Hydrogen production by feedstock

The category at business/processes/production/hydrogen/consumption provides a methodology for calculating greenhouse gas emissions associated with the production of hydrogen. The methodology is based on a mass-balance approach taking into consideration the carbon content of process feedstocks and and carbon or CO₂ recovered for use in other processes. This methodology is sourced from the guidelines published in conjunction with the EPA's mandatory greenhouse gas reporting requirements, and follows approaches described by the IPCC Guidelines for National Greenhouse Gas Inventories (NGGIP) and the New Mexico Environment Department Air Quality Bureau Emissions Quantification Methods publication.

To use this category, simply create a profile item - there are no drill choices.

Next, specify the quantity of feedstock consumed. This can be done in one of two ways:

• Directly, by setting the quantity using the massFeedstock profile item value.

• By specifying both the total quantity of hydrogen produced and the quantity of feedstock required per unit of production using the massHydrogen and massFeedstockPerMassHydrogen profile item values.

In either case, the carbon content of the feedstock needs to be specified using the feedstockCarbon profile item value. Users can additionally specify the fraction oxidation achieved for the feedstock is appropriate using the feedstockOxidation profile item value (decimal fraction, i.e. 0-1), although this defaults to 1 (i.e. 100% oxidation) if left unspecified. The returned value represents CO₂ emissions associated with the consumption and properties of feedstock specified.

Carbon and CO₂ recovery

User have two options for specifying quantities of recovered carbon which is diverted for use in other processes. These refer to recovered carbon as opposed to recovered CO₂. In both cases, these are subtracted from the emissions associated with feedstock consumption. To specify a quantity of carbon recovered, set the carbonRecovered profile item value. To specify a quantity of CO₂ recovered, set the CO2Recovered profile item value. Users should be careful to specify the appropriate value for recovered carbon, the two options differing by a factor of 3.5.

Time-dependent calculations

Each of the values described above represent data describing the performance and processes of a single or multiple facilities. Each of these values can be expressed in terms of a specific period of time, by using the -Unit and -PerUnit profile item designations. In conjunction, users can set the duration for which the facility was in operation, by setting the operatingDuration profile item value. In this case, Discover automatically takes into account the time basis of each quantity.

For example, users may wish to specify their feedstock consumption in terms of a quantity per day, in which case they could specify;

• massFeedstock=100
• massFeedstockUnit=t
• massFeedstockPerUnit=day

This rate of feedstock consumption will be fed into the algorithm. If users specify an operating time for the facility in terms of say hours (h), days (day) or years (year), for example, Discover will handle the necessary conversions and return a value for emissions during the specified operating time. Users can therefore mix the time bases for the different quantities specified if desirable.

User should note that, in the case where all values use the same basis for time, the emissions calculation simply reflects the absolute values for consumption/recovery specified and is effectively independent of particular timeframe. This is the default condition of the calculation: all values are specified on an annual basis with the operating time assumed to be 1 year. As such, if the operatingDuration is left unspecified the returned emission simply reflects the absolute inputs.