Take back your steam energy
In discussions on how to make today’s steam and hot water systems more efficient, first thoughts often turn to replacing or upgrading boilers or boiler burners, or to reducing the demand for steam or hot water at the point of use. But great opportunities also exist in making major improvements in steam and hot water distribution systems.
Rapid paybacks possible
Often the paybacks from improvements come within weeks or a few months at a cost much lower than replacing or upgrading a boiler or burner. After making these improvements, you may find yourself asking, "Why didn’t I do this sooner?" The first step is evaluating your system and finding those opportunities.
Savings can come from incremental reductions in energy losses by completely insulating hot pipes and devices, improving condensate return systems, assuring correct operation of steam traps, and recovering heat from boiler blowdown water. Individual steps may make only small improvements, but taken together they can make for improvements in steam system efficiency ranging from 10% to 20%. Where do we find these savings?
Insulate to reduce heat losses
Whether it’s an eight-inch main steam line, or a one-inch hot condensate return line, insulation is critical. In an example cited by the U.S. DOE, at a plant where the fuel cost was $8.00/MMBtu, a survey identified 1,120 feet of bare 1-inch steam line, and 175 feet of bare 2-inch line, both operating at 150 psig. An additional 250 ft of bare 4-inch- line operating at 15 psig was found. Taken together, these resulted in a heat loss of 5,069 MMBtu/hour at an annual energy cost of $45,620. These energy losses could be reduced by 90% by the appropriate use of pipe insulation. In a case like this, the payback is very short—a matter of weeks.
Missing insulation common
Reasons for inadequate or missing insulation are numerous. Sometimes in the rush to startup a new system, the final step of pipe insulation is never completed. Sometimes devices such as steam traps and valves are initially wrapped with insulation but during periodic inspection or maintenance, the insulation is removed and not replaced.
Often older insulation is damaged or saturated with water and loses its effectiveness. Sometimes asbestos insulation was removed as part of a plant-wide abatement program, but was never adequately replaced. With today’s higher energy costs and an increased emphasis on system efficiency, it’s time to correct these problems.
Designs for easy removal and replacement
One very useful solution is advanced insulation systems that are highly effective yet allow easy removal and replacement for periodic inspection or service. One provider of these systems is Shannon Enterprises, manufacturers of Insultech blanket thermal and acoustic insulation systems. Shannon manufactures a wide range of custom insulation products, including insulation packages for steam and hot water pipes and devices of all type. Commonly insulation for each steam device is custom-fitted to allow for piping, sensors, valve stems, etc. This fitted insulation is designed for quick removal and replacement to allow for inspection or service, and fits around data links such as steam trap monitoring systems. Three additional benefits of quality insulation are more comfortable working conditions, less pipe noise, and reduced risk of personnel burns.
Complete condensate return a target
Another major area for system efficiency improvement is improving hot condensate return. Too often condensate return piping has not been extended to the full extent of the steam system and hot liquid simply drips away into floor drains. Nevana Iordanova discussed the importance of condensate return at a recent Technology & Market Assessment Forum sponsored by the Energy Solutions Center. Iordanova noted, "Condensate is a tangible item which can be measured in the form of a savings analysis."
She pointed out that 13% to 45% of the total heat in a steam system is represented by hot condensate, most of which can be retained by proper condensate return. Further, this hot condensate is already treated so it does not require additional chemicals. In some locations collection of condensate also significantly reduces the cost of water. Thus, the payback for extension and maintenance of these return lines is often short and should be considered. Another aspect of collecting full value from condensate return improvement is adequate insulation at the steam trap and along the return piping.
Steam traps a major target
Most steam distribution systems have dozens, sometimes hundreds of steam valves and traps of various designs. Iordanova pointed out, "Steam leaks, water hammer, plugged valves and traps lead to process loss, large equipment damage, safety issues, energy loss, and environmental issues."
These are often in locations where inspection is challenging or at least time-consuming. Thus, it is important to verify that these devices are operating as intended, without loss of steam or condensate. Often the best solution is remote steam system device monitoring, with alarming features that indicate malfunctions as soon as they occur, rather than waiting for the next inspection.
Iordanova noted that Armstrong recently introduced SAGE, a cutting-edge innovation in smart utility monitoring, measuring and reporting. It is a powerful software tool to analyze data and track trap’s behavior and performance. A fully integrated solution, it works seamlessly with Armstrong’s real-time monitoring devices, ensuring that it always has access to the most current data on your critical system steam traps. Many owners have chosen to include steam trap monitoring in initial system designs, or to retrofit existing systems with remote monitoring capabilities.
Recover heat from blowdown
One more opportunity for major energy savings in the steam system is boiler blowdown water heat recovery. According to a Steam Tip Sheet of the U.S. DOE, in a plant where the fuel cost is $8/MMBtu and the blowdown ratio is 6% of the hourly steam flow of 50,000 lbs at 150 psi, the potential is for recovery of 90% of the heat, with an annual value of $68,000. Several manufacturers offer these heat recovery devices which can be installed during initial system construction or in retrofits. This is heat energy that has already been paid for, and should be recovered.
These are some of the potential energy conserving steps that can be taken to improve system efficiency. All are worthwhile targets for most applications. In today’s era of increased emphasis on conserving energy and reducing carbon emissions, they are worth acting on. Many older steam systems were designed without the full complement of these tools, but can be upgraded. Major system efficiency improvements are out there, often for a very moderate investment.
This article originally appeared in the Gas Technology Spring 2017 issue.