gas consumption calculations

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vinodbabu
Posts: 2
Joined: Wed Mar 09, 2011 5:53 pm

gas consumption calculations

Post by vinodbabu »

Hello everyone, I just joined the forum.
We have a Batch fryer in our Food Processing plant. There is a sensus Gas flow meter to record the flow of gas. We use LPG which is stored in a sphere, underground. The Gas supplier bills us for LPG in MT.(assume in liquid form). Now how do I calculate consumption and therefore cost of the LPG per pound of cashews /nuts roasted. The flow meter readings in Cub M/hr are recorded at start of fryer and after shut down of fryer, during which time "X" lbs nuts would have been roasted.Obviously we have to trace the consumption in vapour form to liquid form, to find out the costs.

VinodBabu
admin
Site Admin
Posts: 375
Joined: Mon Feb 08, 2010 7:47 pm

Re: gas consumption calculations

Post by admin »

First you need to know if the flow rate of gas mixture that measured is on real condiotions with some pressure that is above atmospheric or is it already converted to standard conditions with volume corrector.

If the flow rate that is measured is alresady converted to standard condition, calculation of mass flow rate is straight forward. You must know the composition of mixture - propane butane ration - like 30-70% or so. Than density of that mixture can be calculated based on the density of every single component and its participation in mixture. Here is the theory on how to calculate fluid mixture density:
http://www.pipeflowcalculations.com/pip ... ixture.php.
Components density should be used on standard conditions and you have table for it at:
http://www.pipeflowcalculations.com/tables/gas.php.

When you have fluid mixture density, than measured flow rate should be multiplied with density to have weight flow rate:
G=Q x rho
G - weight flow rate - which is the same for gas and liquid
Q - measured flow rate - volume
rho - mixture density

If measured gas flow rate is not converted to standard conditions than density of every single component should be used on the pressure and temperature that is on the point of flow rate measurement. Which means you should use component density on standard conditions and using gas state equation, calculate density on given pressure.

p1/rho1=RT1

p1/p2 * rho2/rho1 = T1/T2

if 1 - is for standard conditions than

rho2 = rho1 * T1/T2 * p2/p1
Pipe flow calculations - since 2000
vinodbabu
Posts: 2
Joined: Wed Mar 09, 2011 5:53 pm

Re: gas consumption calculations

Post by vinodbabu »

Dear Administrator,
Thanks!
That was really enlightening!
Vinod
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