Dow Chemical Company is a diversified company that offers a wide range of chemical, plastic, and agricultural products and services in many essential consumer markets. With customers in more than 175 countries and 42,000 employees around the world, the company has annual sales of $46 billion. Over the past 30 years, Dow has been proactive about energy efficiency. In 2005, the company established a goal of improving its energy intensity by 25 percent by 2015.
Formerly owned by Union Carbide Corporation, the 2,000-acre St. Charles facility in Hahnville, La., has been in operation since 1966 and produces glycol ethers and amines. With nearly 3,000 employees, the St. Charles site produces approximately 10 billion pounds of these intermediate chemical products annually. Because steam is required for many processes – including electricity generation, distillation, evaporation and concentration, process heating, and catalytic cracking – it is critical to the site’s production.
Assessment Overview
The Save Energy Now energy assessment at the St. Charles site was sponsored by the U.S. Department of Energy’s Industrial Technologies Program (ITP). It involved an Energy Expert who is a qualified specialist on the use of DOE’s Steam System Assessment Tool (SSAT). Because a secondary objective of the assessment was to teach steam system analysis using the SSAT software, the Energy Expert formed an assessment team with six of the site’s employees and installed the SSAT software on their computers. This enabled the project team to learn the software, model the facility and perform what-if scenarios to determine the most optimal implementation measures for energy savings.
Assessment Recommendations
Once the data collection was complete, the assessment team evaluated the steam system using SSAT and identified several energy efficiency opportunities. The team then calculated the expected savings and payback periods for each opportunity and divided them into near- and medium-term opportunities based on payback periods.
Near-term opportunities
- Implement a Steam Trap Repair Project – A recent steam trap audit performed before the assessment took place identified all failed steam traps. An accurate estimate of steam leakage stemming from the failed traps was generated by inputting the number of failed traps into the SSAT and modeling the impact of implementing a steam trap repair project. Annual savings in natural gas and costs were estimated to be 112,128 MMBtu and $881,000, respectively.
- Improve the Steam Leak Management Program – The amount of steam lost to leaks in the system was estimated in the SSAT by subtracting the amount of steam used in the applications from the total amount of steam generated. The Save Energy Now assessment initially showed that repairing all of the plant’s steam leaks could yield annual energy and cost savings of up to 451,100 MMBtu and $3.3 million. However, subsequent data collection revealed that some steam meters were not functioning optimally and that parasitic demand from other plant assets accounted for a significant portion of the estimated leak load, thus reducing the potential for energy savings.
- Improve Insulation – During an inspection of the plant, several areas of the steam distribution network were found to lack sufficient insulation. Using 3EPlus, DOE’s insulation calculation program, the team estimated total insulation losses to be approximately 1.0 percent. By reducing these insulation losses to 0.1 percent, the assessment showed that annual natural gas and cost savings of 3,030 MMBtu and $25,000 could be achieved.
- Increase Condensate Recovery – At the time of the assessment, about half of the low-pressure condensate was being recovered. Based on the analysis done using the SSAT, a condensate recovery rate of 75 percent was found to be possible for the entire site. Annual natural gas and cost savings from the increased condensate recovery were estimated at 87,600 MMBtu and $649,000.
Medium-term opportunities*
- Install a Blowdown Heat Recovery Exchanger – Although the blowdown was being sent to a flash tank to recover low-pressure steam, the energy assessment found that significant amounts of thermal energy were being lost because there were no heat exchangers in the blowdown systems. By installing a heat recovery exchanger upstream of the blowdown tank, significant heat from the blowdown water could be captured and used to preheat boiler make-up water. The assessment estimated annual natural gas and cost savings resulting from the use of a blowdown heat recovery exchanger at approximately 31,000 MMBtu and $200,000.
- Preheat Reactor Feed with 75-psig Steam – The assessment found that some of the heat needed to preheat the reactor feed from ambient to reaction temperatures could be supplied by 75-psig steam instead of depending only on the 600-psig steam generated at the site. While this opportunity would not save natural gas, it could allow additional electricity generation from the 600-psig steam that was not being used to preheat the reactor feed. This could reduce electricity purchases, leading to estimated annual electricity and cost savings of 1,277 MWh and $79,000.
- Install a Back-Pressure Turbine Drive – Although the site generates steam at 600 psig, most applications require steam at 200 psig. The assessment found that, by installing a back-pressure turbine drive, the chemical plant could generate enough electricity to serve some of its specific critical powered equipment. Annual electricity and cost savings were estimated at 1,946 MWh and $121,000.
If all these measures were implemented, the total annual energy savings that would result were estimated at more than $5 million.
(*These three opportunities pertain to two chemical plants within the St. Charles site that participated in the assessment with the Energy Facility proper.)
Assessment Recommendations
Once the data collection was complete, the assessment team evaluated the steam system using SSAT and identified several energy efficiency opportunities. The team then calculated the expected savings and payback periods for each opportunity and divided them into near- and medium-term opportunities based on payback periods.
Results
The implementation of some Save Energy Now assessment recommendations with short paybacks is already yielding important energy savings. By repairing steam leaks and replacing non-functional steam traps, the St. Charles plant was able to reduce energy costs and improve process efficiency. The steam trap retrofit resulted in annual energy savings of 109,000 MMBtu and energy cost savings of approximately $792,000. The steam leak repairs resulted in annual energy savings of 163,000 MMBtu, worth a little more than $1.1 million. Total annual energy and energy cost savings were 272,000 MMBtu and $1.9 million, respectively. With total implementation costs of approximately $225,000, the simple payback is slightly more than six weeks. In the future, Dow may pursue some other opportunities identified in the Save Energy Now assessment. While the implemented measures and the resulting energy savings are significant, another important result of the Save Energy Now assessment is the permanence of both measures. Steam trap maintenance and leak management are now ongoing programs. As a result, steam leakage from failed traps or fissures in steam headers are identified and repaired in real time. In addition, Dow is sharing the results of the SSAT-based analysis from the Save Energy Now assessment at the St. Charles plant with its other facilities that use steam.
Lessons Learned
Repairing steam traps and leaks in steam headers is one of the quickest ways that an industrial plant can reduce its energy consumption. Compared with other steam-related energy efficiency opportunities, steam leak and trap repair are easy, cost-effective and yield a quick payback. At Dow Chemical’s St. Charles plant, the value of energy efficiency was well understood. However, when steam losses from failed steam traps and leaks were fully quantified with DOE’s SSAT software, the energy savings became more compelling. SSAT and other DOE software tools such as AIRMaster+, the Pumping System Assessment Tool (PSAT), the Process Heating Assessment and Survey Tool (PHAST), MotorMaster+, the Fan System Assessment Tool (FSAT), and 3EPlus can similarly be used to determine how to optimize industrial systems and processes (to download software, visit www.eere.energy.gov/industry/bestpractices/software.html).
Save Energy Now
Save Energy Now (www.eere.energy.gov/industry/saveenergynow) is a national campaign started in 2005 in response to a rapid rise in energy prices. This campaign helps U.S. industry reduce energy use and supports national goals for energy security. Through Save Energy Now, DOE’s Industrial Technologies Program helps industrial plants operate more efficiently and profitably by identifying ways to reduce energy use in key industrial process systems.
Strong Energy Portfolio for a Strong America
Energy efficiency and clean, renewable energy will mean a stronger economy, a cleaner environment and greater energy independence for America. Working with a wide array of state, community, industry and university partners, the U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy invests in a diverse portfolio of energy technologies. For more information, contact the EERE Information Center, 877-EERE-INF (877-337-3463), www.eere.energy.gov. And, visit the DOE Industrial Technologies Program home page at www.eere.energy.gov/industry.
