Proportional, traceable additive dosing into a chemical product is achieved by tying the additive quantity to the signal from the main product meter. An injection controller follows the product throughput, delivers additive at a preset ratio through an injector or dosing pump, verifies the delivered additive with its own measurement, and raises an alarm when the ratio drifts. At the end of each load or transfer, the additive quantity is recorded alongside the product quantity, so it can later be shown that every shipment actually received the right dose.
Additive injection is usually built into the truck loading line, whose general layout is described on our truck loading systems page. Additive injection at biofuel terminals, which revolves around fuel specifications and coordination with blending, has a separate page.
What additives are used for at chemical terminals
At chemical terminals, additives are typically used to protect product properties during transport and storage or to meet a customer-specific specification. Examples include inhibitors for products prone to self-reaction, stabilizers against oxidation, dyes or markers for product identification, and specialty additives defined in a customer contract. Whatever the additive, it is usually dosed at a very small ratio to the main product, and under- or over-dosing affects product quality directly.
How proportional injection works
1. The main product meter generates pulses or a digital signal proportional to throughput.
2. An injection controller, or a batch controller with additive control, reads that signal and calculates the target additive quantity from the set ratio.
3. An injector valve or dosing pump delivers additive into the line, either continuously or at fixed product-volume intervals.
4. Measurement on the additive line compares the delivered amount with product throughput and trims injection in real time.
5. If the ratio leaves its tolerance band an alarm is raised, and depending on project requirements the loading permissive can be withdrawn to stop the transfer.
6. At the end of the transfer, additive total, product quantity and ratio are written to the transaction record and passed to the terminal automation system.
Injection methods compared
Method | How it works | When it is considered |
Metered valve injector | A solenoid valve admits additive from a pressurized supply header, with a small meter measuring each dose | Terminals where several arms share a common additive supply header |
Piston injector | Each stroke delivers a fixed volume; the number of strokes follows product throughput | Low-ratio applications where a constant dose volume is easy to maintain |
Continuous dosing pump | Pump speed or stroke is adjusted to product flow and additive is delivered continuously | Cases needing a uniform ratio throughout the load, or higher additive ratios |
Tank or batch addition | Additive is added in bulk to the storage tank or a preparation vessel | Where proportional injection is not required and the whole inventory takes the same additive; mixing uniformity must be verified separately |
Injection point and mixing
Where the additive enters the line has consequences for both measurement and quality. If it is injected upstream of the main product meter, it is measured as part of the delivered quantity; if injected downstream, the additive has to be accounted for separately. That choice should be made together with how the product is metered for sale. An injection point too close to the loading arm may not leave enough pipe length for mixing, while one too far upstream leaves additized product sitting in the line at the end of a transfer. Keeping additive supply pressure above main line pressure, and a check valve that stops product backing into the additive line, are standard features of any injection point.
Additive compatibility with the product and materials
A concentrated additive can be far more aggressive than the main product. Materials for the additive tank, feed pump, injector, small-bore tubing and seals are therefore selected independently of the main line, based on the stability, reactivity and incompatibility information in the additive's safety data sheet. If one injection skid will handle different additives in turn, their compatibility with each other and with the wetted materials, and the flushing applied at each change, must be defined. For additives whose viscosity changes noticeably with temperature, ambient effects on small-bore lines can upset dosing accuracy.
Dose verification and records
· Per-dose measurement: Giving each injector its own additive measurement prevents a missed dose from going unnoticed.
· Ratio deviation alarm: Target and actual ratio are compared continuously; which deviation triggers an alarm and which stops loading is agreed with operations.
· Periodic verification: Injector output is checked by delivering into a vessel of known volume, and the meter factor is updated if needed.
· Transaction record: Additive type, total, ratio and alarms are kept in the same record as the product transfer and passed to the terminal automation or enterprise systems.
How TLY Enerji supports additive projects
For additive injection at chemical terminals, TLY Enerji can provide engineering support in selecting product and additive measurement, integrating injection control into the existing batch controller, PLC or SCADA architecture, and in field installation, testing and commissioning. Whether additive storage and feed equipment fall within scope is decided by the project specification.
Information to prepare for an additive injection review
· Additive type, target ratio and allowable ratio tolerance
· Main product flow range and number of arms or lines to be additized
· Additive safety data sheet, viscosity and storage conditions
· Number of additives on the same skid and how often they change
· How the product is metered for sale and where injection is wanted relative to the meter
· Expected response to a ratio deviation: alarm only, or stop loading
· Existing batch controller, terminal automation and reporting interface
Related pages
· Additive injection systems for biofuel terminals: Additive injection coordinated with fuel specifications and blending.
· Batch metering systems for chemicals: Target-quantity cutoff and batch records, the transaction structure additive data is tied to.
· Automated truck loading terminals: How additive data joins the order, permissive and reporting flow.
· Chemical metering skids: Technology and material selection for main product metering.
Additive injection FAQ
Should additive be injected upstream or downstream of the product meter?
Both arrangements are used, and the choice depends on how the product is metered for sale. Additive injected upstream is measured within the delivered quantity; additive injected downstream has to be accounted for separately. Mixing length and the amount of additized product left in the line at the end of a transfer also matter. The decision should be made with the metering authority and customer requirements in view.
How can you prove the additive was actually delivered?
Each injector's output is measured separately and compared with main product throughput. A ratio deviation raises an alarm and, depending on project requirements, withdraws the loading permissive. At the end of the transfer the additive total and ratio are written to the transaction record. Periodically checking injectors against a vessel of known volume shows that the additive measurement itself is still accurate.
Can one injection skid handle several additives?
Yes, but the additives' compatibility with one another and with the line materials, the flushing used at each change, and the measures that stop one additive carrying over into the next product all have to be defined. Where additives are incompatible or change frequently, a dedicated injector and supply line per additive is the safer route.
How does chemical additive injection differ from fuel additive injection?
The hardware logic is similar: proportional dosing tied to product metering, plus verification. The difference lies in the product and the purpose. At fuel terminals, additives are mostly considered together with fuel specifications and blending. At chemical terminals, chemical compatibility between additive, product and equipment materials, customer-specific specifications and safe handling of concentrated additives come to the fore.