Reference method for measuring releases of particulate from stationary sources: method C


Method C: Determination of Molecular Weight by Gas Analysis

3.1 Principle

An integrated or grab sample is extracted from a single point in the gas stream and analyzed for its components using an Orsat analyzer, a gas chromatograph, or calibrated continuous analyzers.

3.2 Apparatus

3.2.1 Integrated Gas Sampling Train

The following items are required:

Probe/Filter
A probe made of stainless steel, Pyrex, or other corrosion-resistant material to extract the sample from the stack or duct being tested. A filter is used to remove particulate matter from the gas sample.

Condenser/Water Trap
A condenser and water trap, or impingers to remove and trap moisture contained in the gas sample.

Control Valve
A valve to control the flow of gas in the sampling system.

Pump
A leakless pump to withdraw the sample gas through the sample train.

Rotameter
A rotameter, or equivalent device to measure the sample gas flow in the train. The unit should measure flows up to 2 L/min.

Sample Bag
A flexible bag of a non-reactive material such as Tedlar or Teflon, with a total capacity of 1L for each minute of anticipated sampling to hold the collected sample.

S-type Pitot Tube and Differential Pressure Indicator
A calibrated S-type pitot and a differential pressure device such as an inclined manometer to measure the gas velocity during sampling.

3.2.2 Grab Sample Apparatus

The following items are required:

Probe/Filter
See Subsection 3.2.1.

Pump
A squeeze bulb with a one-way valve to withdraw a sample from the stack or duct under test.

Analyzer
An Orsat analyzer, a gas chromatograph, or calibrated continuous gas analyzers to analyze the major constituents in the gas sample. The components measured should include, as a minimum, carbon dioxide (CO 2), oxygen (O 2), and nitrogen (N 2) by difference. Where an additional gas may affect the molecular weight by greater than 2%, this component must be measured and the resulting concentration included in the calculation.

3.3 Procedure

3.3.1 Integrated Sampling

Leakcheck the bag by connecting it to a water manometer and pressurizing the bag to 5 to 10 cm H2O. Allow to stand for 10 minutes. Repair or replace the bag if there is a decrease in the manometer reading after this time period.

Evacuate the sample bag using the sample pump, then assemble the equipment as shown in Figure C-1, leaving the sample bag disconnected. Ensure that all connections are leak-free. Place the sample probe in the stack or duct under test, and allow at least five minutes for the probe and optional filter to reach stack temperature. Turn on the sample pump and allow sample gas to purge air out of the system for about two minutes using a flow of approximately 1L/min. Turn off the sample pump and connect the sample bag as in Figure C-1.

Figure C-1: Integrated Gas Sampling Train

Integrated Gas Sampling Train

Turn on the sample pump and adjust the sample flow rate to one which will provide an adequate sample size, yet not overfill or burst the sample bag. The sampling rate, Q, is maintained proportional (K) to the stack gas velocity, Us, over the sampling period. Use Equation C-1 to calculate the sampling rate and adjust the control valve to maintain the sampling rate indicated by Equation C-1 throughout the test.

Equation C-1
Sampling rate Equation

At the completion of sampling, turn off the pump, then seal and disconnect the sample bag. Analyze the bag contents using the procedures provided in Section 3.4.

3.3.2 Grab Sampling

This procedure provides an analysis of the stack gas constituents which is not as complete as would be provided by the procedure given in Subsection 3.3.1 and should only be used when the previous procedure cannot be applied.

Set up the apparatus as shown in Figure C-2, but do not connect the analyzer(s). Ensure that all connections are leak-free. Place the probe in the duct or stack and purge the system with stack gas using the squeeze bulb for a minimum of one minute. Connect the analyzer(s) to the discharge side of the squeeze bulb. Follow the manufacturer’s instructions regarding the recommended quantity of gas that should be provided to the analyzer(s) and any flow rate recommendations.

Figure C-2: Grab Sample Apparatus

Grab Sample Apparatus

3.3.3 Continuous Source Monitoring

A continuous (real-time) source monitoring system may be utilized to measure the concentrations of the major gas components. A monitoring system of this nature would normally be operated as part of a larger testing program. The setup and operation of such a system is beyond the scope of this document; therefore, specifics will not be provided in this method. Where data from such a system are used, the system must be calibrated using verified reference gases. A table of the calibration gases used must be provided as well as the procedures followed in calibrating and operating the system. A diagram of the continuous source monitoring system must also be supplied.

3.4 Analysis

Follow the manufacturer’s instructions on the operation of the analytical apparatus utilized.

Calibrate the apparatus using verified reference gas cylinders prior to analyzing the stack gas to ensure that the equipment is operating satisfactorily. Include this calibration data with the reported concentrations of the various components.

When following the integrated sampling procedure, determine the concentrations of the components immediately after sampling. Repeat the analysis of the bag sample until the analyses vary no more than 0.25% (v/v) for each component.

Using the grab sampling procedure, a set of analyses must be carried out at equal time intervals during testing; the time period between analyses not to exceed ten minutes.

3.5 Calculations

Dry Molecular Weight (Md)

The dry molecular weight of the sample is calculated using Equation C-2.

Equation C-2
Dry Molecular Weight Equation

Equation C-2 assumes that the stack gas components measured include carbon dioxide (CO2), nitrogen (N2), and oxygen (O2). Where the concentrations of additional components are determined, the equation can be modified to include these components by adding extra terms to Equation C-2, as shown in Equation C-3.

Equation C-3
Dry Molecular Weight Equation

Wet Molecular Weight (Ms)

The wet molecular weight is calculated using the dry molecular weight (Md) determined using Equation C-2 or C-3, and the stack gas moisture content (Bwo) determined from Method D (Determination of Moisture Content).

Equation C-4
Wet Molecular Weight Equation

3.6 Nomenclature

Bwo
proportion by volume of water vapour in the stack gas, dimensionless

%CO2
percent carbon dioxide by volume, dry basis

%i
percent of additional component, i, measured by volume, dry basis

K
proportionality, constant, (L/min) (s/m)

Md
molecular weight of gas on a dry basis, kg/kmol

Ms
molecular weight of gas on a wet basis, kg/kmol

MWi
molecular weight of component i, kg/kmol

%N2
percent nitrogen by volume, by difference, dry basis

%O2
percent oxygen by volume, dry basis

Q
sampling rate indicated by the rotameter, L/min

Us
stack gas velocity, m/s

Figure C-3: Molecular Weight Data Sheet

Molecular Weight Data Sheet

Page details

Date modified: