November 20, 2018

Steam System Engineering – Steam Terminology Part Two – Flash Steam, Steam Quality and Filtered Steam

Steam System Engineering

My name is Kelly Paffel, technical manager for Inveno Engineering LLC located in Tampa, Florida.

We are Engineering firm specifically for Steam and Condensate systems. We are domestic and international.

Steam system engineering. Types of steam and terminology. This is a part two of a three segment presentation.

Today I want to talk about flash steam, steam quality and filtered steam.

Types of steam and terminology. First one we want to talk about is flash steam. Flash steam; high pressure and higher temperature condensate is discharged into a lower pressure condensate system. Condensate will be at the same pressure and temperature as the steam in the process, which is shown here in picture two.

If we have 100 psi, 338 degrees Fahrenheit, steam comes into the process, latent energy is released and condenses down into condensate at P2. This temperature here will be the same as the pressure and temperature in the process.

When the condensate’s passed through the drain device, control valve or steam trap, sees a lower pressure here in the return system. The higher temperature condensate cannot exist at the lower pressure, so it must get its temperature down to the lower pressure saturation temperature correlation. How it does do this is take a percentage of liquid, changes state from a liquid to a vapor or what is classified as flash steam. Again, condensate discharges at a lower pressure system return line. The higher temperature condensate cannot exist at the lower pressure, therefore the additional sensible energy is released into latent heat of vaporization or what we call flash steam.

Here is an example of a steam trap that’s discharging to atmosphere and the steam trap is operating at 150 psi, 366 degrees. [inaudible 00:02:41].

Flash steam is no different than utility steam which we talked about in part one. It has the energy and the steam quality.

Flash steam describes how the steam is formed from the flashing process.

Always reuse in different processes or systems. Example is a flash tank system that’s located in this picture.

This is the flash steam. The condensate and the flash is coming in here and we take the flash up here. This happens to be a thermal compressor system where we take the steam at low pressure, thermal compressor back up to a higher pressure.

The next term I want to talk about; steam quality.

So many times people talk about this as wet steam, they say I have wet steam. Remember saturated steam is dry and invisible.

Steam quality, no liquid entrainment, correct amount of latent and sensible energy. Wet steam really means poor steam quality.

When somebody says, I have wet steam. They’re really saying I have poor steam quality.

Steam quality, zero equals a 100 percent liquid condensate, while a steam quality of a 100 indicates a 100 percent steam quality.

Here is an example of a steam quality. How we can check. Just take a valve on the steam line, open it to atmosphere. Remember saturated steam is dry invisible gas you cannot see. When looking at the discharge right here, [inaudible 00:04:25] we have pretty god steam quality.

Here’s an example of poor steam quality. [inaudible 00:04:42] This is an example of poor steam quality. Poor steam quality has several negative effects on the process and steam system. [inaudible 00:04:59].

Now how do I measure steam quality. Is really measured by a Calorimeter.

Really if you do a pressure reduction system, the thing is if we know the upstream pressure and we know the downstream pressure and anytime you go through a pressure reduction, you’ll pick up super heat. We have an accurate temperature measurement downstream and we go to our super heat tables and we know the percentage of super heat that we will pick up, then by adding this temperature device in there, and if we achieve that super heat than we have 100 percent steam quality. If we don’t achieve that super heat than we have less than a 100 percent steam quality.

Anytime you’re installing a pressure reducing station, always add the measurement devices, pressure and temperature and you really have an in plant calorimeter.

One fact to remember, steam leaving the boiler is really about 99 percent steam quality. Steam quality is degraded by poorly managed steam systems.

The next one I want to talk about is filtered steam.

Filtered steam is steam that’s been mechanically filtered by several devices. Utility steam prepared by removing any liquid entrainment and corrosion particles.

The thing is that no matter how well we treat the steam system, we will have corrosion inside the piping and there’ll be some corrosion particles coming down into the system and we want to be able to remove that.

Filtered steam is used for applications in proving steam quality and process applications, sterilization, autoclaves, any contamination or liquids condensate can negatively affect the final process.

This here happens to be a mechanical coalescing type separator, which will bring a poor steam quality back up to at least 98 percent or higher, very efficient.

Utility steam can be prepared by the following filtration; strainer as I showed in the previous slide, standard centrifugal separator, coalescing separator and a standard steam filter.

Remember this is a mechanical coalescing or mechanical separator. Mechanical separators are flow dependent.

You have to be sure you’re up at the maximum flow through this to make this device perform.

The previous device was a mechanical coalescing separator which is not flow dependent. You should know the difference between the two devices.

Steam filtration or separation must be capable of removing particle sizes dictated by the company standards or governing rules or regulations. Example; hospital sterilizers must comply with ANSI-AAMI-ST.

Steam is filtered and has been through a separation; all downstream steam components and piping/tubing should be stainless steel. That’s a best practice when we do filtration and separation.

This concludes our section two of our three segment. Again, we’re here to be your partners in steam system assessments, engineering, steam balance, steam system performance, training. To give people knowledge of steam systems. Long term, upgrades, process changes and improve reliability and safety.

Our contact information is right here. Please contact us if you have any questions whatsoever regarding steam systems. Have a great day.