Krohne's Optiflux Overcomes Problems Of Measuring Sewage

Image above: KROHNE's OPTIFLUX is being used to maximise the efficient conversion of sewage filter cake incinerated to generate electricity.

KROHNE's OPTIFLUX electromagnetic flowmeter has been installed at the Emscher Genossenschaft sewage processing plant at Bottrop in Germany. The instrument is being used to maximise the efficient conversion of sewage filter cake incinerated at the plant to generate electricity.

The Emscher Genossenschaft plant has the largest digestion, drainage and dry incinerator system in Europe. Sewage at the plant is processed into filter cake with high TS (total solid) content, which is used to fuel two waste-to-energy systems that each generate 8 MW of electricity for the plant.

To form the filter cake, sludge is drained in compartmentalised filter presses that increase the solid content from 5 per cent to nearly 45 per cent including carbon and with a density of 1.87 kg per litre.

Accurately measuring the flow of filter cake into the incinerator within the waste-to-energy system has historically been difficult using electromagnetic flowmeters because of the large solid bodies and gas bubbles within the material.

Gas bubbles and large solid bodies can create interference in the measurement signal. Rectifying this by using filters introduces sand grains into the sludge - these also make measuring flow rate difficult and sometimes impossible - because contact between the sand and the measuring electrodes can break the electrochemical boundary layer within the flowmeter and cause voltage jumps.

Engineers at Emscher Genossenschaft had previously resorted to using three different methods of measuring the amount of filter cake fuel fed into the furnaces; conventional electromagnetic flowmeters; theoretical feed rates of the high performance piston pumps; and measurements taken from the thermal energy generated from incineration.

However, the difference between the values derived from these measurement methods could be as much as 100 per cent. This made it impossible for engineers at Emscher Genossenschaft to accurately monitor and control emissions because they did not know how much fuel was being burnt. Neither did they know how efficiently the fuel was being converted into electricity.

KROHNE's OPTIFLUX proved itself capable of accurately and reliably measuring the flow of the filter cake. The instrument is unaffected by high solid content or bubbles contained within the sludge. Over a 30 day trial, comparing its measurement value against the volume count of the pumps resulted in a difference of just 3 per cent.

The OPTIFLUX flowmeter uniquely incorporates three levels of diagnostics which sets new industry standards of metrological performance and accuracy.

Traditionally, diagnostic analysis within electromagnetic flowmeters has been limited to checking the devices' microcontroller or memory. KROHNE's OPTIFLUX incorporates revolutionary 3x100% diagnostics. These provide engineers with comprehensive data that makes it possible to anticipate and rectify potential problems before they affect production.

The 3x100% diagnostics include 100% sensor and converter diagnostics, which test the microprocessor, memory and software plus the temperature of the electronics as well as the output. The instrument also carries out internal accuracy checks (100% out of spec) to determine that it is operating within specification. 100% application diagnostics, which exceed SIL 2 and NAMUR standards, are also carried out and displayed.

Contact:

Teresa Kennedy
KROHNE Ltd
Tel: 01933 408500
Fax: 01933 408501
E-mail: info@krohne.co.uk