btu analisis qué,por qué, y cómo how

BTU Anlisis Utilizando un Cromatgrafo de Gases

GC Division

Objetivos

Por qu utilizamos analizadores de BTU?

Qu es unalizador de BTU?

Cmo trabaja un analizador de BTU?

Qu es un Cromtogrado de Gases en Lnea ?

Un Cromatgrafo de Gases en Lnea es

Es un instrumento que mide, ya sea, un componente o varios componentes en una corriente de gas. (Proporciona la composicin de todas las partes del gas).

Algunas propiedades fsicas de interes comn en el rea de aplicacin de gas natural (BTU) son:

1. Poder Calorfico (BTU, Joules, calories, etc.)

2. Densidad Relativa

3. Compresibilidad

Componentes Tpicos MedidosAnalizador de BTU en Gas Natural

Hexanos+ C6+Propano C3Isobutano IC4Normal Butano NC4Neo Pentano Neo C5Isopentano IC5Normal Pentano NC5Nitrogeno N2Methano C1Dioxid de Carbono CO2Ethano C2

Componentes Rangos Tpicos0 0.7 %0 5 %0 1%0 1%0 1%0 1%0 1%0 15%0 100%0 10%0 15%

Por qu utilizamos un Cromatgrafo de Gases (GC)?

Actualmente mas del 80% de las necesidades de energa mundial es proporcionada por combustibles fsiless. Estas necesidades pueden ser divididas entre 40% aceite, 30% gas natural, y 10% carbn.

La demanda global de gas est creciendo alrededor de dos veces mas rpido que la demanda de aceite.

Taken from Pipeline & Gas Indusry (Sept. 2000) WGC Panel

Un Mercado Creciente

Reservas Probadas

United States 164,041 bcfCanada 63,874 bcfWestern Europe 156,578 bcfFormer Soviet Union 2,002,107 bcfLatin America 252,719 bcfMiddle East 1,749,241 bcfAfrica 394,177 bcfAsia Pacific 363,470 bcf

Taken from Oil & GasJounal (June 25 . 2001) Worldwide Gas-Processing Roundup

Transferencia de Custodia (Volumen)

Las compaas han acostumbrado comprar y vender gas por volumen (SCF)

Debera existir un acuerdo contractual de rango aceptable de BTU.

El gas debera ser analizado peridicamente (al menos una ves por mes o mas frecuentemente dependiendo del contrato) para verificar que los BTUs estuviesen en rango.

Transferencia de Custodia Energa

AGA 5 / ISO 6976Energa= Volumen Corregido (del FC) X Poder Calorfico (del GC)

AGA 8 Mtodos de SupercompressibilidadUsado para calcular Volumen Corregido

Gross 1: SG, BTU, CO2 (From GC) Gross 2: SG, N2, CO2 (From GC) Detail Method: Utiliza toda la composicin del Gas Natural (del GC)

Desde el comienzo de los aos 80s ha llegado as er muy comn que las comapas compren y vendar energa (Dekatherm, MMBTU).

Importancia de la medicin exacta de la energa

Ej. Usando 1020 BTUs / SCF y un Volumen of 20,000,000 SCFD con 0.1% error en BTU. @ $4.00 / Dekatherm

1020 BTU/SCF X 20,000,000 SCFD1,000,000 BTU/Dkthm

Pequeos errores en la medicin se suman a las prdidas $$$

= 20,400 Dkthm/Da (asumido)

1018.98 BTU/SCF X 20,000,000 SCFD 1,000,000 BTU/Dkthm

= 20,379.6 Dkthm/Da(actual)

20,400 20,379.6 = 20.4 Dkthm/Da (error)@ $4.00/Dkthm = $81.60/Da

$2,448/Mes $29,376/Ao

Resultado: +/-1 BTU error puede costar cerca de $30,000 al ao

Ejemplo de 1% Error en medicin de BTUEj. Usando 1020 BTUs / SCF y un Volumen de 20,000,000 SCFD con 1% error en BTU. @ $4.00 / Dekatherm

20,400 Dkthm/Da (asumido)

1009.8 BTU/SCF X 20,000,000 SCFD1,000,000 BTU/Dkthm = 20,196 Dkthm/Da (actual)

20,400 20,196 = 204 Dkthm/Da (error)

@ $4.00/Dkthm = $816/Da $24,480/Mes $293,760/Ao

Nota: El error composicional que causara el erro de BTU, tambin causara errores en los clculos de AGA3/ ISO 5167.

. 2 vlvulas(+/- 1 BTU, 12 min. anlisis)

Controlador y analyzador3 vlvulas

(+/- .50 BTU, 4 min. anlisis)

Cromatgrafos Danalyzer BTU/CV

Cromatgrafo de Gases Principio de Operacin

Los Analizadores GC Consisten de Subsistemas

Inyeccin

Separacin

Deteccin

Integracin / Clculos

Reportes

Cerebro del del GC Controlador

Integracin / Clculos

Reportes

El controlador puede estar integrado al analizador omontado remotamente. Enva seales de control (activacin de vlvulas, cambio de corriente, etc.) einterpreta seales provenientes del analyzador.

Corazn del GC Horno

Inyeccn

Separacin

Deteccin

Tpicamente un horno elctrico. Se mantiene a unaTemperatura constante, y tiene flujo constante degas de arrastre (Usualmente Helio de Alta Pureza).

GC Horno

El horno del GC contiene 3 componentes principales montados juntos en un horno calentado elctricamente:

GC Vlvulas (Inyeccin de muestra, direccionamiento flujo de gas de arrastre)

Columnas Micro-empacadas (separacin de los componentes)

Detectores TCD (Deteccin de los componentes separados)

6 purtos, Vlvula de diafragma operada por pistn

Actuacin nica de diafragma basada en un diseo orignal de la NASA

Sin resortes, lavadores o lubricantes. La muestra nunca estpa en contacto

con las las partes internas. >5 Millones de operaciones por vlvula Garanta de por vida.

Tecnologa Vlvulas Cromatogrficas

Vlvulas de inyeccin de muestra y activacin de columnas

.

.043 ID

Tiempos de anlisis menores con consumo de gas de arrastre extremadamente bajo (10-15 cc/min. tpicamente)

Alto grado de separacin de componentes dfine la linea base y una mejor resolucin de forma de los picos.

Combina la durabilidad e las columnas empacadas con la ventaja de las columnas capilares.

Diseadas en forma conjunta con vlvulas y detectores para minimizar el volumen muerto interno.

2 aos de garanta bajo condiciones normales de operacin.

Tecnologa Columnas Micro-empacadas

Utiliza (TCD) termistores para medir la concentracin de cada componente.

Mejora la sensibilidad para mediciones de bajo nivel (elimina el requerimiento de FID para algunas aplicaciones)

Rudo -- Immune a fallas de gas de arrastre y vibracin.

El bloque de detector y el bloque de columnasson calentados. Cuenta con arreglo para prevenir calentamiento por encima de 85 C.

Tecnologa Detector de Conductividad Trmica

El horno elctrico contiene las columnas, vlvulas y detectores TCD

Aprobado para Clase I Div I Grupos B, C, & D

Utilidades Mnims -- No requiere Aire o Hidrgeno

+/- 0.1 C sobre la temperatura ambiente (-18 to 55C)

Asegura mxima estabilidad y repetibilidad a temperatura y condiciones ambientales.

Tecnologa Horno elctrico

HORNOELECTRICO

LAZO DEMUESTRA

COLUMNAS

VALVULA6 PUERTOS

DETECTOR DEMEDICION

DETECTOR DEREFERENCIA

Ruta de Flujo en el horno GC

Paso 1: Inicio de anlisis. Vlvula de muetreo (V-1) OFF, backflush vlvula (V-2) ON, y vlvula de doble columna (V-3) ON. El sistema de purga de muestra mantiene una muestra en fase gaseosa y pasa la muestra a travpes del tuving de transporte hacia la vlvula de muestreo, y a travs del lazo de muestreo.

Horno del Analizador

Paso 2: La vlvula de muestreo es puesta ON para capturar un volumen preciso demuestra y para permitir al gas de arrastre (Helio) barrer el lazo de muestreo hacia la primer columna. La Columna 1 separa C6, y componentes mas pesados (C6+) del resto de los componentes que constituyen la muestra de gas

Horno del Analizador

Paso 3: La vlvula de muestreo es puesta OFF para purgar la prxima corriente. La vlvula backflush es puesta OFF reversing the carrier flowthrough column 1 so that C6+ components elute first (all combined as a singlepeak) to the measure detector. Note: by switching the direction of flowthrough the first column, C6+ components bypass columns 2 and 3. This helps to expedite the analysis.

Analyzer Oven

Analyzer Oven

Step 4: C6+ (heavies combined) is on its way to the detector. Column 2 separates the mediums C3, C4s, and C5s while the lightestcomponents N2, C1, CO2, and C2 continue traveling through column 2 into column 3.

Step 5: Dual column turns OFF after trapping the lightest components N2, C1, CO2, and C2. The medium components bypass column 3 by going through the restrictor column (R-1) and Follow C6+ to the detector. Once again this helps speed up the analysis.

Analyzer Oven

Step 6: After the heavy and medium components elute to the detector the dual column valve is turned back ON freeing the light components and allowing them to cross the detector next. This is the end of the analysis and the next one is ready to begin. Typical Analysis time is 4 minutes.

Analyzer Oven

Qualitative Information

Carrier Gas Flow Is Constant

Temperature Of Oven Is Constant

Sample Size Is Constant

The time each peak elutes across the detectorwill also be constant. This time is known as Retention Time of each peak. This time is programmed into the controller.

Thermal Conductivity DetectorsTCD

Quantitative information

Thermal ConductivityExamples

NAME SYMBOL THERMALCONDUCTIVITY ATZERO DEGREES C

Air 5.8 Hydrogen H2 39.6 Helium He 33.6 Nitrogen N2 5.7 Argon A 3.9 Carbon Dioxide CO2 3.4 Methane CH4 7.2 Propane C3H8 3.6 Acetylene C2H2 4.5 Benzene C6H6 2.2 Butane C4H10 3.2 Chloroform CHCL3 1.6 Freon 12 CL2CF2 2.0 (Dichlorodifluoromethane) Methanol CH3OH 3.4 Acetone C3H6O 2.4

Detector Bridge Circuit

Idealized Chromatogram

The signal from the detector is read by the controller.The controller integrates the area under each peak. Thisis known as the raw area, and is used for quantifying the component concentration.

Response factor is used to tell how much of a component is present in the gas RF = Raw Area / Cal Concentration

NOTE: RF are only updated during a calibration

Response Factors (RF)

We use the RF to calculate the Mole % of each componentin a sample stream

Mole % of Sample = Raw Area / RF

A simplified example of how RF is calculated and used in stream analysis

Given: A calibration was run and a Raw Area for ethane calculated by the controller is 100. The known calibration gas has 5% ethane (programmed into the controller).

RF = 100 / 5 = 20RF = Raw Area / Cal. Conc.

Given: Sample Stream gas is run, and the raw area of ethane calculated by the controller is 200.

Mole % = Raw Area / RFEthane = 200 / 20 = 10%

Typical Chromatograms And Reports

Gas ChromatogramShows retention times and raw area under each peak

A Chromatogram is a picture showing the detector output

Gas Chromatogram Comparison

Typical Raw Data Report

Response Factor (RF) = Area(comp x ) / Cal Conc.(Comp x) Mole % = Area(comp x) / RF (Comp x)

Typical Analysis Report

Typical Calibration Report

Sample System

Sample Conditioning and Sample Transport

The sample conditioning system is a very important component in any analytical system. This is a frequently overlooked component that must deliver a representative sample from the pipeline to the GC without changing the composition.

This is not a difficult task when low BTU gas is measured

in warm climates. When high BTU gas is measured the potential exists to lose the heavier components as they drop into the liquid phase due to sample cooling.


The Joules-Thompson (JT)

Cooling effect causes heavier components to drop into liquid phase.

Will bias energy readings low because the high BTU contributors drop out of the vapor-phase sample before the GC even has a chance to measure it.


Pressure Balancing stream to stream.

Minimizes normalization.Minimizes cross-stream contamination if solenoids do not seal completely.


Calibration Standards

may require heated insulation blankets when installed in High BTU applications in cooler climates.

Sample transport lines require heat tracing to a heated area or all the way to the sample valve.

Instrument Performance

Repeatability

Accuracy

Linearity

Repeatability and Accuracy can be checked by your calibration

Response Factor (RF) = Area(comp x) Cal Conc.(Comp x)

Mole % = Area(comp x) RF(Comp x)

Instrument Performance-Linearity CheckUsing three standards

Component Standard Heating Standard Heating Standard Heating #1 Value 1 #2 Value 2 #3 Value 3

Hexanes + C6+ 0.01 0.53 0.03 1.59 0.20 10.58Propane C3 1.00 25.16 3.00 75.48 7.00 176.13

Iso-Butane IC4 0.50 16.26 0.10 3.25 0.40 13.01N-Butane NC4 0.50 16.31 0.10 3.26 0.40 13.05

Neo Pentane Neo C5 0.08 3.19 0.00 0.00 0.00 0.00Iso-Pentane IC5 0.08 3.20 0.30 12.00 0.80 32.01N Pentane NC5 0.10 4.01 0.30 12.03 0.80 32.07Nitrogen N2 3.32 0.00 2.00 0.00 1.00 0.00Methane C1 89.50 904.15 87.67 885.47 77.40 781.74

Carbon dioxide CO2 2.91 0.00 1.50 0.00 1.00 0.00Ethane C2 2.00 35.39 5.00 88.48 11.00 194.66

Totals 100.00 1008.20 100.00 1081.56 100.00 1253.25

Note: Heating values are based on GPA 98 Engineering Data Book Volume II Section 23. Using 60 F and 14.696 base conditions

Physical Property Calculations-Pressure Base

TypicalNaturalGas

Composition PressureBase @14.73

PressureBase @14.696

PressureBase @15.023

Nitrogen 2.46Methane 89.709C02 1.001Ethane 5.001Propane .999Iso-Butane .300N-Butane .300Iso-Pentane

.100

N-Pentane .100C6+ .03RelativeDensity

.6222 .6222 .6223

Gross DryBTU

1053.70 1051.26 1074.73

Physical Property Calculations-GPA Standards

TypicalNatural Gas

GPA 2145-96 GPA 2145-2000 (Jan 1release)

Rich Gas 1300 BTU +0.0138 BTUTypical USGulf Coast

1078 BTU +0.0032 BTU

Table 4

Constants that are not so constant

Conclusion

BTU Analyzers Play an important part in gas energy measurement

During the analysis the GC uses columns to separate the gas into its constituents

The GC uses thermal conductivity detectors to quantify the mole % of each component present

A BTU is calculated for each constituent based on mole %

By summing up each of these individual values we find the total BTU value of the gas

Questions and Answers

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