Eiji O'Shima

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.

A graphical approach to cause and effect analysis of chemical processing systems

Abstract A method for cause and effect analysis of chemical processing systems has been developed on the concept of a signed directed graph. The signed directed graph, called a “model graph,” is used for representing cause and effect relationships among process variables in a system, and a “Pattern” on the graph is introduced to represent a state of the system, which is specified by “0” for normal state, “ + ” and “ − ” for larger and smaller deviation from the normal state, respectively. For a given model graph and pattern on it, the cause of state changes and the manner of their propagation are easily found out by the present approach, which is mainly based on the depth-first search algorithm developed by Tarjan. As an illustrative example, a propane vaporizer has been taken to show the usefulness of the present approach.

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.

Control of a Distillation Column with a Heat Pump

Abstract Static and dynamic operabilities of two types of distillation systems with a heat pump are investigated based on digital simulation. A heat pump is not installed between a condenser and a reboiler but between a plate in the cooling zone of a distillation column and a reboiler (SC/R System). One of the SC/R systems is a vapor-split type system and the another employs a partial condenser-type system as a side-cooler. Both systems have the broad regions of feasible operation of the the manipulative variables, reflux ratio and heat to a reboiler. The latter system is superior to the another in terms of control performance.

Extraction of the Functional Structure Inhering in a Chemical Plant by Means of the Functional Model.

化学プラントのより知的な運転管理を実現ずるためには, 対象プラントに埋め込まれている諸機能を計算機に認識・理解させることが不可欠である.本研究では, 別報で提案した「機能」モデルに基づいて, 個別のプラントのPFDおよび物質の状態から対象プラントに内在する諸機能の階層構造を抽出し, その説明構造を自動に生成する方法を開発した.機能抽出は, まず「着目ユニット」の考え方に基づいて対象プラントに固有の「主機能」が抽出され, 次に機能間の階層関係に関する知識を用いて, プラントの機能の階層構造が生成される.このとき必要となる「最下位機能」の満たすべき構造的条件や各機能の意味に関する知識は明確なデータ構造で与えられており, これを用いて機能の階層構造についての説明構造が生成できるようになっている.

COMPUTER-AIDED PROCESS DESIGN SYSTEM FOR PLANT OPERATION

Abstract In designing a piping and instrumentation diagram (P&ID) with refer-ence to a process flow diagram (PFD) of a chemical plant, design engineers are used to implicitly or explicitly deal with operational procedures for start-up and shut-down. There is no systematic approach to handle the relationships between plant topology and its operations. This paper states the structure of a computer-aided process design support system for plant operations, specifically, start-up from PFD to P&ID. First, the background of necessity of a design integration environment and the basic concepts are explained, using a representative case study. Developed as a visual system, and databases of operational sequence diagrams, time tables, .preliminary P&ID (Pre-P&ID) and unit specifications are explained.

RELIABILITY ASSURING MAINTENANCE

Recently, the condition monitoring techniques which are capable to detect the deterioration of equipment in advance of the system failures to develop, are attracting the practical interest. This methodology is much more sophisticated than the conventional breakdown or preventive maintenance strategies with respect that the occurrence of the monitored failure can be avoided. With the purpose of reinforcing the maintenance technology, an attempt is being made to apply the systems engineering methodology to the problems of maintenance management and the concept of Reliability Assuring Maintenance system has been developed. The fundamental function of the system is to suggest the maintenance strategy for each type of failure modes of any parts of equipment depending on the characteristics of the deterioration phenomena as well as the criticality of the effect of the failure.

MAINTENANCE PRACTICE IN JAPANESE PROCESS INDUSTRIES

Abstract In accordance with the technical progress in mechanization or system integration, maintenance has been forced to change. When the production system is integrated, a trifle failure in a constituent element might cause a huge loss of production or even a disaster of the plant. The preventive or predictive mode of maintenance is, therefore, strongly needed, particularly in the plant of greater equipment complexity, in order to avoid such unacceptable losses. In the present paper, a new trend of maintenance activity is overviewed, where the importance of the strategic management of maintenance work is pointed out and the total productive maintenance activity is introduced as an example.

Fault diagnosis of chemical processes utilizing the signed digraph. Improvement of accuracy by use of the fault revealing time.

プラントの測定変数が異常を示す時刻を利用して測定変数の経時変化の特徴を表現し, 符号付有向グラフによる異常診断法を改良して, 真の原因である可能性の高い候補だけを選び出すことのできる異常診断法を提案する. また, 槽・配管系の異常診断の実験データに適用してその速度と精度を検討する.

Heat Transfer in a Reacting System

均相瞬間反応系であるN2O4-NO2ガスを円管内に流し, 壁における境膜伝熱係数, 温度および流速分布を測定した。平均のNu数は物性値を平均のエンタルピにおける値を用いると, Colburnの式で整理することができ, その係数は0.023であった。エンタルピーを推進力にとり, 反応による密度と粘度の変化を考慮して, Deisslerのアナロジーを適用して流速分布とエンタルピー分布を求め, 実験値と比較した。