Page 133 from: May 2008

May 2008 133

tion over a distance of up to two metres, thus

facilitating the assembly of extremely com-

pact drive units. The significance of this

option is proven by the figures: roughly 200

drives have been installed in the mechanical-

biological plant section, approximately 130 of

which are driven via ET200S motor starters.

Service-friendly features
While a central solution was selected for the

entire control system, the ET200S input/out-

put devices were distributed throughout 26

on-site control cabinets to provide optimised

routes. The supplier also focused on the aspect

of service friendliness for this sub-system,

such that the control cabinet doors were

equipped with large inspection windows so

that any fault messages could be signalled via

LEDs to passing operating personnel.

Mr Surber emphasises: ‘Even though the

motor starters are installed in a central con-

trol cabinet, the concept of distribution was

also implemented here to some extent. Due to

the option of the motor starters’ transparent

arrangement, we were able to assemble pro-

cess-technical function groups.’ This means

that plant sections can be switched off at any

time without affecting other components.

Revision work thus no longer requires the

plant to be brought to a standstill – a critical

point since the processing, transport and,

above all, the fermentation stage must obvi-

ously never be interrupted.

Also, the transparent arrangement of all plant

components and the devices’ ease of handling

represented crucial requirements. On-site staff

must be multi-functional, in a manner of

speaking, as they not only have to deal with

the process technology but also with electrical

and control technology. In addition to remote

operation from the control station via bus

technology, the individual plant components

are equipped with additional manual operator

panels which were delivered by Siemens com-

pletely pre-assembled.

Standardisation
In the six percolators – which are effectively

large tanks comprising agitators – biodegrad-

able waste is washed using water. This water

flows into the fermentation tanks through

inlets and openings in the bottom while the

refuse is transported into residual presses by a

so-called pushing floor and conveyor screws.

From there, the solid components are fed to

the biological drying unit, after which final

separation by size and type takes place. The

gases that develop during the fermentation

process are directed into the connected com-

bined heat and power plant where four gas

motors produce electrical energy.

The percolators are driven by electric motors

each with a power rating of 75 kW, picked up

by huge gears which then generate a torque at

the agitator shaft of 1.5 million Nm. A car typ-

ically produces approximately 300 Nm and so

this scale of torque corresponds roughly to that

of 5000 cars.

The gears are powered by Micromaster

MM440 frequency converters from Siemens.

These devices are considered extremely rug-

ged, a factor which also proves highly advan-

tageous when it comes to feedback effects

from the drive string, ie regenerative shares.

Thanks to their high overload capacity, these

converters also support the operators’ avail-

ability requirements.

Yet another argument was important to Mr

Surber: ‘Besides the practical load torque

monitoring and the direct connection to Pro-

fibus, the large application area of these drives

was of major interest to us in the context of

standardisation.’ The devices are available

from 0.12 to 250 kW. In the biological trans-

formation section, a further 37 drives such as

pumps and conveyor screws are installed

which require individually adjustable speeds.

‘As the Micromaster 440 was the ideal solu-

tion for this challenge, we even remained

within the same device range,’ he adds.

The new Kahlenberg refuse recovery plant in the Baden region of Germany is based on a patented mechanical-biological treatment concept whereby
the refuse can be used as a resource. (Photo: ZAK)

Sirius ET200S motor starters can be connected in series over a distance
of up to two metres, allowing for the assembly of compact and transpa-
rent drive units. (Photo: Siemens)

The I/O devices of the distributed ET200S I/O bundle all the signals of
the plant in a minimal amount of space. (Photo: Siemens)

RI_019_Waste processing.indd 3 14-05-2008 16:51:58