When the Flame is not the problem
In the case of porous organic materials (such as dried sludge from wastewater treatment plants, granular biomass, generic organic solid waste, etc.), the risk almost never originates from an open flame. It begins earlier, silently, in the form of spontaneous and initially mild self-heating.
This phenomenon is also known as smouldering: a slow, flameless combustion process that can last hours or even days before becoming clearly visible.
And this is precisely what makes it dangerous: by the time it is detected, the process is already underway.
Smouldering: a known but difficult-to-control phenomenon
Dried sludge is particularly prone to smouldering because it combines:
● porous structure
● presence of potentially reactive organic material
● residual moisture
● possibility of prolonged contact with oxygen
In industrial plants, this translates into:
● problems in dryers
● critical issues during storage
● fire hazard
● operational management challenges
Understanding when and why the process is triggered is the only way to prevent it.
The limits of traditional approaches
Studying smouldering is not straightforward: the phenomenon occurs in large, heterogeneous masses, whereas most laboratory techniques work on small, homogeneous samples (DSC, TGA, etc.) to investigate thermo-chemical-physical properties.
This scale gap often makes the following poorly representative:
● standard thermogravimetric test results
● tests conducted on just a few milligrams of material
● purely theoretical models
To bridge this gap, a different experimental approach is required.
Industrial Macro TGA: bringing industrial reality into the laboratory
To address this issue, K-INN Tech developed a dedicated experimental apparatus: the Industrial Macro TGA.
This system allows:
● testing of hundreds of grams of material (up to one kilogram, depending on material density)
● operation under controlled temperatures and atmospheres
● continuous and simultaneous monitoring of weight loss, temperature, and reaction products
Temperature is measured:
● at the core of the material, where ignition typically originates
● at various points in the surrounding atmosphere, enabling precise correlation between reaction and environmental conditions
The sample is placed in a perforated crucible, allowing oxygen (or other atmospheres) to effectively permeate the solid matrix.
What the experimental results show
With this setup, the self-heating phenomenon of porous organic materials can be reproduced in a controlled laboratory-scale environment. The results show that:
● the amount of oxygen governs reaction rates: the more oxygen available, the faster the heating
● low-temperature reactions are chemical in nature, not biological: this is a crucial aspect often misunderstood in industrial practice
● particle size distribution plays a determining role: higher specific surface area increases the risk of ignition
These elements enable a shift from reactive management to data-driven prevention.
From diagnosis to operational prevention
Based on Industrial Macro TGA testing, it is possible to:
● assess the ignition tendency of sludge and granular organic materials
● compare different process and storage conditions
● define operational procedures to reduce or eliminate self-heating risk, thereby improving process safety
● manage and harness, in a controlled manner, the thermal energy produced by the phenomenon
Conclusions
Smouldering is not an unpredictable event: it is a physico-chemical phenomenon that follows precise rules, identifiable through proper monitoring of the specific material and process.
Measuring what happens before a real fire develops is the only way to prevent it.
If you operate dryers or handle dried sludge and/or porous organic materials, understanding the real self-ignition risk in your processes or storage systems requires a representative-scale experimental evaluation. Write to us at info@k-inntech.it
