Evaluation of Plastic Waste Management in Thailand Using Material ...

2.3.2.2 Gasification: Plastics are converted to gas for use as a raw material in the chemical
industry
The gasification process includes heating plastic wastes and supplying oxygen which is
limited. Most of plastic wastes are transformed into hydrocarbon, carbon monoxide and
water. First of all, sand in the reactor is heated at 600-800 ºC, and it is circulated inside a
first-stage gasification furnace. Plastic wastes are fed into the furnace break down on
contact with the sand to form hydrocarbon, carbon monoxide, hydrogen and char.
The gas from the low-temperature gasification furnace is reacted with steam at a
temperature of 1,300-1,500 ºC in a second-stage high-temperature gasification furnace to
produce a gas composed mainly of carbon monoxide and oxygen (see in Figure 2.23). At
the furnace outlet, the gas is rapidly cooled to 200 ºC or below to prevent the formation of
dioxins. Then, the gas passes through a gas scrubber and any remaining hydrogen chloride
is neutralized by alkalis and removed from the synthetic gas. This synthetic gas is used as a
raw material in the chemical industry to produce chemicals such as hydrogen, methanol,
ammonia and acetic acid.
Figure 2.23 Gasification process for converting plastic wastes to chemicals (PCD, 2011)
2.3.2.3 Coke oven chemical feedstock recycling: Plastic waste reused in coke ovens
This recycling makes a coke by baking coal and hydrocarbon oil which can be produced
from plastic wastes. At these plants, plastic waste collected from households is first
shredded, and the other wastes are removed such as iron and glass. The PVC waste is also
removed before heating plastic waste to 100 ºC and granulating. Then plastic wastes are
mixed with coal and fed into the carbonization chamber of a coke oven. The carbonization
chamber has combustion chambers on both sides which heat the content indirectly. This
method only makes plastic wastes crack inside the chamber at a high temperature in order
to produce coke for use as the reducing agent in coke ovens. Hydrocarbon oil can be used
as chemical feedstock in the chemical industry, and coke oven gas is used to generate
electricity (Plastic Waste Management Institute, 2009). Figure 2.24 shows the process of
Coke oven chemical feedstock recycling.
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