Processing of Primary Fischer-Tropsch Products - University of Alberta

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Figure 2 Current (2004) High Temperature Fischer-Tropsch refinery used at Secunda The HTFT reactors at Sasol 1 were decommissioned in the 1990's and the facility was converted to a chemicals production site. The Secunda plants also started to lose their identity as fuels-only refineries as more and more chemicals were targeted for extraction [12]. Yet, most of the production volume still went to fuels and with the more stringent fuel specifications, some fuels refining units were added, such as etherification and skeletal isomerisation (Fig. 2). With the construction of the first commercial HTFT gas-to-liquids (GTL) plant, an all-fuels approach was again followed. The PetroSA GTL plant started operation in 1993 as Mossgas in Mossel Bay, South Africa. The plant is an integrated facility for natural gas processing that makes use of Sasol Synthol technology. The feed is obtained from their own natural gas fields located offshore. The primary gas separation is done at the main production platform where Raw Natural Gas and Natural Gas Liquids (NGL) are produced and transported some 120 km to the GTL plant by pipelines. A secondary separation is done onshore where the natural gas composition is made compatible with the GTL process requirements and the NGL is separated into Liquefied Petroleum Gas (LPG), Naphtha and Diesel. The refinery design resembled that of the Secunda facilities, but some changes were made to the C2-C8 processing (Fig. 3) [13]. Condensate Gas Natural Gas Liquids Recovery T" Fischer- Tropsch process ........................... ~ Skeletal isomerisation I 9 iiiiii ! ili- ,I Alkylation ] ~ Alkylatepetrol Tail !i 9 LPG gas ! i _ _ ~ O lefin oligomerisation I 9 Unhydrogenated petrol llr i. ~ s keletal isom e ris a t ion [ I ~ Isomerate petrol i ~j Naphtha hydrogenation [ Light [ S0111 "11 t ]i~i a b i l i s 9 " "-i I .., "[ e Naphtha d ref~ i -~ LPG -~ Aromatic petrol 9 :_1 Distillate hydrogenation I -~ Kerosene Decanted k.U/ , "-~ A -~ Diesel Oil | '~ ...................................................................... i | L Fuel oil Aqueous product "l Chemical work-up [ -~'~ WaterOXygenate chemicals Figure 3 High Temperature Fischer-Tropsch refinery design of Mossgas (now PetroSA) at Mossel Bay 485
486 Chemical production at the Mossel Bay refinery is possible but lacks economy of scale relative to the Secunda plants. Although not implemented, some chemical production opportunities have been investigated [14]. Future HTFT plants are likely to target bulk commodity chemicals to decrease the reliance on high oil prices for satisfactory economic performance. Chemicals extraction is an attractive option to grow income [ 15] and this can be considered even after the FT plant is in operation provided the remaining plant life is sufficient. Since the Mossel Bay refinery uses natural gas as feed material and not coal, it does not have a tar refinery associated with it. However, the co- processing of natural gas offers its own advantages. The historic evolution of the Sasol HTFT refineries was not only driven by technology advances and market requirements, but also by the strategic positioning of the company. Current thinking favours expansion in the field of polymers and future changes may well have to balance the demands of more stringent fuel specifications with growth in ethylene and propylene production. To meet such an eventuality a change in the refinery configuration to include a Superflex TM Catalytic Cracker (SCC) unit is being implemented [ 16]. 3. UPGRADING OF HIGH TEMPERATURE FISCHER-TROPSCH (HTFT) PRODUCTS 3.1 Influence of feed properties on refining approach To understand HTFT refining, it is necessary to take a closer look at the refinery feed material. Although the feed composition depends strongly on the nature of the FT catalyst and operating conditions [4, 5], a high temperature iron based FT primary product typically has the following attributes: 9 The oil and aqueous products are essentially sulphur-free. 9 The oil and aqueous products are low in nitrogen-containing compounds. 9 The oil and aqueous products contain percentage levels of oxygenates (alcohols, acids, esters and carbonyls). 9 The oil product is rich in olefinic material, especially linear alpha-olefins. 9 The oil product is poor in aromatics and naphthenics (cyclo-paraffins and cyclo-olefins). 9 The oil product is mostly linear or with a low degree of branching. 9 The oil product follows a Schultz-Flory distribution, heavily weighted towards light hydrocarbons. 9 The aqueous product contains most of the short chain oxygenates. The discussion presupposes that the products are typical HTFT products and have not been modified in some way by the addition of a second catalyst type. It may seem desirable to use a second catalyst type to make the HTFT
Page 1 and 2: Studies in Surface Science and Cata
Page 3: 484 Cold separation .~~"~ Condensat
Page 7 and 8: 488 Table 1 Research octane value (
Page 9 and 10: 490 cannot be used with FT products
Page 11 and 12: 492 an attractive refining option f
Page 13 and 14: 494 pose a serious refining problem
Page 15 and 16: 496 offset by the higher capital co
Page 17 and 18: 498 technology that can be used to
Page 19 and 20: 500 includes conventional petroleum
Page 21 and 22: 502 environmental footprint refers
Page 23 and 24: 504 option depending on the scale o
Page 25 and 26: 506 yielding a much higher selectiv
Page 27 and 28: 508 conditions are significantly le
Page 29 and 30: 510 protonated on the acidic cartie
Page 31 and 32: ~ .I Condensat, i ,~ ~l Cond,nsate
Page 33 and 34: 514 product upgrading unit is compa
Page 35 and 36: 516 broad terms, the information re
Page 37 and 38: 518 7.1.1 LTFT diesel as a blending
Page 39 and 40: 520 component e.g. biodiesel and/or
Page 41 and 42: 522 A comparison of the characteris
Page 43 and 44: 524 100 -[ ........................
Page 45 and 46: 526 60.0 . . : . . . i i ! i i i .
Page 47 and 48: 528 of hydrocarbon products, the pr
Page 49 and 50: 530 [41 ] F.D. Rossini, Chemical th
Page 51: 532 [83] J.A. Tilton, W.M. Smith an

Processing of Primary Fischer-Tropsch Products - University of Alberta

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