Calculation of scrap ratio of converter steelmaking: How much scrap can be added in theory?

In the process of iron and steel smelting,scrap steel,as an important raw material,plays an important role in converter steelmaking.The use of scrap steel not only contributes to the recycling of resources,but also affects the smelting effect and economic benefit of the furnace.Converter scrap ratio,that is,the proportion of scrap steel in the smelting process,is one of the important factors affecting the smelting effect.So,in theory,how much scrap steel can be added to converter steelmaking?This requires detailed calculation and practical experience to answer.

1、Definition and calculation method of scrap ratio of converter

Converter scrap ratio refers to the proportion of scrap instead of pig iron in the converter smelting process.The calculation formula is:

Converter scrap ratio=(scrap weight÷(pig iron weight+scrap weight))×100%

Among them,the weight of scrap refers to the weight of scrap added in the smelting process,and the weight of pig iron refers to the weight of pig iron added in the smelting process.

For example,if 100 tons of scrap steel and 200 tons of pig iron are added to a converter smelting process,the converter scrap ratio is:

(100÷(200+100))×100%=33.33%

This proportion directly reflects the use of scrap steel in the smelting process,and is also one of the important parameters to evaluate the smelting effect.

2、Theoretical calculation of the amount of scrap added

In the process of converter steel making,the amount of scrap added is affected by many factors,including the composition of hot metal,smelting temperature,oxidation reaction heat,etc.Through theoretical calculation of heat balance,the amount of scrap added can be determined more accurately.

The first thing to consider is the heat released by the elemental oxidation reaction.Under the condition of 1300℃,the heat absorbed by the molten pool when different elements oxidize 1Kg is as follows:

Carbon oxidation to CO2:32751KJ/Kg

Carbon oxidation to CO:11231KJ/Kg

Iron oxidation produces FPO:4040KJ/Kg

Manganese oxidation to M No:6327KJ/Kg

Silica oxidation to SiO2:19937KJ/Kg

Phosphorus oxidation to P2O5:25101KJ/Kg

According to the composition of hot metal on site and the steel made,the total heat released by oxidation reaction can be calculated.Assume that the composition of molten iron in the furnace is as follows:carbon 3.8%,silicon 0.68%,manganese 0.54%,phosphorus 0.120%,sulfur 0.031%,the end composition:carbon 0.06%,manganese 0.1%,phosphorus 0.030%,sulfur 0.030%,and the temperature rises from 1300℃to 1640℃.

To calculate the total heat released by the oxidation reaction and consider the amount of elemental oxidation,it can be obtained:

C→CO:0.374Kg,release heat 12249KJ

C→CO2:3.37Kg,heat release 37848KJ

Si→SiO2:0.68Kg,release heat 13557KJ

Mn→M No:0.44Kg,heat release 2784KJ

Fe→FPO:1.4Kg,heat release 5656KJ

P→4CaO·P2O5:0.09Kg,the release of heat 2259KJ

The total heat is 74353KJ,considering that the furnace gas and splash loss is calculated at 10%,the actual heat absorbed by the molten pool is 66918KJ.

Next,the heat required to heat the molten pool from 1300℃to 1640℃is calculated.Considering the specific heat and weight of molten steel,molten slag and furnace gas,the required heat can be calculated to be 33667KJ.

Therefore,the excess heat is 66918KJ-33667KJ=33251KJ.According to the melting heat and latent heat of scrap,the amount of scrap added can be calculated.Assuming that the specific heat of scrap is 0.7,the melting point of steel is 1500℃,the latent heat of steel is 272KJ/Kg,the specific heat of liquid steel is 0.837,and the temperature rise interval is 1500℃to 1640℃,then the amount of scrap added is:

33251÷(0.7×(1500-25)+272+0.837×(1640-1500))=23.4Kg

According to the calculation of loading 50 tons of hot metal on site,the loading amount of scrap steel is 11.7 tons.

3、Factors affecting the amount of scrap added

Although theoretical calculation gives the amount of scrap added,in practice,the amount of scrap added is also affected by many factors.

Hot metal composition:the content of each element in hot metal directly affects the heat released by the oxidation reaction.For example,hot metal with a high carbon content can release more heat,allowing more scrap to be added.

Smelting temperature:The higher the smelting temperature,the more heat absorbed by the molten pool,and the amount of scrap added also increases accordingly.But too high a temperature will also increase energy consumption and equipment loss.

Process parameters:smelting process parameters such as blowing strength and blowing time will also affect the amount of scrap added.Reasonable process parameters can ensure full melting of scrap steel and effective use of heat.

Scrap type and quality:Different types of scrap have different melting points and melting heat,and its quality and weight will also affect the amount of scrap added.High-quality scrap is easier to melt and releases more heat.

Equipment conditions:The capacity of the converter,the parameters of the oxygen gun and other equipment conditions will also affect the amount of scrap added.For example,a high-capacity converter can hold more scrap steel,while a high-performance oxygen gun can make more efficient use of oxygen for blowing.

4、high scrap ratio smelting practice exploration

In order to improve the smelting effect and economic benefit,many iron and steel enterprises are exploring high scrap ratio smelting technology.Here are some practical lessons and measures:

Optimize the ratio of scrap steel:according to the type of steel smelted on site and the type of scrap steel,optimize the ratio of scrap steel to ensure that different types of scrap steel can make full use of its heat and chemical composition.

Improve the adding of scrap:The use of multi-point adding scrap process to improve the adding speed and uniformity of scrap,to ensure that scrap can fully melt and absorb heat.

Strengthen equipment management:Upgrade the converter,oxygen gun and other equipment,improve the performance and service life of the equipment,and ensure the stability and safety of the smelting process.

Control smelting parameters:reasonable control of blowing strength,blowing time and other process parameters to ensure that scrap can be fully melted and effectively use heat.

Recycling waste heat:Use the waste heat generated in the smelting process to preheat scrap or other energy-saving measures to improve energy efficiency.

5、Benefits and challenges of high scrap ratio smelting

The high scrap ratio smelting technology has brought about remarkable benefits,including reducing production cost,improving resource utilization and reducing environmental pollution.However,there are also some challenges,such as the instability of the type and quality of scrap steel,the problem of heat balance in the smelting process,and the limitations of equipment conditions.

In order to overcome these challenges,iron and steel enterprises need to continuously optimize the smelting process and equipment conditions,strengthen the management and recycling of scrap steel,and improve the stability and economy of the smelting process.At the same time,it is also necessary to strengthen technology research and development and innovation,and explore more efficient and environmentally friendly smelting technology to meet the development needs of the steel industry.

6、Conclusion

The scrap ratio of converter steel making is one of the important factors affecting the smelting effect and economic benefit.Through theoretical calculation and practical exploration,the amount of scrap added can be determined,and corresponding measures can be taken to improve the smelting effect and economic benefit.However,the high scrap ratio smelting technology is also facing some challenges,requiring steel enterprises to continuously optimize the process and equipment conditions,strengthen technology research and development and innovation,in order to meet the development needs of the steel industry.

In the future,with the continuous development of the steel industry and technological progress,high scrap ratio smelting technology will become one of the important means for steel enterprises to improve their competitiveness.Steel enterprises need to actively explore and apply this technology to promote the sustainable development of the steel industry.