- Email: [email protected]
Evaluation on the natural gas hydrate formation process
Journal Pre-proof Evaluation on the natural gas hydrate formation process
Shuqi Fang, Xinyue Zhang, Jingyi Zhang, Chun Chang, Pan Li, Jing Bai PII:
S1004-9541(20)30002-1
DOI:
https://doi.org/10.1016/j.cjche.2019.12.021
Reference:
CJCHE 1615
To appear in:
Chinese Journal of Chemical Engineering
Received date:
26 May 2019
Revised date:
5 December 2019
Accepted date:
8 December 2019
Please cite this article as: S. Fang, X. Zhang, J. Zhang, et al., Evaluation on the natural gas hydrate formation process, Chinese Journal of Chemical Engineering(2020), https://doi.org/10.1016/j.cjche.2019.12.021
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
© 2020 Published by Elsevier.
Journal Pre-proof
Evaluation on the natural gas hydrate formation process Shuqi Fang1,2,3, Xinyue Zhang1,3, Jingyi Zhang1, Chun Chang1,2,3, Pan Li1,2,3, Jing Bai1,2,3,* 1
School of Chemical Engineering and Energy, Zhengzhou University, Zhengzhou 450001,
China Henan Outstanding Foreign Scientists’ Workroom, Zhengzhou 450001, China
3
Engineering Laboratory of Henan Province for Biorefinery Technology and
oo
f
2
pr
Equipment, Zhengzhou 450001, China
*
e-
Corresponding author.
E-mail addresses: [email protected] (J. Bai)
Jo u
rn
al
Pr
Tel: +86-371-67780093 Fax: +86-371-67780093
Journal Pre-proof ABSTRACT Gas hydrates have endowed with great potential in gas storage and rapid formation of gas hydrates is critical to use this novel technology. This work evaluated the natural gas hydrate formation process, which was compared from six parameters, including conversion of water to hydrate, storage capacity, the rate of hydrate formation, space velocity (SV) of hydrate reaction, energy consumption and hydrate removal. The literature was selected by analyzing and comparing these six parameters mentioned
f
above, meanwhile placing emphasis on the three parameters of storage capacity, the
oo
rate of hydrate formation and space velocity of hydrate reaction. Through analysis and comparison, four conclusions could be obtained as follow. Firstly, the overall
pr
performance of the stirring process and the spraying process were better than other
e-
processes after analyzing the six parameters. Secondly, the additive types, the reactor
Pr
structure and the reactor size had influence on the natural gas hydrate formation process. Thirdly, the energy consumption via reciprocating impact in the hydrate formation process was higher than that via stirring, spraying and static higee. Finally,
al
it was one key for hydrate removal to realize the hydrate industrial production.
rn
Keywords: Natural gas hydrate; Evaluate; Hydrate formation process; Storage
Jo u
capacity; Space velocity of hydrate reaction
Journal Pre-proof
1. Introduction Natural gas hydrate (NGH), mainly composed of methane, is an ice-like crystalline compounds formed by water and natural gas at high pressure and low temperature [1]. Natural gas hydrate has the characteristics of high gas storage capacity and mild storage condition, as unit volume of natural gas hydrate can contain 160~180 m3 (at standard condition) [2,3]. In 1990, Gudmundsson [4] firstly proposed the NGH can be preserved at atmospheric pressure and the temperature lower than
oo
f
258.15 K. Because of the favorable gas storage capacity and pressure-temperature conditions, the storage and transportation in the form of hydrates has huge advantages
pr
over almost other common technologies such as compressed natural gas (CNG), liquefied natural gas (LNG) and pipeline natural gas (PNG), especially in the oceans,
e-
deserts and medium-sized gas fields where scarce energy and fresh water [5]. NGH
Pr
provides a new option for gas storage and transportation, many fundamental researches and technologies of NGH have been investigated extensively in recent
al
years.
rn
Rapid hydrate formation technology is one of the key in the industrialization of NGH. Reactor is the core device of the rapid hydrate formation system, which affects
Jo u
the hydrate formation process to a certain extent. The reactor for natural gas hydrate formation not only provides the temperature and pressure environment needed for gas and water formation, but also provides a disturbance environment to intensify the mass and heat transfer process in gas-liquid-solid phase [6]. Conventional reactors mainly include stirring reactor, spraying reactor and bubbling reactor. Stirring is one of the most common reactors, and Gudmundsson et al. [7] developed a stirring reactor where gas diffuses to the liquid phase rapidly by an impeller. Then, Linga et al. [8] used mechanical agitation to capture CO2 from fuel gases by employing gas hydrate technology. Their experimental result showed that the new apparatus improved CO 2 recovery compared to the previously used laboratory apparatus, which proved stirring can enhanced the rate of gas hydrate formation. Nevertheless, the shortcomings of the
Journal Pre-proof stirring reactors should not be neglected. For example, in order to prevent high pressure gas leakage in the reactor, the stirring shaft needs to have a high dynamic sealing technology. Besides, the power consumption of stirring is usually the fifth power of impeller size which indicates that the mixing reactor is not easy to enlarge in the industry and the stirring time is not easy to be too long [9]. Spraying is a type of reactor for gas-liquid, which can overcome the fact that stirring reactors cannot be used for industrial amplification. Rossi et al [10] had used a 25 L reactor (with 6
f
nozzles) which equipped with atomized spray to perform methane hydrate formation.
oo
The result showed this device could obtain methane hydrates without water left, in
pr
some 10 min only with sodium dodecyl sulfate (SDS) surfactant promotion. Mori [11] proposed and designed a continuous production mode of natural gas hydrate, which is
e-
characterized by spraying in the production of natural gas hydrate [12]. Bubble
Pr
column reactor is another reactor type suitable for gas-liquid reaction system, and it feeds gas into the reactor equipped with water or solution. Luo et al. [13] found the
al
increase of methane flux resulted in the increase of the hydrate formation rate, because higher methane flux produced more bubbles and larger total gas-liquid
rn
interface in a bubbling system. However, it is not encouraging to use bubbling reactor
Jo u
in terms of hydrate formation rate and it can increase the cost of the system [14, 15]. Apart from the conventional hydrate reactors described above, researchers were constantly exploring a number of new reactor devices and applying them in the field of rapid gas hydrate formation. Tetsuya et al. [16] reported a novel device for the continuous, high-rate formation, which was characterized by utilizing twin liquid jets impinging on each other. Park et al. [17] discovered that ultrasonic waves had an obvious promoting effect on methane hydrate formation, the ultrasonic power of 150 W was four times higher than that at 0 W when the subcooling temperature of 0.5 K. Bai et al. [18] proposed a vortex and impinging stream reactor (VIR) to enhance the CO2 gas hydrate formation by generating a high-gravity field. As mentioned above, various types of reactors had been proposed to investigate their effects on hydrate
Journal Pre-proof formation on the laboratory scale. However, the evaluation of gas hydrate formation process is still in its infancy, only a few literature had tried to assessment it. Mori [11] reviewed natural gas storage and divided it into four series of technologies, placing emphasis on the hydrate formation process, and compared and evaluated the rate of hydrate formation. Zhong et al. [19] compared the methane hydrate formation in stirred reactor and silica sand, in which the normalized gas uptake, water conversion to hydrate and storage capacity were mainly considered. Fan et al. [20] indicated that
f
TBAB could accelerate hydrate formation via analyzing hydrate formation rate
oo
constant and space velocity. Considering that the sizes and types of reactors are
pr
different, the thermodynamic conditions required for hydrate formation are not consistent. So far there is still no appropriate and unified standard to evaluate the
e-
performance of various hydrate formation process fairly.
Pr
In this work, relevant data of hydrate formation process in recent years had been compared and evaluated, mainly from six aspects: conversion of water to hydrate,
al
storage capacity (gas volume per unit volume of gas hydrate, V/V), the rate of hydrate formation, space velocity of hydrate reaction, energy consumption required and
rn
hydrate removal. This work placed emphasis on storage capacity, the rate of hydrate
Jo u
formation and space vel9ocity of hydrate reaction. 2. Conversion of water to hydrate Conversion of water to hydrate refers to the percentage of water converted into hydrate, which is expressed as the ratio of the total water mass in the reaction to the water supplied. The calculation formulas are as follows. Conversion %
n gas Hydrate number n H2O
100
(1)
Where nH2 O (mol) is the total number of moles of water in the system. Hydrate number is the number of water molecules needed per methane molecule to form hydrate and ∆ngas (mol) is the number of moles of gas consumed for hydrate
Journal Pre-proof
formation at the end of the experiment, which is determined from the gas uptake measurement, as follows. n gas n gas,t -n
gas,0
P0Vg Z 0 RT0
PV t g
(2)
Z t RTt
Where P0 (MPa) and T0 (K) are the pressure at the initial time respectively, Pt (MPa) and Tt (K) are the pressure at time T=t. Vg is the volume of gas phase of the crystallizer, m3. R is the general gas constant, taking 8.314 J∙mol-1∙K-1 ; Z is the
h
bP RT
e-
B
B Z
oo
1 A h - 1-h B 1 h
pr
Z
f
compression factor of real gas, which can be calculated by the following formula.
Pr
A a B bRT 1.5
a 0.4278
(4) (5) (6)
R 2Tc 2.5 Pc
(7)
RTc Pc
(8)
b 0.0867
al
(3)
rn
Conversion of water to hydrate is an important parameter in the process of
Jo u
hydrate formation, where higher conversion of hydrate to water is desirable. This work compared the data about conversion of water to hydrate in the hydrate formation process from different literature. Zhong [19] compared the effects of the stirred reactor and porous medium on the conversion of water to hydrate, using a reactor with the volume of 600 cm3. Naoki at the Keio University [21] proposed a static reactor with the volume of 942 cm3, and in this experiment investigated the effects of surfactants such as lithium dodecyl sulfate (LDS) and dodecylbenzene sulfonic acid (DBSA) on the conversion of water to hydrate. Linga [22] built a volume bed of silica sand reactor, which placed two copper cylinders in order to investigate the effect of the variable reactor volume on the hydrate formation process. Two years later, Linga [23] aslo investigated the role of the fixed bed column and a stirred vessel on the
Journal Pre-proof conversion of water to hydrate, and the volume of the reactor was 1236 cm3. Besides, Ekta [24] developed a static reactor with the volume of 250 cm3. Table 1 is the conversion of water to hydrate in the above-mentioned literature. Table 1. The comparison of experimental conditions and the conversion of water to hydrate. Additive
Conversion
Reactor Literature
Gas
Reactor
Pressure
volume (cm3)
Additive
concentration
T (K)
of water to (MPa)
(ppm)
hydrate (%)
Stirring 19
76.6
CH4
600
SDS
500
7 78.1
oo
f
Silica sand
274.15
2000
LDS CH4
924
e-
(Unstirring)
CH4
Fixed bed
695
3.9
/
78.2
420
83.6
580
275
4
950
1236
CH4
Jo u
Fixed bed
24
rn
Stirring CH4
Static
86.1 81.2 76.7
/
277.15
8
309
23
80.6
5000
al
22
Pr
DBSA
1236
275
pr
Static, 21
3500
81.8
79.7 84.0 74
/
/
277.15
8 94.7
0
8.36
Castor 250
5000
293.15
13.79
13.80
oil 9000
Table 1 showed the conversion of water to hydrate in different literature. The results could be revealed as follows. (a) On the basis of the conversion of water to hydrate from the literature 19 and 21, it could be found that the conversion rate with LDS and DBSA in static reactor was greater than that with SDS in stirring reactor. And it could be proved that the surfactant had a greater effect than the reactors to the conversion of water to hydrate. The reason was that the surfactant could reduce the gas-liquid surface tension, and decrease the resistance of gas entering the liquid phase, which could achieve more gas
15.91
Journal Pre-proof dissolve in liquid phase and enhance the mass transfer process. (b) According to the conversion of water to hydrate from the literature 23, the conversion of water to hydrate in fixed bed was slightly higher than that in the stirring reactor. Because the padding of the fixed bed was porous medium, which could obviously increase the gas-liquid contact area and provide a large amount of space for the growth of hydrate. Stirring only speeded up the mixing of gas and liquid, but the gas-liquid contact area did not increase greatly.
f
(c) According to the conversion of water to hydrate from the literature 22, the
oo
conversion of water to hydrate decreased slightly with the increase of reactor size.
pr
3. Gas storage capacity of hydrate
Gas storage capacity (GSC) has three kinds of expression way. Including volume
e-
storage capacity, mass storage capacity and molar storage capacity. Gas storage
Pr
capacity was usually defined as gas volumes decomposed from per unit volume of hydrate at standard conditions, m3∙m-3. The calculation formula is as follows. VG VG VNGH VL (1 V )
(9)
al
C
rn
Where C is the gas storage capacity of hydrate, VG (m3) is the volume of gas
Jo u
consumed under the standard condition in the reactor, VNGH (m3) is the volume of hydrate when the reaction ends, VL (m3) is the volume of water consumed, and ∆V is the molar volume change of water turned into hydrate. Makogon [25] demonstrated that the value of ∆V for structure-I hydrate is 4.6 cm3∙mol-1, and, the value of ∆V for structure-II hydrate is 5.3 cm3∙mol-1. Besides the data demonstrated in literature 19 and literature 24 mentioned in Table 1, four sets of data were added in Table 2. China University of petroleum [26] proposed a static reactor with the volume of 220 cm3, which charged with a biosurfactant instead of pure water. North University of China [27] installed a rotating packed bed reactor with the volume of 1413 cm3 to investigate the GSC. Dalian university of technology [28] investigated the effect of stirring rate and stirring time on GSC, using a semi-continuous stirred tank with the volume of 1072 cm3. Besides,
Journal Pre-proof Xiao [29] investigated the function of the three types of mechanical strategies on GSC via a reactor with the volume of 245 cm3, which were rotational stirring only, rotational stirring for a duration of time, followed by reciprocating impact and reciprocating impact only. These data above-mentioned literature were summarized in Table 2. Table 2. The comparison of experimental conditions and the GSC of hydrate. Reactor Literature
Gas
Reactor
Pressure 3
Additive
T (K) (MPa)
Stirring CH4
600
SDS
274.15
7.0
293.15
13.79
277.15
8.0
SDS
277.15
5.0
1072
SDS
274.4
5.0
275
/
273.3
6.0
oo
19
f
volume (cm )
Silica sand CH4
Static
250
pr
Castor 24
CH4
Static
Natural
Rotating
gas
packed bed
220
Mung starch
1413
al
27
/
Pr
26
e-
oil
Stirring CH4
Static
rn
28
Jo u
(Unstirring) Stirring
Reciprocating impact
29
CH4
Stirring+ Reciprocating impact
According to the formula (9) and the data summarized in Table 2, the GSC was calculated and illustrated in Fig. 1.
Journal Pre-proof Literature 19
Silica sand
Literature 24
T = 293.15K, Castor oil
Stirring
Literature 26
T = 277.15K, Pure water T = 277.15K, Mung strach
Literature 27
200
Rotating packed bed
Literature 28
Unstirring
Literature 29
Stirring, 320ppm
Stirring
Impact Stirring + Impact
GSC, V/V
160
120
80
f
40
0
5
10
15
Time, h
oo
0 20
25
pr
Fig. 1. The comparison of GSC of natural gas hydrate formation process from different literature.
Fig.1 investigated the changes of GSC over time. In Fig. 1, the points from
e-
literature 19, 24, 26 and 27 were the value of GSC calculated under the optimal
Pr
conditions, and in rotating packed bed, the maximum value of GSC was obtained. The line from literature 28 and 29 were the trend of GSC in different time periods.
al
According to Fig.1, the following results could be revealed.
rn
(a) According to literature 19, 24 and 26, compared with pure water, the value of GSC with the three additives such as SDS, castor oil and mung bean had a significant
Jo u
increase, which could be inferred that the additives could increase the gas storage capacity of hydrate. It indicated that the solubility of methane was enhanced and the phase equilibrium condition was decreased under the action of additives. (b) In accordance with literature 19 and 28, the GSC was about the same in the silica sand bed, the stirring reactor and the static reactor under the same temperature and pressure. However, the time of rapid hydrate formation in the silica sand bed was lower than that in the stirring reactor, and both were significantly lower than the static reactor. The reason was that the gas-liquid contact area was the largest in the silica sand bed, and that in the static reactor was the smallest. (c) According to literature 29, the maximum GSC value of the reciprocating impact method and the stirring + reciprocating impact method was approximately
Journal Pre-proof equal with the time range of experiment, which was about 3.1 times than that of the stirring method. The main reason was that the stirring method took less time to reach equilibrium on the gas-liquid interface, and it took a long time and consumed too much energy to break the armor effect of hydrate formation. On the contrary, the reciprocating impact method could constantly update the gas-liquid interface, thus shortening the time to reach the maximum value of GSC. (d) During the natural gas hydrate formation process, the theoretical GSC was
f
about 180 V/V. In literature 27, the GSC value of the rotating packed bed reactor was
oo
up to 175 V/V, which was significantly higher than the other types of reactors.
pr
Therefore, this result revealed that the structure of the reactor has a great influence on the hydrate formation process.
e-
(e) Compared literature 27 and 29, the time exponential period of GSC reaching
Pr
the maximum value was the fastest when SDS was used as additive, and the exponential period was the slowest in pure water. This result indicated that the effect
al
of additives was the strongest.
rn
4. Rate of hydrate formation
The formation of hydrate consists of three processes, including dissolution,
Jo u
nucleation and growth. The formation rate of hydrate is a key parameter in evaluating the hydrate formation process. In this work, Vg (m3∙min-1∙m-3) was proposed to represent the gas consumption rate at the standard condition, which could be calculated as. Vg
C t
(10)
Where C is the gas storage capacity of hydrate mentioned in the previous section, and t (min) is the reaction time. Besides the data demonstrated in literature 19 and literature 29 in Table 2, four sets of data were added in Table 3. Hao [30] investigated the effect of additives such as SDS and ethanol on the rate of hydrate formation in a spraying reactor with the volume of 1072 cm3. Korea Advanced Institute of Science and Technology [31]
Journal Pre-proof researched the kinetic promotion effect of sII cyclopentane (CP) hydrate seeds on sI CH4 hydrate formation in sodium dodecyl sulfate (SDS) solutions, using a static reactor with the volume of 44.75 cm3. In order to overcome the foaming of SDS during the process of hydrate dissociation, Wang [32] grafted nano-Ag particles of 2~5 nm on the surface of SDS (Ag&SDS) to improve the promotion efficiency, using a stirring reactor with the volume of 80 cm3. Moreover, University of Chinese Academy of Sciences [33] investigated SDS dry solution (SDS-DS) in a static reactor
f
without stirring. These data above-mentioned literature were summarized in Table 3.
Gas
Reactor volume (cm3)
Reactor
pr
Literature
oo
Table 3. The comparison of experimental conditions on the rate of hydrate formation.
Stirring CH4
600
Silica sand
29
CH4
reciprocating
Spraying
Jo u
31
CH4
Static
(MPa) SDS
7.0
SDS
275
6.0 / SDS
1072
2.4 Ethanol
rn
CH4
al
impact 30
Pr
Static
e-
19
Pressure
Additive
3.5 4.5 44.75
SDS 5.0 6.0
32
CH4
Stirring
80
33
CH4
Static
300
Ag&SDS
6.0
SDS dry 5.0 solution
Combined with the experimental conditions listed in Table 3, the rate of hydrate formation was calculated in accordance with formula (10). In this work, the Vg -T diagram was plotted to compare the rate of hydrate formation, where T (K) is the reaction temperature.
Journal Pre-proof
Literature 19
silica sand
Literature 29
4.0
Static Literature 30
Spraying （ SDS）
Literature 31
5.8 MPa
5 MPa
4.5MPa
3.5MPa
3.5
Spraying （ Ethanol）
3.0
Average rate of gas consumption Vg , min-1
Stirring
Reciprocating impact
2.5
Literature 32
Ag&SDS
Literature 33
SDS-DS
2.0 1.5 1.0
0.0 273
274
275
276
277
278
pr
Temperture, K
oo
f
0.5
Fig. 2. The comparison of the rate of gas hydrate formation during different hydrate formation
e-
process.
Pr
Fig. 2 investigated the variation of gas consumption with temperature. In Fig.2, the points from literature 19, 30, 31, 32 and 33 were the value of average gas
al
consumption rate calculated under the optimal conditions, and the lines from literature 29 were the trend of average gas consumption rate over time. As could be seen in Fig.
rn
2, the conclusions were summarized as follows.
Jo u
(a) In literature 32, the rate of gas consumption was the highest with Ag&SDS as additive in the stirring reactor. The points in literature 31 was approximately equal to it in literature 32, which was much higher than the point in a static reactor. It was found that the volume of the both reactors was much smaller than that of others. Moreover, the volume of spraying reactor was 1072 cm3, which was the largest reactor mentioned above. And the rate of gas consumption was the least although with SDS as the additive. This indicated that not only the type of additives could affect the rate of gas consumption in the hydrate formation process, but also the volume of the reactor could affect the rate of gas consumption to a great extent. The rate of gas consumption increases with the decrease of reactor volume. (b) On the according of the rate of hydrate formation from the literature 30 and
Journal Pre-proof 31, the rate of hydrate formation was influenced by temperature and pressure. The result indicated that the increase of temperature and the decrease of pressure were not conducive to the hydrate formation. 5. Space velocity of hydrate reaction The space velocity (SV), in chemical reactor design, indicated how many reactor volumes of feed that can be treated per time unit and is defined as [34]. SV
v0 VR
(11)
oo
f
Where v0 (m3/h) is the gas volumetric flow rate, and VR (m3) is the volume of the
temperature and pressure (STP).
v0 Vm STP t
(12)
e-
SV
pr
reactor. Besides, the gas volumetric flow rate, v0, is normally measured at standard
Thus, for the process of methane hydrate formation, v0 could be define as. n Vm STP
Pr v0
t
(13)
al
Where Δn is the gas moles that has been consumed during hydrate formation, V m
rn
is the mole volume of the hydrate forming gas mixture at standard temperature and pressure (STP), and Δt is the time for the hydrate formation.
Jo u
Finally, the SV can be expressed by. SV
n Vm STP VR t
(14)
Besides the data in literature 31, five other groups of data from different literature were added. Jeju National University [17] carried out the experiments with the goal of increasing the amount of gas consumption by using an ultrasonic waves reactor with the volume of 350 cm3. Keio University [35] compared the effect of liquid large molecule guest substance (LMGC), such as methylcyclohexane (MCH) and neohexane on hydrate formation process, via a spraying device with the volume of 955 cm3. Shi [36] investigated the kinetics of tetrabutylphosphonium chloride (TBPC) + CH4 hydrate formation in a stirring reactor with the volume of 307 cm3. Lv [37] investigated the effects of the flow rates of cyclopentane (CP) on the formation
Journal Pre-proof of CP-methane hydrate using a novel bubble column reactor. Moreover, it took a long time and consumed too much energy to break the armor effect of hydrate formation. Tang [38] built a natural gas hydrate formation system based on the ejector-type loop reactor (ELR). The hydrate formation experimental conditions were summarized in Table 4. Table 4. The comparison of experimental conditions on the space velocity of hydrate reactor. Literature
Gas
Reactor volume (cm3)
Reactor
Pressure Additive
CH4
350
3~9
44.75
SDS
3.5~6
MCH
oo
/
pr
Ultrasonic 17
waves CH4
Static
35
gas-mixture
Spraying
CH4
Stirring
37
CH4
TBPC
6.0
Bubbling
4000
CP
2.0
ELR
4620
/
3.0
CH4/C2H6/C3H8 (92.01:3.01:4.97)
al
38
2.9 Neohexane
307
Pr
36
955
e-
31
f
(MPa)
rn
In this work, in order to compare SV in different formation process, the SV-∆Tsub diagram was proposed. ∆Tsub (≡Teq－Tw,in) was the water-inlet subcooling, which was
Jo u
often adopted to represent the driving force of hydrate formation. And the probability of hydrate nucleation should increase with increasing subcooling inside the hydrate region, which means that hydrate was more likely to form [39]. Where Tw, in and Teq were the temperature of water at its inlet to the reactor and the three-phase equilibrium temperature corresponding to the pressure inside the reactor. According to formula (14), the space velocity of hydrate reactor was calculated and plotted in Fig. 3.
Journal Pre-proof
16
Literature 17
Ultrasonic waves
Literature 31
5.8MPa
5MPa
4.5MPa
3.5MPa
Literature 35
2.9MPa Spraying(MCH) 2.9MPa Spraying(Neohexane)
14 12
Literature 36
6.0MPa Stirring
Literature 37
2.0MPa Bubbling
Literature 38
3.0MPa ELR
SV, h-1
10 8 6 4
0 1
2
3
4
Tsub , K
5
6
7
8
pr
0
oo
f
2
Fig. 3. The comparison of space velocity of hydrate reactor from different literature.
e-
There were many factors affecting the SV during the hydrate formation process,
Pr
such as pressure, subcooling, reaction time, reactor type and reactor volume. In Fig. 3, the points from literature 31, 35, 36 and 37 were the value of SV under the optimal
al
conditions, and the line from literature 17 and 38 were the trend of SV over
follows.
rn
subcooling. Viewing the data summarized in Fig. 3, the results were summarized as
Jo u
(a) On the according of the literature 35, 36, 37 and 38, the maximum value of SV exceeded 14 h-1 in the spraying and ELR reactors, and the maximum value of SV was less than 2 h-1 in the stirring and bubbling reactors. Water was the dispersed phase in the spraying and ELR reactors, which could increase the gas-liquid contact area and reduce the mass transfer resistance. On the contrary, gas was the dispersed phase in the stirring and bubbling reactors, meanwhile methane was insoluble in water. The result indicated that the mass transfer resistance was the side of the liquid film, and the decrease of liquid particle size was beneficial to the hydrate formation. (b) According to literature 35, the SV of spraying reactor reached 15.4 h-1 at the pressure of 4 MPa and the subcooling of 4.7 K, which far exceeded that of other reactors above mentioned. This reason was the gas consumption of methane by
Journal Pre-proof sH-hydrate formation at a given temperature and pressure was much more than that by sI-hydrate formation. (c) In accordance with the SV of hydrate reactor from the literature 17 and 38, it indicated that the increase of subcooling degree was beneficial to the SV of reactor increased. It was worth mentioning that the four parameters mentioned above were positively correlated with each other, including conversion of water to hydrate, GSC
f
of hydrate, the rate of hydrate formation and SV of hydrate reaction. When the
oo
hydrate conversion rate increasing, the number of host cages which was composed of
pr
hydrogen-bonded water molecules increased. So more gas molecules (small-sized guest molecules) were trapped in host cages, which would lead to the increase of gas
e-
consumption and further increase the GSC of hydrate. Correspondingly, the increase
Pr
of GSC was conducive to the rate of hydrate formation rate increased during the hydrate formation process, and the increase of gas consumption was beneficial to the
rn
6. Energy consumption
al
SV of hydrate reaction increased.
Energy consumption was an important parameter that must be analyzed to realize
Jo u
the industrial production of hydrate. However, the energy consumption analysis on the hydrate formation had rarely been reported until now. Hao [40] compared the energy consumption in the semi-continuous stirred reactor and the spraying reactor under the same conditions. The energy consumption for producing 1 kg hydrate was 2283.93 kJ in the semi-continuous stirred reactor. While the energy consumption for producing 1 kg hydrate was 173.77 kJ in spraying reactor. Xiao [29] found the minimum energy required for the formation of 1 kg hydrate in reciprocating impact test was about 5301.7 kJ via calculating the energy consumption of the reciprocating impact reactor. Bai [41] investigated the energy consumption of a static higee reactor system. In this system, the minimum energy consumption for each 1 kg of hydrate formation was 1438.7 kg. Nevertheless, the
Journal Pre-proof energy consumption of other common hydrate formation reactor such as bubbling and impinging stream reactors had not been reported. The energy consumption of different types of reactors was roughly summarized in Table 5. Table 5. Comparison of energy consumption of different types of reactors.
Reactor type
Stirring
Spraying
Bubbling
Impinging
reciprocating
stream
impact
/
5301.7
Static higee
Energy 2283.93
173.77
/
1437.9
f
consumption
oo
kJ/kg
pr
According to Table 5, the energy consumption for each 1 kg hydrate formation was the largest in the reciprocating impact reactor, followed by the stirring reactor,
e-
and the energy consumption was the least in the spraying reactor. The primary reason
Pr
was that the inefficient energy consumption in reciprocating impact and stirring reactor were too large. For example, energy mainly consumed to lift the impactor and
al
magnets repeatedly in the reciprocating impact reactors. And in stirring reactor, much
rn
energy was consumed to keep the motor running continuously. In addition, it would be found the relationship between energy consumption and
Jo u
the four parameters mentioned above was relatively complex. The increase of conversion of water to hydrate could promote GSC of hydrate, the rate of hydrate formation, SV of hydrate reaction, but the change rule of energy consumption could not be determined, which was related to the technology used to enhance hydrate formation. Mechanical methods such as stirring, static higee and reciprocating impact could increase the gas consumption and SV of hydrate reaction, but mechanical methods may also lead to more energy consumption. 7. Hydrate removal During the process of hydrate formation, most of the hydrates formed stuck to the reactor wall. So how to separate hydrate from water was an urgent problem to be solved. The problem of hydrate removal was less reported till now, and it should be
Journal Pre-proof received more attention. Rossi [10] proposed a novel reactor with a screw conveyor, which was designed to allow conveyance of the solid hydrates to the unloading flang in order to separate the solid products from the reactor. Kim [42] set a scraper in the bubbling reactor to removal gas hydrate particles. This reactor was characterized by the removal of hydrate particles attached to the inner wall with a scraper, and discharge from the slurry discharge outlet on the upper part of it. Meanwhile, the gas hydrate slurry with
f
high purity discharged from the outlet by dehydration, cleaning and compression.
oo
In conclusion, the hydrate removal could be efficient implemented by a screw
pr
conveyor and a scraper. The research about hydrate remove was seldom in the previous literature although it was beneficial for the industrial applications.
e-
8. Conclusions
Pr
At present, the efficient formation of natural gas hydrate is affected by heat and mass transfer process, especially the heat transfer problem after the scale-up on
al
hydrate is enlarged. Therefore, it is necessary not only to provide the cooling capacity
rn
for the natural hydrate formation process, but also to adopt mechanical methods to promote the rapid renewal of gas-liquid-solid surface and removal of hydrate
Jo u
formation heat in the reactor.
In the work, the natural gas hydrate formation process was evaluated from six parameters, including the conversion of water to hydrate, storage capacity (gas volume per unit volume of gas hydrate, V/V), the rate of hydrate formation, space velocity of hydrate formation, energy consumption and hydrate removal. The comprehensive performance of the stirring reactor and the spraying reactor were better than that of other type reactors after analyzing and comparing the six parameters. The stirring process had a distinct superiority in the conversion of water to hydrate and storage capacity, and it is the most common hydrate formation process. The spraying process had good performance on the SV of hydrate reaction and consumed less energy in the hydrate formation process.
Journal Pre-proof The additive types, the reactors structure and the reactors size had influence in the natural gas hydrate formation process. Through comparison and analysis, it was found that the effect of additive types was greatest, followed the effect of the reactors structure. The analyses of energy consumption were not fully investigated in hydrate formation process. According to known reports, the energy consumption was the least in the spraying process and the energy consumption was the largest in the
f
reciprocating impact process. The reduction of energy consumption was the one key
oo
to to realize the scale-up on hydrate, through the continuous improvement of natural
pr
hydrate formation process, the goal of low energy consumption and the scale-up on hydrate can be achieved step by step. And the removal of hydrate had received little
e-
attention, but it was important for the industrial production of NGH. In the future, the
Pr
removal of hydrate will become the focus of the application technology research. Acknowledgments
al
This work was supported by the Scientific and Technological Research Project of the Science and Technology Department of Henan Province, China [grant number
rn
152102210041]; the National Natural Science Fund of China [grant number
Jo u
NSFC-U1404519]; the China Postdoctoral Science Foundation [grant number 2016M602260]; and the Program of Biomass Resources Processing and Efficient Utilization
of
Outstanding
Foreign
Scientists’
Workroom
[grant
number
GZS2018004]. References
[1] E.D. Sloan, C.A. Koh, Clathrate Hydrates of Natural Gases, 3rd ed. New york: CRC press, Taylor & Francis Group, 2008. [2] M.R. Islam, A new recovery technique for gas production from Alaskan gas hydrates,
J.
Petrol.
Sci.
Eng.
11
(1991)
267–281
https://doi.org/10.1016/0920-4105(94)90046-9 [3] A.A. Khokhar, J.S. Gudmundsson, E.D. Sloan, Gas storage in structure H
Journal Pre-proof hydrates,
Fluid.
Phase.
Equil.
151
(1998)
383-392.
https://doi.org/10.1016/S0378-3812(98)00338-0 [4] J.S. Gudmundsson, F. Hveding, Transport of natural gas as frozen hydrate, Proceeding of 5th International Offshore Polar Engineering Conference, Hague, Netherlands, 1995, pp. 282-288. [5] D.E. Sloan, Fundamental principles and applications of natural gas hydrates, Nature. 426 (2003) 353-363. https://doi.org/10.1038/nature02135
f
[6] N. Daraboina, J. Ripmeester, V.K. Walker, Natural gas hydrate formation and
oo
decomposition in the presence of kinetic inhibitors. 1. High pressure calorimetry,
pr
Energy & Fuel. 25 (2011) 4392-4397. https://doi.org/10.1021/ef200812m [7] J.S. Gudmundsson, A. Børrehaug, Frozen hydrate for transport of natural gas,
e-
Proceeding of 2nd International Conference on Gas Hydrate,Toulouse, France,
Pr
1996.
[8] P. Linga, R. Kumar, J.D. L, A new apparatus to enhance the rate of gas hydrate
al
formation: Application to capture of carbon dioxide, Int. J. Greenh. Gas. Con. 4 (2010) 630-637. https://doi.org/10.1016/j.ijggc.2009.12.014
rn
[9] Y.H. Mori, On the scale-up of gas-hydrate-forming reactors: The case of reactors,
Jo u
gas-dispersion-type
Energies.
8
(2015)
1317-1335.
https://doi.org/10.3390/en8021317 [10] F. Rossi, M. Filipponi, B. Castellani, Investigation on a novel reactor for gas hydrate
production,
Appl.
Energ.
99
(2012)
167-172.
https://doi.org/10.1016/j.apenergy.2012.05.005 [11] Mori, Y. H, Recent advances in hydrate-based technologies for natural gas storage-a
review,
J.
Chem.
Ind.
Eng.
54
(2013)
1-17.
https://doi.org/10.3321/j.issn:0438-1157.2003.z1.001 [12] R. Ohmura, S. Kashiwazaki, S. Shiota, H. Tsuji, Y.H. Mori, Structure-I and structure-H hydrate formation using water spraying, Energy & Fuel. 16 (2002) 1141–1147. https://doi.org/10.1021/ef0200727
Journal Pre-proof [13] Y.T. Luo, J.H. Zhu, S.S. Fan, Study on the kinetics of hydrate formation in a bubble
column,
Chem.
Eng.
Sci.
62
(2007)
1000-1009.
https://doi.org/10.1016/j.ces.2006.11.004 [14] A. Kumar, G.Bhattacharjee, B.D. Kulkarni, Role of surfactants in promoting gas hydrate
formation,
Ind.
Eng.
Chem.
Res.
54
(2015).
https://doi.org/10.1021/acs.iecr.5b03476 [15] Y. Zhong, R.E. Rogers, Surfactant effects on gas hydrate formation, Chem. Eng.
f
Sci. 55 (2000) 4175-4187. https://doi.org/10.1016/S0009-2509(00)00072-5
oo
[16] T. Murakami, H. Kuritsuka, H. Fujii, Forming a structure-H hydrate using water
pr
and methylcyclohexane jets impinging on each other in a methane atmosphere, Energy & Fuels. 23 (2009) 1619-1625. https://doi.org/10.1021/ef800880f
Ind.
Eng.
Chem.
19
(2013)
1668-1672.
Pr
J.
e-
[17] S.S. Park, N.J. Kim, Study on methane hydrate formation using ultrasonic waves,
https://doi.org/10.1016/j.jiec.2013.02.004
al
[18] J. Bai, D. Liang, D. Li, Continuous formation process of CO2 gas hydrate via a vortex and impinging stream reactor, Energy & Fuels. 24 (2007) 1207-1212.
rn
https://doi.org/10.1021/ef900694z
Jo u
[19] D.L. Zhong, S.Y. He, D.J. Sun, Comparison of methane hydrate formation in stirred reactor and porous media in the presence of SDS, Energy Procedia. 61 (2014) 1573-1576. https://doi.org/10.1016/j.egypro.2014.12.174 [20] S.S. Fan, S.F. Li, J.Q. Wang, Efficient capture of CO2 from simulated flue gas by formation of TBAB or TBAF semiclathrate hydrates, Energy & Fuels. 23 (2009) 4202-4208. https://doi.org/10.1021/ef9003329 [21] N. Ando, Y. Kuwabara, Y.H. Mori, Surfactant effects on hydrate formation in an unstirred gas/liquid system: An experimental study using methane and micelle-forming surfactants, Chem. Eng. Sci. 73 (2012) 79-85. https://doi.org/10.1016/j.ces.2012.01.038 [22] P. Linga, C. Haligva, S.C. Nam, Gas hydrate formation in a variable volume bed
Journal Pre-proof of silica sand particles, Energy & Fuels. 23 (2009) 5496-5507. https://doi.org/doi:10.1021/ef900542m [23] P. Linga, N. Daraboina, J.A. Ripmeester, Enhanced rate of gas hydrate formation in a fixed bed column filled with sand compared to a stirred vessel, Chem. Eng. Sci. 68 (2012) 617-623. https://doi.org/10.1016/j.ces.2011.10.030 [24] C. Ekta, P. Nitish, M. Ajay, Enhanced formation of methane hydrate using a novel synthesized anionic surfactant for application in storage and transportation of J.
Nat.
Gas
Sci.
https://doi.org/10.1016/j.jngse.2018.06.016
Eng.
56
(2018)
246-257.
f
gas,
oo
natural
pr
[25] Y.F. Makogon, Hydrates of hydrocarbons. Tulas,Oklahoma. 1997,35-37. [26] Q.Sun, B. Chen, Y.Y. Li, Promotion effects of mung starch on methane hydrate
e-
formation equilibria/rate and gas storage capacity, Fluid Phase Equilib. 475
Pr
(2018) 95-99. https://doi.org/10.1016/j.fluid.2018.07.019 [27] Y.Z. Liu, Y.Q. Xing, L.J. Cui, Experimental study on capacity of gas hydrate in a
al
rotating packed bed. Chem. Ind. & Eng. Pro. 26 (2007) 853-856. https://doi.org/10.1016/S1872-5791(07)60010-4
rn
[28] W.F. Hao, J.Q. Wang, S.S. Fan, Study on methane hydration process in a
Jo u
semi-continuous stirred tank reactor, Energy. Convers. Manage. 48 (2007) 954-960. https://doi.org/10.1016/j.enconman.2006.08.007 [29] P. Xiao, X.M. Yang, C.Y. Sun, Enhancing methane hydrate formation in bulk water using vertical reciprocating impact, Chem. Eng. J. 336 (2018) 649–658. https://doi.org/10.1016/j.cej.2017.12.020 [30] W.F. Hao, W. Sheng, S.S. Fan, Experimental investigation of methane hydrate formation in a spraying reactor, J. Wuhan Univ. Technol. 29 (2007) 39-43. [31] S. Baek, Y.H. Ahn, J.S. Zhang, Enhanced methane hydrate formation with cyclopentane
hydrate
seeds,
Appl.
Energ.
202
(2017)
32-41
https://doi.org/10.1016/j.apenergy.2017.05.108 [32] F. Wang, Y. Song, G. Liu, Rapid methane hydrate formation promoted by
Journal Pre-proof Ag&SDS-coated nanospheres for energy storage, Appl. Energ. 213 (2018) 227-234. https://doi.org/10.1016/j.apenergy.2018.01.021 [33] S.S. Fan, L. Yang, Y.H Wang, Rapid and high capacity methane storage in clathrate hydrates using surfactant dry solution, Chem. Eng. Sci. 106 (2014) 53-59. https://doi.org/10.1016/j.ces.2013.11.032 [34] H.S. Fogler, Elements of chemical reaction engineering, 3rd ed, Prentice Hall, New York, 1999.
f
[35] H. Tsuji, T. Kobayashi, R. Ohmura, Y.H. Mori, Hydrate formation by water
oo
spraying in a methane + ethane + propane gas mixture: An attempt at promoting
pr
hydrate formation utilizing large-molecule guest substances for structure-H hydrates, Energy & Fuels. 19 (2005) 869-876. https://doi.org/10.1021/ef049785a
e-
[36] L.L. Shi, D.Q Liang, Kinetic study of CH4 hydrate formation in the presence of
Pr
tetrabutylphosphonium chloride (TBPC), J. Mol. Liq. 271 (2018) 730-737. https://doi.org/10.1016/j.molliq.2018.09.071
al
[37] Q.N. Lv, X.S. Li, C.G Xu, Experimental investigation of the formation of cyclopentane-methane hydrate in a novel and large-size bubble column reactor,
rn
Ind Eng. Chem. Res. 51 (2012) 5967-5975. https://doi.org/10.1021/ie202422c
Jo u
[38] L.G. Tang, X.S. Li, Z.P. Feng, Natural gas hydrate formation in an ejector loop reactor: preliminary study, Ind. Eng. Chem. Res. 45 (2006) 7934-7940. https://doi.org/10.1021/ie0609259 [39] W. Ke, T.M. Svartaas, D.Y. Chen, A review of gas hydrate nucleation theories and growth
models,
J.
Nat.
Gas.
Sci.
Eng.
61
(2019)
169-196.
https://doi.org/10.1016/j.jngse.2018.10.021 [40] W.F. Hao, Study on natural gas hydrate formation with different reactors, Ph. D. Thesis, Dalian Univ. Technol. 2006. [41] J. Bai, D.L. Li, D.Q. Liang, Heat analysis of carbon dioxide hydrate formation process in a static higee reactor, Gas Chem. Ind. 35 (2010) 30-34. https://doi.org/10.3969/j.issn.1001-9219.2010.04.007
Journal Pre-proof [42] J.H. Kim, J.D. Lee, J.H. Yun, Gas-liquid circulating type of hydrate reactor. US
Jo u
rn
al
Pr
e-
pr
oo
f
Patent 9302239 (2016).
Journal Pre-proof
oo
f
Graphical Abstract
The space velocity (SV) of hydrate reactor was compared for evaluating natural gas
Jo u
rn
al
Pr
e-
pr
hydrate formation process from different literature.
Journal Pre-proof
Highlights
Jo u
rn
al
Pr
e-
pr
oo
f
1. The natural gas hydrate formation process was evaluated systematically from six parameters, including conversion of water to hydrate, storage capacity, the rate of hydrate formation, space velocity (SV) of hydrate reaction, energy consumption and hydrate removal. 2. By comparing the conversion of water to hydrate, it could be realized that the surfactant had a greater effect than the reactors to the conversion. 3. Considering the space velocity (SV) of hydrate formation, the value of SV in the spraying and ejector-type loop (ELR) reactors were much larger than the SV in the stirring and bubbling reactor. 4. Comparing the energy consumption of different reactors, the energy consumption per 1 kg hydrate formation was the largest in the reciprocating impact reactor, followed by the stirring reactor, and the energy consumption was the least in the spraying reactor.
Shuqi Fang, Xinyue Zhang, Jingyi Zhang, Chun Chang, Pan Li, Jing Bai PII:
S1004-9541(20)30002-1
DOI:
https://doi.org/10.1016/j.cjche.2019.12.021
Reference:
CJCHE 1615
To appear in:
Chinese Journal of Chemical Engineering
Received date:
26 May 2019
Revised date:
5 December 2019
Accepted date:
8 December 2019
Please cite this article as: S. Fang, X. Zhang, J. Zhang, et al., Evaluation on the natural gas hydrate formation process, Chinese Journal of Chemical Engineering(2020), https://doi.org/10.1016/j.cjche.2019.12.021
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
© 2020 Published by Elsevier.
Journal Pre-proof
Evaluation on the natural gas hydrate formation process Shuqi Fang1,2,3, Xinyue Zhang1,3, Jingyi Zhang1, Chun Chang1,2,3, Pan Li1,2,3, Jing Bai1,2,3,* 1
School of Chemical Engineering and Energy, Zhengzhou University, Zhengzhou 450001,
China Henan Outstanding Foreign Scientists’ Workroom, Zhengzhou 450001, China
3
Engineering Laboratory of Henan Province for Biorefinery Technology and
oo
f
2
pr
Equipment, Zhengzhou 450001, China
*
e-
Corresponding author.
E-mail addresses: [email protected] (J. Bai)
Jo u
rn
al
Pr
Tel: +86-371-67780093 Fax: +86-371-67780093
Journal Pre-proof ABSTRACT Gas hydrates have endowed with great potential in gas storage and rapid formation of gas hydrates is critical to use this novel technology. This work evaluated the natural gas hydrate formation process, which was compared from six parameters, including conversion of water to hydrate, storage capacity, the rate of hydrate formation, space velocity (SV) of hydrate reaction, energy consumption and hydrate removal. The literature was selected by analyzing and comparing these six parameters mentioned
f
above, meanwhile placing emphasis on the three parameters of storage capacity, the
oo
rate of hydrate formation and space velocity of hydrate reaction. Through analysis and comparison, four conclusions could be obtained as follow. Firstly, the overall
pr
performance of the stirring process and the spraying process were better than other
e-
processes after analyzing the six parameters. Secondly, the additive types, the reactor
Pr
structure and the reactor size had influence on the natural gas hydrate formation process. Thirdly, the energy consumption via reciprocating impact in the hydrate formation process was higher than that via stirring, spraying and static higee. Finally,
al
it was one key for hydrate removal to realize the hydrate industrial production.
rn
Keywords: Natural gas hydrate; Evaluate; Hydrate formation process; Storage
Jo u
capacity; Space velocity of hydrate reaction
Journal Pre-proof
1. Introduction Natural gas hydrate (NGH), mainly composed of methane, is an ice-like crystalline compounds formed by water and natural gas at high pressure and low temperature [1]. Natural gas hydrate has the characteristics of high gas storage capacity and mild storage condition, as unit volume of natural gas hydrate can contain 160~180 m3 (at standard condition) [2,3]. In 1990, Gudmundsson [4] firstly proposed the NGH can be preserved at atmospheric pressure and the temperature lower than
oo
f
258.15 K. Because of the favorable gas storage capacity and pressure-temperature conditions, the storage and transportation in the form of hydrates has huge advantages
pr
over almost other common technologies such as compressed natural gas (CNG), liquefied natural gas (LNG) and pipeline natural gas (PNG), especially in the oceans,
e-
deserts and medium-sized gas fields where scarce energy and fresh water [5]. NGH
Pr
provides a new option for gas storage and transportation, many fundamental researches and technologies of NGH have been investigated extensively in recent
al
years.
rn
Rapid hydrate formation technology is one of the key in the industrialization of NGH. Reactor is the core device of the rapid hydrate formation system, which affects
Jo u
the hydrate formation process to a certain extent. The reactor for natural gas hydrate formation not only provides the temperature and pressure environment needed for gas and water formation, but also provides a disturbance environment to intensify the mass and heat transfer process in gas-liquid-solid phase [6]. Conventional reactors mainly include stirring reactor, spraying reactor and bubbling reactor. Stirring is one of the most common reactors, and Gudmundsson et al. [7] developed a stirring reactor where gas diffuses to the liquid phase rapidly by an impeller. Then, Linga et al. [8] used mechanical agitation to capture CO2 from fuel gases by employing gas hydrate technology. Their experimental result showed that the new apparatus improved CO 2 recovery compared to the previously used laboratory apparatus, which proved stirring can enhanced the rate of gas hydrate formation. Nevertheless, the shortcomings of the
Journal Pre-proof stirring reactors should not be neglected. For example, in order to prevent high pressure gas leakage in the reactor, the stirring shaft needs to have a high dynamic sealing technology. Besides, the power consumption of stirring is usually the fifth power of impeller size which indicates that the mixing reactor is not easy to enlarge in the industry and the stirring time is not easy to be too long [9]. Spraying is a type of reactor for gas-liquid, which can overcome the fact that stirring reactors cannot be used for industrial amplification. Rossi et al [10] had used a 25 L reactor (with 6
f
nozzles) which equipped with atomized spray to perform methane hydrate formation.
oo
The result showed this device could obtain methane hydrates without water left, in
pr
some 10 min only with sodium dodecyl sulfate (SDS) surfactant promotion. Mori [11] proposed and designed a continuous production mode of natural gas hydrate, which is
e-
characterized by spraying in the production of natural gas hydrate [12]. Bubble
Pr
column reactor is another reactor type suitable for gas-liquid reaction system, and it feeds gas into the reactor equipped with water or solution. Luo et al. [13] found the
al
increase of methane flux resulted in the increase of the hydrate formation rate, because higher methane flux produced more bubbles and larger total gas-liquid
rn
interface in a bubbling system. However, it is not encouraging to use bubbling reactor
Jo u
in terms of hydrate formation rate and it can increase the cost of the system [14, 15]. Apart from the conventional hydrate reactors described above, researchers were constantly exploring a number of new reactor devices and applying them in the field of rapid gas hydrate formation. Tetsuya et al. [16] reported a novel device for the continuous, high-rate formation, which was characterized by utilizing twin liquid jets impinging on each other. Park et al. [17] discovered that ultrasonic waves had an obvious promoting effect on methane hydrate formation, the ultrasonic power of 150 W was four times higher than that at 0 W when the subcooling temperature of 0.5 K. Bai et al. [18] proposed a vortex and impinging stream reactor (VIR) to enhance the CO2 gas hydrate formation by generating a high-gravity field. As mentioned above, various types of reactors had been proposed to investigate their effects on hydrate
Journal Pre-proof formation on the laboratory scale. However, the evaluation of gas hydrate formation process is still in its infancy, only a few literature had tried to assessment it. Mori [11] reviewed natural gas storage and divided it into four series of technologies, placing emphasis on the hydrate formation process, and compared and evaluated the rate of hydrate formation. Zhong et al. [19] compared the methane hydrate formation in stirred reactor and silica sand, in which the normalized gas uptake, water conversion to hydrate and storage capacity were mainly considered. Fan et al. [20] indicated that
f
TBAB could accelerate hydrate formation via analyzing hydrate formation rate
oo
constant and space velocity. Considering that the sizes and types of reactors are
pr
different, the thermodynamic conditions required for hydrate formation are not consistent. So far there is still no appropriate and unified standard to evaluate the
e-
performance of various hydrate formation process fairly.
Pr
In this work, relevant data of hydrate formation process in recent years had been compared and evaluated, mainly from six aspects: conversion of water to hydrate,
al
storage capacity (gas volume per unit volume of gas hydrate, V/V), the rate of hydrate formation, space velocity of hydrate reaction, energy consumption required and
rn
hydrate removal. This work placed emphasis on storage capacity, the rate of hydrate
Jo u
formation and space vel9ocity of hydrate reaction. 2. Conversion of water to hydrate Conversion of water to hydrate refers to the percentage of water converted into hydrate, which is expressed as the ratio of the total water mass in the reaction to the water supplied. The calculation formulas are as follows. Conversion %
n gas Hydrate number n H2O
100
(1)
Where nH2 O (mol) is the total number of moles of water in the system. Hydrate number is the number of water molecules needed per methane molecule to form hydrate and ∆ngas (mol) is the number of moles of gas consumed for hydrate
Journal Pre-proof
formation at the end of the experiment, which is determined from the gas uptake measurement, as follows. n gas n gas,t -n
gas,0
P0Vg Z 0 RT0
PV t g
(2)
Z t RTt
Where P0 (MPa) and T0 (K) are the pressure at the initial time respectively, Pt (MPa) and Tt (K) are the pressure at time T=t. Vg is the volume of gas phase of the crystallizer, m3. R is the general gas constant, taking 8.314 J∙mol-1∙K-1 ; Z is the
h
bP RT
e-
B
B Z
oo
1 A h - 1-h B 1 h
pr
Z
f
compression factor of real gas, which can be calculated by the following formula.
Pr
A a B bRT 1.5
a 0.4278
(4) (5) (6)
R 2Tc 2.5 Pc
(7)
RTc Pc
(8)
b 0.0867
al
(3)
rn
Conversion of water to hydrate is an important parameter in the process of
Jo u
hydrate formation, where higher conversion of hydrate to water is desirable. This work compared the data about conversion of water to hydrate in the hydrate formation process from different literature. Zhong [19] compared the effects of the stirred reactor and porous medium on the conversion of water to hydrate, using a reactor with the volume of 600 cm3. Naoki at the Keio University [21] proposed a static reactor with the volume of 942 cm3, and in this experiment investigated the effects of surfactants such as lithium dodecyl sulfate (LDS) and dodecylbenzene sulfonic acid (DBSA) on the conversion of water to hydrate. Linga [22] built a volume bed of silica sand reactor, which placed two copper cylinders in order to investigate the effect of the variable reactor volume on the hydrate formation process. Two years later, Linga [23] aslo investigated the role of the fixed bed column and a stirred vessel on the
Journal Pre-proof conversion of water to hydrate, and the volume of the reactor was 1236 cm3. Besides, Ekta [24] developed a static reactor with the volume of 250 cm3. Table 1 is the conversion of water to hydrate in the above-mentioned literature. Table 1. The comparison of experimental conditions and the conversion of water to hydrate. Additive
Conversion
Reactor Literature
Gas
Reactor
Pressure
volume (cm3)
Additive
concentration
T (K)
of water to (MPa)
(ppm)
hydrate (%)
Stirring 19
76.6
CH4
600
SDS
500
7 78.1
oo
f
Silica sand
274.15
2000
LDS CH4
924
e-
(Unstirring)
CH4
Fixed bed
695
3.9
/
78.2
420
83.6
580
275
4
950
1236
CH4
Jo u
Fixed bed
24
rn
Stirring CH4
Static
86.1 81.2 76.7
/
277.15
8
309
23
80.6
5000
al
22
Pr
DBSA
1236
275
pr
Static, 21
3500
81.8
79.7 84.0 74
/
/
277.15
8 94.7
0
8.36
Castor 250
5000
293.15
13.79
13.80
oil 9000
Table 1 showed the conversion of water to hydrate in different literature. The results could be revealed as follows. (a) On the basis of the conversion of water to hydrate from the literature 19 and 21, it could be found that the conversion rate with LDS and DBSA in static reactor was greater than that with SDS in stirring reactor. And it could be proved that the surfactant had a greater effect than the reactors to the conversion of water to hydrate. The reason was that the surfactant could reduce the gas-liquid surface tension, and decrease the resistance of gas entering the liquid phase, which could achieve more gas
15.91
Journal Pre-proof dissolve in liquid phase and enhance the mass transfer process. (b) According to the conversion of water to hydrate from the literature 23, the conversion of water to hydrate in fixed bed was slightly higher than that in the stirring reactor. Because the padding of the fixed bed was porous medium, which could obviously increase the gas-liquid contact area and provide a large amount of space for the growth of hydrate. Stirring only speeded up the mixing of gas and liquid, but the gas-liquid contact area did not increase greatly.
f
(c) According to the conversion of water to hydrate from the literature 22, the
oo
conversion of water to hydrate decreased slightly with the increase of reactor size.
pr
3. Gas storage capacity of hydrate
Gas storage capacity (GSC) has three kinds of expression way. Including volume
e-
storage capacity, mass storage capacity and molar storage capacity. Gas storage
Pr
capacity was usually defined as gas volumes decomposed from per unit volume of hydrate at standard conditions, m3∙m-3. The calculation formula is as follows. VG VG VNGH VL (1 V )
(9)
al
C
rn
Where C is the gas storage capacity of hydrate, VG (m3) is the volume of gas
Jo u
consumed under the standard condition in the reactor, VNGH (m3) is the volume of hydrate when the reaction ends, VL (m3) is the volume of water consumed, and ∆V is the molar volume change of water turned into hydrate. Makogon [25] demonstrated that the value of ∆V for structure-I hydrate is 4.6 cm3∙mol-1, and, the value of ∆V for structure-II hydrate is 5.3 cm3∙mol-1. Besides the data demonstrated in literature 19 and literature 24 mentioned in Table 1, four sets of data were added in Table 2. China University of petroleum [26] proposed a static reactor with the volume of 220 cm3, which charged with a biosurfactant instead of pure water. North University of China [27] installed a rotating packed bed reactor with the volume of 1413 cm3 to investigate the GSC. Dalian university of technology [28] investigated the effect of stirring rate and stirring time on GSC, using a semi-continuous stirred tank with the volume of 1072 cm3. Besides,
Journal Pre-proof Xiao [29] investigated the function of the three types of mechanical strategies on GSC via a reactor with the volume of 245 cm3, which were rotational stirring only, rotational stirring for a duration of time, followed by reciprocating impact and reciprocating impact only. These data above-mentioned literature were summarized in Table 2. Table 2. The comparison of experimental conditions and the GSC of hydrate. Reactor Literature
Gas
Reactor
Pressure 3
Additive
T (K) (MPa)
Stirring CH4
600
SDS
274.15
7.0
293.15
13.79
277.15
8.0
SDS
277.15
5.0
1072
SDS
274.4
5.0
275
/
273.3
6.0
oo
19
f
volume (cm )
Silica sand CH4
Static
250
pr
Castor 24
CH4
Static
Natural
Rotating
gas
packed bed
220
Mung starch
1413
al
27
/
Pr
26
e-
oil
Stirring CH4
Static
rn
28
Jo u
(Unstirring) Stirring
Reciprocating impact
29
CH4
Stirring+ Reciprocating impact
According to the formula (9) and the data summarized in Table 2, the GSC was calculated and illustrated in Fig. 1.
Journal Pre-proof Literature 19
Silica sand
Literature 24
T = 293.15K, Castor oil
Stirring
Literature 26
T = 277.15K, Pure water T = 277.15K, Mung strach
Literature 27
200
Rotating packed bed
Literature 28
Unstirring
Literature 29
Stirring, 320ppm
Stirring
Impact Stirring + Impact
GSC, V/V
160
120
80
f
40
0
5
10
15
Time, h
oo
0 20
25
pr
Fig. 1. The comparison of GSC of natural gas hydrate formation process from different literature.
Fig.1 investigated the changes of GSC over time. In Fig. 1, the points from
e-
literature 19, 24, 26 and 27 were the value of GSC calculated under the optimal
Pr
conditions, and in rotating packed bed, the maximum value of GSC was obtained. The line from literature 28 and 29 were the trend of GSC in different time periods.
al
According to Fig.1, the following results could be revealed.
rn
(a) According to literature 19, 24 and 26, compared with pure water, the value of GSC with the three additives such as SDS, castor oil and mung bean had a significant
Jo u
increase, which could be inferred that the additives could increase the gas storage capacity of hydrate. It indicated that the solubility of methane was enhanced and the phase equilibrium condition was decreased under the action of additives. (b) In accordance with literature 19 and 28, the GSC was about the same in the silica sand bed, the stirring reactor and the static reactor under the same temperature and pressure. However, the time of rapid hydrate formation in the silica sand bed was lower than that in the stirring reactor, and both were significantly lower than the static reactor. The reason was that the gas-liquid contact area was the largest in the silica sand bed, and that in the static reactor was the smallest. (c) According to literature 29, the maximum GSC value of the reciprocating impact method and the stirring + reciprocating impact method was approximately
Journal Pre-proof equal with the time range of experiment, which was about 3.1 times than that of the stirring method. The main reason was that the stirring method took less time to reach equilibrium on the gas-liquid interface, and it took a long time and consumed too much energy to break the armor effect of hydrate formation. On the contrary, the reciprocating impact method could constantly update the gas-liquid interface, thus shortening the time to reach the maximum value of GSC. (d) During the natural gas hydrate formation process, the theoretical GSC was
f
about 180 V/V. In literature 27, the GSC value of the rotating packed bed reactor was
oo
up to 175 V/V, which was significantly higher than the other types of reactors.
pr
Therefore, this result revealed that the structure of the reactor has a great influence on the hydrate formation process.
e-
(e) Compared literature 27 and 29, the time exponential period of GSC reaching
Pr
the maximum value was the fastest when SDS was used as additive, and the exponential period was the slowest in pure water. This result indicated that the effect
al
of additives was the strongest.
rn
4. Rate of hydrate formation
The formation of hydrate consists of three processes, including dissolution,
Jo u
nucleation and growth. The formation rate of hydrate is a key parameter in evaluating the hydrate formation process. In this work, Vg (m3∙min-1∙m-3) was proposed to represent the gas consumption rate at the standard condition, which could be calculated as. Vg
C t
(10)
Where C is the gas storage capacity of hydrate mentioned in the previous section, and t (min) is the reaction time. Besides the data demonstrated in literature 19 and literature 29 in Table 2, four sets of data were added in Table 3. Hao [30] investigated the effect of additives such as SDS and ethanol on the rate of hydrate formation in a spraying reactor with the volume of 1072 cm3. Korea Advanced Institute of Science and Technology [31]
Journal Pre-proof researched the kinetic promotion effect of sII cyclopentane (CP) hydrate seeds on sI CH4 hydrate formation in sodium dodecyl sulfate (SDS) solutions, using a static reactor with the volume of 44.75 cm3. In order to overcome the foaming of SDS during the process of hydrate dissociation, Wang [32] grafted nano-Ag particles of 2~5 nm on the surface of SDS (Ag&SDS) to improve the promotion efficiency, using a stirring reactor with the volume of 80 cm3. Moreover, University of Chinese Academy of Sciences [33] investigated SDS dry solution (SDS-DS) in a static reactor
f
without stirring. These data above-mentioned literature were summarized in Table 3.
Gas
Reactor volume (cm3)
Reactor
pr
Literature
oo
Table 3. The comparison of experimental conditions on the rate of hydrate formation.
Stirring CH4
600
Silica sand
29
CH4
reciprocating
Spraying
Jo u
31
CH4
Static
(MPa) SDS
7.0
SDS
275
6.0 / SDS
1072
2.4 Ethanol
rn
CH4
al
impact 30
Pr
Static
e-
19
Pressure
Additive
3.5 4.5 44.75
SDS 5.0 6.0
32
CH4
Stirring
80
33
CH4
Static
300
Ag&SDS
6.0
SDS dry 5.0 solution
Combined with the experimental conditions listed in Table 3, the rate of hydrate formation was calculated in accordance with formula (10). In this work, the Vg -T diagram was plotted to compare the rate of hydrate formation, where T (K) is the reaction temperature.
Journal Pre-proof
Literature 19
silica sand
Literature 29
4.0
Static Literature 30
Spraying （ SDS）
Literature 31
5.8 MPa
5 MPa
4.5MPa
3.5MPa
3.5
Spraying （ Ethanol）
3.0
Average rate of gas consumption Vg , min-1
Stirring
Reciprocating impact
2.5
Literature 32
Ag&SDS
Literature 33
SDS-DS
2.0 1.5 1.0
0.0 273
274
275
276
277
278
pr
Temperture, K
oo
f
0.5
Fig. 2. The comparison of the rate of gas hydrate formation during different hydrate formation
e-
process.
Pr
Fig. 2 investigated the variation of gas consumption with temperature. In Fig.2, the points from literature 19, 30, 31, 32 and 33 were the value of average gas
al
consumption rate calculated under the optimal conditions, and the lines from literature 29 were the trend of average gas consumption rate over time. As could be seen in Fig.
rn
2, the conclusions were summarized as follows.
Jo u
(a) In literature 32, the rate of gas consumption was the highest with Ag&SDS as additive in the stirring reactor. The points in literature 31 was approximately equal to it in literature 32, which was much higher than the point in a static reactor. It was found that the volume of the both reactors was much smaller than that of others. Moreover, the volume of spraying reactor was 1072 cm3, which was the largest reactor mentioned above. And the rate of gas consumption was the least although with SDS as the additive. This indicated that not only the type of additives could affect the rate of gas consumption in the hydrate formation process, but also the volume of the reactor could affect the rate of gas consumption to a great extent. The rate of gas consumption increases with the decrease of reactor volume. (b) On the according of the rate of hydrate formation from the literature 30 and
Journal Pre-proof 31, the rate of hydrate formation was influenced by temperature and pressure. The result indicated that the increase of temperature and the decrease of pressure were not conducive to the hydrate formation. 5. Space velocity of hydrate reaction The space velocity (SV), in chemical reactor design, indicated how many reactor volumes of feed that can be treated per time unit and is defined as [34]. SV
v0 VR
(11)
oo
f
Where v0 (m3/h) is the gas volumetric flow rate, and VR (m3) is the volume of the
temperature and pressure (STP).
v0 Vm STP t
(12)
e-
SV
pr
reactor. Besides, the gas volumetric flow rate, v0, is normally measured at standard
Thus, for the process of methane hydrate formation, v0 could be define as. n Vm STP
Pr v0
t
(13)
al
Where Δn is the gas moles that has been consumed during hydrate formation, V m
rn
is the mole volume of the hydrate forming gas mixture at standard temperature and pressure (STP), and Δt is the time for the hydrate formation.
Jo u
Finally, the SV can be expressed by. SV
n Vm STP VR t
(14)
Besides the data in literature 31, five other groups of data from different literature were added. Jeju National University [17] carried out the experiments with the goal of increasing the amount of gas consumption by using an ultrasonic waves reactor with the volume of 350 cm3. Keio University [35] compared the effect of liquid large molecule guest substance (LMGC), such as methylcyclohexane (MCH) and neohexane on hydrate formation process, via a spraying device with the volume of 955 cm3. Shi [36] investigated the kinetics of tetrabutylphosphonium chloride (TBPC) + CH4 hydrate formation in a stirring reactor with the volume of 307 cm3. Lv [37] investigated the effects of the flow rates of cyclopentane (CP) on the formation
Journal Pre-proof of CP-methane hydrate using a novel bubble column reactor. Moreover, it took a long time and consumed too much energy to break the armor effect of hydrate formation. Tang [38] built a natural gas hydrate formation system based on the ejector-type loop reactor (ELR). The hydrate formation experimental conditions were summarized in Table 4. Table 4. The comparison of experimental conditions on the space velocity of hydrate reactor. Literature
Gas
Reactor volume (cm3)
Reactor
Pressure Additive
CH4
350
3~9
44.75
SDS
3.5~6
MCH
oo
/
pr
Ultrasonic 17
waves CH4
Static
35
gas-mixture
Spraying
CH4
Stirring
37
CH4
TBPC
6.0
Bubbling
4000
CP
2.0
ELR
4620
/
3.0
CH4/C2H6/C3H8 (92.01:3.01:4.97)
al
38
2.9 Neohexane
307
Pr
36
955
e-
31
f
(MPa)
rn
In this work, in order to compare SV in different formation process, the SV-∆Tsub diagram was proposed. ∆Tsub (≡Teq－Tw,in) was the water-inlet subcooling, which was
Jo u
often adopted to represent the driving force of hydrate formation. And the probability of hydrate nucleation should increase with increasing subcooling inside the hydrate region, which means that hydrate was more likely to form [39]. Where Tw, in and Teq were the temperature of water at its inlet to the reactor and the three-phase equilibrium temperature corresponding to the pressure inside the reactor. According to formula (14), the space velocity of hydrate reactor was calculated and plotted in Fig. 3.
Journal Pre-proof
16
Literature 17
Ultrasonic waves
Literature 31
5.8MPa
5MPa
4.5MPa
3.5MPa
Literature 35
2.9MPa Spraying(MCH) 2.9MPa Spraying(Neohexane)
14 12
Literature 36
6.0MPa Stirring
Literature 37
2.0MPa Bubbling
Literature 38
3.0MPa ELR
SV, h-1
10 8 6 4
0 1
2
3
4
Tsub , K
5
6
7
8
pr
0
oo
f
2
Fig. 3. The comparison of space velocity of hydrate reactor from different literature.
e-
There were many factors affecting the SV during the hydrate formation process,
Pr
such as pressure, subcooling, reaction time, reactor type and reactor volume. In Fig. 3, the points from literature 31, 35, 36 and 37 were the value of SV under the optimal
al
conditions, and the line from literature 17 and 38 were the trend of SV over
follows.
rn
subcooling. Viewing the data summarized in Fig. 3, the results were summarized as
Jo u
(a) On the according of the literature 35, 36, 37 and 38, the maximum value of SV exceeded 14 h-1 in the spraying and ELR reactors, and the maximum value of SV was less than 2 h-1 in the stirring and bubbling reactors. Water was the dispersed phase in the spraying and ELR reactors, which could increase the gas-liquid contact area and reduce the mass transfer resistance. On the contrary, gas was the dispersed phase in the stirring and bubbling reactors, meanwhile methane was insoluble in water. The result indicated that the mass transfer resistance was the side of the liquid film, and the decrease of liquid particle size was beneficial to the hydrate formation. (b) According to literature 35, the SV of spraying reactor reached 15.4 h-1 at the pressure of 4 MPa and the subcooling of 4.7 K, which far exceeded that of other reactors above mentioned. This reason was the gas consumption of methane by
Journal Pre-proof sH-hydrate formation at a given temperature and pressure was much more than that by sI-hydrate formation. (c) In accordance with the SV of hydrate reactor from the literature 17 and 38, it indicated that the increase of subcooling degree was beneficial to the SV of reactor increased. It was worth mentioning that the four parameters mentioned above were positively correlated with each other, including conversion of water to hydrate, GSC
f
of hydrate, the rate of hydrate formation and SV of hydrate reaction. When the
oo
hydrate conversion rate increasing, the number of host cages which was composed of
pr
hydrogen-bonded water molecules increased. So more gas molecules (small-sized guest molecules) were trapped in host cages, which would lead to the increase of gas
e-
consumption and further increase the GSC of hydrate. Correspondingly, the increase
Pr
of GSC was conducive to the rate of hydrate formation rate increased during the hydrate formation process, and the increase of gas consumption was beneficial to the
rn
6. Energy consumption
al
SV of hydrate reaction increased.
Energy consumption was an important parameter that must be analyzed to realize
Jo u
the industrial production of hydrate. However, the energy consumption analysis on the hydrate formation had rarely been reported until now. Hao [40] compared the energy consumption in the semi-continuous stirred reactor and the spraying reactor under the same conditions. The energy consumption for producing 1 kg hydrate was 2283.93 kJ in the semi-continuous stirred reactor. While the energy consumption for producing 1 kg hydrate was 173.77 kJ in spraying reactor. Xiao [29] found the minimum energy required for the formation of 1 kg hydrate in reciprocating impact test was about 5301.7 kJ via calculating the energy consumption of the reciprocating impact reactor. Bai [41] investigated the energy consumption of a static higee reactor system. In this system, the minimum energy consumption for each 1 kg of hydrate formation was 1438.7 kg. Nevertheless, the
Journal Pre-proof energy consumption of other common hydrate formation reactor such as bubbling and impinging stream reactors had not been reported. The energy consumption of different types of reactors was roughly summarized in Table 5. Table 5. Comparison of energy consumption of different types of reactors.
Reactor type
Stirring
Spraying
Bubbling
Impinging
reciprocating
stream
impact
/
5301.7
Static higee
Energy 2283.93
173.77
/
1437.9
f
consumption
oo
kJ/kg
pr
According to Table 5, the energy consumption for each 1 kg hydrate formation was the largest in the reciprocating impact reactor, followed by the stirring reactor,
e-
and the energy consumption was the least in the spraying reactor. The primary reason
Pr
was that the inefficient energy consumption in reciprocating impact and stirring reactor were too large. For example, energy mainly consumed to lift the impactor and
al
magnets repeatedly in the reciprocating impact reactors. And in stirring reactor, much
rn
energy was consumed to keep the motor running continuously. In addition, it would be found the relationship between energy consumption and
Jo u
the four parameters mentioned above was relatively complex. The increase of conversion of water to hydrate could promote GSC of hydrate, the rate of hydrate formation, SV of hydrate reaction, but the change rule of energy consumption could not be determined, which was related to the technology used to enhance hydrate formation. Mechanical methods such as stirring, static higee and reciprocating impact could increase the gas consumption and SV of hydrate reaction, but mechanical methods may also lead to more energy consumption. 7. Hydrate removal During the process of hydrate formation, most of the hydrates formed stuck to the reactor wall. So how to separate hydrate from water was an urgent problem to be solved. The problem of hydrate removal was less reported till now, and it should be
Journal Pre-proof received more attention. Rossi [10] proposed a novel reactor with a screw conveyor, which was designed to allow conveyance of the solid hydrates to the unloading flang in order to separate the solid products from the reactor. Kim [42] set a scraper in the bubbling reactor to removal gas hydrate particles. This reactor was characterized by the removal of hydrate particles attached to the inner wall with a scraper, and discharge from the slurry discharge outlet on the upper part of it. Meanwhile, the gas hydrate slurry with
f
high purity discharged from the outlet by dehydration, cleaning and compression.
oo
In conclusion, the hydrate removal could be efficient implemented by a screw
pr
conveyor and a scraper. The research about hydrate remove was seldom in the previous literature although it was beneficial for the industrial applications.
e-
8. Conclusions
Pr
At present, the efficient formation of natural gas hydrate is affected by heat and mass transfer process, especially the heat transfer problem after the scale-up on
al
hydrate is enlarged. Therefore, it is necessary not only to provide the cooling capacity
rn
for the natural hydrate formation process, but also to adopt mechanical methods to promote the rapid renewal of gas-liquid-solid surface and removal of hydrate
Jo u
formation heat in the reactor.
In the work, the natural gas hydrate formation process was evaluated from six parameters, including the conversion of water to hydrate, storage capacity (gas volume per unit volume of gas hydrate, V/V), the rate of hydrate formation, space velocity of hydrate formation, energy consumption and hydrate removal. The comprehensive performance of the stirring reactor and the spraying reactor were better than that of other type reactors after analyzing and comparing the six parameters. The stirring process had a distinct superiority in the conversion of water to hydrate and storage capacity, and it is the most common hydrate formation process. The spraying process had good performance on the SV of hydrate reaction and consumed less energy in the hydrate formation process.
Journal Pre-proof The additive types, the reactors structure and the reactors size had influence in the natural gas hydrate formation process. Through comparison and analysis, it was found that the effect of additive types was greatest, followed the effect of the reactors structure. The analyses of energy consumption were not fully investigated in hydrate formation process. According to known reports, the energy consumption was the least in the spraying process and the energy consumption was the largest in the
f
reciprocating impact process. The reduction of energy consumption was the one key
oo
to to realize the scale-up on hydrate, through the continuous improvement of natural
pr
hydrate formation process, the goal of low energy consumption and the scale-up on hydrate can be achieved step by step. And the removal of hydrate had received little
e-
attention, but it was important for the industrial production of NGH. In the future, the
Pr
removal of hydrate will become the focus of the application technology research. Acknowledgments
al
This work was supported by the Scientific and Technological Research Project of the Science and Technology Department of Henan Province, China [grant number
rn
152102210041]; the National Natural Science Fund of China [grant number
Jo u
NSFC-U1404519]; the China Postdoctoral Science Foundation [grant number 2016M602260]; and the Program of Biomass Resources Processing and Efficient Utilization
of
Outstanding
Foreign
Scientists’
Workroom
[grant
number
GZS2018004]. References
[1] E.D. Sloan, C.A. Koh, Clathrate Hydrates of Natural Gases, 3rd ed. New york: CRC press, Taylor & Francis Group, 2008. [2] M.R. Islam, A new recovery technique for gas production from Alaskan gas hydrates,
J.
Petrol.
Sci.
Eng.
11
(1991)
267–281
https://doi.org/10.1016/0920-4105(94)90046-9 [3] A.A. Khokhar, J.S. Gudmundsson, E.D. Sloan, Gas storage in structure H
Journal Pre-proof hydrates,
Fluid.
Phase.
Equil.
151
(1998)
383-392.
https://doi.org/10.1016/S0378-3812(98)00338-0 [4] J.S. Gudmundsson, F. Hveding, Transport of natural gas as frozen hydrate, Proceeding of 5th International Offshore Polar Engineering Conference, Hague, Netherlands, 1995, pp. 282-288. [5] D.E. Sloan, Fundamental principles and applications of natural gas hydrates, Nature. 426 (2003) 353-363. https://doi.org/10.1038/nature02135
f
[6] N. Daraboina, J. Ripmeester, V.K. Walker, Natural gas hydrate formation and
oo
decomposition in the presence of kinetic inhibitors. 1. High pressure calorimetry,
pr
Energy & Fuel. 25 (2011) 4392-4397. https://doi.org/10.1021/ef200812m [7] J.S. Gudmundsson, A. Børrehaug, Frozen hydrate for transport of natural gas,
e-
Proceeding of 2nd International Conference on Gas Hydrate,Toulouse, France,
Pr
1996.
[8] P. Linga, R. Kumar, J.D. L, A new apparatus to enhance the rate of gas hydrate
al
formation: Application to capture of carbon dioxide, Int. J. Greenh. Gas. Con. 4 (2010) 630-637. https://doi.org/10.1016/j.ijggc.2009.12.014
rn
[9] Y.H. Mori, On the scale-up of gas-hydrate-forming reactors: The case of reactors,
Jo u
gas-dispersion-type
Energies.
8
(2015)
1317-1335.
https://doi.org/10.3390/en8021317 [10] F. Rossi, M. Filipponi, B. Castellani, Investigation on a novel reactor for gas hydrate
production,
Appl.
Energ.
99
(2012)
167-172.
https://doi.org/10.1016/j.apenergy.2012.05.005 [11] Mori, Y. H, Recent advances in hydrate-based technologies for natural gas storage-a
review,
J.
Chem.
Ind.
Eng.
54
(2013)
1-17.
https://doi.org/10.3321/j.issn:0438-1157.2003.z1.001 [12] R. Ohmura, S. Kashiwazaki, S. Shiota, H. Tsuji, Y.H. Mori, Structure-I and structure-H hydrate formation using water spraying, Energy & Fuel. 16 (2002) 1141–1147. https://doi.org/10.1021/ef0200727
Journal Pre-proof [13] Y.T. Luo, J.H. Zhu, S.S. Fan, Study on the kinetics of hydrate formation in a bubble
column,
Chem.
Eng.
Sci.
62
(2007)
1000-1009.
https://doi.org/10.1016/j.ces.2006.11.004 [14] A. Kumar, G.Bhattacharjee, B.D. Kulkarni, Role of surfactants in promoting gas hydrate
formation,
Ind.
Eng.
Chem.
Res.
54
(2015).
https://doi.org/10.1021/acs.iecr.5b03476 [15] Y. Zhong, R.E. Rogers, Surfactant effects on gas hydrate formation, Chem. Eng.
f
Sci. 55 (2000) 4175-4187. https://doi.org/10.1016/S0009-2509(00)00072-5
oo
[16] T. Murakami, H. Kuritsuka, H. Fujii, Forming a structure-H hydrate using water
pr
and methylcyclohexane jets impinging on each other in a methane atmosphere, Energy & Fuels. 23 (2009) 1619-1625. https://doi.org/10.1021/ef800880f
Ind.
Eng.
Chem.
19
(2013)
1668-1672.
Pr
J.
e-
[17] S.S. Park, N.J. Kim, Study on methane hydrate formation using ultrasonic waves,
https://doi.org/10.1016/j.jiec.2013.02.004
al
[18] J. Bai, D. Liang, D. Li, Continuous formation process of CO2 gas hydrate via a vortex and impinging stream reactor, Energy & Fuels. 24 (2007) 1207-1212.
rn
https://doi.org/10.1021/ef900694z
Jo u
[19] D.L. Zhong, S.Y. He, D.J. Sun, Comparison of methane hydrate formation in stirred reactor and porous media in the presence of SDS, Energy Procedia. 61 (2014) 1573-1576. https://doi.org/10.1016/j.egypro.2014.12.174 [20] S.S. Fan, S.F. Li, J.Q. Wang, Efficient capture of CO2 from simulated flue gas by formation of TBAB or TBAF semiclathrate hydrates, Energy & Fuels. 23 (2009) 4202-4208. https://doi.org/10.1021/ef9003329 [21] N. Ando, Y. Kuwabara, Y.H. Mori, Surfactant effects on hydrate formation in an unstirred gas/liquid system: An experimental study using methane and micelle-forming surfactants, Chem. Eng. Sci. 73 (2012) 79-85. https://doi.org/10.1016/j.ces.2012.01.038 [22] P. Linga, C. Haligva, S.C. Nam, Gas hydrate formation in a variable volume bed
Journal Pre-proof of silica sand particles, Energy & Fuels. 23 (2009) 5496-5507. https://doi.org/doi:10.1021/ef900542m [23] P. Linga, N. Daraboina, J.A. Ripmeester, Enhanced rate of gas hydrate formation in a fixed bed column filled with sand compared to a stirred vessel, Chem. Eng. Sci. 68 (2012) 617-623. https://doi.org/10.1016/j.ces.2011.10.030 [24] C. Ekta, P. Nitish, M. Ajay, Enhanced formation of methane hydrate using a novel synthesized anionic surfactant for application in storage and transportation of J.
Nat.
Gas
Sci.
https://doi.org/10.1016/j.jngse.2018.06.016
Eng.
56
(2018)
246-257.
f
gas,
oo
natural
pr
[25] Y.F. Makogon, Hydrates of hydrocarbons. Tulas,Oklahoma. 1997,35-37. [26] Q.Sun, B. Chen, Y.Y. Li, Promotion effects of mung starch on methane hydrate
e-
formation equilibria/rate and gas storage capacity, Fluid Phase Equilib. 475
Pr
(2018) 95-99. https://doi.org/10.1016/j.fluid.2018.07.019 [27] Y.Z. Liu, Y.Q. Xing, L.J. Cui, Experimental study on capacity of gas hydrate in a
al
rotating packed bed. Chem. Ind. & Eng. Pro. 26 (2007) 853-856. https://doi.org/10.1016/S1872-5791(07)60010-4
rn
[28] W.F. Hao, J.Q. Wang, S.S. Fan, Study on methane hydration process in a
Jo u
semi-continuous stirred tank reactor, Energy. Convers. Manage. 48 (2007) 954-960. https://doi.org/10.1016/j.enconman.2006.08.007 [29] P. Xiao, X.M. Yang, C.Y. Sun, Enhancing methane hydrate formation in bulk water using vertical reciprocating impact, Chem. Eng. J. 336 (2018) 649–658. https://doi.org/10.1016/j.cej.2017.12.020 [30] W.F. Hao, W. Sheng, S.S. Fan, Experimental investigation of methane hydrate formation in a spraying reactor, J. Wuhan Univ. Technol. 29 (2007) 39-43. [31] S. Baek, Y.H. Ahn, J.S. Zhang, Enhanced methane hydrate formation with cyclopentane
hydrate
seeds,
Appl.
Energ.
202
(2017)
32-41
https://doi.org/10.1016/j.apenergy.2017.05.108 [32] F. Wang, Y. Song, G. Liu, Rapid methane hydrate formation promoted by
Journal Pre-proof Ag&SDS-coated nanospheres for energy storage, Appl. Energ. 213 (2018) 227-234. https://doi.org/10.1016/j.apenergy.2018.01.021 [33] S.S. Fan, L. Yang, Y.H Wang, Rapid and high capacity methane storage in clathrate hydrates using surfactant dry solution, Chem. Eng. Sci. 106 (2014) 53-59. https://doi.org/10.1016/j.ces.2013.11.032 [34] H.S. Fogler, Elements of chemical reaction engineering, 3rd ed, Prentice Hall, New York, 1999.
f
[35] H. Tsuji, T. Kobayashi, R. Ohmura, Y.H. Mori, Hydrate formation by water
oo
spraying in a methane + ethane + propane gas mixture: An attempt at promoting
pr
hydrate formation utilizing large-molecule guest substances for structure-H hydrates, Energy & Fuels. 19 (2005) 869-876. https://doi.org/10.1021/ef049785a
e-
[36] L.L. Shi, D.Q Liang, Kinetic study of CH4 hydrate formation in the presence of
Pr
tetrabutylphosphonium chloride (TBPC), J. Mol. Liq. 271 (2018) 730-737. https://doi.org/10.1016/j.molliq.2018.09.071
al
[37] Q.N. Lv, X.S. Li, C.G Xu, Experimental investigation of the formation of cyclopentane-methane hydrate in a novel and large-size bubble column reactor,
rn
Ind Eng. Chem. Res. 51 (2012) 5967-5975. https://doi.org/10.1021/ie202422c
Jo u
[38] L.G. Tang, X.S. Li, Z.P. Feng, Natural gas hydrate formation in an ejector loop reactor: preliminary study, Ind. Eng. Chem. Res. 45 (2006) 7934-7940. https://doi.org/10.1021/ie0609259 [39] W. Ke, T.M. Svartaas, D.Y. Chen, A review of gas hydrate nucleation theories and growth
models,
J.
Nat.
Gas.
Sci.
Eng.
61
(2019)
169-196.
https://doi.org/10.1016/j.jngse.2018.10.021 [40] W.F. Hao, Study on natural gas hydrate formation with different reactors, Ph. D. Thesis, Dalian Univ. Technol. 2006. [41] J. Bai, D.L. Li, D.Q. Liang, Heat analysis of carbon dioxide hydrate formation process in a static higee reactor, Gas Chem. Ind. 35 (2010) 30-34. https://doi.org/10.3969/j.issn.1001-9219.2010.04.007
Journal Pre-proof [42] J.H. Kim, J.D. Lee, J.H. Yun, Gas-liquid circulating type of hydrate reactor. US
Jo u
rn
al
Pr
e-
pr
oo
f
Patent 9302239 (2016).
Journal Pre-proof
oo
f
Graphical Abstract
The space velocity (SV) of hydrate reactor was compared for evaluating natural gas
Jo u
rn
al
Pr
e-
pr
hydrate formation process from different literature.
Journal Pre-proof
Highlights
Jo u
rn
al
Pr
e-
pr
oo
f
1. The natural gas hydrate formation process was evaluated systematically from six parameters, including conversion of water to hydrate, storage capacity, the rate of hydrate formation, space velocity (SV) of hydrate reaction, energy consumption and hydrate removal. 2. By comparing the conversion of water to hydrate, it could be realized that the surfactant had a greater effect than the reactors to the conversion. 3. Considering the space velocity (SV) of hydrate formation, the value of SV in the spraying and ejector-type loop (ELR) reactors were much larger than the SV in the stirring and bubbling reactor. 4. Comparing the energy consumption of different reactors, the energy consumption per 1 kg hydrate formation was the largest in the reciprocating impact reactor, followed by the stirring reactor, and the energy consumption was the least in the spraying reactor.