Reference method for measuring releases of mercury from mercury cell chlor-alkali plants: section 4

Section 4: Apparatus

• 4.1 Sampling Train
• 4.2 Equipment Required for Sample Recovery and Analysis

4.1 Sampling Train

Impingers

Four Greenburg-Smith impingers are connected in series using ball and socket U-connectors and clamps ( Figure 1). The first and second impingers have the standard tip and impaction plate. The third and fourth impingers are modified by replacing the tip and impaction plate of the standard design with a 13-mm (0.5 in.) ID glass tube extending to within 13 mm (0.5 in.) of the flask bottom. Inlet and outlet connectors are ball and socket type with 13-mm (0.5 in.) ID tubing.

Control Valve

A needle valve or equivalent is used to control the sample flow rate.

Pump

A leak-free, vacuum pump is used to withdraw the gas sample.

Dry Gas Meter

A dry gas meter calibrated to within ±1% (according to Method F, Reference Method 1/RM/8) and equipped with a temperature indicator, is used to determine sample volume.

Rate Meter

A calibrated rotameter (or equivalent) with a range of 0 to 5 l/min is required to measure sample flow rate.

Probe

1. Stack sampling
   When sampling within a confined source such as a stack, use a suitable probe made from stainless steel tubing or other material which does not absorb significant amounts of mercury. This is connected to the impinger train using the minimum amount of Teflon tubing required to join the probe to the glass sampling-train inlet.
   
2. Cell room sampling
   If the ventilation air leaving the cell room is confined to ducts or stacks, a suitable probe may be made from stainless steel tubing. However, if ventilation is via large, unconfined vents or roof top openings, a multipoint sampling manifold system is required. Such a system, illustrated in Figure 2, can be made from ABS piping or other suitable material. Maintain the system at or above the ventilation air temperature.
   

Air-flow Measuring Device

A calibrated standard or S-type pilot tube is used (according to Method F, Reference Method 1/RM/8). If the air-flow velocity is below 3 m/s (10 ft/s) a calibrated vane anemometer or other suitable low-flow measuring device is required.

Barometer

A barometer capable of measuring atmospheric pressure to within 2.5 mm Hg (0.1 in. Hg) is required.

Temperature Gauge

A thermocouple or equivalent, capable of measuring temperatures to within 1.5% of the minimum temperature of the process gas, is required.

Differential pressure Gauge

An inclined manometer or equivalent, capable of measuring pitot tube velocity pressure to within 0.127 mm (0.005 in.) of H ₂0, is required.

Figure 1: Mercury Sampling Train

Figure 2: Multipoint Sampling Manifold System

4.2 Equipment Required for Sample Recovery and Analysis

Wash Bottles

Volumetric Flasks

100-, 250-, 500- and 1000-mL capacity.

Pipettes

1-, 2-, 3-, 4- and 5-mL capacity.

Storage Bottles

Amber glass bottles are required to store recovered impinger samples.

Miscellaneous

Beakers and graduated cylinders.

Atomic Absorption Spectrophotometer

A portable unit used only for mercury analysis is used in the field. A research-grade instrument, if available on site, can also be used. Both types of instruments are available commercially. Figure 3 is a schematic diagram of the analysis system which includes a spectrophotometer, optical cell, pumping system and sample bottle. The dimensions and materials shown in Figure 3 are recommended. Equipment which departs from these specifications must be demonstrated to be equivalent. This equipment is usually available as a complete kit from the spectrophotometer manufacturer.

Figure 3: Flameless Atomic Absorption Analysis System