Partial biomass gasification (pyrolysis) is used to produce combustible gases (syngas) mainly containing CO, H2 and CH4, bio-oil condensates (biofuel) and high carbon biochar. Trigeneration or combined cooling, heat and power (CCHP), is the process by which some of the heat produced by a cogeneration plant is used to generate chilled water for air conditioning or refrigeration. An absorption chiller is linked to the combined heat and power (CHP) to provide this functionality.

In most locations, biomass pyrolysis could be Combined Cooling, Heat, Power, Biofuel, Biochar (CCHPBB) Systems. The thermal efficiency of CCHPBB systems can be as high as 90%. Typical yields by weight of slow pyrolysis of acacia wood are 30% bio-oil, 35% biochar, and 35% syngas. Bio-oil and syngas percentages vary greatly with different feedstocks while the biochar % is more stable. Feedstock composition is thus chosen according to the preferred solid : liquid : gas output ratios. Less desirable feedstocks are used elsewhere.

With complete gasification — i.e. no biochar & no bio-oils — the amount of produced syngas depends significantly on the total amount of carbon in the biomass that is fed into the gasifier. On average, one kilogram of wood biomass produces 2.5 m3 of syngas. In CCHPBB systems, we want the biochar and bio-oils, this means that syngas production is reduced. Bio-oil outputs are significant. In the Ecohamlet economy, bio-oils can be used for many purposes, including being used as a biofuel. Biofuel stores very well.

Although most biomass that is pyrolyzed is waste, many Ecohamlets do grow some biomass specifically for their CCHPBB systems. Biomass grown specifically for CCHPBB is designed to always have many functions — from the ecological bio-remediation of water and landscapes to mechanical (i.e. windbreaks, erosion control, flood control, etc.). Biochar is also the best material for long-term to very-long-term storage and use (10 to 100s of years) while wood is best for short to medium-term storage (1 to 10 years) and use.

Biochar is mainly used as an emergency fuel for heat, as a fuel for metallurgy, as a soil amendment and as an adsorption substrate. Biochar has a net calorific value of between 27 and 32 MJ / kg, which is comparable or even higher than good-quality coal (eco pea coal 24–26 MJ / kg). Eco-pea coal is a solid fuel obtained from lignite or bituminous coal (31.2 type granules 5 – 25mm). Eco-pea coal has a low sulphur content and an ash sintering temperature over 1190°C. So, from an energy and metallurgy point of view, biochar is great!

For interest sake, and to dispel the naysayers, here is some stuff you may not know! Historically, pyrolysis technology — char production by using kilns — has been used for 1,000s of years. The industrial scale use of pyrolysis to make char became integral to the production of metals and especially in the steel industry — this remained true until the later stages of the industrial revolution. Coking coal only became popular in the 1800s. Biochar is the key ingredient of terra preta, a type of very dark, highly fertile anthropogenic soil.

and: Syngas has historically mainly been used as a replacement for petrol, when petrol supply has been limited; for example, wood gas was used to power cars in Europe during WWII (in Germany alone half a million cars were built or rebuilt to run on wood gas). Amazingly, in this time, many trucks, buses, tractors, motorcycles, ships and trains were equipped with a wood gasification unit. Wood gasifiers are still manufactured in China and Russia for vehicles. Wood gasifiers are also still being used for trucks in North Korea!

and: The fast pyrolysis process also called flash pyrolysis is for the primary production of bio-oil. The process had a period of rapid development during the 1970s oil crisis (mainly in the US and Europe) because it gave the possibility to use a biomass feedstock to produce oils for transportation and other practices. Furthermore, over 92 percent of Germany’s aviation gasoline and half its total petroleum during World War II had come from synthetic fuel plants using coal as feedstock for the Fischer–Tropsch process.

I hope that the three paragraphs above help you realise that the potential of using wood in a post collapse society goes beyond heat — the past proves it! The only ‘problem’ is that we will have to start planning, designing and implementing a transition strategy for wood gasification ASAP or else it will be too late. That said; Syngas, Biochar & Biofuels are considered to be a highly viable resource in the Ecohamlet Model — and we are working on perfecting their production using current technological knowledge. 

Calculations

Biochar has around 8 kWh of energy per kg.

At 25% biochar yield, 4 kg wood becomes 1 kg biochar

4 kg of completely combusted wood releases around 20 kWh of heat energy.

In terms of energy — the following comes from 4 kg of pyrolyzed wood:

Biochar: energy equals 8 kWh
Syngas: energy equals 4 kWh
Biofuel: energy equals 4 kWh
Heat: energy released equals 4 kWh (N.B. this is waste heat if it is not used)

RSD Course Versions

The pre-alpha version of a lesson is one that has not been peer reviewed yet — however, don’t worry, pre-alpha is good enough to be live! The alpha version is an early version of a peer reviewed lesson that is part of a dedicated evaluation process. The beta version includes almost all of the final content, videos, etc. yet it may still need to be tweaked somewhat.

The first modules of the pre-alpha version of the RSD Course are already live. The reason for making the pre-alpha version live is that we are actively engaging with our ‘early adopter’ crowdfunding students and contributors so that we can build the best course possible. The completed alpha versions of the entire course will be live from the 1st September 2024.

The beta version of the entire RSD Course will hopefully be released by 1st March 2025. The ‘completed & refined’ release of the RSD Course (English) should be available around late-2025. The course will then be translated into other languages — around 10 languages at first, and then more according to demand.