Energy Tips Benchmark the Fuel Cost of Steam Generation

Steam
Compressed Air
Motors
Effective Cost of Steam
The effective cost of steam
depends on the path it follows
from the boiler to the point of
use. Take a systems approach
and consider the entire boiler
island, including effect of blow-
down, parasitic steam consump-
tion, deaeration, etc. Further
complications arise due to the
process steam loads at different
pressures, multiple boilers, and
waste heat recovery systems. To
determine the effective cost of
steam, use a combined heat and
power simulation model that
includes all the significant effects.
Multi-Fuel Capability
For multi-fuel capability boilers,
take advantage of volatility in
fuel prices by periodically ana-
lyzing the steam generation cost
and use the fuel that provides the
lowest steam generation cost.
Higher Versus Lower
Heating Values
Fuel is sold based on its gross or
higher heating value (HHV). If,
at the end of the combustion
process, water remains in the
form of vapor, the HHV must be
reduced by the latent heat of
vaporization of water. This
reduced value is known as the
lower heating value (LHV).
Benchmark the Fuel Cost of Steam
Generation
Benchmarking the fuel cost of steam generation ($/1000 lbs of steam) is an effective way to assess
the efficiency of your steam system. This cost is dependent upon fuel type, unit fuel cost, boiler
efficiency feedwater temperature, and steam pressure. This calculation provides a good first
approximation for the cost of generating steam and serves as a tracking device to allow for boiler
performance monitoring. Table 1 shows the heat input required to produce one pound of saturated
steam at different operating pressures and varying feedwater temperatures. Table 2 lists the typical
energy content and boiler combustion efficiency for several common fuels.
Table 1. Energy Required to Produce One Pound of Saturated Steam (Btu)*
Operating
Pressure, psig
Feedwater Temperature, °F |
50
100
150
200
250
150
1,178
1,128
1,078
1,028
977
450
1,187
1,137
1,087
1,037
986
600
1,184
1,134
1,084
1,034
984
* Calculated from steam tables based on the difference between the enthalpies of saturated steam and feedwater.
Table 2. Energy Content and Combustion Efficiency of Fuels
Fuel Type (sales unit)
Energy Content
(Btu/sales unit)
Combustion
Efficiency (%)
Natural Gas (therm)
100,000
81.7
Natural Gas (cubic foot)
1,030
81.7
Distillate/No. 2 Oil (gallon)
138,700
84.6
Residual/No. 6 Oil (gallon)
149,700
86.1
Coal (ton)
27,000,000
87.6
Note: Combustion efficiency is based on boilers equipped with economizers and air preheaters and 3% oxygen in flue gas.
Data from the above tables can be used to determine the cost of usable heat from a boiler or
other combustion unit. The calculations can also include operating costs of accessories such
as feedwater pumps, fans, fuel heaters, steam for fuel atomizers and soot blowing, treatment
chemicals, and environmental and maintenance costs.
Example
A boiler, fired with natural gas costing $0.30/therm, produces 450 psig saturated steam and is
supplied with 230°F feedwater. Using values from the tables, calculate the cost of producing
steam.
Steam Cost = M H -lerm) » x 1000 x 1006 (Btu/lb) x — = $3.69/1000 lbs
100,000 (Btu/therm) 81.7
For additional information on
industrial energy efficiency
measures, contact the OIT
Clearinghouse at (800) 862-2086.

Suggested Actions
• Determine your annual fuel costs based on utility bills.
• Install a steam flowmeter in your facility and calculate your steam generation cost. Compare
this with the benchmark value.
• Using a systems approach, do a thermoeconomic analysis to determine the effective cost of
steam. (See sidebar: Effective Cost of Steam)
OFFICE OF INDUSTRIALTECHNOLOGIES
ENERGY EFFICIENCY AND RENEWABLE ENERGY • U.S. DEPARTMENT OF ENERGY

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About DOE's Office of Industrial Technologies
The Office of Industrial Technologies (OIT), through partnerships with industry,
government, and non-governmental organizations, develops and delivers advanced
energy efficiency, renewable energy, and pollution prevention technologies for industrial
applications. OIT is part of the U.S. Department of Energy's Office of Energy Efficiency
and Renewable Energy.
OIT encourages industry-wide efforts to boost resource productivity through a strategy
called Industries of the Future (IOF). IOF focuses on the following nine energy and
resource intensive industries:
• Agriculture
• Aluminum
• Chemicals
• Forest Products
• Glass
• Metal Casting
• Mining
• Petroleum
• Steel
OIT and its BestPractices program offer a wide variety of resources to industrial
partners that cover motor, steam, compressed air and process heating systems.
For example, BestPractices software can help you decide whether to replace or rewind
motors (MotorMaster+), assess the efficiency of pumping systems (PSAT), or determine
optimal insulation thickness for pipes and pressure vessels (3E Plus). Training is available
to help you or your staff learn how to use these software programs and learn more
about industrial systems. Workshops are held around the country on topics such as
"Capturing the Value of Steam Efficiency," "Fundamentals and Advanced Management
of Compressed Air Systems," and "Motor System Management." Available technical
publications range from case studies and tip sheets to sourcebooks and market assessments.
The Energy Matters newsletter, for example, provides timely articles and information on
comprehensive energy systems for industry. You can access these resources and more by
visiting the BestPractices Web site at www.oit.doe.gov/bestpractices or by contacting the
OIT Clearinghouse at 800-862-2086 or via email at clearinghouse@ee.doe.gov.
1
BestPractices is part of the Office of
Industrial Technologies' (OIT's) Industries
of the Future strategy, which helps the
country's most energy-intensive
industries improve their competitiveness.
BestPractices brings together the best-
available and emerging technologies
and practices to help companies begin
improving energy efficiency, environmental
performance, and productivity right now.
BestPractices focuses on plant systems,
where significant efficiency improvements
and savings can be achieved. Industry
gains easy access to near-term and
long-term solutions for improving the
performance of motor, steam, compressed
air, and process heating systems. In
addition, the Industrial Assessment Centers
provide comprehensive industrial energy
evaluations to small and medium-size
manufacturers.
FOR ADDITIONAL INFORMATION,
PLEASE CONTACT:
Eric Lightner
Office of Industrial Technologies
Phone: (202) 586-8130
Fax: (202) 586-1658
Eric.Lightner@ee.doe.gov
www.oit.doe.gov/bestpractices
OIT Clearinghouse
Phone: (800) 862-2086
Fax: (360) 586-8303
clearinghouse@ee.doe.gov
Please send any comments,
questions, or suggestions to
webmaster.oit@ee.doe.gov
Visit our home page at
www.oit.doe.gov
Office of Industrial Technologies
Energy Efficiency
and Renewable Energy
U.S. Department of Energy
Washington, D.C. 20585
0IT
D0E/G0-102000-1115
November 2000
Steam Tip Sheet #15

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