Paper details

Title:

Tar Removal in a Catalytic Ceramic Candle Filter Unit at High Temperatures

Author(s):

Simeone, E., Pal, R., Nacken, M., Heidenreich, S., Verkooijen, A.H.M., de Jong, W.

Document(s):

Abstract:

Solid particles and tars are among the non­desirable products of synthesis gas produced during biomass gasification. Removal of fly ashes is necessary in order to comply with emission limits as well as avoid their deposition in downstream units. Condensation of tars, on the other side, can cause clogging. A catalytic hot gas filter can remove both solids and tars, when operating at temperatures as high as 850 °C. Catalytic hot gas filter elements are under development in order to solve this issue. A lab­scale filtration unit has been designed and constructed at Delft University of Technology. It contains one ceramic filter candle which is made of a SiC porous structure coated with a mullite membrane. The integration of a catalyst layer allows the dual function of particle filtration and tar cracking. The set­up operates at atmospheric conditions and is equipped with gas and H2O supply lines, a tar evaporator and a pre­heater, located upstream of the filter vessel. Dry gas composition is measured with an on­line micro gas chromatograph and tar concentration is obtained with SPA method. Water content is measured gravimetrically. The unit was tested with a dust­free model gas which consisted of a mixture of CO (14%), CO2 (14%), H2 (7%), CH4 (5%), and varying concentrations of N2 (30, 40, 50%) and H2O (30, 20, 10%). Naphthalene (2 g/Nm3 and 5 g/Nm3) was adopted as model compound in order to study the catalytic conversion of heavier hydrocarbon species to H2. A filter element containing a MgO­Al2O3 support structure impregnated with 60 wt% NiO has already shown a conversion of 99.4 % with 2 g/Nm3 and 98.5 % with 5 g/Nm3 Naphthalene at 850 °C and 30 vol% H2O. Therefore, a new candle with increased nickel content (189 wt% NiO, on support structure mass basis) was tested under the same operating conditions for comparison purposes. The temperature range varied from 650 to 850 °C and the gas face velocity was 2.5 cm/s. The following findings were obtained: 100 % naphthalene conversion for 2 g/Nm3 at all temperatures and H2O content, while for 5 g/Nm3 100% conversion was achieved at 800 and 850 °C for each H2O concentration. Lower temperatures and 5 g/Nm3 of naphthalene showed increasing conversion with decreasing water content, being 85.6% the lowest conversion obtained at 650°C and 30% H2O. Methane conversion was negatively affected by increased tar concentration, thus indicating a competing effect for the nickel active sites. Among the light hydrocarbons, toluene and xylene appeared to be produced. Based on these results, it can be concluded that increasing nickel load in a filter element provides a higher naphthalene conversion.

Keywords:

catalytic conversion, filtration, gasification, hot gas cleaning, tar

Topic:

Thermochemical conversion - Gasification for synthesis gas production

Subtopic:

Catalytic upgrading and syngas cleaning

Event:

18th European Biomass Conference and Exhibition

Session:

OB8.1

Pages:

787 - 796

ISBN-13:

978-88-89407-56-1

ISBN-10:

88-89407-56-5

Paper DOI:

10.5071/18thEUBCE2010-OB8.1

Price:

FREE