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.

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


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.


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

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.


Innovations decreasing electricity generation costs: quantitative estimations till 2025 for solid fuel plants

Very recently InnoEnergy commissioned a study to BVG Associates to evaluate how innovation would impact the electricity generating cost, in Europe and till 2025, from new gas CHP (combined heat and power) plants and retrofitted coal plants.

The study [1] outlines that for a 500 kW gas CHP plant, the levelized cost of energy (LCOE) shall drop by about 17% between 2016 (the baseline) and 2025, while for a 225 MWe solid fuel power plant (coal retrofitted) such decrease is estimated to be about 27%.

For the solid fuel plant, according to the authors [1] and as evidenced in Fig. 1, over half of the LCOE savings arise from innovations in the modification, pre-treatment and combustion of new fuels.

Screen Shot 2017-02-21 at 19.23.00.png
Fig. 1. LCOE decrease between 2016 and 2025 for solid fuels energy plants. Adapted from [1].
The identified major innovations for the solid fuel plant are reported in the following [1]:

  • Topic 1 – Improvements in fuels through modification, switching; hybrid fuels (-10% LCOE). The use of low quality fuels is limited by operational challenges (e.g. slagging and fouling). Today, fuel additives are still limited to basic minerals (e.g. kaolinite) to reduce slagging and fouling and fuel blending is still limited to fuels that are not classified as waste. The use of advanced mineral or artificial additives to reduce ash challenges and influence emissions and the blending of low quality fuels/wastes shall be increased. According to the study, 80% of the benefit of these innovations is already realisable in 2016, with 100% realisable by 2020 onwards, however with an implementation limited to 40% of plants in 2025 because of local policy and regulations limitations.
  • Topic 2 –Introduction of thermal pre-treatment of solid fuels (-7% LCOE). As an example, torrefaction, by upgrading the properties of biomass and waste fuels, could reduce fuel transportation and handling costs (but might increase processing costs). According to the study, 40% of such benefit is already realisable in 2016, with 100% realisable by 2025 onwards, with an implementation limited to 30% of plants in 2025 because of local policy and regulations limitations.
  • Topic 3 –Improvements in preventive maintenance, power plant start-up system and boiler flexibility (-5% LCOE). Innovations cover advanced burners to reply heavy oil start up burners with liquid biofuel waste (70% of the benefit of these innovations is realisable in 2016) and the increase in boiler’s flexibility to enable plant operation at below 40% of maximum output (e.g. improving electronic/digital control and using high temperature heat accumulation systems). Moreover, modern preventative maintenance algorithms,  based on real operations, could provide information about failure in advance (e.g. material failures due to corrosion, especially when using biomass).
  • Among other 10 innovations (-5% LCOE): improvements in treatment of solid fuel combustion byproducts (today used by the cement industry, tomorrow to produce artificial zeolites, geopolymers and cenospheres, or vitrified), improvements in steam circuit design (optimal turbine blades, valves and condenser designs), introduction of superconducting technology in transformers/cables, integration of the main three pollution control systems (NOx, SOx, dust emissions), today in series, by using single sorbents and oxidisers in single wet scrubbers.

As a summary, reduced fuel OPEX in solid fuel plants by 2025 is achieved through innovations that enable the use of lower cost fuel and waste products (Topic 1), with thermal pre-treatment (Topic 2) and additives. Improvements in operations (Topic 3) also deliver significant savings, with preventative maintenance, operational flexibility and treatment of the byproducts of solid fuel combustion.

Topic 1 is addressed by many research projects (e.g. [2]) and now also with an operational, available tool called BIOFACT (BIOmass Fuel Advisory Characterization Tool) which wants to disclose a tool to characterize solid biomass for its utilization as a fuel in existing and new units, by estimating the impact of its utilization in terms of operational problems. In fact, fuel characterization tools are supposed to unlock the 8% reduction of the solid fuels generation costs already realisable today, with the final objective of providing flexible back-up plants for wind and solar energy technologies as well as renewable heat production.


[1] InnoEnergy, “Future Energy Costs: Coal and Gas Technologies“, BVG Associates, 2016, (accessed 21/02/2017).

[2] European Union’s Horizon 2020 research project: Biofficiency. Developing the next generation of CHP plants, (accessed 21/02/2017).

By Lucio De Fusco, InnoEnergy PhD School Fellow

Fuelsim: a useful tool for energy and mass balances in biomass combustion

Fuelsim is a useful mass, volume and energy balance Excel tool, by Dr. Øyvind Skreiberg, for computations related to biomass combustion processes. It might be useful for preliminary simulations to compute heat output, adiabatic combustion temperature and system efficiencies. Report here, tool download here.