Engineering Data
Engineering Publication by Preferred Instruments
Useful Combustion Engineering Data
Combustion Theory
In light of the continued rise in fuel and labor costs, a good understanding of basic combustion theory is more important today than ever before. Click on the link below to find out more about the Combustion Theory.
Combustion System Design
A good, well thought design is an important aspect in creating a long lasting Combustion System. Click the link below to find out more about how to design your combustion system properly.
Combustion Control Strategies
Not sure which control strategy will be best for your application? Click the link below to learn more about advantages and disadvantages of each control strategies: Single Point Positioning, Parallel Positioning, and Fully Metered Combustion Control.
Combustion Control Strategies.PDF
Efficiency Calculation
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Conservation of Energy
- Fuel energy “in” equals heat energy “out”
- Energy leaves in steam or in losses
- Efficiency = 100% minus all losses
Typical boiler efficiency is 80% to 85%
- The remaining 15% to 20% is lost
- Largest loss is a typical 15% “stack loss”
- Radiation loss may be 3% at full input
- Miscellaneous losses might be 1 to 2%
Rules of Thumb To Approximate Operating Cost
- Cost of Fuel = $6.25 per thousand lbs. Of steam per hour (based on gas @ $5/thousand Cu. Ft.)
- Normal firing hours per year = 8500
- 10% reduction in excess air = 1% reduction in fuel input
- On a packaged water tube boiler, each on-off cycle costs an additional $.50 per thousand pounds of maximum boiler rating (based on heat losses during purge and increased maintenance)
- Horsepower cost = $333.00 per horsepower per year (based on electricity cost of $.05/KW hr)
Combustion Efficiency Table
Combustion Efficiency (#2 Oil)
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Efficiency = (Heat Added to Incoming Feedwater) / Heat Input (Fuel)
Fuel Oil Rate Of Boilers Operating At 80 % Efficiency
No. 1 Oil average equals 31.4 gallons per hour per 100 horsepower
No. 2 Oil average equals 30.0 gallons per hour per 100 horsepower
No. 4 Oil average equals 28.9 gallons per hour per 100 horsepower
No. 5 Oil average equals 28.1 gallons per hour per 100 horsepower
No. 6 Oil average equals 27.5 gallons per hour per 100 horsepower
Combustion Efficiency (Natural Gas)
)
Efficiency = (Heat Added to Incoming Feedwater) / Heat Input (Fuel)
Fuel Oil Rate Of Boilers Operating At 80 % Efficiency
No. 1 Oil average equals 31.4 gallons per hour per 100 horsepower
No. 2 Oil average equals 30.0 gallons per hour per 100 horsepower
No. 4 Oil average equals 28.9 gallons per hour per 100 horsepower
No. 5 Oil average equals 28.1 gallons per hour per 100 horsepower
No. 6 Oil average equals 27.5 gallons per hour per 100 horsepower
Combustion Efficiency (#6 Oil)
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Efficiency = (Heat Added to Incoming Feedwater) / Heat Input (Fuel)
Fuel Oil Rate Of Boilers Operating At 80 % Efficiency
No. 1 Oil average equals 31.4 gallons per hour per 100 horsepower
No. 2 Oil average equals 30.0 gallons per hour per 100 horsepower
No. 4 Oil average equals 28.9 gallons per hour per 100 horsepower
No. 5 Oil average equals 28.1 gallons per hour per 100 horsepower
No. 6 Oil average equals 27.5 gallons per hour per 100 horsepower
Multiple Boiler Header Pressure or Temperature Control Recommendation
| Boilers Type | Boiler Horsepower (Bhp) | Steam lbs/hr | Control Arrangement |
|---|---|---|---|
| On/Off | 1 | 0.033 | Lead/Lag Control |
| 5 | 3467 | ||
| 10 | 0.335 | ||
| 20 | 0.67 | Modulating Lead/Lag Control |
|
| Cast Iron | 50 | 1.674 | |
| Fintube | 100 | 3.348 | |
| 200 | 6.696 | ||
| Firebox | 300 | 10.044 | |
| 500 | 16.739 | ||
| Firetube | 600 | 20.087 | |
| 800 | 26.783 | ||
| Watertube | 1000 | 33.479 | |
| 1500 | 50.218 | ||
| Watertube | 2000 | 66.958 | Plant Master Control |
| 4000 | 133.915 | ||
| 6000 | 200.873 | ||
| 8000 | 267.83 | ||
| 10000 | 334.788 | ||
| 20000 | 669.576 |
| Lead/Lag Control: | Multiple boiler “on/off” operation is automatically established to satisfy the overall plant hot water or steam demand. Automatic sequencing ensures that the number of boilers in service meets hot water or steam demand. Tripped equipment is automatically replaced with a standby unit. |
| Modulating Lead/Lag Control: | Multiple boiler firing rates and “on/off” operation are automatically adjusted to satisfy the overall plant hot water or steam demand. Either unison (parallel) or series modulation is used. |
| Plant Master Control: | Multiple boiler firing rates are automatically adjusted to satisfy the overall plant hot water or steam demand. Either unison (parallel) or series modulation is used. |
Firing Rate Control Selection Recommendations
For selection recommendation by Application, Click Here
For selection recommendation b y Boiler Type, Click Here
Notes:
- Jackshaft Positioning type systems are a good choice for boilers smaller than 200 Bhp. When there is difficulty installing jackshaft linkage or a FD Fan Variable Speed Drive (VSD) or Oxygen trim is included, a parallel positioning system should be selected.
- Fully Metered type systems are a good choice for boilers larger than 600 Bhp (20 kpph). Fully Metered Systems with Oxygen trim measure and control air flow, fuel flow and flue gas Oxygen to minimize excess air.
When selecting a combustion control system, consider safety first, then control system cost vs. operating cost trade-offs.
Boiler Size Terminology
| Boiler Horsepower (Bhp) (output) | Heat Mbtu/hr (output) | Steam lbs/hr (output) | Electrical Power (MW) (output) | Natural Gas ft3/hr (input) | #2 Fuel Oil gal/hr (input) |
|---|---|---|---|---|---|
| 1 | 0.033 | 34.5 | 39.86 | 0.28 | |
| 5 | 0.167 | 172.5 | 199.28 | 1.42 | |
| 10 | 0.335 | 345.0 | 398.56 | 2.85 | |
| 20 | 0.670 | 690.0 | 797.11 | 5.69 | |
| 50 | 1.674 | 1,725.0 | 1,992.79 | 14.23 | |
| 100 | 3.348 | 3,450.0 | 0 | 3,985.57 | 28.47 |
| 200 | 6.696 | 6,900.0 | 1 | 7,971.14 | 56.94 |
| 300 | 10.044 | 10,350.0 | 1 | 11,956.71 | 85.41 |
| 400 | 13.392 | 13,800.0 | 1 | 15,942.29 | 113.87 |
| 500 | 16.739 | 17,250.0 | 2 | 19,927.86 | 142.34 |
| 600 | 20.087 | 20,700.0 | 2 | 23,913.43 | 170.81 |
| 700 | 23.435 | 24,150.0 | 2 | 27,899.00 | 199.28 |
| 800 | 26.783 | 27,600.0 | 3 | 31,884.57 | 227.75 |
| 900 | 30.131 | 31,050.0 | 3 | 35,870.14 | 256.22 |
| 1000 | 33.479 | 34,500.0 | 3 | 39,855.71 | 284.68 |
| 1100 | 36.827 | 37,980.0 | 4 | 43,841.29 | 313.15 |
| 1200 | 40.175 | 41,400.0 | 4 | 47,826.86 | 341.62 |
| 1300 | 43.522 | 44,850.0 | 4 | 51,812.43 | 370.09 |
| 1400 | 46.870 | 48,300.0 | 5 | 55,798.00 | 398.56 |
| 1500 | 50.218 | 51,750.0 | 5 | 59,783.57 | 427.03 |
| 2000 | 66.958 | 69,000.0 | 7 | 79,711.43 | 569.37 |
| 4000 | 133.915 | 138,000.0 | 14 | 159,422.86 | 1,138.73 |
| 6000 | 200.873 | 207,000.0 | 21 | 239,134.29 | 1,708.10 |
| 8000 | 267.830 | 276,000.0 | 28 | 318,845.71 | 2,277.47 |
| 10000 | 334.788 | 345,000.0 | 35 | 398,557.14 | 2,846.84 |
| 20000 | 669.576 | 690,000.0 | 69 | 797,114.29 | 5,693.67 |
Chart data is based on a steam enthalpy of 970.4 Btu/lb and boiler efficiency of 80% when firing natural gas and 84% when firing oil.
Boiler Horsepower: A boiler horsepower is the evaporation of 34.5 lbs. of water per hour at a temperature of
212° F. and a pressure of 14.7 psia into dry saturated steam at the same temperature and pressure. The term “boiler horsepower” started because early boilers were used to drive engines with one engine horsepower.
RULES OF THUMB
Boiler Horespower
- 10,000 PPH Steam Output = 300 Boiler HP Developed
- Developed HP / 200 = GPM Fuel Oil Burned
- Developed HP x 45 = CFH Natural Gas Burned
- Developed HP x 9 = CFM Combustion Air Required (20% Excess Air)
- Developed HP x 20 = CFM Hot Flue Gases (580° F) Used for Sizing I.D. Fan (20% E.A.)
Flow Meter Piping Requirements
Flow Meter Piping Requirements
Instrument Installation Details
- Boiler Drum Level Transmitter Installation Details
- Pressure Transmitter Installation Details
- Boiler Outlet Draft Control Transmitter Installation Details
- Orifice Plate Installation Details for Horizontal Liquid Pipes with Flange Taps
- Orifice Plate Installation Details for Horizontal Steam Pipes with Flange Taps
Typical Burner System Arrangements
Click on the following links to view the Burner System Arrangements:
- Typical Main Burner Fuel Supply System for Fuel Gas-Fired Multiple Burner Boiler
- Typical Fuel and Atomizing Medium Supply Systems and Safety Controls for Oil Burner
- Typical Fuel Supply System and Safety Controls for Gas Burner
- Typical Ignition Systems for Gas or Oil-Fired Burner
- Typical Steam or Air Atomizing Main Oil Burner System
Unit Conversion Tables
Pressure or Force Per Unit Area
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Power or Rate of Doing Work
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Boiler Horsepower and Quantity of Fuel Oil Burned
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Electrical Formulas
W = Power (Watts)
E = Voltage (Volts)
I = Current (Amperes)
R = Resistance (Ohms)
Electrical Units
- Volts: The units of electrical motive force. Force required to send one ampere of current through one ohm of resistance.
- Ohms: The units of resistance. The resistance offered to the passage of one ampere, when impelled by one volt.
- Amperes: The units of current. The current which one volt can send through a resistance of one ohm.
- Watts: The unit of electrical energy or power, and is the product of one ampere and one volt. That is, one ampere of current flowing under a force of one volt gives one watt of energy.
- Volt Amperes: The product of the volts and amperes as shown by a voltmeter and ammeter. In direct current systems, this is the same as watts (energy delivered). In alternating current systems, the volts and amperes may or may not lie in step. When in step, the volt amperes equal the watts shown directly on a wattmeter. When out of step, volt amperes exceed watts.
- Kilovolt Ampere: One kilovolt ampere (KVA) is equal to 1,000 volt amperes.
- Power Factor: The ratio of watts to volt amperes.
- Farad: The unit of capacity of a condenser charged to the potential of one volt by one ampere of electricity per second.
- Micro-Farad (Mfd): Equal to 1/100,000,000th part of a Farad.
Electric Consumption
The cost to run electric auxiliaries should not be overlooked when considering the total cost to run a facility. The cost of electric auxiliaries can be found by determining the Kilowatt - hours used and your cost per kilowatt - hour. The following are some "rule of thumb" relationships:
One Horsepower of Electricity is equal to 0.746 kilowatt-hours.
A 1 H.P. motor running at full load for 24 hours would use 17.90 Kilowatt-hours of electricity.
Boiler Emissions
Units of Measurement
Emission levels can be presented in many different units depending on whether the measurement is volume or mass based.
| PPM | Parts per Million - Indicates emission levels on a volume basis. Sometimes may be shown as ppmv. Part per million must be referenced and corrected to some oxygen level (excess air level) which, for industrial boilers, is typically 3% oxygen. Actual measurements recorded during boiler testing are usually in ppm. |
| lb/MMBtu | Pounds per Million Btu - Indicates emission levels on a mass basis. Emission levels are shown in pounds of pollutant per million Btu input. This level is useful when hourly or annual emission levels must be determined. |
| TPY | Tons per Year - Indicates emission levels on a mass basis. This unit corresponds to the annual pollutant levels. |
Correcting Emissions to 3% Oxygen
The following equation shows how to correct emission readings to 3% oxygen. Because boilers do not always operate at 3% oxygen, it is necessary to convert ppm values measured at various excess air levels to 3% oxygen for comparison and regulation compliance purposes. To correct emission levels to 3% oxygen that are referenced to excess air levels other than 3%, use the following equation:
ppm (@3%) = (21-3/21-O2 (actual)) x ppm (actual)
Example: What is the NOx level corrected to 3% oxygen for a measured level of 27 ppm at 7.1% oxygen?
ppm (@3%) = (21-3/21-7.1) x 27 = 35 ppm NOx
Converting Emissions
Between PPM & lb/MMBtu
Although emission levels can be given in many different units, the most common are ppm (corrected to 3% oxygen) and lb/MMBtu. Conversion between these two types of units is very simple, however, it does depend on the fuel type and excess air level.
NOx Emissions Conversions at 3.0% O2
#2 & #6 Oil
ppm = (lbs/MMBtu) x 750
lbs/MMBtu = ppm/750
Nat Gas
ppm = (lbs/MMBtu) x 850
lbs/MMBtu = ppm/850
CO Emissions Conversions at 3.0% O2
#2 Oil
ppm = (lbs/MMBtu) x 1290
lbs/MMBtu = ppm/1290
#6 Oil
ppm = (lbs/MMBtu) x 1260
lbs/MMBtu = ppm/1260
Nat Gas
ppm = (lbs/MMBtu) x 1370
lbs/MMBtu = ppm/1370
Combustion Data
Common fuels are classified as hydrocarbons meaning that they are predominantly composed of varying amounts of carbon and hydrogen.
Typical Analysis of Common Fuels–Percent by Weight
| #2 Fuel Oil | #6 Fuel Oil | Natural Gas | Coal | |
|---|---|---|---|---|
| Hydrogen (H2) | 12.6 | 9.7 | 23.5 | 5.0 |
| Carbon (C) | 87.3 | 87.1 | 75.2 | 75.0 |
| Sulfur (S) | 0.1 | 0.3 | --- | 2.3 |
| Nitrogen (N2) | 0.02 | 0.5 | 1.3 | 1.5 |
| Oxygen (O2) | --- | 1.5 | --- | 6.7 |
| Ash | --- | 0.2 | --- | 7.0 |
| Water (H2O) | --- | 0.2 | --- | 2.5 |
Combustion is a rapid chemical reaction that combines the fuel constituents and air to release heat, light, and by-products.
By-products of Combustion
| #2 Fuel Oil | Btu/hr Released | Natural Gas | |
|---|---|---|---|
| Hydrogen | (H2O) Water | 61,100 | 8.94 Ibs H2O |
| Carbon | (CO2) Carbon Dioxide | 14,100 | 3.66 Ibs CO2 |
| Carbon | (CO) Carbon Monoxide | 4,000 | 2.09 Ibs CO |
| Carbon Monoxide | (CO2) Carbon Dioxide | 4,345 | 1.57 Ibs CO2 |
| Sulfur | (SO2) Sulfur Dioxide | 3,980 | 2.0 Ibs SO2 |
Combustion Rules of Thumb
- Standard air @ sea level and 70° F = 0.07495 lbs/ft3
- 1 lb of standard air @ sea level and 70° F = 13.34 ft3
Required Air For Combustion
(no excess air)
- lbs. air/lb. natural gas = 17.5
- lbs. air/lbs. oil = 14.0
- lbs. air/lbs. coal = 12.0
- lbs. air/mmBtu. oil = 750
- lbs. air/mmBtu. nat gas = 720
- Required air for combustion increases 4.0% for every 1000 ft. above sea level
- lbs./hr. air = (SCFM) X 4.5 @ 70° F.
- Required air for combustion in CFM increases 1.9% for every 10° above 70° F.
Changes in combustion air temperature directly affect the pounds of combustion air supplied to the burner and will increase or decrease the excess air level. The table below shows how changes in temperature change the excess air level for a fixed damper position and fan speed.
| Air Temp | lbs/cu.ft. | CFM | Ibs Air/hr | O2 (dry) | Excess Air % |
|---|---|---|---|---|---|
| 40° F | .0795 | 2600 | 12,402 | 5.3 | 31 |
| 60° F | .0764 | 2600 | 11,922 | 4.4 | 26 |
| 70° F | .07495 | 2600 | 11,700 | 4.0 | 24 |
| 80° F | .0736 | 2600 | 11,489 | 3.6 | 21 |
| 100° F | .0710 | 2600 | 11,068 | 2.9 | 17 |
| 120° F | .0686 | 2600 | 10,694 | 2.2 | 13 |
Properties of Saturated Steam & Saturated Water
Properties of Saturated Steam & Saturated Water table