Process Simulation for CO2 Capture with the ...

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Process simulation for CO2 capture with the aqueous solution of 1- methylpiperazine and its mixture with piperazine. Jian Chen a,. *, Han Li a. , Yann Le Moullec.
Available online at www.sciencedirect.com

ScienceDirect Energy Procedia 114 (2017) 1388 – 1393

13th International Conference on Greenhouse Gas Control Technologies, GHGT-13, 14-18 November 2016, Lausanne, Switzerland

Process simulation for CO2 capture with the aqueous solution of 1methylpiperazine and its mixture with piperazine Jian Chena,*, Han Lia, Yann Le Moullecb, Jiahui Lub, Jose Carlos Valle Marcosb, Guofei Chenb a

State Key Laboratory of Chemical Engineering, Tsinghua University, Beijing 100084, CHINA EDF China R&D Center, EDF Asia Pacific Direction, China Division, Beijing 100005, CHINA

b

Abstract Carbon dioxide capture with absorption is the main method to reduce CO2 emission. In this article CO2 solubility data were measured and thermodynamic models are established for CO2 capture with a new solvent 1-methylpiperazine (1-MPZ) with piperazine (PZ). Then the simulations are carried out with commercial software to calculate energy consumption of absorption processes with different operating parameters including amine concentration, CO2 partial pressure, regeneration pressure, and the results are compared with the MEA and AMP solvent. The energy consumption with the new solvent 1-MPZ+PZ is smaller than those with MEA by 20%. 2017The TheAuthors. Authors.Published Published Elsevier © 2017 byby Elsevier Ltd.Ltd. This is an open access article under the CC BY-NC-ND license Peer-review under responsibility of the organizing committee of GHGT-13. (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of GHGT-13. Keywords: CO2 Capture; absorption; solvent; 1-methylpiperazine; process simulation

1. Introduction Carbon dioxide capture and storage technology is considered to be the most effective technology to reduce greenhouse gas emissions in the future [1]. The absorption with amine solutions is most likely to be widely applied in fossil fuel power plants at present. The biggest problem this method faces now is great energy consumption of the capture process.

* Corresponding author. Tel.: +86-10-62798627; fax: +86-10-62770304. E-mail address: [email protected]

1876-6102 © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of GHGT-13. doi:10.1016/j.egypro.2017.03.1262

Jian Chen et al. / Energy Procedia 114 (2017) 1388 – 1393

Process simulation for CO2 capture with the solvent 1-methylpiperazine (1-MPZ) with piperazine (PZ) was studied. First, the basic thermodynamic data as vapor-liquid equilibrium and heat capacity of pure components and mixtures, CO2 solubility in aqueous solution of mixed amines were measured and used to establish the thermodynamic models[2]. Then the simulations are carried out with commercial software Aspen Plus to calculate energy consumption of absorption processes with different operating parameters including amine concentration, CO 2 partial pressure, regeneration pressure, and the results are compared with the MEA and AMP solvent as [3]. The energy consumption for CO2 capture can be divided to three parts, CO 2 desorption energy, H2O vaporization energy and solvent heating energy. In total energy, CO2 desorption energy occupies more than 60%, even up to 70%, for these solvent. The amine concentration is not the bigger the better. There is a best value, which can be calculated from circling loading for CO2 in the solvent. For MEA, AMP, AMP+PZ, 1-MPZ, 1-MPA+PZ, best concentration values are 40wt%, 40wt%, 30wt%+10wt%, 40wt%, 30wt%+10wt%. The lean loading at the least energy consumption is far small than the equilibrium lean loading at the absorption temperature and the CO 2 partial pressure in the purified gas. So the method for estimation of circling loading is that the loading at 313K and CO2 partial pressure is set as the rich loading and that at 393K and CO2 partial pressure is set as the lean one. The energy consumption is decreased when the CO2 partial pressure in the flue gas becomes bigger, and the decrease range is reversely related to the gradient of CO2 solubility curve at the absorption temperature. The gradient in MEA is the highest, and the increase of CO2 partial has almost no effects on the energy consumption. The gradient of CO2 solubility line in AMP and 1-MPZ is less than that in MEA, and when CO2 partial pressure is increased from 5kPa to 10kPa, the energy consumption is decreased by 0.3GJ/tCO 2 and 0.2GJ/tCO2. Further when CO2 partial pressure is increased from 10kPa to 15kPa, the energy consumption is almost not changed. The effect of reboiler pressure on the energy consumption is small, while the effect on the reboiler temperature is large. This situation for various amines is similar. When the reboiler pressure is increased by 0.5bar, the energy consumption is decreased by 0.1GJ/tCO2, while the reboiler temperature is increased by 10 degrees. When CO2 partial pressure in the flue gas is in the range from 5kPa to 15kPa, the energy consumption in the new solvent 1-MPZ+PZ is kept as the smallest one in all solvents, and is smaller than those in MEA by 20%. Later the capture process with the new solvent could be incorporated with different power generation processes to find out final real energy consumption and related capture cost. 2. Thermodynamic models for CO2+1-MPZ+PZ+H2O

Fig. 1. CO2 solubility in aqueous 10wt%1MPZ+5wt%PZ solution(ƹ, 313.15K˗■, 343.15K˗▲, 373.15K˗●, 393.15K).

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With the available thermodynamic models for CO2 in aqueous PZ solution and 1MPZ solutions [2], reaction equilibrium constants are correlated and can be used. So only cross ion-ion parameters need to be regressed, i.e., (1MPZH+, PZCOO-), (1MPZH+, PZ(COO-)2), (PZH+, 1MPZCOO-) with molecules, (PZH+, PZCOO-), (PZH+, PZ(COO-)2), (PZH+, HCO3-), (PZH+, CO32-) with molecules 1MPZ and H1MPZCOO, (1MPZH+, 1MPZCOO-), (1MPZH+, HCO3-), (1MPZH+, CO32-) with molecules PZ and HPZCOO. CO2 solubility in aqueous 1-MPZ+PZ solutions were measured at temperatures 313.15Kǃ343.15Kǃ373.15Kǃ393.15K, and 1-MPZ+PZ concentrations at 10wt%+5wt%ǃ20wt%+10wt%ǃ25wt%+5wt%ǃ35wt%+5wt%. The following figures 1-4 show comparison the results with the calculation ones, with mean relative deviations 10.3%, 15.9%, 16.3% and 15.2%.

Fig. 2. CO2 solubility in aqueous 20wt%1MPZ+10wt%PZ solution(ƹ, 313.15K˗■, 343.15K˗▲, 373.15K˗●, 393.15K).

Fig. 3. CO2 solubility in aqueous 25wt%1MPZ+5wt%PZ solution (ƹ, 313.15K˗■, 343.15K˗▲, 373.15K˗●, 393.15K).

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Jian Chen et al. / Energy Procedia 114 (2017) 1388 – 1393

Fig. 4. CO2 solubility in aqueous 35wt%1MPZ+5wt%PZ solution (ƹ, 313.15K˗■, 343.15K˗▲, 373.15K˗●, 393.15K).

3. Process simulation 3.1. Aqueous 1-MPZ solution Table 1 lists CO2 cyclic solubility in aqueous solutions of different 1-MPZ concentrations. Figure 5 shows the effect of 1-MPZ concentration on energy consumption at CO2 partial pressure of 10kPa and stripper pressure of 2.2bar. In Figure 5, Qabs is the desorption heat (same as absorption heat) for CO 2 from the rich solution to the lean solution, QT is the heat for heating the liquid also from the input rich solution to output lean solution, and Q con is the condensation heat of water in the top condenser. Qreb is the total reboiler heat. As listed in Table 1, along with the increase of 1-MPZ concentration, CO2 cyclic solubility is increased also with both methods[3]. From the comparison with Figure 5, CO2 cyclic solubility from the method 2 has the same position for the lowest point with the lowest point for the energy consumption. At the same time, as shown in Figure 5, with the increase of 1-MPZ concentration, Qabs increases, and the total energy consumption Qreb decrease. The best concentration for 1-MPZ is 40wt%. Same as MEA and AMP, the operation lean loading for the lowest energy consumption point is far lower than the equilibrium lean loading. For 40wt% 1-MPZ concentration, CO2 desorption heat Qabs is about 66% in total energy consumption Qreb, while water vaporization heat is about 20% in Qreb. Table 1. Cyclic CO2 solubility in aqueous 1-MPZ solutions 1-MPZ wt%

Method 1 αlean

αrich

Δα

mol/mol

Method 2

Cyclic solubility

αlean

g CO2/kg solution

αrich

Δα

mol/mol

Cyclic solubility g CO2/kg solution

20

0.392

0.624

0.232

20.38

0.119

0.666

0.547

48.06

30

0.392

0.595

0.203

26.75

0.107

0.633

0.526

69.32

40

0.402

0.581

0.179

31.45

0.096

0.617

0.521

91.55

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Jian Chen et al. / Energy Procedia 114 (2017) 1388 – 1393

Fig. 5. Effect of 1-MPZ concentration on energy consumption at CO2 partial pressure of 10kPa and stripper pressure of 2.2bar.

3.2. Mixed amines Table 2 and 3 shows the lowest energy consumption of different 1-MPZ+PZ, AMP+PZ solutions for CO2 partial pressure 10kPa and regeneration pressure 2.2bar, and they arecompared with aqueous 1-MPZ, AMP solutions. The total amine concentrations are 30wt%, 40wt% with PZ concentrations as 5wt% or 10wt%. For 1-MPZ, along with the increase of PZ, lean loading and rich loading are increased also, and cyclic loading is increased. Then the L/G ratio is decreased, liquid heating energy QT is decreased also. Meanwhile, CO2 Qabs is decreased clearly, the total energy consumption Qreb is decreased along with the addition of PZ. The best concentration for 1-MPZ+PZ is 30wt%+10wt%. Compared with 3.8GJ/tCO2 with MEA solution, the energy consumption with the new solvent 1-MPZ+PZ is decreased by about 20%. Table 2. Energy consumption of different 1-MPZ+PZ solutions for CO2 partial pressure 10kPa and regeneration pressure 2.2bar. PZ

αlean

20

10

0.10

0.682

25

5

0.08

30

0

0.05

30

10

35 40

1-MPZ

αrich

Treb

L/G

ºC

kg/kg

124.2

0.627 0.577

0.10

5 0

wt%

Qreb

-Qcon

1.717

3.177

0.929

123.9

1.868

3.218

123.9

2.399

3.315

0.648

124.7

1.390

0.06

0.607

124.9

0.05

0.565

124.5

mol/mol

Qabs

QT

-Qcon

Qabs

1.808

0.441

29.2

56.9

13.9

0.856

1.875

0.486

26.6

58.3

15.1

0.858

1.930

0.528

25.9

58.2

15.9

2.988

0.730

1.918

0.340

24.4

64.2

11.4

1.411

3.037

0.684

2.001

0.352

22.5

65.9

11.6

1.641

3.136

0.662

2.084

0.392

21.1

66.4

12.5

GJ/ton CO2

QT

%

As listed in Table 3, different than 1-MPZ+PZ, for the system AMP+PZ, along with the addition of PZ, liquid-gas ratio L/G is increased somewhat, Qcon and QT in increased somewhat, while Qabs in decreased, then the total energy consumption Qreb is increased. The best concentration for AMP+PZ is 30wt%+10wt%.

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Jian Chen et al. / Energy Procedia 114 (2017) 1388 – 1393 Table 3. Energy consumption of different AMP+PZ solutions for CO2 partial pressure 10kPa and regeneration pressure 2.2bar. PZ

αlean

ºC

kg/kg

20

10

0.14

0.732

124.5

25

5

0.20

0.679

30

0

0.02

0.601

30

10

0.25

35

5

40

0

AMP wt%

αrich

Qreb

-Qcon

1.898

3.333

0.898

121.9

2.358

3.364

124.5

1.604

3.288

0.672

121.8

1.795

0.20

0.608

122.7

0.01

0.520

125.3

mol/mol

Treb

L/G

Qabs

QT

-Qcon

Qabs

2.061

0.374

26.9

61.8

11.2

0.869

2.026

0.469

25.8

60.2

14.0

0.736

2.161

0.391

22.4

65.7

11.9

3.171

0.779

2.039

0.354

24.6

64.3

11.2

1.860

3.209

0.766

2.074

0.370

23.9

64.6

11.5

1.361

3.168

0.670

2.184

0.315

21.1

68.9

9.9

GJ/ton CO2

QT

%

4. Conclusions With CO2 solubility in mixed amine of 1-methylpiperazine and piperazine, thermodynamic models for CO2 absorption with the mixture are established and used for process simulation. Effects of amine concentrations, liquid/gas ratios on capture energy consumption are analyzed. The best concentration for 1-MPZ+PZ is 30wt%+10wt%, and compared with MEA solution, the energy consumption with the new solvent is decreased by about 20%.

Acknowledgement This work was supported by National Science and Technology Support Plan of China (No. 2015BAC04B01) and EDF Research Foundation.

Reference [1] Rochelle GT. Amine Scrubbing for CO2 Capture. Science 2009; 325: 1652–4. [2] Li H, Le Moullec Y, Lu J, Chen J, Valle Marcos JC, Chen G, Chopin F. CO 2 solubility measurement and thermodynamic modelling for 1methylpiperazine/water/CO2. Fluid Phase Equilib. 2015, 394: 118–28. [3] Li H, Le Moullec Y, Lu J, Chen J, Valle Marcos JC, Chen G. Solubility and energy analysis for CO2 absorption in piperazine derivatives and their mixtures. Int. J. Greenh. Gas Control 2014; 31: 25–32.