Preferred Utilities Manufacturing Corp

Preferred Utilities Mfg. Corp.31-35 South Street • Danbury • CT

www.preferred-mfg.com

Fuel Oil Handling Systems

Fuel System Design Considerations

Part 1

Is it Common Knowledge?Or

Not So Common Knowledge

A review of a few important basics

We Hate to Assume

Pressure Basics

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

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

Head Pressure

For Water 1 psi = 27.7 inches of “water column”No matter how wide or large.

Inches of Head

Attached to process

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

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

The Rules of Thumb

Unit Conversion Rule of THUMB

Pressure Head Pressure Head1 psi = 2.31 ft of water 3 psi = 7 ft of water1 psi = 2.60 ft of No. 2 Oil 2 psi = 5 ft of No. 2 Oil

Vacuum Head Vacuum Head1 " Hg = 1.28 ft of No. 2 Oil 4 " Hg = 5 ft of No. 2 Oil

Head Vacuum Head Vacuum1 ft of No. 2 Oil = 0.78 " Hg 4 ft of No. 2 Oil = 3 " Hg

Head Pressure Head Pressure1 ft of No. 2 Oil = 0.38 psi 3 ft of No. 2 Oil = 1 psi

Pressure Scales and Gauges

All different names for the same thing, “Pressure”.

Gauge Type: "Compound" "Gauge" "Absolute" "Gauge" "Absolute" "Gauge"

Units -> psig psig psia " Hg " Hg " H20

19 19 33.70 38.68 68.61 526.517 17 31.70 34.61 64.54 471.115 15 29.70 30.54 60.47 415.713 13 27.70 26.47 56.40 360.211 11 25.70 22.40 52.33 304.8

9 9 23.70 18.32 48.25 249.47 7 21.70 14.25 44.18 194.05 5 19.70 10.18 40.11 138.63 3 17.70 6.11 36.04 83.11 1 15.70 2.04 31.97 27.7

Atmospheric -> 0 0 14.70 0.00 29.92 0.02 -0.98 13.72 -2.00 27.93 -27.26 -2.95 11.75 -6.00 23.93 -81.7

10 -4.91 9.79 -10.00 19.93 -136.114 -6.88 7.82 -14.00 15.93 -190.518 -8.84 5.86 -18.00 11.93 -245.022 -10.81 3.89 -22.00 7.93 -299.426 -12.77 1.93 -26.00 3.93 -353.9

Outer Space Vacuum -> 29.92 -14.70 0.00 -29.92 0.00 -407.2

Units -> " Hg psig psia " Hg " Hg " H20

Traditional Reading is Reading is (60 F)Compund Relative to Relative toPressure Local Outer Space

Gauge Atmosphere Vacuum

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

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

Spur Gear Pump

Internal Gear Pumps

Screw Pump

Twin rotor Screw Pump Three rotor Screw Pump

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

Typical Properties of Fuel

Viscosity as a Function of Temp.

Designing a Fuel Oil Pumping System

The Five Basic Steps in designing a fuel oil pumping system.

1. Calculate the required flow rate.

2. Estimate the maximum inlet suction pressure.

3. Estimate the required discharge pressure.

4. Choose a fuel oil pumping system

5. Select the proper control strategy

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 4:1 ratio so the pump runs

only 25% of time. (Strictly engineer’s 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.

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.

Day Tank Schematic

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.

Some city codes limit the amount of oil that can be stored above ground level

locating near tank will help prevent free-fall into tank and causing foaming

keep at max distance apart

Use an RBS, it’s expensive to dump oil on the roof

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.

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 4:1 run ratio.

Requirements: Very Basic

1. Generator usage is 56 GPH

2. Minimum day tank is 168 gallons

3. Minimum pump flow rate is 3.73 GPM (224 GPH)

Example Continued

Apply that information to the real world:1. The recommended day tank depends on how the E-

Gen is using the oil.2. Local fire codes may limit the amount of storage

above ground level.3. The day tank may have to be larger to act as a heat

sink for hotter return oil from the generator.4. Spill containment size is based on local code

requirements.5. The pump capacity should have a 20% margin of

error.

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).

“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.

Burner Loop Piped in Series

Burner Loop Piped in Parallel

“High or Low Pressure Loop”Use BPR to

Insure min. PSI at Burner inlet

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.

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.

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

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 10”Hg 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.

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

Pressure Drop through Pipe

Flow, Gallons per hour

Pressure drop through pipe,Number 2 Fuel Oil

Example:250 GPH in a 1” pipe has a 1.0 PSI per100 ft of pipe

And it’s not linear- Twice the flow triples the pressure drop.

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 1,2&3 inch pipe:Fitting 1 inch 2 inch 3 inch

Gate Valve .60 1.2 1.7Globe Valve 27 53 8090 Deg. Elbow 2.7 5.2 845 Deg. Elbow 1.23 2.4

3.6Tee (straight thru) 1.7 3.5 5.2Tee (rt. Angle flow) 5.7 12 16180 Deg. Return 6 13 18

Choose fittings and valves with the least pressure drop.

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

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.

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 manufacturer’s

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”

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?

Fuel Management System

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 doesn’t 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

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.

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

Automatic Pump Set Features

Built In Run Time MetersBAS Modbus StandardBuilt In Tank GaugeAuto Pump Prime & Suction Line

Integrity Checking based on day of weekAutomatic Alternation Based on Run hrsLarge 16 line x 40 character display200 Point Alarm and Event Summary

with Time and Date Stamp

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 SwitchDuplex StrainerDuplex Strainer DP Switch & Indicator

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

What About Automatic Testing

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

Will that pump set be ready when you need it the most?

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.

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

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

Preferred Utilities Manufacturing Corp

31-35 South Street • Danbury • CTT: (203) 743-6741 • F: (203) 798-7313

www.preferred-mfg.com