The Re-Use of Calcareous Mud in the Sintering Plant of Hadisolb: A Techno-Economic Study

The chemical analysis of the calcareous mud (C.M.) was the corner stone behind the idea of replacing the limestone (L.S.) used in the sintering of el-Bahareya iron ores in the Egyptian Iron and Steel Company (Hadisolb) by the calcareous mud produced as a waste from the sugar beet companies. The aim of this investigation is to examine the possibility of replacing the limestone used in the sintering plant in the Iron and Steel Company at Helwan by the C.M. of the sugar beet companies. Several experiments were performed in the pilot plant of the company. The pilot scale experiments covered replacement of the limestone in the sintering process by C.M. for ranges starting from zero% C.M., i.e. 100% L.S., and up to 100% C.M. and zero% L.S., at an increment of 10% each time. The chemical analysis and testing of the mechanical properties were performed to characterize each run of experiments. The results of the pilot scale experiments performed in the Egyptian Iron and Steel Company proved that 10% reduction in coke consumption in the sintering plant can be achieved as a result of the replacement of L.S. by C.M. Taking into consideration both the productivity of the sintering machine and the quality of the produced sinter, the annual return for the Egyptian Iron and Steel Company (Hadisolb) as a result of using C.M. in the sintering plant instead of Limestone was estimated to be about 100 million Egyptian pounds every year, in addition to the gains of the sugar beet companies as a result of getting rid of its waste material, i.e. the C.M.


Introduction
In Egypt nowadays, there are about eight sugar beet factories. Beside sugar they produce several DOI: 10.35840/2631-5076/9242 a waste material which is accumulated year after year; consequently, it has a negative impact on both the environment and the economy.
As a matter of fact, the amount of C.M. from the eight sugar beet factories is estimated to be about 800,000 tons/year, i.e. it represents 8-12 w/o of the processed beet [1].
It may be worth it to mention that in Europe the C.M. is reused in several aspects, such as: − As an additive to animal feed. − As a filling material in some industrial products (e.g. rubber, plastic, paper, …). − In the building industry. − In water treatment. However, in Egypt the C.M. is still unused by-product, in spite of the fact that the sugar beet factories offer to give it for no charge.
In this investigation, a scientific approach for reusing the C.M. is adopted. This approach is based on considering some important facts about the C.M., the complete chemical analysis of the C.M. is the most important of them. The chemical analysis for a representative sample of C.M. was performed using XRF -9800 ARL technique. The results of the chemical analysis are given in Table 1.
The chemical analysis given in Table 1 shows that the C.M. is composed mainly of CuCO 3 , MgCO 3 and a significant amount of organic matter -given as organic CO 2 -which varies between 8-15%, and its value obviously depends on the beet juice composition [2]. The presence of the organic matter in the C.M. should be considered by all means an added value to the C.M., and this ought to be taken into consideration when searching for its reuse.
Based on the chemical analysis of the C.M. given in Table 1. We can assume that the annual production of the eight sugar beet factories in Egypt, which is estimated to be about 800,000 tons, will contain about 80,000 tons of combustible organic matter (taking it as 10% content). Accordingly, it was suggested to reuse the C.M. in pyro-industrial applications, such as Portland cement production, or in the Iron & Steel making as a substitute for the limestone used in any of them.
It was found that about 5% in the charge of the calcining furnace will save about 1% of the consumed energy/ton of clinker. However, this amount of energy saving was not enough to make the reuse of C.M. in this respect feasible. The conclusion may be attributed to the fact that the cement companies in Egypt are using highly subsidized raw material.
In many cases, sintering is considered as an essential step in ore preparation for the blast furnace operation. Sintering may be defined as the agglomeration of fine particles into a strong porous mass. The process is carried out by heating the sintering charge at a temperature approaching its fusion. The sintering charge usually includes, beside the iron ores, the required amounts of L.S., coke and water to produce sinter of a specific composition and quality.
In this investigation, several pilot scale experiments were performed in which L.S. was replaced by C.M. to produce the self-fluxed sinter.

Material and Experiments
The Egyptian Iron & Steel company (Hadisolb) is the only company among all the other steel making companies which adopts blast furnace/sintering route. The blast furnaces in Hadisolb use selffluxed sinter in its burden. Self-fluxed sinter, as was mentioned before, requires an iron ore, a fluxing material such as L.S. or C.M., of course in addition to coke and water.

Material
The iron ore: The iron ore deposits at El-Gedida are the only ores used now in Hadisolb. These ores are located in three different localities. At El-Gedida mines, ores from the three localities are extracted and blended according to predetermined program to meet the previously agreed upon composition, which is Fe > 51%, Cl < 0.6%, MnO < 2.4%, SiO 2 < 8%, CaO > 0.5%, and Al 2 O 3 < 2%. Calcareous Mud (C.M.): The idea of replacing L.S. by C.M. in the sintering process is based on the chemical composition of both materials given in Table 2 [3].

Experimental work
Sintering of different mixtures under investigation is conducted in a pilot scale unit of 20 kg capacity, as shown in Figure 1.
The following steps should be carefully fulfilled prior to the sintering process: 1. Separate weighing of the different constituents of the charge.

Dry blending the charge constituents.
3. Spray water carefully and slowly into the charge till the required moistening is reached.
The well-mixed charge then should be transferred into the sintering crucible, after putting enough coarse sinter return at its bottom on the perforated plate.
A thin layer of fine coke should be added on the surface of the charge to initiate the combustion process.

Limestone (L.S.):
The Limestone used as a flux in the pilot-scale experiments is that brought from Bani-Khalid quarries nearby Samalut. The quarry is owned by Hadisolb, and is one of the highest quality limestone in Egypt.
The Limestone was crushed and sieved up to -3 mm size.    After the sintering is completed, suction of air was continued for a few minutes to cool the sinter cake. The cake was then punched out of the crucible, weighed, analyzed, and tested for strength (the drum test (DT) was the only test performed in all experiments). One of the experimental sheets is given in Table 3 [4].

Results and Discussion
In order to investigate the effect of replacement of L.S. by C.M. in the sintering process, several sintering experiments were performed, using different percentages of replacements, as mentioned previously.
Representative samples were taken from each three similar experiments (replacement percent), for chemical analysis, for each three experiments of similar replacement ratio. Table 2 gives the average chemical analysis calculated for each degree of replacement (C.M.%).
From Table 4, it is noticed that the CuO% in the sinter decreases and the MgO% increases as the C.M. percent increases, which is in favor for the blast furnace operation.  In Table 5, the savings in the coke consumption in the sintering process as the result of replacing L.S. by C.M. is given. From Table 5, it is clear that the saving in coke increases as the C.M.% in the sintering charge increases. It can be concluded from the Table 5, that the total saving of coke in