Characterization of physicochemical and combustion properties of densified fuels

As energy prices continue to rise and concerns about the environmental impact of fossil fuel
depletion and traditional biomass (i.e. firewood) grow, an increasing number of households
and commercial businesses are seeking alternatives. One such alternative is densified fuels
from biomass waste, which can be used for cooking or heating. But did you know that not
all fuels are produced equally in terms of their quality? Some burn more efficiently, last
longer, produce less smoke, and produce less ash. So, how can we determine the quality of
these solid fuels? Before being used or marketed, densified fuels typically undergo a series of
tests to evaluate their properties, including assessments of durability, moisture content,
calorific value, among others. These tests ensure that densified fuels are efficient, safe, and
eco-friendly. In this article, we will explain why testing fuel is essential, when these tests are
performed, and, most importantly, how they are conducted. We’ll discover together that
behind every solid fuel lies a gold mine!

1. Why is it important to characterize the properties of densified solid fuels?

• Ensuring high-quality densified fuels
  The quality of a fuel is determined by several properties, including its density, water and
  impact resistance indexes, moisture content, ash content, calorific value, and combustion rate,
  for instance. Without thorough characterization, it is impossible to ensure consistent quality,
  which directly impacts the product's energy efficiency and market acceptance. Additionally,
  producing high-quality fuels aids in storage and handling while also reducing transportation
  costs.

• Meeting technical standards and regulatory requirements
  The marketing of densified fuels is governed by standard norms (i.e. ISO 17225, for instance)
  which specify value ranges for various properties, including calorific value, ash content, and
  size of solid fuels. The characterization of these fuels indeed allows to verify that the end
  products meet the standard norms.

• Optimizing the production operating parameters
  By analyzing the properties of densified fuels produced under various conditions (such as
  pressure, temperature, binders, if the carbonized raw biomass is considered, and particle size,
  among others), the machine operator can adjust their processes to maximize their quality.

• Improving end-user acceptability
  Parameters such as durability, ease of ignition, smoke emissions, and residual ash levels
  significantly impact user satisfaction. Analyzing these properties helps to produce
  pellets/briquettes that perform better and are more eco-friendly.

2. When should characterization be carried out?

• Before solid fuel production (feedstock characterization)
  Before solid fuels are produced, it is essential to assess the properties of the raw materials.
  Key parameters to evaluate include moisture content, biochemical composition (specifically lignin, hemicellulose, proteins and starch), particle size distribution, ash content, volatile matter content, and calorific value. These factors directly influence the choice of densification technology and help to predict the quality of the final product.
• During the process development test: In this stage, any modifications or adjustments made to the process, such as changes in biomass type, compaction pressure, or the use of binders, should be followed by an evaluation of the properties of the produced briquettes. This assessment is necessary to elucidate the interactions between operating parameters and fuel quality.
• After fuel production (characterization of the final product) once the fuel has been produced, regular quality control tests are conducted. This stage is essential for detecting any deviations in the process, comparing different batches, and providing technical data to users or distributors.

3. How to characterize fuel properties?

The analysis of the properties of densified fuels can be categorized into four main areas:
physical, mechanical, chemical, and thermal properties.

• Physical properties
  This stage involves determining the apparent density, which is the ratio of the briquette's mass
  to its volume, as well as the water content of the briquettes, following E871 ASTM standards.
• Chemical properties
  This analysis measures the ash content (in accordance with ASTM D1102), volatile matter
  (ASTM D3175), fixed carbon (calculated by difference), and calorific value (which is
  measured by using a calorimetric bomb).
• Mechanical properties
  This assessment evaluates the briquettes' water resistance, indicating their ability to absorb
  moisture when exposed to wet environments, as well as their impact resistance, reflecting the
  durability of the briquettes when shifting from one location to another or discharging them
  from trucks onto to ground.
• Thermal properties
  This includes measuring ignition time, which indicates ease of ignition, along with
  combustion time and rate.

To conclude, densified fuel characterization is an essential step in ensuring the quality of these
biofuels. It not only helps us comply with regulatory requirements but also enables to
optimize the production process and meet user expectations. This process is conducted at
various stages, from raw material to final end product, and employs a range of rigorous scientific methods. For researchers, engineers, and producers, mastering this characterization
process is vital for the sustainable recovery of lignocellulosic biomass waste and for reducing
dependence on conventional fuels.