Charcoal Testing Data

As noted in a previous blog post, we are entering the charcoal business in western Kenya with a sustainable alternative to conventional lump charcoal that can compete on both cost and quality bases. We have spent the last month experimenting with different binders and charcoal made from different parent material to find the optimal charcoal briquette.

Our initial market research revealed that the most important qualities of a briquette to Kenyans are cost and burn duration. As such, we used thermocouples and an Arduino-based system to test each variety of briquette for burn duration and calorific value — the latter to ensure that charcoal alternatives offered similar heat production to traditional charcoal. Briquettes were aligned in the bottom of a typically-sized and -used metal jiko stove. We did not stack the charcoal; we allowed for only one base row. The thermocouple tip was placed in the middle of the jiko at the same height for each test. Find a graph of the results below. There is a link at the end of the document to download the data spreadsheet.

Apologies for bad formatting, but it's better to see the whole graph!

One of the first noticeable results from the graph is the climb to peak temperature. Each of the re:char briquette blends reached peak temperature long before lump charcoal. As long as the duration of the burn is sustained, this is a desirable quality as there is less wait time for the charcoal to reach appropriate cooking temperatures.

While the briquettes made from sugarcane char and woodchips reached a high peak temperature the most quickly, the burn did not last. What cannot be detected in the graph is that this blend was very smoky – a quality not usually associated with charcoal. Given that traditional wood cooking stoves produce a lot of smoke, this finding is not surprising.

The extruder screw press that we use.

The best performers from our study were traditional lump charcoal, sugarcane charcoal that had been put through an electric extruder screw press without any binder, and the same extruded sugarcane charcoal bound with an unusual binder: dog food. It was on a whim that we decided to try the dog food as a binder. Because the local variety is starchy – the usual requirement for binders – has a consistency similar to porridge and thus the other binders we used, and because it was available, we thought to try it.

The lump charcoal and dog food-bound briquettes reached similar temperatures and declined at a similar rate once they reached roughly 300 degrees Celsius. The dog food briquettes outperformed traditional charcoal in that they reached peak temperature more quickly, maintained peak temperature for a longer period of time, and then initially declined at a slower rate. The sugarcane charcoal that passed through the extruder press but was bound by water moisture alone outperformed the other two briquettes in its duration. It took an extra 30 minutes to reach 100 degrees Celsius.

Whereas loose sugarcane char is a collection of straw-like pieces that do not adhere together particularly well, when the sugarcane char is passed through the extruder screw press, it is homogenized into a uniform charcoal slick through pressure and a small amount of heat. (See previous post for more information on the extruder press and briquette production.)

A critical component of producing any type of briquette is moisture content. An update from our previous “Step by Step Guide to Making Biochar Briquettes” post: the wetter a briquette is before compression, the looser the briquette will be once it is dry. Loose briquettes break easily under pressure from transport and heat, and they typically burn for shorter amounts of time. We still maintain that charcoal needs to be moist before compression is applied so that the moisture can aid in binding the briquette. We recommend that producers wring out wet charcoal before compressing it.

Moving forward, we look forward to receiving market feedback in the next two weeks about which of the extruder press-produced briquettes is preferred. Once we have identified the favorite, we will ramp up production!

re:char Charcoal Testing Excel Spreadsheet

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