economics of steam

Animal Feed Technologies

Economics of Steam

Improving overall steam plant efficiencies in the Feed Mill


Basic Steam Principles Review

• 1 pound mass of steam addition is equal to 1 pound of water addition.

• Water at 32 deg F has 0 BTU/lb of energy.

• Water at 212 deg F has 180.2 BTU/lb of energy.

• Steam at 212 deg and 0 psig has 1150.5 BTU/lb of energy.


Basic Steam Principles Review

• Sensible Heat:

Heat which results in a temperature increase.

Water at 212 deg F has 180.2 BTU/lb of sensible heat.

• Latent Heat:

Heat which causes a change of state (Water to vapor).

Steam at 212 deg F and 0 psig, has a total energy of 1150.5 BTU/lb. 970.3 BTU of latent heat and 180 .2 BTU/lb of sensible heat


Basic Steam Generation Graph


Steam Generation Graph


Basic HP Steam design


Calculating Energy Requirements(Optimum)

Heating Requirements• Q=cm▲T

Q = Energy

c = Specific heat

m = Mass

▲T= Temperature Increase.

Calculation

Q = (.504) * 2000*112

C = .477 btu/lb F(14%)

C = .531 btu/lb F(20%)

C avg = .504 btu/lb F

Q = 112,896 btu

Q = 1.128 therms/ton


Factors effecting Energy Requirements

• Boiler Efficiency = Output / InputOutput = Input – LossesBoiler Efficiency = 100% - % losses

• Losses:Burner – Tube Transfer (Scale, Sludge)Radiation – Stack

• Steam Quality • Distribution System


Factors effecting Energy Requirements(Losses)

Combustion Efficiency

(Natural Gas)

• Curves relate %CO2

net stack temperature.

• 10% CO2 and 400 deg net stack temp equals a combustion efficiency of 81%.

Tube Transfer

(Chemistry)• 1/50th of an inch of

scale build up on the boiler tubes can increase fuel cost as much as $20,000 yr at a fuel cost of $0.65/therm.


Factors effecting Energy Requirements(Losses)

Radiation Loss• A comprehensive term

covering conduction, radiation and convection losses to the ambient air.

• Anything that can loose heat, should be insulated.


Factors effecting Energy Requirements(Steam Quality)

• Steam Quality is defined as the percentage of steam contained in a mixture.

• “Wet Steam” – A term commonly used for steam qualities of less than 100%

• “Dry Steam” – A term commonly used for steam qualities equal to 100%

• A number of factors can affect steam quality


Steam Quality


Steam QualityOther problems with Low quality Steam:

• Surging Boiler water levels or Nuisance low water Cut-Out operations.

• Difficulty in maintaining boiler chemical levels or over use of boiler chemicals.

• Apparent decrease in Boiler Capacity.• Increase in Overall Maintenance – Steam

trap and control component failure, and increased corrosion problems.


Factors effecting Energy Requirements(Distribution System)

• Overall length from steam source to end use.

• Use and operation of steam separators and traps.

• Proper insulation on steam lines and headers.


Factors effecting Energy Requirements(Distribution System)

Steam leaks in the steam lines or Traps can be a large source of energy loss.

• A 1/16th inch leak in a 100 psi steam line results in 13.2 lb/hr loss.

• A 1/8th in leak in a 100 psi steam line results in a 52.8 lb/hr loss.


Calculating Energy Requirements• Optimum energy requirement = 112.896 btu

Some assumptions for this calculation:

Combustion Efficiency = 85%

Tube Transfer = 90%

Radiation Loss = 10%

Steam Quality = 90%

Steam leaks = 2 @ 1/16th and 1 @ 1/8th inch.

Production rate of 60 ton/hr


Calculations

We need to Calculate from the Steam Chest Back to the boiler and then add any raw steam losses.

• Optimum Energy Required = 112,896 Btu/ton

• Steam Quality of 90% causes a loss in energy of 8.4%:

(112,896 btu / .916 = 123,249 btu)

• Radiation loss of 10%:

(123,249 btu / .9 = 136,943 btu)

• Tube Transfer of 90%:

(136,943 btu / .9 = 152,159 btu)


Calculations• Combustion Efficiency of 85%:

(152,159 btu / .85 = 179,011 btu)

• This calculations shows that while our optimum energy requirement is only 112,896 btu/ton, after adding the system losses, the required energy changes to 179,011 btu/ton.


CalculationsAdding in the effect of steam leaks:

• 2 1/16th inch steam leaks with a header pressure of 100 psi• 1 1/8th inch steam leak with a header pressure of 100 psi.

• 2 @13.2 lbs/hr = 26.4 lbs/hr• 1 @ 52.8 lbs/hr = 52.8 lbs/hr• Total steam loss = 79.2 lbs/hr• 79.2 lbs of steam at 100 psi:

(79.2 lbs @ 1187 btu/lb = 94,010 btu’s)• 94,010 btu’s / 60 ton/hr = 1,567 btu’s/ton

• 179,011 btu/ton + 1,567 btu/ton = 180,578 btu/ton


CalculationsFeed water temperature:

• All Steam tables are calculated with the assumption that feed water temperature is 212 deg.

• When feed water temperature drops below 212 deg. The amount of energy input to the boiler increases dramatically.

• British Thermal Unit (Btu): The heat required to raise one pound of water one degree F between 32 and 212 degrees F.


Calculations• If we assume that we are adding 4 points of

moisture with steam in the chest then we are adding approx. 128 lbs or water per ton of grain.

• If the feed water temperature is at 190 deg., we need to add an additional 22 btu’s per pound of water.

(128 lbs x 22 btu/lb = 2,816 btu)• We still need to calculate the efficiency losses to

get the total energy requirement for this added energy.


Calculations• 2,816 btu / 85% = 3,313 btu (Combustion)

• 3,313 btu / .9 = 3,681 btu (Tube x-fer)

Adding all together.• Boiler system requirement = 179,011 btu• Steam leaks and traps = 1,567 btu• Feedwater temperature = 3,681 btu

• Total Btu required = 184,259 btu / ton• Total Therm requirement = 1.84 therms/ton


Calculations• Optimum energy requirement = 112,896 btu

• Calculated energy req’d = 184,259 btu

• As we can see, due to losses in the steam system, distribution system, and the boiler make-up system we are actually required to add 63% more energy input to provide us with our energy need.


Calculating energy requirement.

To increase the temperature of 2000 lbs of grain from 100 F to 212 F the following calculations is used.

Q = C M ? T C = .504 Btu/lb F (Average of grain moistures from 14 to 20%)M = 2,000 lbs? T = 112 deg F (212 – 100)

This calculation shows an optimum steam requirement of 112,896 btu’s per ton of grain.

Calculating your individual energy needs with system losses.

1. Steam Quality : ______________ Your steam quality.

112,896 btu’s / (100% - _________ ) = ____________________ Btu’s Your steam qlty


2. Radiation Loss: _____________ Your radiation loss. (Minimum of 10%)

__________ btu’s / (100% - __________ ) = ________________ Btu’sBtu’s from step 1 Your radiation loss

3. Tube Transfer : ______________ Your tube transfer loss (Minimum of 5%)

__________ btu’s / (100% - __________ ) = ________________ Btu’sBtu’s from step 2 Your tube x-fer loss

4. Combustion Efficiency: ____________ Your Combustion Efficiency.

___________ btu’s / _____________ = __________________ Btu’sBtu’s from step 3 Your burner efficiency


5. Steam Leaks: Consult the steam flow thru steam trap orifice table to calculate flow rate.

Total lbs/hr of steam leakage = _______________ lbs

Total tons production per hour = ______________ tons

Btu’s hr loss from steam = ________ lbs/steam x ________ btu/lb mass (from

steam table) = ______________ Btu/hr energy loss due to leaks.

___________ Btu/hr loss / ____________ tons/hr = _____________ btu loss/ton


6. Feed water temperature:

Temperature of boiler feedwater tank = ___________ deg F.

212 Deg F - ___________ = __________ deg below 212.Feedwater temp

Moisture added in the steam chest = _______________ %

2000 lbs / (100% - __________ ) = ____________ total weight with moisture. Moisture in chest

_________ Total weight – 2000 lbs = _________ Lbs of water added in chest

___________ x ____________ = ____________ Additional Btu’s needed.Deg below 212 Lbs of water added


Total energy required:

Total from item 4 (Steam quality, radiation, Tube and Combustions) ____________ btu

Total from item 5 (Steam leaks and faulty traps) ____________ btu

Total from item 6 (Low boiler water make-up temperature ____________ btu

Total calculation for your system ____________ btu

Overall calculated system efficiency:

__________________ btu - 112,896 btu’s = _________________ btu’sYour total system calculation Additional btu’s required

__________________ btu / 112,896 btu’s = _______ % energy required over optimal.Additional btu’s required


Example of energy requirement

• Commercial feed mill processing 75 ton/hr

• Gas meter shows a usage of 164 therms/hr

• Therm per ton usage of 2.19

• Optimum calculation shows a need of 1.13 therms/ton.

• Energy usage is 93% higher than optimal.


Example of energy requirement

Some possible reasons for this difference:

• Adding more than 4 pt’s moisture with steam in the chest.

• Boiler make-up water temperature.

• Steam leaks

• Auxiliary steam loads not in the calculation.


Improving Energy Requirements

• Combustion Efficiency:Work with your boiler company to ensure that your burner efficiency is optimal for the load and cycles for your needs.

• Tube heat transfer efficiency:Maintain proper chemistry, have qualified operators responsible for maintaining your boiler chemistry and make-up water chemistry.


Improving Energy Requirements• Radiation Loss:

If you can feel heat, then is should be insulated. Remember that insulation thickness needs to be based on your coldest expected ambient temperatures.

• Steam Quality: Again, Proper chemistry is important. Also, make sure all of the boiler trim system is maintained and operating properly


Improving Energy Requirements• Steam Leaks:

Maintain proper operation on all steam traps. Have a good preventative maintenance program to take care of leaks.

• Feed Water Temperature:Make sure you are using some kind of heat recovery or heat input to your boiler make up water. Condensate returns will also lower chemical requirements.


Managing Energy Usage

• Steam Flow Meters:These meters can be used to monitor the actual pounds mass of steam being applied to the steam chest or total system.

• Natural Gas Meters:It is possible to work with your gas company and install gas meters with analog outputs to monitor therm per ton usage.


Managing Energy Usage• Automatic Steam valve controls:

Have the ability to more effectively control steam application to the steam chest. Must insure that the PID loop control is continually limiting.

• Ensure you have quality well trained operators:This could be the most important management item of all. Do not expect untrained operators to understand the importance of what they do.


Conclusion• There are a multitude of factors in steam

production that effect your overall steam system efficiency.

• Monitoring your energy usage per ton is important.

• Make sure your operators know what they are doing and the impact that they can have on the total cost of production.

economics of steam

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