Urea and Ammonia Consumption Calculator

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Engineering Guide · Design Calculators

Urea and Ammonia Consumption Calculator

The amount of reagent needed for DeNOx is the number of moles of NOx to be removed multiplied by the normalized stoichiometric ratio (NSR). In theory, ammonia (NH₃) reacts with NO mole for mole, and one mole of urea (CO(NH₂)₂) treats two moles of NO.

How Is Reagent Consumption Calculated?

4NO + 4NH₃ + O₂ → 4N₂ + 6H₂OAmmonia reacts with NO in a 1:1 ratioCO(NH₂)₂ + H₂O → 2NH₃ + CO₂One mole of urea yields two moles of ammonian = Q × (Cin − Cout) × 10⁻⁶ ÷ 22.414n NO to be removed (kmol/h), Q flue gas flow (Nm³/h), C concentration (ppm)NH₃ = n × NSR × 17.031, Urea = n × NSR ÷ 2 × 60.06kg/h. Solution consumption = active ingredient ÷ strength; volume = mass ÷ specific gravity

This calculation treats all NOx as NO. If the NO₂ share is high, consumption increases, because each mole of NO₂ needs 4/3 moles of ammonia.

Worked Example

StepCalculationResult
NO to be removed50,000 × 100 × 10⁻⁶ ÷ 22.4140.2231 kmol/h
Urea (100%)0.2231 × 1.0 ÷ 2 × 60.066.70 kg/h
40% urea solution6.70 ÷ 0.4016.75 kg/h
Urea solution volume16.75 ÷ 1.1115.1 L/h
As ammonia0.2231 × 17.0313.80 kg/h

Flue gas of 50,000 Nm³/h with inlet NOx of 150 ppm reduced to 50 ppm, at NSR 1.0, using 40 wt% urea solution (specific gravity 1.11).

Why Is Actual Consumption Higher Than Calculated?

  • Reaction efficiency: Not all of the reagent reacts with NOx. Some passes through unreacted (ammonia slip) or is consumed by side reactions.
  • Mixing: Poor injection location or uneven mixing means more reagent is needed to remove the same NOx.
  • Temperature: SNCR works in a high-temperature window, while SCR and catalytic filters depend on the catalyst's active temperature range. CataFill™ applies at 120–200°C flue gas, with 180°C or higher recommended for NOx reduction. When urea is used with a catalytic filter or low-temperature SCR, it is usually converted to ammonia in a separate hydrolysis or thermal decomposition unit before injection.

Frequently Asked Questions

What is NSR?

NSR (normalized stoichiometric ratio) is the amount of reagent actually injected divided by the theoretical amount required. An NSR of 1.0 means exactly the stoichiometric amount is injected.

Should I use urea or ammonia?

Both are used as DeNOx reagents. Urea solution is relatively easy to handle and store, while aqueous or anhydrous ammonia requires dedicated storage and safety systems. Review the system configuration together with the applicable safety and permitting requirements.

Should ppm be entered on a dry basis?

Use the same basis for gas flow and concentration. If the gas flow is in dry Nm³/h, enter NOx in dry ppm as well. Also enter the measured concentration before oxygen correction; using an O₂-corrected emission limit value directly will give the wrong consumption.

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By the Micro-one R&D Center · Last updated November 1, 2026 · All Engineering Guide pages →

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