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USING NONUPGRADED BIOGAS AS THE FUEL FOR SOFC SYSTEMS

IP.com Disclosure Number: IPCOM000249473D
Publication Date: 2017-Feb-28
Document File: 5 page(s) / 23K

Publishing Venue

The IP.com Prior Art Database

Related People

David Weingaertner: INVENTOR [+3]

Related Documents

US8685583: PATENT [+2]

Abstract

Provide desulfurized biogas as the fuel for solid oxide fuel cell (SOFC) systems instead of natural gas or upgraded biogas.

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USING NONUPGRADED BIOGAS AS THE FUEL FOR SOFC SYSTEMS

Brief Abstract

Provide desulfurized biogas as the fuel for solid oxide fuel cell (SOFC) systems instead of natural gas or upgraded biogas.

Background

Raw biogas composition is typically:

 CH4 55-65 % dry basis  CO2 35-45 % dry basis  H2S up to 1.5 % dry basis  H2O up to 7 % (saturated at the digester outlet temperature and pressure)

Desulfurized, upgraded biogas has been proposed in previous inventions as the fuel for solid oxide fuel cell (SOFC) systems. Desulfurization can be done with the following methods. Some of the methods can only partially desulfurize the gas.

 Water/caustic absorption  Iron chloride solution addition to the digester  Iron oxide adsorption  Zinc oxide adsorption  Activated carbon adsorption  Biofilter  Other specialized solid adsorbents

Upgrading means rejecting the CO2 in order to increase the methane concentration of the upgraded biogas, typically to natural gas like concentrations – greater than 96 % CH4. Upgrading can be done by any of the following technologies:

 High pressure water scrubbing  Amine scrubbing  Membrane permeation  Pressure swing adsorption  Organic physical solvent scrubbing  Cryogenic separation  Biosling Rotating Water Coil (developing technology)  Metener Ultra High Pressure Water Flash (developing technology)

All of these upgrading technologies suffer all of the following disadvantages:

 Capital investment required  Parasitic power demand to run the technology (gas compression)  Yield loss – some methane is lost with the rejected CO2  Space required for the equipment

Novel Features of the Innovation and Results or Benefits of Its Application

Desulfurization in multiple steps using a mix of site and system level desulfurization steps

SOFC’s still require very low levels (ppb) of sulfur for stable operation. The economic optimum for desulfurization may involve multiple desulfurization steps. For example with purely hypothetical numbers:

 Iron chloride solution addition to the digester – to reduce the digester outlet to 500 ppm H2S

 Site level biofilter – to reduce the H2S concentration to 50 ppm  Site level zinc oxide adsorption – to reduce the H2S concentration to 2 ppm  System level specialized adsorbents – to reduce the H2S concentration to ppb levels, and

to serve as the final guard beds for H2S slippage from the previous steps.

The actual optimum cannot be evaluated independent of site specific design requirements:

 Digester feed, type, typical operating temperature  Site Elevation (impact on atmospheric pressure and thus water concentration)  Biogas production rate  Local raw material availability and costs  Local liquid effluent, digester sludge disposition, adsorbent disposition – regulations and

cost of disposal

No upgrading

It has been previously proposed that it may be advantageous to run SOFC systems on desulfurized biogas that has not been upgraded. The disadvantages of running without an upgrade...