Very Important CNG Station design and development tips as well as information on CNG Fill station service and preventive maintenance.
A well-planned and executed maintenance program is key to the reliability of your CNG Refueling Station. Not only will your station be on-line, all the time, it will also be safer for those fueling and those working at the station. Here is a quick checklist that will help you get you started. Identify the sequence of operation. Determine the actual sequence of operation. Make corrections to operations required. Select onsite personnel to be responsible for daily maintenance. Then provide the training and time to perform the job properly. Set up and use a log sheet to track equipment performance. Keep wiring diagrams, flow schematics and OEM manuals onsite. They are much more useful there for troubleshooting purposes than sitting on a bookshelf miles away from the station. Check OEM maintenance schedules and draw up a plan to carry out required maintenance procedures. Document these procedures when they are completed. Test all equipment safety controls on a regular basis to verify their proper operation. Document these safety checks. If you do not have personnel within your organization qualified to troubleshoot the station equipment, contact qualified, reputable service companies and check the cost of having them run a regular maintenance check on your station. Specify what equipment checks and maintenance procedures you want carried out. Also, request that they state any additional checks they believe should be made. A standard simplex compressor with priority sequencing with a gas dryer and a dispenser can easily require an entire day to PM. Have your gas tested for water content (dewpoint testing) so possible freeze-up problems can be identified. Take dewpoint readings at the suction side as well as the discharge. Plan to stock a minimum of spare parts, such as gasket kits, O-rings, valve rebuild kits, control relays, etc. These should be kept onsite so minor repairs can be done with a minimum of...read more
Many of you are already documenting the performance of your CNG stations / NGV refueling stations. This provides you with a daily history, a means of comparing past performance with the present with an eye on future performance. We encourage our customers to fill out log sheets on a daily basis. In one instance we had an individual that had never seen an NGV station before but was responsible for filling out the log sheet. We marked each point alphabetically for them and keyed this into our log sheet. Within weeks he could log the station in less than 10 minutes and was able to identify problem areas! If you are not already completing daily checks of your NGV refueling station and recording your findings on a log-sheet, you may wish to start today! This information will prove most helpful in the efforts to keep your station up and running. A daily log-sheet is simply a form that an operator completes on a daily basis by examining the station instrumentation and recording the findings. Some of these check points include: Inlet Pressure Discharge Pressure Inter-Stage Pressures Oil Consumption Discharge Temperatures When compared against past performance the operator can determine if there might be a problem developing. This ability to compare and predict is the foundation of Planned Preventative Maintenance. There are a number benefits to this type of maintenance approach. First and foremost the station is kept on-line satisfying the customers that depend upon the station. Second it allows for more economical repairs. Parts can be ordered and shipped via regular means and repairs maybe be scheduled for regular working hours. Both save money. Another benefit is the increased safety of the station. A station that is maintained on a daily basis is less likely to experience a catastrophic failure than one that is neglected. One aspect of maintenance that is often overlooked is station cleanliness. Clean equipment not only looks nice, but it also tends to show leaks much more quickly than dirty equipment. Clean equipment tends to send the message to both customers and supervisors that the personnel responsible for maintaining a site are doing exactly that. We have included a sample log-sheet that has been developed for CNG compression packages. Here is a sample log sheet for you CNG Fueling Station that you are welcome to download and...read more
To clock a gas compressor you will need to identify the following: That the only load on the gas meter is the compressor you are clocking. What the gas pressure is at the meter while you are clocking. What the smallest rotary dial on the meter measures in one revolution. Next, record how long it takes for a given amount of gas to go through the meter and what pressure the meter was at when you clocked it. Now the fun part; use the following formulas: Correction Factor = 14.7 + P (pressure at meter in psi) / 14.7 Uncorrected Flow = Cubic feet clocked X 60 seconds / clocking time (seconds) Corrected Flow (scfm) = Flow X Correction Factor Example: You have determined that you need to know what the gas flow at your NGV station is. Pressure at the meter while running is 18 psig. It takes 25 seconds for the 10 cubic foot dial on the meter to rotate once. What is the corrected flow? Correction Factor = 14.7 + 18 psig / 14.7 = 2.224 Uncorrected Flow = 10 scf X 60 / 25 sec = 24 scfm Corrected Flow = 24 scfm X 2.224 = 53...read more
Natural gas is highly explosive when combined with oxygen and an ignition source. In order to operate your NGV station safely, you should remove all the air from the system especially at start-up. We suggest using an inert gas such as nitrogen. Here are some simple steps to follow; remember these are a simple guide and may or may not apply to your specific module. Open the manual drain valve on the vent recovery tank. Turn auto condensate drain manual “dump valves” to the dump position. Open isolation valves to allow inlet pressure to the inlet solenoid valves. Turn the motor starter(s) “ON” and begin normal compressor operation. Open the pulsation tank drain valve slightly to allow gas to flow out while maintaining 1-2 psig on the compressor inlet. After three minutes, close the pulsation tank drain valve. Open each inlet filter bowl manual drain valve slightly to vent gas from the inlet filter bowl. Drain valves for one minute, then close each valve. Vent the compressor frame by removing the snifter valve cap and depressing the valve slightly. While maintaining at least one (1) psig on the compressor inlet, vent the frame until oil mist appears. Continue to run the system while dumping through out the recovery tank manual drain valve for five minutes. Close the manual drain valve. Turn auto condensate drain manual dump valves to the normal position. Vent the compressor frame a second time by depressing the snifter valve slightly while maintaining at least one (1) psig on the compressor inlet. Vent the frame until oil mist appears. Replace the valve cap. Vent the recovery tank through the manual drain valve located on the tank for three minutes. Vent the final discharge line through the user supplied purge valve. Continue to purge gas through all remaining pressurized components downstream of the compressor. If using nitrogen to purge the system, re-purge the entire system with natural gas. Upon completion, recheck position of each manual valve, securing as necessary. After waiting for the areas to be free of gas fumes which might lead to false readings, proceed with a leak check on all connections and valve seats. Remember, air can be reintroduced into the system if the unit is allowed to pull a vacuum anywhere in the system. If this happens, re-purge for your own...read more
The issue of CNG Fueling site safety in the field is one that should never be compromised. We are adamant about this at CNGCenter.com as you should be also. Here are some basic rules that I make sure all of our own service technicians follow: Understand and use good lockout and tag out procedures. Never work on compressor engine internals or rotating externals without locking out all electrical power and closing and securing with lock and tags all gas into and out of the skid. Know how to vent the gas off skid. Secure and lock out air start lines and vent same. Don’t vent down high pressure lines by loosening tubing connections. It is not only slow, IT IS DANGEROUS! Install vent purge plugs if they do not already exist. Most high pressure fitting supply houses stock them. Don’t use carbon steel compression fittings on stainless steel. Don’t intermix different manufacturer’s fitting parts on the same fitting. After having the compressor system open to air for repair, purge the air out of it before restarting. See Start Up Tip! . Leak test with soap or approved gas leak solution or electronic leak detectors and will help with increasing CNG fueling site safety. Avoid loose clothing. Don’t work with watches, rings or loose neck chains on. Always open high pressure vent and drain valves slowly and be sure that the discharge line is securely anchored and venting to a safe area. Avoid sudden high venting rates. Large discharges of high pressure gas can create a static charge, particularly if directed across a moveable surface such as a grass field or weed patch. Keep a fire extinguisher on site and know how to use it. Be aware that compressor piping becomes quite hot when running and remains so for a while after running. Repressurize high pressure lines slowly and in stages, checking for leaks at each stage. Generally this means stopping at 1000, 2000, 3000 and 4000 psi. NEVER TRY TO TIGHTEN A LEAKY FITTING WITH PRESSURE ON IT!!! High pressure compression fittings are designed to use pressure to seat them after they are torqued. Know where all the ESD shutdowns on a station are before performing CNG fueling site safety maintenance work. Never jump out a safety control because it is a nuisance. Please use above mentioned tips to increase the CNG fueling site safety of the cng station. More information on this and other topics related to Natural gas fueling infrastructure development can be found on US Department of Energy...read more