Problem

Today, almost all household waste collected over a long period is located in landfills and emits the volatile components contained in it (about 55%). This factor has a great impact on the pollution and contamination of the environment.

Waste incineration is a complex technology that involves a large volume of production cycles starting with the collection and sorting of waste ending with the disposal or further use of solid combustion products. Currently, the following types of incinerators are used in Japan as well as in the developed countries of America and Europe:

• mechanical furnaces with grate grate;
• the fluidized bed furnace;
• pyrolysis or gasification furnaces.

The most relevant issue in the process of incineration is the environmental friendliness of the technology. Thus, during the combustion process up to 30% of solid waste from the initial amount of raw materials (ash, slag, dust) and a significant amount of flue gases are formed.

Flue gases mainly consist of carbon dioxide and nitrogen oxides, sulfur, chlorine-and hydrogen fluoride, heavy metal compounds (cadmium, lead, mercury). Special attention is paid to emissions of toxic furans and dioxins. However quantitative incineration produces significantly less of them than uncontrolled fires in landfills and private bonfires.

Solid waste in case of poor-quality or incomplete incineration requires disposal at industrial landfills while properly selected technology allows you to export waste to landfills of solid waste disposal or organize their further use as additives to building materials in the construction of industrial structures or expensive.

The methods of incineration of garbage

1. Technology of waste incineration in mechanical furnaces with a grate

Initially, garbage trucks pour waste into a storage bin where they are sorted, ground, rammed and processed by special teams. From there, the solid waste enters the furnace and burns on the grate at a temperature of 600-1300 degrees.

Gorenje products are filtered out in the lower chamber of the boiler, the outgoing flue gases are sent up to the waste boiler and the filter system. Further, the ash and slag are cleaned of heavy metals and the resulting products are used as a filler in the construction of roads. As Gorenje flue gases after the combustion process they initially come through a waste heat boiler which uses the thermal energy of the flue gases to heat the mains water, isothermal oil, or to produce saturated / superheated steam. Then it passes through an electrostatic filter that captures ash dust and a bag filter system where the flue gases are completely cleaned of fine dust and other particles going to the chimney.

The production process is controlled by sensors that show the concentration of harmful chemical compounds in the plant’s emissions in real time.

In addition, the technology of deeper utilization of outgoing flue gases can be used due to the installation of polymer heat exchangers that can cool the flue gases to a temperature of 30-40 °C. This installation allows you to increase the overall thermal efficiency of the boiler unit.

Advantages of waste incineration technology in mechanical furnaces with grate

Picture 1 – Waste incineration technologies in mechanical grate furnaces

2. Technology of waste incineration in mechanical fluidized bed furnaces

The technological process is almost the same as in furnaces with a grate. The main difference is the direct method of incineration: household waste is burned in a furnace with a constant supply of air in a layer of inert material, resulting in a fluidized or fluidized bed.

The advantages of the technology of waste incineration in a mechanical fluidized bed furnaces

1. Net emissions of both flue gases and solid substances due to the higher completeness of solid waste incineration (almost no chemical and physical underburning), which provides a positive environmental effect.
2. Full utilization of the potential energy of the garbage.
3. The ability to obtain electrical and thermal energy by burning solid waste.

If we compare this method of incineration with the previous one the energy consumption is higher and the cost of purchasing inert material is required. In addition, the fractional composition of solid waste is subject to strict requirements, and the process of deep sorting of garbage is also necessary.

3. Gasification of solid household waste

Gasification is the conversion of the organic part of a solid or liquid fuel into combustible gases under high-temperature heating with an insufficient amount of oxidizer for complete combustion: oxygen, air, water vapor, CO2 or more often a mixture of them.

The gasification process begins with the preparation of raw materials, including their proper storage in the warehouse. From the warehouse, the raw materials are fed in batches to the hopper-receiver, and from there it gets to the augers, where it is subjected to the drying process. As a result, the raw material is heated to the required temperature due to the heat coming from the reactors to get rid of excess moisture.

The dried source material is fed through conveyors to a multi-stage reactor of a thermolysis device for flame-free gasification at a temperature of 400 to 950 °C.

During the gasification reaction, synthesized gas is produced, which in the enrichment section is purified from minor impurities and by-products through a system of scrubbers, separators, tanks and superchargers. After passing through all the stages of purification, the process gas flow enters the gas storage facility, which serves not only for receiving and storing synthesis gas, but also for buffering the synthesized gas. This ensures a continuous supply of power to the additional burners of the gas reactors.

The resulting synthesis gas has a high caloric content, comparable to the caloric content of natural gas. Accordingly, it can be used in power boilers and/or as a feedstock for the chemical industry.

Advantages of solid waste gasification technology

1. Eco-friendly process with zero impact on the environment due to the high combustion temperature of the synthesis gas.
2. The ease of use of the synthesis gas.
3. The ability to process industrial waste, as well as to obtain electrical and thermal energy by burning household waste.

This complex technological process requires strict compliance with regulations and high energy consumption for pre-drying of garbage.

4. Technology of high-temperature processing of solid household waste in slag melt

This technology is the combustion of solid waste in a slag melt at a temperature of more than 1400 °C which allows us to fully dispose of waste with zero or positive impact on the environment.

It is developed on the basis of a metallurgical unit for liquid-phase reduction of iron (Vanyukov furnace). The furnace is made in the form of a caisson shaft with heating and blowing devices located above the hearth. The walls of the furnace are water-cooled panels, and two rows of tuyeres are installed on the sides:

• the lower ones are used for bubbling the slag melt with oxygen-enriched air (up to 50-70 %);
• the upper ones are used to supply oxygen and / or air for afterburning furnace gases to the products of complete oxidation.

To form the initial bath granulated blast furnace slag obtained during waste processing is used. During operation, it is formed from the mineral part of the waste (the coarse part of the dust) and the flux which corrects the chemical composition of the slag and ensures its liquid mobility at operating temperatures.

Advantages of high-temperature solid waste recycling technology

1. Positive environmental effect: zero impact on the environment due to the high temperature in the furnace furnace and the slagging of mineral waste, the absence of dioxins and furans in emissions.
2. The ability to burn garbage without pre-sorting.
3. Technological flexibility – co-processing of solid waste with combustible industrial waste in order to save fuel.
4. Recycling of industrial waste: it can be used for the production of building materials, mineral fibers and road surface filler.
5. Reduction of variable costs due to the absence of working personnel who are engaged in sorting garbage.
6. The ability to obtain electrical energy (steam turbine and ORC-turbine) and thermal energy (hot water, heating, technological needs) by burning solid waste.

It is worth noting that the process of high-temperature processing of solid waste is energy-intensive, since the duration of heating the furnace from the cold state and melting the melt in it is from 4 to 6 days.

Decision

Aquaecology has a wide range of developments on the issue of waste incineration with partners from Russia, Europe and China. We develop comprehensive solutions that on the one hand allow us to find a balance between energy intensity, reliability and availability of technology and on the other – have a zero or positive impact on the environment.

Our company qualitatively analyzes and implements the most suitable waste incineration technology for each specific case, depending on the Customer’s requirements, as well as on the actual operating conditions. In Gorenje, we are ready to offer a full cycle of waste management – sorting, recycling of individual useful fractions, thermal processing of waste and recycling of the resulting combustion products after cleaning