ERAtech Group LLC

3508 Wilmington Pike

3508 Wilmington Pike.

Dayton, Ohio 45429

Telephone: (1)937 859 8998

Fax:(1)937 859 9132

Internet e-mail: rkohnen@eratech.com

 

 

 


Questions and Answers Pertaining to the Use of Recycled Liquid Fuels in Cement Kilns

 

 


Cement Manufacturing

 

 

 

Q

How is cement manufactured?

 

 

 

A

Limestone, clay, sand and a small amount of iron-containing materials are heated in a huge kiln at very high temperatures until they chemically combine to become marble-sized modules called "clinker." The clinker is then mixed with gypsum and ground to a fine powder to make cement. Cement, in turn, is a key ingredient in concrete, which is a vital component of roads, buildings, homes and offices.

 

 

 

 

 

Q

What is a cement kiln?

 

 

 

A

The cement kiln is a long, inclined cylinder which can be hundreds of feet in length and up to 25 feet in diameter. Raw materials enter at one end and cement clinker exits at the other. Material temperatures required to make cement clinker must be maintained at a minimum of 1345 oC/2450 oF while gas temperatures inside the kiln can reach in excess of 1925 oC/3500 oF. During the operation, the kiln slowly rotates to ensure a thorough blending and "cooking" of the raw materials.

 

Exhaust gases leaving the kiln pass through air pollution control devices such as baghouse filters or electrostatic precipitators.

 

 

 

 

 

Q

What types of fuels are used to make cement?

 

 

 

A

Traditional fossil fuels, such as coal, petroleum, coke and natural gas, are the primary fuels used to make cement. However, the kilnís high internal temperatures and other aspects of the cement manufacturing process are ideal for the destruction of organic chemical waste, which normally have to be disposed of in some fashion.

 

 

 

 

 

Q

How much coal and oil can be saved by recycling waste in this way?

 

 

 

A

Cement kilns use several hundred tons of coal per day to produce the energy necessary to manufacture cement. At a 30 percent waste derived fuel (WDF) substitution rate, this would amount to a reduction in coal use of approximately 38,300 tons (153,200 barrels of oil) per year for a typical long, wet kiln.

 

 

 

 

 

Q

What types of WDF will be used as fuel?

 

 

 

A

Typical waste materials used as fuels include such familiar items as paint thinners, printing inks, paint residues and industrial cleaning solvents.

 

 

 

 

 

Q

Does the use of WDF affect the cement?

 

 

 

A

Production of high quality cement is the top priority of every cement manufacturer. Therefore, great care is taken to ensue that only those wastes that can be safely recycled and that are compatible with the cement manufacturing process are used.

 

Because the chemistry of cement-making is both sensitive and precise, manufacturers cannot afford to put anything into their kilns that could produce variation in the cement. If they did, the cement would not meet the rigorous, industry-wide product quality set by the appropriate standards group or agency pertaining to the cement industry in the country. In the United States, this group would be the American Society of Testing and Materials (ASTM).

 

 

 

 

 

Q

In the United States, what do the ASTM standards cover?

 

 

 

A

ASTM specifies tests and test methods to ensure uniform controls on cement produced throughout the USA. Before the product can be called portland cement, tests must show it has the required chemical composition. It must also pass tests measuring physical qualities, such as strength and particle fineness. In this way, product quality is assured regardless of what raw materials or fuels are used.

 

 

 

 

 

Q

What regulations govern the transportation of WDF to the plant?

 

 

 

A

Trucks transporting waste derived fuels to cement kilns are regulated just like other trucks on the road. In addition, drivers receive an on-site orientation covering cement plant safety rules and load processing procedures. Transporters who haul these fuels into a facility must meet all of the local regulations.

 

 

 

 

 

Q

What happens to the WDF after it is delivered?

 

 

 

A

The facilities for unloading, storing and transporting WDF to the kiln are designed and built to approved regulatory specifications. Integral to these specifications are fire prevention. Such areas are also designed to meet or exceed federal and local standards for environmental safety, including secondary containment in the unlikely event of a spill.

 

 

 

 

 

Q

What happens to the WDF in the kilns?

 

 

 

A

All WDFs are composed of organic and inorganic compounds. The organic portion of the waste materials is flammable. The organics release heat as they are burned. As they are burned, they get broken down into the basic elements of hydrogen and carbon. Some water vapor is also given off.

 

The high temperatures, counter current gas flows, turbulent conditions and long retention times in the cement kiln destroy more than 99.99 percent of all organic compounds. While the inorganic metals cannot be destroyed, the cement manufacturing process effectively manages them. It should be understood that the raw materials used to make cement contain most of the metals found in WDF. Most dust particles containing metals are returned to the system. There, they are chemically bound into the cement.

 

 

 

 

 

Q

Would it be better not to burn WDF in cement kilns?

 

 

 

A

No. In fact, high temperature destruction is the preferred method of managing organic chemical wastes. There are no better alternatives. Land disposal of untreated organic chemical wastes, for instance, is being banned worldwide because the wastes can move through the soil and pollute groundwater. Land disposal is simply long-term storage, leaving the problem of ultimate disposal to future generations. Cement kilns provide an excellent way to recycle WDF as an energy source.

 

 

 

 

 

Cement Kilns and Air Emissions

 

 

 

Q

What happens to the organic wastes when they are used for fuel in a cement kiln?

 

 

 

A

Cement kilns manage WDF through a process of high temperature combustion. This involves heating the waste to a sufficient temperature, keeping it in the kiln for enough time, and providing the fuel with sufficient oxygen. This method destroys organic chemical wastes, such as paint thinners, printing inks and industrial cleaning solvents.

 

Combustion in an existing manufacturing process, such as cement manufacturing, has become the preferred method of managing these wastes since the energy value is reclaimed. The conditions in the kiln ensure that 99.99 percent or more of them are destroyed, that is, converted to carbon dioxide and water vapor.

 

 

 

 

 

Q

Do organic emissions from cement kilns pose a health risk?

 

 

 

A

Because cement kilns effectively destroy more than 99.99 percent of organic chemical wastes, only trace amounts of organic compounds are emitted. Testing has indicated that these emissions are independent of fuel type. In fact, organic emissions are sometimes reduced through the use of waste derived fuels. The quantity of organic emissions is so small, it does not present a perceptible increase in risks to public health or the environment. Cement kiln exhaust gasses typically contain less than one-tenth the hydrocarbons present in automobile exhaust gases.

 

 

 

 

 

Q

What about dioxins?

 

 

 

A

Dioxins are chemical compounds found throughout our environment, usually in extremely small concentrations. They are formed as contaminants during the production of certain herbicides, germicides, wood preservatives and bleached paper products. They can also be formed when materials are not completely burned as in wood fires, automobiles, and cigarette smoking. When formed in that manner, they are a type of products of incomplete combustion (PIC). Studies have shown that cement kilns are so good at destroying organic chemical wastes, emissions of dioxins (or any other type PIC) are so low that they pose virtually no danger to human health or the environment.

 

 

 

 

 

Q

What would happen if some of the fuel used contained dioxins?

 

 

 

A

Temperatures of 900 oC/1650 oF will destroy dioxins in less than one second. Because cement kilns operate at much higher temperatures (at least 1345 oC/2450 oF) and because the burning wastes have an average residence time in the kiln of at least two seconds, any dioxins are destroyed. However, dioxin waste is not accepted by ERAtech for use in its cement kiln projects.

 

 

 

 

 

Cement Kilns and Metals

 

 

 

Q

How does the cement manufacturing process manage metals?

 

 

 

A

All fuels used in cement kilns contain metals. This is true whether they are fossil fuels, like coal, coke and oil, or WDF. The raw materials (limestone, clay, sand) used to make cement clinker also contain metals. In fact, certain metals, such as iron and aluminium, are essential components of the final product. Whilst metals cannot be destroyed, the cement manufacturing process effectively manages them in three ways.

 

First and foremost, cement kiln operators limit emissions by carefully restricting the metals content in wastes accepted for recycling. Second, dust particles containing metals are returned to the kiln where metals are chemically bound into the cement. Third, particles not returned to the kiln are captured in air pollution control devices. The small amounts emitted from the stack have been demonstrated to be below levels of health concern.

 

 

 

 

 

Q

How are metals incorporated into cement?

 

 

 

A

All fuels contain organic compounds and metals. The kilnís intense heat breaks down the organics, leaving the metallic compounds. These compounds then bond chemically with the line, clay and the raw materials in a tight crystalline structure and become a part of the clinker.

 

 

 

 

 

Q

Is the cement hazardous if it contains metals?

 

 

 

A

No. In fact, cement made with WDF contains essentially the same amount of metals as cement made using traditional fossil fuels such as coal, coke or oil. Also, tests show cement made with WDF has essentially identical leaching characteristics as those of cement produced solely with traditional fuels. Thus means the metals are no more likely to leach out of the cement made using WSF than if it were made using coal, coke or oil.

 

 

 

 

 

Q

Does chemical bonding prevent unsafe levels of metals from washing out of the cement when it is used to make concrete?

 

 

 

A

Yes. Using a regulatory testing procedure, scientists have confirmed that the chemical reactions that must take place in order to make cement, prevent unacceptable concentrations of metals from being released either from cement or the concrete.

 

 

 

 

 

Q

Can the metallic-bonding laboratory results be confirmed by experience with more normal uses of concrete?

 

 

 

A

Yes. One historical use of concrete has been for pipes used to transport drinking water. Drinking water is routinely tested to show that it meets federal standards for a wide variety of contaminants including metals. Testing has shown that there is no reason for concern over the safety of concrete pipes to transport drinking water.

 

 

 

 

 

Q

What kind of air pollution control devices are used to trap metals that might be emitted from the kiln?

 

 

 

A

Electrostatic precipitators and baghouses are used to catch dust particles containing metals. Electrostatic precipitators use an electrical field to remove all the particles. Baghouses use fiberglass filters, similar to vacuum cleaner bags, to catch them. These particles, called cement kiln dust (CKD), are trapped by this equipment and returned to the kiln for incorporation into the cement.

 

 

 

 

 

Q

Is the CKD hazardous if it contains metals?

 

 

 

A

CKD has received extensive testing. These tests have demonstrated that as long as the fuel specifications are met, CKD characteristics are not significantly changed.

 

 

 

 

 

Q

What are the potential health risks from metal emissions to nearby residents and the surrounding environment?

 

 

 

A

Health risk assessments performed by a number of cement facilities in the United States have demonstrated that risks are well within regulatory limits. One particular study in Texas was conducted in an area where three cement plants were in close proximity. Contaminants found during the monitoring of the surrounding air in the vicinity of those three kilns were found to be well below any levels of health concern.

 

 

 

 

 

Use of Waste Derived Fuels

 

 

Q

Will WDF be used simultaneously with the fuel the cement kiln uses today?

 

 

 

A

Yes. WDF will only be substituted for about 25 to 50 percent of the current fuel. Although it is safe to burn WDF as the only fuel, it is more practical to use it along with the current fuel. The main reason for this is the WDF supply is not sufficiently available to maintain it as the primary fuel. Without sufficient supply, there would be a constant switching of fuel types from one to another. We know from experience that this switching of fuels creates problems in the kiln operation, and is a practice to be avoided. It is better to consistently burn WDF as a portion of the kiln fuel.

 

 

 

 

 

Q

How is WDF burned simultaneously with your current fuel?

 

 

 

A

During the early efforts to burn WDF in cement kilns in the 1970s, a separate fuel lance was thrust into the kiln through the kiln hood. The fuel was atomized with air and the resultant plume impinged on the flame from the primary burner. This method is still used today during trials. For kilns that burn WDF on a continuous basis, a burner is designed to handle two different fuels. Generally, the WDF is fed through a separate line that is run down the middle of the primary fuel burner. This way the WDF is atomized as a plume inside the plume of the primary fuel. This gives a very even flame pattern and less fluctuation.

 

 

 

 

 

 

 

Q

Do other cement manufacturers use WDF?

 

 

 

A

Yes. There are about 36 kilns in the U.S. that burn liquid supplemental fuels and used oil. In 1992 these facilities consumed over 650 million liters of WDF. England, Canada, Norway, France, Belgium, Germany Ė nearly every major country burns some type of waste material (frequently hazardous) in cement kilns.

 

 

 

 

 

Q

What difference will cheaper fuel make?

 

 

 

A

One of the major costs in producing cement is the energy needed to make clinker. Substituting a cheaper fuel for the present fuel will reduce this cost. This cost reduction can be translated into more revenues for the cement plant by allowing the price of cement to be less, thereby selling more cement and operating the kiln at higher production rates more efficiently. In the U.S., this type of fuel has allowed older, less-efficient wet kilns to compete effectively against more efficient multistage preheater/precalciner kilns.

 

Lower production costs translate to the manufacture of more cost-competitive cement in the world market along with the preservation of local jobs at the cement plant.

 

 

 

For more detailed information, contact ERAtech
to discuss your waste-derived fuel needs.

USA Tel:1 937 859 8998
USA fax: 1 937 859 9132

E-mail rkohnen@eratech.com

www.eratech.com