Good day,
I have spent some time going through the forum topics and resources. I apologize if I am repeating a previously discussed and resolved topic.
I have a fuel depot project that includes tank API inspections. Part of the work scope is to provide emergency venting to six 83cu.m vertical pencil tanks. The tanks are not API tanks and do not satisfy API 650 5.8.5.3, regarding a frangible tank to roof joint.
API 2000 7th Ed, 2014 has been followed to determine the normal venting required. The emergency vent sizing has provided some queries though.
The tank details are -
Dia: 2.87m
Hgt: 14.4m
Product: Diesel (AGO 50)
Due to the tank being a diesel tank, and will remain in diesel service, the normal venting requirement and the emergency venting requirement will be met with a single free vent.
The required effective discharge area has been calculated from eqn D.27 in Appedix D of API 2000 -
Aeff = qf/(125.15*pi*√((1/M*Tb*Z)*k/(k-1)*((po/pi)2/k-(po/pi)(k+1)/k))
Calculating qf from eqn 14 section 3.3.3.3.2 in API 2000 -
qf = 906.6*(QF/L)*(Tb/M)^0.5
Some of the variables here are -
M = 170g/mol (diesel) or 29g/mol (air)
k = 1.4 (air), diesel not known
pi = 123.84kPa
po = 101.325kPa
L = 250 000 J/kg (diesel)
The queries are as follows:
1. Considering the product is diesel, should the relative molar mass (M) of air be used in determining the venting requirement?
2. In determining the absolute pressure ratio -
i. API 620 9.2.2 states that a supplemental pressure-relieving device shall be capable of preventing the pressure from rising more than 20% above the maximum allowable working pressure.
ii. API 620 5.3.1.1 states that the working pressure shall not exceed 103.2kPa
Based on API 620 is it reasonable to size the emergency vent on an absolute pressure at device inlet (pi) of 20% higher than the maximum allowable working pressure, giving pi = 123.84kPa? Bearing in mind that the tank is not an API tank.
Thank you in advance for any assistance on these queries. The chereresources.com forums and resources are live and provide excellent support based on the reading I have done thus far.
Edited by Hanro Rousseau, 31 March 2016 - 08:42 AM.