Boiler System is a group of many pieces of equipment. A boiler is a horizontal vessel, where water is stored for boiling. Boilers are of two main types:
1 Boiler for hot water
This boiler is used to heat the water. Hot water from this vessel is used for several domestic purposes like :
(1) Heating in the house in winter.
(2) Laundry Use.
(3) Bathing, Cleaning, Disinfecting the utensils in the kitchen.
2 Boilers for steam generation
Vessels are used for steam generation are called boilers or steam generators. They’re the horizontal vessels designed and manufactured for high pressure and temperatures inconsistent with ASME (American Society for mechanical engineers) and ASTM(American Society for Testing materials) code and standards.
Water is continuously fed into the boiler for steam generation. Boiler water is heated with combustible fuels like coal, oil, or gases. Combustible is burnt within the combustion chamber of the boiler and flue gases of Combustion are conveyed to boiler tubes to heat the water for steam generation. The boiler is not a simple pressure vessel but it is a complete system. Boilers have other accessory equipment’s like:
(1) Water feed pump.
(2) water Demineralization plant.
(3) Water feed injector.
(4) Forced draft fans.
(5) Fuel burner.
(7) Deaeration system.
Boilers have various mountings on them. Without these mountings, boilers can’t be operational. These mountings are:
(1) Steam isolation valve.
(2) Safety valve.
(3) fusible plug.
(4) Pressure gauge.
(5)Water level indicator.
(6) Feedwater non-return valve.
(7) Vent valve.
Depending on the waterside and fireside arrangements the boiler systems are mainly classified into two categories:
1)FIRE TUBE BOILERS
2) WATER TUBE BOILERS
FIRE TUBE BOILERS
Combustion gases flow through tubes in the fire tube boiler, and water is contained in a large shell that surrounds the tubes. Fire-water boilers are mostly used for hot water services and low-pressure steam generation up to 400 PSIG.
WATER TUBE BOILERS
Water flows through the tubes in water tube boilers. Combustion flue gases surround the tubes. These boilers contain about 75% less water as compared to fire tube boilers. Water boilers generate the steam from 1000 lb (0.45 t)/hr to 1,000,000 lb/hr. they’re extensively used in industries. They generate pressure up to 1000 PSIG. They’re usually manufactured in two drum construction. The upper drum is named as steam drum and the lower drum is named as mud drum.
BOILER OPERATION PRINCIPLE
Heat is applied to the water, and the boiling of water takes place in the boiler. Water-tube boiler, riser tubes are heated from outside the tubes. Steam is generated in the form of bubbles at the heated surface of water tubes. Vapour bubbles and steam are displaced by heavier water. Thus, the water circulation current brings down the cold water to the mud drum of the boiler, and steam is released. Through the riser of the boiler, a mixture of water and vapor goes up in the steam drum. Heavier water comes down to mud drums through downcomers. This way the hot water goes up and cold water comes down and a natural circulation begins and steam generation starts in the boiler. Continuous running of the boiler is achieved through the forced circulation of the water in the boiler system by boiler feed pumps. This assures the supply of water is available all the time to avoid any overheating and bulging in the boiler tubes.
TO KEEP THE LOGBOOK FOR BOILER
The boiler is continuous operating equipment. Once the boiler lit up, it remains in operation till the next planned shutdown for maintenance. The continuous running of the boiler is assured by monitoring operating parameters precisely. Boiler operating parameters to be logged in every eight-hour shift are as follows:
1 Forced draft air fan
Check the fan prime mover condition
Outside air temp. (degree F)
Airflow in the boiler combustion chamber
Boiler no. in commission
Boiler operation time in hours
Fuel gas quantity used in cubic feet
Amount of fuel in hand
Amount of fuel used
Fuel firing rate
Boiler drum pressure in PSIG
Boiler drum water level (normal, high, low)
Boiler water temp in degree F
Blowdown of the mud drum in every shift
Boiler burner pressure in PSIG
Boiler burner flame observed by the pyrometer
Flue gas analysis leaving the stake
Oil is used as a combustible medium the following parameters to be logged:
The fuel oil pump in use
Oil pressure at the pump in psi
Oil pressure at burner in psi
The pressure of atomizing air or steam in psi
Oil pressure at regulating valve in psi
Steam is used in chemical plants, refineries, petrochemicals as heating media for viscous fluid handling. Steam is used for pre-heating of vessels, reactors for moisture removal. it’s used to run the turbine-driven equipment where electrical drives are not used due to safety reasons. Uses of steam in the plant generate the condensate, which’s sent back to the boiler house and stored in the tanks. This stored condensate is used as feed water to boilers. To maintain a condensate record following parameters to be logged:
Condensate pump in operation
Boiler feed pump in operation
Returned quantity of condensate
Condensate return temperature
During the treatment of water for boiler feed contamination of chlorides, sulfates, and carbonates are to be removed in the demineralization plant. Demineralized water is used to make up water to condensate then fed to the boiler. Removal of salts like chloride, sulfate, and carbonates is necessary, this causes scale formation in boiler tubes. Hence,
Water testing for chloride, sulfate, and carbonate content to be carried out and logged in every shift of boiler operation.
Deaeration of feed water also to be carried out to remove the oxygen content. Oxygen content causes corrosion in boiler tubes. Hence,
Feedwater oxygen content test to be carried out and logged in every shift of boiler operation.
MAINTENANCE OF BOILER
The boiler is continuous operating equipment. The safe, trouble-free, and smooth operation of the boiler system is being achieved by daily, weekly, monthly, and yearly check-ups of the system as follows:
1 Water level and feedwater control equipment.
2 Pressure and temperature gauges and controls.
3 Burner working and their control.
4 prime movers to be checked for bearing noise, temp, and vibration.
5 Auxiliary systems.
6 Blowdowns system and their valves.
WEEKLY CHECK UP
1 Water level trip control
2 Blowdowns system water level gauge
3 Testing of safety and relief valves
4 Cleaning of burners
5 Flame and flame arrester testing
6 Safety sequence testing of all program
7 Testing of all safety switches
8 Flue gas analysis for CO2, SO2, and O2
MONTHLY CHECK UP
1 Combustion air supply to boiler box.
2 Draft fan Prime mover vibration
3 Belts of all belt-driven equipment’s
4 Lubrication of all rotary equipment’s
YEARLY CHECK UP
Yearly check-up for the boiler system to be carried out by an insurance inspector. It is to be planned in advance. The boiler, items to be included for a check-up are as follows:
1 Fireside cleaning and refractory repairing of the boiler
2 Draining of the whole boiler system
3 Opening of all manholes or hand holes for inspection
4 Boiler waterside cleaning
5 Internal inspection of boiler drum and tubing’s to be carried out by boiler inspector
6 Repairing of tubing or the other part
7 Refilling the boiler
8 Hydro-testing of whole boiler system
9 Oil storage check-up
10 Chemical feed system
11 Electrical equipment terminal check-up for tightness.
12 Lit up the boiler and take slowly inline
13 Checkup for all safety sequence operation