Practical Experience in the Development of Waste to Energy Projects Utilizing Landfill Gas

Transcription

1 Practical Experience in the Development of Waste to Energy Projects Utilizing Landfill Gas CONTACT INFORMATION George Deardorff, Golder Associates Inc. Kevin Brown, Golder Associates Inc. George Deardorff Golder Associates Inc Chamblee Tucker Road, Atlanta, Georgia (T) (F) EXECUTIVE SUMMARY As the United States and other countries continue to focus on alternative forms of energy, landfills are being considered as potential energy sources. Although landfill gas has been used as a renewable energy for over a decade, its popularity continues to grow as landfills increase in size. Furthermore, landfills are being considered as areas for solar and wind energy production given the nature of their open area development. These forms of energy can supplement the use of landfill gas and ultimately increase the profitability of such projects. Many of the United States leading waste management companies have undergone a paradigm shift over the past several years. Environmentally friendly landfill operations are now becoming part of the normal landfill development phase, and many companies have established separate divisions for renewable energy, primarily including landfill gas. Further, as the municipalities across the United States continue to grow, alternative forms of energy are investigated. Developments have been recently buoyed by the economic recession, as large capital investments are often required; however, long range plans still include developing renewable energy sources. The capture, treatment and ultimate use of landfill gas can be a complex process involving many parties. Common projects in the United States include direct use projects (also known as medium BTU projects), electrical generation projects (with and without waste heat utilization), and natural gas production projects (also known as high BTU projects). Each project undergoes several phases characterized by planning and negotiations, design, construction and operation. In many cases, several parties including the owner, developer, contractor and engineer have to work together seamlessly to avoid costly modifications and delays. This paper includes a case study of three projects in the southeastern United States that were completed and put into operation within the past two years. The three projects selected represent the most common development projects in the United States and each project presented unique challenges. These projects include: Old Dixie Highway Landfill Medium BTU direct use project;

2 Enoree Landfill Electrical generation project; and Oak Grove Landfill Natural gas production project As an example, the direct use project presented challenges unique to the landfill that serves the carpet capital of the world, as well as conveying landfill gas through public rights of way while complying with the Federal Pipeline Safety regulations. The most challenging aspect of the natural gas production project is maintaining the quality of the landfill gas collected from the landfill and directed to the processing plant. Because natural gas has to be at least 95 percent methane, and the process cannot remove air from the landfill gas, air intrusion to the gas stream must be controlled at the well field. Controlling air intrusion to satisfy the developer, while simultaneously minimizing odors at the facility to satisfy the owner, can be a daunting task. This paper discusses in detail the unique challenges associated with these project developments as well as some lessons learned for each project. Furthermore, the energy park concept will be discussed briefly in order to establish future development concepts and how the development of landfills can become a sustainable endeavor. INTRODUCTION The use of landfill gas as a renewable energy source can present many unique challenges. These challenges depend on the landfill characteristics, the end use of the landfill gas, the interaction of the parties involved and the operational requirements of the project. Discussed below are three case studies of common landfill gas to energy (LFGE) projects in the United States as shown on Figure 1: Old Dixie Highway Landfill Dalton, Georgia Enoree Landfill, Greenville, South Carolina Oak Grove Landfill, Winder, Georgia Figure 1 - Project Locations A detailed description and discussion of unique challenges are provided for each project. The discussion provides lessons learned from each development as well as suggestions for

3 implementation of future projects. In general, the following challenges are discussed for each project: Old Dixie Landfill The benefits of pump tests for assessing the properties of the landfill, permitting of the off-site delivery pipeline and operational issues caused by the end use of the landfill gas Enoree Landfill The benefits of pump tests for designing the system and calibrating gas production models and working with the developer to satisfy the end use of the gas while meeting the owner s objectives. Oak Grove Landfill Operational considerations for high quality inlet gas required to produce pipeline quality gas. In addition, the concept of utilizing landfills as energy parks is also discussed. These parks can supplement the use of landfill gas as renewable fuel with the implementation of solar and/or wind. These other uses can take advantage of the open development nature of landfills and promote the sustainability of landfills as an environmentally friendly waste disposal option. Site Number 1 Old Dixie Landfill The Old Dixie Highway municipal solid waste (MSW) landfill is operated and owned by the Dalton-Whitfield Regional Solid Waste Management Authority (Authority). The site includes various phases of development starting in the late 60 s and continuing to the present day. The landfill facility consists of Phases 2, 4, 5 and 6 with the principal phases considered for the landfill gas to energy project being 2, 5 and 6 located as shown on Figure 2. Phase 4 was not included in the project because of the shallow waste depth. Figure 2 - Old Dixie Landfill Phases 2 and 5 were initiated in 1980 and 1988, and were closed between April 1996 and May Phase 2 (which included a Phase 2a inert site and carpet-waste balefill) provided an original

4 air space capacity of about 3.5 million cubic yards and covered about 55 acres. Phase 5 is about 33 acres in size and contains about 0.8 million cubic yards of waste. Phase 6 will include 11 cells when complete with the latest cell receiving waste (Cell 3) constructed in Cell 1 was started in 1996 and attained a total airspace capacity of about 0.7 million cubic yards. Cell 2 was started in March 1999 and developed a total airspace capacity of about 1.7 million cubic yards. Cells 1 and 2 have a landfill footprint of about 40 acres while Cell 3 covers an area of about 15.6 acres. The primary challenges associated with this project include: System design to accommodate the lower gas generation rate and waste composition; Permitting the off-site pipeline under the Federal Pipeline Safety Regulations; and Accommodating the highly variable demand by the end user. Currently, about 38 percent of the waste received by the Old Dixie landfill is carpet waste consisting of pieces and lengths of synthetic carpet trimmings and associated waste materials. About 27 percent of the waste appears to be commercial waste with an additional 5 percent of construction debris. The remaining 30 percent of the waste is typical household waste with various percentages of paper, wood, textiles, plastics and glass. The Authority intercepts most cardboard received at the site for recycling. Baled carpet waste is directed to the onsite balefills and as such, is not included in the total waste tonnage reported for the site. It is important to note that historically, more carpet waste was received and disposed in Phases 2 and 5. In addition to general waste composition, the moisture content of the waste (as in absorptivity of leachate which moves through the waste mass, field capacity, leachate pass-through time and saturation capacity) is largely controlled by the high percentage of carpet materials in the waste mass as well as the overall rate of surface water infiltration. The carpet trimmings and backings present a poorly compactable mass with an overall high porosity and permeability. This results in accelerated leachate pass-through times and reduced opportunity to perch leachate within the waste mass, subsequently enhancing the open pore spaces between waste particles and facilitating movement of LFG throughout the landfill. This characteristic of the waste significantly impacts the waste compaction density as the carpet waste presents a spongy, elastic mass that resists the high compaction densities common to most MSW landfills. As opposed to a density of 65 pounds per cubic foot of in-place waste currently achieved by many MSW landfill operators, the density of the waste placed during the operation of Phases 2 through 5 did not exceed 30 to 35 pounds per cubic foot. Currently in Phase 6 the reported density is in the range of 50 pounds per cubic foot, utilizing modern landfill compactors in lieu of tracked equipment to achieve compaction. In order to assess the variability of the landfill phases, pump tests were performed in each phase. These tests were designed to determine the flow characteristics of each landfill phase such that extraction wells could be spaced accordingly. Tests were designed with an extraction well where flow, pressure and gas quality were measured as well as observation points and wells to measure the area of influence of the extraction well. In general, the pumping tests indicated that phases 2 and 5 exhibited lower gas generation rates, but they also exhibited a higher permeability due to the nature of the waste and the lower compaction ratios. Phases 5 exhibited characteristics more typical of modern MSW landfills in North America.

5 Figure 3 provides a representation of the landfill pressure observed in an observation well for the pump test conducted in Phase 2. Note that the well exhibited a rapid response to pressure when the test commenced, indicating a zone of relatively high permeability. This test indicated that fewer wells may be required for Phases 2 because of the high permeability. However, the other factor to consider is the nature and quality of the landfill cap. Because Phase 2 is closed, it is capped with a two foot thick soil layer with a maximum permeability of 1 x 10-5 cm/s. A geosynthetic liner was not included in the final cover, which could improve the efficiency of the wells by minimizing air intrusion. The pipeline was permitted through the Georgia Public Service Commission (PSC) and followed guidelines set forth in the Code of Federal Regulations 49 CFR Part 192. This process required communications with the PSC to interpret the regulations as the regulations are not specific to landfill gas or plastic pipelines as were used in this project. A certificate of public convenience and necessity, a public awareness program, a operator qualification program and an operations and maintenance program, including emergency response, were required. In addition, a Drug and Alcohol Misuse Program meeting PHMSA was required. Note that these requirements are typical for pipeline operators, but may present a challenge for landfill owners and operators because specific training is often required for staff. 4 2 WELLHEAD MONITORING INTERFERENCE DUE TO BAROMETRIC PRESSURE CHANGE Vacuum (inches H2O) Blower On Flow = 190 cfm RECOVERY Note rapid response and recovery indicating high permeability zone Pressure Drawdown 12 BLOWER OFF Elapsed Time (in minutes) Starting 10/16/2003 Figure 3 - Old Dixie Landfill Pump Test Results, Phase 2 The startup process involved collaboration between the Authority, the end user, the engineer, the treatment facility manufacturer and the contractor to achieve acceptable operational limits for the treatment facility.

6 Flowrate (SCFM) Pipeline Mass Flowrate Versus Time (April 1, 2009) 12:00 AM 2:38 AM 5:16 AM 7:55 AM 10:33 AM 1:12 PM 3:50 PM 6:28 PM 9:07 PM 11:45 PM Time The boiler at the end user provides steam to more than 20 independent processes that require continuously changing energy requirements. The change in energy demands occur almost instantaneously and the demand for gas fluctuates accordingly. The treatment facility at the landfill was designed to produce a constant pressure to the pipeline. Initially when the boiler required a change in gas flow rate, the valve supplying gas to the boiler was instantaneously opened, creating a surge in gas through the pipeline thus reducing the pressure. Since the treatment facility was designed supply gas at a constant pressure, the surge created a situation where the treatment facility produced a Figure 4 - Pipeline Mass Flowrate higher vacuum on the well field, essentially increasing the flow rates from the collection points on the landfill. Increasing the flow rate on landfill gas wells increases the chance for air intrusion which would harm the methane generation of the landfill. Figure 4 shows the fluctuation in treated landfill gas flowrate through the pipeline during a typical day. To address this problem, the equipment supplier, Perennial Energy (PEI) installed a modulating valve which tempers the collection systems response to the continuously changing demand. The modulating valve combined with the storage capacity of the two mile long pipeline and a small amount of well field tuning have limited the vacuum required to supply the necessary quantity of landfill gas. In addition the boiler is outfitted with a tri-fuel burner that is capable of utilizing natural gas, landfill gas or No. 2 fuel oil simultaneously or independently to meet the overall boiler demand. Thus, this project is a good example of how parties must work together during all phases of the project in order to successfully complete the project. The system included in this project is currently in operation and supplying the end user with 90 to 100 percent of their gas needs for production. Site Number 2 Enoree Landfill The Enoree Municipal Solid Waste Landfill is located in Greenville County, South Carolina, and is operated by the Greenville County Solid Waste Division. The Phase II site is about 71 acres in area, about 40 feet deep on average and has a 4.2 million cubic yard design capacity. Prior to design of the system, a pump test program was initiated to provide a general assessment of the quality and potential quantity of landfill gas generated by the facility. Three extraction wells and nine monitoring points were installed in January 2006 for the test. A short term test (approximately 75

7 hours) was performed on gas extraction well GEW-1. The flow rate and pressure for this well were 185 SCFM and -53-inches of water, respectively. A long term test (approximately 600 hours) was completed for GEW-3. The flow rate and pressure for this test was about 140 SCFM and -50 inches of water, respectively. Gas composition and landfill pressure were measured at all monitoring points for each test. The pumping well was also monitored for gas quality and flow rate (with associated pressure) during the test. The results of the pump test indicated the following: The pressure distribution induced in the landfill by the pumping well (in the vicinity of the test area) tends to remain at or slightly above the screened interval for the well. The landfill in this area appears to exhibit a higher permeability in the north-south direction (approximately 1 x 10-3 cm/s) than the east-west direction (approximately 5 x 10-4 cm/s). Significant air intrusion was not measured at either pump test well during the tests. The gas generation rate estimated from the pump test data appears to be consistent with recommended EPA values. The Lo value ranged from 106 to 104 cubic meters of methane per tonne of waste. This value was obtained through calibration of a spreadsheet landfill gas generation model based on the pump test data. The results of the pump test program and spreadsheet model indicate that the gas recovery from the landfill can vary based on the pump test well (i.e. the location in the landfill) as provided in Figure Calibrated Gas Recovery Model Curves GEW 1 GEW 3 Gas Recovery (SCFM) Year Figure 5 - Gas Recovery Curves

8 Upon installation of the gas collection system and subsequent internal combustion engines, the landfill was producing about 1,000 SCFM in This value falls within the lower boundary of the range provided in Figure 5, which was acceptable to the project. It is interesting to note that the initial gas generation model for the landfill provided an estimated 1,700 SCFM of landfill gas in 2007, using default parameters provided by EPA s Clean Air Act (Lo of 170). Prior to construction of the system, the design engineer developed the preliminary layout of the extraction wells and header piping. This layout was discussed with the owner and future developer of the project, and resulted in some beneficial changes to the design. Because the landfill was about to be closed with a synthetic cap system, the developer and engineer worked to move much of the perimeter header system to a location outside the permitted limit of waste. This allowed the header to remain operational during closure construction activities and allowed operation of the system with minimal interruption. The lateral pipes to the wells from the header system had to be temporarily relocated by the construction contractor for the capping system, so they were left above ground until completion of the construction activities. This project demonstrated the value of performing a resource assessment of the landfill to estimate the realistic landfill gas recovery rates, and also demonstrated the cooperation between the design engineer, developer and contractor. Site Number 3 Oak Grove Landfill The Oak Grove landfill is located approximately 40 miles northeast of Atlanta and serves the northeast region of Georgia. The facility has two landfill units, including a 50 acre unlined closed facility and a 72 acre lined active facility. The active facility began accepting waste in 1996 and has received approximately 2,000 to 3,000 tons of municipal solid waste per day. In 2006, a developer interested in constructing and operating a natural gas processing plant approached the owner and negotiations commenced. The developer began construction of the processing plant in February 2008 and construction was completed in late December, The facility uses an Air Liquide MEDAL membrane separation process to remove carbon dioxide and other trace gases (destroyed in a thermal oxidizer) from the landfill, producing pipeline quality gas (> 95.5% methane) suitable for injection into the local pipeline. The construction of the treatment facility and landfill gas infrastructure was completed with minimal problems, with good cooperation between the owner, developer and contractors. The challenge with the project has occurred during the operational phase of the project. The primary reason for the operational challenges is maintaining the quality of the landfill gas. Prior to operation of the treatment facility, the owner and its representatives were aggressively operating the gas collection system to minimize odor from the landfill. This resulted in gas qualities of 40 to 50 percent methane, and oxygen concentrations of 2 to 3 percent. The treatment facility for the landfill gas cannot remove nitrogen from the gas stream; therefore, this constituent must be minimized by careful operation of the gas collection system. The specification for the landfill gas at the inlet to the treatment facility is 1 percent oxygen and nitrogen or less (combined). This created a challenge for operating the system, because the landfill owner s objectives were to maximize the gas flow to the treatment facility, but also minimize odors at the facility. Figure 6 provides a summary of monitoring data between January 2007 and October This graph provides an indication of the trend in flow based on gas quality improvement. As shown on the figure, the total gas flow would need to decrease to between 2,000 SCFM and 2,500 SCFM to

9 meet the gas quality specification for the plant to operate properly. The graph also shows that when system flows were on the order of 4,000 SCFM to 5,0000 SCFM, the total amount of air (oxygen and balance gas (primarily nitrogen) as measured on the GEM was 15 to 20 percent, which is clearly not acceptable for a natural gas pipeline processing facility. This graph provided an indication to the field monitoring staff on an approximate gas flow range required to achieve the gas quality specification without any physical changes to the gas collection system. 35,0 30,0 Total Flow vs Based on Data Since January 2007 Oxygen+Balance Gas Oxygen Plus Balance Gas (%) 25,0 20,0 15,0 10,0 y = 0,006x 10,82 R² = 0,776 5,0 0, Total Flow (scfm) Figure 6 - Gas Quality versus Total Flow (Oak Grove Landfill) The system is currently operating under the gas specification at a flow of about 2,500 SCFM, and this has been achieved throughh careful operation of the well field. The primary focus of the monitoring team is to reduce leaks of the system, which can be very small, but have a large impact on the gas quality. Significant coordination is needed between the developer and the owner s monitoring team. This coordination involves frequent meetings and communication between alll parties. Interestingly, the project team has improved the gas quality using the information provided in Figure 6 and the approach discussed above without the use of a gas chromatograph, which is usually required to detect very low oxygen and nitrogen concentrations. The team is currently reviewing gas chromatograph models in preparation of further fine tuning of the system to maximize gas flow. Energy Parks

10 As the world continues to evaluate and move towards renewable sources of energy, landfills will continue to play an important role. One concept that is currently being evaluated and even implemented on small scales is the concept of energy parks. Under this idea, landfill gas would not only be reclaimed and used for energy, but other sources of energy may be captured. Another potential renewable energy source at landfills would be solar energy. This can be obtained in the form of typical solar arrays designed to withstand the settlement at landfills or implementing solar landfill caps. These caps are essentially exposed geomembranes with built-in solar panels and are flexible to move with settlement of the landfill. Capture of solar energy can sometimes be used in conjunction with a marginal site with respect to available landfill gas. It is important to note that solar energy generally requires government legislation to be implemented. This is because the cost for solar energy is typically two to three times the avoided cost of producing electricity by other means, rendering it financially unsound without government regulation. If governments require that a portion of a Utility s energy come from a renewable source (such as the Renewable Portfolio Standards or RPS), then implementation of solar projects can become viable. In general, approximately 6 acres of land are required to generate one megawatt of energy in the southern United States using standard solar arrays. Therefore, careful planning of land use at a landfill site is required to avoid disruption to landfill operations. CONCLUSIONS The case studies presented in this paper indicate the following: Pump tests, although sometimes costly, are invaluable for providing landfill information needed for design as well as for calibrating gas production models; The planned end use of the gas is an important factor to consider when designing and operating the collection system. For instance the variable nature of the demand exhibited for the direct use project required post construction augmentation of the system; Significant cooperation and synergies between all parties are necessary for a successful project, regardless of the planned end use of the gas; and Energy parks may be considered for future developments pending government regulations on the use of renewable energy sources. These guidelines should be considered for future landfill gas to energy (and other renewable energy projects at landfills) during the design, construction and operational phases of the project. ACKNOWLEDGEMENTS The authors wish to extend their sincere gratitude to the following individuals for their contributions to this paper: Norman Barashick, Director, Dalton-Whitfield Solid Waste Authority Dirk Verhoeff, Environmental Manager, Dalton-Whitfield Solid Waste Authority Marcia Papin, Director, Greenville County Solid Waste Division Susan Harrison, Engineer, Greenville County Solid Waste Division Timothy Laraway, Environmental Manager, Republic Services, Inc. David Wentworth, President, Renewable Solutions Group, Inc.