Save Energy Now Program Gets Results
Through the Save Energy Now (SEN) program, the Department of Energy’s (DOE’s) Industrial Technologies Program (ITP) helps industrial plants operate more efficiently and profitably by identifying ways to reduce energy use in key industrial process systems. The ITP cosponsors these assessments through a competitive process. The DOE promotes plant-wide energy-efficiency assessments that will lead to improvements in industrial energy efficiency, productivity, and global competitiveness, while reducing waste and environmental emissions.
This case study looks at the Bayer Corporation, which is the largest subsidiary in the Bayer Group, with some 23,200 employees working at more than 50 locations in the United States. The Bayer Polymers1 New Martinsville, West Virginia, plant has 16 production units and employs 950 workers. The plant produces more than 1.2 billion pounds of chemical intermediates, polyurethane materials, food-grade hydrochloric acid, and iron-oxide pigments each year.
The Bayer Corporation’s plant-wide energy assessment focused on the technical and economic evaluation of existing utility systems. The assessment also identified areas—such as insulation, boiler, steam, compressor, and motor-driven pump systems—that could benefit from modifications and upgrades. Improvements in these systems, as well as their accompanying energy and cost savings, can be replicated in other industrial plants. In this case, the DOE contributed $87,000 of the total $181,000 for the assessment, which took place in the spring of 2001. The project evaluation process was unique in that the company had obtained very favorable rates for electricity, even by West Virginia’s favorable standards in the industrial sector. Even so, the company found strong economic justification for several projects that would reduce either electricity or fossil fuel consumption.
The projects, when complete, will reduce the amount of fossil fuel that is burned and leaked, saving the company an estimated 236,000 million British thermal units (MMBtu), or an estimated $1.16 million annually, based on an average cost of fossil fuel. Certain other projects will save the company 6.3 million kilowatt-hours (kWh) of electrical energy. All of the projects are potentially applicable to other chemical manufacturing facilities, and most of the projects have potential applicability to other industries.
The plant-wide energy-efficiency assessment focused on the technical and economic evaluations of existing energy systems in the plant utilities that could benefit from equipment modifications, leak reduction, heat recovery, improved control systems, additional insulation, and burner adjustments.
The systems that were evaluated included those using significant quantities of natural gas (NG), electrical power, and chemically treated water. Reducing production of nitrogen oxide (NOX) and carbon dioxide (CO2) was also a high priority. The assessment team consisted of the Bayer Corporation’s director of utilities and maintenance, the manager of utilities, and a member of process engineering. The review was a joint effort of these management experts and an assessment team from West Virginia University (WVU). The Bayer team prepared a list of energy-efficiency concerns and discussed them with the WVU team. During the summer of 2001, the WVU team made regular site visits to collect necessary energy-use and management data at the plant. The assessment focused on boiler-system operation, insulation needs, steam leaks, steam-system condensate, compressed air, and motor performance.
The WVU team then conducted a detailed analysis of the data, which focused on component-level specifics (heat losses in pipes, flanges, tanks, cooling towers, and valve spool pieces specific to each boiler). The WVU team issued a report in July 2002 describing the analysis and several proposed projects. The utility management staff noted high-priority items (steam and compressed gas leaks) with less than 1-month payback and acted on those immediately.
To ensure that all project goals were met, the Bayer team wanted to: 1) identify significant energy savings and attractive payback, and 2) proceed based on environmental criteria. The company is interested in reducing the production of NOX and CO2, which is frequently an outcome that accompanies energy conservation projects. The Bayer plant operates with a 25-megawatt electric load and is the second largest user of NG in the state. The total annual cost for imported utilities is more than $15 million. The Bayer team recognized that even a small improvement in the efficiency of the plant’s main energy consumers—boilers and large pumps—could create a significant savings.
The plant-wide energy-efficiency assessment identified several attractive projects based on the above criteria. Figure 1 provides a list of five projects that Bayer plans to submit internally for implementation. For each project, the table indicates expected project costs, estimated annual savings, and expected payback periods. The greatest annual energy savings will come from boiler burner replacements, increased condensate return, and a portion of Project 5 that reduces the number of NG leaks (discussed below).
The following discussion provides details of the selected energy-efficiency projects developed during the plant-wide assessment. Because of the similar basic utility processes used in chemical plants, all of the projects are highly applicable to other chemical plants. In addition, these projects seek to improve common utility systems (boilers, steam, compressed air, and motors), so the projects are replicable in many other industries.
Project 1—Burner Replacement
The plant-wide evaluation of boiler operations found that the NG-fired burners in four boilers, as well as the combined NG- and hydrogen-fired burners in two boilers, were not the newer, high-efficiency designs. These designs produce a controlled, slow-burning, low-temperature flame that produces less NOX and CO2. Using a newer burner could increase efficiency by 2 percent. Replacing the burners would yield an energy savings of 74,800 MMBtu per year (MMBtu/yr) and an 8.46-million-pound annual reduction of CO2.
Project 2—Condensate Return
The WVU analysis showed that by increasing the amount of condensate returned to the boilers, the company would pay less for makeup water, save NG in the initial heating of the makeup water, and save the chemical and treatment costs for the makeup water. There would be a small savings from discharging less water into the sewer system. Increasing the condensate return may require separators or filters to remove contaminants and additional piping. Increasing the condensate return from the present 30 percent, or 30,000 pounds per hour (lb/hr), to 75 percent, or 75,000 lb/hr, will produce an overall energy savings of 66,600 MMBtu/yr and a 7.53-million-pound annual reduction of CO2.
Project 3—VSDs on Pumps
The utilities department at the Bayer plant provides cooling tower water to various designated users. The cooling towers’ performance depends on the weather and the needs of the users. At any given time, no more than 60 percent of the users connected to each cooling tower station are operating. Because the 12 motors used in the four cooling towers (three per tower) are all at constant speeds, maximum flow is continuously supplied to all users regardless of individual needs. The plant assessment analysts knew that variable speed drives (VSDs) could adjust flow based on demand and save money by reducing electrical energy consumption and electrical demand charges. The VSDs would provide smoother control; softer starts; and reduced noise, component maintenance, and friction heating of the coolant. Providing 12 VSDs to the towers to control six 75-horsepower (hp) motors and six 200-hp motors would yield total electrical energy savings of 4.64 million kWh annually (a rough but conservative estimate) and a 10.2-million-pound annual reduction of CO2.
Project 4—Compressed Air System Optimization
A limited assessment of the compressor system at the Bayer plant identified one partially loaded compressor that frequently vents up to 500 standard cubic feet per minute of compressed air. This venting occurs when the inlet throttle of the compressor attempts to balance the system supply to the actual plant demand. The WVU team recommended replacing this 800-hp centrifugal compressor with a 400-hp reciprocating compressor. The new compressor would supply the required compressed air flow, but at nearly half the rated power, and no compressed air would be wasted. This should yield total electrical energy savings of 1.53 million kWh annually and reduce electrical demand charges. The reduction in electricity usage will reduce annual CO2 emissions by 3.34 million pounds.
Project 5—Four Low-Cost Projects
The following low-cost projects each will provide a payback for the plant in just 1 month or less:
- Insulating steam system components, including pipe saddles, flanges, boiler end covers, and lines where needed
- Repairing steam leaks in overhead lines
- Adjusting the fuel-to-air ratio in Boiler 7 for a 1-percent efficiency improvement (based on combustion efficiency tables)
- Repairing compressed gas leaks (air, NG, and nitrogen)
Repairing the NG leaks alone will save approximately $321,000 per year. The second greatest savings—$70,000 per year, or 14,300 MMBtu/yr—will come from insulating the steam system components. The four low-cost projects together are projected to prevent 95,000 MMBtu/yr of lost heat energy and reduce CO2 emissions by 11 million pounds annually.
The DOE’s SEN program has completed more than 200 energy assessments—including this one for Bayer—and has identified energy cost savings of $485 million. The program will complete more free energy assessments in 2007. Through SEN, the DOE’s ITP helps industrial plants operate more efficiently and profitably by identifying ways to reduce energy use in key industrial process systems.
This article has been reprinted with permission from the U.S. Department of Energy (DOE). To learn more, visit www1.eere.energy.gov/industry/saveenergynow.