December 2, 2020

1

Chapter 10

10-1.

Relief

Configuration

MAWP

psig

Set

Pressure

psig

Maximum

Set

Pressure

psig

Maximum

Accumulated

Pressure

psig

Allowable

Overpressure

psig

10-2. a. Certified capacity spring-type relief.

Liquid flow = 100 gpm

Set pressure = 50 psig

Here:

Then

2

Substituting into Equation 10-4:

2

10-3. a. Spring operated relief in vapor service – assume a conventional spring relief.

m

Required mass flow, 50 lb / hr

m

Q

Equation 10-12 now applies:

Substituting, being careful of units!

10-4. a. Rupture disc in liquid service.

Liquid flow = 500 gpm

Set pressure = 100 psig

Here:

ref

Then

Substituting into Equation 10-4:

10-5. a. Use Equation 10-12 for vapor service thru a rupture disk.

4

Then:

And

Substituting into Equation 10-12:

The relief diameter is:

Parts b thru d are similar.

10-6. a. Use Equation 10-16:

5

m

This is the heat generation rate in the reactor.

Now apply Equation 10-20

10-7. The original problem as presented in the 1st printing of the 4th edition is confusing and

difficult to work. The revised problem is shown below:

Determine the deflagration vent size for the following structures.

Vapors a b c d

Internal area of structure: 1000 ft2 1000 ft2 300 m2 300 m2

Dusts e f g h

Volume of structure: 1000 ft3 1000 ft3 30 m3 30 m3

c. Use Equation 10-23 with Equation 10-25 to estimate the vent area required.

Start with Equation 10-25:

Substituting into Equation 10-23:

g. Apply Equation 10-29 – being careful to use the correct unit:

unit equation

10-8. Use Equation 10-42:

Here:

Substituting into Equation 10-42:

5 o 1

10-9.

This is a complex problem with many possible approaches. First, let’s state some facts about

this situation:

a. The rate of energy discharge thru the relief device must match the heat input from the

burner in all cases.

8

10-10.

In this casee a vapor space will occur after the relieving starts. Thus, it will be vapor

discharge. Equation 10-12 then applies to size the vapor relief size.

From the steam tables at 50oF:

p m

From Example 10-10, the thermal expansion coefficient at 50oF is 5 o

3.47 10 / F

.

The surface area is the cylinder (excluding the ends) is:

Assume only the top half of the vessel is exposed to the sun, and not the ends. Then,

Substituting into Equation 10-10:

This is a very small expansion.

For fire exposure, assume that the vessel is horizontal. The surface area of the ends must

be added.

The MAWP of the vessel is 200 psig = 214.7 psia. Use this as the set pressure for the

relief and also the pressure inside the vessel during the relief (with no overpressure). The

water will boil at this pressure.

For saturated water at 214.7 psia, from the steam tables:

And,

For vapor relief, the mass discharge rate through the relief is, by an energy balance,

Use Equation 10-12 to size the relief.

Then from Equation 10-13,

From the guidelines in the textbook:

Substituting into Equation 10-12:

The relief diameter is:

10-11. The vent area is estimated using Equations 10-25 and 10-23.

For methane from Table 10-2, u

40 cm/s 0.040 m/s

S .

Assume no turbulent augmentation, then

1

.

Each wall on the structure is 100 ft2. The area of the structure includes the 4 walls + ceiling =

10-12. This is almost identical to the second part of Problem 10-10, but in metric units. Use

Equation 10-12 with Equation 10-14.

Total surface area of vessel =

From the guidelines with Equation 10-30, take 75% of this surface area,

From Equation 10-33 – being careful of units:

Assume no overpressure and a set point equal to the MAWP of 14 barg = 15.013 bara.

For saturated water at 14 barg, from the steam tables:

fg

For vapor relief, the mass discharge rate through the relief is, by an energy balance,

Use Equation 10-12 to size the relief.

Then from Equation 10-14,

From the guidelines in the textbook:

Substituting into Equation 10-12:

The relief diameter is:

Problems and Solutions for Chapter 11

Problem 11-1.

In a pilot plant, toluene is transferred from a drum to an open bucket. Develop a checklist for this procedure.

Include inerting / purging, ventilation, grounding and bonding and any other safety procedures.

Solution for Problem 11-1

FigureofSystembeforeSafetyReview

Problem 11-2. Perform a HAZOP on the reactor in Example 11-2. The reaction is exothermic, so

cooling coils removes the heat of reaction. The temperature is controlled by controlling the flow of

cooling water. Use as a study node the cooling coil (process parameters: flow and temperature) and

the stirrer (process parameter: agitation).

Solution for Problem 11-2

Hazards and Operability Review

Project Name: Date: 9/1/2018 Page of 1 of 2 Completed

No action:

Reply Date

Assigned to:

Process: Reactor of Example 11-2

Section: Reactor Shown in Example 11-2

Item Study

Node

Process

Parameters

Possible Causes Possible

Consequences Safeguards Recommendations

Deviations

(Guide

Words)

Example 11-2

Hazards and Operability Review

Project Name: Date: 9/1/2018 Page of 2 of 2 Completed

No action:

Reply Date

Assigned to:

Process: React or of Example 11-2

Section: Reactor Shown in Example 11-2

Item Study

Node

Process

Parameters

Possible Causes Possible

Consequences Safeguards Recommendations

Deviations

(Guide

Words)

Example 11-2

Problem 11-3. If the monomer in Example 11- 2 is ethylene oxide, identify the hazards by developing

a list of material hazards and a list of process hazards.

Solution for Problem 11-3

Notice:ThefollowinglistisgeneratedwithexperiencedpersonnelandadocumentliketheHAZOPs

helps.Belowarelistedtheprocesshazards,andsomeactionstosafelyoperateinthisenvironment.

Listofprocesshazards

Problem 11-4. The concept of "fail safe" is used to specify the position (fail closed or fail open) of all

process valves in the event of a utility failure. The specified fail open or fail closed puts the process in

a safe mode of operation. Specify the proper fail-safe position for the following situations:

a) A process valve regulates the flow of steam that heats a solvent in a heat exchanger.

b) A valve controls the flow of a reactant (exothermic reaction) to a reactor.

c) A valve controls the flow of a reactant (endothermic reaction) to a reactor.

d) A valve controls the flow of natural gas to a furnace.

e) A remote valve is connected to a storage tank drain line.

f) A remote valve is connected to a fill line to a storage tank.

g) A valve controls the combustion air to a furnace.

h) A valve releases excessive pressures in a steam header.

Solution for Problem 11-4

Problem 11-5. Conduct a safety review for the design of the system described in Example

11-2. This reactor is used to polymerize ethylene oxide to form polyols.

Solution for Problem 11-5

TablesforProblem11‐5

ChecklistforaSafetyReviewfortheDesignoftheReactorshowninExample11‐2