PRACTICAL CONSIDERATONS OF GAS SAMPLING and

GAS SAMPLING SYSTEMS and STANDARDS

by David J. Fish

Welker Engineering Company

Canadian Gas Association

June 2006

Approximately 10 AM, Monday, April 10, 2006

About 1 hour into the fire

Where did I leave that postit note?

Keep your files closed!

2:30 PM with 200,000 gpm into my office window!!

Why is a Gas Sample Taken ?

To Determine the Value of Gas being brought or sold.

What is a Sample ?

A composite representation having the same composition as

the homogenous whole of the material sampled.

GETTING A GOOD SAMPLE IS LIKE A

WALK ON THE BEACH!

ORNOT!

GPA2166 API14.1

ISO10715 ASTMD5287

Why is an Accurate and Representative Sample

Critical?

All of the numbers used to determine the value of natural gas come from a gas sample.

BTU !!

Specific Gravity !!

Compositional Analysis !!

What do these Numbers Represent ?

Money . $, , Fr., Rs., Kr., Pesos Controlling YOUR Companies Bottom Line Profitability

What kind of impact? 3 BTU difference at 5 million per day station

$3.50 per thousand $52.50/day $19,162/yr

$4.50 per thousand $63.75/day $23,268/yr

8 BTU difference at 25 million per day station

$3.50 per thousand $700/day $255,500/yr

$4.50 per thousand $850/day $310,250/yr

How Do You Get a Sample ?

Do you send a summer trainee out to take a sample ?

Do you have a highly trained person who knows the ins and outs of proper sampling and its importance ?!!

OR

Summer Trainees enjoying

breaktime

Sample System Components

Probes

Valves

Filters

Regulators

Probe Regulators

Tubing

Heating Elements

Sample Pumps

Sample Cylinders

Relief Valves

SP2/PP2 Sample Probes

Sample Probe should be positioned on the top of a horizontal line in an area of flowing gas (positive velocity) with no turbulence, and as much straight upstream piping as possible.

Correct Placement of Sample Probe in the Line

No Turbulence No Turbulence means away from control valves, reducing port valves, orifice plates or other obstructions in the line that might cause contaminates to take flight and possibly end up in your sampling system.

THREE IMPORTANT ISSUES ABOUT SAMPLE POINT

LOCATION

LOCATION

LOCATION

HEADERS

While all of the information to this point applies to all gas sampling operations, there are specific sampling methods that require special procedures and techniques to insure accurate samples are gathered.

Spot Sampling

Composite Sampling

Recommended Methods for Taking a Spot Sample

Fill and Empty

Constant Pressure Cylinder

Positive Pressure of Helium

Evacuated Cylinder (Vacuum)

Methods of Spot Sampling NOT Highly Recommended

Continuous Purge

Water or Glycol Displacement

Cylinder screwed directly into the pipeline valve

Spot Sampling Manifold GPA 2166

Constant Pressure Cylinder

IMPORTANT NOTE !!

Tests have proven that condensate collected in a standard cylinder when mishandled in the lab, can increase the BTU of a gas sample by a considerable amount.

PreFabricated Field Office

Composite Sampling

Composite Sampling is a low cost alternative to an online analyzer.

The sample collected by a properly designed and installed composite sampler will provide a representative and accurate sample of the product.

Composite samplers should be interfaced with flow measurement equipment so that the sample collected is proportional to the flow in the line.

Speaking of things that should be interfaced!!!!

Composite samplers must follow the same design and installation guidelines set up for spot samplers.

Correct Sampler Installation

Size and slope of tubing runs

No turbulence

Cylinder mounting

Live flowing stream

Heating for components

Additionally, the composite sampler must be installed above the sample point with a short piece of 1/4 SS tubing sloping upward from the outlet of the probe to the inlet manifold of the sampler. This will ensure that any condensed liquids in the lead line will flow back into the pipeline and be swept away.

Sampler Installations

The sampling of a deadend line will give a nonrepresentative sample of the gas in the flowing stream.

NO!

NO!

NO!

A properly designed gas sampler must be installed and placed in service so as not to be affected by ambient conditions or fluctuations of pressure in the line.

Or turbulence generators!

It is important that all of the components in a sampling system be heated if the gas being sampled is close to its hydrocarbon dew point.

Gas streams above 1050 BTU must be sampled very carefully to ensure that a representative sample is collected.

Hydrocarbon Dew Point Issues Temperature of equipment vs. Gas Stream

vs. Ambient Conditions

20 to 50 F above the HCDP for most cases

JouleThomson Effect 7 F drop / 100 psi drop

Hydrocarbon Dew Point Prediction Chilled Mirror ASTM Method SRK (Soave Redlich Kwong) Peng Robinson Other Equation of State Models

Heated Enclosure

Pipeline Mounted

Opened Enclosure

A composite sampling system should not have filters of any type (cartridge, membrane, etc.) installed between the probe and the sampler. Drip pots should also be avoided. If excessive contamination is noticed call the manufacturer for recommendations on solving the problem. Inlet check valves may also affect the quality of the sample collected.

NOTE: Any type of filter, drip pot or membrane may change the composition of the sample.

One of the most serious problems that occurs with composite samplers is leaks on the outlet piping leading to the cylinder. The sampler pumps a sample into the cylinder and if a leak is present, the sample begins to leak out of the cylinder light ends first leaving an unrepresentative sample in the cylinder.

Typical Installation for Gas Chromatograph

New Energy Meter Technology

Verification Systems for Online Technology

Keeping up with Changing Conditions

Keeping up with Changing Standards

Keeping up with Changing Technology

Pick your currency. Just pay the fine!!!!

Sampling and Analysis is more than a business .

Its also an Art !!!

Questions???