EG55P8-EG55Q4/2015-16

UNIVERSITY OF ABERDEEN SESSION 2015-16

EG55P8-EG55Q4
Degree Examination in EG55P8-EG55Q4 PROCESS DESIGN, LAYOUT & MATERIALS

Tuesday 10th May 2016 Time: 14:00 – 17:00

PLEASE NOTE THE FOLLOWING

(i) You must not have in your possession any material other than that expressly permitted in
the rules appropriate to this examination. Where this is permitted, such material must not
be amended, annotated or modified in any way.

(ii) You must not have in your possession any material that could be determined as giving you
an advantage in the examination.

(iii) You must not attempt to communicate with any candidate during the exam, either orally
or by passing written material, or by showing material to another candidate, nor must you
attempt to view another candidate’s work.

(iv) You must not take to your examination desk any electronic devices such as mobile phones
or other “smart” devices. The only exception to this rule is an approved calculator.

Failure to comply with the above will be regarded as cheating and may lead to disciplinary
action as indicated in the Academic Quality Handbook Section 7 and particularly Appendix 7.1.

Notes: (i) Candidates ARE permitted to use an approved calculator

(ii) Candidates ARE permitted to use Engineering Mathematics Handbook

(iii) Data sheets are attached to the paper

Candidates should attempt ALL questions.

ALL QUESTIONS ARE WORTH 20 MARKS

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 EG55P8-EG55Q4/2015-16

QUESTION 1

a) Name and describe the main features of the three common pressure relief valves.

[9 marks]

b) A high pressure (HP) vessel feeds a low pressure (LP) vessel as shown in Figure Q1. The liquid
level in the HP vessel is controlled by a level control valve. The control valve has a Cv of 1.5 when
fully open and 1.2 when at its normal position. The gas molecular weight is 24 g/mol and the
compressibility (Z1 ) is 0.94. Given the following information calculate the maximum gas blowby
rate from the HP vessel to the LP vessel for the following configuration. The molecular weight of
air is 29 g/mol.

[8 marks]

Figure Q1

c) What is the function of a firewater deluge system.

[3 marks]

END OF QUESTION 1

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 EG55P8-EG55Q4/2015-16

QUESTION 2

a) Figure Q2 shows the key features of an oil and gas separation system. V01 is a high pressure oil
and gas separator designed for 20 bara internal pressure. The feed into V01 is a two-phase oil and
gas mixture. The oil from V01 flows to V02, V02 is a low pressure oil and gas separator (V02)
designed for 4 bara internal pressure. The liquid levels and pressures for V01 and V02 are
controlled by level and pressure controllers as indicated. Between V01 and V02 there is a shell
and tube heater HX01. The oil flows inside the tubes with heating medium in the shell.
Temperature control of the fluid entering V02 is facilitated by TCV01 using heating medium at 10
bara. The design has all expected layers of protection.

A debottlenecking study is undertaken between V01 liquid outlet and V02 liquid outlet. The study
concludes that to accommodate the increased liquid throughput the CV of LCV 01 requires to be
increased. Also to maintain the same liquid residence time in V02 the liquid operating level is to
be increased. Thermal calculations show that there is sufficient heat transfer area and heating
medium capacity to permit operation of HX01 with the same outlet temperature provided the
heating medium flowrate is increased.

As the Process Safety Engineer you are requested to make a list of potential issues you would
require the design team to evaluate to ensure the safety implications of the proposed increase in
flowrate have been fully evaluated.

Identify the topics you would want considered and the reason why.

[14 marks]

Figure Q2

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 EG55P8-EG55Q4/2015-16

Question 2 continued on next page…

b) A single offshore platform is to contain the following systems – Wells, Oil Processing, Gas
Processing, Water Injection, Utilities, Power Generation and Living Quarters (including control
room and temporary refuge). The platform will have a gas export and oil export pipeline. The
platform also requires a flare tower. Describe how you would wish to layout the systems including
the export pipelines recognising safety principles. A sketch may assist and indicate the prevailing
wind direction. Discuss the significance of wind direction.

[6 marks]

END OF QUESTION 2

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 EG55P8-EG55Q4/2015-16

QUESTION 3

a) A 1000m long vertical riser contains a static oil column with a density of 800 kg/m 3 . The pressure
at the top of the riser is 1200 kPa. A 50 m long gas bubble is introduced at the bottom of the
vertical riser at the same pressure as the oil at the bottom of the riser. There is now a 50m gas
bubble with a 950m of oil column on top of the bubble in the riser. At this point, valves at the
bottom and top of the riser are closed. The gas bubble migrates to the top of the riser and, since
the top and bottom valves are closed, no oil leaves the riser. Calculate the pressure at the base of
the riser when the bubble has reached the top. State any assumptions.

[10 Marks]

b) Biological organisms may be exposed to toxicants via the following exposure routes: Dermal
Absorption; Ingestion; Inhalation; Injection. Prepare a plot of Blood Level vs. Time After
Administration showing the generalised relative responses for these exposure routes

[4 marks]

c) In the context of the interactive actions of toxicants on biological organisms, define what is meant
by the following terms: Additive Interaction; Synergistic Interaction; Potentiate Interaction;
Antagonistic Interaction.

[4 marks]

d) What is meant by the terms Effective Dose and Toxic Dose?

[2 marks]

END OF QUESTION 3

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 EG55P8-EG55Q4/2015-16

QUESTION 4

a) Humans breathe in about 500 ml of air per breath and take about 12 breaths per minute during
normal activities. If a person is exposed to an atmosphere containing benzene at a concentration
of 10 ppm (by volume);
(i) How many grams of benzene will be deposited in the lungs during an 8-hour shift if all
the benzene that enters remains in the lungs?
[3 marks]

(ii) If you were the worker, would this be acceptable? How might your analysis be
improved from a technical standpoint?
[2 marks]

Assume a temperature of 25°C in your analysis.

TLV-TWA / ppm TLV-STEL / ppm TLV-C / ppm
Benzene 0.5 2.5 -

b) What concentration of phosgene (ppm by volume) in the atmosphere would result in the death of
25% of an exposed population were the exposure to last for 5 minutes?

[5 marks]

c) On January 23rd 2010 the E.I. DuPont de Nemours & Co., Inc. plant in Belle, West Virginia,
experienced a phosgene release which resulted in one fatality, one confirmed exposure and one
possible exposure. Give an overall discussion of this event in the context of process safety but
ensure that you include in your discussion the materials aspects and the concept of Inherently
Safe Design.

[10 marks]

END OF QUESTION 4

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 EG55P8-EG55Q4/2015-16

QUESTION 5

a) Describe the mechanisms by which hydrogen can result in failure of steels. Consider high
temperature and low temperature environments.

[6 marks]

b) On April 2nd 2010 a heat exchanger within the Naphtha Hydrotreater (NHT) unit at the Tesoro
Anacortes Refinery failed catastrophically resulting in 7 fatalities. Making reference to the
diagrams shown in Figure Q5 and the Nelson Curves shown in the Data Sheet, discuss the incident
in the context of process safety ensuring that you address the key materials aspects.

[14 marks]

a) b)

c)

d)

Figure Q5: a) PFD of NHT unit; b) Fabrication layout of the B and E heat exchangers; c) Heat exchanger
failure schematic; d) Comparison of damage locations in the B and E heat exchangers.

END OF QUESTION 5

END OF EXAM PAPER

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 EG55P8-EG55Q4/2015-16

DATA SHEET

FLOW OF COMPRESSIBLE FLUIDS

Condition for the occurrence of critical/choked flow:

𝑃2
≤ 0.55
𝑃1

Where: 𝑃2 = downstream pressure (bara)

𝑃1 = upstream pressure (bara)

The following valve flow relationships apply:

54𝑊√𝑍1
Critical Flow: 𝐶𝑣 =
900𝑃1 √𝐺
0.0472𝑊√𝑍1
Sub-critical Flow: 𝐶𝑣 =
√∆𝑃(𝑃1 + 𝑃2 )𝐺

Where: 𝑊= Mass flow rate through valve (kg/hr)

𝑍1 = Compressibility
𝐺= Gas specific gravity
∆𝑃 = 𝑃1 − 𝑃2

Page 8 of 12
 EG55P8-EG55Q4/2015-16

TOXICOLOGY

Table 4. Probit correlations for a variety of exposures (the causative variable is representative of the
magnitude of the exposure)

Type of injury or damage Probit parameters

Causative variable k1 k2
Fire a
Burn deaths from flash fire te Ie 4/3 /104 -14.9 2.56
Burn deaths from pool burning tI4/3 /104 -14.9 2.56
Explosiona
Deaths from lung haemorrhage po -77.1 6.91
Eardrum ruptures po -15.6 1.93
Deaths from impact J -46.1 4.82
Injuries from impact J -39.1 4.45
Injuries from flying fragments J -27.1 4.26
Structural damage po -23.8 2.92
Glass breakage po -18.1 2.79
Toxic release b
Ammonia deaths ΣC2.0T -35.9 1.85
Carbon monoxide deaths ΣC1.0T -37.98 3.7
Chlorine deaths ΣC2.0T -8.29 0.92
Ethylene oxide deaths c ΣC1.0T -6.19 1.0
Hydrogen chloride deaths ΣC1.0T -16.85 2.0
Nitrogen dioxide deaths ΣC2.0T -13.79 1.4
Phosgene deaths ΣC1.0T -19.27 3.69
Propylene oxide deaths ΣC2.0T -7.42 0.51
Sulfur dioxide deaths ΣC1.0T -15.67 1.0
Toluene ΣC2.5T -6.79 0.41
te = effective time duration / s
Ie = effective radiation intensity / W·m -2
t = time duration of pool burning / s
I = radiation intensity from pool burning / W·m -2
p o = peak overpressure / N·m -2
J = impulse / N·s·m -2
C = concentration / ppm
T = time interval / min

a Selected from Frank P. Lees, Loss Prevention in the Process Industries (London: Butterworths, 1986), p. 208.
b Center for Chemical Process Safety (CCPS), Guidelines for Consequence Analysis of Chemical Releases (New York: American Institute of
Chemical Engineers, 2000), p. 254.
c Richard W. Prugh, “Quantitative Evaluation of Inhalation Toxicity Hazards,” in Proceedings of the 29 th Loss Prevention Symposium (American

Institute of Chemical Engineers, July 31, 1995).

Equation for Probit Variable: Y = k1 + k 2 ln V (where V is the causative variable)

 Y −5  Y − 5 
Probit to Percentage Approximation: P = 50 1 + erf  

 Y − 5  2 

Page 9 of 12
 EG55P8-EG55Q4/2015-16

Table 4. Transformation from percentages to probits

% 0 1 2 3 4 5 6 7 8 9
0 - 2.67 2.95 3.12 3.25 3.36 3.45 3.52 3.59 3.66
10 3.72 3.77 3.82 3.87 3.92 3.96 4.01 4.05 4.08 4.12
20 4.16 4.19 4.23 4.26 4.29 4.33 4.36 4.39 4.42 4.45
30 4.48 4.50 4.53 4.56 4.59 4.61 4.64 4.67 4.69 4.72
40 4.75 4.77 4.80 4.82 4.85 4.87 4.90 4.92 4.95 4.97
50 5.00 5.03 5.05 5.08 5.10 5.13 5.15 5.18 5.20 5.23
60 5.25 5.28 5.31 5.33 5.36 5.39 5.41 5.44 5.47 5.50
70 5.52 5.55 5.58 5.61 5.64 5.67 5.71 5.74 5.77 5.81
80 5.84 5.88 5.92 5.95 5.99 6.04 6.08 6.13 6.18 6.23
90 6.28 6.34 6.41 6.48 6.55 6.64 6.75 6.88 7.05 7.33
% 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
99 7.33 7.37 7.41 7.46 7.51 7.58 7.65 7.75 7.88 8.09
D.J. Finney, Probit Analysis (Cambridge: Cambridge University Press, 1971), p. 25.

 1  x −  2 
f (x ) =
1
Normal/Gaussian Distribution: exp −   
 2  2   
 
= Standard deviation
= Mean
n n

 xi f ( xi )  (x i −  ) f ( xi )
2

= i =1
n
2 = i =1
n

i =1
f ( xi )  f (x )
i =1
i

Page 10 of 12
 EG55P8-EG55Q4/2015-16

ERROR FUNCTION
TABLE OF VALUES

Hundredths of X
X 0 1 2 3 4 5 6 7 8 9
0.0 0.00000 0.01128 0.02256 0.03384 0.04511 0.05637 0.06762 0.07886 0.09008 0.10128
0.1 0.11246 0.12362 0.13476 0.14587 0.15695 0.16800 0.17901 0.18999 0.20094 0.21184
0.2 0.22270 0.23352 0.24430 0.25502 0.26570 0.27633 0.28690 0.29742 0.30788 0.31828
0.3 0.32863 0.33891 0.34913 0.35928 0.36936 0.37938 0.38933 0.39921 0.40901 0.41874
0.4 0.42839 0.43797 0.44747 0.45689 0.46623 0.47548 0.48466 0.49375 0.50275 0.51167
0.5 0.52050 0.52924 0.53790 0.54646 0.55494 0.56332 0.57162 0.57982 0.58792 0.59594
0.6 0.60386 0.61168 0.61941 0.62705 0.63459 0.64203 0.64938 0.65663 0.66378 0.67084
0.7 0.67780 0.68467 0.69143 0.69810 0.70468 0.71116 0.71754 0.72382 0.73001 0.73610
0.8 0.74210 0.74800 0.75381 0.75952 0.76514 0.77067 0.77610 0.78144 0.78669 0.79184
0.9 0.79691 0.80188 0.80677 0.81156 0.81627 0.82089 0.82542 0.82987 0.83423 0.83851
1.0 0.84270 0.84681 0.85084 0.85478 0.85865 0.86244 0.86614 0.86977 0.87333 0.87680
1.1 0.88021 0.88353 0.88679 0.88997 0.89308 0.89612 0.89910 0.90200 0.90484 0.90761
1.2 0.91031 0.91296 0.91553 0.91805 0.92051 0.92290 0.92524 0.92751 0.92973 0.93190
1.3 0.93401 0.93606 0.93807 0.94002 0.94191 0.94376 0.94556 0.94731 0.94902 0.95067
1.4 0.95229 0.95385 0.95538 0.95686 0.95830 0.95970 0.96105 0.96237 0.96365 0.96490
1.5 0.96611 0.96728 0.96841 0.96952 0.97059 0.97162 0.97263 0.97360 0.97455 0.97546
1.6 0.97635 0.97721 0.97804 0.97884 0.97962 0.98038 0.98110 0.98181 0.98249 0.98315
1.7 0.98379 0.98441 0.98500 0.98558 0.98613 0.98667 0.98719 0.98769 0.98817 0.98864
1.8 0.98909 0.98952 0.98994 0.99035 0.99074 0.99111 0.99147 0.99182 0.99216 0.99248
1.9 0.99279 0.99309 0.99338 0.99366 0.99392 0.99418 0.99443 0.99466 0.99489 0.99511
2.0 0.99532 0.99552 0.99572 0.99591 0.99609 0.99626 0.99642 0.99658 0.99673 0.99688
2.1 0.99702 0.99715 0.99728 0.99741 0.99753 0.99764 0.99775 0.99785 0.99795 0.99805
2.2 0.99814 0.99822 0.99831 0.99839 0.99846 0.99854 0.99861 0.99867 0.99874 0.99880
2.3 0.99886 0.99891 0.99897 0.99902 0.99906 0.99911 0.99915 0.99920 0.99924 0.99928
2.4 0.99931 0.99935 0.99938 0.99941 0.99944 0.99947 0.99950 0.99952 0.99955 0.99957
2.5 0.99959 0.99961 0.99963 0.99965 0.99967 0.99969 0.99971 0.99972 0.99974 0.99975
2.6 0.99976 0.99978 0.99979 0.99980 0.99981 0.99982 0.99983 0.99984 0.99985 0.99986
2.7 0.99987 0.99987 0.99988 0.99989 0.99989 0.99990 0.99991 0.99991 0.99992 0.99992
2.8 0.99992 0.99993 0.99993 0.99994 0.99994 0.99994 0.99995 0.99995 0.99995 0.99996
2.9 0.99996 0.99996 0.99996 0.99997 0.99997 0.99997 0.99997 0.99997 0.99997 0.99998
3.0 0.99998 0.99998 0.99998 0.99998 0.99998 0.99998 0.99998 0.99999 0.99999 0.99999
3.1 0.99999 0.99999 0.99999 0.99999 0.99999 0.99999 0.99999 0.99999 0.99999 0.99999
3.2 0.99999 0.99999 0.99999 1.00000 1.00000 1.00000 1.00000 1.00000 1.00000 1.00000

Page 11 of 12
 EG55P8-EG55Q4/2015-16

Page 12 of 12
 EG55P8/2016-17
EG55Q4/2016-17

UNIVERSITY OF ABERDEEN SESSION 2016-17

EG55P8 / EG55Q4
Degree Examination in EG55P8 / EG55Q4 PROCESS DESIGN, LAYOUT & MATERIALS

Tuesday 9th May 2017 14:00 - 17:00

PLEASE NOTE THE FOLLOWING

(i) You must not have in your possession any material other than that expressly permitted in
the rules appropriate to this examination. Where this is permitted, such material must not
be amended, annotated or modified in any way.

(ii) You must not have in your possession any material that could be determined as giving you
an advantage in the examination.

(iii) You must not attempt to communicate with any candidate during the exam, either orally
or by passing written material, or by showing material to another candidate, nor must you
attempt to view another candidate's work.

(iv) You must not take to your examination desk any electronic devices such as mobile phones
or other "smart" devices. The only exception to this rule is an approved calculator.

Failure to comply with the above will be regarded as cheating and may lead to disciplinary
action as indicated in the Academic Quality Handbook.

Notes: (i) Candidates ARE permitted to use an approved calculator

(H) Candidates ARE NOT permitted to use the Engineering Mathematics Handbook

(Hi) Candidates ARE NOT permitted to use GREEN or RED pen in their exam booklet

Attempt ALL questions.

Each question is worth 20 marks.

Page lof 6
 EG55P8/2016-17
EG55Q4/2016-17

QUESTION 1

a) Inherent Safety Design:

(i) List the four key focus areas of Inhere nt Safety Design and give an example of how each
element could be applied to a chemical process.

[4 marks]

(ii) Give an example of how each element could be applied to a chemical process.

[8 marks]

b) The Reppe process for the manufacture of acrylic esters uses acetylene and carbon monoxide,
with nickel carbonyl catalyst having high acute and chronic toxicity, to react with an alcohol to
make the corresponding acrylic ester. The stoichiometry is as follows;

Ni(C0)4
CH = CH + CO + ROH-^-^ CH2 = CHCO2R

Anhydrous HCI is very toxic by inhalation and is also highly corrosive. The acrylic ester product is
self-reactive and must be stabilized using polymerization inhibitors before being sent to storage (it
will polymerize, which is why it is useful, however if the polymerization occurs in an uncontrolled
manner, it can cause a storage vessel to explode).

An alternative route is propylene oxidation which proceeds according to the following

stoichiometry;

3 Catalyst
ch2 = chch3 + -o2------- > ch2 = chco2h +h2o

H+
CH2 = CHCO2H + ROH CH2 = CHCO2R + H20

Propylene is oxidised to acrylic acid which is then esterified with the appropriate alcohol (for
example, ethanol to make ethyl acrylate) in the presence of a strong acid catalyst to make the
desired ester

Compare and comment on the hazards of the two processes from an inherent safety viewpoint.

[8 marks]

END OF QUESTION 1

Page 2 of 6
 EG55P8/2016-17
EG55Q4/2016-17

QUESTION 2

a) Explain what is meant by gas blowby from a high pressure to low pressure system. Why is it
important to recognise gas blowby?
[4 marks]
b) Explain what is meant by a control valve Cv. Why is the valve Cv important in establishing
overpressure scenarios?
[4 marks]
c) An absorber operating at 54 bara uses triethylene glycol (TEG) to remove water from a gas. The
TEG is taken from the absorber by a level controller, routed to a plate and frame heat exchanger
and then to a flash drum as shown in Figure Q2.

Calculate the gas blowby rate and comment on the capacity and location of the HP/LP interface
overpressure protection provided by the relief valve. Identify any other evaluation you would
wish to undertake.
[12 marks]
Assume the gas blowby rate through the valve can be calculated from:

0.06214?

Where: Cv = 0.9 for normal operation and 1.5 when the valve is fully open
14/ = mass flow rate / kg-hr1
Px = valve upstream pressure / bara

During gas blowby, the pressure drop (AP/ bar) from the plate and frame heat exchanger inlet to
the flash drum can be calculated from:

AP = 0.00014 ■ W • Pin

Where: Pin= pressure at plate and frame inlet / bara

Absorber
pressure
54 bara

Figure Q2

END OF QUESTION 2

Page 3 of 6
 EG55P8/2016-17
EG55Q4/2016-17

QUESTION 3

a) The layouts shown in Figure Q3 are being proposed for an FPSO (floating production storage and
offtake). The FPSO has an internal turret which allows for 360° rotation capability. Discuss the
advantages and disadvantages of the two arrangements.
Internal Turret-Moored FPSO - Accommodation AFT
Prevailing wind and cirrent

Figure Q3
[6 marks]
b) Heat radiation from a burning flare can be described by the following equation in which D
represents the minimum distance from the mid-pointof the flame to the object being considered.
Name and describe the other variables.
rFQ I0,5
----- —
D = Ll2.6tfJ

[4 marks]
c) On August 6th 2012 a pipeline rupture and fire occurred on the #4 crude unit at the Chevron
Richmond Refinery. Give an overall discussion of this event in the context of process safety.
Ensure that you include in your discussion an account of sulfidation corrosion and the materials
issues which impacted upon this incident.
[10 marks]
END OF QUESTION 3

Page 4 of 6
 EG55P8/2016-17
EG55Q4/2016-17

QUESTION 4

a) The first step in the electrochemical process which results in the formation of common rust (ferric
hydroxide, Fe(OH)3) is the formation of ferrous hydroxide (Fe(OH)2) via the oxidation of solid iron
to Fe2+ and the reduction of oxygen in the presence of water to form hydroxide (OH).

Write down the Anode (oxidation), Cathode (reduction) and REDOX reactions for this process and
include the precipitation of solid ferrous hydroxide.

[6 marks]

b) 500 ml of a solution, saturated at 25.0 °C with ferric hydroxide, is evaporated to dryness yielding
5.25 ng of Fe(OH)3 residue. Calculate the solubility product constant, Ksp, for Fe(0H)3 at 25.0 °C.
The molecular weight of Fe(OH)3 is 106.866 g-mol

[6 marks]

c) Consider the closed system shown in Figure Q4in which a gas/vapour phase consisting of air (21
mol% O2, 79 mol% N2), saturated with water, is in equilibrium with liquid water.

Calculate the composition of the liquid phase and express your result in mole fractions.

[8 marks]

The vapour pressure of pure water at 25.0 °C is 0.03166 bar and the Henry's constants for oxygen
and nitrogen, at 25.0 °C, are 44380 bar and 87650 bar respectively.

Page 5 of 6
 EG55P8/2016-17
EG55Q4/2016-17

QUESTION 5

a) Describe each of the following forms of corrosion and give an example of either: where it may be
found to occur or where it did occur in a loss of containment event.
(i) Stress corrosion (stress corrosion cracking)
(ii) Pitting
(iii) Selective leaching (dealloying)
(iv) Galvanic corrosion

[12 marks = 4x3 marks]

b) A shell and tube heat exchanger is to be designed to cool a raw well fluid as it arrives on an
offshore platform. The well fluid is received at 10 bara and contains a small fraction of sand as
well as a three-phase fluid made up of an aqueous phase, a liquid hydrocarbon phase and a
gas/vapour phase. The gas/vapour phase contains carbon dioxide and hydrogen sulfide. The
aqueous phase contains a variety of dissolved mineral species. The well fluid is to be cooled from
105 °C to 85 °C using sea water.

Discuss the materials considerations affecting the design. Highlight specifically the
questions/analyses you would wish to answer/undertake in orderto evaluate the system to
inform materials selection and fluid allocation to tube side or shell side.

[8 marks]

END OF QUESTION 5

END OF EXAM PAPER

Page 6 of 6
 EG55P8/2017-18
EG55Q4/2017-18

UNIVERSITY OF ABERDEEN SESSION 2017-18

EG55P8 / EG55Q4
Degree Examination in EG55P8 / EG55Q4 PROCESS DESIGN, LAYOUT & MATERIALS

Tuesday 8th May 2018 TIME: 14.00-17.00

PLEASE NOTE THE FOLLOWING

(i) You must not have in your possession any material other than that expressly permitted in
the rules appropriate to this examination. Where this is permitted, such material must not
be amended, annotated or modified in any way.

(ii) You must not have in your possession any material that could be determined as giving you
an advantage in the examination.

(iii) You must not attempt to communicate with any candidate during the exam, either orally
or by passing written material, or by showing material to another candidate, nor must you
attempt to view another candidate's work.

(iv) You must not take to your examination desk any electronic devices such as mobile phones
or other "smart" devices. The only exception to this rule is an approved calculator.

Failure to comply with the above will be regarded as cheating and may lead to disciplinary
action as indicated in the Academic Quality Handbook.

Notes: (i) Candidates ARE permitted to use an approved calculator

(H) Candidates ARE NOT permitted to use the Engineering Mathematics Handbook

(Hi) Candidates ARE NOT permitted to use GREEN or RED pen in their exam booklet

Attempt ALL questions.

Each question is worth 20 marks.

Page 1 of 6

Q
 EG55P8/2017-18
EG55Q4/2017-18

QUESTION 1

a) The Bernoulli equation (usual notation applies) for a flowing fluid may be expressed as;

A(u2)
vdP 4- g&x 4----- -— = —Wf — W

Stating any assumptions, show that for compressible flow through an orifice, such as a relief
valve, the equation can be expressed as;

Equation QI

Where: G = Total mass flux / kg m’2 s’1

v = Fluid specific volume / m3 kg’1
P = Downstream pressure / N m’2
and subscript 0 indicates the upstream condition.
[4 marks]

b) Equation QI is referred to as the Homogeneous Equilibrium Model for two phase flow. The
integral can be solved numerically by conducting a series of isentropic flashes across a
valve/orifice starting at the system process pressure. This provides values of fluid specific
volumes that can be used to evaluate the integral.

Such a series of flashes have been conducted to simulate two phase flow through a relief valve,
relieving at 39 bara. The data produced are shown in Table QI. The pressures involved are those
downstream of the valve.

Table QI: Specific volume vs. Pressure data for Qlc

P / bara v/m’kg1 P / bara v / m3 kg 1
39 0.00666 27 0.00947
36 0.00718 24 0.01062
33 0.00780 21 0.01209
30 0.00855 18 0.01407

The maximum flow through the relief valve will occur at the downstream pressure which gives the
highest mass flux. Calculate the maximum mass flux through the relief valve. At what
downstream pressure does this occur?
[10 marks]

c) What are the three key principles of facilities plant layout?

[6 marks]

END OF QUESTION 1

Page 2 of 6
 EG55P8/2017-18
EG55Q4/2017-18

QUESTION 2

a) Figure Q2 shows a two phase horizontal separator with key gas controllers and over pressure
protection. The pressure in the vessel is normally controlled by PCV1 at 27.6 barg. The gas is
forwarded to a compression plant. There is a split range association with PCV2; i.e. if the pressure
in the vessel rises above 27.6 barg, PCV2 starts to control. PCV2 is a 25 cm valve and would
normally be closed. Should the pressure rise to 29.5 barg the PAHH will initiate a process
shutdown; this will close the inlet valve ESDI. ESD 1 is a 40 cm valve. At 30.5 barg the relief valve
will lift.

The plant is debottlenecked to a new gas flow rate of 40 Sm3/hr. In operation, at the new
increased gas flow rate, it is found that if the compression plant trips the relief valve lifts.

Assume the vessel is 50% full of liquid and that a valve will move at 2.5 cm/s. Stating any other
assumptions made, explain by calculation why the relief valve will lift. Note liquid control has
been omitted from the sketch, as it is not pertinent to the problem.
[14 marks]

Two Phase Horizontal Separator

Pressure Controller
set at 27.6 barg - split range

open # *
11.5m

Figure Q2

b) Underpressure is a case that has to be investigated to ensure the integrity of process plant.
Identify six events that could induce an underpressure.
[6 marks]

END OF QUESTION 2

Page 3 of 6
 EG55P8/2017-18
EG55Q4/2017-18

QUESTION 3

a) A gas transportation pipeline has experienced a hydrate blockage. The pipeline situation
following the blockage is shown in Figure Q3.

Hydrate Plug
Upstream Pressure = 100 bara Downstream Pressure = 100 bara

Figure Q3: Pipeline with hydrate plug and upstream/downstream pressures

It has been proposed that the hydrate plug is removed by depressurising the downstream end to
atmospheric pressure. You are asked to comment on this procedure; would you recommend it?
Explain your reasoning.

[6 marks]

b) Compressible flow through a relief valve is defined as critical/choked or sub-critical flow. Describe
both flow conditions and discuss their nature with respect to the pressure drop across the relief
valve.

[4 marks]

c) On April 2nd 2010 the Tesoro refinery in Anacortes experienced a catastrophic rupture of a heat
exchanger in the catalytic reformer / hydrotreater unit which resulted in seven fatalities. Give an
account of this incident which covers the following points;
(i) Process and plant design

[3 marks]

(ii) Materials selection

[2 marks]

(iii) High temperature hydrogen attack

[4 marks]

(iv) Safety culture

[1 mark]

END OF QUESTION 3

Page 4 of 6
 EG55P8/2017-18
EG55Q4/2017-18

QUESTION 4

a) The first step in the electrochemical process which results in the formation of common rust (ferric
hydroxide, Fe(OH)3> is the formation of ferrous hydroxide (Fe(OH)2) via the oxidation of solid iron
to Fe2+ and the reduction of oxygen in the presence of water to form hydroxide (OH j.

Write down the Anode (oxidation), Cathode (reduction) and REDOX reactions for this process and
include the precipitation of solid ferrous hydroxide.

[6 marks]

b) Two streams of produced water, each at 25.0 °C, in an oil and gas facility are to be mixed prior to
treatment. One stream has a flow rate of 50.0 I s'1 and a concentration of Barium Chloride (BaCI2)
of l.OOxlO’3 mol I*1, the other stream has a flow rate of 50.0 I s’1 and a concentration of Sodium
Sulfate (Na2SO4> of l.OOxlO’4 mol I’1. Would you recommend that the process design be reviewed
to address possible scaling when these streams mix?

The solubility product constant for BaSC>4 is l.lxlO’10 at 25.0 °C.

[6 marks]

c) Consider the closed system shown in Figure Q4 in which a gas/vapour phase consisting of air (21
mol% O2, 79 mol% N2) with 8500 ppm H2S, saturated with water, is in equilibrium with liquid
water.

What would be the mole fractions of O2 and H2S in the liquid phase?

[8 marks]

The vapour pressure of pure water at 25.0 °C is 0.03166 bar and the Henry's constants for oxygen,
and hydrogen sulfide, at 25.0 °C, are 44380 bar and 550 bar respectively.

END OF QUESTION 4

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 EG55P8/2017-18
EG55Q4/2017-18

QUESTION 5

a) Describe each of the following forms of corrosion and give an example of either: where it may be
found to occur or where, from knowledge of a case study, it did occur in a loss of containment
event.
(i) Stress corrosion (stress corrosion cracking)
(ii) Pitting
(iii) Selective leaching (dealloying)
(iv) Galvanic corrosion

[12 marks = 4x3 marks]

b) A shell and tube heat exchanger is to be designed to cool a raw well fluid as it arrives on an
offshore platform. The well fluid is received at 10 bara and is three-phase containing an aqueous
phase, a liquid hydrocarbon phase and a gas/vapour phase. The gas/vapour phase contains
carbon dioxide and hydrogen sulfide. The aqueous phase contains a variety of dissolved mineral
species. The well fluid is to be cooled from 105 °C to 85 °C using sea water.

Discuss the materials considerations affecting the design. Highlight specifically the
questions/analyses you would wish to answer/undertake in order to evaluate the system to
inform materials selection and fluid allocation to tube side or shell side.

[8 marks]

END OF QUESTION 5

END OF EXAM PAPER

Page 6 of 6
 EG55P8/2018-19
EG55Q4/2018-19

UNIVERSITY OF ABERDEEN SESSION 2018-19

EG55P8 / EG55Q4
Degree Examination in EG55P8 / EG55Q4 PROCESS DESIGN, LAYOUT & MATERIALS

DATE: Tuesday 7 May 2019 TIME: 14:00 - 17:00

PLEASE NOTE THE FOLLOWING

(i) You must not have in your possession any material other than that expressly permitted in
the rules appropriate to this examination. Where this is permitted, such material must not
be amended, annotated or modified in any way.

(ii) You must not have in your possession any material that could be determined as giving you
an advantage in the examination.

(iii) You must not attempt to communicate with any candidate during the exam, either orally
or by passing written material, or by showing material to another candidate, nor must you
attempt to view another candidate's work.

(iv) You must not take to your examination desk any electronic devices such as mobile phones
or other "smart" devices. The only exception to this rule is an approved calculator.

Failure to comply with the above will be regarded as cheating and may lead to disciplinary
action as indicated in the Academic Quality Handbook.

Notes: (i) Candidates ARE permitted to use an approved calculator

(H) Candidates ARE NOT permitted to use the Engineering Mathematics Handbook

(Hi) Candidates ARE NOT permitted to use GREEN or RED pen in their exam booklet

Attempt ALL questions.

Each question is worth 20 marks.

Page 1 of 7

Q
 EG55P8/2018-19
EG55Q4/2018-19

QUESTION 1

a) On January 23rd 2010 the E.l. DuPont de Nemours & Co., Inc. plant in Belle, West Virginia,
experienced a phosgene release which resulted in one fatality, one confirmed exposure and one
possible exposure. Give an overall discussion of this event in the context of process safety but
ensure that you include in your discussion the materials aspects and the concept of Inherently
Safe Design.

[10 marks]

b) A 1000 m long vertical riser contains a static oil column with a density of 800 kg m’3. The pressure
at the top of the riser is 1200 kPa. A 50 m long gas bubble is introduced at the bottom of the
vertical riser at the same pressure as the oil at the bottom of the riser. There is now a 50m gas
bubble with a 950 m of oil column on top of the bubble in the riser. At this point, valves at the
bottom and top of the riser are closed. The gas bubble migrates to the top of the riser and, since
the top and bottom valves are closed, no oil leaves the riser. Calculate the pressure at the base of
the riser when the bubble has reached the top. State any assumptions.

[10 Marks]

END OF QUESTION 1

Page 2 of 7
 EG55P8/2018-19
EG55Q4/2018-19

QUESTION 2

a) List the four guidewords for Inherently Safe Design (ISD) and give an example of how any two of
the elements could be applied to a chemical process.
[6 marks]

b) The Bernoulli equation (usual notation applies) for a flowing fluid may be expressed as;

f A(u2)
I vdP + gbx + —— = -Wf - W

Stating any assumptions, show that for compressible flow through an orifice, such as a relief
valve, the equation can be expressed as;

Equation Q2.1

Where: G - Total mass flux / kg m'2 s'1

p = Fluid specific volume / m3 kg1
P = Downstream pressure / N m'2
and subscript 0 indicates the upstream condition.
[4 marks]

c) Equation Q2.1 is referred to as the Homogeneous Equilibrium Model for two phase flow. The
integral can be solved numerically by conducting a series of isentropic flashes across a
valve/orifice starting at the system process pressure. This provides values of fluid specific
volumes that can be used to evaluate the integral.

Such a series of flashes have been conducted to simulate two phase flow through a relief valve,
relieving at 39 bara. The data produced are shown in Table Q2. The pressures involved are those
downstream of the valve.

Table Q2: Specific volume vs. Pressure data for Q2c

P / bara v / m3 kg1 P/ bara v I m3 kg 1
39 0.00666 27 0.00947
36 0.00718 24 0.01062
33 0.00780 21 0.01209
30 0.00855 18 0.01407

The maximum flow through the relief valve will occur at the downstream pressure which gives the
highest mass flux. Calculate the maximum mass flux through the relief valve. At what
downstream pressure does this occur?
[10 marks]

END OF QUESTION 2

Page 3 of 7
 EG55P8/2018-19
EG55Q4/2018-19

QUESTION 3

a) A compressible fluid is discharging through an orifice from an upstream pressure, Pi, to a

downstream pressure P2. Sketch a plot of mass flow rate through the orifice versus downstream
pressure, P2, and label the main features. You may assume that you are sketching a plot for a
system which conforms to the following assumptions:

• Negligible velocity upstream of the orifice;

• Negligible change in elevation through the orifice;
• Zero/negligible work/friction effects;
• Ideal gas;
• Adiabatic; and
• Constant heat capacities.
[6 marks]

b) The mass flow rate of gas through the orifice described in part a) may be described, in part, by the
following equation;

2 K+1l
2MW / y
M = CdaoPi
RTr \y - 1/

Show that the downstream pressure, Pw, at which the flow through the orifice becomes critical or
choked is given by the following equation;
Y

[6 marks]

c) As part of the process and plant design for a new ammonia (NH3,17 g mol1) manufacturing
facility, it is necessary to undertake consequence modelling to partly inform the decisions
regarding whether to opt for pressurized ammonia storage at ambient temperature or
refrigerated storage at ambient pressure.

The team evaluating dispersion of ammonia to the surroundings require a worst case scenario
release rate, in kg s1, from a pressurized ammonia storage vessel which develops a 0.00254 m
diameter hole from a small-bore instrument fitting connected to the vapour head space. You
have been given the task of providing the worst case scenario release rate.

The ambient temperature may be taken as 287 K, which corresponds to a storage pressure of
7.045 bara. The heat capacity ratio for ammonia may be assumed to be 1.32. The vessel is
located in a region where the ambient pressure is 1.01325 bara. State any assumptions.

[8 marks]

END OF QUESTION 3

Page 4 of 7
 EG55P8/2018-19
EG55Q4/2018-19

QUESTION 4

a) Describe the concept of Layers of Protection Analysis with respect to process plant safety. In the
description, identify the hierarchy of the layers starting with the basic process design.

[8 marks]

b) 500 ml of a solution, saturated at 25.0 °C with ferric hydroxide, is evaporated to dryness yielding
5.25 ng of Fe(OH)3 residue. Calculate the solubility product constant, 7fsp, for Fe(OH>3 at 25.0 °C.
The molecular weight of Fe(OH)3 is 106.866 g-mol'1.

[6 marks]

c) Two streams of water are isothermally mixed at 25.0 °C. Material balances show that the
concentrations of Ca2+ and SO?’ in the mixed stream will be 0.0110 mol-l1 and 0.0900 mol-l1
respectively. Would you expect calcium sulfate (CaSCU) to precipitate in the mixed stream? The
solubility product constant for calcium sulfate is 2.4xl0‘5.

[6 marks]

END OF QUESTION 4

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 EG55P8/2018-19
EG55Q4/2018-19

QUESTION 5

a) What is the difference between the Flash Point and the Fire Point of a substance?

[2 marks]

b) Referring to the flammability diagram shown in Figure Q5 (Examination booklet, page 7); state the
compositions (vol % oxygen, nitrogen, fuel) at points A, B, and C as shown on the diagram.

[6 marks]

In order to answer the remaining questions, you should remove Figure Q5 from the
examination booklet, write your candidate number in the place provided and submit the
diagram inside your Examination Script.

c) Draw the air line on the flammability diagram.

[2 marks]

d) The Upper Flammable Limit (UFL) and Lower Flammable Limit (LFL) for propane, Vol % fuel in air,
are 9.5 and 2.1 respectively. Plot the UFL and LFL for propane on the diagram and label them
accordingly.

[2 marks]

e) Draw the stoichiometric line for propane on the flammability diagram.

[3 marks]

f) The Minimum Oxygen Concentration (MOC) for propane is 11.6 vol% O2. You are to devise
operations to bring a propane storage tank out of service (from a point at which it is lying at
atmospheric pressure containing 100 vol% propane) for inspection and then bring it back into
service (at atmospheric pressure, change the atmosphere in the tank from 100 vol% air, to 100
vol% propane).

Show your operations on the flammability diagram and clearly state your method and reasoning.

[5 marks]

END OF QUESTION 5

END OF EXAM PAPER

Page 6 of 7
 EG55P8/2018-19
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Candidate Number

Nitrogen, Volume Percent

Figure Q5: Flammability diagram for use in Question 5

Page 7 of 7