Jul-2024

Vessel internals enhance worker safety during plant turnarounds (TiA)

Reducing confined space entry when changing media beds using hold-down screen solutions

Kevin Chase
Global Products Manager, Johnson Screens

Article Summary

The importance of petrochemical products to industry and society emphasises the critical nature of facility maintenance and efficient turnarounds that keep production going. The lost revenue and costs associated with shutting down a process for media bed changeouts, preventative maintenance, or repairs are significant. During these outages, every element of the turnaround must be carefully planned and executed efficiently by plant workers to meet tight schedules and get the plant back online. As a result, worker safety is always critical, especially when entering the confined space and hazardous environment inside petrochemical reactors. Injury or accidents to a worker can significantly impact workers, families, and project schedules.

The problem
Professional process engineers and managers in the industry are well trained, knowledgeable, and equipped to comply with safety standards and guidelines from OSHA,2 API,1 NFPA,3 and ASSP/ANSI4 for continuous worker safety. They are trained to understand and mitigate the risks to workers and make sure that processes and protocols in place are carefully followed to ensure worker safety throughout turnaround activities.

Regulatory and industry safety standards for rendering the internal atmosphere of a reactor inert and allowing workers to enter the confined workspace are detailed and complex. After a vessel is purged and flooded with inert gas to mitigate potential explosions, many significant hazards to workers persist, including asphyxiation, unsafe working conditions, and changes to the internal atmosphere. Fortunately, several regulatory and recommended safety standards are in place to address and minimise these hazards.

Defined as Permit-Required spaces, OSHA 1910.146,2 NFPA3503 standards detail the requirements of the written Permit-Required Confined Space (PRCS) Program that includes area identification and barriers, atmospheric testing, documentation, entry permitting and close-out, emergency retrieval, stand-by personnel, continuous environmental monitoring inside the vessel, vessel purging/inerting, ventilation, worker breathing equipment, personal protection equipment (PPE), worker communications, lighting, rescue and emergency equipment, and ongoing training.

API Recommendation 2217A1 references these standards while providing additional details on each aspect, including maintaining the inert atmosphere with nitrogen and the potential hazards of ‘catalyst crusting’, testing, and mitigation.

Petrochemical plants are well versed in implementing these programmes and guidelines while ensuring they are followed for the safety of workers on the turnaround team, specifically those who will be entering these ‘Entry Permit Required’ spaces to perform maintenance (see Figure 1).

The challenge
Implementation and compliance with regulatory and industry guidelines for entering PRCSs are critical yet complex and expensive to execute and implement. As such, companies are constantly evaluating their turnaround processes and procedures to determine if any changes can be made to minimise risk to workers and the necessity for implementing these protocols at various stages of the turnaround in fixed-bed reactors.

From a regulatory standpoint, anytime workers need to enter a vessel, the protocols for Permitted-Entry for Confined Spaces must be followed. Changing the media when it has reached the end of its useful life, for example, requires that workers enter the vessel to remove the hold-down screens or the manways in top screens to allow access for the media removal equipment.

Of course, once the media is removed, the vessel can be ventilated completely to create a safe and stable atmosphere where workers can enter and service or repair the vessel internals. However, many hazards still exist, and once again, the safety protocols and permitting process for entering the confined space must be followed.

With an eye on lowering costs, reducing risk to workers, and improving turnaround times, many companies and process engineers have begun to ask how the process for simple media bed changes can be simplified to eliminate the need for a worker to enter the vessel to remove the media. This would help to streamline the initial stage of the turnaround and shorten the overall process. In some cases, companies have already begun to mandate that employees do not enter vessels when removing media during a turnaround. These corporate mandates create unique challenges for process engineering teams at the beginning stage of a turnaround.

The solution
Johnson Screens was approached to develop new reactor internals that will help process engineers comply with corporate mandates for reducing the risk to workers and the company to reduce the need for confined space entry for media bed changes. Innovating to meet this challenge required a new approach to standard hold-down screen designs that have been used for decades.

In fixed-bed, downflow reactors that utilise hold-down screens at the top of the bed, accessing the media to change the bed requires first removing the hold-down screen from the vessel. Traditionally, this requires a worker to enter the confined space of the vessel to dismantle the manway in the centre of the screen by removing the bolts that secures the manway. For ‘floating’ hold-down screens, which sit directly to the top of the media bed, workers must enter the vessel to dismantle the entire screen, bolt-by-bolt, and remove the components through the vessel manway.

Entering the vessel requires significant preparation, and although the vessel is flooded with inert gas to displace the volatile gas, risks to workers still exist due to low oxygen levels and continuous off-gassing from media while the work is being performed. Senior process leaders have concluded that this initial stage can be eliminated and have started to mandate that workers will no longer be allowed to enter a vessel just to remove a screen or a manway prior to simple media bed changes, predicating development of two hold-down screen solutions within a new StaySafe product platform.

While both new patent-pending products are hold-down screens, they facilitate a ‘no-entry’ approach for disassembly and removal from a vessel. Each has a unique and distinctive design based on how the screen is positioned in a vessel. The first new product is a ‘floating’ hold-down screen that rests directly on the top of the media bed. Like all ‘floating’ screens, these screens sit on the media bed and must be removed from the vessel before media extraction and replacement can begin. Traditional designs of this type of screen are bolted together and a worker must enter the vessel to disassemble the screen and remove it from the vessel.

This new design approach incorporates interlocking screen components that are assembled in the vessel without tools and secured in place with a central locking hub. This design allows for easy disassembly, capture, and removal of the screen components from outside the vessel. It eliminates the need for workers to enter the confined space to remove the screen. Working from outside the vessel, simplifies compliance with regulatory safety protocols by eliminating the need for confined space entry permits in the initial stage of media bed replacement.

The second new StaySafe product is a ‘supported’ hold-down screen with a manway which rests on support beams within the vessel. Although the main part of the screen follows a standard bolted design, the manway incorporates a unique design so it can be disengaged and removed from the screen from outside the vessel. An integrated manway screen seal ensures media containment with an easily released panel. This gives the turnaround team the option to remove the manway from the vessel or set it aside in the vessel while the media bed is extracted and replaced. The manway can then be reinstalled and locked back into position from outside the vessel.

Both new StaySafe products have already been installed and are in use today. Each screen has been designed to the high-performance specifications and rigorous standards that Johnsons Screens has been delivering to the gas processing industry for decades.

References
1 API (American Petroleum Institute) Recommended Practice 2217A, 5th Edition, July 2017.
2 OSHA (Occupational Safety and Health Association) Standard 1910.146 Permit-Required Confined Spaces.
3 National Fire Protection Association, NFPA350 – Guide for Safe Confined Space Entry and Work.
4 American Society of Safety Professionals and Approved American National Standard (ASSP/ANSI) Z117.1, 2022, Safety Requirements for Entering Confined Spaces.

StaySafe is a mark of Johnson Screens.

This short case study originally appeared in PTQ's Technology In Action Feature - Q3 2024 Issue

For more information: Kevin.chase@johnsonscreens.com