[Terrapreta] small-scale torrefaction for developing countries

[Tom Miles]

Gerrit,

 

Interesting find. 

 

It was a pilot study aimed at processing 16,000 tons of solid waste (of
73,000 tons available) into fuel briquettes. I find a project summary at
http://www.ard-rwanda.org.rw/solidwaste.htm  It looks like there was a
proposal for 2004-2008 but no update. 

 

It's not clear from the ARD site if the torrefaction-briquetting project is
still running. 

http://www.ardinc.com/projects/detail_region.php?id=111

 

The project seems to have stopped when the USAID funding stopped.  

 

Can someone contact ARD or USAID Rwanda for an update?

 

Thanks

 

Tom

 

http://www.henrykellam.com/reports/CoP_version_Rwanda.pdf

 

 

 

From: terrapreta-bounces at bioenergylists.org
[mailto:terrapreta-bounces at bioenergylists.org] On Behalf Of Gerald Van
Koeverden
Sent: Saturday, March 08, 2008 5:03 AM
To: Terra Preta
Subject: [Terrapreta] small-scale torrefaction for developing countries

 

An extract from a USAID report on introducing small-scale torrefaction in
Rwanda.  Unfortunately, the sketch of the equipment  for torrefaction,
grinding and briquetting, would not transfer to this message.   (They use
used car engine oil to heat up their biomass.)  But I included a link at the
bottom.

 

Gerrit

 

Torrefaction Technology 

 

A major concern expressed by many potential users of 

biomass fuel briquettes was the smell emanating from 

the briquettes, and the amount of smoke they emit 

during cooking. A pre-processing technology called 

'torrefaction' was developed to remove the organic 

compounds in the solid waste that emanate bad smell 

and emit excessive smoke in briquettes.  

 

Low temperature carbonization of biomass to obtain 

roasted or "torrefied" products is a relatively recent 

development. Torrefied products can substitute charcoal 

in a variety of applications. Torrefied briquettes have 

superior combustion characteristics as compared with 

ordinary briquettes. They are easier to ignite, burn much 

faster with less smoke, and are essentially odorless 

compared with ordinary briquettes. 

 

The developed torrefaction technology is essentially a 

thermic fluid system comprising of (a) circulating pump; 

(b) oil storage tank; (c) furnace; (d) piping, fittings and 

instruments (Figure 1). The interesting thing about this 

system is its friendliness to the environment. It utilizes 

used car-engine oil, which at present is a nuisance 

waste in almost all the gas stations in Kigali. When 

servicing vehicles, used-oil is usually allowed to drain 

freely from the car engine to a container placed beneath 

the engine. The dirty used-oil is then disposed off in the 

soil where it can cause groundwater pollution, unfriendly 

smell that characterizes most gas stations in the City of 

Kigali, and other adverse effects to the environment. By 

using this oil in the torrefaction system, we are 

essentially cleaning the environment. Secondly, the oil- 

heating furnace is fired using reject briquettes, which 

again perfects the waste recycling system! 

 

The biomass is heated in a modified container system, 

through which hot used-oil is continuously circulated. 

The coil, which is meant to circulate the oil in the 

furnace, is specially designed. The oil gets heated in two 

sections of the furnace, i.e., the radiative and the 

convective zones. First, the oil enters into the coil placed 

in the convective zone and then goes to a portion of the 

coil in the radiative section. After the exit of the oil from 

the coil, its temperature depends upon the temperature 

of the furnace. The oil then goes to the pre-heater where 

the biomass gets heated up. The torrefied material is 

then conveyed to a grinder where it's pulverized before 

being passed into the briquetting machine for 

processing into biomass fuel briquettes. 

 

Also, heating the biomass before processing serves the 

purpose of relaxing the inherent fibers in the biomass 

and apparently softening its structure, resulting in 

release of some bonding or gluing agent on to the 

surface. This phenomenon is also known as 'sweating 

the biomass'. The work requirement for densification 

can be reduced by a factor of about two by preheating 

the raw material. The preheating therefore, lowers the 

power input. This phenomenon of thermally induced 

softening the resistance of fibers is also noticed in the 

everyday domestic activity of ironing cotton clothes. 

Only when the press (iron) is hot enough can the fibers 

in the cotton clothes be oriented in the desired direction 

with minimum effort. Once the biomass fibers are 

softened, a drop in resistance to briquetting results in: 

(a) reduced pressure required for briquetting, resulting in 

reduction in power consumption; (b) reduced frictional 

forces leading to a reduction of wear to contact parts, 

particularly the rotating screw; and (c) reduced 

resistance to flow leading to an enhanced rate of 

production. 

 

Grinding Mill System 

 

This system has been developed/manufactured and 

ready for mounting. Grinding mills are employed to 

pulverize and/or reduce the particle size of the feed 

material. This process results in an increase in the 

surface area of the material for easy, faster and efficient 

processing, to achieve optimum briquetting results.  

 

For biomass materials, it is essential to avoid gravity 

discharge from the grinding mills. We have designed 

and developed a system that utilizes an induced draft 

blower to produce suction that sucks and conveys the 

material pneumatically. 

 

Screw-Press Briquetting Machine 

 

We have manufactured a screw-press briquetting 

machine and currently awaits mounting, testing and 

calibration. Torrefied and pulverized organic waste 

material will be fed continuously into the screw, which 

forces the material into a cylindrical die. The die will be 

heated using a high resistance coil to raise the 

temperature to the point where lignin flow occurred. 

Pressure builds up smoothly along the screw rather than 

discontinuously as is common with piston presses.  

 

Advantages of the Torrefaction, Grinding and 

Briquetting Systems 

 

The above-described systems are homegrown, made by 

local people using local technologies and resources. 

The maintenance costs will be pretty low compared to 

imported systems. Since they are made locally, 

everything is known about the systems, hence, can be 

maintained easily and no need to import any spare parts 

or expertise because they are readily available locally. 

Employment has been created, because in our 

workshop we had no less than 10 technicians working, 

at any given time. Monetary resources were ploughed 

back to the Rwandan economy as opposed to if the 

systems were imported from outside. And more 

importantly, Rwanda stands a very good chance of 

starting to export this system to other neighboring 

countries, when production is scaled up. However, as 

Jamal Sanghir (director for energy and water with the 

World Bank) remarked recently, "renewable energies 

have high upfront costs, and therefore access to 

financing is necessary to scale-up."  

 

Currently, most countries in sub-Saharan Africa are 

importing their briquetting machines from India and 

Europe. Most of these machines have been grounded 

due to high maintenance costs and lack of spare parts. 

Recent cases occurred in Rwanda and Zambia, where 

brand new briquetting machines imported from Europe 

and India stopped functioning just a few weeks after 

being mounted by experts from the exporting countries.  

 

Economic Impact. 

 

Our entire briquetting machinery comprising of a modern 

torrefaction system, grinding mill and a state-of-the-art 

screw-press briquetting machine cost US $ 21,900, 

inclusive of installation, training and 3-6 months free 

maintenance. Investigations reveal that a similar 

system, if imported from India, Europe or USA would 

cost anywhere between US $89,500 and 92,300, 

used to support plant growth and improve soil structure; 

and (iv) to destroy pathogens or unwanted 

microorganisms, insect eggs and weed seeds in the 

organic waste. 

 

http://www.henrykellam.com/reports/CoP_version_Rwanda.pdf

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