Reactor Inlet Research Articles

How sensitive is a dynamic ammonia synthesis process? Global sensitivity analysis of a dynamic Haber-Bosch process (for flexible seasonal energy storage)

The transition towards a sustainable energy sector depends on how we safely manage the transport and storage of energy to keep up with the demand. Large storage (TWh) of renewable energy can be accomplished by producing an energy carrier like ammonia. This power-to-ammonia production process overly depends on the stability of the ammonia reactor where any variations induced by uncertainties could have a large impact on the performance during its dynamic operations. To determine the effect of these variations, we need to identify which of the uncertainties have to be scrutinized during model design. The current work carries out the development of a dynamic Haber-Bosch process, implementing uncertainties in the model and performing an uncertainty quantification analysis on the process. Subsequently, the sensitivity indices quantify the impact of these uncertainties on the design during ramp-up. The global sensitivity analysis indicated that the reactor inlet temperature has the most considerable impact on the performance during ramp-up, where the hydrogen/nitrogen ratio has the second most significant impact. We see that the uncertainty on the reactor inlet temperature dominates (87.8%) the overall standard deviation of the ammonia production. More precise control over the inlet temperature could reduce this impact on the standard deviation. The work can be extended by including a hydrogen and nitrogen production process while powering the full process with renewable power. We can then measure the effect of coupling renewables directly to the dynamic power-to-ammonia process and optimize the design under uncertainty.

Stability of a Feed-Effluent Heat Exchanger/Reactor system for catalytic combustion of VOCs: Influence of variable emission patterns

In this contribution, a theoretical study of the dynamic behaviour (open- and closed-loop) of a Feed-Effluent Heat Exchanger (FEHE) / Reactor system for the catalytic combustion of Volatile Organic Compounds (VOCs) is carried out. An additional supply of energy is provided by means of a furnace to achieve the desired reactor inlet temperature. The positive feedback of energy to the reactor inlet is a source of instability that leads to pronounced limit cycles in the main state variables. The strong thermal oscillations predicted can damage the catalyst and cause considerable stress on both the reactor and heat exchanger materials. To prevent this scenario, a control structure that considers the manipulation of a bypass flow of the feed stream around the FEHE is selected. A single-loop feedback control system is successfully applied to maintain the inlet temperature set-point, rejecting the VOC’s concentration disturbances and enabling a stable operation. The results demonstrate that the controllability of the process is ensured with high external heat supplies (low heat recovery in the FEHE) which increases the fuel demand and the operating costs. Additionally, a high FEHE transfer area enables efficient heat recovery and avoids the controllability loss due to a suitable by-pass valve regulation.

A novel solar hydrogen production system integrating high temperature electrolysis with ammonia based thermochemical energy storage

In this paper, a novel solar hydrogen production system integrating high temperature electrolysis (using solid oxide electrolyzer cell) with ammonia based thermochemical energy storage is proposed for the first time. Without a significantly high concentration ratio, the thermochemical energy storage can upgrade relatively low-temperature solar energy to high-temperature reaction heat for high temperature electrolysis (HTE). Furthermore, thermal coupling of ammonia based thermochemical energy storage system, sCO2 Brayton cycle and HTE will result in substantially higher fuel production efficiency as compared to conventional low-temperature water electrolysis. A system model, including ammonia based thermochemical energy storage, sCO2 Brayton cycle and solid oxide electrolyzer cell (SOEC) system, has been developed using the Aspen Plus software implemented with user-defined Fortran subroutines. The models including reactors, sCO2 Brayton cycle and SOEC have been validated by comparing the model-generated results with the data from references. The effects of the endothermic reactor inlet temperature T2, charging loop ammonia mass flow rate ṁc, turbine inlet temperature T11 and current density J on the system performance have been investigated parametrically. The results show that the solar to hydrogen efficiency ηSTH increases with T2, T11 and J increasing. In addition, there is an optimum ηSTH by varying ṁc. Further, a maximum ηSTH = 26% has been obtained by optimizing the parameters in predefined ranges, which is 7% higher than the state-of-the-art of the solar HTE with TES. Based on a preliminary techno-economic analysis, the capital cost of the proposed system is estimated to be 9.28 $/kg H2, which is 18.9% lower than a typical photovoltaic based electrolyzer system. Therefore, the proposed system is economically feasible.

Numerical modeling of heterogeneous combustion with phase transitions in porous metal-containing media

In this paper, the heterogeneous combustion of porous metal-containing media is studied taking into account the phase transitions of metal in condensed and gas phases. Such process takes place when applying a novel promising method for the extraction of rare metals from various combustible materials, such as coal and petroleum wastes, by means of filtration combustion. A novel mathematical model, based on the conservation laws, is developed for investigating the physicochemical and gas-dynamic processes during the propagation of combustion waves in porous media with admixtures of metals. Using numerical experiments, the possibilities of metal mass transfer and accumulation of condensed metal in a narrow zone of the porous reactor are shown. The effect of the gas velocity at the reactor inlet and initial metal concentration on combustion of porous metal-containing media is studied. It is revealed that by changing the gas velocity at the reactor inlet, it is possible to control the process of metal transfer and accumulation during the extraction of rare metals from various combustible media. It is shown that the investigated method of rare metals extraction can be very effective for combustible media with a low initial metal concentration.

Techno-economic feasibility of a biomass-to-X plant: Fischer-Tropsch wax synthesis from digestate gasification

A techno-economic analysis is performed, assessing the production costs of Fischer-Tropsch syncrude and waxes of carbon number C20+. The products are obtained from the gasification of digestate from anaerobic digestion inside a dual fluidized bed gasifier (3.11 MWth). The results are compared against the same system fed with lignocellulosic biomass. The syngas is cleaned from impurities and conditioned to reach the desired H2/CO molar ratio of 1.8 at the inlet of the Fischer-Tropsch reactor. The Fischer-Tropsch products distribution is based on experimental data of a cobalt-based catalyst. Two process configurations are studied: (1) the Fischer-Tropsch off-gas are employed to produce electricity; (2) the off-gas are recirculated to the gasifier for enhanced wax production. Co-production of steam is also investigated. The results show an advantageous production of Fischer-Tropsch compounds utilizing digestate over wood biomass. The highest plant efficiency (i.e., biomass-to-liquid fuel) of 56.3% is reached with digestate feedstock and off-gas recirculation, outputting 61.5 kgwax/tdig. The minimum wax production cost is of 3.04 €/kgwax, assuming 7.5% discount rate and 25-years plant operation.

Modeling and analysis of microchannel autothermal methane steam reformer focusing on thermal characteristic and thermo-mechanically induced stress behavior

The application of fuel cells boosts the hydrogen demand particularly for distributed hydrogen production facility. As a potential candidate of hydrogen supply, microchannel autothermal methane steam reactor operates at high temperature and results in high thermal impact, which would decrease its stability and lifespan. A three-dimension numerical model based on finite element method was developed to evaluate the thermal characteristic and thermo-mechanically induced stress behavior of the reactor. Three different potential manufacturing materials, Fe–Cr–Al alloy, ceramic and quartz, were chosen. The results indicate that the cold-spot temperature appears near reactor inlet while the hotspot temperature appears near reactor outlet for reactor manufactured by different materials. Corresponding to the hot spot temperature, the maximum Von Mises stress appears near reactor outlet. The difference is the maximum Von Mises stress appears in catalyst layer for quartz reactor while it appears in interconnect rib for both Fe–Cr–Al alloy reactor and ceramic reactor. Meanwhile the maximum Von Mises stress reaches 1830 MPa for ceramic reactor. While the maximum Von Mises stress is 1197 MPa for quartz reactor and 1760 MPa for Fe–Cr–Al alloy reactor respectively. It implies the outlet catalyst layer region is vulnerable for quartz reactor. While the outlet interconnect rib is most vulnerable for both Fe–Cr–Al alloy reactor and ceramic reactor.

The Simulation and Optimization of Flow Field in the Low Temperature SCR Reactor

The uniformity of flue gas velocity at the inlet of selective catalytic reduction denitrification reactor can improve the denitrification efficiency, and the reasonable layout of guide plate can improve the flue gas flow rate. Fluent is used to analyze the flow field in the inlet flue of denitrification reactor, and the flue gas velocity in the guide plate reactor arranged in different ways is simulated. The optimized layout mode is the form of radian plus straight plate, which is helpful to uniform flue gas velocity, improve denitrification efficiency, and help students to improve the understanding of reactor flow field uniformity.

Proportional–Integral Extended State Observer for Monitoring Nuclear Reactors

A proportional-integral extended state observer (PI-ESO) of nuclear reactors is proposed for disturbance estimation, driven by the measurement errors of neutron flux, primary coolant temperatures at reactor inlet and outlet, as well as their integrations. This PI-ESO can provide a globally asymptotically bounded estimation for not only the reactor process variables, including normalized neutron flux and precursor concentrations as well as average temperatures of fuel assemblies and primary coolant, but also the total disturbances in channels of neutron kinetics and coolant thermal hydraulics. Furthermore, the newly built PI-ESO is applied to reconstruct both the unmeasurable state variables and the total disturbances of a nuclear heating reactor (NHR). Numerical simulation results verify the theoretical result, showing both the satisfactory performance and the influence of observer parameters.

Uncertainty quantification in decay heat calculation of spent nuclear fuel by STREAM/RAST-K

This paper addresses the uncertainty quantification and sensitivity analysis of a depleted light-water fuel assembly of the Turkey Point-3 benchmark. The uncertainty of the fuel assembly decay heat and isotopic densities is quantified with respect to three different groups of diverse parameters: nuclear data, assembly design, and reactor core operation. The uncertainty propagation is conducted using a two-step analysis code system comprising the lattice code STREAM, nodal code RAST-K, and spent nuclear fuel module SNF through the random sampling of microscopic cross-sections, fuel rod sizes, number densities, reactor core total power, and temperature distributions. Overall, the statistical analysis of the calculated samples demonstrates that the decay heat uncertainty decreases with the cooling time. The nuclear data and assembly design parameters are proven to be the largest contributors to the decay heat uncertainty, whereas the reactor core power and inlet coolant temperature have a minor effect. The majority of the decay heat uncertainties are delivered by a small number of isotopes such as 241Am, 137Ba, 244Cm, 238Pu, and 90Y.

Causes of deactivation of an amorphous silica-alumina catalyst used for processing of thermally cracked naphtha in a bitumen partial upgrading process

Thermally cracked naphtha represents a challenging feed for many catalytic processes. Its contaminant content and reactivity cause the deactivation of catalysts. Nevertheless, the use of an amorphous silica-alumina acid catalyst to convert and reduce the alkene content in thermally cracked naphtha was possible. The purpose of this study was to determine the cause(s) of catalyst deactivation by analysis of spent catalysts after conversion of cracked naphtha at different conditions in the range 250–350 °C, 6 MPa and WHSV of 0.5–2 h−1. It was found that nitrogen bases, suspected to be important acid catalyst poisons, were not the main cause of catalyst deactivation. Nitrogen was more abundant in deposits on the catalyst at the inlet compared to the outlet of the reactor, but the accumulated nitrogen in deposits represented only a minor fraction of the total amount of basic nitrogen to which the catalyst was exposed. Carbonaceous deposits were the main cause of catalyst deactivation and the profile of the deposition on the catalyst changed with temperature. At 325 °C the amount of deposits at the reactor outlet was higher, with lower H/C ratio and higher persistent free radical content than at the reactor inlet. Although some of the precursor species that formed deposits were present in the feed, some of the precursor species that formed deposits were produced during the conversion process. Although the contribution of acid catalysis was not ruled out, many observations in the study indicated that carbonaceous deposits formed mainly due to free radical reactions.

CFD Modeling of Reactor Concepts to Avoid Carbon Deposition in Pyrolysis Reactions

AbstractMethane pyrolysis in an externally heated tubular reactor inevitably ends with clogging of the reactor. Thin molten metal wall films protect the walls from carbon depositions. A falling film reactor and a rotating film reactor are investigated by CFD simulation. The results show the considerable advantages of a rotating film reactor compared to the vertical film reactor. An alternative route for carbon production from methane is the implementation of an exothermic chlorination reaction. The tubular reactor concept involves the inflow of inert gas at the reactant inlet and through porous walls to ensure that the reaction takes place in the center, thus, largely reducing carbon deposits.

Performance Studies of Proton Exchange Membrane Fuel Cells with Different Flow Field Designs - Review.

Proton Exchange Membrane Fuel Cell (PEMFC) is majorly used for power generation without producing any emission. In PEMFC, the water generated in the cathode heavily affects the performance of fuel cell which needs better water management. The flow channel designs, dimensions, shape and size of the rib/channel, effective area of the flow channel and material properties are considered for better water management and performance enhancement of the PEMFC in addition to the inlet reactant's mass flow rate, flow directions, relative humidity, pressure and temperature. With the purpose of increasing the output energy of the fuel cell, many flow field designs are being developed continuously. In this paper, the performance of various conventional, modified, hybrid and new flow field designs of the PEMFC is studied in detail. Further the effects of channel tapering, channel bending, landing to channels width ratios, channel cross-sections and insertion of baffles/blockages/pin-fins/inserts are reviewed. The power density of the flow field designs, the physical parameters like active area, dimensions of channel/rib, number of channels; and the operating parameters like temperature and pressure are also tabulated.

Adaptive λ-tracking controller for an exothermic chemical plug flow tubular reactor

ABSTRACT This paper deals with the tracking of a prespecified profile temperature for exothermic chemical tubular reactor whose dynamics is described by a set of nonlinear partial differential equations where the state variables are the reactor temperature and the reactant concentration. The coolant temperature, the inlet temperature and the inlet concentration are considered as control actions. For practical reasons, it is preferable to consider a non distributed control law to achieve the control objective. In contrast to our previous work that considers fully distributed control actions where the three control inputs are assumed to be distributed along the reactor, here the last two control inputs are applied at the reactor inlet and only the coolant temperature is distributed along the reactor. We show that the temperature of the reactor tends asymptotically to a ball of arbitrary prescribed radius , centred at the given temperature profile.

To the Theory of Flow SHS Reactors

Operation of a flow SHS reactor was analyzed theoretically. In contrast to classical formulation of the problem for combustion in a flow (Zaidel–Zeldovich, Merzhanov–Rumanov–Khaikin), a reactor with a finite length was modeled. In approximation of high activation energy, basic parameters of the process— such as temperature within the reaction zone, separation between reaction zone and reactor inlet, heat flux through the reactor inlet, and minimal admissible reactor length—were estimated by numerical calculations in terms of steady-state and nonstationary models. Some aspects of practical implementation of flow SHS reactors were discussed, including spatial stabilization of combustion zone within the reactor.

Модель реактивнісної аварії РБМК-1000 енергоблока № 4 Чорнобильської АЕС

The article presents the results of modeling of the reactivity accident, which resulted in the destruction of reactor RBMK-1000 of the 4th power unit of the Chornobyl NPP on April 26, 1986. The RBMK-1000 reactivity accident model was developed on the basis of the kinetics of the nuclear reactor, taking into account the change in the reactivity of the reactor. Reactivity changes as a result of both external influence (movement of control rods; change in the reactor inlet coolant temperature (density)) and due to the action of reactivity feedback by the parameters of the reactor core (change in the fuel temperature, coolant temperature, concentration of 135Хе, graphite stack temperature, etc.). A similar approach was applied by the authors of the article for the study of transient processes with the operation of accelerated unit unloading mode on VVER-1000, and the validity of such model is confirmed. The study of the reactivity accident on RBMK-1000 was carried out for various combinations of values of the effectiveness of control rods; reactivity coefficients of the coolant temperature and fuel temperature; changes in the temperature of the coolant at the inlet to the reactor. In most of the studied RBMK-1000 reactor accident scenarios, the critical values of fuel enthalpy, at which the process of fuel destruction begins, are reached first. An important result of the research is the conclusion that it is not necessary to reach supercriticality on instantaneous neutrons, supercriticality on delayed neutrons is also sufficient to initiate fuel destruction.

Vapor-phase oxidation of propylene glycol-methanol mixture to methyl lactate on CeO2/Al2O3 catalyst

The vapor-phase oxidation of mixtures of propylene glycol with methanol and ethanol to methyl and ethyl lactate, respectively, on supported CeO2/Al2O3 catalyst with 10 wt.% CeO2 content was studied. The steel flow reactor with a fixed catalyst bed (4 cm3) was used. 20 wt.% solution of propylene glycol in alcohol was fed to the reactor inlet by Waters 950 pump at LHSV= 0.5-0.8 h-1. Reaction temperature and pressure were varied in the interval of 190-250 0C and 1.3-1.8 bars respectively. Compressed air was given to the reactor inlet at the molar ratio of propylene glycol/O2 = 1. The reaction products were analyzed using gas chromatography (Agilent 7820A) and 3C NMR (Bruker Avance 400) methods. Studied oxidation of propylene glycol in the presence of methanol describes by total reaction CH3CHOHCH2OH +O2 + СН3OH = CH3CHOHCOOСН3 +2H2O At first, hydroxyacetone is formed that is further oxidized to pyruvic aldehyde, which attaches alcohol to form hemiacetal. Then, hemiacetal of methyl glyoxal rearranges into methyl lactate by Cannizzaro. At 220 0C and load on a catalyst of < 2 mmol PG/gcat/h, the selectivity towards methyl lactate reaches 70 wt.% at 100 % propylene glycol conversion. The main by-products are formed as the result of acetaldehyde transformation. Acetaldehyde could be formed at hydroxyacetone aldol decondensation. In the presence of ethanol, the formation of a significant amount of acetaldehyde and its aldol condensation products as well as the formation of diethoxyethane are observed. Therefore, ethyl lactate selectivity at 100 % propylene glycol conversion does not exceed 45 %. Supported CeO2/SiO2 contact was tested in this oxidation reaction also. However, CeO2/SiO2 provides the low, up to 25%, selectivity towards methyl lactate at full propylene glycol conversion. It was shown that at the same conditions methyl lactate is formed with higher selectivity then ethyl lactate. The high methyl lactate yield up to 70 wt.% could be obtained via vapor-phase oxidation of 20% mixture of propylene glycol with methanol by air oxygen on supported CeO2/Al2O3 catalyst at 210 - 220°С and at time contact of 3-4 seconds.

Mathematical Models for Packed Bed Reactor for Methanation of Carbondioxide<sub>

Models for carbondioxide methanation in a packed bed reactor was developed from first principles by the application of the law of conservation of mass and energy. The kinetic expressions of the process where obtained from relevant literatures and incorporated and solved simultaneously with the developed models using Matlab ODE45 solver. Sensitivity analysis was performed to ascertain the optimal conditions gave reasonable results, which were validated with plant data and was found to be accurate with deviations within allowable range. The research study focuses on carbondioxide methanation reaction for production of synthetic natural gas (SNG) and the performance of the process is characterized by carbondioxide conversion under various operating conditions. One dimensional pseudo-homogeneous packed-bed reactor model neglecting all possible mass and heat constraints was used as a reference and the resulting model equations are solved numerically. The reaction rates and exothermicity (ΔH°=-165KJ/Mol) prevent a packed bed reactor to be operated at high conversions and the reactant inlet temperature is used as a primary parameter, while an optimum inlet temperature is determined at which the carbondioxide conversion has maximum value. With inlet temperature higher than the optimum temperature, CO₂ conversion decreases due to the reverse Sabatier reaction.

Design Theory of a CLC Air Reactor with Oxygen Carrier Recirculation and Its Application to a 3 MWth Pilot

In chemical looping combustion (CLC), oxidation of a reduced oxygen carrier with air occurs in the air reactor and some of the oxygen carrier separated by a cyclone is returned to the air reactor for reoxidation. However, previously developed reactor models did not consider the effect of oxygen carrier recirculation on the oxidation kinetics and could not reasonably predict the oxidation behavior that occurs in a CLC air reactor. This work proposes a design theory of an air reactor with oxygen carrier recirculation to evaluate the effect of recirculation on the oxidation degree of the oxygen carrier. The developed reactor model includes submodels of the reaction kinetics, hydrodynamics, oxygen conversion, and mass and heat balance. Three oxide materials, including ilmenite, manganese ore, and perovskite (CaMn0.375Ti0.5Fe0.125O3-δ) with different oxidation kinetics, are selected as the oxygen carriers for investigating the recirculation effect on kinetic behaviors. The results indicate that only perovskite achieves its full oxidation, while manganese ore and ilmenite cannot achieve the full oxidation even with recirculation. Increasing the recirculation ratio is found to reduce the conversion of the oxygen carrier at the air reactor inlet (Xin,OC) and increase the conversion difference of the oxygen carrier (ΔXOC), which is not beneficial to the oxidation behaviors in the air reactor. The value of the recirculation ratio should be zero, i.e., all of the oxygen carriers from the air reactor should be transported to the fuel reactor. For the oxygen carriers with two-stage kinetic behavior, the initial fast stage should be fully used, while the slower second stage is not suitable for full oxidation because of very slow kinetics. This finding provides a reference for the selection of a suitable oxygen carrier and the design and optimization of the air reactor in chemical looping combustion.

Molecular level analysis on performance of diameter expanding reactor to improve gasoline quality in FCC process

A molecular level model for Fluid Catalytic Cracking (FCC) process was established based on the Structure-Oriented-Lumping (SOL) method to investigate the effects of the diameter expanding reactor on the product distribution. According to the molecular composition characteristics of feed oil, 24 structural increments were adopted to construct a molecular matrix containing 4539 molecules. Combined with the SOL reaction rules, a reaction network consisting of 118,272 reactions was established using MATLAB. The contents of 266 molecules in gasoline and 1189 molecules in diesel oil were calculated using the molecular level models of diameter expanding reactor and conventional reactor. The olefins content in gasoline, which is the summarization of 83 olefins molecules, increased as the reaction temperature went up. Compared with the conventional reactor, the ratio of isopentane to pentene in the diameter expanding reactor increased from 1.38 to 2.59 and the ratio of toluene to methylcyclohexane increased from 2.69 to 3.94. The model illustrated that the diameter expanding reactor could enhance the hydrogen transfer and isomerization reactions from the molecular level to reduce the olefins content and improve the iso-paraffins content in gasoline. The model could describe the molecular level product distribution from the reactor inlet to the outlet.

Effect of heat treatment on microstructure and mechanical properties of boron containing Ti-Stabilized AISI-321 steel for nuclear power plant application

Effect of boron on microstructure and its influence on elevated temperature properties of titanium stabilized AISI 321 steel was studied. A comparative study on mechanical properties of AISI 321 steels with and without boron addition is done. Both steels were worked to get appropriate reduction using forging-rolling process followed by solution annealing (SA) and stabilizing treatment (ST) at the appropriate temperature. Optical micrographs revealed uniform distribution of precipitates in steel. The precipitate count for Ti-stabilized AISI 321 steel with 30 ppm boron (TB30) was higher than Ti-stabilized AISI 321 steel (TB1) in which TiN and TiCN precipitates were observed. In addition to this, for TB30 steel containing boron precipitates of Fe2B and Cr2B were also observed. Precipitates refined the austenite matrix and provided yield strength stability to the AISI 321 steels. Boron addition in TB30 steel improved YS and UTS of AISI 321 steel with a marginal loss in ductility. SA and ST, TB30 steel exhibited best mechanical properties at room and elevated temperature (350 °C). Further, quantification of intergranular corrosion was done by sensitization of samples at 675⁰C for one hour and evaluated as per ASTM A262 specification practice A and practice E. Addition of nearly 30 PPM boron is highly beneficial in titanium stabilized AISI 321 steel that led to increased resistance to sensitization (both according to practice A and practice E) and improved the microstructural stability at elevated temperature resulting a reduction in intergranular corrosion and improved the elevated temperature mechanical properties. Thus, SA and ST, TB30 steels showed superior results as compared to TB1 steel. Study shows that TB30 steel is more suitable material to replace the cooling water inlet and outlet tubes of VVER type nuclear reactor.