Equipment Combined unit operations

The chemical engineer uses flow diagrams to show the sequence of equipment and unit operations in the overall process, to simplify visualization of the manufacturing procedures, and to indicate the quantities of materials and energy transfer. These diagrams may be divided into three general types (1) qualitative, (2) quantitative, and (3) combined-detail. 

An old variation of the conversion type is a catalytic combination unit. Development of this scheme was necessitated by the rising cost of refinery construction after World War II and by the great demand for capital for postwar expansion. The scheme reduced the investment and operating costs for refining equipment. The basic feature of the combination unit lies in the integration of the fractionation facilities of the reduced crude distillation and catalytic cracking sections. 

Ultrafiltration equipment are combined with other unit operations. The unique combination of unit operations depends on the wastewater characteristics and desired effluent quality, and cost considerations. 

The combination of several unit operations into a single piece of equipment can eliminate equipment and simplify a process. There may be inherent safety conflicts resulting from this strategy (see Section 2.4). Combining a number of process operations into a single device increases the complexity of that device, but it also reduces the number of vessels or other pieces of equipment required for the process. Careful evaluation of the options with respect to all hazards is necessary to select the inherently safer overall option. 

Figure 6.1 is presented as an attempt to show the interrelationships between the process metrics categories shown in Table 6.1. Materials (chemicals, solvents, reagents, etc.) choices will directly affect the choice of unit operations and the combination of materials and equipment will directly impact the operability of the process. Materials, equipment and operability all have EHS impacts and opportunities associated with them and ultimately impact product and product quality. 

PHA techniques involve a combination of what if for unit operations and hazard and operability (HAZOP) for both equipment- and procedural-based deviations. 

In the process industry, there are only four basic operations reaction, separation, mixing, and heat transfer. The traditional unit operation is to perform each task in one or more pieces of equipment sequentially, for example, heat transfer in heat exchangers and reaction in reactors. Combining two or more tasks in one piece... 

Equipment that combines more than one unit operation in a single piece of equipment is another approach to process intensification. Reactive distillation is a good... 

In the laboratory, Swagelok pipe fittings are often used to set up plants. The Forschungszentrum Karlsruhe used these interfaces to define a modular platform which consists of modules for a number of standard unit operations. The modules are all equipped with these pipe fittings (Figure 4.10) and can thus be combined using the Swagelok interface standard ([68] see also [69]). 

This is a relatively new technique which is now becoming commercialized. It combines the cell separation and primary product separation stages in a single unit operation, to reduce equipment costs, improve product yields and reduce processing times. 

Control analysis and control system design for chemical and petroleum processes have traditionally followed the unit operations approach" (Stephanopoulos, 1983). First, all of the control loops were established individually for each unit or piece of equipment in the plant. Then the pieces were combined together into an entire plant. This meant that any conflicts among the control loops somehow had to be reconciled. The implicit assumption of this approach was that the sum of the individual parts could effectively comprise the whole of the plant s control system. Over the last few decades, process control researchers and practitioners have developed effective control schemes for many of the traditional chemical unit operations. And for processes where these unit operations are arranged in series, each downstream unit simply sees disturbances from its upstream neighbor. 

The top layer is the procedural layer and this generally defines how unit operations are combined across plant units for the overall process. A feature of S88 is the ability to generate equipment modules, essentially common arrangements of control modules to provide a specific function (e.g., skid-mounted temperature control units for reactors or valve/pump arrangements for transfer routes). 

When a combination of library models is used to simulate a reactor, it is a good idea to group these models in a subflowsheet. The subflowsheet can be given a suitable label such as reactor that indicates that all the unit operations it contains are modeling a single piece of real equipment. This makes it less likely that someone else using the model will misinterpret it as containing additional distinct operations. 

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