Conversion of biomass into paper, board, and energy is discussed in these reviews:

https://www.researchgate.net/publication/315427845_Agricultural_Residues_Wastes_for_Manufacture_of_Paper_Board_and_Miscellaneous_Products_Background_Overview_and_Future_Prospects

https://www.researchgate.net/publication/325803601_Biomass_pyrolysis_past_present_and_future

I'd add to the economic and technical barriers the following elements that need to be taken into consideration:

Human health and environmental impacts associated with centralized and decentralized biomass-to-energy plants. Quantification of human health and environmental impacts require conducting life cycle assessment (LCA) and life cycle impact assessment (LCIA) for both approaches.

The economic barrier needs to take into consideration: a) the economies of scale of using a large centralized biomass-to-energy plant versus a set of decentralized plants and b) the economic cost of transporting the biomass from its source to the plant. I've done studies on the so-called economic distance within which the cost of energy from biomass conversion plants would be more attractive than that from conventional plants. Beyond the economic distance, biomass-to-energy plants would not be an attractive option from the economic standpoint. Hence, such an issue would require cost/benefit analysis.

Lastly, I don't view the technical aspect biomass-to-energy conversion a technology barrier as this technology is well understood.

Hope this helps answer your question and good luck!

There's a lot of challenges in implementing the distributed model, some include: 1) How to incentivise farmers to give up their wastes (financial?), 2) Seasonal variations in production, 3) Transportation issues associated with the remoteness of many sights, 4) Market viability of the products (biochar, bio-oil, etc.), 5) Low HHV of biomass often means long ROI for plants that are built for energy production. All of these challenges can be overcome, I should add, but there will not be a single correct model for every country/waste.

Tamer YA Fahmy thanks for the links. Is there a problem of agro-residue burning in Egypt or lack of collection mechanism for residues?

İbrahim Halil Yılmaz can there be any parallels between the kind of models followed for decentralized solar energy and small scale biomass processing? For example, roof-top solar PV installations for domestic or industrial consumption have been carried out across many countries. If people involved are getting something out of it like energy savings, they don't have a problem installing it. Similarly if farmers are burning their crop because they have no use for it, can't industries/ manufacturers go and process the biomass at source?

Both involve taking the energy production units to people directly and if the benefits of the system are higher than costs to themselves, no one seems to have a problem with it.

Yehia F. Khalil thank you for your reply.

It seems to me that, because biomass sources (agro residue particularly) are so widely distributed, a centralized system of processing would fail in practice because of absence of a reliable supply chain. Supply chain management tends to fall into the trap of incentives for the farmers or lack thereof.

An issue with biomass conversion related LCA studies is that it is hard to compare the two for the same product/ conversion technology. For example, biochar derived from small scale/ decentralized torrefaction of lignocellulose could be economically viable for local consumption for domestic heating or improving nutrient retention in soil but at large scale it would be economically unviable; rather, centralized gasification based power generation might be more suitable.

Lewis Dunnigan I agree with the points that you mentioned. But rather than incentivising the farmer, incentivising an entrepreneur would be a better way to deal with the residue that is being burnt. This is where a mobile/ decentralized unit could be helpful because if you are taking the solution to the farmer they probably won't have a problem in giving it up.

The problem seems to be in valorization of the biomass products like bio-oil, or HTL and torrefaction condensate.

Anubhuti Bhatnagar, you're correct that it is very important to incentivise businesses to embark on such a task. Farmers will always need to be incentivised as not all may be driven from an environmental perspective, and will see burning as convenient. IMO, distributed systems have two major problems that need to be overcome: 1) Establish market viability of biochar/bio-oil/hydrochar etc. That is not quite there for some, and a long way off for others and 2) There needs to be sufficient volume of wastes to enable reactor throughputs that provide returns on a plant. A great number of farmers may only have 10's or 100's of kgs of waste, which is simply not enough for a ROI. Transporting the waste is also likely a no-go, as the bulk density is simply too low and it is often very wet.

Without these barriers being overcome, it will be difficult to implement an economic solution to this problem.