Steam Boiler: Maintenance of Boiler

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Boiler Sootblower

Boiler sootblower is one of important equipment to maximize steam boiler efficiency. Efficiency of boiler is influenced mostly by heat transfer process. One among the most necessary operations to increase heat transfer process is clean metal surfaces for absorb heat. The cleaning metal surfaces is performed to ensures appropriate heat transfer process and in addition avoids parts of steam boiler from growing to be plugged and blocked. Plugged parts could limit gas circulation and lead to load restrictions.

Boiler sootblower is specially needed on coal fired boiler and oil fired boiler. If oil fuel consist of low content of ash and generate small residue, the cleaning method of furnace wall can be performed by water washing for the duration of twelve-monthly shutdown. This is why; boiler sootblower which is installed on furnace wall is not needed on the oil fired boiler.

In the reheater and superheater parts of oil fired boiler, there's ash accumulation on metal surfaces. Excessive-oil vanadium subject matter that contains chemicals to resist high-temperature corrosion, tend to be specifically vulnerable to the following. However while solid powder chemicals are utilized, the deposits of ash boost seriously in the high temperature of gas locations. The good thing is, the deposits fall and easily cleaned with boiler sootblower.

Coal fired boiler need many sootblower which is installed permanently. Reasons like high content of ash and ash-fusion temperatures determine simply what exactly sootblowing area is needed. Boiler sootblower usually utilizes compressed air or superheated steam as medium to eliminate deposits, utilizing rotary or retractable types. The efficient blowing regularity varies according to slag accumulation; however a usual could be four until eight hours. The steam boiler parts such as reheater and superheater is suitable to use long retractable type of sootblower to clean radiant heat surfaces.

Oil Burner Maintenance

Oil burner could very easily be damaged for the duration of cleaning, but oil burner should be cleaned and maintained at regular periods of oil burner maintenance to eliminate little amounts of gum or carbon that often form and also could prevent proper atomisation. An oil burner removed for cleaning and maintenance should be stripped down based on oil burner maker's instructions and drenched in paraffin or diesel oils.

If the solids had melted, the oil burner components must be cleaned by using a smooth rag free from everything which may scratch metal. The leftover deposits can certainly then be eliminated with a wood scraper, really smooth metal or maybe something hard will not certainly damage the oil burner parts surfaces. Several of the oil burner makers supply exclusive ‘dollies ‘of smooth metal intended for cleaning out the compact jets.

These are generally of the proper dimension and design for the oil fired boiler concerned and also no attempt have to be made to push through a mistakenly sized dolly or severe deterioration will occur. When any kind of part of oil burner gets to be worn or damaged, or even an orifice gets to be deformed, a substitution of that part must be provided.

Reliability Centered Maintenance (RCM)

Reliability Centered Maintenance is defined as a process that is used to determine appropriate action to ensure physical asset belong to company can perform its function continuously accordance with desired goal. The process which is carried out in RCM is by proposing 7 questions to each asset / system which is operated by company.

The seventh question is as follows:

What are functions and performance standards that are owned by asset in running its operation (function)?
What is condition if asset fail to perform its function (failure effect)?
What is the cause of each failure (Failure modes)?
What is the effect when failure occur (failure effect)?
How is consequence problem because of failure (failure consequence)?
What is must to do to predict or prevent failure (Pro-active Task)?
What is the next action if pro-active task cannot give its function (default action)

Failure Modes and Effect Analysis (FMEA)

Failure Modes and Effect Analysis (FMEA) is a technique to analyze danger qualitatively that can be used to identify how an equipment, facility or system can be failure and analyze effect that may occur. Analysis of FMEA can be recommendation to enhance reliability and safety of equipment, facility or system. FMEA state failure modes, cause of component can experience failure or damage.

Component that is included in analysis FMEA is component or machine potentially causes function failure from previous maintenance note. FMEA data is obtained based on machine history record and interview with maintainer. Procedures of Failure Modes and Effect Analysis (FMEA) are performed according to following steps:

Determining problem

Determining problem on an equipment, facility or system is carried out by sort parts of equipment, facility or system so the explanation can be more focused.

Review

Review is done on working sheet of FMEA. How to fill working sheet of FMEA is as follow:

a. Item (ID)

In the item column is filled serial number of system which will be analyzed.

b. Identification (component)

In the identification column is filled equipment data which be identified.

c. Function

In the function column is filled data of equipment type, operating configuration and other specified character.

d. Failure Modes

1. Failure mode: it is defined as failure component to apply one of component functions.

2. Failure mechanism: it is possibly generated by failure mode that had been identified.

3. Detection of failure: All possibility of failure mode detection.

e. Effect

1. Local: occurred failure will influence performance of equipment / component.

2. System: occurred failure will influence overall system function.

3. Plant: failure that occurred will influence performance of plant.

f. Safety

Safety features or procedures in the system can eliminate failure that will occur.

g. Action / risk reducing measures

Possibility of action which is performed to prevent seriously effect of failure.

h. Comment

Record other information that cannot be entered in previous column.

Documentation

Documentation is performed by filling working sheet of FMEA to monitor consistently implementation of recommended correction.

Figure 1: Working Sheet of Failure Modes and Effect Analysis (FMEA)

Corrective Maintenance in Steam Boiler

Corrective maintenance in steam boiler is one of maintenance types which is performed repeatedly or maintenance which is performed to correct a part (including tuning and repair) which has been stalled to meet an acceptable condition in steam boiler. Corrective maintenance includes minor maintenance repairs, especially for short-term plans, which may arise between the examination, as well as a planned overhaul.

Maintenance re-occurring due to faulty equipment and should be repaired immediately because of an emergency or because it is a priority. Corrective maintenance is usually an unplanned maintenance, actions that require more attention that must be added, integrated, or replace the previously scheduled job.

Therefore, the implementation of planned maintenance that must be considered is to schedule the steam boiler plant operations, maintenance planning, maintenance planning objectives, the factors to consider in planning maintenance work, organizational systems for effective planning, and estimation of work. Thus, corrective maintenance is the most appropriate use of emergency and to reduce engine idle time.

Corrective maintenance in steam boiler has some advantages as the following below:

Provide information for consideration of replacement of machinery in steam boiler.

Provide budget and cost control are reliable.

Improving the efficiency of the equipment and machine in steam boiler.

Reduction of replacement parts, helped control preparations.

Extends time between overhauls.

Increasing use of labor for maintenance and production of boiler.

Raising the availability for the production of boiler.

Reduction of idle time.

Reduction of emergency maintenance.

Preventive maintenance in Steam Boiler

Preventive maintenance is periodic inspection to detect conditions that may cause production stops or reduce the function of machine or equipment in steam boiler. Preventive maintenance can be combined with other maintenance types to control condition of steam boiler and detect whether the equipment is in good condition or not, so damage can be expected does not occur.

A plan of preventive maintenance requires regular inspection, maintenance and keeping the facilities in good working order so that no damage occurs in the future. Basic works on preventive care are: inspection, lubrication, planning and scheduling, recording, analysis, training for maintenance personnel, and also spare parts storage. Furthermore, all of equipment or machinery in steam boiler plant can avoid damage during operation.

Preventive maintenance in steam boiler can divided in the following actions below:

Alignment: making changes to any of equipment which is specified by variable elements to achieve optimum performance.

Installation: replace the equipment in steam boiler regularly which has limitation usage or the life time of equipment is out to maintain specified level of tolerance.

Servicing: periodic lubrication, filling, cleaning, and so on to any materials of steam boiler to prevent the occurrence of new failure.

Adjustment: make periodic adjustments to certain variables elements to achieve optimum performance.

Testing: testing at regular intervals (periodically) to determine usage and detect damage on electrical or machinery of boiler system.

Calibration: detect and adjust for any differences in accuracy to the material or comparison of parameters for a certain standard.

Inspection: check periodically to certain parts to be used by comparing its physical, machinery, electrical, and other characteristics to certain standard.

Maintenance Types in Steam Boiler

Maintenance of steam boiler must be performed to keep quality of boiler and make boiler has long life. Maintenance has some types as following below:

Running Maintenance

Maintenance is performed when the facilities or equipment of steam boiler in working condition. Running maintenance is applied to the equipment which should operate continuously to serve production process.

Routine maintenance

Routine maintenance is maintenance carried out regularly or continuously.

Predictive Maintenance

Predictive maintenance is performed to determine the occurrence of changes or abnormalities in the physical condition and functionality of equipment system in steam boiler. Predictive maintenance is usually done with the help of senses or sophisticated monitoring tools.

Preventive maintenance

Preventive maintenance is maintenance that aims to prevent damage, or the way of maintenance which is planned to do prevention. The scope of preventive work, including inspections, minor repairs, lubrication and adjustment, so that this maintenance can prevent damage in the equipment or machinery of steam boiler during operation.

Corrective Maintenance

Corrective maintenance is maintenance which is performed to improve and enhance the condition of facilities or equipment in steam boiler so as to achieve a standard that can be received. In the repair can be done in such a way improvements, such as making changes or modifications of design in order to get better equipment.

Shutdown Maintenance

Shutdown maintenance is maintenance which is performed during steam boiler is shutdown and all of equipment stops to operate.

Emergency Maintenance

Emergency maintenance is the maintenance must be done immediately because of congestion or damage which is not unexpected.

Breakdown Maintenance

Breakdown maintenance is done when damage occurs to the equipment of steam boiler and to fix it must be prepared spare parts, tools and labor.

Design out Maintenance

Design out Maintenance is to redesign equipment of steam boiler to eliminate the root causes of failure and result in a failure model that no longer or less need of maintenance.

Drum Level

Fig. 1: Gage Glass Drum Level Indication
Source: Book - Boiler Control System Engineering - GF (Jerry) Gilman

The designer of steam boiler should determine specific limit of drum level both for lowest level and highest level. Drum level must be maintained, do not reach highest or lowest level. If drum level exceed the highest level, the boiler water will be carried over into superheater and may damage turbine generator or steam boiler it self. High cost for maintenance is one of risks because of this condition. But on contrary, if drum level is low will lead to overheating either short term overheating or long term overheating. The most common occurs is crack or rupture in the tubes which connect to steam drum.

Fig. 2: Drum Level Transmitter
Source: Book - Boiler Control System Engineering - GF (Jerry) Gilman

Control drum level is very important to perform steam boiler continuously without damage or outage. Some equipments and instrumentations may be applied to monitor and control the drum level. These equipments are drum level differential pressure transmitter connection, gage glass drum level indication, electrode columns and drum level transmitter. These instrumentation must be located refer to code ABMA (American Boiler Manufacturer Association’s) – Recommendations for Location of Instrument and Control Connection for the Operation and Control of Water tube Boiler.

Optimizing Heat Transfer in Steam Boiler

Heat transfer within steam boiler can be performed by three ways and by their combination; radiation, conduction, and convection. Optimizing heat transfer should be done to maximize efficiency of steam boiler. The followings are the ways to optimize heat transfer:

1. Control excess air

Composition of excess air should be controlled, if excess air is too much will effect temperature of flue gas low because of cooling from excess air, but on contrary if amount of excess air is too low will cause flame temperature is high.

2. Keep clean boiler tubes

Tubes receive heat from combustion furnace by radiation and heat is distributed to all of surface metal tubes by conduction. The presence of soot, ash and scale will obstruct heat transfer because they are poor conductor. Any deposit on outside surface tubes can be cleaned by soot blower, while any scale in inner side tubes can be prevented if water treatment is undertaken well.

3. Keep optimum flue gas and feedwater

Feedwater should be treated free from sludge and scale to ensure water can receive good heat transfer and can flow with a certain velocity. Optimum flue gas can be taken by doing routine maintenance and choose optimum fuel.

Maintenance Tools in Steam Boiler

Steam boiler needs specialized tools to do maintenance properly, so steam boiler can operate continuously and efficiently. The required tools are depending on type of maintenance; these are some variety of tools and equipments:

1. Tube Cleaning Tool, tubes in steam boiler if it is not cleaned will cause scale, sludge, slag, and deposit and other chemical substances on the surface of the tubes, will can disturb flow through the tubes and make corrosion. Steam boiler tubes should be cleaned by tube cleaning tool such as air/water tube cleaning kits, buffing tools, cutter heads, cutter bits, flexible shafts and tube cleaning extension rods.

2. Electronic Instrument Tool, steam boiler need this tool like O₂ Analyzer to observe excess air in the flue gas that will be discharged to atmosphere, tube thickness calculator instrument, test instrument etc

3. Power Tools such as hammer, drill, screwdrivers, impact wrenches, grinder, drill presses, etc

4. Tube expansion tool and removal tool, such as tube expander, tube puller, hydraulic tube cutter, etc

5. Welding equipments such as welding machines, electrode, cutting torch, regulator, welding gage, etc.

6. Hand tools such as punches, pipe threader, pipe wrenches, sockect, knives, etc

7. Pressure washer tools such as hot water pressure washer and its accessories, vapor steam cleaner, etc

Classification of Maintenance Steam Boiler

Maintenance is required to perform and maintain steam boiler in good condition. Maintenance can be classified into two types as the following:

1. The routine and preventive maintenance

The routine and preventive maintenance is maintenance that be made periodically whether daily, monthly and annually. This maintenance is made before equipments of steam boiler damaged, so equipments can work continuously and ready for use any time. The life of steam boiler equipment can be long life and in excellent condition for the best efficiency, safety and reliability if maintenance is well controlled. This maintenance may include cleaning pressure part, draining header, check equipments like valve and the others, burner maintenance, check water level in the steam drum, flame safeguard, refractory, condensate equipment and the like.

2. The forced maintenance

The forced maintenance is maintenance that be made if there is equipment of steam boiler damaged suddenly. The cost of forced maintenance is usually higher than the routine and preventive maintenance. The forced maintenance is commonly caused by overloading of fuel which be burned in the furnace, so steam boiler working extra that could cause the steam boiler to be fatigue and over heat; there are too much slag attached on surface of pressure part; feedwater entering the steam boiler is not pure, there are still solid particle and oxygen in the feedwater, so steam boiler will contain sludge too much and more corrosive; and improper lubrication in the equipment.

Maintenance Program of Steam Boiler

Steam boiler plant should running well, efficiently and safety. The owner must have plan or program to control maintenance of steam boiler plant to avoid unscheduled shutdown occurs. Regular and routine maintenance can make the steam boiler operates continuously and prevent breakdown which cause high cost for repair and loss profit in production downtime.

Fig.1 : Qualified Personnel Doing
Maintenance Program of Steam Boiler

The maintenance should be done by qualified personnel who familiar with all equipment of steam boiler. The personnel can be engineer, operator, or technician. The personnel must have maintenance program to keep steam boiler from possibility of damage and shutdown suddenly. The program which has been prepared must include the following:

§ Routine maintenance

Routine maintenance is performed daily, weekly, monthly and annually. This program include cleaning pressure part, combustion chamber, etc; draining sludge to continuous and intermittent blowdown; protection from erosion and corrosion, inspection of equipments such us valve, burner, etc.

§ Preventive maintenance

Preventive maintenance is performed to prevent possibilities of accident and anticipate if there are unusual something can be happen. This program includes observation of water level in steam drum; check the supply of fuel and feedwater, check equipment for safety like safety valve, flame detection devices; test and perform all of equipment in steam boiler.

§ Stock of spare part

The owner of steam boiler should have stock of spare part and list it and then to be used if there are emergency repair.

§ Shutdown maintenance

Shutdown maintenance can be down annually to check all parts of steam boiler and replace if there are parts that are not working anymore. Procedure of shutdown should be done properly.

§ Personnel training

The qualified personnel who operate and maintain the steam boiler are absolutely required because they are understand about condition and can make solving problem on steam boiler. So, training boiler should be done to each personnel.

§ Upgrading boiler

Upgrading boiler is an effort who need deep analysis to make steam boiler more efficient and reduce cost for production.