Waste Generation

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Waste Generation

• Julia Kitchen

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The Preparation of Cement
Mining, crushing, and grinding of raw materials
calcining (heating a substance so that it
oxidizes or reduces) the materials in a rotary
kiln
cooling the resulting clinker
mixing the clinker with gypsum
milling, storing, and bagging the finished cement
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Areas of Concern

• Particulate matter
• Dusts
• Largest waste produced by cement manufacturing
• NOx
• Nitrogen oxides
• SOx
• Sulfur oxides
• Mercury
• Heavy metal
• Volatile Organic Compounds
• VOC
• Liquid effluent
• From cooling efforts and Storm water

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Particulate Matter (Dusts)

• Sources
• Clinker cooler
• Crushers
• Grinders
• General Handling

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Reason for Concern

• Health Impacts
• Acute and Chronic Illness
• Premature Death
• Size Matters
• The size determines where the particulate matter
  will be deposited in the respiratory system.
• The smaller the particulate, the smaller and most
  sensitive part of the lung it can reach.

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• Goal
• Reduce the emission from the stacks.
• Collection
• Recycling
• Ideal generation
• Less than 0.2 kilograms of dust per metric ton
  (kg/t) of clinker, using dust recovery systems.

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How to Reduce Particulate Matter ?

• Dust can be minimized by reducing gas turbulence
  in the kiln and avoiding excessive flow
  velocities.
• The use of chains near the cool end of the kiln
  can also minimize dust by trapping the dust
  before it is released in the kiln exhaust. Most
  kilns are already equipped with such cool-end
  chain sections.
• The use of fuels with a low ash content, such as
  liquid hazardous wastes, can also reduce the
  amount of cement kiln dust generated.

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NOx and SOx

• Gaseous Emissions
• Mainly nitrogen oxides and sulfur dioxide.
• Process controls
• Including balancing the alkali content in raw
  materials and fuels increasing oxygen partial
  pressure, increasing dust load, and reducing kiln
  volume load, can reduce sulfur emissions in the
  process.
• Process controls to reduce nitrogen oxide
  emissions include avoiding excessive sintering
  temperatures and staged combustion in the
  calciner. Other measures may reduce emissions,
  including the use of ammonia to control nitrogen
  oxide emissions.

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Nitrogen Oxides (NOx)

• Sources
• NOx are formed during high-temperature fuel
  combustion by two primary mechanisms
• the oxidation of molecular nitrogen present in
  the combustion air (thermal NOx)
• the oxidation of nitrogen compounds present in
  the fuel (fuel NOx).
• Also, raw material feeds may contain a
  significant amount of nitrogen compounds, leading
  to NOx formation.  

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Sulfur Oxides (SOx)

• Sources
• oxidation of sulfur present in the raw materials

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Reasons for Concern

• Health Impacts
• Environmental Impacts
• Acid Rain
• Smog

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Maximum Values of NOx and SOx

• Nitrogen Oxides
• Less than 600 mg/Nm3.
• Sulfur Oxides
• Less than 400 mg/Nm3

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How to Control NOx SOx?

• NOx
• Proper kiln design
• Low-NOx burners
• An optimum level of excess air.
• Sox
• SOx emissions are best controlled by using
  low-sulfur fuels and raw materials.

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Mercury

• Heavy metals may also be present in the raw
  materials and fuel used and are released in kiln
  gases.
• Regular testing should determine their presence.

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Volatile Organic Compound

• Volatile organic chemicals (VOCs) are emitted as
  gases from certain solids or liquids
• Sources
• Vary but exposure effects are greater indoors
• Severe Health Effects
• Carcinogenic
• Organ Failure
• Damage to CNS

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Liquid Effluents

• pH should be
• In the range of 69.
• Cooling water should be recycled.

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To Reduce Overall Wastes

• Install equipment covers and filters for
  crushing, grinding, and milling operations.
• Use enclosed adjustable conveyors to minimize
  drop distances.
• Wet down intermediate and finished product
  storage piles.
• Use low-NOx burners with the optimum level of
  excess air.
• Use low sulfur fuels in the kiln.
• Operate control systems to achieve the required
  emissions levels.
• Develop a strong unit or division to undertake
  environmental management responsibilities

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References

• http//www.airimpacts.org/documents/local/M0000749
  3.pdf
• www.epa.gov
• http//www.environmental.usace.army.mil/library/pu
  bs/tsdf/sec5-1/sec5-1.html
• http//www.holcim.com/usa/