Decarbonisation Technology - August 2023 Issue

two objectives: reduce the overall operating expense and process a concentrated benzene stream from the reformer in order to recover benzene for petrochemical production. The scope of the revamp is highlighted in Figure 4 . First, heavy naphtha will be sent to a new splitter, the products from which will be a mid-cut and heavy-cut naphtha. The new mid-cut naphtha (MCN) will be mixed with the benzene concentrate and then treated in a new GT-BTX PluS unit. The raffinate, which contains the olefins, will be sent directly to the gasoline product. The extract, which contains the sulphur and aromatic molecules, will be mixed with the heavy naphtha and then treated in the existing HDS unit. A second new column will be added to recover high-purity benzene. The bottoms product from this column will be mixed with the light and mid-cut naphtha streams to form the final product. The data in Table 2 show the potential benefits. Most notably, with GT-BTX Plus, the final treated gasoline product has retained most of the olefins, which leads to a reduction in RON of only 0.4 instead of 3.0. Hydrogen consumption is reduced, as the HDS unit now operates more efficiently and at lower capacity with the MCN removed. In this case, additional revenue is gained from the new benzene stream and expansion of the gasoline pool. In a revamped case, the new gasoline hydrotreater could produce cleaner-burning gasoline while at

Property

Feed

HDS only

HDS +

GT-BTXPluS

Olefin content, wt% 27.4

17.5 22.5 90.4

26.0 11.0 93.0

Sulphur, wppm Octane, R+M/² H 2 consumption, scf/hr

1,250

93.4

85,000

27,000

The extractive distillation process is especially helpful in an FCC gasoline hydrotreater. Mercaptans and olefins are the dominant species in the lighter fraction, and thiophenes and aromatics are dominant in the heavier cuts. The heaviest fraction has few olefins species to significantly impact the desulphurisation (HDS) unit. However, the heavy naphtha stream in a gasoline hydrotreater also contains middle- boiling components that are primarily olefins and thiophenic hydrocarbons. This mid-cut naphtha is most susceptible to olefin saturation in the HDS units and, consequently, octane loss. Sulzer has been working with a refinery in US PADD 3, which has an FCC naphtha hydrotreater similar to that shown in Figure 3 . It is comprised of selective hydrogenation, a naphtha splitter, heavy naphtha HDS, and a stabiliser. Sulzer is in the process of designing a grassroots GT-BTX PluS unit for this client, with Table 2 Data summary for GT-BTX PluS case study

Stripper

Ranate wash columns

Extractor

Feed

Ranate

Extractor reux

Figure 5 Revamp of an aromatics extraction unit with modified (blue) and eliminated (red) equipment