Batch metering and traceability for pyrolysis oil come from tying every metered quantity, through the record, to one quality lot, to a representative sample drawn from that lot, and to the analysis of that sample. The meter tells you how much product moved; the lot number, the sample and the lab report tell you what moved. If those three never meet in the same record, even a correctly metered quantity cannot be defended in front of the buyer.
Cut-off at the target, staged valve closure and overrun compensation are covered on the batch metering page for chemicals. This page applies them to pyrolysis oil, whose composition changes from lot to lot, and builds quality traceability around the metered quantity.
Two different meanings of batch
At pyrolysis plants the word batch is used in two senses, and the design has to keep them apart:
· Quality lot: Product made from the same feedstock mix under the same process conditions, collected in one tank and treated as homogeneous. The certificate of analysis belongs to the lot.
· Transfer batch: A single delivery of a target quantity from a lot to a truck, a process unit or another tank. The meter ticket and the preset belong to the batch.
One lot can feed several transfer batches. The reverse, two lots ending up in one delivery, should only happen as a deliberate, recorded blending decision. The job of the batch metering system is to record which lot every transfer batch came from in a way that leaves no room for argument.
Why each lot has to be treated on its own
Pyrolysis oil properties depend on the feedstock (tires, plastics, biomass) and on the process. Even the published typical ranges for biomass fast pyrolysis oil are wide: IEA Bioenergy lists 20–30 wt% water, a density of 1.10–1.30 g/ml at 15 °C and a viscosity of 15–35 cSt at 40 °C. No verified general data set exists for tire- or plastic-derived oils; for those products the values must come from their own analyses.
A single lot also changes with time: biomass pyrolysis oil ages, showing a gradual viscosity rise that is fastest in the first weeks and speeds up with temperature. Sample date, the time between analysis and shipment, and storage conditions in between therefore belong in the batch record.
Which quantity should be recorded?
Volume is a weaker basis for pyrolysis oil than it first appears. The general temperature and pressure volume correction procedures used for petroleum are scoped for generalized crude oils, refined products and lubricating oils; nothing supports applying them directly to a water-rich, polar biomass pyrolysis oil. If the contract is based on volume, a product-specific density versus temperature relationship has to be established in the lab and written into the agreement with the buyer.
For this reason, recording mass is often the simpler route. A Coriolis meter measures mass flow, density and temperature at the same time. The average density logged over a transfer can be compared with the density on the lot's certificate of analysis, giving an early warning of a draw from the wrong tank or of phase-separated product. Density alone does not define quality; it is a consistency check. Meter technology selection is covered on the pyrolysis oil metering skids page.
A representative sample is taken during transfer, not from the tank top
Sampling problems with pyrolysis oil come from its tendency not to stay homogeneous. Biomass oils are usually single-phase, but depending on feedstock and process a lighter top phase may separate; with aging, an aqueous phase can separate once total water passes a certain level; and solids can settle into a sludge layer at the tank bottom. A spot sample from the top of such a tank may not represent what the pump is actually drawing.
Flow-proportional automatic sampling on the transfer line builds a composite sample spread across the whole batch. Automatic pipeline sampling standards for petroleum liquids give the framework, but they were written for petroleum products, so sampler mixing, plugging and materials must be checked for pyrolysis oil on each project. The European fast pyrolysis bio-oil standard also has an annex on sampling and materials compatibility.
· Sample container material: Containers and caps must suit an acidic product; for biomass oils, stainless steels and plastics such as PTFE, HDPE and PP are reported as suitable.
· Sample splitting: The composite is split into buyer, seller and retained portions, and each container's seal number goes into the batch record.
· Retention conditions: For a product that ages, storage temperature of the retained sample affects later results, so retention temperature and duration should be defined in the contract.
What upsets the target quantity with pyrolysis oil
The quantity that passes after the close command, the overrun, depends on viscosity and flow rate. Because pyrolysis oil viscosity shifts both from lot to lot and with line temperature, automatic overrun compensation that averages recent batches can drift for a while after switching to a new lot. Holding line temperature steady during transfer and restarting the compensation learning whenever the lot changes reduces this effect.
Solids add a second risk: deposits on the control valve seat can stop full closure and leave a small unmetered leak after the batch. Batch controller no-flow, leakage and overflow detection helps here, together with straining upstream of the valve and periodic seat-tightness checks.
Linking the batch ticket to the quality certificate
Links a transfer batch record needs for traceability
Record field | Why it is needed | Where it comes from |
Lot number and source tank | Connects the delivered product to its certificate of analysis | Tank management or operator selection, confirmed by the control system |
Preset and delivered quantity, with unit | Comparison with the contract quantity | Batch controller |
Average temperature and density | Consistency check against the certificate | Meter and temperature measurement |
Sample ID and seal numbers | Decides which sample governs in a dispute | Sampler and operator entry |
Lab report number and date | Makes the product's age visible | Laboratory system |
Line status and events | Whether the line was full or empty at start and end, interruptions, alarms | Control system event log |
The batch certificate handed to the buyer summarizes this record. Published specifications for biomass pyrolysis liquids define properties such as water, solids, viscosity, density, acidity and flash point, but they cover biomass-derived oils only. For tire- and plastic-derived oils, the contents of the certificate are a matter for the sales contract. If the sale is based on the meter ticket, whether legal metrology requirements apply has to be checked separately against national legislation.
How TLY Enerji can help
Depending on project scope, TLY Enerji provides engineering support for selecting the meter, control valve and sampling equipment based on the oil's analysis data, for supplying that equipment, for integrating batch control into the plant PLC or SCADA system, for collecting and reporting batch records, and for site installation and commissioning. Lot definition and the laboratory process remain the operator's responsibility; the metering system is designed to connect to them.
Information needed to design batch metering
· How a quality lot is defined at your plant: production campaign, tank or feedstock change
· Viscosity versus temperature, density, water and solids data from several lots
· The quantity unit agreed with buyers and the acceptable deviation
· Sample splitting and retention practice, and whether a link to the lab system is needed
· Transfer destinations: trucks, process feed or tank-to-tank moves
· Line heating arrangement and temperature range during transfer
Related pages
· Batch metering systems for chemicals: The general logic of staged closure and overrun compensation.
· Pyrolysis oil metering skids: Choosing meter technology for viscous oil that carries solids.
· Tank-to-tank transfer skids for pyrolysis oil: In-plant tank moves where quality lots are formed.
· Pyrolysis oil truck loading systems: Applying the batch record on the shipping side.
Questions on pyrolysis oil batch metering
Does a sample from the top of the tank represent the lot?
Not necessarily. In pyrolysis oil a lighter top phase can separate, an aqueous phase can form, and solids can build a sludge layer at the bottom. A spot sample from the tank top then does not reflect what the pump is drawing. A flow-proportional composite sample from the transfer line represents the whole batch far better; a tank sample only becomes meaningful after the tank has been homogenized.
Can pyrolysis oil be invoiced by volume?
The invoicing unit is agreed between the parties. Volume-based records, however, need correction to a reference temperature, and the general correction tables written for petroleum products have not been validated for biomass pyrolysis oil. If volume is chosen, product-specific density versus temperature data should be determined in the lab and written into the contract; recording mass avoids that step.
What changes in the batch controller when a new lot starts?
Because viscosity changes, the overrun that passes after the valve closes can change too. A compensation value learned on earlier lots may cause deviations for a while with the new product. Restarting the learning when the lot number changes, using a lower final-stage flow rate for the first transfers and keeping line temperature stable all make the transition smoother.
Which analyses should the batch certificate include?
That depends on the sales contract. Published specifications for biomass pyrolysis liquids cover properties such as water content, solids, kinematic viscosity, density, pH or acidity, ash and flash point. Tire- and plastic-derived oils fall outside those specifications, so for them the certificate content is set by the parties according to where the product will be used.