Waste gasification

Waste gasification has established itself as one of the more promising technologies for the energy recovery of non-recyclable materials. Unlike conventional incineration, this process produces a synthesis gas that can be used as a fuel or converted into other chemical products of industrial value.

Within the transition towards a circular economy, gasification is presented as a viable option for reducing the volume of waste sent to landfill and generating energy in a cleaner way, although its position in the waste hierarchy is below prevention, reuse and recycling.

Fundamentals of the process

Gasification is a thermochemical process that converts carbon-based materials (such as plastics, biomass or municipal solid waste) into a combustible gas through a reaction with a limited amount of oxygen or steam.

The result is a synthesis gas (syngas) composed mainly of carbon monoxide (CO), hydrogen (H₂), carbon dioxide (CO₂) and methane (CH₄), together with small fractions of heavier hydrocarbons and tar compounds.

Basic stages of gasification

1. Drying of the material: removal of moisture.
2. Pyrolysis: initial thermal decomposition in the absence of oxygen.
3. Partial oxidation: part of the carbon is converted into CO and CO₂.
4. Reduction: production of the synthesis gas through chemical equilibrium reactions.

The temperature usually ranges between 800 °C and 1,200 °C, depending on the type of waste and the technology used.

Types of gasifiers

• Fixed bed: the simplest type; suitable for waste with a controlled particle size.
• Fluidised bed: offers greater thermal uniformity and efficiency.
• Entrained flow: used in industrial applications that require high gas purity.

Some modern systems combine gasification with plasma stages to maximise the conversion of the waste.

Applications of the synthesis gas

Syngas can be used:

• To generate electricity through gas engines or turbines.
• As a feedstock in the production of methanol, ammonia or hydrogen.
• In industrial processes that require thermal energy.

Advantages of gasification

• Lower volume of final residues than incineration.
• Versatile energy output (electrical, thermal or chemical).
• Reduced emissions of dioxins and furans, thanks to the controlled, oxygen-deficient environment.
• Recovery of metals and inert materials from the bottom residue (slag).

Limits and challenges

Despite its potential, gasification faces several obstacles:

• High investment and maintenance costs.
• It requires a constant feed of relatively homogeneous waste.
• It produces tars that must be treated with gas-cleaning systems.
• It can be difficult to integrate into existing recycling circuits when materials are highly mixed.

Relevant regulation

• The Waste Framework Directive (2008/98/EC) and Law 7/2022, which set out the recovery hierarchy.
• Regulation (EU) 2019/1009, which can facilitate the use of derived products as fuels or fertilisers where they meet safety requirements.

Gasification is one of several options for managing residual, non-recyclable waste, and it works best as a complement to, not a substitute for, prevention, reuse and recycling. At Manglai we help companies measure their carbon footprint and prepare their sustainability reporting. Discover how Manglai can help you.