Case study of sulfuric acid economizer failure
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Incident details: At 14:10 on April 20, 2014, the water level in the 200,000-ton sulfuric acid waste heat boiler of a certain company dropped from +60 mm to -180 mm, prompting the plant to initiate an emergency shutdown to investigate the cause. The weld at the inspection manhole of the inlet pipe of the No. 2 economizer cracked, causing water to leak out; a large amount of dilute acid flowed out from the condensate acid discharge port. After conducting a water test, it was determined that water was leaking from the pipes in the high-temperature section of the No. 2 economizer and entering the flue box. Analysis of the accident cause: 1. During the major maintenance in January 2014, a pressure test was conducted on No. 2 economizer, and no leaks were detected. 2. On April 7, 2014, sand holes caused leakage at the welds of the main inlet pipe and the branch tee for the high-temperature section of the No. 2 economizer. Taking into account the plant-wide power outage for maintenance on the 15th and the need to ensure a supply of steam for production, the workshop decided to divert the leaking water using color-coated steel sheets. However, on the 14th, during welding repairs due to severe leaks of water and air, it was discovered that there were two holes the size of thumbs in the smokebox. It’s likely that the leaked water splashed onto the smokebox, causing dew point corrosion of its walls. Two small holes are formed, and water enters the economizer through these holes, causing corrosion on the outer walls of the tubes. The pipeline strength decreased, resulting in a pipe rupture on the 20th and significant water leakage. Accident handling: 1. Temporarily bypass the inlet and outlet pipes in the high-temperature section of the economizer; after startup, the outlet temperature of #1 economizer was 205°C, and that of #2 economizer was 180°C. It has little impact on the dry absorber, with only a slight decrease in steam generation capacity. 2. Add new SAP master data, order one 2# economizer, and arrange for its replacement upon return to the factory
One should still approach everything with a rigorous attitude when studying it
Leakage in the economizer is indeed troublesome. . . . On my end, it’s 1 saved#
Actually, this issue has multiple aspects; if the maintenance schedule had been adjusted in time to be carried out 10 days earlier, the accident could have been avoided as well. But it’s mainly related to production performance assessments; if the machine is shut down for maintenance, it is considered an equipment failure, which results in a reduction of more than 6% in the assessment score. There are also assessments based on the machine’s operating rate and the number of accidents – 3% for zero accidents, 1–2% for 1–2 accidents – plus additional deductions due to the reduced operating rate. In total, this can result in losses of tens of thousands of yuan for the entire workshop. The workshop decided to take a risk, but unfortunately it failed; 5% of the performance score was lost due to the equipment malfunction, and the equipment was also damaged.
Production requires stability; don’t rely on luck.
Hehe, this is an external leak; it should be easy to fix. If you’re not good at welding, spend a little money and hire a company specialized in leak sealing under pressure to create a clamp and apply some sealant – that should suffice to get things back in order until the next major repair.
Boilers are crucial; absolutely no carelessness is allowed. This section is extraordinary, so be careful.
Production is at full pace right now, so all our maintenance work has to be done during the times when the furnace is shut down
The system shutdown was caused by a leak in the economizer, which really shouldn’t have happened; it’s related to the company’s evaluation system, and what they said makes sense. However, to maintain operations, a more thorough plan is needed, along with clear definitions of the responsibilities of those in charge and established methods for management; this is part of the task of professional management ； But usually, one should show sufficient respect for professional managers. I’m not aware of the specific structure and location, so I can only offer some suggestions regarding management.
May I ask which manufacturer’s economizer was updated by your company later on, and what has been the performance of it in use?
For special pressure equipment, repairing such damage on its own only allows for temporary use under supervision, as its strength has already been compromised. It is estimated that returning it to the factory for repair or replacement is required to resolve the issue completely.