4 replies to this topic

[jamesj]

Dear all,

I'm having some confusion about several basic words and their definitions in respect to process design. It would be really helpful to have your feedback.

1. What does 'Battery Limit' mean?

2. Difference between Holdup Time and Residence Time in separator design.

3. How does equipment 'load' differ from 'capacity' or 'rated capacity'? whats the significance of the word 'rated'?

4. Difference between Surge and Slug. Is it that surge causes slug flow?

 

Thanks in Advance, and sorry for the noob questions.

[Art Montemayor]

James,

Don’t ever make any apology for asking questions as a student.  There are no stupid questions in Chemical Engineering – there are only smart and intelligent inquiries.

 

The following are responses to your query:

 

1. What does 'Battery Limit' mean?
The term Battery Limit means the legally recognized demarcation (border or “line”) where differences in operation, responsibilities, or ownership are identified.  In an operating plant, you normally have different process units that have been designed by different legal entities or are operating under different business arrangements.  In these cases, each unit has a battery limit that defines the point where, for example, utilities or raw materials are identified as changing “hands” or ownership.

2. Difference between Holdup Time and Residence Time in separator design.
Holdup Time usually means the time that a liquid, solid, or gas are maintained in a system for the purposes of either reaction, treatment, or separation.  Residence  Time is usually used to designate the time that a reactant spends in a reaction system – such as a reactor, adsorber, absorber, or other unit operations.  These terms are often used interchangeably.

3. How does equipment 'load' differ from 'capacity' or 'rated capacity'? whats the significance of the word 'rated'?
Equipment load is a term usually used to identify the required external energy of a unit operation – such as a compressor or pump driver.  Sometimes it is used loosely to also relate to equipment capacity.  Rated capacity is a more specific term.  It designates the certified capacity of an equipment – such as a compressor, pump, boiler, turbine, etc. – under specific operating conditions.

4. Difference between Surge and Slug. Is it that surge causes slug flow?
A surge in a process is a sudden, unexpected change in fluid properties – such as flow rate, pressure, temperature, density, etc.
A slug is a volume of liquid that has been enjoined together from various sources, sites, or conditions to form one continuous within a flowing gaseous volume inside a pipeline or vessel.  This 2-phase mixture flows as a gaseous volumetric flow intermittently and can suddenly change to a single-phase liquid flow with gas phase velocity – the effects of which can be dangerously damaging and inflexible.  The effects of the flow changes instantly from compressible gas flow to incompressible liquid flow – at high gas velocities.

[Padmakar Katre]

Great Answer Art

[jamesj]

Thank you very much Art for this insightful answer, this definitely clears up the confusion.

I definitely look up to many of the members here at Cheresources. Wonderful community, always more than willing to provide guidance.

Any advice you would give someone who is really passionate about pursuing a career in process design?

Edited by jamesj, 21 March 2015 - 12:55 PM.

[fallah]

jamesj,

 

2-Difference between hold up time and residence time in separator design: In a separator normally the hold up time and residence time are equal; but in a reactor the hold up time is usually greater than residence time because a fluid passing through the whole reactor body would spend more time than spend in contact with the catalyst bed...