Oct-2024

Optimising cartridge tray installation

Methodology for tackling site challenges and improving HSE and quality in cartridge tray installations while reducing the overall installation cost and project timeline.

Urmilesh Tiwari
Engineers India Limited

Article Summary

The heart of the refinery, also known as the distillation column, is a critical component due to its role in converting crude oil into various usable products. The hydrocarbon industry, particularly petroleum refineries and petrochemical complexes, involves a higher risk of on-site health, safety, and environment (HSE) challenges during construction and operation. In the case of cartridge trays, in-situ erection and installation of equipment at higher elevations increases the likelihood of accidents.

Improper installation or inadequate quality of work increases the HSE risk due to major modification works required in cartridge trays or columns involving hot works. Current modification practices involve workers entering confined spaces for grinding and repair works, increasing safety hazards. Sometimes, failed modifications also result in material rejection.

Alternate methods to enhance HSE and quality and eliminate the risk involved in installing cartridge trays inside columns are discussed, specifically at construction sites. By analysing real field data from past projects, this research culminates in establishing best practices to mitigate risks and streamline the installation process of cartridge trays. Practical solutions are discussed to enhance HSE practices and reduce installation time on-site, thereby reducing cost and contributing to a net-zero mission and sustainable development goals.

What is a cartridge tray column?
In a hydrocarbon plant, columns are essential for mass transfer. Trays, packings, and internals are used for this purpose, with various design parameters such as chord height, exit weir height, and under down flow clearance (UDFC) to be closely met. These internals are normally installed inside the column by workers entering through the manholes. For trayed columns where the diameter is less than 900mm, manholes cannot be provided for tray installation. Hence, installation is done as a cartridge tray bundle comprising approximately 10-15 trays connected/bolted through tie rods.

Cartridge trays are ideal for small-diameter columns, limiting the use of conventional trays. They also find applications in refineries where precise control over the separation process is required, but there are space constraints.

Design of cartridge tray columns
In larger-diameter trayed columns, tray support rings (TSR) are welded inside the column shell. The trays and other internal accessories are installed through column manholes, allowing personnel to enter through them to facilitate the installation of trays and internals inside the column. Cartridge tray columns, on the other hand, have size limitations, making it infeasible to provide a manhole. The cartridge tray bundles consist of pre-assembled components, including trays, downcomers, seal pans, mass transfer valves, exit weirs, and sealing arrangements connected/bolted through tie rods. These are inserted through column flanges inside the column. Trays facilitate vapour-liquid mass transfer, which is essential for separation.

Trays allow vapour to flow upward through the mass transfer valves/sieves while liquid travels sideways across the tray and down through downcomers. Special sealing arrangements, fixed with cartridge trays, are provided to prevent the bypass of liquid or vapour through gaps between the trays and column wall. Based on the sealing arrangement, two commonly used configurations are:
- Metallic sealing foil configuration: In the metallic sealing foil arrangement, metallic sealing foils fixed with cartridge trays are employed to seal the gap between the shell inner diameter (ID) and the tray decks.
· This configuration aims for the single-step installation of tray bundles within the column.
· If cartridge bundles need to be reinserted into the column, the sealing foils must be replaced. This process introduces rework and necessitates new sealing foils. This rework process has made sealing foil arrangements less preferable.
- Gasket sealing configuration: In the gasket sealing type of arrangement, gaskets of appropriate sizes/shapes fixed with cartridge trays are employed to seal the gap between the shell ID and the tray decks. During installation, these gaskets are compressed/fitted into the gaps between the shell ID and tray decks:
• This type of arrangement effectively seals the gap between the column wall and trays and restricts the flow of liquid/gas through it.
• The advantage of this type of arrangement is its flexibility during installation; the gaskets typically remain undamaged during installation and can be reused if reinsertion is required.

Installation of cartridge trays on-site: Currently, the column and cartridge trays are shipped separately to the construction site. The column manufacturer is responsible for the column, while the tray manufacturer is responsible for the trays. Each item is fabricated independently at their respective workshops and transported to the site. On-site with the help of a crane, the cartridge trays are inserted through column flanges after erection of the column in a vertical configuration.

HSE on-site: HSE management plays a critical role in ensuring the well-being of personnel in the oil and gas sector. This importance is heightened during the refinery construction phase, where workers face a range of challenges and potential risks. Some of these key aspects include:
a) Safety measures: Proper safety protocols are crucial to prevent falls and accidents during work at height.
b) Confined spaces: A confined space encompasses various enclosed areas, including columns, vessels, tanks, containers, pits, bunds, chambers, and cellars. These spaces create conditions that are prone to risk of accidents, harm, or injury.
c) Work-at-height and permit requirement: When workplaces are elevated at more than two metres (approximately 6.5 ft), a work-at-height permit becomes necessary. This applies to tasks involving ladders, scaffolds, mobile elevated work platforms (MEWPs), or any work performed above ground level.
d) Emergency action: Emergency procedures are essential due to the presence (or foreseeable presence) of:
· Flammable or explosive atmospheres
· Harmful gases, fumes, or vapours
· Free-flowing solids or rising liquid levels
· Excessively high temperatures
· The lack (or foreseeable lack) of oxygen.

Vigilance, training, and adherence to safety protocols are paramount to safeguard workers and mitigate risks in these challenging environments.
e) HSE challenges with cartridge tray installation: Installing cartridge trays is inherently challenging. Cranes with extended arms are employed to lift the cartridge trays to elevated heights above the column flanges (see Figure 1).

Workers must stand on temporary scaffolding platforms to guide the bundles into the column. These makeshift platforms must adhere to HSE standards, with proper checks to ensure personnel safety. Despite safety precautions, scaffoldings remain susceptible to failures and accidents. The suspended load of trays hanging from the crane poses a risk to workers below. Workers wear personal protective equipment (PPE) and safety harnesses while working at height. Crane selection has to be based on the loading requirements specified in the load chart to ensure safe operation.

The challenge amplifies when either column or cartridge tray bundles are fabricated outside the respective tolerance range, which makes trays oversized or undersized compared to the column shell. If the tray bundle becomes stuck inside the column due to size discrepancies, in-situ modifications to either the column or trays are necessary. These modifications transform an already high-risk installation practice into a cumbersome and hazardous task.