evan406's version from 2015-12-09 05:21

Ch 7

Procedures for avoiding the flammability zone

Question Answer
Inertingthe process of adding an inert gas to a combustible mixture to reduce the concentration of oxygen below the LOC: usually nitrogen or carbon dioxide, sometimes steam
Characteristics of Inertingvacuum purging is the most common inerting procedure for vessels; not used for large storage vessels because they are not usually designed for vacuums

vessels can be pressure-purged by adding inert gases under pressure

sweep-through purging process adds purge gas into a vessel at one opening and withdraws the mixed gas from the vessel to the atmosphere or scrubber from another opening
Taking a Vessel out of serviceefficient procedure: to inert with nitrogen until a point is reached, then air can be introduced

more efficient: first pump air into the vessel until a point is reached on the air stoichiometric line above the UFL, followed by pumping nitrogen into the vessel, followed by more air
Placing a vessel into servicethe vessel begins with air

followed by nitrogen until a point is reached

then fuel is pumped in until a point is reached
What is considered dangerous static electricity?For industrial operations where flammable vapors may be present, any charge accumulation exceeding 0.1 mJ is considered dangerous (the static buildup created by walking across a carpet averages about 20 mJ and exceeds several thousand volts)
What is the most effective and reliable method for preventing ignition?Inerting

Ways to discharge

Question Answer
spark a discharge between two metallic objects; this is an energetic spark that can ignite a flammable dust or gas
propagating brusha discharge from a grounded conductor when it approaches a charged insulator that is backed by a conductor; these discharges are energetic and can ignite flammable gases and dust
conical pilea form of brush-type discharge that occurs at the conical surface of a pie of powder; these are relatively intense discharges that can ignite flammable gases and dusts
brusha discharge between a relatively sharp-pointed conductor and either another conductor or a charged insulated surface; this discharge is less intense and is unlikely to ignite dusts, however it can ignite flammable gases
lightning-likedischarges from a cloud in the air over the powder; do not occur in small-volume vessels; no evidence that lightning-like discharges have resulted in industrial deflagrations
coronasimilar to a brush discharge; has sufficient energy to ignite only the most sensitive gases

Methods for preventing the buildup of charges on a product

Question Answer
Method 1 for preventing the buildup of charges on a productprevent charges from accumulating to dangerous levels by reducing the rate of charge generation and increasing the rate of charge relaxation; usually used when handling liquids
Method 2 for preventing the buildup of charges on a productprevent charges from accumulating to dangerous levels by designing the system to include charge reduction by means of low-energy discharges; usually used when handling powders
Method 3 for preventing the buildup of charges on a productwhen dangerous discharges cannot be eliminated, then prevent the possibility of an ignition by maintaining oxidant levels below the combustible levels or by maintaining fuel levels below the LFL or above the UFL
Bonding and GroundingBonding and grounding reduces the voltage of an entire system to ground level or zero voltage

The voltage difference between two conductive materials is reduced to zero by bonding the two materials

The voltage between sets of bonded materials is reduced to zero by bonding each set to ground

Ch 9

Question Answer
Conventional Spring Reliefvalve opens based on P drop across valve seat
Spring Relief is?Adjustable spring tension offsets the inlet pressure
Balances Bellows Spring ReliefBellows on the backside of the valve seat ensure that the pressure on that side is always atmospheric
Rupture disks (6 things)1. rupture at specified relief set pressure
2. calibrated sheet of metal
3. remain open after relief
4. flexing-premature fail
5. low cost
6. larger than spring operated
what does a scrubber do?treat toxic exit vapors before venting

Ch 10

Design of relief valves: overpressure, viscosity, and backpressure correction factors

Question Answer
backpressure correction term?Kb, accounts for Discharge at other maximum pressures
The viscosity correction Kv corrects for ?additional frictional losses resulting from flow of high-viscosity material through the valve
Kv - The required relief vent area becomes larger as the viscosity of the liquid? increases
How is the effect of discharge pressure compared to set pressure in the overpressure correction Kp?discharge pressure greater than the set pressure
As the specified overpressure becomes smaller, the correction value decreases, resulting in?larger relief area
Overpressures less than what percent should be avoided?10%
Liquid flow through spring-type reliefs is approximated as?flow through an orifice
For most vapor discharges through spring reliefs the flow is?critical
For liquid reliefs through rupture discs without significant lengths of downstream piping the flow is represented by?flow through a sharp-edged orifice
no corrections are suggested (like for spring-type)
Vapor flow through rupture discs are described similarly to?liquid flow but with the addition of correction factors
Calculation methods for the pilot-operated reliefs are similar to?those used for spring-operated reliefs
What happens to a rupture disc relief valve after the disc has ruptured?The valve does not close again, which may result in the discharge of all the process
Reliefs for fires external to process vessels; how are they sized?Sized based on the constant heat input rate, heat of vaporization of the liquid, volume of the vessel, etc.
Two-phase flow during fire relief can be prevented by providing?a suitable vapor space above the liquid in the vessel
The relationships for computing the heat added to a vessel are dependent on?the area of heat absorption
What is required in the process when installing a rupture disc?Material can get out, air in after rupture
Pieces can dislodge
Must be replaced
Need pressure gauge if put in before spring relief