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ERT 312 SAFETY & LOSS PREVENTION IN BIOPROCESS RELIEF SIZING. Prepared by: Pn. Hairul Nazirah Abdul Halim. OBJECTIVES. Calculate the size of various relief apparatus: a) Spring operated reliefs in liquid & gas service b) Rupture disc reliefs in liquid and gas service.
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ERT 312SAFETY & LOSS PREVENTION IN BIOPROCESSRELIEF SIZING Prepared by: Pn. Hairul Nazirah Abdul Halim
OBJECTIVES • Calculate the size of various relief apparatus: a) Spring operated reliefs in liquid & gas service b) Rupture disc reliefs in liquid and gas service
Relief vent area calculation depends on: a) type of flow (liquid, vapor or two-phase) b) type of relief device (spring or rupture disc)
Spring operated reliefs in liquid service • Liquid velocity through the spring relief: • Relief area: A = the computed relief area (in2). Qv = the volumetric flow through the relief (gpm), C0 = the discharge coefficient (unitless), (ρ / ρref) = the specific gravity of the liquid (unitless), ΔP = the pressure drop across the spring relief (lb/in2). Kv = the viscosity correction (unitless), Kp = the overpressure correction (unitless), Kb = the backpressure correction (unitless), Ps = the gauge set pressure (lb/in2), and Pb = the gauge backpressure (lb/in2).
Example 9-1 A positive displacement pump pumps water at 200 gpm at a pressure of 200 psig. Because a dead- headed pump can be easily damaged, compute the area required to relieve the pump, assuming a backpressure of 20 psig and a 10% overpressure. Solution a. The set pressure is 200 psig. The backpressure is specified as 20 psig and the overpressure is 10% of the set pressure, or 20 psig.
Spring operated reliefs in gas service • Vapor discharge mass flow
Relief vent area for Ideal gas Relief vent area for Non-ideal gas
The constant X can be calculated using Equation 9-10. • Do Example 9-2
Rupture disc reliefs in gas service • Flow of vapor through rupture discs: • Where discharge coefficient C0 = 1.0
Rupture disc reliefs in liquid service • Relief area: A = the computed relief area (in2). Qv = the volumetric flow through the relief (gpm), C0 = is the discharge coefficient (unitless), (ρ / ρref) is the specific gravity of the liquid (unitless), ΔP = the pressure drop across the spring relief (lb/in2).
Example 9-3 Determine the diameter of a rupture disc required to relieve the pump of Example 9-1, part a. Solution The pressure drop across the rupture disc is The specific gravity of the water (ρ/ρref) is 1.0. • A conservative discharge coefficient of 0.61 is assumed.
