Key points
In chemical plants and petrochem refineries, safety procedures, protocols and product technology are critical in addressing risks associated with some of the most hazardous operating conditions any industry presents. These protocols are established and regularly refined to protect both people and production systems from explosions and other hazards that can occur from running process equipment. This equipment includes Mass Flow Controllers (MFCs).
The latest generation of digital MFCs is widely used in chemical and petrochemical facilities due to their precise control and long-term stability for accurate gas flow. MFCs measure and control the flow of gasses in processes where tracking and precisely controlling factors such as flow range, gas conditions, flow accuracy and device communication are important to successful plant operation.
MFCs provide a valuable, precision control and measurement device for chemical and petrochemical research labs and pilot plants. Both kinds of facilities need exact measurement and control of process gasses to efficiently develop new products or evaluate and scale up new refining processes prior to full production.
Given the rugged and hazardous conditions in these facilities, it’s critical to understand how the MFCs are designed in order to specifically meet (or exceed) applicable standards and classification approvals.
The key device factors to consider also include how the MFC is engineered for these kinds of industrial environments: how rugged it is; how well it can stand up to environmental conditions if installed on outdoor process equipment; how much wear and tear it can take and still retain precise, stable flow control over its life cycle.
Hazardous environments can host a concentration of flammable gases, vapours, mists or combustible dust or fibre. These include situations where an explosive chemical or gas is being produced, stored or transported. The risk is twofold: accidental leakage of these explosive gasses or dusts or the gradual buildup of combustible dusts could be ignited by the operation of electronic devices like MFCs.
In some installations, standard Mass Flow Controllers are housed in separate enclosures designed to provide protection from outside hazards. However, this can lead to additional costs, due to the enclosure itself as well as the installation and expenditures related to connecting gas feed lines and wiring for power and device communications. A better alternative is to consider using MFCs designed specifically for hazardous environments.
When assessing whether an MFC can be safely used in a hazardous environment, it’s necessary to understand key classification standards and labeling to determine if the device is right for your needs.
The Zone system is currently used in Europe, Asia and other locations worldwide (North America uses a similar Class/Division system, although the Zone system is gradually being adopted in North America as global companies seek to standardise to one classification system).
The Zone system has two main parts. The Zone specifies the general nature of the hazardous material (gas or dust) and the probability of that hazardous material being present in ignitable concentrations. For hazardous gases, three Zone types are defined: Zone 0 covers long periods of time, Zone 1 covers potential hazardous materials that could be produced under normal operating conditions, and Zone 2 covers gases that are not likely to occur and only present for a short period of time. A similar set of Zones — Zone 20, Zone 21 and Zone 22 — covers the potential for ignitable dust/fibers to be present.
The second part of the Zone system is Groups; these define the type of hazardous material that could be present and (partially) the location: Group I covers mines, Group II covers explosive gas and Group III covers explosive dust. Based on these classifications, it’s important to specify an MFC that’s engineered to operate safely in the presence of Group II explosive gases.
Third-party rating organisations conduct various tests to assign the classification. International approvals are determined by the destination country, as opposed to where the instrument was manufactured. Currently, these international approvals include:
For MFCs, one critical test assesses the potential for autoignition of volatiles that could result from the heat generated by the MFC’s electronics. The rating agency powers up the device and operates it at its highest power draw to determine if the heat could ignite any vapours, such as ethylene, hydrogen, acetylene or others. Since there are different autoignition temperatures for different gasses, a Class 1 rating for an MFC will include additional information specifying which volatiles the MFC has been tested for.
MFCs for hazardous areas also typically receive IP and NEMA ratings. The IP rating identifies the level of ingress protection provided by an enclosure or housing from both dust and liquids. The NEMA rating, primarily used in the United States, defines the enclosure’s ability to withstand various environmental conditions.
For MFC products, the most common classifications are NEMA 4/4x, IP65, IP66 and IP67. For example, IP66-rated MFC housings are dust-tight and protected against heavy water jet spray, which could degrade the housings and potentially allow ingress of explosive gasses or dust that could ignite.
In addition, Mass Flow Controllers with IP66-rated housings are much more rugged and designed to provide longer operating life cycles even if exposed to moisture from wash-down conditions or weather. That makes IP66-rated MFCs reliable devices for use in outdoor process equipment without requiring additional housing or enclosures.
Keeping track of the different ratings and certifications can be challenging. To help ensure you are selecting an MFC that complies with these requirements, it makes sense to work with technology suppliers that have extensive knowledge about these ratings and standards and can help guide you in specifying the right device for a given application. Brooks Instrument, for example, has a dedicated certifications resource webpage to help users understand approvals for flow control instrumentation.
A critical safety area to consider is the design of the electrical and communications connectors on the MFC. To prevent a momentary electrical discharge that can cause a spark, they should be designed so they cannot be easily or accidentally disconnected.
Brooks Instrument, for example, uses special connectors for hazardous-area MFCs that feature simple locking mechanisms that need to be opened with a tool to ensure the connections are only open when there are no gasses or dust concentrations present.
In addition, it’s also important to use communications and power cabling that’s certified for hazardous areas. If the cabling is not approved for hazardous environments, it would need to be run through conduits, adding significant equipment and installation costs and making routine access to the MFCs for service and maintenance more time-consuming.
In MFCs, a key performance characteristic is long-term stability, sometimes referred to as low long-term drift, which represents consistent and accurate gas flow. MFCs are typically calibrated when first delivered from the manufacturer, and end users typically benchmark their stability when the device is first installed.
In some chemical and petrochemical research and pilot plants, a common practice with devices like Mass Flow Controllers is to remove and test/recalibrate them during maintenance intervals or when they change the process gas the MFC is controlling due to running new processes.
However, these recalibration efforts take time and can sideline a system if there are no spare MFCs to replace the one being calibrated. Be sure to work with MFC instrument providers that include a long-term stability specification for the device.
Choosing MFCs with long-term stability specifications can help end users avoid the time and cost of recalibration.
An additional useful feature to look for on a digital MFC is a zero-drift diagnostic. This is a digital test users can access to confirm that the device measurement is not drifting outside the specification, even though the device might have been in use for one or two years. This lets the end user eliminate unnecessary recalibrations from the maintenance schedule and recalibrate only when needed.
Industry 4.0 technology is becoming more prevalent in the chemical and petrochemical industries. When selecting MFCs for hazardous-area applications, it’s important to also consider the digital communications, sensor and other built-in diagnostic capabilities available on the MFCs you are specifying.
High-speed digital communication protocols such as EtherNet/IP and PROFINET are becoming widely adopted within the process control architectures in both industries. Unlike MFCs from past generations that only supported analog interfaces, MFCs with high-speed digital interfaces make it easier to supply critical MFC performance data — such as flow rate, device temperature, valve position, sensor condition and other data — in real time.
This gives end users the ability to incorporate MFC performance data into their process management protocols. This can be particularly helpful in research facilities and pilot plants that are testing new processes and need as much process instrumentation data as they can acquire.
Leading suppliers of hazardous-area MFCs provide a full suite of diagnostics that measure and track the performance and accuracy of the device and correlate the MFC data with other process results for more detailed analysis.
These Mass Flow Controllers also feature multiple alarms that give researchers and process engineers sensor data tied to the gas delivery process. Alarms like Totalizer Overflow and Setpoint Deviation can not only alert users to conditions that fall outside process gas delivery thresholds; they can also help point to potential issues within the gas delivery system or other process equipment.
For example, a Restricted Flow Alarm alerts the user when the MFC is not able to achieve the desired set point flow rate. This could be due to a gas bottle that is empty or near empty, a faulty gas regulator that isn’t maintaining pressure at an appropriate level or a clogged filter causing a restriction in the line.
Some companies support these capabilities with browser-based software packages embedded in the MFC and accessible via high-speed communications interfaces such as EtherNet IP and PROFINET. This makes it convenient for users to access the MFC’s diagnostics capabilities and manage the alarms from a laptop, even while the device is running.
MFCs are crucial instruments for measuring and controlling process gasses in hazardous-area chemical and petrochemical plant operations. To select the right device for these areas, it’s important to understand which locations in a facility are designated hazardous areas, and the level of protection needed for a device, in order to be certain that the MFC is both reliable and safe for long-term use.
In addition, features such as long-term stability, rugged design and support for high-speed digital communications and diagnostic capabilities are equally important to ensuring the device you choose is reliable, accurate and repeatable over its life cycle. Working with technology suppliers that have extensive knowledge about these regulatory requirements and standards can help ensure you select the right device for your applications.
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