First successful firing of bricks in vertical shaft brick kiln

sm_hvc A few decades ago in China a new type of continuous kiln was invented. While the traditional continuous kilns (Hoffmann type) require a high investment, the Chinese kilns are relatively easy to build and were copied in India a few years ago. For the past three years SofoNic has been working on adaptation of the vertical shaft brick kiln to the conditions of Latin America. The principal aspect is that in China and India the firing is done with coke, while in Nicaragua the firing is with wood.

By Kurt Rhyner

hvc_001We traveled to the north of Nicaragua to carry out the second trial of firing the new kiln. As we arrived we encountered Franklin (the young engineer in charge of the project) inside the kiln, placing the first batch of bricks. Each batch has four rows and approx. 180 bricks. Afterwards he was relieved by Marcos and a worker of the cooperative who finished loading of the kiln. There weren't enough bricks with the adequate dimensions, so we partially used smaller ones.

At two a clock in the afternoon we lit the fire. With10 batches of bricks collocated, the kiln was almost full, something that almost gave us problems later on.

As the fire wood was humid (it rained a lot the past few months and that afternoon it also started to rain) and the bricks really green (to not say wet). The burning began with lots of vapor and smoke which came out of all possible openings, even out of the loading zone. Afterwards the situation calmed down somewhat, with lots of vapor coming out of the bricks as well as the chimney. We closed the two combustion openings, and from the first moment on it was evident that in the northern firing compartment the flames would make their way to the inside, and in the southern compartment they would go out. After many discussions and inquiries we came to the conclusion that this is because of a wall that is in front of this compartment, which debilitates the air flow through the ash box. It must be said that this already happened the first time although the wind conditions where very different. While, in this case there was no regular wind, but a light wind changing directions, this different condition of the two fireboxes kept up until the end.

hvc_002At six o clock in the afternoon the technical team took a rest, leaving the cooperative in charge of maintaining the fire until one o´clock in the morning. We considered that at this time the bricks would have lost their humidity and the sintering process would have started.

At one in the morning we arrived at the kiln and lowered the first batch, which of course was cold. These bricks were carried up and again collocated in the kiln. This was extremely hard work as it had to be done inside the kiln, under extreme temperatures and with some smoke. If we had had enough bricks this work would have been much easier as we could have worked outside of the kiln with less heat and smoke.


Afterwards we lowered the second batch and proceeded the same way, and also with the third batch, but suffering the awkward conditions again, which is not a problem of the kiln but a result of the lack of bricks. Kurt decided to lower the intensity of the fire to make sure the bricks wouldn't over cook or melt due to excessive heat, something that would be fatal in this kiln, as it would obstruct the unloading.

In the fourth batch at four in the morning we got the first red bricks that were situated in the lower part of the firebox. We were able to see that the next batch (fifth) would have a majority of baked bricks. Just as expected, it was evident that the firing was better on the northern side than on the southern side. We let this batch cool down while we continued with higher fire as we saw that the baking time or the heat intensity was still low.

hvc_003

At six o clock in the morning we were able to unload the fourth batch without problems (already cooled down) and the fifth was lowered. In this batch all the bricks on the northern side were already red, while on the southern part still lots of bricks didn't cook yet. We broke three bricks and discovered different grades of finishing (in two the center still had not cooked through), but we were clear that the system functions!

hvc_005Together with the director of the cooperative we analyzed the path ahead and decided to enlarge the access of the northern firebox to have more wind movement and, at the same time, make the work in front of the firebox easier. It is also necessary to have a ladder and it was recommended to leave more space between the bricks once they are being collocated in the kiln to facilitate the heat conduction, as well as put doors on the ash boxes in order to be able to control the air flow.

Raul now was sorry not to have had enough bricks, as once the kiln is fire it keeps going with little wood. While this is evident, we still don't have the real calculations. We decided to wait until we have 10 000 bricks ready to do the next burning, to be able to fire during four or five days and get a clear experience and numbers.

It is clear that the oven functions! What we still lack is the practical knowledge about its operation, and still have to optimize.

You are here: Home Past editions Edition 23 - December 2006 First successful firing of bricks in vertical shaft brick kiln

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