Moisture analysis - Citizendia

Moisture analysis covers a variety of methods for measuring moisture content in both high level and trace amounts in solids, liquids, or gases. Water content or moisture content is the quantity of Water contained in a material such as Soil (called soil moisture) rock, Moisture in percentage amounts is monitored as a specification in commercial food production. There are many applications where trace moisture measurements are necessary for manufacturing and process quality assurance. Quality assurance, or QA for short refers to planned and systematic production processes that provide confidence in a product's suitability for its intended purpose Trace moisture in solids must be controlled for plastics, pharmaceuticals and heat treatment processes. Second Album by Rock and roll Singer-songwriter near-legend Graham Parker. Gas or liquid measurement applications include dry air, hydrocarbon processing, pure semiconductor gases, bulk pure gases, insulating gases such as those in transformers and power plants, and natural gas pipeline transport. In Organic chemistry, a hydrocarbon is an Organic compound consisting entirely of Hydrogen and Carbon. A transformer is a device that transfers Electrical energy from one circuit to another through inductively coupled Electrical conductors A power station (also referred to as generating station, power plant or powerhouse) is an industrial facility for the generation of Natural gas is a Gaseous Fossil fuel consisting primarily of Methane but including significant quantities of Ethane, Propane, Pipeline transport is the transportation of goods through a pipe.

1 Loss on drying
2 Karl Fischer titration
3 Natural gas
4 See also

Loss on drying

The classic laboratory method of measuring high level moisture in solid or semi-solid materials is loss on drying (LOD). A laboratory (informally lab) is a facility that provides controlled conditions in which scientific Research, Experiments and In this technique a sample of material is weighed, heated in an oven for an appropriate period, cooled in the dry atmosphere of a desiccator, and then reweighed. An oven is an enclosed compartment for Heating, Baking or Drying. Desiccators are sealable enclosures containing Desiccants used for preserving Moisture -sensitive items If the volatile content of the solid is primarily water, the LOD technique gives a good measure of moisture content. Because the manual laboratory method is relatively slow, automated moisture analyzers have been developed that can reduce the time necessary for a test from a couple hours to just a few minutes. These analyzers incorporate an electronic balance with a sample tray and surrounding heating element. A weighing scale (usually just "scale" in common usage except in Australian English where "scales" is more common is a Measuring instrument for Under microprocessor control the sample can be heated rapidly and a result computed prior to the completion of the process, based on the moisture loss rate, known as a drying curve. A microprocessor incorporates most or all of the functions of a Central processing unit (CPU on a single Integrated

Karl Fischer titration

An accurate method for determining the amount of water is the Karl Fischer titration, developed by the German chemist whose name it bears in 1935. Karl Fischer titration is a classic Titration method in Analytical chemistry that uses coulometric or Volumetric titration to determine trace This method detects only water, contrary to loss on drying, which detects any volatile substances.

Natural gas

Natural gas poses a unique situation since it can have very high levels of solid and liquid contaminants as well as corrosives in varying concentrations.

Water measurements are made in parts per million, pounds of water per million standard cubic feet of gas, mass of water vapor per unit volume, or mass of water vapor per unit mass of dry gas. "Parts-per" notation is used especially in Science and Engineering, to denote Ratios (relative proportions in measured quantities particularly The cubic foot is an imperial and US customary (non- metric) unit of Volume, used in the United States Canada and the United Kingdom The volume of any solid plasma vacuum or theoretical object is how much three- Dimensional space it occupies often quantified numerically Dry gas is an Alcohol -based additive used in Automobiles to prevent any water in the fuel from Freezing, or to restore combustive power to Gasoline That is, humidity is the amount of "vapor-phase" water in a gas. Humidity is the amount of water vapor in the air In daily language the term "humidity" is normally taken to mean Relative humidity. If there are liquids present in the gas, they are often filtered out before reaching a gas analyzer to protect the analyzer from damage.

Measurements of moisture in natural gas are typically performed with one of the following techniques:

Color indicator tubes
Chilled mirrors
Electrolytic
Piezoelectric sorption, also known as Quartz Crystal Microbalance
Aluminum oxide and silicon oxide
Spectroscopy

Other moisture measurement techniques exist but are not used in natural gas applications for various reasons. For example, the Gravimetric Hygrometer and the “Two-Pressure” System used by the National Bureau of Standards are precise “lab” techniques but are not practical for use in industrial applications. Hygrometers are instruments used for measuring Humidity. A simple form of a hygrometer is specifically known as a "psychrometer" and consists of two Thermometers

Color indicator tubes

The color indicator tube (also referred to as the Drager Tube or Stain Tube) is a device many natural gas pipelines use for a quick and rough measurement of moisture. Each tube contains chemicals that react to a specific compound to form a stain or color when passed through the gas. The tubes are used once and discarded. A manufacturer calibrates the tubes, but since the measurement is directly related to exposure time, the flow rate, and the extractive technique, it is susceptible to error. The volumetric flow rate in Fluid dynamics and Hydrometry, (also known as volume flow rate or rate of fluid flow) is the volume of fluid which In practice, the error can be as high as 25 percent. The color indicator tubes are well suited for infrequent, rough estimations of moisture in natural gas; for example, if the tube indicates 30 pounds of water, there is a high degree of certainty that it is over 10 pounds.

Chilled mirrors

When gas flows over a chilled surface, or chilled mirror, the moisture will condense on it. The exact temperature at which this condensation begins is known as the dew point. Temperature is a physical property of a system that underlies the common notions of hot and cold something that is hotter generally has the greater temperature The dew point (sometimes spelled dewpoint) is the Temperature to which a given parcel of Air must be cooled at constant Barometric pressure, The temperature of this mirror is reduced from high to low, and the temperature is read exactly when the dew is observed. By obtaining the dew point temperature, one can calculate moisture content in the gas. The dew point (sometimes spelled dewpoint) is the Temperature to which a given parcel of Air must be cooled at constant Barometric pressure, The mirror temperature is controlled by the flow of a refrigerant over the mirror or by using a thermoelectric cooler. Thermoelectric cooling uses the Peltier effect to create a Heat flux between the junction of two different types of materials

The detection of condensation on the mirror can be achieved using visual or optical means. For example, a light source can be reflected off the mirror into a detector and condensation detected by changes in light reflected. The observation can also be done visually; however the exact point at which condensation begins is not discernible to the eye. Since the temperature is passing through the dew point rather than stopping exactly at the dew point, the measurement tends to be high and with it a high standard deviation. In Probability and Statistics, the standard deviation is a measure of the dispersion of a collection of values Additionally, the condensation of moisture can be confused with condensation of other condensable such as heavy hydrocarbons, alcohol, and glycol. Condensation is the change of the physical state of aggregation (or simply state of matter from gaseous phase into liquid phase In Chemistry, an alcohol is any Organic compound in which a Hydroxyl group ( - O[[hydrogen H]]) is bound to a Carbon A diol or glycol is a Chemical compound containing two Hydroxyl groups (-OH groups Vicinal diols have hydroxyl groups attached to adjacent atoms Automated on-line systems are not able to make these distinctions, and only highly skilled operators can use manual systems.

Electrolytic

The Electrolytic sensor uses two closely spaced, parallel windings coated with a thin film of phosphorus pentoxide (P₂O₅). An electrolyte is any substance containing free Ions that behaves as an electrically conductive medium As this coating absorbs incoming water vapor, an electrical potential is applied to the windings that electrolyzes the water to hydrogen and oxygen. General properties of water vapor Evaporation/sublimation Whenever a water molecule leaves a surface it is said to have evaporated Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1 Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the The current consumed by the electrolysis determines the mass of water vapor entering the sensor. The flow rate and pressure of the incoming sample must be controlled precisely to maintain a standard sample mass flow rate into the sensor.

The method is fairly inexpensive and can be used effectively in pure gas streams where response rates are not critical. Contamination from oils, liquids or glycols on the windings will cause drift in the readings and damage to the sensor. The sensor cannot react to sudden changes in moisture, i. e. , the reaction on the windings’ surfaces takes some time to stabilize. Stability can refer to Aircraft flight Stability (aircraft In atmospheric fluid dynamics atmospheric stability, a measure of the turbulence Large amounts of water in the pipeline (called slugs) will wet the surface and requires tens of minutes or hours to “dry-down. ” Effective sample conditioning and removal of liquids is essential when using this sensor.

Piezoelectric sorption

The piezoelectric sorption instrument compares the changes in frequency of hydroscopically coated quartz oscillators. Piezoelectricity is the ability of some materials (notably Crystals and certain Ceramics including bone to generate an Electric potential in response to Sorption refers to the action of both absorption and Adsorption taking place simultaneously Quartz (from German) is the most abundant Mineral in the Earth 's Continental crust (although Feldspar is more common in Oscillation is the repetitive variation typically in Time, of some measure about a central value (often a point of Equilibrium) or between two or more different states As the mass of the crystal changes due to adsorption of water vapor, the frequency of the oscillator changes. The sensor is a relative measurement, so an integrated calibration system with desiccant dryers, permeations tubes and sample line switching is used to correlate the system on a frequent basis.

The system has success in some applications. However, in natural gas, interference from glycol, methanol, and damage from hydrogen sulfide result in erratic readings. The sensor itself is relatively inexpensive and very precise. The required calibration system is not as precise and adds to the cost and mechanical complexity of the system. The labor for frequent replacement of desiccant dryers, permeation components, and the sensor heads greatly increase the operational costs. Additionally, slugs of water render the system nonfunctional for long periods of time as the sensor head has to “dry-down. ”

Aluminum oxide and silicon oxide

The oxide sensor is made up of an inert substrate material and two dielectric layers, one of which is sensitive to humidity. An oxide is a Chemical compound containing at least one Oxygen atom as well as at least one other element A dielectric is a nonconducting substance ie an insulator. The term was coined by William Whewell in response to a request from Michael Faraday. The moisture molecules pass through the pores on the surface and cause a change to a physical property of the layer beneath it. In Chemistry, a molecule is defined as a sufficiently stable electrically neutral group of at least two Atoms in a definite arrangement held together by

An aluminum oxide sensor has two metal layers that form the electrodes of a capacitor. An electrode is an Electrical conductor used to make contact with a nonmetallic part of a circuit (e A capacitor is a passive electrical component that can store Energy in the Electric field between a pair of conductors The number of water molecules adsorbed will cause a change in the dielectric constant of the sensor. Adsorption is a process that occurs when a gas or liquid Solute accumulates on the surface of a solid or a liquid (adsorbent forming a film of molecules or atoms (the The sensor impedance correlates to the water concentration. In Chemistry, concentration is the measure of how much of a given substance there is mixed with another substance A silicon oxide sensor is an optical device that changes its refractive index as water is absorbed into the sensitive layer. The Chemical compound silicon dioxide, also known as silica or silox (from the Latin " Silex " is an Oxide The refractive index (or index of Refraction) of a medium is a measure for how much the speed of light (or other waves such as sound waves is reduced inside the medium When light is reflected through the substrate, a wavelength shift can be detected on the output which can be precisely correlated to the moisture concentration. In Physics wavelength is the distance between repeating units of a propagating Wave of a given Frequency. Fiber optic connector can be used to separate the sensor head and the electronics. An optical fiber (or fibre) is a Glass or Plastic fiber that carries Light along its length

This type of sensor is not extremely expensive and can be installed at pipeline pressure (in-situ). In situ (ɪn siːˈtuː is a Latin phrase meaning in the place. Water molecules do take time to enter and exit the pores, so some wet-up and dry down delays will be observed, especially after a slug. Contaminants and corrosives may damage and clog the pores causing a “drift” in the calibration, but the sensor heads can be refurbished or replaced and will perform better in very clean gas streams. Pollution is the introduction of contaminants into an environment that causes instability disorder harm or discomfort to the physical systems or living organisms they are in Corrosion means the breaking down of essential properties in a material due to Chemical reactions with its surroundings Calibration is the process of establishing the relationship between a measuring device and the units of measure As with the piezoelectric and electrolytic sensors, the sensor is susceptible to interference from glycol and methanol, the calibration will drift as the sensor’s surface becomes inactive due to damage or blockage, so the calibration is reliable only at the beginning of the sensor’s life.

Spectroscopy

Absorption spectroscopy is a relatively simple method of passing light through a gas sample and measuring the amount of light absorbed at the specific wavelength. Absorption spectroscopy refers to a range of techniques employing the interaction of electromagnetic radiation with matter Traditional spectroscopic techniques have not been successful at doing this in natural gas because methane absorbs light in the same wavelength regions as water. But if one uses a very high resolution spectrometer, it is possible to find some water peaks that are not overlapped by other gas peaks.

The tunable laser provides a narrow, tunable wavelength light source that can be used to analyze these small spectral features. According to the Beer-Lambert law, the amount of light absorbed by the gas is proportional to amount of the gas present in the light’s path; therefore this technique is a direct measurement of moisture. In In order to achieve a long enough path length of light, a mirror is used in the instrument. The mirror may become partially blocked by liquid and solid contaminations, but since the measurement is a ratio of absorbed light over the total light detected, the calibration is unaffected by the partially blocked mirror (if the mirror is totally blocked, it must be cleaned).

The Tunable Diode Laser Absorption Spectroscopy (TDLAS) analyzer has a higher upfront cost compared to the analyzers above. Tunable diode laser absorption spectroscopy ( TDLAS) is a technique for measuring the concentration of certain species such as Methane, Water vapor However, the TDLAS technology is the only one that can meet any one of the following: the necessity for an analyzer that will not suffer from interference or damage from corrosive gases, liquids or solids, or an analyzer that will react very quickly to drastic moisture changes, or an analyzer that will remain calibrated for very long periods of time.

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