TECHNICAL GUIDELINES (WATER MANAGEMENT CONCEPT) FOR PAPER MAKERS IN EUROPEAN REGIONS WITH DIFFICULT BOUNDARY CONDITIONS ON HOW TO OPERATE MILLS WITH MINIMUM WATER USE pdf

Contents 1 Summary ...3 2 Introduction ...4 3 Systematic approach to Water Management...5 4 Minimising water usage...7 4.1 Cooling water network 7 4.2 Preparation and dilution of chemica

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TECHNICAL GUIDELINES (WATER MANAGEMENT CONCEPT) FOR PAPER MAKERS IN EUROPEAN

REGIONS WITH DIFFICULT BOUNDARY CONDITIONS

ON HOW TO OPERATE MILLS WITH

MINIMUM WATER USE

RESPONSIBLE PARTNER: Centre Technique du Papier (CTP)

PROJECT CO-ORDINATOR: LUCENSE SCpA

PARTNERS: Papiertechnische Stiftung (PTS),

Centre Technique du Papier (CTP), A.R.P.A.T.,

Serv.Eco Srl

Project funded by the European Community under the “Energy, Environment and Sustainable Development” Programme (1998-2002)

Contents

1 Summary 3

2 Introduction 4

3 Systematic approach to Water Management 5

4 Minimising water usage 7

4.1 Cooling water network 7 4.2 Preparation and dilution of chemicals 7 4.3 Paper machine showers 7 4.4 Sealing waters 7 5 Optimum Water circuit Layout 8

5.1 Strict separation of water loops together with counter-current flows 8 5.2 Broke system management 8 5.3 Optimal water arrangement, water clarification and recycling of process water for different purposes 8 5.4 Adequate storage capacity 9 5.5 De-inking plant: generation of clarified water 9 6 Appropriate effluent treatment 11

6.1 Installation of an equalization basin and primary treatment of waste water 11 6.2 Secondary treatment 11 6.3 Anaerobic treatment as first stage of biological waste water treatment 12 6.4 Chemical precipitation of waste water from paper mills 13 7 Integration of advanced water treatment as an option to further reduce process water loading 14

7.1 Introduction 14 7.2 Choice of technology 14 7.3 Elimination of organic compound 15 7.4 Elimination of inorganic compounds 15 8 Conclusions 17

9 Literature 18

1 SUMMARY

One important outcome of the EU-funded Project PAPERBREF1 is the water management concept about how to operate mills with minimum water use in European regions with difficult boundary conditions This concept is based upon studies performed in 30 paper mills in the region of Tuscany, Italy, in 2002 and 2003 The paper grades produced in these mills are packaging paper and tissue made of virgin fibre or recovered fibre All conclusions given are based on the results of these studies

It is the aim of this study to describe all methods that have been successfully applied in paper mills operating in typical European regions with difficult boundary conditions with regard to water use All methods mentioned are therefore adapted to these specific conditions Their implementation is a success factor that ensures compliance with local and European standards

The most important fields for achieving optimum water management are:

• a structured approach towards water management in general

• minimised and improved fresh water use

• optimum water circuit layout

• appropriate effluent treatment

• integration of advanced water treatment as an option to reduce process water loading further

The latter should only be adopted if all other methods have been implemented and the process water loadings are still too high In any case, the most challenging part of achieving improved water management is to counteract the build-up of detrimental substances within the process and in the effluent

The solution chosen is always an individual combination of the options described in this document The list of publications given is intended to enable the reader to obtain additional information concerning improved water management in paper mills

2 INTRODUCTION

Knowledge acquired according to the PAPERBREF project concerning packaging paper machine from recovered paper and tissue paper machines from virgin or recovered fibres helps us define technical guidelines on a water management concept This concept is based on the BREF DOCUMENT and analysed through PAPERBREF project experiments to minimise water usage

Water reduction methods in paper and board machines are a complex issue and depend greatly on the degree of closure desired A balance between the advantages and the drawbacks associated with the closing-up of water systems should be established The acceptable level of closure will depend on the paper grade produced, raw materials used and water and pulp circuit management

3 SYSTEMATIC APPROACH TO WATER MANAGEMENT

The enhanced recycling of process water in paper and board machines causes an increase in the concentration of colloidal and dissolved organic and inorganic constituents

in these streams Depending on the characteristics of the pulp in-feed and the used chemicals in paper-making, the closed-up water systems can have an adverse effect on the operation of the machine, the quality of end-product and even the production costs due to the increased use of chemicals

In the different actions listed below, it is very important to estimate the impact on the evolution of physico-chemical quality of the process water The build-up of organic and inorganic materials can be balanced to a certain degree by the use of specific chemicals

in replacement of or in complement to the actual chemicals

Before any investigation to operate with minimum negative environmental impact, paper mills must have a complete overview of their process The methodology applied in the

Paper BREF project provides a detailed global view of the use of fresh water and of the water circuit arrangement A flow diagram of the in-mill stock and water systems must be made to have an overview of the organisation of pulp and water circuits Decrease in fresh water consumption should involve modification in the physico-chemical quality of process water, and analyses at reference points in the water system must be performed to measure the initial load situation All major fresh water consumers are identified and measured

Comprehensive information and the knowledge of experts will enable

1 an estimation of the fresh water saving potential The detailed analysis of the fresh water use will determine the fresh water “losses”, i.e the non-polluted raw water that goes to the effluent treatment plant without being re-used

2 the system to be reorganised to improve water use in the paper-making process and water quality around the paper machine to be improved

The modification needed to operate with minimum fresh water consumption concerns the re-use of non-polluted fresh water, water circuit management and the recycling of fresh water or the substitution of fresh water by process water

As a rule of thumb, the first methods to apply are those that have no effect on the organic and inorganic loading of the process water These methods concern:

1 The cooling water network with the re-use of this non-polluted water (in terms of organic and inorganic load) as raw water for other process applications

2 The decrease in sealing water flow

3 All other fresh water losses identified by a detailed and specific analysis of the fresh water used by the paper machine

To minimise fresh water use and its drawbacks, a combination of the above list is required:

1 Adequate storage capacity and efficient broke system management is of

prime importance with regard to the stability of the process water system

2 Efficient save-alls that produce clarified water with a low suspended solid content

are essential to use process water instead of fresh water for applications such as paper machine showers

3 Backward re-use process water in the systems, counter current to the fibre flow should also be applied

For integrated pulp and paper mills and in particular recovered paper based mills, the

strict separation of water loops together with counter-current flows is of major

importance to restrict the organic load of process water around the paper machine

The measure adopted to minimise water consumption should be applied step by step

The following chapter describes the BAT mentioned above They are classified in 4 groups: BAT concerning water management, BAT concerning the minimising of fresh water consumption, BAT concerning Waste Water management and Advanced Technology that could be applied in extreme cases where the water system closure must

be important

4 MINIMISING WATER USAGE

4.1 Cooling water network

Fresh water used for cooling can reach 6 m3/t Recycling this water in the fresh water network to the paper machine presents real advantages due to the higher temperature There are no disadvantages because the only modification in the physico-chemical quality

of the water leaving the cooling circuit is an increase of temperature

The cooling water network should be fed by the fresh water system and recycled to the raw water tank of the paper machine

If necessary, the cooling water system can be partially closed; in this case, a cooling tower for re-use is then required

4.2 Preparation and dilution of chemicals

The water quality used for the preparation of chemicals should be free from ionic substances because pollutant introduced in this step will greatly alter adjuvant quality and efficiency The preparation of chemicals should be made with clean fresh water Some chemicals need dilution just before sending them to pulp flow The contact between the water of dilution and the chemicals before their contact with the pulp is very short It is then possible to use clarified water instead of fresh water for this application

4.3 Paper machine showers

Clear or super-clear white water from the save-all is increasingly used in wet end wire showers The use of clarified water to feed wire showers requires adequate showers and nozzles: shower cleaning equipment, with an internal brush or other purging equipment is also necessary To avoid plugging of the nozzle due to dysfunction of the save-all, water distribution to such showers should go through a protective in-fine strainer, preferably of the slotted type and equipped with an automatic purge The opening size of this filter should not exceed 1/6th of the spray nozzle diameter To avoid plugging the nozzle, the particle size is more important than the consistency

The use of clarified water to feed felt showers needs a stronger filtration step and a specific study must be carried out to ensure that the use of process water will not affect the felt plugging

4.4 Sealing waters

Sealing water used for circulating pumps can represent a high use of fresh water Pump constructors propose interesting alternatives with mechanical seals or dynamic water tightness

Vacuum pumps also need large quantities of sealing water A recycling loop is recommended for part of the vacuum pump sealing water with integrated cooling and solids removal Paper machine vacuum pumps that recycle used sealing water must have strainers and, in the case of a high recycling rate, cooling systems in recycling lines to maintain a high vacuum

Some paper mills use clarified water as sealing water

5 OPTIMUM WATER CIRCUIT LAYOUT

5.1 Strict separation of water loops together with counter-current flows

This measure concerns integrated pulp and paper mill and in particular the recovered paper based mills When recovered fibres are used, they represent the main polluting

source of soluble organic material This soluble organic substances contaminates the process water during pulping and is then contained within the process water The principle

of strict separation of water loops means, that the pulp department, the bleaching department and the paper mill department each have its own water circuit The white water from paper mill is then introduced into the loops of the pulp mill and thus the water flow is counter-current to the product flow: the excess white water from paper machine loop goes backwards to the previous department where water quality is less demanding, and so on The separation of the water loops is carried out with thickeners The extra thickener leads to an improved separation of the “dirty” stock preparation water and the

“clean” paper machine water and thus to significant reduction of organic substances that enter the machine loop The excess water from the whole system come from the first loop

i.e the pulping department Fresh water is mainly used in the paper machine loop This arrangement can reduced the organic load by a factor of between 2 and 4

With this measure applied the fresh water consumption of the mill can be decreased and

at the same time minimizing drawback of a partial water closure It can be applied to both new and existing plants but needs high investments : thickeners and additional water storage and piping

5.2 Broke system management

Another important factor in closing the white water system regarding the wet-end stability

is to separate the broke and white water systems Under normal operating conditions, the white water from paper machine is relatively constant while the quality of broke varies Mixing broke with the white water system causes significant flow variations in the white water system Suggested broke system involved pumping from the couch pit and the dry-end pulper to a common storage tank From there, it passes through a cleaning device and a deflaker to the blend chest with a controlled flow and a controlled consistency In line consistency control of the stock from the broke chest to blend chest is essential

5.3 Optimal water arrangement, water clarification and recycling of process water for different purposes

The main principle of an optimal water arrangement is to backward re-use process water

in the systems, counter current to the fibre flow The white water from the paper machine

is use for stock dilution before the fan pump (short circulation) The overflow is clarified in saveall One of the most important components of the paper machine white water system

is the saveall which separate liquids from solids The saveall clarified water can be then used in mill applications for adjusting stock consistency and in substitution of fresh water application such as paper machine showers The recovered stock is then re-use in pulp circuit preferably in the machine chest Clarification is achieve by sedimentation, flotation

or filtration Each of these technologies has its own advantages and limitations Sedimentation tank are not any more available as saveall because of the length of time involved for clarification which is not compatible with water circuit closure, risk of anaerobic fermentation is too high The most commonly used clarifiers today for white water clarification are flotation saveall for tissue paper mill and for corrugating paper mill and disk filter for all kind of production (and particularly for fine papers)

Flotation save-alls are effective in removing suspended and colloidal material but need the help of coagulant/flocculant agents At optimum conditions, flotation save-alls have a good TSS removal efficiency They are suitable for grades having fine and colloidal material in stock but not for grades using fillers The main disadvantages of flotation save-alls are:

• difficulties in paper machine operation when recovered stock is added near the fan pump

• the sensitivity of flotation efficiency to process disturbances

• and operational costs

In a disk filter, liquid is forced through the filter layer by applying a vacuum The build-up

of the fibres on the filter wire serves as the main filtration medium The white water filtrate

is typically collected as two separate, cloudy and clear fractions In some cases, even a super clear fraction has been separated The super clear filtrate from a disk filter could have 10-20 mg/l and clear filtrate 20-50 mg/l solids, in comparison with well over 50 mg/l

of other save-alls Thus, clear filtrate can be used in paper machines The cloudy filtrate is readily re-used in machine broke pulping and stock dilution The main disadvantages of disk filter are:

• Space constraints: the disk filter must be installed several metres above the floor

• High maintenance costs

5.4 Adequate storage capacity

The most important item keeping the accident discharges to a minimum is the correct sizing of the process water and broke chests As a rule of thumb, a statistical study on the broke pulp produced by each paper mill should allow the volume of the broke chest to be adapted according to the rated production and significant water and solids discharge to the sewer to be reduced The white water storage capacity must match this broke storage

so that no fresh water is required during sheet breaks or when the broke is returned to the machine But the storage capacity of pulp, broke and process water should be optimised

so that it is not too large, because of microbial activity and not too small to avoid the need

to add fresh water for level control

The white water tank level according to broke inventory, pulp inventory and production plan must be checked to prevent spillage.The low and high tank levels must be optimised and the pulp and process water storage tanks should contain an agitator

In mills that change paper grades frequently, tank control is more difficult, because the inventories are often kept low to minimise losses from clean-ups at grade changes For this reason, machine feed characteristics must be checked more carefully so that the amount of broke stays low

Control of accidental process water discharges is of primary importance in the paper machine and can be applied in existing and new mills However, problems are likely to arise in existing old mills, which often do not have enough space to expand water or pulp storage Moreover, the level of automation in old or small machines should be restricted because of the high costs involved

5.5 De-inking plant: generation of clarified water

To remove upstream the dissolved and colloidal materials generated in the de-inking plant, including anionic colloids that can induce secondary stickies on the paper machine wire, the use of a DAF (Dissolved Air Flotation) to treat water in de-inking plants has proved to be efficient This practice increases efficiency of the ink removal and limits the carry over of contaminant to the paper machine The internal generation of clarified water

from de-inking process water is carried out in micro-flotation systems : the DAF Unlike water clarification in the paper mill, the solid material recovered from the DAF contains contaminants and has to be disposed of as sludge

6 APPROPRIATE EFFLUENT TREATMENT

Minimising water use can result in an increase in pollution load in terms of consistency, and effluent then has to be treated before being sent to the recipient The waste water treatment plant consists of:

• an equalisation basin to ensure that the WWTP is fed with a steady and continuous flow

• a primary treatment: physico-chemical treatment by flotation or settling to remove suspended solids

• a secondary treatment if necessary: biological treatment to remove organic compounds

• sometimes a tertiary treatment to remove specific pollutants

6.1 Installation of an equalization basin and primary treatment of waste water

Equalization and spill collection is of prime importance in the pulp and paper industry: effluents with large variations with regard to flow and content of pollutants are often observed Such variations disturb the functioning of the subsequent treatment processes

An equalization basin before the waste water treatment is essential for the efficiency of the primary and secondary treatments The minimum retention time of the equalization basin depends upon the paper-making process and can be determined by an analysis of the reject flow variation

Primary or mechanical treatment is carried out for the removal of solid particles, such as fibres, bark particles and inorganic particles (fillers, lime particles, etc.) These particles are usually referred to as (total) suspended solids (TSS or SS) This is the first type of treatment to be applied at a pulp and paper mill, and it may be either the only treatment or

a pre-treatment ahead of, for instance, a biological process The result of the primary treatment depends on the effluent properties, but also on the degree of internal fibre recovery in the pulp or paper mill For suspended solids (TSS), the removal rate may be within 60-95% For solids that settle, removal will normally be higher, approximately 90- 95% TSS values after the primary sedimentation may be in the range of 30-200 mg/l The effluent treatment plant produces sludge, which can be burned after dewatering, providing in some cases net positive heat value, or can be used in agriculture

6.2 Secondary treatment

Biological treatment is required if the COD or BOD load is too high with regard to local legislation The basic alternatives are aerobic and anaerobic biological systems Different techniques are available, but the choice of the appropriate technology depends on the organic pollution load of the effluent to be treated

The following table shows the technology that can be chosen according to the COD concentration of the inlet effluent