Over the last decades, there has been considerable attention in industrialized countries given to the development of technologies that help reduce the consumption of energy and raw materials in product manufacturing processes. And metallurgical briquettes are helping to solve one of these problems.
Significant investments are also allocated for the development of production methods and equipment with the minimum adverse effect on the external environment. The problem of metallurgical waste recycling is one such problem.
The situation is especially acute in post-Soviet countries. Heavy industry enterprises in those countries have produced such large amounts of recyclables for many decades of their operation that the storage areas required for them amount to hundreds of thousands of hectares. For example, metallurgical waste covers more than 160,000 hectares in Ukraine.
Pelletizing methods for metallurgical recyclables
Waste recycling not only helps to get rid of prodigious amounts of waste, but to increase the economic benefits of production as well. The most valuable recyclable materials in the steel industry are considered to be the following:
flue dust, mill scale;
steel-melting, agglomeration and blast-furnace, coal sludge;
The small particle size of these materials is a difficulty in recycling such waste. That is why such raw materials are pelleted before reprocessing. Traditional methods of pelletizing are formation of pellets and sintering.
Insufficient efficiency is one of the disadvantages of the latter method. The pellet production requires strict compliance with the waste granulometric composition and moisture conditions, which makes it difficult to perform high-quality processing of recyclables.
Metallurgical briquettes reduce costs by up to 30 % in cast-iron production
Briquetting technology types
Interest in metallurgical scrap briquetting technology has arisen due to such obstacles in the traditional methods of pelletizing metallurgical waste. This method has been actively used by leading enterprises over the past few years. Briquettes made of metallurgical waste are produced by thermal (hot) and cold (unfired) methods.
Hot briquetting of metallurgical waste
Hot briquetting has been used since the 1960s. Briquettes produced in this way have high strength in cold and hot states, excellent moisture resistance and reducibility. This method consists of the following production steps:
Partial recovery of iron ore waste. The operation is performed using multiple-hearth, tube furnaces or fluidized bed reactors at a temperature of 500 to 1000°C.
Plasticizations of ore particles. The process takes place under intense heat.
Pressing of grains softened due to thermal effects. Particles are welded together under pressure.
Hot briquetting has not become widespread due to the additional costs of preliminary scrap heat treatment, as well as the unsatisfactory operation of presses when interacting with hot raw materials.
Cold briquetting of metallurgical recyclables
The essence of this method is to press the waste with or without the use of binders of mineral, organic components. This briquetting option makes it possible to pelletize homogeneous and heterogeneous scrap of different moisture and particle size.
Advantages of cold briquetting:
engineering process simplicity;
no need for technically sophisticated equipment;
environmental friendliness, low energy costs;
the ability to quickly arrange treatment facilities at waste generation sites.
The disadvantages of this method include a higher abrasion index compared to pellets and sinter, and less tolerance for thermal influence. Such disadvantages can be eliminated by optimizing the briquette composition, and correcting melting conditions in oxygen converters, as well as in electric- arc, low-shaft or blast furnaces.
Fields of application of metallurgical scrap briquettes
Currently, many large foreign and domestic companies produce equipment for cold briquetting of metallurgical waste. This is due to the widespread use of material pelletized in this way. Metallurgical scrap waste briquettes are used as:
recovery and fuel components in ferro-alloy, blast-furnace, steel industries;
additions regulating the slag practice of steel remelting units;
iron-containing inclusions, coolants in steel and blast furnace production, metallic charge substitutes;
heat-insulating compositions used in steel casting;
flushing additives for blast-furnace burdens;
deoxidizing, alloying components in the steel industry.
The available experience of melting briquettes includes many positive production examples. Because of this, briquetting is considered a highly efficient and reliable method of metallurgical waste pelletizing.
Metallurgical briquettes reduce the slag formation
Regulations covering production of briquettes from metallurgical scrap waste
Currently, one of the main problems of the processing waste briquetting sector is the lack of clear finished product requirements. Industrial enterprises use individual classifications developed for their own needs.
So far, the most optimal system is the division of briquettes according to their purpose (suggested by I. F. Kurunov):
Class I — self-reducing products with carbon and iron oxides in their composition;
Class II — carbon-free briquettes with fluxing components and iron oxides;
Class III — special purpose products (e.g., being used as a flushing, alloying component).
At the moment, there is work in progress to create clear regulations for the briquetting industry. Properties of raw materials, manufacturing conditions and models of the equipment used are taken into account. Such an approach will help to improve the briquette production process, to develop a comprehensive production approach and create analytical calculations to assess the quality of products being produced.