Dallas, Texas-based TXI developed a production process that increases clinker production at existing cement plants while reducing CO2 emissions, without significant capital expenditures.

Called CemStar, the patented process utilizes steel slag-a co-product of steel manufacturing-as a raw material in the kiln process. The finished product results in high-quality portland cement, rather than the blended product usually associated with the use of slag. According to TXI, portland cement made using this process is indistinguishable from that made with standard raw materials.

TXI has used the process for five years in its Midlothian, Texas, wet process operation and at its Hunter, Texas, dry process plant. Production increases have averaged 10%, and significant per-unit reductions in fuel consumption and CO2 emissions have been realized, according to Jamie Rogers, general sales and marketing manager for TXI.

The company also has implemented the process in its recently acquired Riverside, Calif., dry process plant. In addition, four other cement producers now use CemStar.

"CemStar...can be employed full time with all existing production systems and process-from preheater to wet kilns with excellent production results," Rogers said. "[It] works with existing facilities, not against them, and there is very little lost production time when implementing CemStar."

TXI is the largest producer of cement in Texas and a major producer in California. In steel, TXI is the second largest supplier of structural steel beams in North America.

CemStar was born about six years ago, when the technical leaders of TXI and its steel production division, Chaparral Steel, began investigating cooperative ventures.

Every ton of slag yields a ton of incremental clinker and eliminates a ton of CO2 emissions. In addition, the use of CemStar may reduce or eliminate the need for current raw materials such as clay and shale. These are significant sources of hydrocarbon and sulfur emissions, and, for many plants, also are expensive raw materials.

Due to its chemistry, which is similar to finished clinker, and its low melting point, slag readily mixes and bonds with other ingredients in the kiln. Slag and clinker essentially come from the same raw materials, but slag has already been subjected to the same heat process that clinker receives in the kiln. Many of the chemical changes have taken place in the steel furnace, and less heat is required per unit of product.

Slag's low moisture content also translates into substantial moisture reduction and fuel savings when the CemStar process is used in wet process operations, according to TXI. As a result, there are virtually no additional fuel costs.

Rogers noted that implementation of CemStar typically requires one or two months, a time frame that includes studies, testing, and a brief period of equipment installation, and involves no production downtime. Capital expenditures are generally less than $200,000, primarily for conveyors, elevators, and hoppers to feed slag into the back of the kiln with the other ingredients.

As part of its licensing agreement, TXI provides slag as well as on-site technical assistance. "We will take whatever measures are required to get our licensees up and running quickly and successfully," Rogers added.

Rogers said the process makes sense as an economical method of expanding capacity. "Rather than spending a lot of time and money on plant upgrades or new plants, it makes sense to maximize your existing operations. [It] also presents a more economical alternative to imports," he noted.

The United States will import about 20 million tons of cement and clinker from Europe and Asia in 1998 to supply current demand.

"CemStar is very competitive...because transportation and handling increases those costs significantly," Rogers said.

This article was adapted from materials supplied by TXI. The patented CemStar process utilizes steel slag-a co-product of steel manufacturing-as a raw material in the kiln process, resulting in higher-quality portland cement, lower CO2 emissions, and reduced expenditures, according to its developer, TXI.