Owing to the current healthy state of the mar-ket, the expected growth in local demand for face bricks and the subsequent opportunity to increase the company’s market share in the sector, clay brick producer Rosema is aiming to expand its kiln capacity, says Rosema factory manager Chris Clarke.
He notes that there has been an upswing in the industry since 2013, adding that some companies were unable to survive the previous downswing, which he attributes to the depression of the construction industry and the 2008 housing market slump.
Clarke says capacity expansion can be achieved by either building a new kiln or improving the efficiency of Rosema’s existing gas-fired tunnel kiln.
However, he notes that doubling production by simply duplicating operations and building a new kiln might be too hasty, as Rosema might not be able to immediately sell double the amount of bricks.
While expanding the factory’s capacity is a priority for Rosema, the evolution of this particular market is slow, owing to the cost of the necessary equipment, such as tunnel kilns, Clarke notes.
Clarke highlights that the tunnel kiln, which Rosema currently uses to manufacture bricks, is generally considered the most efficient type of mass-production kiln in the world.
There are about 30 tunnel kilns in use in South Africa, with each kiln on average producing three-million bricks a month, though this represents only about 20% of the market, he adds.
Clarke further highlights that a large portion of the remaining 80% of companies, which are using older, less-efficient firing technologies, such as clamp kilns, are under increasing pressure because of the technologies’ environmental impact.
He predicts that the use of older technologies, which use twice as much energy as tunnel kilns, will gradually be discontinued, with only some businesses being able to convert to using tunnel kilns, creating more opportunity for development in the market.
Clarke highlights that there are about 200 brick manufacturers in South Africa that collectively produce about two-billion bricks a year; however, their bulkiness generally excludes them from being an export product.
The Brickmaking Process
After the clay is mined on site at Rosema’s factory in Olifantsfontein, Gauteng, it is crushed, reduced to fines, mixed with water, shaped into a solid rectangular slug and cut into bricks. Clarke explains that the wet bricks cannot be placed into the furnace, as they would explode – hence, they are placed in the tunnel dryer for about three days to remove the moisture.
The bricks travel on the cars through the 130 m kiln and are exposed to progressively higher temperatures within the firing zone until they reach the soaking zone, which can reach up to 1 085 °C – the kiln’s maximum temperature. After being in the soaking zone for about eight hours, the bricks gradually cool down for another day before they reach the exit mouth of the kiln.
Clarke says manufacturing these bricks from dust takes about seven days.
Rosema assistant manager Marco Da Silva tells Engineering News that building a new kiln of the same size as the company’s existing kiln will cost about R200-million.
Currently, Rosema’s tunnel kiln has the capacity to cure 100 000 bricks simultaneously. A single 2.7 m car of 6 720 bricks takes about three days to pass through the kiln.
Clarke says that improving the efficiency of the kiln will involve reducing this timeframe. He notes that the company’s existing kiln is about 30 years old and that there are new technologies that can improve the efficiency of the kiln.
Another possibility for improving efficiency, says Clarke, is to improve the clay bricks’ receptiveness to heat, which can be achieved by amending the clay recipes.
Rosema is also aiming to improve its brick-drying capabilities, as improving the efficiency of a dryer essentially means that water is removed as efficiently as possible.
Clarke explains that the drying process is made more efficient by increasing the amount of air-flow in the dryer, making the air warmer and enabling the dryer to accommodate air that is slightly more humid.
Meanwhile, he remarks on the superior efficiency achieved when using gas to fire the kiln. Originally, energy and chemicals company Sasol supplied hydrogen-rich gas, converted by Sasol from coal into gas, to the furnace. However, in 1990, Rosema switched to using Sasol’s natural gas from Mozambique, which is more effective than the hydrogen-rich gas.
Clarke says the kiln uses about 16 000 GJ/m of gas and suggests that further efficiencies in terms of the type of gas Rosema uses are quite limited.
However, he suggests that the efficiency can be improved by changing the applications. Burner designs, for example, have improved so that the burners distribute heat more evenly through the stacks of bricks in the kiln.
Da Silva says the holes in bricks allow for more even heat-distribution and airflow in the kiln.
Clarke adds that brick manufacturing changed recently to include more holes, thereby increasing the surface area of the brick, resulting in more efficient drying and firing.
Further, refractory bricks that form the base of the kiln cars and line the kiln’s walls and suspended roof are up to 30% lighter than 30 years ago, he says.
Clarke notes that advancements in ceramic insulating materials that comprise refractory bricks enable them to absorb less heat. Clarke explains that the lighter refractory bricks, which absorb less heat, result in more heat being available for the clay bricks.