Transcript Understanding Steam - Grain Processing Experts

Effective Boiler
Utilization
Why go to all the trouble ?



Steam is an easy method for transferring heat
energy from a heat source to a heat load.
Addition of heat and moisture into the material
improves processing.
Goal is to produce a gelatinized material with
improved feed value.
Benchmark your cost of steam
production.



Determine your annual fuel cost based on utility
bills.
Install a steam flow meter or water flow meter in
your facility and calculate your steam generation
costs.
Compare your actual costs with the benchmark.

(Use a water flow meter on water feed into the boiler
will also cover boiler blow down effects.)
Performing Benchmark

You will need to know
the following.




Operating boiler pressure.
Feedwater Temperature.
Type of fuel used.
Cost of fuel.
Feed
Water
Temp
Op
Pressure
(PSIG)
53
101
162
198
60
1160.7
1112.2
1051.8
1016.2
80
1165.0
1116.5
1056.1
1020.5
90
1166.9
1118.4
1058.0
1022.4
100
1167.6
1119.1
1058.7
1023.1
Energy Required to Produce One Pound of
Saturated Steam, Btu.
Benchmark Continued
Fuel Type and
Sales Unit
Energy Content,
Btu/Sales unit
Combustion
Efficiency, %
Natural Gas,
MMBtu
1,000,000
85.7
Natural Gas,
Thousand cubic
feet
1,030,000
85.7
Distillate/No.2
Oil, gallon
138,700
88.7
Residual/No.6
Oil, gallon
149,700
89.6
27,000,000
90.3
Coal, Ton

Example
Producing 100 psig steam, 101 Deg F
feed water, and $7.50/MMBtu
Natural gas.
Steam Cost = ($7.50/MMBtu/106
Btu/MMBtu) * 1,000 lb * 1,119.1
Btu/lb/0.857
Steam Cost = $9.79/1,000 lb steam
Factors Effecting Steam Cost’s.





Feed Water Temperature.
Heat Transfer (Chemistry).
Burner Efficiency
Steam Application
Distribution System.
Steam Traps
 Condensate Return
 Insulation

Feed Water Temperature


Proper feed water temperature control can be a
major factor when looking at improving steam
system efficiencies.
Compare Benchmark calculation for 90 psig
steam at 53 Deg vs 162 Deg F feed water.
54 Deg F = $10.21/1,000 lb of steam
162 Deg F = $9.26/1,000 lb of steam
A difference of $0.95/1,000 lb of steam
production
Feed Water Temperature

1.
2.
3.
There are a several ways to increase the feed
water temperature in the system. Two of the
most common methods would be:
Direct Steam injection into the feed water
make-up tank with thermostatically controlled
valve.
Install Feedwater Economizer.
Proper condensate return and blowdown heat
exchangers.
Feed Water Temperature

Direct Steam Injection.
Steam injected directly
into the feed water tank
can be used as a heat
source, but it is
important to remember
that this is also a heat
load on the boiler and
will not provide a high
energy savings.

Economizer
Generally, boiler
efficiency can be
increased by 1% for
every 40 Deg. F
reduction in flue gas
temperature.
*Economizers have limits for both cold
end corrosion and exhaust gas
temperatures that must be observed.
Heat Transfer

Proper Boiler Chemistry control is critical in
efficient boiler operation as well as boiler safety.

1/50th of an inch of hard scale buildup on boiler
tubes can result in an increase in fuel usage of
up to $20,000/year.

Find a reliable boiler chemistry company and
perform tests as required.
Burner Efficiency

The purpose of the burner is to mix molecules
of fuel with molecules of air. A boiler will run
only as well as the burner performs. Burners are
designed to maximize combustion while
minimizing the release of emissions.

An efficient natural gas burner requires only 2 to
3% excess oxygen, or 10 to 15% excess air.
Burner Efficiency


Flue Gas Analyzers
The percentage of oxygen in
the flue gas can be measured
by inexpensive gas absorbing
test kits.
More expensive analyzers are
available that display %
Oxygen, stack gas temp., and
boiler efficiency. These are
recommended for boilers
with annual fuel costs over
$50,000.


Oxygen Trim Systems
If fuel composition is highly
variable or in cases where
steam flows are highly
variable, an online oxygen
analyzer should be
considered.
The oxygen “Trim” system
provides feedback to the
burner controls to
automatically minimize
excess combustion air and
maximize the fuel-to-air
ration
Steam Application


Boiler systems in the feed industry have few
similarities with industrial boiler systems. One of
the main differences is with the condensate
return system. Commercial boiler systems can
return over 90% of the condensate while boiler
systems in the feed industry typically return less
than 5% condensate into the feed water system.
In short, almost all of the steam delivered into
the distribution system is used or lost.
Steam Application

Performing the Benchmark test we learned that
even the best situation will result in a given
steam production cost.
60 psig - 198 deg F - $7.50/MMBtu = $8.89/1000 lb steam
100 psig – 198 deg F - $7.75/MMBtu = $8.95/1000 lb steam

By insuring that we are not over-steaming, we
can achieve enough heat input to cook while
minimizing the total steam contribution.
Steam Application
60 psig – 198 Deg F - $7.50/MMBtu
$8.89/1,000 lb of steam
100 psig – 198 Deg F - $7.50/MMBtu
$8.95/1,000 lb of steam
Adding 6% moisture in the steam
chest requires approx. 127 lbs of
steam application. At $0.0089 per
pound of steam that means that
adding 6% moisture (127 lbs) will
have a cost of $1.13 per ton.
Adding 6% moisture in the steam
chest requires approx. 127 lb of
steam application. At $0.0090 per
pound of steam, that means that
adding 6% moisture (127 lbs) will
have a cost of $1.14 per ton.
Compare this to adding only 3%
moisture, 62 lbs, and a cost of
$0.55 per ton.
Compared to $0.56 per ton for 3%
The higher pressure also insures
that enough heat will be added for
cooking with the reduced stem
addition
Steam Application
There are a few options when looking at monitoring steam application. The object
is to provide enough heat input for cooking while minimizing pounds added.

Steam Flow Meters: There
are a number of steam flow
meters that can be installed in
the distribution system to
allow operators to monitor
and adjust steam application
within specified ranges to
insure adequate cooking
while minimizing the pounds
applied.
Distribution System


The steam distribution system includes
everything from the boiler discharge valve out to
the processing units and any condensate return
system that may be in place.
The boiler blow down system, while not actually
part of the distribution system may also offer
some efficiency options and should be looked
at.
Distribution System



Steam Traps
Every distribution system should include steam traps.
Steam traps provide a means for removing water
droplet and condensate from the header prior to
utilizing the steam for heating.
While extremely important in turbine applications, they
also are important in our process to insure the highest
energy and best quality steam is being applied.
Steam Traps

Steam loss from traps.
Trap Orifice
Diameter, Inches

Steam loss, lb/hr
100 psig
1/32
3.3
1/16
13.2
1/8
52.8
3/16
119
¼
211
3/8
475


Steam traps should be
tested to insure they are
not cold plugging or
failing open allowing
steam to escape directly
into the CR line
Four ways to test:
Temp., Sound, Visual,
Electronic
Traps should be tested
monthly to Quarterly.
Condensate Return

Returning hot condensate to the boiler makes
sense for several reasons.
1.
The more condensate that is returned, the less makeup water is required.
Chemicals and Chemical treatment costs.
Fuel savings with higher temperature make-up water.
Reduced boiler blowdown with return of high purity
water.
2.
3.
4.
Insulation



Un-insulated steam piping is a constant source
of wasted energy.
Proper insulation can typically reduce energy
losses by 90% and help insure proper steam
pressure at processing equipment.
Any surface over 120 Deg. F should be insulated
including boiler surfaces, steam piping and
fittings, and CR lines.
Insulation
Pipe Size,
Inches
MMBtu/yr loss per
100 feet
0.5
160
1
240
2
400
4
700
6
985
8
1270
10
1550
12
1820


Proper insulation can
provide a great deal of
energy savings when
properly selects and
maintained.
Use insulating jackets for
valves, flanges and traps.
A 6-inch gate valve may
have more than 6 sq. feet
of surface area.
Conclusion




There are obviously a number of factors that
effect boiler utilization and efficiency.
If you don’t know what your cost of steam
production is, how can you improve it.
If your not monitoring your steam usage, it is
impossible to tell if you are being efficient.
Use the various resources available to you for
better steam and boiler utilization
Resources

www.eere.energy.gov/industry/bestpractices
This site has a lot of information available and can be a great resource for
improving efficiencies.