Easy understand Basics of boiler operating methods 

boiler operation
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boiler test , we will introduce general knowledge regarding the operation and handling of boilers.

This does not mean on-site operation management, but knowledge on equipment protection related to the parts before and after the operation.

Actual operation management varies from site to site, but preparation, start-up, cleanup and maintenance are common to all equipment, so it is easy to ask questions on the exam.

This kind of thinking is not limited to boilers, but applies to various qualification exams as well.

Some equipment engineers think that it has nothing to do with operation, but it is a part that is directly connected to equipment management, so be proactive and learn.

  1. Boiler operation and handling
    1. preparation
    2. ignition
      1. water
      2. air
      3. fuel
    3. pressure rise
    4. driving
  2. Abnormal boiler
    1. boiler water level
    2. carry-over
      1. Effects of lower steam purity
      2. Effects of clogging
      3. instrument malfunction
    3. Combustion gas leak/oil leak
    4. Combustion system problem
      1. secondary combustion
      2. backfire
      3. Carbide (carbon), spark
  3. boiler shutdown
    1. stop fuel
    2. air replacement
    3. Stop water supply
    4. steam valve closed
    5. Damper closed
  4. Handling of accessories
    1. pressure gauge
    2. water gauge
    3. safety valve
    4. Blowing device
    5. Water supply device
    6. automatic controller
  5. Boiler cleaning
    1. mechanical cleaning
    2. acid wash
    3. alkaline cleaning
  6. Storing the boiler
    1. dry storage
    2. Save full water
  7. Terms related to boiler water
    1. pH
    2. hardness
    3. acid consumption
    4. dissolved gas
    5. Evaporation residue
      1. soluble evaporation residue
      2. suspension
  8. Removal of impurities
    1. dissolved gas
    2. Evaporation residue
      1. soluble evaporation residue
      2. suspension
  9. boiler water management
    1. Can cleaning agent
    2. blow
  10. Characteristics of boiler fuel
    1. solid fuel
    2. liquid fuel
      1. Stable quality
      2. easy logistics
      3. Easy to handle
    3. gaseous fuel
      1. equipment is large
      2. High risk of fire and explosion
  11. Liquid fuel combustion method
    1. liquid fuel flow
    2. tank
    3. feed line
      1. pump
      2. Heater
      3. flow rate adjustment
    4. burner
      1. pressure spray
      2. steam injection
      3. air spray
      4. rotary
  12. Gaseous fuel combustion method
    1. There are two combustion methods
      1. Diffusion combustion method
      2. Premixed combustion method
    2. Gas is city gas/LPG
  13. Solid fuel combustion method
    1. 3 ways to burn
      1. grate
      2. pulverized coal burner
      3. fluidized bed
  14. boiler combustion chamber
    1. Combustion chamber conditions
    2. Combustion chamber structure
      1. brick wall
      2. water cooling wall
  15. boiler ventilation
    1. natural ventilation
    2. artificial ventilation
      1. forced ventilation
      2. induced draft
  16. reference
  17. lastly

Boiler operation and handling

We will explain boiler operation and handling within the scope of a second-class boiler engineer.

Preparation → Ignition → Pressure rise → During operation

It is divided into four stages.


The preparatory stage is very important in driving practice.

Use the checklist to check that each item is complete and ready.

A chemical plant also completes a checklist before equipment is commissioned.

About 40 people took turns over the course of several days…

This checklist varies by facility.

Checklists are important even for boilers, but they are difficult to ask in exams.

This is because preparation consists of confirming that there is no problem and that everything is normal .


Extreme care must be taken when lighting the fire.

Before and after ignition, the situation of the boiler changes greatly.

One of the big troubles that can occur during ignition is “explosion” .

Let’s look at it from the perspective of what to check for an explosion.

  • no water
  • There is no air in the furnace
  • too much fuel

There are various items to be careful of when igniting, but it’s easy to understand if you look at the three simple elements: water , air , and fuel .


water in boiler , it will run dry.

It is possible to check the water level with a water level gauge before ignition, and there is no need to pay particular attention to it when igniting.


At the beginning of the ignition process, the inside of the boiler is replaced with air. .

If not replaced with air, residual fuel and impurities from previous operations there may be residual

If you suddenly light a fire in this state, it will explode if you make a mistake. it may explode

Return to neutral before lighting the fire.

In this sense, we perform air replacement.

Start the air fan → Set the damper → Check the ventilation pressure inside the furnace

Verify that the air system has transitioned to proper condition.


If air is good, then fuel .

If fuel is not properly ejected from the burner, it will not ignite.

Start the fuel pump → Check the pressure in the fuel pipe → Preheat the fuel → Light the spark → Open the fuel valve → Ignition

Check the fuel system for fuel in the same way as for air.

Preheating is unique to boilers.

If the fuel is not preheated properly, the viscosity of the fuel will be high.

No spray from burner.

If the burner does not spray properly, stable combustion will not be possible.

Attach the ignition spark first, then add the fuel.

If you do it the other way, it will ignite with too much fuel in the furnace.

Acts in the direction of the explosion.

pressure rise

Even if you can ignite it, you need to be careful while the pressure is rising.

This is because the condition of the boiler changes.

The state of the boiler is OK with the recognition of “pressure” and “temperature” .

  • Burning amountDo not suddenly increase
  • temperatureCheck the effect of expansion due to
  • Check for leaks due to increased pressure

It is easy to understand if we focus on the factors of heat, temperature, and pressure .

When heat is applied, the temperature rises and expands, increasing pressure and causing leakage.

This is the big problem during pressure build-up.

Handling when the pressure rises is as follows.

Steam is generated → Close the air vent valve → Retighten → Pressure monitoring → Combustion amount adjustment → Water level monitoring → Steam blowing

Excess air remains in the water pipe when ignition is started and steam is generated.

The idea is to purge this with steam.

If steam comes out, you can be sure that both the ignition and the water are correct.

When the steam comes out safely and the air vent valve is closed, the steam pressure rises.

If the pressure increases, check for additional tightening. .

Continue to monitor the pressure if no leaks occur.

Depending on the conditions, the amount of combustion may be adjusted in order to transition to a stable state.Depending on the conditions, it may be necessary to

As the temperature and pressure of the water pipe increases to release steam,

The water also expands, causing the water level gauge to shake. .

I’ll keep an eye on it until it settles down and the water level is safe.

At this point, the steam will be released to the user. it will begin releasing


During operation, the main focus is to monitor the condition of the boiler.

  • water
  • vapor
  • air
  • fuel

These four are the main ones.

This is the same as the safe and stable operating condition of a continuous plant.

  • Is the water level appropriate (not too low)?
  • Is the water flow appropriate?
  • Is the water pump current appropriate?
  • Is the steam pressure correct?
  • Is the fan current appropriate?
  • Is the damper opening degree appropriate?
  • Is the fuel pump current appropriate?
  • Is the fuel flow rate appropriate?

This is the phase where we monitor whether everything is appropriate .

We monitor the appropriateness of the meters for each system: water , steam, air , and fuel .

Don’t forget the soot blow .

The heat transfer surface must be cleaned of soot at regular intervals .

Practically speaking, I limit myself to time and clean regularly.

In a real sense, in practical terms, fuel and water must also be regularly supplied to the storage tank.

In the same way as managing raw materials, managing soot as a waste is also important.

If you can think of it as raw materials or waste, it will be easier to imagine operation management.

Abnormal boiler

A second-class boiler engineer explains abnormalities in boiler operation.

boiler water level

Abnormalities in boiler water level are often on the “low water level” side.

There are three main reasons why low water level abnormalities occur.

  • Abnormality on the inflow side
  • Abnormality on the outflow side
  • instrument malfunction

Since the water level is low, the idea is that there is less inflow or more outflow.

Commonly used in boiler operation and plant operation. .

Mechanical and electrical engineers don’t have much to do with driving, so it may be hard to notice.

If the inflow side is low, you can think of causes such as a weak pump or clogged pipes.

If there is a large amount on the outflow side, the possible causes include a high combustion rate or too much steam usage.

This involves carefully looking at the systems on the inflow and outflow sides.

As long as we use a meter to determine low water levels, we must also take into account abnormalities on the meter side.


Carryover is a phenomenon in which water gets mixed into steam .

There are classifications such as priming (watering) and homing (foaming).

The water contained in the steam is

  • high water level in boiler
  • High steam load, etc.


Since there is a lot of water, the steam will be mixed with water, and the more steam you generate, the higher the chance of water being mixed.

This is because the more steam is generated, the more it becomes impossible to generate uniform steam, so there is a possibility that water will remain locally.

Water in the steam as carryover has the following effects on the boiler:

  • Vapor purity drops
  • Water clogs safety valves, instruments, piping, etc.
  • The water level gauge swings, and the water level rises or falls abnormally, and control is activated.

Effects of lower steam purity

A decrease in steam purity affects the degree of superheat.

Since the degree of superheating is decreasing, air preheating and fuel preheating are affected, and the amount of boiler combustion is decreasing.

If the carryover is due to a high steam load, the superheat will decrease and the system will move in the appropriate direction.

If the carryover is due to high water levels, it will not move in the direction of reducing the water level, so be careful.

If you don’t check to see if too much water is flowing in, the water will continue to accumulate and the carryover will continue to develop.

Effects of clogging

The presence of water can clog safety valves, instruments, piping, etc.

Although highly pure water is used for boiler water, it is not possible to eliminate impurities.

There are no impurities present in the part that is released as vapor.

Impurities exist in the area inside the boiler where water exists.

Operation management is done by periodically cleaning the impurities generated here.

If these impurities invade and enclose safety valves, instruments, and piping in areas where they are not expected, it will be a big problem.

instrument malfunction

The water level fluctuates due to carryover, causing abnormalities in the automatic control of meters.

Automatic control goes wild.

The boiler may stop when it should be running, or keep running when it should be stopped.

It’s scary.

Combustion gas leak/oil leak

Combustion gas leaks and oil leaks are more than obvious damage to equipment.

Problems such as fire and explosion, energy loss, heat loss, and equipment damage may occur.

Combustion system problem

secondary combustion

Secondary combustion is when the incompletely burned portion of the fuel burns in the flue.

There is a risk of equipment damage due to combustion in unexpected areas.


Flashback is a phenomenon in which flames blow out of the furnace.

This is more likely to happen when starting the ignition rather than while driving.

  • High pressure in furnace
  • I put fuel in before air.
  • Ignition delay occurred during ignition

High pressure inside the furnace may be caused by, for example, an insufficient opening of the flue damper.

Carbide (carbon), spark

Char can adhere to fuel burners.

This is also an obvious anomaly.

Since the fuel does not burn, there is no boiler steam.

The causes of carbide formation are as follows.

  • Abnormal oil injection angle
  • Abnormal oil pressure/oil temperature
  • Burner tip damage

To monitor proper combustion,

Monitor combustion light or monitor various steam and water gauges.

Sparks may also form in the flame.

This is also a problem of the combustion system in the same way as carbide.

boiler shutdown

I will explain how to stop the boiler operation of the 2nd class boiler engineer.

The boiler shutdown procedure is generally as follows:

Fuel stop → Air replacement → Water supply stop → Steam valve close → Damper close

I will explain each process.

stop fuel

First is the fuel stop process.

As a prerequisite, make sure the user does not use steam.

Once we know that the user will not be using steam, we can turn off the steam coming from the boiler.

First, turn off the fuel .

When you stop the fuel, the fire stops.

Of course.

There are three types of boilers : water , fuel , and air .

air replacement

After stopping fuel, water and steam are not immediately stopped.

Air replacement is also an excellent process.

The furnace, where fuel is burned, is filled with combustion gas.

It also includes incompletely combusted fuel.

To eliminate this, air replacement is performed for a certain period of time.

Stop fuel and continue supplying air

That’s all we’re doing, but the implications are important.

This is exactly the same as nitrogen replacement before operation or air replacement before entering a tank in a chemical plant .

Stop water supply

After stopping the fuel and performing air replacement, the fuel system became safe .

The next thing to stop is water .

The temperature of the furnace does not suddenly drop.

Even if the fuel and air are shut off and the heat source is removed, the structure itself, such as the bricks, still retains heat as sensible heat.

There is also “water” in the sense of cooling this.

Water is supplied to a level higher than the water level during operation, and is used as a cooling source to absorb the sensible heat of the boiler.

It is sometimes called a tension stop.

When the tension is finished, turn off the water supply.

Stop the pump and close the valve.

steam valve closed

When the water supply is finished, close the steam valve.

Avoid sending vapor to the user.

Turn off the water supply and check that the boiler no longer generates sensible heat and no steam is generated.

Make sure steam is no longer coming out and then turn on the steam valve.

At the same time, open the drain valve.

Even if steam is no longer produced, steam remains in the steam piping, and the steam piping itself has sensible heat.

This is cooled by air and forms a drain.

Open the drain valve to remove this drain.

The steam system is now safe .

Damper closed

The ” fuel ” and “steam” systems have become safe, and the ” water ” has stopped, so in the end.

It’s ” air “.

To shut off the air system, turn off the blower and close the damper.

Handling of accessories

Accessories need to be handled with more care than the main unit.

This applies not only to boilers but also to chemical plant equipment.

Once the equipment itself is in a stable state, monitoring is often all that is needed.

On the other hand, accessories require operations and inspections in addition to monitoring.

This means that there are issues to be aware of when handling accessories.

pressure gauge

Pressure gauges have surprisingly detailed rules.

  • Range: 1.5 to 3 times the maximum working pressure
  • Color- coded display of maximum working pressure and normal working pressure range
  • If it is over 80℃, attach a siphon tube.
  • Have a spare pressure gauge

Ranges and color coding may be set as rules for each user company.

The company I work for also uses this rule for microwave settings.

Batch chemical plants use their own color coding.

Why not ask the manufacturer to color it when arranging the pressure gauge?

What I think is the idea of ​​a continuous factory.

Batch chemical plants use the same line for multiple applications.

If the physical properties change, the pressure will change even with the same pump, so the normal operating pressure cannot be fixed.

It is practical for each user to check the normal operating pressure on site and mark it with a pen.

Siphon tubes are often included if you present the usage conditions to the manufacturer.

A spare pressure gauge has two meanings.

“For inspection and replacement in case of malfunction” “For replacement during test maintenance”

In any case, having a spare pressure gauge on hand is important for operation.

It’s not just limited to boilers.

water gauge

The water level gauge has the following rules.

  • 1 set of 2 water level gauges
  • Perform functional tests daily

Although the water level gauge is a rule limited to boilers, there are some interesting rules.

This is because water level gauges are rarely used in chemical plants these days.

The reason why water level gauges are used in sets of two is because one is not reliable.

Check that there is no misalignment between the two water level gauges.

If there is a misalignment, at least one of the water level gauges is malfunctioning.

It would be more accurate to call it a failure or a blockage .

That is why we conduct functional tests every day.

Blow the liquid inside the glass tube → Blow on the water side → Blow on the steam side → Fill the glass tube with liquid

Follow this flow.

Blowing the water side first and the steam side later has meanings such as system separation and blowing efficiency.

The result is the same either way, so don’t worry about the order.

Don’t think too easily, but think about which is better.

safety valve

Safety valves are extremely important accessories, so the rules are strict.

  • Disassemble and maintain during performance inspection
  • Check the safety valve blowout pressure with a pressure gauge.

Inspection and maintenance of safety valves requires specialized skills, so it is often not done in-house but outsourced to a specialist company.

The rules are complete, but

It’s important, so if you think something is suspicious, check it immediately!

I think that stance is fine.

Many safety valves, especially those of a spring type, inevitably become clogged, so there is always the possibility of steam leakage.

Just because it’s a safety valve doesn’t mean it’s safe or won’t break down , so it’s important to handle it properly.

Blowing device

The rules for blowing devices are as follows.

  • Bubble once a day
  • Blow out while looking at the water level gauge
  • Blow-out work is done exclusively

The purpose of blowing is to remove scale and sludge from the boiler.

This is because not only will the heat transfer performance of the boiler deteriorate, but it may also become clogged and malfunction.

The exam includes textbook-like analog operating methods, but automatic blowing is now common.

  • The blow-off valve must be a double valve.
  • Open the quick-opening valve first and the gradual-opening valve later (or vice versa when closing)

The idea behind this is that shipping can also be used in ordinary piping lines in chemical plants.

Water supply device

Water supply equipment is limited to boilers, and is a general inspection of water systems.

  • water tank
  • water pump
  • Valve/pressure gauge

Chemical plants are handled using the same concept.

automatic controller

There are various automatic control devices.

  • pressure regulator
  • temperature controller
  • fuel regulator
  • water level regulator
  • fuel safety device
  • igniter

The most distinctive features are the fuel regulator, fuel safety device, and ignition device.

These accessories are electrical control equipment rather than mechanical equipment.

The inspection also focuses on the control circuit.

Operators and mechanical engineers may not be familiar with it, or rather, they may have little to do with it.

Just like safety valves, specialized knowledge is required.

Boiler cleaning

We will explain how to clean a boiler by a second-class boiler engineer.

mechanical cleaning

Mechanical cleaning is the basis of everything.

This is a manual cleaning method using tools.

Mechanical cleaning is performed as a last resort after other lines are finished .

  • Take the trouble
  • Dangerous as it can get inside the device.
  • Cleaning results can be analyzed

I would like to avoid mechanical cleaning if possible, but usually I always do it.

Manual cleaning is extremely reliable.

Instead, it’s a lot of work.

It will be easy to imagine if you think about cleaning the bath.

Boilers use hammers, files, and wire brushes .

A tube cleaner may also be used to clean the tubes.

Electricity is common, but water pressure and pneumatic pressure also exist.

Additionally, chemical plant equipment often includes detergent and sponges .

acid wash

Acid cleaning is a cleaning method that uses acid as a chemical solution.

If you use acid, you will intentionally corrode the iron.

The iron rust that has corroded like scale is corroded by pressing hard.

This method involves floating it off the iron pipe and washing it off.

If acid cleaning is continued, the acid will remain in the system and corrosion will progress.

Then we add a corrosion inhibitor.

I would leave this to the boiler maintenance man.

In chemical plants, equipment is rarely acid washed.

There are many facilities that are corroded by acid.

I don’t want it to corrode and shorten its life.

Acid cleaning is often used to remove strain during welding when manufacturing stainless steel equipment or piping.

alkaline cleaning

Alkaline cleaning is a cleaning method that uses alkaline as a chemical solution.

Alkaline cleaning uses caustic soda.

The aim is to dissolve the oil in caustic soda.

Oils are often biased towards the acid side and can be dissolved with caustic soda.

The oil remaining is from when the boiler was new.

The oil used during production may remain in the system.

Naturally, it is a direction that deteriorates the performance of the boiler as a foreign substance.

Alkaline cleaning removes this with caustic soda.

The solubility of the oil in the caustic soda is determined, so use the caustic soda warm.

There are also cases of cleaning using this idea in chemical plants.

In glass-lined equipment, care must be taken as raising the temperature of the caustic will accelerate corrosion.

In some cases, you may not use alkaline cleaning but use another method for cleaning.

Storing the boiler

A second-class boiler engineer explains how to preserve a boiler.

There are two patterns: dry storage and water-filled storage.

dry storage

Dry storage, as the name suggests, dries the inside of the boiler.

Corrosion occurs because there is water

This is true not only for boilers but in general.

When the boiler is out of service for a long time, thoroughly remove the water.

  • purge water
  • replaced with air
  • Replace with nitrogen (preferably)
  • Securely closed with a blocking plate
  • Install a desiccant
  • Regular replacement of desiccant

If you do this thoroughly, you can prevent a considerable amount of corrosion.

Drain the water, put the lid on, and you’re done! The point is that it is not.

Chemists pay close attention to air replacement and nitrogen replacement, but many equipment engineers do not notice this.

Moisture absorbers will be boiler specific.

If you think so, isn’t it close to you?


Sweets also contain moisture absorbers. That’s the feeling.

Save full water

To store in full water, do not let it dry out, but fill it with water in the opposite direction.

Use when the outage period is short, about a few months.

If you store it dry, checking and replacing the moisture absorbent is a hassle.

Doesn’t it feel a little strange to fill it with water in an environment where the presence of water can cause harm?

The procedure for storing with water is as follows.

  • Generate water with corrosion inhibitors
  • Fill the boiler with water containing a corrosion inhibitor.
  • Regularly sample and analyze water.
  • If there is an abnormality in the drug concentration, additional drug injections will be given.
  • If there is an abnormality in the iron concentration, refill the water after blowing.

The key is to add a corrosion inhibitor to the water.

It also requires regular inspections.

If the amount of chemical is small, corrosion should progress.

In the early stages, when it is noticed through analysis, it may be sufficient to add a drug.

If you notice it later, it will manifest itself in the form of increased iron levels.

In this case, purge the entire amount once without adding additional chemicals.

It means that it cannot be handled by adding small drugs.

Terms related to boiler water

Let’s organize the terminology for boiler water.

Boiler water management is very important in boiler operation management.

Let’s start by looking at the terminology for this boiler water.


pH is an important index not only for boiler water but also for water systems.

Of course, it is also extremely important in chemical plants.


Hardness indicates the concentration of calcium and magnesium ions.

It is common to convert the amount of calcium ions and magnesium ions called total hardness into calcium carbonate.

It is often expressed in units of mg/l.

Although it is sometimes written in ppm, it can be used in the same way as mg/l.

mg/l → mg/1000g → 10 -6 → ppm

This relationship may be unfamiliar to electromechanical engineers in chemical plants.

acid consumption

Acid consumption indicates alkali content such as hydroxides, carbonates, and hydrogen carbonates contained in water.

dissolved gas

Oxygen and carbon dioxide are dissolved in water.

This is classified as dissolved gas.

Evaporation residue

In addition to gases, water also contains solids.

It is divided into those that are soluble in water and those that are not .

soluble evaporation residue

As the name suggests, soluble evaporation residues are those that dissolve in water .

Compounds such as calcium, magnesium, and sodium.


Suspensions are those that do not dissolve in water .

Dirt, sand, organic microorganisms, etc.

I am interpreting this to include things like silica.

Removal of impurities

Impurities that interfere with boiler operation.

Organize this removal method.

dissolved gas

Degassing to remove dissolved gas is called

There are three main types.

  • Heating degassing: The higher the water temperature, the lower the solubility of the gas in water.
  • Vacuum degassing…The lower the pressure of the gas, the lower the solubility of the gas in water.
  • Membrane degassing: A vacuum is drawn across the polymer membrane to forcefully remove gas.

There are two patterns: the solubility of gases in water, and the convenient equipment of polymer membranes.

Evaporation residue

Evaporation residue removal is divided into soluble evaporation residue and suspended matter.

soluble evaporation residue

Ion exchange is the most common way to forcefully remove substances dissolved in water.

There are three ion exchange methods: simple softening, decarbonation softening, and ion exchange water.

Simple softening is major.

It is called softening because it reduces the hardness of hard water.

In chemical engineering terms, it is adsorption .

Just set it in an adsorption tower filled with ion exchange resin suitable for adsorption and feed it with water.

If you think about it this way, it will be easier for mechanical and electrical engineers working at chemical plants to understand.


Removal of suspended matter includes natural sedimentation, coagulation sedimentation, and filtration.

This is also a major feature for mechanical and electrical engineers working in chemical plants.

Natural sedimentation and coagulated sedimentation are commonly used methods for wastewater treatment.

Filtration is not used alone, but is often used to collect precipitates generated by natural sedimentation or coagulation.

boiler water management

When it comes to boiler water management, the key points are can cleaning agents and blowing.

Can cleaning agent

Can cleaners perform a variety of functions when added to water.

  • pH adjustment
  • decrease in hardness
  • suspension dispersion
  • Deaeration

It skillfully prevents the items mentioned above, such as pH, hardness, suspended solids, and deaeration.

In terms of operational management, it is important to add the appropriate can cleaning agent to the boiler at the appropriate time.


Adding a cleaning agent will only postpone the problem.

Impurities that cannot be completely removed will continue to accumulate in the boiler.

Therefore, the water must be drained.

There are complete blow blows and continuous blow blows.

The blown water is treated as wastewater separately.

The same idea applies to cooling towers in chemical plants.

In a continuous plant, blowing is performed on a daily basis,

When it comes to batch plants, I think the expression “blow” is a bit vague.

The only equipment that operates continuously is the abatement equipment.

Characteristics of boiler fuel

Let’s start by introducing the characteristics of boiler fuel.

It can be divided into three types of fuel.

Solid, liquid, and gas.

The three states of matter itself. It reminds me of science class.

solid fuel

Simply put, solid fuel is “coal . “

It is not much different from the classic story of burning wood and producing heat.

Coal is burned to generate heat, which is used to create steam.

It’s primitive, isn’t it?

The advantage is that it is preserved in large quantities in nature .

We tend to think that this coal is 100% carbon, but it actually contains many impurities.

  • moisture
  • Volatile matter
  • allocation
  • sulfur content

This is a disadvantage for boilers.

Impurities can interfere with stable boiler operation.

This is the same reason why coal power generation continues to exist.

liquid fuel

Simply put, liquid fuel is oil .

The benefits of using oil are as follows:

  • Stable quality
  • easy logistics
  • Easy to handle

I will explain them individually.

The disadvantage is that the number of oil-producing countries is limited.

Stable quality

The quality of the oil is stable because it is distilled.

Because it is a liquid, quality analysis can be performed in a uniformly mixed state, and stable quality can be obtained.

With coal, the quality seems to vary depending on the sampling location.

You can’t even mix them to make them uniform.

Oil undergoes less alteration than coal.

You can seal the tank.

The surface of coal is exposed to the air and deteriorates over time.

Raw material in a stable state is a great advantage when it comes to obtaining a stable boiler output.

easy logistics

Oil is easier to transport than coal.

Since it is a liquid, it can be transported using pumps and piping.

Storage is possible if you have a tank. It is also easy to measure.

There are huge advantages in terms of logistics.

Easy to handle

It means the same thing as easy logistics.

If it is a liquid, it will not scatter even if it leaks, it will not clog the equipment, the pressure will not fluctuate, and it will not scatter into the air.

This is an advantage that liquids have over solids and gases.

gaseous fuel

Gaseous fuel is a mixture of methane, hydrogen, carbon monoxide, etc.

The benefits include:


That’s about it. But this is a very big advantage for stable boiler operation.

Because of this advantage, modern boilers are increasingly using gas.

On the other hand, the disadvantages are greater, so I will introduce them to you.

equipment is large

Equipment that handles gas is always large.

Liquids are denser than gases, so the equipment is usually smaller.

The size of this device directly increases the cost.

High risk of fire and explosion

Gaseous fuels can cause fires and explosions if they leak.

Since it is a gas, leaks are difficult to detect.

Easily forms an explosive atmosphere on contact with air.

The risk of fire and explosion is higher than liquids.

Liquid fuel combustion method

I will explain the combustion method when using the liquid fuel of the boiler.

Liquid fuel combustion schemes are easy to understand even for mechanical and electrical engineers in chemical plants.

As far as handling liquids, it is the same whether it is oil or chemicals in a chemical plant.

liquid fuel flow

Describe the flow of liquid fuel.

Liquid fuel system (boiler)


Tanks are divided into storage tanks and service tanks .

A storage tank is a place where oil transported from outside by lorry etc. is stored.

This will be the raw material storage where the oil for the boiler will be stored.

It is common to have a service tank separate from the storage tank.

A service tank is a tank that allows you to respond when the operating conditions of the burner in use change.

It looks like you can send liquid to the burner with just one storage tank, but

Having a buffer tank is very convenient.

This is the same idea as raw material storage tanks in chemical plants.

feed line

Check the feed line from the service tank to the burner.


A pump is used to send oil to the burner.

To protect this pump, put a strainer on the suction line.

Only one strainer is attached on the flow, but normally two are attached in parallel.

It is a method of using only one side at all times and switching when the clogging becomes large.

Attach a circulation line to the service tank at the pump outlet.

In some cases, a regulating valve is attached to the circulation line to adjust the pressure of the pump.


The heater is necessary to raise the temperature of the oil and reduce its viscosity so that it can be properly atomized by the burner.

The most common equipment type is a heat exchanger type.

The heating method can be steam or electric, but it is common to use electricity to heat the device at startup, and steam to heat it during stable operation.

No steam is generated when starting up.

In terms of flow, we are considering a case of heating with steam.

The temperature of the oil at the outlet of the heater is monitored and the amount of steam is controlled to keep the temperature constant.

flow rate adjustment

You need the ability to adjust the amount of oil fed to the burner.

This is linked to the amount of steam produced by the boiler.

Combined with a flow meter and regulating valve.

It is better to attach the flow meter at the outlet of the heater.

Oil whose viscosity has been lowered by heating will cause fewer problems.

Attach a shutoff valve to the outlet of the regulating valve.

Since the regulating valve cannot completely shut off the leak, an automatic shutoff valve is installed for emergency shutoff purposes.


The burner is also a fairly important part of the boiler.

A very special part of the boiler.

Burners are roughly divided into four types.

pressure spray

Pressure spraying is the simplest method.

In this method, the oil pressurized by the pump is sprayed as it is.

With a simple structure that simply releases oil as it is.

There are two types of structures that return some oil to the service tank.

It is easier to stabilize the spray pressure by releasing some oil from the burner while circulating it.

This leads to expanding the burner load adjustment range.

This is also a commonly used method in chemical plants.

steam injection

Steam injection is a method of spraying oil and steam onto the burner at the same time.

There is a part at the beginning that mixes the oil and steam, and the mixed fuel is released from the burner.

The aim is to use the power of steam to make the oil finer, making it easier to spray evenly.

This will stabilize the burner flame.

air spray

Airflow spraying is a method of spraying oil and air onto the burner at the same time.

The point is to use air instead of steam.


The rotary type is a method of atomizing oil by the centrifugal force of a burner.

Attach the cup to the tip of the burner and stick the oil to the inner surface of the cup.

The oil film is gradually refined by centrifugal force.

For small and medium-sized boilers.

Gaseous fuel combustion method

This section introduces the combustion method of gaseous fuel in boilers.

There are two combustion methods

There are two methods of burning gaseous fuels.

Diffusion combustion method and premixed combustion method.

The difference is where the gas and air are mixed.

Diffusion combustion method

In the diffusion combustion method, air and gas are supplied separately to the burner.

Diffusion and premixing (boiler)

There is no risk of flashback as no combustible mixture is formed in the burner .

The spread, length, and temperature distribution of the flame can be controlled by adjusting the air flow rate, gas injection angle, etc.

Because it is safe and has a high degree of freedom, it is used frequently.

There are several types of gas burners.

  • Center type ・・・ Directly from one gas pipe
  • Ring type: radiates from the gas ring to the circumference
  • Multi-spud: Directly fired from several gas pipes
  • Gun type: Built-in control unit

The gun type is the latest model with a built-in control unit.

It incorporates safety devices and control devices such as burners, fans, igniters, and flame detectors.

The remaining types are simply a matter of physically dividing the gas injection method into several patterns.

Premixed combustion method

As the name suggests, the premix method is a method in which the ingredients are mixed in advance.

Pour the mixture of air and gas into the burner.

Pre-mixed fuel is used to create a stable flame.

Because of the danger of flashback, it is sometimes used as a pilot burner instead of a large-capacity burner.

Gas is city gas/LPG

Gas, one of the fuels, includes city gas and LPG.

City gas is natural gas.

The gas company will install the city gas piping.

Large-capacity boilers are mostly city gas.

LPG is stored in cylinders or storage tanks and transported to the boiler via piping.

Solid fuel combustion method

Introduces the solid fuel combustion method for boilers.

3 ways to burn

There are three methods of burning solids: grates, pulverized coal burners, and fluidized beds.

The difference lies in the position of solid fuel.

The idea is similar to diffusion and premixing of gaseous fuel.


The solid fuel grate is installed on the floor .

Solid fuel is placed in a combustion chamber, air is introduced, and it is combusted.

The image of burning wood in a fireplace or camping is enough.

The only difference with burning wood is that the fuel and equipment are quite specialized.

The key point is that the fuel is on the floor.

pulverized coal burner

A pulverized coal burner is a method that sends coal on top of pulverized coal to a boiler together with air.

Since it is pulverized coal, it is entrained with air .

The idea is similar to the premix combustion method for gaseous fuel.

As for the benefits

  • High contact area and high combustion efficiency
  • There are many types of coal that can be used
  • Easy to respond to combustion load fluctuations

As you can see, there are strong economic benefits to driving.

On the other hand, the disadvantage is

  • Equipment costs and power costs are high
  • There is a risk of explosion

As mentioned above, there are strong disadvantages in terms of equipment and security.

The cost is high, as the air blowing device to send the coal together with air is large, and a combustion chamber larger than the grate is required.

Since the fuel is mixed like in a premix system, there is a possibility of combustion even in the air line.

fluidized bed

The fluidized bed is a system that overlaps a grate and a pulverized coal burner.

This method floats the fuel inside the grate .

In the grate combustion method, a small amount of air is sent to a large amount of solid fuel in the combustion chamber.

In the fluidized bed combustion method, there is little solid fuel in the combustion chamber, so the solid fuel floats due to the force of the air flow.

In the first place, the aim of both pulverized coal and fluidized bed is to increase the contact area .

In order to efficiently burn air and solid coal, it is better to have a large contact area between air and solid.

In the grate combustion method where solids are piled up, some of the fuel inside the piled up coal may not burn.

For this purpose, it is important to create a state in which air and coal are mixed.

The pulverized coal burner combustion method performs this in the air supply line , and the fluidized bed combustion method performs this within the grate .

boiler combustion chamber

Introducing the boiler combustion chamber and ventilation. Let’s start with the combustion chamber

Combustion chamber conditions

As the name suggests, a combustion chamber is a room where combustion occurs.

Let’s sort out the conditions required for this combustion chamber.

  • Combustion chamber maintains high temperature
  • Fuel ignites quickly
  • Mix fuel and air efficiently
  • complete combustion

Once these conditions are met, we will decide on the structure of the combustion chamber.

Combustion chamber structure

Introducing the main parts of the combustion chamber structure.

The main part is the furnace wall .

The furnace wall is the wall of the combustion chamber.

Walls are important even in a room.

brick wall

Furnace walls are often made of bricks.

Brick is highly heat resistant. It will come in handy.

Recently, refractory materials have been developed instead of bricks.

water cooling wall

Water-cooled walls are a method of cooling walls with water.

Some people may imagine a wet wall when I write this.

The water-cooled wall of the boiler places the water tubes on the furnace wall.

If the bricks get too hot, they will release heat to the outside air.

Placing the water pipe in the wall will prevent the brick from getting too hot.

In addition, the heat absorbed by the water pipes can be directly used to generate steam.

It’s a simple idea, just placing water pipes on the wall, but it’s highly effective.

boiler ventilation

Let’s talk about boiler ventilation.

Basically, fuel and air are mixed and burned in the combustion chamber.

Air is also an important element, so let’s check it.

natural ventilation

Natural ventilation utilizes the draft power of the chimney.

The direction of the chimney is the direction in which air flows from the bottom to the top.

Air heated in the combustion chamber becomes less dense.

Light air tends to rise to higher altitudes.

The higher you are, the less dense the air is.

The difference in density of the hot air creates buoyancy and causes it to climb up the chimney.

Draft force is a small force because the only driving force is the difference in air density.

It’s primitive, but I don’t use it these days.

artificial ventilation

If the ventilation is not natural, use artificial ventilation.

Simply put, I’m a fan .

forced ventilation

In forced draft, the fan is located in front of the combustion chamber.

A fan pushes pressurized air into the combustion chamber.

The benefits are as follows

  • No excess outside air leaks into the combustion chamber
  • High combustion efficiency

Because air is forced into the combustion chamber, the pressure force in the combustion chamber is higher than the outside air.

That’s why outside air can’t leak in.

Since the high pressure forced by the fan can be blown into the combustion chamber, fuel and air can be mixed efficiently.

induced draft

Induced draft is the opposite of forced draft.

A fan is located at the outlet of the combustion chamber.

One advantage is that the combustion gas does not leak outside .

Useful in chemical plants.

If flames or high-temperature gas leaks to the outside air, the leaked organic solvent may ignite.

However, there are also disadvantages.

  • Fan power costs are high because it sucks hot, low-density (large volume) air
  • The fan absorbs soot and dust from the combustion gas, corroding the fan.



I explained what you need to know about the operation and handling of a class 2 boiler.

Water/fuel/air/steam balance, start/stop/storage, water quality control, combustion method, combustion chamber, gout

Let’s look at each individual component while keeping in mind the basics that a boiler is made up of four elements: water, fuel, air, and steam.

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