In reference to "PC program estimates TEG circulation rate, number of trays" (OGJ, June 21, 1999, p. 36): Why would someone write a program for estimating circulation rate when this can be easily and quickly achieved on spreadsheets such as Microsoft Excel or any other spreadsheet software?
In addition, it appears from the article that, for a standard tray efficiency of 25%, the program will always estimate either 4 or 6 or 8 trays only. Also, if we look at the data in the example (without calculating), we would say that the number of trays should be 8, not 4 as indicated in the results.
In the nomenclature, density is mentioned in units of kg/cu m. But in the article, it is confusingly in kg/l.
I decided to enter the data from the article into an Excel worksheet. It required half an hour but yielded results different from those in the article, especially on the mass flow rates and circulation rate. There were also minor variations in most other results, which also could be attributed to rounding-off errors.
The results obtained were also different if one enters example data from the API design manual.
Finally, it would be useful if the equivalent in British units were also provided.
Javed Rizvi, P.E.
Pakistan Petroleum Ltd.
The author responds
- For estimating TEG circulation rate, one can use either such spreadsheet programs as Microsoft Excel or any simple program. In this particular case, the program is easier than spreadsheets because the absorption factor and the number of theoretical trays are given for different ranges, as shown in the equation box.
Further, we have to give only six input data and the output will be printed out. Many users may feel that this would be more convenient than using the spreadsheets.
- The plot of absorption-factor equation (as given in Reference 3) is correlated as Equations 8-10 in the article. Hence, this program will always estimate either 4, 6, or 8 trays. It is possible to have 10 or 12 trays, but the correlation is not given in the article, since this may happen very rarely.
- One cannot estimate the number of trays by just looking at the data given in the example. Further, the answer that "the number of trays should be 8" is incorrect. As mentioned in the article, the hand calculation is given in Reference 3 for the same input data, and the number of trays is 4, not 8.
- Although the calculation uses the unit for density as kg/l., the nomenclature gives it as kg/cu m. This will not affect the calculation, per Equation 18, however.
- The results in the article agree well with Reference 3. Some minor variations may exist, because many graphs (such as the water content of inlet gas, the activity coefficient for water in TEG-water solutions, and the absorption factor) are represented by correlated equations.
To several other reader inquiries: This program is written in Fortran and can be easily run with Windows 98 (or earlier version). Click the icon "Microsoft Developer Studio" and get into "Fortran Power Station." Create "Input" and "Output" files. Then "Build" the program with this Power Station and execute it.
King Fahd University of Petroleum and Minerals
Dhahran, Saudi Arabia