What Is Dry Steam?

Despite being a centuries old technology, steam is still an essential part of the industrial world. There are a ton of special uses cases for steam in manufacturing, chemical processing, and elsewhere in heavy industry. We use steam for precise temperature control in specialized vacuum systems, for heating oil and fluids over long distances, for electrical turbines, to push fluids through piping such as in distillation towers, to improve burner efficiency, and for drying things.

You Do WHAT?!

It turns out that steam is actually incredibly useful for drying things, typically clothe things, but it’s been used on paints and other parts of product drying.

You mean for WRINKLES in clothes and pants, right?

NOPE.

Alright, let’s break out the physics. This is actually something weird and incredibly interesting. Starting with the basics. Matter has essentially three states that you’re going to actually experience in day to day life: Solid, Liquid, and Gas. We all know what these look like, right? Solid water is ice. Liquid water is… well tap water, ocean water, lake water, rain. Gas-water is steam, a big, white, puffy, and usually burn-inducing cloud rising up from those noodles I boiled last night (and got the burn on my hand for).

It turns out, we’re not entirely right about how we think of steam. That white, puffy cloud steam makes? It’s not a gas. It’s a liquid. If you physically see steam, the thing you’re seeing isn’t actually steam, it’s a collection of water molecules that have been picked up in the steam. Actual steam is transparent, like air and humidity.

The Suspension of Steam

This phenomenon is called a suspension. When you put chunks of fruit in jello, those bits of fruit are suspended in the jello, they’re held by the fluid around them. When we make steam at home, it’s a suspension of liquid water and gaseous water. This is wet steam. It’s not all a gas. Most of it isn’t a gas.

The liquid water in the steam is either condensed steam, or bits of fluid picked up from the surface of the water itself during the state change. We see condensed water in the air all the time: clouds. Clouds aren’t hot and boiling, they’re in fact, incredibly cold. Water can be somewhere similar but distinctly different from steam: it can be vaporized, billions of microscopic water drops floating in the air. The part of clouds and steam we see are water vapors.

The steam we’re boiling is invisible, and it’s carrying water vapor with it. There’s a massive updraft created by the steam floating upwards, and that carries the incredibly light bits of liquid water with it. This steam will make your hand wet, it’ll make your ceiling wet, and it’s not going to dry anything.

Dry Steam

That’s where Dry Steam comes in. We need to remove that liquid water. Once the liquid water is removed, the steam becomes like a gentler form of a torch. It’s incredible amounts of heat, but in an oxygen-starved environment there won’t be any fires. It can be regulated, providing direct heat at a wide range of temperatures.

This dry steam has a few benefits:

  1. It carries no impurities.
    Liquid water, even as a vapor, can carry contaminants. This can cause debris build up and damage, even in hydronic systems. Dry steam will cause no corrosion or build up. Hardware exposed to dry steam lasts longer than wet-steam hardware. This is most easily observed with power generating turbines. Nuclear plants are generally designed to use superheated steam to prolong turbine life.
  2. It disinfects.
    Dry Steam is common in the pharmaceutical and cleaning industries. The steam itself cannot carries impurities, so it cannot easily contaminate sterile products. The incredible heat allows it to sterilize these products.
  3. It’s highly controllable.
    The temperature of the steam can be easily adjusted by controller it’s pressure, allowing for precise temperature control, more precise than is possible with air and water.
  4. It Doesn’t Burn
    There’s essentially no oxygen content around the steam. It’s almost like heating something with an inert gas like helium. The steam displaces the air. Cleaning can be done at hundreds of degrees celcius without damaging the product (so long as you don’t melt it).

This application of control allows dry steam to be used for cleaning, drying, heating, and more in a massive range of manufacturing. It’s usable everywhere from chemical processing and pharmaceuticals to cleaning applications. It’s an incredible material.

How Do We Make It?

The main difference between wet steam and dry steam is those particles of water vapor, right? We need to make those bits of liquid water turn into gaseous water. We need to put more energy into the system. It all starts with making regular, saturated steam. This is steam that’s been heated to the boiling point. Now we’re going to superheat that steam.

Superheating usually involves heating a liquid beyond its boiling point, without disturbing it’s state. In this case, we’re going to put so much energy into the steam that the liquid water inside the steam, will be converted into pure steam. This can be steam anywhere from just above the boiling point to hundreds of degrees Celsius.

The nice thing is that once you’ve created the dry steam, it can cool down without risk of condensation. Condensation forms UNDER the boiling point. If we keep the steam above 100 degrees Celsius at sea level (and even there we have wiggle room, the steam has to lose some significant energy to actually condense), then there will be no moisture inside the steam, so long as it is not contaminated with liquid water.

This makes dry steam a bit of a production miracle. We can have the incredible heat of an intense flame, without the fire. We can have the gentleness of hot air, without moisture damage. We can have unparalleled control, because the slightest change in pressure impacts the temperature.

Despite being centuries old, steam is far from dead.

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