Cement Kilns - Overview

1. Cement Kilns - Overview Prepared for the CEC North American Strategy for Catalyzing Cooperation on Dioxins, Furans and HCB Source Control Workshop April 17-18, 2008 Leon, Guanajuato, Mexico

2. Cement Kilns - Overview • Cement is manufactured by burning limestone in high temperature kilns to produce clinker, which is then ground and blended with additives to produce cement • Cement is the ‘glue’ used to make concrete, a key construction material used for infrastructure • Feed materials can include limestone, chalk, sand, shale, marl, etc. • Fuels include coal, petroleum coke, oil, gas and alternative fuels such as: • tires, tire derived fuel (TDF), spent solvents, hazardous wastes, etc. • Use of alternative fuels can offset fuel costs, as generally more cost-effective • The combustion process in the kiln has the potential to result in the formation and subsequent release of dioxins/furans and HCB. • Cement kilns firing hazardous waste are noted as having relatively high potential for the formation and release of dioxins/furans, HCB, and unintentional PCBs (UNEP Stockholm Convention on POPs)

3. Cement – typical dry kiln system(Source: CEMBUREAU. Best Available Techniques for the Cement Industry, December 1999; http://www.cembureau.be)

4. General Measures 1 • For new plants and major upgrades, dry kiln system with multi-stage preheating and precalcination is considered state-of-the-art. • Cement plants typically use dust (particulate matter) control measures. BAT for dust control include: • Electrostatic precipitators with appropriate monitoring/ control equipment to minimize the number of CO trips • Fabric filters with bag leak detectors • Achievable performance: 20 to 30 mg/m3 • May also have measures to prevent or reduce emissions of: • NOx: low-NOx burners, selective non-catalytic reduction (SNCR), selective catalytic reduction (SCR) • SO2: absorbent injection, dry scrubber, wet scrubber, activated carbon, switching to low sulphur fuels and/or feeds. 1 European Commission, Reference Document on Best Available Techniques in the Cement and Lime Manufacturing Industries, December 2001, http://eippcb.jrc.es/pages/FActivities.htm

5. Primary Measures 1 Examples: • Process optimization: • rapid cooling of off-gases to below 200OC • Characterize and monitor parameters that corresponde to good operation • Maintain stable operating conditions • Minimize fuel and energy use with use of preheating nad precalcination • Pretreatment of wastes to enable a more homogeneous feed and stable combustion conditions • Avoid use of waste derived fuel during start-up and shutdown • Waste should be fed through the main burner, or secondary burner for preheater/precalciner kilns. • For secondary burners, combustion zone temperature should be maintained at >850OC for a residence time of 2 sec. 1 Part II Source Category (b): Cement kilns firing hazardous waste, Revised Draft Guidelines On Best Available Techniques And Provisional Guidance On Best Environmental Practices Relevant To Article 5 And Annex C Of The Stockholm Convention On Persistent Organic Pollutants, December 2006, http://www.pops.int/documents/guidance/batbep/batbepguide_en.pdf

6. Secondary Measures 1 • Improvement of dust abatement, ESP or fabric filter • Achievable performance of 20 to 30 mg/m3 • Activated carbon injection (combined with use of fabric filters) • Activated carbon filter • Selective catalytic reduction (SCR) • Note, may required increased fuel use for reheating of off-gases • Achievable performance based on BAT for control of D/F should be < 0.1 ng ITEQ/Nm3 with reference conditions of 273 K, 101.3 kPa, 11% O2, dry gas basis. 1 Part II Source Category (b): Cement kilns firing hazardous waste, Revised Draft Guidelines On Best Available Techniques And Provisional Guidance On Best Environmental Practices Relevant To Article 5 And Annex C Of The Stockholm Convention On Persistent Organic Pollutants, December 2006, http://www.pops.int/documents/guidance/batbep/batbepguide_en.pdf