Technical Specification

Technical Specification

Instrument Design Information

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Siloxanes are a class of organic chemicals containing silicon, which burn in CHP engines, producing silica, in effect sand, which is highly damaging to engines and results in major, frequent engine damage and hence overhauls. The solution is to remove the damaging siloxanes in the Biogas or Landfill gas before they reach the CHP engine, this is achieved by using either an activated carbon filter or a regenerative filter. The problem however arises that carbon filters have a finite life span and are relatively expensive to change and that regenerative processes can be energy intensive dependent on the regeneration cycle. By monitoring the gas flow post filter the total siloxane load can be seen and a trend graph produced to show when carbon filter failure is likely or when a regenerative process should be started.
The STS Siloxane Monitor constantly measures the filter output 24/7 putting the operator in possession of accurate and understandable data on which to make an informed decision on plant optimisation.

The instrument should be located outside the ATEX zone but as close to the final filter outlet as possible. Connections to the instrument are as follows. The biogas supply is made with ¼” OD PTFE or SS and is either insulated or in some circumstances (particularly where there is a long run) heated to prevent condensation of the siloxanes.
The Siloxane Monitor requires a nitrogen supply from a cylinder and a vent line, taking the biogas from the instrument after analysis to waste. A 110v 32A mains supply is required to run the instrument and associated water traps.

STS can offer a data communication package for remote access to instrument data. There are a number of options available including GSM and radio repeaters for poor signal areas, email alerts may be set for notification of instrument alarm conditions and threshold breaches for siloxane concentration. Interface into existing systems may also be possible dependent on site systems. A quote will be provided following the conclusion of a site survey and supply of information regarding required protocols.


The Siloxane Monitor is designed to quantify siloxanes in biogas using NDIR technology and is aimed at the sewage and landfill biogas industries.
Applications include monitoring to optimise carbon filter changes or regeneration cycles, determination of likely engine damage, or evaluation of boreholes for siloxane potential.
The instrument contains a pump which draws the biogas into the system, a concentration section and a gas cell which allows very low level detection.
The outputs of the instrument are a 320*240pixel LCD display showing operating parameters and current siloxane value and recent measurement data; an SD card port for data download; and an optional online communications service. Instrument control is by an alphanumeric keypad.
Calibration is required at 6 monthly intervals and is achieved via an injection system.

Performance - detection limit of 0.5mg/m3 total siloxanes.
Rate of measurement – a result is produced every 60 minutes under standard settings
Biogas consumption - 1800 mls are required for every 60 minute cycle.
Weight - 12 Kg
Dimensions - 475 x 170 x 350 mm
Enclosure - painted steel, with aluminium front panel, not weather proof.

The monitor can take up to 3 different samples via a solenoid switching arrangement, these can be monitored in a preset order which is customer selectable.


The monitor utilises an air purged system for safety, this takes fesh air from outside the kiosk and purges the instrument at a rate greater than any potential leakage of biogas.

The unit has onboard methane, temperature and purge control sensors which will shut the instrument down into safe mode should any threshold be exceeded.  

The instrument is supplied with an inline flame arrestor before the unit and an end of line flame arrestor on the instrument exhaust line.

Swagelok high presssure compression fittings are used throughout the instrument and kiosk, these are rated to 10,000 psi, the instrument is regulated to 15psi. All internal pipework is in 1mm ID stainless steel housed in a protective PTFE sheath, this narrow bore acts as a flow limitation restricting the amount of biogas in the instrument at any time.

Although not ATEX rated many of the components used in the monitor are including all the solenoid valves.


Electricity – 110V, 32A
Nitrogen instrument grade, consumption 100 mls/min – a standard X47S cylinder lasts about 80 days.
Suitable exhaust arrangements for waste gas from instrument
The biogas supply must be non-condensing, unless a water coalescing filter is fitted.



The Siloxane Monitor is available in a bespoke GRP kiosk preset so that only the external connections are required to be made.  The kiosk includes a gas management system including valves, solenoid operting valves for line switching, regulators, water and coalescing traps and flame arrestor.  Power is uspplied via an external kill switch to a distribution board which supplied power to the monitor, heated line and cabinet heater.  

The kiosk also houses the remote telemetry unit for access to data via a designated web page.





Technical Specification Data Sheets

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