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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.

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Economics of Steam


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economics of steam

Economics of Steam

Improving overall steam plant efficiencies in the Feed Mill

Animal Feed Technologies

basic steam principles review
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.

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basic steam principles review3
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 Principles Review

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basic steam generation graph
Basic Steam Generation Graph

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steam generation graph
Steam Generation Graph

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basic hp steam design
Basic HP Steam design

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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

Calculating Energy Requirements(Optimum)

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factors effecting energy requirements
Factors effecting Energy Requirements
  • Boiler Efficiency = Output / Input

Output = Input – Losses

Boiler Efficiency = 100% - % losses

  • Losses:

Burner – Tube Transfer (Scale, Sludge)

Radiation – Stack

  • Steam Quality
  • Distribution System

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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)

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factors effecting energy requirements losses10
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.

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factors effecting energy requirements steam quality
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

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steam quality
Steam Quality

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steam quality13
Steam Quality

Other 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.

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factors effecting energy requirements distribution system
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.

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factors effecting energy requirements distribution system15
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.

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calculating energy requirements
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

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calculations
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)

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calculations18
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.

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calculations19
Calculations

Adding 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

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calculations20
Calculations

Feed 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.

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calculations21
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.

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calculations22
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

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calculations23
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.

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example of energy requirement
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.

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example of energy requirement30
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.

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improving energy requirements
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.

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improving energy requirements32
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

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improving energy requirements33
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.

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managing energy usage
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.

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managing energy usage35
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.

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conclusion
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.

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