Q3 What are the principles and features of the fluidized-bed gasification and melting system?

The fluidized-bed gasification and melting facility process flow

Solid waste collected by truck is dumped into waste pit and stored temporally . It is then fed into a gasifier through an air-tight feeder. In the gasifier the waste is pyrolytically decomposed into combustible gas, incombustible materials, and ash. In the melting furnace the combustible gas makes complete combustion, reaching temperatures over 1200 ˚C. The ash is melted at this high temperature, forming slag. The slag is continuously discharged, and is water-granulated in the slag cooler.

The high-temperature exhaust gas generated in the melting furnace is recovered by the waste heat boiler and used for power generation, or as heat for hot water supply or various facilities that utilize waste heat.

The exhaust gas from the waste heat boiler goes through a cooling tower, bag filter, and catalysis tower for treatment, after which it is released through a stack.

Process Flow of Gasification and Melting Facility

Configuration of the fluidized-bed gasification and melting system

A fluidized-bed gasification and melting system is comprised of a fluidized-bed gasifier and a swirl-flow melting furnace. Kobelco Eco-Solutions has over 25 years' experience in operating fluidized-bed waste incinerators and over 15 years' experience in swirl-flow melting furnaces. This strong background ensures high reliability in the company's fluidized-bed gasification and melting system.

Fluidized-Bed Gasification and Melting System

Fluidized-bed gasifier

In the fluidized-bed gasifier, air is blown into a layer of sand to create a fluidized state. The charged waste is disintegrated by the fluidized sand. Here, part of the waste is combusted and the combustion heat is used to pyrolytically decompose waste into combustible gas, incombustible materials, and ash. Fuel is used only at startup and is not necessary during operation. Resources contained in the waste, such as steel and aluminum, are extracted from the bottom of the gasifier in an unoxidized state after being polished by the sand.The features of Kobelco Eco-Solutions' fluidized-bed gasifier are:

1. Cylindrical fluidized-bed: With no corners to interfere with fluidization, stable gasification can take place across the entire furnace bed
2. Compact: Upright, so requires less space than other types for high-load combustion
3. High durability: Has no moving parts, and a long refractory life of over 10 years helps to reduce maintenance and repair costs
4. Highly reliable sand layer and extraction mechanism: For over 25 years, a center-discharge dispersion plate has been used to reliably extract incombustibles
5. High recycling efficiency: Unoxidized steel and aluminum residue in the fluidized-bed gasifier is decomposed and polished into a clean state by the sand before recovery, making it easy to recycle

Features of the Fluidized-Bed Gasifier

Swirl-flow melting furnace

The combustible gas and ash generated in the gasifier are transferred to the melting furnace. Through introduction in tangential direction, a swirl-flow is created inside the melting furnace. Air is supplied for combustion in the melting furnace, where the combustible gas is completely combusted, reaching temperatures over 1200 ˚C. The ash melts at this high temperature, and the centrifugal force generated by the swirling sends the ash into contact with the inner wall surface, turning it into molten slag that flows down on the wall surface. This molten slag is collected in one area, then continuously and stably discharged through the discharger into the slag cooler, where it is cooled to form water-granulated slag. The system employs autothermal melting, using the energy of the waste itself, so no electricity or fuel is needed for the melting. Also, the dioxins in the exhaust gas are reliably decomposed in the high-temperature zone of the melting furnace.

Features of the swirl-flow melting furnace:

1. Vertical alignment: The swirling flow separates solids from gases and forms a uniform molten slag layer on the inner wall surface for efficient melting
2. High durability: The refractory is self-coated by the slag, and water cooling extends the refractory life
3. High melting efficiency: A constriction keeps the high temperature uniform inside the melting furnace (at over 1200 ˚C) for stable melting; also, by increasing the flow rate of the passage gas to hit the slag flow, the unmelted ash collects on the wall surface efficiently, where it melts and forms molten slag with high efficiency
4. Stable slag discharge: Molten slag is collected as a single flow and discharged continuously and stably; no burner is needed for the slag discharger
5. Quality slag for a wide range of uses: The slag can be a substitute for sand or crushed stone for mixing with asphalt, an inter-block admixture, or used for many other purposes

Features of the Swirl-Flow Melting Furnace

What are the features of the fluidized-bed gasification and melting system?

The fluidized-bed gasification and melting system has the following features:

High energy recovery efficiency

• The system employs autothermal melting, using the energy of the waste itself, so no electricity or fuel is needed for the melting
• Low air ratio produces low amount of exhaust gas with highly efficient heat recovery

Reduced environmental impact

• Dioxins and other harmful substances are decomposed at high temperatures sustained by complete combustion
• Ash is turned into recyclable molten slag, thereby reducing the final landfill disposal
• Highly recyclable steel, aluminum and slag are recovered

High economic efficiency

• Simple structure and equipment configuration create a compact, energy-saving system

Processing capacity

• Furnaces suitable for capacity under 300 t/day per furnace

Its superiority to other systems

In comparison to stoker-type incinerator

The fluidized-bed gasification and melting system reduces the volume of ash, turning it into highly recyclable molten slag, thereby decreasing the final disposal load. A stoker-type incineration system (hereafter, "stoker system") requires an additional melting furnace to melt the ash into molten slag.

The stoker system recovers steel with ash adhered to it and aluminum in a molten state making material recycling very difficult. The fluid bed gasification and melting system, in contrast, decomposes the unoxidized steel and aluminum and recovers it polished into a clean state by sand, making material recycling easy.

In comparison to stoker-plus-ash-melting system

The fluidized-bed gasification and melting system makes it possible to have a simpler equipment configuration than with a stoker-plus-ash-melting system. This results in lower power consumption, and because melting takes place using the energy of the waste itself, no extra electricity or fuel is needed for the purpose of ash melting. This results in low energy consumption and low CO2 emissions.

In comparison to shaft furnace-type gasification and melting furnace

A shaft furnace-type gasification and melting furnace (hereafter, "shaft furnace system") requires external fuel such as coke. In terms of energy consumption and CO2 emissions, the fluidized-bed gasification and melting system holds an advantage.

In addition, with the shaft furnace system, metal as well as slag constituents are recovered as molten metal, but the utilizations are limited because the molten metal is a mixture of steel, aluminum, etc. The fluidized-bed gasification and melting system, in contrast, decomposes the unoxidized steel and aluminum and recovers it polished into a clean state by sand, making material recycling possible with high recycling efficiency.

Comparison of fluid bed gasification and melting system with other systems

	Gasification and melting systems		Incineration + ash melting	Incineration only
	Fluid bed	Shaft furnace	Stoker + ash melting	Stoker
1. Recycling efficiency	E	G	G	F
2. Landfill load	G	G	G	F
3. Energy consumption	G	F	F	G
4. CO2 emissions	G	F	F	G
5. Stable operation	G	G	G	E