A.7.1 Brief description of the equipment
The dry ash conveying system of a cement plant is equipped with 3 screw air compressors, with air compressor specifications of 220kW, water-cooled units, and exhaust volume of 36m³/min.
A.7.2 Brief description of the accident
During the operation of the #2 ash conveying air compressor, the air compressor had a high temperature alarm. After inspection, it was confirmed that the water-cooled cooler was blocked. After the maintenance personnel processed the work ticket, they used a high-pressure cleaner to clean the cooler copper pipe. After cleaning, the work ticket was eliminated and the air compressor was put into operation; about 40 minutes later, the operating duty personnel found the low compressed air pressure alarm, and went to the site to check and found that the #2 air compressor was on fire. After disconnecting the power supply, the fire was extinguished.
After inspection, the control system of the #2 ash conveying air compressor was burned and scrapped, the motor and motor cooling fan were burned, and the head needed to be dismantled for overhaul and inspection.
A.7.3 Cause Analysis
(1) The control cabinet was the most severely burned and was the first point of fire. A contactor in the control cabinet was completely burned and the interior was completely burned, which should be the ignition point.
(2) There was a lot of water on the ground around the air compressor. After asking the maintenance personnel, it was confirmed that a high-pressure water gun was used to wash the ground. The door of the control cabinet was not closed and water splashed into the control cabinet. The water entered the contactor and broke through the insulation between the two terminals, causing a two-phase short circuit and igniting the contactor; there was a lot of ash inside the control cabinets of the other two air compressors that had not been cleaned. There was also ash inside the control cabinet of the #2 ash conveying air compressor, which increased the possibility of contactor short circuit and combustion.
(3) There was a lot of oil and dirt deposited on the air compressor pipeline and oil and gas barrels that were not cleaned in time. There was also oil accumulation at the positioning sleeve where the motor and the air compressor were connected due to shaft seal leakage. The presence of oil and dirt caused the combustion area to expand.
A.7.4 Preventive Measures
(1) The doors of the control cabinet and switch cabinet should be closed in time after the operation is completed.
(2) Pay attention to the correct use of tools during maintenance work, and consider the possible consequences when using special tools for other purposes.
(3) Equipment oil leakage should be eliminated and cleaned in time to ensure equipment hygiene and safety.
