boiler utilization

7/29/2019 Boiler Utilization

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Effective BoilerUtilization


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Why go to all the trouble ?

Steam is an easy method for transferring heatenergy from a heat source to a heat load.

Addition of heat and moisture into the materialimproves processing.

Goal is to produce a gelatinized material withimproved feed value.


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Benchmark your cost of steam

production.

Determine your annual fuel cost based on utilitybills.

Install a steam flow meter or water flow meter inyour facility and calculate your steam generationcosts.

Compare your actual costs with the benchmark.

(Use a water flow meter on water feed into the boilerwill also cover boiler blow down effects.)


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Performing Benchmark

You will need to knowthe following.

Operating boiler pressure.

Feedwater Temperature. Type of fuel used.

Cost of fuel.

Feed Water Temp

OpPressure(PSIG)

53 101 162 198

601160.7 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 ofSaturated Steam, Btu.


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Benchmark Continued

Fuel Type andSales Unit

Energy Content,Btu/Sales unit

CombustionEfficiency, %

Natural Gas,MMBtu

1,000,000 85.7

Natural Gas,Thousand cubicfeet

1,030,000 85.7

Distillate/No.2Oil, gallon

138,700 88.7

Residual/No.6Oil, gallon 149,700 89.6

Coal, Ton 27,000,000 90.3

Example

Producing 100 psig steam, 101 Deg F

feed water, and $7.50/MMBtuNatural gas.

Steam Cost = ($7.50/MMBtu/106Btu/MMBtu) * 1,000 lb * 1,119.1Btu/lb/0.857

Steam Cost = $9.79/1,000 lb steam


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Factors Effecting Steam Costs.

Feed Water Temperature.

Heat Transfer (Chemistry).

Burner Efficiency Steam Application

Distribution System.

Steam Traps Condensate Return

Insulation


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Feed Water Temperature

Proper feed water temperature control can be amajor factor when looking at improving steamsystem efficiencies.

Compare Benchmark calculation for 90 psigsteam 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 steamA difference of $0.95/1,000 lb of steamproduction


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There are a several ways to increase the feedwater temperature in the system. Two of themost common methods would be:

1. Direct Steam injection into the feed watermake-up tank with thermostatically controlledvalve.

2. Install Feedwater Economizer.3. Proper condensate return and blowdown heat

exchangers.


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Direct Steam Injection.

Steam injected directlyinto the feed water tank

can be used as a heatsource, but it isimportant to rememberthat this is also a heat

load on the boiler andwill not provide a highenergy savings.

Economizer

Generally, boilerefficiency can be

increased by 1% forevery 40 Deg. Freduction in flue gastemperature.

*Economizers have limits for both coldend corrosion and exhaust gastemperatures that must be observed.


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Heat Transfer

Proper Boiler Chemistry control is critical inefficient boiler operation as well as boiler safety.

1/50th of an inch of hard scale buildup on boilertubes can result in an increase in fuel usage ofup to $20,000/ year.

Find a reliable boiler chemistry company andperform tests as required.


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Burner Efficiency

The purpose of the burner is to mix moleculesof fuel with molecules of air. A boiler will runonly as well as the burner performs. Burners are

designed to maximize combustion whileminimizing the release of emissions.

An efficient natural gas burner requires only 2 to3% excess oxygen, or 10 to 15% excess air.


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Burner Efficiency Flue Gas Analyzers

The percentage of oxygen inthe flue gas can be measuredby inexpensive gas absorbingtest kits.

More expensive analyzers areavailable that display %Oxygen, stack gas temp., andboiler efficiency. These arerecommended for boilers

with annual fuel costs over$50,000.

Oxygen Trim Systems

If fuel composition is highlyvariable or in cases wheresteam flows are highly

variable, an online oxygen

analyzer should beconsidered.

The oxygen Trim systemprovides feedback to theburner controls to

automatically minimizeexcess combustion air andmaximize the fuel-to-airration


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Steam Application

Boiler systems in the feed industry have fewsimilarities with industrial boiler systems. One ofthe main differences is with the condensate

return system. Commercial boiler systems canreturn over 90% of the condensate while boilersystems in the feed industry typically return lessthan 5% condensate into the feed water system.

In short, almost all of the steam delivered intothe distribution system is used or lost.


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Steam Application

Performing the Benchmark test we learned thateven the best situation will result in a givensteam production cost.

60 psig - 198 deg F - $7.50/MMBtu = $8.89/1000 lb steam

100 psig198 deg F - $7.75/MMBtu = $8.95/1000 lb steam

By insuring that we are not over-steaming, wecan achieve enough heat input to cook whileminimizing the total steam contribution.


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Steam Application60 psig198 Deg F - $7.50/MMBtu

$8.89/1,000 lb of steam

Adding 6% moisture in the steamchest requires approx. 127 lbs ofsteam application. At $0.0089 per

pound of steam that means thatadding 6% moisture (127 lbs) willhave a cost of $1.13 per ton.

Compare this to adding only 3%

moisture, 62 lbs, and a cost of$0.55 per ton.

100 psig198 Deg F - $7.50/MMBtu

$8.95/1,000 lb of steam

Adding 6% moisture in the steamchest requires approx. 127 lb ofsteam application. At $0.0090 per

pound of steam, that means thatadding 6% moisture (127 lbs) willhave a cost of $1.14 per ton.

Compared to $0.56 per ton for 3%

The higher pressure also insuresthat enough heat will be added forcooking with the reduced stemaddition


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Steam Application

Steam Flow Meters: Thereare a number of steam flowmeters that can be installed inthe distribution system toallow operators to monitorand adjust steam application

within specified ranges to

insure adequate cookingwhile minimizing the poundsapplied.

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.


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Distribution System

The steam distribution system includeseverything from the boiler discharge valve out tothe processing units and any condensate return

system that may be in place.

The boiler blow down system, while not actuallypart of the distribution system may also offer

some efficiency options and should be lookedat.


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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 toutilizing the steam for heating.

While extremely important in turbine applications, they

also are important in our process to insure the highestenergy and best quality steam is being applied.


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Steam Traps

Steam loss from traps.

Steam traps should betested to insure they arenot cold plugging orfailing open allowingsteam to escape directlyinto the CR line

Four ways to test:Temp., Sound, Visual,Electronic

Traps should be testedmonthly to Quarterly.

Trap OrificeDiameter, Inches

Steam loss, lb/hr

100 psig

1/32 3.3

1/16 13.2

1/8 52.8

3/16 119

211

3/8 475


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Condensate Return

Returning hot condensate to the boiler makessense for several reasons.

1. The more condensate that is returned, the less make-

up water is required.

2. Chemicals and Chemical treatment costs.

3. Fuel savings with higher temperature make-up water.

4. Reduced boiler blowdown with return of high puritywater.


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Insulation

Un-insulated steam piping is a constant sourceof wasted energy.

Proper insulation can typically reduce energylosses by 90% and help insure proper steampressure at processing equipment.

Any surface over 120 Deg. F should be insulatedincluding boiler surfaces, steam piping andfittings, and CR lines.


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Insulation

Proper insulation canprovide a great deal ofenergy savings when

properly selects andmaintained.

Use insulating jackets forvalves, flanges and traps.

A 6-inch gate valve mayhave more than 6 sq. feetof surface area.

Pipe Size,

Inches MMBtu/yr loss per100 feet0.5 1601

240

2 4004 7006 9858 1270

10 155012 1820


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Conclusion

There are obviously a number of factors thateffect boiler utilization and efficiency.

If you dont know what your cost of steam

production is, how can you improve it.

If your not monitoring your steam usage, it isimpossible to tell if you are being efficient.

Use the various resources available to you forbetter steam and boiler utilization


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Resources

www.eere.energy.gov/industry/bestpractices

This site has a lot of information available and can be a great resource for

improving efficiencies.
http://www.eere.energy.gov/industry/bestpracticeshttp://www.eere.energy.gov/industry/bestpractices

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