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Catalytic, environmental-friendly, fuel flexible and cost effective burner for domestic boiler

Final Report Summary - BURNERCAT (Catalytic, environmental-friendly, fuel flexible and cost effective burner for domestic boiler)

The objective of the project was two-fold:
- to obtain two different burners answering basically to the end-user specifications. The first burner was ceramic supported, the second one metallic supported (each support has a different wash coating procedure);
- to assess, the cost-effectiveness of each burner. The consortium analysed the cost effectiveness regarding environmental performances (pollutant emissions).

The technical specifications have been defined by the end-user, the boiler manufacturer. The burner manufacturers have taken into account that specifications in their burner design and catalysts specifications. Two different technologies of supports of burners (ceramics and metallic) are taken in consideration in order to define the lowest cost system.

On the three points, innovative development has been performed:
- the combustion support
- the catalyst
- the deposition methods.

Concerning the catalysts development, during the first year, researchers have identified the best catalytic supports among various supports and determined the best nominal compositions of noble metals Pd, Pt and bimetallic Pd-Pt catalysts. The main conclusions are the followings:
1. The best palladium precursor is Pd(NO3)2.
2.For the palladium supported catalysts, the best supports are commercial Al2O3 and Si stabilised AL2O3 (Si-Al2O3).
3. The best Pd loading on (Si-Al2O3), is comprised between 2 wt% and 3wt%.
4. For the bimetallic Pd-Pt catalysts supported on Al2O3 or Si-Al2O3, the best synthesis method is the successive impregnation one.
5. At last, the physical and chemical characterisations performed on fresh monometallic catalyst (Pd/ Si-Al2O3) synthesised by two different methods used by project partners showed similar results.

Moreover, various combustion supports, both metallic and ceramic, were characterised as combustion supports by Polito. The main goal of the characterisation of new materials is to find some valid economic alternatives to the Acotech metallic supports used as reference.

The different tested supports are:
- metallic fibres from Acotech;
- metallic fibres from Fibertech (two different versions);
- metallic fibres from Worgas;
- metallic stripes from partner NORTA;
- ceramic tiles from partner Schwank (two different versions);
- ceramic fibres from 3M Nextel.

As concerns the metallic fibres (Acotech, Fibertech, Worgas), they present very similar compositions, but different morphological structure. Fibertech's quality is not constant with the various batches provided. WORGAS's supports seem a valid alternative to ACOTECH. As concerns the ceramic supports (Schwank and 3M Nextel), they are very different but both very interesting for the combustion of methane. Before the ageing procedure, the fresh combustion support tests are still in progress at Gaz de France. The Acotech metallic fibre has been tested. For the new supports, the first one tested was the Schwank ceramic tile and problem concerning the distribution grill has been solved. For Polito, the Merloni boiler test rig was assessed in order to obtain a boiler suitable to the characteristics requested by the BURNERCAT project.

During the second and last period of activity, researchers proceeded with their activities concerning the preparation of the second generation catalysts. The goal of this work is to optimise the preparation procedure in order to obtain the best efficient catalyst. Parameters as calcination temperature and the effect of the metal precursor were optimised. At last it was studied the effect of the ageing process on the catalytic performance. Thus, according to the obtained results, it was possible to verify that the best catalyst found was the catalyst prepared with nitrate precursors of Pd and Pt and that the optimal calcinations temperature is 500 degrees Celsius. Comparing both catalysts prepared using exactly the same procedure (Pd-Pt/Al2O3 and Pd-Pt/Si- Al2O3), the Pd/Pt impregnated on alumina stabilised with Si catalyst shows superior catalytic performance.

Ageing process was also applied in order to study the catalyst stability and it was found almost the same results for both mentioned catalyst: no activity decrease was verified at low temperatures and PdO-Pd transition is almost cancelled.

According to the obtained results, only three supports have been chosen for the catalytic tests:
- Worgas fibre
- NEXTEL fibre
- Schwank new generation.

Polito and GDF proceeded with their study in order to determine the catalytic performance of the catalysed burners. GDF continued in the same kind of tests while that Polito proceeded to an evaluation on a commercial Merloni burner which was possible to quantify the CO and NO emissions as a function of air excess introduced and power output. According to GDF results, Worgas can reach lowers air ratios than the no-catalysed one, while that Nextel fibres present better results than the respective catalysed support; however, with Scwank new generation, the catalysed support is better especially for small thermal power. In what concerns Polito results obtained by testing supports and catalysed supports on a commercial Merloni burner, even if no major differences between catalytic and non-catalytic burners were verified, catalytic Schwank tiles and catalytic Biscotto were found as the most interesting burners tested. With Schwank catalytic tiles we reach 16 mg/kWh at 20 kW and 10 mg/kWh at 10 kW instead of 51 and 32 mg/kWh, respectively, obtained with the commercial burner.

Then, the catalysed supports were submitted to an ageing process, in order to study their stability in function of time of working. After ageing, these catalysts were characterised leading to the conclusion that among the three studied substrates (Schwank new generation, Nextel fibre and Worgas fibre), only Worgas catalysed substrate (working in a mixed radiant / blue flame mode-phase) stability is constant in function of time; working in radiant mode it was found Schwank substrates behaviour keeps stable and Nextal and Worgas substrates presented a decrease of NOx emissions in function of time.