Simulating DPM by Editing Various Airways

[Isabela]

Hi,

I am trying to model DPM concentrations by entering the g/kWh and kWh for various equipment in a mine on VentSim 5.2. At the moment, I am able to update this information when I edit an individual airway, but somehow, the EC levels remain at zero throughout the system. 

I was wondering if I am missing any key steps and how I can rectify this?

Thank you,

Isabela

[Martin Griffith]

Hi Isabela, 

To simulate diesel, as well as specifying the rate of diesel emission (g/kW.hr), you need to enter a diesel engine power (kW) as a point source. After that, make sure you are running the Diesel Simulation in the menu under the red Contaminant Simulation button on the toolbar, and not a different simulation type. 

If you still get zero CO, CO2 and DPM throughout the model, if possible please send me your model and we'd be happy to take a look.

regards,

Martin

[Alexandr]

Hi,

I simulate the spread of exhaust gases from diesel engines.
Found 2 ways to solve this problem - slide 1.
Method 1 - modeling of the exhaust gas content and volumetric air flow (which were measured), the "Gas" tab.
Method 2 - through the engine power and the debit of harmful substances, the "Heat" tab.
The recalculation was carried out according to the formulas - slide 2.
The initial data were entered into the model in the appropriate tabs, the results are presented on slides 3, 3.1, 4.

There are questions:
I would like to know which option is more correct?
Why is the ratio of NO and NO2 in NOx different when calculated by heat (slide 5)?
Why do the indicators of CO content differ in variants 1 and 2 of the calculation (slide 6)?
Is there a way to determine the content of harmful substances along the entire path of the vehicle?

 

Best wishes,

Balusov Alexander, lead engineer

Diesel.vsm

[Martin Griffith]

Hi Alex, 

Thank you for your post, I've been investigating. It took me awhile but I think much of the problem comes about here because the fixed flow in the gas part of the model is not Q = 0.1 m3/s, it's in fact 0.13 m3/s. This is an easy mistake to make when dealing with smaller than usual numbers. To fix it, go to Settings | Units, click on Contaminants PPM and Quantity and increase the number of decimal places. 

 

Further to this, I think there is some inconsistency between yourself and Ventsim about how concentrations are converted between mg/m3 and PPM. 

In Ventsim Diesel Simulation, only the CO, NOx and CO2 products are made (the three yield rates available in the Heat, Moisture, Diesel Presets), then a factor of 5% is used to calculate the fraction of NO2 in NOx. From your measurements you have a much higher ratio of NO2:NOx than 5%. You can change this setting in Settings | Simulation | Diesel | DieselNO2NOxratio. From your measured data, you want about 72%. 

I've attached a revised model (which makes the changes above) which gets the 2 simulation methods to agree. I've also attached a spreadsheet which shows how I went from the measured values in mg/m3 to PPM. If there is something about this that you don't agree with, or another way to calculate the concentrations, please let us know and we can discuss further. 

 

dieseldata.xlsx newDiesel.vsm

[Martin Griffith]

There is some further discussion in the Ventsim manual about the NO2:NOx ratio setting: 

"Diesel exhaust gas and particulate matter emissions are normally quoted by
regulatory agencies in terms of grams produced per kW engine output per
hour (g/kWh). Engine emission standards have been improved over time.
For example, a Tier 3 Diesel engine may have an Oxides of Nitrogen (NOx)
output of 9.2 g/kWh and CO 3.5 and PM 0.12, while a Tier 4 Diesel engine has a
considerably reduced NOx requirement of only 0.4 g/kWh NOx. A useful source
of information on engine output is available from the EPA United States
Webpage.

A complicating part of measuring and modelling NOx gases is that this is a
composite of 7 different forms of nitrogen / oxygen molecules. The main health
concern is the NO2 component which has a limit for exposure of around 2-
3ppm, however the presence of NO2 is highly dependent of the presence of
Ozone (O3) which is responsible for much of the formation of NO2 gas from
NOx. Typically in urban environments, the ratio of NO2/NOx may be between
Chapter
22

Tier Standards - Gas Emissions

10% and 30%, however in underground mining, away from the atmosphere
and sunlight, the ratio may drop to only 2%.
To provide an indicative NO2 value for modelling and design improvement
purpose, VentSim assumes a ratio of 5%, however this is highly subjective and
should not be used for designing critical airflows or diesel equipment calculations
without calibration with measured results. The ratio can be adjusted in the
VentSim settings – simulation > Diesel.
settings – simulation > Diesel.
http://www.atmos-chem-phys-discuss.net/5/12723/2005/acpd-5-12723-2005.pdf

"

 

 

 

[Alexandr]

Hi, Martin

Thanks for your comments.

After reviewing your solution and reading additional literature, I am convinced that the actual NO2: NOx ratio is no more than 5%.

The Excel file contains the results of the actual measurements. As can be seen from the document NO2 / NOx is about 80%. As far as I understand, this is possible only in the atmosphere of the earth's surface with the participation of O3 and ultraviolet radiation, but not in the mine workings. Or the measurement was performed with an error.

Converting g / kWhr to mg / m3 and vice versa is similar to my version.

I don't quite understand the ratio of 24.45 in the calculation. I gave 2 options for translating mg / m3 to ppm and the calculation of mg / m3 to gkW / h. Also note how we calculate NOx in ppm and mg / m3.

How do you get NOx (heat preset) if there was only NO (measured) ?

Best wishes,

Balusov Alexander, lead engineer

dieseldata1.xlsx