Closed-Loop Self-Cooling Recuperative N2 Expander Cycle for the

Feb 28, 2018 - Song et al.(10) proposed an empirical modeling (data-driven model) to reduce the required energy consumption for the N2 dual expander L...
0 downloads 9 Views 2MB Size
Subscriber access provided by Kaohsiung Medical University

Article

Closed loop self-cooling recuperative N2-expander cycle for energy efficient and ecological natural gas liquefaction process Muhammad Abdul Qyyum, Kinza Qadeer, and Moonyong Lee ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.7b04679 • Publication Date (Web): 28 Feb 2018 Downloaded from http://pubs.acs.org on March 2, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

ACS Sustainable Chemistry & Engineering is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 37 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Sustainable Chemistry & Engineering

1

Closed loop self-cooling recuperative N2-expander cycle for energy efficient

2

and ecological natural gas liquefaction process

3

Muhammad Abdul Qyyuma, Kinza Qadeera, and Moonyong Leea, * a

4

School of Chemical Engineering, Yeungnam University, Gyeongsan 712-749, Rep. of Korea

5 6

Authors mailing address:

7

1st author: Muhammad Abdul Qyyum

8

Email ID: [email protected]

9

Process System Design and Control Laboratory # 401, School of Chemical Engineering, Yeungnam

10

University, 280, Daehakro, Gyeongsan, GyeongBuk, Republic of Korea.

11

2nd author: Kinza Qadeer

12

Email ID: [email protected]

13

Process System Design and Control Laboratory # 401, School of Chemical Engineering, Yeungnam

14

University, 280, Daehakro, Gyeongsan, GyeongBuk, Republic of Korea.

15

Corresponding author: Moonyong Lee

16

Email ID: [email protected]

17

Process System Design and Control Laboratory # 401, School of Chemical Engineering, Yeungnam

18

University, 280, Daehakro, Gyeongsan, GyeongBuk, Republic of Korea.

19 20 21

*

22

Prof. Moonyong Lee

23

Email: [email protected]

24

Telephone: +82-53-810-2512

Correspondence concerning this article should be addressed to:

25

1 ACS Paragon Plus Environment

ACS Sustainable Chemistry & Engineering 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 37

26

Abstract

27

Liquefied natural gas (LNG) has attracted global attention as a more environmentally friendly energy

28

source when compared to other fossil fuels. The nitrogen (N2) expander liquefaction is the most green

29

and safe process among the different types of commercial natural gas liquefaction processes, but its

30

relatively low energy efficiency is a major issue. In this study, an innovative closed loop self-cooling

31

recuperation technology was proposed to reduce the exergy losses of the N2 expander LNG process.

32

The LNG process with the implementation of the proposed technology was modeled using a

33

commercial process simulation tool, ASPEN HYSYS® v9. Subsequently, a modified coordinate

34

descent optimization algorithm was employed to achieve maximum potential benefits of the proposed

35

technology. The energy efficiency of the proposed LNG process was further improved by energy

36

recovery from end flash gas and high-pressure natural gas feed. Finally, the energy efficiency of the

37

proposed closed loop self-cooling recuperative N2 expander LNG process was significantly improved

38

up to 80.5% compared to the existing N2 expander based LNG processes, depending on the feed

39

natural gas conditions, composition, and design parameters.

40 41 42

Keywords: Natural gas liquefaction; LNG; Closed loop self-cooling recuperation; N2-expander

43

liquefaction process; Ecological liquefaction process; End flash gas.

44

2 ACS Paragon Plus Environment

Page 3 of 37 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

45

ACS Sustainable Chemistry & Engineering

Introduction

46

Compared to other fuels, liquefied natural gas (LNG) mainly has low carbon dioxide emissions

47

and can meet the ever increasing stringent environmental safety rules and regulations. The location of

48

the natural gas reserves is of key importance in the economics of natural gas storage and

49

transportation. The main methods for storing and transporting natural gas is compression, liquefaction,

50

and physical adsorption. Liquefaction of natural gas, resulting in a material with 1/600th the original

51

volume, has been considered to be the most cost effective transportation strategy, especially when

52

compared to gaseous natural gas transportation. However, liquefaction is an energy intensive process,

53

and the liquefaction of 1 kg of natural gas consumes 1,188 kJ of energy 1, which is equivalent to 30–

54

35% of the total energy required for LNG production.2, 3 Although, the energy requirement for LNG

55

production strongly depends on the plant site conditions4, 5 and involved liquefaction process such as

56

SMR, DMR, C3MR, and cascaded.6

57

LNG processes can be categorized by their use of two major technologies, mixed refrigerant

58

based processes, and N2 expander based processes. To optimize these processes for large scale LNG

59

production, a combination of different refrigeration cycles has been developed such as, single mixed

60

refrigerant (SMR), cascade, propane precooled mixed refrigerant (C3MR), and dual mixed refrigerant

61

(DMR) processes. Among these, the SMR and N2 expander processes offer more simplicity with the

62

lowest amount of capital investment, making them the most feasible for offshore LNG production.3, 7-

63

11

64

SMR process has inherent safety and environmental concerns. The presence of highly flammable

65

hydrocarbon based refrigerants makes SMR less attractive due to its environmental hazards and safety

66

concerns.

The SMR process is highly energy efficient when compared to N2 expander processes, however, the

67

Table 1 summarizes the safety and environmental data for different refrigerants. The safety data

68

shows that N2 as a refrigerant has zero occupational exposure limit (OEL), and a zero lower

69

flammability limit (LFL). Furthermore, the American Society of Heating, Refrigerating, and Air-

3 ACS Paragon Plus Environment

ACS Sustainable Chemistry & Engineering 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 4 of 37

70

Conditioning Engineers (ASHRAE) has standardized 34 safety groups (2010a and 2010b), and

71

categorized N2 refrigerant in the A1 category (i.e. no flame propagation), whereas, all other

72

refrigerants are categorized as A3 (i.e. highly flammable). The environmental data shows zero global

73

warming potential (GWP) for N2 refrigeration when compared to the ingredients of the mixed

74

refrigerant. Table 1. Safety and environmental data for refrigerants.12

75

Safety data Refrigerant

Environmental data

OEL

LFL

Std 34 safety

(PPMv)

(%)

group

Methane (CH4)

1000

4.8

A3

0.0

23

Ethane (C2H6)

1000

3.1

A3

0.0

~20

Ethylene (C2H4)

200

3.1

A3

0.0