Carbonate Direct Fuel Cell Operation on Dual Fuel

ABSTRACT

The ability to operate highly-efficient, pollution-free, distributed generation power plants on either natural gas or HD-5 grade propane is of interest to the U.S. Army and the U.S Department of Homeland Security as secure power source for critical power operations. The ability to operate continuously on HD-5 propane also provides a valuable proposition to islands, remote sites, national parks, data centers, military bases, hotels, and hospitals. HD-5 propane, as opposed to other grades of propane, was selected as the back-up fuel of choice because of its availability (even in remote areas), cost, and ease of processing in the fuel cell power plant. Although natural gas distribution through utility pipelines is convenient, it is vulnerable to natural disaster, threats of terrorism, and simple repair outages. Propane, however, is routinely transported and stored as a liquid at ambient temperatures and offers a convenient and secure option for fuel cell operations. An adequate quantity of propane can be stored on site to sustain operations for several days in a variety of weather climates.

In response to the interest for a fuel flexible power plant, Concurrent Technologies Corporation (CTC), under contract to the U.S. Army Engineer Research and Development Center's Construction Engineering Research Laboratory (ERDC-CERL), is working with Fuel Cell Energy (FCE) to test an internally reforming 250 kW carbonate fuel cell. Previous to the demonstration at CTC, FCE operated a 250 kW carbonate direct fuel cell for 1500 hours, which generated 300,000 kilowatt-hours (kWh) net AC electricity using HD-5 propane as fuel. Among the challenges addressed, lessons learned by FCE during initial operation on HD-5 propane included: 1) avoiding carbon deposition during pre-reforming of propane into a methane rich gas, 2) metering and controlling propane flow to account for variations in fuel composition, 3) removing sulfur from the propane, and 4) increasing the steam required for operation on propane. Peripheral issues that required additional investigation included identifying the number and volume of propane tanks and a vaporization system to deliver the required rate and quantity of fuel.