SCERP Project Number: AQ94-5.2
Principal Investigator: Geoffrey D. Silcox and JoAnn S. Lighty
University of Utah
Goal:Experimental evaluation of (1) the use of local fuels to reduce overall demand for natural gas or propane while using small amounts of these gaseous fuels to reduce emissions, (2) modification in combustion characteristics to improve heat transfer and, (3) process changes to improve overall thermal efficiency.
Rationale: Emissions of toxic combustion by-products from the manufacture of bricks can be largely eliminated by the exclusive use of natural gas or propane as energy sources. The cost of these gaseous fuels and the lack of infrastructure in the border area makes this alternative prohibitively expensive. Previous experimental work at the University of Utah has shown that small amounts of gaseous fuels (roughly ten percent), when used in conjunction with low quality solid and liquid fuels, can result in reductions in emissions of CO by up to 80 percent. In addition, any changes that result in increases in thermal efficiency and in heat transfer reduce the amount of fuel that is required to produce the bricks with a consequent reduction in emissions of air pollutants.
Approach: The firing of bricks in small, privately-owned kilns has been identified as a major source of air pollution in the border area. A community group, FEMAP, with support from El Paso Natural Gas and others has built a training and development center in Juárez which is currently helping the local population to convert these kilns from highly polluting waste fuels to natural gas and propane. However, the high cost of natural gas and propane makes it desirable to supplement these clean burning fuels with other fuels such as saw dust, wood scraps, and agricultural waste. This project is designed to directly support the on-going efforts of the FEMAP Training Center. The project focuses on the question of how gas consumption can be reduced through the use of locally available, lower cost fuels (in conjunction with gas firing) and through other changes in the kilns to improve the efficiency of both combustion and heat transfer. All modifications of brick kiln design or operation are being evaluated in terms of their cost to avoid changes which cannot be afforded by the owners of the kilns. The project involves experimental testing in a pilot-scale brick kiln being built at the University of Utah's combustion laboratory and associated modeling of the system. The modeling is being used to evaluate heat transfer and the efficiency of combustion in the kilns.
Status: A pilot-scale brick kiln has been designed and fabricated. The refractory lining for the kiln was poured in December 1995. Testing began in September 1996.
Front and right views of the kiln are shown in Figure 1.
Figure
2 (65K)
A cross-sectional view showing insulating materials and their thicknesses is given in Figure 2. The inside dimensions of the kiln are 3-by-5-by-10.5 ft. The kiln consists of three sections, each four feet tall. The facility is full-scale in height and roughly one-fourth- scale in width and depth. Four layers of insulation line the inside of the facility. The shell is 3/8 in. carbon steel. The bottom section is the combustion zone. The top two sections serve as a quench zone. The combustion zone is separated from the upper sections by an arched, removable refractory barrier, like what is found in field units. An induced draft fan will pull air into the system. The typical firing rate will be 300,000 Btu/h although the facility has been designed to handle firing rates as high as 3,000,000 Btu/h.
The development and testing of a pilot-scale soot sampling system on an existing, wood-fired, pilot-scale furnace at the U. of U. have been completed. A one-dimensional model of the heat transfer in brick kilns has been developed. This will be used with a soot oxidation model to estimate soot burnout.
The new facility will be used primarily for the experimental evaluation of local fuels to reduce overall demand for natural gas or propane while using small amounts of these gaseous fuels to reduce emissions. In these experiments the solid waste fuels, for example, saw dust, wood scraps, and agricultural waste, will be fired on the floor of the kiln while one or more gas burners will be fired above the bed to oxidize soot, CO, and hydrocarbon before the gases enter the quench region.
Figure 3: The effect of using a small amount of natural gas on CO emssions from a pilot-scale spreader stoker furnace firing 20 percent railroad ties and 80 percenter coal. The overall stoichiometric ration at the exit of the facility was 1.28 and the percent of fuel total heat input from natural gas is plotted on the x-axis (Owens, 1994).
The results obtained in this part of the study are expected to be like those shown in Fig. 3 (Owens, 1994) which is a plot of CO concentration (dppm or ppm on a dry basis) as a function of the amount of natural gas being added to the system, expressed as a percentage of the total fuel heat input. The addition of only 10 percent natural gas reduces the CO emissions from 300 dppm to about 50 dppm.
Concentrations of CO, NO, soot, and O2 in the exhaust will be determined for at least three fuels and at firing densities ranging from 20,000 Btu/ft2 to 50,000 Btu/ft2 and at stoichiometric ratios ranging from 1.2 to 2.0.
Typical soot mass concentration measurements obtained as part of a FY93 SCERP project are shown in Fig. 4 (SCERP Year 3 final report, JoAnn Lighty). Soot concentrations are shown for three wood-based fuels: particle board and pallets manufactured in Mexico and the US. The Mexican pallets are made from hardwood while the US pallets are softwood.
Practical Use: The results of this study will be applied directly
to the brick making industry in the border area through our collaborator,
Octavio Chavez, at FEMAP's brick maker training and development center
in Juárez.
The FY94 SCERP-supported phase of this project: AQ94-5.2
The FY95 SCERP-supported phase of this project: AQ95-
9
Find out more about SCERP's other projects involving the Cd. Juárez brickmakers.
Last updated 7/1/99