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The first actions are related to those that each of us of inter fraction, such as RDF. The reactor is able to
can implement. The reduction of the amount of waste melt the ash fraction of the waste to produce a vitrified
produced relies on everyday life activities. Each of us granulate applicable as a raw material for ceramic and
can devote his efforts to reducing the amount of waste concrete production as substitution of minerals.
individually generated. In addition, he can apply the Meanwhile, the reactor is able to convert the
concept reuse, asking himself “should this material combustible fraction of the waste into a valuable gas,
really to be thrown away?”. And if you have to resort to called syngas, composed mainly of hydrogen and
throwing it out, differentiating, if possible. This is where carbon monoxide.
the citizen’s task ends and industry, technology and The waste to chemical process is composed of five
innovation take over. The differentiated product classes main sections, as seen in Figure 2.
can therefore be mechanically
“Waste to chemicals represents recycled. But not all the differentiated 1. High temperature gasification. As mentioned above,
a valid alternative to fractions of fractions can actually be recycled. A this is the core of the overall process, since the
waste that are not mechanically fraction of waste always exists, combustible fraction of the waste is converted into
recyclable, which can then be larger or smaller depending on the syngas, while the inert fraction of the waste is melted
chemically converted to produce, type of material and collection. This – thanks to the high temperature reached – and
for example, fuels is where innovation comes in. Waste collected as a vitrified granulate material.

to chemical represents this: a valid The reactor, according to the temperature profile, can
alternative to fractions of waste that are not mechanically be schematized as divided in three zones, as seen in
recyclable, which can then be chemically converted to Figure 3:
produce, for example, fuels. a. Melting zone. Where pure oxygen is fed as a
The typical feedstock of a Waste to chemical process combustion and gasification agent. The
are Refuse Derived Fuel (RDF), which is the dry fraction exothermal nature of the oxidation reactions
of unsorted municipal solid waste and the non- allows the temperature to reach above 1600°,
recyclable plastic; any other waste fraction that is thus making it possible to melt the inert fraction
impossible to recycle in an alternative way can be sent specifically contained in the waste.
through the process. An example of the average b. Partial oxidation zone. A balance of gasification
compositions, by weight fraction, of the two mentioned reactions implies the further conversion of the
fractions is reported in the table below. combustible fraction, but also a reduction of the
It is important to notice the content of carbon and average working temperature (700°C).
hydrogen. These elements are usually taken from fossil c. Stabilization zone. Called stabilization since the
resources. The rationale in a Waste the chemical gas produced is slowed down when it reaches
process, is instead to produce fuel or chemicals by the enlarged reactor section, and further
converting the carbon and hydrogen contained in the converted by the introduction of more oxygen
waste which would otherwise be disposed of or at best which allows the temperature to elevate up to
recovered only in terms of energy. 1100°. In this way a very valuable syngas is
The conversion of carbon and hydrogen is performed produced: free of TARS or dioxins.
by a high temperature melting gasifier which is the core 2. Syngas cleaning and storage. As the syngas is
of the process. The particularity of this technology is coming out from the gasification reactor, it is abruptly
that it is able to convert feedstock with a high content cooled from 1100°C to 90°C in order to freeze the
composition and avoid the formation of toxic
RDF Non-recyclable plastics compounds. The cold syngas is sent to two scrubbers
and an electrostatic filter to perform a preliminary
C 40-55% 47-61% cleaning. The cleaned syngas is then sent to a gas
H 5-8% 5-7% holder in order to control the potential fluctuation of
flowrate.
O 20-28% 14-20%
3. Syngas compression and purification. Syngas from
Cl 0.5-3% 0.8-1.5% the gas holder is compressed and purified through
N 0.5-1.5% 0.2-0.5% several steps, including adsorption beds, hydrolysis,

S 0.1-1% 0.02-0.3% and sulfur removal, in order to achieve a thoroughly
polished syngas which cannot contaminate the
Moisture 10-20% 5-9% catalysts of the following step.
Ash 5-20% 7-20% 4. Syngas conditioning. Both methanol and ethanol
would require a higher H2/CO ratio than the one
Table 1. Average elemental compositions of Refuse Derived Fuel and Non- coming directly from gasification, which is about 1.
recyclable plastics. Thus, according to the final product desired, the

IndustrIal Plants - May 2023
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