Trace Vent Gas
What are the rules around Dehy’s
The rules around waste gas disposal from Glycol Dehy’s can be confusing and misunderstood. It seems that there are many interpretations of the rules regarding equipment and spacing requirements.
In Alberta, Directive 39 provides the rules and regulations associated with emissions from Glycol Dehydrators. This directive provides details on how an incinerator stack must be at least 9m tall, and it must be designed to meet the performance requirements set out in Directive 60 for waste gas ≥10 mol/kmol H2S.
Directive 39 assign control efficiencies of 95% for an incinerator.
This Directive does a great job identifying which control devices are accepted and even establishes the control efficiencies for each device. The confusion comes from the spacing requirements and where to find this information.
Photo Showing Incinerator installed adjacent to Dehy.
What are the spacing requirements?
An incinerator can be spaced directly adjacent to a Dehy. This spacing variance is outlined in Directive 60, Section 7 where it states:
“25 m from any oil and gas processing equipment. This does not apply to combustion devices that destroy trace vent gases, such as those emitted from gas dehydrators. These devices must be designed to prevent ignition of gas that may leak from surrounding equipment (e.g., combustion devices could be equipped with flame arresters); and”
Directive 60 does not clearly state the spacing requirements for an incinerator; however, the Alberta Energy Regulator (AER) has excepted that an incinerator has no spacing from a Dehy. This does, in some ways , contradict the Enclosed Combustor minimum spacing allowance of 10m stated in Directive 60.
Why the Different Spacing Regulations for Dehydrators?
The spacing regulations for Trace Vent Gas are different because the flammable gas concentration within the trace vent gas stream is quite low. This fact makes it nearly impossible for gas to accumulate in concentrations above the lower explosive limit (LEL) of the gas.
The AER has determined that reduced spacing in this application is safe. They do, however, maintain requirements for a height restriction of 9-meters. This design requirement is to ensure proper dispersion of the exhaust gases.