Boiler mill feeder control system modification
BACKGROUND
Zimbabwe
Power Company is a large power generation government owned organisation. It has
5 power stations 4 thermal and Kariba as the only Hydro power station. Harare
power station is one of the small thermal plants. The first Plant Station 1 was
commissioned in 1942 decommissioned in, station 2 in 19xx and decommissioned in
2014 awaiting boiler upgrade, the current operating plant is station 3 which
was commissioned in 19xx uses pulverised coal to fire the boilers.
Coal
is passed from bunker chutes to coal mills where is gets pulverised to small particles
which are carried into the furnace by Primary air. The amount of coal inside
the mill is monitored to avoid overfilling which may harm the mill motor or under
filling, the mill level value is called Mill differential. To achieve this a
controller was put in place that maintain desired values, this is called Boiler
mill feeder controller.
Boiler
mill feeder control system on all station 3 boilers used pneumatic controllers.
Pneumatic controllers solely on non-electronic components. They have an array
of moving parts, diaphragm contact levers and adjustable nobs. Copper pipework
is run from the point of signal sampling to the control panel into the pneumatic
controllers. A single controller has three diaphragms and four pneumatic input
lines, two for Primary Air signal and two for Mill Differential signal from the
field, the four will enter in either side of two diaphragms. The four inputs
are reduced to two motion signals which become input to the final control
diaphragm which is the regulating diaphragm. This diaphragm is coupled to a flapper.
Employing a similar to the famous flapper nozzle control mechanism the electrically
conducting flapper is connected to a 220VAC. The flappers move is an up-down
motion breaking and making contacts with low and high speed for the two step
motor. Each completed circuit will energise one of the two control relay
concomitantly energising contactors for the two speed feeder motor. The
illustration of the old system which was employed is as below.
MODIFICATION
Due to the inconsistences of the old coal feeder system, there arose
a need to use a more modern error proof and ease to adjust system of
controlling the fuel for the pulverised fuel fired boilers. Electronic
controllers and smart transmitters replace the old system. Each controller has
two analogue inputs and two relay outputs for each mill feeder. Primary air differential
and Mill differential are each a difference of two pressure values. To convert
these into the usable electric signal for the new system will require smart
differential pressure transmitters whose output is a 24vdc driving 4-20mA
signal, these are the analogue inputs to the controller.
MODIFICATION MATERIAL INVENTORY PER MILL
1 x ABB CM50 controller
2 x smart pressure transmitter
1 x single input digital bar graph display
1 x dual input digital bar graph display
2 x relays
20mm din rail
10 x din rail mount connector blocks
1 x 2A miniature breaker
1 x 24Vdc power supply
30 x red 1mm insulated ferrules
20 x black 1mm insulated ferrules
20m x 1mm black instrument cable
15m x 1mm white instrument cable
5m x 1.5mm red instrument cable
2 x Size 0 compression glands
3 x 25mm x m5 screw and nut
TOOLS
Terminal screw driver
Philips screwdriver
Cable cutters
Combination pliers
Cable stripper
Multi meter
Crimping tool
In
the above Figure 2
Point
1 - positive input of Primary Air Differential
Point
4 - Positive input of Mill differential
Point
6 – positive of the power supply
Point
13; 14 - output relay 1 NO
Point
15; 16 - output relay 2 NO
Point
17 - positive of power supply 24 Vdc
Point
18 - negative of power supply 24vdc
The
controller type and model being used is the ABB CM50. The controller is inbuilt
with function maths blocks that can be used to construct mathematical equations
for the feeder controller. The maths blocks and their respective functionality
have been detailed in this document. Also detailed are the step by step
configurations to the controllers.
MILL FEEDER CONTROL H3 BOILERS
The new system of coal
mill feeder controls.
A formula of coal
feeder into the mill is 
Where b is 1
a
is 6.
is Primary Air Differential
is
Mill differential
To compute these values
into the ABB CM50 controller, there is need to break down the formula so as to
fit it into the controller program.
Hence with: 
–
Maths block 1
–
Maths block 1
– Maths block 2
– Maths block 3
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These function blocks
indicate a direct relationship between the two analogue inputs and their ration
factors.
Afters these function
blocks (Maths Blocks) have been created the final analogue value MB3 is
considered the Analogue Output (AO) of the system and from it alarms and relays
are set to give desired output.
A range is assigned to
MB3.
MB3 Range:
To achieve delay of relay de-energising, time hysteresis function is used. The
old system, pneumatic controller used two bellow system to compare two sets of
differential pressures. The different of each bellow would be pivoted on a flat
bar at the centre of the bellows. The bar would deflect back and forth in
response to the differential pressure from the two bellows. The bellow system worked
entirely on pneumatic commands. There would be an electric signal from the
field to the controller and connected to the flat bar end where there is a
flapper. The flapper moves between two connector pins which when connected to
the flapper will complete a circuit to the motor circuit.
For the value of 
mill supply has to be cut. This is achieved by
energising an OFF relay in the control circuit which will in turn switch off
the motor.
mill supply has to be cut. This is achieved by
energising an OFF relay in the control circuit which will in turn switch off
the motor.
For the value of 
mill should go into high speed. This is
achieved by energising a HIGH SPEED relay in the control circuit which will in
turn the motor into high speed.
mill should go into high speed. This is
achieved by energising a HIGH SPEED relay in the control circuit which will in
turn the motor into high speed.
This means for any
value of 
between +3.0 and -1.0 the mill will operate in
low speed.
between +3.0 and -1.0 the mill will operate in
low speed.Configuration of ABB CM50
Menu>Access Level>Basic>
Menu>Advanced>Device Setup
Menu>Advanced>Device setup>
Initial Setting>App.
Template>Dual Indicator
Menu>Advanced>Device setup>
Initial Setting>Inst.
Tag>Boiler (1;2;3:A;B;C) Mill
Menu>Advanced>Device setup>
Initial Setting>Mains
Frequency> 50 Hz
Menu>Advanced>Device setup>
Initial Setting>Config.
Action>Hold
Menu>Advanced>Device setup>
Initial Setting>Reset to Defaults
Menu>Advanced>Device setup>
Initial Setting>Custom> Custom
Template> On
Menu>Advanced>Device setup>
Initial Setting>Custom>Analog
1 Eng. Units> InH2O
Menu>Advanced>Device setup>
Initial Setting>Custom>Analog
2 Eng.> InH2O
Menu>Advanced>Device setup>
Initial Setting>Custom>Tot 1
Eng. Units> InH2O
Menu>Advanced>Device setup>
Initial Setting>Custom>Tot 2
Eng. Units> InH2O
Menu>Advanced>Device setup>
Security Setup>Basic
Password>******
Menu>Advanced>Device setup>
Security Setup>Advanced
Password>******
Menu>Advanced>Device setup>
Security Setup>Reset Passwords
Menu>Advanced>Display
Menu>Advanced>Display>Page
1 Template> Channel 1 & 2 PV
Menu>Advanced>Display>Page
2 Template>No Display Page
Menu>Advanced>Input/Output
Menu>Advanced>Input/Output>Analog Inputs>Analog input 1>Input Type>Milliamps
Menu>Advanced>Input/Output >Analog Inputs>Analog input 1>Elect. Low>4.0000a
Menu>Advanced>Input/Output >Analog Inputs>Analog input 1>Elect. High>20.0000a
Menu>Advanced>Input/Output >Analog Inputs>Analog input 1>Linearizer>None
Menu>Advanced>Input/Output >Analog Inputs>Analog input 1>Eng. Units>InH2O
Menu>Advanced>Input/Output >Analog Inputs>Analog input 1>Eng. Dps>X.X
Menu>Advanced>Input/Output >Analog Inputs>Analog input 1>Eng. Low>0.0 InH2O
Menu>Advanced>Input/Output >Analog Inputs>Analog input 1>Eng. High>3.0 InH2O
Menu>Advanced>Input/Output >Analog Inputs>Analog input 1>Broken Sensor>Upscale
Menu>Advanced>Input/Output >Analog Inputs>Analog input 1>Filter Time>1 secs
Menu>Advanced>Input/Output >Analog Inputs>Analog input 1>Fault Detect>10%
Menu>Advanced>Input/Output >Analog Inputs>Analog input 2>Input Type>Milliamps
Menu>Advanced>Input/Output >Analog Inputs>Analog input 2>Elect. Low>4.0000a
Menu>Advanced>Input/Output >Analog Inputs>Analog input 2>Elect. High>20.0000a
Menu>Advanced>Input/Output >Analog Inputs>Analog input 2>Linearizer>None
Menu>Advanced>Input/Output >Analog Inputs>Analog input 2>Eng. Units>InH2O
Menu>Advanced>Input/Output >Analog Inputs>Analog input 2>Eng. Dps>X.X
Menu>Advanced>Input/Output >Analog Inputs>Analog input 2>Eng. Low>0.0 InH2O
Menu>Advanced>Input/Output >Analog Inputs>Analog input 2>Eng. High>20.0 InH2O
Menu>Advanced>Input/Output >Analog Inputs>Analog input 2>Broken Sensor>Upscale
Menu>Advanced>Input/Output >Analog Inputs>Analog input 2>Filter Time>0 secs
Menu>Advanced>Input/Output >Analog Inputs>Analog input 2>Fault Detect>10%
Menu>Advanced>Input/Output >Analog Outputs>Analogue Output 1>Output Type>Analog
Menu>Advanced>Input/Output >Analog Outputs>Analogue Output 1>Source>None
Menu>Advanced>Input/Output >
Digital I/O>Digital I/O
1>Type>Off
Menu>Advanced>Input/Output >
Digital I/O>Digital I/O
2>Type>Off
Menu>Advanced>Input/Output >Relays> Relay 1> Source>Alarm 1 State
Menu>Advanced>Input/Output >Relays> Relay 1> Polarity> Positive
Menu>Advanced>Input/Output >Relays> Relay 2> Source>Alarm 2 State
Menu>Advanced>Input/Output >Relays> Relay 2> Polarity> Positive
Menu>Advanced>Control
Menu>Advanced>Process Alarm
Menu>Advanced>Process Alarm>Alarm 1>Type>High Process
Menu>Advanced>Process Alarm>Alarm 1>Tag> TURN FEEDER OFF
Menu>Advanced>Process Alarm>Alarm 1>Source> Maths Block 3
Menu>Advanced>Process Alarm>Alarm 1>Trip>1.0
Menu>Advanced>Process Alarm>Alarm 1>Hysteresis>0.5
Menu>Advanced>Process Alarm>Alarm 1>Time Hysteresis>2
Menu>Advanced>Process Alarm>Alarm 1>Display Enable> On
Menu>Advanced>Process Alarm>Alarm 2>Type>Low Process
Menu>Advanced>Process Alarm>Alarm 2>Tag> FEEDER INTO HIGH
Menu>Advanced>Process Alarm>Alarm 2>Source> Maths Block 3
Menu>Advanced>Process Alarm>Alarm 2>Trip>-1.0
Menu>Advanced>Process Alarm>Alarm 2>Hysteresis>0.5
Menu>Advanced>Process Alarm>Alarm 2>Time Hysteresis>2
Menu>Advanced>Process Alarm>Alarm 2>Display Enable> On
Menu>Advanced>Totalizer
Menu>Advanced>Functions
Menu>Advanced>Functions>Math Blocks>Math Block Number>1
Menu>Advanced>Functions>Math Blocks>Block 1> Block Type> Equation
Menu>Advanced>Functions>Math Blocks>Block 1>Eng. Dps> X.X
Menu>Advanced>Functions>Math Blocks>Block 1>Eng. Low>-999.9
Menu>Advanced>Functions>Math Blocks>Block 1>Eng. High>9999.9
Menu>Advanced>Functions>Math Blocks>Block 1>Eng. Units>InH2O
Menu>Advanced>Functions>Math Blocks>Block 1>Operand 1> Analog IP 1
Menu>Advanced>Functions>Math Blocks>Block 1>Operator 1> Multiply
Menu>Advanced>Functions>Math Blocks>Block 1>Operand 2> Constant 1
Menu>Advanced>Functions>Math Blocks>Block 1>Operand 2 Constant>6.6667
Menu>Advanced>Functions>Math Blocks>Block 1>Operator 2>End
Menu>Advanced>Functions>Math Blocks>Block 1>Fault Action>Upscale
Menu>Advanced>Functions>Math Blocks>Math Block Number>2
Menu>Advanced>Functions>Math Blocks>Block 2> Block Type> Equation
Menu>Advanced>Functions>Math Blocks>Block 2>Eng. Dps> X.X
Menu>Advanced>Functions>Math Blocks>Block 2>Eng. Low>-999.9
Menu>Advanced>Functions>Math Blocks>Block 2>Eng. High>9999.9
Menu>Advanced>Functions>Math Blocks>Block 2>Eng. Units>InH2O
Menu>Advanced>Functions>Math Blocks>Block 2>Operand 1> Analog IP 2
Menu>Advanced>Functions>Math Blocks>Block 2>Operator 1> Multiply
Menu>Advanced>Functions>Math Blocks>Block 2>Operand 2> Constant 2
Menu>Advanced>Functions>Math Blocks>Block 2>Operand 2 Constant>1.0000
Menu>Advanced>Functions>Math Blocks>Block 2>Operator 2>End
Menu>Advanced>Functions>Math Blocks>Block 2>Fault Action>Upscale
Menu>Advanced>Functions>Math Blocks>Math Block Number>3
Menu>Advanced>Functions>Math Blocks>Block 3> Block Type> Equation
Menu>Advanced>Functions>Math Blocks>Block 3>Eng. Dps> X.X
Menu>Advanced>Functions>Math Blocks>Block 3>Eng. Low>-999.9
Menu>Advanced>Functions>Math Blocks>Block 3>Eng. High>9999.9
Menu>Advanced>Functions>Math Blocks>Block 3>Eng. Units>InH2O
Menu>Advanced>Functions>Math Blocks>Block 3>Operand 1> Maths Block 1
Menu>Advanced>Functions>Math Blocks>Block 3>Operator 1> Subtract
Menu>Advanced>Functions>Math Blocks>Block 3>Operand 2> Maths Block 2
Menu>Advanced>Functions>Math Blocks>Block 3>Operator 2>End
Menu>Advanced>Functions>Math Blocks>Block 3>Fault Action>Upscale
Menu>Advanced>Diagnostics
Menu>Advanced>Device Info
Menu>Advanced>Device Info>Instrument
Tag>CM50
Menu>Advanced>Device Info>I/O
Build>/0
Menu>Advanced>Device Info>No.
Analog Inputs>2
Menu>Advanced>Device Info>No.
Analog Outputs>1
Menu>Advanced>Device Info>No.
Relays>2
Menu>Advanced>Device Info>No.
Digital I/O>2
Menu>Advanced>Device Info>Functionality>
Dual Loop
Menu>Advanced>Device Info>Serial
No.>3k210000060982
Menu>Advanced>Device Info>Hardware
Revision>1
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