Processes control equipment design

On typical grass-roots, chemical processing facilities, as much as 10% of the total capital investment is allocated to process control equipment, design, implementation, and commissioning. Process control is a very broad topic with many distinct aspects. The following possible sub-topics give some idea of the full breadth of this topic ... 

Spreadsheet Applications. The types of appHcations handled with spreadsheets are a microcosm of the types of problems and situations handled with fuU-blown appHcation programs that are mn on microcomputers, minis, and mainframes and include engineering computations, process simulation, equipment design and rating, process optimization, reactor kinetics—design, cost estimation, feedback control, data analysis, and unsteady-state simulation (eg, batch distillation optimization). 

Many processes require equipment designed to rigid specifications together with automatic control and safety devices. Consideration should be given to the control, and limitation of the effects, of equipment malfunction or maloperation including ... 

Passive controls minimize the hazard by use of process and equipment design features. They reduce either the frequency or consequence of the hazard without the active functioning of any device. Examples include dikes, firewalls, orifice plates or narrow bore piping to control flow, and the... 

The attributes of the extrudate, such as density, thickness, and moisture content, are controlled by variables due to the formulation, extrusion process, and equipment design. The properties of the wet feed material and its ability... 

A formidable obstacle, however, is the development of satisfactory mathematical criteria for automatic operation. As later sections of this chapter will indicate, the satisfactory solution of this type of problem is often difficult enough even when divorced from the urgency of direct process control. The obstacle to further development here seems to lie not so much in the technology of control-equipment design as it does in determining precisely what is expected of a computer in all the situations it can encounter. 

Identification and quantification of the desired reaction conditions, particularly temperature and concentration, are necessary to evaluate what may happen if these conditions are not met. This is particularly true where equilibrium considerations are a significant factor in a rate determining step between or among competing reactions. Where multiple products are possible, temperature variations will often significantly alter the ratios of these products. If one of these is unstable or more toxic, this could lead to more stringent temperature control requirements in the process and equipment design. 

The specific reliability demands on process control equipment are dealt with in Chap. 11. Initially the protection objective for plant design and operation was already mentioned avoiding major hazards for man, environment and valuable property. In order to achieve this so-called protective tasks have to be carried out. Several of these tasks are needed to reach the objective. In general, alternatives... 

True Density - True density is the mass per unit volume of a fertilizer material, excluding voids between particles and the pores within the particles. It is of interest in process control and design of process equipment. The true density carr be determined with an air-comparison pycnometer. The pycnometer has two sample chambers of equal size. One chamber is flooded with a measured volume of air. The other chamber is filled with a weired amount of the ground test sample and then flooded with a measured volume of air. The difference in air volumes is equivalent to the sample volume. The sample weight and volume are used to calculate the true density. Figure 18.6 is an illustration of a Beckman air-comparison pycnometer. Typical true density values for some common fertilizer materials are listed in Table 18.4. 

The melt blowing process responds to process variables more readily than most of the other nonwoven processes to produce a wide variety of end products. The actual process parameters that determine final web properties involve the selection of polymer or resin, conditions in the extruder or melt tank, geometry and condition at the die tip and fiber distribution and separation at laydown. Modem melt-blown lines are designed with highly automated machine and process control equipment, which allow for quick selection of particular parameters and easy machine adjustments. 

In the cement industry there are limits to attainable accuracy imposed by the very nature of the materials handling and processing equipment employed, and not even the best process control system can improve on such limits. Accordingly, in designing the system it is of prime importance to suit the actual accuracy requirements to the conditions of the process itself and not go for the maximum that the makers of the process control equipment are prepared to claim or guarantee. In other words, a realistic approach is needed. 

Extraction, a unit operation, is a complex and rapidly developing subject area (1,2). The chemistry of extraction and extractants has been comprehensively described (3,4). The main advantage of solvent extraction as an industrial process Hes in its versatiHty because of the enormous potential choice of solvents and extractants. The industrial appHcation of solvent extraction, including equipment design and operation, is a subject in itself (5). The fundamentals and technology of metal extraction processes have been described (6,7), as has the role of solvent extraction in relation to the overall development and feasibiHty of processes (8). The control of extraction columns has also been discussed (9). 

An extraction plant should operate at steady state in accordance with the flow-sheet design for the process. However, fluctuation in feed streams can cause changes in product quaUty unless a sophisticated system of feed-forward control is used (103). Upsets of operation caused by flooding in the column always force shutdowns. Therefore, interface control could be of utmost importance. The plant design should be based on (/) process control (qv) decisions made by trained technical personnel, (2) off-line analysis or limited on-line automatic analysis, and (J) control panels equipped with manual and automatic control for motor speed, flow, interface level, pressure, temperature, etc. 

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