Ten rules energy efficient cost effective brick firing
Practical Action
5 Continuous kilns are more efficient than batch kilns
Continuous kilns typically use 'waste' heat to pre-heat green bricks. This means less heat is
lost, and firing is more efficient. Also, the structure of the kiln doesn't need to be heated up
for each batch of bricks. Continuous kilns, such as a Hoffman kiln or a Bull's Trench, are
usually only feasible for brickworks making 10,000 or more bricks per day. There is a lack of
designs for smaller continuous kilns. However, anything brickmakers can do to use waste heat
will cut costs. The Vertical Shaft Brick Kiln (VSBK) is a continuous kiln, originally of Chinese
design, that is being promoted and slowly gaining acceptance in some countries in South and
East Asia.
6 Green bricks should be dry going to the kiln
If green bricks still contain a lot water when they are placed in the kiln, then energy, and
money, is wasted just to dry them. In hot, dry climates bricks should be slowly but completely
dried before firing using energy from the sun.
Example
Señora Jara used to rush her freshly moulded bricks to be fired. The bricks weighed 3.60
kilograms going to the kiln, and 0.60 kilograms was water. It takes at least 2.59 MJ to
raise each kilogram of water to boiling point and evaporate it. So, Senora Jara was using
15,540 MJ in each 10,000 brick clamp just to dry her bricks. This used 0.62 tonnes of
coal and cost her more than $248 per clamp.
7 Fuel should be dry
As with the bricks themselves, if the fuel contains water, then energy is wasted to evaporate
it. If using fuelwood, it should be dry and seasoned. Large, dense, slow burning logs are
generally better than the same mass of small, green twigs.
8 Good kiln control saves energy and money
Kiln temperature should rise quite slowly and constantly, otherwise heat is wasted. And, if the
temperature rises too fast, bricks can be damaged. The temperature shouldn't be allowed to
fall until firing is complete. As a rough guide, a 40,000 brick kiln fired externally might be
slowly heated over a period of 2 or 3 days until no more steam comes from the top. It should
then be fired for 4 to 6 days until the bricks at the top are getting red hot. The kiln is then
sealed at the top, and the fires maintained for about a day. After this 'soaking' stage, the kiln
is completely sealed and allowed to cool. It may take a week or two before it's cool enough to
open. Smaller kilns will burn more quickly, larger ones more slowly.
The flow of air through a kiln should be controlled - too much will cool the bricks and waste
energy, too little and the fuel will not burn completely. The major loss from most kilns is due
to too much cold air being drawn in. Using a permanently set hearth, or fire grate, and
dampers, allowing better control of the firing process, could offer substantial savings.
Protecting the fires from cooling winds by using wind breaks will also promote economy and
help the kiln burn evenly throughout.
9 Record keeping is important
Unless it is known how much fuel, or more precisely energy, a particular kiln used, it will be
impossible to know when improvements have been made: has less fuel been used? Were costs
reduced? Practical Action has developed a system for kiln monitoring which means not only
can one firing be compared with another, but the efficiencies of different processes around
the world can be compared directly.
4