A comprehensive examination of TLUD technology will necessarily involve four essential realms or areas of focus:
Fuels
Combustion Devices
Applications of Heat
Human Factors
Every successful cookstove project must address four essential components: fuels as the source of energy for producing heat, combustion devices (devices to release the energy of fuels as heat and light) to obtain heat, applications of produced heat (i.e., the purposeful capture of heat energy, as in a cooking pot), and human factors such as costs, cooking preferences/traditions, cultural considerations, and user-friendliness. Failure in any of these four components will lead to failure in the project.
Many cookstove projects are differentiated primarily by applications and human factors. With regard to applications (such as single-pot direct heat or plancha griddle tops or baking), primary considerations include stove structure with a focus on the transfer of heat to the pot. Applications are typically defined locally and solved locally. Human factors, on the other hand, are much more personal and cultural, having less to do with the actual physical stove, but often requiring the greatest efforts and investments of time and money.
Let’s introduce the TLUD stove by showing one in action. The first 30 seconds of this video shows an overview and was submitted to Google’s “Project 10 to the 100th” contest. The rest (2:50) shows the processes and issues in more detail.
The Burning Process
In simplified terms, the burning of dry biomass involves three major chemical reactions:
The most visible one is the “combustion” (full or incomplete) of the combustible gases created by the other two reactions. Combustion requires “secondary air” for the necessary oxygen, and gives the visible flames. The other conspicuous reaction is the chemical transformation (“pyrolysis” and “carbonization”) caused by heat (with or without oxygen), resulting in combustible gases and the creation of charcoal. The least visible is the oxidation (“primary air” is required) of the carbon (“char-gasification”) to create carbon monoxide, which is combustible if kept concentrated and hot. Ash is the non-combustible residue after char-gasification.
These three processes occur nearly simultaneously in regular fires, making them difficult to see or to control individually. The simultaneous entry of the primary and secondary air is the major reason why burning wood and other biomass in traditional/typical stoves is incomplete, causing smoke and serious health problems.
But when the gases are generated but not burned immediately, the gasification processes (pyrolysis and char gasification) are more easily understood, seen, and controlled. This separation of gasification from combustion (including the separate entry of the primary and secondary air) is the key distinguishing characteristic of “gasifiers,” and is the main reason they can be so clean burning, even in small cookstoves.
Key References
For all who are new to TLUD cookstoves, a concise set of key reference documents includes the following:
(Note: Click any document’s link to view now in an overlay window, or save a copy for later by right-clicking the paper’s link and choosing the Internet Explorer “Save Target As” or Firefox “Save Link As” menu option.)
“Micro-Gasification: What it is and why it works” by Anderson, Reed, and Wever (Boiling Point, 2007)