Renewable products
Propane, CO , H O
n-para ns
Hydrocarbon mix
Pretreated renewable feed Hydrogen
LPG & naphtha Kero/jet (SAF) Diesel
HDT (de-oxidation)
Isomerisation or mild HCK
Fractionation
Figure 2 A simplified flow chart summarising the various HVO processes
fractionation process and the potential to optimise the fractionator for maximal performance. Most fractionator designs are based on old rules of thumb that limit energy efficiency and product recovery while increasing project Capex. Instead, the fractionator can be optimised with high- efficiency heat exchanger solutions that have been on the market since the early 1990s. Such optimisations can drastically improve efficiency in this part of the HVO process. Fractionator optimisation: feed/bottoms interchanger The first heat exchanger position to consider is the feed/bottoms interchanger. In this position, the aim is to maximise energy recovery from the fractionator bottom stream for use in preheating the feed. Doing so will maximise both the final product cooling and the feed heating, which will reduce the load on both the final product cooler and the fractionator reboiler. The amount of energy that can be recovered is limited by the heat exchanger technology selected. When conventional shell-and-tube
technology is selected, maximising the energy recovery requires a series of several large heat exchangers. This is often too costly or practically infeasible to install in the plant. The alternative is to use a high-efficiency welded plate heat exchanger (WPHE). This technology enables a tight temperature approach down to 3°C, which can be achieved in a single heat exchanger with a minimal flooded weight and plot space requirement. Thus, it becomes economically favourable and practically feasible to maximise energy recovery. Often, at least 25% more energy can be recovered with a WPHE. This reduces the reboiler duty by an equivalent amount and may even eliminate the need for an air cooler upstream of the final trim cooler, as outlined in Figure 3 . Fractionator optimisation: overhead condenser Minimising the column operating pressure is another opportunity to maximise the energy efficiency of the fractionator. Often, this can also improve separation efficiency in regard to fractions with similar or even overlapping boiling
Renewable diesel
O gas
M
Green naphtha
Q min
Product fractionator
M
SAF
T min
M
Q max
T max
Stripper bottoms
Q min
Figure 3 Improved product fractionator design using a WPHE to maximise energy recovery in the feed/bottoms interchanger
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