Chemical Engineering Interview Questions and Answers

• Chemical Engineers are concerned with the designing, supervision, construction, installation and operation of plants and equipment’s for manufacturing chemical products.
• Chemical Technologists deal with the production of substances with new properties which require new methods of production in the fields of petroleum refining & fertilizer technology.
• Chemical Engineers involves in the processing of food and agricultural products, paints and dyes, recycling metals, glass and plastics, cosmetics, mineral based industries and prevention and control of environmental hazards.
• Chemical Engineers involves in the research and development activities in the Bio-Tech firms to find out new drugs.

These are used to treat volatile organic compounds (VOC) and liquid organic streams. Traditionally, these types of streams were combusted to break down the molecules. The disadvantage of this treatment method was the formation of NOx. Flameless oxidizers use electrically heated ceramic packing and a high velocity introduction system to initiate the destruction of the organic compounds into carbon dioxide and water.

Once this oxidation reaction begins, it continues via self-perpetuation. Capital cost for such systems are usually about 25% less than traditional combustion systems and capacities can range from 250 to 40,000 SCFM (standard cubic feet per minute). Thermatrix Inc. is the pioneer for this technology. Visit their website below.

The following compounds are responsible for the foul smells from wastewater plants:

• Hydrogen Sulphide,
• Methyl Mercaptan,
• Dimethyl Sulphide,
• Dimethyl Disulphide.

The threshold limit value was set by American Conference of Governmental industrial Hygienists, Inc (ACGIH) which is defined as the level of concentration of a chemical substance in which a worker can work without an unreasonable risk of disease or injury. It can be expressed in ppm or mg/m3.

For example, the TLV of chlorine for an 8 hrs work day is 0.5ppm or 1.5 mg/m3.

Which indicates a worker can work without any unreasonable risk of disease or injury for 8 hours if and only the chlorine concentration in his/her vicinity is within 0.5ppm.

It is used to measure the sultriness of the environment. The sultriness is calculated on the basis of the humidity affects, the air speed and temperature and also the sun`s radiant heating factor. The sultriness in some cases could be fatal and hence it is very important to keep this under consideration. The wet bulb globe temperature index number was developed in the 1950`s and is now accepted as an industry standard. It is comprised of three temperature readings:

• Wet bulb temperature
• Ordinary dry bulb temperature
• Black bulb globe temperature.

Fractionation and distillation both methods are used to separate the components present in the solution based on the melting points.

Distillation: It is used when boiling point of chemicals are different in the mixtures.

Fractionation: It is used when boiling point of chemicals are close to each other in the mixtures. Fractionation. Fractionation distillation mostly used in petroleum industry.

Oxidation: When there is a loss of hydrogen or electrons, OR gain of oxygen is known as Oxidation reaction.

Reduction: When there is a gain of hydrogen or electron OR loss of oxygen is known as reduction reaction Example of oxidation-reduction reaction is observed in human body, when an electron is transferred into the cell and oxidation of glucose take place from which we get the energy.

CFM and SCFM are both measures of flow rate. CFM might refer to either the flow rate of a gas or a liquid, whereas SCFM refers only to the flow rate of a gas. The same mass flow rate of a gas (i.e., lbs/minute) is equivalent to various volumetric flow rates (i.e., CFM) depending upon the gas pressure and temperature. Thus, when gas flow rates are specified, it is very important to specify at what pressure and temperature the gas was measured.

When the gas flow rate is specified as SCFM, it means that the flow rate was measured at a set of standard pressure and temperature conditions. In the USA, the most common set of standard conditions used in industry is 60 degrees Fahrenheit and one atmosphere of pressure. Note that we have stressed most common, because there are other standard conditions that may be used. It is always best to spell out what standard conditions are being used (i.e., 1200 SCFM at 60⁰F and 1 atmosphere pressure).

When gas flows are expressed simply as CMF, the reader Is can only speculate as to what gas temperature and pressure apply to that flow rate… and, because of that, the CFM flow rate cannot be converted to a mass flow rate.

• High pressure steam should be limited to about 150 ft/s and Low-pressure steam should be limited to about 100 ft/sec.
• Saturated steam at low pressure is common for heating services and secondary process pipes 99 – 131 ft/sec.
• Saturated steam at high pressure is common in powerhouse, boiler and main process lines 82 – 131 ft/sec.
• Superheated steam is common in power generation and turbine plants is 100 – 300 ft/sec.
• Saturated Steam at peak load is < 164 ft/sec.

Seawater is used as a cooling agent in condensers and coolers. Intermittent injection of chlorine gas is used to eliminate marine growth. The system is a once through type. The band screens before the suction of the pumps are supposed to eliminate scales and other suspended materials. The band screens are not properly functioning. Cooling water flow is about 2.6 million gallons per hour.

The pre-screening and mobile screens are not a sufficient protection for the recirculating water. This is a very common problem. In clean salt water the biological grow in the cooling water pipes is the main problem (mussels, barnacle, algae, etc.). After the life cycle is finished they die and blocking the condenser tubes. To solve this debris problems, use self-cleaning Debris Filters (DF) directly installed in front of the water box of the heat exchangers.

 Powder coatings are similar to paint, but they are usually much more durable. Rather than adding a solvent to the pigments and resins in paint, as is typically the case, powder coatings are applied to the surface in a fine granular form. They are typically sprayed on so that they stick to the surface. Once the surface has been sufficiently spray coated, the piece is baked at high temperatures, and the pigment and resins pieces melt and form a durable, color layer.

Fat found in human body is mainly composed of:

• Glycerides
• Glycerides+Phospholipids
• Glycolipids
• Phosphoinotisides

Graphite rod is used in nuclear reactor to convert fast moving neutrons into thermal neutrons.

Iron ore is consisting of Fe₂O₃ Iron ores are rocks and minerals from which metallic iron can be economically extracted. The ores are usually rich in iron oxides and vary in colour from dark grey, bright yellow, or deep purple to rusty red. The iron itself is usually found in the form of

• magnetite (Fe₃O₄, 72.4% Fe),
• hematite (Fe₂O₃, 69.9% Fe),
• goethite (FeO(OH), 62.% Fe),
• limonite (FeO(OH)·n(H₂O), 55% Fe) or siderite (FeCO₃, 48.2% Fe).

When a unit operation is considered changes take place in mass and concentration where energy is provided from an external source without any chemical change. Few examples would be evaporation, distillation, and mixing.

 In the same manner, when a unit process is considered, the reactant is processed in the feed which means that reactants present in the feed are transformed to products by means of chemical reaction and with the assistance of energy being supplied to the system.

A solvent can be defined as a liquid which has the capability to suspend, dissolve or to take out other chemicals where they do not perform any chemical change to the material or solvent. The main process of solvents is to clean, apply, process or to separate materials.

Gibbs free energy is mentioned as the maximum amount of mechanical work or available energy which is done by the system under stable temperature and pressure.

Some characteristics that affect the flow of bulk solids are moisture content where enhanced moisture content in solids makes bulk solids sticky. Absorption of the moisture sometimes by the atmosphere by some solids happens. The other characteristic is a temperature where it affects bulk solids at times when they are exposed to a specific temperature.

Time at rest is a way which affects the solids when they are kept still or rest. The more rest they take, the more slowly the flow of bulk solids takes place. Particle size is one characteristic where it is easy to handle round particles than the odd and asymmetric ones.

The upper pressure range and /or the smaller pipe diameters prompts to investigate the possibility that the gas is reaching critical flow somewhere downstream within the pipe. When a gas gets to critical flow, sonic booms (producing vibration) are expected. In fact, one of the main means by which the additional pressure in the pipe is lost. If the source is a compressor, look for surging. If the source is a tower, look for pressure cycling in the tower Look at critical flow through any control valve that may be in the line.

At 4⁰C the density of water is 1000 kg/cum.

It is the resistance to detonation of a fuel in a spark ignition engine compared to the isooctane-n-heptane mixture.

Many engineers usually point directly to the pneumatic conveying system as a source of such a problem. The truth is that in most cases, segregation occurs because of the differences in sizes of the articles. As a rule-of-thumb, if the size ratio extends outside of around 1:1.3, then there will most likely be segregation.

This being said, one should inspect the equipment responsible for determining the particle size rather than the pneumatic conveying system if this problem is occurring.

Advantages of PFR are Continuous operation, high conversion rate, less cost for operation.

Disadvantages of PFR are temperature gradients, high maintenance cost.

Almost every chemical process, power plant food processing etc. Plant has some type of air operated device from control valves to air operated pumps and all have an air compressor delivering filtered air.

Dense phase pneumatic conveying, typically experiences one common problem from system to system: plugging in the line due to a malfunctioning booster valve. Dense phase systems require these booster systems to introduce new, pressurized air. These boosters are nearly always accompanied by a check valve. If the check valve becomes stuck, the product is allowed to plug the line.

Probably the most common problem encountered in dilute phase pneumatic conveying is the wearing of the rotary valve that serves as an air lock where the product is introduced into the system. If excess air is allowed to pass by the rotary valve, this can cause bridging of the material the flow can be slowed or stopped.

While many applications utilize air as a carrier gas, others are not suited for using air. For example, if the substance being conveyed reactions with moisture in the air or if there is a threat of dust explosions, nitrogen is likely choice.

The third law states that ‘As a system approaches absolute zero, the entropy of the system approaches a minimum value’.

Powder coatings are similar to paint, but they are usually much more durable. Rather than adding a solvent to the pigments and resins in paint, as is typically the case, powder coatings are applied to the surface in a fine granular form. They are typically sprayed on so that they stick to the surface. Once the surface has been sufficiently spraying coated, the piece is baked at high temperatures, and the pigment and resins pieces melt and form a durable, color layer.

Seawater is used as a cooling agent in condensers and coolers. Intermittent injection of chlorine gas is used to eliminate marine growth. The system is a once through type. The band screens before the suction of the pumps are supposed to eliminate scales and other suspended materials. The band screens are not properly functioning. Cooling water flow is about 2.6 million gallons per hour. The pre-screening and mobile screens are not a sufficient protection for the recirculating water.

This is a very common problem. In clean salt water the biological grow in the cooling water pipes is the main problem (mussels, barnacle, algae, etc.). After the life cycle is finished they die and blocking the condenser tubes. To solve this debris problems, use self-cleaning Debris Filters (DF) directly installed in front of the water box of the heat exchangers.

Dense phase pneumatic conveying, typically experiences one common problem from system to system: plugging in the line due to a malfunctioning booster valve. Dense phase systems require these booster systems to introduce new, pressurized air. These boosters are nearly always accompanied by a check valve. If the check valve becomes stuck, the product is allowed to plug the line.

The critical radius of insulation is the thickness of an insulation that does not affect the convection resistance. It is the ratio of the thermal conductivity of the insulator to the convection heat transfer coefficient.

The saltation velocity is defined as the actual gas velocity (in a horizontal pipe run) at which the particles of a homogeneous solid flow will start to fall out of the gas stream. In designing, the saltation velocity is used as a basis for choosing the design gas velocity in a pneumatic conveying system. Usually, the saltation gas velocity is multiplied by a factor, which is dependent on the nature of the solids, to arrive at a design gas velocity.

For example, the saltation velocity factor for fine particles may be about 2.5 while the factor could be as high as five for course particles such as soybeans could.

Pneumatic conveying is a method of moving bulk solids from one place to another with the help of a carrier gas. A differential pressure is applied inside a conveying line. The flow always moves from a region of higher to lower pressure.

A spray condenser is used for the condensation of humid water vapor by direct contact with water. The inlet water is at a temperature less than the dew point of air in the chamber.

Slurry lines should be flushed with a minimum fluid velocity of 10 ft/s and the total flushing liquid volume should equal 3-6 times the total piping volume.

Single-stage or multi-stage steam-jet-ejectors are often used to create a vacuum in a process vessel. The exhaust from such ejector systems will contain steam (and perhaps other condensable vapors) as well as non-condensable vapors. Such exhaust streams can be routed into a “barometric condenser” which is a vertical vessel where the exhaust streams are cooled and condensed by direct contact with downward flowing cold water injected into the top of the vessel.

The vessel is installed so that its bottom is at least 34 feet (10.4 meters) above the ground, and the effluent cooling water and condensed vapors flow through a 34-foot length of vertical pipe called a “barometric leg” into small tank called a “hotwell”. The “barometric leg” allows the effluent coolant and condensed vapors to exit no matter what the vacuum is in the process vessel. Such a system is called a “barometric condenser”.

The non-condensable vapors are withdrawn from the top of the condenser by using a vacuum pump or perhaps a small steam ejector. The effluent coolant and condensed vapors are removed from the Hotwell with a pump.

This is a term that is usually used to indicate how much pressure is required to ‘lift’ condensate from a steam trap or other device to its destination at a condensate return line or condensate vessel. The first image below shows a situation where a properly sized control valve is used on a steam heater. During nominal operation, the utility steam undergoes a nominal 10-25 psi pressure loss through the valve. For typical utility steam (150 psi or higher), this can leave a pressure at the steam trap exit that is often adequate to lift the condensate to its destination.

For example, if the steam losses 20 psi through the valve and another 15 psi through the heater and piping, that can leave up to 265 ft of head to push the condensate to the header. In this case, there is little need for a condensate pump. On the other hand, if the control is too large, it will only be a few percent open during normal operation and the steam can undergo a pressure loss of 50-75psi or even higher.

In addition to supplying terrible control for the heater, it also reduces the available head for condensate lift. In this case, or if the stream supply pressure is relatively low, it may be necessary follow the stream trap with a separation vessel and a condensate pump to push the condensate to the return line.

Generally speaking, cooling tower water should have a pH between 6 and 8, a chloride content no more than 750 ppm, a sulfate content (SO₄) below 1200 ppm, and a sodium bicarbonate (NaHCO₃) content below 200 ppm. Additionally, cooling tower water should not be heated past 120°F to avoid plating out of treatment chemicals in process coolers. In addition, if free chlorine is used for biological growth control, it should be added intermittently with a free residual not to exceed 1 ppm and this should be maintained for short periods.

For normal process plant design liquid pump discharges, look for velocities in the range 5-7 ft/sec. probably not a bad idea to keep design vapor velocities below 125 ft/sec. These guidelines might be applied by an engineering company for design. If you are looking at plant operation, it is common to find velocities in the 9-12 ft/sec range. Erosion problems can also complicate the answer to this question.

Erosion is highly dependent on the nature of the fluid. For example, 98% H₂SO₄ is not corrosive to carbon steel pipe, however it very erosive at “normal design” velocities. Design criteria for 98% H₂SO₄ might be 0.70 ft/sec MAXIMUM. However, it is also well known that if the same 98% H₂SO₄has a little emulsified hydrocarbon, it is substantially less erosive.

The instrument air supply is guaranteed by dedicated air supply with -40⁰C dew point. Apart from this there is about 20 to 30 minutes of back up provided for emergencies like power failure, instrument air-generation failure, etc.

Titration is a process to determine the molarity of a base or an acid. In this process a reaction is carried out between the known volumes of a solution with a known concentration, against the known volume of a solution with an unknown concentration.

Aliquot is a measured sub-volume of original sample. And the Diluent is a Material with which sample is diluted.

The dictionary defines “angle of repose” as “the inclination of a plane at which a body placed on the plane would remain at rest, or if in motion would roll or slide down with uniform velocity; the angle at which the various kinds of earth will stand when abandoned to them”.

Applications to the chemical industry…think about the design of the conical section of a storage bin. The material would not fall out the bottom, as we may want. This concept is also important in the design of system designed to move bulk solids for the same reasons.

The following factors should allow for a reasonable evaluation of cooling towers:

• Purchased cost
• Installed cost
• Fan energy consumption
• Pump energy consumption
• Water use
• Water treatment costs
• Expected maintenance costs
• Worker safety requirements
• Environmental safety
• Expected service life

Graphite rod is used in nuclear reactor to convert fast moving neutrons into thermal neutrons.

Levorotation and Dextrorotation is referred to the properties of plane polarized light, when light rotates clockwise when it approaches the observer is then known as dextro-rotation and when the light rotates anti-clockwise then it is referred as levo-rotation. A compound which exhibits a dextro-rotation is referred as dextro-rotatory and which exhibits levo-rotation is referred as levo-rotatory.

Nitrogen is available in liquid form after compression. If it is exposed to atmosphere directly or comes in contact with heat it would flash (evaporate). So we need to protect the nitrogen storage from the outside temperature. The boiling point of nitrogen is -195.8⁰C. To achieve that it is stored in an inside vessel with an outer vessel surrounding it. The annular space between the two vessels is evacuated to ensure the outside temperature won’t enter inside as no medium is there. This method is similar to what we see in a thermos flask.

The threshold limit value was set by American Conference of Governmental industrial Hygienists, Inc (ACGIH) which is defined as the level of concentration of a chemical substance in which a worker can work without an unreasonable risk of disease or injury. It can be expressed in ppm or mg/m3.

For example, the TLV of chlorine for an 8 hrs work day is 0.5ppm or 1.5 mg/m3. Which indicates a worker can work without any unreasonable risk of disease or injury for 8 hours if and only the chlorine concentration in his/her vicinity is within 0.5ppm.

If we pass the liquid from top to bottom, it will flow fast by gravity itself. So it will have less contact time with the heat exchanger/reactor surface which will result in poor heat transfer. That’s why the hot fluid should be passed from bottom to top to maximize the contact time. The same is applicable for cold fluid also in reactors.

If we pass the steam from bottom side the condensate that is formed after losing the heat won’t have a comfortable passage to get out of the system. In turn the entering steam will start to heat the returning condensate rather than heating the reactor surface. That’s why we have to pass it from the top.

A vapor is formed by heating any liquid and it can be condensed at atmospheric conditions either by reducing temperature or be increasing pressure. But a gas has already above the critical temperature and can’t be condensed by application of above methods. First it has to be brought below critical temperature. Then only it can be condensed.

Biot number is a dimensionless number defined as Bi= hL/kb (No unit). h= convective heat transfer co efficient (unit is W/m2 K) L= characteristic length (Volume of the body/ surface area of the body” unit is metre) kb= thermal conductivity of the body(W/mK)

It is the ratio between conductive heat transfer within a body to that of convective heat transfer away from the body. If it is above one means convection is more and less than one means conduction is more.

Electrolysis is the technical name for using electricity to split water into its constituent elements, hydrogen and oxygen. The splitting of water is accomplished by passing an electric current through water.

Pigments are coloured substances used in paint. Paints are a type of mixture called a colloid. They contain several components, including the pigment, a solvent and a binding medium. Thermochromic and phosphorescent pigments are very useful and extend the normal properties of paints. Paints are used to decorate surfaces or protect them from damage.

A pigment is a coloured substance used in paint. Paints contain these ingredients: a pigment – gives the paint its colour a binding medium – a liquid polymer that hardens to form a continuous layer when the paint dries a solvent – dissolves the binding medium and makes the paint more fluid.

An isochoric process, also called a dash constant-volume process, an isovolumetric process, or an isometric process, is a thermodynamic process during which the volume of the closed system undergoing such a process remains constant.

The abbreviation for CSTR is continuous stirred tank reactor. Here assumptions are steady state, constant temperature, constant density and one irreversible first order reaction.

The main functions of three-way catalytic converter are nitrogen oxide reduction, carbon monoxide oxidation, and uncombusted hydrocarbon oxidation.

The property of particulate solids is mentioned as an angle of repose. When a bulk solid is poured into a flat surface, a conical pile is developed. The angle that is developed between the pile edge and a flat surface is called angle of repose. The angle of repose depends on certain factors which include surface area, density of the material, coefficient of friction.

The production management philosophy which is developed across continuous reduction of waste is called lean manufacturing or just in time. They are mainly used in businesses where production efficiency plays the main role. Any aspect that hinders productivity is considered as waste and enemy in JIT systems.

Wasted many hours, reduction of inbound inventory by a formulation of supplier delivery schedules and minimization of outbound stock and more are few techniques that assist JIT. By this way, cash flow is enhanced and sales margin is maximized.

A surfactant is a chemical that reduces the surface tension of pure liquid or a mixture of liquids.

Flow control is also mentioned as optimized production technology where the effectual flow of material is concentrated by means of the production process. Bottlenecks are the main aspect which the flow control philosophy focuses on. A simple example can be that owner who makes use of flow control process would never intend to purchase machines which have the capacity of 1000 units per hour and supply just 500 units.

The systems are to be analysed and the lowest flow must be identified. The identified point must be addressed and assured that its works to its full capability. When maximum productivity is required, flow control plays its role.

Even long radius elbows should be avoided in slurry pipes and lines. They are often the site of severe erosion or solid/liquid separation. Only gentle pipe bends or sweeps should be used to turn a slurry line. Industrial experience has shown that a bend-radius-to-pipe-diameter ratio of 3-5 is recommended.

Silicon is well known for its chemical inertness, (i.e. it tends not to react with many other chemicals). Depending on what type of silicon you are dealing with, this may or may not be easy to solve. If the silicon is from a lubricant, it is probably the graphitic form, which is soluble in a strong combination of nitric, and hydrofluoric acids, neither of which I would recommend for you to use…nor hydrofluoric acid is not easy to come by.

If it is silicon from an acidic form (probably any other form other than a lubricant), you should try ammonia. In either case, leave your acetone at home it will never work. Update an ammonia solution worked very well in this case.

The first production scale PLA (polylactic acid) facility was built by Cargill Dow in The Blair, Nebraska, and USA. The facility is designed to consume 40,000 bushels of corn per day and produce 300 million lb/year of PLA.

PCB is a commonly used acronym for “Polychlorinated Biphenyls”. These compounds are famous for the disposal problems that they pose to the chemical industry.

An additive is anything that is added to a process that is not a basic raw material. It is usually present in such small quantities that it does not interfere with final product quality. It is usually added to act as an enhancer or to prevent some unwanted reaction. For instance, anti-foam additives are added to columns, evaporators, reactors, etc. to prevent foaming. Inhibitors are added to Styrene systems to prevent polymerization. A well-known additive is a detergent added to motor oils and gasoline to keep your engine clean.

Tank Blanketing Valves provide an effective means of preventing and controlling fires in flammable liquid storage tanks. Vapors cannot be ignited in the absence of an adequate supply of oxygen. In most instances, this oxygen is provided by air drawn into the tank from the atmosphere during tank emptying operations.

Tank Blanketing Valves are installed with their inlet connected to a supply of pressurized inert gas (usually Nitrogen), and their outlet piped into the tank’s vapor space. When the tank pressure drops below a predetermined level, the blanketing valve opens and allows a flow of inert gas into the vapor space. The blanketing valve reseals when pressure in the tank has returned to an acceptable level.

Plate heat exchangers are widely used in ammonia refrigeration systems, and they can be much smaller than the equivalent tubular exchanger can. They work best flooded. A flooded exchanger system needs a way to separate the liquid from the vapor. A typical system has a vessel, which acts as knockout drum, accumulator, and header tank in one, along with the heat exchanger. Liquid ammonia flows from the vessel to the exchanger, and liquid/vapor is returned to the middle of the drum.

Vapor is removed from the top of the drum. The liquid/vapor mixture from the exchanger has a lower density than the liquid entering the exchanger, so gravity provides the driving force to circulate the refrigerant.

[dt_sc_toggle title=”Commonly known as a “secondary cooling loop” or SECOOL, a closed loop water system is circulated through a processing plant near a sea. Process heat is transferred into the closed loop water and then this water is circulated through heat exchangers to transfer (reject) the heat to seawater. This is a hallmark plate and frame heat exchanger application. The higher heat transfer coefficients that are available in plate and frames exchangers (PHEs) will minimize the installed cost because the material of construction of choice it Grade 1 Titanium (higher U-value means lower area).

To combat pluggage the narrow passages in the exchangers, the seawater is typically run through large automatic backflush strainers designed especially for seawater. Periodically, these strainers will reverse flow and “blowdown” debris to clear the strainer. This method has been used for many years with great success.

We can use the Weymouth equation to estimate the gas flow. Below is the equation. The compressibility should be evaluated at P_avg shown below.

Nomenclature is as follows: Q = flow rate, Million Cubic Feet per Day (MCFD) T_b = base Temperature, degrees Rankin P_b = base pressure, p_sia G = gas specific gravity (reference air=1) L = line length, miles T =gas temperature, degrees Rankin Z = gas compressibility factor D = pipe inside diameter, in. E = Efficiency factor E=1 for new pipes with no bends E=0.95 for pipe less than a year old E=0.92 for average operating conditions E=0.85 for unfavorable operating conditions.

Typically, straight-through diaphragm, clamp or pinch, and full-port ball valves with cavity fillers are the preferred type of slurry valves. In general, gate, needle, and globe valves are NOT recommended for slurry services.

Gear pumps are a type of positive displacement pump that are appropriate for pumping relatively high pressures and low capacities. Advantages include the ability to handle a wide range of viscosities, less sensitivity to cavitation (than centrifugal style pumps), relatively simple to maintain and rebuild.

Disadvantages can include a limited array of materials of construction due to tight tolerances required, high shear placed on the liquid, and the fluid must be free of abrasives. Also, note that gear pumps must be controlled via the motor speed. Throttling the discharge is not an acceptable means of control.

For Newtonian fluids, which will have a constant viscosity at all impeller speeds, most design correlations will perform satisfactorily for viscosities up to 5,000cp. Above 5,000cp1, estimating errors from 20% to 50% can result in the sizing of the agitator.

The size of a vapor-liquid separator should be dictated by the anticipated flow rate of vapor and liquid from the vessel. The following sizing methodology is based on the assumption that those flow rates are known. Use a vertical pressure vessel with a length-to-diameter ratio of about 3 to 4, and size the vessel to provide about 5 minutes of liquid inventory between the normal liquid level and the bottom of the vessel (with the normal liquid level being at about the vessel’s half-full level).

At the vapor outlet, provide a de-entraining mesh section within the vessel such that the vapor must pass through that mesh before it can leave the vessel. Depending upon how much liquid flow you expect, the liquid outlet line should probably have a level control valves.

Quicklime is calcium oxide which is in dehydrated stage and an effective scavenger. When a comparison is made with other scavenger’s as silica, oxazolidines, it is cheap. These are usually found in water sensitive paint formulations.