Reactor slurry bubble column

FT synthesis. The multishaft bubble column reactor (type D) has also been utilized for the FT synthesis or at least one of the shafts of 6 inch diameter has been utilized by Exxon. Several laboratory-scale bubble column reactors with static mixers have been evaluated for the FT synthesis at the laboratory scale. 

The slurry-phase methanol process has been developed and commercialized [62-64]. Deckwer has published a major treatise on bubble column reactors [65]. Saxena [66] reviewed the use of bubble column reactors for FTS. A review of more recent studies has been presented [67]. The reader is referred to these for the description of reactor details. In the following, only brief accounts will be given for some of the major topics. 

The US DOE had a major effort to understand the many variables affecting the performance of a bubble column reactor. Dudukovic and Toseland [75] outlined the cooperative study by Air Products and Chemicals (APC), Ohio State University (OSU), Sandia National Laboratory (SNL), and Washington University in St. Louis (WU). The efforts of this group have developed valuable unique experimental techniques for the measurement of gas holdup, velocity, and eddy diffusivities in bubble columns. They have obtained data that allows improved insight in churn-turbulent flow and have assessed the impact of various effects (internals, solid concentration, high gas velocity, pressure, etc.). General ideal flow pattern-based models do not reflect bubble column reality to date the models are based on a combination where some parameters are evaluated from first principles and some from the database. 

The internals of the bubble column reactor may have a dramatic impact on the flow patterns of the bubbles and the liquid. Companies have not divulged details about the internals to date. Some details of the US DOE pilot plant (22.5 inch 0.57 m diameter) have been published [ 106]. In this report the dimensions of the cooling tubes, their location, and their number are provided. These cooling coils occupied about 10% of the total volume of their commercial reactors slurry volume. The gas holdup and bubble characteristics as well as their radial profiles were determined in a column that was about the size of the US DOE reactor [107-109]. Dense internals were found to increase the overall gas holdup and to alter the radial gas profile at various superficial gas velocities. The tube bundle in the column increased the liquid recirculation and eliminated the rise of bubbles in the wall region of the column. These results indicate that further studies of bubble column hydrodynamics are directed toward larger scale units equipped with heat exchange tubes. 

The fate of bubbles in the slurry reactor is a complex issue since they undergo formation and breakup [110, 111]. Single-bubble and two-bubble models have been evaluated [112]. Two models for the churn-turbulent flow regime were developed, and a comparison indicated that increasing reactor 

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Two basically different reactor technologies are currently in operation low temperature and high temperature. The former operates at -220 °C and 25-45 bar, employing either a multitubular, fixed bed (i.e. trickle bed) reactor or a slurry bubble column reactor with the catalyst suspended in the liquid hydrocarbon wax product. 

The development of three-phase reactor technologies in the 1970 s saw renewed interest in the synthetic fuel area due to the energy crisis of 1973. Several processes were developed for direct coal liquefaction using both slurry bubble column reactors (Exxon Donor Solvent process and Solvent Refined Coal process) and three-phase fluidized bed reactors (H-Coal process). These processes were again shelved in the early 1980 s due to the low price of petroleum crudes. 

Saxena, S. C., Rosen, M., Smith, D. N., and Ruether, J. A., Mathematical Modeling of Fischer-Tropsch Slurry Bubble Column Reactors, Chem. Eng. Comm., 40 97 (1986)... 

Toseland, B. A., Brown, D. M., Zou, B. S., and Dudukovi..M., Flow Patterns in a Slurry-Bubble-Column Reactor Conditions, Trans. Inst. Chem. Engrs., 73 297 (1995)... 

Gruver, V., Young, R., Engman, J., and Robota, H. J. 2005. The role of accumulated carbon in deactivating cobalt catalysts during FT synthesis in a slurry-bubble-column reactor. Prepr. Pap.-Am. Chem. Soc. Div. Pet. Chem. 50 164—66. 

A continuous cross-flow filtration process has been utilized to investigate the effectiveness in the separation of nano sized (3-5 nm) iron-based catalyst particles from simulated Fischer-Tropsch (FT) catalyst/wax slurry in a pilot-scale slurry bubble column reactor (SBCR). A prototype stainless steel cross-flow filtration module (nominal pore opening of 0.1 pm) was used. A series of cross-flow filtration experiments were initiated to study the effect of mono-olefins and aliphatic alcohol on the filtration flux and membrane performance. 1-hexadecene and 1-dodecanol were doped into activated iron catalyst slurry (with Polywax 500 and 655 as simulated FT wax) to evaluate the effect of their presence on filtration performance. The 1-hexadecene concentrations were varied from 5 to 25 wt% and 1-dodecanol concentrations were varied from 6 to 17 wt% to simulate a range of FT reactor slurries reported in literature. The addition of 1-dodecanol was found to decrease the permeation rate, while the addition of 1-hexadecene was found to have an insignificant or no effect on the permeation rate. 

Oukaci, R., Singleton, A.H., and Goodwin Jr., J.G. 1999. Comparison of patented Co F-T catalysts using fixed-bed and slurry bubble column reactors. Appl. Catal. A 186 129 14. 

AGC-21 A process for converting natural gas to liquid fuels in three stages generation of syngas in a fluidized bed, Fischer-Tropsch synthesis in a slurry bubble column reactor, and hydrocracking. Piloted in 1997 and proposed for installation in Qatar. 

GTSC [Gas to syncrude] A process for converting natural gas to a synthetic crude oil which may be mixed with natural crude oil and used in conventional oil refineries. Based on F-T technology, but using a proprietary slurry bubble column reactor with a promoted cobalt catalyst. Developed by Syncrude Technology, Pittsburgh, PA, in the 1990s. 

Slurry Bubble Column Reactors (SBCR) This reactor is tubular (Figure 3.12). The liquid is agitated by means of dispersed gas bubbles. Gas bubbles provide the momentum to suspend the catalyst particles. The gas phase flows upward through the reactor at a constant rate. This reactor could be of continuous type or of semibatch type. This type is used only in catalysis. 

There are two types of slurry reactors slurry bubble column reactor (SBCR, Figure 3.25) and agitated slurry reactor (ASR, Figure 3.26). These reactors differ in that the solid... 

Figure 3.25 Slurry bubble column reactor (SBCR)...

In the common case, in slurry bubble column reactors, the catalyst phase remains in the reactor while the liquid phase could remain in the reactor with a continuous flow of gas (semibatch operation). Both gas and liquid could be in plug flow or could be well mixed. 

The most important applications of slurry bubble column reactors ... 

Finally, the relationship between the several rate expressions for slurry bubble column reactors is (see Section 3.1.1 for derivation)... 

The hydrodynamics of bubble columns and slurry bubble column reactors depend strongly on the flow regime (Figure 3.27). There are three flow patterns that prevail in these reactors (Wallis, 1969 Shall et al., 1982) ... 

For maximum utilization of the solid phase in a bubble column, it is essential that all particles be suspended in the reactor (Ramachandran and Chaudhari, 1984). This means that the gas velocity should be sufficiently high to enable suspension of all solids in the liquid. In slurry bubble column reactors, two suspension states exist ... 

This equation has been also proposed for slurry bubble column reactors and has been derived for water-air and glycol-air systems 0.003 < usG < 0.4, 0 < msL < 0.44 m/s. SI units should be used in this equation. 

In this case, the model equations derived for the slurry bubble column reactor are applicable. Note that if the gas-phase concentration is constant, the gas-phase material balance is not needed (where the two reactors have different model equations). 

In the following sections, the solutions of the models as well as various examples will be presented for the case of slurry bubble column reactors. 

Here, it has to be noted that for calculating the Peclet number in fixed beds, the actual velocity has to be used, i.e. the interstitial velocity, which influences the degree of mixing. In slurry bubble column reactors, the real velocity of the fluid is the bubble velocity, which is much higher than the gas superficial velocity. The mean bubble rise velocity for a batch liquid is (eq (3.201))... 

Behkish, A., Hydrodynamic and Mass transfer parameters in large-scale slurry bubble column reactors, PhD Thesis, University of Pittsburgh (2004)... 

Comparison between mechanically stirred reactors and slurry bubble column reactors [71... 

Slurry Bubble Column Reactors As in the case of gas-liquid slurry agitated reactors, bubble column reactors may also be used when solids are present. Most issues associated with multiphase bubble columns are analogous to the gas-liquid bubble columns. In addition, the gas flow and/or the liquid flow have to be sufficient to maintain the solid phase suspended. In the case of a bubble column fermenter, the sparged oxygen is partly used to grow biomass that serves as the catalyst in the system. Many bubble columns operate in semibatch mode with gas sparged continuously and liquid and catalyst in batch mode. 

Bubble Behavior in a Slurry Bubble Column Reactor Model... 

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