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CHEMICAL ENGINEERING TRANSACTIONS

VOL. 45, 2015

A publication of

The Italian Association

of Chemical Engineering

www.aidic.it/cet
Guest Editors: Petar Sabev Varbanov, Jiří Jaromír Klemeš, Sharifah Rafidah Wan Alwi, Jun Yow Yong, Xia Liu

ISBN 978-88-95608-36-5; ISSN 2283-9216 DOI: 10.3303/CET1545046

Please cite this article as: Chavez R.-H., Guadarrama J.J., 2015, Numerical evaluation of co2 capture on post-combustion

processes, Chemical Engineering Transactions, 45, 271-276 DOI:10.3303/CET1545046

271

Numerical Evaluation of CO2 Capture on

Post-combustion Processes

Rosa-Hilda Chavez*
,a

, Javier J. Guadarrama
b

a
Instituto Nacional de Investigaciones Nucleares. Carretera México-Toluca s/n, La Marquesa, Ocoyoacac, Edo. México

C.P. 52750, México
b
Instituto Tecnológico de Toluca. Av. Instituto Tecnológico s/n, Ex-Rancho la Virgen, Metepec, Edo. México, C.P

52140, México

rosahilda.chavez@inin.gob.mx

This paper is focused on the evaluation of a CO2 capture post-combustion process of three Mexican power

plants. They were compared with each other to determine what obtains the biggest CO2 capture flow using

the same size of experimental absorption column, by means of the hydrodynamic behavior and maximum

CO2 absorption with 30 % Monoethanolamine in aqueous solution. The chemical absorption with amines is

the best technology for post-combustion CO2 capture, due to handle large volumes of flue gas, low

pressures of operation, rapid response and low cost, although it is highly energy intensive because of the

thermal energy requirement needed to regenerate the amine solution while another disadvantage is the

loss of amine. Numerical evaluations were developed by computer simulation models applied to the

structured packing. The results shows the greater CO2 capture flow obtained was from a coal-fired Piedras

Negras power plant with 3.03 t/d, followed by caldera gas type of Valley of Mexico power plant with 1.88
t/d, and the lowest one was the gas turbine type of Poza Rica power plant with 0.8011 t/d.

1. Introduction

One of the main challenges of implementing CO2 capture at a power plant is the penalty on electrical

output (De Miguel Mercader et al., 2012). The performance of the combined installation, measured by the

net electrical output is therefore, a key indicator for process optimization (Biliyok et al., 2013), and CO2

capture development (Klemeš et al., 2007).

The post-combustion process using amine, is the most promising technology among post-combustion

processes due to its ability to handle large volumes of flue gas (Canepa et al., 2015), rapid reaction of

CO2, operation at ambient conditions, high efficiency separation of CO2 and low cost, (Sipöcz and

Tobiesen, 2012). However, it is still highly energy intensive (Mores et al., 2012) due to the thermal energy

requirement needed to regenerate the amine solution which increases the operating cost drastically

(Neveux et al., 2013) and another drawback of this method is the loss of amine in the regenerator unit,

because of oxidative and thermal degradation of amine (Porcheron et al., 2011).

The amine absorption processes have the advantage of improving the understanding of the solution

behavior associated with absorption and regeneration reactions (Grncarovska et al., 2013) and thus

provide scientific tools for the objectives of climate change actions and the stabilization of atmospheric

concentrations of greenhouse gases (MacDowell et al., 2011).

2. Methodology

During the last years research activities in CO2 capture have been done in different lines from

experimental studies at laboratory scale and pilot plants (Mores et al., 2012) to the development and

implementation of mathematical models in computers (Kakaras et al., 2013).

Figure 1 shows the flowchart of a system for capturing CO2, used to obtain several parameters needed to

evaluate CO2 capture with this system using diverse study cases with Aspen Plus simulator (Timmerman

2013); the system consist of five several columns, two heat exchangers and a mixer, (Tous et al., 2013) to

272

carry out the CO2 capture process (Moioli and Pellegrini, 2013). The CO2 loaded solvent (rich solvent) is

regenerated in stripper and sent back to the absorber to close the cycle (De Miguel Mercader et al., 2012).

Between the absorber and the stripper (Damartzis et al., 2013), a heat exchanger transfers part of the heat

from the lean to the reach solvent (Meldom, 2011). At the top of the stripper, high purity CO2 is produced

as CO2 capture flow (Lucquiaud and Gibbins, 2011) and is sent to a compression unit for further transport

(Mikulcic et al., 2013) and storage (Saavedra et al., 2013).

Figure 1: Flow diagram of the CO2 capture system, using the Aspen Plus simulator

In order to determine the optimum operational condition of a packed column irrigated, it was determined

hydrodynamic behavior of the column filled with ININ 18 structured packing. Loading or load point is the

maximum gas rate condition above which the efficiency of a packed bed rapidly deteriorates with an

increase in gas rate. Hold up is the amount of liquid held on the surface of the packing and in the voids of

the packed bed. Hold up increases with an increase in liquid rate but the effect of gas rate on hold up

appears minimal up to the load point. The load point usually occurs between 75 to 90 % of the flooding gas

rate for structured packing. Packed columns flood occurs when excessive liquid hold up results from the

interaction of gas and liquid in a packed bed. Characteristic of this condition is very poor separation

efficiency and usually excessive pressure drop in the packed bed. Due to the efficiency decreases very

rapidly at rates beyond the load point, the flood point of packed column usually is not a useful design

criterion parameter as the load point (Yazgi and Kenig, 2013).

Packed columns are mainly used for mass transfer processes and for direct heat transfer between two

phases (Petrova et al., 2013). Their design and operation require knowledge of the operating zone.

Particular interest is attached to the load at which the liquid commences to hold up in the column and

when flooding occurs.

The methodology developed was:

1) Obtain experimental data using an absorption column. The experimental column has 0.30 m

diameter, 3.5 m packed height, and 0.0706 m
2
cross sectional area, and it was used

Monoethanolamine (MEA) at 30 % weight aqueous solution for the chemical absorption of CO2.

The experimental column filled with ININ 18 structured packing has the capacity to process 10.9

t/d of flue gas released from the chimneys of power plant, at 30 ºC and 0.69 bar. The column with

ININ 18 structured packing, was operated at different L/G rates in order to obtain loading

operation.

2) A hydrodynamic model for structured packing (Stichlmair et al., 1989) was used to obtain

parameters such as pressure drops at different liquid and gas flows in the absorption and

desorption columns, energy requirements, were determined with 10.9 t/d fed as flue gas to

absorption column size. Experimental values were fed as known parameters in the numerical

evaluation of pressure drop per liquid and vapor rate at 75 to 90 % with respect to the flooding

vapor rate.

273

The results obtained in this research not only improve the understanding of solution behavior associated

with absorption and regeneration reactions (Linnenberg et al., 2011) but also provide the information

needed to develop a model capable of describing the L/G ratio (Matsuda, 2013) which is fundamental for

simulation and optimization (Sun et al., 2013) of CO2 capture process using amines (Moullec, 2012).

The efficiency of packing is a strong function of packing size, physical properties and proper liquid

distribution. In general, the packing efficiency increases when the height of overall vapor phase transfer

unit decreases, but also becomes progressively more sensitive to the uniformity of the liquid distribution.

In reality, for each industrial plant to meet plant specific demands and conditions (Anantharaman et al.,

2013), each one has specific solution (Semkov et al., 2013).

Table 1 shows the actual characteristics of flue gas of the three power plants in Mexico named and

located: Valle de México, Queretaro State; Poza Rica, Veracruz State and Rio Escondido, Coahuila State,

power plants.

Table 1: Characteristics of flue gas

Characteristics of flue gas Valle de Mexico
(caldera gas type)

Poza Rica
(gas turbine type)

Rio Escondido
(coal type)

Power plant total flue gas (t/h) 627.6 1,645.6 1,338.3
Electrical output (MW) 158.17 170.55 300.00
% mol CO2 (% mass) 7.85 (12.45) 3.70 (5.78) 12.47 (19.46)

% mol SO2 0.0 0.0 0.06
% mol N2 70.53 72.79 72.02
% mol O2 3.28 12.19 4.81

% mol H2O 17.49 10.44 9.78
% mol Ar 0.85 0.8767 0.87

CO2 flow (t/h) 78.13 95.11 260.43
Flue gas temperature (ºC) 126.7 601.1 151.2

Pressure (atm) 1 1 1
Molecular weight of flue gas

(g/gmol)
27.74 28.14 29.31

Flue gas density (kg/m
3
) 1.13

1.15

1.19

Flue gas dynamic viscosity (kg/ms) 1.43x10
-5

1.56x10
-5

1.54x10
-5

Flue gas kinematic viscosity (m

2
/s) 1.26x10

-5
1.35x10

-5
1.29x10

-5

MW equivalent related 10.9 t/d 0.115 0.047 0.100

3. Results and Discussion

The methodology described was developed based on L/G = 1.5 ratio and 0.3 m columns diameter, 90 % of

absorption efficiency and 90 % of CO2 captured. To evaluate the maximum capacity of CO2 absorption and

regeneration of the solvent, numerical simulations were performed to three power plants. Table 2 shows

the results for the hydrodynamic behaviour of each one. Values from Table 1 and 2, as % CO2

concentration flue gas and irrigated pressure drop, were used in the evaluation per each power plant.

Table 2: Hydrodynamic parameters (Stilchmair et al., 1989) with L/G = 1.5 relationship and 0.3m columns

diameter

Hydrodynamic parameters Valle de Mexico
(caldera gas type)

Poza Rica
(gas turbine type)

Rio Escondido
(coal type)

Gas velocity UG (m/s) 2.74 2.75 2.69
Equivalent diameter (m) 1.2×10

-3
1.2×10

-3

Reynolds number 244.66 262.98 251.43
Friction factor 0.5392 0.5304 0.5358

Dry pressure drop (N/m
2
) 473.27 460.59 469.49

Dimensionless factor 0.0477 0.0464 0.0473
Froude number 0.00118 0.001191 0.00113
Liquid holdup 0.0588 0.0588 0.0579
c exponent -0.2323 -0.2238 -0.2291

Irrigated pressure drop (Pa/m) 935.55 907.84 916.88

Figure 2 shows that CO2 production rises when increasing the column diameter, while Figure 3 shows CO2

production is reduced when L/G ratio increase, as these were expected.

274

Figure 2 shows that Rio Escondido power plant is the highest CO2 flow production, and then Valley of

Mexico plant has greater advantage than Poza Rica plant as result of its CO2 concentration in the flue gas.

Figure 3 shows for handling 0.3 m as columns diameter, the best L/G ratio is 1.5 due to optimum

operational condition of a packed column irrigated. From these results presented, it is shown that the

maximum discharge of CO2 from coal-fired with 3.03 t/d was obtained, followed by caldera gas type of

Valley of Mexico, with 1.88 t/d, and the lowest one was gas turbine type of Poza Rica, with 0.8011 t/d. In

contrast, coal-fired power is the one with SO2 and other gases which imply pre-treatment combustion

gases to reduce these before passing them to the capture of CO2 through the amine (see Table 2).

Figure 2: CO2 capture vs column diameter, at

L/G = 1.5

Figure 3: CO2 capture vs L/G ratio

Figure 4 shows the equivalent energy requirements with respect of different values of flue gas processed.

It shows that MWeq raises when flue gas increasing, it was expected as bigger scale of plants. Valle de

Mexico plant, of caldera gas type, has bigger MW equivalent than Rio Escondido plant, of coal type; and

this last one bigger than Poza Rica Plant, of gas turbine type, as the same flue gas processed.

Figure 4: MW equivalent vs flue gas

4. Conclusions

The projection on the amount of CO2 captured requires L/G ratio close to unity, since higher or lower

values lead to failures in the mathematical procedures. In addition, having this magnitude of L/G will

achieve efficiency in capturing within the process interval indicated.

By adding the capture system to power plants, large volumes of CO2 according to the concentration of this

gas produced is captured, taking advantage of modifying the installation of post-combustion system.

The simulation results show that MWeq values to dimensions of capture plants are always lower than those

of generating plant and it is necessary to use many capture units to process volumes observed art real gas

streams obtained and therefore the size of such post-combustion power plants with CO2 capture increases

and thus the amount of energy required for its operation also increases.

0 0.5 1 1.5

C
O

2
c

a
p

tu
re

(
t/

d
)

D (m)

Poza Rica

Valle de
México

Río
Escondido

-0.5

0.5

1.5

2.5

3.5

0 1 2 3 4C
O

2
c

a
p

tu
re

(
t/

d
)

L/G

Poza Rica

Valle de
México
Río
Escondido

0.00

0.05

0.10

0.15

0.20

0.25

10 15 20 25

M
W

e
q

G (t/d)

Poza Rica

Valle de
México
Río
Escondido

275

From these results presented, it is shown that the maximum CO2 capture is from Rio Escondido plant coal-

fired but it is the one with SO2 and other gases which implies pre-treatment combustion gases to reduce

these before passing them to the capture of CO2 through the amine.

Acknowledgements

For the partial financing EDOMEX-2009-C02-135728, SEP-CONACyT-CBII-2007-01-82987, Staff of the

Department of Models and Prototypes of National Institute for Nuclear Research, and pay airfare by

Mexican Ministry of Foreign Affairs (SRE).

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