Analyzer 1 Process Industry Practice [PDF]

Zitiervorschau

August 2000

Process Industry Practices Process Control

PIP PCCPA001 Process Analyzer System Design Criteria

PURPOSE AND USE OF PROCESS INDUSTRY PRACTICES In an effort to minimize the cost of process industry facilities, this Practice has been prepared from the technical requirements in the existing standards of major industrial users, contractors, or standards organizations. By harmonizing these technical requirements into a single set of Practices, administrative, application, and engineering costs to both the purchaser and the manufacturer should be reduced. While this Practice is expected to incorporate the majority of requirements of most users, individual applications may involve requirements that will be appended to and take precedence over this Practice. Determinations concerning fitness for purpose and particular matters or application of the Practice to particular project or engineering situations should not be made solely on information contained in these materials. The use of trade names from time to time should not be viewed as an expression of preference but rather recognized as normal usage in the trade. Other brands having the same specifications are equally correct and may be substituted for those named. All Practices or guidelines are intended to be consistent with applicable laws and regulations including OSHA requirements. To the extent these Practices or guidelines should conflict with OSHA or other applicable laws or regulations, such laws or regulations must be followed. Consult an appropriate professional before applying or acting on any material contained in or suggested by the Practice.

This Practice is subject to revision at any time by the responsible Function Team and will be reviewed every 5 years. This Practice will be revised, reaffirmed, or withdrawn. Information on whether this Practice has been revised may be found at http://www.pipdocs.org.

© Process Industry Practices (PIP), Construction Industry Institute, The University of Texas at Austin, 3208 Red River Street, Suite 300, Austin, Texas 78705. PIP member companies and subscribers may copy this Practice for their internal use.

Not printed with State funds

August 2000

Process Industry Practices Process Control

PIP PCCPA001 Process Analyzer System Design Criteria Table of Contents 1. Introduction................................. 2 1.1 Purpose ............................................. 2 1.2 Scope................................................. 2

2. References .................................. 3 2.1 Process Industry Practices ................ 3 2.2 Industry Codes and Standards .......... 3

3. Definitions ................................... 3 4. Design Criteria ............................ 5 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9

General .............................................. 5 Safety................................................. 5 Process Interface............................... 6 Sample Transport Systems ............... 7 Sample-Conditioning Systems........... 8 Calibration.......................................... 9 Analyzer Shelters............................... 9 Status and Validation Signals .......... 10 Documentation................................. 10

Process Industry Practices

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PIP PCCPA001 Process Analyzer System Design Criteria

1.

August 2000

Introduction 1.1

Purpose The purpose of this document is to convey conventional and widely accepted design practices used in industry for the engineering, design, and assembly of Process Analyzer Systems. Practitioners of this discipline are aware that each Process Analyzer System is a unique and customized entity. This document is intended as a prompt to an experienced analyzer systems engineer to ensure that a safe, reliable, and maintainable system is designed and engineered. The other PIP analyzer documents in this series deal with proven means to specify, purchase, and install Process Analyzer Systems in an engineering and construction environment. These documents collectively provide a framework for obtaining preassembled analyzer systems from third-party vendors who specialize in fabricating complete Process Analyzer Systems. These specialists are frequently called Analyzer System Vendors (ASV).

1.2

Scope Process Analyzer Systems are engineered, designed, and fabricated for one of the following: 1) Process measurement or monitoring 2) Effluent measurement or monitoring 3) Ambient atmospheric measurement or monitoring A properly functioning system requires integration of multiple design tasks: 1) Selection of analytical technology 2) Safety 3) Sample extraction 4) Sample transport 5) Sample conditioning 6) Sample return/disposal 7) Utilities support 8) Analyzer shelter 9) Signal conversions and control system interfaces 10) Status alarms 11) Calibration facilities A Process Analyzer System is not a commodity but is a custom-designed system to meet a specific requirement.

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Process Industry Practices

PIP PCCPA001 Process Analyzer System Design Criteria

August 2000

2.

References Applicable requirements in the latest edition, revision, or addendum of the following codes, standards, and references shall be considered an integral part of this Practice. Requirements modified by this Practice, owner’s referenced drawings, or a purchase order shall take precedence over published specifications. 2.1

Process Industry Practices (PIP) – PIP PCEPA001 - Process Analyzer System Engineering Guidelines – PIP PCEPA002 - Process Analyzer Project Implementation Guidelines – PIP PCIPA001 - Process Analyzer System Field Installation – PIP PCSPA001 - Process Analyzer Project Documentation Data Sheet Instructions – PIP PCSPA01D - Process Analyzer Project Documentation Data Sheet – PIP PCSPA002 - Process Analyzer System Data Sheet Instructions – PIP PCSPA02D - Process Analyzer System Data Sheet – PIP PCSPA003 - Process Analyzer Shelter Data Sheet Instructions – PIP PCSPA03D - Process Analyzer Shelter Data Sheet – PIP PCSPA004 - Process Analyzer Bid Proposal Data Sheet Instructions – PIP PCSPA04D - Process Analyzer Bid Proposal Data Sheet – PIP PCTPA001 - Process Analyzer System Acceptance Testing

2.2

Industry Codes and Standards • National Fire Protection Association (NFPA) – NFPA 30 - Flammable and Combustible Liquids Code – NFPA 70 - National Electrical Code (NEC) – NFPA 496 - Standard for Purged and Pressurized Enclosures for Electrical Equipment – NFPA 497 - Recommended Practice for the Classification of Flammable Liquids, Gases, or Vapors and Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas

3.

Definitions Process Analyzer System: A system that consists of an analyzer, a sample-conditioning system, and one or more readout devices. These are designed and assembled to automatically take a representative portion of a process stream and to identify and measure specific component concentrations or physical properties of the sample. Analyzer Project: A project to design and install one or more analyzer systems, which may involve analyzer enclosures or shelters. Analyzer projects have multiple task requirements and will involve a team of engineering disciplines, each discipline having roles and responsibilities.

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PIP PCCPA001 Process Analyzer System Design Criteria

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Analyzer System Fast Loop: A part of the sample transport system that is designed to bring the process sample close to but not through the analyzer. The purpose is to reduce the time lag in getting sample from the process tie point. The term “bypass sample line” is sometimes used to define the same part of the system. Analyzer Flow: The sample flow (take off from the fast loop) that is delivered to the analyzer for specific component analysis or for physical property determination. Calibration and Automatic Calibration: The introduction of a standard to the analyzer. The measured results are compared with the standard, and the response factors of the analyzer are adjusted so that the measured results match the standard. Automatic calibration is the same activity with no human intervention and is normally on a fixed time cycle. Validation and Automatic Validation: The introduction of a standard to the analyzer. The measured results are compared with historical data and reported, and the response factor is not changed. Automatic validation is the same activity with no human intervention and is normally on a fixed time cycle. Other terms commonly used are “bench mark” and “check peak.” When the historical data trend of a validation sample clearly exceeds the acceptable limit, the instrument should be calibrated. Statistical Quality Control (SQC): A collection of quantitative data that are subjected to analysis, interpretation, and presentation. With an analyzer system, the data are typically the following: 1)

Measurement precision or repeatability – presented in the form of a normal distribution curve.

2)

Calibration or validation response factors – presented as a control chart with upper and lower confidence limits.

3)

Service factor or performance – presented as a percentage of the time that the analyzer system was available.

Original Equipment Manufacturer (OEM) Tests: The acceptance tests that are performed at the Analyzer Manufacturer’s facility. These tests must have defined and measurable parameters with repeatability factors or tolerance factors that are stated in the data sheets or in engineering notes. Examples of these tests are baseline drift, repeatability, resolution, signal ranges, etc. Factory Acceptance Tests (FAT): The tests that are performed at an Analyzer System Vendor’s (ASV) facility after complete fabrication and assembly of the analyzer system(s). These tests must have defined and measurable parameters that encompass the complete analyzer system including any support peripherals such as analyzer shelters or buildings and all ancillary equipment. Reviewing documentation and conducting physical inspection for compliance to codes and standards plus adherence to the analyzer system engineering specification must be part of this acceptance test. Site Acceptance Test (SAT): The transfer of ownership of an analyzer system following a defined period of uninterrupted, on-line operation within acceptable performance parameters. These tests, including the documentation requirements and standards compliance, must be fully defined at the bidding stage of an analyzer project.

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Process Industry Practices

PIP PCCPA001 Process Analyzer System Design Criteria

August 2000

Commissioning: A field demonstration of the operation of an analyzer system and all the associated hardware, software, and peripherals. This activity will include demonstrating that all signals are the correct range and that all alarm status generates the correct sequence of operations and actions. Startup: A demonstrated operation of the analyzer system(s) on actual process samples.

4.

Design Criteria 4.1

General Physical and chemical properties data for each monitored sample stream are required for the system design. Using these data will permit a design considering each of the following aspects:

4.2

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Sample disposal

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Calibration

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Safety relief vents

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Analyzer vents

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Sample-conditioning system design

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Materials of construction

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Maintenance procedures

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Safety monitors

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Safety equipment

Safety Safety shall be the foremost design parameter during all stages of the analyzer selection and system design. All applicable codes and practices shall be adhered to. Examples of safety considerations for some commonly encountered materials are as follows: 4.2.1

For highly toxic process samples, the following shall be optimized in the design of the Process Analyzer System: • The location of the analyzer with regard to the process sample source point • Minimum quantity of sample needed for a reliable, safe, and speedy analysis • Sample disposal or return point for proper disposal of spent samples • Safety support equipment, such as breathing air stations, safety showers, etc. • Emergency escape routes from the analyzer location. • Toxic gas monitors and alarm devices

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PIP PCCPA001 Process Analyzer System Design Criteria

4.2.2

August 2000

For highly flammable process samples, the following shall be optimized in the design of the Process Analyzer System: • Sample stream constituents lower explosive limit (LEL) • Chemical reagent components lower explosive limit (LEL) • Sample system hardware components surface temperature (T-Rating) • Need and location of combustible area monitoring detectors and the calibration of the monitors with regard to the sample stream • Sources of static electricity such as air conditioner blowers, etc. • Safety issues with any other of the process analysis requirements

4.3

4.2.3

The sample transport, conditioning, and disposal shall not create a hazard to personnel, the environment, the process, or the plant that is being monitored.

4.2.4

All hazardous materials shall be properly identified, labeled, or tagged.

Process Interface 4.3.1

Sample Probes 4.3.1.1 When a sample must be extracted from the process, transported, and conditioned, a sample probe shall be installed in lines 3 inches or greater in diameter. The sample point shall be selected to provide easy access, maintainability, fast response time, and a representative sample. Sample points that could be multi-phase must be avoided. 4.3.1.2 Fixed-flange probes are recommended for any operating pressures. These probes shall have the following features: •

An arrow stamped on the flange indicating the direction of flow in the process line

•

Capable of being rodded out or blown back to process

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Welded shutoff valve in compliance with line specifications

•

Sized for approximately 30% immersion beyond the inside pipe wall up to a maximum immersion of 3 inches. A typical fixedflange sample probe is shown in Annex A of IEC 61831, (PIP PCEPA001). Approximate calculations are shown in subsequent annexes.

4.3.1.3 For high-maintenance service, retractable sample probes are also acceptable if the following additional safety features and characteristics are included:

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Arrow stamped for flow orientation

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Marked for insertion depth (scoring tubing reduces mechanical strength)

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Marked for retraction depth to clear the process root valve

Process Industry Practices

PIP PCCPA001 Process Analyzer System Design Criteria

August 2000

•

Expanded section on end of probe to prevent blowout through packing gland

•

Safety chain for blowout prevention

4.3.1.4 Special-purpose, high-pressure, retractable probe devices are commercially available for pipeline or similar demanding service. 4.3.1.5 In any case, fixed or retractable sample probes shall meet the process pipe specification and must have the mechanical strength not to break in high-velocity flow conditions. Harmonic calculations are available to predict the mechanical breakpoint of the sample probe. 4.3.2

In-Line Sensing Elements 4.3.2.1 In-line sensing elements shall be installed such that they can be removed for replacement or maintenance while the process is in operation. 4.3.2.2 Sensing elements and analyzers that are mounted in process slip streams shall be designed to be blocked in, depressurized, and flushed while the process is in operation. 4.3.2.3 All “wet electrolyte” sensing elements must be installed so that the sensing element is constantly wetted to ensure that the sensor does not dry out. 4.3.2.4 In-line sensing elements shall be installed in a manner to ensure that the sensing element does not become fouled with debris.

4.4

Sample Transport Systems 4.4.1

The primary objective of fast loop design shall be to minimize the sample transport time and the mass of sample transported. One or more of the following techniques may be utilized to minimize sample transport time or sample mass: • Pressure reduction • Phase change • Minimum-bore tubing and components • Eductors • Pumps • Heating

4.4.2

The sample return point selected directly influences fast loop design. The sample return point shall be selected to minimize sample conditioning and maintenance.

4.4.3

Sample Phase 4.4.3.1 Phase shall not be changed when the sample phase matches the phase required by the analyzer. 4.4.3.2 Phase shall be changed when required for analyzer system operation.

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PIP PCCPA001 Process Analyzer System Design Criteria

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4.4.3.3 When a phase change is designed into the sample transport system, the phase change must be maintained once it has occurred. If this is not achieved, the analysis results will be erratic.

4.5

4.4.4

The sample transport system materials of construction are a significant factor in design. Sample transport system components are normally stainless steel. When the process sample is not compatible with stainless steel, other materials (as defined in the plant piping specification) shall be required.

4.4.5

Sample transport systems shall be designed and fabricated without low spots, loops, or pockets that can form traps.

Sample-Conditioning Systems Many analyzer system problems can be traced back to the sample-conditioning system. 4.5.1

The sample-conditioning system shall operate as follows: 4.5.1.1 The sample must be representative, and the sample-conditioning system shall not alter the concentration of the measured component. 4.5.1.2 Response time must be consistent with the requirements of control or monitoring. 4.5.1.3 The system must be maintainable and must provide sufficient information to aid in trouble shooting the analyzer system.

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4.5.2

The sample-conditioning system shall be kept as simple as possible yet meet the design objective, which may include such features as auto-calibration and/or auto-verification.

4.5.3

All materials, including elastomers, metals, and composites, shall be verified for compatibility with the process sample.

4.5.4

Isolation valves shall be provided on all sample systems, both at the sample probe/sample return points and at the sample-conditioning system. Frequently, a flush valve is included to run the fast loop with the sample system isolated.

4.5.5

Dead-volume components contributing to increased lag time shall be minimized.

4.5.6

On multi-stream sample systems, cross-contamination from valve leaks is always a possibility. Double block and bleed, or equivalent, shall be utilized for prevention of incorrect analysis caused by leaks.

4.5.7

Pressure or temperature sensitive components or devices used in the sampleconditioning system shall be protected from exposure to excessive pressure or temperature.

4.5.8

Heated sample lines shall enter the sample-conditioning enclosure via heat shrink entry seals to ensure that the sample temperature is uniformly maintained. Ordinary bulkhead unions can be used when sample temperature integrity is not a concern.

4.5.9

Sample-conditioning enclosures shall have windows suitable for viewing measuring devices (e.g., pressure, flow, etc.) if enclosure cannot be opened for viewing due to safety or operating conditions. When high temperatures must be maintained, all adjustments shall be externally accessible.

Process Industry Practices

PIP PCCPA001 Process Analyzer System Design Criteria

August 2000

4.5.10 Sample-conditioning enclosures shall close and seal sufficiently using, at a minimum, a single-handle, three-point latch mechanism. 4.5.11 All sample-conditioning systems, whether enclosed or plate-mounted, shall be provided with a means for decontamination before maintenance. 4.5.12 The location of sample-conditioning systems for samples containing toxic or flammable materials shall be determined by the following: 4.5.12.1 For an analyzer located inside an analyzer building, the sampleconditioning system shall be on an outside exterior wall with flowlimiting devices to and from the analyzer. 4.5.12.2 For field-mounted analyzer enclosures, normal practice shall be to mount the sample-conditioning system adjacent to the analyzer enclosure. 4.5.12.3 For analyzers mounted in three-sided, free-ventilation shelters, the sample-conditioning system shall be mounted where most convenient for maintenance. 4.5.13 Components of all sample-conditioning systems, whether enclosed or platemounted, shall be mounted in such a way that each can readily be removed for maintenance without removing any others. 4.5.14 All components and controls of sample-conditioning systems, whether enclosed or plate-mounted, shall be clearly tagged and labeled for ease of understanding and maintenance. 4.6

4.7

Calibration 4.6.1

All Process Analyzer Systems shall be provided with a means for calibration.

4.6.2

The design of a Process Analyzer System influences its overall precision. The calibration standard used on the system will determine only the relative accuracy. PIP PCSPA002 defines and specifies these terms.

4.6.3

Calibration samples shall be introduced to the analyzer in the same phase as the conditioned process sample.

Analyzer Shelters 4.7.1

The selection of a shelter for a Process Analyzer System shall be based upon the following: • Analyzer manufacturer’s published specifications for operating conditions • Ambient site conditions • Criticality of analysis • Owner company philosophy

4.7.2

The four basic types of analyzer shelters are as follows: • Type I – Field mounted: an analyzer in an integral enclosure mounted on a free-standing support

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PIP PCCPA001 Process Analyzer System Design Criteria

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• Type II – Freely ventilated: typically a three-sided shelter • Type III – Climate controlled: analyzer enclosure interior temperature controlled for proper operation of the analyzer system(s) • Type IV – Controlled for area classification reduction: pressurized and purged to allow operation of analyzer system(s) that are not rated for the exterior area classification of the shelter

4.8

4.9

4.7.3

In Types III and IV shelters, doors shall open outward and shall be equipped with panic hardware, automatic door closers, and windows.

4.7.4

Closed shelters shall also be equipped with appropriate sensors for combustible gas, toxic gas, oxygen deficiency, and loss of pressurization as required.

4.7.5

Alarm conditions shall be shown outside each entry door as well as transmitted to a continuously manned location.

Status and Validation Signals 4.8.1

Regardless of how simple or complex a Process Analyzer System is, valid analytical information shall be conveyed to the end user.

4.8.2

Wherever a Process Analyzer System is on closed loop control and has a fault/status signal available, this signal shall be transmitted along with the measured parameter to the host company computer.

4.8.3

As the complexity of a Process Analyzer System increases, other signals may be required (e.g., calibration, purge fail, no sample flow, etc.).

Documentation 4.9.1

Once a Process Analyzer System is shipped to its final destination, complete and proper documentation shall be supplied.

4.9.2

The final documentation shall contain the following at minimum: • Originals of all OEM documentation for all parts of the system • All ASV drawings and documentation • Original specifications with all agreed-upon changes documented by the ASV • Start-up and shut-down procedures • Calibration procedures • Maintenance procedures • All software documented in a manner to allow changes by the end-user

4.9.3

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PIP PCSPA001 provides a convenient means for specifying and tracking documentation.

Process Industry Practices