Lessons Learned-Mulitpoint Ground Flare Installation/Operation

Paper from the AFRC 2017 conference titled Lessons Learned-Mulitpoint Ground Flare Installation/Operation

During the past ten years, the Dow Chemical Co. has been involved with the design, installation, and operation of four large multipoint ground flares. The first one has been in service for over eight years, and the other three have come into service within the past two years. As one might expect with equipment this large and complicated, the facilities have seen various issues / problems. This paper will be given to allow suppliers and other users in industry to learn from these experiences and to avoid the same problems with future designs / installation and construction / operations.; ; The following general subjects will be covered:; •; Thermal expansion; •; Staging valve bypass valves; •; Flooring materials; •; Shields / protection / bolting; •; First stage operation; •; Pilot operations / ignition; •; Retractable thermocouple system; •; Small bore piping; ; The presentation time allotment can provide opportunities for audience discussion as well.

1 Lessons Learned - Multipoint Ground Flare Installation / Operation Vance Varner Global Flare Subject Matter Expert The Dow Chemical Company AFRC 2017 INDUSTRIAL COMBUSTION SYMPOSIUM Houston, Texas September, 2017 ABSTRACT During the past ten years, the Dow Chemical Co. has been involved with the design, installation, and operation of four large multipoint ground flares. The first one has been in service for over eight years, and the other three have come into service within the past two years. As one might expect with equipment this large and complicated, the facilities have seen various issues / problems. This paper will be given to allow suppliers and other users in industry to learn from these experiences and to avoid the same problems with future designs / installation and construction / operations. The following general subjects will be covered: • Thermal expansion • Staging valve bypass valves • Flooring materials • Shields / protection / bolting • First stage operation • Pilot operations / ignition • Retractable thermocouple system • Small bore piping The presentation time allotment can provide opportunities for audience discussion as well. 21-June-17 2 INTRODUCTION The use of pressure assisted flares in the refining and petrochemical industry started over 30 years ago. The major flare suppliers' (i.e., John Zink, Callidus, Zeeco) can provide user lists as references. In recent times, this type of flare is becoming more common within the industry for use as a part of larger and more complex operating units. There are multiple papers and reports that have been previously presented regarding the advantages, disadvantages, operational characteristics (like radiant heat), and emissions rates from pressure assisted flares. Several of these have been presented as past AFRC Combustion Conferences. Refer to the AFRC web page (www.AFRC.net) for the listing of these papers. This paper considers some of the issues associated with the installations and operations of these flares based on the experiences of the Dow Chemical Co. (Dow). The expectation is that companies and persons associated with flares can utilize these lessons learned to help avoid repeating these issues. INSTALLATIONS Although the pressure assisted units / burners can be elevated, the most common use is with a multipoint ground flare (MPGF). Process technologies that utilize these include: refineries, LNG production, ethylene, aromatics, pipeline, drilling platforms, and several others. During the past ten years, Dow has been involved with the design, installation, and operation of four large MPGFs. While there are other pressure assisted flares within Dow, these are elevated, have a small number of burners, and have only minor issues. A summary of the Dow MPGF designs: Location Kuwait (JV) Texas Saudi Arabia (JV) Texas 1 Year of initial service 2008 2015 2016 2017 The number of burners for these four units range from 300 to 900. The number of stages range from 5 to 19. As one might expect with equipment this large and complicated, the facilities have seen various issues / problems. This paper will be given to allow suppliers and users in industry to learn from these experiences and to avoid the same problems with future designs / installation and construction / operations. The intent is to present the issues in a general way without regard to which supplier, design, or construction company was involved. 1 This MPGF contains 2 separate, independent units of operation within a single fence. 21-June-17 3 ISSUES - DESIGN 1. It is very important that the owner / technology provider supply enough information for the flare supplier to do the proper design. This means to provide as many flow scenarios as practical, not just a normal and maximum. As the flare flow changes upward or downward, the various staging valves will open and close. The staging curve is best developed through the understanding of the multiple scenarios. a. One deficiency that has appeared is that there are not enough burners to handle all the low pressure scenarios. Mostly, these scenarios involve clearing equipment for maintenance. The gas for this operation can contain a high concentration of nitrogen, which lowers the flare gas heating value. If the heating value is too low, it will not burn when flowing at high exit velocity in the pressure assist burners. If the velocity is too low, the flame could smoke without assistance. Assistance is typically found only on stage 1. b. Future designs may have two low pressure, steam assisted stages. 2. Data to be provided for each scenario must include flow, composition, temperature, and maximum allowable pressure at the flare. The number of burners per stage, burner spacing, header spacing, staging pressures, and overall field density are all based on this data. 3. Any limitations on plot space, shape, overall height, atmospheric conditions, etc. will allow the design to be optimized. Any specific safety factors should be included. a. An example: provide an addition height on the fence 10 percent above the expected flame length. 4. Piping layout and orientation must be established early. Examples include: a. Raised manifold or at grade. b. Inlet to manifold in center or from one end. c. Location of manifold relative to the flare field layout. 5. Establish a clear division of scope of supply. Each discipline will have many interface points - mechanical, piping, civil, instrumentation, electrical. This must be established early in the design. a. A decision must be made on which group (owner or supplier) will provide the main manifold. This will establish how many piping tie points between groups, as well as other requirements. 6. The owner must designate any shop testing that must be performed. The requirements may result from the local governmental agency and could be part of the permitting process. These requirements must be established early in the design and fit into the schedule. Burner configuration, number of burners to test, and gases used for testing are all key points to establish in the planning. Potential testing includes: a. Pilot operation / ignition b. Burner cross-lighting c. Burner stability d. Burner pressure operating range e. Emissions testing / how to measure this f. Burner flow testing with air. 7. The use of 3D modeling is very common for plant design. There should be an exchange of information from the flare supplier to the overall plant design which will allow the optimum 21-June-17 4 overall layout, monitor any potential interferences, etc. Many details can be lost if this is not done properly and through-out the design. 8. As part of the layout, establish the piping details. This means things like orientation of both manual and automated valves to ensure operator access and non-interference, flow meter location (need for straight length of pipe), and instrumentation and valve access. a. In one case, the inlet block valve handles were elevated and not readily accessible by operations staff without a ladder or chain operator. b. There are large values used as part of these systems. The owner needs to select the valve type to be used for the stage manual block valve - typically either gate of high performance butterfly valve. 9. The supplier should plan to provide a very detailed set of installation instructions. This is over and above the multiple mechanical drawings that are produced. Some items that have been installed improperly due to lack of instructions: a. Fence panels b. U-bolts - improperly tightened c. Heat shields / bolting d. Gravel - both type and size e. Recommended cleaning methods for all piping f. Utility pipe routing g. Thermocouple tubing installation and required access outside the fence h. Special tools (normally for the thermocouple installation / maintenance). 10. The supplier must take into account the manifold and header expansion due to thermal growth. As the flare operates, heat is generated inside the fence / field. Each header should be designed to grow toward the inside the fence, away from a fixed point at the main manifold area. Off-line headers will grow more since there is no flowing gas inside to cool the piping. a. Proper prediction of how much temperature rise is the critical part. Direct radiant heat from the flames as well as reflected heat from the flare floor must be considered. This will be much higher than any flare gas temperature from a specific flowing scenario. b. Proper / enough shielding of the headers is a factor. c. Allow for ventilation of the heat shield to prevent an oven effect for the headers. d. Proper piping saddles / ability to slide. In one case, saddles were bent and runners damaged due to poor design / saddles in a bind. e. Location of instrumentation and utility piping outside the fence - considerations for the actual fence temperature and heat radiating from it to ensure proper location and movement. ISSUES - FABRICATION / CONSTRUCTION 1. The entire MPGF is fabricated in many parts: structural steel, piping spools, fence panels, header shields, etc. There were several instances that the delivered piping spools were not square / did not properly fit. The manifold and headers are normally large piping. Field adjustments can be difficult. The pipe fittings (like elbows and flanges) are not readily available, so any field re-work can potentially damage the materials and/or cause delays. 21-June-17 5 2. General inspection of all the parts and materials before leaving the fabrication shops is an important step. In many cases, companies use a third party inspector, especially with international fabrication. There should be specific requirements for these inspectors, and review of reports through-out the fabrication process. 3. Construction supervision / consultation by supplier. This is not a straightforward step to include in any contract. This supervision was not utilized on any of these jobs for Dow. Installation and operational issues could have been avoided with the proper use of this service. The service is normally an extra cost, so project managers do not like it. Examples of where a supplier supervisor would have avoid issues: a. Thermocouple tubing routing b. Shield installation / bolt torque c. Utility piping installation / cleaning d. Conduit / wiring routing e. Proper bolting materials f. Proper gravel for flare ground cover. 4. During construction, the alignment of valve handles, instrumentation, actuators, etc. has long term consequences. a. In one case, the valve handles for the stage block valves was about 10 feet (3 meters) above grade. Access was only possible with the use of a ladder or chain operator. b. The operational box for the buckling pin valves needs to be easily accessible for operations / maintenance. For each of the four flares, at least one instance that these boxes ended up inside the piping loop for the bypass valve. Pre-planning in the design should have shown the proper alignment and fabrication by the supplier. ISSUES - OPERATION 1. The pilots are the first equipment to be put in service for the flares. There are multiple considerations that must be evaluated before the actual ignition of the pilots. Dow has examples of pilots no longer functional after only months of service. Since the pilots can only be serviced when the flare is totally out of service, the exact failure mode is unknown. The factors listed will give the highest chance of successful operation during the long operation between flare outages. a. It is critical that the piping inside the fence be cleaned properly. Any debris left in the piping is a potential plugging issue for the pilot mixing nozzle / strainer. Once the pipe has been fabricated and the pilots fit into place, either remove the pilots or offset the connection. Then blow the pipe with steam or high pressure air to remove debris. b. Most suppliers will provide a strainer at the pilot base. This is good protection, but once it plugs, nothing can be done to it until there is access inside the fence. Along with the blowing operation, the best protection is a strainer outside the fence and stainless steel piping inside. c. Thermocouples are routed through tubing from outside the fence to the pilots. The actual tubing and fittings are specially designed for this purpose. Do not use generic tubing. d. Routing of the thermocouple tubing is important. These are long runs in the 21-June-17 6 horizontal plane, so minimization of resistance and bends must be done. Hard bends will cause the thermocouple to bind and not reach the pilot. e. Use of the proper tools for the thermocouples is important for alignment and future extraction. There are specialized straightener and pusher tools that can be used for these very long runs. f. Once the thermocouple is installed, test the tip seating by placing heat on the pilot with a portable torch. Check for a temperature rise reading at the termination wiring. Cold spray can also be utilized. g. Each pilot should be ignited utilizing the high energy spark system and confirm it is burning. Once that is done, extinguish the flame and allow the pilot to cool. Then ignite the pilot utilizing the flame front generator. This method confirms that the pilots and ignition systems are functional well before the time to have the flare in service. In one case, the ignition rod was too short and did not provide a reliable ignition. Since this was discovered early, the rods were changed before there was any flare gas to burn. h. During another pilot ignition test utilizing the FFG system, the ignition lines were found to have a high volume of water. Even with the low point bleed valve opened outside the fence, the line did not drain. In this case, the ignition line between the fence and the pilot connection had a slope toward the pilot rather than back to the fence. It will be critical to blow out the line before operating the FFG. 2. There are bypass safety relief devices around the staging valves to ensure availability of the flare flow area in case of automated valve failure. The most popular relief device currently is a buckling pin type device. There are several suppliers of these. a. These buckling pin valves can have alignment issues. The valve bodies cannot handle uneven torque, as it causes the valve disk to bind and not operate at the proper pressure. This can also lead to seat damage on the disk, allowing for leaking past the valve. In addition, for some systems, the linkage for closure of the disk is not simple and must be handled with care. b. The valves are typically shipped to the construction site with a "shipping" pin, not for service. The service pins are shipped separately. They are normally numbered and specific to particular valve, not interchangeable. Keeping up with the service pins can be a challenge. c. Test the rotation / opening of the disk once the piping is complete to ensure proper opening torque. d. There has been one example of a valve slightly open on a high stage, allowing leakage and a small smoky flame. 3. Control of the MPGF by the opening / closing of the staging valves is based on the inlet pressure for the flare manifold. Programming of whatever control platform is utilized takes time. The suppler should provide a control logic to give the process automation group the ability to program. The considerations on how best to align this logic start at the design stage: a. Staging pressure for each stage to open b. Staging pressure for each stage to close c. Which row / header aligns with which stage in the sequence d. Any time delay for opening once a set point is reached e. Any time delay for closing once a set point is reached 21-June-17 7 f. Control of the low pressure / steam assist 4. Adjustments have been made for the staging curve once the flare was in operation. In one case, there was smoke production at an operational point. With proper operation of the MPGF, there should be no smoke other than a very small amount at the very end of a destage operation. 5. Heat production in some cases has been an issue as well. a. Damage to the heat shields b. Damage to the headers c. Damage to the gravel floor d. Issues with electronics (temperature transmitters) due to heat from fence e. Damage to conduit 6. The flare field should be monitored via video cameras. Location of the cameras is important to make sure the whole field is covered. In most cases, the camera requires some extra cooling and shielding. a. Regulatory agencies may require storage of the video images. CONCLUSIONS The proper design, fabrication, construction, and operation of a MPGF provides a safe and reliable method for the destruction of flare gases. This does not come without continuous efforts throughout the process. This paper along with others outline areas of attention which will help lead to a successful installation. 2 "Considerations when Specifying Multipoint Ground Flares", Ian Fischer, ExxonMobil, AFRC Combustion Symposium, Sept, 2015 2 21-June-17