Demountable flare stack systems in North America

Subsequently, they were also used by many other oil and gas and petrochemical companies. Only in the past 10 years have they become more common in North America.

How do they work?

A demountable flare stack system is a flare system that includes a derrick structure supporting typically one or more flare stacks along with utility piping, a stair tower, access platforms, and a common winch skid. Demountable systems can be designed to support a single flare stack or multiple stacks, with some having as many as 10 stacks. The main components of a demountable flare stack system are shown in Figure 1.

Figure 1. Typical demountable flare system.

The derrick structure is typically fabricated from structural steel pipe and can be designed as a three-leg or four-leg structure. A derrick structure should include a stair tower and the necessary ladders and platforms to access demounting equipment at elevation. Shielding is provided to protect personnel from radiation, which allows personnel to access the flare system safely, even during a flaring event of any active flare stacks.

The flare stack(s) are fabricated in flanged sections between 12 and 24 m (40 to 80 ft) in length and have utility piping pre-mounted to each section to supply pilot gas/ignition/steam to each flare. The flare stacks are installed on one of the flat faces of the derrick structure to allow access for demounting. Flare stacks can be demounted a section at a time, with the stack and utility piping flange connections being unbolted as each section is lowered. Tilting tables and tilting beds are provided at the base of the derrick structure to lower the demounted sections to grade.

A demountable flare stack system is supplied with a demounting winch skid consisting of a single motor servicing a lifting winch and a canting winch. The winches and motor are designed for the heaviest and worst-case loading to enable a single winch system to service any of the flare stacks on the derrick structure.

What are the benefits?

Demountable flare stack systems have become very popular in various refining, petrochemical, and LNG-related applications due to the versatility they provide. Most demountable systems include multiple flare stacks, and most have an installed spare flare stack. This spare flare remains in an idle, standby mode during regular operation of the flare system. When maintenance on any active flare stack in the system is needed, the spare stack is brought into service. A flare tip or stack that requires any inspection or maintenance work can have its associated process units rerouted to the spare stack, while the primary flare stack and tip is demounted to grade level to allow for refurbishment or replacement. This flexible design enables facilities to perform required maintenance without requiring the shutdown of the plant or of process units.

Even demountable flares that do not include an installed spare still provide added flexibility in the facility because the stack/tip requiring maintenance can be lowered to grade without using a tall – and typically expensive – crane. Demountable flares eliminate this significant cost, as the individual stacks can be lowered to grade level for any maintenance, utilising the built-in demounting system and winch package.

This article was originally published in the January 2024 issue of Hydrocarbon Engineering magazine. To read the full article, sign in or register for a free subscription.

Written by Nikki Ebert, Zeeco, USA.

Read the article online at: https://www.hydrocarbonengineering.com/special-reports/31012024/demountable-flare-stack-systems-in-north-america/