Limits

Question 1

NOx Limits

Answer 1

0.09 lb/MBTU 24 hr average

Question 2

SO2 Limits

Answer 2

0.16 lb/MBTU 3hr average

Question 3

CO Limits

Answer 3

1003 lb/hr 30day average
Slag conditions >150ppm

Question 4

Hg Limits

Answer 4

1.2 lb/TBTU 30 day average

Question 5

Opacity Limits

Answer 5

10% 6min average

Question 6

Reheat protection

Answer 6

Total fuel >20% with turbine not in service

Question 7

Furnace pressure Limits

Answer 7

+/- 12inches of water

Question 8

Drum level Limits

Answer 8

+11.25” / -10”

Question 9

Total Air Limits

Answer 9

< 28.7% unit trip
43% minimum in auto
35% for purge

Question 10

DAST lvl

Answer 10

100” set point

> 136” turbine trip
118” dump valve opens
< 12” Both BFPs trip

Question 11

RAH outlet temp Limits

Answer 11

> 350F on 2of3 probes on either RAH trips the plant.

Question 12

Slaking Temp

Answer 12

Normal set point 180F
not to exceed 100degree rise from inlet temp.
High Temp trip 195F
Warming cycle required <120F

Question 13

Dilution water tank Limits

Answer 13

Set point 160”
High level cut off 172”
Pump trip 48”

Question 14

Condenser hotwell Limits

Answer 14

High alarm 37”
Set point 32”
Pump trip 15”

Question 15

Cooling Tower basin Limits

Answer 15

Set point 225”
High 234” (shuts fill valve)
240” overflow
200” point of accelerating concern
172” Pumps trip => unit trip

Question 16

Service Water tank Limits

Answer 16

Normal 35.5’-36.5’
Overflow 37.2’
Pump trip 31’

Question 17

Condenser vacuum Limits

Answer 17

Normal 1.2psia
Turbine reset 1.7
C Vacuum pump auto start 1.9
Turbine trip 3.6

Question 18

Slurry tank

Answer 18

10% - slurry pump trip
75% - normal set point
60-80% batch start/stop
85% - High level shutoff
50% - mixer shut off

Question 19

Main Lube oil pressure Limits

Answer 19

23psi Normal
16psi low alarm (turbine roll permit)
10psi turbine trip (2/3 press switches)
No AC pump running 20 seconds => turbine trip

Question 20

Stator cooling water Limits

Answer 20

203F Return water temp Trip
130-150 normal Return temp
118F supply hdr set point
Low pressure Turbine Trip on 2/3 pressure switches (~30psi)

Question 21

Mill Trips

Answer 21

Coal gate shut
Feeder stop
All cut dampers shut
Air flow <48%
Lube Oil pressure <11psi
Outlet Temp >165F

Question 22

Exhaust Hood temp Limits

Answer 22

125F normal
>175 Alarm
>225F Turbine Trip

Question 23

EHC pressure Limits

Answer 23

Normal 2450psi
1950psi - standby pump starts
1650psi - Turbine Trip

Question 24

Turbine Bearings Limits

Answer 24

Vibrations:
Alarm at 5mils.
Trip at 7mils

Journal bearings
Alarm 225F
Trip 250F

Thrust bearings
Alarm 208F
Trip 221F

Question 25

Boiler Feedpump Limits

Answer 25

Trips:
Strainer DP 7psid
High vibrations
High bearing temp
High LO temp
12psi LO pressure low
or LO pressure BQ
0 NPSH
4080psi Discharge pressure high
475kpph Low flow
(Recirc set point 1200kpph)
12” Low DAST lvl

Question 26

ID Fan inlet duct Limits

Answer 26

-36” on 2/3 trips both Fans
=>MFT

-32” “ID Fan Master Inlet Press Override
Sacrifices furnace pressure control to prevent fan trip

Question 27

Drum metal temp Limits

Answer 27

Max difference top to bottom 100F
Max rate +/-50F/hr up to 212
Max rate +/-100F/hr >212

• differential thermal expansion causes stress fractures which reduce the life of the plant.
  Limits apply to both warming and cooling.

Question 28

Bottom Ash drag chain Limits

Answer 28

Oil pressure > 1850psi
Tensioner > 11”
Tensioners > 2” different
Speed switches ok.

Question 29

PA fan Runback

Answer 29

250MWG
(34%)

Question 30

RAH Runback

Answer 30

250MWG
(34%)

Question 31

ID Fan Runback

Answer 31

333 MWG
(45%)

Question 32

FD Fan Runback

Answer 32

250 MWG
(34%)

Question 33

BFP Runback

Answer 33

333MWG
(45%)

Question 34

2 Mill Runback

Answer 34

333 MWG
(45%)

Question 35

Mill trip Runback
(3 Mills on)

Answer 35

503 MWG
(68%)