Entrained-flow reactor

The principal advance ia technology for SASOL I relative to the German Fischer-Tropsch plants was the development of a fluidized-bed reactor/regenerator system designed by M. W. Kellogg for the synthesis reaction. The reactor consists of an entrained-flow reactor ia series with a fluidized-bed regenerator (Fig. 14). Each fluidized-bed reactor processes 80,000 m /h of feed at a temperature of 320 to 330°C and 2.2 MPa (22 atm), and produces approximately 300 m (2000 barrels) per day of Hquid hydrocarbon product with a catalyst circulation rate of over 6000 t/h (49). 

The company Noell in Germany, currently owned by Future Energy GmbH, has developed a down-fired entrained flow reactor (EFR). Instead of burners at the side of the reactor, this gasifier only consists of a single burner in the top part, which results in a simpler and lower cost reactor. Also, the control of this single burner is easier than the former types mentioned with a resulting lower capital and operational cost related. 

This study shows that limited oxidation at 373 K or weathering (ambient) of coal feedstock reduces the thermoplastic properties of a coal This is manifest as a transformation in char type, from cenospheres to inertoids, at high rates of heating (10 -10 K s" ) in an Entrained Flow Reactor at 1273 K. The specific types of char are related to the chemical structure of the coal and an inverse relationship exists between the occurrence of cenospheric chars and the atomic 0/C ratio of the oxidised or weathered coal from which they are derived... 

To study and examine the effects of oxidation at 373 K and weathering upon the morphology of associated chars and their physical and structural characteristics using an Entrained Flow Reactor at 1273 K. 

Figure 1. A Schematic representation of the Entrained Flow Reactor apparatus.

Entrained flow reactor (riser) This is a fluidized-bed reactor in which the solid is entrained by the fluid phase and is recycled throughout the operation (Figure 3.9). Some applications of this reactor type are the modem FCC process and the calcination of alumina hydrate. 

In a suspended bed or entrained flow reactor technology, the coal is crushed, dried, and then pulverized to fine powder in a crusher and mill. As Table 9.1 shows, the coal particles used in entrained flow reactors are very small. The pulverized coal is transported with air to the furnace (primary air), and secondary air is heated and fed into the combustor to ensure complete combustion. The residence time of the coal in the furnace is typically around 1-2 s, which usually suffices for complete combustion. However, not all coal burns completely, and fly ash will be generated (see Table 9.1). 

Table 1 compares the fluidized-bed reactor with alternative gas-solid reaction systems, i.e. fixed-bed, moving-bed, and entrained-flow reactors. 

In order to achieve rapid heating of the biomass, it should be finely ground. The particle size of the biomass is dependent on the reactor type used. In particular, it was reported [17] that ablative reactors can pyrolyze large-size feedstocks, whereas the fluidized beds require smaller (below 3 mm) particles [16]. The difference is due to lower heat transfer through conduction in the fluidized beds, which is even lower in the entrained flow reactor, being in the range of 4% [17],... 

Existing entrained-flow reactors with solid particle flow can be retrofitted with monoliths in which the channel structure also works as a flow straightener, providing better plug-flow characteristics in large-diameter entrained-flow reactors, which suffer from backmixing of catalyst at the reactor wall (53-55). 

The entrained flow reactor utilized in this study is virtually the same unit described by Scaroni et al. ( ). In order to improve knowledge about, and control of, the time-temperature history of the coal particles, modifications have been made to the reactor and to the predictions of the time-temperature history of particles in the reactor (9,10). 

A schematic diagram of the entrained flow reactor is shown in Figure 1. At the top of the reactor, a screw feeder and semi-venturi system is used to entrain the ground coal particles in the cold primary gas stream. The coal is then injected into the reactor where it is entrained in, and heated by, the preheated secondary gas. The pyrolyzing coal particles fall in a thin stream through the reactor and are collected by a movable water-cooled collector probe. The time which the particles spend in the reactor is controlled by moving the collector probe up and down the reactor axis. The pyrolysis reactions are rapidly quenched in the collector probe, and the particles are separated from the gas stream by a cyclone in the collection system. 

Figure 2. Weight loss in entrained flow reactor in (1173 K) acid washed (A.W.) Montana lignite, raw and calcium exchanged (Cal) lignite, 270 x 400 mesh.

TABLE IV. Effect of Cations on Maximum Weight Loss in Entrained Flow Reactor 1173 K, DICF Basis... 

In order to determine the total pyrolysis yield, another technique was used. Basically, the approach involves capturing the py-rolyzing coal particles in a crucible at the maximum residence distance in the reactor. The captured samples are then held in the reactor for 10 minutes to complete pyrolysis. It is thought that this technique gives a reasonable estimation of the total pyrolysis yield possible in an entrained flow reactor. The results of this study can be seen in Table V in which weight loss values for extended... 

Kinetics of Total Weight Loss. The method chosen is a simple first order Arrhenius treatment in which a single overall activation energy is utilized. The technique has been applied to the kinetics of the initial weight loss, and therefore, the weight loss values were compared to the maximum weight loss in the entrained flow reactor. 

TABLE VII. Tars Released in Entrained Flow Reactor... 

Figure 1. Schematic diagram of entrained-flow reactor and ancillary equipment.

The entrained flow reactor is usually used for biomass, but can be used for mixed plastics. A stoichiometric air-propane burner produces the inert hot flue gas that flows upwards through the vertical reactor and entrains the particles while heating. The Georgia Institute of Technology has developed an entrained flow reactor for biomass (6.4 m height. 

---