We have recently been researching on a fantastic waste management and energy recovery process called Pyrolysis. It is a thermo-chemical decomposition of organic material at elevated temperatures in the absence of oxygen (or any halogen). It involves the simultaneous change of chemical composition and physical phase, and is irreversible.
For example:- Tyre Pyrolysis of 1 ton of Tyres could give you an output of;
- Carbon Black: approx 300kg
- Pyrolysis oil: approx 450kg
- Steel: approx 150kg
- Gas: approx 100kg (at about 40% methane content)
The word is coined from the Greek-derived elements pyro meaning “fire” and lysis “separating”. It is the fundamental chemical reaction that is the precursor of both the combustion and gasification processes and occurs naturally in the first two seconds.
Pyrolysis involves heating organic materials without oxygen to break them down to simpler organic compounds. When organic wastes (e.g., waste tyres) are the feed-stock, products of the process include char or carbon char, oil, and gas. For example, Pyrolysis can convert wood to charcoal and a low-Btu gas.
Pyrolysis processes may operate as either batch feed or continuous feed systems. Batch feed systems process a single charge of feed-stock at a time. After required residence time in the batch thermal reactor, solid products and residue are removed. Conversely, in continuous feed systems, feed-stock is conveyed through the thermal reactor at a uniform rate , and solid products and residue are continuously discharged.
Pyrolysis relies on the addition of heat to break chemical bonds, providing a mechanism by which organics decompose and vaporize. Most projects operate within a temperature range of 250° – 500°C, although some report operating at up to 900°C. At temperatures above approximately 250°C , shredded tires release increasing amounts of liquid oil products and gases. Above 400°C, depending on the process employed, the yield of oil and solid tire-derived char may decrease relative to gas production.
1. Tyres delivered to a site are weighed.
2. Tyres are introduced to systems whole or else halved, chopped, or shredded; Magnetic separation is often used to remove ferrous metals from size reduced Tyres.
3. The feed stock is typically dried and preheated, using tyre-derived gas. Oxygen is purged through a combination of the pyrolysis gas preheater and an inert gas system employing nitrogen.
4. Temperature and residence time in the reactor are key pyrolysis reactor design criteria. Maintaining a positive pressure in the reactor ensures that leaks do not introduce oxygen from the air.
5. The liquid stage, Tyre-derived oil, is condensed and cooled. Light and heavy oil fractions may be handled separately. A separator removes any remaining water vapor. The product is filtered.
6. Solid Tyre-derived char is cooled, typically using a water-cooled stage. The product may be sized and screened to remove fiber. A magnetic separation stage captures magnetic materials remaining in the char. Washing the char and further size reducing it produces the carbon black product.
7. Tyre-derived gas maintains operating pressure in the system and provides heat to the system. Vented gases pass through a pollution control train, which may include a gas flare.
8. Gas can be further treated for power generation. It passes through a venture scrubber to remove particulate matter from gas and then it is passed through a water cooled condenser which can help us to bring down the temperature of Tyre-derived gasses. It is then passed through various filters containing wood waste and saw dust waste to remove moisture from gas and finally cleaned through a fabric filter.
9. Now our Gas is ultra clean and can directly feed to Gas Driven Generating Set. But for continuous operation of generator we use low pressure vessels for the storage of gas. By utilizing these methods we can store power for 24 hours irrespective of the gas production rate through the Pyrolysis processing of waste Tyres.
Below is a beautifully simple video that shows you the process from A-Z.
WASTE TYRE PYROLYSIS
Tyres are shredded and placed on to continuous loader which feeds scrap pieces into main reactor under heat. Discharge is Separated into solid wastes and gasses. Solid waste is made up of:
30-35% Carbon Black
10-15% Steel Gasses that cannot be condensed (5%) are reused to assist with heating reactor.
Condensed gasses are stored as:
40-45% Pyrolysis Fuel Oil. Sizes:2ton,3ton,5ton, 10ton & 15-20ton.
Pyrolysis can be performed at relatively small scale and at remote locations which enhance energy density of the biomass resource and reduce transport and handling costs. Heat transfer is a critical area in pyrolysis as the pyrolysis process is endothermic and sufficient heat transfer surface has to be provided to meet process heat needs. Pyrolysis offers a flexible and attractive way of converting solid biomass into an easily stored and transported liquid, which can be successfully used for the production of heat, power and chemicals.
Source: Wikipedia, Clean Energy Group, Harmonic Energy Inc.