Process Flow Lines

Piping Layout Main Process Flow Lines 

Main process flow lines represent the main process flow. Such streams pass through furnaces. 

Process flow is not always a simple straight through-flow but can split into two or three streams, as is often done with a number of distillation columns. Subsidiary circuits to process flow must also be considered such as the refirigera-tion circuits in ammonia or ethylene units. 

Feed and Product Lines. Feed lines and the usually small-diameter product lines can be minimized if they start at equipment close to that bettery limit where feed and product lines terminate. 

For pipe sizing, process equipment sizes are required. These include types and sizes of vessels, heat exchangers, pumps, compressors, intercoolers, scrubbers, silencers, floor space of lube and seal-oil console, furnace and heater details, control and switch house arrangements. 

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A block flow diagram is used to show the major process equipment and interconnecting process flow lines and flow rates, stream composition, temperatures, and pressures when necessary for clarity. The block flow diagram is a simplified diagram. 

A feature that still often impedes the latter form of analysis, however, is the common need to make many of these relatively sophisticated spectroscopic measurements in controlled, often unrealistic environments, perhaps following periodic extractions of the catalytic materials from process flow lines. As a result, numerous ingenious "minimal disturbance" procedures have been developed to circumvent possible problems (2). Generally, however, all of these schemes are based upon some degree of reliance on a "stop action" or "fix" concept (1 ). In the latter, we assume that the materials in question are usually altered by the previously mentioned catalytic process, but are unchanged ("fixed") following removal from that process. This concept has been shown to have some merit, but detailed analysis has demonstrated that mere exposure to ambient air can often prove deleterious to the chemical status of the surface of some catalytic ingredients (3). Thus, in... 

Figure 7-4. Alternative tower arrangements can shorten main process flow lines.

Piping Layout Main Process Flow Lines... 

Line functions and staff functions within the organisation have to be clearly identified. Line is associated with process flow. Line functions have direct responsibility and have the authority and power for realising the mission of the company. Knowledge of reporting lines is useful. Staff supplies information, materials and advices to the line . Staff functions are e.g. counselling on human resources, on procedures, on analytical methods and on systems, on managing a science based service department handling medical information, complaints and recall. A QP or hospital pharmacist may have both line and staffs function(s). 

For example a process flow scheme for crude oil stabilisation might contain details of equipment, lines, valves, controls and mass and heat balance information where appropriate. This would be the typical level of detail used in the project definition and preliminary design phase described in Section 12.0. 

Esterifica.tlon. The process flow sheet (Fig. 4) outlines the process and equipment of the esterification step in the manufacture of the lower acryflc esters (methyl, ethyl, or butyl). For typical art, see References 69—74. The part of the flow sheet containing the dotted lines is appropriate only for butyl acrylate, since the lower alcohols, methanol and ethanol, are removed in the wash column. Since the butanol is not removed by a water or dilute caustic wash, it is removed in the a2eotrope column as the butyl acrylate a2eotrope this material is recycled to the reactor. 

Russian production may be going to a flow line cell concept (35). In this process, dehydrated camaOite is fed to a chamber where it is mixed with spent electrolyte coming from the electrolytic cells. The spent electrolyte first enters a metal collection chamber, where the molten magnesium is separated. The electrolyte is then enriched with camaOite and any iasoluble impurities are allowed to settle. The enriched electrolyte is then returned to the electrolytic cells. The result is that most of the remaining impurities are removed ia the first electrolytic cell. 

Process flow diagrams are more complex and show all main flow streams including valves to enhance the understanding of the process as well as pressures and temperatures on all feed and product lines within all major vessels and in and out of headers and heat exchangers, and points of pressure and temperature control. Also, information on construction materials, pump capacities and pressure heads, compressor horsepower, and vessel design pressures and temperatures are shown when necessary for clarity. In addition, process flow diagrams usually show major components of control loops along with key utilities. 

Balanced bellows type valves are normally used where the relief valves are piped to a closed flare system and the back-pressure exceeds 10% of the set pressure, where conventional valves can t be used because back-pressure is too high. They are also used in flow lines, multiphase lines, or for ptu affinic or asphaltic crude, where pilot-operated valves can t be used due to possible plugging of the pilot line. An advantage of this type of relief valve is, for corrosive or dirty service, the bellows protects the spring from process fluid. A disadvantage is that the bellows can fatigue, which will allow process fluid to escape through the bonnet. For HjS service, the bonnet vent must be piped to a safe area. 

To understand the mathematics, consider a large empty space into which a number of production units are to be placed, and assume that the major variable to be optimized is the cost of transporting materials between them. If the manufacturing process is essentially a flow-line operation, then the order in which units should be placed is clear (from the point of view of transport costs), and the problem is simply to fit them into the space available. In a job-shop, where materials are flowing between many or all the production units, the decision is more difficult. All the potential combinations of units and locations... 

We can represent states of the system (with constant values specified for all the variables except 9 and at) by a set of isotherms as shown in Figure 2.1 la. Two isotherms, 9 and 92 are shown, with 92 < 9t. State I, which is defined by 9 and A], can be connected to states T and 1" by a series of reversible isothermal processes (horizontal lines in the figure). We remember that heat is absorbed or evolved along a reversible isothermal path, and we will assume that this flow of heat is a continuous function of at along the isotherms, with the absorption or liberation depending upon the direction in which at is varied. That is, suppose... 

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