Plant description
The regenerative combustion plant is based on the concept of achieving a high thermal energy recovery with the aid of large ceramic masses that – during the heat recovery phase – absorb the heat from combustion gases and – during the regeneration phase – release the accumulated heat for the pre-heating of inlet polluted air. The residual fraction of unrecovered thermal energy is partially, or totally, supplied by the heat generated by the combustion of solvents dissolved into the polluted air.
The system is generally composed of three towers with ceramic filling, which alternately operate as a pre-heating chamber, filling cleaning chamber, and thermal recovery chamber. They are physically connected to the upper part by a combustion chamber with one or more modulating burners. The chamber, entirely covered in ceramic fibre insulating panels, ensures the optimal combustion temperature, generally between 750 - 850° C, and its sized is designed to hold treated air for 1 second circa.
Below each tower are positioned the valves of:
- Polluted air inlet
- Inlet of polluted air and exit of the purified air flow
These valves are automatically operated by the plant control system.
Pre-heating, washing, and heat recovery towers contain filling bodies of inert ceramic material; once the optimal inversion temperature is reached, the towers exchange the pre-heating, washing, and heat recovery from the purified gas functions at intervals of 90-120ms. While the reversal happens, the pre-heating vessel contains unpurified polluted gas; with the availability of three towers, it is possible to cyclically move and wash the ceramic filling that has just finished to give out heat before reusing it again in order to recover heat from the purified gas output. In the case of short stops, the system can be kept in temperature, running it with a reduced flow.
Output performance
The regenerative thermal combustion process with three towers easily operates with an air purification yield of 99%, and the limit consists in the capacity of the large valves that command the inlet and outlet of the air.
The theoretical thermal yield of the regenerative thermal recovery system with the redundant sizing of the ceramic masses, can be pushed at almost 97%.
The thermal balance of the combustor must be preferably complete with the contribution of combustion heat coming from solvents present in the polluted air. If this contribution fails, the actual performance of the combustor deviates considerably from the theoretical thermal yield and can be as low as 92%.
Solvents concentration
In the thermal combustion of regenerative type, the desired thermal conditions are achieved with a concentration of solvents in the polluted air between 1,1 and 2,2 g/Nm3, expressed as TOC.
For solvent concentrations ranging from 0,8 to 1 g/Nm3, expressed as TOC, the regenerative thermal combustion process is no longer competitive against the catalytic thermal combustion or the solvent concentration technology, although it is often preferred for its conceptual simplicity.
For solvent concentrations below 0,6 g/Nm3, expressed as TOC, the regenerative thermal combustion process is not available for the exorbitant consumption of auxiliary fuel.
