Preferred Utilities Manufacturing Corp

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Preferred Utilities Manufacturing Corp
Fuel Oil Handling Systems Fuel System Design
Considerations Part 1
Preferred Utilities Mfg. Corp. 31-35 South Street
Danbury CT www.preferred-mfg.com
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Is it Common Knowledge?
We Hate to Assume

• Or
• Not So Common Knowledge
• A review of a few important basics

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Pressure Basics
The Pressure on the surface of the Earth (at
sea level) is 14.7 pounds/square inch (psi).
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More Pressure Basics

• 14.7 psia atmospheric or barometric pressure at
  sea level
• Barometric is absolute pressure expressed as
  inches of mercury (Hg) Sea Level 29.92 in. Hg.
• Psig gauge pressure (reads zero at sea level)
• Psia gauge pressure atmospheric pressure
• 1 psi 2.036 in. Hg
• 1 psi 27.68 in. water

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Head Pressure
Attached to process
Inches of Head
For Water 1 psi 27.7 inches of water
column No matter how wide or large.
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Specific Gravity and Head Pressure
Specific Gravity of water is 1.0 The Specific
Gravity (SG) of any other fluid is a ratio
comparison to water. Numbers below 1.0 mean the
fluid is lighter than water. Numbers above 1.0
means heavier than water. The SG Of 2 oil is
.876 The Specific Gravity of mercury is 13.546
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Head Pressure Comparisons
1 PSI of Head Pressure equals 27.68 inches of
water (SG 1.0) 2.036 inches of mercury (SG
13.546) 31.6 inches of 2 oil (SG .876) 2.31
feet of water 2.60 feet of 2 oil
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The Rules of Thumb
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Pressure Scales and Gauges
All different names for the same thing,
Pressure.
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Positive Displacement Pumps

• Most fuel handling systems use positive
  displacement pumps.
• For most practical purposes
• Positive displacement pumps are self priming
• Flow stops when pump stops
• pump discharge flow is constant for a given rpm
• pressure is determined by downstream restrictions
• when discharge flow is blocked, something breaks
• motor horsepower is proportional to pressure
• A safety relief valve with an unobstructed path
  to a tank is essential to prevent mechanical
  damage.
• Pump-motor combinations produce fixed flows
• Motor HP will determine max capable pressure

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Positive Displacement Pumps

• Spur Gear Pumps- (not that popular)
• two meshed spur gears, one driven, one idling
• suitable for high pressure
• Internal Gear Pumps - (most commonly used)
• two meshed gears, one driven, one idling
• outer gear has internal teeth, inner spur gear
• above 100 gets noisy
• Screw Pump - (best pump, very expensive)
• one driven and two idler screws pull oil through

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Spur Gear Pump
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Internal Gear Pumps
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Screw Pump
Twin rotor Screw Pump
Three rotor Screw Pump
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Pump Slip

• Some oil does bypass the pump internals
• Typically less than 10 of pump displacement
• ie a 100 gpm pump must pump 110 to deliver 100
  gpm
• Higher pressure produces greater slip
• Lower viscosity produces greater slip
• Always size pumps for the expected pressure and
  flow rate
• Size for worst case
• Flow- size for min Viscosity
• Pipe- size for max Viscosity

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Typical Properties of Fuel
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Viscosity as a Function of Temp.
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Designing a Fuel Oil Pumping System

• The Five Basic Steps in designing a fuel oil
  pumping system.
• Calculate the required flow rate.
• Estimate the maximum inlet suction pressure.
• Estimate the required discharge pressure.
• Choose a fuel oil pumping system
• Select the proper control strategy

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Step 1- Determine the Flow Rate

• Fuel Handling System Designs
• For E-Gen day tank systems
• Rate of use vs. duty cycle determines pump flow
• Length of time without power to the pump set
  determines tank size
• E-Gen sets RULE of THUMB 7 GPH per 100kw
• E-Gen sets - RULE of THUMB Use a 41 ratio so
  the pump runs only 25 of time. (Strictly
  engineers preference. Some say 1.5 times the
  E-Gen usage is enough. Each application will be
  different.)
• For burner/boiler systems
• Supply loops to multiple burners are usually
  piped series or parallel.
• Series loops total burning rate plus the pumping
  rate of the last burner only.
• Parallel loops total pumping rate of all burner
  pumps.

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Day Tank Systems

• Day tanks are used when it is desired to provide
  a supply of oil with a gravity head to
• small burners (10 to 50 gph, 100 bhp or smaller)
• diesel generators
• protects pump seals on burner or engine pump
• Multiple day tanks may be filled from one pump
  set.
• Day tanks are used when the burner or generator
  is a great distance from or above the main
  storage tank.
• For emergency generators, day tank provides a
  period of operation without power to the pump
  set.
• Oil in the day tank can be used for cooling
  generator components.
• Day tanks can be drained and refilled
  automatically if oil gets too hot for use.

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Day Tank Schematic
Use an RBS, its expensive to dump oil on the
roof
A motorized ball valve will work better than a
solenoid valve due to low dp across valve may
leak and flood tank not in service.
locating near tank will help prevent free-fall
into tank and causing foaming
keep at max distance apart
Some city codes limit the amount of oil that can
be stored above ground level
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Generators with a Header System
Header could be up 35 floors. 200 ft 76
psi Pressure at pump will be 76 psi plus friction
losses plus the head to reach the overflow
line. Mount a RLS switch in the vent to shut off
the pump. A header pressure switch will back up
the RBS A BPV at the bottom of the return loop
set at a pressure lower then the head will help
prevent foaming in the tank.
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Example of a E-Gen Day Tank System

• Parameters
• Generator is rated for 800 KW.
• The generator must be able to operate for 3 hours
  without power to the pump set.
• Use the recommended 41 run ratio.
• Requirements Very Basic
• Generator usage is 56 GPH
• Minimum day tank is 168 gallons
• Minimum pump flow rate is 3.73 GPM (224 GPH)

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Example Continued

• Apply that information to the real world
• The recommended day tank depends on how the E-Gen
  is using the oil.
• Local fire codes may limit the amount of storage
  above ground level.
• The day tank may have to be larger to act as a
  heat sink for hotter return oil from the
  generator.
• Spill containment size is based on local code
  requirements.
• The pump capacity should have a 20 margin of
  error.

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Burner/Boiler Systems

• Most burners have a supply and return line.
• Burner pumps will usually pump more oil than the
  burner will use.
• 5 gph burner might pump 45 gph
• 100 gph burner might pump 150 gph
• Burners may be piped as parallel or series loops.
• The oil pump set might provide atomizing pressure
  for the burner requiring high pressure loops (100
  PSI)
• Or the pump set may just flood the suction of the
  burner pump requiring a low pressure loop (10
  PSI).

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Burner Loop Piped in Series
Flooded Supply Loop
Return line must be piped to the bottom of the
tank to prevent foaming, air entrainment and
possible loss of prime during off cycles.
All three burners are operating at 100 firing
rate 100 GPH Typical piping of Preferred Inject
Aire Burners.
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Burner Loop Piped in Parallel
High or Low Pressure Loop
Use BPR to Insure min. PSI at Burner inlet
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Advantages of Series vs. Parallel

• With a series loop, pump flow is smaller
• In a series loop if oil is heated, the heaters
  are smaller
• Traditional series loop is usually very low
  pressure
• Parallel loop may operate at high pressures
• for pressure atomizing without burner pumps
• use a back pressure valve where the supply and
  return headers meet to keep pressure only on the
  supply header
• Flooded series loops have less air problems.

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Determine the Pump Capacity

• Once the minimum flow capacity is determined, the
  actual pump capacity must be chosen.
• Allowances must be made for pump wear especially
  with high outlet pressures and low viscosity oil.
• Consider a safety factor to cover design
  approximations.
• Rule of Thumb- Once the actual flow requirement
  is determined, add a 25 margin of safety.
• Your not done yet! You still need to determine
  the system pressures.

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Step 2- Maximum Inlet Suction

• Atmospheric pressure (29.92" Hg)(14.7 PSIA)
  provides the force to get oil into the pump.
• Most pumps can produce a 26" Hg vacuum
• Good practice limits suction to a 15" vacuum or
  less
• Typical design piping loss is 3" Hg or less
• This leaves 10" Hg for static lift with a 2
  margin of safety.
• Pump must not be located more than 12 ft. above
  the bottom of the tank

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Determining Inlet Suction

• Determine gravity head in feet of oil.
• One foot of oil is approximately 0.78" Hg. This
  means a maximum lift of 12 ft to stay at 10Hg or
  less.
• Determine loss through suction piping.
• convert fittings, valves, etc. to equivalent
  diameters
• add total length of pipe to equivalent for
  fittings
• add loss through strainer and Anti-Syphon valves
• If the suction pressure calculation is too high,
  increase the pipe size or lower pump relative to
  the tank.

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Suction Piping Precautions

• If both pumps in a duplex set may be run
  together, use total flow in the calculations
• Figure static lift from bottom of tank
• Use a 100 safety factor for strainer drop
• Use a 40 or 100 mesh strainer for 2 oil
• Use worst case viscosity in figuring loss

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Pressure Drop through Pipe
Pressure drop through pipe, Number 2 Fuel
Oil Example 250 GPH in a 1 pipe has a 1.0 PSI
per 100 ft of pipe And its not linear- Twice
the flow triples the pressure drop.
Flow, Gallons per hour
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Add Equivalent Lengths of Straight Pipe in Feet
for Fittings and Valves

• Measure the straight pipe and add the below
  lengths to determine the total friction loss.
• Example using 1,23 inch pipe
• Fitting 1 inch 2 inch 3 inch
• Gate Valve .60 1.2 1.7
• Globe Valve 27 53 80
• 90 Deg. Elbow 2.7 5.2 8
• 45 Deg. Elbow 1.23 2.4 3.6
• Tee (straight thru) 1.7 3.5 5.2
• Tee (rt. Angle flow) 5.7 12 16
• 180 Deg. Return 6 13 18
• Choose fittings and valves with the least
  pressure drop.

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Step 3- Estimate Discharge Pressure

• Pressure at the pump discharge is a sum of
• pressure needed at point of use plus
• total gravity head and
• pipe losses
• Generally, discharge piping is smaller than
  suction piping

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Miscellaneous Cautions

• Beware of entrained air
• locate return and supply at opposite ends of tank
• Pipe return line to bottom of tank
• Avoid high lifts and traps
• Allow for easy priming of pumps
• Provide adequate vent lines
• Provide properly sized day tank overflow lines
• Design the system so it can be tested regularly
• Provide a means to remove oil from the day tank
  so pump cycle can be tested
• Generator testing usually not often enough or
  long enough to provide pump cycle testing.

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Step 4- Choose a Fuel Oil Pumping Systems

• Pick pump-motor pair with next greater flow rate
• Motor HP based on PSI required (use the
  manufacturers pump curves for the correct
  combination)
• Pump based on required flow- confirm pump curve
  PSI vs Flow
• Duplex and Triplex pumps share common suction and
  discharge piping
• Most common is a duplex set
• two 100 pumps, one for backup
• control system can monitor flow, start lag pump
• Triplex pump sets for large plants
• three 50 pumps allow for one spare
• two 100 winter pumps - one 50 summer pump

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Step 5- Select a Control Strategy

• What determines when the pump will start and
  stop?
• continuous operation is usual for burner pumps
• intermittent operation for day tank systems
• Are you sequencing for filling multiple day
  tanks?
• Do you have provision for automatic pump back-up?
• based on flow or pressure at pump discharge
• flow switch is used where gravity head is
  constant
• What alarms do you need for a malfunction?
• Do you require automatic testing?
• What will cause a safety shutdown?

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Fuel Management System
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Automatic Start-Stop of Pumps

• Burner loop pumps might automatically start with
  a gas changeover
• make certain that the pumps are tested and primed
• might start pumps at 25 degrees if changeover is
  at 20
• Burner loop pumps should run continuously
• Cycling the main pumps with the burner is not
  recommended
• energy saved doesnt pay for nuisance shutdowns
  on loss of prime
• On generator header systems, the supply pumps
  start when a generator runs
• Day tank filling pumps will cycle on and off when
  a tank needs fuel

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Semi-Automatic Pump Set

• Starts and stops based on a remote demand.
• Designed for low cost applications.
• Could be relay logic for simplicity or a small
  PLC for flexibility.
• Usually used when there is a call for operation
  where the pump will stay on during the boiler or
  Egen operation.
• Very limited options.
• Will usually have a pump base leak switch to shut
  down the pumps.
• Lead pump fail back-up.
• Alternates Lead/Lag operation of pumps.

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Automatic Pump Set

• Plant Wide Controller
• UL Labeled Control
• One (1) PWC-Cxxxxxx Controller
• One (1) "D" 120 VAC Discrete Input Card
• One (1) "H" HOA-ROUT Relay Output Board
• Motor Starter Cabinet
• Control circuit transformer (if required)
• Alarm Bell
• Two magnetic motor starters with overload
  protection
• Two motor circuit breakers

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Automatic Pump Set Features

• Built In Run Time Meters
• BAS Modbus Standard
• Built In Tank Gauge
• Auto Pump Prime Suction Line Integrity
  Checking based on day of week
• Automatic Alternation Based on Run hrs
• Large 16 line x 40 character display
• 200 Point Alarm and Event Summary with Time and
  Date Stamp

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Automatic Pump Set Features

• Advanced Communications Modem
• Dial In from PC
• Dial out to pager
• Wire Float and Analog Input Board
• Accepts up to 8 tanks or discriminating sensors
• BAS Discrete Signals for Leak, Overfill etc
• Drip Pan Leak Switch
• Duplex Strainer
• Duplex Strainer DP Switch Indicator

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Sample Alarms

• Failure of a pump to provide flow
• Failure of both pumps to provide flow
• Low level in a day tank
• High pressure in system
• High level in a day tank
• Leak in a day tank or pump set containment
• Leak in double wall piping
• Dirt buildup in strainers and filters
• High oil temperature in the day tank

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What About Automatic Testing
Will that pump set be ready when you need it the
most?

• Start burner loop pumps daily for 10 minutes
• Start generator header pumps daily
• Check for proper flow or pressure
• Alarm on system failure for preemptive repair

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Pump Failure and Backup Operation

• The lead pump is call on for operation.
• Within 15 seconds all inputs must be proven or
  the lead pump will be considered failed.
• -Starter not tripped on overload or failed.
• -Flow switch or pressure switch proven.
• If the lead pump fails the lag pump will
  automatically start.
• If the lead pump starts and runs ok for a time
  beyond the first 15 seconds, a loss of any input
  will result in an immediate start (no timed
  delay) of the lag pump.
• If the lead pump can not keep up with the demand
  and the day tank reaches the low level float, the
  lag pump will start to assist the lead pump.

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Sample Shutdown Conditions

• Leak in piping (oil detected in the containment
  area)
• Day tank leak (oil in the containment basin)
• On multiple day tank applications, all day tanks
  must show a leak condition to stop pumps.
• Pump set leak (oil in the base pan)
• Low level in the main tank
• All pumps failed
• Supply and return valves not properly aligned

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Control System Summary

• Different applications need different strategies
• Control system is as important as the mechanical
  design of the system
• Custom design to suit an application is the key
  to a reliable fuel system
• PLC and PWC logic allows maximum flexibility and
  monitoring of many points
• System may be interfaces with a building
  management system
• Make sure you know the complete scope of the
  system before you complete your design

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Preferred Utilities Manufacturing Corp
31-35 South Street Danbury CT T (203)
743-6741 F [phone] www.preferred-mfg.com