60 Biogas Spotlight Accurate Biogas Measurement
Historically, accurate biogas flow measurement has been problematic and unpredictable due to the difficult and varying nature of the media being measured. Despite suffering from measurement inaccuracies due to installation conditions, thermal and DP flow have been widely used as the best solutions available. Not any more – Endress+Hauser’s (UK) new Prosonic Flow B 200 flowmeter offers accurate biogas measurement.
Using tried and trusted ultrasonic flow technology, the Prosonic Flow B 200 has been specially designed for accurate volumetric biogas measurement. All the usual issues such as moisture, dirt, low pressures, low velocities and changing gas composition no longer pose a problem as ultrasonic technology remains unaffected by these external conditions.
Offering a high accuracy of ±1.5%, negligible pressure loss and a wide operable flow range of 30:1, Prosonic Flow B 200 is an ultrasonic flowmeter to contend with. Available in diameters from DN50 to DN200, it is suitable for applications where gas temperatures could reach +80°C and gas pressures fall as low as 0.8 bar absolute. Better still, as either an Ex d or an intrinsically safe two-wire flowmeter (Ex ia), the Prosonic Flow B 200 is ideal for hazardous area use.
Varying methane content in the biogas is often an issue and ideally this should be constantly monitored. Thanks to ultra-precise sound velocity measurement and its integrated temperature sensor, Prosonic Flow B 200 measures the methane content of a gas as the flow measurement is made, offering an early indication of problems with the biogas production process and information for the protection and efficient running of the CHP engine.
The flanged Prosonic Flow B 200 is easily installed into your biogas pipe. It offers reduced requirements for straight pipe lengths both upstream and downstream of the meter, helping to reduce constraints on the pipework layout and increasing potential measurement points. The real bonus, however, comes in terms of maintenance requirements - Prosonic Flow B 200 is virtually maintenance free.
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25951pr@reply-direct.com Easy Payback for Biogas Monitoring
There is a strong business case for biogas monitoring and CHP protection. A fixed biogas analyser may cost some £6-10,000 and monitor gas every few minutes day and night. By comparison it can save its own cost many times over by protecting CHP engines from expensive unplanned downtime, biogas engine damage repair and help maximise ROI. On a small 0.5kw plant, at around four percent of the CHP cost, an analyser may take five days to pay for itself in avoiding lost downtime. On a £10 million site it could pay for itself in half-a-day’s downtime.
For those who own, fund, build or operate a £1m-£20m AD plant with CHP engines costing £250-750,000 each, this asks a tough question: Why risk such an enormous investment and not have an effective fixed biogas analyser keeping watch, protecting the investment and maximising returns? It seems that there is an acceptance that this damage is unavoidable and therefore businesses are budgeting for and paying out thousands of pounds every year.
Biogas is dirty, wet, explosive, hot, smelly and gives CHP engines a hard time, and with varying feedstocks there can be problems
with increasing levels of hydrogen sulphide (H2S) and siloxanes. Both can cause rapid engine wear and damage requiring processes to minimise them but also frequent oil changes and servicing. CHP engine H2S level limits may be set in manufacturers’ warranty contracts at 400, 900 or 1500ppm of H2S over a specified number of hours. More than that and the warranty may be invalidated and/or the CHP’s sensors may simply shut it down.
Revenue stops when the engine stops. That means analysing biogas before it reaches a CHP not only makes business sense, it
also shows if the operation to remove or neutralise H2S is working. H2S levels going to CHPs are controllable but first operators need to measure, analyse and assess what they need to control. Oxygen content is also a potential problem. A landfill ingress leak of oxygen can cause a burst cylinder head valve which can cost at least £10,000. Clearly limiting damage makes good business sense.
To simultaneously measure high level H2S at 0-10,000ppm before H2S removal and at 0-50ppm after H2S removal, the inclusion of two separate H2S cells in its new GA3000 PLUS is a recent innovation by Geotech (UK) on a user-installed, multi-sample point fixed biogas analyser. For some £6,000-£10,000 it can protect a £1m-£20m plant and engine, and therefore be paid for within half a day of avoided unplanned downtime. It is an ROI many businesses crave.
There are several inconvenient facts. For start-up, spark-ignition CHP gas engines need at least 40% methane with 60% as a good operating level. Low grade biogas with less than 40% methane may need to be flared. So it is essential to monitor and analyse biogas for safe, damage-free engine start-up and running, and to supply to correct quality gas to CHP or to flare if poor quality. Flaring AD gas is necessary in some circumstances, but could be like throwing money away. To avoid producing low quality biogas requires vigilance which is easily achieved with a fixed gas analyser. Reliability, dependability and operator confidence in gas analysers is critically important. Geotech measures its performance and reports over 99% uptime on its installed GA3000 and GA3000 PLUS fixed biogas analysers.
GAS SENSORS FOR BIOGAS APPLICATIONS
Range Infra- Red gas sensors for 0 to 100% Methane and 0 to 100% Carbon Dioxide featuring:-
• Two active gas channels for simultaneous measurement of carbon dioxide and methane
• Sensors for single gas measurement • Lower ranges for gas detection • Fast Response • Rugged stainless steel construction • Resistance to corrosion • Immune from “poisoning” • Suitable for fixed and portable instrumentation • Internal Thermistor for Temperature compensation • Certified ATEX, IECEx, CSA and UL listed
Also available is the long life, RoHS compliant EC410 Oxygen sensor, suitable for use in Biogas where high levels of Carbon Dioxide are present.
For more details phone us on +44 (0) 1245 809110 or e-mail
sales.is@
sgxsensortech.com
Full technical information from
www.sgxsensortech.com
email:
8ad@reply-direct.com IET Annual Buyers Guide 2013
www.envirotech-online.com email:
95ad@reply-direct.com
Estimates of CHP running costs vary. One set of annual operation cost for a 1MW engine, including downtime costs, was stated as £70,000/year. That ties in with a CHP overhaul being done every two years (replace pistons, etc.) for which, the £35,000 cost includes £9,000 of lost revenue due to planned downtime (96 hours). That relates to a revenue or cost of downtime at £2,250 a day. In addition, every 1,000 hours at a cost of £1,200 every time, the CHP must be stopped for an oil and filter change, and to clean and gap spark plugs, and set the tappets. Fixed, automated biogas analysers can help make cost limitation and control much more manageable and achievable. Their cost is a very small fraction of the large sums they can help save which is why there is an easy pay back from biogas monitoring.
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