The Ivanpah Solar Electric Generating System in the Mojave Desert suffered a setback in mid-May when a rupture was found in a tube intended to heat steam for use generating power at Unit 2. Repairs are still continuing, according to a state agency that monitors the energy plant. That rupture followed close on the heels of three "ignition incidents" at the plant's Units 1 and 2.
One of the small fires stemmed from a scaffolding being inadvertently exposed to the plant's concentrated solar "flux," while the other two resulted from improper use of a flammable adhesive.
The Unit 2 pipeline rupture occurred in Mid-May. Repairs are ongoing at the 392-megawatt facility being built by Bechtel for BrightSource Energy and NRG in the Ivanpah Valley near Primm, NV. As California Energy Commission (CEC) press representative Sandy Louey told ReWire;
There was a piping failure involving the auxiliary boiler in Unit 2 on natural gas, which tripped the auxiliary boiler off line during tuning on May 15. An inspection found a ruptured superheater tube in the auxiliary boiler, the result of a manufacturing flaw. Repairs are being made to the super heater section of the Unit 2 auxiliary boiler.
May 14, the day before the failure, marked the first time flux had been achieved at Unit 2 -- meaning that enough of the Unit's heliostats had been aimed at the solar receiver steam generator to create the concentrated solar flux. In the words of BrightSource's Ivanpah website;
On May 14, the Ivanpah team reached another major milestone in the start up of the plant when first flux was achieved at Unit 2. Solar flux is when a significant amount of sunlight is reflected off of the solar field mirrors and concentrated on a surface of the boiler. The flux slowly heated the water inside the boiler to just below the point of steam generation. Overall, Unit 2 is more than 92 percent complete.
According to Louey at the CEC, the rupture -- for which project owners have not filed a detailed incident report -- did not occur while the boiler was "on flux." Each of Ivanpah's three units has a natural gas-fired component intended to supplement sunlight in heating up steam for the project's turbines, especiially at dawn or during especially cloudy weather.
The pipeline rupture capped off what must have been a trying couple of weeks for Ivanpah crews. In three separate incidents reported to the CEC over two weeks in April and May, small ignitions were spotted and extinguished at Ivanpah's Units 1 and 2. We'll refer to them as "fires" here for simplicity's sake, but Bechtel's Sonia Taylor points out that the word might give an impression of larger conflagrations. In one incident, some smouldering wood planks were extinguished: in another, non-fireproof adhesive used to affix insulation to pipes "flash-ignited." Bechtel only characterizes one of the incidents as a "fire." None of the incidents cauused injuries or significant property damage.
On Monday, April 29, concentrated solar flux at the plant's Unit 1 ignited a work platform made of wooden planks near the unit's "superheater" section. The superheater section takes already hot steam and exposes it to concentrated solar flux in the unit's solar receiver steam generator, heating it even further before it enters the unit's steam turbines. At about 1:10 in the afternoon, workers noticed smoke coming from near the top of the tower and notified Bechtel safety crews. According to incident documents Bechtel filed with the CEC, the smoke was coming from wood planks that had been exposed to sufficient solar flux that they were smouldering.
Operations at Unit 1 returned to normal wiithin the hour after the wood had been extinguished and discarded. The wood was in place as part of a scaffolding to hold workers as they reinforced wallls in the Superheater section of the power tower. According to the Bechtel report to CEC,
During the previous week rework of the west wall SH [superheater] panel to install strong back supports, an accessible wood platform was needed from the lower SH panel header to gain access to the weld areas of the buck stay for installation of the insulation strong backs. During the welding operation the weight of the workers standing on the wood planks compressed the header insulation and allowed it to separate from the wall insulation causing a gap which provided an opening from the outside. During flux of the SRSG [solar receiver steam generator], flux entered through the opening and heated up the wood planks causing the wood to smolder.
On May 10, pipe insulation adhesive placed by subcontractor Farwest ignited in separate incidents at Unit 1 and Unit 2, both stemming from the use of non-fireproof adhesives by subcontractor Farwest. Both incidents apparently happened during "steam bllow" testing, in which the plants' natural-gas-fired boilers ramped up steam pressure to test the systems' integrity.
The Unit 1 incident was described as a fire by Bechtel observers:
On the evening of Friday 10 May 2013 a fire was reported in the Unit 1 SRSG at elevation 524 near the steam drum. Somke was witnessed emitting from the partially insulated 10-inch superheat pipe. After the fire was extinguished the insulation was removed and it became apparent that a fire had been burning at a 90-degree elbow... Farwest was using a flammable adhesive product for field applications.
May 10 was a bad day for Farwest, apparently, as its choice of adhesives also contributed to the problem that same evening at Unit 2. According to Bechtel's report on that concurrent incident, a temporary "T" junction in a steam tub left adhesive backing holding insulation on one of the tubes exposed to temperatures of 650°F.
Farwest has been instructed to change its adhesives to more fireproof kinds, and to make sure all temporary junctions are insulated.
All told, a tough spring for Ivanpah. According to Sandy Louey at the CEC, the Commission's staff will be visiting Ivanpah this month to determine whether any of the incidents will affect the agency's approval of the one other solar electric project BrightSource has in the approval pipeline, the Palen Solar Electric Generating System near Joshua Tree National Park in Riverside County. Louey says depending on the results of that visit, the CEC may insist on more detailed "conditions of approval" in order to protect worker safety at Palen.
[Editor's note, July 19: after hearing that some readers were interpreting our earlier headline's reference to a "pipeline rupture" to mean a rupture in a pipe carrying something other than steam, we've edited the headline to help forestall that misinterpretation.]