Design Of Pressure Relief Systems Research Articles

The pool fire case for pressure relief: Radiation exposure limited by fuel supply

In design of pressure relief systems, a pool fire is one of the most typical relief cases. The first step in the fire relief calculation is determining the heat flux input from the fire and methods include the simple to the very complex, covering a myriad of factors and configurations. This article illustrates one method where the heat input is limited by the fuel supply. This method complements one traditional method where the heat input is limited by the equipment exposed area. The scope of the article is limited to the calculation of the heat release, and does not discuss the behavior of the fluid in subject equipment, the relief rate or relief device sizing. © 2014 American Institute of Chemical Engineers Process Saf Prog 34: 214–219, 2015

Study on pressure relief system design for high temperature gas cooled reactor

Under some postulated accidental conditions, the secondary loop of the reactor needs to release its pressure for consequent system action. During the pressure relief transient, the residual fluid mixture of water and the steam will pass through the heat-exchange tubes of the steam generator and the live-steam pipeline, which decreases the steam generator pressure and the steam generator temperature due to taking the heat stored in the components away. The pressure and the temperature during the transient needs to be controlled to protect the steam generator from the potential damage. A 250 MWth high temperature gas cooled reactor is selected to evaluate this countermeasure effect during the pressure relief transient in this paper. A thermal-hydraulic system analysis code is used for modeling and simulating the pressure relief transient after the accident occurs. The temperature change of the fluid and the components in the steam generator are relative to the pressure relief transient, which is dominated by the design of pressure relief valve. Larger diameter of pressure relief valve will result in more intensive blown-down transient which causes faster pressure decrease and stronger heat transfer between the inside walls of the components in the secondary loop and the fluid. The designed pressure value where the pressure relief valve closes will affect the transient also. The designed pressure value dominates the time of the pressure relief transient which affects the amount of the fluid from the pressure relief valve. Different amount of the fluid will take away different quantity of heat from the components in the secondary loop of reactor. The pressure relief transients with a series of different diameter of pressure relief valve under some typical designed pressure value were simulated and compared. The results indicate that the pressure and the temperature of the steam generator during the pressure relief transient could be controlled effectively with reasonable design on the pressure relief system, which will provide protection and benefit for the steam generator after the postulated accident.

Safely scale‐up processes and accommodate recipe changes

AbstractThermal hazards screening can be quickly and cost‐effectively performed to obtain the required data for the safe scale‐up of chemical processes and to accommodate changes to process recipes. Before scale‐up, it is vital to identify safe temperature and pressure operating ranges, quantify the heat generated from a reaction, and the number of moles of gas generated. It is also prudent to determine the heat and gas generation rates to safely accommodate the reaction in the given process equipment. These rate data can also be used to verify the adequacy of the existing pressure relief system design. Process Hazard Analysis (PHA) and Hazard and Operability (HAZOP) reviews identify credible upset scenarios, and data are required to address these issues. When a process recipe or batch size is changed, data are necessary to quantify the effect of the change on the above parameters. For modifications to existing processes, a management of change review should occur. Data addressing issues resulting from these reviews are readily available by performing calorimetry experiments with the Advanced Reactive System Screening Tool and similar calorimeters. Examples of these applications are included in this article. © 2008 American Institute of Chemical Engineers Process Saf Prog, 2009

Kinetics of the reactions of ethylene oxide with water and ethylene glycols

AbstractThis study of the water‐contamination reactions of ethylene oxide was conducted by Arthur D. Little, Inc. with funding from, and under the auspices of, the Ethylene Oxide Industry Council, part of the American Chemistry Council. Significant experimental and technical contributions were also made by staff from Shell Chemicals' Westhollow Technology Center in Houston, Texas, and Union Carbide Corporation's Research Center in South Charleston, West Virginia. Unique fourth‐order kinetics for the reactions of ethylene oxide with water, and ethylene oxide with ethylene glycols were derived and validated, as were kinetics for the reactions of neat ethylene oxide and the decomposition of ethylene glycols. The latter data was incorporated into a reaction model useful for the determination of ethylene oxide storage stability and pressure relief system design under water‐contamination scenarios.

Analysis identifies deficiencies in existing pressure relief systems

AbstractThis article presents a statistical analysis showing that the pressure relief systems on nearly half of the equipment in the oil, gas, and chemical industries lack adequate overpressure protection as defined by recognized and generally accepted good engineering practice. This analysis was based on data collected from a large number of government mandated (per OSHA 1910.119) pressure relief system design audits per‐formed by an independent contractor. The vast majority of these deviations from good practice were not identified during conventional process hazard analyses (PHA) performed on these same facilities. Most of the units had also been designed by reputable design firms.The authors conclude that, as a practical matter, conventional PHA methods are ineffective tools for evaluating pressure relief systems. They also conclude that the pressure relief system design process could be improved. Specifically, the authors recommend that, in order to reduce this deficiency rate in the future, that the industry adopt an equipment based approach to pressure relief system design and maintenance.

Conceptual design of pressure relief systems

Abstract Conceptual design of pressure relief systems is an important stage in the design of a safe process plant. The conceptual design stage consists of the following steps: deciding on the location of pressure relief devices, selecting the general type of pressure relief device for each identified location, i.e. safety valve and/or bursting disc (rupture disc), or other relief device, and selecting the special features for the chosen device type. Some regulations, codes and standards, and a decision tree for the selection of a relief device have been described in the literature. This paper presents four decision trees that have been developed for the different steps in the conceptual design stage. Only positive pressure in pressure vessels is considered here.

Pressure relief system documentation: Equipment based relational database is key to OSHA 1910.119 compliance

AbstractUnder OSHA 1910.119, all Process Safety Management (PSM) facilities are required to keep their pressure relief system design information current. This article demonstrates why a pressure relief system design verification effort must be based on an equipment list, rather than a relief device list, in order to ensure that every piece of equipment is adequately protected. The formerly common practice of simply checking the design bases of all existing relief devices is deficient is deficient since this technique does not systematically ensure that every piece of equipment is protected.The “Berwanger Method” is a step by step process for designing or analyzing a pressure relief system to meet OSHA 1910.119 Process Safety Information (PSI) and Process Hazard Analysis (PHA) mandates. The method uses a relational database which tracks the relationships between protected equipment, potential overpressure scenarios, and protective devices.The challenge facing an operating company does not end once the design basis has been “verified”—the design basis information must also be maintained and be readily accessible to avoid costly reinvention of the wheel down the road. The “Berwanger Method” also addresses these maintenance issues.

Choked gas flow through pipeline restrictions: an explicit formula for the inlet Mach number

A simple analytical formula is derived for the inlet Mach number of a pipeline restriction through which there is choked flow of gas. This formula, valid for all diameter ratios β < 1.0, permits the explicit calculation of choked flow parameters to an accuracy of < 0.1%, thus offering simplicity in comparison with existing iterative procedures. The formula can be applied directly in the design of pressure relief systems.

Drift-flux correlation disengagement models: Part I — Theory: Analytic and numeric integration details

In the design of pressure relief systems for vessels containing liquid, the phase of the flow through the vent line is very important. Mounting the line on the top of the vessel does not necessarily guarantee all vapor flow. One must calculate whether vapor bubbles formed in the liquid will disengage before they reach the vent entrance. Disengagement can be predicted via an axial void fraction profile that is calculated based upon volumetric gas production. It is assumed that the liquid phase is continuous and that pseudo-steady state is reached. The disengagement model is based on a constant energy generation per unit mass of liquid. For non-foaming systems, one of two drift-flux correlations can be chosen on the basis of viscosity. The churn-turbulent drift-flux correlation is for low-viscosity systems, and the DIERS' viscous-bubbly drift-flux correlation is for high-viscosity system [1, 2]. This model reduces to a single ordinary differential equation (ode). Analytic integration results for this model are possible for constant cross-sectional area vessels (e.g., vertical cylinder) and non-unity distribution parameters Co [3–5]. If this calculation shows the bubbles do not disengage, either a partial differential equation model must be solved or the coupling equation must be used. The coupling equation uses the maximum void fraction (calculated from the ode) and ties together the vessel and vent models. The ode solutions relate the local and average void fractions to the dimensionless superficial vapor velocity. For the churn-turbulent drift-flux correlation, explicit relationships are presented for the first time. They validate the earlier approximation of Fauske et al. [6] (see also Ref. [3]). For the DIERS' viscous-bubbly drift-flux correlation, implicit relationships are presented for the first time in the open literature. The earlier approximation of Fauske et al. [6] (see also Ref. [7]) fit the data, but is different than these integration results. Further work is in progress to refit the data [8] and to clarify the best model to use. For non-constant cross-sectional area vessels (e.g., horizontal cylinders and spheres), the analytic integration is difficult, but numeric results have been presented [3, 7]. The details of the numeric integration are presented and discussed here. As the cross-sectional area converges (toward the top of the vessel), the vapor concentration (i.e., the void fraction) and velocity increase. The maximum local void fraction occurs at the top of the vessel. Numerical difficulties are encountered as a result of the cross-sectional area going to zero at the bottom and top of the vessel. The pseudo-steady-state model imposes void fractions of minimum and maximum at these extremes (i.e., 0 and 1/Co).

A risk perspective for emergency pressure relief system design

Improperly sized pressure relief devices have historically been a factor in a significant fraction of serious accidents involving process reactions. The Design Institute for Emergency Relief Systems (DIERS) efforts have provided a methodology which minimizes the potential for inadequate pressure relief capacity. Unfortunately, this methodology can lead to requirements for vent sizes which appear to be unreasonably large. The difficulty may be traceable directly to the selection of the design basis. It is often difficult to justify credible bounds for scenarios to be considered in the design by qualitative methods alone. In these instances, quantitative risk assessment methods can be effective in providing criteria for the elimination of excessive conservatism and thus can lead to a satisfactory design. This paper describes a hypothetical but realistic example which effectively combines the DIERS methodology with quantitative risk assessment methods. The result is a more satisfactory basis for evaluating the adequacy of the vent design.

Transient flow phenomena and reaction forces during blowdown of gas at high pressures through relief lines behind rupture discs

AbstractIn general, rupture discs are designed to give a virtually instantaneous pressure relief opening to a relief system at a predetermined pressure. For safe design of pressure relief systems, consideration must be given to the sizing and the specification of the rupture disc but also to the reaction forces that result when a gas is discharged. These reaction forces can be excessive in the case of venting at high pressures.When a disc ruptures, a shock wave propagates through the gas in the piping behind the rupture disc. This exerts a transient reaction force on the pressure relief system. In the case of steady supersonic flow choking often occurs at one or more points in the pressure relief line and a shock is formed in the pipe. The pressure in the relief line may increase considerably during blowdown as a result of choking at the end of the pipe. Depress‐surization experiments were conducted with nitrogen at high pressures.The results of the pressure measurements in the piping during blowdown are compared with exploratory calculations. The reaction forces exerted on a pressure relief system can be assessed from the pressures and the mass flow rate of the gas as a function of time. For safe design of pressure relief systems, both steady‐state flow reaction forces and the initial transient forces should be considered.