# 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

Or Not So Common Knowledge A review of a few important basics
We Hate to Assume Is it Common Knowledge? Or Not So Common Knowledge A review of a few important basics

Pressure Basics The atmosphere (air) has weight that exerts a pressure which envelopes the earth. This pressure is known as atmospheric pressure, and its force at sea level, under normal conditions is pounds per square inch (psi), or 14.7 psi. As the altitude above sea level is increased, the atmospheric pressure decreases. Have you ever noticed that water boils at a lower temperature at a high elevation? This is due to the reduced pressure on the surface of the water. Although the potatoes are in boiling water, it will take them significantly longer to cook at the lower boiling temperature. NOTES: 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 = in. Hg. Psig= gauge pressure (reads zero at sea level) Psia = gauge pressure + atmospheric pressure 1 psi = in. Hg 1 psi = in. water NOTES:

The atmosphere (air) has weight that exerts a pressure which envelopes the earth. This pressure is known as atmospheric pressure, and its force at sea level, under normal conditions is pounds per square inch (psi), or 14.7 psi. As the altitude above sea level is increased, the atmospheric pressure decreases. Have you ever noticed that water boils at a lower temperature at a high elevation? This is due to the reduced pressure on the surface of the water. Although the potatoes are in boiling water, it will take them significantly longer to cook at the lower boiling temperature. NOTES: For Water 1 psi = 27.7 inches of “water column” No matter how wide or large.

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

1 PSI of Head Pressure equals: 27.68 inches of water (SG = 1.0) 2.036 inches of mercury (SG = ) 31.6 inches of #2 oil (SG = .876) 2.31 feet of water 2.60 feet of #2 oil

The Rules of Thumb The atmosphere (air) has weight that exerts a pressure which envelopes the earth. This pressure is known as atmospheric pressure, and its force at sea level, under normal conditions is pounds per square inch (psi), or 14.7 psi. As the altitude above sea level is increased, the atmospheric pressure decreases. Have you ever noticed that water boils at a lower temperature at a high elevation? This is due to the reduced pressure on the surface of the water. Although the potatoes are in boiling water, it will take them significantly longer to cook at the lower boiling temperature. NOTES:

Pressure Scales and Gauges
The atmosphere (air) has weight that exerts a pressure which envelopes the earth. This pressure is known as atmospheric pressure, and its force at sea level, under normal conditions is pounds per square inch (psi), or 14.7 psi. As the altitude above sea level is increased, the atmospheric pressure decreases. Have you ever noticed that water boils at a lower temperature at a high elevation? This is due to the reduced pressure on the surface of the water. Although the potatoes are in boiling water, it will take them significantly longer to cook at the lower boiling temperature. NOTES: All different names for the same thing, “Pressure”.

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 are the pump of choice of Fuel Oil. Need the lifting and constant flow & self priming - (with a price) These pumps are constant flow (not pressure) machines. Seals leakage, shaft strength govern pump limits Motor determines design pressure: LO-201 is 50 psi, LO-202 is100 psi same pump, different motor. We use IMO/Delaval, Viking and Tutle Typical mechanical engineer sees 10 centrifical pumps for one positive displacement type

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 <> 100 Psi Internal Gear < 100 psi too noisy above 100psi, most ecomical, 80% of appications Screw >< 100psi , IMO type LO-10 - Tutle LO-20 - Viking

Spur Gear Pump more prone to wear, not as mech eff., noisy
Volume pumped Idler Discharge Suction Tight fit prevents back flow Driven

Internal Gear Pumps Discharge Suction Volume pumped Attached to shaft
Oil Film Cresent Piece is stationary

Screw Pump Twin rotor Screw Pump Three rotor Screw Pump
Heavy oil suited, quite, more eff mechanically Balanced construction, no axial thrust IMO, etc. per specification Viking has pump curves in book, press/speed vs flow RPM 1150 on #6 to keep film RPM 3450 for #2 to keep film 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 100 GPM pump pumps 100 GPM to output, but actually pumps 110GPM, Light oils produce up to 20% slip Size pump for worst case sinario so we get desired pressure and flow: Size flow for min viscosity Size inlet piping 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. 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

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 Use an RBS, it’s 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

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 Generator usage is 56 GPH Minimum day tank is 168 gallons Minimum pump flow rate is 3.73 GPM (224 GPH)

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.

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). Flow numbers must come from the burner vendor. There are no rules of thumb Atomizing pressure refers to mechanical atomization Series loop is a low pressure loop - NYC schools must be low pressure Parallel loop is a high pressure loop

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.

Burner Loop Piped in Parallel
“High or Low Pressure Loop” Use BPR to Insure min. PSI at Burner inlet

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
Number 2 Fuel Oil Example: 250 GPH in a 1” pipe has a 1.0 PSI per 100 ft of pipe And it’s not linear- Twice the flow triples the pressure drop. Flow, Gallons per hour

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 Globe Valve 90 Deg. Elbow 45 Deg. Elbow Tee (straight thru) Tee (rt. Angle flow) 180 Deg. Return 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 Motor Starter Cabinet
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 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

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

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

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

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 • CT T: (203) • F: (203)