【Monthly Topic】Discussion on the issue of wastewater gasification
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For chemical wastewater containing large amounts of organic matter, the complexity of the wastewater treatment process and the high treatment costs are indeed significant problems. Converting organic matter through high-temperature gasification represents a very promising prospect. Previously, some people have also proposed practical innovations such as using coking wastewater to quench coke for the production of syngas, but the results are still unknown! There is no theoretical problem with using organic wastewater in water-coal slurry gasification for slurry production, and there are also industrial applications for this. Could everyone discuss the feasibility and theoretical analysis of injecting organic wastewater into gasification furnaces, taking various furnace types into consideration? There are rewards for participation!
In my opinion, aside from the water-coal slurry gasifier, the high-temperature thermochemical conversion method that involves directly injecting organic wastewater into the gasifier does not conform to the principle of hierarchical energy utilization, nor does it align with policies aimed at energy conservation and low carbon emissions. When organic wastewater at room temperature or at a certain temperature is injected into the gasification furnace, the vast majority of water present in it rapidly heats up and evaporates into steam. Under the high temperatures in the gasification furnace, this steam further heats up to the gasification temperature. During this process, a large amount of heat is required to supply the latent heat needed for the water to evaporate into steam, as well as the sensible heat required for both the heating of the water and the heating of the steam; this heat is high-quality heat. This heat needs to be provided by burning more coal, consuming more oxygen or air, which in turn generates more CO2. The H2O that remains unreacted in the gasifier exits the gasifier along with the gas; after heat recovery and cooling, the sensible and latent heat carried by the H2O cannot be fully and effectively recovered or utilized. Taking fluidized bed or circulating fluidized bed gasification as an example, heating 1 kg of organic wastewater to a gasification temperature of around 950–1000°C requires approximately 4.4 MJ of heat. In waste heat recovery, the sensible heat of H2O can be recovered; regardless of the medium used for this purpose, the temperature of the medium after heating remains lower than the temperature of the gas coming out of the gasifier, resulting in an increase in entropy. During the gas cooling stage, circulating cooling water is used to cool the gas; even if the heat absorbed by this circulating cooling water is utilized through a heat pump or other means, the low water temperature results in a low quality of this energy, leading to poor efficiency in its utilization.
The opposing view will surely argue that the difficult-to-treat and biochemically resistant components in the wastewater are vaporized and decomposed at high temperatures, which in turn saves on the costs associated with wastewater treatment.
Water vaporization produces steam that participates in the gasification reaction; organic materials burn or react to produce gases such as CO2 and water, which can then be used for carbon-reduction gasification. It seems feasible! Come to learn*! !