Hydrocarbon Processing - July 2021 - 75
Digitalization
This sequence obtained from simulation models was one of
the bottleneck problems in the debutanizer columns section.
The second problem included the following:
* During a troubleshooting review, it was also observed
that water was continuously being removed from
the debutanizer reflux drum.
* The reflux drum is equipped with a control valve
on the water drain, which normally does not open
during normal operating conditions.
* At lower feed loads, the control valve opening was high,
which corresponded to the discharged water flowrate
from the reflux drum. This was not an expected issue
because dissolved water had to be taken from the
stripper column-and the debutanizer feed had not
contained water composition.
* Simulation models showed that stripper reboilers
(these exchangers used hot debutanizer bottom
products as heating fluid) did not have enough duty
at lower feed rates.
* The lower feed fell to lower temperatures in the
reboilers of the stripper column, and then water
in the reboiled stream could not be removed.
* Water was carried via the stripper bottom to the
debutanizer column at these conditions, thereby
upsetting operations and tripping the PSV in the
debutanizer.
Implementation of model results in the field. As a result
of the simulation modeling, the stripper bottom temperature
began to stay at optimum temperature (it was extracted from
simulation models) and not carry light ends and water to the
debutanizer column, especially at low feed rates. When the water
reached the top of the debutanizer, there was a freezing risk
that could result in a PSV trip. To prevent freezing and blocking,
electrical tracing was used in pipelines and process instruments.
Following the implementation of these model results, highpressure
steam savings increased by 3.36%. Additionally, the
refinery's energy intensity decreased by 0.06, while CO2
emissions
decreased by 1,500 tpy. This was achieved by reducing
high-pressure steam consumption in the process via decreasing
fuel gas rates at conventional boilers in the refinery. Avoiding
PSV trips also helped the refinery decrease losses and mitigate
environmental issues. This was an invaluable gain for the
refinery's reputation.
Takeaway. This study analyzed the effects of each operating
parameter, both individually and collectively. When a system
is viewed in its entirety, some parameters have a snowball effect,
while some have a diminishing effect. Therefore, before
performing any debottleneck study in a process and/or in a
specific section of a process, it is better to check the overall
effects. In this case, by understanding and targeting the source
of the bottleneck, the first step was obtaining the root causes
of the problem based on the symptoms and on the unsteady
operation of the stripper and the debutanizer under turndown
loads. The second step was optimizing operating conditions
according to the simulation results.
In many situations, it is uneconomical to solve the problem-especially
for large-capacity units in a refinery-with
Listen to
Hydrocarbon Processing's
podcast for the latest
technologies in the
downstream industry.
conventional trial-and-error methods, which can cause offspec
products or upsets in refinery units. However, the authors
found alternative solutions via simulation models and
corrected the problems on the unit's data historian. After discovering
the root causes of the problem, alternative solutions
were applied on the models first, prior to implementing them
onsite. This solved the problem in the most economical way.
Therefore, to obtain a correct diagnosis of a problem, it is important
to first understand the underlying principles before
addressing the problem.
ERHAN ÖZSAĞIROĞLU is Simulation Superintendent under
the Process and Equipment Development Department
at Tüpraş headquarters. He previously worked as a senior
process engineer and holds a PhD in chemical engineering
from Istanbul Technical University.
TUĞÇE ÖZKURT ATAGÜN is the Process Superintendent at
Tüpraş' İzmit refinery. She has been working for 8 yr, and is
responsible for the following units: DCU, FCCU, the gasoline
desulfurizer, the kerosene treater, and the LPG and SHU units.
ECEM ARİCİ is the Process Chief Engineer at Tüpraş' İzmit
refinery. She is responsible for the kerosene treatment unit,
the SHU and the LPG merox unit. She previously worked as
an operations engineer and as a process engineer for the
DCU. She earned a BSc degree in chemical engineering
from Boğaziçi University in Turkey.
SUBSCRIBE NOW!
HydrocarbonProcessing.com/Podcasts
Hydrocarbon Processing | JULY 2021 75
http://www.HydrocarbonProcessing.com/Podcasts
Hydrocarbon Processing - July 2021
Table of Contents for the Digital Edition of Hydrocarbon Processing - July 2021
Hydrocarbon Processing - July 2021 - Intro
Hydrocarbon Processing - July 2021 - Cover1
Hydrocarbon Processing - July 2021 - Cover2
Hydrocarbon Processing - July 2021 - 3
Hydrocarbon Processing - July 2021 - 4
Hydrocarbon Processing - July 2021 - 5
Hydrocarbon Processing - July 2021 - 6
Hydrocarbon Processing - July 2021 - 7
Hydrocarbon Processing - July 2021 - 8
Hydrocarbon Processing - July 2021 - 9
Hydrocarbon Processing - July 2021 - 10
Hydrocarbon Processing - July 2021 - 11
Hydrocarbon Processing - July 2021 - 12
Hydrocarbon Processing - July 2021 - 13
Hydrocarbon Processing - July 2021 - 14
Hydrocarbon Processing - July 2021 - 15
Hydrocarbon Processing - July 2021 - 16
Hydrocarbon Processing - July 2021 - 17
Hydrocarbon Processing - July 2021 - 18
Hydrocarbon Processing - July 2021 - 19
Hydrocarbon Processing - July 2021 - 20
Hydrocarbon Processing - July 2021 - 21
Hydrocarbon Processing - July 2021 - 22
Hydrocarbon Processing - July 2021 - 23
Hydrocarbon Processing - July 2021 - 24
Hydrocarbon Processing - July 2021 - 25
Hydrocarbon Processing - July 2021 - 26
Hydrocarbon Processing - July 2021 - 27
Hydrocarbon Processing - July 2021 - 28
Hydrocarbon Processing - July 2021 - 29
Hydrocarbon Processing - July 2021 - 30
Hydrocarbon Processing - July 2021 - 31
Hydrocarbon Processing - July 2021 - 32
Hydrocarbon Processing - July 2021 - 33
Hydrocarbon Processing - July 2021 - 34
Hydrocarbon Processing - July 2021 - 35
Hydrocarbon Processing - July 2021 - 36
Hydrocarbon Processing - July 2021 - 37
Hydrocarbon Processing - July 2021 - 38
Hydrocarbon Processing - July 2021 - 39
Hydrocarbon Processing - July 2021 - 40
Hydrocarbon Processing - July 2021 - 41
Hydrocarbon Processing - July 2021 - 42
Hydrocarbon Processing - July 2021 - 43
Hydrocarbon Processing - July 2021 - 44
Hydrocarbon Processing - July 2021 - 45
Hydrocarbon Processing - July 2021 - 46
Hydrocarbon Processing - July 2021 - 47
Hydrocarbon Processing - July 2021 - 48
Hydrocarbon Processing - July 2021 - 49
Hydrocarbon Processing - July 2021 - 50
Hydrocarbon Processing - July 2021 - 51
Hydrocarbon Processing - July 2021 - 52
Hydrocarbon Processing - July 2021 - 53
Hydrocarbon Processing - July 2021 - 54
Hydrocarbon Processing - July 2021 - 55
Hydrocarbon Processing - July 2021 - 56
Hydrocarbon Processing - July 2021 - 57
Hydrocarbon Processing - July 2021 - 58
Hydrocarbon Processing - July 2021 - 59
Hydrocarbon Processing - July 2021 - 60
Hydrocarbon Processing - July 2021 - 61
Hydrocarbon Processing - July 2021 - 62
Hydrocarbon Processing - July 2021 - 63
Hydrocarbon Processing - July 2021 - 64
Hydrocarbon Processing - July 2021 - 65
Hydrocarbon Processing - July 2021 - 66
Hydrocarbon Processing - July 2021 - 67
Hydrocarbon Processing - July 2021 - 68
Hydrocarbon Processing - July 2021 - 69
Hydrocarbon Processing - July 2021 - 70
Hydrocarbon Processing - July 2021 - 71
Hydrocarbon Processing - July 2021 - 72
Hydrocarbon Processing - July 2021 - 73
Hydrocarbon Processing - July 2021 - 74
Hydrocarbon Processing - July 2021 - 75
Hydrocarbon Processing - July 2021 - 76
Hydrocarbon Processing - July 2021 - 77
Hydrocarbon Processing - July 2021 - 78
Hydrocarbon Processing - July 2021 - 79
Hydrocarbon Processing - July 2021 - 80
Hydrocarbon Processing - July 2021 - 81
Hydrocarbon Processing - July 2021 - 82
Hydrocarbon Processing - July 2021 - 83
Hydrocarbon Processing - July 2021 - 84
Hydrocarbon Processing - July 2021 - 85
Hydrocarbon Processing - July 2021 - 86
Hydrocarbon Processing - July 2021 - 87
Hydrocarbon Processing - July 2021 - 88
Hydrocarbon Processing - July 2021 - 89
Hydrocarbon Processing - July 2021 - 90
Hydrocarbon Processing - July 2021 - Cover3
Hydrocarbon Processing - July 2021 - 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