Boiler and Generator Fuel Oil Pumping and Distribution

March 6, 2012

NJ ASHRAE Chapter Meeting

Presented By: Ed Twiss, PE

Analytical and Combustion Systems www.acs-ny.com

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Fuel Oil Handling Overview Fuel Oil System Layout Unit Conversions/Pump Terminology

Pressure, Vacuum and NPSH Fuel Oil Pumping Basics

Pump Types & Characteristics, Pump Slip Fuel Oil Systems Application Examples

Emergency Generator and Burner Loop Examples Pump Set Selection

Selecting the appropriate pump according to system requirements Fuel System Design

Control Strategy, Fuel Oil Specialties and System Piping NYC Caveats (handout)

Long Term Storage of Fuel Oils-Special Considerations

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Fuel Oil System Layout

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Unit Conversion

Pressure 1 psi = 2.31 feet of water 1 psi = 2.6 feet of #2 oil

Vacuum

1” Hg = 1.28 feet of #2 oil 1” Hg = 1.13 feet of water 1” Hg = 0.49 psi -29.92” Hg = perfect vacuum

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Pump Terminology NPSHa: Net Positive Suction Head Available.

NPSHa is the absolute pressure available at the suction port of the pump Function of the “SYSTEM”

NPSHr: Net Positive Suction Head Required. NPSHr is the minimum pressure required to keep the fluid in the pump from

boiling/flashing/causing cavitation. Function of the “PUMP”

Operating Pump Suction The total summation of all losses encountered on the suction side of the pump

while running. Priming Pump Suction:

This value takes into account the vertical lift of a dry system Often referred to as the priming static lift.

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NPSH and Cavitation High velocity/low pressure at the suction side of a pump can cause

the fluid to start boiling with reduced efficiency cavitation damage

Boiling/cavitation starts when the pressure in the liquid is reduced to the vapor pressure of the fluid at the actual temperature.

To prevent cavitation of the pump, NPSHa MUST always be greater than NPSHr.

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Damaged to Internal gear pump caused by cavitation

NPSH and Cavitation

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Damaged to Internal gear pump caused by cavitation

NPSH and Cavitation

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Pump Location

Pump Location

Positive Displacement Pumps For most practical purposes:

Able to pump viscous liquids Positive displacement pumps are self priming

» Able to lift fluid/operate in vacuum on suction side Discharge flow relatively constant over range of operating pressures

and viscosities Can develop high discharge pressure

» when discharge flow is blocked, something could break

Pump-motor combinations produce fixed flows Pump flow is determined by the motor RPM Motor HP will determine max capable pressure

Safety relief with a path to a tank is essential

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Pump Comparison Positive Displacement Versus Centrifugal

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Internal Gear Pumps

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• Two meshed gears, one driven, one idling • Outer/driven gear has internal teeth, inner is a spur gear/external teeth • In general

• Flow rates up to 1500 gpm • Pressures up to 250 psig

• Low NPSH requirements • Low to very High Viscosity

External/Spur Gear Pump

• Two meshed spur/external tooth gears, one driven, one idling, synchronized by timing gears • In general

• Flow rates up to 750 gpm • Pressures up to 2500 psig

• Low NPSH requirements • Low to High Viscosity

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Screw Pumps

• Pressures up to 4000 psig • Flows > 3000 gpm

Twin rotor Screw Pump Three rotor Screw Pump

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• More Costly • Higher Pressure • Can Handle some solids

Pump Slip

Some oil does bypass the pump internals Typically less than 10% of pump displacement Typical catalog flow rates reflect 10% slippage

Higher pressure produces greater slip Lower viscosity produces greater slip Typical catalog pump flow rates account for 10% pump

slip

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Fuel Oil Systems Applications Boiler Loops Generator Systems (Day Tanks/Headers) Most common is duplex pump set

two 100% pumps, one for backup

Triplex pump sets for large plants three 50% pumps allow for one spare two 100% “winter pumps” - one 50% “summer pump”

Other systems available Thermo-Pump Sets (Outdoor Tanks) Jockey Pumps (tank to tank transfer) Day tank return pumps

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Boiler Supply Loop Systems Most burners have a supply and return line Burners pump more oil than they burn

5 gph burner might pump 45 gph 100 gph burner might pump 150 gph

Burners may be piped in parallel or series Pump set might provide atomizing pressure (high pressure

loop) Pump set floods the burner loop (low pressure)

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Example – Atomizing Air Burner #2 Fuel Oil Train

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Example – Burner Fuel Oil Pump Capacities

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Piping and Flow for Single Burner Return line at Higher elevation and full size, could use BPRV

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Burners in a Series Loop “Low Pressure 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.

Rule of thumb safety factor – size pump set 1.5 to 2X minimum capacity.

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Burners Piped in Parallel “High Pressure Loop”

Use BPRV

Rule of thumb safety factor – size pump set 1.5X to 2X minimum capacity.

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Series vs. Parallel Boiler Loops

Series loop Required pump flow is lower If oil is heated, heaters are smaller Usually very low pressure (< 5 psig) Lower motor HP

Parallel loop Typically operate at high pressures Requires larger motor HP Typically for burners without pumps Higher flow = larger pipe size Greater risk of system leaks

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Day Tank Systems

Day tanks are used for remote inventory for: diesel generators small burners and/or boilers on higher floors

Protects pump seals on burner or engine pump Day tank provides a period of operation without power Precautions needed to prevent foam problems Overflow from day tanks are costly mishaps In critical applications design should include a means to

test fuel pump set and suction line integrity Supply/Return lines at opposite ends of tank

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Generator/Day Tank Considerations Each 100 kw of generator capacity will consume ~ 7 gallons per hour. Diesel generators use fuel oil for combustion and engine cooling – there is a

large difference between the generator “burn” rate versus actual pumping rate. When the Emergency Generators unburned fuel is returned to the day tank,

size pump set to meet generator burn rate When the Emergency Generators unburned fuel is returned to the main

storage tank, size pump set to meet generators total pump capacity Generator fuel oil return piping configuration

Day tank versus Main tank Generator fuel oil return temperature determines the fuel oil return path. If too hot?

Return main tank Install fuel oil cooling radiator to prevent day tank overheating Increase day tank capacity

Determine duty cycle of pump set (Rule of Thumb 4:1)

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Day Tank Schematic

NYC code limits the amount of oil that can be stored above ground level

Use vent switch, as hi-hi level switch

keep at max distance apart

Vent Outdoors

For Venting Refer to Local Code

NYC

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NYC – any tank above lowest floor, vent must be piped to main storage tank,

Pump Set Suction Line Integrity Test

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• Tank Level Controls • High & Low Level Alarms • Fill Control

• Pump On/Off Control • Fill Valve On/Off Control

• Fuel Temperature Monitoring • Secondary Containment Leak

Detection • Motor controls on tanks with

return pumps

Day Tank Controls

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Multi-Point level controller

Rupture Basin Leak Switch

Weighted Emergency Vent*

Vent To System

From Main Pumpset

Generators with a Header System Greater than 330 gallons of total volume requires variance in NYC

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Pump Set Design Summary

Determining Pump Capacity For day tank systems

Rate of use + safety factor/duty-cycle determines pump flow Length of time without power or local code determines day tank size E-Gen sets – “RULE of THUMB” 7 GPH / 100kw E-Gen/Day tank - “RULE of THUMB” 4:1 duty cycle

For burner systems parallel loop, total burner(s) pumping rate X 2 series loop, 2 X (total required flow rate)

Pick pump-motor pair with next greater flow rate

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Pump Inlet Suction Guidelines

Keep pumps close to tank Avoid long suction piping runs and inverted loops

Safe practice limits suction to a 15“ Hg vacuum or less Most gear pumps can produce a 20" Hg vacuum Typical piping loss is 5" Hg This leaves 10" Hg for static lift, or 12.8' of oil Select strainer for < 0.5” Hg pressure drop

Pump should not be located more than 15’ above the bottom of the tank

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Determining Inlet Suction Determine gravity head in feet oil Determine loss through suction piping

Figure static lift from bottom of tank convert fittings, valves, etc. to equivalent feet add total length of pipe to equivalent for fittings add loss through strainer

Increase pipe size or lower pump flow to suit

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Discharge Piping Pressure at pump discharge =

pressure needed at point of use plus: » total gravity head » pipe and fitting losses

A BPRV is typically used to regulate pressure in boiler loops

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Fuel Oil Sizing Program

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Pump Set Components

Base Assembly with Integrated PS-LDS Leak Detector

Duplex Pump & Motor Assembly

Relief Valve

Duplex Oil Strainer

Pressure Gauges

Check Valve

Flow Switch

Ball Valve

Compound Pressure Gauge

Strainer DP Switch/Gauge

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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

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Fuel System Design

Select The Appropriate Pump Size & Type Flow, Pressure and Supply Voltage Required

Select Components and Features Instrumentation (Level, Leak etc…) Fuel Oil Specialties (Fill box, anti-siphon valve, fire valve…) Tanks (size, type and location)

Determine system pipe sizing Determine a Control Strategy

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Control System Considerations Starting and stopping pumps automatically

Call for operation is typical for boiler loops intermittent operation typical for day tanks/level systems Lead/Lag and alternating schemes

Sequencing for filling multiple day/main tanks Motorized ball valves with end switches

Provision for automatic pump back-up based on flow or pressure at pump discharge flow switch

Alarms on malfunction Automatic testing

Pump started on weekly basis for testing

System safety shutdowns

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Fuel Management Systems

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Typical FOS 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 PLC Failure

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Typical Shutdown Conditions Leak in riser piping* Leak in containment piping Leak in day tank* Leak in pump set Low level in main tank Loss of flow in pump, to protect pump Day tank high level* Oil in day tank vent line

*NYC Code requirements

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Control System Summary

Different applications need different strategies Control system is as important as the pumps Custom design is key to a reliable fuel system PLC allows monitoring of many points System may interface with a building management system

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Long Term Storage Of Fuel Oils Special Considerations

Diesel Fuel is an organic product that begins to decay as soon as it is refined.

Emergency generator fuel may store for 10 years Diesel fuel is prone to degradation

moisture accumulates in fuel, corroding injectors and/or seizing valves

bacteria grow in fuel, clogging filters and injectors fuel oxidizes and Cetane rating drops

Fuel can become a “hazardous waste” in 5 years Proper maintenance of stored fuel extends life

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Water collects at the bottom of the fuel tank. Sludge grows at the fuel-water boundary at the bottom of the tank.

Sludge builds up

Monthly generator tests will NOT consume enough fuel to keep the fuel fresh and turned over.

Fuel Maintenance

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Filtration systems are recommended for diesel generator systems where the fuel is likely to sit for long periods of time. A typical system will:

• Filter the sludge from the oil down to 5 microns

• Remove water from the fuel

• Inventory determines system design

Fuel Maintenance

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Emergency Fuel Life Extension Filtration to 5 microns Water removal Chemical treatment Automatic controls Doubles fuel life Engines start reliably Mutli-tank sequencing Inventory determines system

design

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NYC Fuel Oil Code Caveats Day tanks above lowest floor

Must have 200% containment 330 gallons maximum fuel oil storage per floor Vent lines must be piped back to main tank

1 day tank per pump set Tank fill-box must have spill containment Riser pipe requires leak detection/pump shutdown Anti-siphon valve required when tank inventory is above pumpset Foot valve required for tanks below pumpset Fire valve must be provided on pump suction line

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Summary

We discussed... Rules of thumb/conversion and NYC caveats Positive displacement pumps How to determine the required oil flow How to determine the required oil pressure Selecting the appropriate pump size and type Sizing suction and discharge piping Selection of control strategy Problems with long term storage of fuel oils

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