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