In the face of rising energy costs, steam waste is becoming even more of an issue for chemical plants. Traditional manual surveys are time consuming and expensive. Even when audits are carried out annually, up to 15% of steam traps will fail between surveys, says Emerson Process Management. A two- or three-year gap between inspections can push this figure up to 30%.
Failed steam traps can do more than waste steam. For example, a trap failing closed, instead of open, can lead to water hammer and physical damage to a facility — with potentially catastrophic results.
However, many steam traps are in hard-to-access or potentially dangerous locations that make surveying them hazardous.
Fortunately, wireless monitoring systems can ease the checking of steam traps at chemical plants. Vendors offering such systems include Spirax Sarco, Cheltenham, U.K.; Cypress Envirosystems, San Jose, Calif.; Emerson Process Management, Round Rock, Texas; and Armstrong International, Three Rivers, Mich.
NOW ATEX APPROVED
Spirax Sarco's new STAPS wireless steam-trap monitoring system, which was developed at the company's global R&D center in Cheltenham, currently is undergoing beta testing at the company's own sites around the world and with a major food manufacturer. Beta testing at chemical plants was hampered by lack of ATEX approval. However, this approval came in the last week of February. "We can now offer two versions, the standard one and the ATEX-approved one, and we anticipate trial sites in the chemical industry will be forthcoming," explains Simon Geuley, group product manager for condensate management.
The main driver for investment in steam trap monitoring is heat loss, says Geuley. The numbers associated with such losses can be dramatic. For instance, if roughly 10% of the steam traps fail annually at a process plant with 200 traps and the plant has an average trap size of DN20, steam pressure of 14 barg and operates 24/7 for 50 weeks/year, the cost of ignoring the failures would be £89,000 (about $150,000), he notes. This is equivalent to well over one million liters of fuel oil plus 3,000 metric tons of carbon dioxide released to the environment, he adds.
Wired monitoring systems are an option but can be expensive to install and maintain. "There are issues with intrinsic safety, particularly within the chemical industry. So, there has been a huge move to wireless solutions, particularly in the field of condition monitoring," Geuley explains.
The heart of the system is a head unit assembly that is mounted on the pipe upstream of the trap to be monitored and that is powered by a lithium battery that can last for up to ten years. It features vibration and temperature sensors as well as an advanced processor to carry out calculations. The head unit "listens" to the sound signature of the trap (Figure 1). This sound signature is categorized and transmitted via a 2.4-GHz wireless network.
The system also includes a receiver that the head unit communicates with and a repeater. These create a network and can communicate with each other and pass on the steam trap data to a supervisory PC that determines the trap condition and calculates any steam loss.
The monitoring is semi-continuous — occurring a minimum of every 15 minutes depending upon the customer's requirement. The information appears in a very simple format on the PC: green denotes "good," amber is "caution" and red indicates a leak. Two other displays show battery condition and wireless signal strength. The latter also notes when the last successful communication took place in case there's a problem with the wireless network.
STAPS' leak-detection intelligence differentiates it from other wireless steam-trap monitoring systems, says Geuley. Using information from the tens of thousands of steam trap installations it has worldwide, the company has developed a device that can account for the operating principals of different types of steam traps — Spirax's offerings include bimetallic, fixed temperature discharge, ball float, inverted bucket, sealed thermostatic and thermodynamic traps — plus their respective loads and pressures. "So our algorithm is very difficult to replicate," he claims.
The wireless steam trap monitor (WSTM) from Cypress Envirosystems mounts non-invasively onto existing steam traps in minutes and uses a proven algorithm to detect trap failures, particularly expensive steam leaks. It has been designed to augment manual audits to detect failures in a timely manner.
One of its most successful applications has been at the main technology center of a major U.S. pharmaceutical company. The center includes a number of manufacturing buildings, each supplied with steam, chilled water and compressed air from a dedicated utility plant. Each building is responsible for its own energy consumption and is billed separately by the utility plant. Overall, the center houses more than 2,400 steam traps, many operating in hazardous locations where temperatures can reach up to 500°F.
The utility plant installed WSTMs to continuously monitor the steam system — to provide transparent accountability for each building and close the loop on energy reduction goals for the company as a whole. The payback on this project was under 12 months.