Flowsheets 7981 Subject

The present description pertaining to copper refers to solvent extraction of copper at the Bluebird Mine, Miami. When the plant became operational in the first quarter of 1968 it used L1X 64, but L1X 64N was introduced in to its operation from late 1968. The ore consists of the oxidized minerals, chrysocolla and lesser amounts of azurite and malachite. A heap leaching process is adopted for this copper resource. Heap-leached copper solution is subjected to solvent extraction operation, the extractant being a solution of 7-8% L1X 64N incorporated in kerosene diluent. The extraction process flowsheet is shown in Figure 5.20. The extraction equilibrium diagram portrayed in Figure 5.21 (A) shows the condi-... 

In Chapter 1, two alternative ways were discussed that can be used to develop the structure of a flowsheet. In the first way, an irreducible structure is built by successively adding new features if these can be justified technically and economically. The second way to develop the structure of a flowsheet is to first create a superstructure. This superstructure involves redundant features but includes the structural options that should be considered. This superstructure is then subjected to optimization. The optimization varies the settings of the process parameters (e.g. temperature, flowrate) and also optimizes the structural features. Thus to adopt this approach, both structural and parameter optimization must be carried out. So far, the discussion of optimization has been restricted to parameter optimization. Consider now how structural optimization can be carried out. 

The second mathematical formulation presented, is a design model based on the PIS operational philosophy. This formulation is an MINLP model due to the capital cost objective function. The model is applied to a literature example and an improved design is achieved when compared to the flowsheet. The design model is then applied to an industrial case study from the phenols production facility to determine its effectiveness. The data for the case study are subject to a secrecy agreement and as such the names and details of the case study are altered. 

The flowsheet used for apatite flotation is shown in Figure 25.10. The ore was ground to a Algo of 80 pm, followed by magnetic separation. The non-magnetic fraction was subjected to apatite flotation and upgrading. 

The final flowsheet that was developed for chromium removal is shown in Figure 25.13. The concentrate was scrubbed with alkaline followed by desliming. The deslimed concentrate was subjected to chromium flotation followed by a single cleaning stage. 

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. 

This is the fun (and frustration) of chemical reaction engineering. While thermodynamics, mass and heat transfer, and separations can be said to be finished subjects for many engineering apphcations, we have to reexamine every new reaction system from first principles. You can find data and construct process flowsheets for separation units using sophisticated computer programs such as ASPEN, but for the chemical reactors in a process these programs are not much help unless you give the program the kinetics or assume equihhrium yields. 

Sequential Modular. By far the most experience with flowsheeting systems has been with the sequential modular architecture (59- 3). It is this architecture that is most easily understood by the process engineer. Each module calculates all output streams from input streams subject to module parameters. Generally, the stream variables consist of component flows, temperature (or enthalpy) and pressure as the independent variables. Other dependent variables such as total flow, fraction vapor and total enthalpy (or temperature) are often carried in the stream. 

Equation-based flowsheet simulators have not reached the level of commercialization of their sequential modular counterparts as of the time of this writing, and the development of efficient equation-solving algorithms is the subject of much continuing research. 

The classes of problems to be identified in the contemporary CAPE concern the problem of conceptualizing change of scale, intensification, and integration. There are two main subjects of conceptualization. The first one is generation of alternatives and selection of appropriate one for the identification of the chemical path that transforms the given raw materials into the required product. The second is identification of the structure of the flowsheet, i.e., what units are to be used to produce the required material and how they should be connected. More detailed information about the solvents and the control structure is also decided in the conceptualization phase. 

The effiuant streams from the first separator are examined and, if necessary, subjected to further separation. The sequence [s developed, gnided by the cost factor and the heuristic to choose the cheapest of all candidate separations next. The flowsheet is complete when all final effluent streams contain only one of the products of the predetermined set. 

Develop Approximate Criteria. Fianl design criteria cannot be applied without an initial design in hand. Therefore, use approxiatete criteria, such as henristics, to generate altemete flowsheets that can be subjected to more stringeal standards. 

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

The current practice has shown that there is a gap between process and control engineers. Filling this gap is a challenge for education. Only very recently plantwide controllability issues have been included in a book dealing with process design (Seider, Seader Lewin, 1999). This chapter aims to give another perspective on the same subject, with emphasis on integrating controllability aspects in flowsheet synthesis. 

Finally, before leaving this section on preliminary process synthesis, the limitations of the heuristic approaches should not be overlooked. Many algorithmic methods are very effective for the synthesis of alternative flowsheets, their analysis, and optimization. These methods are usually used by design teams in parallel with their work on the development of the base-case design, which is the subject of the next section. The algorithmic methods are easily implemented and are illustrated with many examples in Part Two of this text (Chapters 6-12). 

---