2. What is Steam?
Steam is the gas formed when water passes from
the liquid to the gaseous state. At the molecular
level, the is is when H2O molecules manage to
break free from the bonds (i.e. hydrogen bonds)
keeping them together.
3. Introduction:
Steam has been a popular mode of conveying energy since the
industrial revolution. Steam is used for generating power and
also used in process industries such as sugar, paper, fertilizer,
refineries, petrochemicals, chemical, food, synthetic fiber and
textiles. The following characteristics of steam make it so popular
and useful to the industry:
•Highest specific heat and latent heat
• Highest heat transfer coefficient
• Easy to control and distribute
• Cheap and inert
4. Properties of Steam:
Water can exist in the form of solid, liquid and gas as ice, water
and steam respectively. If heat energy is added to water, its
temperature rises until a value is reached at which the water can
no longer exist as a liquid. We call this the saturation point and
with any further addition of energy, some of the water will boil
off as steam. This evaporation requires relatively large amounts
of energy, and while it is being added, the water and the steam
released are both at the same temperature. Equally, if steam is
made to release the energy that was added to evaporate it, then
the steam will condense and water at same temperature will be
formed.
5. How steam works
In liquid water, H2O molecules are constantly being joined together and
separated. As the water molecules are heated, however, the bonds connecting
the molecules start breaking more rapidly than they can form. Eventually,
when enough heat is supplied, some molecules will break free. These 'free'
molecules form the transparent gas we know as steam, or more specifically
dry steam.
6. Dry Steam vs. Wet Steam
Dry steam:
Dry steam is entirely in the vapor state, and has no liquid in it. Superheated
steam is always dry, because any liquid would be immediately heated into
steam. Saturated steam can be essentially dry, or at least dry enough to do the
job! In order to keep your saturated steam dry, it is necessary to trap it
effectively so that any water is removed before the steam gets to its use point.
Wet Steam:
Wet steam is simply the opposite of dry steam. It has both liquid and vapor
present. The liquid takes up space in the flow, but does not contribute
effectively to the heat transfer since it has already given up its heat of
vaporization. Unsaturated steam can also be described as Wet Steam.
7. The Different Types of Steam in Industrial Steam
Generation
Saturated Steam
Saturated steam is the most common, especially in pharmaceutical industry
applications. Saturated steam is essentially steam at its boiling point. The most
common example is steam at atmospheric pressure. At this pressure, saturated steam
would be at 212°F (100°C). As the pressure of the steam goes up, so does its
corresponding boiling point temperature. This relationship can be seen in steam tables,
which are charts of industrial steam temperature versus pressure for saturated steam
8. Superheated Steam
Super heated stem is steam that is hotter than its boiling point for a given
pressure . For the example above ,superheated steam would be hotter than 212F
(100) , but still at atmospheric pressure.
9. Principal Applications for Steam
Steam is used in a wide range of industries. Common applications for steam
are, for example, steam heated processes in plants and factories and steam
driven turbines in electric power plants, but the uses of steam in industry
extend far beyond this.
Here are some typical applications for steam in industry:
1-Heating/Sterilization
2-Propulsion/Drive
3-Motive
4-Atomization
5-Cleaning
6-Moisturization
7-Humidification
10. Steam of heating:
Steam is typically generated and distributed at a positive pressure. In most cases, this
means that it is supplied to equipment at pressures above 0 MPaG (0 psig) and
temperatures higher than 100°C (212°F).
Heating applications for positive pressure steam can be found in food processing
factories, refineries, and chemical plants to name a few. Saturated steam is used as the
heating source for process fluid heat exchangers, reboilers, reactors, combustion air
preheaters, and other types of heat transfer equipment
11. Steam for Propulsion/Drive:
Steam is regularly used for propulsion (as a driving force) in applications such as
steam turbines, Superheated steam is often used in steam turbines to prevent damage
to equipment caused by the inflow of condensate.
The driving force from the steam causes the fins
to turn, which then causes the rotor on the
attached power generator to rotate, and this
rotation generates electricity.
Besides power generation, other typical propulsion
/drive applications are usually for either
turbine-driven compressors or pumps, ex. gas
compressors, cooling tower pumps, etc
12. Steam as Motive Fluid:
Steam can also be used as a direct “motive” force to move liquid and gas streams in
piping. Steam jet ejectors are used to pull vacuum on process equipment such as
distillation towers to separate and purify process vapor streams. They are also used for
continuous removal of air from surface condensers, in order to maintain desired vacuum
pressure on condensing (vacuum) turbines
High pressure motive steam enters the jet ejector
through the inlet nozzle and is then diffused.
This creates a low pressure zone which entrains air
from the surface condenser.
In a similar type of application, steam is also
the primary motive fluid for secondary pressure
drainers, which are used for pumping condensate
from vented receiver tanks, flash vessels, or steam
equipment that experiences stall conditions
13. Steam for Atomization:
Steam atomization is a process where steam is used to mechanically separate a
fluid. In some burners, for example, steam is injected into the fuel in order to
maximize combustion efficiency and minimize the production of hydrocarbons
(soot). Steam boilers and generators that use fuel oil will use this method to
break up the viscous oil into smaller droplets to allow for more efficient
combustion. Flares also commonly use steam atomization to reduce pollutants in
the exhaust
In flares, steam is often mixed in with the waste gas before combustion.
14. Steam for Cleaning:
Steam is used to clean a wide range of surfaces. One such example from industry
is the use of steam in soot blowers. Boilers that use oil or coal as the fuel source
must be equipped with soot blowers for cyclic cleaning of the furnace walls and
removing combusted deposits from convection surfaces to maintain boiler
capacity, efficiency, and reliability.
Steam released out of the soot blower
nozzle dislodges the dry or sintered ash
and slag, which then fall into hoppers or
are carried out with the combusted gasses.
15. Steam for Moisturization:
Steam is sometimes used to add moisture to a process while at the same time
supplying heat. For example, steam is used for moisturization in the production
of paper, so that paper moving over rolls at high speed does not suffer
microscopic breaks or tears. Another example is pellet mills. Often mills that
produce animal feed in pellet form use direct-injected steam to both heat and
provide additional water content to the feed material in the conditioner section of
the mill.
The moisturizing of the feed softens the feed and partially gelatinizes the starch
content of the ingredients, resulting in firmer pellets
16. Steam for Humidification:
Many large commercial and industrial facilities, especially in colder climates, use
low pressure saturated steam as the predominant heat source for indoor seasonal
heating. HVAC coils, often combined with steam humidifiers, are the equipment
used for conditioning the air for indoor comfort, preservation of books and records,
and infection control. When the cold air is heated by the steam coils, the relative
humidity of the air drops, and it must then be adjusted to normal levels with
addition of a controlled injection of dry saturated steam into the downstream air
flow.
Steam Humidifier in Air Duct
Steam is used to humidify air within an air duct
before the air is distributed to other regions of a
building.
