The way of measuring biogas:
– Lower pressure, normally the pressure of biogas lower 1bar; low pressure and low flow rate.
– Gas components changes:
– Vapor contain: fermentation of sludge biomass also bring the vapor into the medium that makes the measurement more complete.
– Corrosive: biogas also contain hydrogen sulfide even if in very low PPM but once it contain with water it will be high corrosive.
– Vibration of flow rate, the flow rate of biogas varies with temperature, and other factors changes it also require the flow meter with wide turndown ratio.
Flow meter in measure biogas in the marketplace.
Orifice flow meter: Orifice flow meter the tradition method to measured the biogas with lower costs and compact design also very popular in biogas market. The disadvantages is orifice flow meter have big pressure drop and low turndown ration, obviously it’s not very suitable in biogas industrial nowadays.
Thermal mass flow meter: Based on the thermal diffusion working theory can measure the mass flow directly and without pressure drop and can in very wide range ratio. But be sure the medium is dry is very important when select thermal mass flow meters.
Vortex flow meter: Vortex flow meter is an ideal equipment for biogas or steam application measurement, the results will not influenced by the gas components and medium contain vapor. But due to the low pressure and low velocity of biogas makes most of the vortex type meters can’t take the job.
Ultrasonic flow meters : In the fluid, there is a time difference between the upstream and downstream ultrasonic waves, and the converter can measure this time difference. The flow rate is proportional to the time difference, so the flow can be obtained. Based on this ultrasonic flow meter measurement is not affected by low pressure, gas composition fluctuations and water vapor, and the range ratio can reach 1:100, which can fully meet the measurement requirements.