ChE Plus Newsletter Volume 3, Issue 3

 In this issue:

The More You Know: Process Safety Information (PSI)
From our guest author, Mike McCue, learn the basics of process safety information management.  Read the full article.

Steam Tracing with MS Excel

Wondering who won the 2005 Spreadsheet Competition here at Cheresources.com?  Read this in-depth article from Andre de Lange as he details the brains behind this years winning spreadsheet, "Steam Tracing".  Read the full article.

 Results of the MS Excel Spreadsheet Content While we had many impressive entries for our spreadsheet competition, we could have only one winner.  As shown above, Andre de Lange of South Africa was the winner of our \$100 prize for his impressive work on modeling steam tracing.  We received too many entries to feature everyone's work, but these particular entries are available for download here at the site.  We'd like to thank everyone for participating.  Stay tuned for more promotions and chance to win from Cheresources.com. Vapor Pressures from Antoine Coefficients - by Chetan Mittal Column Diameter and HETP Calculation - by Joyy Dass Packed Column Scrubber Design Calculation - by Joyy Dass Reactor Particle Size and Velocity Calculation - by Miguel Larocca Condensate Line Sizing - by V. Velmurugan ** To download, right-click and select "Save As"

Cooling Tower Equations

Cooling towers are part of nearly every chemical processing facility.  Here are some crucial equations used to understand what is happening in your cooling tower.  These equations were submitted by Mr. Milton Beychok.  You can read more about cooling towers here at Cheresourc.com in our article titled "Cooling Towers: Design and Operation Considerations".

Here are the governing relationships for the makeup flow rate, the evaporation and windage losses, the draw-off rate, and the concentration cycles in an evaporative cooling tower system:

 M = Make-up water in gal/min C = Circulating water in gal/min D = Draw-off water in gal/min E = Evaporated water in gal/min W = Windage loss of water in gal/min X = Concentration in ppmw (of any completely soluble salts  … usually chlorides) XM = Concentration of chlorides in make-up water (M), in ppmw XC = Concentration of chlorides in circulating water (C), in ppmw Cycles = Cycles of concentration = XC / XM ppmw = parts per million by weight

A water balance around the entire system is:

M = E + D + W

Since the evaporated water (E) has no salts, a chloride balance around the system is:

M (XM) = D (XC) + W (XC)   = XC (D + W)

and, therefore:

XC / Xm = Cycles = M / (D + W) = M / (M – E) = 1 + {E / (D + W)}

From a simplified heat balance around the cooling tower:

(E) = (C) (DT) (cp) / HV

 where:    HV DT cp = latent heat of vaporization of water = ca. 1,000 Btu/pound = temperature difference from tower top to  tower bottom, in °0F = specific heat of water = 1 Btu/pound/°F

Windage losses (W), in the absence of manufacturer's data, may be assumed to be:

W = 0.3 to 1.0 percent of C for a natural draft cooling tower

W = 0.1 to 0.3 percent of C for an induced draft cooling tower

W = about 0.01 percent of C if the cooling tower has windage drift eliminators

Concentration cycles in petroleum refinery cooling towers usually range from 3 to 7.  In some large power plants, the cooling tower concentration cycles may be much higher.

Website Spotlight

Looking for another great engineering website?   Checkout XCalcs.com.  They feature a list of useful calculations online in real time from their site.   Calculations include beams, vessel, plates, pipes, and others.

New Category Available in ChE Links
Dr. Bernhard Spang has added a new category to ChE Links.  Stop by and visit some of the new sites listed under "Nanotechnology".   Some of the new sites include an Introduction to Nanotechnology, Friction at the Nano-Scale, What is Nanotechnology, and several others.

Overheard in the Online Forum

Learn How to Use BB Code to Enhance Your Posting
One of our loyal message board participates (Milton Beychok) has posted a guide to use BB code to properly format your messages.  Read it here.

Reboilers: Kettle versus Thermosiphon Designs

"I would like some guidance on the relative benefits of kettle vs. vertical thermosiphon reboilers in NGL (DeC3 and DeC4) service.  Specifically we are looking at a turndown of 4:1 and some are concerned that a thermosiphon would not turndown well.  I am unconviced as the drive mechanism is based on relative densities and would therefore (I think) be independent of flow through the exchanger. Alternatively does anyone forsee turndown issues with a kettle?"

Software Spotlight

EZZE AIRE is a utility designed to replace (supplement) the Psychrometric charts used by Engineers and HVAC specialists in heating, drying and air conditioning design and operations applications.  Currently, to determine air properties one needs to know two properties to determine the other 5 properties by using a ruler to extrapolate their values on two paper psychrometric charts.   This is a very confusing and inconsistent means of determining values to use in your design or process calculations.  EZZE AIRE removes inconsistencies by transforming the two Psychrometric charts into a paperless electronic chart which with a few key strokes produces air property values quickly and with good reproducibility.   In addition, there are sample problems which cover the most common process and air conditioning applications solved using EZZE AIRE.   The interface is extremely user-friendly and can be previewed here.

Discounts on CE Credits

Did you know that you can get a 10% discount on a variety of online CE courses offered by RedVector.com?  Visit the CE Credit section of our online store for instructions.   Remember, don't put the course in your "basket", use the link provided with each course description to order from RedVector.com.