Polaris solar PV net news: world’s largest has been installed into a molten salt Crescent dunes Tower power station power plant recently took small molten salt tanks of molten salt leakage accident, leading to the power station from late October this year the removal of network outage, next January is expected to be back to normal operation. Exclude SolarReserve referred to in December as planned maintenance period, the power plant accident in November to at least a month unable to power.
In addition to the economic losses of the heat storage tank maintenance, the greater is the loss of power outage led to the loss of income from electricity sales. According to the latest data, the station in September this year, monthly output of 30514MWh, PPA contract price of the item $0.135 per kWh, according to rough estimates, caused by a month of stopping about about $4 million for loss of income from electricity sales.
From this point of view, molten salt economic losses from the spill to run power stations should not be underestimated. It is understood that salt spills in solar-thermal power generation projects especially in molten salt Tower power station more likely, commercialization of world’s first molten salt Tower power station Gemasolar plant allegedly similar incidents also occurred. So, solar thermal demonstration project either under domestic construction, how to prevent such accidents as much as possible? First of all, we need to understand what causes salt tank leakage accident.
Related topics for discussion, many enthusiasts who shared their views on the causes of the accident. According to industry feedback, a total of seven reasons is possible salt tank leakage accident, including temperature in welding process and quality control problems, tank after welding stress, stress relief heat treatment, tank of steel corrosion problems, a low proportion of non-destructive testing of welds, salt tank size is too large, and so on.
Due to the Crescent dunes power station leaked details of the developers did not release specific, the domestic industry is only from their own professional perspective and analysis on this issue, is for informational purposes only.
Welding process quality problems?
“I think the weld leak and construction is not strictly according to the temperature control of welding process the welding process. Different materials, welding temperature is not the same, and this temperature depends on the material of the tank, flux, Groove. “Bin valve fluid control Ltd company greater China Sales Manager Yu Xiaohua said.
In addition to welding temperature, the third Shandong electric power construction engineering company on a trade point out that may also be because of a thick plate and Groove size standards, caused by welding without penetration. In addition, may be used during automatic welding machine, no precautions.
Yantai or.en electromechanical technology services limited, Wang added, “welding problems also include welding welding before cleaning out after welding, welding gas shield not ready, strain relief didn’t do, weld flaw did not do. ”
Second, large tank internal leaks caused by stress?
Many people in the industry believe that is because inside the heat storage tank temperature cause stress concentration. Tank possible causes of stress is caused by fluctuation in temperature molten salt salt, cause stress cracks in some cracks such as under alternating hot and cold.
“Weld is the weakest parts of the tank, the stress concentration of the most vulnerable places. And tank, thermal analysis and thermal control should be set to ensure uniform heating, stress is not concentrated. “Yu Xiaohua said.
Third, the flux material corrosion-resistant enough?
Problem with the tank weld, solder materials corrosion resistance is a factor worthy of consideration. So in order to prevent similar problems, experts suggest may be appropriate to improve solder corrosion specification or added corrosion-resistant components.
But Wang believes that this statement does not apply to Crescent dune plants. Because the developer’s argument, the leak was small, if insufficient solder corrosion, it should be a large area of cracks. Therefore, from a long-term perspective, tank especially the welding position should do about pickling and passivation-surface treatment as well.
Four tanks, molten salt corrosion of steel led to spill salt?
Beijing rich technology, Tong Guang Hua pointed out that molten salt thermal expansion and contraction would cause material stress, thus breaking the steel lattice, the tank corrosion.
While the he Yuan speculation, weld leak here, was not caused by corrosion. “For big diameter melt salt tank, I personal compared worried of is big diameter high temperature poor Xia of tank body expansion problem, tank end of in based Shang sliding expansion volume larger, if structure Shang appeared local card delay, for example heater, within pieces expansion direction and tank end of expansion direction not synchronization, or distribution tube stress calculation Shi, on tank body diameter of expansion volume consider insufficient, is has may caused weld tear. (The line at the top of the molten salt tanks, piping stress may not be the cause) “
Five, eliminating residual welding stress (heat treatment) work not been done?
Yu Xiaohua believes that for such a large container, use thick plate heat treatment after welding should be done in order to eliminate stress. Also, tanks and other equipment for welding of pipelines, heat treatment after welding should be done. So speculate that spill salt is likely relevant.
BSS (Beijing) energy-saving environmental protection equipment limited company He Yuanzhi hold different views about this, he said, large storage, import/export of material, instruments, tank bottom inspection manholes, etc, will focus on the arrangement of pieces on the wall plate. Large tank wall plate is low-alloy steel plate, these pieces of siding with pipe/manhole is to stress-relief heat treatment after welding, heat treatment is carried out in factory heat treatment furnaces, often without heat treatment defects.
For low-alloy tanks, design-time will adjust the tank dimensions, making the thickness of the wall thickness is less than the required post weld heat treatment. Austenitic stainless steels do not stress-relief heat treatment after welding. And with molten-salt tank volume and condition of construction site, weld is unlikely or stabilizing treatment solution treatment on the spot.
Operating temperature of molten salt tanks of up to 560, has reached the target of reducing heat stress-relief heat treatment after welding, use naturally eliminating welding stress.
So, how far do not think eliminating residual welding stress (heat treatment) no problem.
Crescent dunes solar-thermal power station tank salt spill temporarily suspended
Liu, tank lower the proportion of non-destructive testing of welds?
Lower proportion of non-destructive testing of welds for large storage tank is always a potential problem, if there is no 100% non-destructive testing, you may be left with hidden dangers. Sun Bao Yin Jianping, Chairman of Jiangsu province noted that one of the three reasons also include welding test not 100%, there are holes in question.
He Yuan further explained that usually requires about 10% of large tank weld inspection “, that is entirely in accordance with welding and welding procedure specification for welding, welding conditions, welding quality problems may also occur.
“From a design perspective, you can increase the proportion of non-destructive testing, t-shape weld radiography and elsewhere increase the proportion of ultrasonic testing, lower two-ring and the bottom of the tank wall penetration testing all of the weld. But if you want to increase the proportion of non-destructive testing takes a lot of money, even if the tank wall is the end of the 100% ultrasonic testing of welds. “He Yuan said.
Seven, molten salt tanks uneven Foundation settlement?
He Yuan pointed out that molten salt tanks uneven Foundation settlement is also a potential problem.
Molten Salt tanks for the end of conventional storage tank based on the surface, increased refractory castable (lightweight aggregate concrete, refractory cement) and refractory bricks. Refractory pouring material is characterized by a low intensity low thermal conductivity, high thermal conductivity.
From the angle of insulation should use low heat conductivity, compressive strength of high strength should be chosen in terms of. These two requirements for tank bottom based castable is a contradiction. Low strength refractory castable, even ASTMC401ClassV, the density is 1680kg/m ³, bottom heat intensity does not exceed 10MPa.
Common castable composition is of high alumina cement + aggregate + additives aggregates are made up of multiple particles, such as ceramic, vermiculite, perlite, fine, once the particles are not uniform, crushed in a construction, may cause small tilt of the tank wall, increasing stress of the tank wall, tearing may cause weak welds.
In addition, the industry also points out that desert cause differential settlement of Foundation, cause weld cracking.
In view of the various possible reasons leading to salt molten salt storage tank leakage, solar-thermal power projects in the country can absorb the useful experience, avoid a similar fate.
Crescent dunes solar-thermal power station tank salt spill temporarily suspended
Original title: the Crescent dunes solar-thermal power station seven reasons analysis of molten salt leakage accident