Monday, May 25, 2015
6 High Demand Anaerobic Digestion and Biogas Plant Products
In this article we have identified 6 popular anaerobic digestion and biogas plant products, which with the rising rate of biogas plant installation, has meant that these products are in high demand to ensure the proper running of an ever increasing number of anaerobic digestion plants.
(If you have suggestions for products that you think we should add, just add them to this page via our commenting facility below.)
It is important to measure pH and Redox potential is all anaerobic digestion plant fermenters, other than perhaps some of the most basic un-mixed plastic membrane covered anaerobic digestion lagoons which are used in hot countries, and are not optimized or controlled.
For all other plants this measurement is essential, and also needs to be reliable, and very accurate even if not re-calibrated over long periods. That's because the pH and redox information the device provides is used to adjust the operation of the fermenter. Get that wrong and the production of biogas can cease!
Keeping a biogas plant running at close to its full design gas yield, is done mostly through adjusting the feed material type and quantity day by day, and also at times, to decide on how much of any dosing chemicals must be supplied to bring the pH or Redox back within the optimum operating range. These adjustments are used to ensure that the micro-organisms in the digester are maintained in the chemical conditions in which they will thrive and produce the most biogas, at a high methane quality.
One company that has a pH/Redox monitoring instrument which is in high demand, and is designed for the extreme conditions found in biogas plant reactors is Hach Lange.
It is best to provide their technical details to describe this pH robe system. They state the following in their downloadable pdf file:
“The digital pHD electrode used to measure pH and redox is fully encapsulated so that it does not come into contact with the fluid being measured. A special, soil resistant salt bridge forms the direct contact to the fluid to enable the measurements to be made."
"In contrast to conventional membrane based electrodes, this electrode can be used for very long periods even in fluids with a high particulate content, e.g. digester water. The intervals between cleaning are especially long. Electrode poisoning, e.g. by any H2S that may be present, is prevented and dilution of the electrolytes is avoided.”
There is more information about this popular product at:
pH test strips have been around for many years, but nowadays the technology behind the best of these strips enables the user to assess the pH value, and not just whether the liquid tested is acid or alkaline. They are still not as accurate as using a good quality pH probe, however, they can be very useful when an immediate assessment of approximate pH value is needed, and when there is no probe, such as the Hach Lange pH/Redox probe discussed in 1., above.
For that reason we have included pH Test Strips in this list of our "in demand" anaerobic digestion products.
Probably the best known test strips are those made by Merck in their Millipore range. They offer a large number of products for pH measurements with various methods of operation. These include pH indicator papers, and MColorpHast™ pH test strips, and pH indicator solution, however it is the simple test strips that are most used and can be an essential tool, especially when carrying out process troubleshooting site checks on anaerobic digestion plants.
For anyone that wishes to find out more about pH test strips by Merck we suggest the following link as a starting point:
NPL, once the UK's National Physical Laboratory is a private company which specialises in carrying out trace-level impurity analyses for gases, especially for biogas. Knowing what may be present in biogas as trace-level impurities is critical for the design of the gas-engine for power generation, and also increasingly for upgrading biogas to biomethane by removing these impurities.
The concentrations of both the trace-level impurities which cause corrosion and those that cause the build-up of hard silica materials on valves, and combustion cylinders, are assessed by using these tests. Also, very sticky tar-like substances within a gas-engine used for electrical power generation, can build-up, and trace-level gas impurity tests will when used skilfully by an expert, allow the need for pre-treatment of the biogas before it enters gas engines to be investigated, thus avoiding the risk of very expensive remedial maintenance on the power generation and biomethane upgrading system later.
Traceable gas standards containing each of the following components are available, from NPL as follows:
• Siloxanes (multi-component mixtures of the siloxanes most commonly found in biogas)
• Hydrogen sulphide
Further information on this in-demand service can be obtained from:
Almost all anaerobic digestion systems require the monitoring of flow, and it is particularly important to measure the flow and volume of the substrate feed continuously and accurately, so that the calorific value feed that is added is known, and can be controlled. The Prosonic Flow B 200 by Endress and Hauser Ltd is a well-known example of such a flowmeter.
An inexperienced biogas plant designer might think that a cheaper, vane type flowmeter would be satisfactory, but due to the presence of fibrous materials in the flow, these get caught around the vane of a cheap flowmeter and cause malfunction of the device. As a "non-intrusive" flowmeter the ultrasonic types are very well suited to biogas applications, and ATEX rated explosion proof versions are also available to avoid explosion risks where these occur.
Further details are available at:
Biogas plant mixing systems have traditionally been under-specified for completely stirred mixed reactor type biogas plants. With inadequate stirring, their performance can be far below what would be achieved if well designed, good quality mixing, was installed and operated.
Anaerobic digestion operators can experience problems with the build-up of a hard cap of biomass floating on the surface. It can impede the circulation of biogas through this "hard crust", and as the crust can contain a large proportion of the organic material in the reactor, the rate of biogas production can be significantly reduced.
The installed mixers may be incapable of breaking up the "hard crust" and opening the top of a reactor to physically smash up a floating crust, means significant plant down-time, and loss of biogas production.
The Landia GasMix has not been around for even 18 months (time of writing is May 2015), and yet it is a biogas plant reactor mixing system that is in high-demand. Users report that once installed, and using the cleverly designed combination of biogas and substrate purging, hard crust accumulations can be broken up and re-submerged in not much more than half an hour of operation using this system. Once initial crust break-up and re-suspension has been achieved, the system is run on an automatic setting and runs for only short periods daily, to prevent any further significant build-up of floating material.
Further information of the Landia GasMix is available here:
If there is one thing that all biogas plants have in common is that they produce gas which must be stored, until needed. Suppliers of biogas storage covers and vessels, have been in increasing demand for their products, as the rate of anaerobic digestion plant construction has accelerated.
VERGAS Ltd is a leading company in biogas storage systems, and specialises in the design, manufacture and installation of high quality flexible membrane biogas management equipment, worldwide.
The following is a link to VERGAS Ltd's website where further information on biogas storage covers and vessels is available:
We hope that this article has been useful. If it has, or even if it has not and you have suggestions on improvement you would like us to make, please provide us with feedback via the "commenting" facility below, or via our contact page.