According to OSHA, the chemical industry has one of the most stringent safety regulations. Regular inspections, servicing, and maintenance work are required due to the intense stress that is often placed on the equipment because of the exposure to very aggressive substances and extreme high temperatures and pressures. Depending on the size and type of plants and operations concerned, maintenance often involves a complete shutdown, however, maintenance and servicing operations in localized production areas are common.
In recent times, chemical plants are adapting new recommendations and incorporating newer processes to meet the highest safety guidelines prescribed across industries. Faced with many harsh process conditions such as low pH environments, boiling liquids and extreme pressures at a typical site, companies are turning to automation and upgrading their activities from simplified manual operations to more sophisticated equipment, driving greater production efficiency and safety management practices.
Figure1: Typical applications in Petrochemical and Chemical Plants
Pulsed radar systems which is a Non-Contacting Radar type using an antenna, measure level based on the time-of-flight principle and use a method called time expansion to convert extremely short time delay to a slower timescale. The surface echo is built up of tens of thousands of short radar pulses emitted from an antenna positioned at the tank top, directly towards the process material below. These pulses are reflected from the surface of the material back to the transmitter. The transmitter measures the time delay between the transmitted and received echo
signal, and the on-board microprocessor calculates the distance to the process media surface using the following formula: distance = (speed of light x time delay) /2. Once the transmitter is programmed with the reference gauge height of the application— usually the distance from the flange face to the bottom of the tank or chamber—the level measurement is then calculated by the microprocessor.
Instead of measuring time, Non-Contacting Radar using FMCW technology transmits a radar signal with a frequency, increasing over time to create a signal sweep. After the signal is reflected by the process media surface, the echo is picked up by the antenna. As the transmitted signal varies in frequency, the echo has a slightly different frequency compared to the signal being transmitted at that moment. The difference between these frequencies is directly proportional to the echo delay (i.e., the distance from the transmitter to the process media surface), which enables the level to be accurately measured. An advantage of this technique is that the process variable information is in the frequency domain instead of the amplitude modulated (AM) or time difference domain, which allows more accurate signal conversion. This is the same advantage that FM radio has over AM radio. Most tank noise sources are in the amplitude domain and thus FM signal processing can ignore them, and accuracy is not affected.
Two of the major challenges customers in the Chemical and Petrochemical industry face are:
We have developed two specific features to assist in solving these issues. The first is the Signal Quality Metrics (SQM). By looking at the Signal to Noise margin, our device enables predictive maintenance before the instrument encounters error due to failure such as build up on the antenna or the probe.
To solve the issue of limited data for troubleshooting, we have developed a unique 7-day data historian, to allow users to revisit and check echo curve at the time of event in an on-board memory. The data collected by the Rosemount 5408 and 5408:SIS are compliant with NAMUR NE 107 Field Diagnostics for standardized device diagnostic information.
Figure 2a (left): Rosemount 5408 Non-Contacting Radar Historian Dashboard showing active (colored) and inactive (grey) failures and alerts; Figure 2b (right): Rosemount 5408 Non-Contacting Radar installed on a Chemical Tank
We will be discussing many more features around the Level portfolio in the presentation including topics of Functional Safety for Level Measurement including Proof Testing, Interface measurement and Reactor Level measurement specific.
Figure 3: The Rosemount Level Solution Portfolio including all the technologies from Guided Wave Radars, Non-Contacting Radars, Custody Grade High Precision Non-Contacting Radars, and Point Level Switches & Level Detectors
Join us at Emerson Exchange Asia Pacific, coming on October 26-28, 2021. Register for the event via our webpage, Emerson Exchange Asia Pacific.
The post Solving Level Measurement Challenges for Chemical and Petrochemical Plants appeared first on the Emerson Automation Experts blog.
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