Gas measurement professionals know that gas measurement is a complicated process. It takes place in real-world settings with many variables thrown into the mix.
Accounting for these variables, performing accurate calculations, and having a firm grasp of the fundamentals of gas measurement will ensure an accurate measurement each time.
The key is understanding how to get the conditions right to perform an accurate measurement of natural gas. Meeting this objective will ensure that your company, third-party contract holders, and back-office support personnel can rely on the measurement you are reporting from the field.
What Are the Base Conditions for Measuring Gas?
One of the building blocks for an accurate natural gas measurement is understanding the base conditions for measuring gas. These are the three most important components:
- Contract pressure base
– Consider the types of pressures involved in gas measurement.
Absolute pressure is measured relative to “zero pressure” or what the pressure would be inside a vacuum. Comparatively, atmospheric pressure is a measurement of the force applied by an external factor — the atmosphere.
Then, gauge pressure is defined relative to atmospheric pressure — positive for pressures above atmospheric pressure and negative for pressures below atmospheric pressure.
– Understanding temperature requires a brief chemistry lesson. Specifically, Charles’ Law states that “the volume of an ideal gas at constant pressure is directly proportional to the absolute temperature.”
However, there are times when temperature needs to be “corrected” in natural gas measurement. Why is this? As noted by ASGMT, there is about a 1 percent change in volume for each 5 degrees Fahrenheit change in temperature. That is significant in gas measurement.
– The contract pressure base is another critical determinant. The contract between your company and third-parties will typically state the base pressure and base temperature values.
It’s also important to understand the role of atmospheric pressure in contracts. This measurement is typically influenced by a combination of the sea level where the measurement takes place and a barometer reading of the atmosphere at the time of the measurement.
Understanding these factors at the time of the measurement is critical to get the conditions right for accurate measurement.
What Other Factors Affect Gas Measurement Conditions?
We will also consider three additional factors that need to be taken into consideration to achieve an accurate natural gas measurement.
1. Standard Cubic Feet
A standard cubic feet (scf) is the universally-accepted gas measurement unit that governs the contract between two parties.
The scf unit is known as the accepted standard where 1 cubic foot is measured at 14.73 psia (pressure) and 60 degrees Fahrenheit (temperature).
Being able to achieve accurate readings of both the pressure and temperature is critical, especially when dealing with a large volume of gas. A slight error or misreading could become a significant error when multiplied by thousands, millions, or billions of standard cubic feet.
2. The Heating Valve
Another unit of measurement that affects natural gas measurement is the Btu (British Thermal Unit). This is the baseline measurement unit used to determine the energy content of gas exchanged. Said another way, the amount of heat necessary to raise 1 pound of water by 1 degree Fahrenheit.
In gas measurement, the natural gas heating valve is expressed as Btu per square foot. This measurement can vary significantly because of factors such as the atmospheric pressure and the external temperature (is it very hot or very cold where the measurement is taking place?).
Accounting for these variables is critical to support an accurate measurement of the heating valve.
3. Calculating Mass
One of the most important calculations in physics is determining the density of gas, which is mass divided by volume. In natural gas measurement, it’s important to identify the mass or weight of the gas to align with the stated terms in the contract.
Using the Ideal Gas Equation, we can rearrange the formula to calculate the mass of a gas sample. But, we are reminded that pressure and temperature affect the accuracy of the measurement.
To obtain an accurate measurement, pressure and temperature must be factored into the equation to accurately calculate the mass.
Receive Training on the Fundamentals of Gas Measurement
Getting the conditions right for natural gas measurement requires a fundamental understanding of the factors that need to be accounted for. This will allow you to perform an accurate measurement each time.
To ensure that you are supporting contracts and back-office reporting, consider receiving training on gas measurement.
We offer a Gas Measurement Fundamentals certification course that covers the base conditions for gas measurement, plus several other critical modules from the AGA white paper, Natural Gas Measurement Technician Training and Development Guidelines.
We teach directly from the AGA industry standard to ensure that you return to the field with confidence to support your company with accurate measurement.