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combustion-theory-efficiency

Understanding Combustion Efficiency

The efficiency of a burner-boiler combination is simply the amount of useful energy leaving the system expressed as a percentage of the chemical energy in the fuel entering the system.

Why should I care about efficiency?

Accounting for the loss of useful energy is an important step in evaluating overall cost.

For instance, a change in efficiency by as little as 5% can have a major impact on the operational expense of a facility. The larger the facility’s consumption of fuel and electricity, the more drastic the cost.

General rules of conservation of energy are:

  • Fuel energy “in” equals heat energy “out.”
  • Energy leaves in steam or in losses.
  • Efficiency + 100% minus all losses.

The typical efficiency of a boiler is 80% to 85%. The remaining 15% to 20% is lost. These losses usually fall in the following percentages:

  • 15% typical “stack loss.”
  • 3% radiation loss.
  • 1% to 2% miscellaneous loss.

The table below shows you how to calculate your cost with your efficiency as the variable.

table-operating-costs

Operator / Install Tips

Since a burner must be set up to operate cleanly under worst-case conditions, you must provide enough excess air in order to burn any additional fuel that the metering device at the burner may introduce.

You should also ensure that there is sufficient excess air available on a hot, humid summer day. Remember: there is no way to prevent heat and humidity, but with the proper control systems, you should be able to control fuel flow precisely and efficiently.

Other posts in this series:

  • Understanding Local Law 87 – and laws like it
  • Combustion Theory: The Basics
  • Combustion Theory: Variables – Account for variations in oxygen and fuel
  • Combustion Theory: Efficiency – Calculate efficiency and losses
  • Combustion Theory: FGR – See how flue gas recirculation reduces NOx
  • Combustion Theory: Combustion Controls – Learn how cutting-edge tech can cut your emissions
  • Combustion Systems: Design – Basic principles to follow when designing your combustion system
  • Combustion Systems: Troubleshooting: Burner problems and their causes
  • Combustion Control: Strategies – Linkage vs. Linkageless, and why you should care
 

combustion-theory-variables-header

 Accounting for variations in oxygen and fuel

For any burner-boiler combination, there is an ideal “minimum excess air” level for each firing rate over the turn-down range. Usually, burners require much higher levels of excess air when operating near their minimum firing rates than they do at “high fire.”

More serious factors than dirty fan wheels and dampers inhibit air flow. Varying oxygen content in the air changes the ambient air conditions and effects the input of oxygen into the combustion process.

Hot and Cold Days

On a “standard” day of 60°F, 30 inches barometric pressure, and 45% relative humidity, seasonal temperature and pressure changes, you must take into account that a burner has to deal with additional variables.

When it seems harder for us to breathe on a hot, humid summer day, burners have a problem too. On a hot, humid day, the oxygen flow drops by almost 20% and burners that can’t adapt for this “oxygen lean” air will smoke, soot, and produce noxious emissions.

On a cold, dry winter day, the air flow would increase by 10%, and the burner must adapt.

Viscosity

Variations in pressure across the metering valve and fluid viscosity have the greatest effect on fuel flow.  Viscosity can vary from delivery to delivery and can be affected further by temperature changes.

Having thick oil in burner supply line can reduce the pressure at the metering valve while having thick oil in the return line can increase the pressure at the valve.

Since the burner must be set up to operate cleanly under worst case conditions, enough excess air must be provided to burn any additional fuel that the metering device at the burner may introduce as well as to ensure that the metering device at the burner may introduce as well as to ensure that there will be sufficient excess air available on a hot, humid summer day.

There is no way to prevent heat and humidity, but fuel flow can be closely controlled with the appropriate controls.

Controls are essential to the boiler-burner combination because they will reduce the amount of excess air wasted during weather and fuel changes.

Other posts in this series:

  • Understanding Local Law 87 – and laws like it
  • Combustion Theory: The Basics
  • Combustion Theory: Variables – Account for variations in oxygen and fuel
  • Combustion Theory: Efficiency – Calculate efficiency and losses
  • Combustion Theory: FGR – See how flue gas recirculation reduces NOx
  • Combustion Theory: Combustion Controls – Learn how cutting-edge tech can cut your emissions
  • Combustion Systems: Design – Basic principles to follow when designing your combustion system
  • Combustion Systems: Troubleshooting: Burner problems and their causes
  • Combustion Control: Strategies – Linkage vs. Linkageless, and why you should care
 

Boiler Control RetrofitIn conjunction with Puerto Rico representative M.R. Franceschini Inc., Preferred recently replaced an existing flame safeguard and oxygen trim system with the Preferred BurnerMate Universal (BMU) system on a 500 HP boiler at a pharmaceutical plant outside of San Juan.

In addition to oxygen trim, the BMU is controlling the forced draft fan variable speed drive (VSD), and providing first out annunciation of boiler trips. The BMU was integrated with the existing proprietary feedwater control system and all existing boiler limits.Boiler Control Retrofit with BMU

This steam boiler runs continuously on No. 2 oil, which is expensive in Puerto Rico, so the boiler was tuned for the lowest excess air possible at all firing rates to reduce fuel consumption.

In addition to expensive fuel, Puerto Rico has some of the most expensive electricity rates in the U.S. according to the U.S. Energy Information Administration. Industrial users in Puerto Rico currently pay an average of 14.6 cents/kW-hr compared to the national average of 6.54 cents/kW-hr.

Rate hikes averaging 26%BurnerMate Universal have been announced effective in 2017 for the island. With the new Preferred BMU controller, the forced draft fan VSD speed was kept under 30 Hz from low fire to mid-fire, resulting in electricity savings of over 85% compared to 60 Hz operation.

For more information on the BMU Boiler Control System, click here.

 


How much will you save?
Check out the Preferred Utilities Energy Savings Payback Calculator

Ever tried to justify a retrofit project? Now there’s a better way to crunch the numbers. This app will save you time and money. It analyzes your existing boiler and burner system data and compares it against a proposed modern upgrade, complete with energy savings estimates.

The calculation output in this application is extensive. It includes a fuel analysis, combustion efficiency (existing and projected), fuel consumption, electrical consumption, and C02 credit calculations. Use this tool if you are considering a boiler/burner upgrade.

Used for:

  • Boiler retrofits
  • Burner upgrades
  • Control upgrades
  • Energy auditing

Features:

  • Save your work
  • Recall past projects
  • Print your data
  • Compare Preferred equipment

Energy Saver Payback Tool

 

Combustion Theory

Introduction

Welcome to the Combustion blog series by Preferred Utilities Manufacturing Corporation. To read the introductory post, click here.

This series was inspired by Local Law 87, an environmental regulation passed by New York City legislators. LL87 seeks to reduce the city’s emissions by 50% while increasing the overall efficiency of large residential buildings (over 50,000 gross sq. ft.).

With additional state and local governments instituting similar environmental regulations across the United States, combustion system design and theory is more important now than ever.

Whether you’re a building owner, plant operator, building designer, or system engineer, this blog series will help you make informed decisions on your projects, especially as they pertain to LL87 and laws like it.

Why listen to us?

Because we’ve been doing combustion since 1920. Our rotary-style burners, invented in the 1960s, are still in operation all across New York City–almost half-a-century later.

But we’ve learned a lot since then.

We’re not like a lot of other burner companies. We don’t cut corners. Our products aren’t flimsy and they don’t come cheap. They last. And they perform.

Ultra low emissions. High efficiency. High turn down. Rugged durability. We reached for these marks because we believe in what we do. We love combustion. We love doing it right.

If this sounds like you, then read on.

Basics

The most common industrial fuels are hydrocarbons. This means that they are predominantly composed of carbon and hydrogen. Table 1 lists some common fuels and gives typical values for the hydrogen and carbon contents as percentages by weight. Note that there are some other components besides hydrogen and carbon. Some of these, such as sulfur, are combustible and will contribute to the heat released by the fuel. Other components are not combustible and contribute no positive energy to the combustion process.

Combustion Theory - the basics [table 2]

Table 1

The Chemistry

Table 2 reviews the basic chemical equations, which represent the most common combustion reactions. Note that nitrogen (N2) is shown on both sides of the equations. Except for the formation of NOx (in the parts per million range) nitrogen does not react in the combustion process. The nitrogen must be considered in fan sizing and stoichiometry calculations. Each atom of carbon in the fuel will combine with two atoms of oxygen (or one molecule of O2) from the atmosphere to form one molecule of CO2. On a weight basis, each pound of carbon requires 2.66 pounds of oxygen for complete combustion resulting in the production of 3.66 lb of carbon dioxide.

Combustion Theory - the basics [table 1]

Table 2

Each pair of hydrogen atoms (or each molecule of H2) will combine with one atom of oxygen (or one half molecule of O2) to form one molecule of H2O, or water. On a weight basis, each pound of hydrogen requires 7.94 pounds of oxygen for complete combustion, resulting in the production of 8.94 pounds of water.

By the Numbers

The air we breathe is only about 21% oxygen by volume. For all practical purposes, the remaining 79% is nitrogen. Since oxygen is a little heavier than nitrogen, the percentages by weight are somewhat different. The percentage of oxygen by weight is 23%, and the remaining 77% is nitrogen. Thus, it requires about 4.35 pound of air to deliver one pound of oxygen. Table 3 shows the composition of air.

Combustion Theory - the basics [table 3]

Table 3

A typical gallon of No. 6 fuel oil weighs 8 pounds and is 87% carbon and 12 % hydrogen (the missing percent is sulfur, ash, water and sediment). This gallon contains 6.95 pounds of carbon and 0.96 pound of hydrogen. From the data presented earlier, we can compute that 18.49 pounds of oxygen are needed to burn the carbon and 7.62 pounds of oxygen must be provided to burn the hydrogen in this gallon of fuel oil. This represents a total requirement of 26.11 pounds of oxygen. Since air is only 23% oxygen by weight, it will take 113.5 pounds of air (26.1 ÷ 0.23) for the complete and perfect (0% excess air) combustion of this gallon of fuel. Assuming there are 13 cubic feet of air to the pound, 1476 cubic feet of air are required to burn each gallon of fuel. A 50 gallon per hour burner (about 200 boiler HP) would need nearly 74,000 cubic feet of air per hour (or 1230 scfm) to fire without any allowance for excess air.

The Real World

In the real world, however, there must always be more air supplied to the combustion process than the theoretical or stoichiometric air requirement. This is because no burner made is this “perfect”. This “extra” air is referred to as “excess air.” If 20% more than the theoretical air requirement is supplied, we say that the burner is operating at 20% excess air. Another way of stating the same thing is to say that the burner is operating with 120% “total air.”

Complete combustion of our one gallon of No. 6 fuel oil with 20% excess air would require 136 pounds of air. The 50 gallon per hour burner would actually require about 90,000 cubic feet of air per hour.

For any particular burner-boiler combination, there is an ideal “minimum excess air” level for each firing rate over the turn-down range. Greater air flows would waste fuel because of the increased mass flow of hot gases leaving the stack. Lesser amounts of air would cause fuel waste because the fuel would not be burned completely. Typically, burners require much higher levels of excess air when operating near their minimum firing rates than they do at “high fire.” Table 4 shows a typical relationship between percent firing rate and the excess air required to insure complete combustion of the fuel. In many cases, even though stack temperature might decrease at low fire, efficiency suffers because so much of the fuel energy is lost to heat this excess air.

Combustion Theory - the basics [table 4]

Table 4

 

Other posts in this series:

  • Understanding Local Law 87 – and laws like it
  • Combustion Theory: The Basics
  • Combustion Theory: Variables – Account for variations in oxygen and fuel
  • Combustion Theory: Efficiency – Calculate efficiency and losses
  • Combustion Theory: FGR – See how flue gas recirculation reduces NOx
  • Combustion Theory: Combustion Controls – Learn how cutting-edge tech can cut your emissions
  • Combustion Systems: Design – Basic principles to follow when designing your combustion system
  • Combustion Systems: Troubleshooting: Burner problems and their causes
  • Combustion Control: Strategies – Linkage vs. Linkageless, and why you should care
 

Local Law 87 - NYCThe New Paradigm

What does Local Law 87 – and laws like it – mean for you?

With increasing regulatory effort to protect the environment, preserve energy, and reduce carbon emissions, states and cities have taken matters into their own hands by way of local legislation.

New York City’s Local Law 87 (LL87) mandates that buildings over 50,000 gross square feet undergo periodic energy audit and retro-commissioning measures, as part of the Greener, Greater Buildings Plan (GGBP).

The intent of this law, and laws like it, is to inform building owners of their energy consumption through energy audits. Energy auditors analyze a building’s energy use and aid in retro-commissioning, which is the process of ensuring correct equipment installation and performance. Ultimately, these audits will help make buildings more efficient.

Why this matters:

Environmental regulations like LL87  make the selection, design and maintenance of modern combustion systems extremely important.

This blog series will educate building owners, operators, and engineers affected by LL87 and laws like it. It will cover the basics of combustion theory, how to properly design a combustion system, and how to effectively control your combustion processes with modern technology.

By the conclusion of this series, you will be armed with the knowledge you need  to make informed decisions regarding your projects and efforts to meet these expected environmental regulatory requirements.


Combustion Terms

Combustion is the process by which the hydrogen and carbon in fuel is combined with oxygen from the air to release heat.

Byproducts include carbon dioxide, water vapor, left-over nitrogen from the air, and possibly unreacted oxygen and/or fuel components.

Combustion Control is the maintenance of the proper fuel and air flows into this process to produce the amount of heat energy required while consuming the least possible fuel and generating the lowest amount of pollution.

The following blog posts will contain further information regarding the combustion process as a whole. Among some of the topics we will cover:

  • Combustion Theory: The Basics
  • Combustion Theory: Variables – Account for variations in oxygen and fuel
  • Combustion Theory: Efficiency – Calculate efficiency and losses
  • Combustion Theory: FGR – See how flue gas recirculation reduces NOx
  • Combustion Theory: Combustion Controls – Learn how cutting-edge tech can cut your emissions
  • Combustion Systems: Design – Basic principles to follow when designing your combustion system
  • Combustion Systems: Troubleshooting: Burner problems and their causes
  • Combustion Control: Strategies – Linkage vs. Linkageless, and why you should care

 

 
SCADA Preferred Utilities

SCADA System by Preferred Utilities

SCADA stands for Supervisory Control and Data Acquisition system. It is a type of industrial control system (ICS), which is basically a computer system designed to monitor industrial processes in the real world. But unlike other industrial control systems, SCADA systems can compute multiple sets of data over long distances.

The primary benefit of a SCADA system is the ability to see a visual representation of a complex system. This screen allows the user to see what their application is doing at any given time, while also providing increased control over the entire system.

Another benefit of a SCADA system is its versatility. Practical applications of SCADA can be found in HVAC, water treatment, and power generation facilities. Each SCADA system can be specifically configured for a wide variety of scenarios–if you think it up, we will build it.

One of the unique characteristic of a SCADA system is its ability to withstand temperature, vibration, and voltage extremes. This factor allows it to be placed in almost any HVAC or process plant without fear of breakage.

Preferred Utilities started installing SCADA systems in 1982–that’s over 25 years of experience. We’ve installed them on thousands of burners and hundreds of process plants. Today, we lead the industry as a trusted supplier of cutting-edge SCADA systems designed to meet the standards of the modern energy industry.

To learn more about the SCADA system and how we can help you get the right results in your facility, visit the product page here.

 

2015 was an exciting year for us at Preferred Utilities. We launched a series of new online engineering tools, we released the new Flexible System Controller (FSC), and we saw several of our engineers published in energy industry trade magazines.

To cap off the year, we attended the Power-Gen International trade show in Las Vegas, NV. The show featured a new 20×20 island booth and a never-before-seen video highlighting Preferred Special Combustion Engineering.

 

Take a look at the video below for an insight into Preferred’s many combustion capabilities:

 

 

Writing a Spec? Gotta Retrofit?

Try these tools.

Finally, there’s a better way to manage your projects thanks to Preferred Utilities’ Web Applications. We designed these free tools with engineers in mind – and they’re meant to be your shortcut to success.

Pipe Sizing Calculator

The Preferred Pipe Sizing Calculator has returned! A long-time favorite used by engineers
everywhere, we’ve repackaged this program for web and mobile use. With it, you’ll be able to calculate the pipe sizes for your customized fuel system.

If your project involves fuel systems for data centers, generators, or boilers, this tool will help you get the right results.

EnergySaver Payback Analysis

EnergySaver

EnergySaver Payback Analysis

Ever tried to justify a retrofit project? Now there’s a better way to crunch the numbers. This app will save you time and money. It analyzes your existing boiler and burner system data and compares it against a proposed modern upgrade, complete with energy savings estimates.

The calculation output in this application is extensive. It includes a fuel analysis, combustion efficiency (existing and projected), fuel consumption, electrical consumption, and C02 credit calculations. Use this tool if you are considering a boiler/burner upgrade.

Fuel Load Calculator

Tested by our proven engineers, this app calculates the total fuel tank capacity required for your emergency generator fuel system.

If you know the runtime and the number of generators in your system, you’re good to go. We’ve handled the guesswork and added our recommendations for ullage, drop tube gap, and generator testing.

Fuel Oil System Specification Configurator [Coming Soon]

What would you say if there was a program that could write fuel oil specifications for you? This app will do just that.

Just take a minute to answer our questions and we’ll create a custom specification for your fuel system job. You’ll be able to take charge of your project and adapt this specification to your needs. We’ve included recommendations for line sizes, pumps, and strainer selections. Feel free to save your project. You can come back to it at any time for an updated specification. No other tool offers this much flexibility.

We hope you’ll get comfortable with these tools and use them for your current projects. And don’t worry – you’ll be able to save all of your data and return to it whenever you like. For your convenience, we’ve optimized most of these apps for PC, tablet, and mobile viewing.

Be sure to check back for future applications, because this is just the beginning.

But enough talking – let’s get results!

P.S. – Got an idea for a future web application? We’d love to hear from you!

 

 

 
Automatic Fuel Oil Transfer Pump Set (ATPSF)

Automatic Fuel Oil Transfer Pump Set (ATPSF)

The Automatic Transfer Pump Set (ATPSF) is one of our best-selling products. Our customers love it for its reliability and rugged industrial construction. We consistently beat out our competitors because we build our products out of the highest-quality components. Behind each of our systems, you will find a team of engineers and technicians who are dedicated to getting you the best results possible. People. Products. Results.

Thanks to our new Flexible System Controller (FSC), we have added several exciting features to our  ATPS:

1. Redundant Communication

The FSC is masterless, and uses dual redundant, optically-isolated RS485 cables. RS485 cables eliminate hubs, switches, and repeater failure modes. Because both NodeNet cables communicate continuously, one cable can go down while the other continues communicating with no interruption. If any node fails, all the other nodes will continue to function.

As far as we are aware, Preferred Utilities is the only manufacturer offering this multiple failure backup system.

Sample System Diagram

Sample System Diagram

2. Faster Troubleshooting

FSC OIT Screen

FSC OIT Screen

Another feature of NodeNet communications is that it allows the operator to control or view any device, status, or alarm anywhere in the system from any touchscreen in the network. Because operators can see both digital and analog inputs and outputs from anywhere in the system, troubleshooting becomes streamlined, and much faster than it would be otherwise.

3. Distributed Controls

NodeNet communications provide the additional advantage of distributed control. The NodeNet system employs multiple distributed modular controllers, which are hard-wired to local devices. Even if both NodeNet cables are lost, local automatic control will continue. This modular aspect of NodeNet allows for maximum mission critical reliability.

4. Reduced Wiring Costs

The NodeNet communications network can reduce wiring cost significantly. The average number of wires per day tank (14 home runs) can be reduced to as little as 2 redundant communication cables in a loop between FSCs.

Distributed Controls

 

Preferred Featured in Today's Boiler

 

The Spring 2015 edition of Today’s Boiler magazine published Dr. Jianhui Hong’s article “NOx Emissions Reduction Strategies.” In the article Dr. Hong explains the importance of low NOx and provides solutions for complying with low NOx emissions regulations.

He explains that “NOx is a term used to include two important air pollutants: NO (nitric oxide) and NO₂ (nitrogen dioxide). These pollutants are sometimes called mono-nitrogen oxides…NOx is a term used to include two important air pollutants: NO (nitric oxide) and NO₂ (nitrogen dioxide). These pollutants are sometimes called mono-nitrogen oxides.”

NOx gases are harmful in a number of ways. Exposure to NOx gases is harmful to human health by irritating the mucous membranes and penetrating the lungs, “causing oxidizing damage to the tissues.”

When NOx reacts with water or water vapor, “it forms nitrous acid (HNO₂) and nitric acid (HNO₃). These acids in the rain can make ‘acid rain.’ Acid rain can damage plants and man-made structures such as buildings, bridges, and outdoor sculptures.”

In highly populated areas, “NOx emissions from combustion processes are primarily in the form of NO. In the air, NO reacts with oxygen to produce NO₂. In the presence of sunlight, NOx can react with hydrocarbons, especially VOC (volatile organic compounds) in the air to form ground-level ozone, which is an important ingredient of smog. The reddish brown color of the hazes hanging over the skies of some major cities comes from NO₂ gas… It can cause irritation to eyes, noses, throats, and lungs. It can even cause asthma and other chronic lung diseases such as emphysema and chronic bronchitis.” NOx can also combine with moisture in the air which “induces changes in phytoplankton and produces toxic brown or red algal blooms (i.e. “red tides”). The algal blooms can cause the death of other plants and marine animals in the water.

Thermal NOx, Fuel NOx, and Prompt NOx create the conditions for NOx emission.

Dr. Hong presented five solutions for the combustion community to reduce NOx emissions.

  • Flue Gas Recirculation “targets the thermal NOx by reducing the peak flame temperature and also oxygen concentration…The use of external FGR increases the requirements for the combustion fan” which “become a significant factor in the overall costs of the burners (including fixed costs and operating costs).”
  • Steam/water injection “works similarly to external FGR. It targets thermal NOx by reducing peak flame temperature and oxygen concentration.”
  • Ultra lean premixing “aims to reduce the flame temperature by staying away from stoichiometric condition. Ultra Lean Premixing, if used alone, has the downside of high oxygen level (up to 9%) in the flue gas, and the loss of fuel efficiency due to the very high excess air.”
  • Air Staging supplies combustion air in two or more stages. “The general goal is to reduce flame temperature, and create fuel rich conditions in the early stages, before the final stage of air is supplied.”
  • Fuel Staging supplies fuel in two or more stages. “The general goal again is to reduce peak flame temperature. This technique is often combined with Ultra Lean Premixing to overcome the efficiency issue of the latter.”

In conclusion, Dr. Hong cites that although NOx emissions can be controlled by the mentioned techniques, “the most cost-effective methods tend to be combustion modifications, especially using low NOx and ultra-low NOx burners.”

Dr. Hong’s greatest contribution to the combustion community is his ability to present solutions for common problems in the industry and the stringent regulations placed on emissions.

Read the full article here.