Chemical Technology April 2016

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8 Chemical Technology • April 2016
and capacity losses. Improvements in online monitoring and
analysis enables refineries to better understand accelerated
fouling due to crude incompatibilities, and identify which
tube bundles require cleaning. Fouling across the bundles
is not linear, so determining which bundle is fouled and
needs cleaning can be difficult to determine without all
the process measurements like temperature, flow, and
differential pressure.
For example, a gulf coast refiner that was one of the first
to use tight oil experienced severe and unexpected fouling
in the crude unit pre-heat exchangers. Unfortunately for the
refinery, they were forced to shut down to clean the exces-
sive fouled heat exchangers resulting in lost production
and additional cleaning costs. The refiner has since added
online temperature and pressure measurements on all
heat exchanger bundles, implemented software to analyse
fouling, and the crude unit process engineer reviews fouling
every day. They also have a better understanding on the
percentage of different crudes blended to determine what
crude blends are incompatible, resulting in accelerated
fouling; this information is forwarded to the schedulers and
planners. Although tempting to buy any discounted oppor-
tunity crude on the market, now crude oil purchasers also
utilise crude incompatibility information along with crude
properties and price to determine ‘compatible’ feedstocks
for the refinery.
Even with knowledge about crude blend incompatibili-
ties, a refiner may still experience accelerated fouling issues
when the supply chain is disrupted. For example, a crude
shipment may be delayed owing to severe weather in the
gulf, thus a refinery will run with what crude is available
onsite which may not be the preferred crude blend.
A further challenge processing light tight oils is hydrogen
sulfide (H 2S) and the added amine-based H2S scavengers
prior to transporting. Although tight oil is considered sweet
(little sulfur content in the crude oil itself), there is H2S that
needs to be addressed at the drill site, during transporting,
and when offloading. While amine-based H2S scavengers
are added, tight oil loaded in the cold of winter can have safe
conditions at the site prior to leaving – and then transported
to a warmer climate. The mixing during transport along with
a change in temperature, can result in higher vapour pres-
sure and the release of entrained H2S making the offload-
ing a potential safety hazard. To mitigate the safety risk,
hydrogen sulfide monitoring and vapour recovery should
be standard for loading and offloading tight oil.
Figure 1: World Shale Resource Assessments (US Energy Information Administration, September 24, 2015)
Figure 2: EIA expands monthly reporting of crude oil production
with new data on API gravity
PETROCHEMICALS