US hydrotreating capacity
Hydrogen generation
Current demand
Future demand
Current demand
Future demand
Feedstock supply Feedstock quality must match the process line-up being considered. The types of feeds define the renewable feed processing limitations for each unit. The issues encountered are like the current fossil fuels crude purchasing optimisa- tion systems. The renewable challenge is to get feedstock to the processing facilities on a scalable basis, along with associated costs in a sustainable matter. A reasonable scale biofeed facility would be less than 15 MBPD, with the range being 5-60 MBPD. The best pos - sible economic outcome is to leverage existing fossil fuel refineries and the associated supply chain. The use of exist - ing storage and transportation to market is desirable. The feedstocks are different enough in composition that the feedstock storage considerations are modified compared to fossil fuels. The feeds with longer chain fatty acids favour diesel, whereas shorter chain feedstocks favour jet (see Figure 2 ). The range of saturate (high (C+H)/O), for example, is tallow oil, while low (C+H)/O is represented by tall oil, which is also more difficult to process. Often, raw feeds cost more than resultant products and may not be competitive without price incentives. Hydrogen dilemma To meet future biofuels and renewable demands, US hydrotreating capacity will likely have to double, and hydro - gen generation will need to double or triple. There is an anticipated increase in hydrogen generation from the cur- rent capacity of 3 billion scf/day to 11 billion scf/day (see Figure 3 ). There is a desire to shift from grey to blue to green hydrogen. Oxygen content creates H2O, CO2, and CO byproducts that must be managed in hydrotreaters. This results in catalyst activity, corrosion, and removal concerns. Product qualities The two main products from renewable feed processing are diesel and/or jet. The units also produce naphtha, LPG, and light ends. The green naphtha market is in the beginning Figure 2 Tallow oil high (C+H)/O compared to low tall oil (C+H)/O
Figure 3 US Hydrotreating capacity vs generation
stages. Propane LPG is a fungible product with fossil fuels. However, currently the market is still developing, but the focus in this article is on renewable diesel and jet. Renewable diesel quality Renewable diesel production is fully fungible with fossil die - sel. The energy density requirements are similar, with the target being a C/H or H/C target (~2 H/C mol/mol or 6.5 C/H wt/wt). The linear alkanes produced from the treat reactor are converted to isomers, which have a high cetane blend - ing value. Renewable jet quality Renewable jet has low aromatics and requires blending with fossil fuels to meet the minimum aromatics content require- ment. ASTM D7566 provides renewable jet specifications. Blending renewable and fossil jet meets ASTM D1655, pro - ducing sustainable aviation fuel, or SAF. Renewable content tracking Particularly problematic for co-processing is the require- ment for ASTM D866 Carbon-14 analysis/testing (14C). The content of 14C allows estimation of the renewable die - sel concentration in the rundown. The batch testing requires collecting the biodiesel co-processing product into a tank, sampling then certifying the results. Renewables from triglycerides Seed oils and animal fats are the primary feeds for the renewable system. A typical triglyceride is shown in Figure 4 . Typical feed qualities are shown in Table 1 . 2,3,4,5,6,7 ,8,9 Advanced renewables Feeds not readily processed using current technology are considered advanced renewable feeds: • Cashew nut oil • High oleic sunflower oil extract • Animal fat • Brown grease • Tall oil pitch • Wastewater oil collections (such as fats oil, FOG). These feeds are the next level processing opportunities as the edible feedstocks are removed from renewable feed processing. Receipt and storage Renewable feeds are much more reactive than fractions
O O O
Oleic acid Linoleic acid
O O
Linolenic acid
Figure 4 Typical triglyceride
48
PTQ Q3 2022
www.digitalrefining.com
Powered by FlippingBook