Different Types of Steam
Steam System Engineering
When we communicate about steam system engineering and steam systems; one of the first steps is understanding the different types of steam and terminologies used in steam systems. This video will be part one of several series that will review all the different types of steam and their terminology used in steam systems. Part one will review three specific types of steam: Utility, Saturated and superheated steam.
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Utility steam is sometimes called live steam, plant steam, essential steam, generator steam, but it really means utility steam. No matter what type of boiler we have to generate the steam. The international accepted terminology is utility steam. Utility steam can be saturated or super-heated steam depending on the process, applications, and how we are generating the steam. Steam produced from steam generating sources such as fire tube boilers, water tube boilers, HRSGs [inaudible 00:01:21] heat recovery steam generators, re boilers, et cetera.
There’s a multitude of ways that we can generate utility steam, but at the end of the day, it’s utility steam, which can be into saturated or super-heated conditions.
Now, the water source that we use for the boilers can be water softeners, reverse osmosis, other means for water preparation. But remember one thing, utility steam is pure. No chemicals or minerals will be carried out of the boiler by the steam. Sometimes when we use a corrosion inhibitor, amine can be injected into the steam line to assist in preventing corrosion in the steam system.
We get into types of steam and terminology. First one I want to talk about is saturated steam. Saturated steam is a dry, invisible fluid. Saturated steam is not wet steam. Wet steam is steam quality, which we’ll be talking about that in part two. Saturated steam means saturated with energy, contains both sensible and latent energy. Remember, saturated steam is a dry, invisible gas.
As you can see right here, when the steam is discharging to atmosphere, that right here it’s invisible. You really cannot see it. Remember, saturated steam is a dry, invisible gas. You cannot see it. Contains both sensible and latent energy. Saturated with energy, not wet. Now 98% of industrial processes will only use the latent energy of the saturated steam. Remember there’s two energies in steam, latent energy and sensible energy. So, when the steam comes into the heat transfer from here into here, the latent energy is given up, condenses down and a condensate is removed as quickly as it’s formed to get the maximum efficiency out of the heat transfer. Sensible energy will be in the condensate and return to the boiler plate. Remember one thing: 16% of your energy sits in the condensate, so we want to make sure that we recover it.
Now, latent and sensible energy of saturated steam content will depend on steam pressures and temperature. A higher pressure, higher temperature for less usable energy. People always say “I want higher pressure, more usable energy.” You have less usable energy. Remember, I said, processes use latent energy. At 5 PSIG, the latent is 960.5 BTU per pound. At 200 PSI, the latent energy is 837.7 BTU per pound, so as you go up in pressure, you reduce the amount of usable energy. But the thing about it is when I go up in pressure, I get temperature. And really, what the process is looking at, the temperature I need to make the process work.
Saturated steam occurs when both liquid and gas phases are present at the same temperature and pressure. Many advantages: even heating throughout the heat transfer is probably the number one; ability to control temperature through the pressure, so I can control pressure to process and control temperature; high heat transfer coefficient, high co-efficiency is why heat transfer primarily uses saturated steam as the super heat.
The next one is super-heated steam. So, we produce super-heated steam, we take the saturated steam, which is off of this drum here, and we put it through this bank of coils or tubes inside the boiler here, giving more sensible energy and increase the temperature of the steam without increasing the pressure. Remember, increase of temperature of the steam without increasing pressure. Super-heated steam higher temperature, lower density than saturated steam at the same pressure.
Why use super heat? One thing does not occur in super heat conditions is phase change or condensation, so as I’m going through multiple stages in a high pressure turbine, here that I do not want condensation to occur. Condensation will have erosion effect on the nozzles and the blades inside the turbine. So, therefore, I do not want condensation to occur. So the applications: turbines, [inaudible 00:06:35], and a few high-temperature processes. So, one of the things that we use super-heated steam besides turbines is [inaudible 00:06:47] for the boilers. So a [inaudible 00:06:49] system is a tube here that injects steam inside or in a boiler between the two bangs and blows set of the boilers. Quite commonly used on boilers that burn coal, wood or black liquor, or some off heal that we must get rid of the buildup under the tubes. That’s another application that we use super-heated steam.
With these advantages of super heat, we could be talking about all the advantages that condensation will not occur, but this advantage has a low heat-transfer coefficient. Variable steam temperatures at constant pressures: the temperature can vary, it’s not a direct relationship to the pressure. More expensive components do it at high temperatures. As we go up in super heat temperatures, of course, the materials will change due to the temperature. The vast amount of latent energy cannot be released until the steam reaches saturated conditions. So when we take super heat and send it out into the plant operation where we want to consume the thermal energy as steam, here, is that we’ll add these super-heaters in the system, bringing the steam back to saturated conditions. Thus, when we go onto the heat transfer surfaces, the latent energy will be released.
So that kind of concludes part one, and there will be several other parts to this because we’re going to talk about steam quality, flash steam, pure steam, clean steam, the other terminologies that we use in steam. Remember, we are your partners in steam systems. We can assist in steam system assessment, steam balancing, steam system performance, engineering, steam engineering, design, and long term impacts, upgrades, process changes, improvement, liability and of course, number one in any steam system, is safety of the system. So if you need any help or information, please contact at this email addresses below and a have a great day. Thank you.