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New Burner Technologies for Low Grade Biofuels to Supply Clean Energy for Processes in Biorefineries (BIO-PRO)

Final Report Summary - BIO-PRO (New Burner Technologies for Low Grade Biofuels to Supply Clean Energy for Processes in Biorefineries)

The project BIO-PRO aimed on developing new combustion technologies for bio-residues. Innovative combustion technologies like flameless oxidation (FLOX) and continuous air staging (COSTAIR) were enhanced by re-burning and co-firing in order to meet this goal.

Two basic types of BIO-PRO burners were developed to meet this goal:
- a pilot burner for gas and liquid fuels;
- a pilot burner for solid fuels applying a pre-gasification step for the solids without gas cooling.

The technology developed shall be able to self adjust to different fuel qualities (fuel moisture 10-50%). For emissions of the investigated fuels the upper limit for CO will be 30 mg/m3 (currently 50 mg/m3 are typical) and NOx will be reduced by 50% (starting point for dry wood chips in available combustion systems = 210 mg/m3).

The project was structured into six work packages (WP), as follows:
-WP1: characterisation of biorefinery processes and bio fuels;
-WP2: burner development - gaseous and liquid fuels;
-WP3: process development unit of pre-gasifier for solid fuels;
-WP4: development of the control system;
-WP5: industrial testing of prototype burners;
-WP6: socio-economic evaluation and dissemination, technical exploitation.

In order to apply slurries and wet biomass to thermal conversion the aspects of storage, milling, feeding and pre-drying of such fuels has been investigated. Different concepts for drying of wood fuels for use in small-scale heat plants (< 10 MW) were tested. The investigations related to an adapted FLOX-burner for LCV gases has shown that gases with heating values down to 2.5 MJ/m3 can be utilised.

Parallel activities related to solid residues did result in an optimised combustion system for low-grade biomasses by integrating a newly developed FLOX-burner for the direct combustion of hot and tar-loaded LCV gases. This combustion system showed several benefits compared to the conventional system, e.g. better burnout, stable operation and higher efficiency. Regarding the utilisation of solid biomasses with high nitrogen content the project results have show that the application of the FLOX technologies is not sufficiently reducing the NO emissions. Therefore, the development of an air staged FLOX-burner for solid biomasses was brought forward.

The objective of this work was to show how moist wood fuels can be made technically and economically available for small scale heat generation where dry fuels so far has been the only option. The work has included both theoretical and experimental work.

A further advanced combustion technology, the continuous air-staging (COSTAIR), was adapted within the project to the combustion of LCV gases. Furthermore, a state-of-the-art burner for biomass fuels was developed where a BIOSWIRL gasifier was used together with a burner developed from the COSTAIR concept.

Within the BIO-PRO project, a new online heating value analyser for a wide variety of low calorific value gases was developed. The analyser is aimed at forming a part of a feed-forward burner control loop in order to anticipate to the changing heating value of the incoming fuel gas, with the target to maintain the (very) low pollutant emissions of the novel flameless oxidation combustion technology (CO and NOx in particular). This analyser can be used for the control of boilers, gas engines, fuel cells operation on different types of gas.

A CFD model of the LCV-FLOX-burner was set-up and simulations for this flameless oxidation burner type were performed. This analysis can be used to improve the CFD models extending the simulations to off-specification fuels for which no data are available in literature. This approach can be used to explain qualitatively the difference between syngas and natural gas combustion.

Several flameless combustion experiments were conducted to establish improved boundary conditions for the combustor modelling and to obtain a better insight into burner control strategies aimed at minimising CO and NO. These experiments showed very low CO and NO concentration values using the burner on syngas. CO concentrations well below 30 mg/mn3 (even below 10 mg/mn3 at 3% O2) were obtained with a hydrogen rich gas. An outlet temperature control strategy was applied acting on the (secondary) air of wall cooling.

At the end of the project three prototype FLOX-burners were tested: unstaged burner at FW site, air-staged FLOX-burner at ZAMER site, FLOX-flare for landfill gases at a landfill site in Ticino/Switzerland. Summarising the experiences of the first FLOX burner tests using product gas from a 1.5 MW biomass gasifier as fuel, the burner operation was fully reliable throughout the 176-hour test period. Carbon monoxide emissions were negligible, but the NOx emissions were at the same level as with the old burner of the facility. This has been attributed to NOx formation from reduced nitrogen species in the syngas (mainly NH3, HCN), suppression of which would require further measures.

After applying the modification at burner design there were performed further investigations at Zamer's facility. During these tests strong pulsations in the burner occurred. During scheduled test runs there was not possible to investigate this problem deeply. Probably these pulsations caused damage of one of burners elements - ceramic tube that works as combustion stabiliser. Decreasing of NOx emission with decreasing of primary airflow and increasing of secondary airflow (under stoichiometric operation in the first stage) can be noticed.
Still, monitoring time of the burner performance was too short to investigate the burner more in detail and to identify the best operation conditions. Nevertheless, the commissioning of the air-staged burner was successful and the reduction potential for NOx emissions was shown.

It can be stated, that the adopted burner clearly overbids the project targets of 50% NOx emission reduction compared to state of art (would be 40 mg/m3n @ 3% O2) and reduction of CO-emission below 20 mg/m3n @ 3% O2. Besides landfill sites the burner can also be applied to biorefineries, e.g. for the utilisation of off-gases from the methanisation of biogas to be fed into the gas-grid. Information about the project as well as contact details of the participating partners is available on the project website, found at online.

The new burner technologies can be applied for the energy production in all conversion processes that use fuels and chemicals produced from biomass. Another application can be the integration of the new burners in power plants as well as already existing biomass combustion systems to ensure low emission combustion of bio-fuels. Bio-ethanol production generates only a 30% renewable energy surplus, comparing the generated ethanol to the fossil fuel energy input.

These figures show that there is a considerable need for the envisaged technology to utilise the process residues for energy generation within the process. The BIO-PRO burner technology will be able to serve this global market. Therefore, it does not only support European bio-refinery technology, it generates its own global market.