Pressure-Volume+calculations

=Pressure/Volume Calculations= A “floating drum” storage offers a good, simple way of measuring gas production. You just record the change in height of the drum and volume of gas = area * height (area of a circle = pi Dsquared/4 or pi Rsquared and there are 1000 litres in a cubic metre). If you want more accuracy use a small diameter drum with greater height to get the necessary capacity. Pressure and volume of any gas are related by p1v1=p2v2, where p is pressure, v is volume and 1 represents the initial conditions and 2 is the final conditions. Mass and volume are related by density, where Density = Mass/Volume and the density of biogas is about 1.18 kg/m3. The easiest way to develop the pressure needed for burners etc is to add weight to the drum (bigger diameter – more weight, since Pressure = kg*9.8/sq.metres) and if you measure “pressure” in mm of water you need to know Pressure (Pa) = 9.8 *Height (mm). I think that should let you calculate anything you need and I hope you understand the “useful” metric units I have used.

I have set up a spreadsheet to do the hard work, which provides the example below for you to practice on.


 * ===Calculations for gas volume=== |||||||||| C Paul Harris, November 2010 Version 1.0 ||
 * ====Volume of gas==== ||  ||   ||   ||   ||   ||   ||   ||
 * Diameter of Container || 1.3 || m ||  ||   ||   ||   ||   ||
 * Height || 1.2 || m ||  ||   ||   ||   ||   ||
 * __Volume Contained__ || 1.593 || m3 or || 1593 || litres ||  ||   ||   ||
 * ====Volume change with pressure==== ||  ||   ||   ||   ||   ||   ||
 * || mm Water || Pa ||  ||   ||   ||   ||   ||
 * Initial Pressure || 10 || 101398 ||  ||   ||   ||   ||   ||
 * Final Pressure || 20 || 101496 || Requires || 13.3 || extra kg ||  ||   ||
 * __Final Volume__ ||  || 1.591 || m3 or || 1591 || litres ||   ||   ||
 * Volume at Atmospheric Pressure || 1.594 || m3 ||  ||   ||   ||   ||
 * ====Mass of gas==== ||  ||   ||   ||   ||   ||   ||   ||
 * Density (Cmp 60% CH4) || 1.1607 || kgm-3 |||||| (At Atmospheric pressure) ||  ||   ||
 * __Mass__ || 1.851 || kg or || 1851 || g ||  ||   ||   ||
 * ====Volume change with temperature==== ||  ||   ||   ||   ||   ||
 * (based on Final pressure and volume!) ||  ||   ||   ||   ||   ||
 * ||  || Fixed Vol. |||| Fixed Press. ||   ||   ||   ||
 * ||  || Pressure || Volume ||   ||   ||   ||   ||
 * ||  || (Pa) || (m3) ||   ||   ||   ||   ||
 * Initial Temperature (C) || 20.0 || 101496 || 1.591 ||  ||   ||   ||   ||
 * __Final Temperature (C)__ || 30.0 || 104958 || 1.646 ||  ||   ||   ||   ||
 * || Notes ||  ||   ||   ||   ||   ||   ||
 * |||||||| Enter initial data in yellow cells ||  ||   ||   ||
 * |||||||||||| Enter Final pressure and temperature in the orange cells ||  ||
 * |||||||||||| If you know the mass adjust the Final Pressure to get the pressure resulting from that mass. ||  ||
 * || Notes ||  ||   ||   ||   ||   ||   ||
 * |||||||| Enter initial data in yellow cells ||  ||   ||   ||
 * |||||||||||| Enter Final pressure and temperature in the orange cells ||  ||
 * |||||||||||| If you know the mass adjust the Final Pressure to get the pressure resulting from that mass. ||  ||
 * |||||||||||| If you know the mass adjust the Final Pressure to get the pressure resulting from that mass. ||  ||