Method for clean and low-carbon in-situ disposal of waste incineration fly ash

1 . A method for clean and low-carbon in-situ disposal of waste incineration fly ash, using a system for clean and low-carbon in-situ disposal of waste incineration fly ash comprising a waste incineration system and a fly ash disposal system, wherein the fly ash disposal system is coupled with the waste incineration system of a waste incineration power plant in-situ, the waste incineration fly ash and a flue gas are disposed nearby, and flue gas residual heat and self-generated electricity of the waste incineration power plant are used for providing energy demand and in-situ energy supply for the clean and low-carbon in-situ disposal of waste incineration fly ash;

wherein the waste incineration system comprises a waste incinerator, a flue gas purification system, a bag dust collector, and a chimney connected sequentially by a flue; heat exchange equipment is arranged in a flue for recovering heat energy from flue gas; a waste activated carbon adding port is arranged at a front end of the waste incinerator, an original fly ash outlet is arranged at a bottom of the bag dust collector, and a hot flue gas outlet is arranged at a lower middle part of the chimney;

wherein the fly ash disposal system comprises a water washing system, a mechanical vapor recompression system, and a dioxin removal system;

wherein the water washing system comprises a water washing device and a press filtering device; the water washing device is provided with an original fly ash inlet, a cold flue gas inlet, a tail gas outlet, a sodium carbonate adding port, and a condensed water inlet; the water washing device is connected to the press filtering device, and the press filtering device is provided with a water washing fly ash outlet and a cold water washing solution outlet;

wherein the dioxin removal system comprises a heating device, an activated carbon adsorption device, and a heat pump system; the heating device is provided with an air and nitrogen inlet, a water washing fly ash inlet, a wet tail gas outlet, a to-be-desorbed tail gas outlet, and a treated fly ash outlet, and the to-be-desorbed tail gas outlet is connected to the activated carbon adsorption device; the activated carbon adsorption device is internally filled with activated carbon and is provided with a waste activated carbon discharge outlet and a thermal desorption tail gas outlet; the heat pump system is configured to provide heat to the heating device and is provided with a hot flue gas inlet and a cold flue gas outlet, and the wet tail gas outlet of the heating device is connected to the hot flue gas inlet;

wherein the mechanical vapor recompression system comprises a crystallizer, a heater, a vapor compressor, a circulating pump, a centrifuge, and a condensed water pump, and is provided with a hot water washing solution inlet, a condensed water discharge outlet, and a salt crystal outlet;

wherein the original fly ash outlet of the bag dust collector is connected to the original fly ash inlet of the water washing device through a conveying channel, the water washing fly ash outlet of the press filtering device is connected to the water washing fly ash inlet of the heating device through a conveying channel, and the waste activated carbon discharge outlet of the activated carbon adsorption device is connected to the waste activated carbon adding port of the waste incinerator through a conveying channel; the hot flue gas outlet of the chimney is connected to the hot flue gas inlet of the heat pump system through a pipeline, and the cold flue gas outlet of the heat pump system is connected to the cold flue gas inlet of the water washing device through a pipeline; the cold water washing solution outlet of the water washing device is connected to heat exchange equipment in the flue through a pipeline, the heat exchange equipment is connected to the hot water washing solution inlet of the mechanical vapor recompression system through a pipeline after heat exchange; the condensed water discharge outlet of the mechanical vapor recompression system is connected to the condensed water inlet of the water washing system through a pipeline;

wherein the method comprises

(1) sending original fly ash collected by the bag dust collector to the water washing device of the water washing system, and introducing cold flue gas that has been heat exchanged by the heat pump system, wherein alkaline substances and heavy metals in the original fly ash undergo carbonation reaction with carbon dioxide in the flue gas; when a pH value of a water washing solution is less than 7, stopping introducing the flue gas and adding sodium carbonate to adjust the pH value to between 9 and 10; and the cold flue gas is directly discharged from the tail gas outlet of the water washing device after the carbonation reaction;

(2) sending a suspension obtained by water washing to the press filtering device for press filtration to achieve solid-liquid separation, wherein the water washing solution of (1) is sent to the heat exchange equipment of the waste incineration system for preheating, and a solid waste incineration fly ash washed with water is sent to the heating device of the dioxin removal system for dioxin removal treatment;

(3) enabling a pre-heated water washing solution having a temperature of 70-80° C. to enter the mechanical vapor recompression system and undergo multi-effect staged evaporation to obtain salt crystals and condensed water, wherein the salt crystals are recycled for resource utilization, while condensed water is sent to the water washing device for fly ash washing; and

(4) enabling the original fly ash washed with water to undergo drying and thermal desorption in the dioxin removal system,

where during the drying, a temperature in the heating device is controlled at 100-110° C. for 10-12 hours; at this time, the heat pump system introduces hot flue gas from the chimney and achieves heat supply by recovering sensible heat and latent heat contained in the flue gas; meanwhile, wet tail gas generated during a drying process is sent to the heat pump system by blowing in air to further recover latent heat of water vapor; the treated wet tail gas is sent to the inlet of the heat pump system, and mixed with the hot flue gas for heat supply;

wherein during the thermal desorption, a temperature in the heating device is controlled at 200-350° C. for 1-2 hours; at this time, a thermal desorption tail gas generated during the drying process is sent to the activated carbon adsorption device by blowing in nitrogen, dioxins contained in the thermal desorption tail gas are adsorbed by activated carbon; a waste activated carbon generated by adsorption is sent to a feed adding inlet of the waste incinerator for high-temperature degradation of the dioxins through combustion; a tail gas after thermal desorption disposal is sent to an upper part of the chimney to achieve clean emission; and the original fly ash after thermal desorption disposal is discharged from a bottom of the heating device for further resource utilization.

2 . The method according to claim 1 , wherein the waste incineration system is located in a waste incineration power plant, the heat exchange equipment in the flue is connected to a steam turbine through a steam pipeline, the steam turbine is connected to a generator set; and the generator set is connected to electrical equipment in the fly ash disposal system through a cable, and uses self-generation of the waste incineration power plant to achieve power supply.

3 . The method according to claim 1 , wherein the heat pump system is further provided with a condensed water discharge outlet, and the condensed water discharge outlet of the heat pump system is connected to the cold water washing solution outlet of the water washing device through a pipeline.

4 . The method according to claim 1 , wherein the chimney is provided with a partition device that can adjust an opening degree, the hot flue gas outlet of the chimney is located below the partition device; a thermal desorption tail gas inlet is arranged above the partition device, and is connected to the thermal desorption tail gas outlet of the activated carbon adsorption device through a pipeline for achieving clean tail gas emission.

5 . The method according to claim 1 , wherein the heat exchange equipment is at least one of a superheater, an economizer, or an air preheater; and a water washing solution preheating device is arranged inside the heat exchange equipment, and is separately connected to the cold water washing solution outlet of the water washing device and the hot water washing solution inlet of the mechanical vapor recompression system through pipelines.

6 . The method according to claim 1 , wherein the condensed water discharge outlet of the mechanical vapor recompression system is also connected to a condensed water discharge pipeline.

7 . The method according to claim 1 , wherein the condensed water generated by the heat pump system during heat exchange is sent to the water washing device for recycling as a water washing solution.

8 . The method according to claim 1 , wherein a flow of the flue gas entering the fly ash disposal system is controlled by adjusting an opening degree of a partition device in the chimney according to operating conditions of the heat pump system and the water washing system, and excess flue gas is discharged from the chimney.

9 . The method according to claim 1 , wherein a generator set of the waste incineration power plant is configured to power the electrical equipment in the fly ash disposal system.