Page 573 - APPLIED PROCESS DESIGN FOR CHEMICAL AND PETROCHEMICAL PLANTS, Volume 1, 3rd Edition

Applied Process Design 539

R' = adjusted value of R, for NFPA Code-69 VL = flow rate at flowing temperature, U.S. gallons
Rexp = distance from center of explosion source to the per minute, or required liquid capacity in U.S.
point of interest, ft gallons per minute
Re = Reynolds number (or sometimes, R) v = shock velocity, ft/sec or ft/min (depends on
Rg = Universal gas constant= 1544 = MR units selected)
Rge = individual gas constant = MR/M v 1 = specific volume of gas or vapor at upstream or
R; = inside radius of vessel, no corrosion allowance relief pressure and temperature conditions, cu
added, in. ft/lb
R = temperature, absolute, degrees Rankin v, = sonic velocity of gas, ft/sec
0
r = re = ratio of back pressure to upstream pressure, v 1 ,v 2 = volume percent of each combustible mixture,
P 2/P 1, or critical pressure ratio, PjP 1 free from air or inert gas
r 1 = relative humidity, percent \,V = required vapor capacity in pounds per hour, or
S = maximum allowable stress in vessel wall, from any flow rate in pounds per hour, vapor relief
ASME Code, psi., UCS-23.1-23.5; UHA-23, rate to flare stack, lbs/hr
UHT-'.23 We = charge weight of explosive, lb
S' = SpGr = specific gravity of liquid, referenced to We= effective charge weight, pounds of TNT for esti-
water at the same temperature mating surface burst effects in free air
Sc = Sg = SpGr of gas relative to air, equals ratio of W, = required steam capacity flow or rate in pounds
mol wt of gas to that of air, or liquid fluid spe- per hour, or other flow rate, lb/hr
cific gravity relative to water, with water = 1.0 at \,Vhc = hydrocarbon to be flared, lbs/hr
60°F WTNT = equivalent charge weight of TNT, lb
SpGr = specific gravity of fluid, relative to water = 1.0 WL = liquid flow rate, gal per min (gpm)
St = dust hazard class Wsteam = steam injected into flare, lbs/hr
St St = stainless steel w = charge weight of explosives of interest, lb
SSU = viscosity Saybolt universal seconds Yr= final oxidant concentration, mo! fraction
S = degrees of superheat, °F
0 Yj = specified component concentration after 'T'
T = absolute inlet or gas temperature, degrees purges
Rankin °R = °F + 460, or temperature of relief y0 = initial concentration of component (oxidant)
vapor [26], R under low pressure, mol fraction
0
T 11 = normal operating gas temperature, R Z = compressibility factor, deviation of actual gas
0
T; = operating temperature, °C (NFPA Code-69) from perfect gas law. Usually Z = 1.0 at low
0
T = temperature of service, R pressure below 300 psig.
O
TL = equilibrium temperature at which the lower Z, or Z 1-:--:T = scaled distance for explosive blasts, ft/ (lb) I/ 3
flammable limit composition exists over liquid z = actual distance for explosion damage, feet
in dry air at one atmosphere (theoretical flash
point), °C or °F Subscripts
Ts, = equilibrium temperature at which C,, exists over
liquid in dry air at one atmosphere, °C or °F
Tu = equilibrium temperature at which the upper I = condition I
flammable limit composition exists over liquid 2 = condition 2
in dry air at one atmosphere, °C or °F
T w = vessel wall temperature, R Greek Symbols
0
T 1 = gas temperature, R, at the upstream pressure,
0
determined from T1 = (P 1 /P 11) (T 11) � = beta ratio orifice diameter to pipe diameter (or
t = minimum required thickness of shell of vessel, nozzle inlet diameter)
no corrosion, inches E = (epsilon) emissivity value
Uoo = viscosity at flowing temperature, Saybolt univer- ),,, = (lambda) yield factor, (\A//W 0) 1 13, with subscript
sal seconds "o" referring to reference value
U = lateral wind velocity, fl/sec µ = (mu) absolute viscosity at flowing temperature,
Uj = flare tip velocity, ft/sec centi poise ( cp)
UEL = upper explosive or flammable limit, percenr of n = (pi), 3.1418
mixture of flammable gases only in air p = (rho) fluid density, lb/cu ft
V = velocity, ft/sec, or dust vessel volume, cu ft 't: = (tau) fraction heat intensity transmitted
or, V = vessel volume, cubic meters or cubic feet, or
required gas capacity in SCF!'vl
or, V = vapor flow required through valve (sub-critical), References
_ Std cu ft/min at 14.7 psia and 60°F
V = specific volume of fluid, Cl! ft/lb l. American Society of Mechanical Engineers (ASME) Boil-
V,. = required air capacity, SCF"lv[ er and Pressure Vessel Code, Section Vll l, Pressure \lessels,
Ve = cubic feet of free air per hour from Table 7-17, published by American Society of Mechanical Engineers,
which is 14.7 psia and 60°F, or from Equation 7- New York, N.Y., 1989.
49, for wetted area A,. > 2800 sq ft 2. Ibid., Section VII, Power Boilers, 1974.
V' = venting requirement, cubic feet free air per 3. Bigham, J. E., "Spring-Loaded Relief Valves," Chem. Eng.,
hour at 14.7 psia and 60°F Feb. 10, 1958, p. 133.