this article, cogeneration tech-
nology and benets are explained, and what
cogeneration can bring to the candy indus-
try specically is explored.
WHAT IS COGENERATION (OR CHP)?
Energy is a major driving force in our econ-
omy. All buildings need electric power for
lighting and operating equipment and appli-
ances. Major consumers of energy in buildings
are cooling, heating and humidity control.
Two-thirds of all the fuel used to make
electricity in the United States is generally
wasted from power generation equipment
into the air or into water streams. While
there have been impressive energy effi-
ciency gains in other sectors of the econ-
omy since the oil price shocks of the 1970s,
the average efficiency of power generation
within the United States has remained
around 33 percent since 1960.
Integrated systems for cooling, heating
and power systems signicantly increase the
efficiency of energy utilization by using ther-
mal energy from power generation equip-
ment for cooling, heating and humidity con-
trol systems. These systems are located at
or near the building using power and space
conditioning (Figures 1 and 2).
BCHP SYSTEM BENEFITS
Reduced Energy Costs
Building owners can reduce their energy
costs by deploying cogeneration building
cooling, heating and power (bchp) systems
because compared to conventional sys-
tems these systems provide the following
advantages: Increased energy efficiency Reduced demand charges Reduced peak electric energy costs
B c h p systems offer much higher energy
efficiency than conventional stand-alone
equipment for a similar degree of power
reliability, comfort cooling, heating and
indoor air quality. Because of the higher
energy efficiency of the bchp system, it can
consume up to 47 percent less fuel than con-
ventional systems. The reduced fuel con-
sumption signicantly reduces energy cost.
The cost of electricity to buildings is gen-
erally based on power demand (measured
in kW) and electric energy usage (measured
in kWh). Power demand charge is gener-
ally a monthly charge ($/kW) based on the
peak/maximum power used during a month.
Power demand charge rates can vary with
time of year.
B c h p systems reduce power demand in
Cogeneration for
Confectioners
William Ryan, PhD
University of Illinois
William Ryan, PhD
Dr. Ryan teaches at
the Energy Resources
Center at the Univer-
sity of Illinois Chicago. Typical Method of Power Delivery
Efficiency Advantages of Cooling, Heating and Power
Figure 2
(U.S. Department of Energy)
two ways: one, by generating some of the
power at site, and, two, by using thermal
energy from power generation equipment,
instead of electricity, for operating cooling,
heating and/or humidity control equipment.
The charge for electric energy usage
generally varies with the time of year and
the time of day. This charge is the high-
est during peak periods, generally from
9 a m until 3 p m , and the least during off-
peak periods, generally from midnight till
7 a m . A major portion of the cost savings
for using b c h p systems may come from
avoiding purchase of electric energy dur-
ing peak periods.
Improved Power Reliability
Economic losses due to power outages in
the United States have cost American busi-
nesses billions of dollars. Since b c h p sys-
tems generate power on-site or near-site,
these systems improve power reliability by
reducing the buildings dependency on the
electric power grid, and may provide back-
up power to the building. The greater the
number of buildings that use cogeneration,
the lower the demand on the electric grid.
In areas where the grid is at or near capac-
ity, the reduced demand provided by bchp
will result in increased grid reliability.
Improved Economics for Enhancing
Indoor Air Quality
Controlling indoor humidity improves
indoor air quality in buildings. It is important
to keep indoor humidity to below 60 per-
cent to prevent growth of mold, mildew and
bacteria. Desiccant systems can control
indoor humidity more effectively than con-
ventional systems. In addition, desiccant sys-
tems can be driven by low-temperature heat,
such as the heat rejected by power genera-
tion equipment. This can enhance indoor
air quality at very low operating costs.
Reduced Life-Cycle Costs
The initial cost of b c h p systems is higher
than purchasing electric power and using
conventional chillers and boilers. However,
the life-cycle cost of the b c h p system is
often lower because of the energy cost sav-
ings over its useful life of more than 20 years.
Attractive Return on Investment
Bc h p systems reduce energy costs for
Cogeneration for Confectioners
B
C H P
systems offer
much higher energy
efficiency than
conventional stand-
alone equipment
for a similar degree
of power reliability,
comfort cooling,
heating and indoor
air quality.
102 December
2004
The Manufacturing Confectioner
®
By productively using the waste heat from electric generation, the overall effi-
ciency of energy delivery to the customer can signicantly improve. However,
transporting this heat for long distances is expensive. One solution is to move
the generator nearer to the customer.
Power Sources Compared
Combined Heat
and Power Plant
Standard
Power Plant
40%
Useful energy produced for electricity
100%
Fuel Input
60%
Waste heat rejected to environment
40%
Useful energy produced for heat and/or
cooling via district energy system
40%
Useful energy produced for electricity
100%
Fuel Input
20%
Waste heat rejected to environment
Cogeneration is the process of generating power at your site and using the waste heat for heat-
ing and cooling. A cogeneration system generally involves generating power or work (shaft out-
put) from a prime mover (engine, turbine or fuel cell) and recovering the waste heat from the prime
mover to deliver space heating, hot water and/or space cooling.
Figure 1
(U.S. Department of Energy)
What is Cogeneration?
Steam Turbine
(Bottoming Cycle)
Hot Water Loop (Heating)
electricity
Generator
Prime
Mover
Wout
Qout
Qin
(fuel input)
Heat Exchanger
Steam Loop (Heating)
Absorption Chiller (Cooling) buildings. If the incremental installed cost
of b c h p systems over conventional sys-
tems is viewed as an investment, the return
annual cost savings is often very attractive.
DOES COGENERATION MAKE
ECONOMIC SENSE FOR YOU?
Cogeneration can be a great investment for
some energy users and not for others, even
in the same locations. To nd out if it may
make sense for you, try the following test.
Step 1 Determine your current gas price
or estimate a future gas price.
Step 2 Determine your current electric
price per kWh, including demand charges
and taxes. The easiest way to do this is to
take your current electric bill total and
subtract any xed fees like a at monthly
meter and billing charge. Do not subtract
out any demand charges. Divide the
remainder by the kWhs purchased to get
an overall cost of electricity per kWh.
Step 3 Look at your operation. Are there
heat loads, currently served by a boiler,
which can productively consume the heat
a cogeneration system can provide? If so,
for how many hours of the year? To deter-
mine what type of loads can be served, see
Figure 3.
Step 4 Perform the calculation shown in
Figure 4.
COGENERATION TECHNOLOGY
Power Generation Equipment
Technologies commercially available for
generating electric power or mechanical
shaft power include combustion turbines,
microturbines and engines.
Combustion Turbines
Combustion turbines burn natural gas or
fuel oil to produce high-temperature,
high-pressure gas and to expand this gas
through a series of specially designed
blades to provide power. Many turbines
also use a heat exchanger called a recu-
perator, which utilizes some of the ther-
mal energy in the turbine exhaust heat
to preheat the air/fuel mixture for the
combustor section of the combustion tur-
bine system.
The efficiency of combustion turbines,
operating alone, ranges from 21 to 40 per-
cent. Combustion turbines also produce
high-quality heat that can be used to gen-
erate steam and hot water for other appli-
cations, including heating and cooling
(using absorption chillers).
Utilization of thermal energy in the
combustion turbine exhaust significantly
enhances the efficiency of energy uti-
lization. Maintenance costs per unit of
Cogeneration for Confectioners
If the incremental
installed cost of
B C H P
systems over
conventional
systems is viewed
as an investment,
the return annual
cost savings is often
very attractive.
The Manufacturing Confectioner December
2004
103
®
Use the heat recovery rate found in Step 3
Figure 4b
Cost of Electricity from
On-site Generation
$0.00
$0.00
No Heat Rec.
1,500 Btu/kWh
6,000 Btu/kWh
4,500 Btu/kWh
3,000 Btu/kWh
Cost of Electr
icity ($/kWh)
Cost of Gas ($/MMBtu)
32% Efficient Engine Generator
$12.00
$10.00
$8.00
$6.00
$4.00
$2.00
$0.15
$0.12
$0.09
$0.06
$0.03
200 kW-4 MW
>4 MW
Engine Gas
Turbine
Generator
Generator
Hot Water to 140°F
Service Water Heating
6,000
6,000
Hot Water to 180°F
Space Heating
4,500
4,500
Steam to 15
p s i g
Process & Space Heating Loads
1,500
4,500
Steam 15125
p s i g
Hospitals and Industrial Loads
Not Recomm.
4,500
Figure 3
Estimate of Possible Heat Recovery Factors (Btu/kWh)
1 Purchased cost of electricity
From utility bills in step 2
$0.__ /kwh
2 Cost of generated electricity
Use Fig. 4b with your gas rate
$0.__ /kwh
3 Cost savings
Subtract line 2 from line 1
$0.__ /kwh
If line 3 is not greater than zero stop,
cogeneration will not pay in your applicati