METHOD AND DEVICE FOR THERMOCHEMICAL RECYCLING OF COMBUSTIBLE WASTES IN VERTICAL TWO-SHAFT FURNACE FOR BURNING CARBONATE MATERIALS Russian patent published in 2024 - IPC F23G7/12 F23G5/16 F27B1/02 C04B2/12 

FIELD: destruction of wastes by burning.

SUBSTANCE: group of inventions relates to method and device of incinerators intended for destruction of specific wastes or specific low-grade fuels. Thermochemical recycling of combustible industrial wastes, halogen-containing wastes and polyvinyl chloride plastics, residues after sorting solid municipal wastes, plastics and polyethylenes, alternative fuels RDF, SRF, TDF are performed in vertical two-shaft furnace for calcination of lump carbonate material into lime. Charge is prepared in bunker trestle according to recipe. Fractional recycled wastes, additives and lumpy carbonate material with fraction of 20 mm to 120 mm are dosed from the feed bins. Charge is loaded into the first direct-flow shaft-gas generator through the first sealed conical loading device equipped with an aspiration unit of gasification products. Carbonate material is loaded with fraction from 20 mm to 120 mm into the second shaft of counterflow roasting through the second sealed conical loading device equipped with aspiration unit of gasification products. Charge is gasified in the first shaft-gas generator in the medium of limited supply of oxidizer with excess air coefficient α=0.5 to obtain gasification products from wastes in the form of a mixture of generator synthesis gas, consisting mainly of H₂ and CO, in the medium of alkali-earth metals CaCO₃ and CaO by heating from the upper combined burners at a temperature of more than +1,300 °C. Lump carbonate material CaCO₃ limestone is burnt in the second counterflow shaft for decomposition into gas CO₂ and commercial lime CaO. Wastes gasification products are evacuated by blowing into the second shaft through the transition channel, where gasification products are repeatedly afterburned in the medium of excess air by suction from bottom to top through a layer of incandescent lime CaO in the entire roasting and heating zone in the second shaft of counterflow roasting. Products of gasification leakage from mines are evacuated by rarefaction from both sluice loading devices and supplied to the transition channel-gas duct to the secondary afterburning tuyere with suction through the layer of incandescent lime CaO. Technical lime CaO mixed with recycled waste ash is unloaded from the first shaft-gas generator, and commercial lump lime CaO is discharged from the second counterflow calcination shaft. Waste flue gases are discharged from the two-shaft furnace for gas cleaning due to vacuum of the smoke exhauster from the upper part of the second firing shaft. Reacted finely dispersed CaO is trapped from flue gases by dust-gas cleaning filters. Flue gases are cleaned. After the furnace flue ash is deposited with coal-fabric and electric filters. Residual acid gases HCl, SO₂, HF are removed by dry or wet method. Nitrogen oxides — nitrogen monoxide NO and nitrogen dioxide NO₂ — are catalytically decomposed with ammonia solution at temperatures from +170 °C to +380 °C with formation of gaseous nitrogen and water vapor. In the first shaft-gas generator, gasification of wastes with oxidizer deficiency is performed, with excess air coefficient α=0.5, obtaining generator synthesis gas, which then enters the second carbonate annealing shaft for secondary afterburning, where it burns in excess air with α≥1.2 with heat release, thereby replacing the main fuel of the commercial lime production process. Additionally, incandescent commercial lime CaO in the burning zone of the second counterflow shaft is continuous, replaceable, adsorbing filtering bed for sucked in products of high-temperature gasification of utilized wastes of the first straight-flow shaft-gas generator. Required conditions of dioxins and furans thermochemical destruction are realized on CaO surface with provision of gasification products residence time in medium of alkali-earth metals CaCO₃ and CaO at temperature from +1,300 °C to +1,700 °C for more than 2 seconds with excess air α=1.08–1.2. CaO lime adsorbs on its surface and removes from both mines chlorine, fluorine, bromine and sulphur compounds converted into stable neutral compounds, thereby excluding reverse recombination of dioxins and furans, also binding heavy metals Pb, Zn, Cd, Hg with lime CaO, transforming into stable solid neutral compounds. Additionally, the charge composition provides gas permeability and mobility of the mixed-component charge, prevents the charge from hanging on the arches in the furnace shafts, recycled waste is crushed by grinding with lumpy carbonate material in the process of the charge layer descent in the gas generator shaft and the lining skull is cleaned from soot and crusts, gas, liquid fuel is used as fuel, and by transfer method and solid fuel. Method is carried out in a vertical two-shaft furnace containing service bins of recycled wastes, additives, lump carbonate material with fraction of 20 mm to 120 mm, bunker trestle with proportioners and conveyors for forming charge according to the recipe, charge feed conveyor, two upper loading devices with sealed sluices. Furnace comprises two vertical lined furnace shafts with heating, burning and cooling zones, connected by hollow lined transition channel-gas duct at the level between burning and cooling zones, two lower unloading devices, burners for natural gas, mixture of gases or liquid fuels, tuyere for secondary afterburning of gases of loading devices in transition channel, aspiration unit, smoke exhausters and air blowers, dust and gas cleaning facilities. Structurally, it combines two units: and second — shaft for counterflow calcination of lumpy carbonate material into commercial lime CaO and afterburning of generator synthesis gas, connected to each other by hollow lined transition channel-gas duct at the level between calcination and cooling zones. First shaft-gas generator is made with possibility of operation only in direct-flow mode of gas and charge movement from top to bottom, with upper arrangement of fuel and air supply burners, charge is loaded from above by transfer method and operation in combined mode of gasification of utilized wastes and burning of lump carbonate material included into composition of charge. Second shaft of counterflow firing is made with possibility of operation only in counterflow mode, loading from above by lumpy carbonate material with supply of fuel and air to its lower part by burners together with gasification products from upper loading devices, fed by the tuyere into the transition channel for mixing and secondary afterburning in the CaO layer of the second shaft. It has the possibility of overflow of products of gasification of wastes from the shaft-gas generator into the shaft of counterflow roasting through the hollow lined transitional channel-gas duct for supply of the entire volume of gasification products for secondary afterburning by suction in a layer of incandescent commercial lime CaO in the entire burning zone and heating of the second counterflow shaft. It has the possibility of evacuation of flue gases with dusty lime CaO reacted with pollutants by rarefaction of the smoke exhauster from the upper part of the second shaft of counterflow firing. It has the possibility of heating air supplied from below to the furnace shaft for lime cooling through unloading devices, and supply to the second shaft of counterflow firing for blowing.

EFFECT: improved environmental situation, cleaning of flue gases and elimination of recombination of dioxins and furans, high-efficiency recycling of halogen-containing wastes, simple design of a two-shaft furnace without the presence of moving parts in the high-temperature zone, recycling wastes by releasing commercial lime, which is a continuous replaceable filtering adsorbent, partial replacement of the main fuel with generator synthesis gas obtained from wastes during calcination of commercial lime, possibility of using gaseous or liquid fuel or solid fuel using an upper filling method.

3 cl, 4 dwg