Operational excellence in biomass energy plants

Operations costs, in biomass energy plants, depend on input feedstock quality. To optimize operations and find economic optima, three preliminary steps could be considered.

1) Fuel costs [€/MWth], how do they vary depending on the fuel quality?

Fuel Such as Cost variation (average)
Easy Sawdust, whole tree chips 100%
Average Bark, stumps, forest residues 67%
Challenging Demolition wood, plywood residues 56%
Very challenging Agrofuels, SRF 44%

Note: figures, averaged for solid fuels (Europe).

2) O&M costs [€/y]: chemicals (~20%), electricity (~20%), maintenance (~60%), how do they vary depending on the fuel quality?

Fuel Such as Cost variation (average)
Easy Sawdust, whole tree chips 100%
Average Bark, stumps, forest residues 124%
Challenging Demolition wood, plywood residues 154%
Very challenging Agrofuels, SRF 194%

Note: Values averaged for thermal energy generation (50-500 MWth, fluidized beds boilers), including data from virtual.vtt.fi/virtual/combust.

3) Evaluate the economic feasibility balance including the reduction of fuel costs and the increased O&M costs for the specific installation.


As a summary, first, it is necessary to classify fuels according to operational risks (not a trivial task: even the same fuel type could be Easy/Average/Challenging/Very challenging depending on its origin and properties). It might be smart to use predictive analyses (e.g. BIOFACT-C) and previous return of experience.

Second, based on such 3-step preliminary analysis (and the technical constraint of the specific installation with its components), it is possible to assess with which new fuels it would be possible to operate the energy plant.

How do you perform your operational excellence analyses? Are you expanding the capabilities of your technologies? Any considerations is welcomed.

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Torrefaction of biomass: does it reduce the risks of fuel ash slagging, fouling and corrosion in combustion?

Introduction

The torrefaction of biomass is a thermal process performed at 240-300°C to upgrade a raw material to an output solid with increased energy density (MJ/kg), more homogenous and less vulnerable to biodegradation. The fuel obtained after torrefaction has properties which allow an easier handling and improved thermal performances in combustion. Beside physical properties, the fuel chemical composition is changed. Such changes influence the inorganic matter content, composition, association, and therefore the operational risks in combustion due to inorganic matter.

Methodology

With this brief work, the potential of torrefaction to reduce the risks of fuel slagging, fouling and corrosion in combustion (due to the changes in the inorganic matter), by using a fuel characterization tool called BIOFACT, is verified. The analysis only refers to fuel composition. Specifically, the module to characterize the fuel for combustion BIOFACT-C is used. This module considers (v. 1.2): fouling, agglomeration/slagging, corrosion (high temperature), HCl emissions, particulate matter (PM10), SOx emissions. For each of such risks considered, the tool computes a semi-quantitative evaluation from 0 (lowest risk) to 100 (highest risk).

Two fuel samples are analyzed, considering the properties of the fuels before and after torrefaction, at different temperatures:

  • Eucalyptus wood, raw and torrefied at 220, 250, and 280°C
  • Birch wood, raw and torrefied at 240 and 280°C
Results

The results are presented below.


Depending on the fuel, torrefaction could influence the risk of operational issues related to the fuel ash. Emissions (SOx, HCl) and high temperature corrosion might be reduced, depending on Cl and the other ash constituents. Nevertheless, based on the preliminary analysis – valid for those specific fuels – fouling and agglomeration/slagging are not reduced. PM10 emission risk could increase, due to the higher relative concentration of some PM forming inorganic matter in the fuel (on weight).

This preliminary analysis shall be confirmed by experimental results. The interested reader could look at the related working paper (which includes references), accessible here.

 

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