Like any other piece of machinery, boilers require regular maintenance for the highest safety, reliability, and efficiency. The key to ensuring your boiler continues working properly is through regular inspections so you can proactively avoid big issues. This article gives an overview of how boiler systems work, the parts of a boiler system, how to clean a boiler, as well as common problems that arise with boilers.
How Does a Boiler Work?
Boilers are used to generate hot water or steam via either burning of a fuel (typically natural gas, but fuel oil, biogas, wood, and other fuels are available), or through electricity (resistive element, or electrode-type units). Hot water boilers rely on pumps to move the hot water from the boiler to the end heat users and back to the boiler. In steam boilers, the steam is its own motive force as it moves to fill the available space (from the boiler through the piping). Once the steam gives up its heat, it becomes condensate – depending on pressure, this condensate can be trapped back in the boiler system or may need to be collected and pumped back.
Boiler systems are utilized widely across industries because they are both reliable and efficient in their operation. Steam and hot water are still very practical means to move heat from one space to another, efficiently.
Starting a Boiler
Non-process boilers (comfort heating boilers, those that are used in a manufacturing-type setting) are often turned off during the warmer parts of the year when buildings don’t need to be heated. This temporary shutdown is called a “lay-up”. Boiler operators must follow a specific set of steps when re-starting a boiler after a lay-up that will closely mirror these steps:
- Conduct a pre-start-up check that includes confirming the ventilation and combustion air openings are unobstructed. Also, confirm there is sufficient water in the system and that any isolation valves are in their “run” positions (whether they are normally opened or closed)..
- To start the boiler, if you are manually controlling the boiler’s firing rate, set the manual/auto switch to manual, then set the manual firing rate control to the low fire position, confirm there is power to the boiler through its disconnect (per code, this switch should be within eyesight of the boiler), confirm the boiler has a call for heat, move the boiler’s power switch to the on position, the boilers flame safeguard control should begin the startup process consisting of running the fan to purge the furnace and perform prestart safety checks.
- After the pre-purge, the boiler should go to its Pilot Trial for Ignition, where the pilot flame attempts to light. After the pilot flame is proven, the boiler will move to its Main Flame Trial for Ignition. At this point, the main flame should light.
- At this point the boiler will begin heating the water. Depending on the type of boiler, this may warmup may take place at low fire (typical for firetube boilers). This low fire start will release once the boiler reaches a safe temperature, typically around 180 degrees F. If your boiler has a low-fire start feature, it is important that you allow this process to take place, and that you not manually force the boiler to high fire so it heats faster. Depending on the type of boiler, this can cause damage to the boiler that will require repairs.
- Continue to monitor the boiler as it reaches its desired operating temperature or pressure. Once at that temperature/pressure, the boiler can be tied into the rest of the system either by pumps or valving, depending on the heating plant’s design.
Parts of a Boiler System
Most boiler systems operate somewhat similarly with the same general makeup of parts. The main components of all boiler systems include:
- The burner is where the air mixes with fuel, creating combustion. Proper airflow is important to maintain a clean and efficient process.
- The boiler (proper) is the pressure vessel where the working fluid (water) is contained. The construction of the boiler and materials used (based on code), varies depending on the service (hot water, low-pressure steam, high-pressure steam, etc.)
- The combustion chamber is a part of the boiler where the burner’s fuel and air burn. It creates a safe environment for combustion. It must be regularly serviced /inspected to avoid and repair corrosion or cracks.
- The heat exchanger is the part of the boiler that transfers heat produced in the burners to water in the boiler. It’s made out of metal that conducts heat and is very durable. The type of metal is determined based on the design and operating conditions of the boiler. For example, a condensing boiler will use corrosion-resistant varieties of steel (stainless steel). The type of heat exchanger falls into a few different categories: fire tube (heat from the furnace goes through tubes, surrounded by water), water tube (the water is in the tubes, surrounded by the heat from the furnace), and cast-sectional (cast-iron) types.
- The controls allow the user to operate the system. Controls broadly break down into two main categories. The flame safeguard is responsible for safety functions. The combustion control is responsible for controlling the air/fuel mixture and possibly other functions related to the proper burning of the fuel.
- The supply lines carry the steam or hot water throughout the building. On a hot water boiler, the return lines carry the water back to the boiler after circulating through the building. In a steam boiler, after the steam gives up its heat, it becomes condensate. This condensate travels back to the boiler room via what is known as the condensate return system – this can be made up of condensate at varying temperatures/pressures and moved by motive means.
- In hot water systems, the circulator pump is responsible for maintaining the flow of water through the supply and return lines.
- In steam systems, the condensate will return to the boiler’s feed system, this can be made up of a feedwater tank, or deaerator (may or may not have a surge tank). This system receives the condensate and then sends it to the boiler as needed.
- The exhaust stack carries away the products of combustion, discharging into the atmosphere. This stack can be made up of different grades of materials, depending on the fuel being burned, stack temperature, and local conditions.
Even though natural gas and oil have replaced coal-fired boilers, most modern boilers still operate similarly to the way older models did decades ago – fuel is burned, and the heat created is transferred into the working fluid.
When considering maintenance, you should keep essential spare parts in your boiler room, so you’re prepared for critical situations.
How is Boiler Capacity Defined?
To calculate the boiler capacity, you’ll need to know your building’s heating or process needs. The capacity of a boiler is determined by the amount of heat transferred over time. This capacity is commonly stated in a few ways: BTU/hr (or MBH for thousand BTU/hr) for hot water boilers, Boiler Horsepower for commercial/industrial steam boilers, and PPH (or kPPH) for larger Industrial Water Tube boilers. For hot water boilers, the capacity listed is commonly the gross input of the boiler, not its output. For steam boilers, the listed values are usually based on boiler output. In either case, make sure you are ultimately looking at the output as that is what your building/process will need.
British Thermal Units (BTU) denote the amount of energy (work) needed for 1lb of water to increase by 1 degree Fahrenheit. Energy over a given amount of time is power, i.e. BTU/hr equals the work a boiler can perform over an hour. This is typically written as BTU/hr, MBH (thousand BTU/hr), or MMBH (million BTU/hr). The unit of measure is used for both the (fuel) input into the boiler and the output of the boiler. This unit of measure is commonly used on smaller, commercial hot water boilers.
The boiler’s horsepower (BHP) is commonly used to refer to the output in commercial/ industrial steam boilers. BHP denotes the amount of energy required to produce 34.5 pounds of steam per hour from a pressure of 0 Psig and at a temperature of 212 degrees Fahrenheit. It considers the amount of water the boiler can convert to steam at those conditions.
Pounds per hour of steam (PPH) is a unit of measure commonly used in larger industrial water tube applications, typically expressed in thousands of pounds per hour (kpph). Similar to boiler horsepower this is a measure of the boiler’s output. Unlike boiler horsepower, these sorts of units are at a project-specific pressure and temperature (including feedwater conditions). Note: boiler horsepower can also be calculated for varying temperatures and pressures, but most commonly at the 0psig/212F conditions.
Since these are all units of power, you can easily convert from one unit of measure to another.
Converting BHP to pounds of steam delivered can be done by multiplying it by 34.5. The reverse can be done by dividing the pounds of steam by 34.5.1 BHP is equivalent to 33479 Btu/hr, and 1 Btu/hr is equivalent to 0.293 Watts.
Preventive Maintenance Tasks for Boiler Systems
As mentioned prior, the best way to ensure that your boiler system is running efficiently is through a regular maintenance routine. This involves performing a number of inspections and tasks each week, month, or year.
A great resource can be found in your boiler manufacturer’s Installation and Operating Manuals (IOM). This information will help determine how often you should perform certain checks and inspections on your machine. It can serve as a good foundation to build maintenance practices pertinent to your facility. It’s also important to determine what type of fuel you’re using; if it’s natural gas or oil-based fuel, there may be some additional tasks specific to those types of fuels. When fuel oil is used as a backup, there are fuel treatment and fuel system testing considerations. Also, electric boilers will require different types of maintenance than natural gas models due to their differences in operating principles.
How to Setup a PM Schedule?
There are many ways to set up your PM schedule, but it is generally a good idea to break the tasks down into daily, weekly, monthly, semi-annual/quarterly, and annual procedures. The following example is made up of recommendations regarding the maintenance of steam boilers, courtesy of Superior Boiler.
Daily boiler checks are important for several reasons. Mainly with a consistent routine checking on the health of your boiler, you can spot and address small problems before they become major issues. Daily checks consist of items like:
- Observe and record the water level in the boiler’s site glass
- Blow primary LWCO down while the burner is firing. Verify that the feedwater pump cycles normally and that burner shuts off.
- Observe the burner starting sequence and flame characteristics to verify normal behavior. Check the furnace for debris and sooting, and inspect the refractory through the flame.
- If an operating log is kept, enter readings; otherwise, conduct a visual check of all pressure and temperature gauge readings.
- Check safety valves, handholes, and manways for signs of leakage.
- If the boiler is firing oil, check the level in the oil storage tank. If the burner has an atomizing air compressor, check its lubricating oil level.
- Check stack temperature. If the temperature is higher than normal, check the burner operation for overfiring or improper combustion.
- Check the temperature of water supplied to the unit and if below 140ºF preheat return to at least 165ºF.
- Check water sample readings for proper chemical treatment.
- Check combustion control operation as outlined in the checklist section of the service manual. Investigate and correct at once any failure.
- Check the pressure limit shutdown.Observe the operation of the programming control to make sure that it occurs as described in the sequence of operation section of the service manual.
- Wipe the entire unit, particularly the operating parts, so that oil and dust do not accumulate.
- If firing heavy oil, clean the oil nozzle as detailed in the burner manufacturer’s instructions. Nozzle and electrode settings must be returned to original adjustments.
- Check chemical feed equipment against the checklist supplied by the water treatment company. Treatment should be introduced directly into the boiler or device located on the discharge side of the feedwater pump.
- Check auxiliary LWCO to verify that it shuts the burner off.
- Clean the feedwater strainer between the pump and the condensate return tank.
- Clean the air intake filter on the atomizing air compressor if present. Replace filter oil with clean compressor lubricating oil.
- Clean combustion air fan and air inlet assembly.
- Check the rear door for flue gas leaks and tighten bolts as required. Tighten bolts evenly – uneven tightening could cause leakage.
- Check airflow and fuel pressure switches.
- Manually blow boiler safety valves.
Semi-Annual or Quarterly* Procedure
- Cool boiler slowly to room temperature. NOTE: Failure to cool the boiler slowly will affect the life of your boiler and possibly cause tubes to leak. This is important!
- Remove all the nuts and clamps around the front door flange, pry the door loose from the boiler, and swing it away on the davits.
- Using a flue brush and vacuum cleaner, brush through the tubes to the rear end of the boiler.
- Soot and scale may be removed from the rear end of the boiler by removing the cleanout plug located at the bottom of the rear door and inserting a vacuum cleaner hose. (Does not require the large door to be opened.)
- Check the rear door refractory and patch any cracks or spalled areas with high-temperature cement. If the refractory requires replacement, a sectional assembly may be obtained from the factory.
- Always replace the 1” ceramic fiber seal around the edge of the rear refractory with a new seal when the rear door is opened and the gasket is damaged.
- Tighten front and rear door nuts evenly to take up any slack created through drying out.
- Clean the peep sight glass or replace it if required.
- Flush the air compressor as directed in its service manual.
- If the boiler is used for a steam process with a high percentage of feedwater makeup, follow the Annual Procedure items 2 & 3.
- Have a qualified boiler service company perform a combustion tune-up (primary and backup fuels) and safety/operations check of all controls.
- Follow steps 1 through 11 listed under Semi-Annual Procedure.
- Clean the water side of the boiler as follows:
- Open upper tri-cocks and any other available vent valves to prove that the boiler contains no steam.
- Drain the boiler through the blowdown valve.
- Remove all handhole covers and the manhole cover.
- Wash down the inside (water side) of the boiler with a hose, making sure to get all sludge out of the bottom of the boiler.
- Inspect shell and tube surfaces for signs of corrosion or scale formation. If scale is forming (to any degree) on internal surfaces, chemical treatment is not correct. Consult chemical supplier.
- Remove plugs from low water cutoff equalizer crosses and rod piping if scale is present. Remove the low water cutoff head and clean the float chamber. Reassemble with a new gasket.
- Using new gaskets, install the handhole covers and manhole cover.
- Disconnect the piping on the discharge side of the feedwater pump and inspect for scale build-up. Check stop and check valves for proper operation and replace them if necessary.
- Install new safety valves of proper pressure and capacity rating. Old valves may be refurbished and kept as spares.
- Fill the boiler by means of the feedwater pump and reset the low water cutoff.
- At the time of this yearly inspection and cleaning, it is recommended that the local SUPERIOR factory-trained representative, be called in to check the condition of the equipment. Chemical suppliers should also be present.
Common Problems You May Encounter With Boilers
- Boiler leaks
- Tripping out on manual reset safety controls
- Higher than normal stack temperature
- Low / High Water level
- Excessive Vibration and noise
- Performance problems (i.e., inadequate heat output, reduced efficiency, etc.)
If you experience any of these problems, we recommend first starting with a thorough inspection. If that does not reveal the issue, it’s time to call in experts, such as WC Rouse & Sons.
What are The Three Primary Areas of Responsibility for Operators of Boilers?
The three main areas of responsibility for operators are boiler operation, maintenance, and safety.
Boiler Operation: Operators must be able to safely operate the boiler to ensure the building is powered efficiently. This includes having a thorough understanding of the control systems and the boiler’s principles of operation.
Boiler Maintenance: Operators should also perform routine maintenance tasks such as daily safety checks and planning annual inspections for the boiler and related components.
Boiler Safety: Safety starts with the prevention of problems by keeping equipment in good operating condition, performing routine safety checks, and monitoring the boiler’s condition continuously. Operators should also keep the boiler room organized and clear of clutter – nothing blocking aisles, exits, combustion air supply, etc. – and make sure that emergency stop buttons are readily accessible at each exit from the boiler room.
Important Safety Tips
As a safety precaution, you should do the following when inspecting your boiler:
- Wear protective clothing (PPE). Always select PPE that is appropriate for the task at hand, including heat/flame resistant materials, eye protection, dust masks/respirators, hearing protection, etc.
- Perform proper lock-out tag-out (LOTO) procedures to take the boiler out of service, for inspection. This includes isolating the boiler from water, steam, fuel, and electrical sources.
- Make sure the boiler water is cool before draining, and ensure the boiler stop valves have completely isolated the boiler from the steam system, prior to draining or opening the unit.
- Never use an exposed flame near the boiler or its gas lines—including cigarettes and cigars!
- If you are performing an internal inspection, follow plant safety procedures related to confined space entry.
- Keep unauthorized personnel from the area entirely while operating or repairing any parts of your boiler; you will want them at a safe distance where they cannot accidentally touch buttons, pull levers, etc., which could pose a safety risk.
As you can see, boiler operation and maintenance is a complex process that requires careful attention. Proper care and maintenance can keep your boiler running safely and efficiently for years to come. If you have boiler-related questions or want to know about boiler options for your facility, reach out to the experts at W.C. Rouse today for more information!