Transcript Boiler Efficiency and Combustion Control

Preferred Utilities Manufacturing Corp
Electrical Energy &
Fuel Savings Using
Advanced Boiler Controls
Preferred Utilities Mfg. Corp.
31-35 South St. • Danbury • CT
www.preferred-mfg.com
Introduction
 Introduction
 Fuel

Savings
Stack Losses
 Electrical



Savings
Fan Basics
Fan and System Curves
VFD Basics
 Savings
Summary
Introduction
This discussion focuses on upgrading existing
burners from Jackshaft Control to FD Fan
Variable Frequency Drives (VFD) Speed
Control with Oxygen Trim to Save Energy and
Provide Rapid Payback.
VFD are currently being applied to motors
through out industry.
Typical Applications
 Firetube
Boilers over 400 Bhp
 Watertube Boilers
 Boilers with Seasonal Load Swings:





Hospitals
Universities
Prisons
Airports
Military Bases
Fuel Savings
Combustion Efficiency
Combustion Theory
Chemistry:
Air = O2 + N2
Fuel = C + H
3O2 + N2 + 2C + 4H  2CO2 + 2H2O + N2
Time + Temperature + Turbulence
Excess Air
Excess Air Required for Burners
Excess Versus Deficient Air
Variations in Air Composition
 “Standard”
air has 0.0177 LB. O2 per FT3
 Hot, humid air has less O2 per cubic ft

20% less at 95% RH, 120OF, and 29.9 in. Hg
 Dry,

cold air has more O2 per cubic ft
10% more at 0% RH, 32OF, and 30.5 in. Hg
 Combustion


controls must:
Adapt to changing air composition or
Allow at least extra excess air at “standard”
conditions
Variations in Air Composition
Forced Draft Fan
Combustion Air
(Constant Volume)*
( O 2 + N2 )
Temperature = 120 F
Relative Humidity = 95%
Pressure = 29.9 in Hg
Less lbs of O2 + N2 per cu ft
H2O
N2
N2
N2
N2
N2
H2O
O2
N2
N2
N2 O 2
N2
N2 O 2
N2
Fuel Flow
(C+H)
O2
O2
N2
N2
H2O
N2 N 2
N2
N2
N2
N2
N2
N2
H2O
O2
N2
O2
O 2 N2
N2
N2
N2
N2
N2
N2
N2
N2
N2
N2
N2
O2
N2
O2
Burner
N2
N2
N2
N2
N2
N2
N2
N2
O2
N2
O2
N2
O2
H2O
Variations in Air Composition
Forced Draft Fan
Combustion Air
(Constant Volume)*
( O2 + N2 )
Temperature = 32 F
Relative Humidity = 0%
Pressure = 30.5 in Hg
More lbs of O2 + N2 per cu ft
Fuel Flow
(C+H)
O2
N2
O 2 N2
N2
N2
N2
N2
O 2 N2
N2 O 2
N2
N2
N2N2
O 2 O2
N2 O 2
N2
N2
N2
N2
N2
N2
N2 O 2
N2
N2
N2 N 2
N
2
N2
O2
N2
N2
O2
N2 O 2 N2
N2
N 2 N2
O2
N2
N2 N2
N2
O 2 N2
O2
N2
N2
N2 N2
N2
N2 N 2
O2
N2
N2
N2
N2
N2
O2
N2
O2
N2
N2
N2
O 2 N2
N2
N 2 N2
O 2 N2
N2
N2
O 2 N2
N2
N2
N2
N2 N2 N 2
N2
N2
N2
N2
O2
N2
N2
N2
O2
N2
N 2 N2 O 2
N2
Burner
At these ambient conditions the burner has extra O2 & N2
Control System Errors
Combustion control system can not perfectly
regulate fuel and oxygen flows. Therefore, extra
excess air must be supplied to the burner to
account for control system errors…


Hysteresis (non-repeatability): linkage slop,
valves, dampers, and fuel pressure regulator
Fuel flow for a given valve position varies with
temperature and pressure
Combustion Control Objectives
 Maintain



proper fuel to air ratio at all times
Too little air causes unburned fuel losses
Too much air causes excessive stack losses
Improper fuel air ratio can be DANGEROUS
 Always
keep fuel to air ratio SAFE
 Interface with burner management for:



Purge
Low fire light off
Modulate fuel and air when safe to do so
Jackshaft Fuel-Air Ratio Control
To / From L91 Pressuretrol
STEAM
PT
Existing
Jackshaft
Actuator
Existing Jackshaft Burner
OIL
GAS
Electrical Savings
 Fan
Basics
 Fan and System
Curves
 Motor & Electrical
Systems Basics
 VFD Basics
VFD System Basics
 Variable




Frequency Drive
The Inputs are a 4-20mA FD Fan Speed Demand
and Motor AC Voltage
Output is a “Variable Frequency” AC
Motor speed follows the 4-20mA input
Motor manufactures strongly recommend a
Motor rated for Inverter Service for long life
» These motors can with stand higher surge voltages
VFD System Basics
 VFD
provides Electrical Energy Savings due
to:




Oversized Fans
Oversized Motors
Partially Loaded Boilers
Minimizing Damper Hp Losses
Centrifugal Fan Exploded View
Reference 1
Vortex Dampers
 Inlet
vanes give an initial spin (or vortex) to
air entering a centrifugal fan. By adjusting
angle of vanes the degree of spin and
volumetric output are regulated.
Reference 3
Inlet Control Vanes
Reference 2
Inlet or Outlet Dampers
 Inlet
or opposed blade dampers assure
even distribution of air immediately
downstream from the damper. By
adjusting angle of blades the volumetric
output are regulated.
Reference 1
Flow vs Fan Hp
Non-Vortex Dampers
Vortex Damper
Speed Control
Reference 1
Fan Hp Summary
Dampers substantially increase Fan Hp and Fan
kW Consumption.
 Dampers are Evil!
 Inlet Vortex Dampers waste less Hp than any type
of inlet and outlet Blade Dampers.
 Variable Speed Fans Control air flow with
minimum fan shaft Hp.
 Variable Speed Fans have been field proven in
thousands of HVAC air handler applications.

Variable Frequency Drives

Adjustable Frequency Drive (AFD)
Adjustable SPEED Drives (ASD)
VARIABLE Frequency Drives (VFD)
VARIABLE SPEED Drives (VSD)
Inverters
Frequency Converters
Drives

Different names for the same thing.






Motor Speed Control
Pulse Width Modulation (PWM)



On or Off, voltage does
NOT modulate.
PWM allows IGBT’s to
run cool for long life, so
all VFD’s use PWM.
However, PWM dV/dt
causes spike voltages
Voltage Spikes

dv/dt - Change in Voltage over Time



Poor Drives - up to 3500V/us
Good Drives - 900V/us on 500 feet
Lower Peak Voltages Extend Motor Insulation Life
Do we need a VFD rated Motor ?

NO


Strong Probability: NO




230 V Motors
460 V motors with: < 50 ft wire run, good drives almost
eliminate problems.
However, you can NOT guarantee it. Motor age and heat
naturally degrade the motor wire insulation. The customer
should know that there is a small risk.
If motor insulation fails, the VFD is not damaged, but the
user must pay to have the motor re-wound or replaced.
YES

575 V Motors
Combustion Air Fan Hp Savings
Damper Control
HP Savings
Variable Speed Control
Combustion Air Flow, %Full Load
Reference 1
Savings Summary
F u e l S a v in g s
E le c tric a l S a v in g s
Fuel
Savings
$3,500
Operating Cost Savings
$3,000
$2,500
+
$2,000
Electrical
Savings
$1,500
$1,000
$500
$0
20%
40%
60%
80%
B oiler Load (%)
100%
Energy Savings

Fuel Savings:




Seasonal Air Density
and Humidity Changes
Fuel Pressure and
Temperature Changes
Fuel Btu and Viscosity
Variations
Worn Linkage
Components
(Hysteresis)

Electrical Savings:




Minimizing Damper
Pressure Drop - damper is
100% open for maximum
kWh savings, (Partially
closed at low fire to
maximize burner turndown)
Oversized Fans
Oversized Motors
Partially Loaded Boilers
Advanced Burner Control
Energy Savings
 Important






Factors
Boiler Size?
Loading Service?
Exit Gas Temperature? (Boiler Pressure
Determines)
Electrical Cost? (10 cents, 4 cents?)
Fuel Cost?
Utility Rebate?
Unique Energy Savings Tool

Savings Estimate
Based on:









Boiler size
Motor HP
Air Damper Type
Current O2 Level
Projected O2 Level
Flue Gas Temperature
Seasonal Loading Data
Fuel Cost
Electrical Cost
If You Can’t Get Field Data
Conservative Assumptions
% O2 Improvement = 1 - 2 %
 Heating Boiler Seasonal Loading =




Boiler Firing Rate 0% 20% 40% 60% 80% 100%
% Per Year
25% 5% 20% 15% 30% 5%
Process Boiler Seasonal Loading =


Boiler Firing Rate 0% 20% 40% 60% 80% 100%
% Per Year
5% 5% 20% 20% 30% 20%
Natural Gas Cost $4.50 / 1000ft3
 Fuel Oil Cost $0.90 / gal
 Electricity Cost $0.75 kWh
 Flue Gas Temperatures - 10 psi-350 F, 120 psi-475 F

Things You Need To Know
 Utility




Energy Rebates
North East Utilities, CL&P - offers a 50 % rebate
of the VFD price and cost of installation.
They use standard numbers.
They require paper work to be submitted
Local VFD rep will be able to give the local
rebate offer.
Large Firetube Scenario

Steam Boiler: 600 bhp capacity @ 10 psi (193 F), 350 F flue gas temp.
20 ppm, 60 hp fan motor, parallel blade outlet damper controls air flow

Utilities Cost: Fuel Gas: $4.5 / 1000 ft3) / Electricity: 5 cents / kwh

Operation: Process boiler, 50 weeks a year service,
» Shutdown - 10 % of year / 20 % Load - 20 % of year
» 40 % Load - 20 % of year / 60 % Load - 20 % of year
» 80 % Load - 20 % of year / 100 % Load - 10 % of year
Oxygen Trim Improvement: Field service engineer has determined that
the burner excess air performance can be improved as follows:
» 20 % Load - 6% to 4.5 % O2 / 40 % Load - 6% to 4.5 % O2 Wet
» 60 % Load - 5% to 3.5 % O2 / 80 % Load - 4% to 2.5 % O2 Wet
» 100 % Load - 4% to 2.5 % O2 Wet


Utility Rebate: 50% of VFD Cost and installation
» (use VFD list price as an estimate)
» Existing Jackshaft Actuator: 150in-lbs
Large Firetube Scenario
Large Firetube Scenario
Installed System Payback
Oxygen Trim / VFD Payback Comparison
(with 0% VFD & VFD Installation Rebate, 1% O2 Wet Improvement)
4.50
4.00
Payback (Years)
3.50
3.00
2.50
2.00
1.50
1.00
0.50
0.00
20%
40%
60%
80%
100%
Boiler Load (%)
300 bhp
500 bhp
600 bhp
900 bhp
1200 bhp
300 Bhp Payback vs.O2 Decrease
300 BHP Oxygen Trim / VFD Payback Comparison
(with 50% VFD & VFD Installation Rebate)
6
Payback (Years)
5
4
4.83
3.97
3.47
3
2.84
3.40
3.28
3.46
2.77
2.69
2.59
2.47
2.43
2.05
2
1.82
1.70
1.46
1.59
1.58
1.23
1.16
1
0
20%
40%
60%
80%
100%
Boiler Load (%)
0.5% O2 Decrease
1% O2 Decrease
2% O2 Decrease
3% O2 Decrease
Preferred Utilities Manufacturing Corp
For further information, contact...
Preferred Utilities Manufacturing Corporation
31-35 South Street. • Danbury • CT
T: (203) 743-6741 • F: (203) 798-7313
www.preferred-mfg.com