5 replies to this topic

[Ra v]

Hi everyone,

 

The Capacity of cryogenic air separation plant is expressed in TPD of the main product.

The flow of air products is generally termed in Nm3/hr.

 

How can we determine the actual production in ASU ??

 

For example :

 

1000 TPD plant means, Is it  Liquid / Gas Oxygen capacity or Nitrogen capacity??

 

What is the 1000 Means ??

 

Rgs

Ravi

 

[Bodhisatya]

Capacity of any Air Separation unit is determined by Gaseous Oxygen Flow.

 

Convert the Flow in Nm3/hr into Kg/hr and multiply the same with 24,to get kg per day and subsequently Tonnes per day. (1 metric Ton =1000 Kg)

 

 

1000 TPD corresponds to Gaseous Oxygen flow of 29,166 Nm3/hr.

 

Bodhisatya.

[Ra v]

Thanks Bodhisatya,

 

I got it now but please check the attachment. 

 

What happens if operating mode is liquid oxygen,can we able to produce the total liquid production of plant  3283 Nm3/hr as shown in the sheet.??

 

In this sheet it is given that Gaseous Nitrogen production is 3000 Nm3/hr. So does it mean if the plant is expressed as 3000 Nm3/hr it signifies as Gaseous Nitrogen???

 

What is the actual sheet expressing in both 3000 and  5000 Nm3/hr plants ??? Please try to explain, i am bit confused in this now. hope you can try to resolve my query. 

 

Regards

A Ravi   

Attached Files

•  Example.bmp   1.93MB   58 downloads

[Art Montemayor]

Ravi:

 

I think what you have submitted is a copy of a Universal Boschi specification sheet for one of their air separation plants.  I have found numerous errors, flaws, typos, and mistaken descriptions in their literature and website and for that reason I have taken their information and attempted to organize and list it in a logical, correct manner.  Attached is my version of what they publish in their website.  From the listing I have formatted, you will get a better description of what they produce and the capacities of their various columns - in liquid and gaseous states.

 

Contrary to what Bodhisatya states, I have always found that designers/fabricators of air separation columns identify their plants in any variety of units as they please.  The large, "tonnage" plants have been traditionally labeled in "tons/day".  This has been used because the large plants almost always produce a base load, liquid product that is stored and distributed as such.  Consequently, metering, invoicing, and accounting units are usually tons of product.  When a gaseous product is required, vaporizers (usually ambient) are employed to produce the gas product.  From a distribution, logistical, and sales point of view  it is much more efficient and economical to handle the product in the liquid state - whenever that is possible.  Since I believe that you are in the industrial gas business, you will recognize the fact that the transport and handling of liquefied gases is exceedingly much more efficient and cost effective than it is in the gaseous state.  In the USA, for example, I doubt if you will find any reasonable consumer of compressed gases - such as Oxygen, Nitrogen, and CO₂ - receiving and storing gas in high pressure cylinders anymore.  Almost all major customers resort to the liquefied product and vaporize it on site as needed.  Hospitals are a very good example of this where oxygen is concerned; carbonated beverage bottlers are another in the case of CO₂.  In the developing countries, however, high pressure cylinders are still used - mainly because of a lack of supporting infrastructure and technology.

 

It is always much easier to accurately and efficiently account for compressed gases in MASS units than it is in gaseous units.  Everyone has their own version of what is a "standard"  or "normal" state and not every customer knows how to make the conversions correctly or accurately.  That's why CO₂ is always invoiced and accounted for in mass units - regardless of the quantities involved.  You will note that even Universal Boschi is guilty of failing to identify accurately what the capacity of their air requirement is for each plant size.  They fail to identify what they mean by "m³/hr" when specifying gas flow rate.  That is just bad engineering identification and, unfortunately, very prevalent in the engineering world.

Attached Files

•  Boschi Air Separation Process.xlsx   3.53MB   116 downloads

[Ra v]

Thank you Art for your explanation. It is clear now.

 

But if we look at the specific power  i.e  Power consumed/oxygen produced is higher in low capacity plants and when it comes to higher capacity plants ,where liquid is produced then it is reducing. why is that so??

 

Can you please explain, How the Expansion Engine or Turbo Expander is decided for a particular production capacity?? I mean what are the main factors to be considered while putting a certain capacity of EE or TE??

 

Rgeards

A Ravi

Edited by Ra v, 02 May 2014 - 04:10 AM.

[Bodhisatya]

As Raw material is free and abundant,the major cost of any air separation unit is Power,so basic engineering of such plants focus on choosing cycles that will yield least specific power which in turn becomes the USP.

 

A classic example is evolution of Internal compression  of Liquid Oxygen against the old External Compression of Gaseous Oxygen.

 

For Liquid Plants the spec power becomes more important because the work load of booster air compressor increases.

 

The criteria of choosing an Expansion Turbine depends solely on the amount of refrigeration load required.

 

Obviously the refrigeration load will increase for liquid plants.

 

Carry out an enthalpy balance of the incoming and the outgoing streams ex cold box ,the difference gives you the refrigeration load and accordingly the turbine selection will be decided.Can be an Oil brake,Generator Brake or a booster brake.

 

Bodhisatya.