Calcium carbide slag calcination furnace

Calcium carbide slag calcination furnace：Calcium carbide slag is a precipitate (industrial waste residue) produced by the hydrolysis of calcium carbide (CaC2) during the production of industrial products such as acetylene gas, polyvinyl chloride, and polyvinyl alcohol. Its main component is Ca (OH) 2.

CaC2 (calcium carbide)+2H2O C2H2 ↑ (acetylene gas)+Ca (OH) 2 ↓ (carbide slag)

About 1.15 tons of carbide slag are produced per ton of carbide hydrolysis. The stacking of carbide slag not only occupies a large amount of land, but also pollutes the water resources and alkalized land near the stacking site due to the easy loss and diffusion of carbide slag; Long term storage may also cause dust accumulation due to air drying, polluting the surrounding environment. Calcium carbide slag is one of the difficult industrial wastes to dispose of.

The chemical composition of carbide slag is as follows:

The average particle size of carbide slag is 1.89 μ m; Weight average particle size: 9.19 μ m; Area average particle size: 5.75 μ m; Median particle size: 8.29 μ m; Specific surface area:947.32m2/Kg. The higher the specific surface area of carbide slag, the higher its water absorption and the greater the difficulty of drying.
Through the analysis of the physical and chemical properties of carbide slag, it can be seen that the CaO content in carbide slag is very high, making it a high-quality calcium raw material for manufacturing cement clinker. Its particle size is very fine, and it can meet the requirements of cement clinker production almost without grinding. The main problem that needs to be solved is to effectively dehydrate and accurately mix the calcium carbide slag slurry.

1. Pre drying of carbide slag

After mechanical dehydration, the moisture content of carbide slag slurry generally fluctuates within the range of 28-35%, which poses difficulties for the transportation, storage, and accurate batching of carbide slag. Therefore, it is necessary to pre dry the carbide slag; Due to the fact that carbide slag is a lightweight waste residue with high moisture content, drying treatment is very difficult, and the following technical challenges need to be solved:

(1) Resolve feeding and blockage issues. The calcium carbide slag after pressure filtration is in a "toothpaste" state, which cannot be stored or fed for measurement during transportation, and is not easy to be sent into the dryer. After falling into the dryer, it is prone to material stacking and blockage.

(2) When drying carbide slag, it is necessary to overcome the disadvantages of low evaporation rate and high moisture content.

(3) After the drying of carbide slag, the dust concentration in the exhaust gas is high, and the dust collection equipment is prone to sticking and corrosion.

Selection of drying machine:

To avoid the problems encountered by general drying machines during the above drying process, we have chosen the Stedt Cyclone Dynamic Drying Machine, which works on the following principle:

The cyclone dynamic dryer first uses a shaftless spiral feeder to solve the problem of feeding blockage. Hot air from the heat source enters the main body of the dryer at high speed from the bottom of the dryer. The carbide slag is dispersed at the bottom, and under the strong rotating wind field, the carbide slag fed into the dryer by the spiral feeding is fully contacted with hot air, heated, dried, and collided and rubbed with each other under strong centrifugal action, resulting in particle size reduction. The high-temperature zone from the feed inlet to the drying bottom is also known as the 'fluidization section'. Most of the moisture in the material evaporates in the fluidization section. The dried particles are carried into the upper drying section by hot air and continue to dry in the cyclone field.
There is a circular baffle on the upper part of the dryer - the classification section (referred to as the 'classification section' above the classifier). For materials with larger particles or higher water content, they are thrown towards the dryer cylinder wall due to centrifugal force, and are blocked back to the drying section by the classifier for re drying. Only those materials that have reached the drying degree and smaller particle size are carried out of the circular hole of the classifier with hot air and enter the cyclone separation. This drying method is not limited by high moisture content. The dried carbide slag is continuously discharged from the star shaped unloader and bagged. The humid and hot air is discharged through bag dust removal and induced draft fan, and the bag dust collector uses corrosion-resistant materials to solve the corrosion problem.

There are several traditional calcination modes, which I will briefly describe here:

The application of rotary kilns in powder drying and calcination is quite extensive, with different designs for different materials. The advantages are mature technology and low cost. The disadvantage is that local high stress can cause fatigue pitting, pitting peeling, and crushing of pins, which are extremely difficult and expensive to repair. For calcined carbide slag, the decomposition rate is low and the operating cost is high.

It is a rapid air flow calcination equipment that integrates grinding, drying, and calcination. It is a German CLAUDIS calcination equipment
Developed by PETERS company, abbreviated as Peters mill. It is a circular ball mill, with the bottom of the mill as the main transmission device, which drives the lower grinding disc to rotate. There are multiple grinding discs with a diameter of 600~800mmThe hollow ball has a non rotating upper grinding disc above it. Gypsum is fed into the center of the grinding body from the upper feeding pipe, with a maximum feed particle size of up to60 millimetersUnder the action of centrifugal force, the material is pushed outward and crushed and ground between the lower part of the sphere and the grinding ring.

Calcium carbide slag calcination furnaceThe characteristics are: small equipment size, high production efficiency, low energy consumption, stable product quality, suitable for large-scale continuous production lines.

The advantage is mature technology, but the disadvantage is that the price is too high (for calcined carbide slag), and there is no need for a rotating grinding disc, resulting in wasted power consumption and low cost-effectiveness.

Introduction to the Drying and Calcination Process of Calcium Carbide (Calcium Hydroxide, Calcium Carbonate Mixture)

The cyclone dynamic calcination furnace uses coal gas (oil, natural gas) as the heating fuel, and selects automatic burners (combustion machines) for full atomization combustion, providing direct heating to reach the calcination temperature inside the furnace. The metering feeder sends the dry powder of calcium carbide (a mixture of calcium hydroxide and calcium carbonate) into the furnace, where it is mixed with the high-temperature gas to achieve rapid mass and heat transfer, and rapidly rotates and rises, completing calcination in 8-10 seconds. After the gas-solid mixture enters the combined cyclone, gas-solid separation occurs. The calcined product (calcium oxide) is then packaged in the silo. The calcined tail gas serves as a heat source and enters the dryer to dry the wet calcium carbide material (calcium hydroxide, calcium carbonate mixture) into powder. The dried tail gas enters the first and second stage cyclones together and undergoes gas-solid separation in the pulse bag filter. The purified tail gas is drawn out by a high-pressure induced draft fan, and the calcium carbide dry powder (calcium hydroxide, calcium carbonate mixture) enters the calcination furnace for calcination into calcium oxide finished products.

Process characteristics:

Short calcination time, continuous operation, uniform heating of materials, controllable temperature, good sealing, negative pressure operation, high product recovery rate, decomposition *, uniform color, no dust leakage, no pollution, reducing labor intensity. (The product quality is stable, the environment meets the standards, and the energy utilization is fully utilized.)

The cyclone dynamic calcination furnace technology has achieved successful experience in industrial production of cryolite, boron magnesium ore, molybdenum concentrate, kaolin, zinc oxide, active zinc oxide, nano zinc oxide, high-purity zinc oxide, magnesium oxide, nickel oxide, and cobalt oxide powder, making the technology more mature. Due to different physical properties and processes, selecting a properly configured process system is necessary to ensure the normal operation of the system and produce qualified products.