Spray booth

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A spray booth (or paint booth ) is the core component of a wet paint system. In it, lacquers or coating materials are applied to substrates using a wide variety of application techniques and degrees of effectiveness .

business

For the operation of a spray booth, filtered, heated, humidified or air-conditioned supply air is advantageous. Compliance with ATEX regulations and high safety standards are mandatory. The air is guided vertically (from top to bottom) mostly with countercurrent venturi scrubbers , or horizontally mostly with cocurrent venturi scrubbers . The Venturi scrubber forms a system for paint separation .

The paint mist that arises during spray painting is extracted and cleaned by wet or dry separation systems . With dry separation, the paint mist is separated using filter mats made of fiberglass or other flame-resistant materials (e.g. cardboard filters). In smaller systems, baffle plates serve as pre-separators. With wet separation , the paint mist is separated out in wet scrubbers and the sludge content is usually fed to paint sludge separation. In Germany a solid-state emission of max. 3.0 mg / m 3 allowed.

For some time now, exhaust air cleaning systems have been integrated to reduce volatile organic compounds (VOC) before exhaust air is discharged into the open . The concentration of solvents in spray booths or a downstream adsorption system with thermal or regenerative afterburning (TNV or RNV) has proven itself in practice. With thermal post-combustion, the exhaust air to be cleaned is preheated and then burned in a combustion chamber at 720–750 ° C with the aid of additional fuels (e.g. natural gas or heating oil). With regenerative post-combustion, preheating takes place via a regenerator , which is used alternately for cooling and heating. From 2 g / m 3 this works autothermally, i.e. without additional fuel. These so-called RNV systems are ideal for large air volume flows. RNV systems reduce the organic components particularly well and release relatively little nitrogen oxides (NO x ) and carbon monoxide (CO).

Adsorption systems

adsorption Concentration with RNV
Amount of exhaust air in the washer 30,000 m 3 / h 30,000 m 3 / h
Amount of circulating air as supply air 0 m 3 / h 27,000 m 3 / h
Concentration of solvent 0.1 g / m 3 0.01 g / m 3
Duration per year 3,500 h / a 3,500 h / a
Total solvent load 10.5 t / a 0.105 t / a

The inlet concentration of solvents upstream of the paint mist separator is usually very low, e.g. B. only 0.2 g / m 3 . Adsorption systems usually only reduce this value to approx. 0.04 to 0.1 g / m 3 . An RNV system normally reaches approx. 0.004 to 0.01 gr / m 3, i.e. a pollutant concentration that is 10 times lower. Problems arise when zeolites are blocked by substances that interfere with the zeolite or can no longer be desorbed. All paint solvents must be tested for compatibility before use, otherwise the cleaning effect will be greatly reduced. Activated carbon as adsorber material is questionable because of its flammability. The safest method is the concentration process in spray booths. Spray booth exhaust air can usually be concentrated well and without any loss of quality (vehicle quality is achievable). So far, this has only been done in automatic zones. Recently, hand spray zones can also be operated in this way.

Despite the very good cleaning performance of an adsorption system, the solvent load is 2 powers of ten higher than in a concentration process. This means that a concentration system that still works with an autothermal RNV system is the more environmentally friendly and energetically better alternative. However, this cannot always be implemented, as hand spray zones often cannot be equipped with a concentration process and therefore adsorption has to be used. The alternative are high-solid paints, with their relatively high solid content, or water-based paints , which naturally release few solvents.

Water-based paint Concentration with RNV
Amount of exhaust air in the washer 30,000 m 3 / h 30,000 m 3 / h
Amount of circulating air as supply air 0 m 3 / h 27,000 m 3 / h
Concentration of solvent 0.05 g / m 3 0.01 g / m 3
(value is assumed)
Duration per year 3,500 h / a 3,500 h / a
Total solvent load 5.25 t / a 0.105 t / a
Surface throughput 400 m 2 / h 400 m 2 / h
Specific solvent release 3.75 g / m 2 0.075 g / m 2

Even the comparison of solvent paint with a concentrating system and a spray booth with environmentally friendly water-based paint shows advantages for the former, because for an environmental balance it is not the exhaust air concentration that should be taken into account, but always the load of solvent per square meter of the surface. It has been shown that modern spray booths in connection with water-based paint or a concentration system with RNV are less polluting.

power consumption

Spray booths are big energy guzzlers. Heating with several megawatts (MW) is quite common. The use of sensitive paints, especially water-based paints, means that the supply air must also be moistened. This increases the energy requirement considerably, especially in winter. Often the supply air has to be preheated to approx. 50 ° C before humidification in order to increase it to, for example, 24 ° C and 65% rel. To condition moisture. In summer, such climate windows can often not be reached without air conditioning. Therefore, large air conditioning systems were installed for some spray booths in order to reduce the humidity of the supply air. The cooling capacity provided is so high that it is uneconomical. To save energy, a circulating air system was developed that cleans, filters and air-condition the spray booth exhaust air to a high quality and uses this prepared exhaust air as spray booth supply air. Although this represents an enormous energy saving, high cooling and heating capacities still have to be provided. As a side effect, the solvents and odorous substances are also concentrated. This creates a basis for branching off a partial air flow of the so-called circulating air and for example feeding it to an RNV system.

Classification

Types

  • Continuous spray booths and cycle spray booths (series production)
  • Large-scale spray booths (large parts and series production)
  • Omega spray booths (with ESTA washer for small parts)
  • Flat injection molding machines (for flat parts)
  • Combi cabins (special design with own regulations)

Separation systems

  • DC venturi scrubber (e.g. for small parts - series production)
  • Countercurrent venturi scrubber (e.g. in series production - vehicle painting)
  • Dry separation with glass fiber mats or flame-retardant cardboard goods, baffle plate pre-separator
  • Nozzle washer (old)
  • Vortex cascade, vortex scrubber (old)

Application technology

Handling techniques

  • Manually
  • Working platforms for painters for large parts
  • tripod
  • Side lifting device
  • Roof machine
  • robot
  • Motion automatons

Energy saving opportunities

  • Reducing temperatures
  • Reduction of the air volume, as far as this is justifiable
  • Exhaust air heat exchanger
  • Closer hanging of the parts on the conveyor
  • Increase in lot sizes
  • Recirculation mode
  • Few breaks and short running times
  • No air conditioning or humidification
  • On and off when no substrates are present.
  • Air reduction when there are no substrates.
  • Enercoat air conditioning

Savings opportunities

  • Recovery of water-based paint with ultrafiltration technology
  • Increase of the application efficiency of the application
  • Higher first run rate (i.e. 100% error-free in the first run)
  • Optimization whether wet or dry separation

Laws and norms

Federal Immission Control Act

The 31st ordinance for the implementation of the Federal Immission Control Act (ordinance to limit emissions of volatile organic compounds when using organic solvents in certain systems - 31st BImSchV) sets the following exhaust air limit values ​​in Germany:

8. Coating of other metal or plastic surfaces
8.1 Systems for coating other metal or plastic
surfaces 8.1.1 Emission limit values ​​for collected treated exhaust gases> in this case for spray booths

  • below 5 t / a >> no limit value
  • at 5–15 t / a >> limit value 100 mgC / m 3
  • at over 15 t / a >> limit value 50 mgC / m 3 without post-combustion
  • at over 15 t / a >> limit value 20 mgC / m 3 with post-combustion

Exceptions can be made; especially in metropolitan areas. The solvent consumption applies to the entire systems in a company. The solids ejection may be max. 3.0 mg / m 3 .

EN norm

The most important EN standard is:

  • Coating systems - Spray booths for liquid organic coating materials - Safety requirements; German version EN 12215: 2004

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