The global shipping industry has been under pressure since long before the economic crisis. Rising costs and falling utilisation of capacity are the prominent aspects of the fraught competitive situation. Even more now than ever, time is money and consistent optimisation of all operational processes is essential to survival.

The pressure to meet repair and maintenance deadlines for freight ships is immense. Idle time for cleaning and renewing the outer shell coating is only a few days. Technologies which effectively treat process water offer a significant competitive advantage. Increasingly stringent environmental requirements, particularly in regard to wastewater, mean the washing water used in paint removal and its subsequent economic disposal play an even greater role.

Legislators are currently working on stricter regulations intended to ensure complete proof of proper waste removal. A mobile filter station has been introduced which minimises the expense of treating wastewater and properly disposes of the solid waste. The filter station was developed by the company Renetex S.r.L. in Bozen, which specialises in the development, production and sale of process water treatment equipment. The heart of the unit is the compact filter system MAXFLOW – made by GKD, Gebr. Kufferath AG – that combines filtration and briquetting in one device.

The pivotal impulse for the development of this mobile filter station was Volkert Meinz's passion for filtration and shipping. The CEO of Beinlich Pumpen GmbH, supplier of gear and radial piston pump systems headquartered in Gevelsberg, spent many years going to sea as a technical officer and knows all about the challenges of removing old paint from ships. He applied his background to developing the technology for this filtering system. The prototype has been in operation for a year in Hamburg at one of the most renowned shipyards in the world. Another year was spent on development before that. Findings from previous successful applications of the equipment were integrated, for example in pipe rehabilitation of water supply lines to power plant turbines.

Less water for greater economy

Stripping the paint from freight and container ships, which can be more than 350 metres long, is extremely time-consuming. Several thick and hard protective coatings of varying consistencies comprise a layer between 700 μm and 2 mm thick, which has to be partially or completely removed before a new coating can be applied. Today, these massive coatings are usually stripped using high-pressure water jets. This method, also called water blasting, allows paint to be removed without harming the workers or polluting the environment with dust. Pressure of up to 4,000 bar is applied quickly and gently to remove the old surface coating, a process that is much less harmful than former dry blasting with quartz sand or fine-grained copper slag grit.

An added benefit of this new method is that the fresh coatings last longer, because the salt is purged out of the surface pores of the ship's hull. But the ultimate benefit of water blasting is that there is no contaminated abrasive to dispose of afterwards. Modern high-pressure jet systems include suction mechanisms that apply a vacuum to collect the paint-contaminated water right at the hull of the ship. The water flows into an intermediate storage vessel at the dock and is then conveyed to the wastewater treatment system. Depending on the size and the number of high-pressure pumps used, 50–200 litres of water are required per minute, which corresponds to 3–12 m3/hr. this process is economic only with a closed process water circulation system that drastically reduces the consumption of fresh water. Efficient wastewater treatment is the key element. That was the weak point until now.

The sedimentation procedure commonly used at construction sites requires space, time, and a multitude of chemicals and costly disposal. The new mobile filter station offers an effective alternative. By combining a series of filtration steps – one of which is the crucial mechanical particle separation – with simultaneous compression of the solid matter, the fresh water consumption decreases from up to 12 m3/hr to the same quantity over several weeks.

Maxflow for mechanical filtration

The mobile filter station which separates the paint residue from the water is shipped by a truck to the site where it is needed. A pump conveys the wastewater from the tanks at the docks to the filter station. The integral system for chemical and mechanical filtration purifies the contaminated process water to fully-fledged service water, and at the same time permits cost-efficient disposal of the old paint. The MAXFLOW 504 compact filter system, consisting of a filter head with built-in press as well as a controller and other process water inlet and outlet components made by Beinlich, takes care of the mechanical filtration. Two tanks which feed the water to the filter round off the ensemble. The MAXFLOW 504 filter head is composed of statically positioned vertical filter disks made from the multi-dimensional stainless steel composite mesh, YMAX, designed specifically for this process.

The filter head was developed by GKD-CompactFiltration, an independent business unit of GKD specialising in filter technology and equipment engineering. The feed material cross-flows around the disks and automatic backwashing disengage the filter cake from the disks. The integrated press compresses it to form a non-drip briquette. The specific parameter settings are entered directly on the system via the PROFIBUS-capsule controller. A remote maintenance feature allows data to be queried and settings to be adjusted through an interface accessible by mobile phone.

Fluctuating consistencies

The wastewater produced when paint is stripped from the ships poses a tough challenge to the filter. In addition to paint particles, the water contains organic substances such as algae and other oceanic organisms which settle on the hull or in the seawater. And then there are heavy metals from the paint or even asbestos particles, matter for which the filter, which normally works without the addition of filter aids, was not designed for. Fluctuating inlet concentrations – particularly dilution from rain or variable environmental factors – mean the filter has to work even harder.

To counteract these factors, the wastewater is chemically pre-treated before mechanical filtration. In order to achieve a formation of filter cake during the mechanical filtration of the fine particles, the MAXFLOW filter head in the mobile filter station – unlike other applications – uses filter aids. The integrated press compresses the filtered solid matter to form non-drip briquettes. The solid blocks, with remaining moisture of less than 60%, drastically reduce the amount of hazardous waste and thus the disposal costs. The purified water is then treated to produce fully-fledged process water. An additional chemical filtration step treats the wastewater again, ensuring that it meets the stringent requirements for feeding it into the local sewage system.

Efficient and legally compliant

Based on a rate of €80/tonne of water, the savings potential of this method of water disposal is up to €960/hour. A significant saving considering the current economic pressure placed on businesses. And this method also ensures the legal consent levels are met – levels which will be further tightened again in 2012. The compact design of the filter station is well suited to the time and space limitations on the docks. Because of the enormous time constraints and a chronic lack of space, the system provides the shipyard operators with a solution they have been urgently seeking – a solution that can be quickly implemented on land without structural modifications. Because it is so mobile, the system can easily be moved to any dock where it is needed, so utilisation capacity is ideal. Not only shipyards can profit from this system, cleaning companies that offer paint stripping services can also reap the benefits.

Solution for process water

Volkert Meinz, the mind behind the patent-pending system, is convinced the mobile filter system is a significant milestone for economic ship stripping. He said: “The ship maintenance industry has been waiting for such a solution for years. The treatment method for process water from paint stripping will be significantly faster and more economical.” He can also envisage applications in bridge and tank cleaning. He sees the anticipated tightening of the law as even more reason to promote the equipment. “Keeping the new laws in mind, which will require proof of disposal, the new mobile filter station offers shipyards and cleaning firms the operational reliability they need at an affordable price,” he added.

Sascha Schoenecken, sales manager of GKD-CompactFiltration, sees the success of the MAXFLOW 504 filter head as additional proof of the superiority of the compact filter concept. “The combination of the process-dependent selection of filter materials and the process-specific settings makes MAXFLOW the perfect choice for such complex challenges.”