6.3.3 Tests and test results

Based on Renzmann’s experiences fixed parameters have been chosen for each plant. Moreover, the tests have been conducted with combinations of vessels in stainless/plain black steel, lacquer film dry/wet, washing media and washing time. Dry lacquer film is after drying/hardening for 5 days. The numerous combinations can be grouped according to type of plant in series tests a, b and c.

Each combination has been tested on a number of lacquer and paints chosen by Teknos Technology A/S. The chosen types are stated together with the test results in table 6.2.

Water-based cleaning (Stripper 303 G/E and NaOH-solvent) is carried out in cleaning plant SKM. For comparison the same lacquer and paints are cleaned by means of equipment with brushes or pressure washing by use of mixed/multilevel thinner.

Besides use as standard of comparison for water-based cleaning the tests with multilevel thinner can inform something about efficiency of different pressure and cleaning times.

The test combinations are shown in table 6.1.

Table 6.1 Look here!
Test parameters and variants

Table 6.2 Look here!
Test results

6.3.4 Assessment of test results

Water-based cleaning with alkaline special product (Stipper 303 G/E) is generally suitable. For isocyanate it is not absolutely suitable, however it should be noted that isocyanate generally is difficult to clean which is also the fact with multilevel thinner, cf. the test results.

As for a large number of the investigated types of lacquer the NaOH-solution is suitable. However, there is a demand for longer washing time than with Stripper 303 G/E. For the types of lacquer with limited efficiency, similar or other problems appear also by use of multilevel thinner. For some of these types of lacquer solution-based cleaning demands at the same time a mechanical impact.

The NaOH-solution is somewhat cheaper than Stripper 303 G/E both as to buying and as to subsequent treatment/removal of waste.

In case complete or partly cleaning with solvents is chosen tests show that the best efficiency is reached with a mechanical impact with brushes instead of pressure washing. A plant like "Robus" will not reduce the VOC emission considerably compared to known and more manual cleaning methods, however depending on the construction of the plant an improvement of the working environment may take place.

Each company has to assess relevant cleaning methods and cleaning media based on types of lacquer. It might be necessary to choose more methods and media, in case the product mix of the company is very different and varied. After choice of method the cleaning time can be optimized to each type of lacquer.

It would also be relevant to let existing types of vessels, materials and sizes be part of an overall assessment. Valves may demand additional cleaning. A general replacement of vessels will be very costly.

Chapter 8 shows a calculating example of the economy by using water-based cleaning in the "SKM" plant.

Subsequently advantages and disadvantages for the tested plants are stated.

A – Cleaning plant of the type "SKM"

Advantages:

	Efficient cleaning of the vessels
	Can be used with vessels of different sizes. However, it will be relatively costly to clean very small vessels
	Closed system, considering the working environment
	The vessel is completely dry after the process

Limitations/disadvantages:

	Possible problems with cleaning of the valves
	The process leaves invisible, basic film on the vessel – requires increased amount of rinsing water

B – "Robus" washing equipment with brushes

Advantages:

	Satisfactory cleaning with the most solvent–born lacquers
	Cleaning of the valve
	The process runs at ambient temperature and atmospheric pressure
	Can be extended with equipment for drying after cleaning

Limitations/disadvantages:

	Problematic as for air-drying lacquers and partly as for isocyanate reactor
	The system is not completely tight
	Can only be used for vessels/containers with valve
	Cleaning at the top edge is unsatisfactory
	Loose residues of lacquer at the bottom of the vessel is difficult to flush out
	Brushes shall be chosen/replaced according to the size of the vessel

C – Pressure washer equipment – type "SP50/80"

Advantages:

	The process runs at ambient temperature
	Cleaning of valve
	Can be extended with equipment for emptying after cleaning

Limitations/disadvantages:

	Not suitable for all types of lacquers
	Can only be used for vessels/containers with valve or manhole
	Requires adapter adjustable for each type of vessel
	Cleaning at the top edge is unsatisfactory
	Vessels and containers of plastic may be problematic due to static electricity (when using solvent as washing medium)
	Loose residues of lacquer at the bottom of the vessel is difficult to flush out

7. Experience with Implementation and Operation of Water-based Cleaning Technology

7.1 General remarks

Because many manufacturers of solvent-borne paints and coatings will, as a rule, have a wide range of products, the technology selected for cleaning mixing vessels and equipment as well as the rinsing solutions used must be suitable for a broad spectrum of products and feedstocks.

Differentiation of cleaning prcesses

For conceptual design of a cleaning plant, generally a range of basic aspects must be considered.

So, for quality reasons it may be necessary to employ different processes for cleaning colored and clear pigmented painting systems. For water-borne coating materials, as a rule the same washing medium may be used, but at most supported by admixing (NMP, n-methyl-pyrrolidone), which forms an azeotrope with water.

For cleaning of isocyanate containing coatings, these processes should be segregated from other systems for known reasons, such as their reaction with water.

As a rule, water-borne paints can only be removed with water or alkaline media while they are still in a wet condition.

Process segregation is to be understood as separation of both stocked materials and the complete piping system in the shop, right up to different nozzle installations. Only this will ensure complete segregation.

Storage

Past experience of operation with alkaline or pure water-based systems has shown that in certain cases unwanted reactions (strong generation of heat) in the rinsing tanks may occur. Frequently, the resulting sediments must be disposed of at great expense.

By deploying an appropriately designed filter system and, as far as needed, additionally equipping the tank farms with agitators, this can be counteracted.

To save investment costs in this area, centralized storage of washing and rinsing media would be desirable. This is widely accepted today as the state of the art.

Logistics

When selecting the washing medium that is optimal for the operator, the existing production logistics must also be considered.

For water-borne paints and air-drying coating systems in particular, the period between filling/emptying and cleaning is decisive. For example, water-borne paints, while still wet, can be relatively easily cleaned with water. But as soon as they become tacky or even dried out completely, they can only be removed with appropriately effective media.

It is best to clean production equipment, such as mixing vessels, immediately after they have been emptied, or at least as long as the paint residues are still wet.

Cleaning of solvent-borne paints while they are still wet using high-pressure water-based jets is problematic, as it is not possible to completely remove the solvent film from the vessel. Cleaning with the paint residues when they are already tacky is therefore usually more satisfactory.

Staff qualifications

Which cleaning medium is optimum in a specific application depends not only on technical and economic considerations, but also on acceptance by the shop floor personnel. A high degree of acceptance will also generally be combined with satisfactory operation as well as high quality servicing and maintenance.

Experience from past practice shows that staff acceptance of an installation for water-based cleaning is greater if personnel receive intensive training, repeated at regular intervals, in handling the equipment, or if they are already familiar with the technology. This applies particularly for companies previously applying solvent-based cleaning processes, and now wish to switch to a water-based system. This is because handling of such systems and coping with the associated risks differ greatly from solvent-based systems.

Regulatory conditions, regulations etc.

When switching from solvent- to water-based cleaning systems in particular, statutory requirements and regulations, for example pertaining to pollution control, maximum allow concentrations (MAC) at places of work, protection of land and water resources etc., must be included in the considerations.

General considerations for cleaning installations

When selecting the optimum cleaning medium, generally operational trade-offs must be accepted. When choosing the cleaning technology, this should not be the case. The cleaning technology must be matched to the specific technical and economic constraints and conditions prevailing at the site and for the production facilities.

7.2 Cleaning Agents

Water

Due to its low cost and easy handling, water without additives is always a very economical cleaning medium. It is primarily used for cleaning emulsion paints in washing installations equipped with brushes or with pressurized jets.

Alkaline solution

Alkaline solution is a mixture of water and, for example, caustic soda at a concentration of 5% to 15%. For maximum effectiveness, this has to be brought up to a temperature of 60^o to 80^oC . Hot water with a low content of carbonate and magnesium is used for rinsing.

Up to about 20 years ago, caustic soda was used primarily for cleaning. Such media are suitable for cleaning off most water- and solvent-borne paints for protection of structures, wood, motor vehicles, general industrial applications, household needs and most printing inks. Heightened risks to persons, loss of quality due to solution residues, increased operating and capital costs as well as stricter legislation governing their disposal meant that these washing media have little chance of survival over the long term.

Special cleaning agents

These cleaning agents are usually a mixture of potassium hydroxide, tensides and high-boiling point solvents. They are highly effective, and may be used in nearly all sectors. They find application wherever all other media have produced unsatisfactory cleaning results. Basically, these are very efficient cleaning agents, suitable for universal application. Originally, these products were created for stripping paint from wood and metal surfaces etc. Usually, they are supplied in the form of gels. It must be borne in mind that these special cleaning agents cost three to four times as much as NaOH solution, and their disposal is more problematic.

Flammable solvents

Where flammable solvents are used, they consist usually of a regenerate (blend) of several solvent components that are normally contained in the paint and coating products. To reduce costs in general, a non-volatile base solvent is employed, which is then enriched with efficient solvents. Preferably the operator optimizes the composition.

The following must be borne in mind when selecting the composition:

	low toxicity
	inflammability
	non-volatile
	rapid, effective action

For rinsing, a regenerate of identical composition is used.

Problems arise because of the high vapor pressure of the solvents used for cleaning, they must be explosion-proof and cleaning pressure is limited to 50 bar so that static electricity will not build up. A system for nitrogen purging could be installed, but this is not necessary if equipment and installations are designed according to the regulations.

Non-flammable solvents

Non-flammable solvents exhibit a high flash point (according to the manufacturer's information). Among the solvents falling under this classification are:

DBE is classified non-hazardous according to all EC criteria and its handling is therefore straightforward. This solvent has a very low vapor pressure, a high flash point and high solvency. Consequently the emissions associated with the use of this solvent are well within the limits required by law

DBE = di-basic ester (dimethyl esters of adipic acid, glutaric acid and succinic acid).

NMP = n-methyl-pyrrolidone

For rinsing, a non-hazardous solvent of identical structure is used.

A disadvantage of both these chemicals is that because of their low vapor pressures these solvents do not dry as quickly as the previous mixtures of volatile and quickly evaporating solvents. A film remains on the vessel surface and needs to be washed away with warm water after the solvent cleaning process. A wastewater treatment plant for this rinsing water is required.

Solvent-based cleaning equipment therefore needs a certain amount of redesign of the cleaning process.

A further decisive factor is the high costs for capital investment and for residues disposal.

Washing medium containing active substances

To be understood by this term products by ALKAREN etc. ALKAREN were used as cleaning agent in earlier tests, see Appendix B.

For rinsing, hot water with a low content of carbonate and magnesium is used.

7.3 Cleaning technology

The cleaning medium is allowed to soak into the residue on the equipment to be washed - a chemico-physical process - and this is then dislodged by the mechanical action of the jet and/or rotating brushes. The washing process consists of several steps that are combined and varied depending on plant type, equipment design and cleaning task. Common to all washing processes is the strict separation of cleaning medium from rinsing water, so that there will be no dilution or concentration of the media and they can continue in use for longer without the need for replacement. Optimized technology will result in proper functioning of the equipment.

Appendix A.1 shows a schematic of water-based and alternative cleaning processes. Examples of implemented cleaning plants are shown in Appendix A.2.

The usual washing process is as follows:

	main wash with alkaline solution (NaOH 15% or KOH; stripper) at a temperature of 60°C to 80°C and pressure up to 80 bar
	rinsing step of approx. 10 s with water (with recirculated rinsing water) to remove most of the alkaline solution and to cool down the vessel
	final rinsing step with fresh water to remove all remaining alkaline solution from the vessel
	venting of steam from the closed washing chamber to atmosphere (drying step)

The cleaning time is 5 to 15 minutes, dependent on chemical and physical characteristics of the paints or coatings.

The washing water has to be directed to a wastewater treatment plant (e.g. chemico-physical treatment and/or thermal treatment). This wastewater treatment plant has to be attended by skilled personnel. After about four months, alkaline solution becomes spent, and has to be disposed of. Recovery of spent alkaline solution would be very expensive, and is not economic.

The washing action could be provided by a high pressure rotating nozzle or by a rotary brush. Cleaning with brushes is usually done at a lower pressure of up to 10 bar. The advantage of brushes is the mechanical cleaning action and dislodging of paints adhering to the vessel wall. Their disadvantage is that they are subject to wear and have to be changed after approximately 100 –150 cleaning operations.

A further factor to consider is the material of the vessel and the valves. Posing a problem is mild steel, since the cleaning process will also scrape away the surface protection layer, so that it will be exposed to moisture in the ambient air and will corrode. Non-ferrous metals are problematic because they are not resistant to hot alkaline solutions.

This means that if the operator switches to or adopts water-based cleaning, the mild steel vessels will have to be replaced completely with stainless steel ones, giving rise to high costs.

Pressure jets

The pressure jet technique is based on a combination of hydrodynamic energy, admixed chemicals that decompose and dissolve paint and coating compounds, the time factor as well as effective guidance of the pressure jet itself.

Pressure, flow rate and temperature of the washing medium likewise play important parts.

The harder the residues have become, the better is the action of the liquid jet. Example: cleaning of residues that have become rubbery in their consistency is generally only possible with difficulty, or with the application of a very high hydrodynamic energy.

Brush cleaning technique

The brush technique is based on a combination of mechanical surface treatment, admixed chemicals that decompose and dissolve paint and coating compounds, the time factor as well as contact of brushes with the entire surface to be cleaned.

The washing medium itself is generally of lesser importance, as the actual removal action is achieved by mechanical means. Basically it has two functions: supporting destruction and softening of the residue compounds and transportation away of the residue-medium mixture.

Alternative technologies

Alternative technologies, like sandblasting, ultrasonic cleaning, plasma cleaning, freezing and application of dry ice pellets are tried out from time to time, but up to now have not met with any notable acceptance.

7.4 Personnel protection and safety precautions

The risk of handling solvents is well known. Much effort has to be done to protect the operators against inhalation (neuro toxic effects) and physical contact (absorption through skin). Risks due to inflammability and explosions have to be eliminated.

The risk when handling cleaning processes with water-based/alternative cleaning agents, depending on the aggressiveness, can also be high, out of another character.

Dangers arise less during the actual washing process in the closed system or covered vessels and containers and more when filling and emptying mobile tanks and due to the risk of coming into contact with cleaning media during maintenance work.

Appropriate protection equipment and training of the operating staff are necessary, both for solvents and water-based/alternative cleaning agents.

7.5 Environmental impact

Emissions of fumes to the surroundings or within working areas are appreciably less than when working with solvent cleaning equipment. Instead, pollutant emissions are shifted to the wastewater as shown in Figure 7.1.

During operation of the equipment as intended, there shall be no possibility of emissions to the working areas.

Figure 7.1
Emissions to surroundings.

7.5.2 Wastewater treatment

The rinsing water with its content of cleaning medium as well as the spent cleaning medium, must be directed to a wastewater treatment facility before discharge to the sewer system, or disposed of in some alternative way.

Possibilities are:

	disposal of wastewaters by a specialist company
	directing the water to an on-site wastewater treatment plant
	distillation of wastewater, recycling the distillate as rinsing water and disposal of residues through a specialist company
	chemico-physical wastewater treatment (precipitation/flocculation)

The wastewaters contain primarily paint and coating constituents, such as resins, pigments, small amounts of solvent etc. and residues of cleaning agents, like alkalies, tensides, salts and small amounts of solvent.

Characteristic parameters are:

	pH from 9.5 to14
	solids content up to 3%
	COD value up to 40 g/l

For treatment, chemico-physical processes or distillation are suitable. However, thermal wastewater treatment is only economic if primary energy is already available.

Manufacturers of water-based cleaning systems normally also supply the required wastewater treatment plants in collaboration with qualified suppliers.

In Appendix A.3 a standard solution of wastewater treatment is shown. The plant consists of buffer tank, reactor for neutralization and coagulation, belt filter for dewatering.

The treated water can normally be let to the municipal sewage system. Sludge from the belt filter has to be disposed of as chemical water.

Normal operation time for treatment of 900 l will be approx. 1 hour.

7.5.3 Residues

The spent alkaline solution has to be disposed of after around four months’ use. Recovery of spent alkaline solution is very expensive and is not economic.

8. Cost Comparison between Water– and Solvent-based Cleaning

For a water-based cleaning plant, depending on its design, the procurement costs may be higher than for a solvent-based plant of equivalent capacity. But if all operating costs are taken into consideration, for example explosion protection, fume treatment, disposal of spent solvent etc., then the total costs for water-based cleaning are comparable. However, use of comparatively expensive special cleaning agents will lead to increased operating costs.

There follows, by way of example, a tabulated comparison of the specific costs as well as of the operating and capital costs for water- and solvent-based cleaning. These examples are taken from the practical experience of Renzmann, and are accordingly customer specific. Precise figures for capital and operating costs can only be determined when the prevailing constraints and conditions are known.

The capital costs stated in this project are based on costs in Germany and are converted from DM to DKK with a conversion rate of 4. Differences in the size of taxes etc. are not included.

8.1 Costs for water-based and alternative cleaning agents

The cost example is based on a cleaning system "SKM", manufactured by Renzmann. Further description of this plant can be seen in section 6.3.

Table 8.1
Assumptions for cost comparison in Table 8.2 and Table 8.4. Further assumptions and explanations can be seen in Table 8.3 and Table 8.5.

Table 8.2 Look here!
Cost comparison between solvent- and water-based cleaning agents for type SKM washing equipment. 20 washing operations per day.

Table 8.3
Assumptions/explanations.

Flow sheet  Look here!

Appendix A.2

Photo 1:
Washing machine type Robus (SP70) for inside cleaning with brushes, (Renzmann).

Photo 2:
Washing machine type Robus (SP70) for inside cleaning with brushes, (Renzmann).

Photo 3:
Washing machine type SKM for inside and outside cleaning by spray (Renzmann).

Photo 4:
Washing machine type SKM for inside and outside cleaning by spray (Renzmann).

Photo 5:
Washing machine type SP50/SP80 for container and vessels by spray (Renzmann).

Photo 6:
External rinsing station (Riobeer, IBC cleaning plant CW-III-ex 3D).

Photo 7:
View of rear with runback unit and drying air unit, (Riobeer, IBC cleaning plant CW-III-ex 3D).

Photo 8:
Charging, side view, integrated valve cleaning with telescope brush, (Riobeer, Mixing vat cleaning plant F-ex 0I RMT).

Photo 9:
Charging, turntable, traversing radial brush, (Riobeer, Mixing vat cleaning plant F-ex 0I RMT).

Photo 10:
Additional equipment (from left):
Precleaning station, manual cleaning station, lid cleaner, agitator cleaner, precleaning station (Riobeer).

Photo 11:
Precleaning station (Riobeer).

Photo 12:
Manual cleaning station (Riobeer).

Photo 13:
Lid cleaner (Riobeer).

Photo 14:
Agitator cleaner (Riobeer).

Photo 15:
Special washing tanks for transparent and isocyanate coatings (Riobeer).

Photo 16:
Equipment for cleaning of mobile bin (Riobeer).

Appendix A.3

Look here!

Appendix B

TRANSLATION of

1 Aim of the project

The mapping of waste flows from the lacquer and paint industry which was carried out by the Danish Paintmakers’ Association for lacquer and paint manufacturers for the Danish National Environmental Protection Agency in 1996, shows that the VOC-emission is in an area where it is possible to reduce the environmental impact.

Based on the above an assessment of the VOC-emission has been carried out in each department of the reference company. The VOC-emission from cleaning the mobile mixing vessels is estimated to 25-30% of the total VOC-emission from the production of solvent-borne paint.

The total VOC-emission from the Danish lacquer and paint production is estimated to approx. 450 tons per year. In other words it will be possible to abate the emission of VOC with approx. 110 tons per year by changing to a water-based cleaning of the mixing vessels. The reduction will correspond to approx. 10% of the total VOC-emission from the chemical industry in Denmark.

Another considerable argument for transition to water-based cleaning of the mixing vessels is a significant improvement of the working environment in the vessel cleaning area.

2 Thinner-based cleaning

Today, the cleaning of the mixing vessels takes place in a heavily loaded working environment. The premises are equipped with powerful ventilation, but nevertheless it is necessary to wear personal respiratory protective device.

First the mixing vessel is cleaned manually with organic solvents in order to remove the major part of the paint residues. Subsequently the vessel is placed on the cleaning machine. The machine cleans the vessel with rotating brushes in presence of organic solvents.

Organic solvents and paint sludge are collected by means of a grating in the floor and are lead to distillation. The solvents distilled off are reused for cleaning of mixing vessels. Due to this process it is impossible to determine the exact composition and with that the dangerousness of this mixture of organic solvents.

The distillation residues are collected and sent to destruction at the Intermunicipal Chemical Waste Treatment Plant, "Kommunekemi".

Hot alkaline bath

Removal of paint can be carried out by alkaline cleaning (pH > 13), at a temperature of 50-95 degr. C.

The chemical paint binders are hydrolysed due to the high alkalinity. The penetration of the lacquer film and the migration during this can be increased by addition of surface-active agents.

Strong hydrolysed and aggressive leaching solutions can be used to remove paint from steel whereas strong organic bases are used for other metals.

Alkaline cleaning is very economical and is capable of removing most kinds of paints /2/, /3/.

Acid paint remover

These are based on strong inorganic acid. They are effective by degenerating the paint binder in the lacquer film. Sulphuric acid (pH < 1) is often used.

The acidic paint removers are used to remove epoxy and polyamide paint from hot sensitive items. By choice of acid, the acid resistance of the material must be considered. The temperature in the cleaning vessel is usually from 20-50 degr. C /2/, /3/.

Neutral paint removers

Neutral paint removers are based on glycol, glycol ether, N-Methyl-pyrrolidone or mixtures from this. The temperature of the cleaning vessel is 20-40 degr. C.

The use of neutral paint removers is confined to the physically drying lacquers /2/, /3/.

Mechanical removal of paint

By means of airless cleaning with water paint can be removed from hard surfaces (700 - 1000 bar).

Blasting with sand, plastic or other suitable materials may also be used /2/, /5/.

Thermal removal of paint

The methods are based on combustion and incineration of the paint at temperatures of 300-500 degr. C for 20-60 min.

The incineration may also take place in salt baths increasing the speed to 30-120 sec.

These pyrolytic methods are very energy-demanding and the construction and operating costs are considerable /2/, /4/.

Low temperature paint removers

Due to the fact that the paint shrinks by cooling with liquid nitrogen (-196 degr. C) this is also a suitable method for removal of paint (the cooling

process last 1-3 min.) /2/.

Airless cleaning with water

Airless cleaning with water and subsequent filtration must be considered the most pollution free cleaning method. This type of plant will approx. amount to DKK 250,000 (everything included).

WORMA in Düisburg, Germany is represented by O & J Højtryk in Esbjerg /5/.

The method is only reported used on soft lacquers, however it is considered suitable for the purpose.

CIP-cleaning with leaching solution/acid

These methods are well-known from among others the pharmaceutical industry and the food processing industry. The suppliers of the plant say/declare concurrently that approx. 2.5% ALKAREN 45 or a similar product is used. Based on this information the preliminary tests with this concentration are carried out.

The temperature in the cleaning vessels fluctuates from 70-80 degr. C. Søren Hauritz from Akzo Nobel is of the opinion that alkaline cleaning is the best solution. The reasons adduced for this opinion is the bad experience with alkaline CIP-cleaning of mixing vessels. Akzo Nobel use a 30% sodium hydroxide (corresponding to approx. 15% NaOH) with a bath temperature of approx. 70 degr. C.

However, it should be investigated if a combined product like ALKAREN 45 may be used in a lower concentration (possible 2.5% as stated by the suppliers of the plant).

Neutral paint removers

Glycols, glycol ethers and N-pyrrolidone are organic compounds acting as organic solvents. Due to their high boiling point and low evaporative pressure the substances are not defined as organic solvents. These substances will contribute to a strong increase of COD in the wastewater.

Preliminary laboratory tests are made to examine the efficiency of the substances.

Thermal methods

The pyrolytic methods will cause considerably initial costs and besides, these methods demand a lot of energy. Obviously, it is estimated that these methods are not applicable for this purpose.

Cooling with liquid nitrogen must be considered as a pure academic method, being possibly applicable within the laboratory area.

Nothing further will be done in relation to these methods.

5 Laboratory tests

The investigations are instituted with a view to prove that it is possible to remove paint with acidic or alkaline CIP-cleaning materials. Further the efficiency of the Neutral paint remover, especially developed for this project, is investigated.

Apply paint on the sheets and air-dry for one hour at ambient temperature. After this the sheets are dipped in the cleaning solvent while stirring carefully. The solvent has been heated to the temperature required.

The paint is completely removed after 10 min. In case the paint is not removed after expiration of the time, the test is repeated either with a higher temperature or a larger concentration of the cleaning solvent.

Alkaline bath: COMBIREN is a leaching-based combined cleaning solvent, which is widely used within the food processing industry. COMBIREN is mainly used in cases where most other alkaline CIP-cleaning materials cannot remove the paint.

COMBIREN contains: Sodium hydroxide, potassium hydroxide and complex agents.

Acid bath: NOVASYRE is based on sulphamic acid and a combination of organic acid. The product is used within the food processing industry where a strong phosphate free cleaning is required. The composition of the different organic acids provides a high acid strength without utilizing traditional acid such as phosphoric acid and nitric acid.

NOVASYRE contains: Sulphamic acid, organic acids and tensides.

Neutral bath: NOVALAK is a N-methyl-pyrrolidone based paint remover which is specially developed to comply with possible problems with leaching solution and acid. The product does not give rise to anxiety as regards corrosion and can be used on all metals.

NOVALAK contains: N-methyl-pyrrolidone and tensides.

The results carried out on steel sheets appear from enclosure 1.

Beyond the tests on steel, a number of tests have been made on teflon-coated aluminium. These sheets have been delivered from ACCOAT A/S.

However, results from these tests are not included. During the tests the aluminium corroded and after 1-2 preliminary tests it was impossible to make further tests.

IAT Kolding

The preliminary tests are carried out with a view to investigate if it is possible to remove the paint with water, pressure and heat.

The CIP-plant performs a constant pressure of 110 bar and the temperature can be adjusted from 8-100 degr. C.

The tests are carried out on teflon-coated vessels and steel vessels. Two types of teflon-coatings are used ACCOFAL 2G and ACCOPON 2G.

ACCOFAL 2G is softer and seems smoother (more dirt-repellant) than ACCOPON 2G. Alkyd simply crawls off when the coating is applied. It is possible to clean the vessel for paint having dried up for approx. 30 min. at ambient temperature. During the tests it appeared that it is very important with a cold rinse before the actual cleaning is carried out. In case the pre-rinse is left undone the paint will polymerize and become rubbery and it is then impossible to remove the paint (the results appear from enclosure 2).

ACCOPON 2G seems very hard and is rather rough to look at. After the cleaning a small edge was left, however it was easy to remove with a nail. During the test of removing the paint edge it turned out that the coating of the vessel left green pigments in the white lacquer. Later, ACCOAT A/S investigated the vessel and had to admit that the coating was not carried out properly - the teflon was undercured.

Generally speaking, the teflon-coating sticks very poorly and is easily removed. The coatings are "very" soft and that is why the production management in the reference company has expressed their doubts that teflon-coatings can be used in mobile mixing vessels. Today, the company utilizes teflon-coatings on stationary mixing vessels.

A test has been made on a steel vessel according to above conditions. Altogether the water had no effect on the paint (the results appear from enclosure 2).

O & J Højtryk, Esbjerg

Tests have been made with pressure from 400-1150 bar. It clearly appeared from the tests that it is impossible to remove a paint film from a steel surface with water and pressure being undercured (the paint was moved around in the vessel).

Tests on undercured epoxy were also carried out. At a pressure of 1150 bar it was very easy to remove the lacquer.

IAT Kolding

IAT Kolding undertakes cleaning of tankers and pallet tanks. We are in a position to rent the plant for cleaning of pallet tanks. The plant is a modified Kärcher high-pressure cleaner for industrial cleaning with a rotating spud.

First a pre-rinse for 5 min. The plant performs 18-20 litres of water/min. and a pressure of 90-100 bar. It is not possible either to adjust the pressure or the concentration of cleaning solvent on the plant.

Alkyd: After a total cleaning time of 30 min. a ALKAREN 45 concentration of 1.2% and a bath temperature of 70 degr. C the paint was completely removed from the steel surface.

Epoxy: After a cleaning time of 60 min. 75% of the paint was removed. The remaining 25% was easy to remove with a slight mechanical effect. The concentration of the cleaning solvent and the bath temperature was 1.2% ALKAREN 45 and 70 degr. C respectively.

Similar tests were carried out on the teflon-coatings. It was not possible to remove any of the paint from the teflon-coatings - even after 60 min.

Brüel International A/S

Brüel International manufactures tunnel washers and cabins for the chemical, pharmaceutical and food processing industries. The company has experiences with cleaning of mixing vessels from a Norwegian producer of paint and lacquer.

The Norwegian paint and lacquer manufacturer uses an alkaline combined cleaning solvent corresponding to ALKAREN 45 from NOVADAN A/S. The concentration of the cleaning solvent is approx. 2.5%, the bath temperature is 75 degr. C, and the pressure is approx. 7 bar.

Brüel International’s own experiences draw attention to the fact that a too high pressure (above 10 bar) makes the cleaning difficult. This fact is identical with our results with high pressure.

The tests are carried out on a Wemag washer. The machine is a cabinet washer, manufactured for washing butcher’s vans within the slaughterhouse industry, the so-called Wemag van (machine type CB1-42).

The machine performs 100 litres per min., the pressure is 7 bar and the temperature can be adjusted from 8-95 degr. C.

After some unsuccessful attempts a short pre-rinse for 300 sec. is chosen, the cleaning time is set to 900 sec. and the bath temperature is set to 80 degr. C.

During the unsuccessful attempts with temperatures below 80 degr. C, the ALKAREN 45 concentration was gradually increased from 3% to 5.7%. It was not possible to thin the leaching solution in the plant and due to lack of time it was not possible to start up a new attempt (the plant had to be sent to Sweden).

Tests with above cleaning procedure were carried out on alkyd, epoxy, acrylic, and polyester. All types of lacquer were completely removed after the cleaning (the results appear from enclosure 5).

8 Discussion

The investigations show that the temperature plays an essential part as to the cleaning results. Thus, it was not possible to achieve a reasonable cleaning result without a cold pre-rinse. At a bath temperature below 80 degr. C it is impossible to remove the paint completely.

The total cleaning time of 20-25 min. must be considered as too long. However, it should be noted that neither time nor leaching solution is optimised. Therefore, future work should be concentrated about optimising these parameters.

The pre-rinse was set to 300 sec. in order to ensure a sufficient cooling of the paint film. During normal operation this time is probably too long. The reason for the longer rinse time is that the tests are carried out on the same vessel. Thus the vessel was not cold at the beginning of the test and due to this the drying time of the paint was also reduced. The vessel was approx. 80 degr. C by the time it was taken out of the cabin.

The cleaning cycle of 15 min. is also too long. A satisfactory cleaning result within a shorter period with the concentration of ALKAREN 45 should be obtainable.

It should be investigated how fast it is possible to clean a vessel with the chosen parameters. In case the time of the cleaning cycle is reduced to less than 300 sec. the following tests should concentrate about reducing the concentration of ALKAREN 45.

After optimizing the cleaning at 80 degr. C an investigation should take place aiming at the influence of a possible change of temperature on the cleaning result.

After optimizing the total cleaning procedure a test on all colour and lacquer systems in the production at the reference company should be carried out (see enclosure 1).

During tests on the cabinet washer it should be investigated further how large a dirt load the cleaning solvent manages before it has to be replaced. This condition will not only affect the wastewater amount and the water amount on the plant, but also the usability of the procedure as such. If the cleaning solvent needs to be replaced more than two times a day this may affect the capacity of the plant considerably. It may be very time-consuming to heat up the 800 liters of cleaning solution. Pumping of liquid from and to the machine also takes a long time.

The optimal solution would be to replace the cleaning solution one time every 24 hours. The regeneration of the liquid may take place by means of filters.

9 Conclusion

It is conceivable that a considerable low leaching solution may clean the mixing vessels from the production of paint and lacquer.

However, the cleaning time of 20-25 min. per vessel is too long. The future work must therefore be concentrated about optimizing the cleaning procedure. The total cleaning time per vessel must be between 5 and 7 min. corresponding to a capacity of 8-12 vessels per hour.

The concentration of the cleaning solvent is reduced so that the cleaning solvent is non-corroding. Thus, the ALKAREN 45 concentration must be below 3% corresponding to a NaOH concentration less than 1% (local irritating).

The used cabinet washer must also be considered applicable for the purpose.

Reference list

1. NOVADAN A/S, results from laboratory tests
2. IAT Kolding, results from cleaning tests with water
3. Data sheet on ALKAREN 45
4. IAT Kolding, results from cleaning tests with leaching solution
5. Brüel, results from cleaning tests with leaching solution in cabinet washer

Enclosure 1

Solubility tests carried out by NOVADAN A/S

The test results carried out on steel plates on 19 February 1997 by Mr. Ole Christensen.

Enclosure 2

Cleaning tests with water at IAT on 10 May 1997

The plant performs 18-20 litres of water/min. and performs a pressure of approx. 110 bar.

The tests have been carried out on a vessel coated with ACCOFAL 2G from ACCOAT. The cleaning time shall be considered with reservation as all the tests have been carried out on the same layer of paint (accumulated).

The tests have been carried out on a vessel coated with ACCOPON 2G from ACCOAT.

The test has been carried out on steel.

The tests have been carried out on a vessel coated with ACCOFAL 2G from ACCOAT. The cleaning times shall be considered with reservation as all the tests have been carried out on the same layer of paint (accumulated).

The tests have been carried out on a vessel coated with ACCOPON 2G from ACCOAT. The cleaning times shall be considered with reservation as all the tests have been carried out on the same layer of paint (accumulated).

Enclosure 4

Cleaning tests with leaching solution at IAT on 7 June 1997

The plant performs 18-20 liters of water/min. and performs a pressure of 90-100 bar.

The test has been carried out on steel. The cleaning times shall be considered with reservation as all the tests have been carried out on the same layer of paint (accumulated).

The test has been carried out on steel. The remaining 25% of paint shall easily be removed by means of mechanical effect (a nail). The cleaning times shall be considered with reservation as it has not been registered when the paint has become soft.

Similar tests have been carried out on teflon-coatings, but the leaching solution had no effect.

Enclosure 5

Cleaning tests in cabinet washer at Brüel on 18 June 1997

The cabinet washer performs a constant pressure of 7 bar.

The test has been carried out on steel. The cleaning times shall be considered with reservation as all the tests have been carried out on the same layer of paint (accumulated).

The test has been carried out on steel.

The test has been carried out on steel.

The test has been carried out on steel.

The test has been carried out on steel.

Appendix C

Photos from preliminary tests (Renzmann)

Figure 1
Mixing vessel applied with products from Teknos Technology A/S.

Figure 2
Mixing vessel after cleaning in SKM plant (Stripper 303 G/E, 80^oC, 12 minutes).