2 PRINTING
treatment 0 Total input:
54 BVT-Merkblatt Oberflächenbehandlung mit Lösemitteln Input based on 1000 kg printing ink Process step Output
Included in the printing process Ink conditioning 3180 kWh electric drives
1010 kWh electric cooling
580 kWh electric compressed air Printing process
Included in the printing process Interim cleaning 5500 kWh thermal oil
(approx. 42 % intermediate driers and
58 % bridge driers) 980 kWh electric fans
Ink drying
Included in the printing process Finishing 1300 kWh thermal
350 kWh electric fans Waste gas
treatment 0
BVT-Merkblatt Oberflächenbehandlung mit Lösemitteln 55 Table 2.33 below gives, for many sources, a typical emission value, possible reduction measures for that source and a typical emission value after the reduction measures have been taken. Note:
• ‘typical’ emission values are provided to give an impression of the order of magnitude. The emission is expressed as a percentage of the solvent consumption of the plant. Actual emissions values may vary widely
• ‘n.a.’ means that no typical emission value can be given. Emissions from sources such as
‘defects in bypasses’ or ‘solvent content water-based products’ obviously vary enormously from plant to plant
• ‘very small’ means that the total emissions of all the ‘very small’ sources may be less than 1 % of the solvent consumption
• ‘negligible’ means that the emission is either zero or an order of magnitude smaller than the
‘small’ emissions. Their total volume is smaller than the margin of error in the larger emissions.
Group Activity or source Typical
emission Possible reduction measures After reduction
P Evaporation from the ink fountains
during production 5 %
1. Adequate coverage of the ink fountains 2. Use chamber doctor blades
3. Encapsulation of varnishing or lamination units
4. Use of adhesives with reduced solvent content (see relevant techniques in Section 2.4.2)
5. Floor extraction through driers 6. Floor extraction sent to incinerator (see Section 2.4.2.5.2)
2.5 %
Evaporation from open viscosity
adjustment units Very small None Very small
Leaking driers through defects or drier pressure higher than atmospheric
n.a. Proper maintenance, correct operation,
periodic checks (see Section 20.11.1.2) Negligible
Defects in the bypass of the driers (waste gases sent to atmosphere rather than to the incinerator)
n.a.
Give priority, proper maintenance, correct operation, periodic checks, instruction for manual operation if possible, speedy repairs (see Section 20.11.1.2)
n.a.
Waste gas emissions from presses when these are filled with ink, but not yet printing
Negligible None Negligible
Waste gas emissions from presses when these are printing at minimum
speed 0.1 % None 0.1 %
Waste gas emissions from presses in the case of defects to production machines
Very small None Very small
Waste gas emissions from presses when printing at make-ready speed.
(30 to 60 m/min)
3 – 8 % Automatic closure of bypass before make-ready speed is reached (see Section 2.4.2.5.5)
Negligible
Cleaning floors 1 %
1. Prevention of soiling 2. Use of squeezable sweeps 3. Use non volatile cleaning agents (see Sections 20.9and 20.10.1)
Very small
Evaporation from open drums Negligible Keep closed as much as possible (see
Section 20.2.2.1) Negligible
Residual solvent packaging materials
for food Very small None Very small
Residual solvent in printed materials
that are not packaging for food 3 – 10 % Improve drying 0.1 %
O Emissions from the incinerator 0.5 – 1.5 % (May increase if additional solvent laden
air stream are sent to incinerator) 0.5 – 1.5 %
56 BVT-Merkblatt Oberflächenbehandlung mit Lösemitteln
Group Activity or source Typical
emission Possible reduction measures After reduction
Defects in the incinerator causing waste gases to be sent to the air
n.a.
(0.4 % of input per defect day)
High priority: proper maintenance, correct operation, periodic check, instruction for manual operation if possible, speedy repairs (Section 2.4.2.5.2)
Equip with computer techniques, connect to supplier (see Section 20.2.3)
Very small
The use of solvent-based inks, varnishes and adhesives on machines not attached to the incinerator n.a.
Connect to incinerator at times when incinerator has enough capacity (see
Section 20.11.1.4) n.a.
The use of solvent-based inks, varnishes and adhesives on driers not attached to the incinerator
n.a.
Refrain from using these driers for solvent-based inks
Connect to incinerator at times when incinerator has enough capacity (see Section 20.11.1.4)
n.a.
Solvent content of water-based products (inks contain approx. 5 % solvent, varnishes and adhesives may be fully solvent-free)
n.a.
Priority: Use water-based products with solvent content as low as possible.
Otherwise: none
(see relevant techniques in Section 2.4.2) n.a.
C
Drying process and ventilation in automatic washing machines using
solvents 5 %
1. Ventilation to incinerator (Section 2.4.2.5.2)
2. Use non-volatile cleaning agents (see Sections 20.9 and 20.10.1)
Negligible
Evaporation during manual cleaning
operations 1 %
1. Prevent useless evaporation 2. Prevent cleaning and drying by hand after washing automatically
3. Use automatic washing machine as much as possible
4. Use non-volatile cleaning agents as much as possible
5. In press room, prevent contamination of objects that cannot be cleaned in washing machine as much as possible
6. In-depth cleaning of anilox rollers and cylinders with solvent-free methods (see Sections 20.9 and 20.10.1)
0.5 %
Cleaning and drying by hand after
washing automatically Included See manual cleaning (see Sections 20.9
and 20.10.1) Included
Cleaning with machines other than
automatic washing machines Included See manual cleaning (see Sections 20.9
and 20.10.1) Included
Cleaning of the floors Included
1. Prevention of soiling 2. Use of squeezable sweeps 3. Use of non-volatile cleaning agents (see Sections 20.9 and 20.10.1)
Included
Evaporation from open drums
(solvent, waste, etc.) Included Keep closed Included
I Evaporation resulting from the
mixing of inks Very small
Automatic ink mixing systems, drum close to nozzles, quickly close drums after filling
(see Sections 20.2.3 and 20.2.2.1) Very small Evaporation resulting from making
colour tests Negligible None Negligible
Cleaning of the floors and other
cleaning 1 %
1. Prevention of soiling 2. Use of squeezable sweeps 3. Use of non-volatile cleaning agents (see Sections 20.9 and 20.10.1)
0.5 %
Evaporation losses from tanks Negligible None Negligible
Evaporation from open drums Very small Keep closed (see Section 20.2.2.1) Very small Table 2.33: Reduction of fugitive emissions from flexible packing printing
[127, VROM, 2004]
BVT-Merkblatt Oberflächenbehandlung mit Lösemitteln 57 The emissions caused by defects in driers, bypasses or in the incinerator itself may be considerable. The same is true for machines and driers not attached to the incinerator and the solvent content of water-based inks. No typical emission values are given, but the total of the emissions from these sources may easily be several per cent of the annual solvent consumption.
It can be seen that the total of the emissions from all the other sources may vary enormously. If none of the reduction measures mentioned in Table 2.33 are applied, this total may amount to well over 25 % of solvent consumption. If all possible reduction measures are applied, the total of these emissions may be well below 10 % of solvent consumption.
Allowing for several per cent of emissions due to defects and the solvent content of water-based inks, the total emissions can be expected to vary between 30 and 10 % in most plants.
In order to attain a total emission lower than 10 % of solvent consumption, it is necessary to carry out all or most of the following:
• prevent defects to incinerator, bypasses, driers; etc. (see Section 20.11.1.2)
• send waste gases from the driers to the incinerator both automatically and before make-ready press speed is reached (see Section 2.4.2.5.5)
• connect the ventilation exhaust of the automatic washing machines to the incinerator (see Section 2.4.2.5.2)
• reduce emissions due to evaporation from ink fountains during production (see Section 2.4.2.5.2)
• avoid the use of solvent-based products on machines not connected to the abatement equipment
• reduce the residual solvent in printed matter not intended to be used as packaging for food
• reduce the use of volatile solvents for cleaning floors (see Sections 20.9 and 20.10.1).
Inks
For water-based inks, 0.5 - 1.0 % ammonia emissions per kg ink input can be expected. On average, water-based inks contain 0 - 10 % organic solvent (ethanol or IPA) which will, in the end, be emitted [18, UBA Germany, 2003].
There are no emissions to air from UV inks.
Lamination and varnishing
When using solvent-based (SB) materials, the emissions from these processes are higher than from printing. With solvent-based adhesives, a large amount of air has to moved through the drier to keep the solvent/air ratio well below the lower explosive limit (LEL) [4, Intergraf and EGF, 1999] [76, TWG, 2004].
Increasingly 2-component, solvent-free adhesives and water-based varnishes are used for lamination of plastic foil and varnishing of aluminium respectively. Water-based adhesives are often used to adhere paper to aluminium. Where water-based inks mostly still contain some solvent, water-based adhesives and varnishes are generally solvent-free.
Cleaning
Fugitive solvent emissions arise from cleaning where the quantity depends on the handling.
Waste gas treatment
Modern regenerative incinerators can work without the addition of fuel (autothermic operation) when the solvent concentration in the air to be treated is >1 g/m3. At higher concentrations, the incinerator may produce excess heat, which may be recovered and used in production processes.
In flexo and packaging gravure plants where the airflow has been optimised, and a large amount of the work is with 100 % coverage (such as white ink, adhesives and varnishes) concentrations of 4 to 6 g/m3 are attainable, otherwise lower concentrations are found [76, TWG, 2004].
58 BVT-Merkblatt Oberflächenbehandlung mit Lösemitteln With incineration, emission levels of <100 C/Nm³ can be achieved and often levels of 20 - 50 C/Nm³, see Section 20.11.4.2 [76, TWG, 2004, 128, TWG, 2005]
Adsorption is also applied, although to a lesser extent, see Section 20.11.6. Adsorption can achieve a removal efficiency of up to 99 % in publication gravure (see Section 2.3.4.3), although this is not usual as it requires a high energy input in regeneration of the absorbent. In the clean gas, concentrations of <20 mg/m3 are achieved, The hot steam desorption generates about 3 – 6 m3 per kg of recovered solvent. In flexible packaging, solvent recovery through adsorption to activated carbon is also applied; frequently in Italy, rarely elsewhere. Where solvent recovery is applied, solvent consumption is limited as far as technically possible to ethyl acetate, in order to reduce the size of the adsorption unit, reduce dehydration problems and reduce the occurrence of azeotropic mixtures of ethylacetate with ethanol and MEK. Hot steam desorption is used less and less in flexible packaging, and currently inert gas desorption is usual.
Recovery rates are generally 95 to 95.5 %, with a waste gas concentration of 50 to 150 mgC/m3. [14, DFIU and IFARE, 2002] [4, Intergraf and EGF, 1999, 128, TWG, 2005]
2.3.3.3.2 Waste [128, TWG, 2005]
Printing substrate
Printing substrate is wasted when starting a new printing job and also arises from misprints because of defects and when the edge of the printed web roll requires trimming. The quantity depends on the product produced, however it often accounts for 10 % of the final product in weight [18, UBA Germany, 2003] [76, TWG, 2004].
Ink
Ink losses arise from three areas [4, Intergraf and EGF, 1999]:
• the amount of ink prepared always exceeds the need to avoid presses running out of ink
• ink supplied to the inking unit, but not used, is stored and later used on a repeat job for the same client. Most plants have a large stock of these readymade inks waiting for repeat jobs.
Periodically, inks that are not expected to be used again are removed
• the mixing of the ink results in the wrong colour. To correct this mistake, more ink has to be added and, as a result, too much ink is prepared.
Surplus inks are disposed of as waste, or alternatively are distilled in-house. Their solvent content is then recovered and used for cleaning purposes; the ink sludge is disposed of as waste.
However, modern practice with computerised colour-matching systems enables better first time quality resulting in very little ink wastage and minimal leftover batches, which can be used again in slightly different colours (see Section 20.6.3.6). In situations where no computerised systems for mixing the right colour are applied, some 10 – 20 % of the ink purchased ends up as waste. Where computerised systems are used, the amount of waste ink is reduced by at least 25 - 75 % [18, UBA Germany, 2003] [76, TWG, 2004].
Cleaning
Dirty wipes containing solvents, dirty cleaning mixtures of water and solvent, and ink residues stem from interim cleaning. When the cleaning agents are distilled, the resulting waste, i.e. ink sludge, is far less than without recovery [18, UBA Germany, 2003].
When cleaning is done without using solvents, the waste water might be treated and discharged.
Cleaning solutions with solvents are normally treated as hazardous waste [4, Intergraf and EGF, 1999] [76, TWG, 2004].
Cleaning agents can be successfully recovered by distillation.
BVT-Merkblatt Oberflächenbehandlung mit Lösemitteln 59 Others
Other wastes are, for example [4, Intergraf and EGF, 1999] [76, TWG, 2004]:
• photopolymer and rubber printing plates: The steel, polyester or aluminium sleeves are re-used repeatedly: the polyester or rubber materials are glued to these
• non-returnable metal containers
• reel cores
• film wastes.
2.3.3.3.3 Waste water
Waste water from water-based ink processes can be treated and disposed of to the sewerage system. The total amount of waste water is highly dependent on the working methods, and on average 2 – 3 m3/t ink is used and discharged, mainly from interim cleaning and cleaning the machinery after a job. The characteristics of this waste water before and after treatment are shown in Table 2.34. Copper is not present to the extent shown in Table 2.34 in inks, and is likely to come from the paper (see Section 2.3.2.3.3) [76, TWG, 2004].
Contaminant Before treatment
(mg/l) After treatment (mg/l)
AOX 1500 1
Cu 20