Nitrous Oxide emissions associated with 100% hydrogen boilers: research

Scope of Work

Measurements were performed using two instrumental continuous analysis systems as described below.

Nitrous Oxide and Water Vapour

These components were determined by a Fourier Transform Infrared (FTIR) analyser. A sample was extracted from the boiler flue via a heated sample transport and conditioning system.

The sample is passed to an Infrared measuring cell in which the absorbance of infrared radiation throughout the IR band is recorded. Fourier transform mathematics is then used to identify and quantify the compound of interest from a reference library which contains the absorbance characteristics of that compound. The instrument output was logged at 20 second intervals resulting in continuous real-time analysis.

Oxides of Nitrogen and Oxygen

Oxides of nitrogen, expressed as NOx and Oxygen were determined by a multi-gas analyser employing the following measurement techniques:

The sample is extracted from the boiler flue via a heated sample transport and conditioning system.

Oxides of nitrogen: The dried sample is passed to a chemiluminescence analyser which measures the light produced during the oxidation of NO to NO₂. Any NO₂ in the initial sample is first reduced to NO prior to analysis. The analyser therefore measures total NO + NO₂ as NOx. The instrument output was logged at 15 second intervals resulting in continuous real-time analysis.

Oxygen: The dried sample is passed to a zirconium oxide cell heated to approximately 650°C. The movement of oxygen ions across the zirconium oxide produces a voltage between the two electrodes which is proportional to the oxygen concentration. The instrument output was logged at 15 second intervals resulting in continuous real-time analysis.

Samples were taken during three modes of boiler operation.

1. Modulation – Similar to normal day to day domestic operation.

2. Low Fire – Central heating on.

3. High Fire – Central heating high, hot water running constantly.

The low fire rate is approximately equivalent to 6.40 kWh and the high fire rate approximately equivalent to 29.00 kWh.

The recorded sample data are expressed as average values for each test period.