(By Kamal Hossain, Chief Engineer)
Q. (a) Explain why regular testing of water in auxiliary boiler is advisable
(b) How to take correct sample
(c) Discuss what factors are necessary when measured value differ appreciably from desired value in each test.
(d) Give reasons for the situation when alkalinity is found to have fallen unaccountably.
(a) For the well boiler operation, boiler water should be tested regularly and accurately. Then correct chemical treatment should be followed based on the test results for the following reasons.
– To keep the boiler water in alkaline condition
– To precipitate all scale forming , both dissolved and suspended salts in the boiler water , in the forms of removable and non-adherent sludge.
– To remove dissolved oxygen , carbon dioxide and other gases
– To produces substances which will be well below the limits for carry over , foaming and priming..
Boiler Automatic Burning System:
1. With correct water level, steam pressure transmitter initiates cut-in at about 1.0 bar below working pressure.
2. Steam pressure transmitter initiates Master Relay to allow ‘Air On’ signal to force draught fan.
3. Air feedback signal confirms ‘Air On’ and allows 30-sec. delay for purge period.
4. Then Master Relay allows Electrode to strike ‘Arc’.
5. Arc striking feedback signal confirms through electrode relay and allows 3-sec. delay.
6. Then Master Relay allows burner solenoid valve for ‘Fuel On’ operation.
7. Fuel On feedback signal allows 5-sec. delay to proceed.
8. As soon as receiving Fuel On feedback signal, Master Relay checks ‘Photocell’, which is electrically balanced when light scatter continuously on it.
9. Result is OK and cycle is completed.
10. If not, fuel is shut-off, Alarm rings and cycle is repeated.
11. Steam pressure transmitter initiates cut out automatically at about 1/15 bar above W.P.
Exhaust Gas Boilers:
- About 30% – 34% of Fuel Energy input to engine are discharged to Exhaust Gas, as Thermal Energy.
- This thermal energy is converted into useful work in Exhaust Gas Boiler.
Cochran Exhaust Gas Boiler:
1. A double-pass, vertical type, in which Exhaust gases from ME pass through 2 banks of tube.
2. Served as an efficient silencer, when the boiler is in use.
3. A separate Silencer, always fitted along with exhaust gas boiler, to be used when the boiler is generating more steam than required.
4. All or part of exhaust gases can be directed to the Silencer and atmosphere, without going through the boiler.
5. Working Pressure is around 7 bars.
Composite Boiler (Composite type Cochran boiler):
1. If Exhaust Gases and Oil fire can be used at the same time, it is termed Composite Boiler.
2. In double-pass, composite type Cochran Boiler, it provides a separate tube nest for exhaust gas passage, situated immediately above the return tube nest from Oil-fired Furnace.
3. Exhaust gases from Oil-fired Furnace and ME; pass through the tubes, which are surrounded by boiler water.
4. Separate Uptakes provided for Exhaust Gases and Oil-fired Smoke.
5. Heavy Changeover Valves are fitted, to divert the gases straight to the funnel, when desired.
In the draft “Code of practice for the design, safe operation, maintenance and servicing of boilers”, a requirement is made for regular water-quality monitoring of both limited-attendance boilers and unattended boilers.