Managing trace contaminants in ethylene steam cracking systems is crucial for plant safety, regulatory compliance, and product quality. Acetylene is one of the most important byproducts of this process. This highly reactive gas can potentially cause hazardous reactions and downstream process disruptions if it is not tightly controlled.
Acetylene Control
Many chemical processing plants leverage thermal-catalytic hydrogenation to selectively convert acetylene (C2H2) into ethylene (C2H4) in order to prevent unwanted side reactions and avoid risks of downstream polymerization catalysts.
Over- or under-conversion can be costly, however. Too much conversion wastes hydrogen and risks producing undesired side products, while too little conversion leaves harmful acetylene in the stream.
Reliable and precise gas sampling is, therefore, vital. This is particularly important in hazardous areas such as Class I, Division 1 (C1D1) or Zone 0 locations, where electrical safety is essential.
The Challenge in Hazardous Location Sampling
Sample handling systems employed in post-hydrogenation acetylene analysis are required to:
- Deliver gas to the analyzer at a known and stable flow rate
- Maintain sample integrity
- Function without introducing ignition hazards into classified areas
Recently, a North American company showed that intrinsically safe, integrated mass flow, and pressure control can simplify system design while continuing to meet all three of these requirements.
Closed-Loop Lab-Based Sampling
Image Credit: Alicat Scientific
This installation routed a side-stream from the process line through:
- Heated transfer lines to prevent premature condensation
- A chilled impinger train to remove particulates and volatiles
- An intrinsically safe mass flow controller maintaining 0–200 CCM at 15 PSIG with ± 0.5 % of reading accuracy
The controller integrated closed-loop actuation, laminar differential pressure sensing, and multi-parameter monitoring in a single enclosure. Real-time measurement of mass temperature, flow, totalized flow, and absolute/ gauge/ barometric pressure allowed operators to:
- Detect fluctuations in pressure, upstream, and downstream
- Verify sample stability prior to analysis
- Correlate the actual delivered sample volume with the analyzer data
- Identify condensation or heating issues at an early stage
- Evaluate valve usage to better optimize preventive maintenance
Modbus RTU was used to directly send all control parameters to the plant’s PLC, ensuring seamless integration with digital process control systems.
Benefits of an Integrated, Intrinsically Safe Controller
If employing separate control valves, sensors, and data loggers, these instruments must be interconnected before use. In contrast, an integrated instrument:
- Reduces panel space and wiring requirements
- Shortens commissioning and installation time
- Minimizes potential failure modes and leak points
- Enhances measurement repeatability under shifting process conditions
This offers several benefits for oil and gas analyzers, especially those handling flammable or toxic gases. These include:
- Reduced total cost of ownership
- Increased uptime due to lower maintenance complexity
- Improved data integrity for quality assurance and compliance
Benefits Beyond Acetylene
The example presented here focused on acetylene removal verification, but this intrinsically safe flow and pressure control approach can also be applied to:
- VOC sampling in petrochemical production
- Hydrogen sulfide (H2S) monitoring in refinery streams
- Contaminant and moisture testing in natural gas transmission
The adoption of compact and high-accuracy certified control systems allows operators to reduce hazardous-area engineering effort, standardize sampling methods across facilities, and improve confidence in analytical data.
International organizations can also use the same communication protocols and data collection criteria in each facility, as this approach is compatible with hazardous location certification for North America, Europe, and IECEx.
This information has been sourced, reviewed, and adapted from materials provided by Alicat Scientific.
For more information on this source, please visit Alicat Scientific.