A New  Ferrochrome Granulation Process

Ferrochrome is one of the principal raw materials for stainless steel smelting. In order to meet the requirement of stainless steel production, the ferrochrome should be processed to a certain size.

Traditional Ferralloy Granulation Process

At present, ferroalloy plants mainly use three ways to break ferroalloy.

1. Ground mold or ingot mold casting, hand crushed after cooling.
2. Ground mold or ingot mold casting, crusher after cooling.
3. Molten ferrochrome was transfered from ladle to cast iron machine, and processed to a certain size.

There are different defects in all three processes, the artificial crushing produces much powder which causes pollution of the environment, and with high processing costs. The product granularity produced by the crusher is not uniform, and the product has many edges and corners. The cast iron machine pollutes the product, and with low yield.

Ferro Chrome Granulation

In order to improve the production efficiency, and ensure ferrochrome quality, a new granulation process of ferrochrome was applied to the production. 

Granulation is the process of forming grains or granules from a powdery or solid substance, producing a granular material. (Wikipedia) The process appeared in the 1950s. The initial granulation equipment used for the production of pig iron is similar to the furnace slag granulation process. A later developed process is performed by impinging molten metal against a stationary or rotating disc for alloy granulation.

GRANSHOT granulation system is a set of high-efficiency granulation equipment with the functions such as solidification, cooling, drying, separation, and storage. It only takes 3 minutes from the molten metal to the finished product.

The Granulation Equipment of Ferrochrome

Granulating systems consist of a ladle, chute, rotary device, ejector, toaster, etc.

The water system consists of cold water pump, cold water pool, hot water pump, hot water pool, waterjet pump, etc.

The drying system consists of a dewatering screen, vibrating feeder, drying kiln, etc.

The storage system consists of a large inclination belt, silo, vibrating feeder, etc.

The packing system consists of a large inclination belt, buffer tank, and packer.

Ferrochrome Granulation Process

After slag picking in the ladle, the molten ferrochrome is poured into the chute and into the tundish.  Through the installation at the bottom of the tundish nozzle, divided into small iron flow out. The molten ferrochrome gets into the water,  solidifies instantly, and sinks to the bottom of the cooling tank. The solid ferrochrome is put into the dewatering screen, and then through the drying kiln drying, finally into the silo and packaging.

Production Practice of Ferrochrome Granulation

The ferrochrome granulation is affected by temperature and silicon content, the purity of ferrochrome granulated by this method is higher than the traditional method.

Ferrochrome Granulation Temperature

The degree of superheat is one of the key factors of ferrochrome granulation.

The temperature of the molten ferrochrome is 1570-1600℃. The granulation production is difficult because the temperature is not high enough.

The experimental results show that ferrochrome can be successfully granulated at a temperature of 1600℃. The ferrochrome can’t be granulated if the temperature is below 1570℃.

The success of granulation needs to ensure the stability of the tapping temperature, shorten the slag removal time and transportation time, increase the temperature of the chute.

Ferrochrome Composition

The silicon content is one of the key factors of ferrochrome granulation.

1. The higher the silicon content in the molten ferrochrome, the lower the melting point of the ferrochrome and the better the fluidity of the molten ferrochrome.
2. The higher the silicon content in the molten ferrochrome, the lower the toughness of the ferrochrome particles and the particle size less than 2mm increases.

Si/%	Temperature/℃	＜2mm	2-5mm	＞5mm
4.75	1578	10	45	45
3.17	1577	5	20	75
3.20	1573	3	55	43
3.60	1599	2	34	64
2.90	1615	2	45	53
2.07	1614	2	34	64
2.28	1620	6	31	63

Comparison Between GRANSHOT and Other Processes

The cleanliness and composition uniformity of the granulated products are obviously better than those of other processes. The particle size of the granulated products is small, which affects the further use and promotion of the process.

Purity of the Ferrochrome Granulation Products

The cleanliness and composition uniformity of the granulated products are obviously better than those of other processes. At present, the ferrochrome plant applies ground mold or ingot mold casting. Due to the thick ingot, there is certain segregation in the ferrochrome alloy. Meanwhile, both manual and machine crushing contaminate the product slightly.

Cr	Si	Granulated Cr	Granulated Si	Increase: Cr
49.28	3.65	49.51	3.82	0.23
49.13	3.71	49.51	3.82	0.38
49.29	3.54	49.65	3.41	0.36
49.69	2.64	49.86	2.51	0.17
50.73	1.93	50.01	2.16	-0.72
51.04	1.97	50.86	1.95	-0.18

The table shows that During the granulation process, the molten ferrochrome is not polluted and the composition is uniform.

Granularity of the Ferrochrome Granulation Products

The granularity of the product is one of the key factors of the product application. The main particle size is concentrated in 2-10mm, which is far away from the steelmaking requirement. We need to do that below.

1. Further improvement of the granulation process to increase the product particle size.

2. Study with the users (stainless steel mills) to find the way to use the product, such as improve the feeders, change the smelting process, etc.

Conclusion:

The granulation process takes a shorter time to treat the high carbon ferrochrome. And Reduce the production cost.

The purity and composition uniformity of the granulated products are obviously better than those of other products.

To further improve the process and solve the problem of particle size, the prospect of the ferrochrome granulation process is better.