Q6 How is stable operation achieved?

If the feeding of waste into the furnace fluctuates, doesn't the process become unstable?

It is crucial to feed the waste into the system in a stable manner in order to maintain the furnace temperature and minimize fluctuations in the exhaust gas volume. Kobelco Eco-Solutions' proprietary dual-axis screw-type feeding system prevents the compaction of the waste and enables volumetric feeding. The structure of feed conveyor apron was improved, greatly reducing problems related to feeding. By operating the waste crusher offline, problems with the crusher causing feed stoppage have been overcome.
(Refer to (1) on the following diagram. Specifics regarding shapes, materials etc. are proprietary.)

Doesn't the slag cool and adhere around the discharge outlet, obstructing the outflow?

If the slag does not melt sufficiently or the temperature drops around the discharge outlet, it becomes easier for the slag around the discharge outlet to adhere, which tends to cause obstruction. Based on numerical analysis and actual equipment data analysis, Kobelco Eco-Solutions was able to optimize the structure of the discharge outlet by separating exhaust gas from slag and by reducing slag scattering and maintain high temperatures at the discharge outlet to prevent adhesion and obstruction. Normally a slag burner does not need to operate. In addition, by adjusting the basicity (CaO/SiO2) of the slag, the slag's melting temperature can be kept to 1200 ?C or lower for stable discharge.

Note: Basicity is the ratio of CaO to SiO2 in the slag. Incinerated ash has three chief components: SiO2, Al2O3, and CaO. The melting temperature and viscosity will vary according to the basicity. In general, it is considered that: (1) if the basicity is high, the melting point will be high and when the temperature drops the viscosity rapidly increases; and (2) if the basicity is low, melting takes place at a comparatively low temperature, and even if the temperature rises there is little decrease in viscosity.
(Refer to (2) on the following diagram. Specifics regarding shapes,materials, etc. are proprietary.)

What is the service life of the refractory?

At Kobelco Eco-Solutions we applied our know-how from incinerators, melting furnaces, and gasification and melting systems to optimize the refractory material and improve durability by water cooling the melting furnace. Moreover, the slag melting temperature is kept to 1200 ?C or lower by adjusting the basicity. Ensuring that the temperature does not rise higher than necessary level extends the service life of the refractory. We thus estimate the service life of the refractory to be 10 years.
(Refer to (3) on the following diagram. Specifics regarding shapes,materials, etc. are proprietary.)

Doesn't the exhaust gas line become obstructed?

Kobelco Eco-Solutions takes the following measures to prevent obstruction of the exhaust gas line.

Preventing obstruction at the gasifier exhaust duct

By minimizing the volume of air leaked through feeding, the temperature at the gasifier exhaust duct is kept from rising. In addition, reducing the temperature of the sand layer (with slow combustion) prevents clinker adhesion at the furnace exhaust duct.

Preventing clinker adhesion at the melting furnace outlet

Numerical analysis and other methods were used to optimize the furnace shape. Plus, by considering the melting furnace outlet temperature and improving the method of injecting combustion air, clinker formation was minimized.

Preventing ash adhesion in the cooling tower

The shape, dimensions, and spray nozzle specifications of the cooling tower were determined based on numerical analysis and measurement data analysis to prevent the inner wall and dust from becoming wet, and the dust from sticking.
(Refer to (4), (5), and (6) on the following diagram. Specifics regarding shapes,materials, etc. are proprietary.)

(1) Feeding system... Stabilization

Feeding mechanism
Proprietary feeding system prevents compaction of waste and enables volumetric feeding

Feed conveyor
Apron structure of feed conveyor was remodeled, greatly reducing problems inside the conveyor

Double pit
By operating the waste crusher offline, problems with the crusher causing feed stoppage are overcome

Feeding system enables volumetric feeding and stable feeding of waste to contribute to stable furnace operation

(2) Melting furnace discharge outlet... Stable discharge

• Numerical analysis and actual equipment data analysis used to optimize the outlet shape; exhaust gas and slag are properly separated
• Temperature at outlet is kept at around 1200 ?C so slag burner normally does not need to operate
• Slag basicity (CaO/SiO2) is adjusted to keep the slag's melting temperature at 1200 ?C or lower

Maintains stable discharge conditions
Temperature in furnace does not rise higher than necessary level, helping to extend the service life of the refractory

(3) Gasifier exhaust duct... Obstruction prevention

• Temperature of the sand layer is reduced (slow combustion)
• Volume of air leaked from feeding is minimized to prevent rise in temperature at gasifier outlet

Prevents clinker adhesion at furnace exhaust duct

(4) Melting furnace... Clinker adhesion prevention

• Numerical analysis is used to optimize furnace shape and design
• Melting furnace outlet temperature considered for optimal injection method of combustion air.

Prevents clinker formation in the vicinity of the melting furnace outlet
Contributes to stable, long-term continuous operation

(5) Cooling tower... Ash adhesion prevention

• Numerical analysis and measurement data analysis are used to determine the cooling tower shape, dimensions, and spray nozzle specifications.

Prevents inner wall and dust from becoming wet, and the dust from sticking