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Propane/Air System Pumps
150
USG
200
250
300
100
50
Propane/Air System Pumps Page 1
A pumpset for use in a propane/air mixing system is similar in design to the familiar pumps used for liquid propane transfer operations such as storage tank or truck filling. But unlike liquid transfer opera-tions which use a varying differential pressure to effect the product transfer, a mixing system requires a steady elevated pressure to ensure a consistent velocity through the venturi to maintain an accurate mix. This requires a few specialized components in the pumpset.
Bypass ValvesThe bypass valve which controls the pump discharge pressure must be of the so-called absolute style. A conventional bypass valve commonly used in liquid transfer operations senses the difference in pressure between the storage tank and the pump discharge. This style bypass valve by design allows the line de-livery pressure to vary with changing tank pressure and is inappropriate for a mixer system. By contrast, the absolute style bypass valve senses the difference in the line delivery pressure and atmospheric pres-sure. The line delivery pressure can be held at a constant value as required by the venturi regardless of the tank storage pressure.
Many industrial firms purchase their natural gas on an interruptible basis. Most of these firms use a pro-pane/air mixing system as a substitute fuel during times of curtailment. While other styles of gas mixing equipment is available, the most common style is a venturi system mainly due to initial cost consider-ations.
The venturi mixer requires an elevated propane pressure to operate. If we drive gas through a venturi at an adequate velocity, we can entrain enough air to develop a usable mixture and then store this mixture in a holding tank to be used in the building’s gas system. A typical venturi mixer requires an inlet pres-sure between 80 and 125 psig. Because this required pressure is not naturally available from a propane storage tank, we use a pressurizing pumpset to deliver the elevated pressure to the mixer.
Pump Considerations for Propane/Air Mixers
Mixer Components
Venturi Diagram
Propane/Air Mixers
Venturi
Solenoid
Mixed GasHolding Tank
Vaporizer
GAS ORIFICE
THROATGas
Air
Air
MIXED GAS
Propane/Air System Pumps Page 2
Check ValvesA check valve is required on the pump discharge to isolate the pump from the line delivery pressure. It is important to understand that the pump is delivering product to a vaporizer on the mixer assembly and not to a venturi. As the liquid propane is heated in the vaporizer, it expands significantly and drives liquid back toward the pump. The check valve “hides” the pump from this back flow which streams through the bypass and back to the storage tank.
System PressureThe required delivery pressure to a particular venturi mixer is set by the mixer manufacturer and can be found in the spec sheets for the unit. In general, a higher mixed gas delivery pressure from the mixer to the load will require a corresponding higher pump delivery pressure to the mixer. As an example, a mixer with a 2 psig discharge pressure may only require a pump pressure of 60 psig. A similar mixer with a 5 psig discharge pressure may require a pump pressure of 80 psig.
Because a pump’s capacity falls and the the motor’s HP climbs with increasing discharge pressures, great care must be taken in selecting the correct pump for any particular application. Additionally, cur-tailment from natural gas nearly always occurs during the coldest days of the year when the storage tank pressure is low (even down to 5 psig). The pump is quite often required to provide nearly all the motive pressure to the mixer without the aid of any inlet pressure from the storage tank.
Pressurizing Pumpset
Pump Considerations for Propane/Air Mixers (cont.)
150
USG
200
250
300
100
50
BackCheck
AbsoluteBypass
Return to Tank
To Load
Propane/Air System Pumps Page 3
Pump VolumeAs mentioned earlier in our discussion, the pump is delivering product to a vaporizer on the mixer as-sembly and not to the venturi. This is very important to understand during pump selection. When the mixed gas holding tank is fully charged, the venturi solenoid valve turns off stopping the flow through the venturi. The vaporizer continues to heat and boils the remaining liquid out of the vaporizer chamber until it is filled with vapor. The liquid volume displaced by this expanding vapor is pushed back toward the pump. The entire pump volume is now flowing through the bypass valve and is returning to storage.
When the venturi solenoid valve reopens to provide mixed gas to the load, the vapor volume in the va-porizer tank empties rapidly. To maintain the operating pressure, this vapor volume must be replaced just as rapidly by a liquid volume from the pump. The resulting surge in liquid volume is quite a bit larger than the system’s normal load and can create extreme vapor formation in the pump and the line feeding the pump. A pump not sized with this additional volume requirement in mind will surely vapor lock and drop the system out.
We must also keep in mind that during venturi off time, the entire pump volume is running through the bypass valve. During the short but definite time that it takes for the bypass valve to close in reaction to the new load, the pump must supply both the liquid volume surge to refill the vaporizer and the liquid volume still running through the bypass valve.
Pump Considerations for Propane/Air Mixers (cont.)
Vapor Out
Vaporizer ChamberUnder LoadVenturi On
Vaporizer ChamberNo Load
Venturi Off
Liquid
Liquid
Vapor Out
Liquid
Liquid
Vaporizer Chamber Diagram
Propane/Air System Pumps Page 4
For Propane/Air mixer feeds, the preferred pump design incorporates the regenerative turbine such as the Corken Coro-Flo models. The Coro-Flo pump handles volatile liquids smoothly and quietly without the noise, vibration and pulsations of positive displacement gear and sliding vane pumps. The one moving part, the impeller, floats on the shaft with no rubbing, grinding or metal-to metal con-tact. The free floating impeller with teeth cut on both sides picks up the fluid and creates a spiraling motion around the circumference of each side. The fluid is slightly ac-celerated and pressurized in dozens of small steps creating a smooth, quiet, overall product flow. With only a single pump seal and it’s free-floating impeller, the maintenence on these pumps is easy and very infrequent.From both an operational and maintenence perspective, the Coro-Flo pump provides superior perfor-mance. As just mentioned, propane is a volatile fluid. Because the product is stored at its boiling point, any fluid flow, say from the storage tank to the pump inlet, creates vapor bubbles in the liquid stream. This makes smooth, consistent flow difficult even under the best of conditions. The regenerative turbine tends to smooth out these blips in flow in large part by a stepwise fluid accelleration within the pump.
Pumps used in Propane/Air mixer service are also called upon to perform nonstop for extended periods of time. When the facility is required to go on propane backup service, the pump is turned on and runs continuously while the mixer is running. The pump may run nonstop for hours or even days. The Coro-Flo pump with no abrading parts is designed for this service.
The required load capacity of a mixing system is commonly given in BTU/HR. Because there is approx-imately 91,690 BTU/gallon of propane, dividing by this number will convert the load to the required GPH of liquid propane (that’s Gallons per Hour). Because the pumps are rated in GPM, we must also divide the GPH by 60.
Example:A 14,000,000 BTU/HR mixer represents a pump load of 2.5 GPM (14,000,000 ÷ 91,690 ÷ 60). This is the rated full load of the mixer is terms of GPM. It is the GPM the pump is required to provide to the mixer when the mixer is running at full capacity. But as discussed earlier, the pump also needs to provide capacity to vaporizer chamber refill and pump bypass flow. The pump we select must be 2 to 3 times this value. A pump with a rating of 7.5 GPM (2.5 X 3) is the correct choice for this 14,000,000 BTU/HR system.
Pump Design
Pump Flow Requirements
Pump Flow = Mixer Flow + Vaporizer Chamber Flow + Bypass Flow
Regenerative Turbine Pump
Propane/Air System Pumps Page 5
Coro-Flo F Series Pumps
18”
3”
3”
4: 12
32”
F SERIES
A
C
B 2.375”
2
HP PHASE FRAME A
1
1
10.875”
10.875”
11.875”
11.875”
3 10.875”
10.875”3
145T
145T
184T
145T
184
3
F12
PUMP
3 184T5F14
F13
B
8.125”
8.125”
9.125”
9.125”
8.125”
8.125”
C
29.11”
30.42”
28.55”
31.12”
28.23”
30.48”
WEIGHTNO MOTOR
125#
125#
125#
140#
127#
125#
WEIGHTW/MOTOR
185#
206#
189#
218#
177#
194#
VOLTS
115/208-230
230/460
115/230
230/460
208-230/460
230/460
SPECIFICATIONS
INLETPUMP
1-1/2”F12
CAPACITIES (AT 80 PSID)
OUTLET
1”
GPM
11
1-1/2”F13 1” 16
1-1/2”F14 1” 24
150
USG
200
250
300
100
50
These assemblies provide a complete pump pressurizing package specifically for con-tinuous duty, steady pressure applications. Well suited to standby work.
Assemblies include a single Corken pump, inlet strainer, absolute bypass, discharge check valve and all necessary relief valves and gauges. All components are prepiped on a common base for ease of installation.
Propane/Air System Pumps Page 6
Coro-Flo FF Series PumpsThese assemblies provide a complete pump pressurizing package specifically for con-tinuous duty, steady pressure applications. Well suited to standby work.
Assemblies include a single Corken pump, inlet strainer, absolute bypass, discharge check valve and all necessary relief valves and gauges. All components are prepiped on a common base for ease of installation.
INLET OUTLETPUMP
1-1/2”FF075
1-1/2”FF150
1”
1”
GPM
32
1-1/2”FF060 1” 16
44
CAPACITIES(AT 80 PSID)
INLET
OUTLET
18”
3”
3”
4: 12
32”
A
B
2.375”
7.5
5
HP PHASE FRAME A
3
3
12.078”184T
184T
FF075or
FF150
FF060
PUMP B
31.125”
WEIGHTNO MOTOR
140#
12.078” 31.125” 140#
WEIGHTW/MOTOR
234#
193#
VOLTS
230/460
230/460
10 3 12.078”215T 31.125” 140# 302#230/460
5 1 215FF060 12.078” 31.125” 140# 265#230
SPECIFICATIONS
150
USG
200
250
300
100
50
Propane/Air System Pumps Page 7
MODEL 14
MODEL 14
HO
RSE
POW
ER
MODEL 13
MODEL 13
CAPACITY, GALLONS / MIN.
MODEL 12
MODEL 12
DIF
FER
ENTI
AL
PRES
SUR
E, P
SIG
MODEL 10
MODEL 10
MODEL 9
MODEL 9
0
0 5 10 15 20 25 300
1
2
3
4
5
620
30
40
50
60
70
80
90
100
110
120
10
CORO-FLO F SERIES PUMPSCHARACTERISTIC CURVES3450 RPM
CAPACITY - Enter curves at pressure in PSIG, read horizontally to intersect solid capacity line formodel required, then vertically down to read capacity in Gals/Min.
Curves Are Based On LPG
BRAKE HORSEPOWER - Enter curves at pressure in PSIG, read horizontally to intersect solid capacity line formodel required, then vertically down to intersect dashed horsepower line, then across horizontally to read brakehorsepower.
Propane/Air System Pumps Page 8
00 5 10 15 20 24
20
40
60
80
100
120
140
160 8
7
6
5
4
3
2
1
0
CAPACITY, GALLONS / MIN.
HO
RSE
POW
ER
DIF
FER
ENTI
AL
PRES
SUR
E / P
SIG
CAPACITY - Enter curves at pressure in PSIG, read horizontally to intersect solid capacity line, thenvertically down to read capacity in Gals/Min.
Curves Are Based On LPG
BRAKE HORSEPOWER - Enter curves at pressure in PSIG, read horizontally to intersect solid capacity line,then vertically down to intersect dashed horsepower line, then across horizontally to read brakehorsepower.
CORO-FLO FF-060 PUMPCHARACTERISTIC CURVES3450 RPM
Propane/Air System Pumps Page 9
000.51.01.52.02.53.03.54.04.55.05.56.06.57.07.58.08.59.0
0
25
50
75
100
125
150
175
200
5 10 15 20CAPACITY, GALLONS / MIN.
HO
RSE
POW
ER
DIF
FER
ENTI
AL
PRES
SUR
E / P
SIG
25 30 35 40 45
CAPACITY - Enter curves at pressure in PSIG, read horizontally to intersect solid capacity line, thenvertically down to read capacity in Gals/Min.
Curves Are Based On LPG
BRAKE HORSEPOWER - Enter curves at pressure in PSIG, read horizontally to intersect solid capacity line,then vertically up to intersect dashed horsepower line, then across horizontally to read brakehorsepower.
CORO-FLO FF-075 PUMPCHARACTERISTIC CURVES3450 RPM
Propane/Air System Pumps Page 10
0 10 20CAPACITY, GALLONS / MIN.
30 40 50 600
50
100
150
200
250
DIF
FER
ENTI
AL
PRES
SUR
E / P
SIG
0
3.0
7.5
15.0
10.0
HO
RSE
POW
ER5.0
20.0
CAPACITY - Enter curves at pressure in PSIG, read horizontally to intersect solid capacity line, thenvertically down to read capacity in Gals/Min.
Curves Are Based On LPG
BRAKE HORSEPOWER - Enter curves at pressure in PSIG, read horizontally to intersect solid capacity line,then vertically down to intersect dashed horsepower line, then across horizontally to read brakehorsepower.
CORO-FLO FF-150 PUMPCHARACTERISTIC CURVES3450 RPM
Propane/Air System Pumps Page 11
Typi
cal P
ipin
g A
rran
gem
ent
Vapo
rizer
/Mix
ing
Syst
em
Mix
ed G
asD
isch
arge
150
USG
200 25
0
300
100
50
NO
TES
1. S
ketc
h is
not
to s
cale
and
is s
impl
ified
for c
once
ptua
l cla
rity.
2. In
stal
l sys
tem
per
NFP
A 58
, 70
and
othe
r app
licab
le c
odes
.
E
quip
men
t loc
atio
n m
ust m
eet a
pplic
able
sep
arat
ion
dist
ance
s.
P
ipe,
pip
e fit
tings
, val
ves
etc.
sui
tabl
e fo
r liq
uid
prop
ane
serv
ice.
3. T
ake
spec
ial c
are
in m
ount
ing
the
pum
p.
P
ump
inle
t pip
ing
mus
t be
full
size
, as
shor
t as
prac
ticab
le a
nd
s
lope
upw
ard
tow
ard
the
stor
age
tank
.
M
aint
ain
a m
inim
um ri
se o
f 12"
from
pum
p in
let t
o ta
nk o
utle
t val
ve.
The
byp
ass
disc
harg
e sh
ould
retu
rn to
the
top
vapo
r spa
ce a
s sh
own
to a
id in
vap
or e
limin
atio
n.
Quality Products for the LP Gas Industry881 HERSEY STREET ST. PAUL, MINNESOTA 55114PHONE: (651) 646-1177 FAX: (651) 646-1676
IN MINNESOTA: 1-800-652-9072 OUT-OF-STATE: 1-800-328-9222Visit us on the web www.lp-gasequipment.com