Chemical Engineering Interview Questions and Answers

1 :: Is there any way to remove residual product left in pipes after a batch operation?

OEG Company in Osaka, Japan commercialized a device called Pushkun that runs through pipes and "pushes" out left over product. The system is particularly valuable in batch operations where product recovery is chief concern. The manufacturer claims that at one installation, the system paid for itself in four months through product recovery. System costs depend on the scale of the system, but are typically around $10,000 US (1998).

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2 :: What particle sizes are electrostatic precipitators used to remove?

A. Duprey conducted testing on an electrostatic precipitator in a pulp mill. The results were published in a National Air Pollution Control Administration report called "Compilation of air Pollutant Emission Factors”.

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3 :: What are flameless oxidizers?

Flameless oxidizers 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.

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4 :: Are there any special considerations to be taken into account for combusting ammonia?

The heat of combustion of ammonia is 8,000 Btu per pound. There is no reason why it cannot be combusted with or without auxiliary fuel. However, ammonia combustion does result in a flue gas having a high concentration of NOx and the design of a combustion chamber for ammonia requires special conditions to mitigate or reduce the level of NOx emissions.

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5 :: What are some common causes of control valve noise?

If you have excessive pressure drop across the control valve and the downstream pressure is low enough to cause the liquid to flash, a great deal of noise in the control valve can result. Excessive damage can be done as well. This is a common problem at low flows. Review the design information on the valve and the process to see if low flow may be the problem. If the valve is incorrectly sized the noise will be apparent from the day of installation. If flows have recently been changed, the valve may have been designed correctly at the time, but is too large for current operation.

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