We have put together some helpful tips to keep your boiler up and running smoothly. Maintenance is the single most important thing you can do to increase the life of your boiler.
- A safe way of starting and shutting down the burner. This can be accomplished either automatically or manually.
- A flame safeguard system also starts the burner in the proper sequence. For example it will purge the combustion chamber of gas, light the pilot and then open the main gas valve.
- The flame safeguard system will also continually monitor burner operation when the boiler is on-line.
- The system will protect the boiler from excessive pressure or temperature conditions
- It will also regulate the firing rate according to the demand for heat or steam
- Finally, it will standby during down time, waiting for the signal to start the burner once again.
So why toss this term about? For the simple reason that it gives us a target in which we might compare our combustion conditions against. For example if we supply too little air, the burner will run “rich”. This means that not all the fuel was burned. Not only is this inefficient it also results in sooting that will decrease the heat transfer in the boiler.
Introduce too much air into the process and again, you reduce efficiencies. Not all the fuel is burned. This is why we strive for the perfect balance – Stoichiometric Combustion.
Want to know more about the calculations to determine how much air is required? Just e-mail us.
To calculate Excess Air, % use the following formula:
The theoretical air required will vary depending on the fuel that is being fired. I found a table in the ASHRAE 1985 Fundamentals Handbook (pg. 15.8) that lists these values. For example Natural Gas requires 9.6 lb of cu. ft.air/cu. ft of fuel, Propane requires 24 cu.ft. of air/cu. ft. of fuel, No. 2 fuel oil requires 12.7 lb of air/gal of fuel.
As for a general rule of thumb…how about 0.9 cubic feet of air for 100 Btu of fuel.
When these little foam bubbles pop, they create a liquid that, in turn form slugs of water. Not only does your steam quality suffer, so may your entire system. Remember steam can reach velocities of over 80 miles an hour. Push a slug of water through at that speed and you can seriously damage turbine blades, piping systems and actuators.
First a definition: Turndown ratio is the ratio of maximum fuel input rate to minimum fuel rate of a variable input burner. Traditionally burners on firetube boilers operate in the 5:1 turndown ratio range depending on fuel and size. High turndown burners are considered those with ratios of 10:1 or greater.
Advantages of high turndown burners include:
- Reduction of standby losses
- Limiting thermal cycling
- Saves wear and tear of burner components
- Initial cost and complexity
- Requires more maintenance
- Limitations of Boiler/burner system
The limitations include fuel/air mixing requirements, material temperature issues, flame shape characteristics, flow control limitations and pressure vessel limitations.
- For boilers, refractory is generally a harden brick type material orcastable cement that is designed to handle extreme heat. At one time this refractory had asbestos as the main component, but this has changed. I have included a link below to the Refractories Institute who will have more detailed information on the components of refractory. Some of the things we look for when servicing refractory in a boiler is for loose or broken tile along with flaking or chipping of refractory surfaces. These we repair immediately. www.refractoriesinstitute.org
- Re-bricking a boiler may be a little more difficult especially in firetube (marine) designs. The reason for this difficulty is found in the circular furnace. Make sure you have the right replacement brick and you follow the manufacturers instructions. Depending upon the manufacturer you may also have an inner door and a rear door that will require pouring new refractory. Remember, if you are doing refractory work, make sure the old refractory does not contain any hazardous material and that you have all the closing gaskets needed in order to close the boiler when you are finished. Let me know if we can answer any other questions for you.
- Your boiler plant operates over 75 psig
- Any boiler plant with limited standby capacity
- Boiler plants that use 25% or more cold make-up water
- Any boiler plant that relies on continuous boiler operation
Remember the deaerator is a preventative maintenance tool. It really should be used in every boiler application with the exception of a hot water heating system that uses absolutely no make-up water.
BHP (Boiler Horsepower) X 34.5 / 8.337 / 60 X 10 = gallons of water needed
So, if you have a 500 bhp boiler your formula will be as follows:
500 x 34.5/ 8.337 / 60 x 10 = 345 gallons But wait, you can’t operate a tank completely flooded so you will have to include a 1.5 safety factor. This will take you to about 517 gallons, so a 500 gallon tank will work.
Maybe an easier way is to plan for 1 gallon storage for every boiler horsepower.
500 bhp = 500 gallon tank
300 bhp = 300 gallon tank
But, be careful! Depending upon your particular process you may need a bigger tank. Especially if you are using your steam for process and large slugs of water are returned in an unpredictable manner! When in doubt call us.
If you provide us with your burner/boiler information we can help you locate what you need. Also, a digital picture is great when trying to figure out what part is actually need. I am betting what you are calling air deflectors is actually the burner’s diffuser.
We provide complete burner/boiler service, parts and training in and (far) around the Pittsburgh area, if you ever need help just give us a call. 412-257-8866
The bottom blow down is done at least daily (more often depending on boiler water conditions) to blow out scale and mud from the bottom of the boiler. If possible you should lower the firing rate of your boiler when you do the bottom blow down then return to normal firing rate after the blow down.
There are two pieces of information that you will need. The first is the stack temperature. Simply put, the lower the stack temperature the more heat you are transferring within the boiler. The second bit of information you will need is the amount of CO2 in the flue gas. High CO2 readings with no CO and very little O2 throughout your entire firing range indicate good burner control.
You are going to need some simple equipment to check your fuel-to-steam efficiency. This includes a flue gas analyzer, a stack thermometer, a room thermometer, charts for heat loss in the stack for the fuels you are firing and a correction chart for radiation and convection losses. (ask your boiler supplier for these charts if you do not have them)
Here is an example:
Stack Temperature = 340 degree F.
Room Temperature = 80 degree F.
Gas analyzer reports CO2 = 10% and CO = 0
Subtract room temp from flue gas temp. 340 – 80 = 260 deg. F.
From the Hays Chart, at 260 deg. F. and 10% CO2 you find a stack loss of 15.6% exiting the stack.
Add for radiation and convection losses (available from your boiler manufacturer). We will assume 1% in this example. So 15.6% = 1% = 16.6%
Now subtract that from 100% efficiency
100% – 16.6% = 83.4% Fuel-to-Steam efficiency.
To calculate your actual Turndown you need to know what your actual input is at Maximum and Minimum firing rates. The easiest way to do this is meter the fuel usage be it either a flow meter on the fuel oil supply or a gas meter on the natural gas supply line.
Lets do an example:
Assume that at Maximum Input we clocked the Natural Gas meter and found that the meter clocked 1000 cubic feet (pressure corrected) per hour.
Note: You do not need to have the boiler at Maximum Fire for and hour. You can take the reading over a few minutes and correct to one hour.
So, 1000 cubic feet/hour X 1050 btu/ cubic foot = 1,050,000 btu/hr at maximum input
Minimum Input meter clocked is 100 cubic feet/hour
100 cubic feet/hour X 1050 btu/cubic boot = 105000 btu/hr at minimum input
1,050,000 = 10 giving us a 10 to 1 turndown in this case.
My assumptions: Natural Gas but value = 1050 btu/cubic foot
2. Make sure threads on the nuts and bolts/studs are clean and nuts turn freely over the length of the threads.
3. The tricky part is to make sure the gasket is centered on the backing plate and the backing plate is centered in the manhole or handhole. Tighten (evenly where there is more than one bolt/stud involved) making sure the backing plate and gasket stay centered. Once you are sure everything is properly in place and snugged torque to the proper torque spec. for the size of the bolt/stud and materials that you are using or manufacturers recommendations if you have them.
Note: NEVER EVER TRY TO TIGHTEN A MANWAY OR HANDHOLE WHILE THE BOILER IS HOT AND PRESSURIZED! THE MANWAY OR HANDHOLE COULD MOVE CAUSING YOU TO BE SPRAYED WITH HOT WATER AND/OR STEAM!!!!!!!!
After initial firing of a repaired read door, the door metal will become exceptionally warm or hot. This is due to water conduction of heat. This condition will exist until such time as all moisture has been driven out of the refractory.
The following heat curing schedule is recommended:
Operate burner for brief intervals at low fire, bringing the reading of the stack thermometer up to 150 F and hold this for six hours. The raise the stack temperature at a rate of 50 F per hour until normal operating temperature is reached and hold this for another 6 hours. The boiler may now be operated in the normal manner or shut down if desired.
The securing bolts around the heads should be tightened periodically as the temperature is equalized and when the boiler is at high fire. The tightness of the sight glass retainer should be checked and the retainer and sight glass should be examined for gas leakage. The air line from the front head of the boiler should be checked for possible blockage.
If a loss of heat for 1/2 hour to 1 hours would not cause any problems then running only one boiler is the preferred method. In your case I would run only one boiler at a time. Have one boiler in standby fired every few hours just to keep warm and the last boiler completely off and isolated.
Now, everyone has their own opinion. The above is based on my experiences in the boiler field. Boilers that are turned on and off are heated/cooled/heated/cooled, this can shorten the life of the boiler refractory, cause condensation of flue gas, shorten motor starter contact life among other things. A boiler will last the longest with the least failures if its kept hot and cycled off as few times as possible.
Another possibility for chemical carryover is that you are dropping too big of a load too fast onto the boiler which drops boiler pressure suddenly causing the boiler to suddenly boil excessively and carrying over into the steam line. This is a bit harder to fix but can be done.
Now, the gauge glass problem! I am assuming you have the hollow tubular 5/8″ in gauge glass. These never hold up well on a high pressure boiler. They tend to erode from the top and start leaking steam. As long as you stay with the 5/8″ tubular gauge glass you will have this problem. To eliminate this problem you need to change your gauge glass to a prismatic type gauge glass that uses a thick flat glass that is sandwiched into a strong metal housing. It will not fail! Our Parts Department will be happy to quote a prismatic gauge glass assembly to you. We will need the Center to Center dimension and pipe size of your gauge glass connections. We need to know the MAWP of your boiler also.