External circulation reactor system

In the external circulation reactor system, it introduces small amounts of fresh feed Fo continuously, and at the same time, small amounts of gas after reaction is expelled from the outlet of the reactor allowing the system to maintain constant pressure. If the volume of circulation is Fr, the mole fraction of the B-component in Fo is yo, is the mole fraction of B into the catalytic bed (Fq - - Fr), and yp is for the outlet, the material balance equation (7.13) can be obtained ... 

Table 1 shows a number of aerobic fermentation systems which are schematically classified into (i) internal mechanical agitation reactors, (ii) external circulation reactors, and (Hi) bubble column and air-lift loop reactors. This classification is based on both agitation and aeration as it relates to oxygen supply. In this table, reactor 1 is often used at the industrial level and reactors (a)2, (b)2, (c)2, and (c)3, can be fitted with draught tubes to improve both mixing and oxygen supply efficiencies. 

For purposes of illustration an external circulating 40 system for the coolant is shown in Fig. 4, wherein water, as the coolant, after passing through the reactor 25 and extracting heat, is treated and filtered and then passed in heat exchange relationship with a secondary coolant and finally is recirculated through the reactor. 

The reaction takes place at low temperature (40-60 °C), without any solvent, in two (or more, up to four) well-mixed reactors in series. The pressure is sufficient to maintain the reactants in the liquid phase (no gas phase). Mixing and heat removal are ensured by an external circulation loop. The two components of the catalytic system are injected separately into this reaction loop with precise flow control. The residence time could be between 5 and 10 hours. At the output of the reaction section, the effluent containing the catalyst is chemically neutralized and the catalyst residue is separated from the products by aqueous washing. The catalyst components are not recycled. Unconverted olefin and inert hydrocarbons are separated from the octenes by distillation columns. The catalytic system is sensitive to impurities that can coordinate strongly to the nickel metal center or can react with the alkylaluminium derivative (polyunsaturated hydrocarbons and polar compounds such as water). 

Three-phase reactor systems are ideally suited for methanol production because of the ability to provide intimate contact between the gaseous phase reactants and the solid phase catalysts and to remove the large amounts of heat created by the high heats of reaction. In the three-phase system, an inert liquid phase circulates between the reactor and an external... 

Many circulating systems are characterized by an external cyclone return system that usually has as large a footprint as the reactor itself. The axial solids density profile is relatively flat, as indicated in Fig. 17-6. There is a parabolic radial solids density profile that is termed core... 

The second heat removal system is an independent cooling system (ICS), which includes, besides a part of primary and secondary circuit equipment, a loop separator-cooling condenser with natural circulation. Via this loop the heat is removed to the intermediate circuit water. This system ensures independent (from the turbine generator systems) reactor cooling and independent reactor plant operation at a constant power level up to 6 % N om at the nominal steam pressure. In case of total RI de-energizig the system ensures cooling of the reactor over several days. Connection/disconnection of ICS is realized with no operator action and without using external power supply systems. 

It was found during studies of ammonia synthesis on iron that the incorporation of a condenser downstream of the sample valve in the external circulation loop of the HPLP apparatus (Fig. 7), enabled the system to be run as a flow rather than a batch reactor. This is true for any reaction system where the reactants are more volatile than the products, since the condenser temperature can be adjusted to trap the products almost exclusively, allowing a nearly pure stream of reactants to impinge on the catalyst. In the case of ammonia synthesis, (where, next to the product, nitrogen at a partial pressure of 5 atm was the most condensable species) a slurry of isopentane (— 159.9 °C) was found to be the ideal condenser medium. During a study of rhenium-catalyzed ammonia synthesis the isopentane condenser was switched in periodically to reduce the ammonia partial pressure to below that at which it appeared to poison the catalyst. In this way, the rhenium was able to produce ammonia in excess of the amount usually leading to poisoning. 

In recent years, the term circulating fluidized bed has also been used for liquid-solid systems and gas-liquid-solid (three-phase) systems. These are treated in Chapters 26 and 27. However, the predominant interest in CFB systems continues to be for gas-solid (two-phase) systems, and we restrict this chapter to this case. Some mention is also made in the literature of internally circulating fluidized beds where the particles circulate around one or more loops within a main reactor space or vessel. This chapter deals principally with gas-solid systems where solids recirculate through an external solids flow system, usually involving one or more eyelones, a standpipe, and a valve or seal, either non-meehanieal (e.g., L-valve or loop seal see Chapter 21) or meehanical (e.g., slide valve). 

Non-gradient reactor. Non-gradient reactors have many different names and types, and can be roughly divided into external circulation, internal circulation and continuous stirred kettle -style by the gas flowing mode. However, it is necessary to achieve the flow phase with constant temperature and ideal mixing, and the elimination of mass transfer resistance between phases in reactor. At the same time, on the premise of elimination of the gradient of temperature and concentration, it should be the same that the reaction rate equation is obtained from the circulation flow system or the ideal hybrid system. 

Primary sodium is circulated in the reactor by four electromagnetic (EM) pumps. These pumps are self-cooled by the pumped sodium. This results in higher temperature for the electrical insulation material than for an arrangement with an external gas cooling system. However, suitable ceramic and mica-based materials have been developed and qualified for a life expectancy in excess of 30 years. The self-cooled EM pump simplifies the head... 

Different technical solutions are used in the temperature control of industrial reactors. The heat carriers mentioned in Section 9.2.f may be used by different technical means the direct way whereby the heat carrier is directly mixed with the reaction mass, internal or external coils, jacket, simple circuits, and indirect systems with a double circulating system. These techniques with their advantages and drawbacks, in terms or process safety, are reviewed in the following sections. 

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