Hey folks, Brad Suttlef here for another chemical engineering concept video. Today we're going to
talk about steam boiler systems, process flow, diagrams and material balances. In addition to that
we're going to take a walk out in the field and see what all this stuff looks like in real life
for our small batch processing facility here in Lockhaven Pennsylvania. Start with the process flow
diagram for the boiler system which i have drawn up here on the whiteboard in our conference room.
It all starts with the feed water. We basically get city water from the city of Lockhaven,
goes through a water softener system, we're not going to talk about a lot of these components
of detail you could research them at your leisure, but the purpose of a water softener
is to substitute any of the heavier ions that come in
with the city water, such as magnesium and calcium which cause scaling issues in boilers,
and replace them with softened sodium ions. This actually goes through a regeneration purge cycle
with a salt brine solution, which displaces these ions and then moves the softened water through.
So from there the softened water goes into what's called a deaerator, and we have what's called a
spray type deaerator, where effectively the water comes into this tray type thing which drops down
into what looks like a bucket and a sparge with steam. The purpose of that is to heat up the water
coming in, to drive off any dissolved oxygen and carbon dioxide which cause corrosion issues and
boilers through the vent and we'll get back around to the steam purge later. From there the feed water
goes into a feed water pump which gets pumped into the boiler for boiling and steam generation.
In addition to that, we have two other smaller liquid streams. Boilers require chemical treatment
to prevent corrosion scaling and other problems. We have two we have a small sulfite solution
drum that we have with a small metering pump. That sulfite solution gets injected into the
deaerator and the sulfite scavenges any remaining oxygen that the aeration process doesn't eliminate.
And we have another drum with a cocktail of various ingredients that prevent corrosion,
scaling, other boiler issues, also ph adjustment as there's a little bit of caustic in it. They
get fed into the feed water which also goes into the boiler, keeps the boiler healthy. From there,
water gets boiled and we have steam generation and our plant steam goes two main places.
We have one stream which purges the deaerator causes contact through this
little scrubber plot system to drive off the dissolved oxygen and carbon dioxide.
And we also have steam that goes to all the other major areas in the plant and the steam
we produce in our boiler is 80 psig saturated steam. After going through various heating uses,
it gets condensed into liquid water again and pumped transferred back to the boiler system or
dump the drain. So we have some streams that are returned condensate, they go all the way
back through the plant into the boiler system along with the feed water into the deherator.
And then we have some streams which are simply dump right to the drain. In
addition to condensate, there's two other streams that get dumped to the drain.
We have what's called blow down, and the purpose of that is to balance the treatment chemicals
to make sure they don't build up in the boiler and you keep the proper balance
for the concentrations that are needed. We have a daily 30 to 60 second sediment blow down
where we purge the water out and any dirt that may be collecting in the mud drum, as we call it.
We also have a small amount of treatment chemicals that come out with it. We also have a surface
blow down which is a very small half inch line continuous flow. The main purpose of this is to
balance the treatment chemical concentration in the boiler to make sure we don't have an excess,
and we don't have too much. So this takes a little bit of trial and error to get that, but if you
sample and analyze for your treatment chemicals, you can figure out quite easily how to balance it.
So that pretty much goes over all the liquid streamsM, now let's talk about the combustion
side. Very simple, we get natural gas from our utility company which happens to be UGI.
We also get combustion air which comes right in from the atmosphere with a blower.
Those two get mixed in the firebox and obviously there's a burner in there
creating the flame and the heat. That heat passes over the tubes of our water tube boiler
and then the liquid that's contained in the mud drum and part of the steam drum gets boiled.
Given off of steam as we already discussed. Then the combustion gases come out the boiler
stack in the roof of the boiler room, where we have some excess air carbon dioxide, maybe
some carbon monoxide and water vapor from the combustion reaction. And we could spend
days and weeks talking about boiler efficiency, combustion efficiency, so on and so forth, but
we're just here to give you a general idea of what's going on. So now that we've gone over that,
let's go take a walk out in the field and see the boiler system in real
life. Let's try to put a visual to the diagram that we just reviewed. Right here is the plant boiler.
This is a water tube style boiler and we're going to go ahead and kind of walk through
the different components of the system that'll follow right along with the process.
Here's your very first input stream which is the actual feed water that goes to the boiler
de-aerator. This is a small water softener system, actually kind of similar to what you
might find in a home. Basically city water from the city of Lockhaven comes in and goes through
the softener system and the higher metals exchange with sodium ions to soften the water,
and from there it goes to the actual de-aerator. So here is the aerator for the boiler
and if you look up here and we zoom in that is the control valve that regulates the flow of the
all the oxygen. And from there, all the oxygen
From there, the transfer line progresses up through the boiler room down through
a series of check valves to prevent backflow. And then finally up into the boiler steam drum.
From there water gets in, turns into steam and exits through the main steam header to various different areas of the plant.
Here's two of our smaller input streams for the boiler system which are the treatment chemicals.
We have two, the first one here is a sulfite powder and the purpose of the sulfite powder is to help
tie up and chemically consume any of the oxygen that doesn't get driven off by the aerator system.
So that slowly gets fed and dosed directly into the aerator it gets carried over with the boiler
feed water. Next stream of chemical we have is kind of a all-in-one cocktail for boiler treatment
with a corrosion inhibitor anti-scaling agent and all kinds of other good stuff.
You get these from various manufacturers that make water treatment chemicals. From here it gets
dose from the makeup drum up and directly into the boiler feed water line on its way into the boiler.
So as we continue on our path of the water which goes from feed water, to steam, out to
plant distribution, we have two situations then. One for example like we have on this wastewater tank,
is steam goes into the heating coil to keep the waste water warm in the winter time, but
in this particular case we dump it right to the drain and it goes to waste water.
So some of the water that gets converted into steam ends up just going
right down the drain. And again in other situations sometimes the steam gets condensed from various heating processes and collected.
like in this example here where the steam condensate gets collected into
a small tank. and then from here the tank actually gets pumped back into a piping.
We also have two very small waste streams from the boiler that's required so chemicals and
also conductivity creating elements doesn't get collected into the boiler system. We have what
we call a surface blow down which has a small valve that's continuously cracked to bleed just
a little bit of water out of the boiler and into our blow down drums straight down to the drain.
And then once a day, for about 30 to 60 seconds, to remove any sediment that's collected on the bottom
mud drum of the boiler we open our blow down valves blow out down for about 30 seconds to
a minute we evacuate any buildup of sediment in the bottom which also goes right down the drain.
That concludes the lock down of the water side of the boiler now let's look at the combustion side
of the boiler. So we have natural gas from the utility company that comes into the boiler room.
It goes through a series of pressure reducing regulators to drop the pressure.
So the pressure of the natural gas coming into the boiler is only about six psi. From there it
goes through a series of safety valves, which shut and killed hold of the boiler in case any
issues occur. From there the natural gas goes through a control valve, which regulates the
flow of natural gas into the boiler for heating demand requirements. And in this particular case
right here, we have very low demand as we're on the minimum setting and lowest speed pressure.
And from there, natural gas goes into the boiler into the actual combustion chamber.
We have a nice viewing window of where it gets heated and reacts with the oxygen in the air.
We have a basic natural gas oxygen combustion reaction which provides the heat,
which then heats the tubes of the water tube boiler. So the tubes actually extend
kind of in this shape right here from top to bottom. If you look up the water to boiler
you'll see various examples. Lower drum they call the mud drum which we talked about, where
the sediment collects and gets blown out. And then as the tubes get heated by the natural gas,
and boils up into the steam drum and steam comes off the top into the steam distribution header
which we saw in our water sidewalk. So now we're standing on the very top of the boiler
where it's quite warm. The air for the combustion reaction comes in with a combustion fan.
You can see there's a little mechanism on it for the combustion control that actually regulates
the flow of air in and out instead of dampers. From there it reacts with natural gas and cluster
reaction for heat, and after it passes over the tubes it goes out the ceiling in the boiler stack.
Well that concludes the field walk through of the boiler system, both the water and combustion side. I hope you all enjoyed the video and maybe learned a little something new today.
Thanks again, and let's have one last look at that raging inferno!