CFD Modeling of a LabScale Microwave Plasma Reactor for WastetoEnergy Applications: A Review
Abstract
:1. Introduction
2. Materials and Methods
3. EMIPG System and Process Description
3.1. EMIPG System Physical Description
3.2. EMIPG Reactor Physical Description
3.3. Reaction Kinetics within an EMIPG Reactor
3.4. Governing Equations within an EMIPG Reactor
3.5. Modeling Tools/Software for an EMIPG Reactor
4. Forward Look and Conclusions
4.1. Forward Look
4.2. Conclusions
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Conflicts of Interest
Disclaimer
References
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Source  Advantage 

[16]  Lower voltage requirement than other plasma generator methods. 
[17]  Lower setup cost due to its ability to operate under atmospheric conditions, also allowing the system to be much more compact in size. 
[16,18]  Works without an electrode arrangement so that it avoids operational problems specific to electrode utilization. 
[19]  Microwave energy has already shown its ability to safely combust a variety of hazardous wastes through previous remedial applications. 
Source  Power Setting  Magnetron  Waveguide  MFC  ThreeStub Tuner  Data Collection Equipment  Other Equipment 

[28]  1–6 kW  2.45 GHz (Sairem GMP G4 60 K T400)  WR340  Alicat Scientific, Tucson AZ, USA  Yes  3 thermocouples, HR 2000+ES spectrometer (Ocean Optics Inc., Largo, FL, USA)  E3000 precision steam generators 
[29]  2–5 kW  2.45 GHz (Sairem GMP G4 60 K T400)  WR340  Alicat Scientific, Tucson AZ, USA  Yes  4 type K thermocouples, HR2000+ ES spectrometer (Ocean Optics Inc., Largo, FL, USA)  E3000 precision steam generators 
[18]  Up to 6 kW  2.45 GHz (N.S.)  WR340  Bronkhorst F210 AV50 K  N.S.  Offline microgas chromatograph (microGC, Varian CP4900), sampling bags (Tedlar, 15 L)  Impedance tuner, solid feeder 
[30,31]  1–1.8 kW  2.45 GHz (SM 745, Richardson Electronics)  N.S.  Brooks 5850  Yes  2 Rtype and 5 Ktype thermocouples, GC HP 6890, TCD Carbosphere 80/100 packed column, Alltech  Glycerol preheater and feeder, steam supplier, gear pump (Cole Parmer, 74014750), syringe pump, band heater 
[25]  4 kW  2.45 GHz (N.S.)  WR340  N.S.  Yes  Gas analyzer (N.S.)  Quartz plate installed in the end of tapered waveguide 
[32]  5 kW  2.45 GHz (N.S.)  Twisted Waveguide  N.S.  Yes  Gas analyzer (N.S.)  Quartz plate installed in the end of tapered waveguide 
[33]  1.2–1.6 kW  2.45 GHz (N.S.)  WR248  N.S.  Yes  Optical emission spectroscopy system, transmission stage, optical fiber bundle, spectrometer, CCD camera, data acquisition unit  Forward and backward power meter controller 
[34]  0.8, 0.9, and 1 kW  Not specified  N.S.  N.S.  Yes  GC/TCD, RGA, ESEM, EA (N.S.)  Voltage regulator, cooling water 
[35]  0.8–1.8 kW  2.45 GHz (National Electronics YJ1600)  WR340  N.S.  Yes  GC, FTIR  Cavity resonator 
[36]  0.8–1.4 kW  2.45 GHz (National Electronics YJ1600)  ASTEX WR340  N.S.  Yes  GC/TCD, FTIR, MS  Cavity resonator 
[37]  Up to 6 kW  2.45 GHz (N.S.)  WR340  Bronkhorst F201 AV50 K  Yes  GC, collection bags (N.S.)  Variable reflector, Sairem SAS for all microwave circuits, impedance transformer 
[38]  Up to 6 kW  915 MHz, 2.45 GHz  WR975, WR430  N.S.  GC (Shimadzu GC2014 and SRI 8610 C), FTIR (Thermo Nicolet 380), optical emission spectroscopy (CVI DK480), CCD camera  Water cooling, ferrite circulator with water load, directional coupler, moveable plunger 
Source  Feedstock  Rate of Feedstock Input  Reactor Geometry  Operating Pressure  Carrier Gases/PlasmaForming Gases  Rate of Carrier Gas/PlasmaForming Gases Input  Ignition Source  Reactor Temperature 

[28]  None  None  Quartz tube (L: 450 mm, OD: 25.6 mm, ID: 30 mm)  Atmospheric  H_{2}O, CO_{2}  20–50 g/min, 20–80 SLPM  Inserted tungsten rod  Up to 6300 °C 
[29]  None  None  Quartz tube (L: 35 cm, OD: 25.6 mm, ID: 30 mm)  Atmospheric  H_{2}O, CO_{2}, Air  10–50 g/min (up to 200 °C), 0–100 SLPM, 0–100 SLPM  Inserted tungsten rod  Up to 6300 °C 
[18]  CH_{1.5}O_{.49}  09–13 g/s  Quartz Tube (L: 50 mm, OD: 34 mm, ID: 30 mm)  Atmospheric  Air, N_{2}  8.5–10 NL/min, 17.9–25 NL/min  Used plasmaforming gas (N_{2})  973–2173 K 
[30,31]  Coal  1 g/min  Quartz Tube (L:100 cm, ID: 5.8 cm)  Atmospheric  N_{2}, O_{2}, steam  15 L/min, 0–1.0 L/min, 0–1.5 mL/min  Used plasmaforming gas (N_{2})  Above 3000 °C 
[31]  Glycerol  3 g/min  Quartz Tube (L:100cm, ID: 5.8 cm)  Atmospheric  N_{2}, O_{2}, steam  15 L/min, 0–2.6 L/min, 0–7.2 mL/min  Used plasmaforming gas (N_{2})  N.S. 
[25]  Coal  0–3.75 kg/h  Quartz tube (L: N.S., OD: 30 mm, thickness: 1.5 mm)  Atmospheric  O_{2}, air  20 L/min, 15 L/min  Inserted tungsten rod  2000–6500 K 
[32]  Coal  160 mol coal powder/h  Quartz tube (L: N.S., OD: 30 mm, thickness: 1.5 mm)  Atmospheric  O_{2}  14 mol/h  N.S.  5000 °C 
[33]  None  None  Quartz tube (2.54 cm in diameter and 22.5 cm in length)  Atmospheric  Air, N_{2}, Ar  30 L/min60 L/min  Inserted tungsten rod  5446–6100 K 
[34]  Spirulina algae  1 g of dry Spirulina algae  Quartz tube (L: 35 cm, OD: 3.3 cm, ID: 2.9 cm)  Atmospheric  N_{2}  12 L/min  N.S.  1063–1121 K 
[35]  CH_{4}  12–18 SLPM  Quartz tube (OD: 3.3 cm)  Atmospheric  N_{2}  12–18 SLPM  N.S.  N.S. 
[36]  Methanol  12.4 SLPM  Quartz tube (ID: 2.9 cm)  Atmospheric  N_{2}  N.S.  N.S.  1500 K 
[37]  Cellulose  0.5 g/s  Quartz tube (ID: 31 mm, wall thickness: 2 mm)  Atmospheric  Air  15–20 NL/min  Inserted ignition electrode system  4000–5000 K 
[38]  Ethanol  Introduced into system via bubbler @ 20 °C and 3% v/v  Quartz tube (N.S.)  Atmospheric  CO_{2}, N_{2}, Ar  1500–3900 NL/h  N.S.  Up to 6000 K 
Relationship  Effect 

O_{2}tofeedstock ratio 

Steamtofeedstock ratio 

Gasification efficiency 

Microwave power 

Rate of feedstock input 

Reaction Name  Stoichiometric Description 

Devolatilization  $C{H}_{x}{O}_{y}{N}_{z}{S}_{w}\to Char+Volatiles$ 
Oxidation  $C+0.5{O}_{2}\to CO,\Delta {H}^{0}=268{\mathrm{kJ}\text{}\mathrm{mol}}^{1}$ $C+{O}_{2}\to C{O}_{2},\Delta {H}^{0}=406{\mathrm{kJ}\text{}\mathrm{mol}}^{1}$ 
Water gas reaction  $C+{H}_{2}O\to CO+{H}_{2},\Delta {H}^{0}=131.4{\mathrm{kJ}\text{}\mathrm{mol}}^{1}$ 
Water gas shift  $CO+{H}_{2}O\leftrightarrow C{O}_{2}+{H}_{2},\Delta {H}^{0}=42{\text{}\mathrm{kJ}\text{}\mathrm{mol}}^{1}$ 
Boudouard  $C+C{O}_{2}\to 2CO,\Delta {H}^{0}=172.6{\mathrm{kJ}\text{}\mathrm{mol}}^{1}$ 
Methanation  $C+2{H}_{2}\leftrightarrow C{H}_{4},\Delta {H}^{0}=75{\mathrm{kJ}\text{}\mathrm{mol}}^{1}$ 
Steam methane reforming  $C{H}_{4}+{H}_{2}O\leftrightarrow CO+3{H}_{2},\Delta {H}^{0}=206{\mathrm{kJ}\text{}\mathrm{mol}}^{1}$ 
Nitrogenous species  $CharN\stackrel{H}{\to}HCN$ $HCN+{H}_{2}O\to N{H}_{3}+CO$ 
Sulfur species  ${H}_{2}S+C{O}_{2}\to COS+{H}_{2}O$ ${H}_{2}S+CO\to COS+{H}_{2}$ 
Source  Reactor Type  Modeling Software  Model Used  Devolatilization Considered  Equations/Models Implemented 

[47]  Downdraft Plasma Coal and Biomass Gasifier Reactor  ANSYS Fluent  FRC/EDM  Yes  FRC/EDM Devolatilization: single rate model 
[54]  Downdraft plasma coal gasifier reactor  ANSYS Fluent  FRC/EDM  Yes  FRC/EDM Devolatilization: single rate model 
[55]  Pilotscale plasma bubbling fluidized bed reactor  ANSYS Fluent  FRC/EDM  Yes  FRC/EDM Devolatilization: userdefined function (UDF) using single rate model developed by Badzioch and Hawsley [56]. 
[6]  Updraft plasma gasifier reactor  ANSYS Fluent  FRC/EDM  Yes  FRC/EDM Devolatilization: UDF 
[50]  Downdraft plasma gasifier reactor  Aspen Plus  N.S.  Yes  HCOALGEN model: used to estimate the heat of combustion, heat of formation, and heat capacity of feedstock. DCOALIGT model: used to calculate the density of the feedstock. 
[57]  Plasma spouted bed gasifier  OpenFOAM  N.S.  Yes  Multiphase particleincell approach (MPPICFoam) CoalChemistryFoam 
Source  Mass Balance Model  Momentum Model  Energy Conservation Model  Turbulence Model 

[55]  Solid phase: $\frac{\partial}{\partial t}\left({\alpha}_{s}{\rho}_{s}\right)+\nabla \xb7\left({\alpha}_{s}{\rho}_{s}{\overrightarrow{v}}_{s}\right)={S}_{sg}$ Gas phase: $\frac{\partial}{\partial t}\left({\alpha}_{g}{\rho}_{g}\right)+\nabla \xb7\left({\alpha}_{g}{\rho}_{g}{\overrightarrow{v}}_{g}\right)={S}_{gs}$ Supporting equations: ${S}_{sg}={S}_{gs}={M}_{c}{{\displaystyle \sum}}^{\text{}}{\gamma}_{c}{R}_{c}$ $\frac{1}{{\rho}_{g}}=\frac{RT}{p}{\displaystyle \sum}_{i=1}^{n}\frac{{Y}_{i}}{{M}_{i}}$  Solid phase: $\frac{\partial}{\partial t}\left({\alpha}_{s}{\rho}_{s}{\overrightarrow{v}}_{s}\right)+\nabla \xb7\left({\alpha}_{s}{\rho}_{s}{\overrightarrow{v}}_{s}{\overrightarrow{v}}_{s}\right)={\alpha}_{s}\xb7\nabla {p}_{s}+\nabla \xb7{\alpha}_{s}{\overline{\tau}}_{s}+{\alpha}_{s}{p}_{s}\overrightarrow{g}+\beta \left({\overrightarrow{v}}_{g}{\overrightarrow{v}}_{s}\right)+{S}_{sg}{U}_{s}$ Gas phase: $\frac{\partial}{\partial t}\left({\alpha}_{g}{\rho}_{g}{\overrightarrow{v}}_{g}\right)+\nabla \xb7\left({\alpha}_{g}{\rho}_{g}{\overrightarrow{v}}_{g}{\overrightarrow{v}}_{g}\right)={\alpha}_{g}\xb7\nabla {p}_{g}+\nabla \xb7{\alpha}_{g}{\overline{\tau}}_{g}+{\alpha}_{g}{p}_{g}\overrightarrow{g}+\beta \left({\overrightarrow{v}}_{g}{\overrightarrow{v}}_{s}\right)+{S}_{gs}{U}_{s}$  Gas and solid phases: $\frac{\partial}{\partial t}\left({\alpha}_{q}{\rho}_{q}{h}_{q}\right)+\nabla \xb7\left({\alpha}_{q}{\rho}_{q}{\overrightarrow{v}}_{q}{h}_{q}\right)={\alpha}_{q}\frac{\partial}{\partial t}\left({\rho}_{q}\right)+{\overline{\tau}}_{q}:\nabla \xb7{\overrightarrow{v}}_{q}:\nabla \xb7{\overrightarrow{q}}_{q}+{S}_{q}+{\displaystyle \sum}_{p=1}^{n}\left({\overrightarrow{Q}}_{pq}+{\dot{m}}_{pq}{h}_{pq}{\dot{m}}_{pq}{h}_{pq}\right)$ Supporting equations: ${\overrightarrow{Q}}_{pq}={h}_{pq}\left({T}_{p}{T}_{q}\right)$ ${h}_{pq}=\frac{6{k}_{p}{\alpha}_{q}{\alpha}_{p}{N}_{{u}_{q}}}{{d}_{p}^{2}}$ ${N}_{{u}_{s}}=\frac{{h}_{gs}{d}_{s}}{{k}_{g}}=\left(710{\alpha}_{g}+5{\alpha}_{g}^{2}\right)\left(1+0.7R{e}_{s}{}_{s}^{0.2}P{r}_{g}^{0.33}\right)+\left(1.332.4{\alpha}_{g}+1.2{\alpha}_{g}^{2}\right)R{e}_{s}^{0.7}P{r}_{g}^{0.33}$  $\mathit{k}\mathbf{}\mathit{\epsilon}$model: $\frac{\partial}{\partial t}\left(\rho k\right)+\frac{\partial}{\partial {x}_{i}}\left(\rho {k}_{{u}_{i}}\right)=\frac{\partial}{\partial {x}_{j}}\left[\left(\mu +\frac{{\mu}_{i}}{{\sigma}_{k}}\right)\right]+{G}_{k}+{G}_{b}\rho \epsilon {Y}_{m}+{S}_{k}$ $\frac{\partial}{\partial t}\left(\rho \epsilon \right)+\frac{\partial}{\partial {x}_{i}}\left(\rho {\epsilon}_{{v}_{i}}\right)=\frac{\partial}{\partial {x}_{j}}\left[\left(\mu +\frac{{\mu}_{i}}{{\sigma}_{\epsilon}}\right)\frac{\partial \epsilon}{\partial {x}_{j}}\right]+{C}_{1\epsilon}\frac{\epsilon}{k}({G}_{k}+{C}_{3\epsilon}{G}_{b}){C}_{2\epsilon}\rho \frac{{\epsilon}^{2}}{k}+{S}_{\epsilon}$ 
Variable  Term  Variable  Term 

$\rho $  Density  ${\overline{\tau}}_{g}$  Gasphase stress tensor 
$v$  Instantaneous velocity of gas/solid phase  $\beta $  Gas–solid interphase drag coefficient 
$s$  Solidphase subscript  ${U}_{s}$  Mean velocity of solid 
$g$  Gasphase subscript  ${G}_{k}$  Generation of turbulence kinetic energy due to the mean velocity gradients 
S  Mass source term  ${G}_{b}$  Generation of turbulence kinetic energy due to buoyancy 
${R}_{c}$  Reaction rate  ${Y}_{m}$  Contribution of fluctuating dilatation in compressible turbulence to the overall dissipation rate 
${\gamma}_{c}$  Stoichiometric coefficient  ${S}_{\epsilon}$  Userdefined source term 
${M}_{c}$  Molecular weight  ${S}_{k}$  Userdefined source term 
R  Universal gas constant  ${\overrightarrow{Q}}_{pq}$  Heat transfer intensity between fluid phase $p$ and solid phase $q$ 
T  Temperature of gas mixture  ${\overrightarrow{q}}_{q}$  Heat flux 
$p$  Gas pressure  ${S}_{q}$  Source term due to chemical reactions 
${Y}_{i}$  Mass fraction  ${h}_{pq}$  Enthalpy of the interface 
${M}_{i}$  Molecular weight of each species  ${k}_{p}$  Thermal conductivity for phase $p$ 
$R{e}_{s}$  Reynolds number based on diameter of solid phase and relative velocity  $P{r}_{g}$  Prandtl number of the gas phase 
Sources  CFD Software  Developer  Quick Specifications 

[55,61,62]  Fluent  ANSYS 

[55,63,64]  OpenFoam  Open CFD Ltd. 

[55,65,66]  CFX  ANSYS 

[55,67,68]  COMSOL Multiphysics  COMSOL Inc. 

[55,69,70]  Barracuda  CPFD Software LLC. 

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Sedej, O.; Mbonimpa, E. CFD Modeling of a LabScale Microwave Plasma Reactor for WastetoEnergy Applications: A Review. Gases 2021, 1, 133147. https://doi.org/10.3390/gases1030011
Sedej O, Mbonimpa E. CFD Modeling of a LabScale Microwave Plasma Reactor for WastetoEnergy Applications: A Review. Gases. 2021; 1(3):133147. https://doi.org/10.3390/gases1030011
Chicago/Turabian StyleSedej, Owen, and Eric Mbonimpa. 2021. "CFD Modeling of a LabScale Microwave Plasma Reactor for WastetoEnergy Applications: A Review" Gases 1, no. 3: 133147. https://doi.org/10.3390/gases1030011