Results of a Plant-wide Assessment at an Integrated Carpet Yarn Plant

Transcription

1 46 Energy Engineering Vol. 104, No Results of a Plant-wide Assessment at an Integrated Carpet Yarn Plant Michael Brown Matt Soderlund Jerry Zolkowski Georgia Tech Georgia Tech Shaw Industries Savannah, GA Atlanta, GA Dalton, GA ABSTRACT The Georgia Tech Energy and Environmental Management Center (EEMC) and Shaw Industries partnered to conduct a plant-wide energy assessment at a South Carolina carpet yarn plant. The study was jointly funded by Shaw and the US Department of Energy. The plant manufacturing process begins with the conversion of caprolactum monomer into nylon, and concludes with the twisting of nylon filaments into yarn and heat setting. The energy assessment addressed every phase of the production process. Energy saving improvements for boilers, air compressors, HVAC, yarn extruders, and twisters were discovered. In addition, opportunities to improve general energy management practice at the facility were found. The final energy assessment report contained 18 recommendations with an estimated energy savings of $925,853, or 13.8 percent of the plant s annual energy cost. INTRODUCTION Plant-wide assessments are in-depth energy surveys conducted at large, energy-intensive manufacturing plants. The plant-side assessment program is sponsored by the US Department of Energy. The assessment is expected to require 9-12 months to complete. The cost of the study is shared by the Department of Energy and the organization receiving the assistance. Plant-wide assessment awards are distributed on a competitive basis with the decision based on the energy intensity of the industrial process, comprehensiveness of the proposed energy assessment process, perceived ability to complete the proposed project, and the ability to readily transfer

2 47 and replicate the estimated savings in similar associated facilities. The plant-wide assessment proposal from Shaw contained all of the required factors: large energy budget, unique assessment methodology, knowledgeable assessment team, and well-defined replication plan. A unique aspect of the proposal was the economic sector which it addressed. Prior to this proposal, plant-wide assessments were mostly limited to primary metals, chemical, and forest products sectors. While the plant for the proposed assessment was in the chemical sector, the parent company, several plant processes, and the output is in the textile sector. Thus, completing a plant-wide assessment in this plant exposes an entirely new industrial sector to the advantages of conducting in-depth energy assessments. PLANT BACKGROUND The energy assessment was conducted at a carpet yarn formation plant. The process consists of converting caprolactum monomer to nylon polymer, extruding the nylon chips to form nylon filament, treating the filament to achieve desired properties, twisting multiple filaments into yarn, and heat setting the finished yarn to achieve the memory. Fiber formation, extrusion, filament conditioning, twisting, and heat setting are relatively energy intensive processes. Nylon formation, extrusion and heat setting are thermal processes with heat supplied by steam and thermal oil. The nylon formation, filament conditioning, extrusion, and twisting processes all use significant amounts of electricity. Major energy systems at the plant are listed in Table 1. Table 1. Major Energy Systems at Fiber Plant Steam Boilers hp (20,100 lb/hr) Chillers ton, ton, ton Cooling Towers 2 w/2-75 hp fans; 4 w/2-50 hp fans Air Washers 4-75 hp, hp, hp Extruders hp (165 kw DC) Twisters hp (AC) Air Compressors hp, hp (Centrifugal) Thermal Oil Heaters kw (Extrusion) kw, kw, kw, 4-33 kw (Nylon Formation) Bake-off Ovens 1-28 kw, 1-32 kw

3 48 Energy Engineering Vol. 104, No ASSESSMENT PROCESS The objective of the energy assessment process is to gain an understanding of the manufacturing operation and identify the major energy users. Locating the large energy users is an integral part of the assessment process because, in most cases, the consumption of the user is directly related the potential for energy and/or cost savings. The process used during this assessment is presented in Table 2. As stated earlier, each plant-wide assessment proposal is judged on the assessment methodology used during the study. The assessment process followed at Shaw included six major steps. First, the utility data for the plant were collected, entered into a spreadsheet, and analyzed. The analysis process consists of identifying base usage, seasonal variations, average costs, and marginal costs for energy. The utility data show the overall energy usage pattern at a facility. The next step is to develop a process map whose purpose is to help define the internal energy usage pattern at the facility. The process map presents where energy entering the facility eventually ends up. This is important because the analysis of internal energy use identifies areas of highest usage that have the greatest potential for significant savings. After the development of a rough process map, the next step is a walkthrough of the site. This helps the assessment team visualize the process and verify the process map. During the walk-through, the assessment team verified equipment capacity ratings and collected missing capacity information. Table 2. General Energy Assessment Process Enter and analyze utility data. Develop map of process. Walk-through to observe process flow and equipment arrangement. Identify and quantify significant energy users. Formulate preliminary opportunity list. Collect needed data, analyze, and accept or reject. The outcome of the process flow and facility walk-through is an energy balance that accurately distributes the utility usage among the energy users in the facility. From the energy balance, the plant energy systems can be tabulated from the largest to the smallest. Various small users are put together in the miscellaneous user category.

4 49 Table 3. List of Significant Energy Users in Order of Total Consumption System Percent of Total Energy Boilers 19.5 Air Compressors 17 Twisters 13.7 Extruders 12 Miscellaneous 10.3 Thermal Oil Heaters 8.3 Chillers 6.4 Air Washers 5.5 Total 92.7 Using the significant energy users list as a guide, a preliminary opportunity list was generated. The opportunity list included all classes of energy savings measures, purchasing, operation, maintenance, and capital improvement. Because the organization is doing reasonably well managing the existing equipment and resource acquisition, only limited energy purchasing and equipment operation opportunities were discovered. The greatest number of opportunities identified was maintenance and capital improvement types. The number of potential opportunities, by system, was seven boiler/steam, nine air compressor, six HVAC, four extruder, two twister, three heat set, two fuel switching, and seven miscellaneous. The seven miscellaneous measures included one lighting, one purchasing, two building envelope, three process improvement, and one combined heat and power. Table 4 shows the complete list of potential opportunities by system. As expected, the greatest number of potential opportunities was found for the air compressors and boiler/steam system, the plant s two largest energy consumers. Similarly, HVAC and extruders had a significant number of potential opportunities identified. Extrusion is the fourth largest energy consumer. When the chiller and air washer usage is combined, it represents the fifth largest energy consuming system in the plant. Thus, it is not surprising that six potential measures were identified for HVAC.

5 50 Energy Engineering Vol. 104, No Table 4. List of Potential Opportunities by System System: Compressed Air (9) Potential Opportunities: Repair air leaks. Use synthetic lubrication. Install compressor sequencer control. Replace air aspirators with vacuum. Reduce plant air pressure. Install separate compressor for low pressure applications. Increase air storage. Install rotary screw compressor for trim. Reverse cooling water flow direction in after-cooler. System Boiler/Steam (7) Potential Opportunities: Add drip legs to steam header. Use compressor cooling water as boiler feed. Blowdown heat recovery. Shutdown backup boiler. Reduce steam pressure. Verify operation of oxygen trim control. Decrease boiler blowdown. System: HVAC (6) Potential Opportunities: ASD controls on air wash fans, spray pumps and cooling tower fans. Repair enthalpy control (economizer) on air washers. Replace chillers. Add inverter to fixed pitch fan. Chilled water reset control. Improve cooling tower control and performance. System: Polymer extrusion (4) Potential Opportunities: Replace DC drives with AC VFD. Upgrade belts from standard V to cogged V. Use synthetic oil in extruder gear drive. Upgrade insulation on extruder thermal oil piping. System: Yarn twisting (2) Potential Opportunities: Install VFD controller on twister motors. Replace standard V-belts with cogged V-belts. (Continued)

6 51 System: Heat set (3) Potential Opportunities: Isolate heat set with strip curtains and install exhaust fans to eliminate heat buildup. Install backpressure turbine to reduce heat set steam flow. Recover condensate from heat set operation. System: Thermal oil heaters, bakeoff ovens (2) Potential Opportunities: Replace electric thermal oil heaters in extrusion and poly-tower with natural gas fired heaters. Replace electric bakeoff oven with natural gas fired oven. System: Other miscellaneous (7) Potential Opportunities: CHP. Fast chargers for fork lifts. Use poly-tower nitrogen exhaust for cooling. Increase efficiency of nylon conversion process. Improve natural gas purchasing practice. Cover AGV doorway. Improve warehouse lighting efficiency. OPPORTUNITY ANALYSIS Once the list of potential measures was complete, the opportunities were analyzed for expected savings and investment. Following completion of the analysis, the opportunities are accepted or rejected based on organizational capital investment and risk parameters. While the general rule for acceptance of an opportunity at this facility is a simple payback of two years or less, in some situations there are considerations other than economic that can influence the selection process. Initial data collection resulted in the elimination of a number of impractical opportunities. Because the list of opportunities is assembled prior to any detailed collection of equipment data, inclusion of some impractical measures in the list cannot be avoided. Table 5 presents the list of impractical measures and the reason that renders them inappropriate for consideration. Several other recommendations were rejected after further measurement and analysis. One compressed air recommendation was to replace the compressed air generated vacuum aspirators with vacuum

7 52 Energy Engineering Vol. 104, No Table 5. List of Impractical Energy Saving Opportunities Opportunity Reason Impractical Combine heat and power (CHP) Because of facility energy prices (low electricity, high natural gas), the payback exceeded 15 years. Fast battery chargers Decrease the time for charging but no documented energy savings found. Improve natural gas purchasing Already purchase at month-end close price. Use synthetic lubrication on Already in place. air compressors Boiler blowdown heat recovery Blowdown rate is low (5 percent) and with improvements to makeup water may be reduced even more. Increase efficiency of nylon While the conversion of caprolactum to conversion process nylon can approach 90 percent under laboratory conditions, at the throughput of a manufacturing operation conversion rates of percent are exceptional. Replace chillers Chillers use R-123, which will be phased out in 2030, but the savings from converting to a R-134a refrigerant chiller do not justify the investment. Replace standard V-belts with Twisters are equipped with flat belts. cogged V-belt on twisters Reverse cooling water flow Refrigerated dryer does not cycle, lower air direction in compressor temperature will not generate savings. after-cooler Reduce steam pressure Size of plant and length of steam header run makes this impractical.

8 generated by pump. Vacuum pumps use less energy to create vacuum than compressed air aspirators. When the volume of air used to create the vacuum in the aspirators was determined, it was found to be substantially less than expected. Even though some energy savings would result from this conversion, the complexity of installing a vacuum pump and piping was not viewed as worth the trouble of changing the existing system. Another rejected recommendation was to use air compressor cooling water as boiler makeup. This would increase the temperature of makeup water from 60 to 90 F. While any gain in temperature results in savings, this opportunity was rejected because the mass flows are not well matched, and an alternative boiler makeup water measure offers greater savings. Instead of using compressor cooling water, boiler makeup with reverse osmosis (RO) water was selected. Because one boiler is operated at low fire to meet steam demand if the lead boiler goes off-line, shutting down the backup boiler to save fuel was studied. Steam is required at all times by the polymerization process to prevent solidification. Boiler instrumentation indicated that the standby boiler was operating at 10 percent load. The energy balance indicated that the actual load was less. The standby losses were reduced because the boiler was equipped with a low turndown burner. This allows the unit to operate at lightly loaded conditions without constantly cycling off and on. Since no alternative to one boiler on hot standby could be developed, polymerization operations demand that the backup boiler remain on standby for emergency. Since the twisters operate at different speeds to produce yarns with differing twist ratios (turns per inch), changes in speed are required. Because twisters are equipped with induction (constant speed) motors, to accomplish the change a twister must be shutdown, belt loosened, pulley removed and replaced, belt retightened, then restarted. Installing a variable frequency control would allow motor speed to be changed by adjusting the controller. Experiments on a VFD twister at a sister plant revealed that reducing motor speed to accomplish a change in yarn twist would only reduce motor energy consumption by 6 percent. Although additional savings accrue with VFD twisters from productivity increases and a reduction in maintenance labor, the estimated simple payback on investment is almost five years. With approximately half the savings due to increased production from faster changeovers, VFD twisters could not be justified at this location because the yarn twist ratio is almost never changed. 53

9 54 Energy Engineering Vol. 104, No Plant boilers operate at 165 psig, but the pressure required for the heat set process is only 29 psig. An energy saving opportunity for this situation is to substitute a steam turbine for the throttling valve and generate electricity. Using the calculated steam, the resulting generator is 50 kw. The value of the electrical energy saved is $25,000. The investment cost for a steam-turbine generator of this size is approximately $175,000. Since the annual cost of turbine maintenance is $10,000, the net savings is only $15,000. The resulting simple payback is over 10 years, and the opportunity was rejected. Another potential opportunity in the heat set area was to use plastic strip curtains suspended from the ceiling to retain heat in the area and prevent it from escaping to the surrounding conditioned space. The analysis indicated there was some merit to this idea because it limits the heat gain and, consequently, air conditioning costs in the remaining manufacturing areas. Because of the difficulty of implementation and potential problems with employee comfort in heat set, this idea was rejected. The final opportunity in heat set was to recover condensate that does not directly contact the yarn. Condensate from the traps in heat set is discharged into a floor drain and contaminated with other, cold process water. While the traps could be piped into a separate condensate receiver, the required investment and marginal amount of condensate recoverable does not make this opportunity feasible. Liquid nitrogen is evaporated in a heat exchanger and used to dry nylon chips produced in the poly-tower. The evaporation process uses outside air to vaporize nitrogen. If, instead of outside air, inside air is used for evaporation, the latent heat of nitrogen vaporization could be captured for plant cooling. When the cooling potential of nitrogen was calculated, the current usage translates to only 14 tons of potential capacity. The estimated value of 14 tons of cooling is about $4,000. While this is not insignificant, the cost and difficulty of capturing this savings was not deemed feasible. Since electricity is typically more expensive than natural gas for heating, another opportunity was to switch the thermal oil heaters in nylon formation and extrusion from electricity to natural gas. While the analysis revealed some cost savings would result from this conversion, the high cost of natural gas relative to electricity minimized the savings. Another unfavorable factor is the cost and complexity of gas-fired boilers and heaters. The combination of low savings and high investment made this opportunity unfeasible.

10 55 The final three rejected measures were all related to the HVAC system. One opportunity, a VFD controller on fixed pitch air wash fan, was rejected because examination of the operating conditions indicated that the flow did not vary appreciably and speed control was not justified. The measure to improve cooling tower performance was rejected because tests of tower performance indicated that little improvement was possible. The final HVAC opportunity, chilled water reset, was not included because examination of the existing chiller controls did not indicate this could easily be incorporated. After the list of potential opportunities was evaluated, ten opportunities were found impractical and twelve were found unfeasible, giving a total of 22 measures eliminated from the initial list of 40. The remaining 18 recommendations were included in the final report. OPPORTUNITIES SELECTED The eighteen selected measures are presented in Table 6. By plant energy system, there were five measures for extrusion, five for compressed air, four for boiler/steam, three for HVAC, and one for lighting. Three measures had non-energy cost savings. Non-energy savings are reported in Table 7. The combined savings from energy and non-energy improvements is $1,021,183. This is equivalent to 14.5 percent of the plant s annual energy expense. Table 6 reveals that two measures were included that exceeded the simple payback selection criterion. Another measure with a marginal simple payback was also included. ESO #5, upgrade insulation on thermal oil lines in extrusion, was included because of safety considerations. Although the estimated payback was 10.5 years, the plant s insurance company recommended that the absorbent calcium silicate insulation be replaced with closed cell fiberglass. Closed cell insulation resists liquid absorption. The concern was that any thermal oil leaks are absorbed by calcium silicate, creating a potential fire hazard. Thus, safety and not energy savings was the deciding factor for inclusion of this measure. ESO #1, replace DC extruder motors with ASD-AC, was included because maintenance personnel prefer AC motors due to the simpler maintenance. Even though this is no energy savings, there would be considerable maintenance cost savings. ESO#4, replace electric bake-off oven with natural gas, had a 3.4-year payback. Despite a payback that

11 56 Energy Engineering Vol. 104, No Table 6. Plant-wide Assessment Recommendations Energy Simple Cost Invest- Payback ESO # ESO Saved ($) ment (yr) Extrusion 1 Replace DC extruder motors w/asd 0 256, Install cogged V-belts 16,800 7, Use synthetic oil in gear drive 17,500 1, Replace electric bake-off oven with natural gas 9,690 32, Upgrade insulation on thermal oil lines 6,020 63, Boiler/Steam 6 Add drip legs to steam header 54,200 10, Use RO for makeup water 6,550 2, Replace/repair O 2 trim sensors 25,900 1,000 9 Install vent condenser on receiver 92,400 9, Compressed Air 10 Repair air leaks 187,000 25, Increase primary air storage 113,000 39, Reduce plant air pressure 102,000 51, Install compressor sequencer control 187,000 20, Install dedicated compressor for heat set 9,530 14, HVAC 15 ASD on air wash spray pumps 9,800 36, Repair enthalpy controller on air washers 74,500 94, Cover AGV entrance Lighting 18 Install fixtures with occupancy sensors in warehouse 13,300 35, TOTAL 925, , exceeds the target of 2 years, this measure was included because natural gas ovens have greater heat input capacity and will yield shorter cleaning cycles. The payback for this measure depends on the cost differential between gas and electricity. During the time of the study, the cost of natural gas had risen but electricity had not. Because of the amount of natural gas generation, electricity will mimic the price of gas but with a slight delay.

12 57 Table 7. Non-energy Cost Savings Measure Savings Description Amount ($) Replace DC extruder motors w/asd DC motor maintenance savings $43,200 Add drip legs to steam header Water cost savings from increased condensate return $46,780 Use RO for makeup water Water cost savings from reduced boiler blowdown $5,350 TOTAL $95,330 LESSONS LEARNED 1. Unusual measures seldom prove feasible. Because this assessment had an extended time for survey and analysis, several non-routine opportunities were examined. When studied, these unusual measures were found to yield limited savings and, because of the risk involved, seldom proved feasible. Example opportunities in the category included replacing compressed air aspirators with a vacuum pump, using compressed air cooling water as boiler feed, a combined heat and power system, a backpressure steam turbine to reduce steam pressure for heat set, and recovering liquid nitrogen vaporization energy for cooling. While each of these measures may generate some savings, the magnitude of savings is small and the risk to reward ratio is too great to make consideration of the opportunity feasible. 2. The most inefficient energy systems yield the greatest opportunities. When reviewing the list of recommended opportunities, most of the report s savings (84 percent) comes from two energy systems compressed air and steam. Because these two systems have the greatest inefficiencies, finding huge savings for them is not unexpected. The magnitude of savings and low paybacks associated with these systems indicates that energy assessments should emphasize these areas.

13 58 Energy Engineering Vol. 104, No Variable speed drive AC motors are not warranted for every application. ASDs for AC motors is a popular and oftrecommended opportunity. While one ASD measure, variable speed controller for air washer spray pumps, yielded savings, the other two ASD opportunities, on the extruder and twister drives, gave little or no savings. The conclusion reached was that while ASD control will produce savings on centrifugal drives like pumps and fans, paybacks of greater than three years or more can be expected. When ASD control replaces a DC motor, there is no energy savings because the system efficiencies are essentially identical. Lastly, tests for an ASD on a linear load like yarn twisters will only yield limited savings. Because the cost savings for linear loads is reduced, the economic payback for this type of application approaches seven years. When considering ASDs, centrifugal loads and accurate partload information are recommended. 4. O&M practices yield quick paybacks, good savings, and low risk: The most favorable savings and paybacks were associated with operation and maintenance measures. Examples include reducing air pressure, switching to the lowest cost fuel, synthetic lubrication, and more efficient V-belts. Although the savings from these measures may not be the greatest, the simplicity of implementation renders quick paybacks and low risk. ABOUT THE AUTHORS Michael L. Brown, P.E., C.E.M., is one of the principle developers of ANSI/MSE 2000, the management system for energy standard and a senior research engineer with Georgia Tech s Energy and Environmental Management Center (EEMC). He has over 25 years of experience providing energy conservation, alternate fuel, and energy efficiency assistance to industrial, commercial, and institutional facilities. A registered Professional Engineer and Certified Energy Manager, Mr. Brown has completed over 200 energy assessments at industrial facilities, 50 commercial energy assessments at public schools and hospitals, and several energy surveys at institutional facilities including military bases, correctional buildings, and universities. He instructs training courses on implementation of the MSE 2000 standard. He also has experience in optimizing processes to reduce waste and instructs numerous technical courses related to industrial energy

14 systems. Mr. Brown has degrees from the Georgia Institute of Technology and Texas A&M University. Matthew R. Soderlund, program manager and research engineer at Georgia Tech s Energy and Environmental Management Center (EEMC), comes from a merchant generation background. In his merchant generation position, he worked on both power plant project development and regulatory policy development. One of his current responsibilities includes being the assistant director of the DOE/ITP sponsored Industrial Assessment Center (IAC) where he has coordinated over 70 energy assessments since He has conducted 25 energy assessments for industrial facilities. In addition, he has conducted energy assessments for commercial, institutional, and military facilities. The focus of his work has included analysis and recommendations on combined heat and power, distributed generation, energy purchasing, motor systems, compressed air, combustion systems, steam, chilled water, lighting, and others. Mr. Soderlund has both bachelor s and master s degrees in mechanical engineering from the Georgia Institute of Technology. matt. soderlund@innovate.gatech.edu Jerry Zolkowski, PE, CEM, is the demand-side engineer manager spearheading energy conservation efforts for Shaw Industries since Prior to Shaw, Jerry was employed by the Georgia Tech EEMC as a project manager specializing in energy efficiency and environmental compliance assistance to industry. Before Georgia Tech, Mr. Zolkowski was an environmental engineer at the Pratt and Whitney Division of United Technologies in Columbus, Georgia. He holds a BS in mechanical engineering from the University of Rochester and an MBA from Columbus State College. In 2004, Shaw started establishing formal energy efficiency measures, goals, and ways to improve. Shaw Industries has 60 manufacturing plants and is the world s largest carpet manufacturer. jerry.zolkowski@shawinc.com 59