Posted: 12/12/2008 12:36:11 PM EDT
|
My mind is not working so good today.
Thanks. A glue-making process releases ethylene glycol that becomes generally diluted and interspersed throughout the plant atmosphere. The rate of release is 2.4 cubic feet per hour vapor volume at standard plant temperature and pressure. The plant ventilation system is of the general dilution type with make-up air being supplied at windows and doors throughout the plant area. The plant area is 4000 square feet and the average ceiling height is 12 feet. The problem is to specify the capacity of the general ventilation system required to maintain a steady state condition throughout this process area that protects against both health and safety hazards due to ethylene glycol. For your information in performing calculations the following data is provided: ETHYLENE GLYCOL (CH2OHCH2OH) Molecular weight: 62.1 Boiling point: 197.5o Celsius LEL: 3.2% Firepoint: -13o Celsius Flash point: 232o Fahrenheit Autoignition temperature: 752o Fahrenheit Vapor Pressure: 0.05 mm @ 20o Celsius PEL: 50 ppm (Ceiling) (a) Calculate how much exhaust ventilation (in cubic feet per hour, general dilution type) is required to maintain safety hazards below explosive levels. (b) Calculate how much exhaust ventilation (in cubic feet per hour, general dilution type) is required to maintain health hazards below OSHA-Permissible Exposure Limits (PEL). Is this the correct answer? 2/X = 50/1,000,000 X = (2 x 1,000,000)/50 X = 40,000 cu ft hr (c) Calculate how many plant area room changes per hour the level of ventilation calculated in part (b) would represent. |
|
a) LEL = 3.2% To compute the volume of air required to meet this limit, knowing that the gas release rate is 2.4 cuft/hr, we just use a simple ratio.
3.2/100 = 2.4/x (where x is the total volume of the mixture, INCLUDING the hazard gas) x = 75 cuft/hr 75 cuft/hr - 2.4 cuft/hr = volume flow of change air = 72.6 cuft/hr. Your answer for b) is incorrect. You have a 2.4 cuft per hour release that needs to be dilluted to below 50ppm. Now, ppm is not computed by volume (strictly speaking) but because all measurements are taken at the same temperature and pressure, Avogadro's remains consistent and you can use volume. So to dilute 2.4 cuft to 50ppm, you need to add 2.4/x = 50/1,000,000 You were close, but you have the release rate incorrect. x = 48,000 cuft/hr. You'll want to multiply that by whatever your safety factor is as well. c) If we assume that plant volume = 4000 sqft * 12 ft = 48000 cuft, that's exactly one room change per hour. |
Win a FREE Membership!
Sign up for the ARFCOM weekly newsletter and be entered to win a free ARFCOM membership. One new winner* is announced every week!
You will receive an email every Friday morning featuring the latest chatter from the hottest topics, breaking news surrounding legislation, as well as exclusive deals only available to ARFCOM email subscribers.