Explosion in an Urea Manufactory
In this plant, after conversion of the major part of the carbon dioxide into urea, the off-gasses from the reactor consist of ammonia, carbon dioxide, hydrogen, oxygen and nitrogen. Prior to venting this gas into the atmosphere it is washed with a carbamate solution. This absorption is carried out in a high pressure scrubber, where the explosion occurred. The internals were damaged without affecting the vessel itself as it was designed to take an explosion. A second explosion occurred in April 1974 and also damaged the internals.
Event Date
February 1, 1974
Record Quality Indicator
Region / Country
Event Initiating System
Classification of the Physical Effects
Nature of the Consequences
Causes
Cause Comments
The presence of hydrogen traces in the carbon dioxide is unavoidable. Oxygen is injected in the system because the urea reactor is made of steel. Formation of hydrogen-oxygen explosive mixture was caused by a very effective adsorption of the other off-gas components.The ignition source was probably oil traces in the absorption part of the scrubber caused explosion.
Facility Information
Application Type
Application
Specific Application Supply Chain Stage
Components Involved
reaction vessel and scrubber
Location Type
Location description
Industrial Area
Lessons Learned
Lessons Learned
CORRECTIVE MEASURESAccording to the Doyeweerd (1975, see reference), 3 methods for explosion prevention were available:1 .removal of hydrogen from the carbon dioxide feed stream. Disadvantage: expensive, as additional to the investment to be made for the catalytic hydrogen removal system.2. elimination of ignition sources. This would imply to avoid any possible presence of oil in the high pressure scrubber; this is unrealistic becasue of the use of a reciprocating carbon dioxide compressor 3. avoiding explosive gas mixtures in presence of high partial oxygen pressures.The company went for this 3rd option, and changed the operating conditions, resulting in an off-gas contained a higher fraction of ammonia and carbon dioxide, reducing considerably the oxygen partial pressure. To eliminate further ammonia and carbon dioxide the off-gas was then passed through an additional absorption system at a pressure of only some atmospheres.
Event Nature
Emergency Action
none
Detonation
No
Deflagration
No
High Pressure Explosion
No
High Voltage Explosion
No
Source Category
References
References
DOOYEWEERD E, EXPLOSION IN AN EAST ASIAN UREA PLANT, AMMONIA PLANT SAFETY VOL.17, 1975, 152-153.