What is foundry coke

News 2020-12-03

What is foundry coke

Concept and brief introduce

Foundry coke is a special coke used to melt iron in an iron furnace. It is a kind of metallurgical coke, named after molten iron is used for cast iron parts. Therefore, foundry coke should have the characteristics of large agglomeration, low reactivity, low porosity, adequate impact resistance and crushing strength, and low ash and sulfur ingredient. Foundry coke is the main fuel for iron melting in the furnace. Its function is to melt the charge and overheat the molten iron, and to support the column to maintain its good air permeability.

Industrial developed countries such as the United States and the United Kingdom began to produce foundry coke in the early 20th century.

In China, by the end of 1990, an equipment production capacity with an annual output of nearly one million tons of foundry coke had been formed, and progress was made in the research of batching technology, foundry coke quality, micro structure and the development of foundry coke.

Quality requirement

(1) The lumpiness is large and uniform. In order to ensure the good air permeability of the material column in the iron furnace, so that the wind can blow through the center, it is generally required that the coke lump degree is above 60mm.

The lumpiness of foundry coke is related to the inner diameter of the furnace. For the iron furnace with a production capacity of more than 10t/h, the lumpiness of the cast coke is required to be 1/10～1/12 of the inner diameter of the furnace; for small and medium-sized iron furnaces, coke lump is required The degree is 1/6 to 1/9 of its inner diameter.

• It has sufficient strength against impact and crushing. In addition to impact and wear during transportation in front of the furnace, foundry coke is mainly subjected to the impact of large iron blocks when entering the furnace and after entering the furnace. In order to maintain the uniformity of the coke in the furnace and the stability of the bottom coke, the  coke is required to have a certain drum strength and drop strength, which plays an important role in ensuring the temperature of the molten iron and improving the heat efficiency of the iron furnace.

(3) Low ash ingredient. As the ash ingredient of foundry coke increases, its fixed carbon and calorific value decrease, which will directly affect the temperature of the molten iron in the furnace. Generally, for every 1% reduction in coke ash content, the molten iron temperature will increase by about 10°C.

(4) Low sulfur ingredient. About 30-70%  sulfur content of foundry coke enters the molten iron, especially when the amount of steel scrap in the furnace increases, the molten iron increases sulfur more, which directly affects the quality of the castings. Smelting iron furnaces generally use acidic linings, which cannot desulfurize. Therefore, the sulfur  of coke is required to be less than 0.8%.

(5) Suitable and stable moisture. The evaporation of water requires the consumption of heat; however, if the water ingredient is too low, the coke will easily catch fire when it is put into the iron furnace. In order to prevent the top of the furnace from catching fire, the foundry coke must have a certain amount of moisture and remain stable. Fluctuations of moisture will make batch measurement inaccurate and affect the operation of the furnace. Generally, the moisture ingredient of coke into the furnace is controlled below 5%.

(6) Volatile ingredient should not be too high. High volatile ingredient will affect the strength of cast coke when used, and will also reduce the fixed carbon ingredient of coke. All countries have established quality standards for foundry coke. Lumpiness, ash ingredient, sulfur ingredient and mechanical strength indicators are the quality assessment indicators for foundry coke. If any of the above indicators fails to reach the specified value, it does not meet the qualified quality standards of that level. Drum strength and falling strength are combined indicators. When there is a contradiction between the two index values, M40 shall prevail. Moisture, volatile matter, apparent porosity and broken coke rate are not considered as the main quality acceptance indicators.

Ways to produce

Most of the domestic and foreign production of foundry coke uses chamber coke ovens for the production of metallurgical coke. In order to produce qualified foundry coke, the following four methods are generally adopted in production:

Add pitch and petroleum delayed coke to coal blending

The conventional analysis of the foundry coke produced in this way can reach the special grade index, but its strength after reaction is extremely poor, which reduces its price.

Select large coke from metallurgical coke as foundry coke

Large pieces of coke relatively have more cracks, and are first broken along the cracks under the action of mechanical force. Therefore, large pieces of coke are the coke with the worst stability. In the production of metallurgical coke, in order to increase the strength of coke, some domestic and foreign companies have adopted stabilization  facilities.

Mass production of foundry coke from chemical recovery coke oven

Some chemical recovery coke ovens can produce foundry coke by virtue of their resource advantages, but the temperature generally drops to 1100℃. This temperature condition is not conducive to protecting the furnace body, and the output is reduced by more than 30%, so this type of factory can only produce Limited foundry coke.

Using heat recovery coke oven to produce foundry coke

The earliest used for foundry coke production was the “Seventh Five-Year” furnace adopted by the Dongjiao Chemical Plant in the 1980s. This furnace type was the embryonic heat recovery coke oven type, while the Zhenjiang Coking Plant was the first to adopt chemical production in my country. One of the manufacturers that recycle coke ovens to produce foundry coke

Production status

In 1981, the State Planning Commission and the Ministry of Metallurgy requested the Anshan Thermal Energy Institute to cooperate with Zhenjiang Coking Plant to use the favorable conditions of the plant to produce petroleum coke and try to produce first-class cast coke as soon as possible. Through joint efforts, we successfully developed fat coal, 5% coking coal, 45% delayed coke, petroleum coke and pitch, and successfully developed the original 61-type and type coke oven by reducing the furnace temperature and extending the carbonization time. First-level foundry coke is produced. Later, through the “Sixth Five-Year Plan” scientific and technological research, after slightly adjusting the ratio of raw materials, it successfully trial-produced special-grade cast coke.

For more than ten years, my country’s foundry coke production technology has developed greatly in Zhenjiang, Shanxi and Ningxia, which produce foundry coke. They have a basic grasp of several main production processes, but the disadvantage is that the principle of low freight should be appropriately divided. Then supply rationally. At low prices, the annual production volume is still less than 300,000 tons, and most of them are produced by small coke ovens with narrow furnace holes and improved coke ovens.

Market scale

   Coke from all over the world is mainly used in the steel industry. From the general trend, the world’s steel production has been increasing in recent years, while the coke production has been declining. Global crude steel production has risen, and China’s coke orders have soared.