Rotary incinerator is suitably studied for burning industrial and hazardous waste as well as municipal wastes.
It consists of a rotary kiln inside lined with refractory materials slightly inclined to the horizontal.
The revolving action of the kiln, provides a mixing action of the waste material which results into a more efficient burning and the variable rotation, regulated by frequency converter, and slope give enough residence time to assure optimal combustion efficiency.
A burner located on the front face of the kiln ensures that the temperature in the kiln does not fall below the requested combustion temperature (up to 1000 °C).
The burner is also used to pre-heat the temperature of the kiln before any waste is fed to the kiln.
At the discharge end the cylinder is provided of an air cooled section to which the alloy steel segments are bolted for refractory held in place.
The feed end of the kiln is closed by breeching provided with feed chute and positive seal ring. The seal consists of a set of cast iron segments spring actuated with guide.
The discharge end of the kiln is closed by a breeching provided of hoppered bottom to discharge ashes to the ashes conveyor.
The breeching is sealed to the revolving cylinder with a positive seal ring in the same manner as the feed end.
Both breechings are inside lined with refractory and insulating materials.
The combustion air for the wastes is blown into the kiln through a suitable regulator and distributor.
The air blower has a capacity for 150% excess air for this reason high combustion efficiency can be assured over a wide range of operating conditions.
A further burner can be installed at the end of the cylinder on the discharge side to remove when requested slags formed on discharge ring.
Post Combustion Chamber
The volatile products (flue gases with gaseous unburnt organic compounds and particulates) resulting from the thermal process occurring in the rotary kiln, are drawn into the Post-Combustion Chamber for a further oxidation.
The Post Combustion Chamber is designed to assure enough residence time (2 seconds or more), turbulence and temperature to flue gases in order to guarantee the complete destruction of volatiles.
The Post Combustion Chamber is provided with an emergency stack and with a pneumatically operated butterfly valve.
Flue Gas Treatment
Idreco can propose different solutions for flue gas treatment at the outlet of Rotary Incinerators.
- Heat Recovery
Heat in the flue gases coming from the Post Combustion Chamber can be recovered inside a steam boiler to decrease gas temperature before successive treatment.
Heat can be also recovered by preheating combustion air inside a heat exchanger.
- Flue Gas Conditioning
Whereas to heat recovery from flue gases is not requested they can be thermally conditioned with water by atomization lances in a tower internally lined in order to bring gas temperature complying with successive dry flue gas treatment inside baghouse.
- Flue Gas Depuration
Flue gas which can come downstream from either a boiler or a conditioning tower are cleaned or by dry absorption or by wet absorption.
3.1 Dry Absorption
With dry absorption flue gases acid pollutants (HCl, HF, SO2) are transferred into a solid.
Depending on the availability and on the requested performances Calcium Hydrate or Sodium Bicarbonate are used as sorbent
The adjustable injection of reagent is done upstream a vertical reactor tower sized to ensure the optimum residence time (at least 2 seconds) for the reagents in order to assure the intimate contact between flue gases and reagent.
The flue gas with particulate, reaction products and unreacted reagents then enters the filtration section, where a Baghouse removes almost all the particulate matter, and allows to complete the deacidification reactions on the cake layer formed on the bags.
Depending on the characteristics of waste activated carbon can be also injected before reaction tower for the removal of heavy metals, dioxins and furans. Exhaust activated carbon is discharged from baghouse together with by-products.
3.2 Wet Absorption
Alternatively a Wet Absorption system can be used.
In this case flue gases are cooled down and adiabatically saturated by means of a Quencher, fed with fresh water (make-up) and with a part of the recycled water liquor. Then, gases enter the adjustable Venturi and are accelerated in velocity in the throat section. The intimate turbulent contact adiabatically saturates the gas stream. The droplets generated trap the particles (dust) by impaction and Brownian diffusion and so the dust and the particulate are collected and discharged with the blow down.
Gases coming from the Venturi, purified from dust and particulate, enter the absorbing tower through the inlet nozzle and flow upward through special trays (or packed beds) in counter-current with the flue gas.
The tower is divided in two parts by means the stack-plate.
In the lower part, which is provided with the liquor tank, an acidic solution (pH 3÷4 approx.) is circulated to recover mainly HCl, HF and Heavy Metals.
In the upper part, which is provided with the packed beds or with special plates, a basic solution (pH 7,5 approx.) is circulated to recover mainly SO2.
Caustic Soda is fed in required quantity to keep the pH in relation to the acidic gases. Salts and heavy metals are discharged with the blow down, which is transferred to the waste water treatment plant.
Before leaving the tower, the saturated gases flow through a Mist Eliminator which separates the entrained droplets containing the trapped dust.
ID Fan and stack
Whatever it is the selected flue gas treatment an induced draft fan, with speed controlled by an inverter, is used to control the draft through the entire complex by maintaining a lightly negative pressure in the rotary kiln and to discharge the gases into the atmosphere through a stack.
