Stepped Hearth incinerators (click here) have multiple hearths in cascading steps. Waste is loaded by a ram feeder and begins combustion on the first level. As new waste is loaded on the first level, it pushes partially burned waste to the next lower step or level. A tumbling action results, exposing more surface to the combustion chamber and ensuring more complete destruction of the waste.
Each successive charge moves waste to the next lower level. Automatic de-ashing systems can be used to remove the ash without needing the system to cool, so true continuous operation can be achieved.
Due to the methane content of landfills and the ever increasing need for landfill lands, the incinerator takes shape as an important process to handle solid industrial waste.
The stepped hearth incinerator has several burning chambers, whereby one is hotter than the next in exposing surface area in tumbling and prolonging the burning process to completion of all solid waste.
Both the ash and the emissions of greenhouse gases into the troposphere is an issue. The question regarding the incineration of waste to produce energy is, will the offset of producing CO2 rather than methane in landfills be better in the long view to the troposphere and reducing anthropogenic footprint of Earth's physics.
The technology to capture CO2 from these processes are taking shape. The most innovative currently is in the Netherlands.
Patrick Huttenhuis, Andy Roeloffzenb , Geert Versteega. CO2 capture and reuse at a waste incinerator. Energy Procedia 86 ( 2016 ) 47 – 55
Twence is a waste processing and energy generation company (click here) located in the eastern part of the Netherlands. In the Twence plant waste is incinerated and in this process the waste is converted to valuable products like heat and power. In the flue gas produced from this Waste-To-Energy (WTE) plant a significant amount of CO2 is released to the atmosphere. Recently a new innovative process developed by Procede Gas Treating B.V. has been commissioned at line 3 of the Twence plant. In this process CO2 emitted to atmosphere, is scrubbed from the flue gas and this CO2 is used for mineralization. The CO2 is converted in an innovative new reactor configuration from sodium carbonate directly to sodium bicarbonate (SBC). The produced SBC slurry will directly be used at the WTE plant to purify the flue gas stream, before it is released to atmosphere. Due to the implementation of this process, which is unique in the world, the carbon footprint of the Twence installation is reduced. The new SBC plant produces 8,000 tons of sodium bicarbonate annually and to produce this amount of SBC 2,000 ton per year CO2 is captured from the flue gas.
Another venture in Norway seeks to deposit captured CO2 into the deep ocean where it will ultimately form hydrates. They also see CO2 capture as a method to bring oil and gas out of wells that have become low in gas pressure.
While these efforts by many countries pursuing carbon capture may prove to be only a temporary solution. The upper oceans are known to be melting methane hydrates. If that is the case the deep ocean can be an answer, but, in order to deposit the gas in the deep ocean, the gas has to remain either gaseous or liquid until the delivery point.
"Gas hydrates for deep ocean storage of CO2" (click here)
