Gas Technology: Smartening up your steam system

01/07/2011


Steam systems provide heating, cooling, humidification, water heating and process heat for hundreds of different industrial activities. According to the U.S. Dept. of Energy (DOE), 45% of all the energy purchased by U.S. manufacturers is used to produce steam. These systems are reliable and often operate adequately with minimal attention. That’s why owners may be incurring major energy losses and drops in system effectiveness without knowing it.

The solution is to install modern equipment for steam system monitoring, and to intensify basic plant maintenance procedures. Help is available for you to get a better grip on your system. Doing this will assure trouble-free, efficient operation.

The boiler, and beyond

Kelly Paffel, a Technical Manager from Swagelok Energy Advisors, recently made a presentation at a Technology and Market Assessment Forum sponsored by the Energy Solutions Center. His topic was “Steam System Thermal Cycle Efficiency.” In a recent extensively monitored example installation, total energy losses in the boiler were measured as 18.6%. Steam distribution losses were measured at 14.5%. Only a limited number of steps were available to reduce boiler energy losses, so the major opportunities for system efficiency improvements were at the distribution and energy use end.

According to Paffel, 3.8% of the energy loss was in condensate energy not reclaimed, 4.4% in uninsulated lines and equipment, plus 7.4% in steam leaks and losses to the atmosphere. Paffel indicated that before thorough steam management programs are initiated, 44.3% of the energy provided to the boiler did not result in useful steam. By implementing appropriate steam management improvements, this could be reduced to 25.6%.

Start with the basics

Often owners install new, high-efficiency boilers, and then are disappointed that energy bills continue to be surprisingly high. The reason may be that the plant downstream from the boiler isn’t providing maximum efficiency. The elements of steam system energy improvement include thermal insulation of piping and equipment, improving the condensate return system, assuring proper steam trap operation, and taking advantage of new tools for steam system monitoring.

Improving thermal insulation reduces system heat losses. Paffel says, “To prevent thermal losses, all devices in the steam and condensate system should be insulated, including valves, expansions joints, heat transfer components, tanks, condensate pipe and fittings. In the DOE’s tip sheet on insulation for valves and fittings, insulating a 6-in. gate valve could save approximately $525 per year.” Manufacturers such as Insultech offer durable fitted insulation systems for a wide range of pipes and fittings.

Target wet insulation

Often, old insulation is no longer effective, especially if it has become saturated with condensate. It is important to eliminate sources of moisture prior to insulation replacement. Problems may include leaking steam valves, pipe leaks, or leaks from associated steam equipment. If significant insulation replacement is undertaken, it may be necessary to rebalance steam flows and delivery temperatures in the system.

Paffel indicates that to improve plant efficiency, one of the highest returns on investment is to properly return condensate to the boiler plant. He indicates, “Condensate can contain as much as 16% of the total energy in the steam vapor, depending on steam pressures. Because condensate also contains boiler treatment chemicals transferred during steam generation, improving condensate return also reduces chemical costs, make-up water costs and sewer system disposal costs.  All of this adds up.”

Extend condensate return system

Owners should ensure that condensate piping extends to as many condensate sources as possible and is adequately sized. It has to accommodate both liquid and vapor. Condensate piping that is sized for the liquid portion only will be undersized. Ask your engineer or contractor to evaluate the feasibility of extending condensate return piping to all parts of the system. Just like steam lines, condensate lines should be insulated to minimize energy losses.

Steam trap evaluation

The purpose of a steam trap is to return accumulated condensate and remove non-condensable gases while allowing the free passage of steam. Steam traps come in a wide variety of types and sizes, but have in common the need to be regularly checked to assure proper operation. The difficulty is that many traps are located in areas where access is difficult or even dangerous. Too often these steam traps are not inspected with sufficient frequency, and where they are not functioning correctly, repair or replacement is too often postponed.

Paffel points out that plant operators need to look at steam trap stations, not just the singular steam trap components. “A station consists of isolation valves, strainer, strainer blowdown valve, universal connector and in some cases, a check valve. The steam trap station should be free of threaded connections, which are prone to failure.” He says that the two biggest culprits for steam trap station failure are incorrect sizing and incorrect installation. “Incorrect sizing can negate proper steam trap design and installation and can cause condensate backup and/or steam loss. Incorrect installation can result in a faulty trap and potentially unsafe condensate conditions in the steam system.”

Steam traps can represent major losses

The DOE cites as an example of potential energy losses in steam traps a survey at a large government-owned facility. Each trap in the system was identified, and its in-service performance evaluated to determine the total cost of wasted steam energy. Of the 910 traps identified, 207 were found to be wasting a total of 4,783 lb of steam per hour at an annual cost of more than $60,000.

It is important to choose the correct type of steam trap and to install it in the right location in the system. As an example, a fixed orifice steam trap can be quite effective and is relatively inexpensive to install. However it doesn’t handle fluctuating steam flows well and its orifice can be plugged, or conversely can be eroded into too large an opening. In either case, the inexpensive solution has suddenly become quite expensive.

According to T.J. Secord of Armstrong International, a recent presenter at a conference sponsored by the Energy Solutions Center, the monthly cost of a failed steam trap can range from $210 to over $1,000, depending on the size of the trap and the operating pressure of the system. Multiply this by the number of failed traps in the steam system, and the results are staggering. Armstrong offers its SteamEye™ steam trap monitoring system to provide immediate notification of a steam trap failure. The system uses various types of trap status transmitters for remote placement to detect abnormal trap operation.

The beauty of remote monitoring

For example, a conductivity remote monitor is used with Armstrong bucket and inverted-bucket type traps to monitor the liquid level inside the trap. An ultrasonic monitor is used with other types of traps including fixed orifice traps to detect improper operation. All transmitters communicate via a wireless link to a data gateway which provides communication to a computer display showing trap status and possible alarm conditions. The system can also monitor the status of safety relief valves, liquid levels or coils.

Secord points out that this type of immediate notification of steam trap failure not only minimizes energy losses but helps a plant manager allocate labor resources effectively. The gateway unit used with the system allows users access from any computer connected to the network, and can be programmed to link with BAS and distributed control systems in manufacturing operations.

Monitoring system at airport

An example of a successful monitoring installation is included in a case study at an airport by the University of Minnesota. It describes the installation of the SteamEye monitoring system on over 700 traps in a steam system used to generate domestic hot water and to provide air tempering. Steve Shuppert, chief engineer at the Metropolitan Airport Commission (MAC) explains, “We’re restricted on personnel so we’ve never had the time to monitor our steam traps as often as we’d like to. We had no way of knowing if a trap failed until there was noise in the line or people complained about the temperature.”

After learning about SteamEye at a workshop sponsored by its gas supplier, CenterPoint Energy, MAC decided to pilot the system. Maintenance staff installed sensors on 66 steam traps in its energy management center and tested the system for one year. “It worked fantastic,” says Shuppert. The MAC then installed the complete trap monitoring system at the airport in three phases. Shuppert estimates MAC’s system has a 2.5 year payback.

Bring in an expert

Swagelok Energy Advisors, Armstrong International, and similar firms can do a complete steam system evaluation, including insulation, condensate return, and steam trap station monitoring. Paffel from Swagelok indicates their customers have obtained energy savings of up to 22% and steam cost reductions up to 16%. Payback on the cost of such an evaluation averages less than 40 days. Recommendations are classified to assist owners in prioritizing improvement projects at each facility. Suggested improvements range from safety and/or code issues requiring immediate fixes, to longer-term system improvement projects.

If your steam system isn’t living up to the potential of your boiler plant, now is the time to have an evaluation done and get started on improvements that will pay for themselves in short order. Both the hardware and the consulting help are out there to get you on the right track.



No comments