OFFLINE Hg SAMPLING IN FLAMMABLE GASES AT HIGH PRESSURE
Mercury may be present in pressurized gas samples in trace and significant quantities. Even in trace quantities mercury is undesirable because of its high toxicity and potential to damage the environment and expensive industrial equipment.
Accurate measurements of mercury are needed to understand the effect of mercury on various processes and to monitor the efficiency of mercury abatement systems.
The PSA 10.525 Sir Galahad Mercury Analyser is the ideal analyser for the application. The gas sample is passed over a gold impregnated silica trap (AmasilTM) and the Hg in the sample is collected by amalgamation. This type of sampling can be done offline using remote traps. The traps are then analysed on the PSA 10.525 Sir Galahad. The advantage of this approach is that multiple samples can be collected at the same time in remote and hazardous areas where locating the analyser is not permitted or not suitable.
The sampling of gases at high pressure is not trivial especially if the gas sample has high flammability, condensing liquids and low levels of mercury. A representative sample has to be extracted from the process which then has to be filtered and depressurized before it is passed the across the Amasil trap at a controlled flow rate. An accurate volume of sample also needs to be measured so that the mass of mercury collected from the sample can be related to the volume of gas sampled to enable the concentration to be reported in mass/volume units. This can be achieved by using a Wet Gas Flow Meter.
In recognition of these analytical and practical challenges PSA have developed the PSA 10.547 offline sampling device for all sampling needs including Hazardous Areas.
PSA 10.547 Sampling System
The 10.547 has replaced its well-established and successful predecessor 10.537 offline sampling system. The unit is semi-portable so it can be easily transported between sample points or moved to test different locations. It can also be installed on a permanent basis by mounting to a wall or free standing frame. It may also be put into a 19 inch rack cabinet for additional environment protection if needed.
The sampling system can be used for any type of gas and it may be used in hazardous area locations. The unit contains Ex d components with ATEX and IECEx certifications, the system classification is Ex d IIC T3.
The sampling system is connected to the sample point using a filter and appropriate length of stainless steel braided Teflon hose. A high flow primary bypass is used to ensure that a representative sample is obtained and prevent losses of mercury on upstream sampling components. A Rotameter can be used to get this flow or a Primary Bypass Control Kit can be installed for permanent installation. The depressurized sample is then passed over two Amasil gold traps which can be mounted in series to comply with ISO 6978:B and ASTM 6350 or in parallel mode. The sample flow is controlled using a flow meter and the volume of gas passed over the Amasil traps is recorded using a dry or wet gas meter. Once the gas sample has been collected, the traps are returned to the laboratory to be analysed using the PSA 10.525 Sir Galahad mercury analyser.
The Amasil traps will collect all forms of mercury so the measurement corresponds to total gaseous mercury. The system is designed to have low carryover of mercury by using components with low affinity for mercury. A specially coated version is also available 10.547/110V/C or 10.547/230V/C for customers who encounter wide Hg concentration ranges.
The main features of the product are as follows:
The unit is typically used for sampling mercury in hydrocarbon gases and liquefied gases such as natural gas, methane, sour gas, ethane, propane, butane, ethylene, propylene and butadiene. It is also used for sampling mercury in other pressurised gases such as compressed air, argon, helium, hydrogen, nitrogen and carbon monoxide and carbon dioxide.
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