Cocurrently circulated

After the SO converter has stabilized, the 6—7% SO gas stream can be further diluted with dry air, I, to provide the SO reaction gas at a prescribed concentration, ca 4 vol % for LAB sulfonation and ca 2.5% for alcohol ethoxylate sulfation. The molten sulfur is accurately measured and controlled by mass flow meters. The organic feedstock is also accurately controlled by mass flow meters and a variable speed-driven gear pump. The high velocity SO reaction gas and organic feedstock are introduced into the top of the sulfonation reactor,, in cocurrent downward flow where the reaction product and gas are separated in a cyclone separator, K, then pumped to a cooler, L, and circulated back into a quench cooling reservoir at the base of the reactor, unique to Chemithon concentric reactor systems. The gas stream from the cyclone separator, M, is sent to an electrostatic precipitator (ESP), N, which removes entrained acidic organics, and then sent to the packed tower, H, where SO2 and any SO traces are adsorbed in a dilute NaOH solution and finally vented, O. Even a 99% conversion of SO2 to SO contributes ca 500 ppm SO2 to the effluent gas. 

Compare quantitatively by digital simulation tbc dynamic performance of the three coolers sketched below with countercurrent flow, cocurrent flow, and circulating water systems. Assume the tube and shell sides can each be represented by four perfectly mixed lumps. 

Circulation systems with parallel and crossed cocurrent or countercurrent flow of the heat transfer medium (Fig. 16) arc commonly employed for liquid heat transfer media. The main part of the heat transfer medium is generally circulated with a high-capacity pump in order to achieve uniform heat exchange conditions. A partial stream is passed through a heat exchanger for supplying or removing the heat of reaction. The desired heat transfer medium temperature is at-... 

Figure 20 shows temperature profiles for three different ways of controlling the cooling stream in a partial oxidation reaction. If the coolant is circulated so fast that its temperature in the reactor scarcely changes, then its flow direction is irrelevant and a temperature profile with a pronounced temperature maximum becomes established this is typical for strongly exothermic reactions (Fig. 20A). If the coolant is circulated in cocurrent and its velocity is chosen so that it becomes noticeably hotter over its path, an almost isothermal temperature behavior can be achieved (Fig. 20B). This is because the reactive gas at the inlet is in contact with the coldest coolant and the cooling temperature rises in step with the consumption of the reactants, so that the reaction rate remains virtually constant over a fairly long section [33-35, 40],...

A significant advantage of nonisothcrmal control of the heat transfer medium in cocurrent or counter-current flow is the saving in circulation energy, since much smaller heat transfer medium streams must be circulated. Overall, the combination of several heat-transfer medium circuits (Fig. 16C) and the purposeful... 

Wei, F., Chen, W., Jin, Y., and Yu, Z. Axial solids mixing in cocurrent downflow circulating fluidized bed, in Proceeding of 5th National Meeting on Chemical Reaction Engineering (in Chinese), Tianjing (1993). 

Monolithic Loop Reactor A novel MLR was developed af Air Products and Chemicals (Figure 17) (144). The reactor contains a monolithic catalyst operating under cocurrent downflow condifions. Because the residence time in the monolith is short and the heat of reaction has to be removed, the liquid is continually circulated via an external heat exchanger until the desired conversion is reached. The concept was patented for the hydrogenation of dinifrofoluene fo give toluenediamine (37). 

The effect of liquid velocity can be qualitatively explained as follows. In the heterogeneous regime, liquid circulation is developed that is upward in the central region and downward in the annular region. With cocurrent liquid upflow, the downward annular flow is restricted, resulting into a reduction in the liquid circulation. Therefore, the cocurrent liquid flow delays the transition. The countercurrent liquid flow has the opposite effect. 

Yang, YL. (1991), Experimental and theoretical studies on hydrodynamics in cocurrent upflow and downflow circulating fluidized beds, PhD diss., Tsinhua University, Beijing, China. 

Gas flow and solids flow are usually cocurrent, one exception being a countercurrent flow spray dryer. The method of gas-solids contacting is best described as through-circulation however, in the dilute condition, solids particles are so widely dispersed in the gas that they exhibit apparently no effect upon one another, and they offer essentially no resistance to the passage of gas among them. 

The double pipe, cocurrent heat exchanger is used to cool a distillate product using cold water circulating through the jacket as illustrated in Fig. 2.3. The overall heat transfer coefficient is taken to be U and the mass flow of distillate and water is and Wq, respectively. Under turbulent flow conditions, the fluid temperatures are taken to be uniform across individual flow cross sections. Find the relationship to predict how steady-state temperature changes with axial position, and from this, deduce an expression to compute the average AT... 

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