1 / 39

Performance and Economics of Currently Available Technologies for Removal of Siloxane from Biogas

Explore the impacts of siloxanes on power equipment and different methods for sampling and analyzing siloxanes. Learn about various siloxane removal technologies and their performance and cost considerations.

gbrooks
Download Presentation

Performance and Economics of Currently Available Technologies for Removal of Siloxane from Biogas

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Performance and Economics of Currently Available Technologies for Removal of Siloxane from Biogas Jeffrey L. Pierce, P.E. Senior Vice President SCS Energy jpierce@scsengineers.com SWANA WasteCon 2010 August 15-17, 2010 Boston, Massachusetts

  2. Siloxanes – What and Why? • Siloxanes are volatile organic silicon compounds (VOSCs) • Widely used in personal health and beauty products and in commercial applications • Found in the ppmv level in landfill gas and WWTP digester gas • When burned as a fuel, the silicon (Si) in siloxane oxidizes to silica (SiO2) • Silica deposits cause performance and maintenance problems • Silanes and silanols are also VOSCs

  3. Impacts on Microturbines

  4. Impacts on Engines

  5. Impacts on Turbines

  6. Impacts on Post-Combustion Catalysts

  7. Impacts on Boilers

  8. Impacts on Boilers

  9. Common VOSC Compounds in Landfill Gas

  10. Properties of SelectedVOSC Compounds

  11. Methods of Sampling and Analyzing for Siloxanes • Methanol impinger method (Air Toxics) • Jet Care method • OSB method • AtmAA method • AnSol method • Deutz method • Jenbacher method

  12. Methanol Impinger Sample Train

  13. Jet Care Sampling Kit

  14. Siloxanes in Landfill Gasper SCS Database • Most common siloxanes are D4 (found 90% of the time); D5 (found 83% of time); and MOH (found 77% of the time) • Next most frequently found are L2 (45% of the time) and D3 (20% of the time) • Ten other siloxane species were seen (each no more than 7% of the time) • Siloxanes varied from 4.5 mg/m3 (0.41 ppmv) to 120.4 mg/m3 (8.88 ppmv) by Air Toxics method

  15. Current Siloxane Limits byPower Equipment Manufacturer All limits cited at 50% LFG methane content

  16. Siloxane Removal Theory • Siloxanes are a “gas in a gas” • Siloxanes cannot be filtered, since they are not in a particulate form • Must apply “advanced” physical operations • Condensation • Absorption • Adsorption

  17. Siloxane Removal Technology • Condensation • Conventional chilling • Advanced chilling • Absorption • Water • Solvent • Adsorption • Activated carbon • Silica gel • Molecular sieve

  18. Mountaingate Gas Plant • All three technology categories in simultaneous operation • Conventional chilling = 25% removal • Selexol absorption = 77% removal • Non-regenerative activated carbon = 95% removal • Overall removal = 99.2% • Product gas = 10 ppbv siloxane or 0.04 mg Si/m3

  19. Conventional Chilling • Typically 40º F • Effect may largely be due to absorption of siloxane into condensing water • Effective post-chilling water separation is critical to the performance of this technology • Generally used for moisture removal – so siloxane removal is an added benefit • Generally installed after gas pressurization and air-to-gas cooling – thus, an incremental cost • When specifically installed in siloxane removal service, chilling is usually installed to support a downstream process

  20. Conventional Chilling • SCS’s experience is that conventional chilling will remove 15% to 35% of raw landfill gas siloxanes • Incremental installed capital costs range from $300/scfm to $350/scfm • Operating costs range from $25/mmscf to $30/mmscf at a power cost of $0.10/kWh • Cost ranges from the equivalent of $0.0019/kWh to $0.0022/kWh of power produced

  21. Non-Regenerative Activated Carbon or Silica Gel • Gas is chilled to 40º F and reheated by 30º F to 40º F to prepare the gas for treatment • Chilling/reheat reduces moisture and siloxanes and improves performance and life of activated carbon or silica gel • Activated carbon and/or silica gel is placed in one or more vessels (in parallel or in series) • Vessels sized typically for changeout every six to nine months

  22. Non-Regenerative Activated Carbon or Silica Gel (cont…) • Activated carbon nor silica gel is specifically selective for siloxane; hence, media life is affected by other contaminants • Media exhaustion is detected by siloxane breakthrough • Certain siloxane specie (e.g., L2 break through earlier than others)

  23. Non-Regenerative Activated Carbon or Silica Gel (cont…) • Applicable to low pressure applications (5 psig) and high pressure applications (80 psig+) • Can also be used as a final polishing step after other processes – like at Mountaingate • Media loading rates vary from 7,000 scf/lb media to 70,000 scf/lb of media depending on many factors

  24. Non-Regenerative Activated Carbon or Silica Gel (cont…) • SCS’s experience is that non-regenerative systems will remove virtually 100% of the raw landfill gas siloxanes – when media is virgin • Performance deteriorates over time • Incremental installed capital costs range from $300/scfm to $1,500/scfm (including chiller) • Operating costs range from $40/mmscf to $210/mmscf at a power cost of $0.10/kWh • Cost ranges from the equivalent of $0.003/kWh to $0.011/kWh of power produced

  25. Regenerative Desiccant • Regenerative systems become more cost-effective as flow rates increase • Desiccant-based systems employ media similar to those used in air dryers (e.g., a silica gel) • Regeneration is accomplished by taking a bed offline and heating it with a backflow of hot air • The hot air desorbs the water and the siloxane that was captured by the media

  26. Regenerative Desiccant (cont…) • Process is called thermal swing adsorption (TSA) • The siloxane, VOC and H2S laden off-gas is directed to a small enclosed flare for combustion • Domnick Hunter manufactures and has sold several of these systems under a trade name “GES Siloxane Removal System”

  27. Regenerative Desiccant (cont…) • Domnick Hunter guarantees offers varying mg Si/m3. The guarantee appears to match the requirements specified by the power equipment suppliers, rather than the technology capability. • SCS has seen data showing performance to much better than their typical guarantees, particularly at high pressure installations • Inlet gas temperature should be limited to 80º F, which in most climates imposes a small pre-chiller requirement

  28. Regenerative Desiccant (cont…) • Installed capital costs range from $380/scfm to $650/scfm • Operating costs range from $90/mmscf to $120/mmscf at a power cost of $0.10/kWh • Cost ranges from the equivalent of $0.0035/kWh to $0.0055/kWh of power produced

  29. Regenerative Activated Carbon • Concept is similar to the non-regenerative dessicant concept – it is TSA • Jenbacher markets a proprietary TSA system for use in conjunction with their engines • SCS configures generic systems – normally in support of PSA high-Btu plants • A gas other than air must be used in the regeneration cycle – landfill gas or carbon dioxide can be used

  30. Regenerative Activated Carbon (cont…) • Jenbacher applies heat through electric coils in the activated carbon beds. The beds are relatively small • SCS uses hot carbon dioxide gas, back flowed through the beds to head the activated carbon • Regeneration gas in both cases is sent to an enclosed flare • Gas is chilled prior to being sent to the TSA

  31. Regenerative Activated Carbon (cont…) • Jenbacher’s TSA reportedly achieves low siloxane levels on virgin media, but degrades to a “roughing” removal mode, due to its low media volume, and their lack of need for “ultra-pure” gas • SCS configured systems are delivering siloxane levels in the 0.1 to 0.2 mg Si/m3 well after six months into their media cycle, largely due to their larger media volume and their more thorough regeneration cycle

  32. Regenerative Activated Carbon (cont…) • Incremental installed capital costs range from $720/scfm to $820/scfm • Operating costs range from $50/mmscf to $105/mmscf at a power cost of $0.10/kWh • Cost ranges from the equivalent of $0.0045/kWh to $0.0065/kWh of power produced

  33. Conclusions • There is a lack of consistency in the methods of siloxane sampling and analysis now employed • Power equipment manufacturers appear to have set overly conservative siloxane limits • Most siloxane removal applications require only “coarse” levels of siloxane removal – microturbines and high-Btu gas are notable exceptions • Commerically proven siloxane removal technologies are available • The technologies are fairly generic, although they are often presented as highly proprietary processes by equipment manufacturers

More Related