The Good Old Vent Valve!
The biggest concern about the vent valves of a combustion gas valve train is not only the potential of failure but, more importantly, the mode of failure when it occurs. Most gas trains on boilers and industrial gas fired equipment are indoors. The vent valve is run to a vent stack going up through the roof and venting to atmosphere above the roof. Natural gas rises due to its low specific gravity, so it floats out to atmosphere, in theory. A vent valve is a “normally open” valve, typically a solenoid. When power is not on the coil of the solenoid, the valve will be in the opened position, allowing venting. When the burner or equipment is to run, the solenoid coil is energized with the safety valves and the vent line is therefore closed. in theory!
That’s the problem! Many of these vent lines are old and are not maintained. When they fail to operate, the vent line stays open or, sometimes, partially open. That results in raw gas pouring out the vent on the roof when the equipment is running. This type of failure goes unchecked all the time and usually only gets found when someone reports a “whiff of gas”. Well, that whiff tells you that, due to winds and air currents, the gas does not always just “float away”! NFPA does state in the guideline that all safety and vent valves shall be tested on a regular basis. Lets be realistic, how many of us regularly check the vent lines or walk the roof checking to see that things are proper? In a recent local high profile case, a school full of children were evacuated due to a vent line failure that was leaking gas right into one of the fresh air in-takes to a Make Up Air Unit. Luckily, no one was harmed, but it sure shows the danger!
In addition, what about the money down the drain, or should I say up the vent! If that is not enough, what about the damage it is doing to the environment? This directly impacts our atmosphere as pollution. As we have stated, agencies have amended their rules and manufacturers have created new products. Today, you can put in a completely ventless system that includes pressure switches, regulators, and shut-off valves and not have to run a single line through the roof! As they say, WE HAVE THE TECHNOLOGY! If you have any questions or wish further information feel free to write to us at firstname.lastname@example.org or contact us 800-444-1962.
Intro to Commercial and Industrial Burners
By: Herb H Etter
The number and variety of gas burner installations in commercial and industrial establishments defy any simple generalization. However, in this series of continuing editorial we will attempt to provide some useful tips that will apply to the maintenance and operation of typical burners. Many applications, such as boiler burners, have their own very specific requirements and codes, and it is not our intent to delve into detailed requirements but rather present information that will be applicable to a wide variety of burner installations.
The function of any burner is to convert and transfer energy to a process or product. As with any energy source, whether it be a toaster, a campfire or a huge gas burner, the potential for disaster caused by neglect or ignorance is very real.
Our first topic covers the area of Safety, with the intent that the reader will research further as regards his specific installation.
Various codes and regulations have proliferated over the years, and these can be divided into two arbitrary categories – governmental and commercial. Local state and federal codes can encompass a variety of things ranging from building permits to emissions. It goes without saying that your burner installation should comply with these requirements, even if all of them are not safety related. The commercial type requirements would include any requirements of your gas utility company, plus those required by your insurance carrier. Fortunately, most insurers subscribe to a common set of requirements as set forth in publications of the National Fire Protection Association. NFPA bulletin 86 covers ovens and furnaces and many miscellaneous applications, and other individual bulletins cover specialized equipment such as boilers, etc. It is reasonable to assume that if your installation met the above requirements, it was installed safely. However, these requirements require continuing participation on your part, and do not end with the initial installation. Continued and regular maintenance and safety checks are an essential part of any safety program.
At the low end of the spectrum there are old burner systems, presumably installed before many of today’s requirements and technologies. Owners of these systems may think that since they have operated for years without a problem there is no cause to upgrade. They are aware that there is better and safer equipment available, but nobody has come around and told them to make any changes. They have probably never seriously faced the fact that a comparatively inexpensive upgrade would greatly enhance the safety of their business and property, not to mention the human considerations. This might be a good time for anyone with a questionable installation to check his or her installation against modern safety standards.
The more typical installation probably meets most if not all of current safety requirements. The system includes electronic flame safety system, approved type gas valve train, interlocked pressure and flow switches, proper exhaust and vents, etc. This is the type of installation with which we will concern ourselves in this series. In future articles we will review in some depth the various components which comprise a safe system, and the care and feeding of same.
Basic Burning Tuning
By: Jon Moore
With our most recent edition of Tech Tips, Herb had touched upon the numerous types of gas burners & how they are similar yet different. The next logical step is to discuss the basics of combustion as it relates to the burner. Again, this column is to be taken as a broad overview, and is not intended to resolve or address specific needs or problems. Tuning of combustion equipment should be left to a trained professional (do not try this at home!).
For combustion to take place, you not only need the fuel & air, but also the “three T’s of combustion”, without which the process will extinguish itself, be dangerously poor in its performance, or fail to ignite. The three T’s are: Time, Temperature & Turbulence. You need to expose the fuel to the air for the proper amount of TIME to complete combustion. This is technically referred to as residence time, the time of exposure. The reaction needs TEMPERATURE in order to take place. Once the process is started, this heat is usually self-sustaining coming from the fire itself. Initially, the temperature or energy is usually provided using an external means, most typically a high voltage ignition transformer providing a spark just like your car’s ignition. The TURBULENCE insures that the fuel & the air are mixed properly. If these two streams stratify or segregate, combustion will be adversely affected. On an atomic level, the oxygen molecules must be able to rub shoulders with the carbon & hydrogen molecules or they cannot burn.
Should you loose any of the 3 T’s your process & system efficiency will pay the price. Incomplete combustion results in abnormally high levels of CO (a noxious & toxic gas), low levels of heat, cost you money & present a danger when it comes to potential puffs (that’s what we in the combustion business like to call uncontrolled combustion, also sometimes referred to as explosions). This is a serious financial & safety matter that’s why it is best left to the professional.
With now knowing the 3 T’s, what about stoichiometry? Huh, What did you say? Well, stoichiometry is the measurement of fuel to air ratio. Providing exactly the right molecular amount of Oxygen required to liberate the heat of the reaction from Carbon & Hydrogen molecules and chains is referred to as a “Stoichiometric Burn,” or a stoichiometric ratio (SR) equal to 1.0. Providing 10% excess air would be SR = 1.10, & a 5% deficiency of air (or sub-stoichiometric burn) would be SR = 0.95. Yes, you can burn fuel in an oxygen deficient atmosphere; usually the burnout air (the air required to complete the reaction) is added downstream. An oxygen deficient atmosphere is called RICH or fuel rich, while an atmosphere that has more than enough excess air for the combustion is called LEAN. Most process & industrial heat applications are LEAN applications with plenty of excess air. Great care should be used in “on ratio” or sub-stoichiometric applications. If the burnout air is added suddenly and the three T’s are present, the probable result is a BANG (that’s another one of those words we use in the industry)!
Lean Fires: Lean fires using natural gas get quite blue, sometimes even violet. When firing oil, lean burns are very bright yellow, almost white, & this flame ought to be looked at through a blue lens so as not to harm your eyes. A fire on either fuel with excessive amounts of excess air can actually be quenched (losing the Temperature of the three T’s) which will create high levels of CO and potentially white smoke.
Rich Fires: A rich fire on gas turns yellow, and if it even starts to look orange shut off the FUEL, it is getting to a dangerous point. A dark smoking gas fire is very dangerous. A rich fire on oil will get very orange and dirty, producing a dark smoke.
In either case, the most important thing to leave you with is this: If you ever have a RICH fire, do not add or increase the AIR to clean the fire up. You just gave the fire just what it needs to reach out and touch you, going BOOM! ALWAYS cut back on fuel in a rich condition, never add the air! When manually tuning & increasing your firing rate, bring air up first, then fuel, keeping yourself LEAN. When decreasing your firing rate, bring fuel down first, and then decrease the air to the fuel, again staying LEAN. Remember, let a professional tune your combustion equipment. Those who play with fire may get burned!
Basic Burner Types
By: Herb H Etter
In an earlier article we concentrated on the safety aspects of commercial and industrial gas burner operation. As with any equipment, the more we understand of the operation, the better equipped we are to safely get the most productivity from the unit. We will start our equipment review by beginning with the gas line that comes into the building.
The most common gas fuel is natural gas, as distributed by your local gas company. Gas is odorless ( they add the distinctive smell) and lighter than air ( 0.6 specific gravity, air is 1.0 ). One cubic foot of natural gas contains approximately 1000 Btus. One British Thermal Unit has a heat content about equal to that obtained in burning one wooden match. Natural gas is a hydrocarbon, mostly methane, CH4. When burned ( united with oxygen) the products of combustion are mostly CO2 and H2O vapor. The part we are mostly interested in is the heat generated by the burning or chemical reaction. A proper combustion mix involves 1 part of natural gas and 10 parts of air. More than 1 part gas, the mix is called rich, less than 1 part gas the mix is lean. Flame from a rich mix tends toward being yellow, a lean flame more on the blue side.
Having mastered the “short-short” gas course above, we move on to burners. With the great variety of burner styles available, it is probably easier to first list some of the ways air and gas get mixed and delivered to the various burners.
– Atmospheric Mixers: In this type mixer, gas is discharged through a small orifice into the open end of a venturi tube. The gas velocity entrains ambient air ( about 80% of that needed for complete combustion) and delivers the mix to the burner. The remaining 20% of air comes from the air surrounding the flame.
– Low Pressure or Proportional Mixers: These mixers utilize a zero governor, which is a diaphragm-actuated valve similar to a gas pressure regulator. This downward opening valve is held up and shut by a spring, and opens only when a negative pressure is sensed at the valve outlet. The zero governor is piped to the negative chamber of a venturi tube or mixer. A combustion air blower directs air into the venturi, creating a negative pressure at the zero governor outlet, causing gas to flow and mix with the combustion air. Varying the air flow to the venturi varies the negative pressure and consequently the gas flow. This provides single air valve control for both the air and gas flow.
– Premix: This system provides 100% air-gas mix through a mechanical mixer, usually a centrifugal blower that pulls air in one side inlet and gas in the other side. The resultant mix is delivered to the burner or burners through appropriate flame arresters, etc.
Burner types are endless, but a generalization would include these groups:
– Drilled pipe burners, ring burners, nozzle burners, can be supplied with air-gas mix via atmospheric mixers described above.
– Nozzle burners equipped with proportional mixers will have a higher heat release than when equipped with atmospheric mixers. This is due to the higher mixture pressure available. Other burners using these mixers would include line burners, and some infrared burners.
– Nozzle or Burner mix burners keep the air and gas separate until they mix within the burner housing. This is typical of burners used on high temperature furnaces.
– Packaged burners, sometimes called power burners, have a combustion air blower as an integral part of the burner assembly. This design is typical of boiler burners and air heating burners.
While the above listing is by no means complete, hopefully it will enable you to identify your burner type, and provide an indication as to how it functions. Our future discussions will cover how safety and temperature control accessories are applied to the burner.
Cash for Burners vs. Cash for Clunkers
For big savings, keep the car and upgrade your burners instead!
By: Tom Etter
You heard about the program for cars, but what about your burners? We are going to show you from a savings standpoint how much better a commercial or industrial burner replacement is than the recent hot government program.
The car program was based on fuel efficiency improvements, and rebated the consumer anywhere from $3,500 up to $4,500 on a car that was replaced with a new one getting between four and ten or more miles per gallon better than their trade-in. For a driver that puts 12,000 miles per year on their vehicle, and with the average price of gas at $2.75 per gallon, it will take about 6 years before seeing a return on the government’s investment. Since the life of an average car is just over 6 years, this new car will likely be off the road just when it finally starts paying back for the program. As we all know, in the real world this is not a good plan. And remember, as a taxpayer, the government’s investment is your money!
Now, look at your commercial or industrial burners. If we take a typical burner at 5 MM Btu/hr, running 16 hours a day, and replace it with a new burner with an increase in efficiency of five to seven percent, this is what happens: The annual operating costs of the burner, at $10.00 per Deca-therm, goes from $230,400 per year to $207,360 per year. That’s a savings of $16,000 per year!
Your burner upgrade will only cost you about $8,000, so this upgrade pays back the investment in 5 to 6 months, not years. Given that the average life of a burner is well over 10 years, this course of action will save you piles of money over its lifetime.
But wait – there’s more! The efficiency increases can be further improved by upgrading old fashioned controls with new linkageless controls. This can increase your efficiency savings by another six to ten percent, making your short and long term savings that much greater.
If you’re really looking to hit one out of the park, adding active exhaust control or LEL monitoring can reduce your system fuel requirements by over 20% by minimizing latent heat losses going out of your stack.
Do you want to help the enviroment while still saving money? Upgrading your burner equipment to Low Emissions burners and controls can reduce your NOx and CO outputs by 30 to 40 percent, all while saving money. That’s “GG2” – Going Green Squared!
Other benefits to keep in mind that can justify a burner upgrade alone are improved process quality, reduced maintenance and down time, increased safety, reduced insurance costs when upgrading to satisfy current code controls, and potential rebates from local utilities.