(29d) Autothermal Reforming of Landfill Gases

According to the EPA Landfill Methane Outreach Program landfills generate about 26% of the U.S. methane emissions from landfill gas (LFG), which is typically 50% CH₄ and 50% CO₂. Since land filling will continue to be used in the foreseeable future, it makes sense to design landfills that capture the maximum possible amount of methane for use in generating power. However, because of the low heating value of LFG, most engines need to be modified considerably and once modified; they require a consistent composition of the fuel. LFG variation leads to higher pollutant emissions, such as NO_x, CO and unburned hydrocarbons (UHC) and emissions waiver are often required before LFG thermal energy projects are permitted. One solution to this issue is to reform a portion of the LFG to produce synthesis gas which can be mixed with the remaining un-processed LFG to yield a more reactive mixture to enhance the combustion performance.

To understand the operating regimes of such a reforming reactor, a series of tests were done on a Rh-containing monolith reactor. The tests focused on reacting CO₂ and CH₄ with air to obtain an autothermal condition to generate synthesis gas (i.e. dry reforming). Specific issues were investigated such as carbon formation (coke) and the effect of air to landfill gas ratio. In addition performance variations for a range of CH₄ to CO₂ ratios and operating temperatures were investigated. Effluent species concentrations were measured versus varying reactor temperatures from 550 – 590°C and space velocities from 7,600 – 16,000 hr^-1. Reactant gas mixtures consisted of 0.08 atm CH₄, CO_2, partial pressures from 0.08 – 0.25 atm, and a balance of argon totaling 1 atm total pressure.