Sentry Equipment Corp Sampling Solutions Specialty Heat Exchangers Process Sampling Sentry Equipment...

Sentry Equipment CorpSentry Equipment CorpSampling Solutions • Specialty Heat Sampling Solutions • Specialty Heat ExchangersExchangers

Process SamplingProcess Sampling

Sentry Equipment Corporation


ObjectiveObjective

• Gain an understanding of the methods to obtain representative samples

• Review the fundamentals of gases, liquids and bulk solids

• Overview of analyzing methods• Review the integration of sampling

with on-line instrumentation


Why do we sample?Why do we sample?

• Product mix characteristics– Examples: Particle size, bacteria

count, chemistry, etc.• Identify process variations• Process control• Environmental monitoring• Product quality assurance• Custody transfer


What kind of sample?What kind of sample?

• “True” overall average of the entire lot for one or many characteristics

• Representative sample– Characteristics of the sample equal

that of the entire lot or batch• Consistent, accurate, and repeatable


How to get a representative How to get a representative samplesample

• Follow protocol that gets a consistent, accurate, and repeatable sample

• Understand the material physical properties• Use techniques that have as little sample bias as

possible– Profile the process and sampling system (i.e..

Liquids, slurries, gases, bulk solids, etc.)• Reduce sample to sample variation• Sample methods and results must be repeatable


Sampling ErrorsSampling Errors

• Process analysis is only as good as the quality and representivity of the sample itself

• Sampling errors are costly because they can lead to:– Unnecessary process changes– Additional analysis of more samples– Release of off-spec product to the

customers– Scrap of good material

• The Sampling Scapegoat


General Sampling PracticesGeneral Sampling Practices

• Understand the process and the sampling objective to help select the proper device– I.e. Gas concentration, liquid chemistry, bulk

solids particle size analysis• Determine the best sampler location• Take several increments and composite them to

form the “sample”– Composite Sample – A sample obtained by

combining several distinct sub-samples or increments

• Sample frequently enough to identify process cycles


• Typically includes dipping a cup or container into an open vessel or opening a spigot on a vessel that may be under pressure– May require the process to be

interrupted in order to sample

• This sampling technique is generally considered unsafe– Operator is exposed to any process or

environmental hazards

• Direct sampling introduces the ability for sample variations due to human error and sample contamination

Direct SamplingDirect Sampling


Indirect SamplingIndirect Sampling

• Indirect sampling isolates the operator from the process hazards

• Maintains a closed system

• Sample integrity preserved

• Allows the process to be sampled during normal production cycle


A few general sampling A few general sampling practicespractices

• Mix the material prior to sampling (if possible)• Take several increments and composite them

to form the “sample”– Composite Sample – A sample obtained by combining

several distinct sub samples or increments

• Collect the sample in a container that will not react with the sample

• Sample frequently enough to identify process cycles


• Determine the correct size required for the sample

• Use a sampler and sampling process that removes bias

• Understand the process– Sampling practices may vary from process

to process

A few general sampling A few general sampling practices (cont.)practices (cont.)


Three categories for Three categories for sampling variationsampling variation

• Process variations/cycles• Material variation• Tool and techniques

– Including sample handling


Process VariationsProcess Variations

• Be aware that the process and its conditions may vary over time

• Examine the sampling results and the effects of sampling frequency

• Use the sampler and sampling system to verify the process


Ways to reduce material Ways to reduce material variationvariation

• Determine the appropriate mass of the actual sample– Provides a better idea about the overall properties

of the lot

• Collect several increments from the lot and form a composite sample

• Condition the material prior to sampling– Mix the sample if possible– Control the temperature, pressure, flow, etc.– Control the particle size


Product CharacteristicsProduct Characteristics

• Identification of the product characteristics is critical for obtaining a representative sample

• Every gas, liquid, and bulk solid has its own unique physical property

• Many processes contain entrained gases that can expand when decompressed– Venting provisions must be taken into account

• Bulk solid characteristics can be very unpredictable– Some may pack one moment and fluidize the next– Two grades of the same material may act

differently


• Mass Flow• Funnel Flow• Arching/Bridging• Rat-holing• Flooding• Segregation

Flow CharacteristicsFlow Characteristics


Material PropertiesMaterial Properties

• Abrasive – Materials that wear, grind, or rub on the inside of the sampler or any moving part

• Arching/Bridging – Materials that tend to form a bridge-like structure

• Free-Flowing – Materials that generally flow under the influence of gravity without the aid of agitation

• Floodable – Materials that aerate to a point where they begin to flow like a liquid

• Hygroscopic – Materials that tend to absorb and retain moisture from the atmosphere


Material PropertiesMaterial Properties

• Cohesive – Materials that tend to stick to itself• Adhesive – Materials that tend to adhere or

stick to components of the sampler• Friable – Materials that are easily pulverized or

broken apart • Static Generating – Materials that generate

static from friction on itself or within the sampler


Bulk DensityBulk Density• Mass per unit of volume in powder form,

including the air trapped between the particles

• Measured in g/cc, kg/l, lb/ft3• Examples:

– Cake Mix = 44 lb/ft3 (0.705 g/cc)– Cement Powder = 85 lb/ft3 (1.361 g/cc)– Oats = 27 lb/ft3 (0.432 g/cc)– Parsley Flakes = 3 lb/ft3 (0.048 g/cc)– Sand = 99 lb/ft3 (1.586 g/cc)– Tungsten Carbide = 250 lb/ft3 (4.004 g/cc)


Tools and TechniquesTools and Techniques


Sampling ToolSampling Tool

• The sampling tool is critical for providing a representative sample– The sampler must assure the sample integrity is

preserved

• Understand the analysis requirements to help determine which sampler to choose

• Understand the process variables that may impact the sampler design

• The sampler should keep the operator safe from any process or environmental hazards


Principle for correct samplingPrinciple for correct sampling

• Every part of the lot has an equal chance of being in the sample

• Integrity of the sample is preserved before, during, and after sampling– Oxidation, abrasion, evaporation, and

contamination are examples of improper handling– Vapor pressure is an important characteristic to

take into account when sampling– The measure of the tendency of a material to

form a vapor.


Manual “Grab” SamplesManual “Grab” Samples

• Typically, manual grab sampling is a poor, but common practice because it is taken from the most accessible part of the batch/process– Exception is when the sampler is located in a

proper/acceptable sample point and other good practices are recognized


Gas SamplingGas Sampling

• Maintain pressure and sample integrity

• Monitor H2S, VOCs, water content

• Speed loops and analyzers are common


Liquid SamplingLiquid Sampling

• Control pressure, temperature, flow rate

• Monitor pH, DO, Sodium, conductivity, TOCs, chemistry, etc.

• On-line analysis is common


Bulk Solids SamplingBulk Solids Sampling

• Material characteristics and flow properties vary

• Monitor moisture, particle size, shape, etc

• Difficult to analyze on-line– Material waste


Bulk Solids SamplingBulk Solids Sampling

Point Sample

Strip Sample

Cross Cut Sample


Point SamplersPoint Samplers• Takes a sample from a

point in the material stream

• Used when conducting chemical analysis or when material is homogenous


Strip SamplersStrip Samplers

• Takes a sample from a narrow portion of the stream

• Used in situations where product segregation exists


Cross Cut SamplersCross Cut Samplers

• Takes a cross-section of the entire product stream

• Provides the most representative sample, but requires a lot of headroom


Types of Measurements and Types of Measurements and TechnologyTechnology


Off, At and On-Line Off, At and On-Line

Lab Testing

Infrequent Samples sent to a remote location

At-Line

Sample removed and tested locally

On-Line

Frequent Sample analysis

conducted in real time

Off-Line


Measurements/AnalysisMeasurements/Analysis

• Particle Size• Moisture• Chemical

Composition• Surface Area• Shape• Temperature• Dissolved Oxygen

• Effusivity• NIR• IR• Laser Induced

Fluorescence• Light Scattering• Imaging


KnowledgeKnowledge

• Monitoring multiple properties provides insights into areas and mechanisms that have not been investigated

What you know

What you don’t know

What you don’t know that you don’t know


SummarySummary

• Sampling is a critical part of process control and is often overlooked

• Indirect methods of sampling are the safest, yet most challenging

• The goal is to get representative samples• Material and process variations as well as

sampling techniques and tools effect our ability to get representative samples

• Understand the process and sampling objectives

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