Monday, July 7, 2014

Sequence of Distillation Column Piping Study

The designer now starts thinking about the proper orientation of nozzles and provisions for access to the points of operation and maintenance.

Considerations of the pipeline leaving the tower area and the adjacent piping shall be visualised.

The first step is to orient the manholes preferably all in same directions. Normally, manholes shall be oriented towards dropout area within a 30° segment of column as this facilitates the lowering of tower internals to the main access way. The manhole segment of platform should not be occupied by any piperack.
A break in ladder rise (normal 5m, maximum 7m) will occupy another segment of column for platform.

The levels of platforms are to be decided on the elevation view based on the manholes and access to relief valves, instrument for viewing.

All the available information/ data from equipment specification & P&I D will be written on the elevation view of the column
All platform levels in the proper segments of the tower with ladder location should be drawn on plan view. The manhole shall be shown in proper segment with the angle of orientation, and the space for the swing of manhole cover taking davit hinge as centre. 

Layout should be started from the top of the column with the designer visualising the layout as a whole. There will be no difficulty in dropping large overhead line straight down the side of a column, and leaves the column at a high level and crosses directly to the condenser. This clears a segment at lower elevations for piping or for a ladder from grade level to the first platform.

Flexibility and thermal load connected with the large-dia overhead lines to the condenser at grade level or higher level shall be considered. The relief valve protecting the tower is usually connected to the overhead line. A relief valve discharging to atmosphere should be located on the highest tower platform.

In a closed relief-line system, the relief-valve should be located on the lowest tower platform above the relief -system header. This will result in the shortest relief-valve discharge leads to the flare header. The entire relief-line system should be self-draining.

From layout point of view, it is preferable to space the platform brackets on the tower equally and to align the brackets over each other for the entire length of the tower. This will minimise interferences between piping and structural members.

Nozzles and piping must meet process requirements while platforms must satisfy maintenance and operating needs. Access for tower piping, valves and instruments influence placement of ladders.

In routing pipelines, the problem is faced to interconnected tower nozzles with other remote points. The tentative orientation of a given tower nozzle is on the line between tower centre and the point to which he line is supposed to run. Segments for piping going to equipment at grade e.g. condenser and re-boiler lines are available between ladders and both sides of manhole.

Line approaching the yard/piperack can tum left or right depending on the overall arrangement of the plant. The respective segments of these lines are between the ladders and 180 deg. The segment at 180 deg is convenient for lines without valves and instruments, because this is the point farthest from manhole platforms.

The sequence of lines around the tower is influenced by conditions at grade level. Piping arrangements without lines crossing over each other give a neat appearance and usually a more convenient installation.

The correct relationship between process nozzles and tower internals is very important. An angle is usually chosen between the radial centreline of internals and tower-shell centrelines. By proper choice of this angle (usually 45deg or 90deg to the piperack) many hours of work and future inconvenience can be saved. Tower piping, simplicity of internal piping and manholes access into the tower are affected by this angle. Alter this, the information produced by the designer results in selecting the correct orientation of tower nozzles.

A davit usually handles heavy equipment such as large-size relief valves and large-diameter blinds. If the davit is at the top of the tower. it can also serve for lifting and lowering tower internals to grade.

Clearance for the lifting tackle to all points from Which handling is required, and good access should be provided.

Very often, interpretation of process requirements inside a tower is more exact than for exterior piping design. The location of an internal part determines, within strict physical limits, the location of tower nozzles. instruments, piping and the steelwork. The layout designer have to concentrate on a large-scale drawing of tower internal details and arrangement of process piping to finalise the piping Study.

Access. whether internal or external is very important. This includes accessibility of connections from ladders and platforms and internal accessibility through shell manholes, handholes or removable sections of trays. A manhole openings must not be obstructed by internal piping.

Re-boiler-line elevations are determined by the draw off and return nozzles and their orientation is influenced by thermal flexibility considerations. Re-boiler lines and the overhead lines should be as simple and direct as possible.


Tall Column (Here after called “TOWERS ”) requires large Transportation access through the Unit facilities for lifting after adjacent structures are Erected. Check the foundation clearance when locating the towers adjacent to structures & between towers. If additional supports are required for the overhead vapour lines, consider extending the structure column to assist.

• Where possible link the Platforms & ladders to adjacent structure, Providing the additional access & escape Routes. Check with stress section for Piping Flexibility & Reboiler supports.

• Also check the Pump NPSH Requirement while going for the Bottom pump Piping

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