Reference documents

Activity

Industrial Cooling Systems (ICS)

Industrial cooling systems, e.g. cooling towers, plate heat exchangers

Economics and Cross-Media Effects (ECM)

Economics and cross-media effects of techniques

Emissions from Storage (EFS)

Emissions from tanks, pipework and stored chemicals

Energy Efficiency (ENE)

General energy efficiency

Large Combustion Plants (LCP)

Generation of steam and electricity in pulp and paper mills by combustion plants

General Principles of Monitoring (MON)

Emissions monitoring

Waste Incineration (WI)

On-site incineration and co-incineration of waste

Waste Treatments Industries (WT)

Preparation of waste as fuels

Daily average

Average over a sampling period of 24 hours taken as a flow-proportional composite sample (1) or, provided that sufficient flow stability is demonstrated, from a time-proportional sample (1)

Yearly average

Average of all daily averages taken within a year, weighted according to the daily production, and expressed as mass of emitted substances per unit of mass of products/materials generated or processed

Daily average

Average over a period of 24 hours based on valid hourly averages from continuous measurement

Average over the sampling period

Average value of three consecutive measurements of at least 30 minutes each

Yearly average

In the case of continuous measurement: average of all valid hourly averages. In the case of periodic measurements: average of all ‘averages over the sampling period’ obtained during one year.

Term used

Definition

New plant

A plant first permitted on the site of the installation following the publication of these BAT conclusions or a complete replacement of a plant on the existing foundations of the installation following the publication of these BAT conclusions.

Existing plant

A plant which is not a new plant.

Major refurbishment

A major change in design or technology of a plant/abatement system and with major adjustments or replacements of the process units and associated equipment.

New dust abatement system

A dust abatement system first operated on the site of the installation following the publication of these BAT conclusions.

Existing dust abatement system

A dust abatement system which is not a new dust abatement system.

Non-condensable odorous gases (NCG)

Non-condensable odorous gases, referring to malodorous gases of kraft pulping.

Concentrated non-condensable odorous gases (CNCG)

Concentrated non-condensable odorous gases (or ‘strong odorous gases’): TRS-containing gases from cooking, evaporation and from stripping of condensates.

Strong odorous gases

Concentrated non-condensable odorous gases (CNCG).

Weak odorous gases

Diluted non-condensable odorous gases: TRS-containing gases which are not strong odorous gases (e.g. gases coming from tanks, washing filters, chip bins, lime mud filters, drying machines).

Residual weak gases

Weak gases that are emitted in ways other than through a recovery boiler, a lime kiln or a TRS-burner.

Continuous measurement

Measurements using an automated measuring system (AMS) permanently installed on site.

Periodic measurement

Determination of a measurand (particular quantity subject to measurement) at specified time intervals using manual or automated methods.

Diffuse emissions

Emissions arising from a direct (non-channelled) contact of volatile substances or dust with the environment under normal operating conditions.

Integrated production

Both pulp and paper/board are produced at the same site. The pulp is normally not dried before paper/board manufacture.

Non-integrated production

Either (a) production of market pulp (for sale) in mills that do not operate paper machines, or (b) production of paper/board using only pulp produced in other plants (market pulp).

Net production

Speciality paper mill

A mill producing numerous paper and board grades for special purposes (industrial and/or non-industrial) that are characterised by particular properties, relatively small end use market or niche applications that are often especially designed for a particular customer or end-user group. Examples of speciality papers include cigarette papers, filter papers, metallised paper, thermal paper, self-copy paper, sticking labels, cast coated paper, as well as gypsum liners and special papers for waxing, insulating, roofing, asphalting, and other specific applications or treatments. All of these grades fall outside of the standard paper categories.

Hardwood

Group of wood species including e.g. aspen, beech, birch and eucalyptus. The term hardwood is used as opposite to softwood.

Softwood

Wood from conifers including e.g. pine and spruce. The term softwood is used as opposite to hardwood.

Causticising

Process in the lime cycle in which hydroxide (white liquor) is regenerated by the reaction Ca(OH)2 + CO3 2– → CaCO3 (s) + 2 OH–

Term used

Definition

ADt

Air Dry tonnes (of pulp) expressed as 90 % dryness.

AOX

Adsorbable organic halides measured according to the EN ISO: 9562 standard method for waste waters.

BOD

Biochemical oxygen demand. The quantity of dissolved oxygen required by microorganisms to decompose organic matter in waste water.

CMP

Chemimechanical pulp.

CTMP

Chemithermomechanical pulp.

COD

Chemical oxygen demand; the amount of chemically oxidisable organic matter in waste water (normally referring to analysis with dichromate oxidation).

DS

Dry solids, expressed as weight %.

DTPA

Diethlyene triamine pentaacetic acid (complexing/chelating agent used in peroxide bleaching).

ECF

Elemental Chlorine Free.

EDTA

Ethylene diamine tetraacetic acid (complexing/chelating agent).

H2S

Hydrogen sulphide.

LWC

Light weight coated paper.

NOX

The sum of nitrogen oxide (NO) and nitrogen dioxide (NO2), expressed as NO2.

NSSC

Neutral sulphite semi chemical.

RCF

Recycled fibres.

SO2

Sulphur dioxide.

TCF

Totally Chlorine Free.

Total nitrogen (Tot-N)

Total nitrogen (Tot-N) given as N, includes organic nitrogen, free ammonia and ammonium (NH4 +-N), nitrites (NO2 --N) and nitrates (NO3 --N).

Total phosphorus (Tot-P)

Total phosphorus (Tot-P) given as P, includes dissolved phosphorus plus any insoluble phosphorus carried over into the effluent in the form of precipitates or within microbes.

TMP

Thermomechanical pulp.

TOC

Total organic carbon.

TRS

Total reduced sulphur. The sum of the following reduced malodorous sulphur compounds generated in the pulping process: hydrogen sulphide, methyl mercaptan, dimethylsulphide and dimethyldisulphide, expressed as sulphur.

TSS

Total suspended solids (in waste water). Suspended solids consist of small fibre fragments, fillers, fines, non-settled biomass (agglomeration of microorganisms) and other small particles.

VOC

Volatile organic compounds as defined in Article 3(45) of Directive 2010/75/EU.

Technique

a

Careful selection and control of chemicals and additives

b

Input-output analysis with a chemical inventory, including quantities and toxicological properties

c

Minimise the use of chemicals to the minimum level required by the quality specifications of the final product

d

Avoid the use of harmful substances (e.g. nonylphenol ethoxylate-containing dispersion or cleaning agents or surfactants) and substitution by less harmful alternatives

e

Minimise the input of substances into the soil by leakage, aerial deposition and the inappropriate storage of raw materials, products or residues

f

Establish a spill management programme and extend the containment of relevant sources, thus preventing the contamination of soil and groundwater

g

Proper design of the piping and storage systems to keep the surfaces clean and to reduce the need for washing and cleaning

Technique

Applicability

a

Determination of quantity of chelating agents released to the environment through periodic measurements

Not applicable for mills that do not use chelating agents

b

Process optimisation to reduce consumption and emission of not readily biodegradable chelating agents

Not applicable for plants that eliminate 70 % or more of EDTA/DTPA in their waste water treatment plant or process

c

Preferential use of biodegradable or eliminable chelating agents, gradually phasing out non-degradable products

Applicability depends on the availability of appropriate substitutes (biodegradable agents meeting e.g. brightness requirements of pulp)

Technique

Applicability

a

Dry debarking (description see Section 1.7.2.1)

Restricted applicability when high purity and brightness is required with TCF bleaching

b

Handling of wood logs in such a way as to avoid the contamination of bark and wood with sand and stones

Generally applicable

c

Paving of the wood yard area and particularly the surfaces used for the storage of chips

Applicability may be restricted due to the size of the wood yard and storage area

d

Controlling the flow of sprinkling water and minimising surface run-off water from the wood yard

Generally applicable

e

Collecting of contaminated run-off water from the wood yard and separating out suspended solids effluent before biological treatment

Applicability may be restricted by the degree of contamination of run-off water (low concentration) and/or the size of the waste water treatment plant (large volumes)

Technique

Applicability

a

Monitoring and optimising water usage

Generally applicable

b

Evaluation of water recirculation options

c

Balancing the degree of closure of water circuits and potential drawbacks; adding additional equipment if necessary

d

Separation of less contaminated sealing water from pumps for vacuum generation and reuse

e

Separation of clean cooling water from contaminated process water and reuse

f

Reusing process water to substitute for fresh water (water recirculation and closing of water loops)

Applicable to new plants and major refurbishments.

Applicability may be limited due to water quality and/or product quality requirements or due to technical constraints (such as precipitation/incrustation in water system) or increase odour nuisance

g

In-line treatment of (parts of) process water to improve water quality to allow for recirculation or reuse

Generally applicable

Sector

BAT-associated waste water flow

Bleached kraft

25 – 50 m3/ADt

Unbleached kraft

15 – 40 m3/ADt

Bleached sulphite paper grade pulp

25 – 50 m3/ADt

Magnefite pulp

45 – 70 m3/ADt

Dissolving pulp

40 – 60 m3/ADt

NSSC pulp

11 – 20 m3/ADt

Mechanical pulp

9 – 16 m3/t

CTMP and CMP

9 – 16 m3/ADt

RCF paper mills without deinking

1,5 – 10 m3/t (the higher end of the range is mainly associated with folding boxboard production)

RCF paper mills with deinking

8 – 15 m3/t

RCF-based tissue paper mills with deinking

10 – 25 m3/t

Non-integrated paper mills

3,5 – 20 m3/t

Technique

Applicability

a

Use an energy management system that includes all of the following features:

Generally applicable

b

Recover energy by incinerating those wastes and residues from the production of pulp and paper that have high organic content and calorific value, taking into account BAT 12

Only applicable if the recycling or reuse of wastes and residues from the production of pulp and paper with a high organic content and high calorific value is not possible

c

Cover the steam and power demand of the production processes as far as possible by the cogeneration of heat and power (CHP)

Applicable for all new plants and for major refurbishments of the energy plant. Applicability in existing plants may be limited due to the mill layout and available space

d

Use excess heat for the drying of biomass and sludge, to heat boiler feedwater and process water, to heat buildings, etc.

Applicability of this technique may be limited in cases where the heat sources and locations are far apart

e

Use thermo compressors

Applicable to both new and existing plants for all grades of paper and for coating machines, as long as medium pressure steam is available

f

Insulate steam and condensate pipe fittings

Generally applicable

g

Use energy efficient vacuum systems for dewatering

h

Use high efficiency electrical motors, pumps and agitators

i

Use frequency inverters for fans, compressors and pumps

j

Match steam pressure levels with actual pressure needs

Technique

a

Design paper mill processes, stock and water storage tanks, pipes and chests in such a way as to avoid prolonged retention times, dead zones or areas with poor mixing in water circuits and related units, in order to avoid uncontrolled deposits and the decay and decomposition of organic and biological matter.

b

Use biocides, dispersants or of oxidising agents (e.g. catalytic disinfection with hydrogen peroxide) to control odour and decaying bacteria growth.

c

Install internal treatment processes (‘kidneys’) to reduce the concentrations of organic matter and consequently possible odour problems in the white water system.

a

Implement closed sewer systems with controlled vents, using chemicals in some cases to reduce the formation of and to oxidise hydrogen sulphide in sewer systems.

b

Avoid over-aeration in equalisation basins but maintain sufficient mixing.

c

Ensure sufficient aeration capacity and mixing properties in aeration tanks; revise the aeration system regularly.

d

Guarantee proper operation of secondary clarifier sludge collection and return sludge pumping

e

Limit the retention time of sludge in sludge storages by sending the sludge continuously to the dewatering units.

f

Avoid the storage of waste water in the spill basin longer than is necessary; keep the spill basin empty.

g

If sludge dryers are used, treatment of thermal sludge dryer vent gases by scrubbing and/or bio filtration (such as compost filters).

h

Avoid air cooling towers for untreated water effluent by applying plate heat exchangers.

Parameter

Monitoring frequency

Pressure, temperature, oxygen, CO and water vapour content in flue-gas for combustion processes

Continuous

Parameter

Monitoring frequency

Water flow, temperature and pH

Continuous

P and N content in biomass, sludge volume index, excess ammonia and ortho-phosphate in the effluent, and microscopy checks of the biomass

Periodic

Volume flow and CH4 content of biogas produced in anaerobic waste water treatment

Continuous

H2S and CO2 contents of biogas produced in anaerobic waste water treatment

Periodic

Parameter

Monitoring frequency

Emission source

Monitoring associated with

a

NOx and SO2

Continuous

Recovery boiler

BAT 21

BAT 22

BAT 36

BAT 37

Periodic or continuous

Lime kiln

BAT 24

BAT 26

Periodic or continuous

Dedicated TRS burner

BAT 28

BAT 29

b

Dust

Periodic or continuous

Recovery boiler (kraft) and lime kiln

BAT 23

BAT 27

Periodic

Recovery boiler (sulphite)

BAT 37

c

TRS (including H2S)

Continuous

Recovery boiler

BAT 21

Periodic or continuous

Lime kiln and dedicated TRS burner

BAT 24

BAT 25

BAT 28

Periodic

Diffuse emissions from different sources (e.g. the fibre line, tanks, chip bins, etc.) and residual weak gases

BAT 11

BAT 20

d

NH3

Periodic

Recovery boiler equipped with SNCR

BAT 36

Parameter

Monitoring frequency

Monitoring associated with

a

Chemical oxygen demand (COD) or

Total organic carbon (TOC) (2)

Daily (3)  (4)

BAT 19

BAT 33

BAT 40

BAT 45

BAT 50

b

BOD5 or BOD7

Weekly (once a week)

c

Total suspended solids (TSS)

Daily (3)  (4)

d

Total nitrogen

Weekly (once a week) (3)

e

Total phosphorus

Weekly (once a week) (3)

f

EDTA, DTPA (5)

Monthly (once a month)

g

AOX (according to EN ISO 9562:2004) (6)

Monthly (once a month)

BAT 19: bleached kraft

Once every two months

BAT 33: except TCF and NSSC mills

BAT 40: except CTMP and CMP mills

BAT 45

BAT 50

h

Relevant metals (e.g. Zn, Cu, Cd, Pb, Ni)

Once a year

Technique

Description

Applicability

a

Separate collection of different waste fractions (including separation and classification of hazardous waste)

See Section 1.7.3

Generally applicable

b

Merging of suitable fractions of residues to obtain mixtures that can be better utilised

Generally applicable

c

Pretreatment of process residues before reuse or recycling

Generally applicable

d

Material recovery and recycling of process residues on site

Generally applicable

e

Energy recovery on- or off-site from wastes with high organic content

For off-site utilisation, the applicability depends on the availability of a third party

f

External material utilisation

Depending on the availability of a third party

g

Pretreatment of waste before disposal

Generally applicable

Technique

Description

a

Primary (physico-chemical) treatment

See Section 1.7.2.2

b

Secondary (biological) treatment (7)

Technique

a

Proper design and operation of the biological treatment plant

b

Regularly controlling the active biomass

c

Adjustment of nutrition supply (nitrogen and phosphorus) to the actual need of the active biomass

Technique

Description

Applicability

a

Noise-reduction programme

A noise-reduction programme includes identification of sources and affected areas, calculations and measurements of noise levels in order to rank sources according to noise levels, and identification of the most cost effective combination of techniques, their implementation and monitoring.

Generally applicable.

b

Strategic planning of the location of equipment, units and buildings

Noise levels can be reduced by increasing the distance between the emitter and the receiver and by using buildings as noise screens.

Generally applicable to new plants. In the case of existing plants, the relocation of equipment and production units may be restricted by the lack of space or by excessive costs.

c

Operational and management techniques in buildings containing noisy equipment

This includes:

Generally applicable.

d

Enclosing noisy equipment and units

Enclosure of noisy equipment, such as wood handling, hydraulic units, and compressors in separate structures, such as buildings or soundproofed cabinets, where internal-external lining is made of impact-absorbent material.

e

Use of low-noise equipment and noise-reducers on equipment and ducts.

f

Vibration insulation

Vibration insulation of machinery and decoupled arrangement of noise sources and potentially resonant components.

g

Soundproofing of buildings

This potentially includes use of:

h

Noise abatement

Noise propagation can be reduced by inserting barriers between emitters and receivers. Appropriate barriers include protection walls, embankments and buildings. Suitable noise abatement techniques include fitting silencers and attenuators to noisy equipment such as steam releases and dryer vents.

Generally applicable to new plants. In the case of existing plants, the insertion of obstacles may be restricted by the lack of space.

i

Use of larger wood-handling machines to reduce lifting and transport times and noise from logs falling onto log piles or the feed table.

Generally applicable.

j

Improved ways of working, e.g. releasing logs from a lower height onto the log piles or the feed table; immediate feedback of the level of noise for the workers.

Technique

a

Ensure that underground tanks and piping are either avoided in the design phase or that their location is well known and documented.

b

Establish instructions for emptying process equipment, vessels and piping.

c

Ensure a clean closure when the facility is shut down, e.g. to clean up and rehabilitate the site. Natural soil functions should be safeguarded, if feasible.

d

Use a monitoring programme, especially relative to groundwater, in order to detect possible future impacts on site or in neighbouring areas.

e

Develop and maintain a site closure or cessation scheme, based on risk analysis, that includes a transparent organisation of the shutdown work, taking into account relevant local specific conditions.

Technique

Description

Applicability

a

Modified cooking before bleaching

See Section 1.7.2.1

Generally applicable

b

Oxygen delignification before bleaching

c

Closed brown stock screening and efficient brown stock washing

d

Partial process water recycling in the bleach plant

Water recycling may be limited due to incrustation in bleaching

e

Effective spill monitoring and containment with a suitable recovery system

Generally applicable

f

Maintaining sufficient black liquor evaporation and recovery boiler capacity to cope with peak loads

Generally applicable

g

Stripping the contaminated (foul) condensates and reusing the condensates in the process

Parameter

Yearly average

kg/ADt (8)

Chemical oxygen demand (COD)

7 – 20

Total suspended solids (TSS)

0,3 – 1,5

Total nitrogen

0,05 – 0,25 (9)

Total phosphorus

0,01 – 0,03 (9)

Eucalyptus: 0,02 – 0,11 kg/ADt (10)

Adsorbable organically bound halogens (AOX) (11)  (12)

0 – 0,2

Parameter

Yearly average

kg/ADt (13)

Chemical oxygen demand (COD)

2,5 – 8

Total suspended solids (TSS)

0,3 – 1,0

Total nitrogen

0,1 – 0,2 (14)

Total phosphorus

0,01 – 0,02 (14)

Technique

Description

a

Collection systems for strong and weak odorous gases, comprising the following features:

b

Incineration of strong and weak non-condensable gases

Incineration can be carried out using:

To ensure the constant availability of incineration for odorous strong gases, back-up systems are installed. Lime kilns can serve as back-up for recovery boilers; further back-up equipment are flares and package boiler

c

Recording unavailability of the incineration system and any resulting emissions (17)

Technique

Description

a

Increasing the dry solids (DS) content of black liquor

The black liquor can be concentrated by an evaporation process before burning

b

Optimised firing

Firing conditions can be improved e.g. by good mixing of air and fuel, control of furnace load etc.

c

Wet scrubber

See Section 1.7.1.3

Parameter

Daily average (18)  (19)

mg/Nm3 at 6 % O2

Yearly average (18)

mg/Nm3 at 6 % O2

Yearly average (18)

kg S/ADt

SO2

DS < 75 %

10 – 70

5 – 50

—

DS 75 – 83 % (20)

10 – 50

5 – 25

—

Total reduced sulphur (TRS)

1 – 10 (21)

1 – 5

—

Gaseous S (TRS-S + SO2-S)

DS < 75 %

—

—

0,03 – 0,17

DS 75 – 83 % (20)

0,03 – 0,13

Technique

a

Computerised combustion control

b

Good mixing of fuel and air

c

Staged air feed systems, e.g. by using different air registers and air inlet ports

Parameter

Yearly average (22)

mg/Nm3 at 6 % O2

Yearly average (22)

kg NOx/ADt

NOx

Softwood

120 – 200 (23)

DS < 75 %: 0,8 – 1,4

DS 75 – 83 % (24): 1,0 – 1,6

Hardwood

120 – 200 (23)

DS < 75 %: 0,8 – 1,4

DS 75 – 83 % (24): 1,0 – 1,7

Parameter

Dust abatement system

Yearly average

mg/Nm3 at 6 % O2

Yearly average

kg dust/ADt

Dust

New or major refurbishment

10 – 25

0,02 – 0,20

Existing

10 – 40 (25)

0,02 — 0,3 (25)

Technique

Description

a

Fuel selection/low sulphur fuel

See Section 1.7.1.3

b

Limit incineration of sulphur-containing odorous strong gases in the lime kiln

c

Control of Na2S content in lime mud feed

d

Alkaline scrubber

Parameter (26)

Yearly average

mg SO2/Nm3 at 6 % O2

Yearly average

kg S/ADt

SO2 when strong gases are not burnt in the lime kiln

5 – 70

—

SO2 when strong gases are burnt in the lime kiln

55 – 120

—

Gaseous S (TRS-S + SO2-S) when strong gases are not burnt in the lime kiln

—

0,005 – 0,07

Gaseous S (TRS-S + SO2-S) when strong gases are burnt in the lime kiln

—

0,055 – 0,12

Technique

Description

a

Control of the excess oxygen

See Section 1.7.1.3

b

Control of Na2S content in lime mud feed

c

Combination of ESP and alkaline scrubber

See Section 1.7.1.1

Parameter

Yearly average

mg S/Nm3 at 6 % O2

Total reduced sulphur (TRS)

< 1 – 10 (27)

Technique

Description

a

Optimised combustion and combustion control

See Section 1.7.1.2

b

Good mixing of fuel and air

c

Low-NOx burner

d

Fuel selection/low-N fuel

Parameter

Yearly average

mg/Nm3 at 6 % O2

Yearly average

kg NOx/ADt

NOx

Liquid fuels

100 – 200 (28)

0,1 – 0,2 (28)

Gaseous fuels

100 – 350 (29)

0,1 – 0,3 (29)

Parameter

Dust abatement system

Yearly average

mg/Nm3 at 6 % O2

Yearly average

kg dust/ADt

Dust

New or major refurbishments

10 – 25

0,005 – 0,02

Existing

10 – 30 (30)

0,005 – 0,03 (30)

Parameter

Yearly average

mg/Nm3 at 9 % O2

Yearly average

kg S/ADt

SO2

20 – 120

—

TRS

1 – 5

Gaseous S (TRS-S + SO2-S)

—

0,002 – 0,05 (31)

Technique

Description

Applicability

a

Burner/firing optimisation

See Section 1.7.1.2

Generally applicable

b

Staged incineration

See Section 1.7.1.2

Generally applicable for new plants and for major refurbishments. For existing mills, applicable only if space allows for the insertion of equipment

Parameter

Yearly average

mg/Nm3 at 9 % O2

Yearly average

kg NOx/ADt

NOx

50 – 400 (32)

0,01 – 0,1 (32)

Technique

a

High dry solid content of bark, by use of efficient presses or drying

b

High efficiency steam boilers, e.g. low flue-gas temperatures

c

Effective secondary heating systems

d

Closing water systems, including bleach plant

e

High pulp concentration (middle or high consistency technique)

f

High efficiency evaporation plant

g

Recovery of heat from dissolving tanks e.g. by vent scrubbers

h

Recovery and use of the low temperature streams from effluents and other waste heat sources to heat buildings, boiler feedwater and process water

i

Appropriate use of secondary heat and secondary condensate

j

Monitoring and control of processes, using advanced control systems

k

Optimise integrated heat exchanger network

l

Heat recovery from the flue-gas from the recovery boiler between the ESP and the fan

m

Ensuring as high a pulp consistency as possible in screening and cleaning

n

Use of speed control of various large motors

o

Use of efficient vacuum pumps

p

Proper sizing of pipes, pumps and fans

q

Optimised tank levels

Technique

a

High black liquor dry solid content (increases boiler efficiency, steam generation and thus electricity generation)

b

High recovery boiler pressure and temperature; in new recovery boilers the pressure can be at least 100 bars and the temperature 510 °C

c

Outlet steam pressure in the back-pressure turbine as low as technically feasible

d

Condensing turbine for power production from excess steam

e

High turbine efficiency

f

Preheating feedwater to a temperature close to the boiling temperature

g

Preheating the combustion air and fuel charged to the boilers

Technique

Description

Applicability

a

Extended modified cooking before bleaching.

See Section 1.7.2.1

Applicability may be limited due to pulp quality requirements (when high strength is required).

b

Oxygen delignification before bleaching.

c

Closed brown stock screening and efficient brown stock washing.

Generally applicable.

d

Evaporation of effluents from the hot alkaline extraction stage and incineration of concentrates in a soda boiler.

Limited applicability for dissolving pulp mills, when multistage biological treatment of the effluents provides a more favourable overall environmental situation.

e

TCF bleaching.

Limited applicability for market paper pulp mills producing high brightness pulp and for mills manufacturing speciality pulp for chemical applications.

f

Closed-loop bleaching.

Only applicable to plants that use the same base for cooking and pH adjustment in bleaching.

g

MgO-based pre-bleaching and recirculation of washing liquids from pre-bleaching to brown stock washing.

Applicability may be limited by factors such as product quality (e.g. purity, cleanliness and brightness), kappa number after cooking, hydraulic capacity of the installation and capacity of tanks, evaporators and recovery boilers, and a possibility to clean the washing equipment.

h

pH adjustment of weak liquor before/inside the evaporation plant.

Generally applicable to magnesium-based plants. Spare capacity in the recovery boiler and ash circuit is needed.

i

Anaerobic treatment of the condensates from the evaporators.

Generally applicable.

j

Stripping and recovery of SO2 from the condensates of evaporators.

Applicable if it is necessary to protect anaerobic effluent treatment.

k

Effective spill monitoring and containment, also with chemical and energy recovery system.

Generally applicable.

Parameter

Bleached sulphite paper grade pulp (33)

Magnefite paper grade pulp (33)

Yearly average

kg/ADt (34)

Yearly average

kg/ADt

Chemical oxygen demand (COD)

10 – 30 (35)

20 – 35

Total suspended solids (TSS)

0,4 – 1,5

0,5 – 2,0

Total nitrogen

0,15 – 0,3

0,1 – 0,25

Total phosphorus

0,01 – 0,05 (35)

0,01 – 0,07

Yearly average

mg/l

Adsorbable organically bound halogens (AOX)

0,5 – 1,5 (36)  (37)

Parameter

Yearly average

kg/ADt (38)

Chemical oxygen demand (COD)

3,2 – 11

Total suspended solids (TSS)

0,5 – 1,3

Total nitrogen

0,1 – 0,2 (39)

Total phosphorus

0,01 – 0,02

Technique

Description

Applicability

a

Incineration in a recovery boiler

See Section 1.7.1.3

Not applicable to sulphite pulp mills using calcium-based cooking. These mills do not operate a recovery boiler

b

Wet scrubber

See Section 1.7.1.3

Generally applicable

Technique

Description

Applicability

a

Optimising the recovery boiler by controlling the firing conditions

See Section 1.7.1.2

Generally applicable

b

Staged injection of spent liquor

Applicable to new large recovery boilers and major recovery boilers refurbishments

c

Selective non-catalytic reduction (SNCR)

Retrofitting of existing recovery boilers may be limited due to scaling problems and associated increased cleaning and maintenance requirements. For ammonium-based mills, no application was reported; but due to specific conditions in the waste gas, SNCR is expected to be without effect. Not applicable to sodium-based mills due to explosion risk

Parameter

Daily average

mg/Nm3 at 5 % O2

Yearly average

mg/Nm3 at 5 % O2

NOx

100 – 350 (40)

100 – 270 (40)

NH3 (ammonia slip for SNCR)

< 5

Technique

Description

a

ESP or multicyclones with multistage venturi scrubbers

See Section 1.7.1.3

b

ESP or multicyclones with multistage double inlet downstream scrubbers

Parameter

Average over the sampling period

mg/Nm3 at 5 % O2

Dust

5 – 20 (41)  (42)

Daily average

mg/Nm3 at 5 % O2

Yearly average

mg/Nm3 at 5 % O2

SO2

100 – 300 (43)  (44)  (45)

50 – 250 (43)  (44)

Technique

a

High dry solids content of bark, by use of efficient presses or drying

b

High efficiency steam boilers, e.g. low exhaust-gas temperatures

c

Effective secondary heating system

d

Closing water systems, including bleach plant

e

High pulp concentration (middle or high consistency techniques)

f

Recovery and use of the low temperature streams from effluents and other waste heat sources to heat buildings, boiler feedwater and process water

g

Appropriate use of secondary heat and secondary condensate

h

Monitoring and control of processes, using advanced control systems

i

Optimise integrated heat exchanger network

j

Ensuring as high pulp consistency as possible in screening and cleaning

k

Optimised tank levels

Technique

a

High recovery boiler pressure and temperature

b

Outlet steam pressure in the back-pressure turbine as low as technically feasible

c

Condensing turbine for power production from excess steam

d

High turbine efficiency

e

Preheating feedwater to a temperature close to the boiling temperature

f

Preheating the combustion air and fuel charged to the boilers

Technique

Description

Applicability

a

Counter-current flow of process water and separation of water systems.

See Section 1.7.2.1

Generally applicable

b

High consistency bleaching.

c

Washing stage before the refining of softwood mechanical pulp using chip pre-treatment.

d

Substitution of NaOH by Ca(OH)2 or Mg(OH)2 as alkali in peroxide bleaching.

Applicability for the highest brightness levels may be restricted

e

Fibre and filler recovery and treatment of white water (papermaking).

Generally applicable

f

Optimum design and construction of tanks and chests (papermaking).

Parameter

Yearly average

kg/t

Chemical oxygen demand (COD)

0,9 – 4,5 (46)

Total suspended solids (TSS)

0,06 – 0,45

Total nitrogen

0,03 – 0,1 (47)

Total phosphorus

0,001 – 0,01

Parameter

Yearly average

kg/ADt

Chemical oxygen demand (COD)

12 – 20

Total suspended solids (TSS)

0,5 – 0,9

Total nitrogen

0,15 – 0,18 (48)

Total phosphorus

0,001 – 0,01

Technique

Applicability

a

Use of energy efficient refiners

Applicable when replacing, rebuilding or upgrading process equipment

b

Extensive recovery of secondary heat from TMP and CTMP refiners and reuse of recovered steam in paper or pulp drying

Generally applicable

c

Minimisation of fibre losses by using efficient reject refining systems (secondary refiners)

d

Installation of energy saving equipment, including automated process control instead of manual systems

e

Reduction of fresh water use by internal process water treatment and recirculation systems

f

Reduction of the direct use of steam by careful process integration using e.g. pinch analysis

Technique

Applicability

a

Hard surfacing of the storage area for paper for recycling

Generally applicable

b

Collection of contaminated run-off water from the paper for recycling storage area and treatment in a waste water treatment plant (uncontaminated rainwater e.g. from roofs can be discharged separately)

Applicability may be restricted by the degree of contamination of run-off water (low concentration) and/or the size of the waste water treatment plants (large volumes)

c

Surrounding the terrain of the paper for recycling yard with fences against wind drift

Generally applicable

d

Regularly cleaning the storage area and sweeping associated roadways and emptying gully pots to reduce diffuse dust emissions. This reduces wind-blown paper debris, fibres and the crushing of paper by on-site traffic, which can cause additional dust emission, especially in the dry season

Generally applicable

e

Storing of bales or loose paper under a roof to protect the material from weather influences (moisture, microbiological degradation processes, etc.)

Applicability may be restricted by the size of the area

Technique

Description

a

Separation of the water systems

See Section 1.7.2.1

b

Counter-current flow of process water and water recirculation

c

Partial recycling of treated waste water after biological treatment

Many RCF paper mills recycle a partial stream of biologically treated waste water back into the water circuit, especially mills producing corrugated medium or Testliner

d

Clarification of white water

See Section 1.7.2.1

Technique

Description

a

Monitoring and continuous control of the process water quality

See Section 1.7.2.1

b

Prevention and elimination of biofilms by using methods that minimise emissions of biocides

c

Removal of calcium from process water by a controlled precipitation of calcium carbonate

Parameter

Yearly average

kg/t

Chemical oxygen demand (COD)

0,4 (49) – 1,4

Total suspended solids (TSS)

0,02 – 0,2 (50)

Total nitrogen

0,008 – 0,09

Total phosphorus

0,001 – 0,005 (51)

Adsorbable organically bound halogens (AOX)

0,05 for wet strength paper

Parameter

Yearly average

kg/t

Chemical oxygen demand (COD)

0,9 – 3,0

0,9 – 4,0 for tissue paper

Total suspended solids (TSS)

0,08 – 0,3

0,1 – 0,4 for tissue paper

Total nitrogen

0,01 – 0,1

0,01 – 0,15 for tissue paper

Total phosphorus

0,002 – 0,01

0,002 – 0,015 for tissue paper

Adsorbable organically bound halogens (AOX)

0,05 for wet strength paper

Technique

Applicability

a

High consistency pulping for disintegrating paper for recycling into separated fibres

Generally applicable for new plants and for existing plants in the case of a major refurbishment

b

Efficient coarse and fine screening by optimising rotor design, screens and screen operation, which allows the use of smaller equipment with lower specific energy consumption

c

Energy saving stock preparation concepts extracting impurities as early as possible in the re-pulping process, using fewer and optimised machine components, thus restricting the energy intensive processing of the fibres

Technique

Description

Applicability

a

Optimum design and construction of tanks and chests

See Section 1.7.2.1

Applicable to new plants and to existing plants in the case of a major refurbishment

b

Fibre and filler recovery and treatment of white water

Generally applicable

c

Water recirculation

Generally applicable. Dissolved organic, inorganic, and colloidal materials may restrict the water reuse in the wire section

d

Optimisation of showers in the paper machine

Generally applicable

Technique

Description

Applicability

a

Improvement of paper production planning

Improved planning to optimise production batch combinations and length

Generally applicable

b

Management of water circuits to fit changes

Adjust water circuits to be able to cope with changes of paper grades, colours and chemical additives used

c

Waste water treatment plant ready to cope with changes

Adjust waste water treatment to be able to cope with variations of flows, low concentrations and varying types and amounts of chemical additives

d

Adjustment of the broke system and of chest capacities

e

Minimisation of release of chemical additives (e.g. grease-/water proof agents) containing per- or polyflourinated compounds or contributing to their formation

Applicable only for plants producing paper with grease- or water-repellent properties

f

Switch to low AOX-containing product aids (e.g. to substitute use of wet strength agents based on epichlorohydrin resins)

Applicable only for plants producing paper grades with high wet strength

Technique

Description

Applicability

a

Recovery of coating colours/recycling of pigments

Effluents containing coating colours are collected separately. The coating chemicals are recovered by e.g.:

For ultrafiltration, the applicability may be restricted when:

b

Pretreatment of effluents which contain coating colours

Effluents which contain coating colours are treated e.g. by flocculation to protect the subsequent biological waste water treatment

Generally applicable

Parameter

Yearly average

kg/t

Chemical oxygen demand (COD)

0,15 – 1,5 (52)

Total suspended solids (TSS)

0,02 – 0,35

Total nitrogen

0,01 – 0,1

0,01 – 0,15 for tissue paper

Total phosphorus

0,003 – 0,012

Adsorbable organically bound halogens (AOX)

0,05 for decor and wet strength paper

Parameter

Yearly average

kg/t (53)

Chemical oxygen demand (COD)

0,3 – 5 (54)

Total suspended solids (TSS)

0,10 – 1

Total nitrogen

0,015 – 0,4

Total phosphorus

0,002 – 0,04

Adsorbable organically bound halogens (AOX)

0,05 for decor and wet strength paper

Technique

Description

Applicability

a

Fibre and filler recovery and treatment of white water

See Section 1.7.2.1

Generally applicable

b

Broke recirculation system

Broke from different locations/phases of paper making process is collected, re-pulped and returned to the fibre feedstock

Generally applicable

c

Recovery of coating colours/recycling of pigments

See Section 1.7.2.1

d

Reuse of fibre sludge from primary waste water treatment

Sludge with a high fibre content from the primary treatment of waste water can be reutilised in a production process

Applicability may be limited by product quality requirements

Technique

Applicability

a

Energy saving screening techniques (optimised rotor design, screens and screen operation)

Applicable to new mills or major refurbishments

b

Best practice refining with heat recovery from the refiners

c

Optimised dewatering in the press section of paper machine/wide nip press

Not applicable to tissue paper and many speciality papers grades

d

Steam condensate recovery and use of efficient exhaust air heat recovery systems

Generally applicable

e

Reduction of direct use of steam by careful process integration using e.g. pinch analysis

f

High efficient refiners

Applicable to new plants

g

Optimisation of the operating mode in existing refiners (e.g. reduction of ‘no load power requirements)

Generally applicable

h

Optimised pumping design, variable speed drive control for pumps, gearless drives

i

Cutting edge refining technologies

j

Steam box heating of the paper web to improve the drainage properties/dewatering capacity

Not applicable to tissue paper and many speciality papers grades

k

Optimised vacuum system (e.g. turbo fans instead of water ring pumps)

Generally applicable

l

Generation optimisation and distribution network maintenance

m

Optimisation of heat recovery, air system, insulation

n

Use of high efficient motors (EFF1)

o

Preheating of shower water with a heat exchanger

p

Use of waste heat for sludge drying or upgrading of dewatered biomass

q

Heat recovery from axial blowers (if used) for the supply air of the drying hood

r

Heat recovery of exhaust air from the Yankee hood with a trickling tower

s

Heat recovery from the infrared exhaust hot air

Technique

Description

Electrostatic precipitator (ESP)

Electrostatic precipitators operate such that particles are charged and separated under the influence of an electrical field. They are capable of operating over a wide range of conditions.

Alkaline scrubber

See Section 1.7.1.3 (wet scrubber).

Technique

Description

Reduction of air/fuel ratio

The technique is mainly based on the following features:

Optimised combustion and combustion control

Based on permanent monitoring of appropriate combustion parameters (e.g. O2, CO content, fuel/air ratio, un-burnt components), this technique uses control technology for achieving the best combustion conditions.

NOx formation and emissions can be decreased by adjusting the running parameters, the air distribution, excess oxygen, flame shaping and the temperature profile.

Staged incineration

Staged incineration is based on the use of two burning zones, with controlled air ratios and temperatures in a first chamber. The first burning zone operates at sub-stoichiometric conditions to convert ammonia compounds into elementary nitrogen at high temperature. In the second zone, additional air feed completes combustion at a lower temperature. After the two-stage incineration, the flue-gas flows to a second chamber to recover the heat from the gases, producing steam to the process.

Fuel selection/low-N fuel

The use of fuels with a low nitrogen content reduces the amount of NOx emissions from the oxidation of nitrogen contained in the fuel during combustion.

The combustion of CNCG or biomass-based fuels increases NOx emissions compared to oil and natural gas, as CNCG and all wood-derived fuels contain more nitrogen than oil and natural gas.

Due to higher combustion temperatures, gas firing leads to higher NOx levels than oil firing.

Low-NOx burner

Low-NOx burners are based on the principles of reducing peak flame temperatures, delaying but completing the combustion and increasing the heat transfer (increased emissivity of the flame). It may be associated with a modified design of the furnace combustion chamber.

Staged injection of spent liquor

The injection of spent sulphite liquor into the boiler at various vertically staged levels prevents the formation of NOx, and provides for complete combustion.

Selective non-catalytic reduction (SNCR)

The technique is based on the reduction of NOx to nitrogen by reaction with ammonia or urea at a high temperature. Ammonia water (up to 25 % NH3), ammonia precursor compounds or urea solution is injected into the combustion gas to reduce NO to N2. The reaction has an optimum effect in a temperature window of about 830 °C to 1 050 °C, and sufficient retention time must be provided for the injected agents to react with NO. Dosing rates of ammonia or urea have to be controlled to keep NH3 slip at low levels.

Technique

Description

High dry solid black liquor

With a higher dry solid content of the black liquor, the combustion temperature increases. This vaporises more sodium (Na), which can bind the SO2 forming Na2SO4 thus reducing SO2 emissions from the recovery boiler. A drawback to the higher temperature is that emissions of NOx may increase

Fuel selection/low-S fuel

The use of low-sulphur content fuels with a sulphur content of about 0,02 – 0,05 % by weight (e.g. forest biomass, bark, low-sulphur oil, gas) reduces SO2 emissions generated by the oxidation of sulphur in the fuel during combustion

Optimised firing

Techniques such as efficient firing rate control system (air-fuel, temperature, residence time), control of excess oxygen or good mixing of air and fuel

Control of Na2S content in lime mud feed

Efficient washing and filtration of the lime mud reduces the concentration of Na2S, thus reducing the formation of hydrogen sulphide in the kiln during the re-burning process

Collection and recovery of SO2 emissions

Highly concentrated SO2-gas streams from acid liquor production, digesters, diffusers or blow tanks are collected. SO2 is recovered in absorption tanks with different pressure levels, both for economic and environmental reasons

Incineration of odorous gases and TRS

Collected strong gases can be destroyed by burning them in the recovery boiler, in dedicated TRS burners, or in the lime kiln. Collected weak gases are suitable for burning in the recovery boiler, lime kiln, power boiler or in the TRS burner. Dissolving tank vent gases can be burnt in modern recovery boilers

Collection and incineration of weak gases in a recovery boiler

Combustion of weak gases (large volume, low SO2 concentrations) combined with a back-up system.

Weak gases and other odorous components are simultaneously collected to be burnt in the recovery boiler. From the exhaust gas of the recovery boiler, the sulphur dioxide is then recovered by counter-current multistage scrubbers and reused as a cooking chemical. As a back-up system, scrubbers are used.

Wet scrubber

Gaseous compounds are dissolved in a suitable liquid (water or alkaline solution). Simultaneous removal of solid and gaseous compounds may be achieved. Downstream of the wet scrubber, the flue-gases are saturated with water and a separation of the droplets is required before discharging the flue-gases. The resulting liquid has to be treated by a waste water process and the insoluble matter is collected by sedimentation or filtration

ESP or multicyclones with multistage venturi scrubbers or multistage double inlet downstream scrubbers

The separation of dust is carried out in an electrostatic precipitator or multistage cyclone. For the magnesium sulphite process, the dust retained in the ESP consists mainly of MgO but also to a minor extent, K, Na or Ca compounds. The recovered MgO ash is suspended with water and cleaned by washing and slaking to form Mg(OH)2 which is then used as an alkaline scrubbing solution in the multistage scrubbers in order to recover the sulphur component of the cooking chemicals. For the ammonium sulphite process, the ammonia base (NH3) is not recovered, as it is decomposed in the combustion process in nitrogen. After the removal of dust, the flue-gas is cooled down by passing through a cooling scrubber operated with water and it then enters a three or more staged scrubber of the flue-gas where the SO2 emissions are scrubbed with the Mg(OH)2 alkaline solution in the case of the magnesium sulphite process, and with a 100 % fresh NH3 solution in the case of the ammonium sulphite process.

Technique

Description

Dry debarking

Dry debarking of wood logs in dry tumbling drums (water being used only in washing of the logs, and then recycled with only a minimum purge to the waste water treatment plant)

Totally chlorine free bleaching (TCF)

In TCF bleaching, the use of chlorine containing bleaching chemicals is completely avoided and thus so are the emissions of organic and organochlorinated substances from bleaching

Modern elemental chlorine free (ECF) bleaching

Modern ECF bleaching minimises the consumption of chlorine dioxide by using one or a combination of the following bleaching stages: oxygen, hot acid hydrolysis stage, ozone stage at medium and high consistency, stages with atmospheric hydrogen peroxide and pressurised hydrogen peroxide or the use of a hot chlorine dioxide stage

Extended delignification

Extended delignification by (a) modified cooking or (b) oxygen delignification enhances the degree of delignification of pulp (lowering the kappa number) before bleaching and thus reduces the use of bleaching chemicals and the COD load of waste water. Lowering the kappa number by one unit before bleaching can reduce the COD released in the bleach plant by approximately 2 kg COD/ADt. The lignin removed can be recovered and sent to the chemicals and energy recovery system

Extended cooking (batch or continuous systems) comprises longer cooking periods under optimised conditions (e.g. alkali concentration in the cooking liquor is adjusted to be lower at the beginning and higher at the end of the cooking process), to extract a maximum amount of lignin before bleaching, without undue carbohydrate degradation or excessive loss of pulp strength. Thus, the use of chemicals in the subsequent bleaching stage and the organic load of the waste water from the bleach plant can be reduced

Oxygen delignification is an option to remove a substantial fraction of the lignin remaining after cooking, in case the cooking plant has to be operated with higher kappa numbers. The pulp reacts under alkaline conditions with oxygen to remove some of the residual lignin

Closed and efficient brown stock screening and washing

Brown stock screening is carried out with slotted pressure screens in a multistage closed cycle. Impurities and shives are thus removed at an early stage in the process.

Brown stock washing separates dissolved organic and inorganic chemicals from the pulp fibres. The brown stock pulp may be washed first in the digester, then in high-efficiency washers before and after oxygen delignification, i.e. before bleaching. Carry-over, chemical consumption in bleaching, and the emission load of waste water are all reduced. Additionally, it allows for recovery of the cooking chemicals from the washing water. Efficient washing is done by counter-current multistage washing, using filters and presses. The water system in the brown stock screening plant is completely closed

Partial process water recycling in the bleach plant

Acid and alkaline filtrates are recycled within the bleach plant counter-currently to the pulp flow. Water is purged either to the waste water treatment plant or, in a few cases, to post-oxygen washing.

Efficient washers in the intermediate washing stages are a prerequisite for low emissions. A bleach plant effluent flow of 12 – 25 m3/ADt is achieved in efficient mills (Kraft)

Effective spill monitoring and containment, also with chemical and energy recovery

An effective spill control, catchment and recovery system that prevents accidental releases of high organic and sometimes toxic loads or peak pH values (to the secondary waste water treatment plant) comprises:

Maintaining sufficient black liquor evaporation and recovery boiler capacity to cope with peak loads

Sufficient capacity in the black liquor evaporation plant and in the recovery boiler ensure that additional liquor and dry solids loads due to the collection of spills or bleach plant effluents can be dealt with. This reduces losses of weak black liquor, other concentrated process effluents and potentially bleach plant filtrates.

The multi-effect evaporator concentrates weak black liquor from brown stock washing and, in some cases, also biosludge from the effluent treatment plant and/or salt cake from the ClO2 plant. Additional evaporation capacity above normal operation gives sufficient contingency to recover spills and to treat potential bleach filtrate recycle streams

Stripping the contaminated (foul) condensates and reusing the condensates in the process

Stripping of contaminated (foul) condensates and reuse of condensates in the process reduces the fresh water intake of a mill and the organic load to the waste water treatment plant.

In a stripping column, steam is lead counter-currently through the previously filtered process condensates that contain reduced sulphur compounds, terpenes, methanol and other organic compounds. The volatile substances of the condensate accumulate in the overhead vapour as non-condensable gases and methanol and are withdrawn from the system. The purified condensates can be reused in the process, e.g. for washing in the bleach plant, in brown stock washing, in the causticising area (mud washing and dilution, mud filter showers), as TRS scrubbing liquor for lime kilns, or as white liquor make-up water.

The stripped non-condensable gases from the most concentrated condensates are fed into the collection system for strong malodorous gases and are incinerated. Stripped gases from moderately contaminated condensates are collected into the low volume high concentration gas system (LVHC) and incinerated

Evaporating and incinerating effluents from the hot alkaline extraction stage

The effluents are first concentrated by evaporation and then combusted as biofuel in a recovery boiler. Sodium carbonate containing dust and melt from the furnace bottom are dissolved to recover soda solution

Recirculation of washing liquids from pre-bleaching to brown stock washing and evaporation to reduce emissions from MgO-based pre-bleaching

Prerequisites for the use of this technique are a relatively low kappa number after cooking (e.g. 14 – 16), sufficient capacity of tanks, evaporators and recovery boiler to cope with additional flows, the possibility to clean the washing equipment from deposits, and a moderate brightness level of the pulp (≤ 87 % ISO) as this technique may lead to a slight loss of brightness in some cases.

For market paper pulp producers or others that have to reach very high brightness levels (> 87 % ISO), it may be difficult to apply MgO pre-bleaching

Counter-current flow of process water

In integrated mills, fresh water is introduced mainly through the paper machine showers from which it is fed upstream towards the pulping department

Separation of water systems

Water systems of different process units (e.g. pulping unit, bleaching and paper machine) are separated by washing and dewatering the pulp (e.g. by wash presses). This separation prevents carry-over of pollutants to subsequent process steps and allows for removing disturbing substances from smaller volumes

High consistency (peroxide) bleaching

For high consistency bleaching, the pulp is dewatered e.g. by a twin wire or other press before bleaching chemicals are added. This allows for more efficient use of bleaching chemicals and results in a cleaner pulp, less carry-over of detrimental substances to the paper machine and generates less COD. Residual peroxide may be recirculated and reused

Fibre and filler recovery and treatment of white water

White water from the paper machine can be treated by the following techniques:

Clarification of white water

The systems for water clarification used almost exclusively in the paper industry are based on sedimentation, filtration (disc filter) and flotation. The most used technique is dissolved air flotation. Anionic trash and fines are agglomerated into physically treatable flocs by using additives. High-molecular, water-soluble polymers or inorganic electrolytes are used as flocculants. The generated agglomerates (flocs) are then floated off in the clarification basin. In dissolved air flotation (DAF), the suspended solid material is attached to air bubbles

Water recirculation

Clarified water is recirculated as process water within a unit or in integrated mills from the paper machine to the pulp mill and from the pulping to the debarking plant. Effluent is mainly discharged from the points with the highest pollution load (e.g. clear filtrate of the disc filter in pulping, debarking)

Optimum design and construction of tanks and chests (papermaking)

Holding tanks for stock and white water storage are designed so that they can cope with process fluctuations and varying flows also during start-ups and shutdowns

Washing stage before refining softwood mechanical pulp

Some mills pretreat softwood chips by combining pressurised preheating, high compression and impregnation to improve pulp properties. A washing stage before refining and bleaching significantly reduces COD by removing a small, but highly concentrated effluent stream that can be treated separately

Substitution of NaOH by Ca(OH)2 or Mg (OH)2 as alkali in peroxide bleaching

The use of Ca(OH)2 as alkali results in approximately 30 % lower COD emission loads; while keeping brightness levels high. Also Mg(OH)2 is used to replace NaOH

Closed-loop bleaching

In sulphite pulp mills using sodium as a cooking base, the bleach plant effluent can be treated, e.g. by ultrafiltration, flotation and separation of resin and fatty acids which enables closed-loop bleaching. The filtrates from bleaching and washing are reused in the first washing stage after cooking and finally recycled back to the chemical recovery units

pH adjustment of weak liquor before/inside the evaporation plant

Neutralisation is done before evaporation or after the first evaporation stage, to keep organic acids dissolved in the concentrate, in order for them to be sent with the spent liquor to the recovery boiler

Anaerobic treatment of the condensates from the evaporators

See Section 1.7.2.2 (combined anaerobic/aerobic treatment)

Stripping and recovery of SO2 from condensates of evaporators

SO2 is stripped from the condensates; concentrates are treated biologically, while the stripped SO2 is sent for recovery as a cooking chemical.

Monitoring and continuous control of the process water quality

Optimisation of the entire ‘fibre-water-chemical additive-energy system’ is necessary for advanced closed water systems. This requires a continuous monitoring of the water quality and staff motivation, knowledge and action related to the measures needed to ensure the required water quality

Prevention and elimination of biofilms by using methods that minimise emissions of biocides

A continuous input of microorganisms by water and fibres leads to a specific microbiological equilibrium in each paper plant. To prevent extensive growth of the microorganisms, deposits of agglomerated biomass or biofilms in water circuits and equipment, often bio-dispersants or biocides are used. When using catalytic disinfection with hydrogen peroxide, biofilms and free germs in process water and paper slurry are eliminated without using any biocides

Removal of calcium from process water by controlled precipitation of calcium carbonate

Lowering the calcium concentration by controlled removal of calcium carbonate (e.g. in a dissolved air flotation cell) reduces the risk of undesired precipitation of calcium carbonate or scaling in water systems and equipment, e.g. in section rolls, wires, felts and shower nozzles, pipes or biological waste water treatment plants

Optimisation of showers in paper machine

Optimising showers involves: a) the reuse of process water (e.g. clarified white water) to reduce fresh water use, and b) the application of special design nozzles for the showers

Technique

Description

Primary treatment

Physico-chemical treatment, such as equalisation, neutralisation or sedimentation.

Equalisation (e.g. in equalising basins) is used to prevent large variations in flow rate, temperature and contaminant concentrations and thus to avoid overloading the waste water treatment system

Secondary (biological) treatment

For the treatment of waste water by means of microorganisms, the available processes are aerobic and anaerobic treatment. In a secondary clarification step, solids and biomass are separated from effluents by sedimentation, sometimes combined with flocculation

In aerobic biological waste water treatment, biodegradable dissolved and colloidal material in the water is transformed in the presence of air by microorganisms partly into a solid cell substance (biomass) and partly into carbon dioxide and water. Processes used are:

The generated biomass (excess sludge) is separated from the effluent before the water is discharged

Anaerobic waste water treatment converts the organic content of waste water by means of microorganisms in the absence of air, into methane, carbon dioxide, sulphide, etc. The process is carried out in an airtight tank reactor. The microorganisms are retained in the tank as biomass (sludge). The biogas formed by this biological process consists of methane, carbon dioxide and other gases such as hydrogen and hydrogen sulphide and is suitable for energy generation.

Anaerobic treatment is to be seen as pretreatment before aerobic treatment, due to the remaining COD loads. Anaerobic pretreatment reduces the amount of sludge generated from biological treatment

Tertiary treatment

Advanced treatment comprises techniques, such as filtration for further solids removal, nitrification and denitrification for nitrogen removal or flocculation/precipitation followed by filtration for phosphorus removal. Tertiary treatment is normally used in cases where primary and biological treatment are not sufficient to achieve low levels of TSS, nitrogen or phosphorus, which may be required e.g. due to local conditions

Properly designed and operated biological treatment plant

A properly designed and operated biological treatment plant includes the appropriate design and dimensioning of treatment tanks/basins (e.g. sedimentation tanks) according to hydraulic and contaminant loads. Low TSS emissions are achieved by ensuring the good settling of the active biomass. Periodical revisions of the design, dimensioning and operation of the waste water treatment plant facilitate achieving these objectives

Technique

Description

Waste assessment and waste management system

Waste assessment and waste management systems are used to identify feasible options for optimising prevention, reuse, recovery, recycling and final disposal of waste. Waste inventories allow for identifying and classifying type, characteristics, amount and origin of each waste fraction

Separate collection of different waste fractions

The separate collection of different waste fractions at the points of origin and, if appropriate, intermediate storage can enhance the options for reuse or recirculation. Separate collection also includes segregation and classification of hazardous waste fractions (e.g. oil and grease residues, hydraulic and transformer oils, waste batteries, scrap electrical equipment, solvents, paints, biocides or chemical residues)

Merging of suitable residue fractions

Merging of suitable fractions of residue depending on the preferred options for reuse/recycling, further treatment and disposal

Pretreatment of process residues before reuse or recycling

Pretreatment comprises techniques such as:

Material recovery and recycling of process residues on site

Processes for material recovery comprise techniques such as:

Energy recovery on- or off-site from wastes with high organic content

Residues from debarking, chipping, screening etc. like bark, fibre sludge or other mainly organic residues are burnt due to their calorific value in incinerators or biomass power plants for energy recovery

External material utilisation

Material utilisation of suitable waste from pulp and paper production can be done in other industrial sectors, e.g. by:

The suitability of waste fractions for off-site utilisation is determined by the composition of the waste (e.g. inorganic/mineral content) and the evidence that the foreseen recycling operation does not cause harm to the environment or health

Pretreatment of waste fraction before disposal

Pretreatment of waste before disposal comprises measures (dewatering, drying etc.) reducing the weight and volume for transport or disposal