Base case operating conditions

Base Case Operating Conditions for Process Design and Membrane Specifications for Commercial Nanofiltration Plant... 

Since, in the last section, the base-case operating condition that optimizes TAC is not able to handle properly the impmity disturbance changes in the +20% range, the side-stream flowrate is set to be higher than the optimum case of 50 kg/h in order to handle these disturbances better in the feed F3. A side-stream flowrate of 60 kg/h is used here for illustration purposes. Notice that when the side-stream flowrate increases from 50 kg/h to 60 kg/h, the TAC only increases by 0.66% (see Fig. 9.33). 

Figure 9.37 shows the closed-loop simulation with 20% changes in the feed F3 impurity (m-xylene) component flowrate at this new base-case condition. Notice that for the +20% case, the bottom product purity returns to the product specification of 99.5 wt% acetic acid and the top aqueous product purity is also much better than the one shown in Figure 9.36 (0.113 wt% in this figure versus 0.134 wt% in Fig. 9.36). With the alternative selection of the base-case operating condition only slightly different to the optimum TAC case, the capability of handling the feed impurity variations is improved.

TABLE 9.19 Comparison of Base-Case Operating Conditions in Sections 9.3 and 9.4. 

By modifying heat transfer coefficients for streams requiring non-base-case operating conditions using Equation (15.141. the same cost equation can be used to calculate all exchanger costs in a given network. 

Case (a) On Figure IS.ltbl. the base-case operating condition is Point a. From Point a, follow the constant flow line, M = 1.0, to a vaporizer duty, Q = 3.78 x 10 kJ/h. This is line segment a - c, and, from this, we get that the inlet oil tenperature, T, 2 = 332°C. 

The base-case operating conditions (temperature and pressure) of the reactor were used throughout this study. It is not expected that significant savings can be realized by altering these conditions since the reactor cost has very litde impact on the overall break-even price of benzene. 

For the base case operating conditions, membrane properties, and economic parameters assumed in the study, membrane processes were found to be more economical than DEA over the entire range of CO2 concentrations considered (with no H2S in the feed). When H2S is also present, the results showed that the cost of meeting product gas specifications (<2 mole% CO2 and <4 ppmv H2S) increases with increased H2S concentration. For example, with feed containing 1,000 ppm H2S, the membrane process was found to be more economical than DEA only when the total acid gas in the feed exceeded about 16 mole%. 

For reaction systems without solvents, the time at the test temperature is important. In these cases, the elected period of time and temperature should be based on the worst case operating conditions. 

At the initial stages in design, we identified only the general hazards—for example, instabihty of the robot base and the related system design constraint that the mobile base must not be capable of falling over under worst-case operational conditions. As design decisions are proposed and analyzed, they will lead to additional refinements in the hazards and the design constraints. 

Defining a base case is to determine the base case operation of the tower of interest. This requires extracting two kinds of data. One kind is process data in terms of feed and product conditions, such as flows and compositions, while the other is tower operating data including temperature, pressure, and reflux rate. The former defines the mass and composition balances and the latter sets the heat balance around the tower with Table 13.2 giving such an example of the C2 splitter column. 

With each model description, component best estimates are revised and, in some cases, completely altered from previous revision descriptions. Since the arrangement process evolved using best estimates and resulted in several revisions, there is not yet a single preferred arrangement. The component dimensions used in the models are based on operational conditions of the system and its components to achieve rated power level and minimize pressure drop. 

Clock Spring design required a safety factor of 2 based on a maximum anticipated load of 10 ksi (69 MPa). The composite was designed to withstand 20 ksi (138 MPa) loads at 50 years of exposure to worst case operating conditions. Based on this equation the Clock Spring 20 ksi (138 MPa) design life is 67 years. This equation shows the minimum new (t= 1) tensile strength of the composite should exceed 42 ksi (290 MPa) (GRI, 1998). 

Table II summarizes the yields obtained from the CONGAS computer output variable study of the gas phase polymerization of propylene. The reactor is assumed to be a perfect backmix type. The base case for this comparison corresponds to the most active BASF TiC 3 operated at almost the same conditions used by Wisseroth, 80 C and 400 psig. Agitation speed is assumed to have no effect on yield provided there is sufficient mixing. The variable study is divided into two parts for discussion catalyst parameters and reactor conditions. The catalyst is characterized by kg , X, and d7. Percent solubles is not considered because there is presently so little kinetic data to describe this. The reactor conditions chosen for study are those that have some significant effect on the kinetics temperature, pressure, and gas composition.

The value of the extra chlorine recovered will pay for the membranes in about nine months. Addition of operating costs still gives an attractive pay-out. However, the base case for Table 7.4 assumes that nothing is done to handle the chlorine issuing from liquefaction. This is not an option. The real question is how the membrane process compares with the alternatives, and this is the subject of Table 7.5. The basis assumed is an 800 tonnes per day plant with gas composition 93.16% CI2,2.40% O2, 3.82% N2, 0.37% CO2, and 0.25% H2. The table covers costs only. Product values are highly sensitive to local conditions and are not included. In all cases, the membrane option is based on the field test in order to give the most reliable numbers available. Technological development will improve the case for the use of membranes. 

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