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## Economics of Steam

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### Economics of Steam

Improving overall steam plant efficiencies in the Feed Mill

Animal Feed Technologies

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.

Animal Feed Technologies

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 ReviewAnimal Feed Technologies

Basic Steam Generation Graph

Animal Feed Technologies

Steam Generation Graph

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Basic HP Steam design

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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)Animal Feed Technologies

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

Animal Feed Technologies

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)Animal Feed Technologies

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.

Animal Feed Technologies

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

Animal Feed Technologies

Steam Quality

Animal Feed Technologies

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.

Animal Feed Technologies

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.

Animal Feed Technologies

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.

Animal Feed Technologies

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

Animal Feed Technologies

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)

Animal Feed Technologies

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.

Animal Feed Technologies

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

Animal Feed Technologies

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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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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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

Animal Feed Technologies

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.

Animal Feed Technologies

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.

Animal Feed Technologies

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.

Animal Feed Technologies

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.

Animal Feed Technologies

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

Animal Feed Technologies

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.

Animal Feed Technologies

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.

Animal Feed Technologies

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.

Animal Feed Technologies

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.

Animal Feed Technologies

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