Hisayoshi Matsuyama

An algorithm for diagnosis of system failures in the chemical process

Abstract An attempt was made to apply graph theory to the diagnosis of the system failures in the chemical process. A signed digraph is used for a mathematical model representing the influences among elements of the system. The concept of a pattern on the signed digraph is introduced for representing a state of the system. In order to eliminate carrying out the complicated and inefficient quantitative simulation, the mathematical model of the system structure to represent the rpopagation of failures is simplified in a qualitative fashion. The origin of the system failure can be located at the maximal strongly-connected component in the cause-effect graph reflecting the pattern of abnormality. Even when the pattern is observed only partially, the assumption of single origin of the failure reduces, to some extent, the range of possible candidates to be the first cause of the failure.

An improved algorithm for diagnosis of system failures in the chemical process

Abstract The detailed techniques for improving the efficiency of a fault-diagnosis algorithm can be based on the signed directed graph. This graph represents the structure of the system, and the pattern on the graph represents a state of the system. The usefulness of the improved algorithm is demonstrated using a model of a chemical process comprising a reactor, a heat exchanger and a distillation tower.

Measurement of local fines movement in a fluidized bed of coarse particles by a fluorescent tracer technique

Abstract The movement of fines in a fluidized bed of coarse particles is an important factor for an understanding of multi-size particle systems. In this work, porous catalyst particles of 60 – 65 μm in size were coated with a fluorescent dye and were used as the tracer. The fluorescence emitted from the tracer particles was detected with a set of bifurcated optical fiber probes. The fluidized bed consisted of a transparent 19-cm i.d. pipe with silica gel spheres of diameter 1.54 mm. The percolation velocity of fines in a quiescent bed was well expressed by the model assuming the successive collision of fines on coarse particles. With the presence of gas bubbles, however, the fines percolation increased with increasing gas velocity and height from the gas distributor. The uptake and shedding of fines by bubble wake was found to play an important role in this case. The lateral spread and the downward movement of fines was not dominant unless large bubbles were generated.

Stability of catalytic reactors: a critical review

A critical review of stability studies of heterogenous catalytic systems, including biochemical systems, which can be effectively used to design and operate commercial reactors covers definitions and theoretical concepts of instability; the stability of catalyst pellets, including multiple steady states in a catalyst pellet, intraparticle stability, and parameter ranges and conditions of industrial practice; the stability of fixed-bed reactors, including the phenomena of multiplicity due to macroscale thermal feedback, creeping, parametric sensitivity, stability of a group of multistable particles, and hot spots; the stability of fluidized beds; and the stability of biochemical reactors.

Identification of Fuzzy Rule Based System for Fault Diagnosis in Chemical Plants

Abstract A simplified fuzzy reasoning algorithmic approach for describing the cause -effect relationships in a real technological system is proposed. It uses rule based fuzzy model with simple triangular shape of all the membership functions. In order to determine the number of the fuzzy sets (membership functions) as well as the number of the fuzzy rules, an identification algorithm is proposed. The adjustment of the right part of the rules is done by using real input-output data and Steepest Descent Method. The main features of the proposed identification method are discussed on a numerical example for fuzzy modelling. A method for use of the fuzzy models created in this way for fault diagnosis of an industrial system is also proposed and discus sed in the paper.

A fault detection and diagnosis for the continuous process with load-fluctuations using orthogonal wavelets

Abstract Fault detection and diagnosis of a continuous process with input fluctuations such as load fluctuations can not be simply performed because of the difficulty of detecting the abnormality in the process, where normal values of state variables are uncertainly time-varying according to the input fluctuations. In this study, normal values of output variables are predicted by the use of the approximation function that is drawn from a family of orthogonal wavelets. Measured value of an output variable is classified to five-range signs (+, +?, 0, −?, −) by simultaneously performing two sequential probability ratio tests (SPRTs) based on the error residual between predicted and measured values: one test examines whether it is normal or higher than normal, the other examines whether it is normal or lower than normal. A combination of signs given to all the output variables is called a pattern, which is considered to represent an abnormal situation occurring in the process. Then, the fault diagnosis algorithm, based on signed directed graph (SDG), can deduce the fault origin that causes the pattern. The effectiveness of this approach is demonstrated through experiments by a tank—pipeline system.

The Improvement of Fault Diagnosis Algorithm Using Signed Directed Graph

Abstract As a fault diagnosis method for a large-scale chemical plant, qualitative model-based method using signed directed graph has been proposed. This method has high diagnostic reliability (high probability of finding the real fault cause) but low diagnostic accuracy (poor information content obtained from diagnostic result). To overcome low diagnostic accuracy, the method is improved to use information about delays in fault propagation among state variables, representing the delays by fuzzy numbers. Furthermore, the diagnostic accuracy of the improved method is evaluated by introducing a concept of information content Finally, diagnostic experiments with the use of a mini-plant demonstrate that the improved method has higher diagnostic accuracy and the robustness for ambiguity contained in the delays.

FAULT DIAGNOSIS OF THE CHEMICAL PROCESS UTILIZING SIGNED DIRECTED GRAPH; Improvement and Evaluation of the Diagnosis Accuracy

Abstract The fault diagnosis algorithm using a signed directed graph as a model of the system is useful to real-time diagnosis of failures that occur in processes. The accuracy of the algorithm has been improved so much that it can select the candidates that are the most likely to be the real cause of failure, utilizing the concept of amplifying branch. The accuracy of the improved algorithm has been examined by its application to data obtained in the experiments of fault diagnosis in tank-pipeline systems, and estimated by the size of the greatest set of candidates.

Optimal Allocation of Sensors for Fault Diagnosis System Using the Signed Directed Graph

Abstract An allocation of sensors in a chemical plant is usually decided for the purpose of not fault diagnosis but process control, production control and so on. This is one reason for poor accuracy of fault diagnosis. This paper discusses the problem to search the optimal allocation of sensors with the constraint of the required specification (especially, diagnostic accuracy) for a fault diagnosis system using a signed directed graph. An algorithm to solve the problem is successfully applied to a mini-plant to demonstrate its usefulness.

MEASUREMENT OF FLOW OF SOLID PARTICLES IN GAS FLUIDIZED BED

The flow of fine solid particles was measured in a gas fluidized bed of 12-cm i.d., where silica alumina particles, 60-65 μm in diameter, were fluidized by air. The minimum fluidizing velocity of the solid particles was 0.2-0.4 cm/s. The measuring system was composed of bifurcated optical fiber probes and a data processing unit. Silica fibers and plastic fibers were used for guiding ultraviolet light and collecting fluorescent visible light, respectively. Sensitivity and accuracy of the system were substantially improved over that of the previous system. The pulse response curves of fluorescent tracer particles were measured more than 100 times under the same conditions and were statistically analyzed. The time-averaged velocity and the root mean square of velocity fluctuation of solid particles were determined in upward, radial and oblique directions at the center of the fluidized bed. The results were in agreement with literature data.