POWER PLANT BOILER STEAM DRUM INTERNALS - ASKPOWERPLANT
STEAM DRUM working and its INTERNALS
BOILER COMMISSIONING
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POWER PLANT BOILER STEAM DRUM INTERNALS

Boiler steam drum is very important part of any power plant .it is also called “heart of boiler “Because of its importance in steam generation. Boiler steam drum acts as reservoir which provides necessary head for circulation of water through evaporation zone. Boiler steam drum has own feed water storage capacity it change according to the design of plant requirement. Steam drum supplied the water to boiler after that unit suddenly stopped or tripping of plant. In steam drum steam is purified with the help of steam drum internal like baffle separators, cyclone separator, chevron separators, demisters pad / screen driers. Feed water distribution arrangement and chemical dosing arrangement is made inside the steam drum.

In this article we are discuss about power plant steam drum internal there working and importance of their installation Drum internals include steam separation and purification equipment and other secondary equipment such as the following:-

1. DRUM LEVEL GAUGE
2. CONTINUOUS BLOW DOWN PIPE
3. CHEMICAL DOSING PIPE
4. SAFETY VALVE
5. SATURATED STEAM OUTLET PIPES
6. PURIFIER / STEAM DRIERS / DEMISTER
7. CYCLONE BOX CHAMBER
8. INTERMITTENT BLOW DOWN PIPE
9. DOWN COMER

1. DRUM LEVEL GAUGE

This is a glass tube, or pair of flat glass, fitted to boiler drum to provide a visual indication of water level of boiler drum. Through this device, boiler operator can determine both water level and general condition of water in the boiler. This glass is manufactured from highly chemical and corrosion resistance low expansion Borosilicate glass. This glass is well known for its clarity and mechanical strength. Gauge glass should be regularly checked for any signs of clouding, scratching, erosion or corrosion.
In power plant boiler mainly four type of gauge glass used for showing the exact level of water in steam drum. These gauge glass are fowling:-
a. Flat Glass Type
b. Ported Type
c. Tubular Type
d. Reflex Type
Ported Type gauge glass can be used up to 210 Kg/Cm2.
Flat glass type can be used for pressure up to 140 Kg/Cm2.
Reflex type can be used for the pressure up to 24 Kg/Cm2.
Tubular type water level Gauge glass limited to 17Kg/Cm2 operating pressure.

2. CONTINUOUS BLOW DOWN PIPE

In boiler steam drum CBD (CONTINUOUS BLOW DOWN) pipe header is also uniformly distributed throughout the steam drum length. Continuous blow down header is placed just below the working water level of drum. This header is connected to the drum blow down pipe. Blow down is given to maintained concentration level of boiler water. When the concentration TDS (total dissolved solids ) of boiler water is increase its a highly chances to deposits of solids on turbine blades so blow down is given to maintain the concentration of these solid and protect the turbine blades for further deposition.

3. CHEMICAL DOSING PIPE

In steam drum chemical dosing pump is connected to the dosing pump header inside the steam drum which is evenly distributed with steam drum length. This dosing pump pressure is always greater than the steam drums. TSP ( Tri sodium phosphate ) chemical which is used to maintained the feed water chemistry inside the boiler steam drum. Chemical dosing header distributed the chemical evenly throughout the boiler steam drum. Chemical dosing piping should be made of stainless steel because due to chemical reaction it can be chocked. The hole diameter shall be 6 mm. Holes shall be pitched at 300 mm. The chemical which added to boiler drum should not get drained out through the blow down pipe. It should be so located that the chemical gets mixed well with the fresh water before entering in to the down comers .The chemical could be dosed in feed water pipe just before drum. This will ensure a good mixing of the water & chemical. It would also ensure a very good distribution.

4. SAFETY VALVE:-

Safety valve is also a very important part of steam drum. When the steam pressure is exceeding beyond a safe working limit then safety valve popup and relised the exceeding pressure and safety valve closed at predetermined pressure limit. It should not lead to starvation of Super heater. Hence it is generally located outside the steam drier unit.

5. STEAM PURIFIER / STEAM DRIES / DEMISTERS

Steam is allowed to pass through closely spaced screen. Dry steam can pass easily through these screen and the suspended water particles carried by steam is collected and falls back by gravity. Many boilers have number of screen called primary screen and secondary screen. This screen is called demisters pad.

6.SATURATED STEAM OUTLET PIPE

After heaviest particles separate from the steam with the help of demisters pads and steam comes out for dryer after that steam goes for saturated steam outlet pipe. Baffle plate is used for protect the steam directly enter into the steam outlet pipe line.

7.CYCLONE BOX CHAMBER

It’s a very important part of steam drum. It plays a vital role in purified the steam in this chamber separation of moisture and steam is done by help of centrifugal force. Steam and water mixture is passed through a cyclone separator chamber . The cyclone separator chamber creates the spinning action on the steam. Due to centrifugal action, the heavier water particles through away and collides at the cyclone wall and fall down.

8. INTERMITTENT BLOW DOWN PIPE

IBD (Intermittent blow down) its name indicate that it is a emergency drain valve through which the water level is brought down in case of high level. In low pressure boilers, the intermittent blow off valve was strategically located for removal of settled sludge’s generated by phosphates reaction with calcium and magnesium salts. And also used for the maintaining the feed water chemistry for getting the highest purity steam.

9. DOWN-COMER

Down comers tube is connected the bottom of the steam drum. These tubes are usually seen by the outside of the field . these tubes taking the water for boiler to down comer ring header of the boiler . These tubes takes the water equally throughout the boiler length and does not causes the boiler drum level fluctuations. And maintain the circulation ratio of boiler.

 

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STEAM DRUM iNTERNALS
Please let me know if do you have an idea, what are the best limits for the steam-water separation within the boiler drum for the steam leaving to the superheater circuit, normally I have heard about 99.5 % efficiency of separators is a must for the separation devices within the drum

I am from PAKISTAN and I recently visited your website. It is very helpful. For a fresh Engineer like it is nothing less than a blessing. Keep posting boss. Can you please write more about waste heat boiler and package type?

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