Taking the carbon transfer efficiency of natural gas RX gas as 1.0, nitrogen-methanol (20% CO, 40% H₂) is about 1.0, propane RX gas is about 0.9, and pure methanol (33% CO, 67% H₂) is about 2.7. Pure methanol has the fastest permeability but is the most difficult to control; nitrogen-methanol is flexible to implement but the CO content will fluctuate with furnace temperature and dripping; RX gas composition is the most stable and carbon potential is the easiest to control, making it suitable for production lines that require high precision and consistency.
- Carbon transfer efficiency (relative): natural gas RX 1.0, nitrogen-methanol 1.0, propane RX 0.9, pure methanol 2.7
- After the RX gas enters the furnace, CO and CO₂ are stable and CH₄ is low.
- Nitrogen-methanol CO fluctuation can cause a carbon potential deviation of approximately ±0.12 (field case)
- The choice requires weighing accuracy, output, investment and hazardous chemicals management.
Basic parameters of the three atmospheres
| Project | Natural Gas RX Gas | Nitrogen-methanol (40/60) | Pure methanol |
|---|---|---|---|
| Main ingredients | About 20% CO, 40% H₂, 40% N₂ | About 20% CO, 40% H₂, 40% N₂ | Theoretical 33% CO, 67% H₂ |
| preparation | Generator external lysis | Inject methanol + nitrogen into the furnace | Injecting methanol into the furnace |
| Relative carbon transfer efficiency | 1.0 | 1.0 | 2.7 |
| Difficulty in controlling carbon potential | Low | middle | high |
(For relative carbon transfer efficiency data, please refer to "Carbon Potential Management Method Based on Heat Treatment CQI-9" by Gos Control.)
Stability: Why RX gas is easier to control
Carbon potential calculations rely on "known and stable CO%".
- RX gas: Directional cracking in the generator at a fixed ratio. After entering the furnace, both CO and CO₂ are in a stable state, and CH₄ remains at a low level;
- Nitrogen-methanol: Methanol is cracked in the furnace. The degree of cracking changes with the furnace temperature, furnace type and drip stability. The lower the temperature, the less complete the cracking will be. One month of continuous monitoring of a nitrogen-methanol integral-quench furnace by Gauss Control showed that CO fluctuated between about 19.3%–22.2%, corresponding to a carbon potential deviation of about ±0.12, and the CH₄ concentration was significantly higher than the RX atmosphere;
- pure methanol: The CO concentration is high, the carbon transfer is fast, and the penetration rate is fast, but the process is radical and the carbon potential is easy to overshoot, producing carbon black and excessive carbides.
Cost and management
| Dimensions | RX gas | Nitrogen-methanol |
|---|---|---|
| initial investment | Requires generator and pipeline | Lower, just drip system and nitrogen source |
| running costs | Mainly natural gas and electricity, which have advantages when using large quantities | Methanol and nitrogen costs increase linearly with usage |
| Hazardous chemicals management | No need to store large amounts of methanol | Methanol storage, transportation, fire protection and environmental impact assessment costs |
| Centralized gas supply for multiple furnaces | Suitable | Independent drip injection for each furnace |
How to choose
- Few furnaces, various varieties, small gas consumption: nitrogen-methanol is flexible and starts quickly;
- Continuous production of multiple furnaces requires high carbon potential accuracy and consistency (such as automotive parts, which need to meet CQI-9): centralized gas supply from the RX generator is more suitable;
- Pursuing the ultimate penetration rate: The methanol proportion can be increased if the control ability is sufficient, but monitoring needs to be strengthened.
Frequently asked questions
Can nitrogen-methanol meet CQI-9 carbon potential accuracy requirements?
Yes, but more stringent monitoring is required, such as installing CO online analysis, correcting the carbon potential calculation with measured CO%, and strengthening daily calibration.
Switching from nitrogen-methanol to RX gas, does the process need to be re-validated?
need. Changes in the carrier gas will affect the carbon transfer speed and surface carbon content. The layer depth, surface hardness and metallographic structure should be verified through samples before mass production.
Can RX gas be mixed with methanol?
It can be mixed under certain conditions (such as mainly RX and supplemented with methanol), but the control system needs to consider changes in CO%, otherwise the carbon potential calculation will be biased.