Steam traps are often ignored or poorly maintained - which can be a very expensive mistake. Sean Ottewell reports.
The issue of wasted steam is becoming more important as the costs involved with generating it rise and emissions regulations get ever tougher. However, lack of steam trap maintenance is common on many process plants, often because the manual surveys required can be very time consuming and therefore expensive, and also because the steam traps can be located in difficult to access places.
Nevertheless, this is a false economy. Figures from steam trap suppliers suggest that where limited annual maintenance is in place, 5-10 per cent of a process plant's total energy costs are typically lost through steam trap leaks.
When maintenance drops off to every 3-5 years, this figure can escalate to 15-30 per cent.
According to Spirax Sarco, fast and correct identification of trap failure is the key to saving process energy, optimising process performance, and optimising safety levels. Together, these reduce productivity costs and times, cut the cost of raising steam, slash emission losses from boiler plant - and reduce environmental impact, maintenance costs, and repair costs.
Company figures show that a typical process with 200 steam traps could be losing 8900t/y of steam at a cost of over £90,000/y - or a million litres of fuel oil. In environmental terms, this is over 3000t of carbon dioxide released into the atmosphere.
Spirax Sarco's answer to this comes in the form of its new STAPS wireless steam trap monitoring system which has been designed to efficiently monitor and evaluate steam trap operation.
STAPS surveys the operation of the steam trap at regular intervals and identifies poor performance that can cause reduced plant efficiency and increased energy consumption (Fig.1). It can diagnose both failed-open steam traps that leak live steam and those that have failed-closed or are blocked that result in waterlogging leading to plant damage, product spoilage and health and safety concerns.
Using non-intrusive installation technology combined with a 2.4GHz wireless network, the company says it is an ideal solution for steam trap monitoring.
It is suitable for use with all types of steam trap and can be connected to pipework up to 100mm (4-in), via an adjustable clamp.
The head unit assembly mounted on the pipe upstream of the trap to be monitored 'listens' to the sound signature of the trap in operation. This sound signature is categorised and transmitted via the wireless network to a central PC. The PC determines the trap condition and calculates any steam loss.
Each STAPS head unit assembly is powered by a long life lithium battery which can last up to ten years. It can communicate directly to a receiver that is connected to the PC software via a LAN connection or via another intelligent head or repeater. The PC software can be installed onto a PC on the sites internal network, or onto a standalone local PC.
The STAPS head, repeater and receiver create a network and can communicate with each other, passing on the steam trap data to the supervisory PC.
Developed at the company's global R&D centre in Cheltenham, UK, and tested at its own and customer facilities around the world, STAPS is now on the market.
Meanwhile Emerson reports success from a wireless steam trap monitoring project it has just completed for a major food processor in the USA. In an effort to prevent steam trap failures the company had already implemented a preventative maintenance (PM) schedule.
However, with close to 100 traps in the plant, PM could only be performed once per year - taking up to 100 hours in total.
For steam trap monitoring, the company decided to install nine 708 Rosemount wireless acoustic transmitters which provide acoustic event detection, including leaks in steam traps and pressure relief valves. These were placed on steam lines throughout the plant and integrated into the existing Smart Wireless Gateway, which communicates to a plant host system, data historians or energy management software.
The 708 transmitter, with a combination of temperature measurement and acoustic 'listening', gives unparalleled visibility into steam trap states.
"Manual monitoring of temperature did not give us enough information to conclusively target a steam trap for replacement when we saw water-hammering," noted a project engineer from the food processing company. "But when we installed the wireless acoustic transmitter, we could tell immediately which steam trap was stuck."
It was quickly fixed, and a trend of the new trap showed normal acoustics and temperature. Now the plant has real time alerts for each of the nine steam traps with wireless acoustic transmitters. Some are in wash down areas, and one is in a high humidity environment. All are communicating reliably.
Overall the food processor has managed to reduce energy use by minimising steam blow-through and/or blocked flow; improved productivity by eliminating preventative maitenance activities on steam traps; and reduced mechanical/asset failures by minimising water-hammering
Steam trap assessments are crucial
So concerned was the US Department of Energy (DOE) about energy wastage that it launched a Save Energy Now campaign to highlight the issues involved. As part of this campaign, the DOE performed a steam assessment at Dow Chemical's plant in Hahnville, Louisiana, USA. The main objective was to identify opportunities for natural gas savings in the plant's steam system.
The key findings of the assessment included: quantifying potential energy savings, especially with the assistance of an outside expert, can provide the impetus for management to take action. Although Dow Chemical had an active energy management programme, the Save Energy Now assessment was able to uncover substantial additional opportunities for energy savings by focusing on a specific system; repairing leaks and failed steam traps.
Making these activities permanent can yield substantial energy savings; and, once positive results are achieved, projects implemented as part of an active energy management programme are more likely to be sustained.
The personnel at the site improved their steam trap programme and enhanced their ongoing leak repair campaign.
Although Dow was aware that the efficiency of these systems could be improved, the assessment quantified the potential energy savings in a manner that made it more compelling to implement the improvements.
The combined annual energy and cost savings resulting from these two efficiency measures amounted to 272,000 MMBtu and US$1.9 million, respectively.
With project costs of approximately US$225,000, the simple payback was around six weeks.