Chemical Technology April 2016

PETROCHEMICALS

Figure 1: World Shale Resource Assessments (US Energy Information Administration, September 24, 2015)

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 2 S) and the added amine-based H 2 S scavengers prior to transporting. Although tight oil is considered sweet (little sulfur content in the crude oil itself), there is H 2 S that needs to be addressed at the drill site, during transporting, and when offloading. While amine-based H 2 S 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 H 2 S 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.

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 Figure 2: EIA expands monthly reporting of crude oil production with new data on API gravity (https://www.eia.gov/todayinenergy/detail.cfm?id=23952

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Chemical Technology • April 2016