How to Calculate Hydrogen Pipeline Odorant Injection

Definition and compliance context

Odorant injection rate expresses the mass or volume of odorant required per hour to maintain a specified concentration in a flowing hydrogen stream. Regulators typically define target concentrations in milligrams per standard cubic metre (mg/Sm³) or equivalent units. Because hydrogen projects often operate at lower pressures and with different odorants than natural gas, engineering teams must recompute setpoints rather than rely on legacy tables.

The calculation here assumes steady-state flow at standard conditions. When the pipeline experiences large transients or when batch odorization strategies are deployed, apply the same equations to each distinct operating window and document the highest requirement as the controlling setpoint. Pair this work with emissions tracking such as the hydrogen blend emissions intensity walkthrough to keep safety and climate objectives aligned.

Variables, symbols, and units

Collect the following inputs when preparing an odorization plan:

• Q – Pipeline flow rate (Sm³/h). Hydrogen throughput expressed at standard temperature and pressure.
• C_t – Target odorant concentration (mg/Sm³). Regulatory or internal safety requirement.
• ρ_o – Odorant density (kg/L). Measured at storage temperature; often 0.98 kg/L for tetrahydrothiophene blends.
• A – Injection availability fraction (unitless). Portion of time the dosing system can operate (e.g., 0.95 for 95% uptime).

Flow should reflect the maximum credible operating scenario. If hydrogen is blended with natural gas, base Q on the total standard volumetric flow of the blended stream. Adjust concentration targets when regulatory requirements specify minimum odor intensity rather than a mass fraction; the equations still apply once that intensity is translated into mg/Sm³.

Formulas for mass and volumetric injection

With the inputs defined, compute the dosing requirement as follows:

M represents odorant demand in milligrams per hour. Divide by 1,000 to obtain grams per hour (ṁ) or by 1,000,000 to obtain kilograms per hour (ṁ). Finally, divide by density to convert to litres per hour (V̇) for pump setpoints. The availability factor A rescales the requirement when pumps, storage, or redundancy limit continuous operation; A defaults to 1 when injection is available 100% of the time.

Always round the resulting flow upward to maintain compliance under meter uncertainty. Document any safety margin applied so inspectors understand the relationship between the calculated minimum and the installed setpoint. When designing multi-pump skids, allocate the required V̇ across duty and standby pumps, ensuring the duty unit can meet the full rate should the standby be offline.

Step-by-step dosing workflow

1. Confirm regulatory targets

Review national codes, project-specific permits, and offtake agreements to identify the minimum odorant concentration. Some jurisdictions specify a range or allow temporary deviations during startups; note these clauses so the dosing system can adapt if conditions change.

2. Characterise flow scenarios

Use network simulations or operational history to determine peak, average, and minimum flow rates. For storage-connected systems, include drawdown scenarios where flow may spike as linepack is used, referencing the results of your linepack flexibility study to ensure coverage across the full operating envelope.

3. Select odorant blend and density

Choose an odorant compatible with hydrogen and downstream equipment. Measure or obtain the density at storage temperature. If the supplier provides a range, use the highest density to avoid underdosing when temperature rises.

4. Determine availability allowance

Evaluate pump redundancy, maintenance schedules, and energy supply reliability. Convert the expected uptime into fraction A. A lower A increases the nominal rate so the dosing system meets the concentration requirement even when operating intermittently.

5. Compute and document setpoints

Apply the formulas to each flow scenario. Record the highest grams-per-hour and litres-per-hour requirements as the controlling setpoints. Archive calculations with supporting assumptions, including temperature corrections and supply chain notes, for regulatory review.

Validation and monitoring

After commissioning, validate odorization by sampling gas at representative downstream points. Compare measured concentrations against the target, adjusting pump stroke lengths or speed controls as necessary. Align sampling frequency with risk assessments and integrate alarms that trigger when injection deviates beyond tolerance for more than a defined interval.

Monitor storage tank levels and pump performance to confirm the assumed availability fraction remains accurate. Unexpected downtime should prompt a recalculation of setpoints or an operational change—such as rotating pumps or increasing preventive maintenance—to maintain compliance.

Limitations and considerations

The calculation presumes standard conditions; real gas effects can introduce small deviations at elevated pressures or temperatures. Incorporate compressibility factors if regulators mandate in-situ concentration verification under non-standard conditions. Additionally, some odorants degrade in storage or adsorb onto pipeline walls—track these losses separately and adjust the setpoint if audits reveal significant depletion.

Finally, remember that odorant selection can influence downstream processes such as fuel cell catalysts. Collaborate with offtakers to verify compatibility and to define contingency plans should odorant carryover exceed their thresholds.

Embed: Hydrogen pipeline odorant injection calculator

Provide standard flow, concentration target, density, and optional availability to calculate the mass and volume rates required for your odorant dosing skid.