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Steam and Vacuum Related Q and A

I received 2 interesting questions at my "Vacuum Dropped Alert" post last June. I think its better for me to answer them in a new post for the benefits of others. I discussed the questions/problems with my colleague at work. I hope Mr Owais and Mr Vinay do not mind we discuss it here.

The first questions from Mr Owais (as adopted from the comment section);

"I'm working as a chemical engineer in GamaLux OleoChemical, Fat Splitting Unit.We're facing the same problem. Our main boiler is under maintenance and smaller one in progress time and again vacuum drop and our production get effected but when we don't have good vacuum then we hold the plant or lower down the feed input and product out put but the main problem is that if we lower down the product Fatty acid flow rate then it get chance to stuck in the pipeline then we have to flush the line which is more troublesome. What will u suggest me about how to solve the problem."

My respond/answer;

First of all, I need more informations in order to answer this issue. What is the design requirement of the steam for the plant to get its vacuum? This should be known from the plant manufacturer or current practice. The steam from the boiler house must be supplied as per the requirement of the plant(s). Maybe your smaller boiler do not produce the same amount of steam as your main boiler. Hence, if your plant vacuum system is fragile, slight pressure drop or fluctuation from the small boiler will trigger vacuum dropped and destroy the oil quality.

As for your fatty acid, you probably need a better insulation for the piping and / or steam tracing along the line. This will prevent blockage in the line (hindering fatty acid from solidifying). Sometimes you need jacketed steam tracing if the product have a lower melting point.

If everything above is not an issue, check your cooling water temperature condensing the steam. Is the temperature low enough as per design. Is the pressure from the cooling tower sufficient? Is the strainer nearby the pump suction blocked?

If everything above is still not an issue, when you stop your plant, conduct a complete air test to check and find any leakages in the vacuum system. I hope I answer your questions.

Example of a fire tube boiler that produces steam for general heating and vacuum system.

The second questions from Mr Vinay (as adopted from the comment section);

"I am working in a textile plant as a maintenance engineer. My steam requirement is about 5500 kgs/hr. The main line from boiler to header is 4 inch. Can a smaller pipeline size lead to water carryover. We maintain TDS level in boiler of about 4000-4500. Our's is a water tube boiler."
My respond/answer;

First of all, I need more informations in order to answer this issue. Is it true your plant need 5,500kgs/hr steam? For me, that is very high. Or maybe your production capacity is very big that it require huge amount of steam. I'm just checking some information/facts...I fear, if you reduce the diameter of the pipeline, the flow rate of steam will be slightly affected/restricted. From my observation/experience, if the boiler deliver water carry over, and the water is still in the line (no where to escape), that means wet steam will occur. This will make the vacuum weak. Hopefully no water hammering takes place!!! That means, reducing the line would not help.

Install some steam trap along the line to eliminate water carry over. Spirax Sarco have a number of good steam traps (I'm not related to them).

I think your TDS is on the higher side. Do your water treatment chemicals work at more than 4000 ppm? Please check with your chemical supplier on this matter. For my case, we control the TDS at 2000, the most 2300ppm. This applies to any type of boiler.

I hope I gave a reasonably acceptable answer/suggestion/comment. If anybody want to further comment or discuss about those two issues, you are most welcome...

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posted by zaki yamani @ 1:25 AM,


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The Author


I’m Zaki. I used to be a project, process and chemical engineer. Few years ago I successfully became a Chartered Engineer (IChemE) and Professional Engineer (BEM). I'm now employed as a chemical engineering educator/researcher/consultant. Hope you like reading my blog. I welcome any feedback from you. My email: zaki.yz[alias]gmail.com. TQ!

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