Time To Maximum Rate Under Adiabatic Conditions Research Articles

Thermal behaviors and kinetic analysis of dicyclohexylmethane-4,4′-diisocyanate (HMDI)

Programmed heating measurements were performed by differential scanning calorimeter (DSC) to obtain thermal parameters. The expression of the optimal kinetic mechanism model for the thermal behaviors of dicyclohexylmethane-4,4′-diisocyanate (HMDI) under the five heating rates is f(α)=α0.41(1−α)0.93 by fitting DSC curves. The thermal behaviors under adiabatic conditions and the time to conversion limit (TCL) were further simulated based on kinetic parameters to provide effective safety information concerning HMDI. Estimation of time to maximum rate under adiabatic conditions (TMRad) indicated that the temperature should not be too high by reference to TD24 = 230.95 °C during the production and storage. For 14 % limit value, TCL requires 7 d when the material reaches its maximal rate at 211.15 °C, while it just only 1 d at 236.90 °C.

Thermal stability and kinetic analysis of isophorone diisocyanate (IPDI)

Dynamic experiments were performed by differential scanning calorimeter (DSC) to obtain thermodynamic parameters to evaluate the thermal hazards of isophorone diisocyanante (IPDI). The apparent activation energy was calculated by the isoconversional Friedman method. And the kinetic model was evaluated by fitting experimental curves, which consisted of two stages: the initiation stage of the n-order type, and the autocatalytic stage. Furthermore, thermal behaviors under isothermal and adiabatic conditions were simulated, and the results indicated that a large amount of thermal energy was released. Estimation of time to maximum rate under adiabatic conditions (TMRad) demonstrated that the operational temperature should not exceed 223.64±0.30°C during production and operation. For a limit value of 10%, the time to conversion limit of IPDI is 11.36 d with an error of less than 0.66 at 200°C, while it only took within 0.1 d at 260°C.

Thermal stability and decomposition mechanism analysis of 1, 1’-Azobis(cyclohexanecarbonitrile) by STA, DSC, ARC and TG-FTIR

1, 1′-Azobis(cyclohexanecarbonitrile) (ABCN) is a kind of azo compound, which is widely used as an initiator in the polymer industry. Plenty of heat will be released during the thermal decomposition, and fire or explosive accidents could happen when the cooling system of the polymerization reactor fails. In this manuscript, the thermal decomposition behavior of ABCN under a dynamic temperature environment was investigated by simultaneous thermogravimetric analyzer (STA). Differential scanning calorimeter (DSC) was used to detect the thermal effects of different stages of mass loss. The apparent activation energy was calculated by Kissinger-Akahira-Sunose methods (K-A-S methods). The thermal runaway behavior was investigated by accelerating rate calorimeter (ARC), which was used to predict time to maximum rate under adiabatic condition (TMRad). The results show that the temperatures at TMRad = 8 h and 24 h are 93.0 °C and 89.7 °C, respectively. The self-accelerating decomposition temperature (SADT) is 86.6 °C, which is calculated based on the thermal theory of Semenov. Since ABCN is used at 60–90 °C, a major accident could happen when the heat accumulated in the reactor is not removed timely. The risk of thermal runaway reactions for ABCN was defined against the risk matrix as level Ⅲ, which is an unacceptable risk. The carbon radicals and nitrogen were released during the decomposition of ABCN based on the experiment result of thermal gravimetric analyzer-Fourier transform infrared spectrometer (TG-FTIR) system. Several safety assessment parameters could supply references for the industry to alleviate thermal hazards and prevent critical incidents.

PH-Based Control of the Kinetics and Process Safety of the Highly Exothermic Reaction Between Ammonium Chloride and Sodium Nitrite for Flow-Assurance Applications

Summary The highly exothermic reaction between ammonium chloride (NH4Cl) and sodium nitrite (NaNO2) has an important application in the area of flow assurance. Because of the high heat generation, this reaction has been used as a heat source for the fluidization of low-melting-point deposits formed during oil and gas production. Because this reaction is strongly pH dependent, the incorrect choice of pH can result in an uncontrollable temperature increase caused by the system’s inability to dissipate the large amount of heat generated in a short time, causing accidents such as structural damage and explosions. Thus, the aim of this work was to study a method that involved adjusting the pH over time to ensure controlled heat generation, with high calorimetric conversion, and avoid the development of a thermal-runaway reaction (pH-based control of the kinetics and process safety). The kinetics and thermodynamics of this reaction were studied using heat-flow reaction calorimetry and attenuated total reflection (ATR)-Fourier-transform infrared (FTIR) (ATR-FTIR) spectroscopy. Following a semiempirical approach, calorimetric and spectroscopic data were fitted to a kinetic equation using nitrite, ammonium (NH4+), and hydronium concentrations. The molar enthalpy calculated was –322.92 kJ/mol, and the Arrhenius parameters were determined as the frequency factor [ln(A)] = 22.21 and the apparent activation energy (Ea) = 63.40 kJ/mol. The kinetic model constructed made it possible to properly evaluate the pH profile that should be maintained to control the kinetics (heat-generation rate) and process safety [time to maximum rate under adiabatic conditions (TMRAD)] of the reaction. The strategy of adjusting the pH over time ensured controlled heat generation and high calorimetric conversion, which cannot be achieved by simply adding catalyst at the beginning of the reaction, and minimized the risk of developing a runaway reaction. However, in real applications, the pH control must be made using the balance between the thermal risk (TMRAD) and the performance of the method (qr), because although it is possible to decrease the thermal risk (increase the value of TMRAD) by increasing the pH, this increase is accompanied by a decrease in the heat-generation rate. Thus, from the proper balance of these factors (qr and TMRAD), pH control can ensure adequate levels of heat production within an acceptable thermal risk.

Analysis of thermal hazards of tert-butylperoxy-2-ethylhexyl carbonate by calorimetric technique

Tert-butylperoxy-2-ethylhexyl carbonate (TBEC) is a colorless clear liquid with the molecular formula of C13H26O4, and it is often used as an initiator in polystyrene production. However, it has a high degree of thermal sensitivity. In order to study the thermal hazard of TBEC, the theoretical and experimental methods were combined to yield results. In the theoretical section, the bond energies of TBEC were calculated by Gaussian16 software to analyze the instability of TBEC from the microscopic point of view. In the experimental section, the combustion test, Easy Max and Phi-tec II were utilized to study the thermal characteristic of TBEC. The adiabatic kinetic parameters were calculated; then time to maximum rate under adiabatic conditions (TMRad) and self-accelerated decomposition temperature (SADT) were also estimated. The results demonstrate that TBEC can evaporate to produce combustible gas during heating, and will burn violently when encountering an ignition source. According to the calculation results, the activation energy (Ea) of TBEC under adiabatic conditions is 156.16 kJ mol−1. And based on the value of SADT, the ambient temperature during storage and transportation of TBEC should be lower than 51.83 °C. The results can help designers decide whether it is necessary to take extra measures to reduce risk.

Determination of SADT and TMRad of 3-bromo-1-(3,5-dichloropyridin-2-yl)-4,5-dihydro-1H-pyrazole-5-carboxylic acid: Applying thermal decomposition kinetics

The aim of this study was the evaluation of the safety parameters: Time to Maximum Rate under adiabatic conditions (TMRad) and self-accelerating decomposition temperature (SADT) for 3-bromo-1-(3,5-dichloropyridin-2-yl)-4,5-dihydro-1H-pyrazole −5-carboxylic acid (BDPCA) using evaluated kinetic parameters. The required decomposition kinetics was determined from the results of differential scanning calorimetry (DSC), microcalorimetry (C600), and adiabatic accelerating calorimeter (ARC). AKTS Thermokinetics (TK) and Thermal Safety (TS) Software were used for evaluation of the kinetic parameters of a decomposition reaction. The kinetic analysis was based on the isoconversional Friedman method. The values of TMRad amount to 110.2 °C, 107.3 °C, and 104.9 °C when calculated from the data collected by DSC, C600, and ARC, respectively. The simulated values of SADT for a 50 kg package of BDPCA amount to 101 °C and 96 °C when elaborating the DSC and C600 signals, respectively. Obtained results indicate that the application of kinetic parameters evaluated from the experiments carried out by three different calorimetric devices resulted in the evaluation of consistent safety parameters.

Research on thermal decomposition characteristics of H foaming agent with different moisture contents

N, N-Dinitroso pentamethylene tetramine, also known as H foaming agent, is a self-reactive chemical substance commonly used in the rubber industry. Decomposition, explosion and combustion may be caused by the presence of fire or high temperature. As a high-risk chemical that is strictly regulated in China, H foaming agent has ever triggered multiple accidents. During the study of the decomposition thermal process of H foaming agent, it was found that the presence of moisture content at different levels had a significant effect on its thermal stability. The thermal characteristics of H foaming agent under different moisture contents was studied through the test means such as adiabatic calorimetry and high-pressure differential scanning calorimetry. Through isothermal calorimetry experiment, it was found that the decomposition of H foaming agent had obvious auto-catalytic characteristics. In the moisture content within the range of 0–40%, with the increase of moisture content, the initial exothermic temperature Tonset of the mixture system of H foaming agent and water decreased, while the time from initial heat release to rapid temperature rise of the reaction system (induction period) was gradually prolonged, and the temperature increment of the reaction system was increased gradually. As the proportion of moisture content in the system increased, the adiabatic temperature rise ΔTad of the mixture system of H foaming agent and water gradually decreased, meanwhile the time to maximum rate under adiabatic condition (TMRad) gradually decreased. The research results have guiding significance for finding the reasonable moisture content of H foaming agent in the drying process and determining the upper temperature limit during storage and transportation.

Thermal Decomposition Behavior and Thermal Hazard of Benzoyl Peroxide under Different Environmental Conditions

AbstractThermal decomposition characteristics of benzoyl peroxide (BPO) were preliminary studied by differential scanning calorimetry (DSC), microcalorimeter (C600) and high‐pressure calorimeter (DSC 204 HP). DSC and C600 were used to research the effect of thermal history on the thermal decomposition characteristics of BPO. The time to maximum rate under adiabatic conditions (TMRad) and the self‐accelerating decomposition temperature (SADT) were calculated by combining with the thermal equilibrium equation. The results reveal that the initial decomposition temperature, the highest decomposition temperature and the decomposition completion temperature of BPO increased with the increase of heating rate. The mass scale and thermal history have significant effects on its thermal decomposition. The apparent activation energy of the BPO was calculated by the Kissinger method to be 146.8 kJ mol−1, the apparent activation energy calculated by Friedman method presents that BPO has different apparent activation energy at different stages of the reaction. TD2, TD4, TD8 and TD24 were gained to be 83.5, 80.2, 77.0 and 72.2 °C, respectively. With the increase of the packing quality, the SADT gradually decreased, resulting in a further increased in the risk. To prevent accidents, the initial temperature of BPO should be well governed and massive storage should be avoided.

Research on the decomposition kinetics and thermal hazards of 2,2'-azobis(2-methylpropionamidine) dihydrochloride by experimental and simulation approach

The thermal behaviors of azo-compounds have been a topic received extensive attention. This paper attempted to obtain the decomposition kinetics of 2,2′-azobis(2-methylpropionamidine) dihydrochloride (AIBA) by applying differential scanning calorimeter (DSC) experiments and slow cook-off test. Moreover, the thermal hazards parameters, such as self-accelerating decomposition temperature (SADT), time to maximum rate under adiabatic conditions (TMRad), time to conversion limit (TCL), were predicted. The results indicate that AIBA is a highly exothermic and hazardous substance, and the kinetic model including two-step parallel reaction paths, the n-order reaction and the autocatalytic reaction, is credible to evaluate the decomposition process of AIBA. Based on the kinetic model and fiberboard packaging, the simulated SADT of 50 kg drum and 25 kg box are 94 °C and 91 °C, respectively. The TMRad is 104.66 °C under 24 h, and 113.05 °C of 8 h.

Thermal hazard evaluation of AIBME by micro-calorimetric technique coupled with kinetic investigation

2,2′-Azobis (2-methylpropionate) (AIBME) is a new type of environmental-friendly oil-soluble azo initiator, extensively applied in the radical polymerization industry relying on its extraordinary thermal and physicochemical properties. Nevertheless, the special structure makes AIBME decompose easily under low ambient temperature with a tremendous amount of heat release. To qualify its thermal hazard and obtain the specific safety parameters such as time to maximum rate under adiabatic condition (TMRad) and self-accelerating decomposition temperature (SADT), differential scanning calorimeter (DSC), simultaneous thermogravimetric analyzer (STA), and accelerating rate calorimeter (ARC) were applied to analyze the thermal behaviors of AIBME while conducting the thermokinetic analysis and numerical curve fitting. The results indicate that AIBME decomposes at low temperature, and the SADT of AIBME in 25 kg UN package is 35.2 °C. Moreover, the temperature at TMRad = 8 h is determined at 51.6 °C using Townsend method. Compared with commercially used azo compounds, such as 2,2′-azobisisobutyronitrile (AIBN) and 2,2-azobis(2-methylbutyronitrile) (AMBN)), the predominant heat of decomposition, more gaseous degradation products, quicker heat release rate, and lower decomposition temperature make AIBME more hazardous during production, storage, and transportation. The results of this study can provide the references for the process safety assessment and the design of appropriate safety system in scale-up applications with the wish to avoid the occurrence of AIBME involved accidents.

Thermal hazard assessment and ranking for organic peroxides using quantitative structure–property relationship approaches

Chemical reactivity hazards of organic peroxides are major concerns of the chemical industry due to many serious incidents every year. Thermal hazard assessment for organic peroxides is of great importance for safe operations in chemical process industries. A new hazard evaluation method based on quantitative structure–property relationship (QSPR) was proposed to assess thermal hazard of organic peroxides from their molecular structures. Optimal molecular descriptors were determined to characterize thermal hazard parameters, including onset temperature (To), time to maximum rate under adiabatic condition (TMRad) and heat of reaction (ΔH), respectively. Both the probability and severity of the thermal risk were considered to evaluate the thermal hazards of organic peroxides comprehensively. To and TMRad were employed to describe the probability of thermal risk, while ΔH was used to describe the severity. Then, the thermal hazard rating was developed based on the molecular descriptors and a corresponding ranking criterion was also proposed with the thermal hazards being divided into five levels. After comparing and verifying with previously developed evaluation methods, the proposed assessment method in this work would be reasonably expected to provide an accurate ranking of the thermal hazards for organic peroxides.

Evaluation of thermal hazards based on thermokinetic parameters of 2-(1-cyano-1-methylethyl)azocarboxamide by ARC and DSC

Azo compounds (azos) are widely used as radical initiators in the polymerization industry. Nonetheless, due to the azo group molecular structure, azos gravitate toward thermal decomposition and lead to thermal runaway accidents. In this paper, the thermal decomposition behaviors of 2-(1-cyano-1-methylethyl)azocarboxamide (CABN) under the dynamic and adiabatic environments were investigated using differential scanning calorimetry and accelerating rate calorimeter. Several safety assessment parameters such as time to maximum rate under adiabatic condition (TMRad), temperature of no return, and self-accelerating decomposition (SADT) temperature were calculated based on thermokinetic analysis as well as curve fitting. The results indicated that CABN decomposes at low temperatures (90.0–100.0 °C) and releases huge volumes of gaseous products, which may set off a fire, deflagration, or even explosion if the decomposition occurs uncontrolled in a confined space. Compared with commonly used azos, the shorter TMRad, lower SADT, and more heat from thermal decomposition reflect the potential thermal explosion hazards of CABN. To investigate emergency response procedure in terms of industrial applications, the oxygen-balance method was further used to evaluate the explosion hazard of CABN, and several recommendations on alleviating the thermal hazards of CABN were established to prevent catastrophic accidents.

Thermal instability and kinetic analysis on m-chloroperbenzoic acid

m-Chloroperbenzoic acid (MCPBA) has been widely applied as an oxidant agent for various oxidations in organic chemistry. The understanding of thermal instability and kinetics is a prerequisite for safer storage and transportation. This study investigated the thermal decomposition characteristics of MCPBA under dynamic and adiabatic conditions by performing TG, DSC and ARC tests, respectively. Kinetic parameters were computed using Starink method and compensation effect. Thermal safety parameters, including critical temperature of thermal explosion (Tb) and time to maximum rate under adiabatic conditions (TMRad), were determined to assess the thermal hazard of MCPBA. The experimental results showed two major thermal decomposition processes and a coupling phenomenon of heat absorption and generation. The mean value of Ea was determined as 57.630 kJ mol−1, and the best model to describe the overall reaction mechanism was three-dimensional diffusion model with integral form \(G\left( \alpha \right) = \left[ {1 - \left( {1 - \alpha } \right)^{1/3} } \right]^{2}\) for 0.05 < α < 0.80. The TMRad was 24 h with an apparent onset temperature of 345.82 K. This study provided a guidance to determine the safety measures in MCPBA storage and transportation.

Kinetic analysis of the thermal decomposition of liquid ammonium nitrate based on thermal analysis and detailed reaction simulations

A detailed reaction mechanism for the liquid-phase decomposition of ammonium nitrate (AN) was modeled based on ab initio calculations, and this model was employed to simulate heat flow curves associated with the decomposition of AN at various heating rates (1, 2, 4, 5, and 8 K min−1) over the temperature range of 443–623 K. A kinetic analysis using the model-free Friedman method determined the kinetic triplet for AN decomposition. The predicted activation energy for the exothermic decomposition had a range of approximately 162–168 kJ mol−1 with $$\alpha$$ values between 0.1 and 0.5. The activation energy value is good agreement with the experimental one of 170 kJ mol−1. The Friedman kinetic model was used to predict the time to maximum rate under adiabatic conditions (TMRad) at various initial temperatures, and these values were compared to the TMRad values obtained directly using the detailed reaction mechanism. Accurate predictions for TMRad were obtained at initial temperatures below 623 K. The difference between the TMRad values obtained from the thermal analysis and detailed reaction models at 823 K was larger than one order of magnitude. It was also found that the dominant decomposition mechanism changes from ionic to radical with increasing temperature, and this explains the difference in the TMRad values at 823 K.

Process safety evaluation of the synthesis of tert-butyl peracetate

To explore the thermal hazard of tert-butyl peracetate (TBPA), various instruments were applied to investigate the synthesis and decomposition of TBPA. Reaction calorimeter (RC1e) was used to analyze the exothermic characteristics during synthesis of TBPA in acid and alkaline medium, respectively. The thermal parameters, such as adiabatic temperature rise (ΔTad,r) and maximum temperature of the synthesis reaction (MTSR), were calculated for assessing the thermal hazard of TBPA synthesis. Differential scanning calorimetry (DSC) and Phi-TEC II adiabatic calorimeter were used to understand thermal characteristics of TBPA decomposition. According to the exothermic curves from the interruption and rescanning experiments and isothermal experiments by DSC, TBPA decomposed following the nth-order law. Thermal parameters of TBPA decomposition at different heating rates were obtained from non-isothermal experiments and the corresponding apparent activation energy (Ea) was calculated by Kissinger method and Starink method. Phi-TEC II was, in turn, used to obtain the thermokinetic parameters of TBPA decomposition under adiabatic conditions. The thermokinetic parameters, such as Ea, the pre-exponential factor (A) and reaction order (n), were used to calculate the time to maximum rate under adiabatic conditions (TMRad) and TD24 (Temperature at which TMRad is 24.0 h). To further understand the decomposition process, thermal decomposition products were studied using gas chromatography/mass spectrometry (GC/MS). Then the reaction scheme of TBPA decomposition was proposed. The thermal hazard of TBPA synthesis was evaluated according to the risk matrix and the Stoessel criticality diagram. Results shows that compared to synthesis in acid medium, TBPA synthesis in alkaline medium was preferred. However, the operating conditions of synthesis also need to be redesigned to improve the process safety level. These studies were considered to have potential applications in inherently safer operating measures and safer storage and transportation.

Zero-Order Versus Intrinsic Kinetics for the Determination of the Time to Maximum Rate under Adiabatic Conditions (TMRad): Application to the Decomposition of Hydrogen Peroxide

The thermal safety of chemical processes requires knowledge of the safety parameters that quantify the probability, such as time to maximum rate under adiabatic conditions (TMRad), and the severity, such as adiabatic temperature rise under adiabatic conditions (ΔTad). The zero-order approximation is used to ease the determination of TMRad values at different process temperatures; but how can one be sure that this approximation is acceptable, compared to the use of an intrinsic kinetic model? In the literature, there are no such studies that compare the values of TMRad by using zero-order and intrinsic kinetic models. For that, decomposition of hydrogen peroxide in the presence (and in the absence) of copper sulfate was studied in an advanced reactive system screening tool (ARSST) unit. This calorimeter operates under near-adiabatic conditions, based on heat loss compensation principle, and by using a background heating rate (β). In a first stage, a kinetic model was built to estimate the intrinsic kinetic...

Preparation, characterization and thermal risk evaluation of dihydroxylammonium 5, 5′-bistetrazole-1, 1′-diolate based polymer bonded explosive

Dihydroxylammonium 5,5′- bistetrazole-1,1′-diolate (TKX-50) was used to prepare TKX-50-based polymer bonded explosive (PBX) for the first time in this study. The thermal stabilities and the kinetic parameters of TKX-50 and TKX-50-based PBX were compared via Differential Scanning Calorimetry (DSC), Thermal Gravity-Differential Thermal Gravity (TG-DTG) and Accelerating Rate Calorimeter (ARC). Furthermore, in order to know about their thermal safeties comprehensively, an advanced thermal analysis program based on Friedman method was employed to calculate the thermal safety parameters for TKX-50 and its PBX. With its help, two important safety parameters (time to maximum rate under adiabatic conditions (TMRad) and self-accelerating decomposition temperature (SADT)) for the two energetic materials were calculated and discussed. Finally, based on the safety parameters, effects of storage conditions and ambient temperatures on the thermal explosions of TKX-50 and TKX-50-based PBX were further studied by using finite element analysis (FEA).

Thermal Safety Assessment through the Concept of Structure–Reactivity: Application to Vegetable Oil Valorization

The concept of linear free-energy relationships, and more particularly the Taft equation, was extended to a multiphase system with several reactions and reaction centers: the epoxidation of vegetable oils and free fatty acids. The epoxidation of vegetable oils and free fatty acids by different percarboxylic acids produced in situ is an exothermic reaction system which can lead to a thermal runaway. The safety criterion time-to-maximum-rate under adiabatic conditions (TMRad), linked to the kinetics of the system, was determined with the advanced reactive system screening tool (ARSST). We have demonstrated that TMRad values for the epoxidation of vegetable oils and free fatty acids by using different carboxylic acids follow the Taft equation. The epoxidation reaction series by different carboxylic acids was found to be more sensitive to the polar effect than steric effect. It was demonstrated that, by knowing the carboxylic acid used for the epoxidation, it is possible to predict the values of TMRad.

Prediction of thermal hazard for TBPTMH mixed with BPO through DSC and isoconversional kinetics analysis

tert-Butyl peroxy-3,5,5-trimethylhexanoate (TBPTMH), generally used as an initiator, can replace tert-butyl peroxybenzoate (TBPB) in polymerization processes. The thermal behavior of TBPTMH added to this reaction was analyzed. Furthermore, we compared the influence on thermal hazards with TBPB and benzoyl peroxide. Through differential scanning calorimetry and isoconversional kinetics analysis, thermokinetic parameters and simulation results, including apparent activation energy (Ea), time to maximum rate under adiabatic conditions (TMRad), and self-accelerating decomposition temperature (SADT), can be used to identify a safer handling environment when TBPTMH is mixed with tert-butyl peroxide. According to DSC thermal curves, the apparent exothermic onset temperature of TBPTMH was from 100 to 124 °C, and the heat of decomposition of TBPTMH was from 748.81 to 950.48 J g−1. Ea values as calculated using three methods (Ozawa–Flynn–Wall, Friedman, and ASTM E698) were 122.4, 122.7, and 122.0 kJ mol−1, respectively. From the point of view of thermal loss prevention, TMRad and SADT are two crucial safety parameters, which were obtained as 61.3 °C under 24 h and 55.0 °C, respectively.

Cooling and stirring failure for semi-batch reactor: Application to exothermic reactions in multiphase reactor

Thermal safety assessment for multiple exothermic reaction systems in multiphase reactors is challenging. One of the first step is to determine the presence or absence of secondary reactions producing non-condensable gaseous products. Then, a kinetic and thermal study should be performed to evaluate the value of the heat-flow rates due to chemical reactions. Epoxidation of a free fatty acid by a percarboxylic acid produced in-situ was studied. A classical approach by determining the adiabatic temperature rise (ΔTad) and the time to maximum rate under adiabatic conditions (TMRad) by microcalorimetry was used. Then, different cooling and stirring failure scenarii in a semi-batch lab-scale reactor under isoperibolic mode were performed. It was confirmed that the formation of peroxyformic acid governs the overall reaction kinetics and the reaction temperature. It was confirmed that in case of cooling failure, mechanical agitation should be maintained.