Border Environment Research Reports (Number 2 - June 1996)

Reducing Emissions from Brick Kilns in Ciudad Juárez: Three Approaches

Summary

Background

The Southwest Center for Environmental Research and Policy (SCERP) is currently supporting three studies on the problems of the brick kilns. SCERP researchers at the Ciudad Juárez campus of the Instituto de Estudios Superiores de Monterrey (ITESM, or Monterrey Tech) have been working with private and governmental organizations on both sides of the border to bring the first of the three projects to fruition. This project on co-firing waste fuels with less polluting fuels actually began in 1991 when a Mexican nonprofit organization, the Mexican Federation of Private Health and Community Development (FEMAP), and Empresas de Solidaridad established a training center for brickmakers called the Instituto de Investigaciones Ecotecnológicas (IIET). El Paso Natural Gas Company provided funds for the center's operation and the Los Alamos National Laboratories have provided technical assistance. The goal of this training center is to teach brickmakers, through a series of four courses, methods of brick firing that both improve environmental conditions and do not strain the limited resources of kiln owners.

In another study, researchers from the University of Texas at El Paso (UTEP) are cooperating with FEMAP to investigate the possibility of reducing pollution by shortening the firing time of the bricks. Current methods require that up to a third of total firing time be used in order to remove moisture from the bricks. Researchers are therefore exploring the use of low temperature solar collectors as a drying device.

The University of Utah is conducting yet another experiment to substitute less polluting natural gas or propane fuels for a portion of the waste fuels. While complete substitution of these cleaner fuels for the tires and scrap wood customarily used by the kiln owners would be ideal for air quality improvement, this solution is not economically feasible given the owners' financial resources and the higher cost of propane and natural gas. The objective of this project is to find the least costly combination of fuels that will produce the least amount of pollution.

The Brick Industry

Brickmakers. The brickmakers are generally very poor and minimally educated, with an average of only three and one-half years of schooling. The mean age of the brickmakers is 46. The homes of the brickmakers are extremely modest, with an average of 1.1 rooms per home, and a mean of almost five persons per home. Brickmakers are paid very little, and their "homes" are often made of cardboard or scrap wood, shoddily erected on land next to the kilns. Less than half of these homes (43%) have sewer facilities. Thirty-nine percent of all brickmakers' families have had at least one child die.

Process. The brickmakers work an average of seven months per year due to weather conditions that limit production. The process of making bricks begins when workers mix clay, water, and sand, often using their feet near the end of the mixing to ensure the correct consistency. The finished mix should be smooth and evenly moist, and it is left covered with plastic overnight. The mix is then thrown by hand into open brick molds that hold three to five bricks.

The bricks must then be dried before they are fired. To dry them, the brickmakers place the molded bricks on the ground and periodically rotate them. An experienced brickmaker can tell when a brick is ready for firing by the sound it makes when it is hit against another brick.

At the beginning of the firing process, the kiln is left uncovered so that all of the moisture remaining in the bricks can evaporate. When the workers no longer see water vapor above the kiln, the kiln can then be covered. After 16 to 24 hours of firing, the bricks are ready. The most common fuel used for firing is waste fuel that can be obtained at virtually no cost to the owners, including tires, battery cases, plastics, wood, sawdust, particle board, and used motor oil. Some owners also use more expensive fuels such as fuel oil, diesel, natural gas, or propane.

Costs. Kilns average 10,000 bricks per bake, and the mean number of bakes per month is .98. About five percent of each batch of fired bricks is unusable. The primary cost to kiln owners is labor. Even the kilns themselves cost little to build, since they are made of adobe brick. Kiln owners who operate within the city must pay a bit more, however, since they must also cover the cost of transporting materials to the kiln site. Fuel costs range from 15% to 30% of total production costs, depending on the type of fuel used. A good production cost is about US$635, and a good profit per bake is about US$127.

Not only does this process of brickmaking generate a great deal of harmful pollution, it also fails to produce a quality brick. Brickmakers claim to be able to produce bricks of higher quality. However, because builders most often choose the cheapest bricks regardless of quality, there is little incentive for brickmakers to improve quality. The bricks on the market in Mexico, therefore, have poor strength, high water absorption characteristics, and inadequate insulation properties.

The Brickmakers' Training Center

• to conduct research on improving the brickmaking process within the resource limits of the kiln owners;
• to train brickmakers in improved processes and better technologies; and
• to alter market forces that encourage polluting brickmaking practices.

Courses. The Training Center offers four technical courses:

• Brick Production Process and Alternative Products,
• Fuel, Combustion, and Pollution,
• Heat Transfer, and
• Industrial Safety.

These classes are designed to be easily understood even with low levels of education, since most of the brickmakers have not completed elementary school. To further simplify the transfer of new technology from researchers to brickmakers, instructors have developed four comic book style texts to accompany each course (Figure 1).

Figure 1. Text for Course on Fuel, Combustion and Contamination

As of June 1996, a number of the courses have been offered with a total of some 325 brickmaker participants, most of them kiln owners. Eighty of the participants were from Ciudad Juárez, which represents only about 5% of the total number of brickmakers in the city. However, because most participants were kiln owners, their employees represented close to 50% of all brickmakers in the city. The remainder of the participants were from Zacatecas, Torreón, Saltillo, San Luis Potosí, San Luis Río Colorado, Agua Prieta, Chihuahua, and from even as far away as Mexico City. Dormitories are available at the Training Center for out-of-town participants.

Results. The training courses have seen very positive results in the form of changes made by many brick kiln owners in the Ciudad Juárez area. The number of kilns using tires, plastics, and other high polluting fuels has been greatly reduced, with the majority of them turning to sawdust and wood chips. Up to 60% of all brick kilns in Ciudad Juárez have used liquid propane, although the number of kiln owners purchasing gas fuels at any one time depends on the market price of these fuels. The course on how to use liquid propane and natural gas has been beneficial, since those who were using gas fuels prior to the class were able to reduce fuel consumption by nearly 30%. This was mainly due to tips provided during the courses on how to conserve heat during bakes. Other positive results have been that brickmakers have nearly doubled the number of bakes per month by making changes in labor practices, and suggestions on improving the brick mixtures by using better quality materials have resulted in an improved quality brick. Many of these courses cover ideas that the brick kiln owners may have already known, but by emphasizing these better procedures and giving the owners a chance to practice them helps the new techniques to become common practice.

Researchers from ITESM have also been working with the local and federal governments to improve building regulations. In proposed legislation drafted by the university, new building construction would require bricks fired with liquid propane or natural gas. This would assure that environmentally cleaner fuels would be used and the benefits to the region would be significant.

Research on Drying Bricks

Field tests of small-scale solar dryers have been performed to see if significantly more moisture is removed from the bricks this way than by open air drying (Figure 2). The moisture content of a brick right out of the mold is about 27%. After baking in the sun-about three days in the summer, six in the winter-5% to 10% of the total brick content is still water. The water is stored in the brick in two ways-as chemical (bonded) water and as mechanical (unbonded) water. Mechanical water can be removed via solar dryers, but chemical water cannot be removed except when temperatures of at least 400degC are reached. In other words, even when solar dryers are used, bricks will require at least some firing to remove the chemical water.

Figure 2. Solar Dryer Side View

UTEP performed several tests over time on three different methods of drying:

• placing bricks in convection ovens, set at 65.6degC and 104degC,
• drying in solar dryers, and
• sealing bricks in plastic bags in the sun.

Figure 3. Weight Change of Bricks with Different Drying Methods

In another test, solar dryers were again compared with convection ovens and natural drying where the bricks were not sealed in plastic bags. The solar dryer and convection oven performed similarly, bringing the bricks to a 5% moisture content sooner than those dried in the sun reached this content. The total amount of moisture removed was also greater in the solar dryers than with natural dryers.

This study is scheduled to be completed in the summer of 1996, when more complete information on these tests will be available.

University of Utah: Co-Firing Waste and Gas Fuels

The focus of the University of Utah research is to decrease emissions of pollutants and to decrease consumption of gas by:

• co-firing gas with other fuels, and
• changing kiln operation and/or design in order to improve heat efficiency.

A pilot-scale brick kiln has recently been designed and completed at the University of Utah, and testing began in February 1996. The kiln is full-scale in height and one quarter-scale in width and depth. The facility will burn locally available waste fuels that include sawdust, wood scraps, and agricultural wastes. Gas will be fired above the kiln bed to reduce emissions. Researchers will monitor kiln exhaust for concentrations of polluting emissions. Results of the study will be included in the brickmakers' training courses in Ciudad Juárez so that the outcomes can be effectively transferred to brick producers.

Conclusion

Sources