Sizing of Process Vessels

Reactors must be sized during steady-state design. AU other vessels must be sized before going into dynamics. 

We must also calculate the size of the reflux drum and the column base. These provide liquid surge capacity, which helps to filter disturbances in both flow and composition to downstream units. They also permit the column to ride through large disturbances without upsetting the column to the point where liquid or vapor hydraulic limitations are encountered (flooding or weeping), which can result in the loss of separation and the production of off-specification products. 

Assuming the reflux drum has an aspect ratio (length over diameter) L/D of 2, the total volume is 

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Closed drain headers are normally provided for safe drainage of equipment containing severely toxic, corrosive, pollutant or high cost chemicals (e.g., phenol, sulfuric acid, monoethanolamine, sulfur dioxide, catacarb) where there is an appreciable inventory in a number of processing vessels in a plant. The header should be at least 50 mm in diameter, and should be tied into the major vessels and equipment with 25 mm minimum size connections (20 mm is considered adequate for pumps). The header may be routed to a gravity drain drum (with recovery to the process by pump or gas pressurization), or to a pumpout pump returning to the process, or in the case of sulfuric acid, to an acid blowdown drum. 

A credible spill for Probable Maximum Loss Potential. The minimum spill source is the largest process vessel. The maximum spill size is the combined contents of the largest process vessel, or train of process vessels connected together if not readily isolated. Between these extremes, a credible spill may be estimated after taking into account the presence of remotely operated shutoff valves adequate for an emergency, and automatic dump or flare systems. 

Two formulations were derived. The first deals with minimising the amount of effluent produced from an operation where wastewater can be reused in product formulation and the plant structure is known. The minimisation is achieved by scheduling the operation in such a manner as to maximise the opportunity for wastewater reuse. The second deals with the synthesis of a batch process operating in zero effluent mode. The formulation determines the number and size of processing and storage vessels as to minimise the cost of the equipment and the amount of effluent produced from the resulting operation, while achieving the required production. 

Many investigators consider neutralization as a poorly understood process in the gas phase. While in the best possible cases it may be considered as a homogeneous second-order process, detailed experimentation in specific cases sometimes fails to establish that (Freeman, 1968 Meisels, 1968). At low dose rates and low gas pressures, wall effects can be seen as a major inhibiting factor, as most neutralizations would then be expected to occur on the walls. Coating the wall with specific chemicals has not lead to a uniform conclusion. On the other hand, wall effects are also present at high dose rates. In such cases, and with gas pressure greater than about 0.1 atm, normal positive ions cannot reach the walls if the size of the vessel is 10 cm or more (Freeman, 1968). Even for electrons, it is hard. Large-scale convection is supposed to be the chief transport mechanism this, however, is difficult to establish experimentally. 

The process design of a PFR typically involves determining the size of a vessel required to achieve a specified rate of production. The size is initially determined as a volume, which must then be expressed in terms of, for example, the length and diameter of a cylindrical vessel, or length and number of tubes of a given size. Additional matters to consider are effects of temperature resulting from the energetics of the reaction,... 

In most sensing situations, the analyte molecules are transported to and from the sensor by diffusion. This is particularly true for sensors in which the analyte is chemically transformed, such as sensors that rely on catalysis or in amperometric sensors. Diffusion is another activated (see (B.5)) process in which time and temperature have to be considered. It is driven by the gradient of chemical potential (A. 19). Two kinds of diffusion are most relevant. These are the Fickian diffusion, which depends on molecular properties of both the diffusing medium and of the diffusing species, and the Knudsen diffusion which depends on the size of the vessel. 

From an industrial viewpoint, scale-up means process development and highest possible throughput that virtually excludes the use of batch reactors. In fact, the productivity and not the size of the vessel is important, which clearly indicates that flow systems, regardless of whether applied in SF or CF manner, have distinct benefits over batch process reactors. 

The objective function in the formulation is the minimisation of overall cost. In this instance the overall cost arises from the cost of the processing vessels, the cost of the storage vessels and the treatment costs of the effluent water. The objective function is given in Equation (3). The objective function is linear, as it was assumed that the cost of a processing vessel and storage vessel is a linear function of the size of the vessel. 

A methodology for the synthesis of batch plants incorporating the zero effluent mode of operation has been presented. In the zero effluent mode of operation, the wastewater generated in the operation is reused as a constituent in a batch of subsequent compatible product. The methodology determines the optimal size and number of processing vessels and wastewater storage vessels. 

What happens to fmx upon scaleup Mixing times in mechanically agitated vessels typically range from a few seconds in laboratory glassware to a few minutes in large industrial reactors. As the size of the vessel increases, will increase, and the increase will eventually limit the size at which the reactor is operable. No process is infinitely scaleable. Sooner or later, additional scaleup becomes impossible, and further increases in production cannot be achieved in single-train plants but must use units in parallel. Fortunately for the economics of the chemical industry, this size limit is often very large. 

In Section 13.3.1, the concept of batch/reactor residence time was presented. For batch/semibatch processes, batch time is often simply dictated by the maximum polymerization rate possible for a given piece of equipment and the time required to reduce monomer residuals or end groups to within speciflcation. For a continuous bulk or solution process, reactor residence time is simply a function of the size of the vessel and how fast monomer can be pumped... 

Two different sized measuring volumes were used in the experiments. One had a capacity of 104 ml and the other 312 ml. The size of the vessels was chosen so that tests near the triple-point pressure could be completed before the liquid upstream of the orifice started boiling. The actual sizes used were picked by a very rough trial-and-error process and are not necessarily the best sizes that could have been selected. 

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