ecoinvent Forum Archive

Hi,

the process "natural gas production [DE]" delivers "natural gas, high pressure" in m³. Is there any information about the exact pressure of the product to calculate the mass?

Thank you very much for your time.

Best regards,

Lukas

Dear Lukas,

thank you for your question. You are right that the exact conditions for natural gas networks at different pressure levels are not specified in ecoinvent. These will differ from system to system and with the gas compostion. We therefore recommend to scale the amount of natural gas required for your system based on itsheating value. The heating value for natural gas in ecoinvent is standardized to 39MJ/m3. Moreover, what you can find in the properties of the mentioned dataset is the dry mass of the ´natural gas, high pressure´, which in this case is 1kg/m3.

I hope this answer serves you.
Kind Regards,

Florentine Brunner
Data Analyst at ecoinvent

Hello

Are you sure about the density of 1kg/m3? I may be wrong but crunching some numbers that does not make sense to me.

CH4 has a density of 0.67 kg/m3 at 15 degC and 1 atm (the conditions used as reference in ecoinvent data quality guidelines).

C3H8 (propane) has a density of 1.86 kg/m3 at the same conditions

if we assume NG is only methane and propane, to have 1 kg/m3 you would need to have 72% of methane by volume, which is very low. usual ranges are 87%-97%

I did some back on the envelope calculations and I think that to have 39 MJ/m3 it would need to be 97.6% methane by volume, which seems more reasonable.

could you please confirm the density value?

another way to look it is emissions. I've been checking this and for other datasets and if you assume total oxidation of the fuel, you get a very good aproximation of CO2 emissions.

in the case of combusting natural gas, if density was 1kg/m3 it does not work.

take the Swish process "

" as an example.

it emits 2.18 kg CO2 per m3 of NG. NG is reported to have C content of 69% by mass. if 1 m3 was one kg, then we'd combust 0.69 kg of C per m3. For each 12kg C we have 44 Kg CO2, that is 2.53 kg CO2/m3 combusted. To be consistent with emissions density would need to be 0.86 kg/m3. Something does not work.

Dear Miguel,

thank you for pointing this out. The density of natural gas specified in the dataset ‘natural gas production, DE’ should indeed be in line with the density of 0.84 kg/m3, which matches the standard heating value of 39 MJ/kg.

Regards,

Florentine Brunner, Data Analyst, ecoinvent

Dear Florentine

where does the 0.84 kg/m3 value come from? I checked the UPR description of the process and I have not found a reference to the density.

You mention that the heating value of natural gas is standardised in ecoinvent to 39 MJ/m3. Does it mean all the datasets assume this value?

By chance I was checking the natural gas use "electricity production, natural gas, combined cycle power plant" in CA-ON and the natural_gas_net_heat_value is 39 MJ/m3. The comment specifies that is the lower heating value measured at 0C 1 atm. Other datasets refer to gross heating value of 39 MJ (without specifying the reference conditions of pressure and temperature).

is the 39 MJ (gross) heating value a standard and thus the reference to net heating value an error of the CA-ON dataset? or do different datasets have different heating values ? that would imply that there's no standard heating value for gas in ecoinvent.

thanks for the clarifications! Miguel

Thanks Florentine for the answers and thanks Miguel for the hints. I would be also interested in the source for the density of 0,84 kg/m3 as well as the standard lower heating value and if they are consistent within the database. I was not able to find it in the ecoinvent dataset documentation.

Thank you very much.

Lukas

Dear Miguel and Lukas,

The standard heating value for natural gas of 39 MJ/Nm3 refers to the Higher/Gross Heating Value. Although this is meant to be the default assumption for all datasets producing or using natural gas, you are right that there is a number of datasets in which the property “heating value, net” is set to 39 MJ/Nm3. I agree this is confusing and we are therefore doing our best to correct the issue and provide more explicit documentation on the matter.

Values for the density of natural gas originate from ecoinvent version 2, where a density of 0.84kg/Nm3 was defined for sweet gas and of 1 kg/Nm3 for sour gas (see Tab. 3.4, p. 6 in Faist Emmenegger et al. 2007, pdf report 06_V_Erdgas accessible in the report section of ecoinvent version 2). With the standardization of the gas quality to (sweet) gas of 39 MJ/Nm3 gross heating value, the density was standardized to 0.84 kg/m3. The density of 1kg/m3 in the dataset “natural gas production, DE” was hence mistakenly retained from before the introduction of standardized gas quality and stems from the sour nature of natural gas in Germany.

Reference: Faist Emmenegger M., Heck T. and Jungbluth N. (2007) Erdgas. In: Sachbilanzen von Energiesystemen: Grundlagen für den ökologischen Vergleich von Energiesystemen und den Einbezug von Energiesystemen in Ökobilanzen für die Schweiz (ed. Dones R.). Swiss Centre for Life Cycle Inventories, Dübendorf, CH

Kind regards,
Florentine Brunner
Data Analyst, ecoinvent

Hi, maybe the answer to the initial question is hidden in the upper discussion. I could however not find it.Is there a final answer on what is the mass of the process "natural gas production [DE]" delivering "natural gas, high pressure" in m³? Thank you very much.

Dear Christoph, The general comment of the dataset “natural gas production, DE” mentions 50% of produced gas to be sour gas. Using the densities of sour and sweet gas in (Faist Emmenegger et al. 2007, pdf report 06_V_Erdgas, mentioned above) of 1.00 kg/m3 and 0.84 kg/m3 (Tab. 3.4) respectively we arrive at a density of 0.92 kg/m3 for this particular producing activity.Best regards,Johannes Müller, Junior Data Analyst, ecoinvent association