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In the following article we talk about a very important practice in fumes treatment: the neutralization (inertization) of fumes. What does this process consist of ? When and why is it realized? Let’s find out together!
Inertization is a practice that is carried out in filtering plants for fumes treatment and it is realized to protect filtering elements from acid substances and unburnt particles. Usually, the product used in this process is calcium hydroxide (also known as slaked lime or hydrated lime), also called lime or quicklime, chemical formula Ca(OH)2. Lime results from dry hydration of calcium oxide. Hydrated lime looks like a white powder (lime powder) that, due to its chemical characteristics, is able to reduce the acidity present in the fumes (it is used also in agriculture and in other contexts).
Using lime we can:
This neutralizing process, therefore, led to a series of important advantages, but what are the fields of application?
As we have seen, it is used for the treatment of high temperature fumes that, for example, can be generated by biomass plants, thermoelectric power plants, incinerators and from the treatment of hazardous and non-hazardous waste.
We have analyzed the general characteristics of this process (definition, product used and main advantages), but how does the inertization of fumes work? To understand this, we can analyze the following figure, which represents a typical fume treatment plant complete with inerting system with hydrated lime.
As we can see, the air flow is conveyed into the multi-cyclone Turbovortex® which is suitable as a pre-filter for dust present in the fumes.
This first step, however, may not be necessary for some types of plants as it is closely linked to the nature of the pollutants present: in case of high dust loads, the multi-cyclone allows to protect the main filtering unit(s) from excessive working conditions. After this first phase, the polluted flow passes through the reactor where fumes come into contact with calcium hydroxide. This step is very important because, in order to be effective on fume’s acidity, it is important to gain a very good mixing and an adequate contact time between the two elements.
As shown in the previous drawing, the reactor is connected to a storage silos which, by means of a dosing system, supplies the necessary quantity of lime. After fumes are homogeneously mixed with lime, the flow is conveyed to the bag filter where the particulate is treated.
Large systems, like the one in the figure, can also be equipped with other elements such as:
Smaller plants, usually, are not equipped with pre-heating systems so, during start-up phase, bags are covered with lime to reduce their permeability and filter is by-passed until fumes have reached target operating temperatures, usually higher than 150/160 °C and below 230 °C.
When a bag filter is designed for high temperatures, it is very important to choose filtering media that are most suitable for the process type and operating temperatures. In the following table we show some details regarding filtering media for high temperatures:
TYPE | WEIGHT | TEMPERATURE |
Bag with polyphenylsulfide needle felt on polyphenylsulfide support | 550 g/m2 | Max 150° with peaks of 160° |
Bag with polyphenylsulfide needle felt on PTFE support | 550 g/m2 | Max 160° with peaks of 180° |
Bag in glass fibre with microporous membrane | 750 g/m2 | 250° with peaks of 260° |
Bag with PTFE needle felt on PTFE support | 750 g/m2 | 250° with peaks of 260° |
How does they work? Which benefits they imply? Check out our new article!
How does they work? Which benefits they imply? Check out our new article!
How does they work? Which benefits they imply? Check out our new article!
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