NOTE --- When unzipping the ESPMODEL.ZIP file be sure to use the "-d" option (ie., PKUNZIP -d ESPMODEL.ZIP). If this option is not used the setup program included will not be able to find the files it needs. (FYI - The "-d" option in PKUNZIP restores the directory structure stored into the ZIP file.) --------------------------------------------------------------------------- ÉÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍ» º º º ESPVI VERSION 4.0a º º º ÈÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍͼ This file contains information about relatively minor changes that have been made to ESPVI 4.0 for the purposes of improving its operation and stability. The primary description of the use and operation of ESPVI 4.0 remains the documentation provided with the original version, but this file contains additional information about the program. In general, the changes have been made to improve the operation of the model with regard to data entry and automation. Several months' use of the model showed that some operations were performed repeatedly with manual adjustments of parameter values. Some of these have been automated to obtain the same results faster and more accurately. INTERNAL CHANGES In a recent paper, Hutchins, et al., (Aerosol Sci. Tech. 22:202-218), present measurements of the Cunningham correction factor and give viscosity and mean free path formulas they use in their data reduction. All these factors have been incorporated into ESPVI 4.0a, because they now seem to be the best values to use. The mean free path and Cunningham Factor do not show up directly in the results, but the gas viscosity calculated with the new expression is roughly 10 percent larger than previously. The new viscosity value should be transferred to your data files and saved (see below about data files). The overall change in collection efficiency is small, but the changes do affect the submicron particles noticeably. In the file DATA.CNF, a number of values related to coal have been removed because they were not used. In addition, the number of available wave forms has been increased. Therefore, if you want to maintain the previous version of ESPVI 4.0, you must also maintain a copy of the old version of DATA.CNF. There are more data stored in some of the data files now. Every effort has been made to allow data files from the previous version (ESPVI 4.0) to be used in this version, but some values may require manual editing. When files are saved under this version, the newly added data are appended to the end of the file. In some cases, it has been noted that data files from the previous ver- sion give poor and inaccurate results. Therefore, it is recommended that the results from files created with ESPVI 4.0 be checked. If there are any doubts, the data files should be recreated. The Help system has been updated to be more sensitive to the context of the current screen. There are more help topics and improved descriptions of the options available. Where help is not appropriate, it does not display when is pressed. There have been a few other internal changes for improved predictions. First, the PM10 values have been corrected to be based on aerodynamic particle diameter (as described in the Federal Register) rather than physical diameter (as done in ESPVI 4.0). The resulting changes are relatively small, but if you see a discrepancy from previously calculated PM10 values, this is one reason. Second, particle charging has been modified to use an improved algorithm. The algorithm is faster, more accurate, and allows for effects of bipolar charging. The predicted charges are slightly smaller than in the previous version. Third, since the new charging algorithm easily accounts for bipolar charging effects, a back corona model has been incorporated. The back corona model detects the onset of back corona as in the previous version, but now adds a back corona charging current to the charging model and reduces the corona onset voltage slightly. Together, these effects mimic most of the known effects of back corona. In cases with severe back corona (high resistivities and high current densities), the model will probably predict very much higher current densities than ESPVI 4.0 would with the same peak-to-average ratios. The peak-to-average ratios should be decreased to bring the calculated current densities into better agreement with the measured values. Despite the improvements in back corona prediction with ESPVI 4.0a, there are still cases of back corona that remain difficult to explain. Such cases may have back corona in only a small fraction of the electrodes, but to such a degree that it determines the voltage and current density for the whole section. In the file DATA.CNF, there is a parameter under the title "Back Corona Multiplier" that can be used to change the program's response to back corona. If the parameter is set to 1000 or larger, all the back corona modeling is turned off (detection of back corona is still reported.) If the parameter is set to any other number, the modeling is on but the number describes the maximum charge degradation that can occur. The value 10 has been chosen to fit a number of cases where back corona is a problem. Although the user can modify the back corona multiplier with a text editor, we can give no guidance about a better value to use. Fourth, even though the dust layer thickness was a parameter is the previous version, its only effect was to modify the effective wire-plate spacing. In this version, the voltage drop in the dust layer is also computed. The dust layer voltage drop affects the electric field in the wire-plate gap. Generally, you will see little effect until the layer is 2 or 3 mm thick and the resistivity is above 10E11 ohm-cm. When back corona is detected, the voltage drop across the layer is held fixed at the value of the breakdown voltage. CHANGES IN FEATURES The following features have been added, in the order of their appearance in ESPVI. COLOR - The visual appearance of the program has been modified by changing the screen colors. Whether or not the colors are an improvement, a new program, COLORSET, has been added to the package for the purpose of allowing you to change the colors. COLORSET reads the color values from the file MENU.CNF and displays them on the screen. By choosing and saving new colors to MENU.CNF, you may customize the program's appearance to a large degree. The graphs have been modified to use a white background and cannot be modified. MAIN MENU - The previous main menu contained the entry "Calculate V-I & Performance." These two functions have been split into separate items for "Calculate V-I Curves" and "Performance Calculation." The two functions have been separated because they are used differently. In addition, arrow symbols () have been added beside menu items that lead to another menu, while the absence of an arrow means that a direct action will be taken or a data entry form will be obtained. The bottom line of the display is used to indicate active function keys or to display messages that may be of help during calculations. FILE OPERATIONS MENU - two options have been added to the file choices: "Create New Master File" and "Access Data Directory." The first of these choices will make a whole new set of data files from the data currently in use. The user is prompted for a file name that has not been used before and the files are created. This should make the creation of a new ESP data set from an existing one much easier. Of course, the newly created files will need to be edited to put in correct values. "Access Data Directory" calls an auxiliary program to allow direct access to data files. This option has been added to allow for deletion of obsolete data files and to provide a quick way to see all the data files together. The access makes use of the Ziff-Davis program DR.COM (used with permission.) FILE/BROWSE MENU - another option has been added, "Incremental Results." This option allows viewing of a file that stores electric field, current density, and space charge values at each increment of the calculation. It may be helpful in understanding the detailed operation of the ESP. The increments in the file are the upstream and downstream values for each element. Sparking conditions are indicated with an asterisk (*) next to the gas field values; back corona conditions are indicated with and asterisk next to the dust field values. The local current density and particulate space charge are also shown in the file. Values of local electric field in the gas and in the dust layer are displayed in files named "master.INC", with "master" being the name of the Master file. Some increment files are too long for the simple file browse viewer to display entirely. These files may be viewed whole under "Access Data Directory" as described above. DATA ENTRY - There have been no changes in the submenu, but there have been several changes in the actual data entry menus and in some of the default actions. DATA/DESIGN/OVERALL PARAMETERS - Previously, when the number of sections in an ESP was changed, the user was required to save each of the affected files separately: design, operating voltages, and sneakage/rapping/turbulence. Failure to do so would cause problems in subsequent attempts to use the file. Now, when the number of sections is changed, all three files will be saved together, using whatever values are current when the save operation is performed. We recommend performing the save while still in the Design menu; then modify whatever values are needed in the voltage and SRT menus and save again in each of those. Remember that whenever the number of sections is increased, the new sections receive all the values from the previous final section. DATA/OPERATING VOLTAGES - Two items on the menu have been changed or added. There is a bias reset option and the wave form input is now a section-wise menu. The bias reset removes the effect of one of the automatic performance calculations. When the corona onset is adjusted automatically, all the corona onset factors for the section are shifted by the same amount (biased); usually, the biases are different for each section. The Bias Reset simply returns all the bias values to zero. The WAVE FORM menu now requires entering a distinct "wave form number" for each section. This is aimed toward the use of intermittent energization, where common practice is to adjust the duty cycle for optimum section performance. With the copying ability of the data entry menu, the setting of values is not much harder than previously. DATA/OPERATING VOLTAGES/JINPUT&CINPUT - Three new inputs are /requested in both these menus related to the power supplies: maximum voltage (average), maximum peak voltage, and maximum current (average). These values can usually be obtained from the manufacturer's specifications. The maximum peak voltage can also be estimated as 1.414 times the maximum average voltage. If the values are not known, then set them to 0 as a sign that there are no valid numbers for the parameters. These power supply limits are used to terminate V-I calculations and adjustment calculations when they are reached. However, values of zero will not terminate any calculations. The maximum current rating for a section should be the sum of the ratings for all TR sets that supply the section plate area. The total current may exceed the rating of one power supply, but should not exceed the rating of all supplies together. Some common TR set maximum ratings are 45 or 55 kV average voltage, 63 or 70 kV peak voltage, and 500, 1000, or 1500 mA average current. ESPs that require more current will have multiple units operating in parallel. DATA/ELECTRODE - In this version, when the displayed section number is changed, the electrode data for that section is automatically loaded. This means that some operations will need to be performed in a different order, but review and modification of existing data will be easier. Specifically, to edit the electrode file for a section, display its section number and proceed to ELECTRODE description. However, to copy the electrode data from one section to another, move to the destination section, load the data from the other section's file, and then, save the destination's data under a new file name. The graph option now displays whatever data is current, not the data that exists in the current file. This allows the user to see the effects of changes without saving the changed data to the current file. Once the changes are satisfactory, however, the user must save them explicitly before moving to another section, or the changes will be lost. Another menu, OPTIONS for input, has been added to facilitate electrode spacing. The OPTIONS allow for setting the element locations with a constant spacing (Average) or setting an inlet and outlet offset distance and spacing the remaining elements equally among those locations. This menu may help more with wire electrodes than with mast electrodes. DATA/SNEAKAGE/BY SECTION - There are three changes in this menu. The turbulence parameter has been designated "Turbulent core number", and the two misalignment inputs have been expanded from single values for the whole ESP to sectional values in the SNEAKAGE menu to allow for section-to-section variations. The Turbulent Core Number represents a different way to calculate the effects of turbulence. Essentially, the change is from a Highly turbulent Deutsch-type collection to a series of laminar collection zones separated by regions of complete mixing. The core number describes the number of laminar zones per element and generally should have the value 1. That is, as particles pass under and element (wire), they experience an electrical force much stronger than the turbulent forces that cause mixing and are collected as if the mixing did not exist; once past the element, the mixing dominates again. To allow the mixing to continue under each element, set the core number to 5 or 10. Then, there would be five or ten mixing zones as the particles pass the element. To allow for very low turbulence, set the core number to 0.2 to 0.5; then the particles would pass two to five elements before mixing would occur. In ESPVI 4.0, the Turbulent Core Fraction served the same purpose but represented a different concept and could not exceed 1. The new Turbulent Core Number allows a meaningful parameter to cover the range from full laminar flow to full turbulent flow. The files for the Sneakage/Rapping/Turbulence now contain velocity maldistribution factors, saved into the file whenever maldistribution is calculated (see below). These values are then used to modify the ideal performance without requiring the maldistribution calculation each time. A consequence of this storage is that all the SRT values are saved when the maldistribution is calculated; you therefore need to be certain the right parameter values are current when the operation is performed. DATA/FLUE GAS/COMPOSITION - The EXCESS AIR entry has been removed since it was not used in the calculations. The gas composition should be the composition at the inlet of the ESP, where any excess air or leakage would be included. DATA/PARTICLE - A new input menu has been added, FREQUENCY. This is the differential form of the HISTOGRAM input menu that deals with the cumulative distribution. The cumulative values are used to derive relative frequency values that can be edited in FREQUENCY. If FREQUENCY is used for editing, the resulting cumulative values may change slightly, because the frequency values are normalized to 100 percent (sum of frequency percentages = 100), while the cumulative input does not require that the final cumulative total be 100 percent. FREQUENCY may be useful in emphasizing or reducing particular particle size contributions, such as in submicron sizes, or in transferring differential size distributions from published graphs. HISTOGRAM is still the preferred method for entering data from impactors. With FREQUENCY, it is easy to zero out a particular size contribution; with HISTOGRAM, you must consider the effect on the whole distribution. The cumulative distribution graph has been changed to a logarithmic scale to show more detail at the small diameters and the relative frequency of each particle size has been added to the display. V-I CALCULATION - There is one new choice on the menu, "Automatic V-I Calculation." This choice will calculate a V-I operating point by stepping the peak voltage upward in the increments determined by Set V-I Options. However, "Automatic" will terminate the ramping of voltage according to three criteria: sparking onset, heavy back corona onset, or power supply limits. This option differs from "V-I Curve Calculation" in having the termination procedure. The computation may be viewed as printed values or graphical values, according to the Graphics On/Off switch. A message describing the reason for the termination is written at the bottom of the screen each time the V-I curve for one section is finished. The power supply limits (voltage and current) are new inputs requested under "Operating Voltages," as described later. If zero values are used for the power supply limits (to indicate unknown values), the termination will be only for sparking or back corona. PERFORMANCE CALCULATION - Most of the changes and additions to ESPVI 4 appear in this menu. What was formerly a single choice, "Performance Calculation," has been expanded into several. There is "Standard Method," three types of adjustments, and "Compute Maldistribution." "Standard Method" comes closest to the original "Performance." The reasons for the additions are as follows. Repeated testing with ESPVI has convinced us that the model will accurately predict total section currents if all the input parameters are correct (voltage, peak-to-average ratio, corona onset factor, particle size distribution, etc.) Unfortunately, in most cases, one or more of the parameters are not known, but the total current or current density is known. The adjustment calculations are designed to seek out values for parameters that match the predicted current to the known current. In addition, the velocity maldistribution correction that was used in the original ESPVI was an approximation. As we gained better understanding of the effects of maldistribution, it became apparent that another type of calculation was needed. The present approach computes the ESP performance at seven gas velocities distributed around the mean value according to the velocity standard deviation. The individual computed performances are then combined in a weighted manner to obtain the total maldistribution effect. Factors that indicate the ratio of performance with maldistribution to the performance without maldistribution are computed and stored for future computations. "Compute Maldistribution" performs the seven-fold computation explicitly and should be performed whenever the total efficiency of the ESP changes by more than a few percent. "Standard" will also perform the maldistribution computation if 1) it has never been performed before, or 2) certain parameters have changed enough to require a new computation. The parameters that are checked for changes are SCA, plate area, gas volume flow, gas velocity, and rapping or steady reentrainment factors. All of these require a recomputation if they are changed by more than a few percent. The maldistribution factors are stored in the Sneakage/Rapping/Turbulence files automatically after each seven-fold computation. If the Standard computation is used without the maldistribution computation being required, then the prestored maldistribution factors are used to modify the ideal performance calculation. The "Adjust xxx" choices use the given current density and the computed current density to adjust a parameter. "Adjust Peak Factor" varies the peak-to-average ratio for a match. "Adjust Onset Factor" changes the corona onset factors for the whole section by the same amount to reach a matching condition. "Adjust Particle Dist" changes the number concentration at 0.2 æm to match only the first section's current density. These are explained in more detail below. The peak-to-average ratio is a critical parameter whose value is rarely known. Very few measurements have been reported in the literature, and it is sensitive to the electrode geometry and power supply configuration. Therefore, we think it reasonable to adjust the parameter for a current density match, within bounds. If power supply limits have been provided, the peak-to-average ratio will not be allowed to produce voltages above the supply peak voltage limit. The corona onset for each element is set in the electrode input menu. The adjustment is applied to all elements of the section at one time in the form of an additive constant, called a corona onset bias. The values of the bias may be displayed and stored in the Operating Voltage menu; they may also be rest to zero there. By using a section-wise bias, the same electrode file may be used for many sections without requiring a separate electrode file to accommodate each corona onset value. It is also difficult to justify adjusting the corona onsets of single elements to match the current for the whole section, at the present level of knowledge of ESP operation. In fitting ESP measurements with the model, cases of high voltages and low currents in the first section of an ESP have been encountered. These cases suggest the presence of a strong particulate space charge, yet opacity measurements do not show abnormally high particle concentrations. It seems likely that submicron particles are present, contributing to the space charge, but invisible as far as opacity is concerned. Such submicron peaks have been observed experimentally. "Adjust Particle" varies the concentration of particles of about 0.2 æm diameter to match the current in the first section only. Later sections might have to be adjusted by other means, but often fall in line when the first section is made to match. This choice is really only effective when the computed current density is well above the measured current density. Each of the Adjust xxx operations is independent of the others. They can be applied sequentially in any order, but the results may well be different. For instance, if adjusting the corona onset improves the match between calculated and measured currents but does not match them precisely, the peak-to-average ratios can then be adjusted to finish the match. This may result in a different set of operating conditions and collection performance than if the peak-to-average ratios were adjusted first. Remember, the adjustments are included to compensate for imperfect knowledge of the operating conditions. If the corona onset voltages are known, even roughly, the corona onset factors should be set to give the proper onset voltages and not be adjusted to match the measured currents. If the peak-to-average ratios have been measured, they should be set at the measured values and not be adjusted to match the measured currents. The user will have to develop some awareness of appropriate and inappropriate values for the adjusted parameters. VIEW RESULTS - In the particle description page, the differential inlet concentrations have been added. These can be used with the penetrations to compute the outlet differential distributions. GRAPH RESULTS - A new graph has been added, Wave Form. This graph shows the computed wave form one section at a time. When half-wave or intermittent wave forms are displayed, the inactive half-cycles are displayed at low amplitude along the lower axis. The internal TR set voltage is shown as a dotted sinusoidal curve. The actual electrode voltage is the solid curve. A double-dotted horizontal line represents the average voltage of the wave form. A black, dashed line below the wave form represents the lowest voltage reached by one wire in the section; other wires may not be as low. The red, dot-dashed line represents the corona onset voltage for the section under clean gas conditions. In the size-dependent penetration and cumulative mass graphs, the pure log- arithmic scale has been changed to a bounded logarithmic scale. A bounded logarithmic scale has the values in the lowest decade compressed so that all values down to and including zero can be plotted. This scale has been incor- porated because the graphs used fixed lower bounds anyway, so many low values were simply not plotted. Now they will be plotted, but at very low resolution. Except for the baseline (0 value) on the plot, all the other grid lines shown are precisely the same as their counterparts on a pure logarithmic scale. UTILITIES & CONFIGURATION - The only change here is that the configuration is automatically saved when the menu is exited, whether or not any changes have been made. The same configuration file is read whenever entrance is made into the menu. ADDITIONAL OUTPUTS The internal values of several calculations are now stored in output files for further use. In general, if you don't want these files, you can turn them off by setting Print Details to OFF in the configuration menu. The charge on particles at the outlet of each section is stored in the file named "master.CHG", where "master" is the Master File name. The values are stored as the number of electrons on each particle and as the ratio of actual charge to the calculated saturation charge. These files may be viewed from within the program under FILE/BROWSE/CHARGE. Values of local electric field in the gas and in the dust layer are displayed in files named "master.INC", with the same naming convention as for the charge files. The increments in the file are the upstream and downstream values for each element. Sparking conditions are indicated with an asterisk (*) next to the gas field values; back corona conditions are indicated with and asterisk next to the dust field values. The local current density and particulate space charge are also shown in the file. These files may be viewed from within the program under FILE/BROWSE/INCREMENTAL (or FILE/ACCESS if the results are too long.) Finally, outlet particle concentrations for each particle size are displayed in files named "master.PTn", where n is a digit from 0 to 9. These files represent the last ten outputs that have been calculated. The files also contain the gas velocity used during the calculation. These files are intended to be used in cases where the flow or electrical conditions are so different that one pass of the model is not adequate. Consider a 4 chamber ESP with unequal division of flows. The collection performance of each chamber can be predicted with the velocity and voltages appropriate for each, one after another. The output concentrations would be stored in "master.PT0", "master.PT1", "master.PT2", and "master.PT3". If you then load each file into a spreadsheet program (or calculate by hand), you should multiply each particle concentration by the gas velocity of that data set, then add the velocity-concentration products for each size in all the data sets, and then divide by the sum of the gas velocities for the four sets. This produces a velocity-weighted average outlet concentration that can be used to obtain total emissions, opacity, etc. Three files have been supplied for use in printing the graphical screens: VGAEGRAF.COM, VGAHGRAF.COM, and VGAHRSYS.SYS. The file VGAEGRAF.COM can be installed with a line in the AUTOEXEC.BAT file; it translates the graphics screens into a form that EPSON-compatible printers can print. The file VGAHGRAF.COM can be installed the same way and translates the screens for Hewlett-Packard-compatible printers. Either of the two files should be installed in a location such as the DOS directory from where it could be loaded by the appropriate line in the AUTOEXEC.BAT file. Some printers such as the Hewlett-Packard Deskjet will reverse the black/white values on the printed page with the above files. In that case the file VGAHRSYS.SYS should be installed in the ESPVI 4.0a directory, and the following line inserted in the CONFIG.SYS file: DEVICE=C:\ESPVI\VGAHRSYS.SYS This file translates for Hewlett-Packard Deskjet type printers, reversing the black/white values on the page. If VGAHRSYS.SYS is used neither of the other two files should be loaded. If either a drive other than C or a directory other than ESPVI is used for ESPVI 4.0a, appropriate changes should be made to the CONFIG.SYS line. Another option is to install the DOS program, GRAPHICS.COM, contained in MSDOS 6.x, with an appropriate command in the AUTOEXEC.BAT file. With this option use the appropriate profile (see DOS help) for the printer you have. An advantage with this option is that it provides full size printouts with a higher level of detail than does the other options, which only provides half-page printouts.