Vessels process design

FIG. 16-46 Pressurized adsorber vessel. (Reptinted with peirrussion of EPA. Reference EPA, Process Design Manual for Carbon Adsorption, U.S. Envir. Protect. Agency., Cincinnati, 1973.)... 

Gravity decanter, illustration, 243, 244 Happel/Jordan method, 241 Horizontal gravity, 239 Lamella classifiers, 239 Settler vessel, illustration, 240 Time planning and scheduling, process design, 36... 

Whenever chemical reactions occur these are the key to the process design. The engineer must be aware of what kinds of reactions are possible. He must also keep in mind that there are no such things as pure reactants, nor does the stream emerging from his reaction vessel ever contain just the desired product. Nearly always, a number of reactions occur and other products than those desired are produced. The engineer s purpose in investigating the reaction step is to increase the yields of desired products while reducing the quantity of unwanted substances. 

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,... 

The process design of an LFR, like that of other types of reactors, may involve, for a specified throughput (q or FAo), calculation of the fractional conversion (/A) achieved at the outlet of a vessel of given size, or the size of vessel required for a specified /A. 

Hazard and Operability Analysis (Hazop) (Kletz, 1992) is one of the most used safety analysis methods in the process industry. It is one of the simplest approaches to hazard identification. Hazop involves a vessel to vessel and a pipe to pipe review of a plant. For each vessel and pipe the possible disturbances and their potential consequences are identified. Hazop is based on guide words such as no, more, less, reverse, other than, which should be asked for every pipe and vessel (Table 1). The intention of the quide words is to stimulate the imagination, and the method relies very much on the expertise of the persons performing the analysis. The idea behind the questions is that any disturbance in a chemical plant can be described in terms of physical state variables. Hazop can be used in different stages of process design but in restricted mode. A complete Hazop study requires final process plannings with flow sheets and PID s. 

The basic adsorption process design. Sub-tasks within that include the adsorbent selection, made in view of aU of the requirements imposed on the dehydration process. The adsorption step time, regeneration and cooHng step times all need to be settled and these in view of mechanical details. The overall vessel configuration, for example, the vessel ID and length, which quantities are typically sized based on pressure drop. Finally we need to make some estimate of the expected service Hfetime for the adsorbent product. 

Mechanical design of the adsorber then takes up the remainder of the engineering effort to produce a workable adsorption process design. Once a vessel is sized to provide the required inventory of adsorbenf we need to provide the mechanical details, which include flow distribution devices, bed supports and the required vessel wall thickness to withstand the working pressure and added stresses encountered during regeneration and repeated de-pressurization and re-pressurization. 

Figure 8 is a schematic flow diagram for the hydrolysis of waste newsprint. Most of the process design criteria and the economic evaluations of the saccharification process have been based on newsprint as substrate. Notable analyses are those of Wilke and co-workers (21) and Humphrey (22). In the hydrolysis, the substrate is first pretreated (milling), to make it more accessible to the enzyme. Saccharification takes place in a reaction vessel, where the substrate is contacted with the enzyme solution from the fermentation vessel. Glucose solution is separated from unreacted substrate at the outlet of the vessel and the solution passes on to a concentration stage before the sugar is used in the yeast fermentation to produce alcohol. 

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