Block Flowsheets

Used to present the heat and material balance of a process. This may be in broad block form with specific key points delineated, or in more detailed form identifying essentially every flow, temperature and pressure for each basic piece of process equipment or processing step. This may and usually does include auxiliary services to the process, such as steam, water, air, fuel gas, refrigeration, circulating oil, etc. This type of sheet is not necessarily distributed to the same groups as would receive and need the piping flowsheet described next, because it may contain detailed confidential process data. 

Equipment abbreviations, 25 Instruments, 29 Flowsheets, 1-11 Block diagram, 4... 

A computational sequence for modular flowsheeting. Initial values of both recycles are guessed, then the modules are solved in the order 1, 2, 3, 4, 5, and 6. Calculated values for recycle streams S9 and S10 are compared with guessed values in a convergence block, and unless the difference is less than some prescribed tolerance, another iteration takes place with the calculated values, or estimates based on them, forming the new initial guessed values of the recycle streams. 

Figure 2.1. Coal carbonization block flowsheet. Quantities are in Ib/hr.

Figure 2.2. Block flowsheet of the revamp of a 30,000 Bbl/day refinery with supplementary light stocks (The C. IV. Nofsinger Co )... 

Processes often differ in terms of the process conditions, e.g. high-pressure and low-pressure processes, or the type of reactor that is used, e.g. gas-phase catalytic reactor or liquid-phase CSTR. These differences should be clearly marked on both the simple block diagrams for each process and the detailed process flowsheets, they often determine which process route is ultimately selected. Many older, established processes were operated under conditions of high pressure or high temperature (mainly in the reactor), whereas the newer processes have often been improved by operation under less severe conditions. 

To install streams for feeds, product, and intermediate connections, click the arrow to the right of the Material Streams box on the bottom left of the window and select Material. Moving the cursor to the flowsheet produces a number of arrows on the inlets and outlets of the various blocks. A feedstream is installed by first clicking the flowsheet and then clicking the arrow pointing to a feed valve. Figure 2.32 shows stream 1 connected to valve VI. Figure 2.33 shows the final flowsheet with all lines installed and some streams renamed for clarity. Save the file in an appropriate directory. 

The properties of all the blocks in the flowsheet must be set. Clicking on the + to the left of Blocks generates a list of all the blocks. Selecting the pump block PI opens the window shown in Figure 2.43. We specify a pressure increase of 5 atm. Selecting the valve V1 block opens the window shown in Figure 2.44. Since the reactor pressure is 10 atm, the outlet pressure of VI (the benzene feed) is specified at 10 atm. The valve V2 (the ethylene feed) is defined in the same way. The valve V3 is set to take a 3 atm pressure drop, as shown in Figure 2.45. 

IS- m Components m sa Properties S Qfl Flowsheet CS j Streams -rj Utilities Blocks... 

The disturbance considered is a step increase in the flowrate of the ethylene feed. We want to increase the benzene feed whenever the ethylene feed is increased, so a ratio control structure is installed. Figure 3.89 shows a Mulitply block selected from the list of ControlModels, dropped on the flowsheet, and renamed ratio. A control signal is attached to the FE stream and connected to ratio.Inputl, as shown in the upper window of Figure 3.90. Another control signal is attached from the output of the multiply block to the setpoint of the benzene flow controller. Clicking the ratio icon, clicking the right... 

The tubular reactor in Aspen Plus is called RPLUG and is installed on the flowsheet as shown in Figure 5.21. Two different tubular reactors with their feed and product streams are shown. The five possible types of reactors are listed on the Specifications page tab when Setup under the reactor block is clicked. 

The next issue is how to select the internal temperatures in the reactor. These are not available as normal output signals for the reactor block when you drag a control signal to the flowsheet. The temperatures can be seen by clicking the reactor icon, selecting Forms and AW Variables. With a 30-lump model, there are 30 temperatures. The temperature at 2 m down the 10 m reactor is T(6). 

Aspen Dynamics has the capability of using flowsheet equations for specifying a desired relationship. We illustrate this by setting up an equation that defines the PV signal to a temperature controller as T(6). The reactor block is COOLANT, so the T(6) temperature is BLOCKS( COOLANT ).T(6). 

The control structure is changed to control the temperature at 2 m from the inlet of the reactor T(6). Figure 6.62 shows the flowsheet equation Text Editor with the input to the deadtime block set equal to the temperature in the reactor block COCUR at lump 6. The input to the deadtime block is changed to Free. 

Cf si Properties (fl si flowsheet FJ a Streams. Q Utflifes Itl di Blocks Fl Gfl Reactions f l a Convergence El Qj Fbwsheebng Options 1=1 a Design Spec... 

Block diagrams of the linear openloop process are shown in Figure 7.4. The two alternative flowsheets are labeled FS1, in which no furnace is used, and FS2, in which a furnace is used. The reactor transfer function is GR(s), representing the adiabatic tubular reactor. The reactor by itself is openloop-stable. In Figure 7.4a a simple first-order... 

A simplified flowsheet for an ammonia plant that processes natural gas via steam reforming is shown in Figure 6.7. A block diagram of this same plant is shown in Figure 6.8. This diagram lists typical stream compositions, typical operating conditions, catalyst types (recommended by Synetix) and catalyst volumes82. 

Lin (100) suggested breaking the process flowsheet into one or more blocks of modules. Each block of modules contains one or more modules and all of the modules in the same block are solved simultaneously. The whole process flowsheet is then solved by conventional sequential modular approach by treating each block as a module. 

Synthesis is the step in design where one conjectures the building blocks and their interconnection to create a structure which can meet stated design requirements. This review paper first defines chemical process synthesis and indicates the nature of the research problems—to find representations, evaluation functions and search strategies for a potentially nearly infinite problem. It then discusses synthesis research and the most significant results in each of six areas—heat exchanger networks, separation systems, separation systems with heat integration, reaction paths, total flowsheets and control systems. 

In order to focus on the main issues of process integration, we disregard the distillation column for heavies, as well as the transalkylation section. A preliminary simulated flowsheet in Aspen Plus [9] is shown in Figure 6.8, with values of temperatures, pressures and heat duties. The fresh feed of propylene is llOkmol/h. Note that design specifications are used for the fine tuning of the simulation blocks. The fresh benzene is added in the recycle loop as makeup stream so as to keep the recycle flow rate constant. This approach makes the convergence easier. 

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