SMDS process

Fig. 3. The Shell middle distillate synthesis (SMDS) process. HPS = heavy paraffin synthesis. HPC = heavy paraffin conversion.

Shell Gas B.V. has constructed a 1987 mVd (12,500 bbhd) Fischer-Tropsch plant in Malaysia, start-up occurring in 1994. The Shell Middle Distillate Synthesis (SMDS) process, as it is called, uses natural gas as the feedstock to fixed-bed reactors containing cobalt-based cat- yst. The heavy hydrocarbons from the Fischer-Tropsch reactors are converted to distillate fuels by hydrocracking and hydroisomerization. The quality of the products is very high, the diesel fuel having a cetane number in excess of 75. 

The development of the Shell Middle Distillate Synthesis (SMDS) process began in 1983, when a pilot plant was constructed at the Shell Research and Technology Centre in Amsterdam. This eventually culminated in the design and construction of the Shell gas-to-liquids facility in Bintulu, Malaysia, which was completed and... 

In many respects the SMDS process (Figure 18.8) precipitated a change in the Fischer-Tropsch community with respect to the preferred catalyst for Fischer-Tropsch synthesis and the approach to product workup. It is therefore instructive to understand why Shell moved away from iron-based Fischer-Tropsch catalysts (and as a consequence also high-temperature synthesis) and opted for a Co-LTFT process with an uncomplicated refinery design that does not produce... 

Typical Product Properties Obtained from the Co-LTFT-Based SMDS Process... 

Important points about the SMDS process as applied at Bintulu are ... 

The selection of a fixed bed Co-LTFT process supported the objective to apply the SMDS process for beneficiation of remote gas fields. The Co-LTFT catalyst has a useful lifetime of 5 years and the robustness of fixed bed reactor technology has been proven. For example, the fixed bed Arge Fe-LTFT process has now been in operation for more than 50 years at Sasol 1. 

Short-chain olefins are not refined and the gaseous LTFT products are employed as fuel gas. Production of this fraction is limited by Co-LTFT synthesis, and with the product being less olefinic than iron-based Fischer-Tropsch syncrude, less benefit would be derived from the inclusion of an olefin oligomerization unit. Furthermore, adding complexity would go against the design objectives of the SMDS process. 

Superficially the Oryx GTL refinery design has much in common with the SMDS process, but there are important differences. There is no separate hydrotreater, which limits production of chemicals, such as waxes. The hydrocracker employs the Chevron Isocracking technology, which is based on a sulfided supported base-metal catalyst that was designed for crude oil conversion. The operating conditions of the hydrocracker are also more severe (>350°C, 7 MPa) than those required by the SMDS process (300-350°C, 3-5 MPa). Only intermediate products are produced (Table 18.13),5 with the naphtha slated as cracker feed and the distillate as blending component for diesel fuel. 

The selection of Co-LTFT synthesis, the associated refinery design, and the product slate for Oryx GTL all mimicked the SMDS process. Likewise, no provision has been made for the upgrading of short-chain olefins or oxygenates. 

Unlike the SMDS process, the refining technology selection did not specifically cater to the properties of LTFT syncrude.10... 

LTFT syncrude is more difficult to refine to on-specification transportation fuels, but has become almost synonymous with distillate production from Fischer-Tropsch-based GTL conversion. In this application the SMDS process has been the trailblazer. However, there are two potential misconceptions that should be pointed out. First, Fischer-Tropsch distillate produced from LTFT syncrude is... 

It is of interest to analyze the paradigm shift caused by the SMDS process in context of the original Shell design objectives (refer to Section 18.8) and the current situation. 

The design objectives for the SMDS process were developed to exploit small or remote gas fields where the cost of liquefied natural gas production or a gas pipeline system is not warranted. In many of the present GTL applications this is not... 

It will be interesting to see whether the GTL trend started by the SMDS process will continue. The inclusion of lubricating oil production as part of the Pearl GTL design indicates that it may not. In a related field there also seems to be movement. In oil sands processing, where the product traditionally had been a synthetic crude oil that was sold for refining elsewhere, there seems to be increasing interest in adding value to the product.71... 

Schrauwen, F. J. M. 2004. Shell Middle Distillate Synthesis (SMDS) process. In Handbook of petroleum refining processes, ed. R. A. Meyers, 15.25—40. New York McGraw-Hill. 

Shell materials. See also Microencapsulation biodegradable, 76 441-442 types of, 76 439t water-soluble, 76 456-457 Shell Middle Distillate Synthesis (SMDS) process, 6 778, 829... 

Consecutively, the heavy paraffins are cracked into lighter hydrocarbon fractions by hydro-cracking. For example, for the Shell Middle Distillate Synthesis (SMDS) process, the liquid product stream is composed of 60% gasoil (diesel), 25% kerosene and 15% naphtha. The gaseous product mainly consists of LPG (a mixture of propane and butane) (Eilers et al., 1990). Figure 7.3 shows a simplified diagram comprising all process steps to produce synthetic hydrocarbons from biomass, natural gas and coal. 

The SMDS process, as shown in Figure 12.15, produces high-quality diesel fuel from natural gas. Although synthesis gas generated from coal gasification would, presumably, be equally suitable, it is a process being considered in many GTL processes in oil production. 

A description is given of the Shell Middle Distillate Synthesis (SMDS) process. In this two-stage process, which has been developed specifically for the production of middle distillates, a liquid product is obtained which consists typically of naphtha, kerosine and gasoil in the ratios 15 25 60 to 25 50 25. 

The low-density products manufactured in the SMDS process are predominantly paraffinic and free from impurities such as nitrogen and sulphur. Both the kerosine and gas oil have excellent combustion properties (smoke point and cetane number), and their cold-flow characteristics meet all relevant specifications - even the stringent freezing point requirements of aviation turbine kerosine. They also make excellent blending components for upgrading low-quality stock that would otherwise have to be used in fuel oil. The excellent quality of the products was proved in extensive engine tests. 

The two-stage concept of the SMDS process provides considerable flexibility with regard to the product slate i.e. product yields can be varied as illustrated in Fig. 4, whilst all relevant product specifications can be met or will be exceeded (Table 3). Alternative outlets for SMDS products are, for instance, as paraffinic solvents and as feed material for XHVI (extra high viscosity index) luboils. 

A number of catalysts have been examined and optimized, leading to the development of proprietary Shell catalysts both for the selective production of heavy wax in the first stage of the SMDS process or for the direct production of syncrude. For the hydroconversion of heavy wax a totally different catalyst has been developed. 

In the Shell Middle Distillates Synthesis (SMDS) process starting from natural gas, the reactor configuration chosen for the first commercial unit in Malaysia, successfully commercialized in 1993, is the multi-tubular downflow trickle bed with catalyst inside the tubes (Sie et al., 1991) see Fig. 30e. Because of the enormous exothermicity of the synthesis reaction and the relatively poor heat transfer an extremely large heat transfer area is required. The reactor volume is largely governed by the installable heat transfer area in a vessel of given volume. Use of the multi-tubular three-phase fluidized bed or slurry reactor (see Fig. 30k and 301) provides much better heat transfer characteristics (an improvement of a factor of five over fixed bed units) and could lead to considerably lower reactor volumes. However, the anticipated scale-up problems with three-phase... 

Engineering aspects of the SMDS process are reviewed here. They include the manufacture of synthesis gas, the production of paraffinic Fischer-Tropsch waxes and the control of the chain length distribution by a selective hydrocracking step. The close interaction between the properties of the individual catalyst particles, the choice of the reactor technology and the overall process performance is discussed in detail. 

The Shell Middle Distillate Synthesis (SMDS) process has been developed with these considerations in mind. It produces high-quality middle distillates from natural gas via synthesis gas and a hydrocarbon synthesis/cracking step. In August 1989, it was announced that the world s first commercial SMDS plant will be built in Bintulu in Sarawak, Malaysia, and that it will come on stream in the last quarter of 1992. 

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