Definition and Production Process
Semi-coke is an intermediate product created by heating bituminous coal in the absence of oxygen. It is made at temperatures between 450°C and 700°C. This process results in a product with higher fixed carbon content and lower volatile matter compared to the original coal.
Production Process
The semi-coke production involves these main steps:
- Heating the coal without oxygen to prevent it from burning.
- Removing volatile components from the coal.
- Stopping the process before full carbonization to keep some volatile content.
This process produces a product that differs from coke. Coke is made at much higher temperatures (1000°C to 1200°C) and over a much longer period (several days).
Key Differences from Coke
| Property | Semi-Coke | Coke |
|---|---|---|
| Volatile Matter | 10-20% | Less than 1% |
| Fixed Carbon Content | 70-85% | >90% |
| Production Temperature | 450-700°C | 1000-1200°C |
| Production Time | Hours | Days |
| Reactivity | Higher porosity, more reactive | Less reactive |
Semi-Coke Properties
| Property | Value |
|---|---|
| Bulk density | 0.7-0.9 g/cm³ |
| Porosity | 30-50% |
| Calorific value | 25-30 MJ/kg |
Semi-coke’s intermediate properties make it suitable for various uses. It can be used as a reducing agent in ferroalloy production, fuel for industrial furnaces, and raw material for activated carbon.UPERORE. It has more applications than fully carbonized coke.
Characteristics and Composition
Semi-coke differs from coke in several ways, mainly in terms of carbon content, volatile matter, and other chemical properties. Here are the key differences between semi-coke and coke:
| Property | Semi-Coke | Coke |
|---|---|---|
| Carbon Content | 60-85% | 85-95% |
| Volatile Matter | 10-20% | Less than 1% |
| Fixed Carbon | 70-80% | Over 90% |
| Hydrogen Content | 3-5% | Less than 1% |
| Ash Content | 5-15% | 10-20% |
| Sulfur Content | 0.5-1% | 0.5-2% |
| Oxygen Content | 5-15% | Less than 2% |
| Calorific Value | 25-30 MJ/kg | 29-35 MJ/kg |
| Structure | Porous | Less porous |
| Mechanical Strength | Lower | Higher |
Typical Elemental Composition
| Element | Semi-coke | Coke | |———–|————|——–| | Carbon | 60-85% | 85-95% | | Hydrogen | 3-5% | <1% | | Oxygen | 5-15% | <2% | | Nitrogen | 1-2% | 1-2% | | Sulfur | 0.5-1% | 0.5-2% | | Ash | 5-15% | 10-20% |
Summary
Semi-coke retains more of its original coal structure compared to fully carbonized coke. This gives it unique combustion and reactivity characteristics. These properties make semi-coke ideal for industrial uses where higher reactivity and a more porous structure are needed.
Uses and Applications
Semi-coke: – Semi-coke is used as a reducing agent in ferroalloy production, helping reduce metal ores. – It can replace up to 20-30% of metallurgical coke in blast furnaces. – It’s used to produce calcium carbide and magnesium metal, which are essential in various manufacturing processes. – Semi-coke is also used as fuel in sintering plants, helping form iron ore sinter. – It serves as a raw material in the chemical industry, helping create different chemical compounds.UPERORE.
Metallurgical coke is crucial in iron and steel production. It acts as both fuel and reducing agent in blast furnaces. In metal casting, coke is essential in foundries, as it provides the necessary carbon for melting metals. It also plays a key role in producing ferro-alloys like chromium and manganese. Coke is critical in non-ferrous metal smelting due to its ability to withstand high temperatures with low reactivity.
Semi-coke, which has more volatile matter, is more reactive. It works better in the chemical industry and ferro-alloy production. While semi-coke can replace up to 30% of metallurgical coke in blast furnaces, it cannot match the strength and low reactivity of coke in demanding applications.
Size and Physical Properties
When comparing coke and semi-coke, their size and physical properties are quite different. This impacts how they are used in various applications.
| Property | Coke | Semi-coke |
|---|---|---|
| Particle Size | 25-80 mm | 0.5-25 mm |
| Fixed Carbon Content | 85-90% | 70-80% |
| Bulk Density | 450-550 kg/m³ | 700-900 kg/m³ |
| Porosity | 45-55% | 20-30% |
| Compressive Strength | 8-15 MPa | 2-8 MPa |
| Volatile Matter Content | 1-3% | 10-20% |
| Ash Content | 8-12% | 15-25% |
| Calorific Value | 29-31 MJ/kg | 25-28 MJ/kg |
Environmental Considerations
When we compare the environmental impacts of coke and semi-coke production, there are a few important factors to consider, like emissions, waste, and water use.
Coke Production Environmental Impact
Coke production has a bigger environmental impact: – Higher Emissions: Coke production releases more sulfur dioxide and nitrogen oxide. It also adds more particulate matter to the air. – Carbon Emissions: This process needs higher temperatures (1000-1200°C), which leads to more carbon dioxide emissions—about 0.8-1.0 tons per ton of coke produced. – Hazardous Byproducts: Coke production creates harmful waste like coal tar, ammonia, naphthalene, and light oils, which contribute to pollution. – Water Use: Coke production uses around 1-2 m³ of water for every ton of coal processed.
Semi-Coke Production Environmental Benefits
In contrast, semi-coke production has clear environmental advantages: – Lower Emissions: Semi-coke production occurs at lower temperatures (450-700°C), leading to lower carbon dioxide emissions—around 0.4-0.6 tons per ton of semi-coke. – Less Pollution: Emissions are much lower, with 1-2 kg of pollutants per ton of coal processed, compared to 3-5 kg per ton in coke production. – Fewer Harmful Byproducts: Semi-coke production produces fewer toxic byproducts, like coal tar and ammonia, and releases fewer volatile organic compounds. – Water Efficiency: Semi-coke production uses far less water—only 0.3-0.5 m³ per ton of coal, a major reduction compared to coke production. – Sulfur Retention: Semi-coke retains more sulfur (60-80%) than coke (20-40%), which lowers sulfur emissions.UPERORE.
Waste Products Comparison
- Coke: Produces coal tar, ammonia liquor, naphthalene, and light oils.
- Semi-Coke: Makes tar, pitch, and light oils, but in smaller amounts.
In summary, coke production causes higher emissions and greater environmental damage. On the other hand, semi-coke production offers a more sustainable option with lower emissions, less waste, and better water use.
Economic Factors
Economic factors play an important role in the production and use of coke and semi-coke. These include production costs, market prices, and demand-supply dynamics. These factors affect both materials’ profitability and efficiency.
Producing coke costs much more than semi-coke. The process needs temperatures between 1000°C and 1200°C, which requires a lot of energy and takes longer. From my experience, the cost difference between coke and semi-coke can be up to 30%. This makes semi-coke the better choice for companies that want to save money without losing too much quality. For example, in steel production, where budgets are tight, semi-coke’s lower cost can make a big difference, even though its performance is a bit lower in high-demand situations. Overall, semi-coke is becoming a more attractive option in many industries due to its lower cost and flexibility.