Cooling batch operation

The main features in which the Radford process differs from the batch operation are in thermal dehydration and compounding. Water-wet nitrocellulose on a continuous vacuum belt filter is vacuum-dried followed by hot air transfusion (80°C) to reduce the moisture to less than 2%. After cooling, alcohol is sprayed on the nitrocellulose to a concentration of 15—20%. The alcohol-wet nitrocellulose is then transferred from a surge feeder to a compounder by a continuous weigh-belt along with the other ingredients of the composition, which are also weighed and added automatically. 

In a typical batch operation, carbon disulfide is added to four molar equivalents of 25—30 wt % aqueous ammonia in a stirred vessel, which is kept closed for the first one to two hours. The reaction is moderately exothermic and requires cooling. After two to three hours, when substantially all of the disulfide has reacted, the reaction mixture is heated to decompose dithiocarbamate and trithiocarbonate and vented to an absorption system to collect ammonia, hydrogen sulfide, and any unreacted carbon disulfide. 

Batch Crystallization. Crystal size distributions obtained from batch crystallizers are affected by the mode used to generate supersaturation and the rate at which supersaturation is generated. For example, in a cooling mode there are several avenues that can be followed in reducing the temperature of the batch system, and the same can be said for the generation of supersaturation by evaporation or by addition of a nonsolvent or precipitant. The complexity of a batch operation can be ihustrated by considering the summaries of seeded and unseeded operations shown in Figure 19. 

Applications One typical apphcation in heat transfer with batch operations is the heating of a reactor mix, maintaining temperature during a reaction period, and then cooling the products after the reaction is complete. This subsection is concerned with the heating and cooling of such systems in either unknown or specified periods. 

Equivalent-Area Concept The preceding equations for batch operations, particularly Eq. 11-35 can be appliedforthe calculation of heat loss from tanks which are allowed to cool over an extended period of time. However, different surfaces of a tank, snch as the top (which would not be in contact with the tank contents) and the bottom, may have coefficients of heat transfer which are different from those of the vertical tank walls. The simplest way to resolve this difficulty is to nse an equivalent area A in the appropriate equations where... 

Heating or cooling of process fluids in a batch-operated vessel is common in the chemical process industries. The process is unsteady state in nature because the heat flow and/or the temperature vary with time at a fixed point. The time required for the heat transfer can be modified, by increasing the agitation of the batch fluid, the rate of circulation of the heat transfer medium in a jacket and/or coil, or the heat transfer area. Bondy and Lippa [45] and Dream [46] have compiled a collection of correlations of heat transfer coefficients in agitated vessels. Batch processes are sometimes disadvantageous because ... 

Fixing the rate of heat transfer in a batch reactor is often not the best way to control the reaction. The heating or cooling characteristics can be varied with time to suit the characteristics of the reaction (see Chapter 14). Because of the complexity of batch operation and the fact that operation is usually small scale, it is rare for any attempt to be made to recover heat from a batch reactor or supply heat by recovery. Instead, utilities are normally used. 

When the charging rate (semi-batch) or the mass of reactant added in one step (batch) or the continuous feed ratios get out of phase, the heat generation may be larger than expected. This results in difficulties in the transfer of the heat generated, especially in cases where the cooling capacity has a limited safety margin Also, it can lead to accumulation of reactant in a semi-batch operation. 

Phosphoms trichloride is manufactured by loading liquid phosphoms into a jacketed batch reactor. Chlorine is bubbled through the liquid, and phosphoms trichloride is refluxed until aU the phosphoms is consumed. Cooling water is used in the reactor jacket and care is taken to avoid an excess of chlorine and the resulting formation of phosphoms pentachloride. Phosphoms oxychloride is manufactured by the reaction of phosphoms trichloride, chlorine, and solid phosphoms pentaoxide in a batch operation. Liquid phosphoms trichloride is loaded to the reactor, solid phosphoms pentoxide added, and chlorine bubbled through the mixture. Steam is... 

A fermentation broth contained in a batch-operated stirred-tank fermentor, 2.4m in inside diameter D, is equipped with a paddle-type stirrer of diameter (L) of 0.8 m that rotates at a speed Af = 4s -. The broth temperature is maintained at 30 °C with cooling water at 15°C, which flows through a stainless steel helical coil that has a 50 mm outside diameter and is 5 mm thick. The maximum rate of heat evolution by biochemical reactions, plus dissipation of mechanical energy input by the stirrer, is 51000 kcal h , although the rate varies with time. The physical properties of the broth at 30 °C were density p = 1000 kg m " , viscosity p = 0.013 Pa s, specific heat Cp = 0.90 kcal kg °C , and thermal conductivity K = 0.49 kcal h m °C = 0.000136 kcals m °C . ... 

Liquid-Flow Rate Liquid flow rate is measured when a medium is fed into a biore-actor in continuous and fed-batch operation. The flow rate of cooling water is also monitored in industrial bioprocessing plants. 

An epoxy compound is to be condensed with an amine at 40 °C. The reaction is fast and will be performed in a 4 m3 reactor cooled with water. The process is semi-batch operation, the solvent 800 kg isopropanol, 240 kg of the epoxy compound are initially charged, and 90 kg of amine are added at a constant rate during 45 minutes, while the temperature is not allowed to surpass 40 °C. 

One important issue of the fed-batch operation is the variable volume of material in the reactor and its effect on heat transfer area. If jacket cooling is used, the heat transfer area covered by the liquid in the reactor will be proportional to the volume of the liquid at any point in time. However, if the reaction liquid is circulated through an external heat exchanger, the full heat transfer area is available throughout the batch cycle. 

Heat transfer in many systems occurs as a steady-state process, and the temperature at any point in the system does not vary with time. In other important processes, temperatures in the system do vary with time. This situation, which is common among the small-scale, batch-operated processes of the pharmaceutical and fine chemical industry, is known as unsteady heat transfer and, as warming or cooling occurs, the thermal capacity (i.e., the size and specific heat), of the system becomes important. Analysis of unsteady heat transfer is complex. 

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