REDUCTION OF ATMOSPHERIC POLLUTION THROUGH TECHNOLOGICAL CHANGE IN THE CLAY-BAKING INDUSTRIES IN THE SOGAMOSO VALLEY, BOYACÁ, COLOMBIA

The Sogamoso Valley is located in the central part of Colombia, 260 kilometers to the northeast of the capital city of Bogotá . It comprises an area of 23,189 square kilometers and has a population of close to 150,000. Brick manufacturing is the primary economic activity: 140 kilns are located within the urban area and 80 in the rural area, with an annual production of 5,002,504 units.

CURRENT SITUATION

Most of the operations in this area are characterized as informal and use inappropriate technology. Coal—approximately 14,063 tons annually—is used to bake the bricks, and as a result, the valley has a high level of air pollution. The inefficient combustion systems used in these facilities, known as chircales, is another cause of environmental degradation.

Emissions levels from coal burning in the area are as follows:

Average Atmospheric Emissions (1996) *

Particulates (t/year)	CO (t/year)**	CO2 (t/year)	SO2 (t/year)	NOx (t/year)
678	3,940	1,690	1,318	216

* Estimated from coal consumption

** Considering a 29% combustion efficiency in Slow Burning kilns

The socioeconomic situation of the owners of these brickmaking facilities is best described as: family-owned operations run by people with a low level of education, poor health conditions, and difficult access to basic services. This means that these chircales, or brick factories, are strictly a subsistence type of industry with no growth potential; family income is U.S.$1,475 per year[1]. They also have weak marketing systems, lack product diversification, and make inefficient use of energy.

Inefficiency in combustion systems causes high coal consumption, which wastes the energy potential of coal in the process. This waste of a resource could be considerably reduced if combustion systems could be improved. However, unwillingness on the part of the brickmakers themselves and the fact that this industry is so informal make such improvement difficult.

The following table illustrates the energy efficiency levels for the different kinds of kilns used to bake bricks:

Energy Efficiency of Kilns*

Type of Kiln	kcal/kg	kg of coal/unit
Slow Burning**	2,800	2.8
Inverted Burner	1,400	1.4
Zig Zag	500	0.5
Hoffman	450	0.45
Tunnel	350	0.35

*In making this table, coal was assumed to have a heating potential of 7,000 kcal, with each brick unit having a weight of 7 kg

** Type of kiln most often used in Sogamoso Valley

STRATEGIES

The overall strategy involved a series of alternatives for solutions:

ACTIONS IMPLEMENTED

The second alternative was the one selected to improve the situation in the region. Slow Burning kilns were replaced by the Inverted Burner type, a change that provides some benefits, such as decreased coal consumption and a resulting decrease in emissions. These kilns do present a problem, however, in that they actually utilize only 40% of the total amount of energy supplied for baking brick, while 50% remains in combustion gases. This means that most of the inefficiency is concentrated in this part of the process.

The proposal put forth by PROPEL emphasized optimization of energy use in kilns of this type, through recovery of heat from combustion gases for preheating primary air and regulating the fuel/air mixture. Excess air was regulated to keep it under 100%, and energy from combustion gases was recovered so that they were emitted at a temperature of under 120 °C, with a savings in coal consumption amounting to up to 40%. Thus, a functional efficiency close to that of the Zig Zag kiln may be achieved with considerably less investment.

RESULTS

The immediate benefit of the changeover from the Slow Burning kiln to an Inverted Burner type kiln—operated with energy recovery and regulation of excess air—is a reduction in coal consumption of 2.8 to 0.8 kg per unit. When current average annual production is used as a reference, a substantial decrease in coal consumption is involved in this kiln change:

Slow Burning Kiln:   14,063 t/year

Inverted Burner Kiln: 4,018 t/year

The above data show a 70% decrease in coal consumption. Through the productive centers concept, it is possible to achieve a significant increase in production, thus decreasing the impact that the clay-baking industry could have on the environment from gas and particulate emissions.

Under this system, annual emissions from these improved systems amount to:

Estimated Emissions from Improving Combustion Efficiency in Kilns

Particulates (t/year)	CO (t/year)*	CO2 (t/year)	SO2 (t/year)	NOx (t/year)
34	160	1,446	53	36

*Considering 90% combustion efficiency in the Slow Burning kiln

Lastly, to summarize the benefits of this technological change, the following comparative table shows the ecoefficiency indicators obtained using conventional technology versus cleaner technology:

Ecoefficiency Indicators

Factor	Conventional Technology	Cleaner Technology*	Percentage decrease (%)
T raw material/t product	1.17	0.9	20
J / t product	11,725.3	3,350.1	70

* Improved Inverted Burner Kiln

CONCLUSIONS

Given the current situation of the Sogamoso Valley, the area with the highest atmospheric pollution rates in Colombia, the need exists to start reconversion processes to improve both the environmental situation and  the efficient use of energy in the clay-baking industry.

The data on energy-use improvement in kilns have been derived from data obtained by using a Model for the Evaluation of Drying and Baking Systems in Brick Manufacturing (Spanish acronym MESSYC), developed at the National University of Colombia through support by PROPEL.

Use of the MESSYC enabled the current functioning of kilns to be evaluated. It also allowed predictions of kiln performance to be made after certain changes were introduced to enhance energy use at different stages of production, such as recovery of heat from gases, preheating, and regulation of excess primary air.

The productive centers model has not yet been implemented because of social and cultural difficulties that have already been mentioned. Efforts are now being made, however, to start using this concept, due to the interest that exists in improving the situation of these small industry producers. This solution arose from the working experiences that PROPEL has accumulated with brickmakers in Ibagu and the Sogamoso Valley, and therefore it is firmly believed that this is the best way to move these industries along the road to ecoefficiency, with all its accompanying benefits.

GLOSSARY[2]
Slow Burning Kiln: An artisan-type kiln composed of a semicircular dome upon which bricks are placed, leaving spaces for ventilation windows and the release of combustion gases.
Inverted Burner Kiln: An intermittent kiln with a round roof, stack, loading door, and three to five burners arranged symmetrically around the side of the kiln, depending on its size.
Zig Zag and Hoffman Kilns: These are continuous, high-production-type kilns. The Zig Zag Kiln has more than two chambers, with burners located at the top of the kiln, whereas the Hoffman has two long galleries with barrel arches connected by fire holes at the ends. In these kilns, burners are moveable while the load remains stationary.
Tunnel Kiln: A kiln made up of a gallery faced with refractory brick, which has platforms running through it in all three sections of the kiln (preheating, baking, and cooling), where stacks of brick are placed. In this type of kiln, the load is moveable and the baking areas are stationary.

CONTACT

Ing. Carlos Humberto Barragán
PROPEL
Carrera 12 # 93-31, Oficina 406
Bogotá, Colombia
Tel. (57-1) 622 1314/1336
Fax (57-1) 622 1247
E-mail: propel@colomsat.net.co

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[1] Camargo, Elizabeth. Diagnóstico de la industria consumidora de carbón en el sector ladrillero de Sogamoso y calero de Nobsa. (Diagnosis of Coal-Using Industries in the Brickmaking Sector of Sogamoso and Nobsa Lime Deposit). Ecocarbon, April, 1996.

[2] Corpoboyacá . Estudio de Impacto Ambiental para el establecimiento de la planta piloto de producción de ladrillos de Pantanitos. (Environmental Impact Study for Establishment of a Pilot Plant for Brick Production in Pantanitos). Sogamoso City Government, January, 1997.