Two-Step Electric Gas Heating for DRI Plants
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Solution Overview
Problem
In direct reduction plants using electric heaters, carbon deposition on heater elements occurs when producing DRI containing carbon, leading to overheating and potential damage, especially when using hydrogen or natural gas, which requires frequent idling for carbon burnout, reducing plant availability.
Innovation Solution
Implementing a two-step electric gas heating system with separate power controls, where the primary unit heats the reduction gas to a temperature below 600°C or above 700°C to avoid carbon formation, and the secondary unit heats it to 900–1100°C using a direct heating mechanism, thereby preventing carbon deposition and eliminating the need for carbon burnout.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a single-stage electric heater is used to heat reduction gas to high temperatures (900-1100°C), then the heating efficiency is improved, but carbon deposition occurs on the heater elements causing overheating and damage
Solution Approach 1:
The heating process is divided into two distinct stages: a first electric heater raises the gas temperature to an intermediate range (200-600°C), and a second electric heater completes the heating to the final high temperature (900-1100°C). This segmentation prevents carbon deposition by ensuring the gas temperature remains below the carbon formation threshold in the first heater while achieving the required high temperature in the second heater.
Solution Approach 2:
Different heating zones are created with different temperature characteristics. The first heating zone maintains temperatures below 600°C to avoid carbon deposition, while the second heating zone achieves temperatures up to 1100°C for effective reduction. Each zone is optimized for its specific function, with the first zone prioritizing prevention of carbon deposition and the second zone prioritizing achieving high reduction temperatures.
2Reliability
If carbon burnout is performed to remove carbon deposits from heater elements, then the heater reliability is improved, but plant availability decreases due to required idling
Solution Approach 1:
The system performs preliminary action by maintaining the reduction gas temperature below 600°C in the first heating zone, which prevents carbon deposition on the heater elements before it can occur. This proactive prevention eliminates the need for subsequent carbon burnout operations and plant idling, thereby maintaining continuous production availability.
3Object-generated harmful factors
If hydrogen is used as the primary reducing agent to minimize CO2 emissions, then environmental performance is improved, but carbon deposition risk increases when carbonaceous materials are introduced
Solution Approach 1:
The heating system is segmented into two stages with the first stage specifically designed to heat the gas to below 600°C before carbonaceous materials are introduced. This segmentation allows the use of hydrogen as the primary reducing agent for environmental benefits while the controlled temperature in the first heating zone prevents carbon deposition issues that would otherwise occur with hydrogen-based reduction processes.
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 solution effectively prevents carbon deposition on electric heater elements, maintains high plant availability by eliminating the need for idling, and ensures efficient heating of reduction gases to the required high temperatures.
Implementation Method 1
the primary electric gas heating unit with a direct heating mechanism is configured to heat the reduction gas to a temperature about or below 600° C.
Implementation Method 2
the secondary electric gas heating unit with a direct heating mechanism is configured to heat the reduction gas to 900 ̃1100° C.
Data Source
AI summary
Direct reduction systems and methods utilize a direct reduction shaft furnace to reduce the iron oxide with a reduction gas received from a reduction/recycle gas loop. An electric gas heating system disposed in the reduction/recycle gas loop heats up the reduction gas with make-up hydrogen and/or natural gas before introducing to the shaft furnace. The gas heating system includes, in sequence, a primary gas heating unit utilizing a direct or indirect heating mechanism to first heat the reduction gas to a temperature below 600° C. or above 700° C. to avoid carbon deposition in the gas heating system and a secondary gas heating unit utilizing a direct heating mechanism to second heat the reduction gas to the temperature between 900° C. and 1100° C.