Fuel analytics: residual bran boiler operated with Ca-based additive

The grate boiler analyzed is fired primarily with bran, which is a residue from the milling of wheat grain (outer shell of wheat) used for the production of ethanol. Bran has an ash content up to 7%wt. dry basis.

The vertical type boiler is installed in the largest bioethanol factory in Wanze, Belgium. The boiler was built 11 years ago, in 2009. Bran can be used for animal feed, but also for generating energy. The bran boiler was unable to supply all the required steam for the production plant so it was decided to use natural gas (n-gas) for the remaining energy input. The n-gas is utilized in an external superheater and the flue gas is led to the bran boiler. The plant has a capacity of burning 20 tonnes bran/hour, for a total of 75 MWth, 25 MWel (100 ton/h steam at 92 bar, 520°C including the n-gas external SH). The bran is delivered to the boiler-dosing silo and fed into the boiler with feeding screws.

The combustion takes place on a water-cooled vibrating grate, suitable for the 13.5 – 17.0 MJ/kg moist and high ash bran. The grate consists panel walls mounted on leaf springs. These panels are activated in pairs, in counter phase, by a vibrating unit. Primary combustion air is injected through holes drilled in the fins of the grate panel. The flue gas from the n-gas external superheater is mixed into the bran boiler in front of the convection section reaching a final flue gas temperature of 520°C. The bottom ash is removed with a submerged chain conveyor and carried to an open ash pit.

In order to avoid clogging, the boiler is designed with two empty boiler passes to ensure sufficient cooling of the fuel gas before entering the convection part. In that way, ash will deposit in solid form. The bran fuel is expected to generate fouling and slag on the walls in the empty boiler passes, which have therefore been equipped with water soot blowers. Downstream of the economizers, baghouse filters were installed to remove the fly ash particles from flue gas. To reduce the emissions of SO2 and HCl, NaHCO3 particles were injected before the baghouse filters.

The plant was initially operated with pure bran. However, after successful operation of a few months, according to published literature, the baghouse filters were found to be blocked by “sintered” fly ash, which could not be removed by pressurized air and hindered the continuous operation of the plant. In addition, severe ash deposition was observed in the economizers of the plant, with flue gas temperatures of 380-180°C. To minimize these problems, the plant was operated with the addition of 5-8 wt % CaCO3. It appeared that the baghouse filter problem was mitigated by addition of CaCO3 and by changing the operational condition of the filter, whereas the ash deposition problem in the economizers still appeared occasionally, based on the reported published return on experience.

BIOFACT Dashboard is a tool to predict ash related risks in combustion units. The tool has been applied to bran, and the results is reported in the following.


It should be noted that the composition of the bran used on the grate-fired plant varied over time, and deviates from that shown in the BIOFACT Dashboard. Moreover, CaCO3 was applied in the boiler. Due to these factors, the full-scale results can only be compared with the results from predicted data qualitatively. Emission guarantees out of the boiler (6% dry O2) according to boiler manufacturer:

  • NOx: 278 mg/Nm3 (including primary mitigation measures)
  • Dust: 18 mg/Nm3 (after flue gas treatment)
  • HCI: 25 mg/Nm3 (after flue gas treatment)
  • SO2:  179 mg/Nm3 (after flue gas treatment)

Today, the biomass-fired boiler uses bran, biogas and a by-product derived from distillation such as fusel oil.

Reference: volund.dk/References_and_cases/Biomass_energy_solutions/Biowanze

Technico-economical analysis of additive scenarios for a biomass plant operations optimization

In a recent project, we have further developed a technical-economic framework to analyse the potential opportunity to include mineral additives for the operations optimization of a 13-MWel biomass plant. The plant is processing low quality woody fuels, with slagging and fouling challenges.

Different commercial possibilities are available and additive prices are varying. The techno-economic choice must take into account different variables including, for example, variations on:

  • boiler performance
  • boiler operating hours and/or downtime reduction
  • SHs/heat exchangers lifetime, conventional cleaning programme variation
  • additive dosing and injection equipment (CAPEX and OPEX)
  • additive prices
  • flue gas cleaning impact and adjustment
  • ash disposal costs and ash handling arrangement

As a result of the full techno-economic modelling, additive type selection and break even point related to additive price was computed, for the specific plant.

A snapshot of some of the results is published below: the variation of O&M (fixed and variable) costs for the specific plant (€/year) is evaluated for two specific Ca- and Al-Si based additives (additivation rate 1,0 wt%) with respect to the baseline case (no additive), as a function of the additives price.

The wide range of the computed O&M cost variation is caused by mixing optimistic and pessimistic predictions related to the variables mentioned in the list above. After selecting the additive type, results were further refined reducing the uncertainty on the O&M cost variation prediction for the specific additivation rate.

Do not hesitate to contact us for further discussion!

New Year, new look. BIOFACT Fuel Dashboard for 2019

Thanks to feedback from users, further development and giving a response to the need of digitization of the reports, with the need of an online accessible dashboard, we are glad to present the new version (5.0) of the BIOFACT tool for the biomass and waste fuels advanced characterization.

Here some snapshots!

We would be very glad to get your feedback!

Best regards,

BIOFACT successfully applied for analysing RDF fuel delivered to two side-by-side boilers

Analysis of the fuel mix of the world largest 100% biomass FB boiler

Polaniec (PO) is the World’s largest 100% solid biomass firing CFB boiler operating today (190 MW el. gross, 447 MWth) [1]. Previously owned by ENGIE, it is now managed by the Polish state (ENEA).

The plant uses agricultural biomass in addition to virgin biomass and the combustion technology is a Circulating Fluidized Bed boiler [1]. The steam cycle has a single reheat, for 175 MWel. net/447 MWth, SH/RH 158/135 kg/s, SH/RH 535/535ºC and 127/20 bar [1]. Steam temperature is limited to reduce potential issues of hot temperature corrosion.

To cope with agglomeration, fouling and corrosion, typical concerns with in agro biomass combustion, the boiler technology was adapted as follows [1]:

  • use of active bed materials and application of additives with worst quality agro (kaolin and elementary sulphur may be fed into the combustor to control agglomeration, fouling and hot corrosion [2])
  • conservative flue gas velocities,
  • effective temperature control (homogenous) in the combustion chamber,
  • correct flue gas temperature (to avoid ash melting) in the convective sections, to reduce fouling and corrosion,
  • proper design for the convective heat transfer surfaces (spacing, pitch etc.),
  • proper fuel quality management and boiler diagnostic tools,
  • in the combustion chamber: use of a step grid, use of the wall kick out at fuel inlet, use of the final SH and RH as Intrex (TM): integrated steam cooled solid separator and return leg.

The plant operates with a range of biomass according to the mix: 80% clean forestry wood chips and 20% of agro-fuels such as PKS, straw, sunflower pellets, dried fruit (marc).

The Design Fuel Mixture was analysed with BIOFACT, in order to evaluate operational risks (especially related to inorganic matter). 

The result is presented below.

The Design Fuel Mixture is expected to induce relatively low high temperature fouling on heat exchangers (6/100) and a relatively low agglomeration risk (8/100). High temperature corrosion (19/100, low with respect to 100% agro-firing) still shall be monitored (e.g. evaluate KCl presence in flue gases). Emissions are not expected to be a problem (primary and secondary reduction measures can be defined). Fuel logistic can be critical for high moisture wood chips and depending, for example,  on the physical properties of the agro-fuels used in the fuel mix.

The same boiler manufacturer shall provide a 299 MWel CHP plant (Tees Renewable Energy Project) to MGT Teesside (U. K.), therefore larger than Polaniec boiler, but operated with virgin wood pellets (70%) and wood chips (30%, forest by products from North America) [3]. Differently from Polaniec, this boiler design has been developed to fire “easy-to-burn biomass” [3]. Steam data are 229/205 kg/s, SH/RH 176/43 bar, 568/568°C. The plant shall be in operations in 2020 [3]. Fuel data are not yet available.

[1] Natunen et al., First operating experiences of 55 MWel Konin and 205 MWel Polaniec CFB boilers firing 100% biomass, Amec Foster Wheeler Energia Oy.

[2] Barišić  et al., Modeling of Fouling in CFB Boilers, Foster Wheeler Energia Oy, Presented at 11th International Conference on Fluidized Bed Technology Beijing China 14 – 17 May, 2014.

[3] Nuortimo et al., Large scale utility CFB technology in worlds largest greenfield 100% biomass power plant, Amec Foster Wheeler Energia Oy, Presented at 25th European Biomass Conference and Exhibition, 12-15 June 2017.

BIOFACT case study: corn cobs

BIOFACT – Biomass Fuels Advisory Characterization Tool – is a recently developed fuel characterization tool which aims at rapidly detecting operational risks due to the use of biomass in energy plants. It is build to support engineers to have a better idea about non-conventional fuels and buyers to safely expand the fuels portfolio.

It does not substitute CFD analyses and pilot experimental testing. It is built to minimize the use of such time- and budget-consuming methods to the most interesting fuels. After filling in the fuel data (biofact.eu/analyze), it is possible to download a report with the results. Here a case study for corn cobs.

In the report, four sections are present: the Input section (with the data submitted), the BIOFACT-C (Combustion) section, the BIOFACT-T (Technology coupling) section and a short wrap up.


[pdf-embedder url=”http://www.biofact.eu/wp-content/uploads/2017/07/Example-1.3.pdf”]

The BIOFACT-C section is a quick assessment of operational risks during combustion of the specific fuel, namely the risks of/for: fouling, agglomeration and slagging, corrosion (high temperature), HCl emissions, particulate matter (PM10), SOx emissions, fuel NOx emissions, handling and storage. Each risk is computed with models based on the input data. As a complementary information, a suggestion of

The BIOFACT-T section is build to suggest the most suitable energy conversion Technologies for the specific fuel analyzed. The major combustion technologies are here considered: Bubbling Fluidized Bed combustion, Circulating Fluidized Bed combustion, Fixed Bed combustion (industrial or residential), Pulverized Fuel combustion, Thermal and material recovery (incineration). Fuel characteristics (at the moment 10 properties) and technologies requirements are matched on a matrix (which is kept updated with Best Available Technologies data). The results are the list of suitable (green) / borderline (orange) / inadequate (red) properties. For this corn cobs sample, because of agglomeration is a major risk, the tool evidences that fluidized beds might not be the most suited solution. However, such risk is not problematic for applications in fixed-bed, industrial scale units (e.g. due to fine bed temperature control). Grate furnaces might be more suitable to handle molten slag – agglomerated ash particles than fluidized beds. Beside complementary information such as the computed LHV are indicated.

The wrap up is a summary of the brief comments reported above.

Would you use such tool to screen unconventional fuels? Would this be an effective help for the preliminary fuel characterization?

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.