AEIC

Vertical Shaft Brick Kiln

The process of rehabilitation and reconstruction requires construction material of all types, including burned bricks. Bricks traditionally bum in Afghanistan with wood or bushes. Millions of tons of wood are thus burned every year. The AREA kiln uses coal. fines as its only source of energy. The kiln around the clock and employs ca. 40 persons on a permanent basis. In spite of utilizing coal there is no visible smoke.

Advantages:

1. 70% energy efficiency.
2. High quality at low cost.
3. Environmentally and socially healthy.
4. Promotion of small entrepreneurship.
5. Self sustaining program.
6. Environmentally and socially healthy.
7. Self sustaining program.

1. A Vertical Shaft Brick Kiln (VSBK) is an energy efficient technology for fired clay brick production. This technology originated in China and has about 10,000 kilns running at present. In India, the VSBK technology has introduced at a pilot scale in 1996 and presently 20 kilns are operational. It essentially consists of one or more rectangular, vertical shafts within the kiln structure. Rectangular arrays of dried green bricks and crushed fuel (coal) are carefully stacked into batches, which are loaded into the shaft from the top and finally batches of fired clay bricks are removed from the bottom end. During this process, the batches of bricks pass through the preheating, firing and cooling zones before they reach the shaft exit.

2. This technology relies on the principle of counter correct heat exchanger in order to achieve high thermal efficiency. When the shaft lid is in the closed position, the entire kiln functions as a chimney. The heating cycle for the green bricks is between 22-24 hours. A kiln with 2 shaft of 1.25m x 2m - produce upto 10,000 bricks in a day, which equals to the annual brick production of around 2.5 million.

3. The VSBK technology considerably economizes on fuel cost, with savings of between 30 to 50% when compared with other common firing technologies such as clamps or Bull’s Trench Kilns. Pollution levels are extremely reduced compared to other prevalent methods of brick firing.

VSBK Technology Transfer to Afghanistan

In April 2004 an international VSBK conference was held in Katmandu. A participating delegation from Afghanistan expressed thereafter a strong interest to introduce the VSBK technology in their country. Skat conducted a feasibility study in November/ December 2005, supported by SDC. This was based on the need for cleaner brick production and a potential for overall improvement of the brick manufacturing sector. In addition, the persistence and willingness of private entrepreneurs to contribute led to an in-depth assessment.

The study revealed a booming Afghan construction sector due to large numbers of public and private post-war reconstruction initiatives resulted in a significant increase in demand for bricks and therefore in a growing brick making industry. A detailed assessment of the current brick production sector with regard to technological, environmental, economic, social, and institutional aspects confirmed a high need for improvement. The existing brick making technologies create heavy environmental pollution, such as serious air pollution. Ongoing inefficient firing methods include the burning of tyres and scarcely available wood.

Furthermore, the study shows that there is high potential for change towards the environment and social friendly VSBK technology. The VSBK technology saves energy between 40 to 50%, reduces emissions by 80 to 90 %, improves drastically working conditions, and is economically viable.

As a technology shift does not only concern the firing method but also the entire production system, a technology transfer is only effective and sustainable if a holistic approach is applied. A holistic approach considers besides the technology and environment also economic, institutional, and social aspects. Experiences in India and Nepal have shown that a pilot project approach is most appropriate to adapt and optimize the technology to the local context and to anchor know-how and expertise within the existing institutional set up.

In 2006 the VSBK Technology Transfer to Afghanistan was launched. This includes the active involvement of key stakeholders such as pilot entrepreneurs, support service providers, government departments, etc. Skat has implemented first knowledge sharing and capacity building activities which have been organized by the ongoing VSBK Programs in Nepal and India. Stakeholders receive and exchange tangible information about the VSBK technology for informed decision making as well as to be enabled to arrange for the required pilot project preparations.

Introduction

The vertical shaft brick kiln (VSBK) is classed as a continuous updraft kiln and represents a comparatively new and unique method of firing bricks. It was developed in China in the late 1960s during the cultural revolution, when there was a large demand for bricks in the rural areas of China. There are thousands of this type of kiln currently operating in China, but only a few proto types have so far been built in other countries.

It is a revolutionary type of brick kiln, combining the simplicity and low cost of updraft firing with very impressive fuel economy, plus the benefits of continuous operation. It is used in China as a single or double shaft kiln by small scale seasonal brick making entrepreneurs, wherever there is an abundance of good brick making clay and a reliable supply of coal fines. Its operation is very similar to that of a vertical shaft lime kiln, with coal and bricks being loaded at the top, and fired bricks combined with a small amount of ash being unloaded at the bottom.

Figure 1

A single shafted vertical brick kiln in China

Kiln design

Within a roofed and buttressed rectangular support building is a well insulated fire-brick lined firing shaft, open at the top and bottom. This shaft is approximately 6.5 meters in height with the central 4 meters being lined with a single layer of firebrick. There are two versions of the kiln currently in use: a single shafted model with a 1.5 x 1 meter rectangular shaft and a double shafted model where the shafts are 1 meter square.

At the base of each shaft is an arched unloading tunnel running through the centre of the kiln. This tunnel allows access to both sides of the base of the firing shaft and contains the brick support and unloading equipment.

Loading the kilns

Bricks and coal, a batch at a time, are loaded at the top of the shaft, the coal fines being sprinkled among the green bricks one layer at a time.

In the single wider shaft kiln, each batch of bricks is made up of four layers making a total of 320 bricks, and the shaft holds twelve batches to give a firing capacity of 3840 bricks every 12 hrs. The bottom layer of bricks in each batch, which is the first loaded, consists of 68 bricks arranged in 7 rows to provide six open channels running across the firing shaft. These channels are to allow the placement of the steel beams that support the bricks in the kiln. The second layer of 84 bricks is placed at right angles to the first layer bridging the channels. The third and fourth layers, each of 84 bricks, are added at alternating right angles to make up a complete batch. The bricks in each layer are carefully spaced apart to provide a gap of 1 to 1.5 cm around each brick. Coal is spread evenly on top of each layer of bricks, except the first layer with the cross channels. It is then brushed off the top surface of the bricks into the gaps around the sides before the next layer of bricks is added. A fresh batch of bricks is added each time a batch of fired bricks is removed from the base of the kiln.

With the double smaller shafted kiln the shafts are loaded and unloaded alternately with 188 bricks in each batch, 12 batches per shaft, making a total firing capacity of 4512 bricks every 12 hrs. Ideally a batch of bricks is unloaded every 45 minutes to 1 hour, but the usual practice is to unload and load 3 or 4 batches at a time. The number of batches and the time of unloading is decided by the fire master, who judges this by the colour and position of the firing zone in the shaft. The quantity and quality of the coal fines and condition of the green bricks will determine the speed of firing.

Figure 2

View down the firing shaft showing firebrick lining (China)

Kiln efficiency

Despite there being no controllable fireboxes and the kiln working on the normally least efficient up draught system, it is extremely fuel efficient. This is because the firing shaft creates just enough natural draught for complete and efficient combustion of the fuel spread evenly throughout the firing zone. The packing of the bricks restricts the draught enough to limit the amount of excess air not required for combustion. The cooling bricks below the firing zone heat up the air for combustion. The hot exhaust gases from the firing zone pre-heat the green bricks and fuel prior to combustion. The firing shaft is very well insulated on all four sides, so heat loss is minimized. Once the kiln is up to temperature, all the heat from the coal fines goes into the firing of the bricks. Very little heat is 1ost in the exhaust gases or in steady state heat loss through the fabric of the kiln.

Figure 4

Loading bricks and coal in the vertical shaft brick kiln

Brick wastage is very low when compared with the Hoffmann and Bull's Trench kiln, being 2 to 5% in China and 5

to 7% in Pakistan. This is mainly due to the fact that the kiln fires so evenly, with no over or under-fired bricks. Any wastage results from careless brick handling and low quality green bricks being loaded.

Kiln maintenance is low, because the only machinery involved is the basic unloading system

Advantages of the vertical shaft brick kiln

It represents a very energy efficient low cost method of firing bricks on low grade coal fines. Its efficiency is twice that of Hoffmann or Bull's Trench kilns running on coal. The fired quality of the bricks is high with a low wastage.
The kiln is cheap and straightforward to build, and requires very little maintenance once constructed. It does not require an external power source, except for electric lighting during night operation.
The kiln is very compact, not requiring a large area of land and can be built near to the clay source. It is small and straightforward enough to be considered for rural brick production, where coal fines are available, to replace the less efficient coal and wood burning brick clamps used in many countries. In China, the kilns are easily taken apart and rebuilt with the original materials, when the clay source in one location is worked out, so it has the flexibility, in this respect, to be used in a similar manner to brick clamps.
The construction cost is low and several shafts can be linked together in a row to cope with larger capacity brick works.
The kiln is not effected by variations in the weather, as long as dry green bricks are available.

Figure 6 Cross-section of a VSBK with single shaft, chain block unloading.

Because of the highly efficient combustion of coal in the kiln, localized air pollution is minimal. There is little or no visible smoke while the kiln is running. Steam and combustion gases are quickly dispersed from the top of the firing shaft, which is well ventilated.

More than one shaft allows for firing flexibility to cope with seasonal and economic variations in brick production and demand.
Labor requirements are low, requiring one man to load and two men to unload, during an 8 or 12 hour shift. The labourers are not working continuously, as there are 3 or 4 hours between each loading/unloading session.

Disadvantages of the vertical shaft brick kiln

It is a new type of kiln and method of firing bricks that has only recently been introduced to countries outside China. Despite there being thousands of this type of kiln operating in China, the technology has not yet been adopted anywhere else in any quantity.
The kiln requires good quality green bricks, because they have to be able to withstand being stacked 5 meters high in the firing shaft. This does not exclude hand molded bricks, as has been demonstrated in Pakistan, where all the bricks were slop molded.

Figure 7

View of the top of the vertical shaft brick kiln