# Material Treatment in the Pulsation Reactor—From Flame Spray Pyrolysis to Industrial Scale

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## Abstract

**:**

## 1. Introduction

## 2. Material Synthesis with Flame Spray Pyrolysis

_{x}[3], different hydrocarbons and volatile organic compounds (VOCs) [4,5,6], and carbon monoxide [7]. For example, Li et al. reported on the synthesis of Sr-doped lanthanum cobalt oxide perovskites and the higher NO

_{x}conversion rates achieved by them than common Pt-containing catalysts [8]. In order to synthesize those compounds on a laboratory scale, which is a vital first step for the discovery and development of novel materials, different approaches were chosen. Usually, facile synthesis paths such as the precipitation or sol-gel method are preferred.

## 3. Material Synthesis in a Pulsation Reactor

## 4. FSS and PR Comparison—Empirical Studies

_{2}) and silica (SiO

_{2}). Liquid Zr(IV)-propoxide was thermally treated in the PR directly while, for the FSS, the precursor was dissolved in 2-propanol, since Zr(IV)-propoxide is not combustible and, hence, not suitable for this kind of reactor in its pure form. The applied operating parameters are shown in Table 2. For both presented FSS syntheses, the fuel gas flows were 3 L/min oxygen and 1.5 L/min methane. The dispersion gas flow was 7.5 L/min, with a dispersion pressure drop of 2 bar.

_{2}reference plotted in red.

_{2}nanoparticles were synthesized in the FSS and PR [21]. In addition, the desired ability to upscale material production can be highlighted, since an almost twenty-fold increase in material throughput without any decline of the product quality was achieved. Additionally, the use of an additional solvent was not necessary, which makes production more cost effective and sustainable. After conducting this successful trial, the production of SiO

_{2}was studied following the same procedure. Tetraethyl orthosilicate (TEOS) was used as a precursor. Again, 2-propanol had to be used as a solvent for the FSS, while in the PR it was applied purely. The hourly product throughput was comparable to the first trial. This and the used precursor concentrations are summarized in Table 3.

_{2}, many characteristics of the resulting samples were similar. Both are amorphous, and the morphology shown in the TEM images depicted in Figure 7 resembles those of the previous samples, as expected. In this TEM measurement, even the particle size and overall optics are very similar between the different synthesis methods.

_{2}, however, there is a large difference concerning the SSA of the powders. The FSS sample exhibits an SSA of 260 m

^{2}/g, while the PR sample has less than half of that, at 114 m

^{2}/g. In both cases, ZrO

_{2}and SiO

_{2}, the educt feed rate and the material throughput were similar. The same was true for the FSS. However, the material properties in the case of SiO

_{2}, especially the SSA, differ strongly.

## 5. Interdisciplinary Approach

- (1)
- New materials with advantageous properties are synthesized in the FSS, while the precursor properties and the process conditions leading to the product properties are determined;
- (2)
- The relations between the PR operation parameters and the resulting process conditions must be understood. For given operation parameters, the process conditions in a PR can then be predicted, for which purpose a numerical model might be used;
- (3)
- Similarly, the influence the process conditions have on the final product properties must be discovered. With these effects understood, the product properties might also be predicted;
- (4)
- Experimental data are required for an empirical investigation, as well as for validation of the theoretical models. In order to retrieve the parameters and conditions of interest, measurement setups must be designed for both the laboratory and the industrial environment and tailored to the specific conditions of the FSS and the PR;
- (5)
- The experimental and the theoretical findings and the developed models are to be transferred to pilot and industrial plants, which will help to upscale and optimize the material treatment process.

## 6. Process Model of a Pulsation Reactor

## 7. Heat Transfer at Particles in Steady and Pulsating Flows

## 8. Measurement and Model Validation

## 9. Conclusions

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Acknowledgments

## Conflicts of Interest

## Abbreviations

AKT | Zero-dimensional PR model by Ahrens, Kim, and Tam [25] |

BDB | One-dimensional PR model by Barr, Dwyer, and Bramlette [27] |

BET | Brunauer–Emmett–Teller |

CFD | Computational Fluid Dynamics |

EFR | Entrained Flow Reactor |

FFT | Fast Fourier Transformation |

FTIR | Fourier Transformed Infrared Spectroscopy |

FSP | Flame Spray Pyrolysis |

FSS | Flame Spray Synthesis |

PIV | Particle Image Velocimetry |

PR | Pulsation Reactor |

RMS | Zero-dimensional PR model by Richards, Morris, Shaw et al. [26] |

SSA | Specific Surface Area |

TEM | Transmission Electron Microscopy |

UV | Ultraviolet |

VOCs | Volatile Organic Compounds |

XRD | X-ray Diffractometry |

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**Figure 3.**The pulsating combustion cycle [16]. 1. Ignition & Combustion: combustible mixture is driven into the combustion chamber, where it is ignited; 2. Expansion: the rapid increase in pressure accompanying the combustion blocks further combustible mixture from entering the PR and the combustion products are pushed out of the combustion chamber; 3. Intake: inertia of the outgoing flue gas causes a negative gauge pressure to form in the combustion chamber, which sucks fresh combustible mixture inside; 4. Compression: the negative gauge pressure causes a portion of the hot flue gas to travel back into the combustion chamber as well, which compresses the fresh combustible mixture and supplies thermal energy for re-ignition. The combustion cycle then repeats.

**Figure 4.**Pilot plant pulsation reactor (Kleinmengen-PR) at IBU-tec Advanced Materials AG, Weimar. View including the production hall (left) and a close-up view (right).

**Figure 8.**Approach applied in order to transfer the synthesis of novel materials from the FSS to the PR.

**Figure 9.**General plot of particle velocity, relative (slip) velocity, and gas velocity along the reactor (

**a**) without pulsation (EFR); (

**b**) with pulsation (PR).

**Figure 10.**Initial slip velocity between gas and particle in respect of the phase shift at injection.

**Figure 12.**Design of the pulsation reactor test rig at the Chair of Energy Process Engineering, TU Dresden.

**Table 1.**Operational and constructional parameter ranges of the pilot scale pulsation reactor [16].

Parameter | Range (Pilot Plant) | Often Applied |
---|---|---|

Fuel | natural gas | - |

Thermal energy consumption | up to 70 $\mathrm{k}$$\mathrm{W}$ | - |

Temperature | 250 $\xb0\mathrm{C}$ to 1300 $\xb0\mathrm{C}$ | 450 $\xb0\mathrm{C}$ to 950 $\xb0\mathrm{C}$ |

Pressure | up to 20 $\mathrm{m}$ | 3.5 $\mathrm{m}$ to 15 $\mathrm{m}$ |

Residence time | 0.05 $\mathrm{s}$ to 2 $\mathrm{s}$ | $0.5\mathrm{s}$ |

Reaction pipe length | 1.2 $\mathrm{m}$ to 7 $\mathrm{m}$ | 5 $\mathrm{m}$ |

Flow velocity | 5 $\mathrm{m}$/$\mathrm{s}$ to 20 $\mathrm{m}$/$\mathrm{s}$ | 10 $\mathrm{m}$/$\mathrm{s}$ |

Throughput (raw material) | 0.1 $\mathrm{k}$$\mathrm{g}$/$\mathrm{h}$ to 20 $\mathrm{k}$$\mathrm{g}$/$\mathrm{h}$ | 3 $\mathrm{k}$$\mathrm{g}$/$\mathrm{h}$ |

Product separation | cyclone and cartridge filter | - |

**Table 2.**Comparison of operation parameters and process conditions at FSS and PR for the synthesis of ZrO

_{2}.

FSS Reactor | Pulsation Reactor | |
---|---|---|

ZrO_{2} content feed material | 1.5 mol/L | 2.2 mol/L |

Solvent | 2-Propanol | none |

Educt feed | 0.3 L/h | 3.9 L/h |

Product throughput | 55 $\mathrm{g}$/$\mathrm{h}$ | 1050 $\mathrm{g}$/$\mathrm{h}$ |

Residence time | approx. $0.1$ $\mathrm{s}$ | $0.4$$\mathrm{s}$ |

Absolute pressure | 1 | 1 |

Temperature | > 2000 $\xb0\mathrm{C}$ | 1000 $\xb0\mathrm{C}$ |

Pulsation frequency | - | 20 $\mathrm{Hz}$ |

Energy consumption | 47 $\mathrm{M}$$\mathrm{J}$/kg_{material} | 80 $\mathrm{M}$$\mathrm{J}$/kg_{material} |

**Table 3.**Comparison of operating parameters and process conditions between FSS and PR for the synthesis of SiO

_{2}.

FSS Reactor | Pulsation Reactor | |
---|---|---|

SiO_{2} content feed material | 1.3 mol/L | 4.4 mol/L |

Solvent | 2-Propanol | none |

Educt feed | 0.3 L/h | 3.3 L/h |

Product throughput | 55 $\mathrm{g}$/$\mathrm{h}$ | 870 $\mathrm{g}$/$\mathrm{h}$ |

Residence time | approx. $0.1$ $\mathrm{s}$ | $0.4$$\mathrm{s}$ |

Absolute pressure | 1 | 1 |

Temperature | > 2000 $\xb0\mathrm{C}$ | 1000 $\xb0\mathrm{C}$ |

Pulsation frequency | - | 20 $\mathrm{Hz}$ |

Energy consumption | 47 $\mathrm{M}$$\mathrm{J}$/kg_{material} | 90 $\mathrm{M}$$\mathrm{J}$/kg_{material} |

Model | AKT (1978) [25] | RMS (1993) [26] | BDB (1988) [27] |
---|---|---|---|

Spatial complexity | 0D | 0D | 1D |

Balance equations | 2× 0D: energy balance for the combustion chamber; momentum balance for the tailpipe | 4× 0D: energy, mass, and species balance for the combustion chamber; momentum balance for the tailpipe | 3× 1D: momentum, continuity, and energy balance for the entire domain |

PR type | Helmholtz type PR | Rijke type PR | Helmholtz type PR |

Inflow modeling | Aerovalves modeled as flapper valves (having no backflow) | Continuous air and gas supply (no valves) | Time-varying mass flow rate originally defined as input |

Combustion modeling | Combustion rate explicitly defined as constant | Single-step Arrhenius model | Released heat originally defined as input (results from experiments) |

Thermal losses | Neglected | Explicitly defined heat transfer coefficient (combustion chamber only) | Explicitly defined overall heat transfer coefficient (convection at the inner PR wall, convection and radiation at the outer PR wall) |

Further improvements | Inflow model without discontinuities; Explicitly defined overall heat transfer coefficient (convective and radiative heat loss from the combustion chamber); Friction modeled by a damping coefficient | No further improvements | Sub-models for inlet valves, combustion, heat transfer, and mixing |

Author(s) | Computational Domain | Balance Equations | Turbulence Model | Combustion Model | Source of Pulsations |
---|---|---|---|---|---|

Inflow Modeling | |||||

Benelli et al. (1992) [28] | Inlet part, combustion chamber, tailpipe | Momentum, mass, and energy balance for the mixture; mass balance for individual components | k-ε, ASM | Single-step Arrhenius model | Flow-combustion interaction |

Constraint between pressure and velocity, specified pressure loss coefficient | |||||

Möller and Lindholm (1999) [29] | Inlet part, combustion chamber, tailpipe, decoupler | Momentum, mass, and energy balance for the mixture; mass balance for individual components | LES | Two-step Westbrook–Dryer model | Explicitly specified in boundary condition |

Specified mass flow rate | |||||

Tajiri and Menon (2001) [30] | Inlet part, combustion chamber, tailpipe | Momentum, mass, and energy balance for the mixture; mass balance for individual components | LES | Single-step Arrhenius model | Flow-combustion interaction |

Specified stagnation pressure and temperature, inflow adjusts naturally | |||||

Liewkongsataporn (2006) [31] | Tailpipe, decoupler | Momentum, mass, and energy balance for the mixture | V2F | Combustion not included | Explicitly specified in boundary condition |

Specified total pressure | |||||

Thyageswaran (2004) [32] | Tailpipe, decoupler | Momentum, mass, and energy balance for the mixture | k-ε | Combustion not included | Explicitly specified in boundary condition |

Specified mass flow rate | |||||

Zhonghua (2007) [33] | Inlet part, combustion chamber, tailpipe | Momentum, mass, and energy balance for the mixture; mass balance for individual components | k-ε | Single-step Arrhenius model | Flow-combustion interaction |

Dynamic mesh for the flapper valve | |||||

Yufen et al. (2013) [34] | Inlet part, combustion chamber, tailpipe | Momentum, mass, and energy balance for the mixture; mass balance for individual components | k-ε | Single-step Arrhenius model | Explicitly specified in boundary condition |

Specified mass flow rate |

**Table 6.**Measurement quantities and methods as well as inferred knowledge for experimental investigations of the pulsation reactor.

Quantity | Measurement Method | Measurement Position | Inferred Knowledge |
---|---|---|---|

Flow velocity | PIV | Glass sections of tailpipe | (1) Amplitude of velocity oscillations (2) Degree of harmonic behavior of velocity (3) Model validation |

Flow pattern | PIV | Glass sections of tailpipe | (1) Degree of turbulence (2) Degree of rotational symmetry in the flow (3) Change in boundary layer compared to steady flow |

Temperature | Thermo couple | Steel port rings | (1) Density of gas (2) Heat losses (3) Input for energy balance (4) Model validation |

Pressure | Microphone | Steel port rings | (1) Amplitude of pressure oscillations (2) Frequency of pressure oscillations (3) Degree of harmonic behavior of pressure (4) Model validation |

Exhaust gas composition | FTIR | Steel port rings | (1) Input for mass balance (2) Occurring chemical reactions |

Particle | Extraction | Steel port rings | (1) Secondary testing (2) Occurring chemical reactions |

Natural gas inflow | Flow sensor | Before combustion chamber | (1) Input for energy balance (2) Input for mass balance |

Air inflow | Flow sensor | Before combustion chamber | (1) Input for energy balance (2) Input for mass balance |

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**MDPI and ACS Style**

Heidinger, S.; Spranger, F.; Dostál, J.; Zhang, C.; Klaus, C.
Material Treatment in the Pulsation Reactor—From Flame Spray Pyrolysis to Industrial Scale. *Sustainability* **2022**, *14*, 3232.
https://doi.org/10.3390/su14063232

**AMA Style**

Heidinger S, Spranger F, Dostál J, Zhang C, Klaus C.
Material Treatment in the Pulsation Reactor—From Flame Spray Pyrolysis to Industrial Scale. *Sustainability*. 2022; 14(6):3232.
https://doi.org/10.3390/su14063232

**Chicago/Turabian Style**

Heidinger, Stefan, Felix Spranger, Jakub Dostál, Chunliang Zhang, and Christian Klaus.
2022. "Material Treatment in the Pulsation Reactor—From Flame Spray Pyrolysis to Industrial Scale" *Sustainability* 14, no. 6: 3232.
https://doi.org/10.3390/su14063232