Abstract
Currently, a demand for alternative energy sources to replace traditional fossil fuels is growing. Although there are still found new reserves or mining techniques – e.g. Shale gas, searching for new substitute solutions is needed. Waste from the wood processing industry could be serving as a potential feedstock for energy production, e.g. hydrogen.
Microwave irradiation is an alternative heating method and has already been successfully applied to biomass pyrolysis. Compared with convectional heating processes where heat is transferred from the surface to the core of the material through conduction driven by temperature gradient, microwaves induce heat at the molecular level by direct conversion of the electromagnetic energy into heat, and therefore, they can provide uniform internal heating for material particles. Microwave pyrolysis promotes the heterogeneous catalytic reaction and produces greater concentration of syngas and hydrogen in the product gas than convectional pyrolysis. In addition, it is easier for a rapid start-up and shut-down.
The biomass is mixed with a suitable material which significantly absorbs microwave radiation for generation of intensive heating in the reactor. In our case, the spruce sawdust was mixed with char from previous pyrolysis of spruce sawdust. Char from the pyrolysis of sawdust also contains small amounts of ash (up to 5 %), which includes alkali metals and alkaline earth metals. The presence of such char has a catalytic effect on the pyrolysis process, the cracking of tars and phenolic compounds to the simple gases (H2 and CO).
In this work the influence of various parameters of microwave pyrolysis of spruce sawdust (microwave power, particle size, ratio of sawdust and char, pyrolysis duration, etc.) was studied to maximize the yield of hydrogen, or syngas. Experiments were carried out in a conventional microwave oven with power up to 1 kW. The influence of parameters on the quantity of products (gas, liquid and solid), but also the amount of waste water in the liquid condensate were studied.
