isa 2008 remote injection montgomery

Analytical Solutions for Process Control & ComplianceThe 53rd Annual Symposium of the Analysis DivisionCalgary, Alberta Canada; 20-24 April 2008

PROCESS GC ANALYSIS OF A HAZARDOUS SAMPLE USING A

DISCRETE SAMPLE VALVE IN A REMOTE LOCATION

Tom G. MontgomerySiemens Energy & Automation, Inc.

Process Analytics

Presented in Calgary by Bob Farmer, SE&A

AD 2008: Analysis Division SymposiumCalgary, AB Canada; 20-24 April 2008

Slide 2

Outline

• Introduction and Abstract

• Background and the project requirement

• Solution to project requirements

• Possible issues with solution and investigations

• Result


Slide 3

Introduction and Abstract

• Practical example of discrete remote sample injection– Many thanks to Dr. Jimmy Converse

• Owner’s requirement– Hydrocarbon components in hazardous stream matrix– The owner made severe constraints regarding sample handling

• Solution– Description of remote discrete sample injection technique– Discussion of potential negative impacts

• Investigations– Discussion of possible negative effects on the measurement


Slide 4

Background

• GC is a sample extractive technique– To minimize lag time, a “large” quantity

of sample is removed from process and transported to the analyzer at high flow rates

– At the analyzer, a small quantity of sample is extracted again and conditioned for presentation to the analyzer at low flow rates

– Unused sample is returned to process or to flare

– In the analyzer a tiny quantity of sample is extracted again and inserted onto the columns

• Original extraction and transport issues

– Flow 1: typical 3.5 l/min to ½” tubing– Flow 2: typical 30-40 ml/min to 1/16” or

1/8” tubing– Sample 3: typical 0.5 µl sample or less

Process Stream

ElectronicsOven

Carrier Gas

Gas Chromatograph

Sampling System

Sample Valve

Columns and Valves

Detector

Temperature Controlled

2

1

3


Slide 5

Standard GC Extractive Sampling Technique

Illustration Ref. Dr. J. Converse

Analyzer ShelterUnused sample to flare or return to process


Slide 6

Benefits of Standard Technique

• Ensures fresh sample is present at inlet of GC (reduces time lag)– In this application, transport-related lag time = ~30 sec

• No affect on chromatographic method



Slide 7

Problems of Standard Technique

• Extracts large quantities of sample from process

• Excess sample must be disposed or returned to process

• Failure conditions, including leakage on the transport line must be accommodated

• Leakage can result in hazards of fire or injury to personnel– On this project, the stream contained ~2% Hydrofluoric Acid (HF)– Lethal to humans: STEL <3ppm; Extremely corrosive



Slide 8

Solution – Remote Discrete Sampling

Illustration Ref. Dr. J. Converse

Analyzer Shelter

Sample valve located near process


Slide 9

Benefits of Remote Sampling

• Eliminates transport of large quantities of sample

• Minimizes waste

• Reduces issues of leakage away from process– Reduces human hazards– Reduces potential for damage


Slide 10

Potential Negative Effects on Analysis

• Increased cycle time (or lag time)

• Retention time shift– Effect on valve operating times– Effect on gating reliability

• Peak effects– Peak broadening– Measurement performance


Slide 11

Transport Tubing “Part Of Oven”

45

21

36

45

21

36

Vents

Car. Ref.

Car. 2

Car. 1

Sample fromProcess

KOh

Ref BF Main ITC

Oven Temp: 60°C ±0.05°CValves and wetted tubing of Hastelloy C

C1b

C2

C3

60 Ft

Transport Tubing must be at a controlled temperature: ±?°

“The heated transfer line can be perceived as a very long, slender oven.”(Dr. J. Converse)


Slide 12

Questions To Be Investigated

• How much lag time is introduced?

• How good does the temperature control of transport tubing have to be?– Effect on Backflush Valve operation– Effect on gating of components

• Any other analytical issues?


Slide 13

Test Set

• Maxum GC with divided oven– Two isothermal halves– Each temperature

independently controlled

• Application with SV and CV and columns at 60°C (analysis temperature)

• Coil (60’) of 0.032” ID / 1/16” OD tubing to simulate process transport tubing on other side

• Carrier pressure 51 psig and resulting flow 30 ml/min

• Varied coil temperature from 40° to 80°C in 10°C increments and plotted chromatograms

2 valves

Detector

Divided Oven

Application Side

Test Coil Side

(Photos representative of actual test set.)


Slide 14






Slide 15

Lag Time Observed

Ref. Propane:Elution: ~42sec 151secAdditional Lag: ~109sec

ITC Without Tubing

ITC With Tubing at 60°C


Slide 16






Slide 17

How Much Shift in BF Time Can Be Allowed?Same as previous slide with BF time set out to 240 sec.

Ref. Propane elution = 151sec.

Acceptable retention time shift: <±3 sec.



Slide 18

How Much Retention Shift Is Acceptable for Gating?

• Adequate separation suggests retention time shifts of ~10 seconds can be accommodated by normal gating technique.

• Therefore, the BF time requirement will be the primary control. (<±3 sec)

Main Detector – No Tubing


Slide 19

A Quick Test At the ITCITC With Tubing at 60°C


Retention Times:40°C : 177 (not shown)60°C : 171.380°C : 166.3


Slide 20

Main Detector; Tubing 60°C


Slide 21



Slide 22



Slide 23

Retention Time Effects Summary

• ±20°C shift in temperature of transport tubing causes retention time changes of >10 sec

• Transport tubing temperature should be controlled to at least ±5°C to ensure reliable performance of the analyzer

• (Note: Sample Valve temperature may also vary ±5°C since this is a liquid sample.)


Slide 24






Slide 25

Peak Shape

• Columns used: 0.53 mm ID “megabore” capillary– Normal response is sharp (Eg; Methane ~5 sec wide

even when retained 2.5 minutes at 40ml/min flow rate)

– Therefore, negligible peak broadening was expected

• No significant broadening was observed


Slide 26

Measurement Performance

• Due to good peak shape performance, measurement performance is expected to be good

• All peaks performed well except C5+ (backflush peak) 40C 7.46%

50C 7.57%

60C 7.69%

70C 7.944%

80C 8.086%

10°C swing in transport tubing temperature cause about a relative 1.6% change in the C5+ concentration.

Note: C5+ in this sample is made of Isopentane through n-Hexane. May be a result of backflush of C5s and possibly C4s at lower temperatures.


Slide 27

Summary Of Observations

• Lag Time– Consistent with predictions from flow calculations– Acceptable in overall system performance

• Retention Shift– Tubing must be kept at a constant temperature ±5°C

• Analytical Issues– Negligible in some cases – but poor performance of

backflush “plus” peak also requires tubing to be kept at a constant temperature ±5°C


Slide 28

Results

• Remote discrete sampling resolves problems of hazardous sample handling

• Lag time effects are predictable

• Transport tubing must be kept at a controlled temperature – but not as tightly controlled as an analytical oven

• Measurement performance effects are acceptable if transport tubing temperature is controlled

• Additional benefit: HF neutralization can be accomplished with a small column instead of a large pot


Slide 29

Other Limitations

• This test was with a liquid sample– Simpler transport of sample aliquot– Simpler temperature control requirements on sample

valve (and transport tubing)

• Distance from process to analyzer was not large (~60ft)– Lag time increase is acceptable even at relatively low

flow rates of chromatographic columns


Slide 30

Acknowledgements

• Dr. Jimmy Converse (research and publications)

• Steve Trimble (Siemens Process Analytics)

isa 2008 remote injection montgomery

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