Coils, heat transfer

Heat evolution is 0.94 to 1.10 kcaJ/(kg oil)(unit drop of IV) (1.69 to 1.98 Btu/[lbm oil][unit drop of IV]). Because space for heat-transfer coils in the vessel is limited, the process is organized to give a maximum IV drop of about 2.0/min. The rate of reaction, of course, drops off rapidly as the reaction proceeds, so a process may take several hours. The end point of a hydrogenation is a specified IV of the prod-... 

Heat Transfer Coils in Tank, Liquid Agitated... 

Figure 10-160. Platecoils on tank walls and cone bottoms. Note See Figure 10-163 for use of heat transfer mastic between vessel and heat transfer coils/plates. (Used by permission Bui. 5-63, 1994. Tranter , Inc..)...

In considering heat transfer in gas-solid fluidization it is important to distinguish between, on the one hand, heat transfer between the bed and a heat transfer surface (be it heated bed walls or heat transfer coils in the bed) and, on the other hand, heat transfer between particles and the fluidizing gas. Much of the fluidization literature is concerned with the former because of its relevance to the use of fluidized beds as heterogeneous chemical reactors. Gas-particle heat transfer is rather more relevant to the food processing applications of fluidization such as drying, where the transfer of heat from the inlet gas to the wet food particle is crucial. 

As this trend levels off with larger columns, it is recommended that values estimated for a 60 cm column are used. If heat transfer is a problem, then heat transfer coils within the column, or even an external heat exchanger, may become necessary when operating a large, industrial bubble column-type fermentor. Scale-up of an internal loop airlift-type fermentor can be achieved in the same way as for bubble column-type fermentors for external loop airhfts see Section 7.7. 

LMTD. This mode is equivalent to an internal heat transfer coil where the temperature driving force is a log-mean average of the differences between the reactor temperature... 

FIGURE 9 Sectional view of a stirred-tank reactor/heat exchanger with both an external jacket and internal heat transfer coils. 

Although, as shown in this monograph, mechanical agitation is provided in a number of different ways, the most common method is by a stirrer in a standard vessel. In many mechanically agitated reactors, the vessel contains internals such as baffles (particularly for low-viscosity fluids), feed and drain pipes, heat transfer coils, and probes (e.g., thermometers or thermocouples, pressure transducers, level indicators). The degree of mixing and power requirement depend on the nature of the internals present in the vessel. 

The entire pilot-scale installation consists of a coal combustor, cyclone separator, two heat exchangers, scrubber, regenerator, and exhaust fan. The scrubber and regenerator are equipped with heat-transfer coils, and all equipment in contact with the scrubber liquid is made of stainless steel. Gas-sampling ports are installed upstream and down-... 

Inhomogeneity in supersaturation has a similar effect on encrustation, also a strong function of supersaturation. Small high supersaturation zones may be the trigger to initiate encrustation, which then may spread to cover a much broader area of the crystallizer wall. In this case, a local cold spot on a wall or at the entrance of a heat transfer coil may be where the supersaturation becomes higher locally. 

Costs of Fluidization Systems. Published cost information on these systems is lacking. As a method of approach for preconstruction cost estimation of installed fluidization equipment, use the cost figures from Fig. 6-28 for the reactor, increasing these by 35 per cent if heat-transfer coils or jacketing is required. Add to this the cost of a dust-collection system of the required gas-handling capacity as obtained from Fig. 6-4. 

Further, plan a process in which the reaction is to be carried out with a charge of 5000 pounds of benzene in a vessel equipped with internal heat-transfer coils and with sufficient surface area to satisfy an allowable temperature rise of 10°C. Cooling water is available at 20°C. In the reactor the heat-transfer area is 300 ft, and an overall heat-transfer coefficient of 200 Btu/ft -h-°F can be maintained. The reaction is to be carried out at 40° C, and under these conditions the nitrie acid dissolved in the organic layer may be neglected. The acid is to be fed at a constant rate such that if it were all converted the limiting heat-removal rate would not be exceeded. 

AIR HANDLER - The fan blower, heat transfer coil, filter, and housing parts, of a system. 

Water circulation in the heat transfer coils takes place by natural convection currents as it gets heated up due to the heat given by the hot gases. No pump is required for this purpose and hence the power consumption is very low. 

Four primary reactor auxiliary cooling systems (PRACS) are used A cooling coil is installed in the inlet plenum of each IHX and a heat transfer coil is installed in the mr cooler of ultimate heat sink Coolant is circulated by EM pumps supported by emergency AC power The air cooler consists of a blower, a stack, vanes and dampers The blower is supported by the emergency AC power The vanes and the dampers are operated by the emergency DC power Decay heat removal by natural circulation is possible to mitigate a total blackout event (loss of all AC power)... 

The reactor, or Contactor, is basically a special type of a continuous-flow stirred tank reactor, as shown in Figure 1 (6). It is a cylindrical vessel positioned horizontally in which the acid/hydrocarbon dispersion is repeatedly circulated over and around heat transfer coils (tube bundle). The impeller employed to promote the dispersion of the feed mixture of isobutane and olefins in the acid phase is located at one end of the reactor. The impeller causes the dispersion to enter the annular region between the shell of the reactor and the tube bundle the dispersion flows rapidly in this region, which extends over most of the length of the reactor. As the dispersion reaches the exit end of the annulus, a small portion of the dispersion is withdrawn and fed to the decanter, which is discussed later. The remainder of the dispersion leaving the annular region makes a 180° turn at the end of the reactor and flows back toward the impeller. As it returns, the dispersion passes over and around U-shaped heat transfer coils that remove the exothermic heats of reaction and the energy added to the reactor by the impeller. 

Manipulated variables These input variables are adjusted dynamically to keep the controlled variables at their setpoints. There are two manipulated variables in Fig. 18.49, namely, the exit flow rate Wc and the steam pressure Pj to the heat transfer coil in the tank. 

That vapor is cooled as it passes through a zone botmded by cold thermal coils arotmd the walls of the degreaser. At and near the cooler walls, solvent condenses into droplets, some of which are collected in a trough (channel) beneath the cold heat transfer coils. External to the degreaser, liquid from the trough drains into a receiver, from which it is recycled to the rinse sump (perhaps through a water separator). 

Above the cold heat transfer coils, cooled solvent vapor is heavier than the ambient air above it, and no longer rises to penetrate the air. 

At locations far from the walls where the cold heat transfer coils are located, the solvent vapor is less cooled. So, it can continue to rise further. The result is that the shape of the vapor cloud is bulged upward at its center — farthest from the walls. Figure 1.4 is a diagram of this situation. 

An important quantity in the design of bubbling-bed reactors containing internal heat transfer coils is the bed expansion ratio, 8. A model for 8 in terms of a dimensionless drag force, F, was developed by Lofstrand et al. (1995) and compared with experimental work carried out with the pressurized unit at Chalmers University and an atmospheric pressure fluidized bed boiler fitted with bed internals. The bed expansion ratio is defined as... 

The heat transfer coefficient between the fluidized bed and the immersed heat transfer coils (the... 

Calcium carbonate is usually added during the batch fermentation to control the pH, and the highest concentration of lactic acid (12-15 %) is limited by the precipitation of calcium lactate from the broth. Temperature control is maintained with heat transfer coils using circulating water, and the cells are retained in a mixed suspension by mechanical agitators or... 

Most actual reactors deviate from these idealized systems primarily because of nonuniform velocity profiles, channeling and bypassing of fluids, and the presence of stagnant regions caused by reactor shape and internal components such as baffles, heat-transfer coils, and measurement probes. Disruptions to the flow path are common when dealing with heterogeneous systems, particularly when solids are present. To model these actual reactors, various regions are compartmentalized and... 

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