Comment Log Display

Clarification is needed regarding the appropriate location to
obtain samples of crude oil and produced water to apply the
Appendix B flash liberation methodology specified in
95153(v)(1)(A)(1) for calculating emissions from “crude oil,
condensate, and produced water sent to storage tanks, ponds, and
holding facilities”.  As currently written, the method requires
sampling from a “primary vessel located in a separator and tank
system”.  “Primary vessel” is defined in 95102 as "a separator or
tank that receives crude oil, condensate, produced water, natural
gas, or emulsion from one or more crude oil, condensate, or natural
gas wells or field gathering systems”.  This seems to leave
considerable flexibility in the sampling location.  Because the
objective is to calculate emissions from “crude oil, condensate,
and produced water sent to storage tanks, ponds, and holding
facilities”, it seems appropriate to sample such liquids at the
vessel immediately upstream of the storage tanks, ponds, or holding
facilities.  This is because the CO2 and CH4 dissolved in liquid
discharged from such a vessel is the CO2 and CH4 potentially
liberated from the liquid when it “flashes” in the storage tanks,
ponds, and holding facilities.  However, ARB staff has recently
(verbally) advised samplers and operators that samples must be
obtained from the FIRST (i.e., furthest upstream) vessel in a
separator and tank system.  Sampling at the furthest upstream
vessel in a separator and tank system that consists of more than
one separation vessel (e.g., a free water knockout followed by a
heater treater) is likely to result in overstating emissions from
the downstream storage tanks, ponds, and holding facilities.  This
is because some of the gas entrained in the liquids discharged from
the upstream vessel is liberated in downstream vessels that operate
at lower pressure and / or higher temperature and, therefore, is no
longer dissolved in the liquid conveyed to the storage units. 
Rather, it is directed elsewhere in the facility (i.e., a fuel gas
system, reinjection system, gas processing / sales system, or a
flare) via a closed gas collection / conveyance system.  This gas
only contributes to facility emissions if it is then combusted as
fuel gas or in a flare, leaks to atmosphere via equipment
components in the gas collection / conveyance system, or is vented
to atmosphere via a gas processing / sales system (e.g., an acid
gas removal unit that vents CO2 to atmosphere).  But the MRR
requires these categories of emissions to be separately quantified
and reported in accordance with other specified methodologies.  So,
requiring samples to be obtained at a point further upstream in the
system from the vessel immediately upstream of the storage tanks,
ponds, and holding facilities would likely result in emissions from
the storage tanks, ponds, and holding facilities to be overstated.