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The Sound of Temperature

Measuring flue gas temperature with an acoustic pyrometer In order of : Refineria Isla (Curazao) S. A. Prepared by : Duarte N. de Jesus Marques University mentor : Rob A. van Leeuwen Industrial mentor : Henry Hernandez Educational institution : Fontys Hogeschool. Applied Sciences, dept. of Engineering

Physics with Commerce Curaçao, December 2002

The sound of temperature Summary

Summary Heat flux distribution in process furnaces has been a concern for quite some time at Refineria Isla (Curazao) S.A. (RICSA). In December 2001 Scientific Engineering Instruments (SEI) Inc. had installed a test setup to determine the requirements for introduction of an acoustic pyrometer to measure flue gas temperature. Objectives were to control and optimize emissions, process and flame pattern by means of possible correlations. The acoustic pyrometer measures on the principle that temperature of a gas is a function of composition and speed of sound. By measuring the time it takes for a sound wave to propagate in a straight path through a volume of gas, temperature can be determined. Multiple paths are defined and used for visualization of temperature distribution by means of a software. With the Thermal Mapping System 2000, which is the software used for visualization, windows of convenience can be displayed for analyzing data. To interpret these windows it is important to understand the properties of a flame and the principles of heat transfer. Although flame in a process heater is the source of heat it should be emphasized that the acoustic pyrometer measures only flue gas temperature and not radiation emitted by the flame. In the furnace where the test setup is installed, dynamics of flue gas in the combustion chambers have influence on the measurement system. Introducing the AP in the present control system needs more tests and experience. It is recommended that the gas measurement system should be used as a monitoring tool rather than as control tool. Defining and identifying an ideal flame pattern can be a good start for the use of the acoustic pyrometer as a monitoring tool.

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The sound of temperature Foreword

Foreword In the scope of my Industrial Placement Period (IPP) I had the opportunity to study a technology introduced by Scientific Engineering Instruments (SEI) Inc. to measure the temperature of flue gas by using an acoustic pyrometer. About a year ago SEI Inc. agreed with Petroleos de Venezuela S.A. (PDVSA) to install a test setup in Refineria Isla (Curazao) S.A. PDVSA is a worldwide company of energy that has operational and commercial activities in and outside of Venezuela. This company is a property of the Venezuelan State. Its operations are exploration, exportation, refining, transport and distribution of hydrocarbons. Refineria Isla (Curazao) S.A. is a part of the PDVSA group, which is situated on Curaçao, Netherlands Antilles. This refinery provides processing and storage services to PDVSA and has a capacity of 330.000 barrels a day. The products are marketed and distributed by PDVSA. During the time was at the refinery some delays were encountered. The first setup had limited sensors, which did not measure reliable enough. Hardware limitations forced us to install a new acoustic pyrometer only in one radiant cell. Further these circumstances have given me a better insight of real time situations that are not to compare with university projects. In this assignment heat transfer was the main subject. Understanding heat transfer in process heaters has given me the opportunity to interpret the mapping system of the acoustic pyrometer better. It gets more challenging when multiple variables have to be studied. When trouble shooting causes of temperature differences many persons have helped me out. For this reason I want to dedicate these last sentences to all who has helped me. Naming all of them would create a long list but the departments are MTI, TSI, TSR, especially TSP and OPDM. Special thanks go to the below mentioned persons for their cooperation and advice.

Douglas van der Veen Giovanni Con Henry Hernandez Roberto Roubicek Ruben Roosberg

Duarte N. de Jesus Marques December 2002 Curaçao Netherlands Antilles

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The sound of temperature Table of contents

Table of contents Page Summary i Foreword ii Table of contents iii List of figures v List of symbols vi 1. Introduction 1 1.2 Problem definition 1 1.3 Assignment 1 1.4 Project objectives 1 1.5 Argumentation 1 2. Heat transfer 2 2.1 Conduction 2 2.2 Convection 3 2.3 Radiation 6 3. Combustion 11 3.1 Theoretical amount of air 11 3.2 Percentage volume oxygen 14 4. Acoustic Pyrometer 19 4.1 Applications 19 4.2 Principle 19 4.3 Setup 20 4.4 Thermal Mapping System (TMS 2000) 20 5. Process heater 24 6. Discussion 30 6.1 Manipulation of stack damper 30 6.2 Manipulation of air registers 30 7. Conclusion & Recommendations 31 7.1 Conclusion 31 7.2 Recommendation 31 Afterthought 32 References 33 Appendix 1 34 Appendix 2 45

iii

The sound of temperature Table of contents

Appendix 3 50 Appendix 4 59 Appendix 5 72

iv

The sound of temperature List of figures

List of figures Page Figure 1 Heat through a single wall system 4 Figure 2 Heat through multiple wall system 5 Figure 3 Heat transfer with turbulent flow 8 Figure 4 Radiation in furnace F-1202 10 Figure 5 Mole map 12 Figure 6 Excess air versus percentage CO2 in flue gas 18 Figure 7 First setup of the gas measurement system 21 Figure 8 Second setup of the gas measurement system 21 Figure 9 Both area configuration 22 Figure 10 Mapping examples of the TMS 2000 23 Figure 11 Sketch of furnace F-1202 25 Figure 12 Sketch of a burner with magnified head with tip and plug 27 Figure 13 Simplification of draft system of a furnace 27 Figure 14 Schematical layout of furnace F-1202 29 List of tables Table 1 Heat transfer formulae for coordinate systems of convenience 5 Table 2 Spectrum of Electromagnetic Radiation 8 Table 3 The amount of reactants formed on combustion of one Kg of liquid fuel 15 Table 4 The amount of air required to combust on one Kg liquid fuel 15

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The sound of temperature List of symbols

List of symbols Symbol Description S.I. Unit A Area 2m

c0 Speed of light in vacuum ( ) 810998,2 ⋅sm

C Specific Heat KkgJ⋅

Cp Specific Heat at constant pressure KkgJ⋅

h Planck’s constant ( 6 ) 34106256, −⋅ sJ ⋅

Ib Intensity of a black body 2mW

k Thermal conductivity Km

W⋅

k Boltzmann constant (1 ) 23103805, −⋅KJ

L Length m n Excess combustion air -

q Heat transfer rate sJ,W

qx Heat transfer rate at position x sJW ,

q’ Rate of heat generation per volume sm

W⋅3

Q Heat J t Time s Ts Temperature of the surface K Tx Temperature at position x K

vi

The sound of temperature List of symbols

u Velocity in the x direction sm

v Velocity in the y direction sm

w Velocity in the z direction sm

α Coefficient of heat transfer Ksm

J⋅⋅2

β Weight percentage of carbon - ε Emissivity factor - γ Weight percentage of hydrogen - ϕ Weight percentage of sulphur - λ Wavelength m

ρ Mass density 3mkg

σ Stefan-Boltzmann constant (5 ) 810670, −⋅ 42 KmW⋅

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The sound of temperature Introduction

1. Introduction Heat flux distribution in process furnaces has been a concern for quite some time at Refineria Isla (Curazao) S.A. (RICSA). The dimensions of the furnace have a major influence on the distribution of heat. In the seventies when these furnaces were build relatively low priority was given to combustion efficiency. Nowadays environmental and cost reducing issues have a huge impact on all refinery processes. The objective of Refineria Isla is to increase combustion efficiency by controlling the heat flux within the furnace. At present Scientific Engineering Instruments Inc. (SEI Inc.) is setting up test to use Acoustic Pyrometer to measure flue gas temperatures in one of RICSA’s furnaces. The test hardware called Boilerwatch MMP can measure flue gas temperatures up to 2273 K. This temperature can be seen on a computer with the thermal mapping system, TMS-2000, which is a visual representation of the flue gas dynamics in the combustion or radiant chamber of the furnace. 1.2 Problem definition To determine the requirements for the introduction of the Acoustic Pyrometer as a part of the process controlling and monitoring system.

• How to approach the investigation? • Understanding the process dynamics of the furnace • Identify the various variables of influence on the process • What is the correlation between the flue gas temperature, the process variables and

the combustion variables? 1.3 Assignment The assignment is integrating the Acoustic Pyrometer (AP) with the present control system without interrupting the production process of crude distillation. 1.4 Project objectives Trimming the combustion by using the Acoustic Pyrometer with the objective of:

• Controlling and optimizing the emissions • Controlling and optimizing the process • Controlling and optimizing the flame pattern

1.5 Argumentation Like mentioned before heat flux distribution is a concern for Refineria Isla (Curazao) S.A. Understanding the underlying theories of heat transfer and heat dissipation are of importance for economical and environmental reasons. There fore the principles of heat transfer and combustion (source of heat in a furnace) will be discussed in a few chapters. Objectives of the assignment of using the acoustic pyrometer as a control tool was not achieved, instead a lot of time was dedicated to interpret the mapping system of the pyrometer. In most of the times it was difficult to interpret the data, because of many parameters that have influence on the flue gas temperature. These topics are also discussed in this report.

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The sound of temperature Heat Transfer

2. Heat transfer Heat propagates in three fundamental ways respectively conduction, convection and radiation. Although each type of heat transfer may occur at the same time, it is preferable to consider each type apart at a particular case. 2.1 Conduction [1] Conduction heat transfer is the transfer of energy within a substance, or two substances if in physical contact, from the more generic particles to the less generic particles. Conduction also called diffusion of energy is the net transfer of energy by random molecular motion. The Fourier Law is the fundamental differential equation for heat transfer by conduction:

dxdTkA

dtdQ

−= (1)

where the factor is called the thermal conductivity. This is a property of material through which the heat is flowing and varies with temperature. Further it can be shown that for an isotropic media a more general equation can be used:

k

tTq

zTk

zyTk

yxTk

x cp δδ

ρδδ

δδ

δδ

δδ

δδ

δδ

=+

+

+

' (2)

where ρCpδT/δt is the time rate of change of sensible energy of the system. Sensible heat is defined as the quantity of heat needed to raise one unit weight of a substance with one unit of temperature (also called specific heat). For a steady flow of heat, the term on the right of the equal sign in eq.1 is constant and may be replaced by Q/t or q. The same counts for the term δT/δt in eq.2, it becomes zero. Hence eq.2 may be expressed as:

kqT '2 =∇ (3)

where is the Laplacian operator, defined in the Cartesian coordinates as: 2∇

2

2

2

2

2

22

zyx δδ

δδ

δδ

++=∇ (4)

For one dimensional heat transfer eq.2 becomes:

kq

dxTd '2

2

−= (5)

Many heat conduction problems can be simplified by choosing a coordinate system of convenience. Forms of conduction for different coordinate systems are shown in table 1. For a plane wall illustrated in figure 1 the next calculations can be made for constant thermal conductivity (k).

2


hotshotscolds

x TxLTT

T ,,, )(

+−

= (6)

The heat transfer rate can be determined by using eq.1 for a steady state condition.

( )2,1, ssx TTLkAq −= (7)

where the factor L/kA is called the thermal resistance. In industrial applications several walls (bodies) in series are mounted to increase strength and to minimize heat loss. The heat equation for walls in series is be expressed as:

∑−

=t

ssx R

TTq 2,1, (8)

where Rt is the total thermal resistance:

AkL

AkL

AkLRt

3

3

2

2

1

1 ++=∑

Figure 2 illustrates the above-discussed issue. 2.2 Convection [1,2] Heat transfer by convection takes place in fluids. A macroscopic motion of fluid contributes to the heat transfer. Convection takes place on boundaries where fluid passes at the to be heated surfaces. In majority of the cases met in industrial practice, heat is transferred from one fluid through a solid wall to another fluid. These fluids propagate mostly in turbulent flows when passing along solid walls. As one approaches the adjacent of the body the turbulent flow becomes more laminar. This quite zone is called the film layer (figure 3) The film has the properties, which is essential for heat transfer by molecular conduction. The layer possesses all the characteristics for heat resistance or transfer, depending on the thickness and thermal properties of the flowing fluid. For a general overview of energy balance on a flowing fluid where heat is transferred, the equation below is given.

Φ++

∂∂

+∂∂

∂∂

=

∂+

∂+

∂+

∂∂ '2

2

2

2

2

2

qzT

yT

xTk

zTw

yTv

xTu

tTCp (9)

The term Φ is given for energy dissipation due to fluid viscosity, which can be high in high-speed gas flow or for very viscous fluids. The above equation exists only for some simple laminar flow situations. The equation shows that it is very dependent on solutions of momentum equations. When dealing with turbulent flow, expressing flow viscosity as function of time and direction can become complicated. If this is the case eq.9 becomes difficult to use. For simplification most of the time when turbulent flow is the case, empirical or computational fluid dynamics (CFD) is used. For a local rate of heat transfer in laminar flow and small temperature differences between fluid and solid in steady state, eq.10 can be used.

α)( 2,1, sx TTdAdq −= (10)

3


This equation includes all the properties of eq.9. The heat transfer coefficient (α) used includes both temperature gradients of the solid and fluid. In many cases applications where some process is heated, determining the coefficient α is very complicated.

Figure 1 Heat through a single wall system Source: Charles E. Baukal, Jr The John Zink combustion handbook John Zink

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Figure 2 Heat through multiple wall system Source: Charles E. Baukal, Jr The John Zink combustion handbook John Zink

Coordinates Heat transfer formulae

Cartesian (rectangular) coordinates kq

dxTd '2

2

−=

Cylindrical coordinates kq

drdTr

drd

r'1

−=

Spherical coordinates kq

drdTr

drd

r'1 2

2 −=

Table 1 Heat transfer formulae for coordinate systems of convenience Source: Robert H. Perry and Don Green Perry's chemical engineers' handbook sixth edition

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Logarithmic mean temperature difference [3] When dealing with fluid passing through tubes convective heat transfer becomes more complicated. The above discussed convection theory is applied when there is a steady state and temperature differences between two points are not relatively high. In the case of process heaters (sensible) heat is transferred to hydrocarbons and its temperature varies over the entire length of the tube. For calculations of convection in pipes there are three temperatures necessary namely inlet, outlet and tube temperatures (figure 3). Assuming that the tube temperature is constant over the entire length and inlet temperature is less then outlet temperature the next formulae’s can be used. The heat transfer coefficient of the hydrocarbon is constant. Eq. 10 can be rewritten and used for the total heat transferred to the fluid when passing through the tube.

αTdAdq ∆=

21

12

12

TTTTTTTTT

t

t

−=∆−=∆

∆−∆=∆

The increasing slope of T is the temperature as a function of q. The decreasing slope defines the temperature difference as a function of q.

qTT

dqTd 12 ∆−∆

=∆

( ) ∫∆

∆ ∆∆

=∆−∆⇒∆−∆

=∆∆ 2

1

1212

T

T TTdTT

qdA

qTT

TdATd α

α

Integrating

( )

1

2

12

ln TT

TTAq

∆∆

∆−∆= α (11)

The last factor in the above formulae is called the logarithmic mean temperature difference. When temperature difference is low increase can be considered to be linear otherwise there is a logarithmic relationship. 2.3 Radiation [1] Thermal radiation heat transfer is heat transfer by means of electromagnetic waves. Contrary to conduction and convection radiation does not require an intervening medium to propagate. All surfaces emit and absorb radiation. The ideal radiator is called a black body. The black body absorbs all the energy that strikes its surface regardless the direction of the wave. It also radiates the theoretical maximum that any surface can radiate. According to the Stefan-Boltzmann law, radiation energy depends on the surface properties and absolute temperature.

4sr TAQ σε= (12)

6


where ε = 1 for a black body and the emissive power is given by:

4TEb σ= (13) Taking into account that the emission of a black body is diffuse, the intensity is given by:

πb

bE

I = (14)

The blackbody is used as reference in discussions and calculations of radiation heat transfer. Further when radiation strikes a surface some waves are converted into internal energy and some are reflected or transmitted. Because radiation is a wave it has all the properties of a wave. Properties like wavelength and frequency and it also can be refracted and reflected. The spectrum of electromagnetic radiation is shown in table 2. The spectral distribution of an ideal emitter is given by the Planck distribution equation.

−

=1exp

2),(

*05

20

,

Tkhchc

TI b

λλ

λλ (15)

*Note: In this paragraph k is the Boltzmann constant. Taken to assumption that a blackbody is a diffuse emitter, its spectral emissive power is given by:

−

=∗=1exp

2),(

05

20

,,

kThchc

TIE bb

λλ

πλπ λλ (16)

As it can be seen in the above equation, the emissive power is a function of wavelength and absolute temperature. Further when radiation strikes a surface some few aspects have to be considered. First, factors like the angle of incoming rays relative to the normal of the absorbing area. In many literatures it is called the view factor. Secondly, the correction factors for the emissive power when dealing with conditions that are not ideal. When dealing with radiations of different surfaces simultaneously, calculations get too complicated. Most of the time empirical numbers are used for industrial situations. It is important to distinguish and understand that the approach for solids is different than the approach for gases. When dealing with gas radiation scattering and gas composition becomes also important factors. Composition of gases is important, because gases that contain diatomic molecules and inert do emit relatively low. Examples are N2 and O2. On the other hand water in vapor phase and carbon dioxide do emit radiation significantly. Gases like these are a participating medium between two bodies when transferring heat by radiation.For an in depth analysis of these subjects it is recommended to go through the references of the literature list.

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Source: Robert H. Perry and Don Green Perry's chemical engineers' handbook sixth edition ;

Figure 3 Heat transfer with turbulent flow

Donald Q. Kern Process heat transfer International student edition

Spectrum of Electromagnetic Radiation Region Wavelength

(Angstroms) Wavelength

(centimetres) Frequency

(Hz) Energy

(eV) Radio > 109 > 10 < 3 x 109 < 10-5

Microwave 109 - 106 10 - 0.01 3 x 109 - 3 x 1012 10-5 - 0.01 Infrared 106 - 7000 0.01 - 7 x 10-5 3 x 1012 - 4.3 x 1014 0.01 - 2 Visible 7000 - 4000 7 x 10-5 - 4 x 10-5 4.3 x 1014 - 7.5 x 1014 2 - 3

Ultraviolet 4000 - 10 4 x 10-5 - 10-7 7.5 x 1014 - 3 x 1017 3 - 103 X-Rays 10 - 0.1 10-7 - 10-9 3 x 1017 - 3 x 1019 103 - 105

Gamma Rays < 0.1 < 10-9 > 3 x 1019 > 105

Table 2 Spectrum of Electromagnetic Radiation Source: http://csep10.phys.utk.edu/astr162/lect/light/spectrum.html

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http://csep10.phys.utk.edu/astr162/lect/light/spectrum.html


Radiation of a flame A precise calculation of a flame radiation is very difficult. Reasons for this are:

• Temperature of the flame is not known. Still when it is possible to determine the adiabatic flame temperature for a given fuel in practice it will be lower. This because the flame emits radiant heat. The adiabatic flame temperature is defined as the theoretical temperature that can be reached with a certain amount of fuel and a stochiometric air quantity, assuming heat transfer to the surroundings is zero.

• Under flame radiation is often misunderstood that some reaction is the cause that the flame emits electromagnetic waves. Only gases and solids of the flame emit the radiant energy, particularly carbon, because of their high energy content due the reactions in the flame.

• The presence of solid carbon particles can dominate the emission of heat in a flame. Determining the concentration and temperature of the carbon is difficult.

The fuel composition determines the amount of energy that is transmitted by the flame. It is important not to confuse two subjects like high-energy content gases and gases that have a relatively high emissivity coefficient. High-energy content gases have a high temperature, but this doesn’t mean that these gases emit radiation. The items that determine the quantity of radiation to be emitted are the gas properties and composition. Figure 4 illustrates the effects of radiation in a furnace.

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Figure 4 Radiation in furnace F-1202

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The sound of temperature Combustion

3.0 Combustion [4]* Combustion is a chemical reaction between combustible matter and oxygen, resulting in combustion products and liberation of heat. The combustion product is flue gas that contains carbon dioxide (CO2), water (H2O), nitrogen dioxide (NO2) and sulphur dioxide (SO2). Other substances in the flue gas can be neglected, because of the relatively low mass percentage. Before combustion can take place two conditions are required:

• Fuel and oxygen (air), both in gaseous phase, must be mixed and concentrations must be in proper flammability ratio. If there is too much fuel in the air the mixture is saturated and will not burn. Below a certain quantity of fuel in the air the mixture is too poor to burn. These boundaries are called upper and lower flammability limit.

• When the first condition is fulfilled heat input is necessary, unless the mixture has a certain temperature.

Fuels differ according to the different elements they contain, such as carbon, hydrogen, sulphur, nitrogen and oxygen. To obtain general formulas for combustion simplification has to be made.

• Fuels are considered to contain H, C and S; hence N, O, ash/metals are neglected. • Combustion air consists of 21% volume (vol.) O2 and 79% volume N2; humidity is

considered to be zero. • Molecular weights are: C=12 u, H=1 u, S=32 u, O=16 u, air=29 u

3.1 Theoretical amount of air In refineries when furnaces are used, calculations can be made to determine the exact amount of air needed for combustion of one mass unit of fuel. Two types of fuel can be distinguished respectively liquid and gas fuel. To determine for both the quantity of air, the same technique is used. In the calculations below it is assumed that the fuels only contain hydrogen, carbon and sulphur and that the weight % of these components are given. Determining stochiometric air quantity can be done as follows. Calculations for combustion of carbon Assuming that liquid fuel contains only H, C, S, the following general equations can be made. The equation for combustion of carbon is given by:

C (l) + O2 (g) → CO2 (g) The above chemical equation means that one mole of carbon and oxygen reacts to one mole of carbon dioxide. When calculations are made where gases are present, volume percentages have to be taken into account. Here is where the law of Avogardo implies. According to the law one mole of a gaseous substance is equivalent to 22,4 Normal liters. This is illustrated in figure 5.

12 Kg C (l) +32 Kg O2 (g) → 44Kg CO2 (g)

1 Kg C (l) +1232

Kg O2 (g) → 1244

Kg CO2 (g)

Calculating the volume per unit weight of the reacted oxygen gives:

1 Kg C (l) +32

4,221232

× Nm3 O2 (g) → 44

4,221244

× Nm3 CO2 (g)

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Figure 5 Mole map

12


In industrial applications air is used as oxidizing agent instead of pure oxygen. Air consists of 21 % O2 by vol. and 79 % N2 by vol. This means that the oxygen quantity has to be multiplied by 100/21.

1 Kg C (l) +12

4,2221

100× Nm3 air (g) →

124,22

Nm3 CO2 (g) + 2179

124,22

× Nm3 N2 (g)

A general equation can be made if the fuel used for combustion contains ϕ % wt C:

100ϕ

Kg C (l) +10012

4,2221

100 ϕ×× Nm3 air (g) →

100124,22 ϕ

× Nm3 CO2 (g) +

1002179

124,22 ϕ

×× Nm3 N2 (g)

Rewriting gives:

100ϕ

Kg C (l) + 0,089 ϕ Nm3 air (g) → 0,0187 ϕ Nm3 CO2 (g) + 0,0702 ϕ Nm3 N2 (g) (16)

Calculations for combustion of hydrogen

4 H (l) + O2 (g) → 2 H2O (g) To calculate the amount of air needed for combustion of hydrogen is the same way as for carbon.

4 Kg H (l) + 32 Kg O2 (g) → 36 Kg H2O (g)

1 Kg H (l) + 8 Kg O2 (g) → 9 Kg H2O (g)

1 Kg H (l) + 32

4,228× Nm3 O2 (g) → 18

4,229× Nm3 H2O (g)

For the amount of air needed:

1 Kg H (l) + 21

1004

4,22× Nm3 air (g) →

184,229× Nm3 H2O (g) +

2179

44,22

× Nm3 N2 (g)

A general equation can be made if the fuel used for combustion contains β % of H:

100β

Kg H (l) + 21

1004

4,22100

××β

Nm3 air → 2

4,22100

×β

Nm3 H2O (g) + 2179

44,22

100××

βNm3

N2 (g) per Kg fuel Rewriting gives:

100β

Kg H (l) + 0,267β Nm3 air → 0,112β Nm3 H2O (l) + 0,211β Nm3 N2 (g) (17)

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Calculations for combustion of sulphur

S (l) + O2 (g) → SO2 (g)

32 Kg S (l) + 32 Kg O2 (g) → 64 Kg SO2 (g)

1 Kg S (l) + 1 Kg O2 (g) → 2 Kg SO2 (g)

1 Kg S (l) + 32

4,22Nm3 O2 (g) →

644,222× Nm3 SO2 (g)

1 Kg S (l) + 32

4,22Nm3 O2 (g) →

644,222× Nm3 SO2 (g)

Oxygen quantity converted to air quantity:

1 Kg S (l) + 21

10032

4,22× Nm3 air →

644,222× Nm3 SO2 (g) +

2179

324,22

× Nm3 N2 (g)

Rewriting gives:

100γ

Kg S (l) + 0,033γ Nm3 air → 0,007γ Nm3 SO2 (g) +0,0263γ Nm3 N2 (g) per Kg fuel (18)

The total amount of air that is required to for a theoretical combustion is:

0,089 (ϕ + 3β + 0,375γ) Air quantity and content of the flue gas are summarized in table 3 and 4. 3.2 Percentage volume oxygen For reasons of limitations of a burner, it is impossible to achieve complete combustion with stoichiometric air quantity. For this reason excess of air is required. The disadvantage of this method is that it influences the % vol. of oxygen in the flue gas. The value of % vol. of oxygen in flue gases is used in many efficiency calculations. It indicates e.g. how efficient fuel is fired. Reason for using oxygen as an important variable is, that it is independent of fuel composition. In case of combustion with air excess, the theoretical amount of air needed is then multiplied by the factor n.

n = amount of air flow / stoichiometric air The stoichiometric air for combustion of fuel in a simplified situation is given by

0,089 (ϕ + 3β + 0,375γ) Nm3 air per Kg fuel (table 3 and 4) The air excess is then calculated:

0,089 (n-1) (ϕ + 3β + 0,375γ) Nm3 air per Kg fuel oil

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S H C Total N2 0,0263γ 0,211β 0,0702ϕ 0,0702(ϕ + 3β + 0,375γ)

H2O - 0,112β - 0,112β SO2 0,007γ - - 0,007γ CO2 - - 0,0187ϕ 0,0187ϕ

*Note: This table must be read from left to right

Table 3 The amount of reactants formed on combustion of one Kg of liquid fuel

Air 0,033γ 0,267β 0,089ϕ 0,089(ϕ + 3β + 0,375γ)

Table 4 The amount of air required to combust on one Kg of liquid fuel

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When there is complete combustion with stochiometric air the % vol. of oxygen is zero. Thus if oxygen is present in flue gas, it is from the air excess. For oxygen in the excess air the above formula has to be multiplied by 0,21. That is the ratio of oxygen in the air.

0,21×0,089 (n-1) (ϕ + 3β + 0,375γ) Nm3 air per Kg fuel oil (19) Flue gas: Substituting the obtained values in Table 3 by: K = 0,089 A = (ϕ + 3β + 0,375γ) *Note: 0,089 (ϕ + 3β + 0,375γ) is the amount of air needed for combustion. This has to be multiplied by 0,21, because only 21% of the air (oxygen) is heated and converted to reaction products of combustion. Dry flue gas = Flue gas + N2 - H2O +O2 0,21AK + 0,79KAn- 0,21K3β + 0,21KA(n - 1) 0,21Akn + 0,79Akn - 0, 21K3β K(An - 3β0, 21) = K(An - β0, 63) Wet flue gas = K(An - β0, 63) + 0,112β (table 3 and 4) K(An - 0, 63β + 1,26β) K(An + 0,63β) Substituting back Dry flue gas:

0,089{n(ϕ + 3β + 0,375γ) – 0,63β} Nm3 air per Kg fuel oil (20) The total quantity of the flue gas with water is then given by:

0,089 {n (ϕ + 3β + 0,375γ) + 0,63β} Nm3 air per Kg fuel oil (21) Theoretically humidity in gases may have some influence on the % vol. O2. In practice these amounts are very small to have some influence on measurements.

%O2 = 10020.19.

×eqeq

% ⇒ ( )(

( ))

βγβαγβα

63,0375,03375,03121

−++++−×

nn

% (22)

For wet flue gas:

%O2 = 10021.19.

×eqeq

% ⇒ ( )(

( ))

βγβαγβα

63,0375,03375,03121

+++++−×

nn

% (23)

The value of 0,63β is very small comparing to the other values. This is why it can be neglected and the percentage of O2 in both dry and wet flue gas is determined by the next formula:

16


% O2 = ( )nn 121 −

(24)

For comparing the above formula with percentage CO2 a diagram is used. This is showed on figure 6. For the fuels used at Refineria Isla the API number is two. API stands for American Petroleum Institute and is a measure for the gravity of hydrocarbons, which is calculated by:

1,131..

5,141−=°

GrSpAPI (25)

Whereby specific gravity (Sp. Gr.) is defined as the ratio of the density of liquid at 60 °F to the density of the water at 60 °F. On the horizontal axis percentage air is given. This includes the 100% stochiometric air quantity. On the vertical axis percentage CO2 is given. In the past carbon dioxide in flue gas was measured and then oxygen was calculated. At present analyzers are in such way developed that one can measure the oxygen in the flue gas instead of calculating it.

17


% C

O2

% e

xces

s ai

r Fi

gure

6 P

erce

ntag

e ex

cess

air

vers

us p

erce

ntag

e C

O2

Sour

ce: J

.B. M

axw

ell D

ata

book

on

hydr

ocar

bons

, App

licat

ion

to p

roce

ss e

ngin

eerin

g

18

The sound of temperature Acoustic pyrometer

4. Acoustic Pyrometer The Acoustic Pyrometer (AP) is an instrument that is able to measure gas temperature. This measurement is based on the principle that propagation of acoustic signal is primary a function of absolute temperature. For many years acoustic pyrometry has been successful in a lot of applications around the world. Nowadays application of this device in refineries can be more complicated, the ideology of using gas temperature as control tool is the same. 4.1 Applications [5,6] In the late eighties when incineration became an alternative of handling trash problems in the United States, Waste-To-Energy (WTE) plants were constructed. As environmental awareness increased it became important to be able to control the burning of trash. Considering temperature, time and turbulence as important parameters for burning of trash cleanly, gas temperature becomes a key variable in this process. For technical reasons measuring gas temperature with accuracy and without effect of radiation on the instrument was a problem. Not much could be done to improve this inefficiency without influencing the temperature measurement. Taking this into account acoustic pyrometry has an advantage. Here the effect of radiation does not influence the instrument. With this the AP was incorporated in the system of a WTE plant and used as a control tool. Since then emissions of non-environmental friendly gases were minimized. Waste-To-Energy plant is only one application of the Acoustic Pyrometer. Since 1984 SEI Inc. has introduced The AP in coal, oil and gas fired utility boilers. Other applications are in black liquor chemical recovery boilers, metal heat treat furnaces and cement plants. Analyzing applications, all are based on the same principle, namely gas temperature control of emissions. Controlling flue gas temperature in fired furnaces is complicated since a lot of variables are involved. This is why the AP has to be used as a multifunctional tool. 4.2 Principle [7] The BoilerwatchMMP Acoustic Pyrometer system is based on the principle that the speed of sound traveling through a gas volume is proportional to the temperature of that gas. The velocity at witch an acoustic signal propagates is a primary function of absolute temperature. Secondly, composition of gas has less influence on the determining temperature but it cannot be neglected. Knowing the distance between transmitter and receiver, measuring the time taking for the wave to travel the distance, average velocity of the wave for that particular path can be computed. The equation below describes the relationships between the variables used to calculate gas temperature.

16,27310 62

−⋅

= −

BtdTc (26)

where Tc = temperature (°C) d = distance between transmitter and receiver (m) t = duration for the wave to travel (ms) B = acoustic constant which is determined by among other

things like the molecular weight of the gas. Combining several paths together a two-dimensional temperature distribution can be made for a furnace.

19


4.3 Setup The setup of the measurement system is very simple. There are sensors mounted on the furnace at equal elevation. This forms a two dimensional plane where the flue gas temperature is measured. The first setup (before 27 November 2002) had only four sensors in each combustion cell. The sensors were mounted on the observation doors at equal level as the burners. Figure 7 shows a sketch of the setup. At the end of October it was recommended to add extra sensors because of inaccurate measurement (appendix 2). To install extra sensors at the burner level it would require a shutdown of the furnace, which was not possible. Solution for this was instead of measuring in one plane, three planes were used. The extra sensors were placed above the burners while the others remained on their position beside the burners (Figure 8). Mounting the sensors above the burners was possible because of existing openings. After measuring in three planes the software plots the temperature distribution as if it was measuring in a single plane. The difference in length of the inclined planes is very small. Calculating the cosine of this angle has a result of one. This means that the inclined plane has the same length as the one at burner level. The configuration of area mapping of both setups are shown in figure 9. The first configuration shows that a combustion cell is divided in four equal areas. The second one is divided in sixteen areas where area 1-8 are equal in surface and 9-16 have smaller surfaces then the first eight. The smaller areas are the ones in the neighborhood of the tubes. 4.4 Thermal Mapping System 2000 The software used to visualize the temperature measurement is the TMS 2000. It displays windows of convenience with information of the measured gas temperature. Some windows are:

• Statistics Here information for each area is given. Information like mean temperature, maximum temperature, minimum temperature, rate of change, standard deviation and mean temperature.

• Path temperature graph Temperature for each area is given as a function of time.

• Area plot This window displays continuously the mean temperature of each area in the furnace.

• Isothermal mapping Here the isothermal graphs are visualized as continuously given at a specific location in the furnace.

• Path plot This windows shows the paths used and where the transmitters and receivers are located.

Figure 10 shows three of the above-mentioned windows.

20


21

Figure 7 First setup of the gas measurement system

Figure 8 Second setup of the gas measurement system


22

Figure 9 Both area configurations Left: First setup

Right: Second setup

Figure 10 Mapping examples of the TMS 2000
23

The sound of temperature Process heater

24

5. Process heater A furnace also called process heater is a device that heats up a bank of tubes as purpose to increase temperature of the flow inside. In process heaters the three fundamental ways of heat transfer are present. Energy transfer by means of convection and radiation are the most important. The furnace mentioned in this assignment is used to heat up hydrocarbons for distillation in a mild vacuum tower. This furnace consists of two radiant cells and one convection bank. The hydrocarbons pass through steel tubes, which receive heat on the outside area. The tube then transfers its heat to the process stream. To improve heat transfer a coil is splitted into parallel passes. The velocity of the flow in each pass is controlled in such way for optimal heat transfer, without causing excessive pressure drop due to friction. The passes of coils are uniformly distributed in the radiant cell. Purpose is for each to receive the same amount of heat. Radiant section Combustion takes place in the radiant section where the burners are located (figure 11). In this section fuel is fired and energy is transferred to tubes by radiation. The flames have temperatures above 1600 K and the flue gas temperature varies between 350 K - 1400 K. For areas around the tubes it is important not to have too high temperatures. This is to prevent coke formation inside the tube. Coke is an undesired solid that is the result of heating up hydroc*arbons for a prolonged time and has the characteristics of an insulator. The variables that have to be manipulated to prevent coke forming are tube temperature and retention time of the process stream. The transfer of heat is not efficient when there is coke present in the tubes. Subsequently heat will accumulate on the tube area until equilibrium is reached with the surroundings. Unfortunately the tubes have a maximum operating temperature. If there is a local overheated area on the tube it will damage the tube and lead to a rupture. Overheating of areas occurs when a flame is continuously hitting furnace tubes adjacent to the burners. This is classified as a flame impingement. It can be caused by:

• Operating without all burners in service • Insufficient primary and secondary air supply (air registers) • Excessive firing rates • Fouled burner tips • Eroded burner tips

Convection section Prior to the radiant cell the hydrocarbons are heated up in the convection bank. The heat transfer in this section is less then in the radiant section. According to the design data of the furnace 41.6 % of the total heat is picked up by the hydrocarbons in the convective section. Temperatures measured in the convection section are bridge wall and stack temperature. Bridge wall is the duct connecting the radiant cell and the convection bank. The temperature here is used to estimate flue gas temperature in the radiant cell. Nowadays implementation of the acoustic pyrometer makes it possible to actually measure flue gas temperature in the radiant cell instead of estimate it. As combustion gases propagate in the convective section it transfers its energy to the tubes. This means that more heat is transferred at the bridge wall then at the outlet of the convection cell. The temperature measured at the outlet is the stack temperature. The larger the difference is between bridge wall and stack temperature, the more effective the convection section is. On the other hand it is not recommended to operate F-1202 with stack temperatures lower then approximately 413 K. The SO2 and water vapor present in the flue gas will react with each other and form H2SO4 / H2SO3. For the furnace this means excessive corrosion of the steel tubes and frame.


25

Figure 11 Sketch of furnace F-1202


26

Burners Burners are designed to mix the combustion reactants in order to achieve a proper combustion. From chapter one it is known that fuel and oxygen has to be mixed thoroughly for complete combustion. This is done by means of atomization of fuel with high-pressure steam. The liquid fuel is dispersed into small droplets that will be mixed later with air. Figure 12 shows a burner layout. The top of the burner is magnified in order to analyze the atomization better. At the burner tip fuel and steam are mixed just before combustion. Further burners are designed to fire different types of fuel respectively, asphalt, fuel oil and refinery fuel gas. Each of the above mentioned fuels are process residues that do have low market value. So they are fired in furnaces. Air registers Due to mechanical limitations of the burner air registers are used. These are blades settled in circular position around the burner tip. The blades have an adjustable pitch, which is used to control flame pattern and creates a swirl in the flame zone to optimize the mixing of combustion reactants. Registers are also a secondary air supply. Flames can be compared as cylinders with a volume that has a relationship with fuel pressure. The diameter and length are variables that can be adjusted by the air registers. It is important for the process of heating up hydrocarbon that all the flames in the cells are equal. If this is not the case then an asymmetrical burning situation is present. It means that the radiation is no equally distributed in the cell. Draft In process heaters draft is present in order to maintain a flue gas current. It is important to keep draft in the furnace otherwise flue gas will leave the furnace through other openings which are not safe for employees. To keep explanation straightforward only text is used. If draft calculations or formulae’s are included it will become too complicated and unclear. For simplification, the furnace and the stack are substituted by a duct with different sections (figure 13). The left side of the duct is the one combustion cell and the right side is the outlet of the stack to the atmosphere. If all variables are constant the law of mass conservation can be applied. The same amount of mass entering the duct will leave the duct. At the outlet of the duct (stack) there is a wind velocity of the atmosphere. This develops an absolute pressure lower then the atmosphere (vacuum). This phenomenon can be compared to the Ventouri theorem that relates mass velocity to pressure. Beside this difference in flue gas density also causes draft in the system. It is known that flue gas in combustion cell possesses a higher temperature and lower density then at the stack outlet. A small amount of mass with a low density leaving the system will have a huge effect on the volume displacement in the furnace causing a current to the highest draft, which is the stack outlet. For the operation of a furnace a so-called stack damper located at the top of the convection section controls the draft. The draft form convection section outlet to the atmosphere is determined by the construction of the stack. Operating controls Although furnaces operate on simple principals, their controls can be very complicated. One can imagine that safety has a major priority in a refinery. The key in operating a furnace is to have a high compromise between safety and environmental boundaries and heat transfer efficiency.


27

Figure 12 Sketch of a burner with a magnified burner head with tip and plug Source: Verbrandings techniek

Figure 13 Simplification of draft system of a furnace


28

Like:

• Preventing overpressure in a furnace Flue gas will leave the furnace through other gaps instead of leaving through the stack. This is dangerous for an employee that is using e.g. an observation window.

• Preventing excessive high temperatures High temperatures can cause coke formation that is disastrous for the continuation of the process.

• Maintaining fuel pressure between safe ranges If fuel pressure is low then back firing at the burner is possible and too high pressure causes the furnace to operate beyond its design condition due to over firing.

Taking the above-mentioned circumstances into consideration control of the process and combustion variables must be in equilibrium. Figure 14 is a sketch of furnace F-1202. In here the controls are schematically shown.


29

Figure 14 Schematical layout of furnace F-1202

The sound of temperature Discussion

30

6. Discussion At Refineria Isla tests are discussed prepared and then data is collected after a manipulation for analysis. For this reason when every test is made a so-called “test prospectus” is prepared. A test prospectus has all the procedures and / or requests that are necessary for a test. A test has a theoretical background and reasoning. Implementing this requires a safety and operational evaluation. After an approval for the prospectus the shift supervisors and operators have to be informed about the execution of the test. When tests are done and data is collected the part of analysis starts. It is preferred to present data as simple as possible. In this assignment two kinds of test were done namely manipulation of draft and registers. The test of the draft was to determine if draft had influence on the temperature measured by the acoustic pyrometer. (In refineries it is preferred to use draft instead of pressure to prevent confusion.) A scale of convenience was introduced to be able to reproduce the operating conditions. Position 1 is fully open and position 5 is closed at the safety minimum opening. After the new setup there was more emphasis on registers. In chapter 4 it is showed that the second setup has a better resolution then the first one. There were also more areas added. For the register test it was more important to reproduce the data acquired in every register manipulation. The objective is identifying an ideal flame pattern by means of temperature distribution. The results of the tests are separately given in appendix 1, 3, 4 and 5. In every appendix there are prospectus, results and conclusions. 6.1 Manipulation of stack damper From the data gathered in the different tests it is showed that operating conditions were almost similar. Like mentioned before intentions were to reproduce data whenever operating conditions where the same during the test. From the results it can be noticed that every time stack damper and / or register were manipulated the temperature distribution changed. In the appendix of the tests it is showed that at relative low draft average temperature measured by the acoustic pyrometer is at its maximum. This can be explained by summarizing some facts:

• Decreasing draft in the furnace • During the tests of the stack damper no incomplete combustion was visually

confirmed • When % vol. oxygen in flue gas decreases • Combustion air was not measured accurately in every test by the flow indicator.

All this means that less air was supplied to the furnace when stack damper was closed. By decreasing the excess air more heat is transferred to the process stream and less to the air. In appendix 1 and 3 it is concluded that this leads to a better heat pick up in the radiant cell. This could be interpreted in a decrease in fuel flow. 6.2 Manipulation of air registers In the two tests of manipulation of registers it is showed that no reproducible data is found. In the first register test (appendix 4) some adjustments were repeated. The charts show that there is no relative equal temperature distribution. Here draft should have not sufficient influence on the temperature, because of a fixed stack damper position. It was visually confirmed that when registers were below position 5, incomplete combustion was determined. Further for all the tests done no conclusive data were found.

The sound of temperature Conclusion & Recommendations

31

7. Conclusion & Recommendations 7.1 Conclusion The proposed objectives for this assignment were too ambitious to achieve in such short time. Each objective should be studied separately. From the obtained data no correlation were found. It is possible that not sufficient tests were done in order to obtain better results or the most important conclusion is that there are quite a number of variables that influence the flue gas temperature. Introducing the acoustic pyrometer as a control tool would require more then just a few tests and this assignment. The system can be used at present better as a monitoring tool. This would help in developing required knowledge for understanding and defining possible flame patterns. 7.2 Recommendations It is proposed for further studies to change assignment objectives of controlling emissions and process. The acoustic pyrometer should be introduced as a monitoring tool. When this is the case then an ideal flame pattern should be defined, qualitative. After this as much data as possible mush be gathered to identify this flame. All other patterns will then be considered as none desired. For example flame impingement can have various patterns but an ideal flame has only one pattern. It cannot be affirmed that the best measuring plane is parallel or perpendicular to the burner. Yet for this box type of furnace measuring parallel to the flame can be better. Once having these basics under control personnel can rely on these temperatures and work can be done more efficiently. Also this would be a better step for introducing the acoustic pyrometer as control tool. Tests of process stream flow should be done. This is only one example of tests that are possible to do. With possible influence of process stream temperature one can investigate the behavior of the flue gas temperature distribution. Repeating every test will give better information about the furnace. Possible combination with this test is if there was a possibility to measure in a plan parallel to the tubes. This test setup can be installed in the next shut down when there is a turnaround. Understanding the data gathered by software used (TMS 2000) requires a better insight of the operational conditions of a furnace. This is a reason for informing the personnel of operations about the possibilities of the gas measurement system and explaining them what is plotted. The feed back of operations should not be underestimated. For better analysis a position indicator can be placed at the air registers and stack damper for recording the positions. With this there would be data about the positions of the registers. It is also more accurate.

The sound of temperature Afterthought

32

Afterthought At the beginning of this assignment I expected to achieve all the objectives that were set. During my placement period it was noticed that these goals could not be reached. This, because a change in setup was required. Further the flue gas dynamics in this type of furnace did not make it easier. Less positive is that all the data collected before the second setup could not be used any more. In the first week of December data was reliable enough to do some extra tests, which caused some delay in preparing this report. Although none of the objectives were achieved still I am satisfied with the things I have learned. A great help in gathering and analyzing data was the software Plant Information (PI) by Osisoft. This is a function that can be added to MS Excel. This function gathers information that is required from the database and translates it to the Excel system. Beside doing this it also has many options for calculations. These are options that make it easier for analyzing data.

The sound of temperature References

33

References Manuals [1] Charles E. Baukal, Jr The John Zink combustion handbook John Zink Co., 2001 [2] Robert H. Perry and Don Green Perry's chemical engineers' handbook sixth edition [3] Donald Q. Kern Process heat transfer International student edition [4] Refineria Isla proprietary course on combustion [5] Applications of acoustic gas temperature measuring systems in waste to energy plants Bonnen & Drescher ingenieursgesellschaft mbH, January 2000, Adenhoven, Germany [6] International Cement Review Hear the difference? SEI Inc. June 2002, Nevada, USA [7] Technical manual of acoustic gas temperature measurement SEI Inc., April 2001, Nevada, USA [8] J.B. Maxwell Data book on hydrocarbons, Application to process engineering ninth edition, Florida Internet http://csep10.phys.utk.edu/astr162/lect/light/spectrum.html http://www.pdvsa.com

The sound of temperature Appendix 1

34

Appendix 1 (Test 1)


35

Test prospectus 1 From: Duarte Marques To: H.Hernandez / TSPP, G.Con / TSPP3, D. van der Veen / OPDM, Date: September 24, 2002 Subject: Measurement run at CD-3 F-1202 1. Introduction It is proposed to have a measurement run the 4th and 5th of October at F-1202. The scope of the test is to determine what influences the pressure in the different sections of the furnace have on the flue gas temperature measured by the Acoustic Pyrometer. 2. Operating conditions It is important for the test to maintain the process variables of F-1202 as steady as possible. The waste gas of the column C-1202 has to be vented to the atmosphere. Fuel burned is asphalt. During the test request goes to the shift supervisor not to switch to refinery fuel gas. If necessary to fire fuel gas this will have to be done in furnace F1201, A, B, C. 3. Procedure Before the experiment stoichiometric air quantity will be determined qualitatively. At the beginning of the test, all the air registers will be fixed at position 7. After checking that the flames do not destabilize the process flow or impinge, data will be collected. The test will consist of changing the stack damper position every day during the time scheduled. Every day data is collected and evaluated before changing position of the damper. The effect of the air register position on the AP temperature, will be evaluated. 4. Measurement Measurements of importance during the test are draft, O2, airflow, fuel flow. Data will be collected during the test period. A few days before the experiment, MTI will be requested to check and calibrate instruments of importance. Below a table of the instruments to be checked. The change of stack damper position will be every time one quart of the total range. The total range of the damper is defined as the scale between fully open and fully closed. Any type of comment on change in process condition without variables change will be appreciated. List of instruments to be checked

Tag number Description 1 D2:12FC111.M COMBUSTION AIR TO F1202 2 D2:12Q017.M F1202 OXYGEN IN FLUE GAS 3 D2:12FI103.M FUEL OIL TO F1202


36

Results of test 1 Date : 12 October 2002 Writer : Duarte N. de Jesus Marques 1. Objective To determine what influences of pressure in different sections of furnace have on the flue gas temperature measured by the acoustic pyrometer. 2. Analysis It was scheduled to adjust the combustion airflow to stoichiometric air quantity. After this an excess air of 30% was planned to be added. For technical reasons it was not possible to do this. The bailey that controls the damper of the combustion air was not properly aligned. Important was to determine the influence of the stack opening on the combustion airflow to the furnace. Thus testing closing the stack damper would decrease the airflow. Chart 1 shows the course of the combustion air during the time of the test. It shows that no considerable change in flow was measured when the stack damper and air registers were manipulated. Chart 2 shows that the oxygen level decreases during the test. Visual inspection confirmed that the combustion was complete. Thus the decreasing oxygen level indicates a decrease in combustion air. This indicates that the flow instrument of air was not accurate enough. The time when the variables were changed is given in table 1 and the settings of registers are given in table 2. It is known that when the stack damper is closed the absolute pressure will increase, meaning that draft decreases. The flue gas remains longer in the furnace, which stabilizes the flue gas dynamics and increases the average temperature in the radiant cells. Charts 3 and 4 shows the temperature of the acoustic pyrometer during the test. It is noticed that when the positions of the stack damper and registers are changed, immediate temperature difference is observed in the measurement. Determining what the relationships are between register position, stack damper position and temperature is difficult. This, because separate tests of registers and damper have to be made. In this test both were done simultaneously, which makes it difficult to quantify the influence of the variables. An issue that cannot be either neglected or prevented is the drop in fuel flow around 14:00 hours (chart 1). This is an effect of petroleum temperature increase measured by the temperature control at the outlet of the radiant cell (chart 5). The cause of this is the cascade arrangement of the combined outlet temperature control and the flow control of the fuel valve. Increasing the flue gas temperature in the radiant cell, keeping the fuel pressure constant, the temperature of the heated crude will also increase. Because of the fixed set point of the temperature control, this closes the fuel valve if the temperature of the crude increases. Also it the chart 2 shows that the bridge wall temperature decreases. The flue gas temperature in radiant cell increases. This means that there was an increase of heat transfer of the flue gas. Chart 6 shows that the draft at -14 mmH2O, flue gas temperature is at its maximum. This could be the optimum draft for the furnace.


37

3. Conclusion The test results are not conclusive. With regards to the individual impact of the stack damper and/or air register. However, it is clearly noticed that the flue gas temperature increased by closing the stack damper. This resulted in a reduction of the asphalt flow at constant heater outlet temperature. (The process temperature controller takes care of this when in automatic control.) All this is translated in an improved heat pick up in the furnace. 4. Recommendation It is recommended to perform additional tests manipulating the stack damper or register alternately keeping the other in a fixed position.


38

Posi

tion

stac

k da

mpe

r

Tim

e ch

ange

Setti

ng

regi

ster

s

Tim

e ch

ange

1 friday 1 friday 2 8:48 2 10:37 3 11:30 3 12:58

4 14:03 4 14:58

5 15:47

Table 1 Time when variable were changed

Position air registers

Air r

egis

ters

@

burn

er

setti

ng 1

setti

ng 2

setti

ng 3

setti

ng 4

13 *7 *7 *7 *7

14 7 7 9 6

19 7 2 2 2

Rad

iant

cel

l Nor

th

F-12

02

20 7 2 2 6

15 7 7 9 9

16 7 7 9 6

17 7 2 2 2

Rad

iant

cel

l Sou

th

F-12

02

18 7 2 2 6

* Indicates that register of burner 13 was stuck at position 7

Table 2 Settings of registers


39

1. Combustion

0,00

200,00

400,00

600,00

800,00

1000,00

1200,00

1400,00

1600,00

7:12 8:24 9:36 10:48 12:00 13:12 14:24 15:36 16:48 18:00

Time

Com

bust

ion

air (

T/D

)

0,00

10,00

20,00

30,00

40,00

50,00

60,00

Fuel

flow

(T/D

)

comb.air flow asph.

time when stack damper was movedtime when air register was moved


40

2. B.W.T & O2

400

500

600

700

800

900

1000

1100

1200

1300

7:12 8:24 9:36 10:48 12:00 13:12 14:24 15:36 16:48 18:00

Time

Tem

pera

ture

(K)

0,00

2,00

4,00

6,00

8,00

10,00

12,00

14,00

16,00

18,00

O2

(%-v

ol.)

bwt O2



41

3. A.P. Temperature north cell

400

500

600

700

800

900

1000

1100

1200

1300

7:12 8:24 9:36 10:48 12:00 13:12 14:24 15:36 16:48 18:00

Time

A.P

. tem

pera

ture

(K)

AN1 AN2 AN3 AN4



42

4. A.P. Temperature south cell

400

500

600

700

800

900

1000

1100

1200

1300

7:12 8:24 9:36 10:48 12:00 13:12 14:24 15:36 16:48 18:00

Time

A.P

. tem

pera

ture

(K

)

AS1 AS2 AS3 AS4



43

5. T.C. Outlet

616

617

618

619

620

621

622

623

624

625

7:12 8:24 9:36 10:48 12:00 13:12 14:24 15:36 16:48 18:00

Time

Tem

pera

ture

(K)

temp.outlet



44

6. Average draft - Average A.P. Temperature

y = 0,0969x4 + 5,2447x3 + 102,61x2 + 858,74x + 3789R2 = 1

400

500

600

700

800

900

1000

1100

1200

1300

-20,00 -18,00 -16,00 -14,00 -12,00 -10,00 -8,00 -6,00 -4,00 -2,00 0,00

Average draft (mmH2O)

Ave

rage

A.P

. Tem

pera

ture

(K)

aver. draft - aver. A.P. temp. Polynoom (aver. draft - aver. A.P. temp.)



45

Appendix 2 (Memorandum)


46

Memorandum Objective of meeting : Discussion setup of AP at F-1202 Date : 28 October 2002 Present : Giovanni Con, Henry Hernandez, Duarte Marques,

Roberto Roubicek, Douglas van der Veen Topics of discussion Introduction → Problem explanation (Intensity level of radiation is at wrong position)

Measured Expected Draft has to much influence Explained with q = ε A T4 Option 1 → Install two sensors one at the south and at the north side of

each cell Disadvantage: Not executable on short term Advantage: Closer to tubes, better for tube skin calculations

Option 2 → Use thermo wells above burners as openings for sensors. Disadvantage: Eight sensors needed, four not enough Advantage: Steady pattern expected

Burner area

Burner area

Burner area

Burner area


47

Sensor at each arrow In case option 2 is possible the smothering steam line has to be relocated. Minutes: During the meeting it was explained that the actual setup is not reliable enough. This because the peak heat flux is not at the expected location. The 'hot areas' in the furnace should be in the neighborhood of the flames, witch is not the case right now. The measured values of temperature with the present setup are mostly influenced by draft. The two options on the agenda were discussed and a solution was proposed. For the first option a shutdown of the unit is required and it is the most adequate setup. Optional methods of installation without shutting down were explained and proposed by Mr. Roberto Roubicek. Methods like thermal welding and other similar to this were discussed, but not approved. This for limited knowledge of reliability and safety of these techniques of the ones present in the meeting. The second option was immediately approved by Mr. Douglas van der Veen (CD-3 supervisor). He explained that there would be no problem in relocating the smothering steam line while operating the furnace. After further discussion a third option was proposed by Mr. Roberto Roubicek. The third setup constitutes of a two-plane measurement system. The actual setup will be used and a secondary plane of measurement would be added. The second plane is located above the flames and the sensors would be located in the thermo wells above the burners. One issue that ended undefined was the availability of sensors. Depending on the quantity of sensors available, the last setup is done in one or both cells. Further topics like confidentiality of the report of Mr. Duarte Marques was mentioned. It was agreed that the report would be written in a non-confidential form. Uncertainty of setup of the acoustic pyrometer leads to the decision to qualify the report as confidential.

flame flame

Smothering steam line


48

Memorandum From : Duarte Marques To : H. Hernandez / TSPP, G. Con / TSPP3, D. van der Veen / OPDM,

R. Roubicek / SEI Inc. Date : November 4, 2002 Subject : New setup at CD-3 F-1202 Reasoning Since the beginning of this project it was noticed that the concentration of the hottest flue gas were always found on the vertical acoustic paths. During the analysis of a test made on October 5 it was found that when almost all variables were in control, still the hottest flue gas was changing constantly of position. The visualization of temperature distribution was not stable. The changes were always on the vertical acoustic paths. After reviewing some literature again, it was found that the mapping of The TMS 2000 was contradicting the theory concerning flame temperature and radiation heat transfer. None of the acoustic paths were in the surroundings of the flame. Still the hot areas were on the vertical acoustic paths. Analyzing straight forward there can never be an area in the process heater hotter than the source of radiation which is the flame. Knowing that radiation does not have any effects on the measurement of the acoustic pyrometer, it can be assumed that the flue gas leaving the flame on the top should be measured as the hottest part in the furnace by the acoustic system. From the studied literature the top of the flame is supposed to be the hottest part of the flame. Knowing this it was concluded that the gas measurement system was not visualizing the data accurately. Not because of a failure of the system, but this was a consequence of insufficient sensors present in the furnace. After these preliminary conclusions a meeting was called with the concerning engineers to convince them that the setup was useless and to discuss a new setup. When a new provisory setup was discussed and installed the new mapping system was plotting a more stable temperature distribution. The concentration of the hottest flue gas was also in the surroundings of the top of the flames. Comparing both data before and after the new setup it is suspected that the hot areas in the prior setup were actually the surroundings of the "real" hot areas in the new setup. The figures below shows the mapping of the first setup and the second one. The combustion and process variable were almost the same in both situations. The second mapping shows a much better temperature measurement and visualization of temperature distribution.


49

Resolution of the prior setup

Figure 1 Date: 9 August 2002

A B

Figure 2 Date: 27 November 2002

Resolution of the new setup

A B


50

Appendix 3 (Test 2)


51

Test prospectus 2 From: Duarte Marques To: H. Hernandez / TSPP, G. Con / TSPP3, D. van der Veen / OPDM, Date: November 11, 2002 Subject: Measurement run at CD-3 F-1202 Addendum It is planned to have a measurement run on the 20 November at F-1202. The objective is to determine what influences the pressure in the different sections of the furnace have on the temperature measured by the acoustic pyrometer with a provisory setup. It is requested to the shift supervisor to maintain process and combustion variables as steady as possible. Condition will be similar as outlined in test prospectus dated 24 September (Appendix 1). This time air registers will stay fixed at position 7. Also there is no need to check or calibrate the instruments of importance.


52

Results of test 2 Date : 20 November 2002 Writer : Duarte N. de Jesus Marques 1. Objective To determine what influences of pressure in different sections of furnace have on the flue gas temperature measured by the acoustic pyrometer. 2. Analysis After installing a provisory setup it was scheduled to repeat the first test. This time only the stack damper was manipulated. Difference this time is that only in the radiant south cell is measured. It was scheduled to fire asphalt fuel in the furnace. Due to operational circumstances fuel type was switched to refinery fuel gas. These are procedures to prevent not controlled burning of fuel. An other issue was that Maintenance Technicians (MTI) has confirmed that the temperature controller of the furnace outlet have great inaccuracies. This is the reason that fluctuations in process stream temperature has upset the combustion and process variables (chart 1). Visual inspection did not confirm any incomplete combustion. The decrease in oxygen level on chart 2 means that combustion air flow decreased during the test. This was also measured this time with the flow indicator of the combustion air. Subsequently heat emitted by the flames is used more efficiently, because less excess air is heated during the combustion process. Keeping the registers fixed a linear relationship is found between average draft and average acoustic temperature in the south cell (chart 4). Comparing BWT and average flue gas temperature in the cell, only difference of approximated 35K is measured (chart 5). This means that the heat pick up has improved. The linear relationship found is yet to be proved that it can be reproduced. Comparing the first test with is not correct, because the register positions were manipulated then. Although a relationship is found in this test still it is not much of use in the present control system. 3. Conclusion The result obtained is not much of use. Still this relationship has to be proved and repeated with other tests. However, it is clearly noticed that the flue gas temperature increased by closing the stack damper. This resulted in a reduction of the asphalt flow at constant heater outlet temperature. All this is translated in an improved heat pick up in the radiant cell of the furnace. 4. Recommendation It is recommended to perform additional tests manipulating the stack damper to confirm the obtained relationship.


53

Posi

tion

stac

k da

mpe

r

Tim

e ch

ange

1 tuesday 2 8:32

3 12:22 4 14:05

5 15:47

Table 1 Time when stack damper was manipulated


54

1. Combustion

1110,00

1120,00

1130,00

1140,00

1150,00

1160,00

1170,00

1180,00

1190,00

1200,00

7:12 8:24 9:36 10:48 12:00 13:12 14:24 15:36 16:48 18:00

Time

Com

butio

n ai

r (T/

D)

0,00

5,00

10,00

15,00

20,00

25,00

30,00

35,00

40,00

45,00

Fuel

flow

(T/D

)

comb.air flow gas


55

2. B.W.T. & O2

400

500

600

700

800

900

1000

1100

1200

1300

7:12 8:24 9:36 10:48 12:00 13:12 14:24 15:36 16:48 18:00

Time

Tem

pera

ture

(K)

0,00

2,00

4,00

6,00

8,00

10,00

12,00

14,00

16,00

18,00

O2

(%-v

ol.)

bwt O2


56

3. T.C. Outlet

595

600

605

610

615

620

625

630

635

7:12 8:24 9:36 10:48 12:00 13:12 14:24 15:36 16:48 18:00

Time

Tem

pera

ture

(K)

temp.outlet


57

4. Average draft SRC - Average A.P. Temp SRC

y = 8,76x + 1336R2 = 0,9909

1160

1180

1200

1220

1240

1260

1280

-20,00 -18,00 -16,00 -14,00 -12,00 -10,00 -8,00 -6,00 -4,00 -2,00 0,00

Average draft SRC (mmH20)

Ave

rage

A.P

. Tem

pera

ture

SR

C (K

)

Aver. Draft src - Aver. AP src Lineair (Aver. Draft src - Aver. AP src)


58

5. B.W.T & Average AP temperature

500,00

600,00

700,00

800,00

900,00

1000,00

1100,00

7:12 8:24 9:36 10:48 12:00 13:12 14:24 15:36 16:48 18:00

Time

Tem

pera

ture

(K)

bwt aver. AP. temp.


59

Appendix 4 (Test 3)


60

Test prospectus From: Duarte Marques To: H.Hernandez / TSPP, G.Con / TSPP3, D. van der Veen / OPDM, Date: December 6, 2002 Subject: Measurement run at CD-3 F-1202 1. Introduction It is proposed to have a measurement run on December 7 at F-1202. The scope of the test is to determine what influences the pressure in the different sections of the furnace have on the flue gas temperature measured by the acoustic pyrometer using the new setup. 2. Operating conditions It is important for the test to maintain the process variables of F-1202 as steady as possible. The waste gas of the column C-1202 has to be vented to the atmosphere. The test will be done at F-1202 firing asphalt. All actions must be taken to maintain the process and combustion variables as steady as possible. In the event that fuel gas has to be fired it is requested to maintain F-1202 on asphalt and switch F-1201 A / B and / or F-1201 C on gas. 3. Procedure At the beginning of the test, all the air registers will be fixed at position 7. Data will be collected after evaluation of flame pattern. The test will consist of changing the stack damper position every 1.5 hours during the time scheduled. Every time data is collected and evaluated prior to changing the position of the damper. The test will cover all five positions of the stack damper. A second test will be conducted maintaining a fixed stack damper position while adjusting the air registers of all four burners in cell B. Any deviation in the crude quality and / or process condition that can affect the behavior of F-1202 must be recorded. Kind regards Duarte Marques


61

Results of test 3 Date : 6 December 2002 Writer : Duarte N. de Jesus Marques 1. Objective To determine what influences of pressure in different sections of furnace have on the flue gas temperature measured by the acoustic pyrometer. 2. Results According to the test prospectus, it was proposed to perform two separate tests. The first part of the analysis are the results of the test with the stack damper. The second ones are from the register test. The time when stack damper was manipulated is given in table 1. It is noticed that during the test the asphalt flow (chart 1) dropped, while other variables remained constant. The measured combustion air and oxygen level also decreased, which was expected. This, because closing the stack damper creates less draft. Chart 3 shows a relationship found between average draft in the south cell and average gas temperature in the same cell (New setup, only one cell has sensors). This correlation should not be compared with the previous one of the first test. This test had variable register positions. Chart 3 also shows that the highest average temperature is at a draft of -10 mmH2O. Here high temperatures are achieved while fuel flow decreased. Comparing the average temperature obtain from the AP with the BWT it is showed that heat pick up in the radiant cell remained normal. Fluctuations in temperature cannot be explained, because other variables were constant. Chart 4 and 5 shows that position 5 of the damper gives a better distribution of temperature. This can be noticed by comparing the differences of the columns of position 5 with the other ones. Air register In chart 6 to 9 average temperatures are showed of the areas with different register settings. These settings are given in table 1. It is showed that the areas where the burners are located 1, 4, 5 and 8 do not have considerable temperatures differences between settings 1 and 6. Chart 7 shows two identical settings (6 and 9) but the measured temperature distribution is not reproduced. This shows that flue gas dynamics have influence on the measurement or the dead time of the temperature distribution is too long. It means that it takes too long for the furnace to change it temperature distribution pattern after changing position of a register. Chart 9 shows that in setting 2 and 3 when one register position is changed small temperature differences are measured. In setting 4 two register positions are manipulated. It is noticed that the difference in temperature between each setting increased. Still it seems that the distribution of temperature remains steady. 3. Conclusion The test results are not conclusive. With regards to the individual impact of the stack damper and/or air register. However, it is clearly noticed that the flue gas temperature did not increase by closing the stack damper. However still the asphalt flow decreased. (The process temperature controller takes care of this when in automatic control.) Regarding the register test, the results were not reproduced when settings were repeated. This indicates that differences are measured but still no results are conclusive.


62

Time Position 7:30 1 9:00 2

10:30 3 12:00 4 13:30 5 15:00 finish

Table 1 Time when stack damper position was manipulated

Setti

ng

Tim

e

posi

tion

regi

ster

@

bu

rner

15

posi

tion

regi

ster

@

bu

rner

16

posi

tion

regi

ster

@

bu

rner

17

posi

tion

regi

ster

@

bu

rner

18

1 16:00 10 10 10 10 2 16:10 10 7 10 10 3 16:40 10 3 10 10 4 17:10 7 3 10 10 5 17:25 3 3 10 10 6 17:40 3 3 3 3 7 17:55 3 3 7 7 8 18:10 3 3 10 10 9 18:25 8 8 8 8

Table 2 Settings of the registers


63

1. Com bustion

1100,00

1110,00

1120,00

1130,00

1140,00

1150,00

1160,00

1170,00

1180,00

1190,00

1200,00

1210,00

6:00 7:12 8:24 9:36 10:48 12:00 13:12 14:24 15:36

Tim e

Com

bust

ion

air (

T/D

)

0,00

10,00

20,00

30,00

40,00

50,00

60,00

70,00

80,00

Asp

halt

flow

(T/D

)

com b.air asph.f low


64

2. B.W.T & O2

400

500

600

700

800

900

1000

1100

1200

1300

6:00 7:12 8:24 9:36 10:48 12:00 13:12 14:24 15:36

Time

Tem

pera

ture

(K)

0,00

2,00

4,00

6,00

8,00

10,00

12,00

14,00

O2

(%-v

ol.)

bwt O2


65

3. Draft - Temperature

y = -0,2497x3 - 9,9777x2 - 125,25x + 534,83R2 = 0,9965

1005

1010

1015

1020

1025

1030

1035

1040

1045

-20,00 -18,00 -16,00 -14,00 -12,00 -10,00 -8,00 -6,00 -4,00 -2,00 0,00

Average draft (mmH2O)

Ave

rage

tem

pera

ture

(K)


66

4. Average temperature (1-8)

700720740760780800820840860880900920940960980

10001020104010601080110011201140116011801200

1 2 3 4 5 6 7 8

Areas

Ave

rage

tem

pera

ture

(K)

pos.1 pos.2 pos.3 pos.4 pos.5


67

5. Average temperature (9-16)

700720740760780800820840860880900920940960980

10001020104010601080110011201140116011801200

9 10 11 12 13 14 15 16

Areas

Ave

rage

tem

pera

ture

(K)

pos.1 pos.2 pos.3 pos.4 pos.5


68

6. Short register test

700720740760780800820840860880900920940960980

10001020104010601080110011201140116011801200

1 2 3 4 5 6 7 8

Areas (1-8)

Ave

rage

tem

pera

ture

(K)

set.1 set.6 set.9


69


700720740760780800820840860880900920940960980

10001020104010601080110011201140116011801200

9 10 11 12 13 14 15 16

Areas (9-16)

Ave

rage

tem

pera

ture

(K)

set.1 set.6 set.9


70


700720740760780800820840860880900920940960980

10001020104010601080110011201140116011801200

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Areas

Ave

rage

tem

pera

ture

(K)

set.5 set.8


71


700720740760780800820840860880900920940960980

1000102010401060108011001120114011601180

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Areas

Ave

rage

tem

pera

ture

(K)

set.2 set.3 set.4


72

Appendix 5 (Test 4)


73

Test prospectus 4 From: Duarte Marques To: H.Hernandez / TSPP, G.Con / TSPP3, D. van der Veen / OPDM, Date: December 6, 2002 Subject: Measurement run at CD-3 F-1202 1. Introduction It is proposed to have a measurement run on December 16 at F-1202. The scope of the test is to determine the influence of a single register have on the temperature distribution measured by the new setup of the acoustic pyrometer. 2. Operating conditions For this test it is requested to maintain the process stream flows equal for coils one to four. This to prevent influence of the process temperature on the temperature distribution. It is important for the test to maintain the process variables of F-1202 as steady as possible. The waste gas of the column C-1202 has to be vented to the atmosphere. The test will be done at F-1202 firing asphalt. All actions must be taken to maintain the process and combustion variables as steady as possible. In the event that fuel gas has to be fired it is requested to maintain F-1202 on asphalt and switch F-1201 A / B and / or F-1201 C on gas. 3. Procedure At the beginning of the test, all the air registers will be fixed at position 10. Data will be collected after evaluation of flame pattern. The test will consist of manipulating register position in the order of position 10, 8, 5 and 2. After collecting data for the several positions, the register position is returned to its initial state. This procedure is also repeated for registers at burners 17 and 18. Any deviation in the crude quality and / or process condition that can affect the behavior of F-1202 must be recorded. Kind regards Duarte Marques


74

Results of test 4 Date : 16 December 2002 Writer : Duarte N. de Jesus Marques 1. Objective To determine the influence of a single register have on the temperature distribution measured by the new setup of the acoustic pyrometer. 2. Analysis The data is presented in such way that each area is showed independently in the diagram. Every column represents the average acoustic temperature when register was manipulated. In charts 1-10 sequence of areas are given horizontally with their correspondent register. Every chart has a fixed position of the air register. Chart 7 and 8 where position of registers are at 10. It is noticed that after manipulating the register average temperature of the areas do not return to its initial value. These two charts are important, because after manipulating a register it is returned to position 10. Subsequently the next register is manipulated while the others remain fixed. Interpreting this into the graphs all three columns showed per area should have the same average temperature (height). Not only these two charts shows not repetitive data but also the other ones. On the other hand temperature difference is noticed when register position are changed. Possible explanation for these results are that the registers are not positioned equally. Second the range of the opening may also not be equal. An other possibility is that the dead time of the furnace is to long, resulting in a very slow reaction of dynamics if registers are manipulated. 3. Conclusion The data acquired is not conclusive. The fact that data is not repetitive for equal positions while other variable are constant, determines this. 4. Recommendation More tests should be done to determine that the registers are not equally calibrated. If temperature distribution is different then dead time and / or dynamics of the furnace have to much influence to obtain reliable data.


75

1. Register position 2

600620640660680700720740760780800820840860880900920940960980

10001020104010601080110011201140116011801200

16/A117/A118/A1

A2A2A2

A3A3A3

A4A4A4

A5A5A5

A6A6A6

A7A7A7

A8A8A8

Areas

Ave

rage

tem

pera

ture

(K)

reg.16 reg.17 reg.18


76


600620640660680700720740760780800820840860880900920940960980

10001020104010601080110011201140116011801200

16/A917/A918/A9

A10A10A10

A11A11A11

A12A12A12

A13A13A13

A14A14A14

A15A15A15

A16A16A16

Areas

Ave

rage

tem

pera

ture

(K)



77


600620640660680700720740760780800820840860880900920940960980

10001020104010601080110011201140116011801200

16/A117/A118/A1

A2A2A2

A3A3A3

A4A4A4

A5A5A5

A6A6A6

A7A7A7

A8A8A8

Areas

Ave

rage

tem

pera

ture

(K)



78


600620640660680700720740760780800820840860880900920940960980

10001020104010601080110011201140116011801200

16/A917/A918/A9

A10A10A10

A11A11A11

A12A12A12

A13A13A13

A14A14A14

A15A15A15

A16A16A16

Areas

Ave

rage

tem

pera

ture

(K)



79


600620640660680700720740760780800820840860880900920940960980

10001020104010601080110011201140116011801200

16/A117/A118/A1

A2A2A2

A3A3A3

A4A4A4

A5A5A5

A6A6A6

A7A7A7

A8A8A8

Areas

Ave

rage

tem

pera

ture

(K)



80


600620640660680700720740760780800820840860880900920940960980

10001020104010601080110011201140116011801200

16/A917/A918/A9

A10A10A10

A11A11A11

A12A12A12

A13A13A13

A14A14A14

A15A15A15

A16A16A16

Areas

Ave

rage

tem

pera

ture

(K)



81


600620640660680700720740760780800820840860880900920940960980

10001020104010601080110011201140116011801200

16/A117/A118/A1

A2A2A2

A3A3A3

A4A4A4

A5A5A5

A6A6A6

A7A7A7

A8A8A8

Areas

Ave

rage

tem

pera

ture

(K)



82


600620640660680700720740760780800820840860880900920940960980

10001020104010601080110011201140116011801200

16/A917/A918/A9

A10A10A10

A11A11A11

A12A12A12

A13A13A13

A14A14A14

A15A15A15

A16A16A16

Areas

Ave

rage

tem

pera

ture

(K)


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