Introduction to Oxidation and Mass & Energy Balances IT3/HWC Baltimore Baton 2014LA Rouge, 2016

Michael Mannuzza OBG

Combustion • Combustion is an oxidation reaction:

Fuel + O2 ---> Products of Combustion + Heat Energy

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• In addition to traditional burner fuels, incinerator fuel can include solid, gaseous and liquid waste. • The Products of Combustion (POC) are the primary concern from an Air Pollution Control (APC) perspective.

Air Pollutants and Regulatory Drivers • The type of APC system required for an incinerator will be decided based on the system’s POCs and the regulatory limits mandated for specific pollutants. • Emissions of the following pollutants are typically regulated for most incinerator applications: IT3/HWC Baltimore Baton 2014LA Rouge, 2016

• • • • •

Dioxin/Furans Mercury (Hg) Semi-Volatile Metals (Cd, Pb) Low-Volatility Metals (As, Be, Cr) SOx

• • • • • •

NOx Particulate Matter VOCs & Total Hydrocarbons Carbon Monoxide HCl & Cl2 Others

Identifying APC Requirements

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Three Steps: 1. Quantify anticipated POCs 2. Identify Regulatory Emission Constraints (establish abatement requirements) 3. Quantify the discharge flow rate of the system.

Waste Feed Properties I.

Begin by identifying the properties of the waste feed and quantifying the constituency of the waste:

1. 2. 3. 4.

Material Take-Offs Proximate, Ultimate, and Ash Analysis Sample & Analyze for Specific Compounds Employ Other Empirical Methods

PROXIMATE ANALYSIS

ASH ANALYSIS

ULTIMATE ANALYSIS

Category

wt %

Category

wt %

Category

wt %

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Moisture

3.3

Carbon (C)

61.1

Silicon Dioxide (SiO2)

74.1

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Ash

22.1

Hydrogen (H)

3.0

Aluminum Oxide (Al2O3)

20.0

Volatile Matter

27.3

Nitrogen (N)

1.35

Iron Oxide (Fe2O3)

3.25

Fixed Carbon

47.3

Sulfur (S)

0.4

Calcium Oxide (CaO)

0.68

Gross Calorific Value

24.73

Oxygen (O)

8.8

Magnesium Oxide (MgO)

0.48

Other

25.25

Other

1.49

*Ash

Fusion Point = 1104 ⁰C

Waste Feed Properties •If possible, identifying specific compounds in the waste is the best approach. GASEOUS WASTE STREAMS

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LIQUID WASTE STREAMS

COMPOUND NAME

% VOLUME

COMPOUND NAME

Wt. %

Methane Ethane Propane Butane Octane Pentane Hexane Carbon Monoxide Benzene Toluene Methylene Chloride Water (g)

56.33 - 66.40 1.27 - 3.8 0.75 -1.2 0.05 -1.0 0.02 -.08 0.13 – 1.1 0.11 – 1.0 17.40 -21.0 0.00 -0.21 0.00 – 0.46 0.01 – 0.8 2.95-23.93

Toluene Xylene Propanol Isopropylbenzene Acetic Acid 1,2 Dichloroethane Methanol Methyl Bromide Formaldehyde Sodium Fluoride Hydrogen Chloride Water (L)

8.4 -11.0 1.2 – 3.1 1.9 -17.1 0.08 – 9.3 0.5 – 0.9 1.1 – 13.1 0.9 – 5.0 0.9 -1.5 1.1 -6.7 1.0 – 1.5 4.5 – 9.5 21.3 – 78.42

Waste Feed Properties I.

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Waste feed rates and constituencies are rarely constant. It is important to establish a realistic waste feed design basis. The waste feed design basis must address the following:

I. II. III. IV. V.

Worst case feed rate Highest heating value condition (kJ/kg of waste) Lowest heating value condition (kJ/kg of waste) Worst case sulfur condition, chlorine condition,NOx condition, metals condition, particulate condition, etc. Any other critical regulatory or production related criteria associated with the waste.

Stoichiometry of Combustion I.

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As a starting point, it is necessary to make some Initial assumptions. If adequate Oxygen will be made available for complete combustion, assume the following:

I. II. III. IV. V.

All Carbon converts toCO2 All halogens convert to acids (e.g., Cl  HCl, Br  HBr) All alkali metals convert to hydroxides (e.g., Na  NaOH) All remaining hydrogen converts to H2O All non-alkali metals convert to metal oxides in their most common oxidation state (e.g., MgO, Fe2O3) VI. Bound Nitrogen in the waste converts to NO2 VII. All Sulfur converts to SO2 VIII. Non-combustible constituents pass through unchanged or thermally decompose to known compounds

Stoichiometry of Combustion I.

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In reality, it is possible that additional products or congeners can be formed.

I. II. III. IV. V. VI.

SO3 Diatomic Halogens (Cl2, Br2 ) N2, NO, N2O CO Dioxin/Furans Others

I. II. III. IV. V.

Temperature Contaminant Concentrations O2 and H2O Concentrations Catalysts Other factors

II. Formation of these tertiary compounds can be a function of:

Stoichiometry of Combustion I.

The initial assumptions outlined usually provide a reasonable estimate of the products of combustion that are generated.

I. II.

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Allows the elemental contaminants to be quantified. Provides a mechanism for identifying combustion air requirements and exhaust flow rates

II. The resulting POCs can then be refined if necessary by applying: I. II.

Empirical Data Advanced Methods

Stoichiometry of Combustion • Example: Dichlorobenzene, C6H4Cl2 C6H4Cl2 + ?O2  ?CO2 + ?H2O + ?HCl

C6H4Cl2 + 6.5O2  6CO2 + 1H2O + 2HCl IT3/HWC Baltimore Baton 2014LA Rouge, 2016

1. 2. 3. 4.

Balance Carbon atoms first Balance halogens, metals, Nitrogen & Sulfur next. Balance Hydrogen atoms Balance Oxygen atoms last

Stoichiometry of Combustion 1. Balance Carbon & CO2 first: C6H4Cl2 + ?O2  ?CO2 + ?H2O + ?HCl How many moles of CO2?

Answer: IT3/HWC Baltimore Baton 2014LA Rouge, 2016

6

C6H4Cl2 + ?O2  6CO2 + ?H2O + ?HCl

Stoichiometry of Combustion 2. Balance halogens, metals, Nitrogen & Sulfur next: C6H4Cl2 + ?O2  6CO2 + ?H2O + ?HCl How many moles of HCl? Answer: IT3/HWC Baltimore Baton 2014LA Rouge, 2016

2

C6H4Cl2 + ?O2  6CO2 + ?H2O + 2HCl

Stoichiometry of Combustion 3. Balance Hydrogen atoms: C6H4Cl2 + ?O2  6CO2 + ?H2O + 2HCl How many moles of H2O? Answer:

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1

C6H4Cl2 + ?O2  6CO2 + 1H2O + 2HCl

Stoichiometry of Combustion 4. Balance Oxygen atoms last: C6H4Cl2 + ?O2  6CO2 + 1H2O + 2HCl How many moles of O2?

Answer: IT3/HWC Baltimore Baton 2014LA Rouge, 2016

6.5

C6H4Cl2 + 6.5O2  6CO2 + 1H2O + 2HCl

Stoichiometry of Combustion – Mass Balance C6H4Cl2 + 6.5O2  6CO2 + 1H2O + 2HCl Compound:

Molecular Wt. (g/mol):

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C6H4Cl2

O2

CO2

H2O

HCl

147.004

32.00

44.011

18.0158

36.461

No. of Moles:

1

6.5

6

1

2

1Total Wt. (g):

147.004

208.00

264.066

18.0158

72.9218

1

1.415

1.796

0.123

0.496

2Normalized

Ratio:

1Total Wt. =

(Molecular Wt.) * (No. of Moles) 2Normalized Ratio = Total Wt. divided by the molecular wt of C H Cl (147.004 g/mol). 6 4 2

Thus: 1kg C6H4Cl2 + 1.415kg O2  1.796kg CO2 + 0.123kg H2O + 0.496 kg HCl Same applies for grams, pounds or any unit other unit of mass.

Stoichiometry Calculations

This approach can be applied to each constituent identified in a waste stream: STEP 1: Balance the moles

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STEP 2: Balance the mass

Stoichiometry Calculations •

•

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Each constituent can be factored by its mass ratio and then summed to generate a representative compound that reflects the properties of the overall waste stream. Similarly, a weighted calculation can be performed to determine the net heat of combustion of the waste stream.

Heat of Combustion

Definitions:

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• Heat of Combustion: The heat released by combustion of a unit quantity of fuel with its stoichiometrically correct amount of combustion air, measured either in calories or Btu. • Gross Heating Value:The heat released by combustion of a unit quantity of fuel with both the combustion air and fuel at a known reference temperature prior to combustion (e.g. 60 ⁰F) after the products of combustion are allowed to cool to the initial temperature. Also known as Higher Heating Value (HHV). • Net Heating Value: The heat release measured prior to the products of combustion being allowed to cool. Also known as Lower Heating Value (LHV).

Heat of Combustion

• For most incinerator applications, we are concerned only with the LHV of the fuel/waste. • Numerous data sources are available (reference books, internet, etc.). • Can be estimated or obtained through testing. IT3/HWC Baltimore Baton 2014LA Rouge, 2016

• Heat of formation • Dulong’s Approximation (Btu/lb = 14,544C+62,028(H2-0.125O2)+4,050S)

• Empirical formula based on coal. • Can be applied to other carbonaceous waste, but accuracy is questionable.

• 410 Btu (103.3 kcal) per Mole of O 2 Consumed

• Good approximation for hydrocarbons. • Accuracy diminishes if Oxygen, Nitrogen, Halogens and other elements are present.

Mass & Energy Balance Mass in = Mass out Energy in = Energy out

• Mass of exhaust stream constituents (solid, gas) • Heat content of constituents

Thermal losses

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Control volume

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• Mass of waste stream constituents (solid, liquid, gas) • Heat content of constituents • Net heat of combustion of combustibles

• Mass of burner fuel and combustion air • Heat content of constituents • Net heat of combustion of burner fuel

Mass & Energy Balance

Conservation of Mass & Energy mstream1 + mstream2 + mstream3 =mstream4 Qstream1+Qstream2+Qstream3 =Qstream4 + Thermal Losses

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Mass & Energy Balance –Key Points

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I. Mass in must equal mass out (m in – mout = 0). II. Energy in must equal energy out (Q in – Qout = 0). III. Combustion air volume will generally be a direct function of the fuel input, however, additional air may be needed to maintain O2 levels or control temperature. IV. Adjust the mass of the fuel input until the system energy is balanced. I. Cannot solve directly - must be an iteration. II. The Goalseek function in Excel is useful for this approach (modulate fuel input until Qin – Qout = 0

III. Determine energy of waste gas streams by applying specific heats.

Mass & Energy Balance

Conservation of Mass & Energy mstream1 + mstream2 + mstream3 =mstream4 Qstream1+Qstream2+Qstream3 =Qstream4 + Thermal Losses

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Applying Specific Heats

• Q=m* Cp*DT • • • •

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Q = Heat flow (Btu/hr, MJ/hr, Watts, etc.) m = mass flow (lb/hr, kg/hr, etc.) Cp = Constant pressure specific heat (Btu/lb-⁰F, J/kg-⁰K, etc.) DT = Temperature difference between actual temperature and reference temperature (T-Tref) (⁰F, ⁰C, etc.)

• Specific heat varies based on temperature and is tabulated for commonly encountered gases in many reference books. It is also frequently presented as a polynomial function of temperature. • Cp = a + bT +cT2

• A very accurate mean Cp can be obtained by integrating this polynomial across the temperature range.

Cpmean = ∫[a + bT +cT2]/(T-Tref)  [a(T-Tref)+(1/2)b(T2-Tref2)+(1/3)c(T3-Tref3)]/(T-Tref)

Radiation Losses

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Shell losses are a function of numerous variables: • Shell temperature • Wind velocity • Shell color • Shell area • Emissivity

Furnace Radiation Losses1

Furnace Rate (MBtu/hr)

Radiation Losses (%)

35

1.5

1 Handbook of Incineration Systems, Brunner, C.

1991 McGraw-Hill

R.,

Mass & Energy Balance

Conservation of Mass & Energy mstream1 + mstream2 + mstream3 =mstream4 Qstream1+Qstream2+Qstream3 =Qstream4 + Thermal Losses

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Converting Mass to Volume

• When calculating process emissions, we routinely need to convert between mass & volume. • Avogadro’s Law: Equal volumes of all gases under the same conditions of temperature and pressure contain the same number of molecules. • Definitions & Conversions:

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• lb-mol = mass (lbs) ÷ MW • 1 lb-mol = 386.728 ft3 @ 70 ⁰F and 14.6959 psi • g-mol = mass (grams) ÷ MW • 1 g-mol = 22.414 L @ 0 ⁰C and 760 mm Hg

• ppmv = 106 * Volume of Component ÷ Overall Volume

Converting Mass to Volume

• Volume is temperature & pressure dependent. It is common to normalize volume to a standard temperature, to facilitate mass/volume conversions • Nm3/hr & m3/hr • m3/hr = Nm3/hr * (273 + T)/(273 +Tref) • T = Process Temp. (⁰C) • Tref = Reference Temp. (⁰C) usually 0 ⁰C

• SCFM & ACFM IT3/HWC Baltimore Baton 2014LA Rouge, 2016

• ACFM = SCFM *(460+ T)/(460 +Tref) • T = Process Temp. (⁰F) • Tref = Reference Temp. (⁰F)

• Be aware, different reference temps are used for SCFM • 60 ⁰F, 68 ⁰F, 70⁰F

• Nm3/hr * 0.6341 = SCFM (@ 70 ⁰F)

Converting Mass to Volume I. Volume is also effected by pressure, including pressure due to elevation changes: I.

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SCFM is referenced to standard atmospheric pressure at sea level = 14.6959 psi (406.8 inches H2O) II. Nm3/hr is referenced to 760 mm Hg. III. When pressure effects must be accounted for: I. II.

ACFM =SCFM *(406.8/ Pactual)*(460+T)/530 m3/hr = Nm3/hr * (760/Pactual)*(273+T)/273

Combustion Air Composition of Dry Atmospheric Air

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Gas Nitrogen Oxygen Argon Carbon Dioxide Neon Helium Methane

Volume 78.084% 20.946% 0.9340% 0.0397% 0.001818% 0.000524% 0.000179%

Typical C.A. Constituency (Assumed) Nitrogen Oxygen

% Weight 76.85 23.15

% Volume 79.1 20.9

Excess Air

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• Excess Air: The air remaining after a fuel has been completely burned or that air supplied in addition to the amount required for stoichiometric combustion. • Increased O 2 content can enhance combustion, or it can lead to the formation of problematic compounds (i.e., SO3, CO2, NO2) • Excess air may be required to control exothermic temperature rise or flammability levels. • Regulatory emission limits are typically referenced to a specific O2 level and a correction factor must frequently be applied to actual data. ppmvcorrected = ppmvtest * [21-%O2base]/[21-O2test]

Particulate Matter • Particulate Matter (PM) can be solid, or liquid aerosol. • Can include condensables

• Particle Size Distribution (PSD) is important. • Will drive APC Technology Selection • Determined by source testing.

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• Units for PM

• Micrograms per dry cubic meter (μg/m3) • Grains per standard cubic ft ( gr/scf). • 7,000 gr = 1 lb

• Measurements are dry basis

QUESTIONS? IT3/HWC Baltimore Baton 2014LA Rouge, 2016