Reactor Failure Research Articles

The Impact of the Bisubstituted Aromatics Functional Groups on the Inhibition of Methane Biosynthesis (Biogas)

Inhibitory compounds are often found to be the leading cause of anaerobic reactor upset and failure since they are present in substantial concentration in wastewaters and organic solid wastes. Among these inhibitory compounds, organic compounds are mentioned and more especially aromatic compounds. The purpose of this work was to evaluate the effect of bisubstituted aromatics functional groups on the methanogenic inhibition. The toxicity to acetoclastic methanogenic bacteria has performed in serum flasks, utilizing digested pig manure as inoculums, by measuring cumulative methane production. The results obtained indicate that some general relationships exist between the bisubstituted aromatic structures and their inhibitory effects on methanogenic bacteria. This demonstrates sufficiently that the grafting of hydrophobic or hydrophilic substituent on the benzene or monofunctional aromatic compound, make the obtained compound more or less toxic as the case and that in the same order of toxicity. A significant correlation was obtained indicating that the partitioning of bisubstituted aromatics into lipophilic membranes in bacteria may have a role in the inhibition of methane biosynthesis.

Controlling bubbles using bubbles—microfluidic synthesis of ultra-small gold nanocrystals with gas-evolving reducing agents

Microfluidic wet-chemical synthesis of nanoparticles is a growing area of research in chemical microfluidics, enabling the development of continuous manufacturing processes that overcome the drawbacks of conventional batch-based synthesis methods. The synthesis of ultra-small (<5 nm) metallic nanocrystals is an interesting area with many applications in diverse fields, but is typically very challenging to accomplish in a microfluidics-based system due to the use of a strong gas-evolving reducing agent, aqueous sodium borohydride (NaBH(4)), which causes uncontrolled out-gassing and bubble formation, flow disruption and ultimately reactor failure. Here we present a simple method, rooted in the concepts of multiphase mass transfer that completely overcomes this challenge-we simply inject a stream of inert gas bubbles into our channels that essentially capture the evolving gas from the reactive aqueous solution, thereby preventing aqueous dissolved gas concentration from reaching the solubility threshold for bubble nucleation. We present a simple model for coupled mass transfer and chemical reaction that adequately captures device behaviour. We demonstrate the applicability of our method by synthesizing ultra-small gold nanocrystals (<5 nm); the quality of nanocrystals thus synthesized is further demonstrated by their use in an off-chip synthesis of high-quality gold nanorods. This is a general approach that can be extended to a variety of metallic nanomaterials.

Kinetic study of mesophilic anaerobic digestion of pulp &amp; paper sludge

Abstract Anaerobic digestion of pulp and paper sludge (PPS) and monosodium glutamate waste liquor (MGWL) was studied in completely stirred tank reactors (CSTR) at 37 ± 2 °C. This work focused on the effect of increased organic loading rate (OLR) on the methane production in long-term experiments. For OLR in the range of (1.5–5.0) kg m −3 d −1 based on VS fed, VFA and SCOD concentrations decreased for the first 10 days and then kept stable at about 2.3 kg m −3 and 4.0 kg m −3 respectively until to the critical OLR of 5.0 kg m −3 d −1 ; and the methane generation rate enhanced to 0.838 m 3 m −3 d −1 during this period until to the reactor failure. Additionally, reaction rate constant k and sludge retention time (SRT) are described on the basis of a mass balance in a CSTR followed a first order kinetic equation. In the present study, values for y m and k were obtained as 0.733 m 3 kg −1 of removed VS and 0.07 d −1 , respectively. The simple model can apply for dimensioning a CSTR digesting of organic wastes from pulp and paper industries, food processing industries, sewage treatment plants or biogas crops.

Effects of metal deactivator concentration upon the gassing characteristics of transformer oils

Recent years have witnessed a relatively large number of power transformer and shunt reactor failures, which were attributed to the presence of corrosive sulfur compounds in the insulating oils and their attending reactions with copper to form electrically conductive copper sulphides. The associated problems appeared to be initially resolved by the addition to the insulating oil small amounts of a metal deactivator (more commonly called passivator), a derivative of 1,2,3 benzotriazole (BTA). However, over the past four years, additional problems arose that were principally associated with the evolution of gases from the electrical insulating oils, containing the metal deactivator. These observations, recorded in the field as well as reproduced in laboratories, are examined in this paper.

Reduction of produced elementary sulfur in denitrifying sulfide removal process

Denitrifying sulfide removal (DSR) processes simultaneously convert sulfide, nitrate, and chemical oxygen demand from industrial wastewater into elemental sulfur, dinitrogen gas, and carbon dioxide, respectively. The failure of a DSR process is signaled by high concentrations of sulfide in reactor effluent. Conventionally, DSR reactor failure is blamed for overcompetition for heterotroph to autotroph communities. This study indicates that the elementary sulfur produced by oxidizing sulfide that is a recoverable resource from sulfide-laden wastewaters can be reduced back to sulfide by sulfur-reducing Methanobacterium sp. The Methanobacterium sp. was stimulated with excess organic carbon (acetate) when nitrite was completely consumed by heterotrophic denitrifiers. Adjusting hydraulic retention time of a DSR reactor when nitrite is completely consumed provides an additional control variable for maximizing DSR performance.

Effects of the antimicrobial tylosin on the microbial community structure of an anaerobic sequencing batch reactor

The effects of the antimicrobial tylosin on a methanogenic microbial community were studied in a glucose-fed laboratory-scale anaerobic sequencing batch reactor (ASBR) exposed to stepwise increases of tylosin (0, 1.67, and 167 mg/L). The microbial community structure was determined using quantitative fluorescence in situ hybridization (FISH) and phylogenetic analyses of bacterial 16S ribosomal RNA (rRNA) gene clone libraries of biomass samples. During the periods without tylosin addition and with an influent tylosin concentration of 1.67 mg/L, 16S rRNA gene sequences related to Syntrophobacter were detected and the relative abundance of Methanosaeta species was high. During the highest tylosin dose of 167 mg/L, 16S rRNA gene sequences related to Syntrophobacter species were not detected and the relative abundance of Methanosaeta decreased considerably. Throughout the experimental period, Propionibacteriaceae and high GC Gram-positive bacteria were present, based on 16S rRNA gene sequences and FISH analyses, respectively. The accumulation of propionate and subsequent reactor failure after long-term exposure to tylosin are attributed to the direct inhibition of propionate-oxidizing syntrophic bacteria closely related to Syntrophobacter and the indirect inhibition of Methanosaeta by high propionate concentrations and low pH.

Dynamic Simulation of a Space Reactor System with Closed Brayton Cycle Loops

A dynamic simulation model for space reactor power systems with multiple closed Brayton cycle loops for energy conversion is developed and demonstrated for a startup transient. The simulated power system employs a submersion-subcritical safe space S ^ 4 reactor with a negative temperature reactivity feedback and has no single-point failures in reactor cooling and energy conversion. The S ^ 4 reactor core is divided into three hydraulically independent sectors, and each sector has a separate closed Brayton cycle loop that is thermal-hydraulically coupled to a circulating liquid NaK-78 secondary loop with two water heat pipe heat rejection radiator panels. Each closed Brayton cycle loop has a Brayton rotating unit designed and optimized for high thermal efficiency and low specific mass (1.16 kg/kW e ). The reactor coolant and the closed Brayton cycle working fluid is a He-Xe binary gas mixture with a molecular weight of 40 g/mol. Results are presented for a startup transient of the S ^ 4 closed Brayton cycle power system to full-power operation at a reactor thermal power 471 kW th , a Brayton rotating unit shaft speed of 45 krpm, and turbine and compressor inlet temperatures of 1149 and 400 K, respectively. At these conditions, the nominal electrical power and thermal efficiency of the power system are 130.8 kW e and 27.8%.

SIPPING TEST: CHECKING FOR FAILURE OF FUEL ELEMENTS AT THE OPAL REACTOR

Sipping measurements were implemented at the Open Pool Australian Light water reactor (OPAL) to test for failure in reactor fuel elements. Fission product released by the fuel element into the pool water was measured using both High Purity Germanium (HPGe) detection via samples and a NaI(Tl) detection in-situ with the sipping device. Results from two fuel elements are presented.

Thermal-hydraulic and neutronic analyses of the submersion-subcritical, safe space (S 4) reactor

The solid-core Submersion-Subcritical Safe Space (S 4) reactor is cooled with He-28% Xe gas (molecular weight of 40 g/mole) and nominally generates 471 kWth for at least 7 years. To avoid single point failures in reactor cooling and energy conversion, the S 4 reactor core is divided into three hydraulically independent, but neutronically and thermally coupled sectors. Each sector feeds a separate Closed Brayton Cycle (CBC) power conversion loop with separate heat rejection radiator panels. Detailed thermal-hydraulic analyses of the S 4 reactor core are performed to ensure that the maximum fuel temperature during nominal operation stays below 1300 K. In addition, a neutronics analysis performed using MCNP 5 confirms that the S 4 reactor satisfies the design reactivity requirements. These are at least $ 4 of cold clean excess reactivity, at least $ 2.25 of shutdown margin, and at least $ 1 subcritical in the worst-case of submersion and flooding, following a launch abort accident. Mass estimates of the S 4 reactor design that meets both the thermal and the reactivity requirements are provided.

Fate of LCFA in the co-digestion of cow manure, food waste and discontinuous addition of oil

Different concentrations of oily waste were added in a discontinuous mode and recurrently to anaerobic continuous stirred tank reactors fed with cow manure and food waste. Four continuous stirred tank reactors were run in parallel. A control reactor (R1) received no additional oil and R2, R3 and R4 received increasing concentrations of oil in two different experimental approaches. First, the lipids composition was forced to change suddenly, in three moments, without changing the total chemical oxygen demand (COD) fed to the reactors. The only long chain fatty acid (LCFA) detected onto the R1 solid matrix was palmitic acid (C16:0). Nevertheless in the solid matrix of R2, R3 and R4 C16:0 and stearic acid were detected. For occasional increase in the oil concentration up to 7.7 gCOD oil/L reactor (55% Oil COD/Total COD) no statistical differences were detected between the reactors, in terms of methane production, effluent soluble COD, effluent volatile fatty acids and total and volatile solids removal. Therefore this experiment allowed to conclude that cow manure–food waste co-digestion presents sufficient buffer capacity to endure solid-associated LCFA concentration up to 20–25 gCOD-LCFA/kgTS. In a second experiment higher concentrations of oil were added, raising occasionally the concentration in the reactors to 9, 12, 15 and 18 gCOD oil/L reactor. All pulses had a positive effect in methane production, with the exception of the highest oil pulse concentration, that persistently impaired the reactor performance. This experiment demonstrates that threshold values for LCFA and C16:0 accumulation onto the solid matrix, of about 180–220 gCOD-LCFA/kgTS and 120–150 gCOD-C16:0/kgTS, should not be surpassed in order to prevent persistent reactor failure, as occurs in some full scale co-digestion plants.

Performance and radiological analyses of a space reactor power system deployed into a 1000–3000 km earth orbit

This paper presents the results of performance and radiological analyses of a space reactor power system to support space-based, radar satellites in a 1000–3000 km orbit for global civilian air and ocean traffic control. The power system with six primary and secondary loops to avoid single point failures in reactor cooling and energy conversion employs a sectored, liquid NaK-78 cooled fission reactor that has a negative temperature reactivity feedback and SiGe thermoelectric energy conversion modules, nominally generating 37.1 kW e for up to 6 years. The reactor nominally generates 1183.6 kW th at an exit temperature of ∼992 K. Thermoelectric–electromagnetic (TEM) pumps circulate the liquid NaK-78 in the primary and secondary loops and passively remove the decay heat from the reactor core after shutdown. The system parameters during the startup and shutdown transients and nominal steady-state operation are calculated. The effects of the period of incrementally inserting external reactivity on the system parameters during nominal operation are also investigated. The radioactivity buildup in the reactor during nominal operation up to 6 years and the decay in radioactivity after shutdown and as a function of storage time in orbit up to 1000 years are calculated.

Application of a fuzzy logic control system for continuous anaerobic digestion of low buffered, acidic energy crops as mono‐substrate

A fuzzy logic control (FLC) system was developed at the Hamburg University of Applied Sciences (HAW Hamburg) for operation of biogas reactors running on energy crops. Three commercially available measuring parameters, namely pH, the methane (CH4) content, and the specific gas production rate (spec. GPR = m(3)/kg VS/day) were included. The objective was to avoid stabilization of pH with use of buffering supplements, like lime or manure. The developed FLC system can cover most of all applications, such as a careful start-up process and a gentle recovery strategy after a severe reactor failure, also enabling a process with a high organic loading rate (OLR) and a low hydraulic retention time (HRT), that is, a high throughput anaerobic digestion process with a stable pH and CH4 content. A precondition for a high load process was the concept of interval feeding, for example, with 8 h of interval. The FLC system was proved to be reliable during the long term fermentation studies over 3 years in one-stage, completely stirred tank reactors (CSTR) with acidic beet silage as mono-input (pH 3.3-3.4). During fermentation of the fodder beet silage (FBS), a stable HRT of 6.0 days with an OLR of up to 15 kg VS/m(3)/day and a volumetric GPR of 9 m(3)/m(3)/day could be reached. The FLC enabled an automatic recovery of the digester after two induced severe reactor failures. In another attempt to prove the feasibility of the FLC, substrate FBS was changed to sugar beet silage (SBS), which had a substantially lower buffering capacity than that of the FBS. With SBS, the FLC accomplished a stable fermentation at a pH level between 6.5 and 6.6, and a volatile fatty acid level (VFA) below 500 mg/L, but the FLC had to interact and to change the substrate dosage permanently. In a further experiment, the reactor temperature was increased from 41 to 50 degrees C. Concomitantly, the specific GPR, pH and CH4 dropped down. Finally, the FLC automatically enabled a complete recovery in 16 days.

Nitrifying bacterial communities and its activities in aerobic biofilm reactors under different temperature conditions

Tests were performed to investigate nitrifying bacterial communities and activities in aerobic biofilm reactors with different temperature conditions, denaturing gradient gel electrophoresis (DGGE) based on polymerase chain reaction targeting 16S rRNA and amoA gene, fluorescence in situ hybridization (FISH) and dehydrogenase activity (DHA). T1, T2 and T3 reactors operated at different temperatures (5, 10 and 30 °C, respectively) were set up in the thermostat and acclimated. Nitrification was considerably limited in T1 and T2 reactors. DGGE revealed specific genera of ammonium-oxidizing bacteria (AOB) and some Nitrosomonas genera endured at the low temperatures. FISH revealed a decreased distribution ratio between AOB and nitrate-oxidizing bacteria at 5 °C, and showed that the decrease of AOB also affected the nitrification failure in the aerobic biofilm reactor. The mean attached biomass of the T1, T2 and T3 reactors was 69.6, 80.6 and 112.9 mg/L, respectively, and the 2-(p-iodophenyl)-3-(p-nitrophenyl)-5-phenyl tetrazolium chloride dehydrogenase activity of the respective reactors was 73.6, 87.4 and 134.2 mgO 2 * /g VSS/day. The results demonstrate that a low temperature condition in an aerobic biofilm reactor decreases the attached biomass, distribution ratio and activity of nitrifying bacteria, and produces a change in the composition of the AOB species, which results in the failure of nitrification.

The Assessment of Remaining Life of Chemical Reactor Exposed to Creep and Fatigue

The paper presents an application according the reliability and remining life assessment of the reactor (coxing box) from a petrochemical plant, after failure in welding joint of plated shell from W1.5423 (16Mo5) steel with 25 mm thickness, plated with W1.4002 stainless steel with 3 mm thickness. The reactor failure it has associated with initial flaws from welding process, which have accelerated remaining life exhaustion. The assessment made in two steps. It has used VII section of ASME code specifications and iRiS-Thermo expert system for preliminary remaining life assessment. Concomitantly, it was performed the experimental creep and thermal fatigue testing. The program results have defined creep and thermal fatigue exhaustion and its remaining life at common creep-fatigue action, in condition of safety exploitation. It was emphasized the possibility of use an extra 40,000 hours of rehabilitated reactor in the safety condition of normal parameters.

A Dual-Growth Kinetic Model for Biological Wastewater Reactors

Biological wastewater reactors are traditionally divided into two groups based on modes of cell growth: suspension and attached (biofilm) growth. Kinetic descriptions of these reactors are based on confining cell growth to solid surfaces or void space. Because suspended cells grow in void space and biofilms grow on surfaces, both forms of microbial growth must in principle occur in a biological reactor, unless the surface is inhabitable by a biofilm. Cell growth and substrate utilization in both modes, suspension and attached, are fully accounted for in the model developed here. Simulations based on this model show that biofilms growing on the walls of a reactor, classified as a suspension culture, can contribute substantially to the total organics removal. Similarly, suspended cells in the voids of a "traditional biofilm" reactor can contribute significantly to degradation of organic substrates. The presence of biofilms can obviate total washout of suspended cells and avert reactor failure. Model simulations enable a comparison of attached and suspended biomass in terms of biomass accumulation, substrate degradation, and effectiveness of substrate utilization and illustrate interactions between the two forms of biomass. The model provides a unified way to analyze and design biological wastewater processes.

Space reactor power systems with no single point failures

Nuclear reactor power systems could revolutionize space exploration and support human outpost on the moon and Mars. This paper reviews various energy conversion technologies for use in space reactor power systems and provides estimates of the system's net efficiency and specific power, and the specific area of the radiator. The suitable combinations of the energy conversion technologies and the nuclear reactors, classified based on the coolant type and cooling method, for best system performance and highest specific power, are also discussed. In addition, a number of power system concepts with both static and dynamic energy conversion, but with no single point failures in reactor cooling, energy conversion and heat rejection, and for nominal electrical powers up to 110 kW e, are presented. The first two power systems employ reactors cooled with lithium and sodium heat pipes, SiGe thermoelectric (TE) and alkali-metal thermal-to-electric conversion (AMTEC), and potassium heat pipes radiators. The reactors heat pipes operate at a fraction of the prevailing capillary or sonic limit, and in the case of a multiple heat pipes failure, those in the adjacent modules remove the additional heat load, thus maintaining the reactor adequately cooled and the power system operating at a reduced power. The third power system employs SiGe TE converters and a liquid metal cooled reactor with a divided core into six sectors that are neurotically and thermally coupled, but hydraulically decoupled. Each sector has a separate energy conversion loop, a heat rejection loop, and a rubidium heat pipes radiator panel. When a core sector experiences a loss-of-coolant, the fission power of the reactor is reduced, and that generated in the sector in question is removed by the circulating coolant in the adjacent sectors. The fourth power system employs a gas cooled reactor with a core divided into three identical sectors, and each sector is coupled to a separate Closed Brayton Cycle (CBC) loop with He–Xe binary mixture (40 g/mol) working fluid, a secondary loop with circulating liquid Nak-78, and two water heat pipes radiator panels.

Sectored Compact Space Reactor (SCoRe) concepts with a supplementary lunar regolith reflector

Design concepts of the Sectored Compact Space Reactor for Small power (SCoRe-S) have been developed for the avoidance of single-point failures in reactor cooling and energy conversion and a wide range of thermal powers. These modular, fast neutron spectrum, lithium cooled reactors with 16.0 cm thick BeO radial reflector are designed for at least +$2.00 hot-clean excess reactivity, and with a sufficient reactivity shutdown margin. They employ 157GdN additives in the UN fuel and a 0.10 mm thick coating of 157Gd 2O 3 on the outer surface of the reactor vessel to ensure that the bare reactors, when submerged in wet sand and flooded with seawater following a launch abort accident, remain at least −$1.00 subcritical. In addition to identifying the smallest SCoRe-S concept that satisfies the design reactivity requirements, the benefit of using a lunar regolith as a supplementary reflector to decrease the thickness of the BeO radial reflector and hence, the launch mass of the SCoRe-S concepts for a lunar outpost is investigated. Calculations performed using MCNP5 confirmed that SCoRe-S 7 with a 16 cm thick BeO reflector is the smallest to satisfy the stated reactivity requirements. Results also show that a lunar regolith reflector alone is inadequate for this reactor to achieve a critical state at the beginning of life. However, when the regolith is used in conjunction with a BeO reflector of a reduced thickness, this reactor not only becomes critical, but also satisfies the reactivity design requirements at a significantly reduced launch mass. Using a supplementary reflector of regolith decreases the thickness of the BeO reflector for the SCoRe-S 7 from 16 cm to 8.0 cm, and to 5.7 cm for the SCoRe-S 11 of the largest core. The resulting decreases in the launch mass of the SCoRe-S concepts are ∼34% or 150–200 kg.

Space nuclear reactor power system concepts with static and dynamic energy conversion

Nuclear reactor power systems could revolutionize space exploration and support human outpost on the Moon and Mars. This paper reviews current static and dynamic energy conversion technologies for use in space reactor power systems and provides estimates of the system’s net efficiency and specific power, and the specific area of the radiator. The suitable combinations of the energy conversion technologies and the nuclear reactors, classified based on the coolant type and cooling method, for best system performance and highest specific power, are also discussed. In addition, four space reactor power system concepts with both static and dynamic energy conversion are presented. These systems concepts are for nominal electrical powers up to 110 kW e and have no single point failures in reactor cooling, energy conversion and heat rejection. Two power systems employ liquid metal heat pipes cooled reactors, thermoelectric (TE) and alkali-metal thermal-to-electric conversion (AMTEC) units for converting the reactor power to electricity, and potassium heat pipes radiators. The third power system employs SiGe TE converters and a liquid metal cooled reactor, with a core divided into six identical sectors. Each sector has a separate energy conversion loop, a heat rejection loop, and a rubidium heat pipes radiator panel. The fourth power system has a gas cooled reactor, with a sectored core. Each of the three sectors in the core is coupled to a separate closed Brayton cycle (CBC) loop with He–Xe (40 g/mol) working fluid and a NaK-78 secondary loop, and two separate water heat pipes radiator panels.

Implementation of IWA anaerobic digestion model No. 1 (ADM1) for simulating the thermophilic anaerobic co-digestion of olive mill wastewater with olive mill solid waste in a semi-continuous tubular digester

Abstract The anaerobic digestion model No. 1 (ADM1) developed by the international water association (IWA) task group for mathematical modelling of anaerobic digestion processes is the most sophisticated model established for full-scale industrial plants design, systems operational analysis and control, assisting technology transfer from research to industry and a common basis for further model development and validation studies. In this work the original ADM1, implemented in the simulation software package MATLAB/Simulink, was adapted and applied to replicate with reasonable degree of accuracy the thermophilic anaerobic co-digestion of olive mill wastewater (OMW) with olive mill solid waste (OMSW) in a semi-continuous tubular digester. The data set from lab-scale experiments described in our previous work was used to calibrate and validate the model. The simulations results indicated that the modified ADM1 was able to predict reasonably well the steady-state results of gas flows, methane and carbon dioxide contents, pH and total volatile fatty acids (TVFA) observed with all influents concentrations (43, 67 and 130 g COD/l) digested at the hydraulic retention times (HRTs) of 24 and 36 days. Also the reactor failure observed at a HRT of 12 days for an influent concentration of 67 g COD/l was predicted and well justified by the modified ADM1.

A Study of Two-Stage Anaerobic Digestion of Solid Potato Waste using Reactors under Mesophilic and Thermophilic Conditions

A two-stage anaerobic digestion process operated under mesophilic and thermophilic conditions was investigated for the treatment of solid potato waste to determine optimal methane yield, efficiency of operation and process stability. A solid-bed reactor was used for hydrolysis/acidification stage while an upflow anaerobic sludge blanket (UASB) reactor was used in the second stage, for methanogenesis. Three sets of conditions were investigated: (I) mesophilic + mesophilic, (II) mesophilic + thermophilic and (III) thermophilic + thermophilic in the hydrolysis/acidification and methanogenesis reactors, respectively. The methane yield was higher under mesophilic conditions (0.49 1 CH4 g COD−1 degraded) than thermophilic conditions (0.41 1 CH4 g COD−1 degraded) with reference to the methanogenic reactors. (COD) - chemical oxygen demand. However, the digestion period was shorter in systems II and III than in system I. Also, in system III the UASB reactor (thermophilic conditions) could handle a higher organic loading rate (OLR) (36 g COD 1−1d−1) than in system I (11 g COD 1−1d−1) (mesophilic conditions) with stable operation. Higher OLRs in the methanogenic reactors resulted in reactor failure due to increasing total volatile fatty acid levels. In all systems, the concentration of propionate was one of the highest, higher than acetic acid, among the volatile fatty acids in the effluent. The results show the feasibility of using a two-stage system to treat solid potato waste under both mesophilic and thermophilic conditions. If the aim is to treat solid potato waste completely within a short period of time thermophilic conditions are to be preferred, but to obtain higher methane yield mesophilic conditions are preferable and therefore there is a need to balance methane yield and complete digestion period when dealing with large quantities of solid potato waste.