Gas turbine O&M crews typically apply masking tape on the bolted flanges connecting the natural gas supply manifold to the burners with masking tape, make a small hole in the tape and use a portable combustible gas detector to determine if any gas is leaking from the flange. The tape contains any gas that is leaking from the flange and directs it to the hole in the tape. A combustible gas detector is then placed above the hole to detect any gas that is leaking from the flange.
However, gas turbines get hot. The tape bakes on to the flange, becomes brittle and difficult to remove. Eventually many layers are applied. The brittle tape flakes off and migrates into the process piping, blocking gas nozzles. Unfortunately for the O&M crews, this is usually not detected until the gas turbine is started. The resulting failed start results in lost revenue and increased maintenance cost to disassemble, clean and re-assemble the piping.
The Flange Leak Detector is the solution to the tape problem. It is made from a material that does not come apart or flake, thus eliminating any chances of tape blockage.
Cost benefits of using the are listed below.
Case #1- Labor Savings
Using a wire wheel and a scraper typically takes 15 to 30 minutes to properly remove old tape from a bolted flange before breaking apart the flange.
The can be removed or installed in 30 seconds or less.
Assume your technicians have forty flanges to remove tape, disassemble, inspect, reassemble, re-apply tape and perform a leak check. Disassembly, inspection and reassembly shall be assumed to take the same amount of time for both methods-taping and using the .
The cost of removing and installing the tape is calculated by multiplying 40 flanges by 30 minutes per flange multiplied by one technician. This equals 20 man-hours. 20 man-hours multiplied by your labor rate (assume $50/hour) equals $1,000.
The cost of removing the Flange Leak Detector is calculated by multiplying 40 flanges by 30 seconds per flange multiplied by one technician. This equals 0.3 man-hours. 0.3 man-hours multiplied by your labor rate (assume $50/hour) equals $15.
This results in a cost savings of $985.
Case #2- Startup Failure
Substantial costs can result from gas turbine startup failures. When a unit is scheduled for operation, it has designated as the least cost generating unit to be started at that time. Any variation from the startup schedule will result in a more expensive generating unit being put into service, or require the utility to purchase power at a higher cost.
Cost incurred by a utility due to failed start are listed below.
The substantially reduces the chance of fuel system contamination, reducing the chance of failed starts.
Case #3- Base Load Unit Trip
Substantial costs can result from CT startup failures. However, these costs pale in comparison to the economic impact of a baseload unit trip. As mentioned in Case #2, when a unit is scheduled by a utility system dispatcher, it has been scheduled as the least cost generating unit to be operated at that time.
Assume a unit has a rating of net mw 500. Lost of one CT will result in the loss of 250 mw of generation capacity.
Assume natural gas cost of $5.00/mmbtu and a unit net heat rate of 7,500 btu/kwh, the cost of power generated (fuel only) is $37.50/mwh. Total cost per hour for 250 mw of capacity is $9,375 per hour.
Assume replacement power cost is $75/mwh. This is a cost differential per mwh of $37.5. Multiplied by 250 mw, this is cost of $9,375 for every hour the unit is unavailable.
Other considerations are the expense in future maintenance cost associated with a base load trip, potentially tens of thousands of dollars.
Additional cost associated with a unit trip are lost sales revenue and additional labor to return the unit to service.
The can be installed for a fraction of the cost of a unit trip and can substantially reduce the chance of a unit trip due to fuel system contamination.