Latest Chemical Engineering LAB VIVA Questions and Answers pdf free Download

Chemical Engineering Questions and Answers: 

1. What are some common causes of gas pipeline vibration 20 Carbon Steel line?
Check / consider the following:
? The upper pressure range and /or the smaller pipe diameters prompts me 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.
? Are there any vapors in the line, which can condense and produce two-phase flow? Two-phase flow can cause vibration.
In chemical plant design, if we suspect two-phase flow, we instruct the piping designers to provide special anchoring.

2. While there, are many tests available to detect leaks on vessels, is there a technology available to quantify the leak, or measure the flow through a leak?
The RheoVac air in-leak monitor by Intek, Inc. in Westerville, OH is a viable meter that gives the actual air in-leakage flow rate. It also gives you exhauster capacity and a vacuum quality reading. If you want to find more information, you can view their web site below.

3. Is there any way to repair a valve that is passing leaking internally without taking our process offline?
A 600 psig, 3" steam line is experiencing "passing" or internal leakage. If you order to replace the valve, the process would have to be taken offline. A temporary solution to the problem is sought to get the plant to their next scheduled shut down ANSWER Research on-stream leak sealing services. This problem is quite common. What they would do in this case is drill a hole into the bypass valve on the upstream side but not completely into the line. They would then tap the hole and install one of your injection fittings, which is like a small plug valve. They would then take a long 1/8" drill bit and drill through the open injection fitting and into the pressurized line. The drill bit is then removed and our injection equipment is then attached. Sealant (heavy fibers and grease) is pumped into the line and caught in the flow, which will bind up against the leaking seat on the bypass valve. If done properly, this technique can be both effective and safe.

4. When using a pumping loop to mix two miscible fluids in a tank, when can the content are considered well mixed?
A rule of thumb is to turn the tank over three (3) times and then sample the tank for mixture properties. By "turn the tank over”, we mean to force the entire volume of the tank through the pump at least three times. More turnovers may be necessary, but three times is a good starting point.

5. What are some good uses of low-grade steam at 12 atm and 1920C?
There are various traditional methods to employ waste steam in an operating plant:
1. You can generate electricity through a steam turbine-generator set. The electricity is usually put back in the line; this is the idea behind the "Co-Gen" concept used today in many USA plants. Steam turbines can effectively use saturated steam supply down to 75 - 100 psig. In special conditions, they have used down to 50 psig as a turbine steam supply. I have used steam as low as 100 psig.
2. You can pre-heat process streams that require pre-heating; this is done by applying heat exchangers.
3. You can employ the waste steam as a refrigeration source by employing it in vacuum jet ejectors and producing 50 of cooling water.
You have to consider these as viable options if you can identify the heating, cooling and energy conservation requirements. An economic analysis is required to identify the most attractive option. You usually utilize a Discounted Cash Flow analysis to base your decision and that means you must study each case as to savings generated. A fourth method might be that you can use the steam for environmental heating (if you live in a cold climate).

6. What is a good way to get started in doing a plant-wide steam consumption analysis?
It is unclear as to whether or not you know the total steam consumption. If you do not, one way to get it is to take the nominal capacity of the boiler in terms of heat, i.e. the total rated Btu/hr. This is usually available either through the documentation you have for the boiler or even on the nameplate. You also must know the steam pressure you are producing. Using the steam tables, get the enthalpy of the steam and divide it into the nominal boiler capacity to get the total rate. I hope that you also know how much of the capacity you are using, 50%, 75% etc. Multiply this by the total lb/hr to get your rate. Another way to get the capacity is by using the amount of boiler feed water you are sending to the boiler and the known level of steam you are producing. Do not forget to include the blow down in your heat & mass balance. Getting the rate to each plant is more difficult if you are lacking in instrumentation. Use as much plant instrumentation as possible; flow meters, pressure and temperature indicators. If you do not have a meter in each header to each plant, then see if you have them in sections or to pieces of equipment using the steam. Another way is to measure the amount of condensate you are returning to the boiler. If you are dumping the condensate, you may be able to collect and measure the amount in a pail from each source. Another way is to use the process instrumentation and do some mass and energy balances around the steam users.

7. Are there any general rules for flushing slurry lines?
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.

8. How can you determine the proper pipe thickness for a slurry line?
Design of slurry piping systems should follow ANSI/ASME B31.1 and B31.11 Codes. A simple equation for this calculation is as follows: t = (PD) / (2S) + C where: t = pipe wall thickness, in. P = maximum design pressure of the pipe, psig S = maximum allowable design stress, psig C = corrosion or erosion allowance, in.

9. What is the best way to handle bend or turns in slurry piping systems?
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.

10. How can you prevent bridging in a dilute phase pneumatic conveying system?
Manufacturers of these systems recommend bin agitation or blowing air into the top of the feeding bin. These methods can prevent fine particle from bridging near the rotators valve. Two types of particles that are especially prone to bridging include titanium dioxide and calcined- kaolin clay.

11. What is some common piping materials used to transport slurries?
When selecting a piping material to transport slurries, corrosion and erosion considerations must be accounted for. Some of the most popular piping materials include:
? Carbon Steel
? Stainless Steel
? High Density Polyethylene (HDPE)
? Acrylonitrile butadiene stryene (ABS)
? Unplasticized polyvinyl chloride (uPVC)
? Fiberglass reinforced plastic (FRP)
? Elastomer-lined carbon steel

12. What are some common problems associated with dilute phase pneumatic conveying?
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.

13. What are some common problems associated with dense phase pneumatic conveying?
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.

14. What is the most common carrier gas used in pneumatic conveying?
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.

15. What types of pneumatic conveying systems are typically used?
Essentially, there are two types of pneumatic conveying systems. In dilute phase systems, the solids are suspended in the carrier gas and transported to their destination. In dense phase systems, the solids-to-gas ratio is much higher. The gas in these systems acts more like a piston to push the product to its final destination. Dilute phase systems are more typical than dense phase systems because they can employ positive pressure displacement or a vaccum system. Dense phase conveying is useful if the product degrades easily (works at lower velocities) or is particularly abrasive.

16. What is pneumatic conveying?
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.

17. What is the practical particle size limit for pneumatic conveying?
As a rule, pneumatic conveying will work for particles up to 2 inches in diameter with a typical density. By "typical density”, we mean that a 2 inch particle of a polymer resin can be moved via pneumatic conveying, but a 2 inch lead ball would not.

18. What can cause bulk solids to stop flowing from a bin?
Causes of such problems can fall into one of two categories: Material strength or Bin Geometry: Factors that can affect material strength include. Moisture is especially with particles, which fuse together with moisture.

19. What is the most common cause of solid size segregation in bulk solid systems?
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. Reference: Richard Farnish, the Wolfson Centre for Bulk Solids Handling Technology

20. How can one determine the particle size distribution for a given bulk solid?
While there are high-tech methods of performing such an analysis (laser-diffraction and video imaging system are available), the simplest way is to use a sieve stack. For example, to analyze a particular solid, one would stack several different mesh sizes into a cylinder with the largest mesh opening on the top and progress down through the cylinder to finer mesh. The cylinder would contain a pan on the bottom. Before beginning, weight the test sample, each piece of mesh, and the pan. Then, the sample is loaded into the top of the test cylinder and the cylinder is exposed to a combination of movements (shaken) to allow the solids to pass through the appropriate mesh sizes.
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21. What is a "saltation velocity" and how is it used in designing pneumatic conveying systems?
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.

22. What are some characteristics of bulk solids that can affect their ability to flow properly?
Four (4) main factors to consider include moisture content, temperature, particle size (and shape), and time at rest.
1) An increase in moisture content will generally make solids more "sticky". Some solids will absorb moisture from the air, which is why nitrogen is often used as a carrier gas (among other reasons).
2) For some solids, their ability to flow can be adversely impacted by temperature or even the length of time that the particles are exposed to a specific temperature. For example, soybean meal flows nicely at 90 °F but start to form large bridges at 100 °F.
3) Generally, the finer a bulk solid becomes, the more cohesive the particles. Round particles are generally easier to handle than "stringy" or oddly shaped particles.
As particles rest in a bin, they can compact together from their own weight. This can create strong bonds between the particles.
4) Often times, re-initiating flow can break these bonds and the solids will flow as normal, but this can depend on the load at given locations in the bin.

23. After conducting an internet search for ways to reduce energy costs, I found a recipe for whitewashing that is said to reflect sunlight. The recipe calls for 20 pounds hydrated lime to 5 gallons water to 1-quart polyvinyl acetate. What is a good source of polyvinyl acetate that I can buy at a local store?
Well your recipe sounds exciting. Finding your polyvinyl acetate should be easy. Go to your nearest department store and pick up a large container of plain white glue! The chief active ingredient in this glue is polyvinyl acetate. Good luck with your project!

24. We wanted to know how to impart various colors to copper wire by simply dipping them into various chemicals, formulations, etc. This copper wire is to be used by us for our hobby of making various art objects from copper wire.
Changing the color of copper by means of chemical reactions is a dangerous Endeavour that I really do not recommend. However, there is something you can do to get a green color, if fact if you are familiar with the Statue of Liberty here in America, this would explain why it is green. You see, the outside of the statue is coated with copper and being in New York City, it is subjected to acid rain. This causes the formation of another chemical that coats the copper and gives the statue its green color. The two acids that you can use are nitric acid (which works best) or sulfuric acid (which will probably require some gentle heating along with the acid). I am not sure if there were a good way to get nitric acid out of something you may have around the house, you would probably have to buy it.
Sulfuric acid can be obtained from car batteries (the liquid inside). You will want to boil the mixture (to concentrate it by evaporating the water), until you see white fumes (which are very dangerous). Then put your copper is while the acid is hot and leave it there until you get the color you would like. If you are going to do this, please do it outside or in a well ventilated area and make sure you have some baking soda handy is case you get some of the acid on your skin. If you are looking for a different color or more colors...

25. What is an effective means of removing silicon from aluminum?
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

26. What does the catalystic converter on an automobile really do?
A catalytic converter is a device that uses a catalyst to convert three harmful compounds in automobile exhaust gas into harmless compounds. The three harmful compounds are:
? Hydrocarbons (in the form of unburned gasoline)
? Carbon monoxide (formed by the combustion of gasoline)
? Nitrogen oxides (created when the heat in the engine forces nitrogen in the air to combine with oxygen).
Carbon monoxide is a poison for any air-breathing animal. Nitrogen oxides lead to smog and acid rain, and hydrocarbons produce smog. In a catalytic converter, the catalyst (in the form of platinum and palladium) is coated onto a ceramic honeycomb or ceramic beads that are housed in a muffler-like package attached to the exhaust pipe. The catalyst helps to convert carbon monoxide into carbon dioxide. It converts the hydrocarbons into carbon dioxide and water. It also converts the nitrogen oxides back into nitrogen and oxygen.

27. What compounds are responsible for the odors that come from wastewater treatment plants?
Compounds such as hydrogen sulfide, methyl mercaptan, dimethyl sulfide, and dimethyl disulfide can all contribute to this foul odor.

28. What is the average salary for chemical engineers?
AIChE just came out with the results of a ChE salary survey (See Chemical Engineering Progress, September 2000). To answer your question depends on years of service, the type of degree, the size of the company and the type of industry, i.e. Engineering, Design & Construction (E&C), Plant work, Self Employed as examples. To summarize briefly, median starting salary is about $50,000 per year. Median salary among all Chemical Engineers is about $77,200 and annual raises are averaging 4.4%. As far as job prospects that again depends in which area you are interested. In general, jobs are still looking good. However, be forewarned, Chemical Engineers no longer command the job security that we once had. In economic downturns, it can get nasty.

29. Who built the first production scale PLA (polylactic acid) facility?
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.

30. What is the largest application for surfactants?
About 60% of total surfactant market is composed of the detergent and cleaning products marketplace. These types of compounds are sold in large volumes at low prices.

31. How can you separate hydrogen peroxide into hydrogen and oxygen?
This is easily done. Just expose hydrogen peroxide to air. The oxygen in the air will oxidize the hydrogen peroxide into its component gases. It happens far too slowly for industrial or most other purposes (an enzyme catalyst can be used to speed up the process). However, neither hydrogen nor oxygen is produced in this manner in industry. The enzyme catalyst is called "catalase".

32. What is the easiest way to extract hydrogen from water and the safest way to store it?
Electrolysis (which means splitting using electricity) of water is the method for producing hydrogen from water. The safest way to commercially store it would be to use a palladium "sponge", because palladium adsorbs several hundred times it's own volume in hydrogen. One would need to produce a compound with a very high surface area, which has a thin coating of palladium. This type of material is commonly used as a catalyst in chemical processes.

33. What is a solvent?
According to the US Solvent Council, "A solvent is a liquid which has the ability to dissolve, suspend, or extract other materials without chemical change to the material or solvent. Solvents make it possible to process, apply, clean, or separate materials.

34. What are the three classes of organic solvents?
Typically, organic solvents can be split up in the following classes: Oxygenated, Hydrocarbon, and Halogenated. Oxygenated solvents include alcohols, glycol ethers, ketones, esters, and glycol ether esters. Hydrocarbon solvents include aliphatics and aromatics. Halogenated solvents include those that are chlorinated primarily.

35. What is happening when paint dries?
During the manufacture of paint, solvents are added to make the paint thinner so that it can be applied to various surfaces. Once the paint is applied, the solvents evaporate and the resins and pigments that make up the paint for a thin, solid layer on the surface.

36. What is quicklime and what are the uses?
Quicklime (Calcium Oxide) is an efficient scavenger of moisture in its dehydrated state. It is also cheap, compared to orthe scavengers such as silica gel, drierite, oxazolidines, etc. It is commonly found in water sensitive paint formulations (such as polyurethanes and polyureas).

37. What are PCBs?
PCB is a commonly used acronym for "PolyChlorinated Biphenyls". These compounds are famous for the disposal problems that they pose to the chemical industry.

38. How can separation of chiral chemicals affect the chemical and/or pharmaceutical industries?
This enantiomers (left [S] or right [R] oriented) versions of the same compound can have very different properties; this development has been significant particularly in the pharmaceutical industry. For example, the drug Seldane is a racemic mixture of both S and R versions of the drug's molecules. Through chiral separation technology, Hoechst was able to bring the drug Allegra to market in only 3 years (far less time than is usually necessary). Hoechst was able to bypass toxicity testing because Allegra is a single chiral form of its molecule. By chiral separation, the most of the side effects of Seldane were avoided in Allegra.

39. Can asphalt be recycled to form a useful product?
Asphalt can be ground into small pieces and emulsified to form a 70% oil/30% water mixture. This fuel can be used to power boilers. It has a heating value of 6,600 kcal/kg and is said to be stable for about 6 months.

40. What is the easiest way to extract hydrogen from water and the safest way to store it?
Electrolysis (which means splitting using electricity) of water is the method for producing hydrogen from water. The safest way to commercially store it would be to use a palladium "sponge", because palladium adsorbs several hundred times it's own volume in hydrogen. One would need to produce a compound with a very high surface area, which has a thin coating of palladium. This type of material is commonly used as a catalyst in chemical processes.

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

42. What is a good source of surfactant information on the internet?
Check out the Surfactant Virtual Library at the link below.

43. What is the Wet Bulb Globe Temperature (WBGT)?
The sultriness of the ambient environment is more than a comfort factor. For workers, soldiers and athletes, high levels of sultriness may result in heat stress that could very well be life threaten. To determine the actual degree of sultriness in a quantifiable manner, the Wet Bulb Globe Temperature (WBGT) index is used. It includes the effects of humidity, air speed, air temperature and the radiant heating factor (from the sun). This index was developed by the U.S. Military in the 1950's and has become widely accepted for industrial temperature measurements to protect employees. It combines three temperature readings: the wet bulb temperature; the ordinary dry bulb temperature and a black bulb globe temperature. There are also instruments available, which measure WBGT index directly, combining the three factors and their appropriate weighting values.

44. How can metals be removed from aqueous waste streams?
Precipitation is widely used to remove metals from waste streams. The soluble heavy-metal salts can be converted to insoluble salts that will precipitate and can then be removed by clarification, filtration, or settling.

45. What are some common precipitating agents used to remove metals from aqueous waste streams?
Perhaps the most common agents used are:
1) Metal hydroxides
2) Lime or caustic soda
3) Metal sulfides
4) Alum or ferric salts
5) Phosphate or carbonate ions

46. What types of metals are typically removed via chemical precipitation?
Some of the more common metals or other substances removed via precipitation include:
1) Aluminum
2) Arsenic
3) Barium
4) Cadmium
5) Calcium
6) Trivalent chromium
7) Hexavelent chromium
8) Copper
9) Iron
10) Lead
11) Magnesium
12) Manganese
13) Mercury
14) Nickel
15) Selenium
16) Zinc

47. How can hexavalent chromium be removed from aqueous waste streams?
One option is to use ferrous sulfate to reduce the hexavalent chromium to a less toxic, trivalent chromium form that wills precipitate out of the solution. Trivalent chromium can then be reduced by sodium hydroxide.

48. How can arsenic be removed from aqueous waste streams?
Often times, ferric chloride is added to such a stream. The ferric chloride aids in the formation of floc to agglomerate fine arsenic particles that can then be removed by mechanical means.

49. How can I treat a waste stream containing both hexavalent chromium and arsenic?
Waste streams that contain these types of mixtures are often treated in two or more reducing tanks. Strong reducing agents such as sodium metabisulfite, sulfur dioxide, and sodium bisulfite are often used.

50. How many grams per liter would there be in a 0.35 N (Normality) Citric acid solution?
The normality of a solution is the number of gram-equivalent weights of the dissolved substance per liter of solution. The gram-equivalent weight of the dissolved substance is the molecular weight of the dissolved substance divided by the hydrogen equivalent of the dissolved substance. Citric acid has a molecular weight of 192.12 and it contains three hydrogen equivalents (i.e., three COOH groups). Thus, the gram equivalent weight of the citric acid dissolved in water is 192.12/3 = 64.04 grams. Therefore 0.35 Normal citric acid would have (0.35)(64.4) = 22.41 grams of citric acid per liter of solution. 

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