There has been an enormous amount of research in recent years in the area of thermo-chemical conversion of biomass into bio-fuels (bio-oil, bio-char and bio-gas) through pyrolysis technology due to its several socio-economic advantages as well as the fact it is an efficient conversion method compared to other thermo-chemical conversion technologies. However, this technology is not yet fully developed with respect to its commercial applications. In this study, more than two hundred publications are reviewed, discussed and summarized, with the emphasis being placed on the current status of pyrolysis technology and its potential for commercial applications for bio-fuel production. Aspects of pyrolysis technology such as pyrolysis principles, biomass sources and characteristics, types of pyrolysis, pyrolysis reactor design, pyrolysis products and their characteristics and economics of bio-fuel production are presented. It is found from this study that conversion of biomass to bio-fuel has to overcome challenges such as understanding the trade-off between the size of the pyrolysis plant and feedstock, improvement of the reliability of pyrolysis reactors and processes to become viable for commercial applications. Further study is required to achieve a better understanding of the economics of biomass pyrolysis for bio-fuel production, as well as resolving issues related to the capabilities of this technology in practical application.

https://cyberleninka.org/article/n/1011788.pdf

Biofuels production through biomass pyrolysis - a technological review.

Biomass is considered to have potential to be used as an alternative energy source. High carbon content present in biomass converts it into high energy biochar on thermochemical treatment. Among few well established thermochemical technologies for the treatment of biomass and biogenic waste to produce high energy char along with oil and gaseous yield, pyrolysis is the most studied and discussed technique in the recent past. A comparison between the existing techniques is established in the present work. Production of char from the biomass and biogenic wastes is reviewed and it was found that yield of the biochar depends upon the biomass composition like moisture content and presence of cellulose or lignin. Pyrolysis product distribution and their quality strongly depend upon the process parameters. Different biomasses which can be used as raw material in pyrolysis are also reviewed and categorized depending upon their source. Pyrolysis process parameters such as temperature, heating rate, residence time etc. also influence the biochar yield. This study discusses the effect of these process parameters on the production of biochar through pyrolysis of biomass.

Effect of process parameters on production of biochar from biomass waste through pyrolysis: A review

https://digital.csic.es/bitstream/10261/78256/1/Microwave%20heating%20processes_JAMD_2010.pdf

Microwave heating processes involving carbon materials

Relative distribution of Pb2+ sorption mechanisms by sludge-derived biochar

Biochar has been heralded as an amendment to revitalize degraded soils, improve soil carbon sequestration, increase agronomic productivity, and enter into future carbon trading markets. However, scientific and economic technicalties may limit the ability of biochar to consistently deliver on these expectations. Past research has demonstrated that biochar is part of the black carbon continuum with variable properties due to the net result of production (e.g., feedstock and pyrolysis conditions) and postproduction factors (storage or activation). Therefore, biochar is not a single entity but rather spans a wide range of black carbon forms. Biochar is black carbon, but not all black carbon is biochar. Agronomic benefits arising from biochar additions to degraded soils have been emphasized, but negligible and negative agronomic effects have also been reported. Fifty percent of the reviewed studies reported yield increases after black carbon or biochar additions, with the remainder of the studies reporting alarming decreases to no significant differences. Hardwood biochar (black carbon) produced by traditional methods (kilns or soil pits) possessed the most consistent yield increases when added to soils. The universality of this conclusion requires further evaluation due to the highly skewed feedstock preferences within existing studies. With global population expanding while the amount of arable land remains limited, restoring soil quality to nonproductive soils could be key to meeting future global food production, food security, and energy supplies; biochar may play a role in this endeavor. Biochar economics are often marginally viable and are tightly tied to the assumed duration of agronomic benefits. Further research is needed to determine the conditions under which biochar can provide economic and agronomic benefits and to elucidate the fundamental mechanisms responsible for these benefits.

/pdf/biochar-a-synthesis-of-its-agronomic-impact-beyond-carbon-4i1qspanh3.pdf

Biochar: a synthesis of its agronomic impact beyond carbon sequestration.

Production of bio-fuels by high temperature pyrolysis of sewage sludge using conventional and microwave heating.

Conventional and microwave induced pyrolysis of coffee hulls for the production of a hydrogen rich fuel gas

Microwave-assisted dry reforming of methane

Microwave pyrolysis of sewage sludge: analysis of the gas fraction

Pellets of coffee hulls were pyrolyzed at different temperatures using microwave and electrical heating. A comparison of the gas composition obtained by both methods suggests that the different mechanisms of heating that take place in the microwave, in comparison to conventional heating, give rise to the formation of “microplasmas”, which induce self-gasification of the char that is being formed. This hypothesis was corroborated by subjecting the char to reaction with CO2 at different temperatures using both methods of heating. The results showed that, whereas the transition in the reaction mechanism controlling the Boudouard reaction (i.e., chemical or diffusional control) takes place at about 800 °C in conventional heating, in the case of microwave heating the temperature is much lower and the reaction never proceeds under pure chemical control, the differences between microwave and conventional heating being quite significant even at low temperatures.

A. Domínguez

Papers

Production of bio-fuels by high temperature pyrolysis of sewage sludge using conventional and microwave heating.

Conventional and microwave induced pyrolysis of coffee hulls for the production of a hydrogen rich fuel gas

Microwave-assisted dry reforming of methane

Microwave pyrolysis of sewage sludge: analysis of the gas fraction

Evidence of self-gasification during the microwave-induced pyrolysis of coffee hulls