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 gt850OC 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/guida
nce/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 lt 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/guida
nce/batbep/batbepguide_en.pdf