©2013 Detroit Stoker Company. All Rights Reserved
Design and Operation
Spreader Grate SystemsBob Morrow – Detroit Stoker
Red Lion Hotel
Port Angeles, WA
March 11-13, 2014
Western Regional
Boiler Association
©2013 Detroit Stoker Company. All Rights Reserved
• Administration, Sales, Engineering &
Manufacturing in Monroe, Michigan
• 85 Employees
• 19 North American Manufacturer Sale Reps
• 12 International Manufacturer Sales Reps
• Privately Owned
Detroit Stoker Company
©2013 Detroit Stoker Company. All Rights Reserved
• Solid Fuel Combustion Systems
• Solid Fuel Feeding/Metering Systems
• Rotary Seal Feeders/Double Flap Airlocks
• Low NOx Gas/Oil Burners
• Aftermarket Parts & Services
• Engineering Studies
– CFD Analysis for Air Systems and Furnace Design
– Pilot Scale Testing
Products & Services
©2013 Detroit Stoker Company. All Rights Reserved
• Spreader Fired Combustion Systems
• Mass Fired Combustion Systems
Solid Fuel Combustion Systems
©2013 Detroit Stoker Company. All Rights Reserved
Detroit’s Supply for Nippon
Fuel Distributors
Secondary Air
Grate System
©2013 Detroit Stoker Company. All Rights Reserved
Nippon – Grate System Design
• MCR Steam Output = 225K lbs/hr
– 945 psig, 900°F, 250°F
• Thermal Input = 383 MBtu/hr
– Fuel = 95K lbs/hr
– HHV = 4050 Btu/lb @ 51% H2O
• 2 module Roto-Stoker type VCG
– Air-cooled, Vibrating grate
– 19’-4” wide X 24’-0” long
– Grate thermal load = 830 Kbtu/ft2/hr
• Primary Air & Secondary Air Temp. = 500°F
©2013 Detroit Stoker Company. All Rights Reserved
• Eccentric design drive arrangement
• Operation initially lifts fuel and ash ahead & forward. As the grate surface moves back, fuel/ash particles deposited farther ahead.
• Low speed operation (385 rpm nominal)
• Small amplitude (1/4” total)
• Intermittent operation• Run cycle 3-5 seconds, Dwell for 10-20 minutes
• Grate surface supported on specifically designed spring (flex) strap arrangement
Basic Principal of Grate Operation
©2013 Detroit Stoker Company. All Rights Reserved
Stationary Frame
Vibrating Frame
Grate Elements
Flex Straps
Grate Assembly
©2013 Detroit Stoker Company. All Rights Reserved
Grate Drive7 ½ HP motor
Speed reduction
sheaves
Pilot Bearings
Eccentric shaft
Eccentric Bearing
©2013 Detroit Stoker Company. All Rights Reserved
Feed Rate Factor Vs Eccentric rpm
0
0.05
0.1
0.15
0.2
0.25
360 365 370 375 380 385 390 395 400 405 410 415
Eccentric Speed (rpm)
Feed
rate
facto
r
Nominal Operating
Range
Structural Design
Point
Grate Ash Discharge Capacity
©2013 Detroit Stoker Company. All Rights Reserved
Spreader Type Combustion Systems
Larger FuelSmaller Fuel
©2013 Detroit Stoker Company. All Rights Reserved
Biomass particle
Thermal Decomposition
Products:
Light Gases, Liquid HC’s, Tars
Charcoal
CO
Combustion Products:
CO2, CO, H2O, PICs
Air Air
Flyash or bottom ash
with unburned C
Distribution
between these
is fuel
dependent, but
typically more
volatile material
with biomass
Glowing Particles
“Sparklers”1 - 2 Seconds
0.1 - 0.3 Seconds
Biomass Fuels
©2013 Detroit Stoker Company. All Rights Reserved
– Suspension Firing
• Smaller particles with low terminal velocities dry/volatilize in
suspension over the bed flame.
• Smaller particles are less dense with lower mass of moisture.
• Smaller particles have higher surface area
• Distribution across entire grate area is constant with small particles
in front zone and larger particles in the rear.
• Immediate reduction of particle mass (H2O & VM), lesser fuel height
on grate surface. Grate designed for higher P for primary air
distribution.
– Enhanced volitazation by pre-heated primary air
Spreader Combustion
Theory ‘Fine Fuel”
©2013 Detroit Stoker Company. All Rights Reserved
– Grate Firing
• Large particles with high terminal velocity deposit on the grate.
• Larger particles include higher mass of moisture, therefore need
more time to dry and volatilize.
• Larger particle trajectories travel through the hottest zone above the
bed therefore radiant heat transfer increases dry / volatilize rates.
• Under grate air is pre-heated to assist and increase drying rates in
bed zone.
• As larger particles dry / volatilize, size and density decrease and
terminal velocity is reduced which re-introduces particles into the
suspension fired combustion zone.
Spreader Combustion
Theory ‘Larger Fuel”
©2013 Detroit Stoker Company. All Rights Reserved
Maximum Entrained
Particle Size for Dry and
Devolitilized, Dry, 30% and
50% Moisture Particles
Fuel Particle Entrainment
©2013 Detroit Stoker Company. All Rights Reserved
0%
20%
40%
60%
80%
100%
0.0 - 2.8 2.8 - 4.0 4.0 - 6.4
Particle Width (mm)
Mass D
istr
ibu
tio
n,
%
Fraction Solid
Carryover
Fraction Entrained
and Burned
Fraction to Grade
Douglas Fir
15 fps (4.5m/s)
1830ºF (1000ºC)
2% O2
20% MC
Mass Distribution of Douglas Fir Particles Which are Caught Overhead, Burned, or
Falling to the Grate as a Function of Particle Size
Mass Distribution of Particles
©2013 Detroit Stoker Company. All Rights Reserved
• Design fuel (<25% H2O & fine size)
• 60-70% Suspension
• 10-20% grate
• Remaining output fractioned from grate area
• Design fuel (>45% H2O & course size)
• 40-50% Suspension
• 30-50% grate
• Remaining output fractioned from grate area
Anticipated Thermal Release Locations
©2013 Detroit Stoker Company. All Rights Reserved
• NOx– Fuel sizing (direct effect)
– OFA (direct effect)
– Excess air (direct effect)
– Fuel Distribution (direct effect)
• CO– Fuel sizing (direct effect)
– OFA (direct effect)
– Excess air (direct effect)
– Fuel Distribution (direct effect)
NOx & CO Emissions Influences
©2013 Detroit Stoker Company. All Rights Reserved
0
0.2
0.4
0.6
0.8
1
1.2
0 1 2 3 4 5 6
Oxygen (blr wet)
Em
issio
ns (
lbs/M
MB
tu)
NOx
CO
Linear (NOx)
Linear (CO)
Inverse Relationships with Excess Air
BIOMASS
©2013 Detroit Stoker Company. All Rights Reserved
• Utilize lower nozzle elevations at all steam loads– Used to assist grate level fuel combustion
• Evaporate fuel moisture
• Volatize fuel
• Begin free burning of fuel carbon
• Utilize middle nozzle elevations based on flame height– Decrease nozzle flow for lower steam loads
– Increase nozzle flow for higher steam loads
• Utilize upper nozzle elevations at higher steam loads.
– Control of thermal NOx
– Provide additional O2 for burning volatile gases (CO)
OFA Theory of Operation
Top Related