The main incentive for using alternative feedstock is to reduce the overall carbon footprint of the refinery, which is a key objective for any operator today. This integration comes with some consequences, especially on hydrotreating units, where those impacts are as diverse as the feedstock types on the overall energy efficiency of the refinery.
For renewable lipids, the oxygenated compounds in those feeds make this type of feed more hydrogen intensive and exothermic than fossil feedstocks. With adequate heat management and high-efficiency heat exchangers like ZPJE spiral tube heat exchangers, those feedstocks can generate sufficient heat to reduce or avoid the use of fired heaters in hydroprocessing. At the same time, it could also generate steam for the refinery net work, which is a plus. In addition, propane is a valuable by-product of glycerides hydroprocessing. It can be either valorised as a bio-LPG product or used to replace advantageously natural gas as a steam reforming feed stock or refinery fuel gas, thus decreasing the overall car bon intensity.
On the other hand, alternative feedstocks also have variable content and impurities that can negatively impact the overall energy efficiency. For example, waste based feedstocks such as plastic pyrolysis oil can have very high levels of metals or chloride due to their various origins and initial treatments, which will have a negative impact on global heat integration. Metals will require increased reactor temperature due to catalyst poison ing and reduced cycle length, while chloride will make heat integration more complex due to corrosion issues. In addition, other contaminants can be sources of pressure drop build-up and subsequent operational issues. In this context, even low incorporation rates of those pyrolysis oils can negatively impact the overall energy efficiency. However, a combination of equipment, specialty grading, specific catalysts, and unique process expertise can mitigate these negative effects.
Axens’ EquiFlow Hy-Clean filtering trays, ACT series specialty bed, the latest HR 700’s series, air preheater (APH) technologies, revamp studies are among Axens’ proven solutions to overcome the challenges of any alternative feedstocks co-processing. They maximise their rate of incorporation in existing assets with an overall positive impact on energy efficiency.