Comprehensive Relief Valve Sizing and Flare Header Evaluations
Relief valve sizing and flare header evaluation studies can be very complex to perform properly. Process Engineering International provides a full range of services for the sizing, verification, and modeling of Flare Systems and Pressure Safety Relief Devices. Proprietary in-house tools are used to efficiently evaluate and document relief device sizes and commercial simulation software is used to perform hydraulic calculations for the entire flare system.
Tailored Solutions for Unique Relieving Scenarios
We perform all of our relief device studies and flare evaluations accurately and efficiently. When unusual relieving scenarios/conditions present themselves, Process Engineering International is qualified to develop a solution that may not be obvious, thus potentially preventing our clients from having to perform expensive modifications or unnecessarily install larger PSV devices.
Relief Device Sizing
Process Engineering International provides a full range of services for the sizing, verification, and modeling of Flare Systems and Pressure Safety Relief Devices (PSVs, RVs, or PSRVs, Rupture Disks, and Conservation Vents). Our service offerings include:
- Collect on-site data when required
- Perform all calculations and prepare associated documentation for the sizing and selection of relief devices per API and/or ASME Code for new or existing installations. This also includes:
- Identification of, and calculations for all credible scenarios (not just the controlling scenario)
- Generation of physical properties using process simulation models for each stream
- Preparation of pressure drop calculations for both inlet and outlet piping.
- Perform calculations to show that flare stack or vent stack sizing (height, diameter, tip configurations, etc.) fall within API Code requirements.
- Flare manufacturers are consulted to ensure the best available technology is applied to the application.
- Knockout drums and blowdown systems are designed and sized for each installation.
- Prepare all documentation needed to meet regulatory compliance and any specific company requirements
- Prepare required PSV specifications (spec sheets)
- Construct a flare or vent header pressure drop simulation model in simulation software, including both inlet and outlet PSV piping configurations to validate hydraulics
- Perform flare or vent header pressure drop evaluations for specific PSV combinations associated with global relief scenarios.
Our Experience
Any changes made to piping systems where relief devices are used can cause the devices to be oversized or undersized for their application. If relief devices feed into a common blowdown or flare header system then the sizing of the header lines and flaring devices also needs to be checked after process modifications are made. It is common to find blowdown and flare systems undersized as a result of multiple small changes that are made to the process over time and result in a cumulative effect on the header loading. Process Engineering International has performed relief valve sizing calculations for thousands of relief devices following API 520, 521, and 2000 guidelines as well as location-specific or client-specific guidelines. Process Engineering International sizes relief devices of all types including traditional spring-loaded relief valves, conservation vents, and rupture disks. It is critical that relief systems be sized appropriately to safely relieve excess pressure under abnormal operating conditions so that personnel and equipment are protected. Process Engineering International can either provide specific relief valve sizing and evaluations or we can perform an entire flare header system evaluation with many relief devices connected to it. In addition, some clients turn their entire relief device program management over to Process Engineering International on a temporary or long-term basis to reduce the load on local staff and to allow their programs to be independently managed.
Relief Device Evaluation:
Systematic Approach to Evaluating Existing Systems
When performing an evaluation to determine if adequate relieving systems are in place for an existing system and if the flare header is adequately designed, the following steps are typical:
- Collect information from the existing process and relief system (relief device data, P&IDs, protected equipment information, flare header isometrics, inlet/outlet line sizes, etc.) To accomplish this, Process Engineering International travels to the operating site when needed.
- Work with the client to develop the credible relief scenarios, both for individual pieces of equipment and especially for those affecting entire units or sections of the plant (blocked flow, external pool fire, loss of cooling, loss of power, etc.).
- Prepare a simulation of the process (if needed) to ensure accurate process conditions and stream compositions are available for all relieving scenarios.
- Calculate the required flow rate capacity for the relieving streams along with the required orifice sizes for all credible scenarios.
- Determine the controlling scenario and the valve size required.
- For evaluation of existing devices, the required flow rate and actual flow rate capacity for the relief valves are calculated along with the required orifice size for each scenario. From this information, the controlling scenario is determined to check if the existing valve is sized appropriately.
Flare System Design and Evaluation
Advanced Techniques for Accurate Flare System Analysis
Process Engineering International performs calculations to determine flare radiation, produces a contour plot and determines specific radiation incidences on personnel and structures. Effects of mitigation measures, such as water spray and shields that may help minimize the flare height and cost can be assessed. Plume dispersion modeling is also performed when needed. Process Engineering International uses advanced techniques (allowable by the industry) when required to determine radiation more accurately than what is often produced by standard software.
Flare Header Evaluation
The standard approach for flare header evaluation is:
- Check individual relief device sizing
- Work with the client to identify credible and governing relief scenarios affecting entire units or sections of the plant where multiple relief devices would discharge simultaneously into the flare header (blocked flow, external pool fire, loss of cooling, loss of power, etc.).
- Create a simulation of the entire flare header system being analyzed and check the system hydraulics for multiple devices and/or global relieving scenarios to determine backpressure issues impacting PSV sizing and type specification (conventional, bellows, etc.).
- Engineer appropriate modifications to alleviate any sections of the system with unacceptable hydraulic parameters.
- Inform the client of findings, any deficiencies, and recommendations for corrective actions.
- Prepare a report detailing the findings.