Total batch cycle time

From diese various estimates, die total batch cycle time t(, is used in batch reactor design to determine die productivity of die reactor. Batch reactors are used in operations dial are small and when multiproducts are required. Pilot plant trials for sales samples in a new market development are carried out in batch reactors. Use of batch reactors can be seen in pharmaceutical, fine chemicals, biochemical, and dye industries. This is because multi-product, changeable demand often requues a single unit to be used in various production campaigns. However, batch reactors are seldom employed on an industrial scale for gas phase reactions. This is due to die limited quantity produced, aldiough batch reactors can be readily employed for kinetic studies of gas phase reactions. Figure 5-4 illustrates die performance equations for batch reactors. 

What we have found so far is the reaction time, the time needed for 90% of A to be converted to B. We have to add to this the time needed for emptying the reactor, repairing/maintaining and refilling it, what we will call operation time (5 h), in order to find the total batch cycle time 28 h. 

Since the initial volume, recovery, membrane area and flux parameters (m, b) are all constant and known or specified, the total batch cycle time is a function of the relative diafiltra-tion volume (Vo/Vd) only. The optimum can be determined by differentiating Equation (5) with respect to Ud and setting the result to zero, i.e. 

For a target value of Cp = 0.4 mol/L, structure 1 is required. The a policy begins with an exponential decline in sidestream addition to a time of approximately 1.536 s, followed by a period of standard batch reaction to termination. The total batch cycle time for this structure is thus 3.5 s. Theoretically, the correct a policy for this structure... 

For Cd = 0.3 mol/L, the recommended operating policy is structure 2. This structure is different compared to structure 1 in that three reaction periods are required. The batch cycle begins with a fed-batch period of constant a in accordance with the equilibrium CSTR concentration, given by point D. The cycle is then brought into a period of varying a, where the sidestream addition is observed to increase sharply to a maximum value of approximately 1.356 s and then completed with a standard batch period lasting approximately 9.24 s the total batch cycle time for this structure is thus roughly 15 s. 

Operating conditions. Optimization variables such as batch cycle time and total amount of reactants have fixed values for a given batch reactor system. However, variables such as temperature, pressure, feed addition rates and product takeoff rates are dynamic variables that change through the batch cycle time. The values of these variables form a profile for each variable across the batch cycle time. 

Typical lengths of cycles for food stuffs are 5-10 hr, for bacterial pellets 2-20 hr, and for biological fluids 20-50 hr. A production unit with capacity of 500 L may have 75 kW for refrigeration and 50 kW for heating. Conditions for the preparation of freeze dried coffee are preparation of an extract with 20-25% solids, freezing at —25—43°C, sublimation at approx. 200Torr to a final final moisture content of 1-3%, total batch processing time of 6-8 hrs. 

A plant operability analysis helps to establish the correct cycle time. In certain situations, the batch cycle of the entire plant is not determined by the units around the main reactor. Additional time may be needed downstream for product finishing in equipment that operates in series with the main reactor. The batch cycle time T is a composite of three contributions (1) the sum of the batch residence times t(i) in the M true batch units of the plant that operate in series (2) the sum of the residence times t(j) in the N semicontinuous trains of the plant that operate in series and (3) the sum of the downtimes t(k) in series encountered in the total batch cycle ... 

A proportional plus derivative pH controller can be used for pulse width and amplitude modulation to mimic the lab titrations where the drop size and frequency is decreased as the vessel pH approaches the end point. The pulse width and amplitude is proportional to the pH controller output. The pulse cycle time (lime between the start of successive pulses) is set equal to the system dead time, which increases the total dead time by 50%. A minimum pH controller output and hence pulse width and amplitude is selected that is a compromise between the need to minimize batch cycle time and prevent overshoot. 

The total cycle time for most production batches is 2.5—3.5 min, considerably shorter than the cold- or warm-coating processes. Although a few... 

Suppose reaction 12.3-1 is carried out in a batch reactor of volume V on a continual basis. To determine the rate of production, we must take into account the time of reaction (t in equation 12.3-2) and the down-time (td) between batches. The total time per batch, or cycle time, is... 

Alkanolamide from Coconut Oil. A 2 1 cocodiethanolamide (CDEA) can be produced using 6 moles of diethanolamine and 1 mole of rehned and bleached coconut oil. The materials are charged with the reactor and a small amount of catalyst (0.25-0.3% sodium methylate or sodium hydroxide) is added. The temperature of the batch is increased to 70-75°C at normal pressure. After 90 min, the reaction is completed. For a 10-t batch, total cycle time from charging the materials, heating them up, allowing the reaction to proceed to completion, and transferring the finished product takes at least 4 h. 

The total cycle time in any batch operation is considerably longer than the reaction time, as one must account for the time necessary to fill (t ) and empty (f,) the reactor together with the time necessaty to clean the reactor between batches, In some cases the reaction time calculated from Equation (4-5) may be only a small fraction of the total cycle time, t,. 

Production efficiency is another factor that should be considered when selecting a blender. The total cycle time from batch-to-batch must be considered, which includes time for loading, blending, sampling (if required), discharge, and cleaning (as required). 

Thus, the total cycle time for the batch reactor is 119.3 + 20 = 139.3 min = 2.322 hr. Therefore, 2.322 hr x 1250 kg/hr = 2902.5 kg of ester that must be produced in each reactor cycle. Since, in this example, the conversion and feed in. the batch reactor are the same as those in the previous illustration, the effluent concentration of the ester is again... 

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