How it Works
Pyrocal Continous Carbonisation Technology (CCT) was developed to satisfy a need for cost effective conversion of biomass to charcoal and energy.
SYSTEM OPERATING PRINCIPLES
Biomass is continuously metered into the top chamber of the rotary hearth, where it rapidly heats, dries and commences to pyrolyse (thermally decompose). The volatile gases released from the biomass mix with a controlled amount of air and ignite. Partial combustion of volatile gases in the hearth provides the heat that makes the process autothermal.
The flaming off-gases travel up through the hearth and then to the thermal oxidiser, where they are mixed with more air and oxidised completely through to water and carbon dioxide.
The biomass is transported through a number of chambers before dropping out into a screw conveyor where it is quenched and discharged as a char product.
The temperature and oxygen profiles in the hearth are controlled to achieve the desired char yield and char quality. Temperatures as low as 450 degrees C or as high as 700 degrees C may be selected.
The thermal oxidiser is controlled to a selected temperature in the range between 725 to 925 degrees C according to the nature of the biomass and the emissions control requirements. Oxygen is monitored and controlled to achieve efficient oxidation of the gases.
Downstream thermal recovery systems (such as a steam boiler) and emissions controls (such as a wet scrubber) are integrated into a complete system.
The entire system is controlled by a PLC programmed to specific installation requirements.
Key Technical Features
- Mechanical moving bed arrangement, which provides maximum flexibility for a wide range of feedstocks, including light fluffy materials, clumping materials, chips and materials with a very diverse size range.
- Direct heat transfer to the incoming biomass. This means there are no heat transfer surfaces in the system to foul or corrode.
- Moderate and controllable temperatures in each stage of the hearth and thermal oxidiser which allow optimisation of char quality and emissions control for a given feedstock.
- Controlled two stage oxidation of the released volatile matter, allowing efficient control of air pollutants.
- Continuous co-mingling of flammable volatile gases with a controlled airflow, to eliminate flammable gas explosion risks (no hazardous zone design requirements).
- Fully autothermal operation (i.e. after startup there is no need for other fuel sources to operate).
- Rapid start-up. Typically, cold to full throughput in 40-60 minutes. The materials of construction allow heating from cold to full operating temperature without damage.
Unique characteristics of CCT
- Low investment cost compared to both conventional and novel biomass thermal treatment technologies.
- Small footprint and mass, requiring very little site preparation. This is especially useful for operations that need to be relocated to follow seasonally available biomass.
- Ease of maintenance. The hearth unit internals can be completely overhauled in under six hours. This would typically be done every 8000 hours.
- Ability to handle feedstocks that cause major fouling, slagging and/or corrosion in other technologies.
- Pyrocal CCT systems are not only “omnivorous” for feedstock but they can be operated to bias for either carbon product or heat yield.
- Separation of the core thermal treatment step from the control of emissions. This allows the optimal processing conditions to be achieved for what are often competing needs.