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

Method D: Determination of Moisture Content

• 4.1 Principle
• 4.2 Apparatus
• 4.3 Procedures
• 4.4 Calculations
• 4.5 Nomenclature

4.1 Principle

A gas sample is extracted from a single point in the enclosed gas stream being sampled. The moisture is condensed and its weight measured. This weight, together with the volume of gas sampled, enable the stack gas moisture content to be calculated. The moisture content of the gas leaving the final impinger is taken into consideration by assuming that the gas stream is saturated at the average impinger outlet temperature. The moisture content is calculated by using a psychrometric table relating temperature and water content.

If liquid water droplets are present, or are suspected, the moisture content of the gas should be determined using the stack gas temperature in association with psychrometric charts.

4.2 Apparatus

The following items are required:

Probe

A stainless-steel, Pyrex or other corrosion-resistant heated probe, equipped with a filter to remove particulate matter.

Impingers

Two 30-mL midget impingers.

Ice-Bath

An ice bath in which the midget impingers are immersed.

Silica Gel Tube

A tube, of approximately 250- to 500-mL capacity, containing indicating silica gel. The use of this tube is optional, as it serves to protect the pump and dry gas meter.

Valve

A valve to control the sample gas flow rate through the sampling train.

Pump

A leakless pump to pull the gas sample through the sampling train,

Dry Gas Meter

A calibrated dry gas meter capable of measuring the sample volume to within 1%. The meter should allow accurate volume determination for a sample flow rate of up to 5 L/min.

Rotameter

A calibrated rotameter or orifice meter to measure the instantaneous sample flow. The unit should be capable of indicating flows of up to 5 L/min

Graduated Cylinder

A 25-ml graduated cylinder to measure the volume of water placed in the impingers.

Barometer

A barometer capable of measuring atmospheric pressure to within 2.5 mm Hg (0.1 in Hg). The device must be calibrated against a primary standard before use. Alternatively, the uncorrected atmospheric pressure provided by the local weather office may be used with an adjustment for the elevation of the sampling site.

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 gas velocity during sampling.

Scale or Balance

A scale or balance, capable of measuring the weights of the impingers and their contents to within 0.1 g.

4.3 Procedure

Measure and place 5 mL of water into each of the two impingers. Weigh and record the initial weight of each of the two impingers to within 0.1 grams. Assemble the sampling train as indicated in Figure D-1, but do not connect the probe. Ensure that all connections are tight and the system is leak-free. Leak check the system by plugging the inlet to the first impinger, turning on the pump and observing the dry gas meter for any movement of the dial.

Figure D-1: Moisture Sampling Train

Connect the probe and place it in the stack at the desired sampling point. Seal the stack access port to prevent the influx of dilution air. Allow the probe to heat up sufficiently to prevent condensation ahead of the impingers. Turn on the sample pump and adjust the sample flow rate to approximately 2 L/min Adjust the sampling rate, maintaining it proportional to changes in the stack gas velocity using Equation D-1 (see Section 4.5 for nomenclature).

Continue sampling for a minimum of 15 minutes, collecting a sample volume of at least 30 L, as indicated on the dry gas meter. Record on the Moisture Data Sheet (Figure D-2), at five-minute intervals, the temperature of the last impinger discharge, the sample flow rate, dry gas meter reading, and the temperatures at the inlet and outlet of the dry gas meter, if applicable. At the conclusion of sampling, measure the final weight of the two impingers with their contents to within 0.1 g.

Figure D-2: Moisture Data Sheet

4.4 Calculations

Volume of Water Vapour Collected

Use Equation D-2 to calculate the volume of water vapour contained in the stack gas sample at reference temperature and pressure conditions.

Sample Gas Volume

Use Equation D-3 to calculate the sample gas volume at reference temperature and pressure conditions.

Moisture Content of Final Impinger Outlet

Using a psychrometric table, look up the corresponding partial pressure of water vapour at the average temperature at the outlet of the final impinger. Use Equation D-4 to calculate the volumetric proportion of water vapour in this gas.

Moisture Content

Use Equation D-5 to calculate the stack gas moisture content.

4.5 Nomenclature

B_wm

proportion by volume of water vapour in gas stream leaving last impinger, dimensionless

B_wo

proportion by volume of water vapour in the gas stream, dimensionless

K

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

M_H2O

molecular weight of water, 18 kg/kmol

p

absolute pressure at last impinger, approximated by the barometric pressure, kPa

p_m

absolute pressure at dry gas meter, kPa

p_ref

reference pressure, 101.3 kPa

p_v

partial pressure of water vapour leaving the last impinger, kPa

Q

sampling rate indicated by the rotameter, L/min

R

universal gas constant, 8.31(kPa)(m ³)(kmol ^-1) (K ^-1)

(T_m)_avg

arithmetic average of dry gas meter temperatures, K

T_ref

reference temperature, 298K

U_s

stack gas velocity, m/s

V_m

volume of stack gas sample at dry gas meter conditions, m ³

(V_m)_ref

volume of stack gas sample at reference temperature and pressure conditions, m ³

(V_w)_ref

volume of water vapour at reference temperature and pressure conditions, m ³

W_H2O

amount of moisture collected in the impingers, g

γ

dry gas meter correction factor, dimensionless