Refiners use a wide array of process heaters. The operation of these heaters poses a number of hazards that must be controlled, and are typically controlled using safety instrumented functions. The number and type of safety instrumented functions that are employed vary to a great degree from refiner to refiner and from site to site. This paper presents a summary of some of the results of a benchmarking study that was performed to determine the most prevalent practices in industry and establish the degree of adoption for some of the more common safety instrumented functions.
2. Introduction
• Most refiners employ fired heaters and are
interested in standard designs
• API 556 is a common basis
• Benchmarking desired, address limitations
– Improper bypass
– Open block valves at light off
– Improper fuel/air ratios
3. Survey Scope
• Automatic Trips
• Alarms
• Permissives
• Shut off valves
• Pilots
• Post-Purge
4. Survey Participants
• Pure-play refiner or integrated oil and gas
• Large market capitalization
• Multiple refineries
• Large processing volume capacity
• Data set is limited
– Acquisitions cause inconsistency
– Attempted to get multiple sites
5. Results Scope and Format
• Practices for new design and for existing
equipment
• Ranked from 1 to 3
– 3 – Almost always implemented
– 2 – Sometimes implemented
– 1 – Almost never implemented
• Results from multiple sites averaged
• Oriented to natural draft
6. Results – Low FG Pressure
3
3
Alw ays
2
Som e tim e s
1 Alm os t Ne ve r
0 Study Re s ult
Re s ult
• Almost always for new and existing
• Even if not required by standard almost always
implemented
7. High FG Pressure
3
2.9
Alw ays
2
Som etim e s
1 Alm os t Ne ve r
0 Study Re s ult
Re sult
• High degree of implementation
• May address hazard not detected by other
means
• Some opt out if not a credible scenario
8. Pilot Gas Shutdowns
Alw ays Alw ays
3 3
2 Som etim es 2 Som etim es
2.3
2.1
1 1 Alm ost
Alm ost
Never Never
0
0 Study Result
Study Result Result
Result
High Pressure Low Pressure
• Considers that some organizations do not
employ pilots in normal operation
• Some consider risk posed by pilot misoperation
to be minor
9. Loss of Flame
Alw ays Alw ays
3 3
2 Som etim es 2 Som etim es
1 1.4 Alm ost 1 1.4 Alm ost
Never Never
0 0
Result Study Result Result Study Result
Main Pilot
• Not very common
• Feel this is addressed by other means
• Expensive, results in high spurious failure rate
• More prevalent in forced draft and boilers
10. Low Pass Flow Shutdown
3
2.8 Alw ays
2
Som e tim e s
1 Alm os t Ne ve r
0 Study Re s ult
Re s ult
• Extremely common
• Required to be reviewed even if not “standard”
• Some opt out of consequence shown small
11. Improper Fuel/Air Shutdown
3
Alw ays
2
Som etim es
1 Alm os t Never
1
0 Study Re sult
Re sult
• Many are concerned but automatic shutdown
very uncommon
• Addressed by operator action or BPCS
12. Combustion Air Shutdown
3 3
2 Alw ays 2 Alw ays
2.3 2.1
Som etim es Som etim es
1 1 Alm ost Never
Alm ost Never
0 Study Result
0 Study Result
Result
Result
• Almost always address for FD/ID systems
• Detection methodology varies
• Fan motor speed also used
13. Air Supply Alarms
3
2.9
2.5 2.7
2
2.1 Always
1.5
Sometimes
1
Almost Never
0.5
Study Result
0
High Draft Pressure Low Oxygen High CO or
Combustibles
• Frequent and consistent
• High CO becoming more prevalent due to
regulatory involvement
14. Temperature Alarms
3
2.5 2.8 2.8
2.6
2 Always
1.5 Sometimes
1 Almost Never
0.5 Study Result
0
High Bridge Wall Temp High Stack Temp High Outlet Temp
15. Purge Flow Permissive
3
Alw ays
2
Som e tim e s
1.7
1 Alm os t Ne ve r
0 Study Re s ult
Re s ult
• Supervised manual function – different from
completely automatic purge
• Typically completely manual
16. Shutoff Valve Position Permissive
3
Alw ays
2 2.4
Som e tim e s
1 Alm os t Ne ve r
0 Study Re s ult
Re s ult
• Common practice although not often addressed
in corporate standards
• Typically limit switches
17. Burner Valve Closed Permissive
3
Alw ays
2
Som etim es
1 1.4 Alm ost Never
0 Study Result
Result
• Not common unless large number of burners are
employed (SMR, olefin cracking)
18. Automatic Firebox Purge
3
Alw ays
2
Som e tim e s
1 1.3 Alm os t Ne ve r
0 Study Re s ult
Re s ult
• Not common for natural draft
• Very common for FD/ID systems
19. Flame Proven Permissive
Alw ays Alw ays
3 3
2 Som etim es 2 Som etim es
1 1.6 1
Alm ost 1.2 Alm ost
Never Never
0 0
Result Study Result Result Study Result
Main Pilot
• Not common
• Only used where loss of flame trip is employed
20. Double-Block and Bleed
Alw ays Alw ays
3 3
2 2.4 Som etim es 2 Som etim es
2.3
1 1 Alm ost
Alm ost
Never Never
0 0
Study Result Result Study Result
Result
Main Pilot
• Somewhat common but not ubiquitous
• Other methods used to achieve goals of positive
isolation and low system failure probability
21. Bypass Valves
3
Alw ays
2
Som e tim e s
1 1.4 Alm os t Ne ve r
0 Study Re s ult
Re s ult
• Not common and getting less so…
• Pressure test systems might employ ¼” “dead
man” valve
22. Continuously Operated Pilots
3
Alw ays
2 2.3
Som e tim e s
1 Alm os t Ne ve r
0 Study Re s ult
Re s ult
• Some consider continuous pilots strong basis of
safety
• Some consider unreliable and not installed at all
23. Pilot Gas Separate Supply
3
Alw ays
2
2.2
Som etim e s
1 Alm ost Ne ve r
0 Study Re s ult
Re s ult
• Very common where continuous pilots are used
and separate supply is feasible
24. Post Purge
3
Alw ays
2
Som e tim e s
1 Alm os t Ne ve r
1.1
0 Study Re s ult
Re s ult
• Automatic steam introduction upon shutdown
initiation
• Not very common
• Some concern over consequence of action
25. Conclusions
• Benchmarking powerful tool for clarifying
implementation of standards
• Assists in determining “Recognized and
Generally Accepted Good Engineering
Practice”
• Results show remarkable consistency for
most applications
