The importance of monitoring Hydrogen Sulphide in Biogas.

Prevent CHP inefficiency or even damage

The case for understanding the levels of methane (CH4 ) in Biogas is well understood. Is the importance of Hydrogen Sulphide (H2S ) measurement quite so widely recognised?

The concentration of methane in Biogas is an indicator of the efficiency of the AD (Anaerobic Digestion) process. The ability to monitor changes in methane levels allows more accurate biomass management. It can also be used to identify problems such as changes to pH or temperature fermentation process.

Understanding the CH4 content is clearly important at the output stage as well because it affects the energy value of the Biogas and the consequent efficiency of the CHP. CHP engines are designed to operate within specific ranges of CH4 concentration, so monitoring is important in preventing damage or at least reducing maintenance costs.

James Gudgeon, Contracts Manager – Energy & Recycling at Yorkshire Water, agrees:

“We carefully monitor methane concentrations at our Waste Water Treatment AD plants. The CHP engines are sensitive to change. If we don’t keep within operating tolerance then at the very least it’s a costly retune plus the downtime.”

So what about monitoring Hydrogen Sulphide?

For H2S, as with methane, the concentrations in Biogas will vary according to the biomass being used and the operation of the AD process. There are three main factors to be taken into account when considering your monitoring strategy.

Odour
The odour of Hydrogen Sulphide (the classic rotten eggs smell) is detectable by humans at very low ppm levels. The need to manage H2S levels at AD and process sites has become particularly important when they are close to centres of population.

Toxicity
Atmospheric concentrations of H2S above 200 ppm can be fatal so monitoring may be an important part of protecting site personnel.

H2S detection in biogas outputCorrosiveness
In its natural state, even at low levels of concentration, Hydrogen Sulphide can cause corrosion in all parts of the AD and CHP infrastructure. When it is combusted it forms Sulphur Dioxide (SO2), which reacts with engine oil to create a highly destructive chemical that can irreparably damage the CHP.

James Gudgeon says that the corrosion factor alone makes H2S monitoring of paramount importance:

“In the past we have suffered from catastrophic CHP failure because methane was seen as the key monitoring parameter. Our processes now put Hydrogen Sulphide in the spotlight and we have different escalation levels in place to cope with increases in its concentration.

Anything above 1,000ppm means an engine switch off. The cost of repair or replacement far outweighs the value of a few hours CHP energy production.”

Yorkshire Water and a growing number of other AD users are using Gas Data’s Click! System to provide comprehensive Biogas monitoring and analysis capability on their sites. The Click! System’s modular approach means that multiple sampling points can be monitored from a single cabinet. It’s capable of highly accurate on-line monitoring (including alarm activation) of both Hydrogen Sulphide and Methane as well as a variety of other gases.

To find out how you can reduce the risk of H2S problems by using the Click! System contact Gas Data today. Call +44 (0) 2476 303311 or email enquiries@gasdata.co.uk