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Combustion & Flue Gas Analysis 1 December 2006 Excellence in measurements Combustion and Flue Gas Analysis

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Page 1: Combustion and Flue Gas Analy

Combustion & Flue Gas Analysis 1December 2006

Excellence in measurements

Combustion

and

Flue Gas Analysis

Page 2: Combustion and Flue Gas Analy

Combustion & Flue Gas Analysis 2December 2006

Excellence in measurements

Summary

� Combustion Theory

� Fuels

� Combustion with Methane / Natural Gas

� Combustion in practice

� Flue Gases

� Boilers

� Loss & Efficiency

� Regulations

Page 3: Combustion and Flue Gas Analy

Combustion & Flue Gas Analysis 3December 2006

Excellence in measurements

Combustion

Combustion or burning is a chemical process, an exothermic reaction between a substance (the fuel) and a gas (the oxidizer), usually O2, to release thermal energy (heat), electromagnetic energy (light), mechanical energy (noise) and electrical energy( free ions and electrons ). In a complete combustion reaction, a compound reacts with an oxidizing element, and the products are compounds of each element in the fuel with the oxidizing element. For example:

CH4 + 2 O2 → CO2 + 2 H2O + Heat ( +light/noise/ions )

Fuel Gas

Page 4: Combustion and Flue Gas Analy

Combustion & Flue Gas Analysis 4December 2006

Excellence in measurements

FuelsFuels composition

Most fuels are mixtures of chemical compounds called hydrocarbons ( combinations of hydrogen H2 and carbon C ).Fuels are available as gaseous, liquid and solid.

Solid fuelsSolid natural fuels include Coal, Peat, Lignite and Wood.Solid artificial fuel is Coke derived from Coal. High contents of Sulphur and Ash.

Liquid FuelsLiquid fuels are processed at refineries from Petroleum.Light, medium and Heavy Fuel Oil, Gasoline and Kerosene are the most common used.

Gaseous FuelsNatural gas is a gaseous natural fossil fuel consisting primarily of methane. It is found in oil fields and natural gas fields. Town gas is manufactured from Coal ( half calorific value of Natural gas ).LPG ( Liquid Propane Gas ) is manufactured from Petroleum and usually supplied in pressurized steel bottles ( cooking is a typical application ).Gaseous fuels include also Coke oven gas and Blast furnace gas.

Page 5: Combustion and Flue Gas Analy

Combustion & Flue Gas Analysis 5December 2006

Excellence in measurements

Calorific Power

The principal characteristic of a fuel is his power calorific. This represents the

amount of heat developed in the reaction of combustion in conditions predefined

standard. Generally is measured in kcal/kg for the solid and liquid, while for the

gases is expressed with kcal/m3. In many fuels, that contain hydrogen, has

distinguished a superior calorific power (that it includes the heat of condensation of

the water vapor that shape in the combustion) and a inferior calorific power (than it

does not consider such heat).

Inferior calorific power of some fuel (p.c.i.)

Fuel p.c.i. (kcal/kg - kcal/m3)

Firewood to burn 2500 - 4500 Diesel oil 10200

Peat 3000 – 4500 Benzine for car 10500

Firewood coal 7500 LPG 11000

Lignite 4000 - 6200 Natural gas 8300

Coke 7000 Coke oven gas 4300

Fuel oil 9800 Blast furnace gas 900

Page 6: Combustion and Flue Gas Analy

Combustion & Flue Gas Analysis 6December 2006

Excellence in measurements

Combustion

Complete combustion

In complete combustion, the reactant will burn in oxygen, producing a limited number of products. When a hydrocarbon burns in oxygen, the reaction will only yield carbon dioxide andwater. When elements such as carbon, nitrogen, sulfur, and iron are burned, they will yield the most common oxides. Carbon will yield carbon dioxide. Nitrogen will yield nitrogen dioxide. Sulfur will yield sulfur dioxide. Iron will yield iron(III) oxide. Complete combustion is generally impossible to achieve unless the reaction occurs where conditions are carefully controlled (e.g. in a lab environment).

Fuel + Oxygen → Heat + Water + Carbon dioxide.

Page 7: Combustion and Flue Gas Analy

Combustion & Flue Gas Analysis 7December 2006

Excellence in measurements

CombustionCombustion Stoichiometry ( Theoretical )

If sufficient oxygen is available, a hydrocarbon fuel can be completely oxidized, the carbon is converted to carbon dioxide (CO2) and the hydrogen is converted to water (H2O).During combustion, each element reacts with Oxygen to release heat :

C + O2 -> CO2 + Heat H2+ ½ O2 -> H20 + Heat

Pure Oxygen is rarely available so Air is mainly used for combustion. It contains 21 percent of Oxygen O2 and 79 percent of Nitrogen N2.

A complete burning, with nothing but Carbon Dioxide, Water, and Nitrogen as the end products is known as the stoichiometric combustion.

The stoichiometric air/fuel ratio refers to the proportion of air and fuel presentduring a theoretical combustion.

The heat released when the fuel burns completely is known as the heat of combustion

Page 8: Combustion and Flue Gas Analy

Combustion & Flue Gas Analysis 8December 2006

Excellence in measurements

Combustion

Practical Combustion ( Excess of Air – λ Lambda )Due to fluctuations in fuel flow and the lack of perfect mixing between fuel and air in the combustion zone, excess air is required to achieve more complete combustion of the fuel.

Without this extra air, the formation of partial products of combustion such as carbon monoxide and soot may occur. However, supplying too much excess air will decrease combustion efficiency and a balance between too much air and not enough air must be

maintained.

Page 9: Combustion and Flue Gas Analy

Combustion & Flue Gas Analysis 9December 2006

Excellence in measurements

Fuels : Methane ( Natural Gas )

Discovered by Alessandro Volta in 1778

The simplest hydrocarbon, methane, is a gas with

a chemical formula of CH4.

Pure methane is odorless, but when used

commercially is usually mixed with small

quantities of odorants, strongly-smelling sulfur

compounds to enable the detection of leaks.

Autoignition Temperature : 537°C

Explosive limits : 5%-15%

Calorific Power inferior: 8500 kcal/m3

Calorific Power superior: 9400 kcal/m3

Page 10: Combustion and Flue Gas Analy

Combustion & Flue Gas Analysis 10December 2006

Excellence in measurements

Combustion of Methane

CH4 + O2 => CO2 + H2O + Heat

CH4 + 2 O2 => CO2 + 2 H2O + Heat

Theoretical with pure O2

1 m3 CH4 + 2 m3 O2

=> 1 m3 CO2 + 2 m3 H2O + Heat

Page 11: Combustion and Flue Gas Analy

Combustion & Flue Gas Analysis 11December 2006

Excellence in measurements

Combustion of Methane

Air : 21% O2 + 79% N2

Theoretical with Air

1 m3 CH4 + ( 2 m3 O2 + 7,52 m

3 N2 )

1 m3 CO2 + 2 m3 H2O + 7,52 m

3 N2

+Heat

Page 12: Combustion and Flue Gas Analy

Combustion & Flue Gas Analysis 12December 2006

Excellence in measurements

• For a complete burning of 1 m3 of Methane

you need 9.52 m3 ( 2+7,52 ) of air ( Stoichiometric ).

• It develops 10.52 m3 ( 1+2+7,52 ) of wet flue gases.

• It develops 8.52 m3 ( 10.52 less 2 H20 ) of dry flue gases.

• 1 m3 of Carbon Dioxide CO2 is generated each 1 m3 of Methane.

On dry flue gas contents is 11.7% ( 1 m3 1/ 8.52 m3).

• Oxygen is not present in flue gases ( Stoichiometric ).

Combustion of Methane

1 m3 CH4 + ( 2 m3 O2 + 7,52 m

3 N2 )

⇒ 1 m3CO2 + 2 m3 H2O + 7,52 m

3 N2 +Heat

Theoretical with Air

Page 13: Combustion and Flue Gas Analy

Combustion & Flue Gas Analysis 13December 2006

Excellence in measurements

• You use for burning 1 m3 of Methane 14.28 m3 ( 2+1+3,76+7,52 ) of air.

• It develops 15.28 m3 ( 1+2+1+11,28 ) of wet flue gases.

• It develops 13.28 m3 ( 15.28 – less 2 H20 ) of dry flue gases.

• 1 m3 of Carbon Dioxide CO2 is generated each 1 m3 of Methane. On

dry flue gas contents is 7.5% ( 1 m3 / 13.28 m3).

• Oxygen is 7.5% ( 1 m3 / 13.28 m3)

Combustion of Methane

1m3 CH4 + (2 m3 O2 + 7,52 m

3 N2) + (1 m3 O2 + 3,76 m

3N2)

Theoretical Air Excess of Air

=> 1 m3 CO2 + 2 m3 H2O + 1 m

3 O2 + 11,28 m3 N2 +Heat

Practical – Excess of Air

Page 14: Combustion and Flue Gas Analy

Combustion & Flue Gas Analysis 14December 2006

Excellence in measurements

• Theoretically you use 9.52 m3 ( 2+7,52 ) of air ( Stoichiometric ).

• Practically you use 14.28 m3 ( 2+1+3,76+7,52 ) of air.

• Lambda = Volume (Practical Air / Theoretical Air) =14.28/9.52= 1.5

• Excess of Air = ( Lambda – 1 ) * 100 = ( 1,5 – 1 ) * 100 = 50%

• Excess of Air measured from O2 ( 7.5% )

= %O2 measured * 100 / ( 20.9 - %O2 measured ) x Coeff KL= 50%

• To little excess of air is inefficient because it permits unburned fuel, in

the form of combustibles, to escape up the stack. But too much excess

of air is also inefficient because it enters the burners at ambient

temperature and leaves the stack hot, thus stealing useful heat from

the process. “Maximum combustion efficiency is achieved when the

correct amount of excess of air is supplied so that the sum of both

unburned fuel loss and flue gas heat loss is minimized”.

Combustion of MethanePractical – Excess of Air

Page 15: Combustion and Flue Gas Analy

Combustion & Flue Gas Analysis 15December 2006

Excellence in measurements

• The carbon dioxide concentration in the flue gas gives and clear

indication of the quality ( efficiency ) of the burner.

Is the proportion of CO2 is as high as possible with a small excess air,

the flue gas losses are at their lowest.

The maximum CO2 concentration on flue gas depends only on carbon

content of the fuel burned.

Carbon Dioxide – CO2

Fuel % CO2 max

Methane/Natural gas 11.7

LPG 13.9

Oil 15.7

Methane is the fuel that produces less quantity of CO2.

Page 16: Combustion and Flue Gas Analy

Combustion & Flue Gas Analysis 16December 2006

Excellence in measurements

Combustion in practice

• To obtain the most efficient combustion you need a

slight excess of air

• Flue gas volume will be more than theoretical

combustion ( stoichiometric ).

• Carbon dioxide will be less than maximum

achievable ( CO2 max )

• Oxygen will be always present in flue gas.

Page 17: Combustion and Flue Gas Analy

Combustion & Flue Gas Analysis 17December 2006

Excellence in measurements

Combustion in practice

Reduce as much as you can the Excess of Air to reach the

maximum level of Carbon Dioxide CO2

Pay attention to Carbon Monoxide CO level!

Page 18: Combustion and Flue Gas Analy

Combustion & Flue Gas Analysis 18December 2006

Excellence in measurements

Combustion in practice

Carbon Monoxide is the result of incomplete

combustion.

This could mean a a deficiency of air at the

burner.

Page 19: Combustion and Flue Gas Analy

Combustion & Flue Gas Analysis 19December 2006

Excellence in measurements

Carbon Monoxide - CO

Carbon monoxide is a colorless, odorless,

tasteless, flammable and highly toxic gas. It is a

major product of the incomplete combustion of

carbon. It is called the “Silent Killer”.

Concentration Effects

9 ppm The maximum allowable concentration for short term exposure in a living ambient ( ASHRAE )

35 ppm The maximum allowable concentration for continuous exposure in any eight hour period. According to US federal law

200 ppm The maximum allowable concentration for any time. According to OSHA. Headaches, fatigue, nausea after 2-3 hours

800 ppm Nausea and convulsion within 45 minutes. Death in 2-3 hours.

3200 ppm Headaches and nausea within 5-10 minutes. Death within 30 minutes.

Page 20: Combustion and Flue Gas Analy

Combustion & Flue Gas Analysis 20December 2006

Excellence in measurements

Flue Gas contents

� Water Vapor (H2O)

� Nitrogen (N2) Typical contents 75-80%

� Carbon Dioxide (CO2) Typical contents 7-15%

� Carbon Dioxide and Hydrogen (CO, H2) due to incomplete combustion. Typical contents 50-150 ppm.

� Oxygen (O2) due to excess of air. Typical contents 2-8%.

� Nitrogen Oxides NOX (NO + NO2) due to N2 and O2combination at high temperatures. Typical contents <100ppm.

� Sulphur Dioxide (SO2) due to S2 presence in solid/oil fuels. Typical contents <200ppm.

� Uncombusted Hydrocarbons and Ashes

Page 21: Combustion and Flue Gas Analy

Combustion & Flue Gas Analysis 21December 2006

Excellence in measurements BoilersWall-hang type : The body of the boiler is fitted on the wall 20-30 KW

Floor-installation type : The boiler is fitted on the support or on the floor. 30-100 KW

Heating + Hot Water or Hot Water only

• Instantaneous supply typeThe main heat exchanger or heat exchanger for hot water inside the boiler body supplies hot water.

• Storage Tank typeHot water is stored in the separate storage tank and is supplied when necessary.

Page 22: Combustion and Flue Gas Analy

Combustion & Flue Gas Analysis 22December 2006

Excellence in measurements Boilers

Atmospheric Boiler Condensing Boiler

Sealed Chamber Boiler Energy Efficiency

(92/42 European Directive)

Classification ( Stars )

European standards (UNI EN 297

and UN 483) classify

boilers in 5 classes according to

their NOx emissions.

Page 23: Combustion and Flue Gas Analy

Combustion & Flue Gas Analysis 23December 2006

Excellence in measurements

Boilers

Boiler Type AIt takes combustion air from the indoors and vents exhaust gas in surrounding ambient.

Boiler Type BIt takes combustion air from the indoors and vents exhaust gas through the exhaust stack

Boiler Type BIt takes combustion-use air from additional strackfrom outside and vents exhaust gas through the exhaust stack ( dual stack ).

Page 24: Combustion and Flue Gas Analy

Combustion & Flue Gas Analysis 24December 2006

Excellence in measurements

Flue Gas Analysis

Combustion analysis is part of a process intended to :

� SAFETY ( Improve safety of fuel burning equipments )

� ENERGY SAVING ( Improve fuel economy )

� POLLUTION (Reduce undesiderable exhaust emissions)

For these reasons combustion analysis is a must and

Flue Gas Analyser is a fundamental tool for plumbers.

Page 25: Combustion and Flue Gas Analy

Combustion & Flue Gas Analysis 25December 2006

Excellence in measurements Analysis MethodsDuring combustion with an excess of air λλλλ=1.1 it develops 11.5 m3 of flue

gases ( for each m3 of burned gas) as :

(CO2) 1.0m3 + (O2) 0.2m

3 + (N2) 8.3m3 + (H2O) 2.0m3 = 11.5 m3

Analysis on Dry basis

If you remove all water contents from flue gases, condensating, the analyzer

will measure Oxygen as O2 = 0.2 : 9.5 = 2.1%.

This is a measurement on “dry basis” as we refer to Oxygen contents to the

volume of dry flu gases (9.5 m3) with excess of air λ=1.1

Analysis on Wet basis

If we don’t remove all water contents the analyzer will

measure Oxygen as O2 = 0.2 : 11.5 = 1.7%

This is a measurement on “wet basis” as we refer to Oxygen contents to the

volume of dry flu gases (11.5 m3) with excess of air λ=1.1

Flue gas analyzers use electrochemical sensors that need dry gas to measure.

For this reason all measurements are obtained on dry basis.

Page 26: Combustion and Flue Gas Analy

Combustion & Flue Gas Analysis 26December 2006

Excellence in measurements

Units of measurements

� The gas concentration is measured in ppm. Ppm means part per millions.100 ppm is equivalent to 0.01%1000 ppm is equivalent to 0.1%10000 ppm is equivalent to 1%

� Pollutants can be measured in

mg/Nm3 ( milligrams per cubic meter ) this is mass refer to a volume in normal condition ( 0°C 1013 mBar ). Ppm is converted in this unit with a coefficient different for each gas. Example : CO mg/Nm3 = CO ppm x 1,25

mg/kWh ( milligrams per kilowatt-hour of energy )the conversion from ppm to energy-related unit will use coefficient different for each fuel. Example : CO mg/kWh = CO ppm x 1,074

Page 27: Combustion and Flue Gas Analy

Combustion & Flue Gas Analysis 27December 2006

Excellence in measurements

CO and Pollutants referred to O2

� To avoid dilution of pollutants during inspections the CO and other toxic gases has to be measured referred to Oxygen.This is required by regulation.

Example :

CO measured 100 ppm and Oxygen measured 6% .

If O2 reference is set by law to 3%.

CO ref O2 = CO x ( 20.9 – O2 reference )/( 20.9 – O2 measured)

CO ref O2 = 100 x ( 20.9 – 3 ) / ( 20.9 – 6 ) = 120 ppm

If O2 reference is set to 0% usually the CO ref O2 is also called CO undiluted.

Page 28: Combustion and Flue Gas Analy

Combustion & Flue Gas Analysis 28December 2006

Excellence in measurements

One of the first task of flue gas analysis is

Energy saving. The regulations require that

all heating generators have to be measured

as Efficiency.

Useful efficiency is the ratio between the

heat transferred to water ( usefull output )

and the heat generated at the burner ( gross

heat input )

Loss and Efficiency

Page 29: Combustion and Flue Gas Analy

Combustion & Flue Gas Analysis 29December 2006

Excellence in measurements

Example

Boiler :

20.000 kcal/hour ( Gross Heat input )

10 liter/minutes. with DT=30°C

Water use 300kCal/minutes that is equivalent

to 18.000 kCal/hour ( useful output )

The useful efficiency will be 90% ( 18.000 / 20.000 ).

1kCal is the heat quantity necessary to grow 1°C in 1 liter of water.

Page 30: Combustion and Flue Gas Analy

Combustion & Flue Gas Analysis 30December 2006

Excellence in measurements

Loss

Loss for radiation, wall, opening and conveyor are negligible on modern

boiler.

Page 31: Combustion and Flue Gas Analy

Combustion & Flue Gas Analysis 31December 2006

Excellence in measurements

Combustion Efficiency

Efficiency = 100 – Qs Stack Flue Loss

Sensible heat is the amount of energy in the form of heat that is

required to grow temperature of water.

Latent heat is the amount of energy in the form of heat that is required

for water to undergo a change "change of state".

Page 32: Combustion and Flue Gas Analy

Combustion & Flue Gas Analysis 32December 2006

Excellence in measurements

Stack Flue Loss

Qs = k * (Tg - Ta) / CO2

Qs Stack Flue Loss

k Factor related to fuel

Tg Flue Gas Temperature

Ta Supplied Combustion Air Temperature

CO2 % of Carbon Dioxide

Regulation UNI 10389 provide similar formula using Oxygen to calculated CO2

and pertinent factors related to different fuels

Page 33: Combustion and Flue Gas Analy

Combustion & Flue Gas Analysis 33December 2006

Excellence in measurements

Italian Regulation

� 1990 - Law 10Energy saving legislation

� 1993 - D.P.R. 412Legislation on efficiency control and reduction of fuel consumption. Minimum Efficiency for boilers.

� 1994 - UNI 10389Technical regulation on flue gas analyzers, how to perform analysis and maximum limit definition for CO and Smoke.

� 2000 - D.P.R. 551Legislation upgrade of D.P.R. 412

� 2005 - D.L 192Execution of European directive 2002/91/CE

Page 34: Combustion and Flue Gas Analy

Combustion & Flue Gas Analysis 34December 2006

Excellence in measurements DIRECTIVE 2002/91/EC OF THE

EUROPEAN PARLIAMENT

Energy performance of buildings ( Active from January 2006 )

Inspection of boilers (Article 8)

Member state compliance with this part of the Directive is either through a system of regular inspections or through the provision of advice leading to an outcome similar to that of a regular inspection system:

Regular inspection of boilers rated 20 kiloWatt to 100 kiloWatt using non-renewable liquid or solid fuels. over 100 kiloWatt are to be inspected at least every two years, although the period for gas boilers may be extended to four years.

For all boilers over 20 kiloWatt and over 15 years old, a one-off inspection of the whole heating system is to be conducted.

This should cover boiler efficiency and sizing compared to the requirements of the building; advice should then include suggestions for replacement, improvements to the heating system and possible alternative solutions, or advice on improvement, replacement or alternative solutions.

Page 35: Combustion and Flue Gas Analy

Combustion & Flue Gas Analysis 35December 2006

Excellence in measurements

UNI 10389 ( 1994 )

• Define technical specification of flue gas analyzers (O2+CO)

• Three measurements every 2 minutes

• Formula to be used for Efficiency Calculation with factors for the different fuels

• Stack Draft measurement

• CO undiluted referred to 0% O2 ( max 1000 ppm )

• CO2 calculation

• Smoke measurement for Oil boiler

Page 36: Combustion and Flue Gas Analy

Combustion & Flue Gas Analysis 36December 2006

Excellence in measurements

EN50379According to the CENELEC, all national directives not compliant with EN 50379-2 will expire as of March 1, 2007 and will be replaced by EN 50379. The norm consists of three parts. Part 1 describes the general requirements and test procedures. Part 2 defines the requirements for devices used in statutory inspections and assessments. This means that inspections and measurements required by law may only be made with EN 50379-2 certified devices. Part 3 describes the requirements for devices in non-regulated areas in the maintenance of gas-fuelled heating facilities. This means that measurement results produced by devices tested according to part 3 have no legal relevance at all but may be used to set up boilers and determine maintenance intervals. Therefore, the user must carefully check the certification of a device. After March 1, 2007, statutory maintenance may only be performedwith EN 50379-2 certified devices

Page 37: Combustion and Flue Gas Analy

Combustion & Flue Gas Analysis 37December 2006

Excellence in measurements

How to perform an analysis

• The boiler has to work at

maximum power in stable condition.

• Insert probe into stack at height

of 2 times diameter and in the middle of tube.

• For Type C boiler use remote combustion air probe

to be inserter in the aspiration stack.

• Perform Draft measurement

• Select the right Fuel on instrument to obtain the right

factor for calculation.

• Perform a Flue Gas Analysis ( more time if required

by legislation ).

• Print the report.