Fired heater safety distance 6

[Crodark]

Recently, we got a requirement for 15 meters (50 feet) safety distance for the fired heater. Despite not being able to find this "number" in any standard (please correct me), I want to understand if my interpretation is correct.
The primary reason for the minimum clearance of 15 meters is to prevent ignition of gases/liquid incoming from adjacent equipment that could leak. Is this correct?

 

[mk3223]

It's the basic plant layout to maintain a minimum and safe distance in the O&G plant for any equipment from the Fire Heater for a concern of the gas or HC liquid leakage. One may check with the applicable NFPA Code and local regulation for the actual requirement as well.

 

[ProSafPlant1]

It's a longtime insurance recommendation dating back to Oil Insurance Association in the 1970s. OIA later became IRI (Industrial Risks Insurers) and then published their standards as GAP (Global Asset Protection. The GAP guidelines were more recently published by AIChE CCPS in their guidelines books.

 

[georgeverghese]

Forced draft heaters are safer to operate than induced draft. Air intake for forced draft heaters should be from a HAC safe area. Thermal plume studies for the exhaust should also show that that the worst case thermal plume does not present plume temperatures approaching ignition temperature for potential leaks from equipment within the plume. Use 2oo3 voting flame UV sensors for each main burner. Enable feed pressure high limiting controls for feed fuel gas to each main burner. See also API RP 14C for other safety devices.

 

[shvet]

Statistically a fire heater (especially liquid fueled) is the most fire-hazardous zone in a process side and is prone to pool fire caused by leaks or coil creep/damage as a fired heater contains uncontrolled sources of fuel release and ignition both. Your idea is to protect fired heater from adjacent equipment, my idea is to protect adjacent equipment from fired heater. So answering your question - partially correct, safe distance is required to prevent escalation of a fire around of a heater (caused by leak) or explosion (caused by improper purging of firebox).

One is not prohibited to designate an uncontrolled source of ignition (open flame and overheated surfaces in your case) close to a process side if release sources are controlled or segregated (e.g. steam curtain).
Your question concerns zoning (fire, ex) - note that any option is possible if it has been justified properly. Resulted risk is the only issue.

1.2.2 Extent of hazardous area
The design intent should always be to minimise the extent of the hazard radii. It is not good practice to classify hazardous zones that would reach uncontrolled sources of ignition, such as site roads, occupied buildings and off-site populations. For typical sites these distances can be between 15 m and 30 m.
In the majority of cases, it is expected that the release rates will result in hazard radii significantly less than 30 m, although releases resulting in potential hazard radii greater than 30 m which occur due to design intent, e.g. discharges from a relief valve, vent or high pressure source, should be included in the area classification review. Arrangements should be made if practical to route the discharge to a flare or to discharge at an appropriate location subject to a risk assessment.
If a hazard radius calculated using the point source method is greater than 30 m, then the size of the release is generally larger than that considered for area classification purposes and measures should be taken where practical to eliminate the source or reduce the size of the release.

3.4.5 Manual Trip (Emergency Shutdown)
A manual trip shall be provided to isolate all fuel sources. ...
Where existing field panels do not allow for safe access and egress during an emergency situation, or where the radiant heat from a heater fire may prohibit access, it is recommended to have a secondary manual trip outside of a 50 ft (16 m) zone. A design consideration is to install a manual quarter turn tight shutoff valve outside battery limits [> 50 ft (> 16 m)] clearly marked for emergency isolation.
A minimum of two emergency shutdown locations is recommended. Therefore, if a manual trip location outside of a 50 ft (16 m) zone is not available, then a remote manual trip from a continuously manned location (always recommended) such as a central control room may be required (e.g. DCS remote trip).

10.3.5. RELATIONSHIPS
...
Buffer distances between equipment, such as those seen in Figure 10.1, may be given in general guidelines and are meant to improve safety considerations by the separation of equipment under given circumstances (above, it is fire consequences that are designed for). These are not requirements, and in many cases with proper engineering, safety systems, and safety instrumentation, the amount of distance between equipment could be lower. Likewise, there are many cases where circumstances dictate that the spacing should be increased from the value given in a general table. These may include ambient weather conditions, presence of population (either workers or civilians), or internal guidelines. Furthermore, there may be situations in which the applicable separation distance is not able to be attained. As it states in CCPS Guidelines for Facility Siting, appropriate risk-reduction measures should be taken to alleviate as much risk as possible.
The miscellaneous separation distances that are shown in Figure 10.2 work in the same manner as the process equipment spacing tables in Figure 10.1, but cover different equipment and facilities. As with the equipment separation distances given in Figure 10.1, not all of the miscellaneous spacings may be applicable in a given facility. The same caveats apply to these spacings as well. The separation may have to be larger than prescribed or may be allowed to be lower depending on the situation. Detailed risk analysis and engineering judgment should be used in any case.

https://files.engineering.com/getfi...796-434c-b58b-05be45490232&file=Tab._10.1.png

https://files.engineering.com/getfi...29e-4a0d-97ea-40c83e67f0f2&file=Tab._10.2.png

 

[Crodark]

Thank you, gents, for your constructive suggestions.
My problem is actually a request from one vendor to have a safety distance of 15 m for the Electrical Heater. Since the electrical heater is contactless i.e, process fluid is in a tube/pipeline surrounded by a heating element, then all is surrounded with insulation closed in the box, which is under slight N2 pressure.
There is no chance that gasses from external leaks (surrounding equipment), reach heating elements and generate explosions.

 

[shvet]

It's a longtime insurance recommendation dating back to Oil Insurance Association in the 1970s. OIA later became IRI (Industrial Risks Insurers) and then published their standards as GAP (Global Asset Protection. The GAP guidelines were more recently published by AIChE