Flow meter technology for pyrolysis oil is selected from a characterization of the oil, not from a meter catalog. Samples from several batches first establish whether water is dissolved in the oil or present as a separate phase, how much solid matter there is and at what particle size, whether free gas or vapor can form in the metering line, how viscosity changes with temperature, and how far the product can be heated. Coriolis, positive displacement, magnetic and ultrasonic meters are then screened one by one against that data. None is unconditionally suitable; the choice among the remaining options depends on the purpose of measurement (process monitoring or custody transfer), the billing unit (mass or volume), and the manufacturer's product-specific assessment.
One condition applies: the numeric ranges here are for biomass fast pyrolysis oil (bio-oil), the type with the most published data. No verified general data set exists for oils from waste tires or plastics, so for those the decision rests on the product's own analysis. Skid structure and a general review of meter types are on the related solution page; this article covers the step before it: which data to collect and which question each data point raises for each technology.
Different fluids under one name
According to IEA Bioenergy, biomass fast pyrolysis oil typically contains 20–30 wt% water, has a pH of 2–3 and a density of 1.10–1.30 g/ml at 15 °C, and is immiscible with petroleum oils. The ASTM D7544 and EN 16900 product specifications also cover only biomass-derived pyrolysis liquids.
Waste tire oil shows a different profile. In a crude tire pyrolysis oil sample examined in a peer-reviewed study, sulfur exceeded 1 wt%, which the author attributes to the vulcanization of tire rubber; the density of the same sample was reported as 921 kg/m³ at 15 °C. This single-sample data is not typical for tire oils; it only shows that bio-oil ranges do not transfer to this product. A review of pyrolysis oils from post-consumer plastic waste states that these oils can contain many contaminants, including chlorine and various metals, which cause corrosion and fouling. Its context is steam cracker feed, but it also shows which parameters belong in the analysis program for wetted-part selection. A datasheet line reading 'fluid: pyrolysis oil' is not an adequate definition for meter selection.
How water, solids and gas enter the measurement
Water: dissolved or a separate phase?
According to VTT's bio-oil report, water in these oils is dissolved or present as a microemulsion and cannot be removed by physical methods such as centrifugation. Even so, the product does not always stay single-phase: aging reactions produce water, and an aqueous phase can separate when total water exceeds about 30 wt%. Oils from forest residues can form a top phase of 5–20 wt%, lower in density and polarity, depending on feedstock and process.
For metering, the problem is different phases passing through the meter in sequence: product drawn from the tank bottom or top can differ well from the average analysis in density, viscosity and conductivity. Water should therefore be requested with its phase state and how that changes in storage, not just as a percentage. VTT gives Karl Fischer titration (ASTM E203) for water determination in bio-oil and states that xylene distillation (ASTM D95) cannot be used for these oils because of their low-boiling compounds. For tire and plastic oils, whether water occurs as a free phase and which method to use should be decided with the laboratory.
Solids: size and hardness matter as much as quantity
Typical bio-oils whose char is removed by cyclones contain less than 0.5 wt% solids with an average particle size of about 5–10 µm. These solids can agglomerate into a sludge layer at the tank bottom during storage and can promote aging. Field trials reported by VTT found that sand or similar hard solids above 0.05 wt% caused erosion in pumps and nozzles. In bio-oil, solids content can be determined by ASTM D7579 and particle size distribution by an optical particle counter or image analysis.
Particle hardness, the size that passes the strainer, and whether tank-bottom sludge is drawn in at the end of unloading matter as much as quantity. In fuel use the solids carry energy, so removing them all is not the primary aim; strainer fineness is set together with the solids load the meter will see.
Gas: air, light compounds and vaporization
The gas in the title usually comes from metering-line conditions rather than the product itself. Bio-oils contain light compounds that can evaporate near ambient temperature (typically below 5 wt%), and VTT also notes that excessive preheating can cause premature evaporation of water and low-boiling compounds. A meter on a heated line may therefore see a product with bubbles.
For dynamic liquid measuring systems subject to legal metrology control, OIML R 117-1:2019 requires air and undissolved gas to be removed from the liquid before it enters the meter; a gas separator is required where the pump inlet pressure may fall, even momentarily, below atmospheric pressure or the saturated vapor pressure of the liquid. It also notes that air pockets can form when the supply tank empties and through thermal contraction during shutdowns. These requirements apply to legal metrology systems, but asking where gas forms is equally valid for process metering. When gas or an air pocket passes through a meter, an error occurs regardless of the measuring principle; technologies differ only in how they detect and tolerate it.
Fluid characterization table
The table below lists the data to request before meter selection and how each item affects the technology decision. A test method is named only where the reviewed source gives it for bio-oil; for tire and plastic oils the method should be agreed with the laboratory.
Pyrolysis oil fluid characterization: data set for meter selection
Property | Why it matters | How it is determined | Effect on technology selection |
Water content and phase state | Density, viscosity and conductivity differ between phases | Karl Fischer titration (ASTM E203); phase observation on a settled sample | A changing phase strains density-based calculations and conductivity-dependent principles; the tank draw-off point is questioned |
Solids and particle size | Erosion, plugging, deposits and bottom sludge | ASTM D7579 (solids); optical particle counter or image analysis (size) | Decisive for meters with narrow clearances and moving parts; assessed together with strainer fineness |
Density and its temperature dependence | Basis for converting between volume and mass | Digital density meter at 15 °C (ASTM D4052) | If billing is by mass, a volumetric meter needs a product-specific density–temperature relationship |
Viscosity–temperature curve | Pressure drop, slippage and flow profile | Kinematic viscosity (ASTM D445) or rotational viscometer | Pressure drop and meter operating range are checked at the highest viscosity |
Thermal stability and aging | Sets the upper heating limit and viscosity rise over time | Viscosity increase at 40 °C after holding at 80 °C for 24 hours (quick comparison test; not a standard method) | Jacketed meters and heated lines must stay within this limit |
Acidity and feedstock-related impurities | Compatibility of wetted parts, liner, electrodes and seals | pH and total acid number (ASTM D664); ICP or AAS methods for metals; sulfur and chlorine for tire and plastic oils | A meter whose material compatibility cannot be confirmed is screened out; pipe material is not evidence for the meter |
Light compounds and gas tendency | Bubble formation under heating and suction conditions | No suitable standard method for bio-oil in the source; the flash point method is unsuitable for bio-oil. Operating temperature, suction pressure and tank-emptying scenario come from process data | Need for gas elimination and downstream back-pressure design; gas tolerance becomes a technology differentiator |
Electrical conductivity | Operating condition of a magnetic flow meter | Measured on a product sample; little published data for bio-oil | If the manufacturer's requirement is not met in every batch and phase, the magnetic option is screened out |
Screening matrix: which data screens out which technology?
The matrix is not a ranking; for each technology it shows the questions that can trigger screening-out and the data that answers them. A negative answer drops the technology or calls for reassessment with an added measure (straining, gas elimination, temperature control).
Technology screening matrix for pyrolysis oil
Technology | Questions that can trigger screening-out | Data that answers them |
Coriolis mass flow meter | Has the manufacturer assessed the wetted tube material against the product's acid and impurity profile? Does pressure drop at the highest viscosity exceed the pump and suction margin? Can gas or air pockets pass through the meter? | Acidity and impurity analysis; viscosity–temperature curve; suction pressure and tank-emptying scenario |
Positive displacement meter | Are the size and hardness of solids reaching the meter acceptable for internal clearances and moving parts? How far is the batch-to-batch viscosity spread from the calibration condition? If mass is required, is product-specific density data available? | Solids, particle size and strainer fineness; viscosity range; density–temperature relationship |
Magnetic flow meter | Does the product's conductivity meet the manufacturer's requirement for the selected model in every batch, every phase and at operating temperature? Are liner and electrode materials compatible with the acidity and abrasive solids? Will the electrodes coat? | Conductivity measured on samples; phase state; acidity and solids analysis |
Ultrasonic liquid flow meter | Do bubbles and solids attenuate the acoustic signal? Does viscosity change push the flow profile outside the range the meter can compensate? Will deposits build up on the pipe wall? | Gas tendency and solids load; viscosity and Reynolds number range; manufacturer's product-sample or application assessment |
Turbine and other viscosity-sensitive principles | Does operating viscosity move, from batch to batch and with temperature, outside the range where the calibration curve is valid? | Viscosity–temperature curve and batch-to-batch variation |
Static method (tank gauging or weighing) | Is continuous flow data and real-time control needed, or is a quantity determined at the end of each batch sufficient? | Purpose of measurement and the billing method agreed with the buyer |
Direct mass measurement is a real Coriolis advantage with variable density, but it does not remove the matrix questions: localized corrosion can initiate fatigue cracks in thin-walled vibrating tubes, so a material suitable for the pipeline is not evidence for the meter. Magnetic and ultrasonic decisions usually rest on the manufacturer's assessment of a product sample.
Linking the data to the metering point design
· Sampling point: The analysis should represent what the meter will see. EN 16900 treats sampling and material compatibility in a separate annex; assess tank-bottom, tank-top and transfer-line samples separately.
· Strainer and meter together: Strainer fineness is selected for the particle size the meter can accept. If strainer differential pressure is not monitored, a loaded strainer can lower suction pressure and increase gas formation.
· Gas elimination and back pressure: Gas eliminator location and downstream pressure holding depend on where gas forms (tank emptying, heater outlet, pump suction).
· Temperature window: The window between the viscosity-driven lower limit and the stability-driven upper limit must also hold at the meter. Bio-oil reacts rapidly when heated to 100 °C or above; the heating architecture is covered on the heated transfer page.
Unsuitable conditions and limits
· Selection based on a single sample or batch: aging, phase separation and batch-to-batch variation are not covered.
· Applying bio-oil ranges or ASTM D7544 and EN 16900 limits to tire and plastic oils.
· Transferring a meter, materials and heating arrangement chosen for fuel oil directly to pyrolysis oil.
· Generalizing one model's datasheet values to a whole technology; meter accuracy is not total measuring-system uncertainty.
· Legal metrology scope, hazardous area classification and safety design are outside this article; national regulations, the project specification and expert review settle them.
Data to share for a technical review
· Feedstock type (biomass, tire, plastic or mixed), production process and storage conditions
· Water content (with method) and phase state for samples from several batches, and if possible after a period of storage
· Solids content, particle size distribution and planned strainer fineness
· Viscosity at different temperatures or a viscosity–temperature curve; a thermal stability or holding test result if available
· Density and its temperature dependence; pH and total acid number; sulfur, chlorine and metals depending on feedstock; electrical conductivity if possible
· Minimum, normal and maximum flow; operating pressure and temperature; pump type, suction condition and tank unloading arrangement
· Purpose of measurement (process monitoring, consumption or sale) and billing unit (mass or volume)
Related pages and articles
Related pages
· Pyrolysis oil metering skids: Skid structure, a general review of meter technologies and the use of density data.
· Pyrolysis oil facilities: Feedstock-dependent product properties and facility-wide design inputs.
· Heated transfer systems for pyrolysis oil: Setting the heating window against the thermal stability limit.
· Coriolis mass flow and density meters: Measuring principle and the effect of entrained gas on Coriolis measurement.
· Coriolis or positive displacement meter for truck loading?: Details of the decision between the two technologies in a loading application.