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Chemical Engineering Interview Questions and Answers

Chemical Engineering Interview Questions and Answers

Question - 1 : - What Are Some Common Causes Of Gas Pipeline Vibration 20 Carbon Steel Line?

Answer - 1 : -

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.

Question - 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?

Answer - 2 : - 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.

Question - 3 : - Is There Any Way To Repair A Valve That Is Passing Leaking Internally Without Taking Our Process Offline?

Answer - 3 : -

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.

Question - 4 : - When Using A Pumping Loop To Mix Two Miscible Fluids In A Tank, When Can The Content Are Considered Well Mixed?

Answer - 4 : - 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.

Question - 5 : - What Are Some Good Uses Of Low-grade Steam At 12 Atm And 1920c?

Answer - 5 : -

There are various traditional methods to employ waste steam in an operating plant:

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.
You can pre-heat process streams that require pre-heating; this is done by applying heat exchangers.
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).

Question - 6 : - What Is A Good Way To Get Started In Doing A Plant-wide Steam Consumption Analysis?

Answer - 6 : -

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.

Question - 7 : - Are There Any General Rules For Flushing Slurry Lines?

Answer - 7 : - 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.

Question - 8 : - What Is Pneumatic Conveying?

Answer - 8 : - 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.

Question - 9 : - What Types Of Pneumatic Conveying Systems Are Typically Used?

Answer - 9 : - 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.

Question - 10 : - What Is The Most Common Carrier Gas Used In Pneumatic Conveying?

Answer - 10 : - 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.

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