Hydrocarbon Processing - August 2021 - GP-21
SPECIAL FOCUS: SMALL-SCALE LNG
Achieve three efficiencies
in MR compressors for SSLNG
T. PATEL, Atlas Copco Gas and Process, Houston, Texas; M. DREWES, Atlas Copco Gas and Process,
Köln, Germany; and J. ZHAO, EnFlex Group, Houston, Texas
In the equipment they use, investors in small-scale LNG
(SSLNG) face a steep challenge: They must achieve cost efficiency,
operational efficiency and energy efficiency-all
with maximum availability. In this context, the design of single
mixed-refrigerant (SMR) compressors, a critical piece of technology
in SSLNG plants, takes on an important role in both the
plant's efficiency and its return on investment (ROI).
As the benefits of integrally geared compressors (IGCs)
have become better known across hydrocarbon processing industries,
this compressor type has achieved broader acceptance.
For SSLNG, this pertains particularly to compressors requiring
gas or electric drives with a rated power of up to 27 MW
(36,200 hp). Demand for IGCs has been especially strong for
SSLNG plants with varying technical and logistical requirements
compared to large-scale LNG facilities. These include
quick deployment, scalability, redeployment capability and the
ability to respond rapidly to market demand.
Until the early 2000s, inline (i.e., single-shaft) compressors
were the dominant compressor technology in the marketplace.
From then, IGCs have become more popular due to their greater
efficiency and reliability, and their inclusion in the 7th edition
of the API (2002, Ch. 3). Nevertheless, universally applicable
statements on the differences between these two technologies
must be carefully considered. This is because the specific use
case and operating conditions are what ultimately drive the decision
on which compression technology is used.
This article examines the deployment of integrally geared
compressor technology, exploring the drivers behind the rising
demand for SSLNG and the qualities that make IGCs an efficient
compression solution in SSLNG plants. Characteristics discussed
include the IGCs' high flexibility and lower initial investment
and operating costs, which enable operators to realize agile
plant deployment and improve the efficiency of a plant once it is
operational. This article uses the example of a mixed-refrigerant
IGC installationa
operating at an SSLNG plant in China.b
Inside the Zhengtai Yida LNG plant. The Zhengtai Yida
LNG plant (COVER PHOTO) is located in China's Inner Mongolia
region, approximately 700 km (440 mi) from China's capital,
Beijing. The plant has a 0.807-MMtpy capacity (based on
350 days of operation), and it uses an SMR cycle, the most-used
cycle for liquefaction trains with a capacity of 1 MMtpy or less.
The SMR cycle uses various components, such as nitrogen,
ethylene, methane, propane, butanes and/or i-pentane in place of
the pure hydrocarbon refrigerants utilized in the discrete cooling
FIG. 1. The IGC unit's deployment within the SMR cycle.
Gas Processing & LNG | JULY/AUGUST 2021 21
steps of a cascade refrigerant cycle. Basically, SMRs operate by
condensing a hydrocarbon gas mixture to a liquid and then using
cooling through its vaporization to cool natural gas close to its
boiling point of −162°C (−260°F). The final phase change into
LNG is often accomplished with a Joule-Thomson valve.
Many proprietary SMR processes utilize a single-pressure
mixed-refrigerant cycle, which compresses the refrigerant to its
highest pressure. It is then sent to a series of condensers and
separators before it is ultimately delivered to the heat exchanger
to cool LNG. To increase efficiency, other SMR processes vaporize
the mixed refrigerant in two steps: one higher-pressure
and one lower-pressure stage, which can be driven either by two
compressors or, ideally, a single compressor with two separate
stage groupings (FIG. 1).
The relatively narrow range of compression specifications
allows for the standardization of a compressor's aerodynamic
design in three- and four-stage mixed-refrigerant compressors.
Such standardization allows for faster compressor delivery at a
lower initial investment. Given that LNG projects are naturally
CAPEX-intensive (the liquefaction process can account for
more than 50% of total project costs), lower compressor investment
costs help improve a plant's ability to operate profitably.
Lower investment and design priorities. Unlike SSLNG
plants, large-scale LNG liquefaction plants require significant
investment commitments across all project phases. SSLNG
plants have lower installation cost, can be built in much shorter
timeframes, and use natural gas as a cost-efficient feedstock in
Hydrocarbon Processing - August 2021
Table of Contents for the Digital Edition of Hydrocarbon Processing - August 2021
Contents
Hydrocarbon Processing - August 2021 - Intro
Hydrocarbon Processing - August 2021 - Cover1
Hydrocarbon Processing - August 2021 - Cover2
Hydrocarbon Processing - August 2021 - Contents
Hydrocarbon Processing - August 2021 - 4
Hydrocarbon Processing - August 2021 - 5
Hydrocarbon Processing - August 2021 - 6
Hydrocarbon Processing - August 2021 - 7
Hydrocarbon Processing - August 2021 - 8
Hydrocarbon Processing - August 2021 - 9
Hydrocarbon Processing - August 2021 - 10
Hydrocarbon Processing - August 2021 - 11
Hydrocarbon Processing - August 2021 - 12
Hydrocarbon Processing - August 2021 - 13
Hydrocarbon Processing - August 2021 - 14
Hydrocarbon Processing - August 2021 - 15
Hydrocarbon Processing - August 2021 - 16
Hydrocarbon Processing - August 2021 - 17
Hydrocarbon Processing - August 2021 - 18
Hydrocarbon Processing - August 2021 - 19
Hydrocarbon Processing - August 2021 - 20
Hydrocarbon Processing - August 2021 - 21
Hydrocarbon Processing - August 2021 - 22
Hydrocarbon Processing - August 2021 - 23
Hydrocarbon Processing - August 2021 - 24
Hydrocarbon Processing - August 2021 - 25
Hydrocarbon Processing - August 2021 - 26
Hydrocarbon Processing - August 2021 - 27
Hydrocarbon Processing - August 2021 - 28
Hydrocarbon Processing - August 2021 - 29
Hydrocarbon Processing - August 2021 - 30
Hydrocarbon Processing - August 2021 - 31
Hydrocarbon Processing - August 2021 - 32
Hydrocarbon Processing - August 2021 - 33
Hydrocarbon Processing - August 2021 - 34
Hydrocarbon Processing - August 2021 - 35
Hydrocarbon Processing - August 2021 - 36
Hydrocarbon Processing - August 2021 - 37
Hydrocarbon Processing - August 2021 - 38
Hydrocarbon Processing - August 2021 - 39
Hydrocarbon Processing - August 2021 - 40
Hydrocarbon Processing - August 2021 - 41
Hydrocarbon Processing - August 2021 - 42
Hydrocarbon Processing - August 2021 - 43
Hydrocarbon Processing - August 2021 - 44
Hydrocarbon Processing - August 2021 - 45
Hydrocarbon Processing - August 2021 - 46
Hydrocarbon Processing - August 2021 - 47
Hydrocarbon Processing - August 2021 - 48
Hydrocarbon Processing - August 2021 - 49
Hydrocarbon Processing - August 2021 - 50
Hydrocarbon Processing - August 2021 - 51
Hydrocarbon Processing - August 2021 - 52
Hydrocarbon Processing - August 2021 - 53
Hydrocarbon Processing - August 2021 - 54
Hydrocarbon Processing - August 2021 - 55
Hydrocarbon Processing - August 2021 - 56
Hydrocarbon Processing - August 2021 - 57
Hydrocarbon Processing - August 2021 - 58
Hydrocarbon Processing - August 2021 - 59
Hydrocarbon Processing - August 2021 - 60
Hydrocarbon Processing - August 2021 - 61
Hydrocarbon Processing - August 2021 - 62
Hydrocarbon Processing - August 2021 - 63
Hydrocarbon Processing - August 2021 - 64
Hydrocarbon Processing - August 2021 - 65
Hydrocarbon Processing - August 2021 - 66
Hydrocarbon Processing - August 2021 - 67
Hydrocarbon Processing - August 2021 - 68
Hydrocarbon Processing - August 2021 - 69
Hydrocarbon Processing - August 2021 - 70
Hydrocarbon Processing - August 2021 - 71
Hydrocarbon Processing - August 2021 - 72
Hydrocarbon Processing - August 2021 - 73
Hydrocarbon Processing - August 2021 - 74
Hydrocarbon Processing - August 2021 - 75
Hydrocarbon Processing - August 2021 - 76
Hydrocarbon Processing - August 2021 - 77
Hydrocarbon Processing - August 2021 - 78
Hydrocarbon Processing - August 2021 - 79
Hydrocarbon Processing - August 2021 - 80
Hydrocarbon Processing - August 2021 - 81
Hydrocarbon Processing - August 2021 - 82
Hydrocarbon Processing - August 2021 - Cover3
Hydrocarbon Processing - August 2021 - Cover4
Hydrocarbon Processing - August 2021 - GP-1
Hydrocarbon Processing - August 2021 - GP-2
Hydrocarbon Processing - August 2021 - GP-3
Hydrocarbon Processing - August 2021 - GP-4
Hydrocarbon Processing - August 2021 - GP-5
Hydrocarbon Processing - August 2021 - GP-6
Hydrocarbon Processing - August 2021 - GP-7
Hydrocarbon Processing - August 2021 - GP-8
Hydrocarbon Processing - August 2021 - GP-9
Hydrocarbon Processing - August 2021 - GP-10
Hydrocarbon Processing - August 2021 - GP-11
Hydrocarbon Processing - August 2021 - GP-12
Hydrocarbon Processing - August 2021 - GP-13
Hydrocarbon Processing - August 2021 - GP-14
Hydrocarbon Processing - August 2021 - GP-15
Hydrocarbon Processing - August 2021 - GP-16
Hydrocarbon Processing - August 2021 - GP-17
Hydrocarbon Processing - August 2021 - GP-18
Hydrocarbon Processing - August 2021 - GP-19
Hydrocarbon Processing - August 2021 - GP-20
Hydrocarbon Processing - August 2021 - GP-21
Hydrocarbon Processing - August 2021 - GP-22
Hydrocarbon Processing - August 2021 - GP-23
Hydrocarbon Processing - August 2021 - GP-24
Hydrocarbon Processing - August 2021 - GP-25
Hydrocarbon Processing - August 2021 - GP-26
Hydrocarbon Processing - August 2021 - GP-27
Hydrocarbon Processing - August 2021 - GP-28
Hydrocarbon Processing - August 2021 - GP-29
Hydrocarbon Processing - August 2021 - GP-30
Hydrocarbon Processing - August 2021 - GP-31
Hydrocarbon Processing - August 2021 - GP-32
Hydrocarbon Processing - August 2021 - GP-33
Hydrocarbon Processing - August 2021 - GP-34
Hydrocarbon Processing - August 2021 - GP-35
Hydrocarbon Processing - August 2021 - GP-36
Hydrocarbon Processing - August 2021 - GP-37
Hydrocarbon Processing - August 2021 - GP-38
Hydrocarbon Processing - August 2021 - GP-39
Hydrocarbon Processing - August 2021 - GP-40
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