Reduction Reactor Research Articles

Dynamic Modeling and Nonlinear Model Predictive Control of a Moving Bed Chemical Looping Combustion Reactor

A partial differential-algebraic equation (PDAE) model of a dynamic moving bed chemical looping combustion reduction reactor is developed in the IDAES process modeling framework for nonlinear model predictive control (NMPC). Numerical stability of the PDAE discretization and the index-1 property of the DAE are validated. An NMPC case study is performed, which manipulates inlet flow rates to control the system to a steady-state setpoint over approximately 6,000 s of simulated time, while respecting a lower bound on outlet oxygen carrier conversion. The dynamic optimization problems are solved for each NMPC cycle with an average of 39 CPUs, indicating that this model has the potential for use in a real-time scenario.

Thermodynamic evaluation on chemical looping conversion of Cd- and Zn-contained phytoremediation plant with different CaO pathways

With the development of phytoremediation for soil contamination, disposal of phytoremediation plant becomes a serious problem. Thermochemical conversion of phytoremediation plant can greatly reduce the volume and mass, meanwhile the clean and reusable utilization is realized. As one of the thermochemical conversion technologies, chemical looping (CL) offers a carbon negative way for clean utilization of biomass. In this technology, CaO has binary roles of heavy metal solidification and CO2 sorption for gasification enhancement. To assess the CaO pathway in CL of phytoremediation plant, two different CL processes are constructed and comparatively studied based on thermodynamic evaluation. The effects of different operating parameters on the products of gasifier (GR) and reduction reactor (RR) are compared and discussed. Results demonstrated that the CaO addition in GR is beneficial to the production of pure combustible gases. Increasing RR temperature can promote the chemical looping reactions in RR. Under lower temperature, CaO in RR can consume more CO2 leading to CO2 free environment. When it is higher than 850 °C, there is no effect of CaO in RR. Increasing the amount of OC in system can enhance the conversion of combustible gases. When αOC is higher than 0.3, the OC is reduced to a mixed state of Fe3O4 and FeO. When the CaO circulates only between GR and calciner, pure CO2 can be captured at the outlet of calciner. Existence of CaO is beneficial to retain Cd and Zn in solid phases. When the gasification temperature increases from 500 °C to 800 °C, the Cd(g) increases while Cd decreases in both CL1 and CL2. For a long lifetime of OC, CaO is suggested to circulates between GR and calciner.

A novel integrated rotary reactor for NOx reduction by CO and air preheating: NOx removal performance and mechanism

AbstractA novel integrated rotary reactor for NOx reduction by CO and air preheating (iNA reactor) was proposed. NOx removal performance was investigated in a fixed‐bed reactor, which was used to simulate the working conditions change in the iNA reactor. Lab‐synthesized Cu/FeCeOx were used as the catalyst. Two different modes were tested with the iNA reactor: short cycles and long cycles. Excellent NOx removal efficiencies of over 95% and 90% for short cycles and long cycles, respectively, were observed in the iNA reactor. Moreover, compared with the constant‐temperature rotary reactor, better H2O and SO2 resistances were also found in the iNA reactor. The reaction mechanism was proposed based on in situ diffuse reflectance infrared Fourier transform study. In the iNA process, NOx was stored as nitrates in the adsorption zone, and then decomposed rapidly by both high temperatures and CO, leading to the deep catalyst regeneration. Therefore, temperature swinging and the feed of CO were key to having high iNA reactor performance for NOx removal.

Solar Fuel Production from CO2 Using a 1 m-Square-Sized Reactor with a Solar-to-Formate Conversion Efficiency of 10.5%

Solar-driven electrochemical (EC) reduction of CO2 combined with photovoltaic (PV) cells is a promising means for carbon neutrality. However, scale-up of the EC reactors for practical realization often lowers the solar-to-chemical energy conversion efficiency (ηSTC). Here, we constructed an EC reactor for CO2 reduction to formate as large as 1 m-square in size powered by a single-crystalline silicon PV module and achieved a high ηSTC of 10.5% with a formate production rate as high as 1167 mmol/h. We used Ru-complex polymer for the cathode catalyst and IrOx nanocolloids for the anode catalyst. The advantageous feature of this combination of a low threshold voltage for the formate production was fully exploited using low-resistive Ti plates for the anode/cathode substrates, resulting in a large operating current of 65 A at a low operating voltage of around 1.65 V (overpotential of 0.22 V). A well-suppressed crossover reaction that is another feature of these catalysts enabled the use of a simple reactor configuration of a single-compartment type suitable for scale-up, with the help of nanoporous separators made of hydrophilic polyethylene that blocked O2 bubbles generated on the anodes from approaching the cathodes.

(Invited) Techno-Economic Analysis of Utilizing Electricity to Produce Intermediates from CO2

CO2 reduction reactions powered by renewable electricity offer a possible route to transform our incumbent linear consumption economic model by utilizing a portion of the over 10 gigatonnes of CO2 emitted globally as a feedstock for producing fuels and organic chemicals. However, there are several emerging technologies in this area (especially at low technology readiness level) ranging from reductive and oxidative approaches using inorganic catalysts with proton or anion exchange membranes to biological approaches whereby microorganisms directly utilize energy from electricity to produce fuels. These emerging technologies combined with cost-competitive renewable electricity generation and advances in material science warrant further investigation of the potential for electricity to be integrated with conversion of CO2, biomass, or waste resources to advance sustainable production of fuels and chemicals. This presentation discusses various techno-economic aspects of these emerging technologies, with an emphasis on (1) understanding the fundamental technical and economic feasibility of utilizing electricity for CO2 conversion strategies, (2) assessing integration of these technologies through mass/energy balance calculations and economic evaluations and (3) materials sciences and reactor engineering needed to advance the performance and scalability of CO2 conversion systems while manufacturing these systems at low costs. Our approach to this feasibility study leverages NREL’s existing core capability and expertise in analysis to identify the top technical barriers for synthesis of accessible CO2 derived intermediates, analyze results of manufacturing and system-wide technoeconomic models, outlined R&D activities and resources needed to overcome each barrier, and categorizing the time horizon for overcoming these barriers as near-, intermediate-, and long-term. The results presented here can help to benchmark and guide research on CO2 reduction reactors, in turn establishing pathways towards circularity in the carbon economy.

Mixing Behavior in a Side-Blown Vortex Smelting Reduction Reactor

Mixing Behavior in a Side-Blown Vortex Smelting Reduction Reactor

Dynamic behaviour of integrated chemical looping process with pressure swing adsorption in small scale on-site H2 and pure CO2 production

The design of a fully integrated Chemical looping reforming (CLR), single adiabatic water gas shift reactor (WGSR) and Pressure swing adsorption (PSA) operated under dynamic conditions for small scale H2 generation with inherent pure CO2 production is carried out. The dynamically operated packed bed reactors taking part in the chemical looping process have been modelled, designed and simulated to operate with transient feeds from an integrated PSA unit used for the production of 130 Nm3/h of pure H2 (99.9999% purity). As by-product, 51 Nm3/h of pure CO2 (>98.8% purity) is also produced. A rapid cycle 8-bed configuration increases the H2 recovery by 4% whilst reducing the tail gas buffer tank volume requirement by 44%. The effect of the PSA dynamic tail gas composition used as fuel for the CLR reduction reactor stage was found negligible regarding the continuity of the process and the performance of the plant, as it affected only the reduction outlet gas composition profile but had little effect on the reactor bed temperature profile. With respect to the design of the chemical looping reactor beds, an analysis has been performed on the effect of heat losses showing that at higher heat transfer coefficient (U = 5.0 W∙m−2∙K−1) CH4 conversion decreased significantly (≈90% compared to adiabatic operation), therefore a different strategy was implemented. The overall study demonstrates the process design feasibility for producing blue H2 or renewable H2 from methane/bio-methane in decentralised and modular units.

Inverse fluidised bed bioreactor enabled high-rate selenate reduction for wastewater treatment

Mine waters often contain selenate, which needs to be removed to avoid harmful human and environmental health impacts. This study evaluated the performance of a laboratory-scale inverse fluidised bed reactor (IFBR) for biological selenate reduction at 30°C. The IFBR with floating biomass carriers was fed with synthetic mine water (pH 6.0–7.0) containing ∼10 mM (1.4 g L−1) selenate, nutrients and 10 mM ethanol as electron donor and inoculated with selenate reducers enriched from anaerobic sludge and environmental samples. The bioreactor achieved a selenate reduction rate of 1.75 mM d−1 (250 mg L−1 d−1 selenate or 138 mg L−1 d−1 Se) representing 94% removal during stable performance at a hydraulic retention time of 5 d. The formation of a red precipitate indicated the formation of elemental selenium, and selenite concentration remained predominately at below 0.1 mM during stable operation. Alkalinity was generated during the biological selenate reduction, increasing the wastewater pH from 6.0 to 8.6. Redox potential gradually approached a value ranging from -500 mV to -600 mV vs. Ag/AgCl. The dominant prokaryotic phylum in the bioreactor was Proteobacteria, followed by Firmicutes and Tenericutes. This study affirmed that IFBR is a promising configuration for high-rate removal of selenate from wastewaters. It has the potential to minimise the liabilities associated with environmental impacts of selenium containing mine drainage.

Feasibility Study of an Iron-Based Composite Added with Al2O3/ZrO2 as an Oxygen Carrier in the Chemical Looping Applications

The chemical looping process is a promising approach for carbon capture. Oxygen carriers play the crucial role of carrying oxygen between oxidation and reduction reactors. In this study, iron-based composites, added with alumina and zirconia, were used as the oxygen carriers. The feasibility study of these composites for chemical looping applications was then evaluated by measuring their properties, including mechanical properties, relative density, microstructures, crystal structure, and their capacity of oxygen. The results suggest that the addition of zirconia led the decrease of the bulk relative density and thus had a negative effect to both crush strength and attrition. Crush strength declined from 57 kgf to 26 kgf when using zirconia, replacing alumina, in an iron-based composite as the inner material. In addition, the phases in oxidizing and reducing reaction were also revealed. The formation of the spinel phase (FeAl2O4) was the major factor that altered the capacity of oxygen. It inhibited Fe2O3’s ability to be completely reduced to Fe and thus decrease the capacity of oxygen. The value was therefore decreased from 9.7% to 6.2% after 50 redox cycles in alumina addition composite. On the other hand, for the zirconia addition, all of the Fe2O3 could transform to Fe, which provided 8.5% of oxygen capacity after 50 redox cycles. A dense layer which was identified as the Fe2O3 in the bulk surface was observed in the samples reacted with 50 redox cycles. The proposed mechanism of the formation of Fe2O3 layer and its corresponding kinetic analysis was also revealed in this study.

Performance assessment of thermochemical CO2/H2O splitting in moving bed and fluidized bed reactors

In this paper, we present the assessment of moving bed reactors and fluidized bed reactors operating in different fluidizing regimes for solar thermochemical redox cycles (STRC) for syngas production. The reduction reactor with a moving bed (MBRED) while the oxidation reactor (OXI) is either a moving bed reactor (MBOXI) or bubbling bed (BBOXI) yields higher performance. It was observed that only water splitting is suitable at 1400 °C and 10−3 bar reduction conditions. The higher reduction temperature and pressure improved the efficiency of the CO2/H2O splitting unit. The requirement of the H2/CO ratio drives the gas feed (CO2/H2O) into OXI. To achieve an H2/CO ratio of 1, MBOXI and BBOXI require an equimolar mixture of CO2 and H2O at 1600 °C. However, to achieve a similar H2/CO ratio at a lower temperature of 1500 °C, the gas feed of the CO2/H2O ratio required is 3. A similar H2/CO ratio is achieved for OXI operating in a turbulent and fast fluidizing, but the selectivity is lower due to lower reaction rates. OXI as a transport bed is least suited based on solid conversion (XOXI), H2/CO, or efficiency. The results are useful in designing the redox reactors for syngas.

Moving and Fixed Biological Biofilm Systems in Wastewater Treatmentwhen dose an Application Makes Sense

This study demonstrates the optimization of different Biofilm applications in wastewater treatment for a cost-effective solution. The increase of wastewater treatment cost because of high treatment efficiency requested and energy consumption makes such applications very interested in this field. Therefore, aerated reactors for wastewater treatment units were designed to work as Submerged Fixed Biofilm Bed, on the basis of biofilm-microorganisms attached to monolithic plastic supports to increase the treatment efficiency. This application depends on the aerobic process and achieved by the aeration in BOD reduction and Nitrifications reactors (Oxidation of organic compounds and nitrification). This was implemented by mixing and transport treatment processes within the biofilm attached to the plastic fixed media. The anaerobic reactor in this study was designed also to be simultaneous the de-nitrification stage by the application of a moving bed de-nitrification reactor which was considered as a part of the wastewater treatment process to achieve high treatment efficiency for the study pilot plant. The one-year-scientific evaluation was conducted onsite for the municipal wastewater pilot plant includes a test series with well-defined treatment parameters (soft mixing of the suspending the moving bed carriers; intermediate solids removal unit prior to the nitrification reactors; the mechanism for preventing the carriers to move with the flow into the subsequent reactor) such as waste-water-flow, quality, temperature, salinity, organic and hydraulic load and extensive sampling). The above application of the compact-container-system is considered as a typical field of application, for the following reasons: Need of quality improvements discharged into water body, which is often in the vicinity of bathing beaches; Need for Nutrient-Removal-Systems to avoid algae growth going into water bodies and; Space limitations in a resort and saving the implementation capital cost). The comparison between the application of the biofilm concept and the activated sludge system saved more than 40% tank size; 85% space/area; and up to 30% construction cost.

Influence of H2 availability in the catalytic reduction of nitrates in fixed bed reactors

The effect of H2 availability in the catalytic reduction of NO3− was studied through experimental tests and theoretical estimations of mass transfer regime for H2, CO2 and NO3−. The experiments were carried out in a fixed bed reactor packed with bimetallic 0.75% (w) Pd-Cu catalysts supported on granular activated carbon at 25 °C. External mass transfer limitations were only significant in the case of H2 and resulted in lower selectivity to NH4+, particularly in the low gas surface velocity range (0.09–0.019 cm/s). Low availability of H2, becoming the limiting reagent for the reaction, contributed to lower selectivity to NH4+ due to lower H:N ratio at the catalyst surface. Decreasing space–time also led to lower selectivity to NH4+, probably due to the neutralization of OH− by the available H+ at catalytic sites, thus controlling local pH and favoring N2 production. Reduction of selectivity to NH4+ was achieved with lower loss of activity and NO3− conversion when gas flow was decreased than when liquid flow was decreased. The results indicate that the design and operation of reactors for the catalytic reduction of NO3− should consider conditions leading to H2 transfer control in order to reduce selectivity to NH4+, even though this could be at the expense of reaction rate and NO3− conversion.

Co3 O4 -CeO2 Nanocomposites for Low-Temperature CO Oxidation.

In an effort to combine the favorable catalytic properties of Co3O4 and CeO2, nanocomposites with different phase distribution and Co3O4 loading were prepared and employed for CO oxidation. Synthesizing Co3O4‐modified CeO2 via three different sol‐gel based routes, each with 10.4 wt % Co3O4 loading, yielded three different nanocomposite morphologies: CeO2‐supported Co3O4 layers, intermixed oxides, and homogeneously dispersed Co. The reactivity of the resulting surface oxygen species towards CO were examined by temperature programmed reduction (CO‐TPR) and flow reactor kinetic tests. The first morphology exhibited the best performance due to its active Co3O4 surface layer, reducing the light‐off temperature of CeO2 by about 200 °C. In contrast, intermixed oxides and Co‐doped CeO2 suffered from lower dispersion and organic residues, respectively. The performance of Co3O4‐CeO2 nanocomposites was optimized by varying the Co3O4 loading, characterized by X‐ray diffraction (XRD) and N2 sorption (BET). The 16–65 wt % Co3O4−CeO2 catalysts approached the conversion of 1 wt % Pt/CeO2, rendering them interesting candidates for low‐temperature CO oxidation.

Design methodology for mass transfer-enhanced large-scale electrochemical reactor for CO[formula omitted] reduction

The electrochemical conversion of CO2 using a continuous flow membrane reactor is a promising technology. This is because the membrane reactor can achieve high productivity and selectivity by enhancing the mass transfer of CO2. In an industrial-scale reactor, the extrinsic properties that facilitate the mass transfer rate are crucial because the uniform flow distribution and high production rate can only be achieved when the interface and flow patterns are properly designed. Herein, we experimentally measured the production rate of CO in a large-scale electrochemical CO2 reduction reactor by varying the pH, interface, and flow pattern. The result indicated that optimization of the flow pattern alone can improve the production rate of CO by 28% indicating that a high convection rate through gas diffusion electrode (GDE) results in a high production rate. A three-dimensional computational fluid dynamic model was developed to quantify the effect of the new flow pattern on the mass transfer. From the model, the Peclet number increased by 28%, which is consistent with the CO partial current increment. This result indicates that the convective mass transfer improves the production rate. Additionally, we proposed a general guideline for the flow pattern design for a large-scale electrochemical CO2 reduction reactor that maximizes convective mass transfer through a GDE.

Kinetic and Mass Transfer Effects of Fly Ash Deposition on the Performance of SCR Monoliths: A Study in Microslab Reactor

Selective Catalytic Reduction (SCR) reactors with ternary vanadium-based catalysts are the state-of-the-art technology for the multipollutant abatement in cofired biomass and coal power plants. Dur...

Application of Reverse Flow Reactor for Vent Gas Emission Reduction in Catalytic Oxidation Unit at Purified Terephthalic Acid Plant

PTA (Purified Terephthalic Acid) manufacturing process generates waste gases containing VOC (Volatile Organic Compounds) that have negative health effects, one of it is benzene. Catalytic oxidation method consists of a recuperative (need external energy to reach the reaction temperature) and reverse flow reactor (RFR) which uses the principles of auto thermal (requires no external energy). Fuel consumption for heating the feed gas is a major operating cost in the catalytic oxidation, so that the fuel reduction becomes important. The objective of this study is to assess the technical possibility of RFR to lower the fuel consumption; and to assess the operating conditions for autothermal conditions. The mathematical model consisted of the unsteady state mass and energy balances and was numerically solved using a software package of FlexPDE verion 6.32. The recuperative system was simulated in the steady state condition, while RFR with the same amount of catalyst was simulated in the unsteady state condition. As the key parameter, the switching time was varied to consider the performance of RFR. At various switching times and inlet concentrations, the autothermal was achievable even heat extraction was required to prevent the catalyst overheat. At the feed gas linear velocity of 1.2 m/s and the switching time of 7.5 s or higher, RFR provides energy saving that is equivalent to US$ 0.1208/ton feed gas up to US$ 0.7248/ton of feed gas compared to recuperative system.

Duplex Process to Produce Ferromanganese and Direct Reduced Iron by Natural Gas

The application of natural gas instead of solid carbon to produce ferromanganese is a way forward in sustainable development. Mass and energy balances for an integrated duplex process to produce ferromanganese and direct reduced iron (DRI) by natural gas were studied. The process consists of natural gas injection into molten ferromanganese yielding carbon and hydrogen in which the dissolved carbon into the molten metal bath reduces MnO from a coexisting molten slag that is produced from the smelting of manganese ore. Hydrogen and CO gases reduce solid manganese oxides and iron oxides in the Mn ore to MnO and Fe in the ferromanganese reactor burden. A hot gas with a significant amount of CO and H2 leaves the reactor and is upgraded to a rich CO–H2 gas mixture via methane use in a gas reformer. The obtained highly reducing gas is then used to reduce iron ore in a direct reduction reactor for DRI production, while the DRI reactor process gas is partly looped into the gas reformer and the rest is used in an energy recovery unit for electric power generation for the ferromanganese reactor. It is shown that the presented duplex process is more sustainable than the current commercial ferromanganese production process and its application is accompanied by about 50% less electric energy consumption and about 40% less CO2 emission, excluding the source of electricity.

Correlation between the carbon isotopic composition of planktonic foraminifera-bound organic matter and surface water pCO2 across the equatorial Pacific

For times prior to those represented by the air trapped in Antarctic ice core records, the concentration of CO2 in the atmosphere must be reconstructed using geochemical proxies. The δ13C of particulate organic carbon (POC) produced in ocean surface waters has previously been observed to covary with the concentration of CO2 in the water. Relative to bulk sedimentary organic carbon, the minute quantity of organic matter trapped within the shell walls of planktonic foraminifera, “foraminifera-bound organic matter” (FBOM), has the potential advantage of being protected from diagenetic alteration and contamination by allochthonous organic matter. Here, with new protocols and instrumentation, FBOM-δ13C is investigated as a potential proxy for the aqueous CO2 concentration ([CO2(aq)]) and thus the partial pressure of CO2 (pCO2) in past surface waters. We achieve a full method precision for FBOM-δ13C of 0.4‰ (1SD) on sample sizes of 20 nanomole C by adding a cryofocus step, a helium sheath flow to the oxidation and reduction reactors, and other modifications to an elemental analyzer and by introducing new approaches to reduce contamination during sample preparation. FBOM-δ13C was analyzed in core-top sediments from the eastern tropical Pacific that span the equatorial maximum in surface water [CO2(aq)]. FBOM-δ13C is lower than predicted for marine phytoplankton, consistent with a substantial lipid component in FBOM. Anticorrelation is observed between FBOM-δ13C and climatological [CO2(aq)]; the relationship is statistically significant (P <0.05) in mixed-species samples and in 4 out of 5 picked species. The slope of the FBOM-δ13C:[CO2(aq)] anticorrelation is equivalent to or greater than has been measured for the δ13C of suspended POC in the surface ocean. Based on the few species analyzed in this study, endosymbiont-bearing and -barren species do not clearly differ from each other either in terms of their average value of FBOM-δ13C or the strength of the FBOM-δ13C:[CO2(aq)] anticorrelation, despite the recognized importance of the photosynthetic endosymbionts as a source of organic carbon for the symbiotic species. Correcting for variations in the δ13C of CO2(aq) and phytoplankton growth rate did not improve the significance of the FBOM-δ13C:[CO2(aq)] anticorrelation. The findings support the possibility that FBOM-δ13C can be used as a paleoceanographic proxy for surface water [CO2(aq)] and thus atmospheric pCO2.

A novel integrated rotary reactor for NO reduction by CO and air preheating: Reactor design and heat transfer modelling

Abstract An integrated reactor for NOx reduction by CO (iNA reactor) was proposed, integrating a rotary air preheater with a decoupled NOx adsorption-reduction reactor. Three zones were created in this reactor: a flue gas zone, a reducing gas zone, and an air zone. It was expected that NOx reduction efficiency could be enhanced by independently controlled temperature and oxygen content. In this paper, heat transfer was investigated for the proposed iNA reactor to understand the temperature evolution. A heat transfer model was first developed for an air preheater for verification. Energy balance equations were proposed for both the gas and the matrix phase. The modelling results showed that the design can meet the targeted temperatures. The developed heat transfer model was further applied to simulate the temperature profiles in the iNA reactor with three zones. The influences of several design and operating parameters on the heat transfer performance were investigated: flow direction of reducing gas, inlet temperature of flue gas, rotating speed of the reactor, inlet temperature and flow rate of reducing gas, and different zone partitions. It was concluded that a slower rotating speed was preferred to maintain large temperature differences between different zones, which benefited the temperature-dependent NOx adsorption-reduction process. For the reducing gas, downward flow direction, higher temperature and flow rates were preferred. The heat transfer performance was not very sensitive to zone partition ratio, although it may have an important effect on the reaction efficiencies.

Spatiotemporal statistical characteristics of multiphase flow behaviors in fuel reactor for separated-gasification chemical looping combustion of solid fuel

Separated-gasification chemical looping combustion (SGCLC) has high conversion efficiency for solid fuels. Fuel reactor (FR) in SGCLC is designed as a gasifier (GR) and a connected reduction reactor (RR) with gas, sand and oxygen carrier (OC) phases. In order to clearly know the multiphase flow characteristics, a FR prototype is designed and the gas-solid hydrodynamics in FR are investigated using computational fluid dynamic (CFD) method. The gas velocity and OC flowrate are changed in simulations to study their effects on flow behaviors. Bubble probability in GR increases from 0 at bottom to 0.64 at 0.33 m while the gas volume fraction reaches 0.80 herein under fundamental condition. Spatiotemporal statistical results of the characteristics of gas and solid phases demonstrate that increasing gas velocity can enhance the heterogeneity of pressure and gas velocity distributions in GR. The mean values of pressure and gas velocity standard deviations increase from 13.71 Pa to 18.66 Pa and from 2.08 m/s to 2.55 m/s at 0.33 m when gas velocity accelerates from 1.8 m/s to 2.2 m/s. On the contrary, it has opposite effect on heterogeneity of pressure distribution in RR. Increasing OC flowrate from 0.6 kg/s to 0.8 kg/s can enlarge OC inventory in RR and enhance the standard deviation of pressure distribution in RR. The mean value of pressure standard deviations in RR increase from 3.12 Pa to 4.82 Pa at 1.85 m. The gas-OC mixing and contact can be improved for sufficient combustion reaction.