Microwave induced destruction of impurities from biogas and nitrogen oxides from engine exhaust

Abstract

Granulated Activated Carbon (GAC) is used to remove hydrogen sulfide (H2S) from the biogas produced in an anaerobic digester. The cleaned biogas is then combusted in a reciprocating engine. The exhaust of the engine is passed through a heat exchanger and then through GAC in an adsorber to adsorb nitrogen oxides (NOx) and any sulfur oxides (SOx). The GACs containing NOx, H2S, and SOx, are transported to a microwave reactor, mixed, and exposed to microwave energy. The H2S and NOx are desorbed from the GAC and chemically combined to produce nitrogen, carbon dioxide, sulfur and water. Unreacted nitrogen oxides or hydrogen sulfide are transported to a second reactor containing carbon media to be reacted by a further microwave process. Sulfur is removed with a filter as a solid and the remaining inert components are vented to the atmosphere. The GAC is regenerated and reused to remove additional H2S and NOx.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application is a division of U.S. patent application Ser. No. 12 / 013,870 filed on Jan. 14, 2008, now U.S. Pat. No. ______, incorporated herein by reference in its entirety, which claims priority from U.S. provisional application Ser. No. 60 / 884,985 filed on Jan. 15, 2007, incorporated herein by reference in its entirety.NOTICE OF MATERIAL SUBJECT TO COPYRIGHT PROTECTION[0002]A portion of the material in this patent document is subject to copyright protection under the copyright laws of the United States and of other countries. The owner of the copyright rights has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the United States Patent and Trademark Office publicly available file or records, but otherwise reserves all copyright rights whatsoever. The copyright owner does not hereby waive any of its rights to have this patent document maintained in secrecy, includi...

AI Technical Summary

Benefits of technology

This method effectively meets or exceeds CARB NOx standards, reduces waste, and lowers operational costs by regenerating and reusing GAC, thereby extending its lifespan and improving the efficiency of biogas utilization in power generation systems.

Problems solved by technology

However, contaminants in the biogas limit the ability to fully develop these resources for electric generation such as fuel cells and turbines.

Hydrogen sulfide (H2S) produced in the biogas causes significant equipment operation and maintenance issues and restricts power equipment options almost exclusively to reciprocating engines.

SNCR uses urea or ammonia to remove NOx but has not been used successfully on IC engines.

Additional fuel and chemicals are needed and the requirement to heat the exhaust complicates installation of heat recovery equipment on the engine exhaust.

The cost to install and operate these post combustion technologies on small to medium reciprocating engines is significant.

Equipment cost coupled with the uncertainty of performance running on biogas makes it difficult to recommend funding for projects without manufacturer assurance of meeting the proposed CARB standards for NOx.

Both the units with SCR report problems with the catalyst and H2S removal system.

Sulfur plugs filters, causes deposits on valves and cylinders and contaminates lubricating oil.

Some of these media have limited regeneration capacity or can be deposited in a landfill.

However, once NO2 is adsorbed in the GAC, it is no longer available in the equilibrium reaction with NO.

At this point, the GAC is no longer effective and must be replaced.

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