Reducing Gas Bypass in Direct Reduction Iron Ore Heating
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Solution Overview
Problem
Existing direct reduction processes for producing metallic iron face issues with carbon deposits in heaters due to the use of reducing gases with high hydrocarbon content, leading to frequent cleaning operations, production interruptions, and increased capital expenditure.
Innovation Solution
A method and apparatus that circulates a significant portion of fresh reducing gas with high hydrocarbon content through a reducing gas circuit, bypassing the heater and directly into the reactor, while maintaining the necessary energy levels for the reduction process, thereby avoiding carbon deposits in the heater.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If reducing gas with high hydrocarbon content is heated in the heater, then the necessary temperature for reduction reactions is achieved, but carbon deposits form inside the heater
Solution Approach 1:
The reducing gas stream is divided into two separate streams: one stream (first stream) is heated in the heater to provide necessary temperature for reduction reactions, while the other stream (second stream) with high hydrocarbon content is injected directly into the reactor without heating. This segmentation prevents carbon deposits in the heater while maintaining efficient production rates through the unheated stream.
Solution Approach 2:
Different portions of the reducing gas are treated differently according to their local requirements: the first stream requiring high temperature is heated to achieve necessary reaction conditions, while the second stream with high hydrocarbon content is injected cold to avoid carbon deposits. Each stream receives the treatment appropriate to its specific characteristics and function in the overall process.
2Reliability
If the heater is cleaned frequently to remove carbon deposits, then the heater performance is maintained, but production is interrupted
Solution Approach 1:
By segmenting the reducing gas into two streams with different treatment paths, the system eliminates carbon deposit formation in the heater, thereby maintaining consistent heater performance over extended periods without requiring frequent cleaning interruptions. The unheated high-hydrocarbon stream bypasses the heater entirely, preventing deposit accumulation that would otherwise necessitate production interruptions for maintenance.
3Object-generated harmful factors
If reformers are added to remove heavier hydrocarbons, then carbon deposits are prevented, but capital expenditure increases
Solution Approach 1:
Instead of removing heavier hydrocarbons from the reducing gas before heating (the conventional approach using reformers), the invention inverts the approach by injecting a portion of the high-hydrocarbon-content gas directly into the reactor without heating or pre-treatment. This reversal eliminates the need for reformers and associated capital expenditure while still preventing carbon deposits in the heater.
Solution Approach 2:
The harmful heavier hydrocarbon components are effectively extracted from the heating process by routing them through the second stream that bypasses the heater entirely. Rather than attempting to remove or convert these hydrocarbons through complex reforming equipment, the solution extracts them from the thermal processing path, preventing carbon deposit formation without requiring additional capital-intensive equipment.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach reduces carbon deposits in the heater, maintains efficient production rates, and avoids the need for additional equipment like reformers, thus minimizing capital expenditure and operational disruptions.
Implementation Method 1
the iron ore react with a stream of reducing gas in a suitable reduction reactor... the oxygen is in fact removed from the iron ore by means of a high temperature chemical reduction (700° C.-1000° C.)
Implementation Method 2
Fe2O3+3H2→2Fe+3H2O
Implementation Method 3
Fe2O3+3CO→2Fe+3CO2
Implementation Method 4
the reducing gas coming from any gas source with high content of CH4 and heavy hydrocarbons (mixed with the recirculated spent reducing gas) is generally heated to increase its temperature to a value comprised between 700° C. and 1100° C. in a gas heater. The reducing gas must be heated to such a high temperature to provide heat to the iron oxides material inside the shaft furnace
Implementation Method 5
when the C2+ hydrocarbon content is not negligible, during the heating the undesired breaking of the chains of the hydrocarbons, and the consequent deposit of solid carbon inside the heater, occur
Data Source
AI summary
A method for producing direct reduced iron is provided. The method includes circulating a first stream of spent reducing gas exiting a reactor in a reducing gas circuit through at least one carbon dioxide removal unit and a reducing gas heater and the reactor. The method also includes mixing the first stream with reducing gas containing heavier hydrocarbons than methane.