Keypoints: LANDFILL GAS MONITORING - VERY LOW FLOW APPLICATIONS - ACCURACY INDEPENDENT OF MEDIA - EXCEPTIONALLY LOW FLOW RESTRICTION
THIS PATENTED TECHNOLOGY REPRESENTS A SIGNIFICANT
PUBLICITY FLYER: TTL01 - LFG - WIDE RANGE GAS FLOWMETER
MARKETS: This technology is intended to impact on markets presently dominated by orifice plate, pitot, vortex shedding, hot wire and mass thermal devices.
APPLICATIONS: Landfill, flare gas and test cell monitoring process control and general flowmetering. Monitoring aggressive and mixed gas flows down to 0.05 m/s without calibration.
BENEFITS: An inexpensive and reliable replacement for conventional methods of continuously monitoring gas flows. One device can safely measure a variety of media and deliver a conditioned electronic output over several kilometers for monitoring recording or control.
COMMERCIAL OPPORTUNITIES: Arigorous
seven year research programme has produced a field trialed pre – production
prototype for which a comprehensive know – how package is in place. The
technology has patent protection. A business partner is now sought to share
in the production and marketing of a commercial instrument.
TECHNICAL PAPER: TTL01 - LFG - WIDE RANGE GAS FLOWMETER
The Timed Thermal Label (TTL) Flowmeter (1) was initially developed to address shortcomings identified in existing instruments such as Hot Wire Anemometers, Pitot Tubes, Orifice Plates and Mass Thermal Transfer devices when applied to the continuous monitoring of passively vented landfill gas. The gas is invariably of mixed constituents, saturated with water vapour and explosive. Minimal pipeline restriction is essential for this type of investigation since flow is dominated by millibaric pressure variations. Positive displacement instruments are independent of constituents but are of no practical value due to back-pressure and condensation. A programme of two laboratory evaluations established that a time of transit method using liquid propane to provide a cold label was both accurate and safe(2).
TTL will find wide application where widely varying flows are encountered and the media is difficult to monitor with conventional instrumentation. Following initial development for flows well below 1 m/s in 50 mm pipes(3), the same instrument has been operated on pumped commercial sites with flows above 25 m/s in 300 mm pipes(4). A typical installation will comprise a number of Head Stations located in the gas field transmitting data to a single Base Station, where the data is processed logged and displayed.
PRINCIPLE OF OPERATION
Figure 1 shows a Head Station located adjacent to a pipeline. A 3 Watt solenoid valve A, located outside the pipe and controlled by circuit B. It is triggered by the remote Base Station and periodically injects a small shot of liquid propane into the pipeline. Temperature sensors C and D are located a suitable mixing distance downstream from the injector and have a typical separation of 200 - 500 mm. The detected signal passes through Zener barriers E low noise DC restoring amplifiers and AGC stages F. These signals are converted to a frequency G, optically isolated and transmitted to the Base Station H. An embedded computer performs a cross correlation analysis of the detected signals, calculates their interval and converts velocity to volume flow. The results are then corrected for laminar, transitional or turbulent flow and recorded by an internal data logger or transmitted to a user interface. The DC supply is isolated I.
A cold pulse method was adopted since labeling the flow with heat was found to exceed all known safety guidelines for explosive gases. Figure 2 shows experimental results for a variety of gases and sensors using a 50 mm closed loop test rig (2). Measurements were made with a Jeavons positive displacement meter from 0.027 l/s / 0.1 m3hr to 18 l/s / 65 m3hr and a BS1042 standard orifice plate to 60 l/s / 230 m3hr. The positive displacement instrument was selected since it is the only conventional device which does not infer results and its accuracy is unaffected by such characteristics of various gases as thermal conductivity, viscosity and density. Table 1 compares the relative characteristics of the gases used in the experiments. Identical results were obtained with the TTL flowmeter and the positive displacement instrument for Air, CO2 and CH4. Similar results were obtained for air saturated with water vapour.
DRAFT PERFORMANCE SPECIFICATION
Velocity…………….…(field and laboratory )…..0.065
– 30 m/s.
Volume flow ………….(laboratory trials)…….. 0.1 to 230 m3hr.
Accuracy….….…….…(subject to flow regime)…...approx. 2%.
Flow restriction ……..(300mm landfill gas pipe).0.65% of area.
Display average time...(sampling interval)………....10 s to 10 m
Power - on settling time ……………...…Less than 20 Seconds.
Display units...…………………..…m/s,.l/s, l/m, l/h, m3hr. e.t.c.
DRAFT ENGINEERING SPECIFICATION
Materials in contact. Critical components
for all applications are typically stainless steel and platinum.
Media compatibility. Landfill and noxious corrosive gases.
Pressure. Untested, cannot exceed limit for propane to boil.
Temperature. Untested, cannot exceed limit for propane to boil.
Enclosure. To suit application, free-wired to stud mounted pipeline components. Typical -IP67.
Telemetry. To suit application. RS232, 4-20 mA, frequency.
DC supply. Unregulated isolated line 5 - 18 Volts 100mA.
Safety. The design embodies limits for hazardous area operation within IEC 79-1 0/CENELEC classification for Zone 0 applications.
(1) Inventors: Mr. J.K.Bartington. Dr. P.Reynolds. Pat No WO94909205
(2) WE 8000/1/BJB Industrial Physics Group University of Essex and WE 8000/2/BJB Industrial Physics Group University of Essex. Technical Feasibility of Measurement of Flow Rates in Pipes Using a Heat Tracer Technique. Dr. B.J.S.Barnard.
(3) Report No DoE 4119. Landfill 2000 A Field Trial of Accelerated Waste Stabilisation. N.Blakey, K.Bradshaw, P.Reynolds, C. Young.
(4) WRc ETSU contract No B/L/F00466/EP for DTI. Landfill Gas EnhancementField Trials Using Leachate Irrigation.
Patents held by BTG International Ltd.