INDUSTRIAL SAFETY – Boiler Safety Operation Standards

Boiler: A Steam Boiler

Boiler is a closed vessel where the combustion heat is flowed into water to form hot water or steam in the form of work energy. Water is a useful and inexpensive medium for transferring heat to a process. Hot water or steam at a certain pressure and temperature has an energy value which is then used to transfer heat in the form of heat energy to a process. If the water is boiled until it becomes cold, the volume will increase about 1600 times, producing power that resembles explosive gunpowder, so the boiler system is a device that must be managed and maintained very well.

Boiler Work Process

The heat energy generated in the boiler system has a value of pressure, temperature, and flow rate that determines the utilization of  steam  to be used. Based on these three things the boiler system recognizes the state of  low pressure (low pressure / LP) , and  high pressure (high pressure / HP) , with the difference that the utilization of steam  coming out of the boiler system is utilized in a process to heat the liquid and run a machine  (commercial and industrial boilers),  or generate electrical energy by converting heat energy into mechanical energy then turning a generator to produce electrical energy  (power boilers). However, there is also a combination of the two boiler systems, which utilize high-temperature pressure to generate electricity, then the remaining  steam  from the turbine with a low-pressure state can be utilized in industrial processes with the help of  boiler heat recovery.

The boiler system consists of a feed water system, a steam system  , and a fuel system. The feed water system provides water to the boiler automatically according to steam needs  . Various taps are provided for maintenance and repair of feed water systems, feed water handling is needed as a form of maintenance to prevent damage to the steam system  . The steam system  collects and controls steam production   in the boiler. Steam is flowed through the piping system to the user’s point. In the whole system, steam pressure  regulated using a faucet and monitored with a pressure monitor. Fuel systems are all equipment used to provide fuel to produce the heat needed. The equipment required in the fuel system depends on the type of fuel used in the system.

Before explaining the diversity of boilers, it is necessary to know the components of the boiler that support the creation of  steam , the following components of the boiler:

1. Furnace

This component is a place for burning fuel. Some parts of the  furnace  include:  refractory , fireplace room,  burner ,  exhaust for flue gas ,  charge and discharge door  .

2. Steam Drum

This component is a hot water reservoir and steam generator  . Steam is  still saturated ( saturated steam ).

3. Superheater

This component is a place for drying  steam  and is ready to be sent through the  main steam pipe  and ready to drive a steam turbine or run an industrial process.

4. Air Heater

This component is a heating chamber that is used to heat the outside air that is absorbed to minimize the humid air that will enter the furnace.

5. Economizer

This component is a heating chamber that is used to heat water from condensed water from the previous system and new feed water.

6. Safety valve

This component is a steam exhaust   in the event that the steam pressure   exceeds the boiler’s ability to withstand steam pressure  .

7. Blowdown valve

This component is a channel that functions to remove deposits that are inside the steam pipe  .

Boiler Classification

After knowing the short process, the boiler system, and the components forming the boiler system, it is necessary to know the diversity of the boiler. Various forms of boilers have evolved following technological advances and evaluations of previous boiler products that are affected by boiler exhaust gases that affect the environment and what kind of steam products will be produced. The following classification of boilers that have been developed:

Based on the pipe type:

1. Fire Tube

Fire pipe boiler types have the following characteristics: produce low steam capacity and pressure .

How it works: the ignition process occurs in the pipe, then the heat generated is delivered directly into the boiler that contains water. The size and construction of the boiler affect the capacity and pressure generated by the boiler.

2. Water Tube

The type of water pipe boiler has the following characteristics: high steam capacity and pressure .

How it works: the ignition process occurs outside the pipe, then the heat generated heats the pipe filled with water and before the water is conditioned first through an economizer, then the steam produced first is collected in a steam- drum. Until the pressure and temperature match, through the secondary superheater and  the new primary superheater, steam is released into the main distribution pipe. In a water pipe, running water must be conditioned to minerals or other contents that are dissolved in the water. This is the main factor that must be considered for this type.

Table 1.1. Boiler advantages and disadvantages based on pipe type.

Based on the fuel used:

1. Solid Fuel

Solid fuel boiler types have the characteristics: the price of combustion raw materials is relatively cheaper compared to boilers that use liquid and electric fuels. The efficiency value of this type is better when compared to electric type boilers.

How it works: heating that occurs due to combustion between mixing of solid fuels (coal, baggase, rejected products, municipal waste, wood) with oxygen and heat sources.

2. Oil Fuel

The type of liquid fuel boiler has the following characteristics: the price of the most expensive combustion raw material compared to all types. The efficiency value of this type is better when compared with solid fuel and electricity boilers.

How it works: heating that occurs due to combustion between the mixing of liquid fuels (diesel, IDO, residues, kerosene) with oxygen and heat sources.

3. Gaseous Fuel

The type of gas fuel boiler has the following characteristics: the price of the combustion raw material is the lowest compared to all types of boilers. The efficiency value of this type is better when compared to all types of boilers based on fuel.

How it works: combustion that occurs due to mixing of gas fuel (LNG) with oxygen and heat sources.

4. Electric

This type of electric boiler has the characteristics: the price of heating raw materials is relatively cheaper compared to boilers that use liquid fuel. The efficiency value of this type is lowest when compared with all types of boilers based on fuel.

How it works: heating that occurs due to a source of electricity that supplies a source of heat.

Table 1.2. Boiler gains and losses based on fuel.

Based on the use of the boiler:

1. Power Boiler

This type of power boiler has characteristics: its main use is as a steam generator as a power plant, and the remaining steam is used to run industrial processes.

How it works: the steam produced by this boiler uses a type of water tube boiler, the resulting steam has a large pressure and capacity, so it is able to turn steam turbines and generate electricity from generators.

2. Industrial Boiler

Industrial boiler types have characteristics: their main use is as a producer of steam or hot water for running industrial processes and as an additional heater.

How it works: steam produced by this boiler can use the type of water tube or fire tube boiler, the resulting steam has a large capacity and moderate pressure.

3. Commercial Boiler

This type of commercial boiler has characteristics: its main use is as a producer of steam or hot water as a heater and in addition to running commercial operations.

How it works: steam produced by this boiler can use a type of water tube or fire tube boiler, the resulting steam has a large capacity and low pressure.

4. Residential Boiler

This type of residential boiler has characteristics: its main use is as a producer of steam or low pressure hot water that is used for housing.

How it works: the steam produced by this boiler uses the type of fire tube boiler, the resulting steam has a low pressure and capacity

5. Heat Recovery Boiler

The type of heat recovery boiler has the characteristics: its main use as a producer of steam from unused hot steam. The results of this steam are used to run industrial processes.

How it works: steam produced by this boiler uses a type of water tube boiler or fire tube boiler, the resulting steam has a large pressure and capacity.

Table 1.3. Boiler gains and losses based on utility.

Based on boiler construction:

1. Package Boiler

The type of boiler package has characteristics: boiler assembly is carried out at the manufacturing plant, direct delivery in the form of a boiler.

2. Site Erected Boiler

The type of site erected boiler has the following characteristics: boiler assembly is carried out at the site where the boiler is to be built, deliveries are carried out per component.

Table 1.4. Boiler gains and losses based on construction.

Based on boiler working pressure:

1. Low Pressure Boilers

Low pressure boiler type has characteristics: this type has an operating steam pressure of less than 15 psig or produces hot water with pressure below 160 psig or temperature below 250 ⁰ F

2. High Pressure Boilers

High pressure boiler type has characteristics: this type has an operating steam pressure above 15 psig or produces hot water with pressure above 160 psig or temperatures above 250 ⁰ F

Table 1.5. Boiler gains and losses based on working pressure.

Based on how to burn fuel:

1. Stoker Combustion

Stoker combustion type has the following characteristics: this type utilizes solid fuel to ignite, solid fuel is put into the combustion chamber via conveyor or manually. This type has combustion residue that must be handled in the form of bottom ash or fly ash  which can pollute the environment.

2. Pulverized Coal

How it works: this process destroys coal with a ball mill or roller mill so that coal has a size of less than 1 mm. then this powdered coal is sprayed into the combustion chamber.

3. Fluidized Coal

How it works: this process destroys coal with a crusher, so that coal has a size of less than 2 mm. In this process combustion is carried out in a layer of sand, coal will immediately burn if it hits the sand.

4. Firing Combustion

Firing type has characteristics: this type utilizes liquid, solid, and gas fuels to do combustion, heating which occurs more evenly.

How it works: liquid fuel used as preliminary firing fuel is put into the combustion chamber through an oil gun . After reaching the appropriate temperature, combustion is taken over by coal nozzle or gas nozzle .

 Table 1.6. Boiler gains and losses based on combustion.

Based on the boiler constituent material:

1. Steel

The type of boiler made of steel has characteristics: the main raw material for boilers is made using steel in the steam area .

2. Cast Iron

The type of boiler made from cast iron has the following characteristics: the main raw material of the boiler is made using cast iron in the steam area .

Table 1.7. Boiler gains and losses based on material.

Boiler safety

600 MW PLTU boiler

Boiler Protection / Safety Function

Boiler safety is intended to maintain and avoid more serious interference with the boiler and its supporting tools, which results in a decrease in boiler capability, or damage to equipment.

Basic principles

The basis of boiler protection and its auxiliary equipment is that the safety device must be able to guarantee the continuity of the boiler’s steam production service.

Protection

A boiler needs safety to maintain the reliability of operation in a long period of time. This boiler safety system in general will describe the safety of the boiler from corrosion, overheating and thermal stress that is caused during the process of startup, normal operation and shutdown.

Boiler vent must be opened during the filling process so that air in the boiler tube can be removed, the aim is to reduce the possibility of corrosion due to oxidation of air trapped in the boiler tube other than air. It also can cause cavitation and water hammer. Before operating the boiler must be rinsed (purge) from the used gas that accumulates in the combustion chamber is important because the waste gas from the combustion that is not wasted will form a hot gas that can cause an explosion in the room at the boiler ignitor startup because during this period many combustible possibilities occur and explosive due to frequent ignitor ignition failures and unstable binding conditions.

Boiler areas that require special attention include:

Economizer

Feedwater is not always added when raising the boiler pressure because the water in the boiler always circulates naturally. But without the presence of feedwater in the filling water will not flow to the economizer. Economizer is secured from the formation of feedwater evaporation in the tube, because the steam trapped inside can cause water hammer, thermal shock and can cause fluctuations in drum level control. To safeguard this problem there needs to be a continuous flow of circulation from the economizer inlet header to one of the downcomers. This valve must be opened when the boiler is experiencing interference with feedwater flow control, the aim is to avoid the evaporation process in the economizer tube due to the cessation of natural circulation. Economizer is subject to both internal and external corrosion. Internal corrosion can be prevented by maintaining PH feedwater between 8 and 9 by chemical injection. External corrosion can be caused by the occurrence of condensation between the low temperature of the feedwater and the high temperature of the combustion gases that pass through the economizer. Overcoming this problem by keeping the economizer in an area far from the dew point, this case must be avoided during the startup process and after the unit is loaded.

Furnace

Furnace is a part that requires serious attention. Because it deals with the problem of vapor pressure and steam temperature and combustion chamber temperatures are very high. Factors of concern are:

–
Boiler operating pressure Boilers must not operate above their working pressure and never exceed their design pressure.
– Balance balance firing operation
This relates to the heat generated by combustion of the combustion chamber in the case of imbalance firing, which will cause disruption of the natural circulation process and interference with the tube due to overheating.

Steam Drum

During normal operating conditions pressure on the drum and drum level and water quality must always be controlled. The surface of the steam drum is very high, so at startup and shutdown the temperature difference in this area must be considered, namely the difference between the top and bottom should be as small as possible in this case it is important to maintain the occurrence of thermal stress on the steam drum.

Limitations that must be considered include:
– When there is a change in the phases of water and steam in the steam drum.
– The difference between top and bottom does not exceed the maximum setpoint of 50 0C for startup and 100 0C for shutdown.

Superheater

Superheater located in an area where heat transfer by convection induction attracts quite serious attention because it is related to the condition of the steam temperature and the safety temperature of the metal tube. overheating due to disrupted production and vapor flow while the combustion gas stream passing through the high induction convection area.

Superheater safety limits include:
– Main steam temperature must always be controlled
– Combustion conditions must be balanced firing / adjusted according to its formation
– Thermocouple superheater exit must be monitored
– Gas temperature superheater entry area must be limited during startup to normal operating unit conditions.

Boiler Safety Mode Operation

Safety Directly

1.  Safety Valve

Before the boiler is declared ready for operation, the safety valve must be checked and if necessary reset in accordance with the working area. This procedure is very important considering that after the boiler firing will produce pressure. This vapor pressure can determine that the safety valve serves as a safety against the occurrence of excess vapor pressure produced by the boiler.

2.  Relief Valve

Relief valve can be classified as a safety as well as a safety valve, but this relief valve serves as a limiting or maximum pressure safety in the liquid work area. The use of relief valve is placed in the following areas:
– Header reheat / HP bypass spray water
– Header auxiliary steam spray
– Ignitor oil level header
– Heavy fuel oil level header

Indirectly Security

1.  Pneumatic Valve

The pneumatic valve as well as the safety valve serves as a safety for over steam pressure on the boiler only equipped with a pressure sensor which is conveyed through an electronic signal to the electro mechanical to open the pilot valve.

2. Safety Boiler Drum Level

Serves to control the level of water level on the boiler drum as a safety for the occurrence of “high level drum boiler trip” and “low level drum boiler boiler”.
The reason for securing a “high level drum trip boiler” is to secure the boiler drum from carrying over in the drum which will result in deposits in the superheater area and turbine blade. Deposits will inhibit the heat transfer of the superheater which results in overheating of the superheater tube and the turbine blade will cause unbalance and vibration of the turbine.
While the condition of “low level drum trip boiler” can cause disruption of natural circulation which will result in overheating in the steam drum and steam production is inhibited.

3. Safety of the Boiler Furnace

Serves to control the pressure of the combustion chamber / boiler as a safety for the occurrence of:
– Furnace pressure & gt; max
– Furnace draft & gt; max
In connection with the type of boiler with a balance draft design where the design pressure allowed is -10mmWg, this is to ensure the stability of the combustion process. Transportation of coal fuel to the combustion chamber and the process of removing coal ash from inside the combustion chamber to a dust catcher etc. If the security limits are exceeded and distorted, the above process will be disrupted.Things that must be maintained to avoid the above conditions are by:
1) Check the water seal through level on the bottom hopper boiler must be in a position above the normal level. Check LCV and bypass valve water supply.
2) Check the boiler manhole condition before the boiler startup must be in a closed condition including desorvation door.
3) The water level at the SDCC boiler bottom is normal.

4. Main Steam Temperature Boiler Safety

Its function is to control the high temperature of the main steam coming out of the second level superheater as a safety for the main steam temperature to exceed the allowable design limit.
This security is intended to avoid the occurrence of thermal stress in a first level turbine due to the temperature difference that is too high between the temperature of the main vapor entering with the metal temperature at the turbine blade. In addition to avoiding material fatigue in superheater tubes due to steam temperatures that exceed the maximum capacity of superheater tubes.

5. Safety of Total Air Flow

Serves to secure the total amount of air entering the windbox / combustion chamber during the boiler purification process. At the time of boiler startup and normal operation must meet the total flow amount greater than the minimum (& gt; 30% when the boiler purge).
At the time of flushing the boiler we expect all the combustion gases that have accumulated in the combustion chamber and exhaust gases to be pushed / released by air in the amount of & gt; 30% or about 600 tons / hour to be discharged into the outside air at least gases remaining clean combustion within 3 minutes (design) then safeguarding at startup and normal operation Toral air plays a role as combustion air so that when the total combustion air is at least 30% then the amount of ratio between air and fuel will not we are absolutely certain that we are worried about repeated ignition failures and one of the causes of combusable in flue gas.

6. Safeguarding the Air Pressure Header Instrument

Instrument air is a major requirement in the pneumatic power control system. The instrument air supply must be properly maintained and very special considering that the source of power for all turbine boiler controls and its assistants lies in the continuous reliability of the instrument air supply and its working pressure.
Considering the virtue and function of the instrument air as a source of power for all turbine boiler controls and assist equipment, if air pressure drops below its working point, this will cause all pneumatic control functions to cease and will cripple the operation of the boiler and turbine.

Anticipate when an instrument low pressure alarm occurs, including:
– Immediately open the SAC backup valve to the instrument air header.
– Immediately check the condition of the instrument air compressor and its supply process.
– Localize the possibility of instrument air leakage on all lines.
– Localize the possibility of an open air drain / vent valve.

7. Security Pressure Cool Scanner

Its function is to secure the cooling system on the flame sensor scanner. The importance of flame detection in a boiler to ensure the existence of combustion, so that there will be no buildup of fuel due to failure of ignition. The flame detector is secured from the heat of the combustion chamber by providing cooling in the form of pressurized air seals on the entire surface of the fire detector.

The disruption of this cooling system will result in a melting point on the flame detector because there is direct contact between the device and the heat of the fire detected in the damage. The fire detector / scanner will signal the burners that are operating for the trip so that the boiler will trip.

If a low pressure alarm blower discharge flame scanner occurs, do the following:
– Check the standby auto start scanner’s blower select in the auto position.
– Check the air filter / filter blower inlet may be dirty.
– Check for possible leaks in the joint line.

Examples of Operating Limits

1.  Drum Level
   High Alarm : 50 mm ; Low Alarm : -50 mm
   High Trip : 250 mm  ; Low Trip : -250 mm
   2.    Temperature Main Steam & Reheat Steam
   High Alarm : 550 oC ;  High Trip : 570 oC (delay 60 second)
   560 oC (delay 600 second)  ; 550 oC (delay 6000 second)
   3.    Furnace Pressure
   High Alarm : 50 mmWg  ; Low Alarm : -50 mmWg
   Furnace Draft High Trip : 225 mmWg ; Furnace Pressure Low : -225 mmWg
   4.     Boiler Safety Valve Main Drum
   RV 39 : 3011 psi , RV 40 : 2975 psi , RV 41 : 3047 psi, RV 42 : 3064 psi , RV 43 : 2993 psi , RV 44 : 3029 psi
   Secondary Superheater Outlet Header / Main Steam ; SV 13 : 195 kg/cm2, SV 14 : 196 kg/cm2, SV 15 : 197 kg/cm2
   Reheat Outlet Header / Hot Reheat ; SV 92 : 57 kg/cm2, SV 102 : 57 kg/cm2 (SV=safety valve)

Water Quality

water that enters the boiler is always conditioned (mineral free water) so that it does not damage the material / pipes of the boiler iron, so the quality is always controlled, and each time a water sample is taken and injected with chemicals where the pH, conductivity, chlorine, phosphate, silica maintained within the allowable value. and if there is poor quality, it must be removed (blow down) and replaced with new water (make up).

Salt water quality : & lt; 20 usings; PH: 9.2 – 9.5 / Silica: & lt 0.0185 ppm / PO4: 0.3 – 3 ppm / Cl-: & lt; 0.5 ppm

Efficiency:

so that the boiler works economically and efficiently in addition to the type of coal used, the combustion process is optimized to achieve perfect combustion. which boiler operator plays an important role to control, including the composition of fuel and combustion air, oxygen analyzer, chimney, sootblowing, etc. are always monitored.

Reliable

 auxiliary equipment on the boiler installed more than one (a pair or more), aiming that if one of these aids occurs interference then it will not be to stop the boiler but the stand-by will be the way to back it up. so that steam production remains available even if not with maximum generator loading.

The following picture is one type of boiler

Boiler and Problems

Failure Tubes (leaked)

 The cause

• ·      Over Heating
• ·      Material grade
• ·      Gas Temperature
• ·      Internal Scale
• ·      Minimum Thickness (Minimum Thickness)
• ·      Fly Ash Erosion
• ·      Blowing Steam  Erosion
• ·      Manufacture defact (manufacturer’s defects)

Impact: Lost of opportunity for production 3 – 5 days

 Slagging and Fouling

 The cause

Varies greatly

 Impact

• Heat transfer is interrupted
•  Boiler Efficiency
•  Threatening Lost of opportunity for production 5 – 10 days.

Mill Failure

 Mill Explosion

 The cause

• Explosive Mixture ( PA and PF)
• Uncomplete inertia
• Internal wear

Boilers and Accidents

Hazard – Risks and Prevention

Some things that must be considered

1. Follow the instructions given by the manufacturer. Use the Operating standards that have been created and reference some jobs to the ASME standard
2. Training – Workers must truly be given training in compliance in operating the equipment. Safety training should be a continuous process that aims to educate workers to recognize and maintain safety in their minds. The training program must be carried out continuously and supervised
3. Cleanliness – environmental hygiene is very important for the safety and good conduct of operations in the factory. Low hygiene increases the risk of accidents
4. Clothing and safety equipment – appropriate clothing must be worn at all times. Avoid exposed clothing and jewelry. Safety equipment must be worn for as long as necessary (for example: work caps, masks, earplugs, goggles, gloves, work shoes.) Never operate large equipment such as rotating equipment, automatic machinery, electrical machinery unless there is a safety device.
5. Hot surfaces – a lot of hot surfaces are found in the boiler and even non-heating surfaces can be uncomfortable due to heat. Therefore, new workers must be made aware of this. Be careful when working, especially if you are in close proximity to the boiler. Never enter the boiler except until the specified stage.
6. Monitor the remote controller – in factories many units use the remote controller. Note whether there are workers in the unit that will start up before the unit is properly turned on
7. Noises occur in the factory and accumulatively cause illnesses for workers. Always use safety equipment, for example ear plugs

Maintenance

Risk control

Engineering control

1. Check the isolation of the boiler surface area and the pipe
2. Automatic shutdown deviceschecking
3. Check the fuel and air controller
4. Check valves
5. Check the water level controller

Administrative Control

1. Tool operator training
2. Review the tool control procedure
3. Review of Operating Procedures
4. Field Inspection
5. Audit
6. Check the boiler water content

Outside inspection

External inspection is carried out by a certified boiler supervisor. The sections that find supervision include:

1. Leakage
2. Instrument indicator
3. Safety instruments
4. System controller
5. Valve
6. Cleanliness
7. Label
8. Piping

Inspection inside

External inspection is carried out by a certified boiler supervisor. The sections that find supervision include:

Combustion Inspection Parts:

1. Door gaskets
2. Fire side insulation
3. Tube sheet
4. Tubes
5. Blowers
6. Stack

Water Parts Inspection:

1. Tube bundle
2. Scale buildup
3. Condensate feed water tanks
4. Chemistry control systems
5. Level floats

Boiler Tests

Here are some tests that must be done regularly on the parts of the boiler

1. Safety / Relief Valve Operational Test(monthly)
2. Check System for Leaks (weekly)
3. Low Water Fuel Cutoff (LWFCO) Rapid Drain Test (weekly and every start up)
4. Burner Check  (monthly)
5. Water Chemistry Check (monthly)
6. LWFCO Slow Drain Test (4 times a year)
7. Circ and / or Condensate Pump Check (4 times a year)
8. Safety Valve Setpoint Test (routine)
9. Drain Water Gage Glass (as needed)