Entrained Systems

An entrainment system (Fig. 3) uses finely sized coal particles blown into the gas steam prior to entry into the reactor and combustion occurs with the coal particles suspended in the gas phase the entrained system is suitable for both caking and noncaking coals. 

Fntrained Systems. In entrained systems, fine grinding and increased retention times intensify combustion but the temperature of the carrier and degree of dispersion are also important. In practice, the coal is introduced at high velocities which may be greater than 30 m/s and involve expansion from a jet to... 

Exploitation of Homogeneous Azeotropes Homogeneous azeotropic distillation refers to a flowsheet structure in which azeotrope formation is exploited or avoided in order to accomplish the desired separation in one or more distillation columns. The azeotropes in the system either do not exhibit two-hquid-phase behavior or the hquid-phase behavior is not or cannot be exploited in the separation sequence. The structure of a particular sequence will depend on the geometry of the residue curve map or distillation region diagram for the feed mixture-entrainer system. Two approaches are possible ... 

The simplest case of combining T E and LLE is the separation of a binaiy heterogeneous azeotropic mixture. One example is the dehydration of 1-butanol, a self-entraining system, in which butanol (117.7°C) and water form a minimum-boiling heterogeneous azeotrope (93.0°C). As shown in Fig. 13-69, the fresh feed may be added... 

Phase Diagram (Zenz and Othmer) Zenz and Othmer (op. cit.) have graphically represented (Fig. 17-2) all gas-solid svstems in which the gas is flowing counter to gravity as a function o pressure drop per unit of height versus velocity. Note that line OAB in Fig. 17-2 is the pressure-drop versus gas-velocity curve for a packed bed and BD the cui ve for a fluid bed. Zenz indicates an instability between D and H because with no sohds flow all the particles will be entrained from the bed however, if sohds are added to replace those entrained, system JJ prevails. The area DHJJ will be discussed further. 

Schibkr So the entrainment system becomes different after the animals are left in DD for a long time. 

The Entrained system is a high temperature, high reaction rate process in which coal, oxygen (or air) and steam combine rapidly to produce LBG or MBG. The commercial processes aim primarily at the use of oxygen. Several developmental processes use oxygen or air. The most widely used commercial process (Koppers-Totzek) is operated at atmospheric pressure. The Texaco partial oxidation process used with oil and gas is under development for use with coal. Shell and Koppers are developing a pressurized version of the current Koppers-Totzek process. The advantages of the entrained... 

The entrained systems are generally high oxygen consumers - almost double the requirement for the fixed bed units. Energy for oxygen production could be recovered from hot gasifier effluent gases if suitable waste heat boilers and superheaters can be developed. 

Additional work has been done using UV absorption measurements to quantify the clustering around solutes in solute/fluid/ entrainer systems 2, 16). The shift in the wavelength of maximum absorption is used to determine the local composition about the solute. This vicinity is shown to be enriched with the entrainer, especially in the highly compressible region nearest the critical point. 

To achieve the required rapid reaction in an entrained system, both a reactive fuel and a means for rapid heating are necessary. The volatile... 

Fig. 2.30. Experimental study of the effect of a (a) stochastic or (b-d) periodic variation of the substrate source on glycolytic oscillations in yeast extracts. The variation of the substrate input is indicated in black at the bottom of each panel. The entrained system oscillates with a period equal to the driving period in (b) and with a period equal to the triple of the external period in (c). In (d), the enzyme fails to be entrained by the external source and oscillates in an irregular (chaotic ) manner (Boiteux etoL, 1975).

In case of processes operating with catalyst systems where pulverized catalyst is circulated with the aid of a carrier liquid (liquid entrained system) or small-lump catalyst maintained in suspension in a liquid (liquid fluidized system), it is possible to transfer the reaction heat inside the reactor to the carrier liquid and to remove it outside of the reactor. The various means of temperature control inside and outside the catalyst chamber are schematically shown in Fig. 3.3. 

Fig.3.3a-d. Various types of methanol synthesis reactors, (a) Cold gas quench (b) cooling by evaporation - multistage, adiabatic (c) cooling by evaporation - tubular, near isothermal (d) liquid entrained system using heat carrier liquid... 

It is noted that nowadays the commercial market for AWJ systems is dominated by entrainment system, so developments related to these systems are considered in detail. 

For example, coal combustion may be achieved using pulverized coal in entrained systems or as sized particles in fixed or slowly moving beds larger pieces may, in certain instances, also be used. In the case of the fixed- or slowly moving bed combustor, it is usual to employ a mechanical stoker to feed the coal and a grate to support the coal particles as well as to admit air for the combustion process. With regard to the pulverized systems, coal that has been crushed to ca. 200 mesh is carried into the system entrained by the air. 

The occidental flash pyrolysis process originally called the Garrett process (Sass, 1974 Howard-Smith and Werner, 1976) (Figure 19.4) involves the pyrolysis of the feed coal particles at a temperature not in excess of 760°C (1400°F) in an entrained system to produce a liquid product, char, and gas. 

In the Schroeder process (Figure 19.19), pulverized, dry coal is hydrogenated at pressures and temperatures of approximately 500°C (930°F) and 2000 psi (13.8) in an entrained system in which the residence time of the feed coal is less than 1 min. The products are separated into light liquids (approximately 30%), heavy liquids (approximately 5%), char (5%), and gases (30%). The heavy liquids can be hydrotreated to produce further quantities of usable (light) liquids. The reaction may be accelerated by the use of ammonium molybdate (1% w/w) that has been impregnated on to the coal. 

---