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êEvgenyP. Zaporozhets, Nikita A. Shostak
Efficiency Estimation of the Single- and Muiticomponent Anti-hydrate Reagents
UDC 622.279.72:548.562
Efficiency Estimation of the Single- and Multicomponent Anti-hydrate Reagents
Evgeny P. ZAPOROZHETS, Nikita A. SHOSTAK ^
Kuban State Technological University, Krasnodar, Russia
Different types of technological and technical problems in the oil, gas and chemical industries are connected with the hydrate formation process and with the using of anti-hydrate chemicals. That is why, it is necessary to estimate thermobaric ranges within which reagents does not let hydrate to grow or is their dissociation. Also, to estimate anti-hydrate influence we need to determine the chemicals' anti-hydrate efficiency and chose the best one. They make the reagents consisting of several chemical components depending on the purpose of their application -for prevention of formation and (or) elimination of hydrates. It demands calculations of the optimum concentration and expenses and also the intensity (speed) of hydrates dissociation causing with the reagents.
The analytical method of the anti-hydrate chemical reagents efficiency determination containing one or several components from different classes of chemical compounds - alcohols, salts, acids, compounds of nitrogen and oxygen - is presented in this paper. With its help it is possible to define decrease in temperature of hydrate formation from reagents influence, to count key parameters of reagents anti-hydrate efficiency depending on component compositions of hydrate gas and a phase condition of a hydrate-gas system, to select types of chemical components and their quantity in multicomponent reagents, i.e., to make new compounds. The method can be used for express assessment of anti-hydrate chemical reagents efficiency on criteria sign for practical application in oil, gas and processing industry.
Key words: absorption; anti-hydrate reagent; gas-water system; hydrate; hydrate formation; concentration of reagent; crystallization temperature
How to cite this article: Zaporozhets E.P., Shostak N.A. Efficiency Estimation of the Single- and Multicomponent Anti-hydrate Reagents. Journal of Mining Institute. 2019. Vol. 238, p. 423-429. DOI: 10.31897/PMI.2019.4.423
Introduction. The prevention of technogenic hydrates formation and elimination and also gas production from natural hydrates are connected with the use of anti-hydrate chemical reagents (further - reagents). Due to a variety of the reagents differing as on chemicals classes (for example, solutions of alcohols, salts, alkalis and acids) and on their mixes, there is a problem of their choice depending on: efficiency, concentration (in solutions), mutually compatibility, compatibility with the contacting environments (hydrocarbons and the components accompanying them, for example, H2S, CO2, the mineralized reservoir waters).
For the solution of this problem calculations are required such as:
• chemicals' anti-hydrate efficiency;
• optimum concentration and expenses of reagents depending on the purpose of their application;
• anti-hydrate influences of the reagents consisting of several chemical components and drawing up their compounds;
• effects of reagents on intensity of hydrates dissociation.
The analytical method of determination of efficiency of the reagents containing one or several components from classes of chemical compounds - alcohols, salts, acids, compounds of nitrogen and oxygen is developed for the solution of these tasks. It can be used for express assessment at use of reagents in oil, gas and processing industry. In the method the following assumptions and restrictions are made: water in an initial hydrate-forming system is in a vaporous, liquid and (or) firm phase; from impact of reagent on a system its equilibrium pressure of hydrate formation remains constant, only equilibrium temperature changes.
Equilibrium thermal conditions of hydrates formation and existence at the reagents influence. The reagent entered into a hydrate-forming system absorbs water component from its vaporous, liquid and (or) firm phases. As a result the new system consisting of a gas-vapor phase with the reduced maintenance of the water component and reagent diluted with water from initial concentration of Хto concentration Xr is formed:
êEvgenyP. Zaporozhets, Nikita A Shostak
Efficiency Estimation of the Single- and Muiticomponent Anti-hydrate Reagents
Xr =-
Xm
m + m,.
(1)
where m is amount of reagent with initial concentration of X, kg; mw - total amount of the water absorbed by reagent, kg.
In case of prevention of hydrates formation the amount of the water absorbed by reagent can be found:
mw = mw +
V (q -Q 2 ),
(2)
where m - the mass of water in liquid and (or) firm phases in an initial system, kg; V - amount of
gas in a system, m ; Q1 and Q2 - content (kg/m ) of water vapors in gas with a pressure of Ph, Pa, and, respectively, at temperatures of T0 and Th.n, K. Quantities Q1 and Q2 can be determined using the corresponding graphic dependences or the equations of equilibrium moisture content in gases [14].
The amount of the water absorbed by reagent from the dissociating hydrate (at its decomposition) calculates with a following equation:
mw = mh& , (3)
where mh - hydrate mass (its content in a system), kg; ro - water content in hydrate.
Exact values of quantity ro are determined by a technique [2] depending on types of hydrates, component composition of gases-hydrate-forming, hydrate numbers, molar masses and density. As these calculations are difficult, for simplification we accept ro ~ 0.9. It is acceptable for engineering calculations with accuracy of 5 %.
In a new system because of absorption by water reagent the equilibrium temperature of hydrate formation decreases from an initial system Th towards lower temperature in a new system Th.n by AT (Fig. 1).
As the baric conditions in the initial and the new system are identical (Ph = const), the amount of decrease in equilibrium temperature of hydrate formation depends only on reagent concentration:
AT = f X ).
In both systems processes of hydrate formation are identical - crystalline hydrates are formed of molecules of the gases adsorbed by ice alike associates of water molecules [3]. Then processes of formation of such associates in crystalline hydrates of initial and new systems are similar to processes of pure water crystallization at a temperature Tw and waters in reagent solution with lower
temperature Tr. Proceeding from this similarity, amounts of decrease in temperatures are equal:
Pressure, Pa
Ph
Ill Line of hydrate-forming equilibrium
! I T 1 T 1 hn I 1 h U
- Y < i AT Temperature, K
T - T ' i
h 1 h.n
T - T =AT .
(4)
Water crystallization temperature Tw is not a constant. It depends on pressure Ph and the type of gas over water:
Tw = 273.16 - Ma (o. w M„ V
0731Phw + 0.0002Phw
), (5)
Fig. 1. Change of the hydrates formation thermal conditions
where Ma u Mg - molar masses of the air and gas-hydrate-former.
Calculation of the amount Tw to within 0.01 K on the equation (5) can be carried out in the range of pressure Ph = = 0.00061173 - 212.9 MPa.
Evgeny P. Zaporozhets, Nikita A. Shostak
Efficiency Estimation of the Single- and Multicomponent Anti-hydrate Reagents
The crystallization temperature the reagent water solutions consisting of one or several chemical components calculate by a following equation:
T =Z XT,
(6)
where xr - mass concentration of an i-component; Tr - water crystallization temperature in the
diluted reagent containing i-component.
The exact value of Tr can be defined by reference books [7-10, 15] or using this equation:
Tr =oX2r + $Xr + y,
(7)
where a, P, y - coefficients for some chemical components with concentration Xn in the ranges specified in Table 1.
Table 1
Coefficients for chemical components
Reagent name Reagent concentration in a solution Xr , kg/kg Coefficients
a ß Y
Alcohols
Methanol 0.10-0.60 -138.93 -40.15 271.89
Ethanol 0.025-0.719 -10.40 -70.26 275.93
Propanol 0.08-0.65 28.83 -63.80 274.40
Ethylene glycol 0.02-0.663 -160.62 11.44 270.20
Diethylene glycol 0.02-0.62 -131.77 13.14 271.73
Triethylene glycol 0.02-0.50 -101.47 7.41 272.16
Propylene glycol 0.05-0.59 -153.29 16.51 269.72
Glycerin 0.050-0.667 -116.58 14.74 270.78
Salts
Lithium chloride 0.05-0.25 -1130.70 19.79 270.55
Magnesium chloride 0.014-0.206 -840.22 16.46 271.84
Sodium chloride 0.015-0.224 -212.97 -45.24 272.86
Calcium chloride 0.059-0.284 -840.90 126.63 263.66
Calcium nitrate 0.02-0.35 -102.86 -16.29 272.86
Calcium permanganate 0.05-0.42 -295.6 48.35 269.16
Acids
Nitric acid 0.02-0.33 -332.73 -14.39 271.75
Sulfuric acid 0.04-0.38 -618.46 50.86 269.68
Hydrochloric acid 0.012-0.239 -479.60 57.50 269.69
Acetic acid 0.065-0.555 -15.27 -31.92 273.29
Ammonia Monoethanol amine Diethanol amine Trietanolamine
Potassium hydroxide Sodium hydroxide Hydrogen peroxide Formaldehyde
Compounds of nitrogen
0.02-0.33 -937.69
0.10-0.50 -480.14
0.10-0.50 -153.57
0.10-0.60 -158.93
Compounds of oxygen
0.02-0.32 -670.91
0.02-0.19 -498.06
0.05-0.50 -87.73
0.015-0.250 -29.81
28.37 122.40 30.64 50.54
25.91 -46.32 -65.31 -57.01
268.27 262.47 269.65 268.65
270.26 272.43 274.14 273.12
The calculated values of decrease in temperatures AT (4) from influence of reagents water solutions are presented in the form of graphic dependences (Fig.2, 3).
In some reagents solutions the water crystallization temperature has no strictly fixed values. It is noted [9] temperatures of emergence of the first crystals and full hardening. The equation (7) is intended for calculation of the first crystals emergence temperature.
Evgeny P. Zaporozhets, Nikita A. Shostak
Efficiency Estimation of the Single- and Multicomponent Anti-hydrate Reagents
AT, K 80 i
70
b
60
50
40
30 -
20
10 -
Methanol Ethanol Propanol Ethylene glycol Diethylene glycol Triethylene glycol Propylene glycol Glycerin
AT, K 70
60 H
50-
40 -
30 -
Lithium chloride
Magnesium chloride
Sodium chloride
Sodium chloride
Calcium permanganate
Calcium nitrate
Calcium nitrite-nitrate Calcium nitrite-nitratechloride
—i-1-1-1-1-1-1
0.1 0.2 0.3 0.4 0.5 0.6 Xr
0.05 0.1 0.15 0.2
a
0
0
AT, K 80 -
70 -
60 -
50 -
40
30 -
20 -
10
Nitric acid Pydrochloric acid Sulfuric acid Acetic acid
AT, K 80
70
60
50
40
30 20
10
Ammonia Monoethanol amine Diethanol amine Trietanolamine
h-1-1-1-1-1-1-1-
0.1 0.2 0.3 0.4 Xr
n-1-1-r
0 0.1 0.2 0.3 0.4 0.5 0.6 Xr
Fig.2. Decrease in temperature of hydrates formation AT from the water solutions influence consisting of alcohols (a), salts (b), acids (c), compounds of nitrogen (d) with concentration Xr
c
d
0
êEvgenyP. Zaporozhets, Nikita A. Shostak
Efficiency Estimation of the Single- and Multicomponent Anti-hydrate Reagents
The difference between these temperatures increases up to 5-7 °C with increase in reagent
concentration Xr in the solution.
'i
In the equation (4) Th - the equilibrium temperature of hydrate formation in a system gas -water is determined by a technique [4]. For a system individual gas - water in the first range (from left to right) to a quadrupole point the I (Fig.1) temperature is calculated by a formula:
i
'■-I f11
(8)
where a, b - coefficients (Table 2).
In the second range between quadrupole points of I and II (Fig. 1) it is possible to use the equation:
ln
T —
l2
d
(9)
where e = 2.718 - basis of a natural logarithm; c, d - coefficients (Table 2).
The nature of a balance line change of a hydrate-former system multicomponent gas - water is identical to balance lines of systems individual gases - water, and its current coordinates submit to the equation:
T -X Y' +X Y'h
i-i i-i
(10)
molar share of a hydrate-former n - number of a hydrate-former
where Y -component; component.
Determination of the reagents efficiency.
The anti-hydrate efficiency of reagents is estimated by criterion for:
• single-component reagent
T - T
Л г --
(11)
multicomponent reagent
АТ, К 60 ■
50 ■
40 -
30 ■
20 ■
10 -
Potassium hydroxide Sodium hydroxide Hydrogen peroxide Formaldehyde
0
0.1
0.2
0.3
0.4
0.5 X
Рис .3. Decrease in temperature of hydrates formation AT from the water solutions influence consisting of compounds of oxygen with concentration Xr
Table 2
Numerical values of the coefficients a, b, c и d
Gas a b c d
Methane 4-10-17 9.3415 10-7 0.1128
Ethane 3-10-26 12.8130 6-10-10 0.1256
Propane 2-10-28 13.4980 8-10-10 0.1281
i-butane 2-10-32 15.0760 8-10-20 0.2052
Carbon dioxide 10-21 11.0890 3 • 10-20 0.2078
Hydrogen sulfide 10-23 11.4690 2-10-8 0.1064
Nitrogen 2-10-12 7.7171 10-5 0.1015
Argon 8-10-12 7.4047 10-7 0.1168
Krypton 5 • 10-26 12.8900 2^10-6 0.0990
Xenon 2-10-24 11.8380 310-7 0.0993
Лг -
T - T
W Г
T
(12)
If nr = 0 - there is no reagent in a system; n > 0 - there is reagent in a system, and the higher quantity corresponds to higher efficiency.
For example, the criterion of the chemical reagent efficiency consisting of water solution of one anti-hydrate reagent - the methanol having mass concentration ofX1 = 0.6 in a hydrate-forming system water - methane:
• in the 1st range of a phase state (Fig.1) at Ph = 2.3-106 Pa equal to
Лг
T - T
* w г
T
273 -198 272
- 0.28;
c
êEvgenyP. Zaporozhets, Nikita A Shostak
Efficiency Estimation of the Single- and Multicomponent Anti-hydrate Reagents
in the 2nd range of a phase state (Fig. 1) at Ph = 4.0-106 Pa equal to
Tw - T 272 -198
r =-- =-= 0.27 .
Th 278
The criterion of inhibitor water solution efficiency with mass concentration of X = 0.6, consisting of two anti-hydrate reagents - methanol (Xi = 0.4) and ammonia (X2 = 0.2):
• in the 1st range of a phase state (Fig. 1) at Ph = 2.3-106 Pa equal to
Tw -T 273-140
r =-- =-= 0.49,
r Th 272
• in the 2nd range of a phase state (Fig. 1) at Ph = 4.0-106 Pa equal to
Tw - Tn 272-140
rr =-L =-= 0.47.
Th 278
As a result, the efficiency of single-component reagent - 60 % of methanol water solution - is approximately identical in both ranges of a phase condition to system water - methane. The efficiency of the two-component reagent consisting of methanol (40 %) and ammonia (20 %) water solution exceeds by 1.75 times the efficiency of a single-component in both ranges phase condition of system water - methane.
It is possible to use the schedules in Fig.2, 3 for determination of individual reagents efficiency. Also it is possible to make effective multicomponent reagents selecting individual reagents and using (6) and (12). However it is necessary to consider chemical interference of reagents of various classes, for example, a negative combination of salts and acids.
Verification. A compliance of the developed method of reagents efficiency determination was established from comparison of AT with the one known experimental. The results of comparison are presented in Table 3.
Table 3
Theoretical and experimental values of AT
Anti-hydrate reagent Water solution concentration, mas % AT, K Reference Divergence, %
Theoretical Experimental
Methanol (CH3OH) 0.10 5.7 5.5 [11] 3.6
0.27 22.0 21.0 [11] 4.7
0.60 57.9 60.0 [6] 3.6
Ethylene glycol [C2H4(OH)2] 0.10 2.9 3.0 [12] 3.4
0.40 19.7 19.0 [6] 3.6
0.60 43.7 42.0 [1] 4.0
Triethylene glycol [C6H12O2(OH)2] 0.20 3.6 3.5 [12] 2.8
0.60 37.3 36.0 [1] 3.5
Lithium chloride (LiCl) 0.15 23.3 23.0 [1] 1.3
Magnesium chloride (MgCl2) 0.11 8.7 8.5 [13] 2.3
0.15 20.1 21.0 [1] 5.0
Calcium chloride (CaCl2) 0.10 5.3 5.5 [5] 4.1
0.20 17.4 17.0 [1] 2.3
Let's compare different AT from reagents influence at various concentrations. It is obvious that the divergence of AT values does not exceed 5 % that is acceptable for engineering purposes.
Conclusion. By means of the developed method of anti-hydrate chemical reagents efficiency determination it is possible:
êEvgenyP. Zaporozhets, Nikita A. Shostak
Efficiency Estimation of the Single- and Multicomponent Anti-hydrate Reagents
• to define decrease in temperature of hydrate formation from reagents influence;
• to calculate key parameters of reagents anti-hydrate efficiency depending on component compositions of gas-hydrate-former and a phase condition of a hydrate-forming system;
• to select types of chemical components and their quantity in multicomponent reagents, i.e. to make their new compounds.
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Authors: Evgeny P. Zaporozhets, Doctor of Engineering Sciences, Professor, [email protected] (Kuban State Technological University, Krasnodar, Russia), Nikita A. Shostak, Candidate of Engineering Sciences, Associate Professor, [email protected] (Kuban State Technological University, Krasnodar, Russia). The paper was received on 12 December, 2018. The paper was accepted for publication on 23 May, 2019.
