• Water Management

Combustion Emissions

The cement industry has an enviable record in reducing air pollutants. It is working closely with the Environmental Protection Agency and state regulators to develop new standards and technology to manage air emissions. Investment in new equipment and technology to reduce emissions totals in the millions of dollars per year.

Cement companies also work with state and local officials to meet the National Ambient Air Quality Standards (NAAQS). For example, the industry is conducting ongoing cooperative efforts with federal, state, and local officials to study emissions controls of fine particulates and other pollutants. Further emission reductions are achieved by utilizing waste fuels that would otherwise be burned unproductively in incinerators.

In a perfect world combustion products would be limited to just water and carbon dioxide, but that is not possible with cement manufacturing. Nitrogen oxides can be formed from nitrogen in the fuel or raw materials, or from a reaction of nitrogen with combustion products (prompt NOx). The great majority of NOx in cement plant exhausts are known as thermal NOx which is the conversion of nitrogen in the air around the fuel combustion flame at temperatures greater than 1200° C. A short hot burning zone can reduce the formation of thermal NOx. Sulfur oxides, or SOx, is formed as sulfur compounds are oxidized at temperatures of 300 to 600° C. Limiting the sources of sulfur or excess oxygen can limit the potential for SOx formation. Carbon monoxide (CO) formation is another concern; it is either formed because of incomplete combustion or the rapid cooling of combustion products below the ignition temperature of 610° C. The particulate matter from the raw materials (cement kiln dust – CKD) can become entrained in the exhaust gas and carried out of the kiln system. The vast majority of the CKD is removed by fabric filters, known as baghouses, or by electrostatic precipitators.

The portland cement industry was among the first to tackle the issue of climate change, and it has remained at the forefront of developing global climate change policies and improving the manufacturing process. Of the several gases which are related to climate change, carbon dioxide (CO₂) is the principal emission from the cement industry. CO₂ results from the combustion of carbon-based fuels and from raw material calcination, which is the conversion of carbonates in the raw materials into the various compounds which give cement its unique properties. From the PCA publication: U.S. and Canadian Labor-Energy Input Survey 2006, from 1972 to 2006 the cement industry reduced energy consumption by 37.5% which means that the fuel CO₂ was reduced by nearly the same amount. In 2000, the industry created a way to measure CO₂ emissions, and by the year 2020, the industry plans to voluntarily reduce CO₂ emissions per ton of cementitious product by 10% below the 1990 baseline.

The most recent progress involves newly introduced cement guidelines that will allow for greater use of unburned ground limestone as a component in finished cement, which will ultimately reduce calcination CO₂ by more than 2.5 million tons per year.

Today, the cement industry fuel CO₂ accounts for less than 3% of U.S. industrial CO₂ emissions, well below other sources such as the petroleum industry (21.8%), chemical industry (22.2%), and iron and steel mills (9%).

By 2020, the industry aims to reduce CO₂ emissions by 10% from the 1990 baseline levels. To achieve this goal, the cement industry has adopted a three-part strategy:

1. Improve the energy efficiency by upgrading plants with state-of-the-art equipment
2. Improve product formulation to reduce manufacturing energy consumption and minimize the use of natural resources
3. Conduct research and develop new applications for cement and concrete that improve energy efficiency and durability

In the 1990’s, PCA and its member companies joined the USEPA ClimateWISE program. This voluntary program assisted companies in improving energy efficiency and reducing CO₂ emissions. As part of this program, an MS-Excel spreadsheet was developed for the calculation of CO₂ cement plant emissions. This farsighted effort was used to develop an international emission calculation spreadsheet (See WBCSD information in the above sidebar). PCA member companies are using this international consensus-developed spreadsheet to calculate current and past CO₂ emissions.

› Next