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Description of RHF process in China



Source: internal company

1. Background Technical Description

China's mainstream iron making process is a long process, using blast furnace - converter process. The use of blast furnace iron making occupies an absolute dominant position in China.


Non-blast furnace iron making technology has grown significantly in recent years, driven by increasing environmental requirements, the need for high-quality steel materials, and especially the Chinese government's commitment to "carbon neutrality" to the world.


Non-blast furnace iron-making technology is dominated by the gas-based shaft furnace process, because the gas-based shaft furnace can use hydrogen reduction technology, which greatly reduces carbon emissions, In addition to the gas - based shaft furnace process, rotary kiln, tunnel kiln, RHF and other technologies are also used.


Tunnel kiln is mainly used for small-scale iron making, because of its high metallization rate, product purity is higher advantages to prepare powder metallurgy materials, The scale of its single production line is generally below 50,000 tons per year.


Rotary kiln is mainly used to process materials such as ferronickel, red mud (about 50% iron), etc. It has been used in mature applications in this type of material, and the "two-step method" is also used (the first step is to prepare oxidized pellets, and the second The first step is the production of DRI) The use of fine iron powder to produce DRI, but due to high operating costs and high failure rate (especially rotary kiln ring formation) and other reasons, the production was stopped.


RHF process is widely used to deal with materials containing zinc and iron, Such as iron and steel enterprises of all kinds of dry dust removal ash, wet dust removal ash and mill scale and so on. Its main product is DRI, used in converter slag coolant, at the same time steelmaking, by-product is zinc oxide and so on. RHF is also useful to deal with the case of iron powder.


In China, RHF can only be used as a supplement to the mainstream ironmaking process, which is inseparable from the mainstream iron and steel process in China.


2.  Summary of RHF process characteristics

2.1 A wide range of raw materials and fuels can be used. Natural gas, coke oven gas can also be used for raw coal gas generation;


2.2 Fine ore does not require high-temperature agglomeration and coke, eliminating the need for coking and sintering procedures, and the process flow is short;


2.3 The requirements for the strength of the charge are not high;

2.4 The carbon-containing pellets can realize self-reduction at high temperature, with fast reduction speed and low energy consumption;


2.5 Short process flow and smelting cycle, high production efficiency;


2.6 RHF system construction investment is low, the process system is compact, the equipment structure is simple, the technology and equipment are relatively mature, the construction difficulty coefficient is low, and the civil engineering investment is low;


2.7 The equipment runs stably, all equipment is of mature technology, the process equipment is widely used, the degree of automation is high, the reliability is high, and it is easy to operate and maintain;


2.8 Low environmental pressure, good RHF sealing, negative pressure operation, CO can be completely consumed in the furnace without escaping, the dust from the flue gas dust can be returned to the raw material system for use, and the harmful exhaust gas dust emission is controllable, which is a kind of low energy consumption , Low-emission and low-cost green metallurgical technology.


3. Problems in the RHF system

3.1 Fuel selection and supply problems, practice shows that the calorific value of gas should not be less than 1600kcal, when lower than the calorific value must be used to support the combustion of high temperature hot air, gas needs a stable supply. That demand should have no problem in Iran.


3.2 Since all the reducing agent is added to the pellets, the residual ash content of the reducing agent and the content of harmful elements sulfur, zinc, etc. will directly affect the quality and use direction of DRI. Therefore, there are certain requirements for the ash content of the reducing agent. When the agent cannot meet the requirements, the application direction of DRI products will change. For example, when the sulfur content is too high, DRI needs to be melted into molten iron for desulfurization before it is suitable for high-quality smelting.


3.3 Due to the use of open flame heating, reduced iron may be reoxidized, the metallization rate of the product is not high, which also depends on the control of the atmosphere in the furnace and the quality of the raw material, the metallization rate of the product is inversely related to the output, and is positively related to the energy consumption. In addition, the flame temperature of radiation heat transfer in the furnace ≤1350℃ will not occur bonding.

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