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News and Features
Tri-fuel
Generators that are true Hybrids!
These machines are
not adaptations...no other generator brand can offer:
1 carburetor
for
3 Fuels
Yamaha Generators
ready to run on gasoline, propane, or natural gas.
Everybody's
talking about GREEN these days. We are pround to say we have always
been green and long before all the hype.
We were green when green wasn't cool!
end * * *
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Here we explain
propane and natural gas consumption, cylinder vaporization, and the size
cylinder required to run a certain horsepower generator. Some links
may take you to our other websites so just use your "Back" button to return
to this page. Propane is discussed first and then natural gas below.
Use this link to jump to
Natural Gas.
Propane Consumption Rate
First thing to keep in mind is that the estimate given by the
manufacturer for the gasoline run time can be used for propane also because
it is just that; an estimate or guess. Propane only has about 10% less Btu
content than gasoline gallon-to-gallon, so the estimate used by Yamaha for
gasoline consumption will be very close for propane if not exact. The
biggest mistake most "experts" make in opinionating that a propane or
natural gas generator will lose power is based solely on these figures and
not on any data they personally have. When figuring power output of
any fuel, the size of the engine has to be a significant factor of the total
equation. For instance, comparing a vehicle with a V8 engine to a
generator with an 11hp generator attached can not be calculated the same.
The characteristics of the fuels and how they mix with air, how far the
piston is in relation the gasoline float bowl effects the power derived from
the fuel among many other things. To presume that just because
the btu content is less, it is less powerful, is erroneous.
But
for those that want even more information we now offer some basic
factors, round numbers and some good estimates to see how run time values of
propane cylinders can be worked out:
BASIC FACTORS
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It requires 2 horsepower to
produce 1000 watts of energy per hour under load |
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Under load, each
horsepower consumes 10,000 BTU per hour |
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Propane contains 92,000 BTU
per gallon |
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Propane weighs 4.2 pounds
per gallon |
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Cylinders are rated by their weight
capacity of propane |
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Bulk tanks are rated by
gallon |
Cylinder Capacities in Gallons and BTU's
| Size |
Gallon Capacity |
Total BTU Capacity |
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20# |
4.8 |
441,600 |
| 30# |
7.1 |
653,200 |
| 40# |
9.5 |
874,000 |
| 60# |
14.3 |
1,315,600 |
| 100# |
23.8 |
2,189,600 |
| 200# |
47.2 |
4,342,400 |
| 420# |
99.1 |
9,117,200 |
Using these factors we can arrive at run times based on average load for
any generator.
For instance:
How long would a 5000 Watt Generator with a 10 HP engine
at 50% load run on a 20# propane cylinder?
10hp at 50% load would be using 5 horse power to generate 2500 watts of
energy.
5hp x 10,000 btu would consume 50,000 btu per hour.
Using a 20# cylinder that produces 441,600 total btu, the engine
consuming 50,000 btu per hour would run for about 8.8 hours.
BTU consumption chart based on generator/engine size and
load
| Generator Wattage |
Engine Horsepower |
Full Load |
75% Load |
50% Load |
| 1850 |
3.5 |
35,000 |
26,250 |
17,500 |
| 4000 |
8 |
80,000 |
60,000 |
40,000 |
| 5000 |
10 |
100,000 |
75,000 |
50,000 |
| 7500 |
15.5 |
155,000 |
116,250 |
77,500 |
| 8000 |
16 |
160,000 |
120,000 |
80,000 |
| 10,000 |
20 |
200,000 |
150,000 |
100,000 |
| 12,000 |
24 |
240,000 |
180,000 |
120,000 |
Many people want to know what size cylinders they need based on their
engine size. Here are some real conservative estimates of the vaporization
rate of various size cylinders based on the outside temperature.
Vaporization Rates of Cylinders
Output in
BTU's per hour - Vertical Cylinder 25% full - Minimum Cylinder Pressure 10
PSI
Cylinder Size
| Outside Temperature |
20 |
30 |
40 |
100 |
200 |
420 |
| +60F |
24,000 |
32,000 |
40,100 |
79,700 |
125,900 |
185,500 |
| +50F |
21,200 |
28,300 |
35,500 |
70,600 |
111,500 |
164,300 |
| +40F |
18,450 |
24,700 |
31,000 |
61,500 |
97,200 |
143,100 |
| +30F |
15,700 |
21,000 |
26,400 |
52,400 |
82,800 |
122,000 |
| +20F |
13,000 |
17,300 |
21,800 |
43,300 |
68,400 |
100,700 |
| +10F |
10,250 |
13,700 |
17,200 |
34,200 |
54,000 |
79,500 |
| 0 |
7,500 |
10,000 |
12,600 |
25,000 |
39,500 |
58,300 |
| -10F |
4,780 |
6,400 |
8,000 |
16,000 |
25,300 |
37,100 |
| -20F |
2,050 |
2,700 |
3,400 |
6,800 |
10,700 |
15,900 |
For the physical properties of each cylinder, click on the "Cylinder
Size" above.
What does
all this mean?
Well, if you went exactly
by the chart, you would need a 420# cylinder to run a 14hp engine if it
was 25% full and 40 degrees outside and keep a minimum of 10 psi in the
cylinder. This is a worse case scenario. For instance, when a 20#
cylinder is full it can run a 16hp engine for quite some time in 40 degree
weather before there will be any freezing problem. But if you wanted to
use up all the gas in a cylinder, it would have to be sized according to
the chart.
Here is why. Propane is
stored as a liquid under pressure and boils to produce a vapor that is
drawn off at the top for the engine to use as the fuel. Because propane
boils at -44° (below zero), the gas will freeze
if it can not absorb enough ambient heat to compensate for the boiling
process. The bigger the cylinder is compared to the amount of load, the
warmer it is outside, the warmer the cylinder is kept, all are a
determining factor in the likelihood of a cylinder freezing up.
If a sweat or frost line forms around the cylinder at the level of the
fuel, this is a telltale sign that the cylinder over worked and is in the
process of freeze up. If the gas does freeze, it will stop producing
vapor and the pressure inside the cylinder will drop to as low as zero psi
which will cause the engine to stop running.
To compensate for an undersize cylinder, two cylinders can be tied
together using a
tee check
and pigtails. Some customers set the cylinder near the exhaust of the
engine to help keep the cylinder warm and have no problem using smaller
tanks on bigger engines. This practice needs to be carefully monitored so
that the cylinder does not overheat and cause the relief valve to check
off.
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Natural gas is billed in THERMS. |
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This represents a unit or block of
100,000 btu of fuel. |
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The average price per therm is around
$0.80. |
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A generator engine running at 3600 rpm
under full load consumes on average about 10,000 btu per horsepower
per hour. |
Using these figures, we can figure the estimated usage for any size
engine. For instance a 10hp engine used on a 5000 watt generator running
at FULL load should use no more than 100,000 btu per hour and cost
approximately $0.80 to operate. 50% load (2500 watts output average)
should use no more than 50,000 btu per hour and cost approximately $0.40
to operate.
To compare that to gasoline (110,000 btu per gallon) times the cost by
1.1 to arrive at $0.88 per gallon.
So if you are paying over $0.88 per gallon for gasoline, you can save
by using natural gas.
For information on Pipe Size requirements visit the
Natural Gas Page on
our USCARB website.
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by
US Carburetion Inc.
