Level measurement for the chemical industry

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Ammonia

Liquid ammonia is a common chemical raw material. To facilitate transportation and storage, gaseous ammonia is usually pressurized or cooled to obtain liquid ammonia. When liquid ammonia is dissolved in water, ammonium ion NH4+ and hydroxide ion OH- are formed, and the solution is alkaline. Liquid ammonia is mostly stored in pressure cylinders or steel tanks. Liquid ammonia is widely used in industry, is corrosive and easily volatile, so its chemical accident rate is very high.


Chemical injection

Level monitoring controls chemical inventory and determines when the tanks require filling. The careful selection and application of level controls to chemical injection systems can effectively protect against tanks running out of chemicals or overfilling. Without reliable, consistent level measurement, accidents and spillage can occur.

Chemical agents employed in natural gas processing include drilling fluid additives, methanol injection for freeze protection, glycol injection for hydrate inhibition, produced water treatment chemicals, foam and corrosion inhibitors, de-emulsifiers, desalting chemicals and drag reduction agents. Chemicals are frequently administered by way of chemical injection skids.


Chlor-alkali

Chlor-alkali (CA) refers to the manufacture of chlorine and alkali (NaOH). They are among the top ten chemicals produced globally and are the main ingredients in the manufacture of drugs, cleaners, disinfectants, herbicides, pesticides and PVC. Chlorine and sodium hydroxide are made from electrolytic saline (NaCl).

In the ion selective permeation membrane technology of chlor-alkali, the liquid level meter should control the feed of saturated brine and desalted water, and the liquid level of sodium hydroxide. Level control keeps a sufficiently high liquid level in the anode chamber and cathode chamber to ensure the saturation of the membrane, thus preventing any gas exchange through the membrane in the upper part of the electrolytic cell.


Condenser

Changes a gas or vapor to a liquid; condensation is employed in the reflux process to improve the efficiency of distillation. Tower vapors are condensed prior to entering an accumulator (reflux drum) where level can assist controlling tower pressure.


Deionization

Highly purified water is essential in processing premium grade and highly purified products in the chemical, pharmaceutical, beverage, cosmetics and electronics industries. Deionization (DI) is frequently used to remove minerals from water by passing water through two separate ion beds - cation and anion - followed by mixed bed saturation.


Distillation

Following desalination, crude oil enters the distillation column where fractional distillation separates hydrocarbons into separate streams, cuts or fractions. For optimum operation of the distillation column, level controls must contend with occurrences of foaming, bubbling and moderate-to-high temperatures.

Level measurement at the bottom of a distillation tower controls the "bottoms" product rate. Poor level control could allow liquid to back up over the stripping trays causing damage and reduced yields. Too low level may cause pump cavitation. In related extraction towers, interface level control provides optimal separation from associated substances.


Mixing & blending

Mixing and blending of liquid ingredients is essential throughout the broader chemical industry. In-line and skid mounted systems include batch and continuous mixing for liquid/liquid formulation and blending. An impeller in the process vessel accomplishes the mixing of miscible liquids. Level controls monitor tank and vessel levels and trigger alarms in underfill and overfill incidents


Reboiler

Reboilers, or vaporizers, are heat exchangers that provide heat to the bottom of a distillation tower. They boil the bottom liquid to generate vapors which are returned to the tower to drive the distillation separation process. The reboiler may partially or completely vaporize the stream it receives from the bottom of the tower. Excess reboiler liquids (bottoms or blow-down) overflow a baffle where level is controlled by means of a level controller. If the reboiler level becomes too low, it will affect the maximum flow rate of bottoms product that can be drawn off. Inaccurate reboiler level can also degrade composition control for material balance control configurations.


Scrubber vessels

Scrubbers remove odors, pollutants, acid gases and chemical wastes from air and liquid streams or from biogas. In a wet scrubber, the polluted stream flows counter current past water or a liquid chemical, which removes the undesirable component of the gas or liquid. Chemical scrubbing typically requires large amounts of caustic chemicals. Scrubbers remove odors, pollutants, acid gases and chemical wastes from air and liquid streams or from biogas. In a wet scrubber, the polluted stream flows counter current past water or a liquid chemical, which removes the undesirable component of the gas or liquid. Chemical scrubbing typically requires large amounts of caustic chemicals.


Fermentation vessels

Industrial fermentation is the process of breaking down organic substances and re-assembling them in order to produce other chemical compounds. Alternative fuels like ethanol and chemicals such as methanol and a wide range of acids can be developed using this process. Chemical fermentation takes place in large tanks called fermenters in a process that can either be aerobic or anaerobic.

Depending upon the type of fermentation vessel and the media being processed, the level control often must contend with agitation and aeration. Froth or foam is typically generated because fermentation agents have surfactant properties. When processing acids, contact level controls must tolerate the very aggressive media.

 


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