The liquid bio-oil product from fast pyrolysis has the considerable advantage of being storable and transportable as well as the potential to supply a number of valuable chemicals. In this respect it offers a unique advantage and should be considered complementary to the other thermal conversion processes. Biomass fast pyrolysis technologies for liquid fuel production have been successfully demonstrated at small-scale, and several large pilot plants or demonstration projects (up to 200 ton/day biomass feed design capacity) are in operation or at an advanced stage of construction. Earlier economic studies suggested that bio-oil is relatively expensive compared to fossil based energy (Bridgwater et al. 2001): however, in light of recent dramatic increases in petroleum prices, bio-oil may be cost competitive for direct utilization and potentially is competitive in the transportation fuel market after catalytic processing for deoxygenation. Commercialization of bio-oil production continues to face economic and other non-technical barriers when trying to penetrate the energy markets.
As with biomass gasification, fast pyrolysis will only be able to penetrate energy markets if completely integrated into a biomass system. Thus the innovation in practically all demonstration projects under implementation lies not only in the technical aspects of the various processes but also in the integration of pyrolysis technologies in existing or newly developed systems where it can be demonstrated that the overall system offers better prospects for economic development. Niche markets are likely to be the most attractive in the short term, such as utilization of bio-oil in a marine environment where bio-oil is much less damaging than fuel oil in case of accidents. The overall challenges include small-scale efficient and cost effective power generation (electricity and mechanical power) and heat production systems, while also taking advantage of the more economically attractive chemicals markets.
There is no obvious best technology. Fluid beds offer robust and scalable reactors, but the problem of heat transfer at large-scales in not yet proven. Circulating fluid beds and transported beds may overcome the heat transfer problem but scaling is not yet proven and there is an added problem of char attrition. Intensive mechanical devices such as ablative and rotating cone reactors offer advantages of compactness and absence of fluidising gas, but may suffer from scaling problems and always the problems associated with moving parts at high temperature.
There are specific challenges facing fast pyrolysis that relate to technology, product and applications including:
The most important issues that need to be addressed are: