Iron

Additional physico-chemical information

Administrative data

Endpoint:

other: Self-heating and water reaction

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: acceptable publication, widely used by the industry. Pilot test simulating the environment of ship transport

Data source

Reference

Reference Type:

other: Article

Title:

Reactions leading to the auto ignition of Direct Reduced Iron

Author:

Neil Birks and Abdul G. F. Alabi

Year:

1986

Bibliographic source:

Fifth International Iron and Steel Congress Proceedings of the 6th Process Technology Conference Volume 6 Washington Meeting, April 6-9, 1986

Materials and methods

Test guideline

Qualifier:

no guideline followed

Principles of method if other than guideline:

A review of the different oxidation reactions of iron compounds is presented and the detailed mechanism (kinetic and morphological steps) by which ignition of Direct Reduced Iron (DRI) is established. Article; no overall test guideline applies.

Test material

Test material information

Constituent 1

Reference substance name:

iron foil specimens

IUPAC Name:

iron foil specimens

Results and discussion

Results:

Oxidation reactions of iron compounds and their kinetics have been reviewed. Dry oxidation reactions proceed slowly at low temperatures, whereas aqueous reactions proceed more rapidly. Moreover the oxidation reactions of a metallic compound are faster with sea water contact. Wet Direct Reduced Iron (DRI) in an oxygenated atmosphere can satisfy all the conditions to become a fire hazards.

A pile of DRI on a ship has been divided in four major zones to explain the mechanism leading to the ignition of the pile:
- “aqueous zone” on the lower part of the pile: Iron is oxidized by water to form rust (exothermic reactions) and hydrogen. Heat is released and leads to the evaporation of water
- “capillarity zone” : water rises by capillarity through the pile until a limit which defines this zone
- “reflux zone” , where water condenses and leads to a rise of temperature. Oxidation processes of iron compounds continue.
- “vapor zone”, oxidation reactions occur with gaseous water (high temperature). This zone has been previously heated by the calories released from the oxidation reactions in the lower part of the pile. Temperature rises and ignition can be established.

Experiences on several carbon grade of iron under different atmospheres and temperatures showed that hydrogen is continuously produced when pellets are in contact with water. Hydrogen plays an important role in the ignition sequence on the upper part of the pile. The corrosion products were investigated: very finely divided oxidation products are formed in the interstitial spaces between the pellets.

The more refined mechanism of the ignition of a DRI pile involves water (under the gaseous form), heat from oxidation reactions, oxygen and hydrogen. Oxidations reactions and compounds produced interfere together and lead to a complex phenomenon and to the pile ignition. This study supports the fact that shallow DRI piles do not readily ignite.

Applicant's summary and conclusion

Executive summary:

The kinetics and morphologies of the oxidation reactions that occur in a pile of Direct Reduced Iron (DRI) on a ship have been studied. A basic mechanism of DRI oxidation has been proposed. Iron foil specimens have been exposed to salt water and to salt water saturated in oxygenated gases to simulate the environment of a pile of DRI during ship transportation. Experiments were carried out at temperatures up to 90°C. This study showed that hydrogen plays a key role in the auto ignition process. Moreover very finely divided oxidation products are formed in the interstitial spaces between the pellets. The more DRI is converted to finely iron products, the more likely the pile can reach high temperature where oxidation reactions can be sustained and succeed in provoking ignition. This study supports the fact that shallow DRI piles do not readily ignite