Industry Applications
Moisture measuring applications are wide-ranging and diverse.
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Air Separation Units & Speciality Gases
A variety of bottled gases are certified for resale as "calibration gases ", specifying the concentration of contaminants in each bottle. Often the water content is specified, and this must be monitored with precision both by the supplier and consumer.
Breathing Air & High Pressure Air Systems
A reliable supply of breathing air is critical for applications in the military, medical and fire fighting sectors. The presence of excess moisture in breathing air can lead to freezing in the pressure regulator and ice blocking the orifice, causing an interruption to the supply of air to the user. Such freezing effects have caused the loss of life and equipment in submarines and aircraft.
Food Packaging
Foil-wrapped foods are often sealed with air, or an inert gas. It is possible to extend the storage life of the food if the air trapped between the foil and the food is replaced with nitrogen of very low moisture content .
High Density Polyethylene (HDPE) Production
The presence of excess moisture in the ethylene feed gas reduces the catalyst activity, thereby decreasing the yield of the polyethylene reactors.
Hydrogen Annealing Ovens
High moisture content in hydrogen gas used in annealing furnaces causes oxidation of the metal to occur, thus resulting in an undesirable surface finish on the product
Hydrogen Cooled Electricity Generators
Hydrogen is used to cool large, stationary generators because of its high heat capacity and low viscosity, and must be kept dry to maintain both of these properties. Ambient moisture is considered a contaminant, which will reduce the heat capacity and increase the viscosity of the cooling hydrogen.
Injection Moulding
Excess humidity in the air used to dry plastic pellets has several adverse effects on the quality of the products produced.
- The strength of the product is decreased.
- The surface of the product can be blemished.
- The product can have a ‘cloudy’ appearance.
All of these production problems reduce yield and increase the overall production cost.
Instrument Air & Compressor Systems
The presence of humidity in a blanketing gas for sensitive instruments can cause corrosion problems, rapid changes in calibration and loss of sensitivity. The presence of oil contamination in compressors can cause similar problems.
Liquid Benzene Feed Stock
Moisture needs to be measured in feed stock gases in the manufacture of polymers . For example, pre-dried benzene is fed in to a reactor containing hydrochloric acid – if the dryers are not operating properly moisture in the benzene promotes acid corrosion of the reactor and process lines. Several processes require water concentrations of specific values to optimise efficiency and yield; in such cases more sophisticated instruments are required.
Natural Gas & LNG
The presence of moisture in high-pressure natural gas from production wells causes pipelines and associated valves to freeze. High moisture content also leads to the formation of hydrates of the liquid hydrocarbons present, thus causing further difficulties. The moisture content of the gas also adversely affects the calorific value of the gas, thus lowering the quality and value of the product. Moisture is therefore measured at the point of extraction, at export stations, at gas storage locations and in the transmission grid. As natural gas often contains high levels of contaminants, more complex systems are required to maintain instrument performance over prolonged periods and to verify data collected in spot-check moisture analysis.
Nuclear Reactors
The Advanced Gas Cooled Reactor uses carbon dioxide gas to transfer heat from the nuclear fission core to the water boiler for steam generation. The moisture content needs to be monitored to avoid corrosion damage, and continuous moisture monitoring acts as a boiler leak detector or bulk moisture meter.
Permeability Testing
Manufacturers of bandages and permeable membranes must comply with tests to determine the extent of permeability of the finished product. Quality can be improved and wastage reduced if the moisture can be measured quickly and reliably.
Refinery Recycle Gas & Plant Start-up
Optimal performance of petrochemical reforming catalysts depends upon maintaining an optimal moisture / chloride ratio within the reforming reactor. When moisture and chloride are out of balance, catalysts suffer from higher deactivation rates and decreased yields. The cost of inadequately controlling the moisture / chloride ratio can be very high in terms of yield losses, off-spec product, increased catalyst regeneration , early catalyst replacement , processing upsets and / or increased downtime.
SF6 / Air Circuit Breakers
SF6 (sulphur hexafluoride ) or air is used as an insulation gas in circuit breakers . Excess moisture in these gases causes arcing, which can trip the circuit breaker and cut off power to the distribution network. More seriously, such arcing can lead to physical damage of equipment and, on occasion, death of plant operatives (please ask for our case study on circuit breakers).
Vacuum Evacuation & Gas Refill on Oil Filled Transformers
Moisture is continuously monitored in the vacuum evacuation and gas refill of oil-filled transformers. The moisture content of blanketing gases used in the transformers directly affects the dielectric properties of the oil, through water vapour dissolution.