

Request for inspection will be submitted after successive 3-6 layers of installation depending upon the access and the type of trays. Wherever small access, each layer shall be offered for inspection.

Method of inspection and criteria of acceptance shall be as per the approved ITP in accordance to the vendor instruction but as minimum the following items to be checked. Tower inside cleanliness (non existence of scales, slag, spatter, sand, paint, oil, mist etc. Prepare or review the inspection sign-off sheet for both the ring levelness and

measurements Confirm the condition of trays free from abnormalities and deformations. Match marks and identification are correct. Tray levelness is within tolerance. Clearance for down comers and tray. Height and horizontality of outlet weir is within tolerance Confirm the clamps are attached in correct direction. Confirm the correctness and tightness of fasteners by torque wrench.

Tolerance for respective dimensions to be followed as mentioned in the specification,

vendor manual and drawings.

manhole

manhole

manhole

Liquid distributor

Reflux from condenser

Bed limiter

Bed limiter Liquid distributor

Supporting plate

Supporting platecollector

Random packing

Random packing

Skirt

Liquid feed

Vapor outlet to condenser

Re boiler returnVapor feed

Circulation to re boiler Bottom product

Installation of packing