Chemical

Vaporized ammonia is used in catalytic and noncatalytic reduction systems for emissions control. Ammonia is injected into the flue gas stream and acts as a reducing agent. It is also used to enhance precipitator efficiency for particulate control. Pure ammonia is stored in a pressure vessel rated for 250 to 300 psig. Aqueous ammonia (70 to 80% water) is stored in a tank rated for 25 to 30 psig. Storage requirements for aqueous ammonia are three to four times that of pure ammonia. Challenge Accidental atmospheric release of pure ammonia vapor can be hazardous, so safety and environmental measures may be required which affect the level control selected.

Mixing finished gasoline requires level monitoring of blending stocks, in-line blending, additive storage, dilution systems and injection systems. Blend stocks are straight-run gasoline, alkylate, reformate, benzene, toluene and xylene. Additives include octane boosters, metal deactivators, anti-oxidant and knock agents, gum and rust inhibitors, and detergents. Challenge Level is normally measured only for inventory control and, in some cases, custody transfer. The precision of level indication that is required varies. If level is used only for internal inventory control, a less accurate measurement can be used. If level is used for custody transfer, highly accurate measurements are required.

The catalytic method of converting compounds into other compounds uses a chemical catalyst to increase the rate of a reaction. The catalyst is chemically unchanged after the reaction has occurred and can be recovered from the reaction mixture. Thirty of the top fifty commodity chemicals are created directly by catalysis. Challenge In the fluidized bed reactor-regenerator (FBRR) a fluid is passed through the catalyst at high enough velocities to suspend the solid and cause it to behave as though it were a fluid. Measurement in the reactor vessel must contend with severe process conditions. Finished product and, in some configurations, spent catalyst, is on level control.

From Active Pharmaceutical Ingredients (APIs) to Vapor Phase Corrosion Inhibitors (VCIs), any one of a thousand additives and agents can be injected into the process stream of a given industry to alter or impart new product properties or enhance processing dynamics. Injection systems and chemical skid systems offer a wide range of dosing control options. Challenge A chemical injection system typically consists of one or more chemical supply tanks or drums, a metering tank, a vessel with a mixer (if required), a variable pump, and process controls. Chemical tanks and chemical skid packages require level monitoring to ensure that the tanks do not overfill or run out of feed chemicals.

Chemical agents employed in field processing include drilling fluid additives, methanol injection for reservoir stimulation, glycol injection for hydrate inhibition, produced water treatment chemicals, foam and corrosion inhibitors, de-emulsifiers, desalting chemicals and drag reduction agents (DRAs). Chemicals are frequently administered by way of chemical injection skids. Challenge Level monitoring controls chemical inventory and determines when the tanks require filling. Though the precise measurement often comes from chemical metering pumps, it is important for the tanks not to run out or overflow.

Chemical, polymerization and pharmaceutical processes utilize reactor vessels to contain chemical reactions. Chemical reaction speed and product quality are frequently controlled by an external heat exchanger for elevating temperature and a cryogenic system for lowering temperature. Reactors typically contain impellers for product mixing. Challenge Level instrumentation in a tank-type reactor vessel must contend with diverse and often aggressive product chemistries, agitation, mixing, surface foam and temperature and pressure variations. Low level monitoring in the discharge line, high level monitoring in the vessel, and interfacial measurement of the foam/emulsion interface is recommended.

Chlor-alkali (CA) refers to chlorine and caustic soda (NaOH) manufacturing. These are among the top ten chemicals produced worldwide and are main ingredients in the manufacture of pharmaceuticals, detergents, disinfectants, herbicides, pesticides and PVC. Chlorine and caustic soda are made by the electrolysis of brine (NaCl). Challenge In the preferred membrane process of CA, level instruments control saturated brine and demineralized water feed, and caustic liquid level. Level control maintains a high enough level in the anode and cathode compartments to ensure membrane saturation, thus preventing any exchange of gases via the membrane in the upper part of the electrolysis cell.

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

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. Challenge Multiple bed DI units have pairs of tanks where an optional CO2 degasser may be placed in between. Single bed DI units incorporate both the cation and anion exchangers mixed in a single tank. In addition to monitoring feed water, a level control in the mixing tank will operate the transfer pump to route the purified water to storage.

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 occurances of foaming, bubbling and moderate-to-high temperatures. Challenge Sight glasses and displacer systems mounted in external chambers have traditionally provided distillation level measurement. Today, radar retrofitted in these existing chambers is gaining popularity due to radar’s less demanding maintenance schedule and ease of retrofit. High product temperatures necessitate temperature-tolerant level sensors.

Selecting a separation technology from among 20 leading varieties depends upon a chemical’s nature, the number of phases, and the capacity, speed and efficiency required. Distillation – separating substances based on differences in volatilities – is the most widely used separation and purification method. Today, approximately 40,000 distillation towers are operating in U.S. chemical plants. Challenge 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.

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. Challenge 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.

Heat Recovery Steam Generator (HRSG) from cracked gases for additional steam and power generation Challenges Improving heat rate efficiency through feedwater heater level control Utilities steam and condensate recovery system Optimizing makeup water treatment, energy management, steam generation cycle, condensate and waste heat recovery

In terms of annual tonnage, lime ranks first among water treatment chemicals. Lime is used for pH adjustment, phosphate removal, sludge and biosolids conditioning, and in association with other chemicals for precipitation. Lime is initially mixed with water in lime slakers to form a slurry referred to as slake lime. The slake lime is then added to raw water for formulation under carefully controlled conditions. Challenge Often contained in an agitated tank, lime slurry is slightly abrasive, and can be corrosive depending upon the other chemicals involved. Contact level sensing should use single rod probes to avoid media buildup.

Liquid-liquid extraction (LLX), or solvent extraction or partitioning, is a selective separation procedure for isolating and concentrating a valuable substance from an aqueous solution by using an organic solvent. LLX can serve as an alternative when distillation is ineffective. LLX is used in pharmaceutical, food and agricultural processing, organic and inorganic chemistry, hydrometallurgy and fragrances. Challenge In mixer-settler type extraction, feed and solvent tanks are monitored for level. The feed and solvent are thoroughly blended in a mixer-settler chamber and the mixture overflows into a separation chamber where it settles into light and heavy phases. The separate phases are monitored and removed on interfacial level control.

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. Challenge A mixing and blending system can be as simple as a vessel with an agitator and graduate in complexity to a fully skid-mounted PLC controlled system with heating, cooling, homogenization and steam injection capabilities. Level controls monitor tank and vessel levels and trigger alarms in underfill and overfill incidents.

To protect neighboring water systems, industrial wastewater must be neutralized so that it is neither acidic nor alkaline prior to its discharge. The neutralization process takes place in a tank where aqueous solutions of an acid and a base are added to wastewater. Sulfuric acid, sodium hydroxide and calcium carbonate are most commonly used. Challenge Level is measured in the neutralization and chemical regeneration tanks which typically involve agitation and aggressive chemicals. Ideally, the tank level monitoring system should be easily removable for frequent cleaning. Contact level sensors should be single rod types to avoid media buildup.

CHALLENGES Loss of interface control of caustic water and hydrocarbon in the quench settler means: • Reduced efficiency of the quench tower, leading to reduced productivity for the plant if the fluid composition negatively changes in the tower and secondary reactions occur (less ethylene produced from the feedstock) • A long residence time in the settler, which creates a thicker emulsion layer due to the caustic and impacts production • Water recirculation back into the quench tower may carry over hydrocarbons, reducing productivity and potentially fouling equipment • As feedstock is increased, more cooling fluids are required, whichincreases the importance of water recirculation and general quench tower operation SOLUTION Magnetrol® level devices allow for reliable control of the quench settler interface to increase ethylene production and product quality • Fast residence time in the settler is important to production in maintaining desirable product quality and preventing secondary reactions in the tower • Fast residence time will also assist level measurement to keep a tighter emulsion layer in the settler (less reaction with the caustic) • Guided wave radar (GWR) can be utilized to measure tighter emulsion layers while magnetostrictive will measure thicker emulsion layers with a float designed to follow the bottom of the emulsion • Total level and interface can both be measured RESULTS Reliable interface measurement leads to efficient quench tower operation • Optimized production and product quality through the quench tower • Potential savings in caustic usage with more efficient quench tower operation • Protection against fouling of equipment and downtime due to hydrocarbon carryover • A level solution that fits the needs of the specific quench settler operation

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. Challenge 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.

Large-scale distillation towers use a reflux system to achieve a more complete product separation. Reflux is that portion of a tower’s condensed overhead liquid product that is cycled back to the top of the tower where it flows downward to provide cooling and condensation of the upflowing vapors. Challenge The reflux drum, or accumulator, serves as a distribution point for reflux and distillate. Condensed liquid leaves the reflux drum under level control. Drum level control is critical to ensure that the proper amount of reflux will return to the distillation tower. Poor liquid level indication can cause expensive operating problems and product degradation.

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. Challenges Accurate level monitoring of water in the scrubber vessel requires a control to feed the correct amount of make-up water to the recycle reservoir. Located in the wet scrubber shell, the level-monitoring device for water-out control should be equipped with a level alarm.

Measuring and ensuring proper liquid levels in your seal pots protects expensive equipment and your brand. Whatever your application, high-quality liquid level instrumentation is crucial. For end-users that means accurate performance, advanced diagnostics, and no calibration necessary regardless of specific gravity changes. For seal pot manufacturers that means a variety of price and performance options, with worldwide safety approvals and simple, easy to stock configurations.

Chemical manufacturers are major users of steam for cleaning, drying, fermentation, steam stripping, and chemical recovery. Steaming-in-place (SIP) is a widely used method for in-line sterilization of vessels, valves, process lines, and filter assemblies. Steam is created in a boiler where heat transforms water under pressure into steam. Challenge Boiler drum level control is critical for safe and efficient steam generation. Drum level control maintains level at constant steam load. Too low a level may expose boiler tubes, which will overheat and sustain damage. Too high a level may interfere with separating moisture from steam, which reduces boiler efficiency and carries moisture into the process.

Surge drums are frequently located between process units to help reduce the effect of flow rate variations between interconnected process units. A low surge drum level can result in reduced capacity while a high level can cause liquid carryover. In an application characterized by alternating inertia and turbulence, stable level output is highly desirable. Challenge Contrary to the normal control objective of keeping a measurement at set point, the purpose of a surge drum level control is to dampen the changes in controlled flow while keeping the liquid level in the vessel between limits. For surge drums it is generally more important to allow levels to “float” in order to minimize flow rate variations.

Nitrogen – the most widely used commercial gas – is the ideal tank blanketing gas when injected into the vapor space of a storage tank. It prevents ignition of flammable liquids, inhibits vapor loss, and protects chemicals, pharmaceuticals and foods from oxygen and moisture degradation. Nitrogen is also used as a purging agent and in cryogenic applications. Challenge Mass flow measurement will monitor the nitrogen blanketing gas. A mass flow meter can track usage as a cost control measure and determine the when, where and by whom of gas usage. Flow monitoring of feed lines can prevent unsafe conditions that may arise when gas supply is insufficient.

Nitrogen is commonly used as a tank blanketing gas in order to prevent ignition of flammable liquids, provide an oxygen and moisture barrier, inhibit vapor loss and maintain a tank’s pressure balance. Nitrogen is the leading gas used for tank blanketing applications. Nitrogen systems are prominent because they are simple to use and require little or no maintenance. Challenge Mass flow measurement will monitor the nitrogen blanketing gas. A mass flow meter can track usage as a cost control measure and determine the when, where and by whom of gas usage.

Where the separation of vapors and liquids is required, a separator drum, or knockout pot, flash drum, or compressor suction drum, is integrated into the process unit. The separation vessel receives the flashing liquid mixture where the liquid is subsequently gravity separated and falls to the bottom as the vapor exits at the top. Challenge Typically, a collection tank located beneath the separation chamber collects the liquid by gravity flow and utilizes a liquid level control for liquid withdrawal. The control also maintains a vapor barrier while discharging the collected liquid at the same rate of accumulation. In some separators, such as flash drums, liquid level must be kept within an extremely narrow span for very tight control.