MINIMIZING WASTE AMOUNT AND SAVING RESOURCES
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Transcript of MINIMIZING WASTE AMOUNT AND SAVING RESOURCES
MINIMIZING WASTE AMOUNT AND SAVING RESOURCES
Paper production
Chemical composition of wood• 50 % water• Solid fraction:• 45 % cellulose• 25 %
hemicellulose• 25 % lignin• 5 % other
Constituents of wood solid part (1)• Cellulose (C6H10O5)n, n = 10000 to
14000 naturally, decreased to 1000-3000 during pulping• Degree of polymerization = n• Acid-hydrolysed
• Hemicellulose consists of different sugar units, branched and amorphous
• Lignin is highly-branched aromatic polymer• Recalcitrant water pollutant in
pulp and paper industry
Image: http://www.life.ku.dk/forskning/online_artikler/artikler/marken_en_stor_solfanger.aspx
Image: Wikipedia
Constituents of wood solid part (2)• Extractives (hot water/organic solvents)• Terpenes, fats, fatty acids and alcohols, waxes and phenols,
tannins• Add colour and odour to wood, influence its physical and
mechanical properties• Resins – lipophylic extractives (non-polar organic solvents)
• resin acids, long chain fatty acids, fats and volatile terpenes
• Inorganic part• 0.2 to 1.0 % of wood mass• calcium (40-70 %), potassium (10-30 %), magnesium (5-10 %),
iron (up to 10 %), and sodium compounds
Pulp and paper production stages
Water consumption: state of the artTo produce 1 t of paper we spend the following amounts of water:• 6 m3 in paper machine showers• 2 m3 for chemicals preparation• 2 m3 for steam production• 2 m3 for feed materials solutions• 1 m3 for vacuum pumps sealing• 2 m3 in cooling towers
• Total: ca. 15-16 m3 for 1 t of paper
Discharges: state of the art• Water used in wood handling/debarking/chipping• Bark has more extractives (incl. phenols) and lignins than wood
• Digester and evaporator condensates• White waters from screening, cleaning and thickening• Bleach plant washer filtrates• Paper machine white water• Fibre and liquor spills from all sections.
Process water recycle• Decreases fresh water consumption• Reduces wastewater amount• Produced waste is more concentrated• White water: fibre-enriched water exiting paper machine• Fresh water consumption is 1-1.5 m3 per 1 t of paper produced
White water treatment• Reduces dissolved and
suspended matter build-up in process water
• Allows higher pulp extraction degree
• UF/NF separates organic compounds and part of salts
• Ozone decomposes organic matter and desinfects water
• Wet air oxidation degrades organic matter and desinfects
Pros and cons of closed water systems• Advantages:• Decreased water consumption• Decreased waste amounts• Decreased fibre losses• Elevated process temperature
• Disadvantages:• Build-up of solids (dissolved and suspended), clogging• More complicated process• Corrosion• Product quality issues
• Unless we want toilet paper, fresh water would have to be added at 4 to 7 m3 per tonne
• This means 2.5 to 5.5 m3 per tonne of wastewater• Elevated temperature
Sulphuric acid production
Contact reactor• H2SO4 production stages
S + O2 SO2
SO2 + ½ O2 SO3 SO3 + H2SO4 H2SO4SO3
H2SO4SO3 + H2O 2 H2SO4
• Uses V2O5 catalyst
• 96 % conversion of SO2
• Pt is more effective, but is quickly poisoned
Image: http://www.dynamicscience.com.au/tester/solutions/chemistry/sulfuricacid.html
Double contact reactor
• 99.8 % SO2 conversion
• 0.003 vol. % of SO2 in tail gas
Image: http://www.greener-industry.org.uk/pages/sulphuric_acid/10SulphuricAcidDouble.htm
Nitric acid production
Ostwald process and modifications4 NH3 (g) + 5 O2 (g) → 4 NO (g) + 6 H2O (g)
2 NO (g) + O2 (g) → 2 NO2 (g) 3 NO2 (g) + H2O (l) → 2 HNO3 (aq) + NO
(g)• NO has very low solubility
• Absorption NOx with nitric acid solution and water addition
• Altering last phase of the reaction:2 NO2 + H2O2 → 2 HNO3
or 4 NO2 (g) + O2 (g) + 2 H2O (l) → 4 HNO3 (aq)
Image: http://chemistry.need.org/curriculum/fertilizer
Phosphoric acid production
Extraction H3PO4
Ca5(PO4)3X + 5 H2SO4 + 10 H2O → 3 H3PO4 + 5 CaSO4·2H2O + HX, X = -OH, -Cl, -Br, -I
• CaSO4 produced is referred to as phosphogypsum
Image: http://www.fao.org/docrep/007/y5053e/y5053e0f.htm
Phosphogypsum• Production of sulphuric acid• Cement• Production of ammonium sulphate• Production of calcium sulphide• Production of sulphur and lime
• For further use, phosphogypsum must be free of radioactive elements present in many phosphate ores
• Treating extraction phosphoric acid to remove radioactive elements may also be necessary
Electrochemical processes
Electrochemical decomposition of NaCl
NaCl + H2O NaOH + ½ H2 + ½ Cl2
• Diaphragm process• Mercury cell process• Membrane process
Diaphragm process• Graphite or titanium anode, iron
catode• Diaphragm: asbestos fibres in
polymer (e.g. PTFE) matrix, resists migration of OH- to Cl2-producing compartment
• Product: 12 % NaOH, 16 % NaCl• Upon evaporation and
crystallisation: 50 % NaOH, 1 % NaCl• Relatively low voltage, requires less
clean input brine• Asbestos-associated hazards,
diaphragm clogging by Ca/Mg, does not produce clean NaOH
Image: http://www.chemguide.co.uk/inorganic/group7/diaphragmcell.html
Mercury cell process• Carbon anode, liquid Hg
cathode• Suppresses hydrogen
production (req. 1.7-1.85 V overvoltage, actual – 1.2 V)
• Produces 50 % NaOH with up to only 30 mg L-1 NaCl
• Mercury toxicity issues, pollution, formation of Hg-organics
Hg2+ + Na2S HgS + 2 Na+
Image: http://electrochem.cwru.edu/encycl/art-b01-brine.htm
Na+ + e- + n Hg NaHgn
NaHgn + H2O NaOH + ½ H2 + n Hg
Membrane process
• Titanium anode, nickel catode, perfluorocarboxylic and perfluorosulfonic acid-based membrane
• Membrane holds back anions• 40 % NaOH with up to 50 mg L-1 NaCl produced
Image: Wikipedia
Current trends• Presently, the majority of
production switches to membrane process
• Asbestos and mercury compounds pollution prevention
• Quality of product unchanged
Image: http://electrochem.cwru.edu/encycl/art-b01-brine.htm
Ultra-low CO2 steelmaking (ULCOS)
Top gas recycling blast furnace
• Up to 26 % carbon input saving• Up to 15 % CO2 emission reduction• Goal: 50 % CO2 emissions reduction by 2020
Image: http://www.ulcos.org/en/docs/Ref25%20-%20ULCOSpublic.pdf
Surface treatment in metallurgy
Surface coating process• Stages• Degreasing with surfactant solution• Surfactant solution removal• Electrolytic surface coating (Zn, Cu, Cr, etc.)• Rinsing baths
• Environmental concern: wastewaters with elevated amounts of metals, many of them carcinogenic (e.g. Ni, Cr6+)
• Solution: precipitation as hydroxides and sulphides• Reduction is sometimes required before precipitation (e.g. Cr6+
Cr3+)
Image: http://www.protocase.com/products/mcf_chemconv.php
Minimizing ultimate waste amounts in wastewater treatment
Paljassaare Wastewater Treatment Plant, Tallinn
Image: https://aktal.tallinnlv.ee/static/Eelnoud/Dokumendid/ddok12933.htm
Image: https://oigusaktid.tallinn.ee/?id=3001&aktid=119834
Main pumping station
ScreensSand grids
Primary clarifiers
Secondary clarifiers
Aeration tanks
Purified water pumping station
Waste active sludge thickening
Mixed sludge storage
Methane tank Stabilised
sludge storage
Sludge thickening and silos
Image: Google
Heat energy reuse
Heat recuperation principles• Thermal waste: e.g. clean water with even slightly elevated
temperature discharged into water body (why?)• Hot stream exiting from one process can serve as a heat
source for another one
Kansha et al., Chem. Eng. Sci. 65 (2010) 330-334
Clusters
Definition and types• Geographical concentration of interconnected businesses,
suppliers, distributors, etc.• Reasons of clusters formation:• Common natural resources, or common research facilities (e.g. Silicon
Valley, USA)• Geographical proximity to markets (e.g. electronics cluster in
Guadalajara, Mexico)• Low-cost labor force• Know-how spreading
• From cleaner production point of view:• Less resource transportation• One process’ product may be another one’s feed (e.g. fertilizer
industry and agriculture, coal and steel production in Ruhr, Germany)• Environment may benefit when several companies at a time try to
solve pollution questions in their operation region
Silicon Valley
Image: http://www.startup-book.com/tag/cluster/
Barets Sea Region
Summary
Cleaner production options• Efficient rinsing, incl. countercurrent rinsing• Materials recirculation• Heat recirculation• Process integration