18 April, 2013

BOILER PRINCIPLES

Highlights

1. Definition boilers & steam forming process

2. Type boiler combustion system based
  1. Furnace bed material
  2. Excess / shortage of type-type boiler
3. System maintenance boiler
  1. New Boiler / renovation
  2. Routine care (internal)
4. Boiler interlocking

1. Boilers and process of formation of steam
  • Boiler (boiler) is a closed pressurized vessel,where water is converted into steam by the provision of heat (heat).
  • When the water is heated in a closed vessel (boiler) with
  • The addition of some heat, there will be a phase change from liquid to gas (evaporation process)
  • With increasing pressure, the boiling temperature of water will also rise.
  • vapor formed during the process of boiling at a certain pressure is still a steam / wet steam.
  • If the steam is still being given extra heat at a constant pressure point, then the volume will increase and temperature steam will pass through the point of saturation. Steam is commonly called steam up.
  • Steam heat up has many advantages because it can be transmitted over long distances with little loss of heat, contains a higher thermal energy, and can reduce the impact of erosion on turbine blades because of the water content in steam has been eliminated
Boilers and process of formation of steam
(Working substance flow diagram on the steam generator)

Internal circulation boiler

There are three types of internal circulation:
1. Forced (economizers) forced circulation (pipe economizer)
2. Natural (wall, roofs, generating section) natural circulation (the pipe wall)
3. Steam pressure difference (superheaters) circulation by pressure difference (steam piping up)
                                     
Circulation water / steam in the boiler
Forced circulation

In forced circulation, fluid (feed water) is pumped through the evaporator kettle. Water filler (feed water) can be pumped using only a small pipe
However, with very high pressures (in our boiler reaches about 100 bar).
High pressure forcing fluid flow in through the control valve to the economizer to be forwarded to the steam drum.

Natural circulation

The heat energy given to the combustion chamber will cause evaporation.
The steam has a lower specific gravity will rise upwards, while the heavier water will collect at the bottom of the steam drum (steam drum). Water is what will go down from the steam drum through the downcomer and enters the tube wall (wall tube boiler) natural (gravity)

Circulation pressure difference

As the laws of gravity and heat flow, vapor always flows from an area
Higher pressure to areas of low pressure. Steam in the steam drum of about 12 bar higher than the pressure of steam turbine header. This pressure difference causes the steam flow to the steam pipe up.

2. Type boiler combustion system based

1. Fixed bed (cb)
Do not have a sand layer with temperature (~ 750oc 900oc) in the bottom of the combustion chamber for burning media.

2. Fluidized bed boiler
Boiler wearing hot sand (800 ~ 900 oc) in the furnace. Fluidization
Using primary air of paf.

2.1. Bubbling fluidized bed boiler (BfB):
Bed experienced bubbling (centered) on the bottom of the boiler, bed material
(Sand) remain in the furnace
         
2.2. Circulating fluidized bed boiler (CFB):
Bed material moving / flying from the combustion chamber and circulating
Back to the combustion chamber with the aid of cyclone separator.

2.1 fixed bed boiler (cb)

The general condition of fixed bed boiler
  • smaller combustion area.
  • smaller boiler capacity
  • Efficiency lower combustion
1. Control fuel with air particles less than perfect
2. O2 (excess water) 3% ~ 10%
3. High carbon content in the ash residue.
  • Fuel type limited (especially bio-fuel)
  • The process of burning fuel down drastically if wet (because no charbed that retain heat combustion chamber)
  • No need oil for start-ups
  • lower operating costs
2.2 fluidized bed boiler. Bubbling fluidized bed boiler (BfB)

Bubbling fluidized bed boiler (BfB)
1. Bed material (sand) had bubbling (move / swirl) in the bottom of the engine, only a small portion of fine sand with a low specific gravity to fly left the combustion chamber.
2. Fluidization / bubbling is due to the primary air flow passing through the nozzle (on the whole) the basis of the combustion chamber with a speed of 2 ~ 3 m / sec.
3. At rest, the height of the sand combustion chamber is 45 ~ 75 cm from the bottom (nozzle). If the conditions of hot sand floating 90 ~ 150 cm.

Bubbling fluidized bed boiler (mb)

Bubbling fluidized bed boiler (pb)

2.2 fluidized bed boiler
Circulating fluidized bed boiler (CFB)

  • fluidization achieved with the primary air flow passing through the nozzle at the base of the engine, at a speed of 2 ~ 3m/detik sand still experiencing turbulence statically.
  • If the air velocity increased until reaching 5 ~ 6 m / sec will be circulating sand.
  • Bed material (sand) moving / swirling and some flew out of the engine and circulates back into the combustion chamber with the aid of cyclone separator.
Circulating fluidized bed boiler-CFB (mb)

Cyclone separator in mb

Specifications bedmaterial (sand) boiler

1. Sand for boiler BfB
  • Particle size = 0.5 ~ 2 mm
  • Density sand = 1.3 ~ 1.6 t/m3
  • Heat resistance> 1100 ° c
2. Sand for CFB boiler
  • Particle size = 0.13 ~ 0.6 mm
  • Sand density = 1.3 ~ 1.6 t/m3
  • Heat resistance> 1100 ° c
2.3 advantage fluidized bed boiler
  • larger boiler capacity (pressure & high temperature)
  • wider area burning, high heat transfer.
  • flexible fuel type, can change or mix and be able to
  • Using high moisturenya fuel.
  • High Efficiency burning and easy to control
  • Excess lower o2 (2 ~ 6%).
  • Environmentally friendly:
- The amount of carbon in the fly ash is lower.
- SO2 can be reduced by limestone injection
                                 (SO2 + CaCO3 à gypsum)
- Low nox emissions due to higher combustion temperatures (750 ~ 900oc)

Type boiler in Sumatra

3. System maintenance boiler

  • New Boiler / renovation of boiler tube

- Alkali boiling
- Magnetic films formation
- Steam flushing

  • Routine care (internal treatment)

- Boiler water treatment system
• Corrosion control
• Scaling control
• Carry over control
- Trouble shooting (water quality)

3.1 Alkali boiling

Aiming to dispose or release a total carat, solids are sticky on the inside of the tube, minerals and oils and other substances that are not expected to be in the tube / drum.

Chemical needed for boiling alkali:
Soda ash / sodium carbonate (Na2CO3) =>
Total consumption 7.5 kg/m3 boiler volume.

  • Trisodium phosphate (na3po4) =>Total consumption 7.5 kg/m3 boiler volume.Chemical injection point:
  • Some through another drain economizer
  • Mostly through boiler blow down
The general procedure alkali boiling

1. Before the ignition process begins, boiler water recharge and do blow down several times, to remove dirt from sticking to the tube.
2. Fill the water boiler to normal levels, start ignition, an increase in temperature in the furnace or boiler water carried out following the curve of refractory curing.
3. When the water temperature reaches 90oc boiler and furnace temp. 90oc ~ 110oc conducted chemical charging through eco drain and blow down boiler.chemical directly charged to the end (+ 1 hour).
4. Perform chemical circulation for 7 ~ 10 hours, keep your furnace controls the temperature and press the starting valve.
5. Further raising the furnace temperature up to + 200oC and pressure (press) 7 ~ 10 bar, keep this condition for 10 ~ 12 hours.
6. Perform Circulate water blow down and boiler. Furnace temperature, drum press and steam drum level is maintained in accordance point 5, do the test water quality during blow down every 2 hours until normal parameter values.

Parameter test in boiling alkali

Sat Parameter Standard Remark
1. Coductivity
2. Ph
3. Phosphate (na3po4)
4. Silica (Si02)
5. Iron (fe)
6. Oil content Us / cm
-
-

Ppm
Ppm
Ppm <150
9.5 ~ 10.5

<3:50
<0.02
UDT

Standard operational
Eachs boiler

Remarks: if the above conditions have been achieved, the process can stop boiling lye.

3.2 Magnetic films formation

Boiler pipes made of stainless steel or mild steel mix. Once done boiling alkali, the conditions inside the boiler piping clean and very sensitive to corrosion. So to protect the surface of the pipe and prevents corrosion, is necessary to form a protective layer called "layer magnetic film"

Magnetic layer of the film will not provide total protection to the piping, but with protection against corrosion magnetic films can be reduced, as long as water quality can be maintained.

Magnetic layer of the film will be lost / damaged if the boiler water ph ph lower than when the formation of magnetic film.

The general procedure magnetic films

1. This process is a continuation of prosesalkali boiling.

2. If the process is done boiling lye, then proceed with the formation of "magnetic layer film".

3. Steam pressure is increased up to 35 ~ 40 bar, the pressure is controlled with a starting valve / steam to the mp header.

4. Ph in the process of measuring magnetic films approaching ph = 7 (normal ph), then do the test water quality parameters until all water boilers, steam as standard normal operations except ph bw remain near ph = 7, the process is carried out for 36 ~ 38 hours.

Reaction movie kimiamagnetic

With clean water and free oxygen reaction will occur below the
Different temperatures

  • At temperatures <60'c
  • 2H2O + Fe fe (oh) 2 + h2

Reaction formed can not protect the steel from corrosive.

  • At temperatures of 60'c ~ 250'c2H2O + Fe fe (oh) 2 + h23fe (oh) 2 
  • 2H2O + H2 + Fe3O4 + 4H2 magnetic layer of the film has begun to take shape through 2 faseferro hydroxide.
1. At temperatures 250'c ~ 570'c
3fe + Fe3O4 + 4H2  4h2o
Film magnetic layer harder than the layer formed at low temperatures to protect the pipe from corrosive reaction.

Graph magnetic films formation (for example mb-12 for 32 hours)

3.3 Steam flushing

Aiming to clear the superheater tube & pipe line of solid material objects contained within the pipes that arise during manufacturing / development boiler. Solid objects such as: rust, powder grinding, sand, dirt, etc. should be cleaned so as not to damage the turbine blades.

The general procedure steam flushing:

All internal equipment drum demister, cyclone separator should be opened and removed the condition of the steam drum.

  • At around steam pipes, made after playing steam outlet valve to blow out blow out steam installed on the target plate of aluminum.
  • Steam fastest flushing done 1 x 4 hours, performed repeatedly until the inside of the boiler tube really clean, marked by conditions of the target plate (alluminium) no longer a solid object goresan-goresan/rusak severe beating.

Internal maintenance (routine) boiler
1. Routine maintenance (internal check)

  • System boiler water treatment

- Corrosion Control
- Carry over control
- Deposition / scaling control

  • Trouble shooting (water quality)

Boiler water treatment system

Things that need to be considered for the water boiler is hardness, chloride salts, silica and acidity and alkalinity of the gases dissolved in the water should not be ignored, such as co2 and o2

Boiler water treatment purposes

1. Prevent corrosion in boiler systems
Corrosion occurs due to the presence of:

  • Oxygen
  • Ph of water is too low / too high

2. Prevent deposition / scaling
 scaling the result of minerals, especially ca, mg, the
 (Deposition in boilers, especially in areas that have a high heat flux).

3. Prevent contamination of steam carry over
As a result of:

  • Water Impurities charging
  • parameter limits too far

CORROSION CONTROL

Prevention of corrosion in boiler systems

Written by : Afridal Walda ~ Lets talk about Power Plant,Recovery Boiler,Function,Black Liquor,Chemical Boiler,Electrostatic Precipator,Information and Blogging

BOILER PRINCIPLESarticle was posted by Afridal Walda on 18 April, 2013. Thank you for your visit and your willingness to read this article. Criticism and suggestions can you convey through the comment box.

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