Accurate and reliable pressure measurement is crucial in a broad range of chemical industry applications such as reactors, distillation columns, heat exchangers and storage tanks. Monitoring pressure in these applications helps to maintain operational stability, ensuring process and worker safety, optimising performance, increasing energy efficiency and helping organisations adhere to regulatory standards. Many pressure measurement applications are relatively straightforward in nature, enabling companies to implement quite basic instrumentation that minimises their capital expenditure costs. In more complex and critical applications, the functionality provided by advanced pressure measurement devices has the potential to create significant benefits for users. However, the industry-wide challenges of a loss of in-house expertise and reduced personnel numbers can create a reluctance to invest in new technology that is easier to install, configure, maintain and use, but requires companies to go through a change management process. Continuing to deploy the same basic instrumentation has therefore often been regarded as the easiest choice, despite the limitations of these devices and the opportunity to reduce operational and lifecycle costs by investing in new technology.
Although basic pressure measurement instruments can be well proven and usually reliable, their limitations – especially the fact that their installation and maintenance can be complicated, labour-intensive and time-consuming – result in increased total cost of ownership.When deployed in applications such as distillation columns, these instruments can be difficult to access, and personnel may need to climb scaffolding to perform maintenance tasks, thereby putting their safety at risk. Proof-testing of these instruments, which is required when they are deployed in safety instrumented systems (SIS), can also be quite a complicated, laborious and time-consuming task.
New technology designed to meet challenges
The latest advanced pressure measurement instruments, such as the Rosemount™ 3051 Pressure Transmitter from Emerson, have been designed to provide outstanding accuracy and reliability but also reduce costs by being easier to install, commission, configure, maintain and use. By enabling commissioning, maintenance and troubleshooting tasks to be completed faster, these devices also help to make facilities safer and operations more efficient and profitable.
Supporting ease of use and cost reduction by simplifying configuration, the latest pressure transmitters have user interfaces designed to provide a straightforward, task-based menu structure. Users are provided with a more intuitive experience, and built-in configuration buttons enable the devices to be easily configured in just a couple of clicks. With plants potentially having hundreds or even thousands of devices to configure, this functionality can save many personnel hours and therefore significantly reduce costs. Further reducing complexity in relation to configuration and maintenance, the latest transmitters offer Bluetooth® connectivity. By removing the need to physically connect to the device via a cable, this enables configuration and maintenance to be performed from a distance, thereby saving time and reducing costs. This is especially the case if devices are installed on large storage tanks or distillations columns.
Simple proof-testing
Pressure transmitters used in SIS must be proof-tested at regular intervals to verify that they are working properly and ensure compliance with the relevant safety standards. Proof-testing, which is performed to uncover dangerous undetected failures, has traditionally been conducted on location and can be a time-consuming, labour-intensive and therefore costly task. To simplify the procedure, the latest pressure transmitters provide guided proof-testing capability. Depending on whether the user is performing a partial or comprehensive proof-test, the device will drive the required steps. With the proof-test method that is built into these transmitters, a device will walk users through the necessary steps to verify the alarm and perform any calibration verification.
Built-in diagnostics
To help ensure safe, efficient and compliant operations while maintaining high product quality and minimising maintenance costs, chemical companies need to identify any issues with instrumentation as quickly as possible. Enabling service technicians to address potential problems faster, the latest pressure transmitters have built-in diagnostics that can identify issues in electrical loops and impulse lines. Advanced pressure transmitters can continuously monitor electrical loops, to detect issues affecting the communication signal, and continuously monitor for plugged impulse line. Users can then be alerted to abnormal conditions so that proactive measures can be taken before the quality of the process is affected. Early detection and correction of instrumentation issues also prevents unplanned shutdowns and enables maintenance to be scheduled during planned downtime, thereby minimising disruption and preventing additional costs from being incurred.
Differential pressure level measurement
One application that often incurs high installation and maintenance costs is level measurement in distillation columns, which has for many years relied upon differential pressure (DP) technologies. Although traditional DP technologies, such as wet leg and dry leg systems – which utilise impulse piping as well as capillary-based solutions – are well-understood, they also have certain disadvantages. For example, impulse lines are prone to plugging and can freeze in extremely cold ambient temperatures, while DP transmitters with remote seals and capillaries have a limited measurement range and are extremely difficult to install. Capillary systems are complicated to calibrate and maintain, have a relatively slow response time, and are sensitive to environmental factors such as temperature changes, vibrations and physical stress. Capillaries are also quite fragile and prone to damage from physical impacts, so these transmitters must be handled very carefully during installation. If a seal gets damaged, the complete capillary system needs to be replaced, making the inventory costs high. Installing these devices requires two people and is complicated by having to avoid the obstacles within the column. With all these challenges, the overall cost of installing a DP transmitter with capillaries can be five times higher than the cost of the device itself.
Benefits of electronic remote sensors
An excellent alternative to these traditional DP technologies is a measurement systems based on electronic remote sensors (ERS), such as the Rosemount 3051S ERS System from Emerson. Rather than using a single DP transmitter with mechanical impulse piping or capillary, ERS systems use two pressure sensors connected with non-proprietary electrical wire that is immune to the effects of temperature variations. The DP is calculated in one of the two sensors and transmitted to the distributed control system or a PLC using a standard two-wire 4-20 mA HART® signal.
At a US chemical plant, a DP transmitter was used to assess the health of packing in a glycerin refining tower, but unreliable measurements made it hard to determine when cleaning or packing replacement was needed. The measurement distance exceeded 8m, requiring extensive impulse piping, which was suboptimal. Condensation in the low side reference leg caused the DP transmitter to shift. Heat tracing was added to keep the reference leg dry, increasing maintenance costs and complications. Ambient temperature variations led to pressure fluctuations, resulting in erroneous packing status, causing maintenance engineers to schedule more outages than necessary. Potential packing issues indicated by DP increases were often false, but engineers couldn’t ignore them due to the risk of process shutdowns and damage to the column.
The DP transmitter, impulse piping, and heat tracing were replaced with a Rosemount 3051S Electronic Remote Sensor system from Emerson. Removing the need for impulse piping eliminated problems like condensation buildup and heat tracing issues. Stable readings, regardless of ambient temperature, improved insight into packing health, enabling better maintenance scheduling and reducing the risk of unplanned shutdowns and damage.
By removing mechanical connections, ERS systems not only provide a faster response time than traditional DP technologies but are also easier to install and less complex to maintain, enabling costs to be reduced. Installation time is drastically reduced because the difficult-to-install impulse piping has been replaced with electrical wire, and installation costs are therefore 60% lower than those of DP transmitters with capillaries. Additionally, whereas cold weather installations of impulse piping and capillaries often require heat tracing or insulation to prevent freezing, the electrical wire requires no heat tracing or insulation. This effectively makes installation a one-person job, saving end users substantial installation costs.
High pressure and vibrations
The cost of installing and maintaining pressure instruments can be also high in applications with challenging process conditions such as high pressure and high vibrations. In these applications, mechanical instruments such as Bourdon tube pressure gauges are typically used to provide pressure monitoring and control. These are simple devices that may be cost-effective in many applications but have certain limitations that make them less suitable for critical applications in modern plants that demand high accuracy, real-time monitoring and data integration capabilities.
Bourdon tube gauges are susceptible to the effects of extreme temperatures, humidity, vibration and shock, which can make the gauge difficult to read, potentially leading to inaccurate readings that could affect product quality and impact profitability. The gauges are sensitive to overpressure, and a lack of diagnostics means it is not possible to see if a device is still functional, which creates a safety risk for personnel. In challenging applications, these devices may require additional options such as syphons, seals and glycol fill, which has a significant cost impact. Also impacting cost is the fact that mechanical gauges have components that can wear out over time, necessitating regular maintenance and calibration, and that they have a high failure rate, requiring frequent replacement. In addition, mechanical gauges provide only a visual display and lack digital output options, meaning that they require manual reading and data recording, which is time-consuming, laborious, costly and prone to human error.
Solving the pain points associated with mechanical gauges, electronic wireless devices, such as the Rosemount Wireless Pressure Gauge from Emerson, support increased reliability by eliminating the Bourdon tube and replacing it with a solid state pressure sensor based on piezoresistive technology. This robust design enables wireless gauges to provide correct pressure information even in high-pressure and high-vibration environments and deliver up to 10 years of maintenance-free operation, thereby reducing costs. Wireless pressure gauges feature a large dial that makes it easy for personnel to accurately read pressure levels on the plant floor, and a blinking diagnostics LED provides a localised indication that the device is operating properly. In addition, WirelessHART® communication technology enables these gauges to deliver reliable pressure readings and device health status back to the control room as frequently as once per minute. This facilitates the central logging of historical data, supporting improved maintenance planning and cost reduction.
Summary
For chemical producers faced with the challenge of reducing operational costs without comprising plant safety, the use of advanced pressure measurement technology is helping to support these goals. Modern transmitters enable easier installation, maintenance and testing procedures that contribute towards lower lifecycle costs. Wireless transmitters reduce the cost of installation in applications without existing wired data infrastructure, but modern devices are also easier to configure, and provide greater reliability and visibility to device health. This not only increases measurement certainty but helps to drive further efficiency and costs savings.
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