why make metallurgical briquette by cold briquetting process
With the development of the global economy, the gradual depletion of various mineral resources, besides, it also caused a variety of serious environmental problems, these have become factors that constrain the development of the global economy.
Countries all over the world are now doing a lot of work in environmental comprehensive management and developing circular economy. Now the global mainstream is the development and application of energy saving and emission reduction technologies.
With the development of global industry, there are fewer and fewer high grade ore in the world. As a processing method of mineral powder, the processing of mineral powder used in the metallurgical industry generally uses sintering or briquetting.
Like the fly ash, it contains many useful ingredients that can be used in smelting, an average of about 25%, but when it is directly used in the furnace for smelting, it will easily lead to energy loss and even smelting safety accidents, therefore, briquetting process is particularly important.
The cold briquetting is a way in which all the materials required in the production of the metallurgical industry are uniformly mixed, then subjected to a roller briquetting press for the cold briquetting work, and dried at a low temperature to get the finished briquette.
The original wet briquette needs to take the process of screening and transporting to the drying house, a certain drop strength is required to ensure that there is no breakage during transportation and little deformation.
The briquette dried by the dryer has to be transported many times and finally dropped into the furnace. Sufficient drop strength is required to ensure that there is no breakage and few deformations during transportation.
Briquette must have a certain compressive strength to withstand the various stresses of the briquette during the drying process, such as the upper layer pressure of the drying, the stacking pressure of the storage silo, etc.
The traditional smelting process is to smelt the lump raw material and the lump coke into the electric furnace at the same time. These lumps will be pulverized when heated, while 20% to 30% of the useful components are collected by the dust collection system.
But cold briquetting combines the mineral powder and coke (coal) together as briquette for smelting and reduction. The mineral powder and reducing agent are in surface contact, with a large contact area. It makes the carbon-containing briquettes have the characteristics of fast reaction and high melting efficiency.
For example, use 20% carbonaceous briquettes in the blast furnace charge (briquette with 5% of coal), the blast furnace smelting coefficient is increased from 1,485 t/m3d to 1,831 t/m3d, the furnace coke ratio was reduced from 789 kg/t to 711kg/t. The same effect is obtained when the ferromanganese alloy is smelted in an electric furnace.
Whether in steel plants or ferroalloy plants, the use of secondary metallurgical resources of fine ore and solids has become an important task in the efficient use of mineral resources and environmental protection.
influence of size and shape on the strength of briquettes - sciencedirect
Char fines obtained from low temperature carbonization of a non-caking coal were subjected to surface dressing with addition of water and briquetted using 2 wt.% of starch-based compound binder on the char fines to make cylindrical and ovoid or pillow-shaped briquettes in a hydraulic and a roll press. The compression strength of the cylindrical briquettes was determined by placing them in different positions, in between the plates giving rise to surface, line and point contacts. It was observed that surface compression strength of cylindrical briquettes is generally about 10 times the strength in the other two positions. The strength of ovoid or pillow shaped briquettes did not depend on the dimensions or weight of the briquettes. The point compression strength of such briquettes was found to be about one-fifth the surface compression strength of the corresponding cylindrical briquettes of the same composition.
4 main factors that will influence the coal briquette quality
Coal fine briquetting system is a briquette system uses the coal fine briquette machine as the core equipement to turn the coal fine to briquette. It includes two types, cold coal briquette and hot coal briquette, and most of the systems are cold briquette systems.
Under certain pressure and proper moisture, the coal fine and binder particles slide into contact with each other, forming electrostatic attraction force, solid bridge bridging force, and liquid bridging particles coupling force and van der Waals force. These forces work together to bond the coal fine particles together to a coal briquette.
Coal fine briquetting conditions include briquette pressure, briquette moisture, binder type and ratio, mixing time and mixing way, material size and composition, curing way and coal briquette drying temperature, etc.
For binder free briquette, finer coal particles are generally used, while coarser particles are suitable for coal fine with higher ash. When there is a binder briquette, particles of different sizes will produce different specific surface areas, which will seriously affect the degree of bonding with the binder particles, which may lead to the loss of the binder in some areas of the briquette.
The higher the coalification degree of coal, the larger the micelle structure of coal, with the increase of the elasticity and hardness of coal, the plasticity is reduced, which will lead to different compressible spaces of coal particles of different coal ranks when briquetting.
Under the briquette pressure, the coal particles of the high rank coal are not easily broken, which we shall be appropriately increased the particle size, while for the low rank coal, the particle size should be appropriately reduced.
The best gradation of coal fine is mainly coarse-grained grade, followed by fine-grained grade, and the middle-grained grade is the smallest. When the coal fine particle size is too concentrated to the upper or lower limit, this will reduce the briquette strength. The composition of any single particle size will reduce the strength of the briquette, so the coal fine grading distribution should be based on different sizes matching.
With the binder free way, increasing of briquette pressure is beneficial to increase the strength of the briquette. For a binder way, when the binder is different, the maximum briquette pressure of the briquette is also different.
Increasing the briquette pressure will compress the coal fine to an extreme value, continue to increase the pressure, the coal fine endurance will exceed the limit and the crushing phenomenon. When the briquette pressure is greater than the limit of the coal fine particles, there will be broken coal splitting phenomena and rebound phenomenon, it will destroy the integrity of the coal particles and cause cracks in the briquette, thereby reducing the strength of the briquette.
The strength of the briquette which first mixes the binder with the coal fine and adds moisture is much greater than the briquette strength of the binder after the first moisture is added. This is because a water film is formed on the surface of the coal particles after preferential moisture distribution, which prevents the binder particles and the coal fine particles from coming into contact with each other.
As the briquette moisture increases, the briquette strength increases first and then decreases. This is because the moisture can bring tiny particles into the infiltrated pores, reduce the porosity and make the coal particles dense and compact, while the excessive water film on the surface of the particles will cause the coal fine to swell and loosen.
For the inorganic binders, the moisture hydration reaction with the combination of the moisturization bonds the pulverized coal to each other. If the moisture is too low, the hydration reaction time will be slowed down and the briquette solidification time will be prolonged.
For organic binders, the moisture acts to lubricate the movement of its molecular groups, promoting the contact of molecular groups with the surface of the coal fine. If the moisture is too high, it will hinder the action of the molecular group, and the excess moisture will overflow during the pressing process and take away some of the binders.
For hydrophilic binders, an appropriate amount of moisturizer not only promotes the movement of coal particles, but also facilitates bonding to each other, but too much moisture will result in poor bonding effect, and suitable moisture is generally between 10% to 15%.
Due to the different binder components and properties, the binder bonding process is different, mainly chemical bonding, cohesive bonding, hydration bonding, adhesion bonding and polycondensation bonding.
Inorganic binder can significantly increase the strength of briquette, but it will increase the briquette ash and the cohesiveness is not high. The organic binder will not increase the briquette ash but the strength sensitivity is high and with poor waterproof performance. The composite binder can make up for the deficiency and shortcomings of the single binder to make the performance of the briquette optimal.
There are two ways in which the same kind of binder affects the strength of briquette: a concentration with a certain quality and a mass with a certain concentration. The optimum concentration of binder has the highest amount of briquette strength, and the influence of different concentrations of binder on briquette strength is also different.
The mixing uniformity is positively correlated with the stirring time. When the stirring time is more than 35 min, the mixing uniformity is the highest and the briquette strength stability is the best.
The influence of briquette additive components on briquette strength varies. For example quick-setting additive will enhance the compressive strength; Phosphate and Fe2O3 hinder the increase in compressive strength.
The hydrothermally treated coal fine, moisture and volatiles were significantly reduced, but the saturated alkanes increased, and the higher the hydrothermal treatment temperature, the greater the compressive strength of the briquette.
The group distribution ratio and production process of cold coal briquette are important means to improve the cold compressive strength of coal briquettes and the adsorption performance of stable coal.
Fully understand the composition, specific gravity and production process of briquette on the strength of cold coal briquette, and on this basis, optimize the production process of the outstanding simulation test briquette.
It is of great significance to make a comparative simulation of similar materials and process research with high physical and mechanical properties and adsorption properties of raw coal and to carry out large-scale outburst simulation experiments using large-size briquette in the future.
physical testing of fuel briquettes - sciencedirect
Four physical properties have been identified as being of greatest value when developing or evaluating fuel briquette formulations or processes. They are resistances to crushing, impact, abrasion and water penetration. Arbitrary tests for these properties have evolved in this laboratory during a decade of investigations of binders and formulations for briquetting coal fines and the like. The simple test methods are described and some typical results are given.
Tests of several types of commercial and pilot process fuel briquettes have been used to set realistic target values for these four physical properties. In the process development stages, it is suggested that the tests should relate to the briquette material, rather than the briquette as an entity, and that this can be achieved by transforming the raw data into various indices. These would allow intra-laboratory or inter-laboratory comparisons of briquette formulations. This approach is illustrated by presenting results for compressive strength, impact resistance and abrasion resistance. The same could apply to water resistance and some suggestions are discussed.
The needs of research and development and of production in respect of briquette testing are seen as different, but complementary. It is hoped that the paper will stimulate researchers and producers alike to work towards the adoption of codes of standard practice in briquette testing.