Part 1: 3 Steps to Integrate "Flare System Management"

Written by Dustin Smith, P.E. | Jun 28, 2017 4:23:00 PM

The Evolution of American Refining:

Refineries and petrochemical facilities today are faced with a choice: either increase efficiencies and throughputs or be put out to pasture. While the capacity of the average refinery has almost doubled in the past 30 years, per Energy Information Administration (EIA) data, the capacity of the average flare system generally has not. This is not a mere academic issue. In the US, the number of operating refineries dwindled from ~200 in 1985 to only 137 thirty years later (per the EIA); over the same thirty years, the total US throughput has increased by 25% (or significantly more depending on how you quantify the increase in complexity).

This growth in capacities and efficiencies is instrumental in succeeding amongst the rigors of a "keep up or be left behind" economy. Driven by major projects, these process changes include adding new equipment, changing existing processes, and creating more integrated heating and cooling.

However, during all the major project pushes, one thing is often lost, overlooked, or left for the last minute: integrating changes into the existing flare system and doing so in a manner that provides the maximum benefit to the organization.

The Solution...

The first step is to determine what type of projects / project characteristics require further consideration when it comes to analyzing the effect on the flare system (not all projects affect the flare in the same manner.) The second step is to establish a responsible entity to act as a caretaker for the flare and all management of change items associated with its operation. The responsible entity would ensure that all changes made to the flare would be documented and the capacity of the flare would be evaluated for significant changes. The final step is to ensure that the management of change for the flare is incorporated into the project lifecycle for any given project.

These three steps will create a foundation for an evergreen flare process basis and help to ensure that the impact to the project is minimized while maximizing the benefits (PSM compliance and decreased risk to project scope and budget.)

Who is Responsible for the Flare Design Basis?

Let us start from the beginning. Where did the design basis of your current flaring system come from? Odds are that it was part of the original design of the facility; here in the US, that was most likely 35-45 years ago. With the PSM standard introduced in the early 1990's, many operating facilities made a proactive effort to re-establish their flare study baselines, which was a great place to start. However, what has happened since either the original design basis or a more current baseline study was complete? Based on past experiences seen at multiple operating facilities, these flare design studies are typically passed around from the project team to project team or contractor to contractor. These project teams or contractors typically only make minimal changes concerning their specific projects and lose sight of the overall disposal system. This is often the case when there is not one true owner responsible for the disposal system.

With all this attention, we are concerned that only 2% of our survey respondents stated that their inspections were "Very Outdated" along with 58% and 32% believing that their inspections were "Very Current" and "Somewhat Outdated", respectively. In almost every PSM audit we have conducted, there are repeated inspection frequency gaps and the required inspection plans don't provide details for compliance.

Typical Projects:

Now let us take a moment to illustrate a few examples of some popular projects over the past 20 years, what drove the changes, and if they had a significant impact on the flare system demands.

TYPE OF PROJECT:	MOTIVATING DRIVER:	IS THERE A FLARE IMPACT?
Increase Throughput	Increased Revenue	Yes - Any throughput increase is likely to increase the demands on a flaring system by increasing the required relief rate for rate-dependent scenarios.
Heat Integration	Decrease Cost	Yes - With any heat integration project you have the possibility of changing the flaring system demands by adding interdependency of flaring loads.
Relief Valve or Control Valve Flare Tie-In	EPA Safe Location Regulations	Yes - Many facilities have tied in existing atmospheric relief devices into their flaring system to address a safe disposal location of hazardous releases, increasing overall demand on the flare system.
Addition of New Units	Clean Fuels Mandates from the EPA	Yes - These additional units will increase the overall load on the flare and therefore change the flare design basis.
Change the Feedstock	Economically Driven based on Increase in Domestic Feedstock	Yes - By changing the feedstock to a unit, the compositional basis used in the disposal system design is likely to change. Changes in the composition can affect the required relief rates.
Utility Additions or Upgrades	Aging Utility Systems and the Need to Invest or Go Out of Business	Yes - Changes to electrical power sources, cooling water systems, or other utilities can change the overpressure scenario rationale and relief loads, resulting in changes to the loads on the flare system.

(While this list is not all-encompassing, it is safe to assume that if a project falls into one or more of the descriptions given here, there is a high likelihood that the flare capacity may be impacted. Resources must be allocated to at least investigate the impact to the flare and its capacity.)

What are the Requirements?

The following excerpt from section 4.8 in API 521 6^th Edition lists the documentation requirements for flare headers:

4.8 Flare Header Design Documentation:

Common examples of information that may need to be provided often include, but are not limited to, the following...

a)  For each flare header scenario, a description of the initiating event and of the intermediate consequences that lead to relief flow. For example, for an electric power failure, this description would include the primary element assumed to fail, a list of all electric power users that would consequently be de-energized, and the consequences of the loss of each electric power user.

b)  Documentation of the basis used to define the flare system configuration for the network-flow simulation model.
(For the base case, this documentation generally consists of a list of piping drawings with revision numbers. For alternate piping configurations, changes from the base case may be marked on the schematic diagram of the system or described in narrative form.)

c) Schematic diagram of the flare system showing a pressure profile for each flare header scenario analyzed. The pressure profile should show calculated backpressure at each relief source discharging in the given scenario.

d)  Electronic copies of input files used for the network-flow simulation. Electronic data files for the existing piping network should be provided.

e) PRV size-selection datasheets showing valve manufacturer (for existing valves), type of valve, set pressure, size and inlet and outlet flange ratings.

f)  List of disposal system loads (e.g. loads from relief devices, depressuring valves, and control valves) including source name, temperature, relative molecular mass ("molecular weight") or composition, and flow rate.

g) List of all credits taken to reduce or eliminate disposal system peak loads, including instrumentation (see 5.3.4 for details).

h)  List of instrumentation assumed not to work for each relieving scenario and basis for selection of failure combination.

i)  Backpressure limit for each source and the basis for limit (e.g. downstream piping design pressure, API 526 [..], manufacturer, critical flow, or derated valve capacity).

j) Acceptance criteria for flare system capacity, including assumptions and design basis for the knockout drum and the flare stack.

Part 2: 3 Steps to Integrate "Flare System Management" into Your Project Life-cycle and Maximize the Benefits

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