Tags: 🅱️ Background and definitions | 🅰️ Analysis of fuel data

🅱️1️⃣ What is solid biomass?
🅱️2️⃣ What is the inorganic content (or “ash forming matter”) of biomass?
🅱️3️⃣ What happens to the inorganic matter during thermal conversion (combustion, gasification etc.)?
🅱️4️⃣ What is ash?
🅱️5️⃣ What are bed materials and combustion additives?
🅱️6️⃣ Which are the ash related problems in thermal processes for biomass fuels?
🅱️7️⃣ Can you suggest a couple of references to understand biomass fuels ash challenges?
🅱️8️⃣ Can you suggest standards to be considered for the fuel analyses?
🅱️9️⃣ Why to use BIOFACT?

🅰️1️⃣ BIOFACT-C: how the indicators are computed?
🅰️2️⃣ BIOFACT-C: how the indicators are validated?
🅰️3️⃣ BIOFACT-T how the indicators are computed and validated?
🅰️4️⃣ What is a calibration fuel?
🅰️5️⃣ When fuel data are not available, which information is used?
🅰️6️⃣ BIOFACT-O: how it works?
🅰️7️⃣ Is it possible to apply BIOFACT to Municipal Solid Wastes, construction wastes, hazardous wastes or liquid effluents?


🅱️1️⃣ What is solid biomass?

✅ Biomass is a heterogeneous matter originating from recently living organisms, such as herbaceous, woody, aquatic matter and some specific wastes, e.g. pulp industry residues or sewage sludges. Multiple outcomes, competitive or not, have been associated to biomass, for example: food and fodder, fibre, furniture and fuel.

🅱️2️⃣ What is the inorganic content (or “ash forming matter”) of biomass?

✅ All solid fuels contain an inorganic fraction, not combustible, which is constituted by inorganic elements, such as: Cl, S, K, Na, Mn, Cd, Cr, Zn, Si, Mg and many others. These inorganic elements are present in the fuel in different phases and minerals (e.g. silicates, oxides/hydroxides, sulphates/sulphides, phosphates, carbonates, chlorides, etc.).

🅱️3️⃣ What happens to the inorganic matter during the fuel thermal conversion (combustion, gasification etc.)?

✅ During thermal processing, the inorganic matter present in the fuel undergoes chemico-physical transformations, changing its association, form, phase and forming an etherogenours (solid, liquid or gaseous) matter called “ash”.

🅱️4️⃣ What is ash?

✅ Ash, the transformed inorganic matter, stays in the plant in solid/liquid phase or is released to the environment in gaseous phase. Ash can be splitted in bottom ash (or grate ash) and fly ash (or filter ash). Fly ash is composed by a fine (or aerosols) and a coarse fractions. The split bottom/fly ash is dependent on the fuel type, technology and plant operating conditions.

🅱️5️⃣ What are bed materials and combustion additives?

Bed materials are inert (at specific conditions) which are used to increase the inertia of the bed, in fluidized bed combustion, allowing to convert the fuel at lower temperatures (850-900°C), increasing the thermal efficiency and reducing the emissions (e.g. NOx) of the thermal system. Example of bed materials are: sand, feldspar, dolomite.

Additives are (usually) minerals injected in the plant (in solid/liquid/gaseous form), or premixed with the fuel, in order to capture critical inorganic elements (e.g. S, Cl, K) and promote specific interactions (e.g. to increase ash melting temperatures). Examples are: aluminosilicates (kaolin), Ca-based (gypsum), S-based (ammonium sulphate) minerals.

🅱️6️⃣ Which are the ash related problems in thermal processes for biomass fuels?

Here some:

⚠️ Ash agglomeration (fluidized beds): rapid formation of agglomerates (due to the stickiness of the ash and bed material particles) in fluidized beds, which causes improper fluidization till interruption of operations. Two agglomeration mechanisms are identified: coating induced and melt induced agglomeration. It happens already at low temperatures (< 800°C).

Agglomerates (photos for didactic purposes).

⚠️ Ash slagging: deposition of (partially) molten ash particles on the furnace water walls, bottom grid/roof, more in general on radiant heat exposed surfaces (high temperatures, e.g. > 1000°C).


Slag (photos for didactic purposes).

⚠️ Ash fouling. High-temperature fouling (around 1000°C) is the deposition condensed alkaline compounds on the banks in the upper and medium temperature section of the boiler (convective heat exposed surfaces). Low-temperature fouling (300-600°C) is the deposition (often solid particles) on the economizers banks of a boiler. Fouling deposits are often (partially) removed with sootblowers, cleaning devices which use steam or water.

Fouled pipes (photos for didactic purposes).

⚠️ Corrosion. High temperature corrosion (already at around 500°C, metal temperature) is a metal wastage mechanisms occurring in superheater sections, often related to chlorine and heavy metals. Low temperature corrosion, in convective sections (e.g. around 200°C), is mainly related to condensation of acidic compounds (e.g. S, Cl).

Corroded pipes (photos for didactic purposes).

⚠️ Erosion/wear: metal wastage, e.g. due to the presence of hard compounds in the fuel ash and increasing with increased gas flow velocities in the installation.

⚠️ Flue gas conditioning disturbances: ash can influence the operation of the flue gas cleaning systems, e.g. by deactivation of catalysts or disturbance of the nominal performance of the components to reduce the pollutants in the flue gases.

Those problems affect the thermal efficiency of the plant, and increase maintenance costs therefore reducing the system’s profitability. Here enclosed some videos about boilers inspections and cleaning (once the maintenance is required).

Inspections

Slightly slagged biomass boiler (1100°C)

Heavily slagged SH in straw boiler

Heavily slagged SH in bagasse boiler

Cleaning

Soot-blowing 720 MW coal boiler

Soot-blowing SH in WTE boiler

🅱️7️⃣ Can you suggest some references to understand biomass ash challenges?

✅ I recommend the keynote lecture from Prof. Mikko Hupa, delivered at the 36th International Symposium on Combustion (by The Combustion Institute), in August 2016.

🅱️8️⃣ Can you suggest standards to be considered for the fuel analyses?

✅ Helpful standards concerning analytical analyses are: moisture (EN 14774), ash content (EN 14775), C, H, N; S, Cl, F (EN 15104; EN 15289), ash oxides (CaO, K2O, SiO2 etc.) (EN 15290, by XRF or better, ICP), volatile matter (EN 15148), calorific value (EN 14918), ash fusibility (e.g. deformation temperature) (CEN/TS 15370, ISO 540), easily (water) soluble K, Na e.g. KpH3, NapH3 (EN 16995).

Further material
Standards’ catalogue ISOStandards’ catalogue EN

🅱️9️⃣ Why to use BIOFACT before/together with other characterization tools?

✅ BIOFACT provides, at low cost, a confidence on results comparable to experimental pilot testing. It is easy to use and rapid to apply for a quick fuel screening and analysis.

The best use of BIOFACT is togheter with more expensive tools, in a funnel strategy, for example: choose 5 fuels on 10 initially selected, based on BIOFACT results, then perform detailed  simulations with CFD to choose 2 fuels on the 5 selected, finally perform pilot/full scale tests on the 2 selected fuels to finalize the choice. Analytical tools (TGA/DSC, SEM/EDX and chemical fractionation) are useful complement.

🅰️1️⃣ BIOFACT-C: how the indicators are computed?

✅ The indicators are computed with theoretically based predictive models, based on the fuel constituents, calibrated with a set of experimental data.

⚠️ Please note that CO, dioxines and furans emissions, organically derived PM (Particulate Matter) such as soot or char, depend much more on the process (and its design) than on fuel characteristics (e.g. see ref. or ref2.). If looking at operational aspects in combustion, it is suggested to check the deliverables of the BeReal project.

🅰️2️⃣ BIOFACT-C: how the indicators are validated?

✅ The BIOFACT-C results are validated with experimental data from the scientific literature (lab-, pilot- and full-scale tests) and from experience from the industrial partners.

🅰️3️⃣ BIOFACT-T how the indicators are computed and validated?

✅ The fuel – technology matching is built linking fuel properties with requirements from conversion technologies. The module is validated with return of experience from the industrial partners.

🅰️4️⃣ What is a calibration fuel?

✅ A calibration fuel is a fuel for which the behaviour is well known, e.g. for which plant results are available. The calibration fuel helps to interpret the BIOFACT results when comparing unknown fuels with the calibration one (relative evaluations).

🅰️5️⃣ When fuel data are not available, which information is used?

✅ When fuel properties are not available, data are retrieved from databases or own data are used.

🅰️6️⃣ BIOFACT-O: how it works?

✅ The simulation is based on commercial softwares and validated with pilot tests at scientific/industrial partners.

🅰️7️⃣ Is it possible to apply BIOFACT to Municipal Solid Wastes, construction wastes, hazardous wastes or liquid effluents?

✅ BIOFACT is primarily built (and validated with) solid biomass fuels (wood, shaving and pruning, wood wasted and forest residues, pulp residues, shrubs, woody/herbaceous crops, agro/food-residues, etc.). It can be applied to waste wood, SRF and RDF as an explorative approach.


Pose your question by sending a message to defusco.biofact@gmail.com.
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