Waste handling at scale

Where “trash” used to be just dumped someplace, today every waste stream is treated individually. No less than 750 to 800 tonnes of residual waste arrive at the AHA Hannover waste treatment centre every day.

October 11, 2021

It’s one of Germany’s largest and ecologically most exemplary of its kind. For mechanical and biological processing, the company has relied on dependable Komptech machinery and service for over ten years. The processing lines cannot be out of operation for more than two business days. A year ago, two worn out shredders in the residual waste treatment line were removed and replaced. The whole process had to be completed in under 96 hours including the weekend, per the bid tender of the Hannover Regional Waste Association (AHA). Komptech got the gig. “For each replacement we also had to switch out the control and control panel – normally for an install of this magnitude we would plan one or two weeks,” says Christian Hüwel, Stationary Machine Sales Director at Komptech. That in itself would be pretty ambitious, but the team made it happen in the specified 96 hours.

RELIABILITY REQUIRED
Fast reaction is a must if there is a machine breakdown in the Association’s mechanical-biological treatment system. Every day 750 to 800 tonnes of residual waste are unloaded at the site east of Hannover, and every day it all needs to be worked through before the next delivery comes. The plant only has room for two days’ worth of waste. Eberhard Lütge, who is in charge of residual waste treatment at AHA, explains: “If one of the four processing lines goes down we get busy. I call Komptech, sometimes with an energetic tone of voice.”
Service technician Dennis Hahne totally understands. He’s taken care of the Association for seven years, and just switched to Komptech Mobile Machine Sales. “That’s how it has to be with volumes like theirs. If need be, we move our other appointments around so we can get them up and running immediately.” AHA works closely with the Komptech Service team. With two double lines, just the necessary maintenance means a visit about every four weeks. “Right now I’m happy. The machines are running,” says Lütge.
Through the window of the meeting room under the roof of the multi-storey hall, Lütge shows visitors how the two mechanical processing lines run from the entry doors on both sides towards each other at a right angle. Each of the lines starts with a Terminator 3400 EF, followed by big drum screens. In total four shredders and two screeners from Komptech work here on residual waste. In the adjacent organic and green waste composting line there are two stationary star screens and one each mobile drum and star screen.
The screen drums in the hall were also replaced by Komptech, working through the roof with two truck-mounted cranes. “Like an open-heart operation,” says Hahne. As he says that, down in hall garbage trucks dump their loads right on the concrete floor inside the open doors. It’s a confusion of plastic bags and everything else imaginable, including things that have no business being in residual waste, like devices with lithium batteries. Residual waste from some 566 thousand households and a good 41 thousand area companies is processed here. The scale is impressive.

INCREMENTAL SPEED ADJUSTMENT
AHA Hannover has had Komptech machines on the job since 2008. They started with the first four Terminators, which were recently replaced. Lütge tells how it was: “Before and during the first bid tender we measured the ideal feed for our drum screens and determined that above a throughput of 30 tonnes per hour, screening results get markedly worse, and with 60 mm screening we get more oversizes for incineration. Of all the shortlisted shredders, the Terminator gave the best throughput control. Later, during use, Komptech further improved the adjustability, so that now we can regulate the machine’s speed in increments of 1 percent.” Thus, the Terminators in the stationary lines, along with the loader drivers, help dose the waste for further processing. The speed is regulated by the system control. If contraries stop the machine, or materials block the line, it has to be run briefly at higher speed by manual control. This is done by the driver of the loader that feeds the Terminators. “For clean operation we need seven or eight people, who mostly operate the mobile machines. Maintenance and repair work is done by the night shift,” says Lütge. 22 people work the residual waste plant in two shifts.

MAKING THE BEST OF THE REST
Degreed chemist Lütge considers the AHA well prepared for residual waste processing for the coming six to eight years. Beyond that they’ll have to see how the technical options develop. As he explains, “right now our goal with mechanical-biological processing is to minimize the amount that gets landfilled. Furthermore, the small amount that is landfilled should cause as few ecological issues as possible.” To accomplish this, after shredding in the Terminators the drum screens separate the material into two fractions. The high-caloric coarse fraction goes to a press container and is used to generate heat in a waste incinerator. The fine fraction passes an overband magnet to recover the recyclable metals, and screened and wind sifted to remove hard inert objects that would interfere with subsequent anaerobic digestion. Fines preparation with two stationary drum screens, two wind sifters and various conveyors was revamped in 2010. After this step the fines from the screen drum (< 15 mm) and the light fraction from the wind sifter go on to biological residual waste treatment in the form of anaerobic digestion, to generate biogas. The solid residue from anaerobic digestion and the heavy material from the wind sifter go to post-rotting for further composting. The result is a soil-like substrate that meets landfill maturation criteria for residual materials. “The machinery is a very important part of what we do,” says Lütge. And what if the replacement of the Terminators had not succeeded in the time allotted? “Then Komptech would have had to pay the addition incineration feeds,” says Lütge with a grin, and adds “but we knew they handle it.”