Flowsheets Material balance

Sood, M. Khanna, R. Reklaitis, G. V., "A Two Level Approach Exploiting Sparsity in Flowsheeting Material Balancing", Paper presented at AIChE Meeting in Houston, April 1979. 

This example shows how plantwide control problems can be understood by the analysis of the flowsheet material balance. Chapter 13 will develop this subject. 

Preliminary Process Flowsheet. This will show major equipment and lines, preliminary equipment details (vessel diameter, number of trays, pump flow and driver horsepower, etc.), major instrumentation, and, it is hoped, have a material balance at the bottom of each drawing with flows keyed to a numbering system on the diagram. The process flowsheets should cover both the process and utility sides of the plant. 

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. 

Figure 1-11. Typical material balance process flowsheet.

This section is a general discussion of the techniques used for the preparation of flowsheets from manual calculations. The stream flows and compositions are calculated from material balances combined with the design equations that arise from the process and equipment design constraints. 

In this case, only the material balance will be solved in order to keep the problem simple. If the material balance is to be solved, then a series of material balance equations can be written for the flowsheet in Figure 13.13a ... 

Figure 5 A simplified flowsheet and materials balance for the recovery of copper from oxidic and transition ores by heap leaching, solvent extraction and electrowinning.

From a computational viewpoint, the presence of recycle streams is one of the impediments in the sequential solution of a flowsheeting problem. Without recycle streams, the flow of information would proceed in a forward direction, and the cal-culational sequence for the modules could easily be determined from the precedence order analysis outlined earlier. With recycle streams present, large groups of modules have to be solved simultaneously, defeating the concept of a sequential solution module by module. For example, in Figure 15.8, you cannot make a material balance on the reactor without knowing the information in stream S6, but you have to carry out the computations for the cooler module first to evaluate S6, which in turn depends on the separator module, which in turn depends on the reactor module. Partitioning identifies those collections of modules that have to be solved simultaneously (termed maximal cyclical subsystems, loops, or irreducible nets). 

Consider the process flowsheet shown in Figure El6.4, which was used by Rollins and Davis (1993) in investigations of gross error detection. The seven stream numbers are identified in Figure El6.4. The overall material balance can be expressed using the constraint matrix Ay = 0, where A is given by... 

In this volume, there is an account of the basic theory underlying the various Unit Operations, and typical items of equipment are described. The equipment items are the essential components of a complete chemical plant, and the way in which such a plant is designed is the subject of Volume 6 of the series which has just appeared. The new volume includes material on flowsheeting, heat and material balances, piping, mechanical construction and costing. It completes the Series and forms an introduction to the very broad subject of Chemical Engineering Design. 

Extractive Distillation Recovery of Isoprene. A typical flowsketch and material balance of distillation and solvent recovery towers for extracting isoprene from a mixture of cracked products with aqueous acetonitrile appears in Figure 13.26. A description of the flowsheet of a complete plant is given in Example 2.10. In spite of the fact that several trays for washing by reflux are provided, some volatilization of solvent still occurs so that the complete plant... 

Linear. Since mass and energy are linearly related between modules, purely linear flowsheet calculations can be formulated as a solution to a set of linear equations once linear models for the modules can be constructed. Linear systems, especially for material balance calculations can be very useful (16). Two general systems, based on linear models, SYMBOL (77) and MPB II (7 ) are indicated in Table 1. MPB II is based on a thesis by Kniele (79). If Y is the vector of stream outputs and the module stream inputs are X, then as discussed by Mahalec, Kluzik and Evans (80)... 

Sood, M. K. Reklaitis, G. V. Woods, J. M., "Solution of Material Balances for Flowsheets Modelled With Elementary Modules The Unconstrained Case" AIChE J (1979) 25, No. 2 209. 

A major development effort has been underway at M.I.T. from 1976 to 1979 to develop a next-generation process simulator and economic evaluation system named ASPEN (Advanced System for Process ENgineering). The 150,000-line computer program will simulate the flowsheet of a proposed or operating plant. In addition to calculating detailed heat and material balances,... 

At the end of the Level 4, the result is a close-to-optimum process flowsheet together with a consistent material balance. The next levels will have as a goal the solution of the problems related with the optimal use of energetic resources and material utilities, as well as with waste minimization and plantwide process control. 

The input/output structure defines the material balance boundary of the flowsheet Often it is referred as the inside battery limit envelope. A golden rule requires that the total mass flow of all components entering the process must be equal with the total mass flow of all components leaving it. It should be kept in mind that the recycles affect only the internal process streams, but not the input/output material balance. 

The economic potential may be used to optimize the flowsheet with respect to the material balance. After Level 4 the mass-balance envelope is closed by completing the synthesis of reaction and separation systems. The economic potential EP4 becomes ... 

Formally, the hierarchical design procedure can be divided in two steps process synthesis and process integration. The first deals with the synthesis of the process flowsheet and basic material balance. The second step handles the problem of efficient use of energy and helping material resources (water, solvents, hydrogen). Clearly, the two steps are interrelated. 

The conceptual flowsheet with heat and material balance built upon supplies the key elements for sizing the units and assessing capital and operation costs, and on this basis establish the process profitability. 

The reactor and separation systems described above can be assembled in a flowsheet In a preliminary simulation, the goal is closing the material balance with recycles. In a first approach shortcut models may be used to simulate the distilla-... 

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