| Front page | | Contents | | Previous | | Next |

Waterbased cleaning of mixing vessels

Summary and conclusions

As summary parts of the text from the project article in the publication "Ny Viden", issued by the Danish EPA are reproduced.

Water-based cleaning – a real alternative

The lacquer and paint industry is able to use water-based cleaning on a number of lacquers and paints. Hereby, the present use of solvents can be reduced or possibly completely avoided with clear advantages for the working environment and the external environment. As to many types of lacquer and paints a water-based alkaline cleaning will be competitive with the solvent based cleaning. Special types of lacquer and paint may naturally cause higher expenses.

Possibilities and limitations are described in this report explaining a number of tests in laboratory and in full scale. The report may inspire companies requesting to establish their own basis for decisions.

Trade project within the lacquer and paint industry

Background and purpose

The lacquer and paint industry in Denmark consists of approx. 20 manufacturers of paints as well as approx. 10 manufacturers of glue and sealing compounds.

During recent years the lacquer and paint industry has worked with possibilities for reducing VOC emissions. This has been done partly through product development with a view to reduce the VOC contents in the product and partly by limiting initiatives in the phase of production at various paint factories.

In 1994-1995 the Danish Paintmakers’ Association carried out a review of the possibilities for using cleaner technology within the lacquer and paint industry. Report regarding this review has previously been published/issued as Trade information for the lacquer and paint industry no. 5, 1996 from the Danish EPA, (Brancheorientering for lak- og farveindustrien nr. 5, 1996 fra Miljøstyrelsen).

In continuation of the review in 1994-1995 the Danish Paintmakers’ Association has completed a project with the intention to verify the possibilities for using water-based cleaning of mixing vessels and other equipment.

Two suppliers of cleaning technology, Renzmann in Germany and Riobeer in Switzerland have kindly participated in laboratory tests. Further, the company Renzmann has placed equipment at our disposal for a number of test in full-scale. Akzo Nobel Coatings GmbH in Berlin has placed an established plant with water-based cleaning (sodium hydroxide) at our disposal for inspection and has kindly informed about operation experiences.

The Danish company Teknos Technology A/S has participated in a group of experts having followed the project.

The Danish EPA, The Danish Directorate for National Labour Inspection, SiD (The General Workers Union in Denmark), The Association of County Councils in Denmark and The Danish Paintmakers’ Association have been represented in a steering committee.

Employees from Fichtner GmbH & Co. KG in Germany and Carl Bro a|s in Denmark have been consultants on the project.

The target group of the project consists of companies within the lacquer and paint industry as well as the environmental authorities. The possibility of implementing the project is created by means of financial support from the Danish EPA.

The project course

The project

By way of introduction laboratory tests have been made being prepared by means of experiences with cleaning processes at suppliers of cleaning plants. In the tests various chosen lacquers and paints from Teknos Technology A/S are included. Subsequently the laboratory tests have formed the basis for arrangement of tests in full-scale with a view to verify the real possibilities of introducing the water-based cleaning at the companies within the lacquer and paint industry.

Approx. 10 companies and suppliers have been interviewed regarding their experiences with water-based cleaning as well as experiences from a workshop (held at Renzmann in Germany) form part of the project.

Water-based cleaning is possible – with limitations, however

Main conclusions

Collecting of experiences and completed tests show that water-based cleaning may be a real alternative to the traditional cleaning with solvents. Thus, there are immediately possibilities for improvements of the working environment and reduction of VOC emissions to the external environment.

However, it is necessary for each company to assess relevant cleaning methods and cleaning media based on actual types of lacquer and paint. Possibly it may be necessary to choose more methods and media in case the product mix of the company is very different and variable. It will also be relevant to let existing types of vessels, materials and sizes enter in an overall assessment. Valves may require additional cleaning. A general replacement of vessels will be very costly.

Based on experiences at interviews the following can be summarized:

	Water-based cleaning takes place with a hot alkaline solvent (sodium hydroxide or special product)
	Cleaning may be difficult when the product dries up. Mechanical influence may be necessary, possibly supplemented with manual final cleaning
	All companies have completed test programs before implementation in full-scale
	Suppliers of cleaning plants usually recommend both laboratory tests and full-scale tests with the products in question prior to establishing the plant

Procedure, method and investigation program

The project

In connection with the project "Cleaner Technology in the Lacquer and Paint Industry" Teknos Technology A/S investigated in 1997 the possibilities of using water-based cleaning. The possibilities showed promising in the laboratory, however problems arose with verifying the possibilities in full-scale.

The previous basis forms the basis for new tests, where experiences from among others Germany are included.

Method and procedure is indicated on figure 1.

Figure 1
Procedure and method.

As erection of plant for full-scale test at Teknos Technology A/S would be costly and time-consuming, the tests have been carried out at the company Renzmann’s own test plant at the development center in Germany. The tests are carried out under realistic conditions together with a number of lacquers and paints from the product range at Teknos Technology A/S. The tests have been followed by an employee from Teknos Technololgy A/S as well as an representative from Fichtner – Carl Bro a|s.

Tests have been carried out with 17 wet-type lacquers (rapid air-drying) to industrial purpose. Both water-borne and solvent-borne lacquers are represented.

The tests are carried out on vessels of stainless steel and mild steel respectively as well as both wet paint and paint after 5 days of drying.

The tests are carried out with 3 types of equipment:

Cleaning plant of the type "SKM"

A closed system for cleaning of vessels of varying diameter is in question. Cleaning is made by means of a rotating spray system on both the inner and outer side of the vessel. Possible cleaning agents are water, alkaline media (i.e. sodium hydroxide) and solvents.

The plant has integrated tank for cleaning agent (800 l) and exhaust of the residual cleaning agent, so that the vessel is left dry. The cleaning takes place during pressure (8-80 bar) and at increased temperature (approx. 60-80^oC) for water and caustic cleaning agents.

During cleaning of vessels with valve additional manual cleaning may be necessary.

The system will demand subsequent treatment of waste. By use of solvents distillation equipment is demanded.

Wastewater cleaning/precipitation will be a necessary by use of water and caustic cleaning agents.

"Robus" cleaning equipment with brushes

The system is for cleaning of the inside of the vessel and tanks with valve. The cleaning takes place with rotating brushes being changeable dependent on type of vessel and tank.

A tight adapter works as lid during the cleaning process. The system is designed for non-pressure cleaning with solvent (or water) and usually takes place at ambient temperature. A subsequent drying of the vessel is possible. The cleaning medium recirculates and will at some point require distillation equipment for treatment of waste (solvents) or wastewater cleaning/precipitation (water-based).

High-pressure washer equipment – type "SP50 / SP80"

The system is for cleaning of inside of containers and mobile tanks with valve.

The cleaning takes place by pressure washing at 50 bar by use of solvent and 80 bar by use of water as cleaning media. A tight adapter is required as lid adjusted for each type of tank/container. The cleaning media recirculates and will at some point require distillation equipment for treatment of waste (solvents) or wastewater cleaning/precipitation (water-based).

The following 3 cleaning media are used for tests in full-scale:

	Stripper 303 G/E (from Foster Chemical GmbH) Alkaline mixture of glycol ether and sodium hydroxide in concentration 5-6%
	Sodium hydroxide solution 12%
	Teknosolv 601 (from Teknos Technology A/S) Multilevel thinner for cleaning

Based on Renzmann’s experiences fixed parameters have been chosen for each plant. Moreover, the tests have been carried out 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 in 5 days. The numerous combinations can be grouped after type of plant in series of experiments a, b and c.