Environmental and Energy Systems, a business unit of the global Dürr group, recently supplied Rexam with an Ecopure® RL system, a special type of regenerative thermal oxidiser (RTO), for use at their beverage can manufacturing plant in Denmark. Because of the ability to treat medium air volumes and pollution loads, sensitivity to specific manufacturing processes, and small physical footprint, the Ecopure RL became the right answer to Rexam’s very detailed compliance requirements.
With an annual production rate of approximately 55 billion cans, Rexam is one of the largest manufacturers of beverage cans in the world. In 2008, Rexam commissioned a new plant at Fredericia in Denmark, where approximately 3,000 cans are manufactured per minute. In spite of ultramodern production processes, Rexam had to meet strict emission limits that go beyond the usual regulations valid in the EU. One of the conditions before the plant could be opened was the installation of an air purification system. Emissions treated by the Ecopure RL are produced by the aluminium can coating process, both for outside clear coating and inside coating, as well as outside decorative coating.
Since Rexam has had previous experience with thermal oxidisers in their other manufacturing plants, they believed that the oxidation of pollutants was the safest method to meet emission limits. An Ecopure RL oxidiser, which operates with a single rotary diverter valve, was chosen for Fredericia from Dürr’s wide product portfolio of regenerative oxidisers (RTO, CTO, RL). Though more than 80 such oxidisers have already been installed in North and South America for this specific type of process, this system in Fredericia is the first time that Dürr is applying the RL for this application in Europe.
The Rexam air purification system has to be very flexible, as the new plant is to be built in phases. While the Ecopure RL is already designed for the maximum air flow capacity planned for the future final phase, the system will still operate perfectly and cost-effectively in the initial production phase, where only a reduced exhaust air volume has to be treated.
An electric actuator operates the single rotary valve, replacing the nine pneumatic dampers and complex control equipment normally used for a typical RTO. Due to uniform air flow with minimal pressure fluctuations during operation, there is no impact on the customer’s very delicate coating process.
As the hot pure gas is always flowing through the body of the rotary valve, keeping it hotter than the exhaust air inlet, any build-up of condensate on the valve is minimised. If condensate deposits are formed over time by the oven exhaust air in the inlet section of the ceramic heat exchanger bed, the bed can be cleaned automatically with the integrated ‘bake-out function’. This can even be done when the system is running in full purification mode, i.e. online, without exceeding emission limits. On conventional multi-chamber RTO systems, this feature can only be realised with highly complex technical solutions.
Dürr’s rotary diverter valve concept without pneumatic dampers and few moving parts has major benefits for the owner, such as a long service life, minor maintenance requirements and uniform air flow with minimal pressure fluctuation during operation. Remarkably, the single rotary valve does not require seal replacement as it does not rely on contacting seals to maintain destruction efficiency.
The Ecopure RL has been in operation at Rexam for over one year now and has fully met all expectations.