Hydrocarbon Processing - May 2022 - 44
Digital Technology
richment gas with a high heating value is
added to control the pressure, the heating
value of the fuel gas increases. The furnaces
will then have to cut their consumption,
which will upset the volume balance, and
the enrichment gases will also be cut back.
This behavior keeps repeating, leadFIG.
1. Fuel gas network pressure and quality interaction.
have shifted dramatically during the past
2 yr, with energy reduction, production
cost reduction and increased agility becoming
the top focus areas.
APC and optimization technologies
are the most cost-effective option to improve
process efficiency and support the
decarbonization process. It is worth noting
that with carbon prices continuing to
increase, the value from CO2
reduction
becomes as significant a benefit as energy
reduction savings.
There are a multitude of efficiency
improvement opportunities available to
refiners. These include:
* Increasing furnace efficiency
* Minimizing distillation
columns' pressure against
actual unit constraints
* Minimizing load and
optimizing the purification
level of distillation columns
* Minimizing quality giveaways to
avoid excess energy consumption
* Minimizing circulation,
reprocessing and recycling
* Making the right product recovery/
energy consumption tradeoffs
* Maximizing heat/cold recovery
* Integrating multiple units and
managing heat balances
* Balancing demand/supply to avoid
losses (e.g., hydrogen, steam)
* Minimizing downgrades (e.g.,
steam, fuels, hydrogen, products)
* Maximizing equipment efficiency
* Optimizing utilities networks:
fuels, hydrogen and steam.
APC is now capable of solving difficult
nonlinear problems. In addition, it
enables an adaptive workflow to maximize
model accuracy, lets users make
changes to economic objectives on the
fly, and embeds AI and deep learning capabilities
to leverage a wealth of histori44
MAY 2022 | HydrocarbonProcessing.com
cal data to obtain models and solve complex
problems-for instance, inferring
highly nonlinear qualities that depend
on the type of run, feedstock qualities or
grade to be produced.
With dynamic, self-adapting optimization
capabilities that automatically
align models and the process, a true overall
optimum can be achieved across a
large process scope.
These capabilities and technology
enhancements enable users to solve complex
problems, such as utilities networks,
which were previously difficult to solve.
The rest of this article focuses on optimization
strategies, which
tremendous energy- and CO2
-saving opportunities
in the three primary site networks:
fuel gas, hydrogen and steam.
Fuel gas network optimization. For
many facilities, fuel gas network optimization
can be a significant issue that must
be addressed. The following are some of
the most common challenges:
* Fuel gas network pressure
(volume) and quality
interact heavily
* Volume balance models are
integrating processes as pressure
builds up as a ramp
* Quality models are nonlinear,
and gains may even change from
positive to negative or vice versa
* Various makeup gases are typically
available, and their quality may
change over time
* Additional makeup gas reduces the
effect on overall network quality
due to nonlinearities from mixing
* Inherent instability due to
disturbances continuously
entering the system.
The quality of gas streams entering
the network varies continuously. If enrepresent
ing
to a self-propagating cycle impacting
the performance of fuel gas users across
the whole site. Fuel gas instability can
result in scenarios such as units cutting
back load, increasing load to blowdown
networks and gas recovery compressors,
and flaring events.
This behavior, illustrated in FIG. 1, can
cause excessive energy consumption and
CO2
emissions. With integrating processes
like volume balance models, which
exhibit strong nonlinearity, model gains
can flip their sign (i.e., go from positive
to negative or vice versa) as the quality
effect of the enrichment gas depends on
the current network's calorific value.
Multiple enrichment gases may be
available to control pressure, and each gas
can increase or decrease the network calorific
value. The impact may change over
time depending on current calorific values
of both gas and the network. Adding
more makeup gas changes the effect as the
gap between the two qualities changes.
FIG. 2 illustrates the potential effects
of these nonlinearities. For instance, the
same changes to the same enrichment
gas may have very different effects on the
network's calorific value. Addressing these
challenges is possible by adopting a nonlinear
adaptive process control solutiona
to solve highly nonlinear and interactive
problems and reach desired outcomes.
The adaptive process control solutiona
lets
users easily revise economic objectives to
continuously minimize the overall cost of
the streams entering the fuel gas network.
The following are some other key
benefits of using such a nonlinear adaptive
process control solution:
* Simultaneously control both
fuel gas pressure and quality
(calorific value), stabilizing
operations throughout the site
* Minimize/avoid flaring
* Minimize blowdown discharge
and subsequently gas recovery
compressor power consumption
* Improve furnace efficiency
through consistent and stable
firing, which enables further
reduction in excess air
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