On-line Temperature Measurements Research Articles

SCHEDULED OPTIMIZATION OF AN MMA POLYMERIZATION PROCESS

In this study, attention is focused on the design of a scheduled-optimization strategy for a batch MMA polymerization process. The objective of this strategy is to track an optimal temperature, despite uncertainties in the heat transfer and the gel ***effect. This strategy makes use of an (uncertain) physical model and on-line temperature measurements. The uncertain parameters are re-estimated on line, so as the optimal temperature trajectory. The good decoupling (in time) between the two major disturbances allows good performance to be achieved.

State Estimator Design for Multicomponent Batch Distillation Columns

In the control of batch distillation columns, one of the problems is the difficulty in monitoring the compositions. This problem can be handled by estimating the compositions from readily available online temperature measurements using a state estimator. In this study, a state estimator that infers the product composition in a multicomponent batch distillation column (MBDC) from the temperature measurements is designed and tested using a batch column simulation. An extended Kalman filter (EKF) is designed as the state estimator and is implemented for performance investigation on the case column with eight trays separating the mixture of cyclo-hexane, n-heptane and toluene. EKF parameters of the diagonal terms of process noise covariance matrix and those of measurement model noise covariance matrix are tuned in the range where the estimator is stable and selected basing on the least IAE score. Although NC-1 temperature measurements is sufficient considering observability criteria, using NC measurements spread through out the column homogeneously improves the performance of EKF estimator. The designed EKF estimator is successfully used in the composition—feedback inferential control of MBDC operated under variable reflux-ratio policy with an acceptable deviation of 0.5–3% from the desired purity level of the products.

Consolidation of scientific and technological expertise to assess the reliability of reactor pressure vessel embrittlement prediction in particular for the arctic area plant (COBRA)

The evaluation and prognosis of reactor pressure vessel (RPV) material embrittlement in WWERs and the allowable period of their safe operation are performed on the basis of impact test results of irradiated surveillance specimens. The main problem concerns the irradiation conditions (irradiation temperature, neutron flux and neutron spectrum) of the surveillance specimens that have not been determined yet with the necessary accuracy. These conditions could differ from the actual RPV wall condition. In particular, the key issue is the possible difference between the irradiation temperature of the surveillance specimens and the actual RPV wall temperature. It is recognized that the direct measurement of the irradiation temperature by thermocouples during reactor operation is the only way to obtain reliable information. In addition, the neutron field's parameters in the surveillance specimens location have not been determined yet with the necessary accuracy. The use of state of the art dosimeters can provide high accuracy in the determination of the neutron exposure level. The COBRA project, which started in August 2000 and had a duration of 3 years, was designed to solve the above-mentioned problems. Surveillance capsules were manufactured which contained state of art dosimeters and temperature monitors (melting alloys). In addition, thermocouples were installed throughout the instrumentation channels of the vessel head to measure directly the irradiation temperature in the surveillance position during reactor operation. The selected reactor for the experiment was the Unit 3 of Kola NPP situated in the arctic area of Russia. Irradiation of capsules and online temperature measurements were performed during one fuel cycle. On the base of statistical processing of thermocouples readings, the temperature of irradiated surveillance specimens in WWER-440/213 reactor can be accepted as 269.5 ± 4 °C. Uncertainties were evaluated also with experimental work carried out in the WWRSZ research reactor and by finite element modelling of surveillance capsules. The results obtained show that there is not need to perform temperature correction when surveillance data of irradiated specimens are used for embrittlement assessment of WWER-440(213) reactor pressure vessels. Maximum neutron flux evaluated using detectors, which were placed in the Charpy specimen simulators, equals ∼2.7 × 10 12 cm −2 s −1 with E > 0.5 MeV. It is established that depending on the orientation of the capsules with respect to the core, the detectors of the standard surveillance capsules can give both overestimated and underestimated neutron flux values, as compared to the actual flux received by the surveillance specimens. The overestimation or underestimation can reach 10%.

EKF and ANFIS Estimator Design in Multicomponent Batch Distillation Columns

In the control of batch distillation columns, one of the problems is the difficulty of monitoring the compositions. This problem can be handled by estimating the compositions from readily available online temperature measurements using a state estimator. In this study, an extended Kalman Filter (EKF) and an Adaptive Neuro-Fuzzy Inference System (ANFIS) state estimators that infer the product composition in a multi component batch distillation column (MBDC) from the temperature measurements are designed and tested using a batch column simulation. The designed EKF and ANFIS estimators are successfully used in the composition – feedback inferential control of MBDC operated under variable reflux-ratio policy with an acceptable deviation from the desired purity level of the products

Calibration-free estimates of batch process yields and detection of process upsets using in situ spectroscopic measurements and nonisothermal kinetic models: 4-(dimethylamino)pyridine- catalyzed esterification of butanol.

In this paper, we report the use of an NIR fiber-optic spectrometer with a high-speed diode array for calibration-free monitoring and modeling of the reaction of acetic anhydride with butanol using the catalyst 4-(dimethylamino)pyridine in a microscale batch reactor. Acquisition of spectra at 5 ms/scan gave information relevant for modeling these fast batch processes with a single multibatch kinetic model. Nonlinear fitting of a first-principles model directly to the reaction spectra gave calibration-free estimates of time-dependent concentration profiles and pure component spectra. The amount of catalyst was varied between different batches to permit accurate estimation of its effect in the multiway model. A wide range of different models with increasing complexity could be fit to each batch individually with low residuals and apparent low lack of fit. However, only one model properly estimated the concentration profiles when all five batches were fitted simultaneously in a multiway kinetic model. Inclusion of on-line temperature measurements and use of an Arrhenius model for the estimated rate constant gave significantly improved model fits compared to an isothermal kinetic model. Augmentation of prerun batches with data from an additional batch permitted model-based forecasts of reaction trajectories, reaction yield, reaction end points, and process upsets. One batch with added water to simulate a process upset was easily detected by the calibration free process model.

Feedback Regulation of Temperature in FCC Regenerator Reactors

Design of regulative control laws for stabilization of regenerator temperature in adiabatic Fluid Catalytic Cracking Units is performed. This is achieved despite the fact that kinetic terms and heat generation are, commonly, unknown. This article presents a control law that makes use of on-line discrete measurements of temperature to estimate the heat of reaction, obtained from a neural-estimation algorithm. The controller design is similar to discrete PID controllers. Some new tuning rules are given in terms of closed loop and measured characteristic times. In order to obtain the simplest neural network and the minimum number of parameters to be adjusted, only one perceptron is used. Moreover, the resulting control law has physical meaning and can be interpreted as a standard PID controller with time varying gain. Performance of the neural-estimation technique is analyzed under closed-loop behavior using numerical simulations considering disturbances to the process and set point changes. The performance obtained when using this new control is compared with the one obtained by using a PID controller tuned following the IMC rules.

Assessment of station cable condition using wireless telemetry and diagnostic tests

Following the premature in-service failure of a 15 kV, XLPE insulated cable in a hydraulic generating station, a program was devised to: determine the root cause of failure; assess the condition of the remaining cables in the station; and ensure that the field modifications proposed to rectify the problem were effective. The underlying mechanism driving the failure was found to be overheating of the cable sheath as a result of the inadvertent formation of ground loops in the cable support structure, and hence circulating currents. Physicochemical tests of cable sections recovered from the failed circuit showed that the cable had experienced temperatures in excess of 115 /spl deg/C. Electrical diagnostic testing of the affected cable circuits indicated that the majority of the cable length was unaffected by the overheating. However, the portion of the cable within the switchgear cubicle may have undergone some ageing as evidenced by higher dielectric loss values. On-line temperature measurements, including those on the current-carrying components using wireless telemetry, confirmed that one of the sources of the high temperatures was the ground structure in the cubicle.

Developmental differences in temporal patterns and potentiation of isolation-induced ultrasonic vocalizations: influence of temperature variables.

The present study examined the relationship between the thermal environment and core body temperature in producing age-related patterns of ultrasonic vocalizations (USVs). Implanted telemetry devices allowed on-line measurement of core body temperature during an extended period of isolation and after maternal contact, both as a function of age and thermal environment. At 12 or 17 days of age, rat pups were isolated for 30 min in either a cool or a warm environment, returned home for 5 min, and then re-isolated for 10 min. Number of USVs, body temperature, and behavioral activity were measured. During initial isolation in a cool environment, 12-day-olds displayed relatively stable patterns of ultrasounding and body temperature across time whereas older animals showed a time-dependent increase in USV calling and in core temperature. During re-isolation, 12-day-olds potentiated their USV calling at both ambient temperatures while 17-day-olds did not. The overall results suggest a strong dependence between USV calling, core body temperature, and ambient temperature during initial isolation at both ages-a finding in agreement with interpretations of USVs as an acoustic by-product of thermal challenge. In contrast, during re-isolation, USV calls, core body temperature, and ambient temperature functioned independently-a finding in agreement with interpretations of USVs as a representation of an emotional state.

Experimental study on an on-line measurement of high temperature circulating ash flux in a circulating fluidized bed boiler

A new kind of measuring method that may be used to measure high temperature circulating solid particles flux in a circulating fluidized bed boiler is studied in this paper. The measuring method is founded on the principle of thermal equilibrium. A series of cold tests and hot tests were carried to optimize the structure and collocation of water-cooling tubes and showed that the method had the advantage of simple, accurate, reliable and good applicability for on-line usage in a circulating fluidized bed boiler.

Effect of Thermal Treatment on Moisture Transport during Steam Cooking of Skipjack Tuna (Katsuwonas pelamis)

ABSTRACT: Moisture and mass loss were determined during atmospheric steam cooking of skipjack tuna by measurement of muscle moisture content in whole fish and on‐line measurement of mass and temperature in fillets. Thermal denaturation temperatures of muscle proteins were measured by differential scanning calorimetry. Muscle moisture content and mass loss were dependent on muscle temperature. Temperature distribution was predicted and mass loss rates were calculated in fillets. A decreasing rate of mass loss was followed by a steady rate period and a resumption of a decreasing rate period. The increased loss of mass during the steady period corresponded to thermal denaturation temperatures of muscle proteins. Changes in mass loss rates resulted from a gradient of muscle changes produced by the temperature gradient created during cooking.

Performance of a Li 2TiO 3 pebble-bed in the CRITIC-III irradiation

Lithium metatitanate (Li 2TiO 3) is a candidate material for tritium breeding in fusion reactor pebble-bed blankets. 173 g of Li 2TiO 3 pebbles were irradiated for 334 full power days (FPD) to a burnup of 0.9% 6Li in the CRITIC-III experiment in AECL's NRU reactor. A key objective was to determine tritium release over a wide temperature band from 200°C to 900°C. On-line release and temperature measurements are reported in this paper. New analytical methods led to calculated inventories ranging from 15 wppm average at the lowest temperature of operation (200°C outer surface to 700°C inner surface) to less than 1.2 wppm average at 375°C outer-surface temperature and 875°C inner-surface temperature. The thermocouples indicated that the bed remained stable during the irradiation, which included thermal shocks from 90 reactor shutdowns. From this swept-capsule irradiation, Li 2TiO 3 appears to be a good candidate for fusion blanket pebble-beds.

Robust estimation of free-radical homopolymer reactors

In this work is presented a practical (i.e. nonlocal) robust estimation design to infer the main safety, production, and quality variables of batch, semibatch, or continuous free-radical homopolymer reactors with on-line measurements of free monomer, temperature, and volume. The solvability of the problem is established a priori , and the design features a robust nonlocal uniform convergence criterion coupled with a systematic construction-tuning procedure. The nonlocal stability framework exhibits the performance-robustness tradeoff, as well as the relationship between the sizes of the estimate error, initial state, exogenous input, and model parameter errors. The tuning of gains of the estimator can be executed with conventional filtering techniques for linear single-output filters. The polymerization of methyl methacrylate with AIBN initiator is considered as an application example, and the robust nonlocal functioning of the estimator is corroborated with numerical simulations.

Inferential estimation of polymer quality using bootstrap aggregated neural networks

Inferential estimation of polymer quality in a batch polymerisation reactor using bootstrap aggregated neural networks is studied in this paper. Number average molecular weight and weight average molecular weight are estimated from the on-line measurements of reactor temperature, jacket inlet and outlet temperatures, coolant flow rate through the jacket, monomer conversion, and the initial batch conditions. Bootstrap aggregated neural networks are used to enhance the accuracy and robustness of neural network models built from a limited amount of training data. The training data set is re-sampled using bootstrap re-sampling with replacement to form several sets of training data. For each set of training data, a neural network model is developed. The individual neural networks are then combined together to form a bootstrap aggregated neural network. Determination of appropriate weights for combining individual networks using principal component regression is proposed in this paper. Confidence bounds for neural network predictions can also be obtained using the bootstrapping technique. The techniques have been successfully applied to the simulation of a batch methyl methacrylate polymerisation reactor.

Non-Linear Observer Based Method for Fault Detection and Isolation: Application to an industrial petrochemical process

This paper deals with the implementation of algorithmic fault diagnosis on an industrial petrochemical reactor. This process is cared out in a perfectly mixed reactor with a heat exchanger. The algorithm is based on a non linear geometric approach of the disturbance rejection. It allows to supervise three faults which may occur on the reactor with online temperature and pressure measurements.

Temperature and mixture fraction measurements in gases by laser-induced electrostrictive gratings

We applied time-resolved light scattering from electrostrictive gratings to measure nonintrusively gas compositions and temperatures. The infrared radiation of a pulsed Nd:YAG laser generates a spatially periodic density grating that oscillates in time, and the beam of a cw laser is used to read it out. The oscillation period of the signal depends on the sound velocity in the medium. If the gas composition is known, the measurement of the sound velocity allows the temperature to be deduced. We evaluated this novel technique in a tube furnace for temperatures in air up to about 1400 K. Although the measured temperatures agree within the error bars with the thermocouple readings, there is some evidence that the temperatures determined by the laser-induced grating technique are systematically too high. For singleshot temperature measurements in air, we determined a statistical error of 70 K at a furnace temperature of 1400 K. On the other hand, if the temperature is known, concentrations in isothermal binary mixtures can be determined by the laser-induced grating technique. We performed measurements in methane-nitrogen and hydrogen-nitrogen mixtures. The limits for the minimum detectable variation of the gas composition of 0.5 mole fraction mixtures were found to be 2% and 0.6%, respectively. One advantage of the proposed method is the simple evaluation process that allows for on-line measurements of temperature or gas compositions.

On-line inference of tube-wall temperature in an industrial olefin pyrolysis plant

A major difficulty in the efficient functioning of industrial pyrolysis is the lack of suitable on-line tube-wall temperature measurements. In this paper, an inferential scheme is developed to predict the tube-wall temperature, which is called skin temperature, in an industrial olefin pyrolysis plant. Based on a theoretically-derived model, the skin temperature is predicted from the available on-line measured process variables, such as gas temperature around the tube, fuel gas flowrate, and naphtha feed flowrate. Using the infrequently off-line measured skin temperature with the on-line measurements, adjustable parameters of the model are updated on-line according to the Kalman filter technique. The application of this scheme then is illustrated using operating data obtained from an industrial olefin pyrolysis plant. The results of the proposed scheme show that, by taking infrequent measurements of the skin temperature for model adaptation, the skin temperature can be predicted successfully for every tube in the pyrolysis over an extended time interval. Simulations suggest that as few as one or two manual measurements of the skin temperature, taken during the entire cracking operation, provide sufficient information to maintain the developed inferential system at a practical level.

Tubular Film Blowing

Abstract The literature on tubular film blowing is contradictory, even on such basic matters as to whether increasing inflation pressure increases or decreases the bubble radius. To provide a solid experimental base for physical understanding and theoretical modelling, detailed on-line measurements were made using three polyethylenes (a low density, a linear low density and a high density material, all of melt index 1.0). The measurements included blow-up ratio as a function of inflation pressure and take-up ratio; the melt temperature and the air flow rate were also varied. On-line radius, velocity and temperature measurements along the film were made in some runs. For the most part the data showed an “intuitive” effect of inflation pressure on blow-up ratio; that is, increasing the pressure caused the final radius (the blow-up ratio) to increase. However, at high blow-up ratios (typically values of 2 to 3, depending on the material and processing conditions), regimes having a “counterintuitive” relationship were observed in some cases. There were not substantial differences among the three materials except that the low density material was less prone to instabilities at high blow-up ratios.

Effect of Impurities on Continuous Solution Methyl Methacrylate Polymerization Reactors. I. Open-Loop Process Identification Results

ABSTRACTAn automated pilot-scale 1-litre experimental reactor system with facilities for on-line measurement of flow rate, temperature and density has been set up for open-loop process identification of impurity effects on the solution polymerization of methyl methacrylate (MMA) in a continuous stirred tank vessel. The desired conversion level is maintained using the initiator flow rate as the manipulated variable. Monomer, initiator and solvent flow rates are all regulated by computer-controlled variable speed pumps to maintain a prespecified monomer/solvent ratio and residence time. During operation, various levels of 2,2-diphenyl-1-picrylhydrazil (DPPH) are injected into the reactor as disturbances. An on-line densitometer, which relies upon changes in the frequency of oscillation of a fixed volume tube through which liquid is flowing, is used to monitor the density change and therefore conversion in the reactor system. The on-line experimental results have been cross-checked by off-line gravimetry and...

Dielectric analysis of epoxy/amine resins using microwave cavity technique

AbstractDielectric properties (permittivity and dielectric loss factor) of stoichiometric mixtures of DGEBA (diglycidylether of bisphenol A) epoxy (DER 332) and amine (diaminodiphenyl sulfone; DDS) as a function of temperature and extent of cure have been measured at a microwave frequency of 2.45 GHz. Permittivity and dielectric loss factor of this resin increase with increasing temperature and decrease with increasing extent of cure. Dielectric loss factor is more dependent on temperature in the early stages of cure but becomes less dependent on temperature as the cure proceeds. Dielectric loss data can be related to extent of cure in order to monitor the cure process. Online measurements of temperature‐ and cure‐dependent dielectric loss factor show three material structure stages and significant changes in dielectric loss factor during the microwave cure process. Dielectric Joss factor is also found to be the same for both thermal and microwave cured samples.