Bronkhorst has become firmly established as the market leader in low flow gas & liquid measurement and control by selecting the correct technology and methodology from their broad product repertoire to not only meet any given application, but to exceed expectation. One of the company’s greatest strengths is its competence with Coriolis measurement techniques and, more specifically, its patented Mini-Cori flow sensor. By using this core technology, together with their knowledge and experience Bronkhorst UK has helped many customers and processes which needed low flow measurement or control.
Following discussions at the AD&B exhibition at the NEC in Birmingham, Bronkhorst knowledge and experience was requested by a UK gas supplier to assist in developing a solution for metering liquid propane being injected into the out-flow from biogas production plants.
This propane injection is part of the careful treatment and assurance process for the biogas prior to it being introduced into the UK national grid. Biogas is produced by a process called Anaerobic Digestion. AD is actually a collection of processes by which microorganisms break down degradable material within an environment that is starved of oxygen. The process is entirely natural, being part of the global ecological cycle, however as an important energy resource the techniques are now industrialised and highly refined. As the biodegradable material breaks down a number of subsequent off products are produced.
This specific end user is using the process to create a source for renewable energy. The main part of the process creates a gas consisting of methane, carbon dioxide and a small amount of contaminant gases. The methane and the CO2 are separated and the contaminants are rigorously scrubbed to remove them from the gas stream. The final part of the process requires detailed analysis of the gas to ensure that it meets the required calorific value as set out by national standards. In the event that the gas is not to the required quality, a very small amount of propane is injected to boost the calorific value thereby ensuring that the contents of the National Grid retain their burn efficiency.
In view of the very low injection rates, the customer approached Bronkhorst as specialists in the field of low and ultra-low gas and liquid flow measurement and control. A significant challenge was matching the extremely accurate low flow control against the relatively high flow within the main line, however, by working in partnership all parties arrived at the optimum solution. After a number of technical and detailed meetings, Bronkhorst suggested the use of Mini-Cori Coriolis Flowmeter directly coupled to a Badger Valve.
Importantly, the controlled medium was taken from a liquid propane source stored in tanks below ground level thereby ensuring a more stable temperature and pressure regime. This combined solution overcame some of the difficulties facing the customer as Propane has a very low Vapour Pressure Line and the system demanded some very tight pressure tolerances.
The system needed to be finely balanced to allow the liquid to be pumped from the source, ultimately converted to gas phase, but without fluctuations caused by phase-change shifts within the control loop e.g. at the restriction caused by the control valve orifice. Furthermore, the pressure required to inject into the main biogas line had to be accurate – if the pressure on the outlet was incorrect then the propane would not mix correctly and measurement of the calorific value would be adversely affected.
As the Anaerobic Digestion & Biogas market matures within the UK, the demand for greener, sustainable and more localised energy sources are being fulfilled. Bronkhorst UK has found itself gaining more traction within difficult niche flow/pressure applications within this very singular niche industry.
Technical specification : accuracy of +/-0.2% Reading, certified for ATEX Zones 1 and 2, on-board PID control is standard, as is over-run protection and a self-learning function, the turn-down ratio is 2000:1, flow rates down to 0.1 grams per hour have been easily achieved and the physical size (“the smallest Coriolis instrument in the world”) has proven to be perfect for multiple injection points within a confined space. This particular application suited a Badger Valve although virtually any actuation device can be integrated – direct pump control, other types of control valve or indeed shut-off valves – should the process conditions demand it.
For more information on the Mini Coriolis instrument please contact us; Bronkhorst UK Ltd, Email: sales@bronkhorst.co.uk, T: 01223 833222
