Process Description and Overview
The ART system thermally depolymerizes organic materials within an oxygen-free, externally heated reaction vessel in a temperature and pressure controlled environment. Feed material is sized for entry into the process and mechanically conveyed through the reaction vessel at a controlled rate. Moisture is minimized as water exacerbates the thermal demand for feedstock decomposition. The reaction vessel is maintained at a temperature of sufficient magnitude to insure complete thermal decomposition of volatile components. Oxidation or “burning” does not occur because the process maintains a near oxygen-free environment. Complete control of time, temperature, turbulence and pressure insure product decomposition. Nitrogen is introduced at the feedstock entry and product exit of the reaction vessel to counter air infiltration and insure safe operation.
The ART recycling process converts feedstocks into liquid, carbon char and vapor gas products.
Two products exit the reaction vessel: solids and vapor gas. The solids are transferred to a classifier for separation of carbon and other feedstock solid components. The solids are transferred to their respective storage vessels. The total gas stream is drawn out of the reaction vessel into a condensing system for oil recovery. The oil is transferred to bulk storage tanks. Part of the remaining non-condensable gas fuels the burners which maintain process temperature. The balance of the gas can fuel other process equipment designed for natural gas or propane or stored for future use.
The liquid product has value as a feedstock to refineries, petrochemical production facilities and as a blend for other petroleum-based products. The carbon char is sold for use in the production of activated carbon, pigments, rubber goods, masterbatching and applications in oil remediation, and agriculture.
The Pyrolysis process consists of four endothermic steps:
1. Melting the feedstock
2. Heating the molten liquid to depolymerization (decomposition) temperature
3. Thermal depolymerization of the feedstock
4. Volatilization of the product
The critical factors which govern the capacity of the unit are feedstock type, temperature, heat transfer and residence time.
The term process severity is used as a relative measure of the process conditions and the feedstock decomposition efficiency. Severity is affected by temperature, feed rate and residence time.
Hydrocarbon product distribution is dependent upon the type of feedstock and process severity. Hydrocarbon partial pressure is often an important variable in Pyrolysis reactors because it determines how long the reactants are in the reactor and can greatly influence the product yields and compositions. Partial pressures do not play a significant role in the ART system due to operating pressures at less than 1” WC and the introduction of nitrogen for safety purges.
At low severity the products resemble the molecular skeleton of the polymer. Polymers depolymerize at different temperatures and some polymers, such as polypropylene and polystyrene can facilitate or catalyze the depolymerization of other polymers.