Time-Dependent Risk Control of Crucial Tube Furnace With SIL Requirement Considered

2010 ◽  
Author(s):  
Jianxin Zhu ◽  
Xuedong Chen ◽  
Zhibin Ai ◽  
Weihe Guan
Keyword(s):  
Control System ◽  
Safety Concern ◽  
Degradation Mechanism ◽  
Economic Loss ◽  
Time Dependent ◽  
Tube Furnace ◽  
Operation Condition ◽  
Control Time ◽  
Dependent Risks ◽  
Tube Failure

Hydrogenator feed tube furnace is of great safety concern due to its rigorous operation condition (up to 550°C, 17MPa) and flammable/explosive materials (H2, crude oil) involved in refining installations. Unlike instruments where the failure may not necessarily cause direct hazards, the failure of tubes in high temperature furnace always cause severe damage and downtime-caused economic loss. Normally the main cause of tube failure is time-dependent material degradation mechanism (such as creep, fatigue and oxidation). The occurrence of two tube rupture accidents gives birth to the consideration whether it is necessary to add a new isolation/mitigation layer in tube furnace in order to control time dependent risks. Taking advantage of the progress of life and probability prediction techniques (such as API581), the time-dependent risk of high pressure tube furnace was studied by taking into account of contributions provided by control system and safety instrumented functions (SIF). The frequency of severe initial events (leakage or rupture) of furnace tube was studied and fault tree analysis method was used to analyze the combined failure probability of time-dependent tube failure rate, basic process control system (BPCS) as well as safety instrumented system (SIS). The necessity of adding a mitigation function to reduce consequence caused by tube failure (leakage or rupture) was studied in order to control time dependent risks. A mitigation SIF at tube’s late service stage to reduce risks was proposed, which is of great significance for furnace safety.

Computational Hydrodynamics for an Autonomous Underwater Vehicle With Moving Control Surfaces

2002 ◽  
Author(s):  
Abdollah Arabshahi ◽  
Howard J. Gibeling
Keyword(s):  
Control System ◽  
Autonomous Underwater Vehicle ◽  
Stokes Equations ◽  
System Development ◽  
Underwater Vehicle ◽  
Time Dependent ◽  
Navier Stokes ◽  
Computational Hydrodynamics ◽  
Flow Solver ◽  
Control Surfaces

The present study was undertaken to provide information for both design improvement and control system development during various stages of an autonomous underwater vehicle (AUV) development project. The need to establish a predictive capability for the hydrodynamic (control) coefficients for an AUV presented an opportunity to apply a multiblock incompressible Navier-Stokes flow solver which has evolved over many years. The solver utilizes a state-of-the-art implicit, upwind numerical scheme to solve the time-dependent Navier-Stokes equations in a generalized time-dependent curvilinear coordinate system. Domain decomposition is accomplished via a general unstructured multiblock approach. In addition, an efficient grid movement capability is incorporated in the code that will handle the relative motion of a multi-component configuration (e.g. oscillating control surfaces). Numerous simulations were conducted during the course of this work. The computations for vehicle and propulsor design consisted mainly of steady state axisymmetric computations, while for control system development both steady and unsteady (prescribed motion) simulations were conducted. The latter cases focus on the forces and moments on the vehicle that are needed for extraction of control information. A brief overview will be presented on the flow solver. This will be followed by a presentation of the numerical results.

Experimental Study on Large Turbine HP-Valve’s Excitation Fault Caused by Steam’s Unsteady Flow and its Economic Solution

2014 ◽  
Vol 536-537 ◽  
pp. 1501-1509 ◽  
Author(s):  
Jie Wan ◽  
Jun Sheng Gu ◽  
Guo Rui Ren ◽  
Qian Guo ◽  
Zhi Hua Li ◽  
...  
Keyword(s):  
Large Scale ◽  
Thermal Power ◽  
Economic Loss ◽  
Random Fluctuation ◽  
Variable Load ◽  
Steam Turbines ◽  
Operation Condition ◽  
Valve Body ◽  
Power Generating Unit ◽  
Unit Depth

In order to stabilize the uncertainty of large-scale new energy power’s random fluctuation in the grid, there is an increasing number of large thermal power generating unit needing to do deep variable load operation. However, the pattern of steam inlet on turbine’s part load has a very significant impact on the unit operation condition of safety, stability and economy. In this paper the HP-valve’s body vibration fault of large steam turbines caused by unsteady steam flow under partial arc admission operating at part of their full load is researched, and an economic solution based on analysis and diagnosis of fault mechanism is provided by designing of complex HP-valve opening sequence rules. This solution solves the safety problem of valve vibration and avoids the economic loss by using full arc admission or replacing the valve body equipment directly, which is of great effective and practical verified by units’s actual operating experiment. As a result, it demonstrates that the optimization of HP-valve iadmission mode can not only change the stress state of high pressure rotor and prevent its vibration caused by the force of unbalanced flow to improve the shafting stability of the unit when running with variable load, but also can improve the steam instability and solve the resulting vibration problem in HP-valve. And it is of great engineering practical value to improve high-power thermal power unit depth secure efficient load operation.

scholarly journals Analysis of time-dependent risks for infection, rejection, and death after pulmonary transplantation

1995 ◽  
Vol 109 (1) ◽  
pp. 49-59 ◽  
Author(s):  
Ko Bando ◽  
Irvin L. Paradis ◽  
Kanshi Komatsu ◽  
Hiroaki Konishi ◽  
Masato Matsushima ◽  
...  
Keyword(s):  
Time Dependent ◽  
Dependent Risks

scholarly journals Time-Dependent Probabilistic Model for Hierarchical Structure in Failure Mode and Effect Analysis

2019 ◽  
Vol 9 (20) ◽  
pp. 4265 ◽  
Author(s):  
Jang ◽  
Min
Keyword(s):  
Failure Mode ◽  
Hierarchical Structure ◽  
Probabilistic Model ◽  
Economic Loss ◽  
Time Instant ◽  
Time Dependent ◽  
Effect Analysis ◽  
Elapsed Time ◽  
The Hierarchical Structure ◽  
Cause Of Failure

Failure mode and effect analysis (FMEA) is a structured technique for identifying risks that may occur during a given stage of a system’s life cycle. However, the use of the risk priority number (RPN) in traditional FMEA results in difficulties with regard to quantification of the degree of risk in the hierarchical failure structure. This study proposes the use of a hierarchical time-dependent FMEA approach to overcome the limitations encountered during the implementation of traditional FMEA approaches. In place of the RPN, a probabilistic loss model is developed under a hierarchical structure considering the elapsed time from the failure-cause (FC) to the system failure. By assuming exponential and case functions for each occurrence and detection time instant, the expected loss corresponding to each FC can be evaluated. As a result of the practical application of the time-dependent probabilistic model through the numerical example, we could reasonably evaluate the risk from the cause of failure in the hierarchical structure in terms of economic loss.

Modeling & Simulating of Hami-Zhengzhou UHVDC Transmission Project and Security & Stability Analysis of Send-Side Power System

2014 ◽  
Vol 1070-1072 ◽  
pp. 790-796
Author(s):  
Tian Xia ◽  
Xiao Xiao Qi ◽  
Li Jun Deng ◽  
Yi Xian Sun
Keyword(s):  
Control System ◽  
Stability Analysis ◽  
High Voltage ◽  
Power Transmission ◽  
Control Strategies ◽  
Operation Condition ◽  
Hvdc Transmission ◽  
Failure Treatment ◽  
Commutation Failure ◽  
Simulation Results

Hami-Zhengzhou ±800kV DC project is the first ultra high-voltage project for Xinjiang power transmission, it is also the first DC transmission project binding thermal and wind power, with bipolar low-end operation in 2013 and bipolar operation in the middle of 2014. The rated power is 8,000MW. This article focused on Hami-Zhengzhou HVDC transmission system, established the electromechanical model, which improved commutation failure treatment in the traditional DC control system and made the simulation results more close to the real operation condition. Based on this model, security and stability analysis of power grid was carried out and the corresponding control strategies/schemes were brought up.

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