Biogas Focus - Air Monitoring
sensors generally have a long life. However, the increasingly popular fixed monitoring systems which communicate directly with site control systems, such as SCADA systems, must be correctly set up to ensure a reasonable sensor life. In addition, H2
S calibration gas, which is important to fine-tune and verify
measurements at the low levels required, can be expensive, complicated, or even impossible to get to where it is required. As a result, pre-calibrated sensors or cross-checking with a portable analyser which has been calibrated elsewhere offer practical solutions to this problem.
S in biogas will vary according to the process and feedstock and can be anything up to 3,000ppm in a municipal sludge plant, but may also be in tens of thousands for industrial or food related AD systems. At these levels, rather than monitoring H2 H2
Incoming H2 S in raw biogas, the challenge is to remove the S effectively and monitor that it has been removed. Alarms
are set to indicate any sudden increases which should shut down vulnerable equipment.
Many proven H2 S desulphurisation methods are used across
Europe such as chemical scrubbing, biological or down flow systems. Biological H2
are cheaper to run and maintain than chemical scrubbers, which require frequent replacement of expensive chemicals. As well as checking H2 also measure O2
will produce very little (close to zero) O2 S scrubbers are commonly used as they S levels, gas monitoring systems must
in the biogas. Whilst a healthy biogas process , a leak which allows
, particularly if following maintenance. Many biogas sites set a tolerance level of 0.5-1% O2
air into the system can prove catastrophic for an engine. In addition, biological scrubbers can introduce small amounts of O2
with alarms set if this figure is exceeded. A reliable O2 sensor is critical and the
system must be carefully set up and managed to ensure long- term performance.
Maintenance
Often an appropriate level of maintenance is difficult to achieve on many sites, due to the availability of trained staff or the remote location and need for minimal downtime. The
best fixed gas monitoring systems take this into consideration and require little on-site maintenance, from changing parts to calibration or management of the moisture, which is an unwelcome feature of biogas from many common feedstocks. Whilst complex gas chilling systems sound appealing and can reduce the humidity of biogas when working well, they are fragile, expensive and often require high maintenance and spare parts. Good monitoring
33
McCain’s lagoon in the UK
system design and passive moisture removal offer a cheaper and ultimately more effective solution.
Using biogas
In Europe biogas is generally burned in CHP engines to generate electricity, which can feed into the grid and can earn a considerable income for the operator, dependent on the kW/ hr of power generated and the financial incentive offered for each unit of renewable energy from the national government. This model also exists in farther Eastern continents, but it is dependent on the site being of a scale to justify the capital expenditure and also local power infrastructure: if the nearest point of the electricity grid is far away, the cost of creating a connection could be prohibitive.
A popular model is to upgrade the biogas from 50-60% CH4 to
over 95% to produce CNG. The gas composition requirements vary between application and country, with limits for use in motor vehicles being more relaxed than for injection to the gas grid. As well as checking that CH4 98%, it is also important to keep H2
is consistently around 97- S and O2
levels very low. A
good monitoring system can also manage the higher pressures involved in biogas upgrading through carefully positioned pressure regulators.
Biogas from landfill
Municipal waste is managed differently throughout Europe, depending on availability of land, government policy and incentives, public opinion, historical legacy and budgets. A well- managed landfill site will also yield high quality biogas in large volumes. As with biogas, some sites do not lend themselves to electricity generation, or for other reasons may find a better business case for generating CNG from landfill gas.
Many monitoring solutions are available for the wide range of biogas applications around the world, whether it is a fixed system installed to protect a CHP engine, or a portable analyser for spot checking gas levels throughout the AD process. A regular monitoring routine will assist with process efficiency and protect against potential damage, ultimately saving time and generating revenue.
More information
www.geotechuk.com
Biogas monitoring
Gas analysis provides early warning of AD problems
Robust and reliable equipment Full support and advice
Self-install fixed system with two-minute service downtime
Payback in months with avoided CHP downtime
Minimal running costs
to avoid CHP downtime BIOGAS 5000 portable and
GA3000 PLUS fixed gas analysers
For More Info, email: email:
For More Info, email:
+44 (0)1926 338111
sales@geotech.co.uk www.geotech.co.uk 1003ad@reply-direct.com
www.envirotech-online.com IET March / April 2014
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