3 replies to this topic

[John Kervin]

1. For a column design of 1.5 ft diameter what is the type of column would you recommend? Why?
a. Packed Column
b. bubble cap column
c. Plate column


2. Based on the available data, which of thew following packing materials can be considered for a gas absorption process involving flue gas from a combustion chamber with high amounts of sulfur being combusted? Why?


a. 16mm pall rings
b. #3 nutter rings
c. 50 mm tellerettes
d. 19 mm raschig rings



Thanks for your help.

[Art Montemayor]

John:

Here are my comments:

1. I cannot recommend ANY type of column, given only the diameter. The reason for this simple response is that other, perhaps more important factors are not being considered – for example: what specific fluids are we talking about inside the column? What are the volumetric rates of each fluid? What are the operating pressures (vacuum?) and temperatures? Do any of the fluids contain suspended solids? Do any of the fluids tend to foam? What are the operating requirements like – 24 hrs/day? 330 days/yr? What is the allowable pressure drop across the column? You are being very naïve (and a bad engineer) if you believe that a column type can be selected based simply on the diameter.

2. WHAT available data? Any of the stated packing materials can be used IF they meet the requirements for the allowable pressure drop (which is probably very low), the maximum operating temperature, and the corrosion resistance required for this process. I know this because I've used all of these materials in direct water and chemical scrubbers on the flue gas outlets of steam boilers. They all worked.

Now MY question: Why are you asking these vague questions? Is this a class assignment? Instead of asking for an "answer", why don't you seek out the methodology and logic of arriving at the correct response(s)? That would make more engineering sense – and it would make you a more successful student AND future engineer.

[katmar]

I agree with Art that there is a lot more information required before you can make a proper choice, but if your column really is 1.5 ft diameter there is a very practical limitation that you have to overcome.

It is very difficult to weld inside such a small column and you will not be able to make a trayed column economically at this size. There are ways of doing it, but it is expensive. You can make up all the trays as a cartridge and insert it into the shell with sealing rings between the tray edges and the inside of the shell. Or you can flange the column at every point where there is a tray. I have only seen columns like this in laboratories and never in industry. This makes a packed column the most likely candidate, but you need to evaluate the full picture as Art recommended.

You did not make it clear whether the second question also relates to this small diameter column. If it does, you may find that the larger packings do not give the expected HETP performance. The rule of thumb is that the main dimension of the packing should be less than 8 to 10% of the ID of the column, or the packing is no longer randomly packed near the column wall.

[siretb]

Hello,


You state it's gas absorption, high sulfur. We cannot, without knowing the reagent (caustic?, ... ?),
the loadings you selected and the other components (CO2? ...) , make a very useful design.

Based on the application and the size you pre selected (1.5 foot) it is likely that a packed column is the best choice.

Now general consideration indicate that the ratio of Column diameter / nominal size should be between 12 and 20. 50mm tellerettes look to large. I have designed and seen many scrubbers in operation. My advice would be that you select a general purpose ring, preferably plastic (I assume, but cannot know for sure that the temperature would be around 60°C) , in your case of size not exceeding 38mm.
That you carefully check the liquid rate and pH conditions Top and Bottom.
That you verify that 1.5 foot is good diameter
That based on mass transfer information, available on the Internet most often you calculate the heigth
Calculate pressure drop
That you add a reasonable margin. The lower the removal efficiency, the higher the margin.

If you need more, provide specific information.

I hope this helps