Ash Grove Launches Major Environmental Initiatives
Environmentally responsible operation is a priority at Ash Grove plants around the country. The company’s efforts in this area range from simple steps to large-scale research, testing and implementation of alternative processes that offer the potential to reduce emissions or conserve energy. In 2007, Ash Grove has made major progress in this area, notably at the company’s plants in Oregon, Texas and Nebraska.

Utilizing new technology to reduce mercury emissions in Oregon
Cement manufacture uses limestone as a raw material, and its local availability is a major criterion for plant location. The limestone quarried at the company’s Durkee, Oregon, plant has a relatively high amount of naturally occurring mercury, and the facility recently launched a proactive effort to explore ways to reduce the amount of mercury from its operations.

On April 11, scientists from the University of North Dakota began work alongside Ash Grove employees to install equipment at the plant to test mercury control technology and collect data about the control of mercury from the facility’s flue gases. That data will assess both the specific potential control technology as well as the impact on mercury recovery of different design and kiln operating parameters. The project represents the most comprehensive test of the potential mercury control technology—activated carbon injection—ever performed on a cement kiln in the United States.

The company has enlisted the assistance of the University of North Dakota’s Energy and Environmental Research Center (EERC) to conduct the test. The EERC has a portable slipstream baghouse, through which flue gases from the kiln are passing during the test. (“Baghouse” is an industry term for a particle collection chamber that contains a number of permeable filters through which exhaust passes.) Activated carbon is injected into the system, and the particulates are collected by a series of filters on the downstream side of the baghouse. Data to determine possible emissions reductions is collected both at the entry to and the exit from the baghouse to permit evaluation of the degree of control achieved.

“Although there are some subtle physical and chemical processes at work,” says Co-Project Manager and University of North Dakota professor Dr. Michael Jones, “the fundamental thing that we believe will happen is that mercury, which is primarily in gaseous form in the flue gas, will attach itself to the carbon. This effectively converts the mercury from a gas to a particulate that can be removed much more easily using standard filtration technology. The effectiveness of this process will also vary with temperature, gas velocity, and a range of other factors, so we’ll attempt to systematically vary those parameters to help identify the combination of conditions that optimize mercury removal.”

Improving local air quality in Texas
The Dallas-Ft. Worth region has been struggling for some time to meet the federal ozone standard, and Ash Grove is doing its part at the Midlothian plant to improve air quality in the area. For some time, we’ve been working to reduce a type of ozone-forming emission from the kiln called NOx (oxides of nitrogen). NOx is produced in combustion processes. Since 1996, we’ve reduced NOx emissions by 43 percent, and we are currently implementing additional technology that will reduce emissions even more. That technology is called Selective Non-Catalytic Reduction (SNCR) and was chosen based on a comprehensive analysis of other cement plants around the world.

SNCR involves the injection of ammonia into the kiln’s flue gas. This converts NOx emissions in the flue gas into elemental nitrogen and water. According to Ash Grove’s Vice President- Environmental Affairs, Fran Streitman, “We are in the process of installing full-scale SNCR technology at our plant in Midlothian, and we anticipate achieving through this recently proven technology a substantial further reduction in NOx emissions in the area.” Overall, the addition of this technology offers the potential for an approximately 30 to 40 percent reduction in NOx emissions.

“These three projects are emblematic of our comprehensive environmental policy. Every day, we’re working to maintain the highest levels of environmental stewardship.”

Chuck Wiedenhoft
President, Ash Grove Cement

Ash Grove has made a significant investment in finalizing the system’s design, and the data that has been collected shows that SNCR has reduced NOx emissions more than 35 percent from the test kiln. That kiln now meets the NOx limit in the state’s plan to improve air quality in the region. Based on the success of this test, and following the required permit applications and regulatory approvals, Ash Grove plans to have SNCR installed on all of the Midlothian plant’s kilns for the 2008 ozone season, helping to meet the state’s plan requirements one year early.

Reducing emissions and improving energy-efficiency in Nebraska Making cement requires the heating of raw materials to about 2,700° F in a large cylindrical kiln. As you can imagine, generating that heat requires large amounts of fuel, and typical fuel sources include coal and natural gas. Recently, however, Ash Grove’s Louisville, Nebraska, plant has applied for a permit to use tire-derived fuel in its manufacturing process.

Ash Grove plants currently using tire-derived fuel

• Durkee, Oregon
• Foreman, Arkansas
• Inkom, Idaho
• Leamington, Utah
• Midlothian, Texas
• Seattle, Washington

Several Ash Grove plants are already using tire-derived fuel, which consists of discarded automobile and truck tires, and the process offers several environmental benefits. First, it helps to reduce emissions. During a July 2005 test at the Louisville plant conducted in cooperation with the Nebraska Department of Environmental Quality, the substitution of scrap tires for coal significantly reduced emissions at the plant, including oxides of nitrogen, sulfur oxides and carbon monoxide. Next, it helps to reduce the demand for imported fuels and limits quantities of domestically produced fuels. Finally, it is helping to reduce the disposal burden faced by a number of states by decreasing the number of tires being placed in landfills and helps to avoid illegal dumping of tires, which can provide a breeding place for disease-bearing mosquitoes.

According to Louisville Plant Manager Dan Peters, “The substitution of scrap tires for coal at Ash Grove’s plants will provide significant environmental benefits to the state, while lessening the facility’s reliance on coal by 10-20 percent annually.”