Applications Set 2

Click on the heading to see a screen shot of the application.

Geyser Simulation

A look at the uncommon phenonena of geysers and the special geology and chemistry that makes them possible is provided in this unusual application. Using calcAQ the dissolution and precipitation of silica along a gesyer column illustrates the mechanism of creating the seal necessary to hold the high pressures that power the geyer eruption. The calcAQ application also demonstrates the ability to create and plot surveys with respect to a nontraditional process variable, in this case depth down the geyser column, where all of the input parameters change independently. In other words, the operating curves of unit operations can be generated where the temperature and pressure, and even the composition, change simultateously. This is in contrast to the usual solubility or pH curve where only one independent variable is varied at a time.

Click here for a more detailed look at the geyser application.

Daily Production Report

Combining macro process functions for calculating the holdup mass in a tank with a customized calcAQ function for calculating the concentration of NaOH from density measurements provides a simple way to generate operations logs. With the ability to add functions and data concerning product price from the accounting system, managers have an additional tool for helping to make operations decisions. This application illustrates an example production report for BaCl2 crystallization.

H2SO4 Heat Exchanger

A simple countercurrent heat exchanger is demonstrated in this application. The inlet and outlet temperatures, pressures, and concentrations of the process and utility streams, the flowrate of the process stream, and the overall heat transfer coefficient are provided by the user. The results calculated by the application are the heat exchanger area and duty, the utility stream flowrate, and the enthalpies and phase amounts (vapor/liquid) of all streams.

The overall structure of the application is fairly simple. The main input screen is the "Countercurrent Heat Exchanger" worksheet. It displays both the user input variables and the output values in two small tables. This worksheet is protected to allow changes to the input variables only. This is a simple way to prevent accidental changes to "locked" areas of the worksheet. (Select the "Tools:Protection:Unprotect Sheet" menu item to unprotect the worksheet.)

The "UserData" worksheet uses the row layout to setup four equilibrium calculations for the Process and Utility inlet and outlet streams. The equilibrium calculation functions are organized to return only the pH, the enthalpies and masses of each possible phase, and the totals for the stream. The values are then used to calculate the log mean temperature differences, the enthalpy changes for each stream, the exchanger heat duty, the energy and mass balance, the flowrate of the utility stream, and the required area of the heat exchanger.

The application can be easily modified to simulate a cocurrent heat exchanger. Other heat exchanger specification options (heat duty, utlity flowrate, etc) can also be added.

Process Variability Study Using Monte Carlo Simulation

Most approaches to simulation make an assumption concerning the values of process variables. That is they assume that the process variables are known exactly (e.g., T=25.0 °C, P=1.0 atm, pH=6.3). This is rarely the case in a production environment. The values of the process variables, even during times of smooth operation of the facility, fluctuate over a range, which itself may or may not be known with any certainty. These fluctuation in turn cause the quality and quantity of the product to also fall within a range, or distribution.

Monte Carlo simulations can extend the use of a deterministic model to the estimation of the distribution of process and product variables by accounting for the distribution in the range of the input variables. This kind of study is sometimes known as a risk and reliability study because it helps to quantify the risk of encountering certain conditions. The question it can answer is: What is the probability of my process running at off spec conditions?

It is generally desired that a crystallizer be run at some level of supersaturation. Below that level the process does not provide the desired product quality. This application uses Monte Carlo simulation to predict the probability of the solution in a crystallizer to be at or below a given level of supersaturation. It uses the range of fluctuation in the process temperature, pH and flowrates to show the risk of being below that supersaturation level or, worse, being below the solubility limit of the desired product.

Click here for a more detailed discussion of scaling tendencies and Monte Carlo simulation.

Equivalence Point Calculator

The equivalence point is defined as the point at which a stoichiometric amount of the titrant has been mixed with the sample. Experimentally, the equivalence point of a pH titration corresponds with the inflection point on the titration curve, or the root of the second derivative of the titration curve. In complex systems, it is possible to have multiple equivalence points, one for each titration endpoint. This application is a calculator that locates the equivalence point for a solution of Ca(OH)2 titrating with HCl. It uses both the isothermal and set pH calculations. It also mixes the row layout and the vertical layout features of the calcAQ.

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