DOI: 10.3303/CET24113017 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Paper Received: 20 June 2024; Revised: 26 July 2024; Accepted: 3 November 2024 
Please cite this article as: Dinh T.S., Tran T.Q., Le N.P.T., 2024, Modeling Syngas Generation from Co-Gasification of Refuse-Derived Fuel and 
Tire Waste in Fixed Bed Gasifier, Chemical Engineering Transactions, 113, 97-102  DOI:10.3303/CET24113017 
  

 CHEMICAL ENGINEERING TRANSACTIONS  
 

VOL. 113, 2024 

A publication of 

 
The Italian Association 

of Chemical Engineering 
Online at www.cetjournal.it 

Guest Editors: Jeng Shiun Lim, Bohong Wang, Guo Ren Mong, Petar S. Varbanov 
Copyright © 2024, AIDIC Servizi S.r.l. 
ISBN 979-12-81206-14-4; ISSN 2283-9216 

Modeling Syngas Generation from Co-Gasification of Refuse-
Derived Fuel and Tire Waste in Fixed Bed Gasifier 

Thanh Son Dinh, Trong Quan Tran, Nguyen Phuc Thien Le* 
Laboratory of Biofuel and Biomass Research, Faculty of Chemical Engineering, Ho Chi Minh City University of Technology 
(HCMUT),VNU-HCM, Ho Chi Minh City, Vietnam. 
phucthien.le@hcmut.edu.vn 

The objective of this research was to investigate the effects of operating parameters on syngas quality and 
process performance metrics during the co-gasification of refuse-derived fuel (RDF) and tire waste (TW). This 
was modeled using simulations by Aspen Plus v10. The influence of gasification temperature, steam flow rate, 
and air flow rate on syngas composition, lower heating value (LHV), cold gas efficiency (CGE), and syngas yield 
were thoroughly evaluated. Simulation results revealed an optimal temperature of 700 °C, combined with 0.5 
kg/h steam and 0.5 kg/h air flow rates, maximizing the LHV at 17.62 MJ/kg (approximately 14.5 MJ/Nm3), CGE 
at 75.38 %, and the weight of syngas at 1.28 kg/kg. The optimized conditions facilitated a balanced formation 
of combustible gases while minimizing carbon losses, generating a high-quality syngas with desirable properties 
from the co-gasification of RDF and TW. 

1. Introduction 
Municipal Solid Waste (MSW) management faces challenges including increasing volume, environmental 
impact of landfills, and failure to recover resources (Srivastava et al., 2015). Refuse-Derived Fuel (RDF) and 
tire waste (TW) are two major components of MSW contributing to these issues. While recycling, composting, 
and anaerobic digestion offer partial solutions, thermal techniques like gasification present significant potential 
for volume reduction, energy recovery, and pathogen/toxin destruction. 
Previous research has explored gasification of RDF and TW separately, with limited studies on their co-
gasification. Le Tan et al. (2022) investigated RDF gasification, focusing on syngas composition and energy 
recovery, but didn't address RDF composition heterogeneity, which significantly impacts gasification 
performance. Haydary et al. (2023) examined RDF as a feedstock but didn't consider its combination with other 
waste streams to enhance gasification efficiency. Rogachuk and Okolie (2023) studied tire waste gasification, 
highlighting its high calorific value and potential as a fuel source, but didn't explore synergistic effects of 
combining tire waste with other feedstocks. 
Co-gasification of RDF and TW in a fixed bed gasifier offers potential advantages, including balanced syngas 
composition and higher calorific value. However, the literature lacks comprehensive studies on optimal operating 
conditions for this feedstock combination. Fernandez-Lopez et al. (2017) demonstrated Aspen Plus's utility for 
gasification process simulation but didn't extend to the complex interactions in RDF and TW co-gasification. 
Significant research gaps exist, including limited understanding of RDF-TW synergistic effects during co-
gasification, lack of optimization studies for these feedstocks in fixed bed gasifiers, insufficient exploration of 
feedstock variability impact on gasification performance and syngas quality, and absence of comprehensive 
techno-economic and environmental assessments for RDF and TW co-gasification systems. 
This research aims to fill these gaps by modeling and simulating RDF and TW co-gasification in a fixed bed 
gasifier using Aspen Plus. Primary objectives include optimizing syngas quality by evaluating critical parameters 
like gasification temperature and equivalence ratio, enhancing process efficiency through maximizing syngas 
yield, lower heating value, and cold gas efficiency, and identifying the optimal operating regime balancing 
syngas quality and overall process efficiency. 
The study's novelty includes developing a comprehensive Aspen Plus model for RDF and TW co-gasification, 
accounting for complex feedstock interactions, identifying optimal operating conditions, analyzing synergistic 

97



effects between RDF and TW, providing insights into feedstock blending strategies, and assessing feedstock 
variability impact on gasification performance. 
By addressing these research gaps and providing novel insights into RDF and TW co-gasification, this study 
will contribute to developing more efficient and sustainable waste management strategies, supporting the 
transition towards a circular economy in the waste sector. 

2. Materials and methods 
2.1 Materials 

The proximate and elemental compositions, as well as the higher heating values (HHV) of the RDF and TW 
used in the modeling are reported in Table 1. RDF and TW were mixed for co-gasification at a mass ratio of 1:1 
and a total material flow rate of 2 kg/h.The HHV of the RDF and TW mixture was calculated as 24.75 MJ/kg. 
The average hydrogen content (H) was 6.31 %, and the average moisture content was 2.52 %. Lower heating 
value (LHV) of material was calculated by Eq(1). 

𝐿𝐿𝐿𝐿𝐿𝐿 =  𝐿𝐿𝐿𝐿𝐿𝐿 (1 −  𝑀𝑀)  −  2.44𝑀𝑀  (1) 

where M is the moisture content. The LHV of the mixture was estimated to be approximately 23.31 MJ/kg. For 
the simulation, the following components were defined: conventional gasification gases: O2, N2, CO, CO2, CH4, 
H2O, and H2. Other relevant components: C, S, ASH, C6H6, C7H8, C8H8, C10H8, C9H8, C6H6O, C8H10, H2S, and 
SO2. These components were included to accurately represent the complex composition of the feedstocks and 
the gasification products in the simulation model. 

Table 1: Proximate and elemental composition and HHV of RDF (Haydary et al., 2023) and TW (TNO, 2022) 

Material Moisture (wt%) Volatile matter (wt%) Fixed carbon (wt%) Ash (wt%) HHV (MJ/kg) 
TW 0.81 63.65 26.28 9.27 34.62 
RDF 4.24 70.29 0.45 25.02 14.88 
RDF and TW 2.52 66.97 13.37 17.15 24.75 
Material C (%) H (%) N (%) S (%) O (%) 
TW 75.36 7.09 0.95 1.76 5.42 
RDF 38.02 5.52 0.77 0.34 26.09 
RDF and TW 56.69 6.31 0.86 1.05 15.76 

2.2 Simulation description 

The co-gasification of RDF and TW was simulated using Aspen Plus process simulation software (Aspen plus 
V10, 2017). The simulation model consisted of several unit operation blocks, including DRYING, PYROLYSI, 
MOIS-SEP, ASH-SEP, GASIFIER, COMBUST, and TAR-SEP (Figure 1), each employing different modules 
such as RStoic, RYield, SSplit, and FSplit to represent the respective processes (Table 2).  

 

Figure 1: Aspen plus flowsheet of the co-gasification RDF and TW model 

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Table 2: Simulation Parameters for co-gasification RDF and TW 

Block Module Describe and Reaction  ref 

DRYING RStoic 

Simulates drying by quantifying water removal from RDF and 
TW based on reaction equations (Eq(2) and Eq(3)). 
WT → 0.0709 H2O 
RDF → 0.0552 H2O 

 
 
(2) 
(3) 

- 

MOIS-SEP SSplit Separates water from the feed stream after drying  
NC split fraction = 1 

 
(4) - 

PYROLYSI RYield 

Simulates pyrolysis/devolatilization of RDF and TW, with 
products like H2, N2, O2, H2O, S determined by mass yield 
coefficients (Eq(5) - Eq(9)). 
C (CISOLID) → 0.9619 
H2 → 0.1405  
N2 → 0.0108  
O2 → 0.3908  
H2O → 0.7262  
S → 0.0112  

 
 
 
(5) 
(6) 
(7) 
(8) 
(9) 

(Parthasarathy 
and Sheeba, 
2015) 

COMBUST RGibbs Simulates combustion process assuming equilibrium reactions.  - 

TAR-SEP FSplit 

Simulates tar cracking reactions during gasification, with 
reactions defined (Eq(10) - Eq(17)). 
C10H8 + 4H2O → C6H6 + 4CO + 5H2  
C10H8 + 4.75H2 → 1.25C6H6 + 2.5CH4  
C7H8 + H2 → C6H6 + CH4  
C6H6 + 5H2O → 5CO + 6H2 + CH4  
C8H10 + 2H2O → C6H6 + 2CO + 4H2  
C6H6O → CO + 0.4C10H8 + 0.15C6H6 + 0.1CH4 + 0.75H2  
C9H8 + 3H2O → C6H6 + 3CO + 4H2  
C6H6O + 3H2O → 4CO + 2CH4 + 2H2 

 
 
(10) 
(11) 
(12) 
(13) 
(14) 
(15) 
(16) 
(17) 

(Babatabar, and 
Saidi, 2021) 

GASIFIER RGibbs 

Simulates combustion and gasification processes assuming 
equilibrium reactions. 
C + CO2 → 2CO  
C + H2O → CO + H2  
C + 2H2O → CO2 + 2H2  
C + 2H2 → CH4  
H2 + S → H2S  
CO + H2O → CO2 + H2  
CH4 + H2O → CO + 3H2 

C + O2 → CO2 

C + 1/2O2 → CO 

 
 
(18) 
(19) 
(20) 
(21) 
(22) 
(23) 
(24) 
(25) 
(26) 

(Babatabar, and 
Saidi, 2021) 
(Sierra et al., 
2021) 

ASH-SEP SSplit 
Separates ash from the feed stream after pyrolysis. 
CISOLID split fraction = 1  
NC split fraction = 1 

 
(27) 
(28) 

- 

The key reactions considered were the drying, pyrolysis, and gasification reactions, with their stoichiometric 
coefficients determined based on the feedstock composition and gasifying agent, all reactions have been 
described from Eq(2) to Eq(28). 
The simulation parameters were set to investigate the effects of varying steam and air flows and temperature 
on the syngas composition, LHV, and CGE. 

2.3 Calculation formula 

The lower heating value of syngas (LHVsyngas) is the caloric of the syngas product calculated by the heat 
multiplied by the composition of the component gases (Le Tan et al., 2022). LHVsyngas was determined by Eq(29). 
 

 𝐿𝐿𝐿𝐿𝐿𝐿𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠 = 10.7𝐿𝐿2 % + 12.6.𝐶𝐶𝐶𝐶 % + 35.8𝐶𝐶𝐿𝐿4 % (𝑀𝑀𝑀𝑀/𝑘𝑘𝑘𝑘 )  (29) 

Cold gas efficiency (CGE) is the percentage of the energy of syngas at standard temperature conditions 
compared to the energy of biomass in theory. CGE was calculated in Eq(30) (Shahadat Hossain, 2022). 

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𝐶𝐶𝐶𝐶𝐶𝐶 = 𝜔𝜔(𝐿𝐿𝐿𝐿𝐿𝐿𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠/LHV).100 (%)  (30) 

Where 𝜔𝜔 is the weight of syngas production (including the weights of the gases CO, CH4, and H2) per the dry 
mixed RDF and TW. 

3. Results and discussions 
3.1 Effect of Gasification Temperature on Co-gasification of RDF and TW 

The gasification temperature exerts a significant influence on the syngas composition, lower heating value (LHV, 
in MJ/kg, and CGE during the co-gasification of RDF and TW (Figure 2 and Figure 3).  

 

Figure 2: Syngas composition (mole%) at different gasification temperatures with 2 kg/h stream flow and 2 kg/h 
air flow 

 

Figure 3: LHV, and CGE at different gasification temperatures with 2 kg/h stream flow and 2 kg/h air flow 

The simulation results highlight the significant influence of temperature on syngas composition, LHV, CGE, and 
𝜔𝜔 during the co-gasification process of RDF and TW. As temperature increases from 500 °C to 700 °C, the 
volume fractions of desirable combustible gases CO and H2 rise substantially, reaching maximum of 0.14 and 
0.23 mole% at 700 °C. The mole fractions of CO2 and CH4 decrease from 0.15 to 0.10 and 0.037 to 0.0048 
mole% over this temperature range. This behavior stems from favorable high-temperature gasification reactions 
like water-gas shift, methane reforming, and Boudouard reactions promoting CO and H2 formation while 
consuming CO2, CH4, and solid carbon. The LHV and CGE mirror this trend, peaking at 9.98 MJ/kg and 48.98 
% at 700 °C due to increased combustible gas concentrations before declining at higher temperatures from 
excessive oxidation. Moreover, the syngas production weight (𝜔𝜔) shows a continuous rise from 0.38 kg/kg at 
500 °C to 1.41 kg/kg at 1,200 °C (Figure 3), indicating higher solid-to-gas conversion at elevated temperatures. 
Ultimately, 700 °C emerges as the optimal temperature balancing syngas quality, energy density, process 
efficiency, and production yield during RDF and TW co-gasification. 

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3.2 Effect of Gasifying Agents on co-gasification RDF and TW 

The Figure 4 presents the effect of varying the steam flow and air flow on the syngas composition, LHV, and 
CGE during the co-gasification of RDF and TW in a gasifier at 700°C. 

(a) 

 

(b) 

 

(c) 

 

(d) 

 

(e) 

 

(f) 

 

(g) 

 

  

Figure 4: Effects of Steam Flow and Air Flow on Syngas Composition and Performance Metrics during Co-
Gasification of RDF and TW. (a) CO Composition, (b) CO₂ Composition, (c) CH₄ Composition, (d) H₂ 
Composition, (e) LHV, and (f) 𝜔𝜔 and CGE 

As the steam flow rate increases, the mole fractions of CO and H2 in the syngas increase due to the promotion 
of the water-gas shift reaction (Eq(23)) and steam reforming reactions (Eq(24)). At an air flow rate of 0.5 kg/h, 
the CO mole fraction rises from 0.21 to 0.27 mole% as the steam flow rate increases from 0.5 to 2 kg/h, while 
the H2 mole fraction increases from 0.41 to 0.47 mole% over the same range. The air flow rate increases, the 
mole fractions of CO and H2 initially rise due to the partial oxidation of the feedstock, promoting reactions like 
Eq(25) and Eq(26). Beyond a certain air flow rate, the mole fractions start decreasing as the excess air oxidizes 
more CO and H2 to CO2 and H2O. This trend is evident at a steam flow rate of 1.5 kg/h, where the CO mole 

101



fraction increases from 0.14 to 0.20 mole% as the air flow rate increases from 0.5 to 1 kg/h, but then decreases 
to 0.05 mole% as the air flow rate further increases to 4 kg/h. 
The LHV, CGE, and weight of syngas production (𝜔𝜔) are also influenced by the steam and air flow rates. An 
optimal condition of 0.5 kg/h steam flow rate and 0.5 kg/h air flow rate, where the LHV reaches a maximum 
value of 17.62 MJ/kg, the CGE peaks at 75.38 %, and 𝜔𝜔 is 1.28 kg/kg. This operating condition balances the 
formation of combustible gases (CO, H2, and CH4) with minimizing carbon losses, resulting in a high-quality 
syngas with balanced energy density, process efficiency, and production yield. Assuming typical syngas 
densities and using the provided mole fractions, the maximum LHV of 17.62 MJ/kg corresponds to approximately 
14.5 MJ/Nm3. In comparison, Juma Haydary et al. (2023) reported lower heating values of 8.26 MJ/Nm3 for the 
dry gasification of RDF and 11.09 MJ/Nm3 for the wet gasification method. Gang Xiao reported LHV ranges of 
4,000–9,000 kJ/Nm3 (4.0–9 MJ/Nm3) for the gasification of tire waste (Xiao et al., 2008). The co-gasification 
process in this study achieves a significantly higher LHV of approximately 14.5 MJ/Nm3, highlighting the 
advantages of co-gasifying RDF and TW in terms of syngas quality compared to their separate gasification. 

4. Conclusions
Co-gasification of RDF and TW at the identified optimal temperature and steam/air flow rates achieved a 
significantly higher lower heating value and cold gas efficiency compared to separate gasification of RDF and 
TW. The balanced operating conditions produced a high-quality, energy-dense syngas (LHV of approximately 
14.5 MJ/Nm3), clearly demonstrating the superior syngas quality attainable through co-gasification. These 
findings highlight the promising potential of co-gasification as a sustainable energy production route. 

Acknowledgments 

We acknowledge Ho Chi Minh City University of Technology (HCMUT), VNU-HCM for supporting this study (via 
the decision number 1688/QĐ-ĐHBK, date 25/06/2021). 

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	Modeling Syngas Generation from Co-Gasification of Refuse-Derived Fuel and Tire Waste in Fixed Bed Gasifier