Jaimee K. Dahl

Rapid solar-thermal dissociation of natural gas in an aerosol flow reactor

A solar-thermal aerosol flow reactor process is being developed to dissociate natural gas (NG) to hy drogen (H2) and carbon black at high rates. Concentrated sunlight approaching 10 kW heats a 9.4 cm long×2.4 cm diameter graphite reaction tube to temperatures ~2000 K using a 74% theoretically efficient secondary concentrator. Pure methane feed has been dissociated to 70% for residence times less than 0.1 s. The resulting carbon black is 20–40 nm in size, amorphous, and pure. A 5 million (M) kg/yr carbon black/1.67 M kg/yr H2 plant is considered for process scale-up. The total permanent investment (TPI) of this plant is

Intrinsic kinetics for rapid decomposition of methane in an aerosol flow reactor

12.7 M. A 15% IRR after tax is achieved when the carbon black is sold for

Rapid Solar-thermal Decarbonization of Methane in a Fluid-wall Aerosol Flow Reactor -- Fundamentals and Application

0.66/kg and the H2 for

Sensitivity analysis of the rapid decomposition of methane in an aerosol flow reactor

13.80/GJ. This plant could supply 0.06% of the world carbon black market. For this scenario, the solar-thermal process avoids 277 MJ fossil fuel and 13.9 kg-equivalent CO2/kg H2 produced as compared to conventional steam-methane reforming and furnace black processing.

Two-Dimensional Axi-Symmetric Model of a Solar-Thermal Fluid-Wall Aerosol Flow Reactor

Abstract A one-dimensional nonisothermal model is developed for the high-temperature rapid dissociation of methane in a fluid-wall graphite aerosol flow reactor. Intrinsic reaction kinetics are identified through simulation of the model and comparison to experimental results. The dissociation rate can be described by d X d t =6×10 11 exp −25000 T (1−X) 4.4 s −1 over the temperature range 1533 K and residence time range 0.9 s . This rate expression is useful for describing high-temperature short residence time processes for producing hydrogen and carbon black by methane decomposition (CH4→C+2H2).

Solar-thermal dissociation of methane in a fluid-wall aerosol flow reactor

A graphite fluid-wall aerosol flow reactor heated with concentrated sunlight has been developed over the past five years for the solar-thermal decarbonization of methane. The fluid-wall is provided by an inert or compatible gas that prevents contact of reactants and products of reaction with a graphite reaction tube. The reactor provides for a low thermal mass that is compatible with intermittent sunlight and the graphite construction allows rapid heating/cooling rates and ultra-high temperatures. The decarbonization of methane has been demonstrated at over 90% for residence times on the order of 10 milliseconds at a reactor wall temperature near 2000 K. The carbon black resulting from the dissociation of methane is nanosized, amorphous, and ash-free and can be used for industrial rubber production. The hydrogen can be supplied to a pipeline and used for chemical processing or to supply fuel cell vehicles.

Dry Reforming of Methane Using a Solar-Thermal Aerosol Flow Reactor

A one-dimensional, nonisothermal model is developed to describe the thermal dissociation of methane to hydrogen and carbon black occurring in a fluid-wall aerosol flow reactor. The model expressions are scaled and nondimensionalized to determine the minimum parametric representation of the system. The sensitivity of this thermal dissociation to three parameters (flow rate of carbon particles fed to initiate the reaction, carbon particle radius, and reactor wall temperature) is studied. The results of the study indicate that in order to achieve nearly complete conversion, high reactor wall temperatures must be maintained. In addition, micron-sized carbon black particles must be fed into the reactor to enhance the heat transfer to the gas phase. The actual flow rate of particles fed is not critical, as long as some flow rate of fine particles is maintained.

Solar-thermal fluid-wall reaction processing

A solar-thermal fluid-wall reactor consisting of three concentric vertical tubes is constructed to dissociate methane to hydrogen and carbon black using concentrated solar power. Several aspects of the design are modeled for scaling the system up: the heat transfer and its effect on the integrity of the materials, and the fluid flow of all gas streams within the reactor. It is determined that the inlet gas temperatures, mass flow rates, and permeability of the porous wall affect the gas flow profile through the porous tube wall. By increasing the inlet gas temperature and/or the tube permeability in the hot zone section of the reactor, a more uniform flow profile can be obtained along the length of the tube.