Hydrocarbon Processing - May 2022 - 86
Heat Transfer
liquid accumulation rate. This does not affect
the thermosiphoning of the reboiler.
FIGS. 9 and 10 show a front view of a
Cd
FIGS. 9 AND 10. A front view of a baffle
with different hole shapes and a side view
of the baffle, respectively.
H/D
even and fine to reduce friction losses.
FIG. 7. Cd of different shapes-the Cd reduces
with diameter and head.
90 TPH
210 TPH
4 in.
20 TPH
Product
190 TPH
FIG. 8. Hole diameter and height of liquid
above hole.
is rectangular, square or circular, or any
random cut (TABLE 1). It is important to
highlight that the issue with different
shapes would be the friction factor and
discharge coefficient of liquid. The discharge
coefficient (Cd) of liquid through
any hole is the ratio of actual flow to ideal
flow. The Cd is inversely proportional to
the friction factor; therefore, friction losses
should be the lowest and the discharge
coefficient should be the highest.
FIG. 7 shows a simple comparison on
practical values. The discharge coefficient
depends on the diameter (d) of the hole
(circular shape) and the head (H) of the
liquid in the product compartment. As the
diameter of the hole or cut in the baffle
increases, velocity reduces and fewer friction
losses lead to a higher discharge coefficient.
This should be optimized.
The head of the liquid in the product
compartment also changes the friction
losses. A higher head enhances the velocity
and increases friction losses. Therefore,
the minimum head should be there.
The cut in the baffle should be smooth,
86 MAY 2022 | HydrocarbonProcessing.com
300 TPH
Size of the hole in the baffle. The diameter
of the hole should be determined
based on the liquid load in the product
compartment. In Part 1, it was seen in
the calculation of the liquid that 20 tph
(tons/hr) were accumulated there. As a
result, the size or diameter of the hole is
determined by the amount of liquid that
accumulates
per hour. Recommendation:
The liquid velocity through the hole
should be approximately 1.4 m/sec, and
the height of the liquid in the product
compartment above the hole should be 4
in., or 100 mm (FIG. 8).
For 20 tph (28.57 M3
/hr with a density
of 700 kg/m3) of flow toward the reboiler
compartment, the hole size should
be 42.5 mm, or approximately 2 in. Based
on this recommendation (Eq. 2):
Q (flow in m3
/hr) =
A × V (m/sec) × 3,600
(2)
where A is the area of the hole and the velocity
(V) is 1.4 m/sec.
Similarly, the hole diameter in the baffle
can be calculated based on the liquid
accumulation rate. A large-diameter hole
in the baffle would equalize both levels
of the compartments and the chances of
bidirectional flow through this hole. This
baffle reboiler has the preference of taking
liquid from the reboiler compartment as
well as the product compartment.
The liquid should not go from the
reboiler compartment to the product
compartment. If the efficiencies of oncethrough,
circulating and preferential baffle
reboilers are compared, the preferential
baffle reboiler earns the second rank
while providing operational flexibility.
FIG. 8 shows an ideal design of the
baffle with a hole. The liquid head in the
product compartment is 4 in. above the
hole to make it unidirectional towards the
reboiler sump, and the hole in the baffle is
circular with a 2-in. diameter based on the
baffle with different hole shapes and a side
view of the baffle, respectively. The circular
hole in the baffle is beveled towards
the reboiler. This reduces the formation
of eddies and friction losses of flowing
liquid. All level transmitters should be in
the product compartment. It might be assumed
that with a hole in the baffle, level
transmitters will work on any side; however,
there is always a delta (difference) in the
height of liquid on both sides. A high-high
level alarm for the product compartment
is helpful to avoid the submerging of the
reboiler return line into the liquid pool.
Takeaway. The proper design of a preferential
baffle reboiler can avoid startup
and liquid accumulation problems and
provide optimum benefits. Recommendations
to enhance the design of the preferential
baffle reboiler include:
1. The hole in the baffle should be
circular rather than a rectangular
or square.
2. The diameter of the hole should
be calculated based on a velocity
of 1.4 m/sec.
3. To avoid thermosiphon flaws, the
elevation or altitude of the hole
must be determined using
a reboiler head calculation.
4. The hole or cut in the baffle should
be smooth and beveled towards
the reboiler compartment.
5. The baffle with an underflow
design should be selected rather
than the circulating reboiler;
otherwise, a once-through
reboiler is preferred.
ACKNOWLEDGMENT
This work is based on the author's experience and
is not affiliated with any company. The author wishes
to express his gratitude to Krishna, who supported and
advised him on this article.
LITERATURE CITED
Complete literature cited available online at
www.HydrocarbonProcessing.com.
ABHISHEK SHARMA is a Process Engineer at an
ethylene plant, and has more than 4 yr of experience
in the steam cracker unit. He completed his B.Tech
degree in chemical engineering from the National
Institute of Technology Raipur, India with honors and
completed a process equipment design course from
IIT Roorkee. He is an active professional member of
the American Institute of Chemical Engineers and
an associate member of IChemE. He has published
three articles and participates in the smooth
operation and troubleshooting of the plant.
http://www.HydrocarbonProcessing.com
http://www.HydrocarbonProcessing.com
Hydrocarbon Processing - May 2022
Table of Contents for the Digital Edition of Hydrocarbon Processing - May 2022
Contents
Hydrocarbon Processing - May 2022 - Cover1
Hydrocarbon Processing - May 2022 - Cover2
Hydrocarbon Processing - May 2022 - Contents
Hydrocarbon Processing - May 2022 - 4
Hydrocarbon Processing - May 2022 - 5
Hydrocarbon Processing - May 2022 - 6
Hydrocarbon Processing - May 2022 - 7
Hydrocarbon Processing - May 2022 - 8
Hydrocarbon Processing - May 2022 - 9
Hydrocarbon Processing - May 2022 - 10
Hydrocarbon Processing - May 2022 - 11
Hydrocarbon Processing - May 2022 - 12
Hydrocarbon Processing - May 2022 - 13
Hydrocarbon Processing - May 2022 - 14
Hydrocarbon Processing - May 2022 - 15
Hydrocarbon Processing - May 2022 - 16
Hydrocarbon Processing - May 2022 - 17
Hydrocarbon Processing - May 2022 - 18
Hydrocarbon Processing - May 2022 - 19
Hydrocarbon Processing - May 2022 - 20
Hydrocarbon Processing - May 2022 - 21
Hydrocarbon Processing - May 2022 - 22
Hydrocarbon Processing - May 2022 - 23
Hydrocarbon Processing - May 2022 - 24
Hydrocarbon Processing - May 2022 - 25
Hydrocarbon Processing - May 2022 - 26
Hydrocarbon Processing - May 2022 - 27
Hydrocarbon Processing - May 2022 - 28
Hydrocarbon Processing - May 2022 - 29
Hydrocarbon Processing - May 2022 - 30
Hydrocarbon Processing - May 2022 - 31
Hydrocarbon Processing - May 2022 - 32
Hydrocarbon Processing - May 2022 - 33
Hydrocarbon Processing - May 2022 - 34
Hydrocarbon Processing - May 2022 - 35
Hydrocarbon Processing - May 2022 - 36
Hydrocarbon Processing - May 2022 - 37
Hydrocarbon Processing - May 2022 - 38
Hydrocarbon Processing - May 2022 - 39
Hydrocarbon Processing - May 2022 - 40
Hydrocarbon Processing - May 2022 - 41
Hydrocarbon Processing - May 2022 - 42
Hydrocarbon Processing - May 2022 - 43
Hydrocarbon Processing - May 2022 - 44
Hydrocarbon Processing - May 2022 - 45
Hydrocarbon Processing - May 2022 - 46
Hydrocarbon Processing - May 2022 - 47
Hydrocarbon Processing - May 2022 - 48
Hydrocarbon Processing - May 2022 - 49
Hydrocarbon Processing - May 2022 - 50
Hydrocarbon Processing - May 2022 - 51
Hydrocarbon Processing - May 2022 - 52
Hydrocarbon Processing - May 2022 - 53
Hydrocarbon Processing - May 2022 - 54
Hydrocarbon Processing - May 2022 - 55
Hydrocarbon Processing - May 2022 - 56
Hydrocarbon Processing - May 2022 - 57
Hydrocarbon Processing - May 2022 - 58
Hydrocarbon Processing - May 2022 - 59
Hydrocarbon Processing - May 2022 - 60
Hydrocarbon Processing - May 2022 - 61
Hydrocarbon Processing - May 2022 - 62
Hydrocarbon Processing - May 2022 - 63
Hydrocarbon Processing - May 2022 - 64
Hydrocarbon Processing - May 2022 - 65
Hydrocarbon Processing - May 2022 - 66
Hydrocarbon Processing - May 2022 - 67
Hydrocarbon Processing - May 2022 - 68
Hydrocarbon Processing - May 2022 - 69
Hydrocarbon Processing - May 2022 - 70
Hydrocarbon Processing - May 2022 - 71
Hydrocarbon Processing - May 2022 - 72
Hydrocarbon Processing - May 2022 - 73
Hydrocarbon Processing - May 2022 - 74
Hydrocarbon Processing - May 2022 - 75
Hydrocarbon Processing - May 2022 - 76
Hydrocarbon Processing - May 2022 - 77
Hydrocarbon Processing - May 2022 - 78
Hydrocarbon Processing - May 2022 - 79
Hydrocarbon Processing - May 2022 - 80
Hydrocarbon Processing - May 2022 - 81
Hydrocarbon Processing - May 2022 - 82
Hydrocarbon Processing - May 2022 - 83
Hydrocarbon Processing - May 2022 - 84
Hydrocarbon Processing - May 2022 - 85
Hydrocarbon Processing - May 2022 - 86
Hydrocarbon Processing - May 2022 - 87
Hydrocarbon Processing - May 2022 - 88
Hydrocarbon Processing - May 2022 - 89
Hydrocarbon Processing - May 2022 - 90
Hydrocarbon Processing - May 2022 - Cover3
Hydrocarbon Processing - May 2022 - Cover4
https://www.nxtbook.com/gulfenergyinfo/gulfpub/HPI-Market-Data-2023-v3
https://www.nxtbook.com/gulfenergyinfo/gulfpub/hpi-market-data-2024-v2
https://www.nxtbook.com/gulfenergyinfo/gulfpub/hpi-market-data-2024
https://www.nxtbook.com/gulfenergyinfo/gulfpub/gas-processes-handbook-2022_v2
https://www.nxtbook.com/gulfenergyinfo/gulfpub/gas-processes-handbook-2022
https://www.nxtbook.com/gulfenergyinfo/gulfpub/hp_202212
https://www.nxtbook.com/gulfenergyinfo/gulfpub/hpi-market-data-2023-v2
https://www.nxtbook.com/gulfenergyinfo/gulfpub/hpi-market-data-2023
https://www.nxtbook.com/gulfenergyinfo/gulfpub/hp_202211
https://www.nxtbook.com/nxtbooks/gulfpub/hp_202210
https://www.nxtbook.com/nxtbooks/gulfpub/hp_202209
https://www.nxtbook.com/nxtbooks/gulfpub/hp_202208
https://www.nxtbook.com/nxtbooks/gulfpub/hp_202207_v2
https://www.nxtbook.com/nxtbooks/gulfpub/hp_202207
https://www.nxtbook.com/nxtbooks/gulfpub/hp_202206_v2
https://www.nxtbook.com/nxtbooks/gulfpub/hp_202206
https://www.nxtbook.com/nxtbooks/gulfpub/hp_202205_v2
https://www.nxtbook.com/nxtbooks/gulfpub/hp_202205
https://www.nxtbook.com/nxtbooks/gulfpub/hp_202204_v2
https://www.nxtbook.com/nxtbooks/gulfpub/hp_202204
https://www.nxtbook.com/nxtbooks/gulfpub/hp_032022
https://www.nxtbook.com/nxtbooks/gulfpub/hp_202203
https://www.nxtbook.com/nxtbooks/gulfpub/hp_202202
https://www.nxtbook.com/nxtbooks/gulfpub/hp_202201
https://www.nxtbook.com/nxtbooks/gulfpub/hp_202112
https://www.nxtbook.com/nxtbooks/gulfpub/hp_202111
https://www.nxtbook.com/nxtbooks/gulfpub/hp_202110
https://www.nxtbook.com/nxtbooks/gulfpub/hpimarket_2022_v2
https://www.nxtbook.com/nxtbooks/gulfpub/hpimarket_2022
https://www.nxtbook.com/nxtbooks/gulfpub/hp_202109
https://www.nxtbook.com/nxtbooks/gulfpub/hp_202108
https://www.nxtbook.com/nxtbooks/gulfpub/petrochemical_processes_handbook_2021_v2
https://www.nxtbook.com/nxtbooks/gulfpub/petrochemical_processes_handbook_2021
https://www.nxtbook.com/nxtbooks/gulfpub/hp_202107
https://www.nxtbook.com/nxtbooks/gulfpub/hp_202106
https://www.nxtbook.com/nxtbooks/gulfpub/hp_202105
https://www.nxtbook.com/nxtbooks/gulfpub/hp_202104
https://www.nxtbook.com/nxtbooks/gulfpub/hp_ebooks
https://www.nxtbook.com/nxtbooks/gulfpub/hp_202103
https://www.nxtbook.com/nxtbooks/gulfpub/hp_202102
https://www.nxtbook.com/nxtbooks/gulfpub/hp_202101
https://www.nxtbook.com/nxtbooks/gulfpub/catalyst_handbook_2020_v2
https://www.nxtbook.com/nxtbooks/gulfpub/catalyst_handbook_2020
https://www.nxtbook.com/nxtbooks/gulfpub/hp_202012
https://www.nxtbook.com/nxtbooks/gulfpub/hp_202011
https://www.nxtbook.com/nxtbooks/gulfpub/hp_202010
https://www.nxtbook.com/nxtbooks/gulfpub/hpimarket_2021
https://www.nxtbook.com/nxtbooks/gulfpub/hp_202009
https://www.nxtbook.com/nxtbooks/gulfpub/hp_202008
https://www.nxtbook.com/nxtbooks/gulfpub/refining_processes_handbook_2020
https://www.nxtbook.com/nxtbooks/gulfpub/refining_processes_handbook_2020_v2
https://www.nxtbook.com/nxtbooks/gulfpub/hp_202007
https://www.nxtbook.com/nxtbooks/gulfpub/hp_202006
https://www.nxtbook.com/nxtbooks/gulfpub/hp_202005
https://www.nxtbook.com/nxtbooks/gulfpub/hp_202004
https://www.nxtbook.com/nxtbooks/gulfpub/hp_202003
https://www.nxtbook.com/nxtbooks/gulfpub/hp_202002
https://www.nxtbook.com/nxtbooks/gulfpub/hp_202001
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201912
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201911
https://www.nxtbook.com/nxtbooks/gulfpub/hpimarket_2020_v2
https://www.nxtbook.com/nxtbooks/gulfpub/hpimarket_2020
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201910
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201909
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201908
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201907
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201906
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201905
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201904
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201903
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201902
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201901
https://www.nxtbook.com/nxtbooks/gulfpub/petrochemical_2018_v2
https://www.nxtbook.com/nxtbooks/gulfpub/petrochemical_2018
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201812
https://www.nxtbook.com/nxtbooks/gulfpub/hpimarket_2019_v2
https://www.nxtbook.com/nxtbooks/gulfpub/hpimarket_2019
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201811
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201810
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201809
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201808
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201807
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201806
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201805
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201804
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201803
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201802
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201801
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201712
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201711
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201710
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201709
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201708
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201707
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201706
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201705
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201704
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201703
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201702
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201701
https://www.nxtbook.com/nxtbooks/gulfpub/hp_2017mediaplanner
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201612
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201611
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201610
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201609
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201608
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201607
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201606
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201605
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201604
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201603
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201602
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201601
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201512
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201511
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201510
https://www.nxtbook.com/nxtbooks/gulfpub/hp_2016mediaplanner
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201509
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201508
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201507
https://www.nxtbook.com/nxtbooks/gulfpub/hp_2015tmsd
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201506
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201505
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201504
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201503
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201502
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201501
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201412
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201411
https://www.nxtbook.com/nxtbooks/gulfpub/hp_2015mediaplanner
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201410
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201409
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201408
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201407
https://www.nxtbook.com/nxtbooks/gulfpub/hp_2014petrochemicalprocesses_v2
https://www.nxtbook.com/nxtbooks/gulfpub/hp_2014petrochemicalprocesses
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201406
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201405
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201404
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201403
https://www.nxtbook.com/nxtbooks/gulfpub/hp_2014calendar
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201402
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201401
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201312
https://www.nxtbook.com/nxtbooks/gulfpub/hp_2014mediaplanner
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201311
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201310
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201309
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201308
https://www.nxtbook.com/nxtbooks/gulfpub/hp_srsguide2013
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201307
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201306
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201305
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201304
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201303
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201302
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201301
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201212
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201211
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201210
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201209
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201208
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201207
https://www.nxtbook.com/nxtbooks/gulfpub/hp_srsguide2012
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201206
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201205
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201204
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201203
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201202
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201201
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201112
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201111
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201110
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201109
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201108
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201107_srsguide
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201107
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201106
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201105
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201104
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201103
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201102
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201101
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201012
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201011
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201010
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201009
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201008
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201007
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201006
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201005
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201004
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201003
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201002
https://www.nxtbook.com/nxtbooks/gulfpub/hp_201001
https://www.nxtbook.com/nxtbooks/gulfpub/hp_200912
https://www.nxtbook.com/nxtbooks/gulfpub/hp_200911
https://www.nxtbook.com/nxtbooks/gulfpub/hp_200910
https://www.nxtbook.com/nxtbooks/gulfpub/hp_200909
https://www.nxtbook.com/nxtbooks/gulfpub/hp_200908
https://www.nxtbook.com/nxtbooks/gulfpub/hp_200907
https://www.nxtbook.com/nxtbooks/gulfpub/hp_200906
https://www.nxtbook.com/nxtbooks/gulfpub/hp_200905
https://www.nxtbook.com/nxtbooks/gulfpub/hp_200904
https://www.nxtbook.com/nxtbooks/gulfpub/hp_200903
https://www.nxtbook.com/nxtbooks/gulfpub/hp_200902
https://www.nxtbook.com/nxtbooks/gulfpub/hp_200901
https://www.nxtbookmedia.com