sumarry phd thesis - pub.rodoctorat.energ.pub.ro/files/abstract/2019/slavu... · sumarry phd thesis...

UNIVERSITY POLITEHNICA OF BUCHAREST

THE POWER ENGEENERING DOCTORAL SCHOOL

SUMARRY

PhD THESIS

Multi-criteria assessment of CO2 capture processes by

chemical absorption using ammonia solutions

Scientific Coordinator:

Prof. phd. eng. Adrian BADEA

Author:

Eng. Nela SLAVU

Bucharest, 2019

https://www.google.ro/imgres?imgurl=https%3A%2F%2Fupload.wikimedia.org%2Fwikipedia%2Fro%2Fthumb%2F5%2F51%2FLogo_Universitatea_Politehnica_din_Bucure%25C8%2599ti.svg%2F1024px-Logo_Universitatea_Politehnica_din_Bucure%25C8%2599ti.svg.png&imgrefurl=https%3A%2F%2Fro.wikipedia.org%2Fwiki%2FFi%25C8%2599ier%3ALogo_Universitatea_Politehnica_din_Bucure%25C8%2599ti.svg&docid=v1HGhAqJQVkzBM&tbnid=LKBsYpcaM77lZM%3A&vet=10ahUKEwjL__6s7IfjAhVloYsKHcNAAcgQMwhRKAAwAA..i&w=1024&h=1024&bih=747&biw=1536&q=sigla%20upb&ved=0ahUKEwjL__6s7IfjAhVloYsKHcNAAcgQMwhRKAAwAA&iact=mrc&uact=8

https://www.google.ro/imgres?imgurl=https%3A%2F%2Fupb.ro%2Fwp-content%2Fuploads%2F2018%2F04%2FSigla-Energeticii_blue-30-55-115-yellow-255-255-50-300x300.png&imgrefurl=https%3A%2F%2Fupb.ro%2Ffacultati%2Ffacultatea-de-energetica%2F&docid=H06j20qSIw_UCM&tbnid=3aJHWXv7tONU4M%3A&vet=10ahUKEwjWzePD7IfjAhVtxosKHdffAMIQMwhEKAAwAA..i&w=300&h=300&bih=747&biw=1536&q=sigla%20energetica&ved=0ahUKEwjWzePD7IfjAhVtxosKHdffAMIQMwhEKAAwAA&iact=mrc&uact=8

Multi-criteria assessment of CO2 capture processes by chemical absorption using ammonia solutions

3

SUMMARY (corresponding to the phd thesis summary)

SUMMARY .......................................................................................................... 3

SUMMARY .......................................................................................................... 4

KEY-WORDS ....................................................................................................... 6

SUMMARY OF PHD THESIS CHAPTERS ....................................................... 7

GENERAL CONCLUSIONS AND FUTURE DEVELOPMENT .................... 28

SELECTIVE BIBLIOGRAPHY ......................................................................... 31


4

SUMMARY (corresponding to the phd thesis)

CHAPTER 1. INTRODUCTION………………………………………………………………..15

1.1 Necessity to reduce the CO2 emissions……………………………………………………...15

1.2 Global energy demand and CO2 emissions for 2017…………………………………………17

1.3 Thesis motivation.…………………………………………………………………………...20

1.4 Purpose and objectives of the thesis.………………………………………………………...21

CHAPTER 2. CURRENT STATUS OF CO2 CAPTURE TECHNOLOGIES………………...23

2.1 CO2 capture……………………………………………………………………………….....23

2.1.1 CO2 capture from energy sector………………………………………………………...24

2.1.2 CO2 capture from industry……………………………………………………………...25

2.2 CO2 utilization……………………………………………………………………………….29

2.3 Challenges of existing CO2 capture technologies ……………………………………….......31

2.4 Hybrid CO2 capture processes……………………………………………………………….36

2.5 Cost progress for new CO2 capture technologies……………………………………………37

2.5.1 Cost learning curves……………………………………………………………………38

2.5.2 Technical evaluation of cost reduction for new technologies …………………………..39

2.5.3 Methodology for comparing CO2 capture costs………………………………………...41

2.6 Comparing costs …………………………………………………………………………….44

2.7 Use of LCOE increase to estimate the cost of CO2 avoided …………………………………45

2.8 Technology Readiness Level (TRL) and LCOE for CO2 capture technologies……………...46

2.9 Conclusions………………………………………………………………………………….51

CHAPTER 3. EXPERIMENTAL AND SIMULATION-MODELING STUDY OF THE CO2

CAPTURE PROCESS USING AMMONIA SOLUTIONS…………………………………………...53

3.1 CO2 capture process using ammonia solutions……………………………………................53

3.2 Advantages and limitations of the CO2 capture process based on ammonia solutions……….54

3.3 Case studies of using CO2 capture process based on ammonia solutions in the energy sector..57

3.4 The CO2 capture process chemistry based on ammonia solutions…………………………...61

3.5 Experimental process description……………………………………………………………63

3.6 Experimental process results………………………………………………………………...66

3.7 Process description in the simulation software………………………………………………67

3.8 Results and discussions……………………………………………………………………...70

3.8.1 The influence of the stream gases temperature on the CO2 capture process

indicators…….…………………………………………………………………………………...70


5

3.8.2 The influence of the ammonia solution temperature on the CO2 capture process

indicators…………………………………………………………………………………………79

3.8.3 The influence of the ammonia concentration temperature on the CO2 capture process

indicators…………………………………………………………………………………………85

3.8.4 Comparative analyses of the study cases……………………………………………….91

3.9 Conclusions………………………………………………………………………………….94

CHAPTER 4. TECHNICAL-ECONOMIC ANALYSIS OF THE CHEMICAL ABSORPTION

PROCESS INTEGRATION IN ENERGY SECTOR………………………………………………….97

4.1 Introduction………………………………………………………………………………….97

4.2 Thermodynamic model……………………………………………………………………...97

4.3 Pulverized coal combustion power plant description………………………………………..98

4.4 Capture process description………………………………………………………………..101

4.5 Performances evaluation of CO2 capture process…………………………………………..102

4.5.1 Absorption column……………………………………………………………………102

4.5.2 Desorption column……………………………………………………………………104

4.6 The integration impact of the capture technology on the power plant technical indicators…110

4.7 The integration impact of the capture technology on the power plant economic indicators...116

4.7.1 Specific economic indicators………………………………………………………....117

4.7.2 Economic-financial indicators………………………………………………………..123

4.8 Conclusions………………………………………………………………………………...129

CHAPTER 5. MULTI-CRITERIA MODEL FOR OPTIMAL CHEMICAL SOLVENT

SELECTION FOR CHEMICAL ABSORPTION PROCESS ………………………………………..133

5.1 Introduction………………………………………………………………………………...133

5.2 Life cycle assessment ………………………………………………...................................134

5.2.1 Data and information collection………………………………………………………134

5.2.2 Environmental indicators……………………………………………………………..139

5.3 Multi-criteria methodology description…………………………………………………....143

5.4 Application of the multi-criteria analysis method - Variant I ………………………………145

5.5 Application of the multi-criteria analysis method - Variant I I……………………………...151

5.5.1 Sensitivity analysis……………………………………………………………………155

5.6 Conclusions………………………………………………………………………………...166

CONCLUSIONS AND FUTURE PERSPECTIVES…………………………………………………169

ANNEXES……………………………………………………………………………………………173

A1. Thermodynamic models……………………………………………………………………….173

A2. Calculation power plant subcritical parameters ……………………………………………….176

A3. Economic-financial indicators………………………………………………………………...191

BIBLIOGRAPHY………………………………………………………………………………….....193


6

ACKNOLEGEMENT

I thank Professor Adrian Badea for opening this way for me, for it accepted to be my

doctoral supervisor, for all the confidence and support given during these years. I also want to

thank him for all the projects that I was involved in the Academy of Romanian Scientists.

I would like to express my sincere gratitude to Professor Cristian Dincă for all the

support given in all these years. I thank him for all the shared knowledges, for all the

confidence, patience and for motivating and encouraging me all the time to trust me and what

I can achieve through a lot of hard work and ambition. I thank him for always having time to

give me advice on all my research work. Also, I want to thank him for all the research projects

in which I was involved, for all the people I have met through him. I express my sincere

gratitude to him for having contributed to my professional development, both in terms of the

research part and the didactic part. Thank you, professor, for this period in which I have

evolved and thanks to collaboration with you I continue to progress and apply what I have

learned so far.

I thank all the professors from Power Engeneering Faculty with I have collaborated,

who have given me advice and for the trust granted.

I would like to thank all the commission members, for they agreed to evaluate my

doctoral thesis. I thank Professor Călin-Cristian Cormos for the introductory course in

Chemcad.

Finally, I express my immense gratitude to my family and dear friends for supporting

me and were being with me all these years.

KEY-WORDS

CO2 capture, power plant, integration, chemical absorption, ammonia solutions,

monoethanolamine, multi-criteria analysis, technical, economic and environmental indicators, optimal

chemical solvent, operating parameters, experiment, simulation, Chemcad, Aspen Plus.


7

SUMMARY OF PHD THESIS CHAPTERS CHAPTER 1. INTRODUCTION

Since the end of the 18th century, the volume concentration of greenhouse gases in the

atmosphere, especially CO2, has increased with about 40%. The main reason for the global

growth of greenhouse gases is due to the use of fossil fuels and global deforestation, from the

period called the Industrial Revolution, the year of the beginning of this period being considered

1750 [1]. The volume concentration of CO2 in the atmosphere increased from 280 to 392.6 ppm

(parts per million) in 2012. In May 2013, at the Mauna Loa atmospheric observatory in Hawaii,

considered the "gold standard" observer in the world, the volume concentration of CO2 in the

atmosphere was 400 ppm. It is for the first time, since the values regarding the volume

concentration of CO2 in the atmosphere are recorded, when a value of 400 ppm is reached.

Scientific analyzes suggest that atmospheric CO2 levels reached values up to 415 ppm in the

Pliocene era, between 5.3 and 2.6 million years ago. During that period, global average

temperatures were estimated to be 3 – 4°C higher than the current average and up to 10°C higher

at poles. Sea levels were estimated to be 5 to 40 m higher than at present [2]. The main effects

of increasing the concentration of greenhouse gases in the atmosphere are: the increase of the

average temperatures on the Earth's surface as a result of the absorption, by the GHG, of the

direct or reflected solar radiation; melting polar ice caps; rising sea levels.

The International Energy Agency (IEA) evaluates the role that low-carbon technology

options can play in transforming the current energy system. The 2012 edition of "Energy

Technology Perspectives" presents different scenarios on global warming [3]. The “2°C”

scenario (2DS) identifies the technological options and the political paths that ensure an 80%

limitation of the global temperature increase to 2°C on long term. [3]. This IEA analysis shows

that Carbon Capture and Storage (CCS) is an integral part of any cost reduction scenario, where

long-term average temperature increases are limited to less than 4°C, especially for Scenario

“2°C” (2DS). Thus, according to these forecasts the CCS must ensure a percentage of 16% of

the total CO2 emissions reduced by 2060. IEA indicates that removing the CCS as an option to

mitigate CO2 emissions would increase significantly the cost of the scenario objectives 2DS.

The additional investment needs in the energy sector to achive the 2DS requirements would

increase by another 40% if CCS technology were not implemented, the total costs in absolute

value reaching 2 trillion dollars. Also, without the implementation of CCS technology, the

pressure on other options to reduce CO2 emissions would be greater.

The IEA Scenario for Sustainable Development presents a path to achieving long-term

climate change objectives. In this scenario, global emissions must reach a peak and drop sharply

by 2020, this reduction will now have to be even greater, given the increase in emissions in

2017. The share of energy sources with low carbon emissions must increase by 1.1 percentage

points each year, more than five times higher than the growth recorded in 2017. Especially in

the energy sector, the amount of energy produced from renewable sources must increase by

approximately 700 TWh annually in this scenario, compared to the increase of 380 TWh

registered in 2017. Carbon Capture, Utilization and Storage (CCUS) have an important role in

reducing emissions in the industrial and energy sector.

Thesis motivation

In the context of the need to reduce greenhouse gases and increase energy consumption

globally, CO2 capture technologies are a solution found in all proposed scenarios worldwide,

to reduce carbon dioxide emissions. Thus, it is necessary to continue studying, developing and

proposing new capture methods, in order to reduce the negative technical, economic and


8

environmental effects that these technologies have after being integrated into an energy or

industrial process.

Purpose and objectives of the thesis

The purpose of this PhD thesis is to identify the optimum capture technology according

to the technical, economic and environmental criteria, which can be integrated into the existing

power plants. Thus, in this study we analyzed the post-combustion integration of a CO2 capture

process based on chemical absorption using as a chemical solvent an ammonia solution, also

compared this process with the conventional process based on amines (reference process -

monoethanolamine with a mass concentration of 30%).

The thesis is structured in 5 chapters. The first chapter includes a brief introduction on

global CO2 emissions and their provenance, energy mix and energy consumption globally, and

the measures to be implemented to achieve the goals set at European and global level to reduce

greenhouse gas emissions.

In the second chapter are presented the capture technologies and their development stage

(the technology readiness level), as well as the implementation in the energy sector and in the

industry, and some aspects regarding the use of carbon dioxide after its capture. General

economic aspects are also discussed regarding the investment costs and the impact on the cost

of electricity produced.

In the third chapter the process of CO2 capture was studied using ammoniacal solutions,

both experimentally and through simulation/modeling. The objective of this study was to

determine the optimal process parameters, such as the temperature of the flue gas, the

temperature of the ammonia solution and the mass concentration of NH3 in the solution, to

diminish the negative effects of the integration of the capture process (energy consumption,

ammonia loss in the absorption process, the dimensions of the absorption/desorption column)

in an energetic process.

Thus, after establishing the optimal parameters of the capture process based on ammonia

solutions, in the fourth chapter we analyzed the integration of such a process in a power plant

with the subcritical parameters of 200 MW. The effects of integration were analyzed according

to the technical and economic criteria, and compared this process with other methods of CO2

capture.

In chapter 5, a multi-criteria analysis was performed for choosing the optimum carbon

dioxide capture process for a power plant, for choosing the solution that has the least impact on

the technical, economic and environmental indicators.

CHAPTER 2. CURRENT STATUS OF CO2 CAPTURE TECHNOLOGIES

Carbon dioxide can be separated depending on the positioning of the capture technology

into power plant. There are three methods of capture, namely, post-combustion, pre-combustion

and oxy-combustion capture. The energy sector, being the largest generator of CO2 emissions,

also has the greatest potential for reducing them, by integrating capture technologies. The

separation of CO2 depends mainly on its partial pressure and its concentration in the gas

mixture, so different capture methods have been developed, such as: chemical absorption,

physical absorption, membranes, adsorption, cryogenics and combinations thereof.

Post-combustion capture by chemical absorption using amines is the technology that

has been commercially validated. The main drawback of this technology is the energy

consumption for the chemical solvent regeneration. Even though significant progress has been

made in energy consumption, in the 1980s studies showed that an amount of about 4.1 GJ was


9

needed to separate a ton of CO2, and today there has been a consumption between 2.5-3.5

GJ/tCO2 (depending on the amine used in the process), there is still a barrier to large-scale

implementation. Because, after integrating this technology into a power plant, the overall

efficiency decreases by up to 20%, having a direct impact on the cost of electricity produced.

It is also important to reduce emissions from the industrial sector, as they represent about 35%

of the global total. Thus, most of the capture projects implemented were in the following

industries: natural gas processing, fertilizer production, hydrogen production, iron and steel

production, chemical manufacturing.

In recent years, the concept of Capture, Utilization and Storage of Carbon (CCUS) has

appeared, because we are looking for solutions of use, not only its storage. The greatest potential

for CO2 utilization is improved oil and gas recovery, but this method of use has several

restrictions, such as geographical constraints, which also occur at storage sites. Thus, to support

this area, the European Union has launched several Horizon 2020 projects on the use of carbon

dioxide for the production of fuels, chemicals and intermediates.

In addition to the high energy consumption associated with regeneration, there are other

limitations of existing capture technologies, such as: additional energy requirement for CO2

compression (for transportation), corrosion of equipment, degradation of chemical solvents (for

example amines), negative environmental impact of chemical solvent emissions. However,

theoretically the thermal energy required for post-combustion capture is much lower, compared

to today's requirements, so it is shown that possibilities of reducing the energy related to the

capture process. In addition, to limit the disadvantages enumerated, some studies have focused

on the development of new solvents, to improve the absorption rate, absorption capacity and

regeneration energy.

Following an assessment of the capital costs for a coal-fired power plant (PC) and for a

integrated gasification combined cycle (IGCC), the cost per unit of capture for IGCC is

substantially lower than in CP case, but the total cost of the IGCC plant with CO2 capture is

higher than the total cost of a CP installation, because the other parts of the IGCC have higher

costs (air separation unit, gasification unit, combined cycle). However, at present these costs

are subject to significant uncertainty, because when these technologies are used in commercial

scale, the costs can change.

The existing technologies can be evaluated by the technology readiness level (TRL), so

if they are in the research stage they can have a TRL between 1-3, if they are in the development

stage they can have a TRL between 4-6, and if is in the demonstration stage can have a TRL

between 7-9. In the case of post-combustion capture, the reference technology

(monoethanolamine process) has a TRL of 9, and the conventional conventional solvents have

a TRL between 6-8. It should be noted that, the readiness level of a technology does not

necessarily show the term until the commercialization of a technology, because it does not show

the degree of difficulty in solving the problems occured from the development of a technology

and does not take into account the costs related to these technologies.

CHAPTER 3. EXPERIMENTAL AND SIMULATION-MODELING STUDY OF THE

CO2 CAPTURE PROCESS USING AMMONIA SOLUTIONS

The ammonia-based solvent can be a promising and alternative solvent for CO2

separation, it is one of the most used chemicals in the world, it offers several advantages such

as [4, 5]:

High CO2 absorption capacity, with a theoretical ratio of 1 mol CO2/1 mol NH3, which can

increase the cyclic CO2 capacity of the NH3 solvent and reduce the circulation rate of the

solvent;


10

There is no thermal and oxidative degradation, thus it is allowed to regenerate the solvent

based on NH3 at high temperatures and pressures;

The purchase cost of NH3 is lower compared to the purchase cost of amines;

The thermal energy requirement for NH3 solvent regeneration is lower, ranging from 0.93-

2.9 MJ/kgCO2, compared to the MEA solvent ranging from 3.7-4.2 MJ/kgCO2 [6, 7];

Simultaneous separation of acid pollutants, such as SOx, NOx, HCl and the production of

value-added products, such as ammonium sulphate and ammonium nitrate, products that

are used as fertilizers in the agricultural industry on a large scale.

Experimental process description

The experimental study was conducted on existing pilot plant in the Laboratory of

Renewable Energy, Power Engeneering Faculty. The technical specifications of the pilot

installation are the following: thermal load: 75 kWt; fuel feed rate: up to 20 kg/h (depending on

fuel type and particle size); combustion air flow: up to 175 m3/h; combustion chamber gas

temperature: 850-1000°C.

The pilot plant is the only one on this scale in Romania (Figure 1). One of the facilities

of pilot plant is the separation of CO2 from the flue gases. The CO2 capture module based on

the chemical absorption process (designed for the use of amines) is located after the combustion

and desulfurization section of the flue gases. The regeneration of the chemical solvent used is

gradually achieved by recovering the heat of the flue gas and by using an electric re-boiler in

order to increase the temperature of the solvent in the desorption unit (up to 90-100°C).

Figure 2 shows the schematic diagram of the pilot installation existing in the laboratory.

The diagram shows different measurement points for: pressure, temperature, analysis of flue

gases and analysis of the CO2 rich loading solvent; and flows of: water, fuel (natural gas, lignite,

biomass) and chemical solvent.

The pilot installation was designed modularly, including the following sections: The

fuel injection system in the boiler; Primary and secondary air supply systems, as well as air

blower; A vertically fluidized bed that supplies the natural gas burner and a screw hopper for

lignite supply; Flue gas cleaning unit consisting of: precipitating cyclone, desulphurisation unit,

CO2 absorption unit and a modular desorption unit; Bottom ash cooling equipment; The flue

gas cooling system; Separation of CO2 and SOx by the use of solvents and sodium hydroxide,

the circulation being performed by the use of pumps; Cooling of the lean CO2 solvent in the

metal plate heat exchanger before entering the CO2 absorption unit.

The aim of the experiment was to determine the CO2 capture efficiency for different

weight concentrations of ammonia in solution. Because the pilot plant was designed for the

capture process by chemical absorption based on amines, which takes place at a temperature

between 40-50°C, in the case of the use of the ammonia solution there is a significant loss at

this temperature, the experiments performed were limited. In addition to the losses in the

absorption column, the losses in the desorption column are also added, due to the desorption

process at atmospheric pressure. In both the experiments and the simulations, lignite (extracted

from the Jiu Valley) was used with the elementary mass composition and the mass composition

of the flue gases presented in Table 1.


11

Figure 1. CFBC experimental pilot plant with post-combustion CO2 capture

Coal/bioMass

tank

Ante-chamber

Fan

Ash recirculation

device

Ash recirculation

cyclone

Convective unit

HeX

Cyclone

HeXRe-

boiler

NaOH tank

Rich solvent

tank

Lean solvent

tank

T

P

T

P

T

P

TT

T

T

T

T

P

P

T

P T T T

TP

T

T

T

T

T

T

T

P

AG

AG

P T

AG

LegendNatural gas

Fuel/Flue gases

Water

Rich solvent

Lean solvent

Rich NaOH

Lean NaOH

T Thermocouple

P Pressure senzor

AG

d

d Flow meter

Gas analyzer

De

sulf

uri

zati

on

un

it

Ab

sorp

tio

n u

nit

Co

mb

ust

ion

ch

am

be

r

Figure 2. Schematic diagram of CFBC pilot installation

Table 1. Mass composition of fuel and flue gases

Lignite mass composition

C

[%]

H

[%]

S

[%]

O

[%]

N

[%]

W

[%]

A

[%]

PCI

[kJ/kg]

23 1 1 1.6 1.5 35.5 36.4 7913

Flue gasses mass composition

CO2

[%]

N2

[%]

H2O

[%]

O2

[%]

12 75.5 8 5.5

Experimental process results

In the experimental process the CO2 capture efficiency was determined for 4 weight

concentrations of NH3 in solution, respectively for 5, 10, 15 and 20%, for the same ammoniacal

solution flow rate. Five sets of analyzes of the flue gases concentration were performed before

and after the absorption column, and the results were compared with those obtained in the

process simulation for a process temperature between 25-45°C (Figure 3).


12

Figure 3. CO2 capture efficiency depending on weight concentration of NH3 in solution

The graph shows the minimum value, the maximum value and the average for the 5 sets

of experiments, and respectively for the 4 weight concentrations studied. It is observed that the

capture efficiency increases with the increase of the NH3 weight concentration for all the

analyzed cases, both in the experimental process and in the simulated process. It can be

observed that there are no very significant differences between the values obtained in the

experimental process and in the simulation. Table 2 shows the standard deviations for each

measurements set, obtaining values between 1.49-1.72, and how much of the experiments is

between average and standard deviation. Thus, for 3 of the 4 wight concentrations, 80% of the

values of the experiments is between within this range.

Table 2. Standard deviation (σ)

Data Parametru

NH3 concentration, [wt.%]

5 10 15 20

CO2 capture efficiency, [%]

Experimental set

Minimum value (x) 23 44 64 79

Maximum value (x) 28 49 68 84

Average value, �� 25 46.4 65.4 81.8

σ 1.6733 1.6248 1.4967 1.7205 (�� − 𝜎; �� + 𝜎), [%] 80 80 80 60

Simulation set 29 52 73 90

Process description in the simulation software

The CO2 capture process based on ammonia solutions can be divided in 5 stages: 1. Flue

gases cooling; 2. CO2 absorption process in aqueous ammonia solution; 3. NH3 recovery

process from the treated flue gases; 4. The regeneration process of the ammoniacal solution rich

in CO2; 5. CO2 pure compression.

The schematic diagram of the CO2 capture process based on ammonia solutions is

shown in Figure 4. For optimal functioning of the CO2 capture process using ammonia solutions

the temperature of the CO2 absorption process in the absorption column is preferable to be in

the range 1-20°C. For this reason it is necessary to cool the flue gases from a power plant, which

usually have a temperature of 110-120°C, before entering the absorption column. Thus, after

the desulfurization process, the flue gases are passed through a direct contact cooler (DCC)

where are cooled. At the top of the cooling tower, cold water is sprayed which comes into

contact with the flue gases introduced at the bottom of the tower. Water is collected at the

bottom of the DCC, being recirculated after cooling. The flue gases leave the DCC at the bottom

of it, and before entering the absorption column, they are also passed through liquid coolers to

reduce the temperature in the range of 50-20°C.

0

10

20

30

40

50

60

70

80

90

100

0% 5% 10% 15% 20% 25%

CO

2ca

ptu

re e

ffic

ien

cy, [

%]

NH3 concentration, [wt.%]

simulation

min

max

average


13

The simulation of the CO2 capture process based on ammonia solution was carried out

in the Chemcad software. For the liquid phase, the thermodynamic package ELECNTRL was

used, and for the vapor phase the Redlich-Kwong state equation was used. The simulation of

this process was performed for treating the flue gases from a lignite-based power plant extracted

from the Jiu Valley, with the elementary mass composition presented in Table 1. The main

technical indicators considered for evaluation the process separation performances were: CO2

capture efficiency; L/G ratio; The amount of NH3 lost in the process; Energy requirements for

regeneration of CO2 rich ammonia solution; Energy requirements for cooling of flue gases;

Energy requirement for cooling the ammonia solution low in CO2.

C

C

R

C

C

R

Direct

contact

coolerCold

water

Refuse

water

Flue

gases Cooler

CO2 rich solution

Pump

Cooler

Cooler

Cooler

Heat

exchanger

CO2 lean solution Reboiler

Reboiler

Pump

Heat

exchanger

Valve

Ammonia rich

solutionAmmonia lean

solution

Ammonia wet

scrubber

Cold water

Recycled water

Recycled

ammoniaClean flue

gasesAmmonia/

water vapour

Ammonia

absorber Ammonia

stripper

CO2 wet

scrubber

Cold

water

Pure CO2

Recycled aqueous

ammonia

CO2

absorber

CO2

stripper

Contaminated

CO2

Make-upAmmonia/

water

Flue gases

CO2 removal

NH3 slip

abatement

Pump

Figure 4. Schematic diagram of CO2 capture process based on NH3

The influence of the stream gases temperature on the CO2 capture process indicators

In the capture process using an ammonia solution, the temperature at which the

absorption process takes place is an important parameter, influencing CO2 separation process

performances. Thus, in this subchapter we studied the influence of the flue gases temperature

at entering the absorption column on the capture process indicators. The flue gases temperature

at the entrance to the absorption column was considered to be 50, 40, 30 and 20°C. In order to

analyze the influence of the flue gases temperature on the capture process performances, the

ammonia solution temperature at the entrance to the absorption column was kept constant,

respectively at 20°C and the NH3 weight concentration in the solution.

In Figure 5 there are presented the results obtained for the capture efficiency according

to the L/G ratio and the flue gases temperature. It is observed that the CO2 capture efficiency

increases with the increase of the L/G ratio, because a higher quantity of ammoniacal solution

is introduced to treat the same amount of flue gases. The ammonia amount released with the


14

treated flue gases is influenced by the temperature at which the absorption process takes place,

as shown in Figure 6. Thus, lower process temperatures are preferable, for re-use of higher

ammonia amounts in the process.

Figure 5. CO2 capture efficiency according to

the L/G ratio

Figure 6. The NH3 amount lost according to

the CO2 capture efficiency

Figure 7. CO2 capture efficiency and NH3

losses

Figure 8. Total energy consumption

according to the L/G ratio

In Figure 7 there are presented comparatively the capture efficiency and NH3 losses in

the absorption column. It is observed that there is not the same percentage increase of

efficiency, even if the temperature of the flue gas has a constant decrease of 10°C. After

determining the energy consumption of the all process, the total energy consumption was

calculated reported one tonne of captured CO2. Thus, Figure 8 shows the variations of the total

energy consumption according to the L/G ratio and the flue gases temperature. It is observed

that the lowest values were obtained for the lowest value of the flue gas temperature, regardless

of the L/G ratio, because it is reported to a higher quantity of CO2, the capture efficiency having

an increase of over 50% for a constant L/G ratio.

The influence of the ammonia solution temperature on the CO2 capture process indicators

The CO2 capture process indicators were analyzed according to the ammonia solution

temperature introduced in the absorption column. In this case, the flue gases temperature at the

inlet to the absorption column and the weight ammonia concentration in solution were

considered constant. The flue gases temperature was considered 20°C due to at this temperature

the best results were obtained in terms of the capture efficiency and the amount of ammonia

lost.

Figure 9 shows the capture efficiency according to the L/G ratio if the temperature of

the ammonia solution changes. As the temperature decreases, the CO2 absorption process is

more efficient in terms of the amount of ammonia used in the process, so for the same efficiency

of capturing at lower temperatures a smaller amount of ammonia is used. Another positive

effect of lowering ammonia solution temperature is that a smaller amount of ammonia is

evaporated in the treated flue gases (Figure 10), and thus it can remove the recovery system to

be implemented if the evaporated quantity is too high, having a negative impact on the


15

environment and on the costs with the addition of a new quantity of ammonia in the process to

maintain the separation efficiency.


the L/G ratio




losses



Figure 11 shows the results obtained for the capture efficiency and the NH3 losses for a

constant L/G ratio, to 0.4 kgsolNH3/kgf.g. It can be observed that in this case, the percentage

increase of efficiency is 6.27%, from a temperature of 20°C to a temperature of -1°C, much

lower than in the case of the decrease of the temperature of the flue gases. In Figure 12 it is

presented the total consumption reported to the amount of CO2 captured. No significant

differences are observed between the analyzed situations, even though in the case of energy

consumption for regeneration and for cooling the solution significant differences were

observed, because with the decrease of the temperature of the absorption process, the amount

of CO2 is higher.

The influence of the ammonia concentration temperature on the CO2 capture process

indicators

The influence of the weight ammonia concentration in solution on the performances of

the capture process was analyzed below. The NH3 mass concentration was considered to be 5%,

10%, 15% and 20%.

Figure 13 shows how efficiency increases with increasing L/G ratio, but with decreasing

NH3 weight concentration in solution a higher L/G ratio is needed to maintain the same

efficiency. Instead, the decrease of the NH3 weight concentration in the solution has a positive

influence on the amount of NH3 lost, therefore at lower weight concentrations a smaller amount

of NH3 is evaporated (Figure 14). In the case of the total energy consumption (Figure 16), for

higher NH3 weight concentrations a smaller amount of energy is needed, and also these

consumptions have an increasing rate as the L/G ratio increases, regardless of the NH3 weight

concentration.


16


the L/G ratio




losses



Comparative analyses of the study cases

The following is presented an analysis of the cases studied from the point of view of the

capture process performances using ammonia solutions for a carbon dioxide capture efficiency

of 90%. The parameters of the analyzed cases are presented in Table 3.

Table 3. CO2 capture process parameters

Parameter 1 2 3 4 5 6 7 8 9 10 11

Tf.g,°C 50 40 30 20 20 20 20 20 20 20 20

TsolNH3,°C 20 20 20 20 15 10 5 -1 -1 -1 -1

NH3,wt.% 20 20 20 20 20 20 20 20 15 10 5

Figure 17 shows the results obtained regarding the L/G ratio for the analyzed cases. It

is observed that the lowest ratio was obtained in variant 8, where the temperature of the flue

gas is 20°C, the temperature of the ammonia solution is -1°C, and the mass concentration of

ammonia is 20%. The amount of ammonia evaporated and evacuated with treated flue gases

depends on the temperature at which the process takes place in the absorption column, so in

Figure 18 is represented the amount of ammonia lost for the 11 cases, expressed in kg/h and the

percentage lost from the initial quantity. It is observed that this has a decreasing allure, which

indicates that Case 11 is optimal from this point of view, with the smallest value.

The energy requirement for the process, both for the ammonia solution, as well as for

the cooling of the flue gas and the solution is shown in Figure 19. If the cases are classified only

according to the thermal energy consumption in the regeneration process, the optimal is the

Case 8. On the other hand, if it is classified according to the total consumption the optimal is

Case 1, but in this variant the amount of ammonia lost is the highest.


17

Figure 17. L/G ratio Figura 18. NH3 losses

Figure 19. Energy consumption for CO2 capture efficiency of 90%

CHAPTER 4. TECHNICAL-ECONOMIC ANALYSIS OF THE CHEMICAL

ABSORPTION PROCESS INTEGRATION IN ENERGY SECTOR

Pulverized coal combustion power plant description

The characteristics of the gases treated are from a coal-fired power plant (PC). The

reference power plant is a PC of 200 MW, with subcritical parameters, modeled in Aspen Plus.

The power plant characteristics are presented in Table 4, and the coal composition used in Table

5.

Table 4. Power plant characteristics with subcritical parameters

Characteristic Unit measure Reference PC

Power installed MW 200

Annual operating h/an 7500

Preheating stages - 7

Intermediate preheating - 2

Electric power MWh/an 1 346 425.27

Steam pressure bar 200

Steam temperature °C 580

Condenser pressure bar 0.054

Condenser temperature °C 34.25

Steam flow kg/s 149.343

Generator losses MW 2.607

Generator efficiency % 98.71

Mechanical losses MW 0.820

Internal power steam turbine MW 203.427

Mechanical efficiency % 99.60

Internal mechanical work of 1 kg steam kJint/kg 1 364.5


18

Heat of 1 kg steam kJ/kg 2 819.63

Specific energy of 1 kg steam kJel/kg 1 341.6

Thermal efficiency % 48.4

Gross efficiency % 47.58

Net efficieny % 42.44

Coal flow kg/s 19.03

Flue gases flow kg/s 241.32

Annual CO2 emission tone/an 788670

Emission factor kgCO2/MWh 585.76

Table 5. Coal composition

Elementary analysis (wt.%)

C H O N S A W

58.00 2.00 1.80 1.00 0.80 18.30 18.1

Low heating value

LHV = 21 421 kJ/kg

The integration impact of the capture technology on the power plant technical indicators

The integration of the CO2 capture process by chemical absorption in a thermoelectric

power plant has a significant impact on its overall efficiency, decreasing the overall efficiency

due to the energy required in the regeneration process and for cooling the flue gas and the

chemical solvent. In this analysis, the electric energy required for the cooling process was not

taken into account. The power installed for the reference case is 200 MW, decreasing for the

cases with CO2 capture, depending on the NH3 concentration in solution or the type of amine

used.

The capture process based on NH3 was analyzed for different weight concentrations of

2, 5, 7, and 15%, comparing the results obtained with the reference process based on MEA of

30% weight concentration. All presented results are for CO2 capture efficiency of 90%. The

thermodynamic cycle analysis was performed for two cases:

1. Fuel=ct. In this case it was used the same amount of fuel.

2. Power=ct. In this case it was used the power installed was maintained constant.

Figure 20 shows the fuel amounts needed for the two cases analyzed. In the case of the

fuel amount was constant, a fuel flow of 19.03 kg/s is required, to have a power of 200 MW at

the generator terminals. If the power installed was constant, the fuel amount needed increased,

obtaining the highest fuel amounts for the NH3 weight concentration in solvent of 2%,

respectively of 22.79 kg/s of fuel, and when used monoethanolamine in weight concentration

of 30%, respectively a fuel requirement of 23.66 kg/s.

Figure 21 shows the results obtained for net efficiency before and after integrating the

CO2 capture process. Before the capture process integration the net efficiency of the power

plant is 42.44%. After integration the net efficiency decreased up to 33% for NH3 = 2 wt.% and

for MEA=30 wt.%. Even if the better results were obtained when using higher weight

concentrations of NH3 in solution, it is not preferable to choose a weight concentration higher

than 7%, due to the volatilization of ammonia in the absorption process.


19

Figure 20. Fuel flow Figure 21. Net efficiency

The integration impact of the capture technology on the power plant economic indicators

In this study, the specific economic calculated are the following: levelized cost of

electricity – LCOE; CO2 capture cost per ton; LCOE with CO2 tax emissions. The investment

costs for the power plant without the CO2 capture process are 2497 €/kW, and after the

integration are 4333 €/kW. The price of the used fuel was considered of 55 €/t, the discount

rate of 8%, and the lifespan of 30 years. An important advantage of using ammonia in the of

chemical absorption process consists in the low purchase price, respectively of 0.672 €/kg,

compared to the purchase price of MEA, of 2 €/kg.

The LCOE in the case of power plant without capture process is 42.48 €/MWh. The

variations of the levelized cost of electricity and the CO2 capture cost for the fuel constant case

are shown in Figure 22. After the integration of the capture process, LCOE had the highest

increase in the case of MEA, up to 95.46 €/MWh. In the case of using ammonia, the highest

electricity price was obtained for a NH3 weight concentration in solution of 2% (87.68

€/MWh)). In the case of a weight concentration of NH3=15%, both LCOE and CO2 capture cost

are higher because the ammonia amount used in the process is higher due to degradation.

In Figure 23 there are presented the values obtained for the LCOE and CO2 capture cost

in the case the power installed was constant. As in the previous case, the same variations are

observed. The CO2 capture cost per ton varied between 49-67 €/tCO2, and the LCOE varied

between 71-82 €/MWh, obtaining the lower costs in the case of ammonia use.

Figure 22. Levelized cost of electricity and

CO2 capture cost for Fuel=ct.

Figure 23. Levelized cost of electricity and

CO2 capture cost for Power=ct.

Further an analysis is presented of the electricity cost in case of considering the price

for one tonne of carbon. Now, due to the energy regulations regarding the reduction of

greenhouse gases, a tax is applied for the carbon dioxide emitted in the atmosphere from the

power plants. CO2 tax varies depending on the certificate market and the amount of electricity

required worldwide. According to the source [8], in 23.05.2018 the CO2 emissions tax was

15.81 €/tCO2, and in 22.05.2019 the tax reached 25.40 €/tCO2. Thus, in this analysis was

considered the price of one tonne of CO2 emitted in the atmosphere between 0 and 120 €/tCO2,

in order to observe when the integration of the process of capture by chemical absorption is


20

better in terms of levelized cost of electricity, compared to the case in which the capture process

is not integrated and the CO2 tax is paid.

Figure 24 shows the levelized cost of electricity for the power plant (Fuel=ct.) with and

without integration of the capture process, according to the NH3 concentration in solution and

according to the CO2 emission tax. For PC with CAP (CO2 emissions tax is avoided in this

case), the price of electricity decreases with the increase of the NH3 weight concentration in

solution, up to a weight concentration of 7%, for a weight concentration of 15% a slight increase

of LCOE is observed. When the CO2 tax is about 61 €/MWh, the LCOE is higher than if the

capture process is integrated, for NH3 weight concentration in solution of 5, 7 and 15%. For a

weight concentration of NH3=2%, the price of one tonne of CO2 emitted must be greater than

90 €/MWh, so that the LCOE with capture to be less than LCOE without the capture process.

For the reference capture case (MEA=30 wt.%), the LCOE value obtained was 96.35 €/MWh,

if the value of the CO2 emissions tax exceeds 110 €/tCO2 is more economically convenient and

this solution.

Figure 2. Levelized cost of electricity for PC

w and w/o CAP (Fuel=ct.)

Figure 25. Levelized cost of electricity for PC

w and w/o CAP (Power=ct.)

In the case of Power=ct. (Figure 25), due to lower levelized cost of electricity, compared

to the case of Fuel=ct., for a CO2 tax of approximately € 60/MWh, all cases in which ammonia

is used they are better in terms of the LCOE. In the case of MEA=30 wt.%, a lower LCOE is

obtained only if the CO2 tax is higher than 80 €/MWh (LCOEMEA=81.91 €/MWh). Thus, if the

cost of one tonne of CO2 emitted continues to increase (it has increased in the last decade,

reaching an average of 25 €/MWh today) [8], capture technologies can become a reliable

alternative for reducing the CO2 emissions from thermoelectric power plants.

In order to say if an investment project, in this case the thermoelectric power plant with

and without carbon dioxide capture, is feasible, an economic-financial analysis is needed in

which to consider all the cash flows entered and exit the set counter. The economic-financial

indicators determined in this analysis are the following: Net Present Value – NPV; Internal Rate

of Return – IRR; Gross Capital Recovery – GCR; Net Capital Recovery – NCR; Profitability

Index – PI.

Regarding the economic criterion NPV, from Figure 26 it is observed that without the

carbon dioxide capture technology integration, the project is profitable up to a value of CO2

emission tax of 120 €/tCO2, after this value the NPV is negative. In the case of solutions with

capture processes, it is observed that the capture process using ammonia solution has higher

values for NPV compared to solution without capture process, from a CO2 emissions tax of 80

€/tCO2. The NH3 capture solutins are economically better than the solution based MEA, due to

the amount of solvent regeneration required is smaller, and thus a smaller amount of fuel is

used to produce the same amount of electric energy, resulting lower fuel consumption costs.

Another advantage of capture solutions based on NH3 consists the purchase cost of ammonia

(it is much lower than the purchase cost of monoethanolamine).


21

Regarding the internal rate of return the results obtained are presented in Figure 27. In

this case, if the CO2 emissions tax is higher than € 100/tCO2, the solution based NH3 in weight

concentration of 7%, is better than the solution without CO2 capture technology. For the solutins

based on NH3 in weight concentration of 2, 5 and 15%, there are no significant differences

between the values obtained for IRR. All solutins based on NH3 are better in terms of the IRR

indicator, compared to the solution based on MEA, as in the case of the NPV indicator.

For the economic indicators GCR and NCR, the obtained results are presented in Figures

28 and 29. For the solution without capture technology, GCR has values between 6-13 years,

having increasing values with the increase of the CO2 emissions tax. In the case of NCR, there

was obtained values between 9-29 years. The period after which the investment is recovered is

higher in the case of NCR, compared to the GCR, because with the levelization, the cash flows

are smaller. For solutions based on NH3, NCR values are between 15-19 years. In the case of

the solution based MEA, NCR are between 17-21 years. Only in the case of solution without

capture process, the investment project is no profitable for a CO2 emissions tax higher than 120

€/tCO2, because the investment recovery time is longer than the life of the energy installation.

Figure 26. Net present value Figure 27. Intern rate of return

Figure 28. Gross capital recovery Figure 29. Net capital recovery

Since, at present, the CO2 emissions tax is 25 €/tCO2, the values obtained for NPV and

NCR in this situation are presented below.

It is observed (according to Figure 30), at this value of the CO2 emissions tax, the net

present value in the case of the thermoelectric power plant without the capture process

integration, is higher than in the case the capture process is integrated, having a value of 598

mil. €. In the case of solutions with capture process, the net present value decreases up to 219

mil. € (MEA=30 wt.%), due to investment costs, the maintenance and operating costs increase,

the revenues realized being the same for all systems energy analyzed. For the capture process

using NH3, the net present values is between 286 and 310 mil. €, with NPV decrease of

approximately 50% compared to the solution without CAP. The best solution based on NH3 is

for weight concentration of 7%, followed by the solutions of 5 wt.%, 15 wt.% and 2 wt.%.

Regarding the term of the net capital recovery (Figure 31), for the solution without CAP,

the investment is recovering after approximately 9 years. As in the case of NPV, in the NH3-

based solutions, the recovery time of the investment is double compared to the version without

CAP, of 16 years. In the case of the solution based on MEA, the investment is recovered after

approximately 18 years.


22

Figure 30. Net present value Figure 31. Net capital recovery

CHAPTER 5. MULTI-CRITERIA MODEL FOR OPTIMAL CHEMICAL SOLVENT

SELECTION FOR CHEMICAL ABSORPTION PROCESS

Choosing the competitive process for CO2 capture from power plant depends on the

characteristics of the type of fuel used, the CO2 capture process performance and economic

scenario considered. Previous studies have focused on the development of CO2 capture

processes, and on reducing the costs associated with integrating the capture process in

accordance with reducing energy consumption for chemical solvent regeneration. [9, 10, 11,

12]. However, considering the concept of sustainable development, focusing only on the

technical and economic aspects is not sufficient for optimum choice of carbon capture process.

In this context, the problem of identifying the ecological influence of the CO2 capture processes

integration in power plants was raised.

In this chapter, life cycle assessment (LCA) is used to collect data for the analyzed

energy systems. In the paper [13], the LCA methodology was applied to technically and

economically compare different life cycles of energy systems based lignite with CCS

technology. In the paper [14], an algorithm was developed to optimize the specific annual total

cost of a post-combustion CO2 capture technology by chemical absorption process.

The purpose of this chapter is to apply a multicriteria model for the selection of the

optimum chemical solvent, taking into account technical, economic and ecological indicators

for a coal-fired power plant. The emphasis was on highlighting the effects of integrating post-

combustion CO2 capture technology with chemical absorption using ammonia in different

weight concentrations, and monoethanolamine in weight concentration of 30%. Thus, we

analyze the effects of reducing CO2 emissions on the increase of capital costs of the power plant

and respectively on the increase of the electricity cost, but also on the general impact on the

environment generated by the pollutants from the process of CO2 capture by chemical

absorption process.

The cases that were considered in the multi-criteria analysis are the following: NH3 in

weight concentration of 2%; NH3 in weight concentration of 5%; NH3 in weight concentration

of 7%; NH3 in weight concentration of 15%; MEA in weight concentration of 30%.

Life cycle assessment

The life cycle assessment is used to collect the data and information of this study.

According to this methodology, the first step consists in clearly identifying the study field of

studied systems (Figure 32). Also, all the incoming and outgoing flows from the processes

taking place in the study field were identified [15]. The data collected, as well as the results

obtained for the analyzed energy systems, are reported to the functional unit (U.F.). In this

study, the functional unit is represented by the amount of annual electricity produced by the

power plant. It was considered the case for Power=constant, in order to have the same amount


23

of energy produced for all the analyzed energy systems. The annual amount of electricity

produced is 1 346 400 MWh/year (U.F.=1 346 400 MWh/year).

Figure 32 shows the limits of the analyzed energy system. The energy system was

analyzed with and without CO2 capture by chemical absorption. In this analysis, the steps of

compression, transport and storage of carbon dioxide were not considered. The distance of

transport of the fuel, from the extraction zone to the area of energy production was considered

250 km.

Extration+Treatment+Transport+Distribution

Fuel combustion

Natural gasCoal

Power turbines

Fuel gas clean-up

CO2 capture unit

Compression unit

Electricity generation

Chemical solvent (MEA)

Emissions

CO2 transport

CO2 storage

CO2

CO2

CO2CO2Flue

gasses

Thermal energy

Electricity

Material flux

Figure 32. Processes considered in the life cycle assessment

Environmental indicators

The quantified impact classes are: a. Abiotic Depletion Potential – ADP, Climate

change - GWP, Eutrophication - EP, Acidification - AP, Photochemical oxidant formation –

POCP, Human toxicity – HTP.

The results of the impact indicators are presented below. They quantify the emissions

from two stages of the fuel life cycle, respectively from the extraction, treatment, transport and

combustion stage. In the case of ADP, only the fuel amount from the extraction stage was taken

into account. From Figure 33 it can be seen that this indicator increased compared to the

reference case (power plant without CO2 capture technology) for all the cases in which the

capture process is integrated. In the case of the ammonia, the highest increase of the ADP

indicator was for a weight concentration of 2%, because in this case the amount of thermal

energy required for regeneration is the highest, and thus a greater amount of fuel is used for the

production the same electricity amount. When comparing the chemical absorption process

using NH3 with MEA in weight concentration of 30%, it is observed that in the case of MEA,

the value of the ADP indicator is the highest, having an increase of 24.3% compared to the

reference case.

The results obtained in the case of climate change are shown in Figure 34. The highest

value was obtained for the case without CAP, because in the other cases the CO2 capture process

was integrated, and thus the CO2 emissions were reduced by 90% in the combustion stage. For

the cases with the CO2 capture process, the GWP values did not show significant differences,

being between 127000 – 157000 techiv_CO2/U.F, with a decrease between 85-89% of this

indicator for the life cycle. Only in the case of this indicator, the percentage of emissions from

the combustion stage participating in the total value is 87.43%, and the remaining 12.57%

represents the emissions from the extraction, treatment and transport stages. For the other

indicators, the emissions from the combustion stage have a percentage of over 96%.

The results obtained for EP are shown in Figure 35. It is observed that in the case of this

indicator, the increases are significant in the case of the integration of the chemical absorption

process based on NH3, due to the amount of ammonia lost in the CO2 capture process is taken

into account. Thus, compared to the case without CCS, for a weight concentration of NH3=2%,

there was an increase of 206.6%, for a weight concentration of NH3=5%, an increase of 579.7%,

for a weight concentration of 7%, an increase of 924.3%, and for a weight concentration of

15%, an increase of 3533.2%, which shows that from the point of view of this indicator, the


24

capture process based NH3 is less advantageous compared to the capture process based on

MEA, which registered a EP growth of only 24.3% compared to the variant of energy

production without a carbon dioxide capture technology.

Figure 33. Abiotic depletion potential Figure 34. Climate change

In the case of the acidification impact indicator, as in the case of eutrophication, a

significant increase is observed for the cases in ammonia is used (Figure 36). However, in this

case there are no such high increases, because the SO2 emissions are also taken into account.

Thus the percentage increases are between 24.3-243.9%, the highest value for NH3=15 wt.%,

and the lowest value for MEA=30 wt.%.

In Figure 37 are presented the results obtained in the case of the POCP indicator, it is

observed that the highest value was obtained when using MEA, because in this case the highest

fuel amount was used to produce the same electricity amount, and the lowest value was obtained

when using NH3 in weight concentration of 15%. And, in Figure 38 are presented the results

obtained for the HTP indicator, observing the same variations as in the case of POCP.

Compared to reference case without CAP, for both POCP and HTP, in the case of MEA the

increase was of 24.3%, and in the case of NH3=15 wt.% the increase was of 1.5%.

Figure 35. Eutrophication Figure 36. Acidification

Figure 3. Photochemical oxidant formation Figure 38. Human toxicity


25

Multi-criteria methodology description

The purpose of this chapter is to identify the optimal chemical solvent for the CO2

capture process by chemical absorption integrated in power plant according to the technical-

economic and environmental criteria requested by the study beneficiary. The multi-criteria

model proposed in this study will allow the comparison of the different chemical solvents

according to the criteria defined by the beneficiary.

The method of multi-criteria analysis is presented below, with which the optimum

chemical solvent was identified, taking into consideration the set of criteria defined above.

Further, each case studied is named ”energy system”, and is noted by S:

Power plant without CO2 capture – S1;

Power plant with CO2 capture process integration by chemical absorption using

NH3 in weight concentration of 2% – S2;








MEA in weight concentration of 30% – S6.

The multi-criterion method is based on the MUNDA and ELECTRE IV method [16,

17]. The multi-criteria methodology is based on the following stages: a) standardization of

evaluations; b) evaluation if energy system belongs to the negative class solutions or,

respectively, to the positive class solutions; c) the global evaluation of the energy systems

corresponding to each family criterion.

Application of the multi-criteria analysis method

Table 5 summarizes the results obtained for the technical, economic and environmental

criteria considered in the multi-criteria analysis, for the cases in the capture process by chemical

absorption is integrated.

Table 5. Input data multi-criteria analysis

Criterion S1 S2 S3 S4 S5 S6

Tehnical

Thermal efficiency, % 48.4 38.27 44.32 45.42 46.87 37.89

Net efficiency, % 42.44 33.59 39.28 40.25 41.52 33.58

Economic

CO2 capture cost, €/tCO2 0.00 53.67 49.44 49.46 52.29 66.45

LCOE (taxă CO2 = 25 €/t),

€/MWh 42.48 73.80 71.66 71.86 73.59 81.10

NPV (taxă CO2 = 25 €/t), € 521.39 152.81 174.40 175.21 158.34 85.28

IRR (taxă CO2 = 25 €/t), % 18.73 11.35 11.59 11.59 11.41 10.60

NCR (taxă CO2 = 25 €/t), ani 10.66 21.13 20.40 20.37 20.93 24.04

PI (taxă CO2 = 25 €), - 2.04 1.18 1.20 1.20 1.18 1.10

Environmental

Abiotic depletion potential -

ADP, techiv_sb 5007.50 5996.90 5378.53 5239.06 5081.18 6225.83

Climate change - GWP,

techiv_CO2 1109204 150622.6 135091.1 131588.2 127622.7 156372.6


26

Eutrophication - EP, techiv_PO 741.78 2274.18 5042.00 7598.22 7574.83 922.26

Acidification - AP, techiv_SO2 10807.92 14329.21 15853.97 18129.84 17789.07 13437.49

Photochemical oxidant

formation - POCP, techiv_C2H4 479.71 574.49 515.25 501.89 486.77 596.42

Human toxicity - HTP,

techiv_DCB 7452.68 8925.21 8004.88 7797.32 7562.34 9265.92

After the results centralization for analyzed criteria, the evaluations were normalized,

in the interval [0.1], the values obtained are presented in Table 6. We started from the value of

the coefficients α and β of 0.5, and the weight factor for all criteria equal to 1.

Table 6. Normalization of evaluations

Criterion S2 S3 S4 S5 S6

Tehnical C1 0.990 0.855 0.834 0.808 1

C2 1 0.855 0.834 0.809 1

Economic

C3 0.963 0.864 0.842 0.816 1

C4 0.963 0.864 0.842 0.816 1

C5 0.084 0.187 0.282 1 0.034

C6 0.386 0.427 0.488 1.000 0.362

C7 0.963 0.864 0.842 0.816 1

C8 0.963 0.864 0.842 0.816 1

Enviromental

C9 0.808 0.744 0.744 0.787 1

C10 0.910 0.884 0.886 0.908 1

C11 0.558 0.489 0.487 0.539 1

C12 0.934 0.915 0.914 0.929 1

C13 0.879 0.848 0.847 0.871 1

C14 0.934 0.914 0.914 0.929 1

As the global evaluation of the solutions according to the three criterion families, from

the radar type diagram, represented in Figure 39, it is observed that the S3 solution presents the

best evaluations. Thus, solution 3 has the best overall assessment, with a percentage of 32.3%,

followed by solutions 4 and 5, with a percentage of 28.3% and 22.1. The lowest global presents

solutions 2 and 6, with a percentage of 13.2% and 4.2% (Figure 40).

Figure 39. Global evaluation of the solutions

according to the three criteria families




27

Sensitivity analysis

In the first sensitivity analysis, we aimed to reduce the appurtenance interval to the

positive class, by reducing the coefficient β, and implicitly increasing the coefficient α,

respectively the appurtenance interval to the negative class.

For α = 0.8, β = 0.2, in case the appurtenance interval of the positive class is reduced

by 70%, the results obtaining for global evaluation are presented in Figure 41. If in cases where

α=0.5, α=0.4 și α=0.3 not changed the solutions classification and scores obtained for the global

evaluation, in this case the order of the solutions has changed, the S4 solution passing the first

place with a percentage of 32.8%. Solution S5 obtained a percentage of 28.3%, and solution

S3, which it was the best evaluated so far, obtained a percentage of 18.9%, being the third

solution. Solution S6 remained the weakest solution, and solution S2 obtained a percentage of

11%.

Regarding the global evaluation for β = 0.1 the S5 solution has the highest percentage

of 41.1%, followed by the S3, S4, S2 and S6 solution (Figure 42). The 80% reduction for

appurtenance interval of the positive class has changed the solution hierarchy, and the 70%

reduction compared to the initial version, where the intervals are equal. It can be said that the

choice of the coefficients α and β has a significant impact on the solutions ordering of the point

of view of the three criteria families.

Figure 43 shows the values of the global evaluation for all the discrimination thresholds

studied. It is observed that there is no change in the solutions order for the positive

discrimination threshold, β, of 0.3, 0.4 and 0.5. Instead, the influence of the positive

discrimination threshold on the optimal solutions classification is observed, for the value of 0.1

and 0.2.



(𝜷 = 𝟎. 𝟐)



(𝜷 = 𝟎. 𝟏)

Figura 43. Global evaluation of solutions according to the positive discrimination threshold


28

GENERAL CONCLUSIONS AND FUTURE DEVELOPMENT

In the context of climate change and carbon dioxide emissions reduction, integrating

CO2 capture technologies into coal-fired power plant is a reliable solution. Thus, the capture

processes integration remains a key solution in all scenarios made worldwide. The purpose of

this PhD thesis was to identify the optimal solution for CO2 capture, with the least negative

impact on the technical, economic and environmental indicators. In Chapter 2, a bibliographic

study was carried out, presenting the current stage development of CO2 capture technologies,

resulting that the chemical absorption process using amines (the case of MEA in mass

concentration of 30%) being the most developed and industrially tested. However, this process

still has disadvantages, such as the overall efficiency decreasing of the power plant, chemical

solvent degrading, electricity price increasing, etc. Thus, the CO2 capture by chemical

absorption process based on ammonia solutions was studied in this thesis, the results obtained

comparing with the reference process based on amines.

In this PhD thesis, the process of CO2 capture by chemical absorption based on

ammoniacal solutions was studied. The original contributions are the following:

The bibliographic study performed in the first part of the thesis, to identify the advantages

and disadvantages of the CO2 capture technologies already developed, in order to apply

solutions to improve these technologies.

Capture process based NH3 simulation for determining optimal process parameters, in order

to determine the best solution in terms of CO2 capture process indicators.

Experimental study of the capture process based on ammonia solutions, carried out in the

Laboratory of Renewable Energy Sources, the Faculty of Power Engineering, on the

existing pilot plant – CFBC.

Conduct of the technical, economic and environmental analysis, regarding the integration

of the capture process into power plant of 200 MW and comparing the obtained results of

the capture process using NH3 with those of the reference capture process based on MEA.

Applying a multi-criteria method to identify the optimal capture process from the point of

view of the three criteria families (technical, economic and environmental) considered.

Developing an excel calculation program, which can be applied for different carbon dioxide

capture processes, in order to choose the process with the best performances.

The chemical solvent based on ammonia has several advantages as against amines such

as: a higher CO2 absorption capacity, there is no thermal and oxidative degradation, the

purchase cost of ammonia is lower, the amount of thermal energy needed for regeneration is

lower and can separate different acid pollutants simultaneously. On the other hand, as

disadvantages, ammonia is volatile at high temperatures, and it requires the operating

temperature in the absorber.

In the experimental study the influence of the weight concentration of NH3 in solution

on the carbon dioxide capture efficiency was analyzed. The weight concentrations considered

were 5, 10, 15 and 20% for a constant flow of ammoniacal solution. It was observed that the

CO2 capture efficiency increases with the increase of the NH3 weight concentration in the

solution, obtaining a capture efficiency of 25%, for a weight concentration of 5%, a capture

efficiency of 46.4% for a weight concentration of 10%, a capture efficiency of 65.4% for a

weight concentration of 15% and a capture efficiency of 81.8% for a weight concentration of

20%. The results obtained experimentally were compared with the results obtained by the

simulation of the process, with no significant differences. In the experiments, the process of


29

CO2 absorption take place at a temperature of 40°C. In the simulation study, the influence of

the following parameters on the indicators of the CO2 capture process was studied: the flue gas

temperature at the inlet in the absorption column (20°C, 30°C, 40°C, 50°C), the ammonia

solution temperature at the inlet in the absorption column (-1°C, 5°C, 10°C, 15°C, 20°C) and

the NH3 weight concentration in the solution (5%, 10%, 15%, 20%). Thus, when comparing the

analyzed cases for a carbon dioxide capture efficiency of 90%, the lowest L/G ratio was

obtained for a flue gas temperature of 20°C, a ammonia solution temperature of -1°C and a NH3

weight concentration of 20%. However, from the point of view of the amount of ammonia lost,

the optimal case is the one in which the same temperatures are maintained but the weight

concentration of NH3 is 5%, but for this situation the energy consumption is the highest.

In the Chapter 4 was studied the technical and economic effects of integrating the CO2

capture process based on NH3 into power plant of 200 MW. The analyzes were performed for

a NH3 weight concentration in solution of 2, 5, 7, and 15%, and for a CO2 capture efficiency of

90%. In the case the fuel flow is maintained constant, thus producing different amounts of

electric energy, for the cases analyzed based on NH3, the overall efficiency penalty was between

2.95 - 22.16%, for the case based on MEA the penalty was 22.19 %. In the case the power is

maintained constant, the amount of fuel used is higher and thus the same amount of energy is

produced, the overall efficiency penalty for cases based on NH3 was between 2.97 - 21.21%,

and for case based on MEA was 21.89%. The specific economic indicators determined were:

the levelized cost of electricity with and without the CO2 emissions tax, and the cost of

capturing one tonne of CO2. In both situations analyzed, the lowest costs were obtained for the

capture process using NH3 in weight concentration of 7%. For the reference capture case

(MEA=30 wt.%) were obtained the highest costs. If the CO2 emissions tax is taken into account,

the solutions with a capture process are better than the solution whitout capture process, when:

the CO2 emissions tax is higher than € 60/tCO2 for the cases based on NH3, the CO2 emissions

tax is higher than 80 €/tCO2 for the case based on MEA. Regarding the impact indicators (ADP,

GWP, EP, AP, POCP, HTP) it was obtained that it are higher for the solutions in which a capture

process is integrated, because the amount of fuel used is higher, except GWP impact indicator,

due to the reduction of the carbon dioxide amount emitted during the combustion stage.

The multi-criteria analysis performed in Chapter 5 consisted of the evaluation of the

solutions analyzed according to the technical, economic and environmental criteria. Therefore

the first multi-criteria analysis, the optimal solution resulted was the solution that does not

integrate a capture process, because in this solution most of the considered criteria have better

results. Thus, in the second multi-criteria analysis, only the solutions with a CO2 capture process

were considered. Therefore this analysis, if the discrimination threshold for appurtenance

solutions to the positive class is the same as that of the appurtenance solutions to the negative

class, the solution with the best global evaluation is solution S3 (NH3=5 wt.%). If the

discrimination threshold of the positive class solutions is reduced by 60%, the optimal solution

is the S4 solution (NH3=7 wt.%). And if the discrimination threshold of the solutions to the

positive class is reduced by 80% the optimal variant is the S5 solution (NH3=15 wt.%).

Currently still looking for solutions to reduce the impact of CO2 capture technology

integration in energy sector or industrial process. The major drawbacks of the CO2 capture

technologies consist of the overall efficiency decrease of energy process and the electricity costs

production increase. As further development perspectives are listed: Decreased energy

consumption for the capture process by chemical absorption through improving process

parameters, by recovering the flue gas heat and its use in the regeneration process of the

chemical solvent; Hybrid CO2 capture processes, such as adsorption-absorption, membrane-


30

absorption to improve the capture efficiency; Minimizing the costs of capture technologies by

developing existing solvents on the market and by developing new solvents with higher CO2

absorption capacities and a lower purchase price.

Scientific articles published during the elaboration of the doctoral thesis:

1. Slavu, N., Dinca, C., Badea, A. (2019). CHILLED AMMONIA PROCESS EVALUATION

FOR CO2 SEPARATION. U.P.B. Sci. Bull., Series C, 81(2), 275-284,

WOS:000469413500021.

2. Dinca, C., Pascu, A., Slavu, N., Badea, A. (2019). PARAMETRIC STUDY OF THE

ETHANOLAMINE DEGRADATION IN THE ABSORPTION PROCESS. U.P.B. Sci.

Bull., Series C, 81(3), 261-272, WOS:000477996400021.

3. Ionescu, C., Tuţică, D., Pătraşcu, R., Dincă, C., Slavu, N. (2019). Evaluation of the energy

efficiency of an industrial consumer in trigeneration mode. In E3S Web of Conferences

(Vol. 85, p. 01005). EDP Sciences, WOS:000468021200005.

4. Dinca, C., Slavu, N., Badea, A. (2018). Benchmarking of the pre/post-combustion chemical

absorption for the CO2 capture. Journal of the Energy Institute, 91(3), 445-456,

WOS:000433014700012.

5. Dinca, C., Slavu, N., Cormoş, C. C., Badea, A. (2018). CO2 capture from syngas generated

by a biomass gasification power plant with chemical absorption process. Energy, 149, 925-

936, WOS:000431162100074.

6. Slavu, N., Dinca, C., Badea, A. (2018, June). Parametrical study of adsorbent materials for

CO2 separation. In The 14th WEC CENTRAL & EASTERN EUROPE REGIONAL

ENERGY FORUM - FOREN.

7. Pascu, A., Slavu, N., Badea, A., Dinca, C. (2017). EVALUATION OF THE PHYSICAL

SOLVENTS USED IN CO2 POST-COMBUSTION PROCESSES. U.P.B. Sci. Bull., Series

C, 79(1), 303-314, WOS:000405770100024.

8. Slavu, N., Dinca, C. (2017, July). Economical aspects of the CCS technology integration

in the conventional power plant. In Proceedings of the International Conference on Business

Excellence (Vol. 11, No. 1, pp. 168-180). De Gruyter Open, WOS:000431004400019.

9. Dinca, C., Slavu, N., Badea, A. (2017, October). CO2 adsorption process simulation in

ASPEN Hysys. In 2017 International Conference on ENERGY and ENVIRONMENT

(CIEM) (pp. 505-509). IEEE. WOS:000427610300107.

10. Slavu, N., Patrascu, R., Dinca, C. (2017, October). MANAGEMENT OF THE CO2

CAPTURE PROCESS INTEGRATION IN THE GLASS TECHNOLOGY INDUSTRY.

In International Conference on Management and Industrial Engineering (No. 8, pp. 169-

181). Niculescu Publishing House.

11. Slavu, N., Dinca, C., Patrascu, R. (2017, October). ENVIRONOMIC CONSEQUENCES

OF CCS TECHNOLOGY INTEGRATION IN THE CEMENT PROCESS CHAIN. In

International Conference on Management and Industrial Engineering (No. 8, pp. 182-194).

Niculescu Publishing House.

12. Cristian DINCA, Cosmin MARCULESCU, Adrian BADEA, Nela SLAVU, Adrian

PASCU, Îndrumar de proiectare a echipamentelor de captare CO2 prin absorbţie chimică.

Bucureşti, 2017, 170 pg., Editura Politehnica Press, ISBN: 978-606-515-744.


31

SELECTIVE BIBLIOGRAPHY

[1] Le, Treut H., et al. "Historical overview of climate change science." (2007).

[2] SIO, 2014. Scripps Institute of Oceanography, https://scripps.ucsd.edu/education.

[3] IEA, CO₂. "Emissions from Fuel Combustion." International Energy Agency 13 (2012):

2895-2902.

[4] Darde, Victor, et al. "Experimental measurement and modeling of the rate of absorption of

carbon dioxide by aqueous ammonia." International Journal of Greenhouse Gas Control 5.5

(2011): 1149-1162.

[5] Slavu, Nela, Dinca, Cristian, Badea, Adrian. “CHILLED AMMONIA PROCESS

EVALUATION FOR CO2 SEPARATION.” U.P.B. Sci. Bull., Series C, 81(2), (2019): 275-

284.

[6] Abu-Zahra, Mohammad RM, et al. "CO2 capture from power plants: Part I. A parametric

study of the technical performance based on monoethanolamine." International Journal of

Greenhouse gas control 1.1 (2007): 37-46.

[7] Tobiesen, Finn Andrew, Hallvard F. Svendsen, and Olav Juliussen. "Experimental

validation of a rigorous absorber model for CO2 postcombustion capture." AIChE Journal 53.4

(2007): 846-865.

[8] https://markets.businessinsider.com/commodities/co2-emissionsrechte. 2019. Accesat:

10.03.2019.

[9] Ruth Nataly, Echevarria Huaman, Sonia Lourenco. ”A review on: CO2 capture technology

on fossil fuel power plant.” J. Fundam. Renew. Energy Appl. 5 (3) (2015) 164.

[10] Oh, Se-Young, et al. "Energy minimization of MEA-based CO2 capture process." Applied

energy 169 (2016): 353-362.

[11] Goto, Kazuya, Katsunori Yogo, Takayuki Higashii. "A review of efficiency penalty in a

coal-fired power plant with post-combustion CO2 capture." Applied Energy 111 (2013): 710-

720.

[12] Raksajati A, Ho MT, Wiley DE. ”Reducing the cost of CO2 capture from flue gases using

aqueous chemical absorption.” Ind Eng Chem Res 2013;52:16887–901.

[13] Man, Yi, et al. "Environmental impact and techno-economic analysis of the coal

gasification process with/without CO2 capture." Journal of cleaner production 71 (2014): 59-

66.

[14] Cormos, Calin-Cristian, et al. "Process Design and Integration of Various Carbon Capture

Approaches into the Energy Sector and Other Energy-intensive Industrial Applications."

Computer Aided Chemical Engineering. Vol. 38. Elsevier, 2016. 265-270.

[15] Goedkoop, Mark, Renilde Spriensma. "The eco-indicator99: A damage oriented method

for life cycle impact assessment: Methodology report." (2001): 1-144.

[16] Blanc, Armelle. Analyse de cycle de vie des filières de traitement des sites industriels

pollués. Diss. Lyon, INSA, 1999.

[17] Dinca, Cristian. Teză de doctorat. ” EVALUATION ENVIRONNEMENTALE ET

TECHNICO – ECONOMIQUE DU CYCLE DE VIE DE LA COMBUSTION DU GAZ

NATUREL ET PROPOSITIONS D`AMELIORATIONS TECHNIQUES, 2006.

https://scripps.ucsd.edu/education

https://markets.businessinsider.com/commodities/co2-emissionsrechte

sumarry phd thesis - pub.rodoctorat.energ.pub.ro/files/abstract/2019/slavu... · sumarry phd thesis...

Documents