Reliability Assessment of the Whistler Propane Vaporizers

Transcription

1 Reliability Assessment of the Whistler Propane Vaporizers Prepared for: Terasen & Fransen Engineering Prepared by: ClearSky Risk Management Inc rd Ave East Vancouver, BC V6B 5Z3 Phone: Fax: June 2005

2 Table of Contents 1.0 Summary of the Reliability Assessment Method Resources Results Lack of Spare Vaporizer During Peak Demand Failure of Propane Supply to the Vaporizers During Peak Demand Generalized System Failures... 7 Tables Table 1. Study Team Members...3 Table 2. Preventative Recommendations for Vaporizer Failure During Peak Demand...4 Table 3. Mitigative Recommendations for Vaporizer Failure During Peak Demand...5 Table 4. Recommendations for Loss of Liquid Propane Feed to the Vaporizers...6 Table 5. General Recommendations for System Reliability...7 Appendix A: Worksheets Appendix B: Recommendations Appendices i

3 1.0 Summary of the Reliability Assessment This summarizes the results from the reliability assessment of the Whistler Propane Plant Vaporizers. The study was conducted on June 6, 2005 at the Terasen office in Whistler, BC. The scope of the study was the equipment downstream of the propane tanks at the North and South Plants, through the propane vaporizers and into the propane distribution header. The objective of the study was to evaluate the potential reliability hazards in the existing system, relating to the ability to provide propane to the customers at all times of the year, during all ranges of demand. As part of a long-term plan, the propane storage system is expected to be decommissioned when a proposed pipeline is built from Squamish to Whistler to introduce natural gas to the community. However, in the interim, the reliability of the existing system is paramount. This review was undertaken to determine if there are any portions of the vaporization system that is prone to failure, in the time prior to the system changes. The primary purpose of the study was to identify equipment or procedures at the site that require attention in order to maintain the integrity of the process. The secondary purpose was to document any obvious safety concerns brought up during the course of the reliability assessment. However, this evaluation did not explicitly review safety hazards, and does not take the place of a Process Hazard Analysis. The study was conducted with the participation of two Terasen staff members from the Whistler Plant, one Terasen technician (instrumentation and controls), a project engineer from Fransen Engineering. A process safety and risk management expert from ClearSky Risk Management facilitated the study. A total of nineteen recommendations relating to operational and safety improvements to the facility were made. These recommendations were made with a team consensus, and are the product of this evaluation. ClearSky Risk Management has expended its best professional efforts in performing this work. However it should be noted that this report describes a work effort where Terasen personnel provided design, operations and maintenance information for the scope of equipment evaluated. This information was not field-verified or confirmed by ClearSky Risk Management. In addition, Terasen personnel were responsible for the assessment of hazards and the development of recommendations. Consequently, ClearSky Risk Management can accept no liability for any use that Terasen may make of the information contained herein. 1

4 2.0 Method The reliability assessment is a subjective evaluation which follows a standardized method for hazard identification, commonly used for process hazard analysis. In this case, the What-If? hazard analysis method was tailored to suit the scope and objectives of the study, which was to focus on reliability concerns at the Nesters site. The system was divided into 3 subsystems:. 1. Liquid supply system from Propane Storage tank through the Vaporizer Feed pumps 2. Tank Vapor header from Propane Storage tanks to the propane distribution header. 3. Liquid propane feed into the Vaporizers, including the glycol/water bath and burners. In each subsystem, the study team brainstormed possible scenarios that would lead to a loss or reduced function of the propane distribution network, stemming from problems at the Vaporizers. For each hazard identified, the potential consequences were documented. The worst-case consequence was evaluated without the benefit of operator or instrumentation interaction. This is typical in hazard evaluation, as both human action and instrumented systems are fallible and prone to fail on demand at some frequency. The existing controls, or safeguards, for each hazard scenario was documented. If the study team felt that the hazards outweighed the existing controls, then recommendations were made to reduce the risk of occurrence. The study was facilitated by a trained hazard analysis expert; however it was the input of the team members from Terasen that primarily guided the outcome of this study. Members from ClearSky and Fransen used their experience at other similar sites to provide advice during the course of the study, but are not solely responsible for the work product. Note a risk evaluation method was not used in this study. The purpose of the study was primarily to identify potential reliability weak spots. The study team recognized that the recommendations put forth during the study would not necessarily receive equal priority, nor be implemented. 2

5 3.0 Resources The PHA study was a team effort, consisting of a trained facilitator, Terasen operations personnel, and an engineering representative from Fransen Engineering. The team members who participated in this PHA are as follows: Table 1. Study Team Members Name Title Company Leslie Parchomchuk Facilitator ClearSky Risk Management Mark Abbott Mechanical Engineer Fransen Engineering Wayne Cankovic Frode Hansen Al Rumbel Operations Manager, Whistler Instrumentation Technician District Service Agent, Whistler Terasen Terasen Terasen The team members from Fransen and ClearSky conducted a site tour of the North Plant, to become familiar with equipment layout, prior to the study. The study team referenced drawings available at the Terasen offices, including: K : Rail Car Unloading & Nesters Propane Plant K : Nesters Propane Plant Liquids System In addition, electrical one-line diagrams and inspection reports were referenced as needed. All worksheets and reference drawings for this short study are appended. 3

6 4.0 Results The review focused on aspects of the equipment and the operating procedures that could reasonably lead to operational upsets in the next few years, prior to the conversion of the grid to natural gas. There were several areas of generalized concern: 4.1 Lack of Spare Vaporizer During Peak Demand The major concern was that during peak demand, all four vaporizers are required to supply the demand. Should a vaporizer, or any of its components, fail for any reason, there would be two consequences of concern: a) Reduced supply of propane to the end users, which can likely be mitigated by increased bath temperatures and increased natural vaporization from the propane tanks. b) Potential for the demand on the distribution header to increase the flow of liquid propane into the remaining vaporizers; the inability of the vaporizers heat input to keep up with the inflowing liquid could cause the vaporizers to flood and trip on high level, which would trip out all vaporizers, and cause a major upset due to loss of supply. The recommendations made to combat this concern focused on both on prevention as well as mitigation of the event, as follows: Table 2. Preventative Recommendations for Vaporizer Failure During Peak Demand Recommendation 16. Inventory spare parts for the entire system, and provide spare parts for critical equipment, such as: Fire eyes Level switches High Temperature switches Bath temperature control switches Flame guard ignition system Microswitches Liquid inlet solenoid valve.. e.g. PRV-1120 (& similar) Comment At a minimum, stocking spare parts and having the knowledge to repair or replace equipment will minimize downtime for vaporizers. 4

7 Table 3. Mitigative Recommendations for Vaporizer Failure During Peak Demand Recommendation 17. Consider developing a procedure to unload the demand on the system, while a vaporizer is down during peak demand. Sacrificing the supply to some customers may be required in order to prevent a total outage. 18. Calculate (estimate) how long it would take at peak demand for the vaporizers to flood and trip on high level, if one of the vaporizers trip. If the time to react is low (.e.g less than one hour), consider implementing options that would mitigate the sudden pressure surge due to losing a vaporizer at peak times, such as: Comment It is expected that a procedure to cut off supply to some users will be an unpopular move. However, having a documented protocol for use in the case of emergency is preferred over leaving the operators to make last-minute decisions. There has been experience with remaining vaporizers flooding if one vaporizer goes down during peak demand. If it happens while the site is unmanned, the time to respond may be too long before a total outage occurs. a) Install temperature controller, remotely activated. Increasing vaporizer temperatures temporarily will allow for increased propane generation. b) Remote start/stop of the Vaporizer Feed pumps. Stopping a pump would reduce the flow of liquid to the vaporizers to minimize the potential for high level trips, and would decrease the system pressure but not stop the flow. 19. Develop an operating procedure to deal with a loss of one Vaporizer during peak demands, to assist in decision-making whether to fix the problem or to reduce the throughput. The first evaluation is to check the demand, and to determine if the existing number of vaporizers can match that demand. The procedure should include a reference table of how much each vaporizer can produce at certain temperature/pressure profiles, for an 'at a glance' reference. In addition to providing operators with a tool to make difficult decisions, this would also provide an understanding between the site and the head office as to how to deal with outages. If existing vaporizers cannot keep up, then reducing the demand or throughput would be necessary to prevent tripping out the remaining vaporizers. 5

8 4.2 Failure of Propane Supply to the Vaporizers During Peak Demand There are two Vaporizer Feed Pumps, run at the same time during peak demands, with a larger Pipeline Evacuation Pump that may be used as a spare on its own. During peak demand time, the vaporizers require liquid feed in order to sustain the propane header pressure. There are various weak points in the liquid delivery process between the Propane Tanks up to Vaporizers, as follows: Pump failures while running are not explicitly monitored, alarmed, and mitigated (e.g. there are no remote or auto-starts). Tank isolation valves are prone to failure, either through loss of pneumatic signal or failure of a microswitch. The following recommendations are concerned with preventing, detecting and mitigating loss of liquid feed into the Vaporizers: Table 4. Recommendations for Loss of Liquid Propane Feed to the Vaporizers Recommendation 1. Consider providing a discreet local pump status indication (e.g. light) for Vaporizer Feed pumps. The location of the feed pumps under the awning makes it difficult to assess if the pump motor is on, especially if there is snow. 2. Consider providing a page status for pump failure. 3. Consider providing remote start/stop of the Vaporizer Feed pumps. This would allow operators to respond to a pump failure quickly, to start a spare pump. Stopping a pump would reduce the flow of liquid to the vaporizers to minimize the potential for high level trips, and would decrease the system pressure but not stop the flow. 4. Verify and ensure that the gen-set is function tested on full load, to ensure it can handle maximum load. Comment Note - history of operators not noticing that pumps were not running. Light would aid in detection. Currently, there is no remote notification of pump status, and the pump(s) are required in winter to sustain pressure. Pumps have been reliable; however as the demand is increased, the pumps will be required more often. As well, when they are needed, they are more critical as losing a pump in peak demand could mean a system outage. The gen-set is function tested, but the inspection reports were unclear if it was tested under a full load. 6

9 5. Lock and tag closed the bypass valve around the liquid supply solenoid valves to each propane vaporizer. These are safety systems which should not be bypassed, except under controlled circumstances. 7. Verify and ensure that that the nitrogen supply header is not vulnerable to snow/ice load, especially the section upstream of the restriction orifice. 8. Implement a formal program for checking and testing the microswitches on the nitrogen system to the tank ESVs. To be treated like any other safety system, e..g. PSV. Icing and snow load have the potential to cause failure of tubing. Informal program in place, but needs to be made standard. 4.3 Generalized System Failures There were a number of generalized operational efficiencies that could be gained from minor modifications to the system. The root cause of these concerns relates back to the detection and response to problems at an unstaffed site. Operators may not be at the plant site, and are required to respond to pages transmitted via a modem on site. There are several opportunities for failure between the alarm system, the modem communication system, and operator response time. Each opportunity for failure has the potential to be coupled with a peak demand time. The following recommendations would limit the potential exposure of the site to failures of the equipment or alert systems: Table 5. General Recommendations for System Reliability Recommendation 6. Consider providing a UPS (battery backup) to the power supply to the Vaporizers and Lighting panel 9. Include both the pump internal relief valves and the safety relief valves on the Vaporizer Feed Pump discharge on the PSV maintenance system. on a maintenance schedule. Comment 15 kva transformer causes loss of power to the instrumentation panel, which would cause the vaporizers to trip. The pumps have gen-set backup, but the vaporizer instrumentation does not, but the required level of reliability would be the same. Since the outlet of the pump discharge PSVs can be blocked in (e.g. valve #221 and 222 can be closed), then the pump internal PSVs are the only reliable form of overpressure protection. 7

10 10. Consider an increased reliability system for alarms and indication. The current system relies on the phone/modem system, and is not self-diagnostic and no immediate alarms if it fails. 11. Consider running the Vaporizer baths at a lower percentage of glycol to improve the heat transfer. 12. Consider implementing a propane vapour temperature control system on the Vaporizers. (only if an RTU is added for information). 13. Consider modifying the temperature control set for the Vaporizer at Function Junction, to provide faster feedback/control tuning. 14. Verify that the safety systems function as designed: e.g. that the loss of flame trip causes the liquid inlet solenoid valve to close. 15. Label the operators in the field, to minimize the likelihood of the setpoints being incorrectly adjusted, or adjusted on the wrong operator. Operators not always on site, and rely on pager system to alert them to problems. The percentage of glycol in water required for maximum heat transfer efficiency is not documented for the site. This would provide more direct control over propane header pressure, as bath temperature control is a delayed control. As well, the provides the potential for remote control, allowing the operators to increase vaporization temperature in the peak demand times in the case of an upset. It has historically had problems with delayed response, causing bath temperatures to drop significantly before the temperature controller turns back on, which results in inefficient propane vaporization. Unable to confirm during the evaluation that a loss of flame trip condition causes the inlet solenoid valve to go closed directly, rather than waiting for the high level trip to happen. One specific area of concern is the South Plant, which is not as well known to operators. In the case that another person, less familiar with the Whistler Sites, needs to respond, the labeling is either unclear or not present. All recommendations are also appended to this report. 8

11 Appendix A Worksheets

12 Appendix B Recommendation List

13 Terasen Whistler, BC Recommendations Whistler Propane Plant Reliability HAZOP Recommendations Comment CAT Resolution 1. Consider providing a discreet local pump status indication (e.g. light) for Vaporizer Feed pumps. The location of the feed pumps under the awning makes it difficult to assess if the pump motor is on, especially if there is snow. 2. Consider providing a page status for pump failure. 3. Consider providing remote start/stop of the Vaporizer Feed pumps. This would allow operators to respond to a pump failure quickly, to start a spare pump. Stopping a pump would reduce the flow of liquid to the vaporizers to minimize the potential for high level trips, and would decrease the system pressure but not stop the flow. 4. Verify and ensure that the gen-set is function tested on full load, to ensure it can handle maximum load. 5. Lock and tag closed the bypass valve around the liquid supply solenoid valves to each propane vaporizer. These are safety systems which should not be bypassed, except under controlled circumstances. 6. Consider providing a UPS (battery backup) to the power supply to the Vaporizers and Lighting panel 7. Verify and ensure that that the nitrogen supply header is not vulnerable to snow/ice load, especially the section upstream of the restriction orifice. 8. Implement a formal program for checking and testing the microswitches on the nitrogen system to the tank ESVs. 9. Include both the pump internal relief valves and the safety relief valves on the Vaporizer Feed Pump discharge on the PSV maintenance system. on a maintenance schedule. Note - history of operators not noticing that pumps were not running. Light would aid in detection. Currently, there is no remote notification of pump status, and the pump(s) are required in winter to sustain pressure. Pumps have been reliable; however as the demand is increased, the pumps will be required more often. As well, when they are needed, they are more critical as losing a pump in peak demand could mean a system outage. The gen-set is function tested, but the inspection reports were unclear if it was tested under a full load. To be treated like any other safety system, e..g. PSV. 15 kva transformer causes loss of power to the instrumentation panel, which would cause the vaporizers to trip. The pumps have gen-set backup, but the vaporizer instrumentation does not, but the required level of reliability would be the same. Icing and snow load have the potential to cause failure of tubing. Informal program in place, but needs to be made standard. Since the outlet of the pump discharge PSVs can be blocked in (e.g. valve #221 and 222 can be closed), then the pump internal PSVs are the only reliable form of overpressure protection. SAF Prepared by ClearSky Risk Management Evaluation Date: June 6, 2005 Page 1 of 3

14 Terasen Whistler, BC Recommendations Whistler Propane Plant Reliability HAZOP Recommendations Comment CAT Resolution 10. Consider an increased reliability system for alarms and indication. The current system relies on the phone/modem system, and is not self-diagnostic and no immediate alarms if it fails. 11. Consider running the Vaporizer baths at a lower percentage of glycol to improve the heat transfer. 12. Consider implementing a propane vapour temperature control system on the Vaporizers. (only if an RTU is added for information). Operators not always on site, and rely on pager system to alert them to problems. The percentage of glycol in water required for maximum heat transfer efficiency is not documented for the site. This would provide more direct control over propane header pressure, as bath temperature control is a delayed control. 13. Consider modifying the temperature control set for the Vaporizer at Function Junction, to provide faster feedback/control tuning. 14. Verify that the safety systems function as designed: e.g. that the loss of flame trip causes the liquid inlet solenoid valve to close. 15. Label the operators in the field, to minimize the likelihood of the setpoints being incorrectly adjusted, or adjusted on the wrong operator. 16. Inventory spare parts for the entire system, and provide spare parts for for critical equipment, such as: Fire eyes Level switches High Temperature switches Bath temperature control switches Flame guard ignition system Microswitches Liquid inlet solenoid valve.. e.g. PRV-1120 (& similar) As well, the provides the potential for remote control, allowing the operators to increase vaporization temperature in the peak demand times in the case of an upset. It has historically had problems with delayed response, causing bath temperatures to drop significantly before the temperature controller turns back on, which results in inefficient propane vaporization. Unable to confirm during the evaluation that a loss of flame trip condition causes the inlet solenoid valve to go closed directly, rather than waiting for the high level trip to happen. One specific area of concern is the South Plant, which is not as well known to operators. In the case that another person, less familiar with the Whistler Sites, needs to respond, the labeling is either unclear or not present. At a minimum, stocking spare parts and having the knowledge to repair or replace equipment will minimize downtime for vaporizers. SAF Prepared by ClearSky Risk Management Evaluation Date: June 6, 2005 Page 2 of 3

15 Terasen Whistler, BC Recommendations Whistler Propane Plant Reliability HAZOP Recommendations Comment CAT Resolution 17. Consider developing a procedure to unload the demand on the system, while a vaporizer is down during peak demand. Sacrificing the supply to some customers may be required in order to prevent a total outage. 18. Calculate (estimate) how long it would take at peak demand for the vaporizers to flood and trip on high level, if one of the vaporizers trip. If the time to react is low (.e.g less than one hour), consider implementing options that would mitigate the sudden pressure surge due to losing a vaporizer at peak times, such as: a) Install temperature controller, remotely activated. Increasing vaporizer temperatures temporarily will allow for increased propane generation. It is expected that a procedure to cut off supply to some users will be an unpopular move. However, having a documented protocol for use in the case of emergency is preferred over leaving the operators to make last-minute decisions. There has been experience with remaining vaporizers flooding if one vaporizer goes down during peak demand. If it happens while the site is unmanned, the time to respond may be too long before a total outage occurs. b) Remote start/stop of the Vaporizer Feed pumps. Stopping a pump would reduce the flow of liquid to the vaporizers to minimize the potential for high level trips, and would decrease the system pressure but not stop the flow. 19. Develop an operating procedure to deal with a loss of one Vaporizer during peak demands, to assist in decision-making whether to fix the problem or to reduce the throughput. The first evaluation is to check the demand, and to determine if the existing number of vaporizers can match that demand. The procedure should include a reference table of how much each vaporizer can produce at certain temperature/pressure profiles, for an 'at a glance' reference. If existing vaporizers cannot keep up, then reducing the demand or throughput would be necessary to prevent tripping out the remaining vaporizers. In addition to providing operators with a tool to make difficult decisions, this would also provide an understanding between the site and the head office as to how to deal with outages. Prepared by ClearSky Risk Management Evaluation Date: June 6, 2005 Page 3 of 3