Case Studies
Landfill Gas Clean-up and Upgrading to Hydrogen System
Quadrogen has extensive knowledge of and experience in biogas and landfill gas clean-up systems technology, design and development. Quadrogen’s Integrated Biogas Clean-up System will remove all sulfur species, siloxanes, chlorides, water, oxygen and other impurities from biogas to the parts per billion level required for reliable and long term operation. Quadrogen also has extensive experience developing cost effective gas cleanup systems and methane reformer designs for Ballard Power Systems’ natural gas and biogas fuelled 250 kW PEM fuel cell power plants installed at more than 10 sites in Canada, the USA, Europe and Japan.
Quadrogen has teamed with Pioneer Air Systems, Inc. based in Tennessee and is uniquely positioned to design and deliver a gas clean-up and upgrading system producing hydrogen from landfill gas. Pioneer Air systems have been installed at numerous locations in the USA.
The Quadrogen and Pioneer Air team has recently delivered a biogas clean-up system operating on anaerobic digestion gas at the Orange County Sanitation District Wastewater Treatment Plant in California. This gas is being cleaned for a DFC300, which is producing renewable power, heat, and hydrogen. Initial testing from the Quadrogen Gas Clean-up System has shown that all sulfur species and all halogen species at the outlet of the Quadrogen clean-up skid are below the minimum detection limit of 25 ppbv.
Los Angeles County Sanitation Districts: Siloxane Removal
Los Angeles County Sanitation Districts have long been involved with recovering landfill and digester gas for energy to power turbines and internal combustion engines. Their experience led them to identify performance issues associated with these gases.
One particular challenge is siloxanes. Cyclic organic silicon monomers (siloxanes) used in the manufacture of personal hygiene, health care and industrial silicone products are found in wastewater and solid wastes deposited in landfills. They volatilize into digester gas and landfill gas. When this gas is combusted to generate power (such as in gas turbines, boilers or internal combustion engines), siloxanes are converted to silicon dioxide (SiO2) precipitants, which in turn deposit in the exhaust stages of the equipment. Deposition on turbine blades, heat exchangers and emissions control equipment is common, resulting in loss of heat transfer efficiency, premature equipment failure and poisoning of catalytic converters.
The Districts first became interested in siloxanes in the mid ‘90s as a result of a requirement to retrofit the gas turbines at the Districts’ Joint Water Pollution Control Plant (JWPCP) with Selective Catalytic Reduction (SCR) to achieve a NOx limit of 9 ppm. Although the quantity of siloxanes in the gas was known, the SCR vendor was confident that the proposed zeolite catalyst would not be affected. The SCRs were installed and subsequently failed in a relative short period. The exact cause of failure is still being debated but siloxanes are suspected to be the major culprits.
To address this issue, the Sanitation Districts evaluated a variety of test methods and removal systems. These included filters with different media and condensation systems. The ultimate combination proved to be a condensation system with a coalescing filter.
At the low temperature of -9° F, almost 100 % siloxane removal was achieved with a coalescing filter of 1 micron. Without the coalescing filter, temperatures as low as -22° F would be required. The condensate at -22° F was tested for its concentration of silicon. It was found to contain 48,000 mg/liter (4.8%) silicon and 113,000 mg/liter (11.3%) carbon, indicative of siloxane and other hydrocarbon removal.
Pioneer’s Total Contaminant Removal (TCR) System provides extremely dry gas and removes siloxanes, sulfur, and halide compounds, and other difficult to remove contaminants; e.g. up to 98-99 % of Moisture, VOC, H2S and SO2, by chilling gas to sub-zero temperatures, down to -10ºF/-23ºC Pressure Dew Point (PDP); because most siloxanes condense at -9ºF.
In addition, the removal of moisture, a base for acid formation, minimizes acid formation.
To prevent freeze up, gas is cooled in steps. Most of the contaminants either condense, or dissolve in condensed fluids. If required, an adsorption system can be added for additional gas cleaning. Gas quality provided by a TCR, without Activated Carbon/Desiccant adsorber, is satisfactory for most applications. A TCR eliminates, or minimizes, the need of an Adsorber. By using the condensation system alone, a Pioneer TCR system can remove 90% of siloxanes. This is a significant advantage; because, disposal of adsorption media can be a serious problem; it can be classified as a hazardous material.
In applications where greater siloxane removal is needed, a TCR combined with the proper dessicant/adsorber can provide siloxane removal of approximately 99%.
To learn more, view the technical paper presented by the Los Angeles County Sanitation Districts and the Pioneer TCR Brochure.