Sunlight to Convert Carbon Dioxide into Transportation Fuels

Abstract

The proposed plant to convert sunlight and carbon dioxide to transportation fuels will utilize a Counter-Rotating Ring Receiver Reactor Recuperator (CR5) to convert carbon dioxide into carbon monoxide gas and oxygen gas. The CR5 is a solar chemical heat engine that provides an environment for the continuous reduction/oxidation of iron oxide, which allows for the reaction of carbon dioxide to carbon monoxide and oxygen. The plant will contain 150 CR5s each attached to its own parabolic mirror dish in order to collect sunlight. A carbon dioxide feed of approximately 25,070 kg/hr will be used to produce 9,520 kg/hr carbon monoxide. The devices will then feed a mixture of carbon dioxide and carbon monoxide gas to both a water gas shift reactor and a Fischer-Tropsch reactor. The Fischer- Tropsch reactor will use the carbon monoxide along with hydrogen gas produced from the water gas shift reactor to produce a range of hydrocarbon products following an Anderson- Schulz-Flory distribution centered around octane. The FT oil products (naphtha, gasoline, diesel, heavy ends) will be sold while the light-end products will be used to meet the utility requirements of the plant itself.\nThe plant will be located in the western part of Texas in the Mojave Desert in order to take advantage of the high solar flux in this region. Due to the necessity of sunlight to provide energy for the CR5 reaction, the production of carbon monoxide will only take place during daylight hours and 2 hours worth of carbon monoxide production along with an excess of 10% of this amount will be stored in floating roof storage tanks. The storage of some extra carbon monoxide will keep the startup and shutdown production of petrol product constant as the sun rises and sets. The water gas shift reactions and Fischer- Tropsch reactors will operate for as long as carbon monoxide is available and will shut down once the carbon monoxide is depleted.\nAssuming a discount rate of 13%, the project yields a -$5.5 billion NPV over a 30 year time period. Based on this negative net present value, the plant proves to be economically unattractive. This result is primarily driven by high operating costs due to the high stress put on expensive catalysts that require frequent replacement as well as daily startup/shutdown costs.\nThe largest negative economic factors in the plant projections are related to operating expenses. Specifically, the daily startup and shutdown costs associated with the CR5, WGS and FT reactors are significant. A related factor is the replacement cost of catalysts due to the high amounts of stress associated with daily shutdown, which requires 1 the catalysts to be replaced every 5 years. Storage tanks for continuous operation were considered, which would require 134 storage tanks total. This option is potentially more economically attractive; however, continuous operation was still discounted because the cost of maintenance, piping equipment costs, and other logistical challenges associated with housing the storage tanks. In addition, this option still produces a negative NPV after 30 years.\nFinally, the compressor operation requires significant electricity, factoring into the economic unattractiveness of the operation of this plant. These variables all lead to a negative net present value and negative cash on hand throughout thirty years of operation. Consequently, unless technological advancements can be made to change the fundamental operations of the sunlight to transportation fuel plant, the investment is not recommended.