Chemical Engineering

Statement of the Problem: Th e internal combustion (IC) engine exhaust contains harmful pollutants such as NOx, CO, and VOCs. These air pollutants need to be removed to comply with air quality control regulations. Th is project used pre-and post-combustion NOx control to reduce air pollutants in the exhaust from biogas powered IC engine. Th e pre-combustion NOx control system has a microwave hydrogen sulfi de (H₂S) removal unit followed by a microwave steam reformer. Approximately 10% of the biogas used to fuel the engine is process to generate hydrogen (H₂). Th e H₂ is injected back into the fuel stream prior to combustion to create H2 enriched fuel gas. Hydrogen Assisted Lean Operation (HALO) is used to ignite ultra-lean air-fuel mixtures. It reduces the peak flame temperatures and signifi cantly decreases NO_x emissions. Pre-combustion NO_x control using HALO, followed by post-combustion NO_x removal with carbon adsorption is the best approach to ensure that the CARB 2007 NO_x emission standards will be consistently met. HALO, may not meet emission standards alone, but will reduce the NOx concentration in the engine exhaust signifi cantly to minimize the amount of NO_x that must be removed by adsorption. Th e post-combustion NOx removal system consists of an exhaust cooler and two carbon adsorbers in series. Th ese adsorbers are fi lled with granular activated carbon (GAC) to remove NOx and VOCs from the exhaust. The beds are operated in a standard Lead-Lag cycle. When the average NOx concentration in the exhaust leaving the Lag bed reaches 5 ppm, the saturated GAC is replaced with the newly regenerated GAC. Th en that adsorber is switched to the Lag bed. Th e saturated GAC is transported to the microwave facility for processing. We expect the adsorbent will be replaced and regenerated once every 2-3 months. An additional benefi t is that the GAC also removes sulfur dioxide (SO2) and VOCs from exhaust. Under the grant awarded by California Energy Commission, CHA Corp built and fi eld tested this pre-and post-combustion NOx control system at Clean World’s Bio Digester Facility at SATS in Sacramento. A six-month long field-testing was successfully completed in January 2017. Throughout the field-testing period, the average NO_x emission did not exceed 5 ppm to confi rm that pre-and post-combustion NO_x control would meet not only the Rule 1110.2 but also CARB 2007 NO_x control standards. Th e result from this fi eld demonstration will be presented.