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Project Description for RNG Facility 7 www.scsengineers.com
Appendix A
BCCB Process Flow Diagram and Description
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RAWFEEDFROMLANDFILLBLOWERSFEEDCOMPRESSORPAIRA/BCONDENSATEH2SPOLISHERIMPURITYPRE-TREATMENTCONDENSATECHILERHXNCHILLERAS BUILTARCHAEA ENERGY LLC.AS FIELD MODIFIED. .DATEDRAWING STATUSPRELIMINARY0.08-4-21.MJM.BYDTBD... .. .MEMBRANETREATMENTDEOXONRU&COMPRESSORSALESPOINTOFF-SPEC GASTO FLARETOXCO2 & IMPURITYREJECTTo DRYER & TOXPA2022-063
COYOTE CANYON PROCESS DESCRIPTION
The raw landfill gas is received downstream of the existing landfill blowers. The gas is
compressed in two stages with high efficiency machines to 200 PSIG. The Feed Compressors
will be protected by an inlet moisture separator. The Feed Compressors will be equipped with
variable frequency drives (VFDs) (to be confirmed), air cooling for discharge LFG and
lubricating oil, and moisture and oil removal.
The inter stage compressed LFG is treated for H2S removal by non-regenerable scavenger media
and then for moisture removal prior to entering the second stage of compression.
At the outlet of the second stage compression the range of VOCs and siloxanes are removed by
chilling, regenerable adsorption beds (TSA), and non-regenerable adsorption beds (VOC
polishing). The temperature of the LFG is reduced with a chilled water/glycol-to-LFG heat
exchanger. The heat exchanger will be followed by a moisture separator where the bulk of the
water from the LFG is removed. The adsorbed contaminants are purged from the TSA beds with
the reject stream from the membrane unit and sent to the thermal oxidizer for destruction. Prior
to regeneration the TSA vessel depressurization biogas is sent to the flare for destruction.
Following VOC removal pre-treatment the feed stream is mixed with the recycled permeate from
the second stage of a two stage membrane CO2 separation unit. At the outlet of the first stage
oxygen in the feed is removed as needed using a heated catalyst De-Oxo unit ensuring that
oxygen concentration levels remain well below the threshold for potential flammable mixtures in
the second stage permeate. The first-stage membrane low pressure permeate stream, rich in CO2
is used to regenerate the TSA, the retentate is a high-pressure product gas that contains less than
1% CO2. The second-stage membrane provides a low pressure permeate stream rich in methane.
This permeate gas is recycled to the front of the first-stage membranes, as mentioned previously,
via recycle compressors boosting its pressure to match inlet conditions.
The product gas then enters the Nitrogen Removal Unit (NRU) where nitrogen in the feed gas is
rejected using a high methane recovery pressure swing adsorption system (PSA). The NRU unit
delivers pipeline quality product gas and a byproduct stream enriched in nitrogen that is
combined with the reject gas from the membrane unit’s first stage permeate and sent to the
thermal oxidizer. The PSA system will consist of five banks of four adsorber vessels filled with
selective media, a product gas buffer tank, and three pairs of recycle and vacuum compressors.
Methane is adsorbed into the pores of the media of the online adsorber vessel bank while
operated under pressure. The media is regenerated by taking the vessel bank offline,
depressurizing the vessel bank, and then pulling a deep vacuum on the media to evacuate the
methane (product gas) trapped in the media pores. During the sequence of this operation, some
gas is recycled back to the inlet of the PSA process using a recycle compressor to improve
overall methane recovery. The waste gas which is produced is a mixture of nitrogen and methane
(14 percent dependent on the inlet N2). The waste gas is destroyed in the Thermal Recuperative
Oxidizer (TRO).
The TRO will destroy a minimum of 99 percent of the VOCs in the waste gas. The methane in
the waste gas itself will provide most of the energy required by the TRO; however, in order to
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achieve complete and continuous destruction of the VOCs, a small quantity of Natural Gas must
be provided to the TRO as a supplemental fuel.
After the PSA step, a gas chromatograph (GC) will be employed to monitor product gas methane
and nitrogen content. The membrane skid has an on-board carbon dioxide analyzer. Oxygen
concentration in the LFG is monitored prior to entering the second stage of compression. O2
concentration exceeding 3.0% is considered off spec. If off-specification LFG or product gas is
detected by any of these devices, Plant operation will be suspended, and/or product gas will be
diverted to the offspec flare, prior to entering the pipeline, until such time that the product gas
can again be made compliant. Flaring from the RNG plant will be limited by the Air Permit at
800 annual hours and thus the duration of off-spec concentration excursions will be limited by
the annual hours of flare use to date. As determined by the control system the plant may go into a
full shutdown until the gas condition meets spec. Prior to shutdown the plant control system will
notify the County flaring facility to prepare to receive LFG allowing it time to prepare the flares
for operation. Following a full plant shutdown the LFG fixed gas concentration taken at the inlet
to the landfill flaring facility will be monitored to determine when conditions are back within
spec.
The pipeline quality gas from the nitrogen rejection unit is delivered to the pipeline interconnect
at the requested delivery pressure by the utility.
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