Theoretical Calculations on Simultaneous Emission Removal from a

Waste Gasification Plant

ILIRJAN MALOLLARI, TERKIDA VASO, GRESADA ÇOÇKA

Chemical Process Engineering Group, Department of Industrial Chemistry,

Faculty of Natural Sciences,

University of Tirana, Boulevard ZOGU I , 25/1, Tirana1057

ALBANIA

Abstract:- This study presents a detailed and comprehensive methodology for theoretical engineering

calculations in a modelled waste gasification plant. The aim is to determine the most effective way to clean

up exhaust gases or emissions from industrial combustion processes. The pollution from chemical processes

is significant due to the direct emission of harmful gases into the atmosphere, such as SOx, NOx, COx, O3,

etc. To achieve this, we utilised the ASPEN PLUS simulation computer program, which facilitated a series

of theoretical calculations during the procedure and optimisation of capturing the abovementioned

dangerous gases and cleaning them out. This work involves two processes: the absorption of chimney's

emissions from waste gasification plants, which consists mainly of a reactor and an absorber, and cleaning

the contaminated remaining liquid from the absorber at the end of the capturing process. Through

meticulous simulation and computer calculations, we have determined the absorbing rate of the polluting

gases and completed a thorough sensitivity analysis for the entire process. This precision in our calculations

instils confidence in our results' reliability and the proposed methods' potential effectiveness, reaffirming

the trust in our research findings.

Key-Words: environmental pollution, pollutant gases, gas oxides, simulation, absorbing solutions, emission

reduction.

Received: April 8, 2023. Revised: October 19, 2024. Accepted: November 13, 2024. Published: December 12, 2024.

1. Introduction

1.1. The process of capturing acidic oxides

consists of a reaction that makes oxidation

possible, followed by a cooler that cools the

oxidised gases. This mixer combines the NaOH

solution and an 'absorption column '. This column

is a critical component that allows the oxidised

gases to be absorbed, a crucial step in the

emission reduction process.

In the procedure below, the currents represent the

following: 1: the stream of ClO2 2: the stream of

polluting gases (NO, NO2, SO2, SO3, etc.); 3-

streams of oxidised gases 4- streams of cold water

5-flow of cold oxidised gases 6-flow of water and

NaOH; 7-stream leaving the mixer and containing

the cold NaOH solution; 8-the stream of steam

that is released from the absorber must contain as

few polluting gases as possible; 9-the solution

stream that leaves the reactor and includes all the

salts formed [1–3].

1.2. The process of the Acidic gases

Captured from the combustion processes

Through the process diagram flowsheet

preliminarily constructed by us (see Figs. 1 and

2), the capture of all the harmful gases that come

out of the chimneys of burning plants is realised

before releasing them into the atmosphere. In

stream 1, we have a mixture of gases where, in

addition to sulfur and nitrogen oxides, we also

have other 'polluting gases', a term used to

describe the gases that contribute to

environmental pollution [4–7].

The reactor used in this case is of the CSTR type,

a crucial component that enables the oxidation of

these gases by forming the corresponding salts of

each pollutant. In stream 2, we have ClO2, which

International Journal on Applied Physics and Engineering

DOI: 10.37394/232030.2024.3.9

Ilirjan Malollari, Terkida Vaso, Gresada Çoçka

E-ISSN: 2945-0489

Volume 3, 2024

is used as an oxidiser. In-stream three, we have

oxidised gases, which pass to a scrubber or an

absorber, where water absorption becomes

possible [8–9].

Fig. 1:

Schematic presentation of the CSTR reactor

followed by an absorber in the simulation

software ASPEN PLUS.

Here, we have the separation of condensable

gases from non-condensable gases. Condensable

gases stay in the water and form 'polluting water',

a byproduct that requires further treatment. At the

fig. 2 it is presented a tentative process diagram

of acidic gases capture, where non-condensable

gases are released into the atmosphere because

they are harmless—the capture of combustion

gases. Through this scheme, we capture all the

gases that come out of the chimneys of plants or

factories as secondary material so as not to release

them directly into the atmosphere. Stream 1 has a

mixture of sulfur, nitrogen oxides, and other

polluting gases [11].

Fig. 2: Acidic gases capture process diagram

using EdrawMax software

In stream 2, we have ClO2, which is used as an

oxidiser. In stream 3, we have oxidised gases,

which then pass to a scrubber or an absorber

where absorption by water becomes possible [10].

Fig. 3 Schematic presentation of the CSTR

absorber in the simulation software ASPEN

PLUS.

Here, we have the separation of condensable

gases from non-condensable gases. Condensable

gases stay in water and form polluting water,

while non-condensable gases are released into the

atmosphere because they are harmless.

1.3.Capture of combustion gases.

Through this scheme, all the gases that come out

of the chimneys of plants or factories as

secondary material make it possible to capture

them so as not to release them directly into the

atmosphere. In stream 1, we have a mixture of

gases where, in addition to sulfur and nitrogen

oxides, we also have other polluting. The reactor

used in this case is of the CSTR type, which

makes it possible to oxidise these gases by

forming the corresponding salts of each pollutant.

In stream 2, we have ClO2 [12], which is used as

an oxidiser. In-stream three, we have oxidised

gases, which then pass to a scrubber or an

absorber where absorption by water becomes

possible. Here, we separate condensable gases

from non-condensable gases, which stay in water

and form polluting water. In contrast, non-

International Journal on Applied Physics and Engineering

DOI: 10.37394/232030.2024.3.9

Ilirjan Malollari, Terkida Vaso, Gresada Çoçka

E-ISSN: 2945-0489

Volume 3, 2024

condensable gases are released into the

atmosphere because they are harmless [13-15].

2. Material and Methods

The general scheme worked on Aspen Plus is

formulated as in the flow sheeting of Fig 4.

Fig. 4: Full absorption process diagram of SOx

and NOx gases with solution ClO2 in ASPEN

PLUS V11.

The modelling and simulation of technological

processes were conducted using a standard

methodology. This approach, widely accepted in

the field, involves determining and optimising

process indicators and engineering capacities.

The physicochemical properties used in the

simulation were taken from the built-in databases

of the ASPEN PLUS software, ensuring the

results' accuracy and reliability.

For many scientific problems, especially

technological development, the data for the

dynamic construction of technological processes

does not exist. However, they are sufficient for

the so-called stationary (steady-state) models.

Because of this, the time dependencies of all

influencing parameters cannot be considered,

which is why the modelling and related

calculations become much more straightforward.

The simulation/modelling scheme represents

technological plants' construction, development,

and operation. Depending on the desired details,

we are dealing with fundamental technological

schemes, piping schemes, and instruments.

The simulation scheme graphically presents a

process, showing the basic operations for the

various parts of the plant, which are connected

through material and energy flows. By calculating

the mass and energy balances, it is possible to

calculate the mass and ratios of productive

currents, such as pressure and temperature.

Regarding the principle that through design and

modelling programs are carried out calculations,

we distinguish sequential modular calculations of

basic operations according to their arrangement in

the process diagram (flowsheet) and simultaneous

calculation of all stages through the passage of all

elements in the equalisation system.

Sequential modular calculation of individual

essential elements has some advantages in

modelling, as it performs comprehensible

simulations, detects errors, and offers the

possibility of adding models. Comparing it with

simultaneous calculations, we found some areas

for improvement in the case of opposite currents

and recycling between basic operations since they

have to be repeated many times. Let us consider

the flow control for the flowsheet simulation

performed throughout the computer program.

Through it, the models for calculating the

functions were obtained one after the other,

International Journal on Applied Physics and Engineering

DOI: 10.37394/232030.2024.3.9

Ilirjan Malollari, Terkida Vaso, Gresada Çoçka

E-ISSN: 2945-0489

Volume 3, 2024

basically mutually related to the data of subjects,

mixtures, or thermodynamic models. Other

numerical subroutines were used to solve linear

and non-linear equations encountered in separate

modules.

It is important to describe some of the essential

technological parts of operation by the chemical

reaction equations used while modelling various

technology processes for producing synthetic

fuels, together with their symbols.

3. Results and Discussion

Specifications for raw materials: In this work, the

raw materials are polluting gases and an oxidiser

that converts gases with a low oxidation number

into gases with the highest oxidation number. We

have raw NOx, SOx, CO2, O2, ClO2, and H2O

raw materials as in table 1.

Table 1 Some specific properties of the gases

Reactor feedstock: Gas flow: Polluting gases are

collected from all the chimneys of plants,

factories, or anywhere there is a combustion

reaction and the release of gases.

We have summarised the input data for the raw

material in the following table, which presents the

input current flows, the percentages of each

current component, the temperature of the input

components, and their pressure (see Table 2).

Values on this table has been taken from the

laboratory experimental characterisation for the

actual situation taken into account for this

research.

Table 2: Typical exhaust gas compositions

The input currents in this table are in ppm or %,

but in the Aspen Plus program, we have replaced

the unit kg/sec as the total flow as well as the

content of the components in the current. Rapid

Tables software was used for unit conversion,

which made it possible to convert ppm to

percentages, knowing the density of each

component and converting these percentages to

the program unit km/hr. First, we find the total

flow in km/hr and mp after each component (see

Table 3).

Table 3: Summary of component input measures

The input currents in this table are in ppm or %,

but in the Aspen Plus program, we have replaced

the unit kg/sec with the total flow and the content

of the components in the current.

Reactor specifications: The reactor used in the

process is of the CSTR type; its function is the

oxidation of gases. Some summary data for the

reactor

Components

(kg/m3)

Content

Density

(kg/m3)

Molar

mass

(kg/kmol)

NOx

200

ppm

1.34

SO2

65 ppm

2.93

9 %

1.43

CO2

13 %

1.98

air

79%

1.29

Components

NOx, ppm

SO2’ppm

O2, %

CO2, %

Humid,ity %

Air

Waste-

burning

treatment

plant

200

78%

Conversion

in %

0,02

0,0065

Components

Kg/s

9.5

SO2

6.06

6.217

CO2

6.17

Air

72.056

International Journal on Applied Physics and Engineering

DOI: 10.37394/232030.2024.3.9

Ilirjan Malollari, Terkida Vaso, Gresada Çoçka

E-ISSN: 2945-0489

Volume 3, 2024

Fig. 5: Reactor completions in Aspen Plus V11

All reactions are kinetic and have their constants,

the release or acquisition of energy.

Fig. 6: Reactions entered in Aspen Plus V11

The feedstock of the reactor are the following

components: the stream of ClO2 and the stream of

International Journal on Applied Physics and Engineering

DOI: 10.37394/232030.2024.3.9

Ilirjan Malollari, Terkida Vaso, Gresada Çoçka

E-ISSN: 2945-0489

Volume 3, 2024

polluting gases (NO, NO2, SO2, SO3, etc.). A

packed tower is chosen as the absorbing device.

The packed towers are filled with packing

materials, such as ceramic Raschig rings.

Fig. 7. Total flowsheet process diagram

Tests in Aspen Plus: Our work in Aspen Plus has

been multiple, and each has an addition or

subtraction of the process. Evidence number 1: In

the program, I entered all the devices and all the

currents as shown in the theory above, but I could

not find a method that included NaOH; the

simulation went to the end, but the results were

not very satisfactory and expected.

The process calculation in the first trial consisted

of a CSTR reactor, a cooler, a mixer and an

absorber. The input streams in the process were

polluted gases, chlorine oxide, cold water in the

cooler, water needed to form the NaOH solution,

and the NaOH stream entering the mixer. The

completion seen in the figure above is done for all

other reactions.

The program entered all the devices and all the

currents, as shown in the theory above, but I

needed help finding a method that included

NaOH. The simulation went to the end, but the

results could have been more satisfactory. The

process in the first trial consisted of a CSTR

reactor, a cooler, a mixer and an absorber.

The input streams in the process were polluted

gases, chlorine oxide, cold water in the cooler,

water needed to form the NaOH solution, and the

NaOH stream entering the mixer. The completion

seen in the figure above is done for all other

reactions.

Fig. 8: Test number 1 in Aspen Plus

Test number 2

In test #2, We tried to dump the NaOH stream

from the mixer since it was not generated using

our method in Aspen Plus.

The process continued to generate results at the

end, but again, they did not obey our theory of

releasing as little gas as possible at the end. Again,

the process had the same equipment and initial

data in all currents and equipment specifications.

Fig. 9: Test number 2 in Aspen Plus

The following figure shows this process:

Test number 3

In test number 3, seeing that the mixer was not

playing an important role but only mixing water

with the temperature coming out of the cooler

with water coming from normal conditions and

seeing that their temperature was close to their

temperature in out of the mixer, we thought we'd

remove one and see what the results would be like

in the end.

International Journal on Applied Physics and Engineering

DOI: 10.37394/232030.2024.3.9

Ilirjan Malollari, Terkida Vaso, Gresada Çoçka

E-ISSN: 2945-0489

Volume 3, 2024

The simulation again ran to completion, and some

data was generated, but we still needed to meet

our expectations. The figure below shows the

process where the mixer is missing.

Fig. 10: Test number 3 in Aspen Plus

Test number 4

In this test, we added another device at the end of

the process where we have the solution output

containing the dissolved gas salts. Suppose these

crypts get out into the environment. In that case,

they can be harmful to the environment, and to

eliminate this occurrence, we have added another

absorption column where it is possible to absorb

these salts. The figure below represents this

simulation:

Test number 5:

Fig. 11: Test number 4 in Aspen Plus

In this test, it was added a second cooler and made

it possible to reduce the surface area of the cooler

by dividing it into two equal parts, that is, since in

the summary table of the supplement for the

cooler, we have an area of 1248 m2 by dividing it

into two equal parts for both exchangers is

624m2.

In Fig. 11, S1 represents the water entering the

cooler, S2 the exit of cold gas oxides, S3 the exit

of warm water from the first cooler (B1), S4 the

NaOH solution that enters the mixer (B2), S5 the

union of the three streams of water at the same

temperature, S6 water under normal conditions

enters the second cooler (B3), S7 warm water

from the second cooler, S8 cold oxides, S9 current

where we have the reduction of polluting gases,

S10 salt solution exit.

Test number 6: We have considered only SOx

reactions in this test, assuming these gases are

present only in the stream. The only difference is

that we have considered only the reactions that

occur for SOx, eliminating all other pollutants.

Test number 7: In this test, we only considered

NOx, eliminating all other pollutants that may be

present in the flue gas stream. So, in the reactor,

we have the kinetic reactions of NOx being

oxidised and then absorbed to prevent their

release directly into the atmosphere.

Although the most critical tests were mentioned

above, many other tests in Aspen are related to

changes in some parameters of currents or

devices.

International Journal on Applied Physics and Engineering

DOI: 10.37394/232030.2024.3.9

Ilirjan Malollari, Terkida Vaso, Gresada Çoçka

E-ISSN: 2945-0489

Volume 3, 2024

Some results and graphs generated by Aspen Plus

Fig. 12: Results when using reactions for SOx only

Fig. 13: Numerical calculations results for the reactor

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DOI: 10.37394/232030.2024.3.9

Ilirjan Malollari, Terkida Vaso, Gresada Çoçka

E-ISSN: 2945-0489

Volume 3, 2024

Fig.14: Results for the absorber

The following charts, 1-4, show the dependence

of mass and the number of plates in the column,

the dependence of mass on plates in different

phases, the dependence of temperature on plates,

and the dependence of temperature in the cooler,

respectively.

Chart 1: Mass and number of plates in the column

Graph 2: Dependence of mass on plates in

different phases

Graph 3: Dependence of temperature on plates

Graph 4: Dependence of temperature in the

cooler

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Ilirjan Malollari, Terkida Vaso, Gresada Çoçka

E-ISSN: 2945-0489

Volume 3, 2024

4. Conclusions and Recommendations

In anticipation of the calculated results that the

Aspen Plus program should have generated, it

should be within the expectations described in the

theory above. The NOx and SOx gases at the outlet

of the gas vapour stream at the outlet of the

absorber should have been sufficiently reduced

about the measures we have set at the inlet. Input

measures were taken from the literature, and some

reports and component measures were found from

the reactions. In conclusion, the polluting gas

should have been reduced so that after oxidation

with chlorine oxide and interaction with different

bases, they could form more salts dissolved in

water than components released in the gas

vapours from the absorber.

If the stream of gases released above the reactor

has more pollutants than the stream below the

reactor, then we have something that could have

been done better with the program, or that needs

to be added to our data. If the stream of salt

solutions has a large amount of pollution, it will

not be a problem since we can add a treatment

plant for these waters and make them harmless to

the environment.

Our interest is only in the one at the outlet of the

absorber gases, and there, we have to minimise

the components of NOx and SOx as much as

possible.

References

[1].https://www.rapidtables.com/convert/number

/PPM_to_Percent.html

[2]. Evaluation of a Novel Concept for Combined

NOx and SOx Removal, Master’s thesis in Master

Programme Sustainable Energy Systems,

(JÜRGEN HAUNSTETTER, NIKO

WEINHART), 2015

[3]. NOx-Emission bei Feuerungsanlagen

Entstehung, Reduktionsmöglichkeiten,

Messtechnik und aktuelle Grenzwerte

[4]. R. Schefflan, Teach yourself the basics of

Aspen Plus, John Wiley & Sons, 2011.

[5]. Aspen Technology Inc., Aspen PLUS V11

(28.0.25), 2013.

[6]. file:///D:/GREENLUNGSBULLETIN2021.pdf

[7].https://www.alentecinc.com/papers/NOx/The

%20formation%20of%20NOx_files/The%20for

mation%20of%20NOx.htm#:~:text=Thermal%2

0NOx%20is%20produced%20during%20the%2

0combustion%20process,O3%2C%20a%20subst

ance%20known%20as%20ground%20level%20

ozone.

[8]. https://en.wikipedia.org/wiki/NOx

[9]. https://lwvworc.org/sq/do-scrubbers-remove-

nox

[10].https://www.eea.europa.eu/data-and-

maps/indicators/eea-32-nitrogen-oxides-nox-

emissions-1/assessment.2010-08-

19.0140149032-3

[11]. https://www.noxfondet.no/en/articles/what-

is-nox/

[12] Application of Gaseous ClO2 on Disinfection

and Air Pollution Control: A Mini Review -

Aerosol and Air Quality Research.

https://aaqr.org/articles/aaqr-20-06-covid-0330

[13] Harvianto, G. R., Ahmad, F., & Lee, M.

(2017). A hybrid reactive distillation process with

high selectivity pervaporation for butyl acetate

production via transesterification.

https://doi.org/10.1016/j.memsci.2017.08.041

[14] Fenty U. Puluhulawa, Jufryanto Puluhulawa,

Mohamad Rusdiyanto U. Puluhulawa, Amanda

Adelina Harun, 2024, "Handling Plastic Waste

based on Sustainable Tourism in the Legal

Framework of Telematics", WSEAS Transactions

on Environment and Development, vol. 20, pp.

16-25, DOI: 10.37394/232015.2024.20.3

[15] Santos SM, Assis AC, Gomes L, Nobre C,

Brito P. Waste Gasification Technologies: A

Brief Overview. Waste. 2023; 1(1):140-165.

https://doi.org/10.3390/waste1010011

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DOI: 10.37394/232030.2024.3.9

Ilirjan Malollari, Terkida Vaso, Gresada Çoçka

E-ISSN: 2945-0489

Volume 3, 2024

Contribution of Individual Authors to the

Creation of a Scientific Article (Ghostwriting

Policy)

The authors equally contributed in the present

research, at all stages from the formulation of the

problem to the final findings and solution.

Sources of Funding for Research Presented in a

Scientific Article or Scientific Article Itself

No funding was received for conducting this study.

Conflict of Interest

The authors have no conflicts of interest to declare

that are relevant to the content of this article.

Creative Commons Attribution License 4.0

(Attribution 4.0 International, CC BY 4.0)

This article is published under the terms of the

Creative Commons Attribution License 4.0

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International Journal on Applied Physics and Engineering

DOI: 10.37394/232030.2024.3.9

Ilirjan Malollari, Terkida Vaso, Gresada Çoçka

E-ISSN: 2945-0489

Volume 3, 2024