Comparatively analyze the corresponding relationship between gas recovery and steam recovery in the converter steelmaking process, and discuss and analyze the feasibility of improving the level of gas recovery and steam recovery.
Key words: gas recovery, steam recovery, heat balance
During the converter steelmaking process, the two by-products of converter gas and vaporization cooling recovery steam support the realization of “negative energy steelmaking” in the entire steelmaking process. According to statistics from the China Iron and Steel Association, in 2016, the lowest process energy consumption of the pure converter process was -33.3kgce/t, and the lowest process energy consumption of the entire steel billet production process including refining and continuous casting was -15.41kgce/t. It can be seen that the recovery of converter gas and vaporization steam is of great significance in reducing energy consumption in the steel production industry.
Converter flue gas vaporization cooling heat balance
The main methods of converter steelmaking flue gas purification and dust removal are the “OG” method and the “LT” method, which are the so-called wet dust removal and dry dust removal systems. There are essential differences between the two in terms of the principles of converter flue gas purification and dust removal, which will not be discussed here. Too much elaboration. The similarity between the two is that the flue gas temperature at the furnace mouth of the converter body is 1600-1700°C. It is cooled down to 800-900°C by the evaporation flue, and then enters the purification and dust removal system for flue gas purification and dust removal, and finally achieves the dust content reaching the standard. Flue gas exhaust or recovery. When the high-temperature flue gas passes through the vaporization cooling flue, it transfers heat to the high-pressure soft water in the flue to vaporize it into steam. The steam and soft water are separated in the steam drum through a steam-water separator and the steam is sent out.
The heat balance of the converter flue gas passing through the evaporation cooling flue process is shown in Table 1.
Table 1 Heat balance of flue gas vaporization cooling process
|Hot income item||Proportion/%||Hot expenditure item||Proportion/%|
|Smoke and furnace gas physical heat||85～90||Heat absorption in the evaporation flue wall||3～5|
|CO oxidation heat release in flue gas||10~15||Cooling soft water vaporizes and absorbs heat||35～4945～55|
|Physical heat of smoke and furnace gas after cooling||3～5|
|total||100||Other forms of heat loss||100|
It can be seen from the heat balance table that the heat source for generating steam comes from the physical heat of the converter flue gas itself and the heat release of CO secondary combustion and oxidation in the flue gas. The secondary combustion of CO in the flue gas directly affects the quantity and quality of converter gas recovery.
Correspondence between converter gas recovery and steam recovery
Based on the above heat balance analysis, the converter gas recovery and emission conditions and the steam delivery setting conditions of the vaporization system during actual production operations are shown in Table 2.
Table 2 Gas system and vaporization system condition settings
|Converter gasvaporized steam||CO%≥25%, start recyclingDrum pressure>1.2MPa, steam delivery||CO%<25%, stop until recyclingDrum pressure ≤1.1MPa, stop until delivery|
During the converter gas recovery process, the CO content percentage in the flue gas measured by the carbon monoxide analyzer and the flow rate data of the metering system at that time are measured by computer PLC, and the recovery time is integrated to obtain the converter gas recovery heat for each heat.
Single furnace converter gas heat
Among them: Q is the total heat recovered, GJ; αco is the instantaneous percentage of CO in the flue gas, %; V is the instantaneous flow rate of the flue gas, m³/h; q is the calorific value of the gas, GJ/m³, with a value of 1.26×10-*.
The heat recovery amount of converter gas and the amount of vaporization steam recovery are both measured in terms of unit steel production. Through data comparison, it can be found that there is a corresponding relationship between the heat recovery amount per ton of steel and the amount of steam recovery per ton of steel, as shown in Figure 1.
Figure 1 Corresponding relationship between heat recovery from converter gas and vaporization steam recovery
Optimize converter smelting hood lowering operation
Through the above theoretical analysis and actual data comparison, it can be found that: under the condition that the flue gas temperature is relatively stable, the change in steam recovery is affected by the secondary combustion of CO in the flue gas. At the same time, the secondary combustion of CO in the flue gas also affects the converter gas. The amount of recovery and heat recovery. Therefore, in the converter smelting process, converter gas recovery heat and vaporization steam recovery are a contradictory unity.
In the actual operation process, the converter smelting hood lowering operation is an important measure to improve the heat recovery of the converter gas. However, when the CO concentration does not reach the recovery condition, the hood lowering operation will hinder the secondary combustion of CO in the flue gas, reduce the amount of heat that promotes steam generation, and is not conducive to steam generation.
Therefore, the timing of lowering the converter fume hood is adjusted from immediately lowering the hood at the beginning of blowing to lowering the hood only when the CO concentration is close to the recovery condition; the timing of raising the hood is adjusted from starting to lower the hood only after blowing is completed to raising the hood immediately after the CO concentration reaches the dispersion condition. . By adjusting the timing of raising and lowering the fume hood, the vaporization steam can be increased by 2 to 5kg/t while ensuring that the heat recovery from the converter gas remains unchanged.
Through the analysis of actual production data of converter gas recovery and steam recovery, the corresponding relationship between converter gas recovery heat and vaporization steam recovery amount and the heat distribution rule were found. Reasonable adjustments to the timing of raising and lowering the hood based on objective laws can increase energy recovery.