Worland Gas Plant - Executive Summary
Devon Energy Worland Gas Plant Risk Management Plan: |
ACCIDENTAL RELEASE PREVENTION AND RESPONSE POLICIES
The Devon Energy Worland gas plant has a long-standing commitment to worker and public safety. This commitment is demonstrated by the resources invested in accident prevention, such as training personnel and a strong record for safety in the design, installation, operation, and maintenance of Devon's equipment and processes. Devon's policy is to implement reasonable controls to prevent foreseeable releases of regulated substances. However, if a release does occur, trained gas plant personnel will respond to control and contain the release.
DESCRIPTION OF THE STATIONARY SOURCE AND REGULATED SUBSTANCES
The Worland gas plant, located 9 miles north of Worland, Wyoming, operates a variety of processes to produce petroleum products (e.g., natural gas, propane, butane, and condensate) from wet (i.e. contains hydrocarbon liquids) natural gas. The Worland gas plan
t produces several regulated flammables, such as propane and butane.
OFFSITE CONSEQUENCE ANALYSIS RESULTS
The worst-case scenario (WCS) associated with flammable substances in Program Level 3 processes at the gas plant is a rupture of a tank car being loaded with propane at the tank car loading rack, with the car almost full and product being pumped into it. A north to south or west to east wind of any velocity could carry released propane to either one of two offsite receptors. These sites are a house 650 feet south of the loading station, and an occupied compressor station 875 feet to the east of the loading station. Ignition of the released propane could cause a vapor cloud explosion, jet fire, pool fire or BLEVE of the tank. No other dwellings are within the endpoint distances calculated for this situation. Approximately 120,000 pounds of propane could be released. The endpoint at 1 psi is 2,112 feet from the loading rack. Ten percent of the released quantity is assumed t
o participate in the resulting explosion. Safety shutoff valves located at a safe distance are present to stop flow to the tank car.
The alternative release scenario (ARS) is a rupture of a propane storage tank at the tank farm with the tank almost full and propane being produced into it. A north to south wind of any velocity could carry released propane to an ignition point creating a potential vapor cloud explosion and subsequent jet fire, pool fire, and/or BLEVE. Affected offsite habitation is one home 1,914 feet south of the storage tanks, and an occupied compressor station 875 feet east of the storage tanks. No other dwellings are within the endpoint distances calculated for this tank. Approximately 144,398 pounds of propane could be released. The endpoint at 1 psi is 2,270 feet. Ten percent of the released quantity is assumed to participate in the resulting explosion. Isolation valves are present at the plant and a PSV (pressure safety valve) is present on the tank.
mical-specific information, including exposure hazards and emergency response/exposure treatment considerations, is provided in material safety data sheets (MSDSs). This information is supplemented by documents that specifically address known corrosion concerns and any known hazards associated with the inadvertent mixing of chemicals. For specific process areas, the gas plant has documented safety-related limits for specific process parameters (e.g., temperature, level, composition) in a key process parameter document. The gas plant ensures that the process is maintained within these limits using highly trained personnel, process controls and monitoring instruments, and protective instrument systems (e.g., manual and automated shutdown systems).
The gas plant also maintains numerous technical documents that provide information about the design and construction of process equipment. This information includes materials of construction, design pressure, volume and temperature ratings
, and electrical rating of equipment. This information, in combination with written procedures and trained personnel, provides a basis for establishing inspection and maintenance activities, as well as for evaluating proposed process and facility changes to ensure that safety features in the process are not compromised.
PROCESS HAZARD ANALYSIS (PHA)
The Worland gas plant has a comprehensive program to help ensure that existing and potential hazards associated with the various processes are identified and controlled. Within this program, each process is systematically examined to identify hazards and ensure that adequate controls are in place to manage these hazards.
The Worland gas plant primarily uses the "what if" analysis technique to perform these evaluations. The analyses are conducted using a multi-disciplined team of people who have operating and maintenance experience as well as engineering expertise. This team identifies and evaluates hazards of the process as well as a
ccident prevention and mitigation measures, and the team makes suggestions for additional prevention and/or mitigation measures when the team believes such measures are necessary.
All approved mitigation options in response to PHA team findings are tracked until they are completed. The final resolution of each finding is documented and retained.
To help ensure that the process controls and/or process hazards do not eventually deviate significantly from the original design safety features, the plant periodically updates and revalidates the hazard analysis results. These periodic reviews are conducted at least every five years and will be conducted at this frequency until the process is no longer operating. The results and findings from these updates are documented and retained. Once again, the team findings are forwarded to management for consideration, and the final resolution of the findings is documented and retained.
PRE-STARTUP SAFETY REVIEWS (PSSRs)
The Worland gas plant
conducts a PSSR for any new facility or facility modification that requires a change in the process safety information. The purpose of the PSSR is to ensure that safety features, procedures, personnel, and equipment are appropriately prepared for startup prior to placing the equipment into service. This review provides one additional check to make sure construction is in accordance with the design specifications and that all supporting systems are operationally ready. The PSSR review team uses checklists to verify all aspects of readiness. A PSSR involves field verification of the construction and serves as a quality assurance function by requiring verification that accident prevention program requirements are properly implemented.
The Worland gas plant has well-established practices and procedures to maintain pressure vessels, piping systems, relief and vent systems, controls, pumps and compressors, and emergency shutdown systems in a safe operating condit
ion. The basic aspects of this program include: (1) conducting training, (2) developing written procedures, (3) performing inspections and tests, (4) correcting identified deficiencies, and (5) applying quality assurance measures. In combination, these activities form a system that maintains the mechanical integrity of the process.
Maintenance personnel receive training on (1) an overview of the process, (2) safety, health, environmental hazards, (3) applicable maintenance procedures, (4) emergency response plans, and (5) applicable safe work practices to help ensure that they can perform their jobs in a safe manner. Written procedures help ensure that work is performed in a consistent manner and provide a basis for training. Inspections and tests are performed to help ensure that equipment functions as intended and to verify that equipment is within acceptable limits (e.g., adequate wall thickness for pressure vessels, relief valve testing). If a deficiency is identified, emplo
yees will correct the deficiency, if it is considered to be a major potential safety problem before placing the equipment back into service, or a management of change team will review the use of the equipment and determine what actions are necessary to ensure the safe operation of the equipment.
Another integral part of the mechanical integrity program is quality assurance. The Worland gas plant incorporates quality assurance measures into equipment purchases and repairs. This helps ensure that equipment is suitable for its intended use and that proper materials and spare parts are used when repairs are made.
SAFE WORK PRACTICES
The Worland gas plant has long-standing safe work practices in place to help ensure worker and process safety. Examples of these include (1) control of the entry/presence/exit of support personnel, (2) a lockout/tagout procedure to ensure isolation of energy sources for equipment undergoing maintenance, (3) a procedure for safe removal of hazardous subst
ances before process piping or equipment is opened, (4) a permit and procedure to control spark-producing activities (i.e., hot work), and (5) a permit and procedure to ensure that adequate precautions are in place before and during entry into a confined space. These procedures (and others), along with training of affected personnel, form a system to help ensure that operations and maintenance activities are performed safely.
SPECIALIZED SAFETY FEATURES
The Worland gas plant has safety features on many units to help (1) contain/control a release, (2) quickly detect a release, and (3) reduce the consequences of (mitigate) a release. The following types of safety features are used in the covered processes:
1. Hydrocarbon detectors with alarms in the process building.
1. Process relief valves that discharge to a flare to incinerate episodic releases;
2. Valves to permit isolation of the process (manual or automated);
3. Automated shut
down systems for specific process parameters (e.g., high/low temperature, pressure and volume);
4. Redundant equipment and instrumentation (i.e., backup firewater pump);
5. Atmospheric relief valves.
1. Fire suppression and extinguishing systems;
2. Trained emergency response personnel;
3. Personal protective equipment (e.g., fire retardant clothing).
PLANNED CHANGES TO IMPROVE SAFETY
The Worland gas plant resolves all findings from PHAs, some of which result in modifications to the process. The following types of changes are planned over the next few years in response to PHA, safety audit, and incident investigation findings:
7 Upgrade process control system to use distributed computerized control system.