Control algorithm for autothermal reformer (U.S. Navy)

CATEGORY: HYDROGEN
PATENT
Control algorithm for autothermal reformer (U.S. Navy)
United States Patent 8430938
Inventors:
Miller, Steven P. (Gibbstown, NJ, US)
Application Number:
11/894637
Publication Date:
04/30/2013
Assignee:
The United States of America as represented by the Secretary of the Navy (Washington, DC, US)
Abstract:
According to typical inventive practice, an algorithm controls a reformer in order to produce a pure hydrogen stream for a hydrogen-using device. The inventive algorithmic feedback control maintains the permeate hydrogen stream at a permeate pressure setpoint. Pressure measurements are performed of the permeate hydrogen stream. Control data (e.g., including a “lookup” table) establishes at least three output levels (scaled from zero output to maximum output) of the permeate hydrogen stream and, for each output level, five variable setpoints (air flow rate, hydrocarbon flow rate, and steam flow rate preceding the reformer reaction; steam flow rate preceding the water-gas shift reaction; shaft rotational speed in the energy recovery device). The pressure signals and the control data are processed to determine the optimal output level and the associated variable setpoints. Control signals are sent to adjust the variables to the determined variable setpoints.
BACKGROUND OF THE INVENTION
The present invention relates to hydrogen production, more particularly to methods and apparatuses for producing hydrogen from hydrogenous-carbonaceous substances such as natural gas (e.g., methane, ethane, or propane), organic waste, gasoline, diesel fuel, oil, coal, methanol, and ethanol.
Hydrogen, the most abundant element in the universe, usually occurs in nature as an element included in a compound (e.g., hydrocarbonaceous or hydrous) that also includes one or more non-hydrogen elements. Pure hydrogen is non-toxic, odorless, tasteless, colorless, and easily flammable, and burns in daylight with no visible flame.
In order to be a standalone element (H2) that is useful as a fuel, hydrogen must be broken from its bonds with the accompanying element(s). Known methodologies for breaking these bonds include reformation, biomass gasification, coal gasification, and electrolysis of water. Generally speaking, reforming involves the splitting of hydrogen and carbon so as to yield a mixture (known as a “synthesis gas,” or “syn-gas”) that contains hydrogen (H2) and carbon monoxide (CO). The resultant carbon monoxide (CO) can then be caused to react with steam (gaseous H2O) so as to turn the carbon monoxide (CO) into carbon dioxide (CO2) and release more hydrogen (H2). Electrolysis involves the use of electricity to split water (liquid H2O) into hydrogen (H2) and oxygen (O2). Contemplated but as yet undeveloped methodologies for producing hydrogen include photo-electricity (involving the splitting of water via sunlight), photobiology (involving the splitting of water via sunlight, using organisms such as algae or bacteria), and thermal dissociation (involving the application of extreme heat, via, e.g., solar power or nuclear power, to split hydrogenous compounds without generating carbon dioxide).
Fossil fuels are beset with environmental and economic concerns. Hydrogen fuel represents a viable alternative to fossil fuels, albeit hydrogen is not a perfect fuel. Safety issues are concomitant production, storage and use of hydrogen fuel, and efficiency/cost-effectiveness deficits remain in current hydrogen production implementations. An advantage of hydrogen as a fuel is its capability of being produced from a variety of feed-stocks, including fossil fuels, water, and organic matter. Efforts continue in many countries to improve hydrogen production in terms of safety, efficiency, and cost-effectiveness.
SUMMARY OF THE INVENTION
In view of the foregoing, it is an object of the present invention to provide an improved methodology for producing pure hydrogen from a hydrocarbon (hydrogenous-carbonaceous substance).
The present invention's control algorithm, as typically embodied, controls the process inputs of an autothermal reformer system (such as a diesel fuel autothermal reformer system) in order to provide pure hydrogen. For instance, practice of the present invention can serve to deliver a constant pressure feed stream of pure hydrogen to a hydrogen-using device (such as a proton exchange membrane fuel cell). According to typical inventive practice, the inventive algorithm controls a hydrogen compressor, an autothermal reformer compressor, an autothermal reformer fuel pump, an autothermal reformer water pump, a water-gas shift reactor water pump, and a gas turbine generator. Control of the hydrogen compressor is provided by a PID controller that maintains a constant outlet pressure by varying input power to the compressor motor. A core process controller monitors the hydrogen compressor inlet pressure and varies the other outputs to different steady state operating levels in order to maximize system efficiency while allowing the system to respond to varying load levels on the hydrogen-using device (e.g., fuel cell).
Practice of the inventive control algorithm can render a thermal reformer system more responsive to rapid changes in system load, and more capable of operating at maximum efficiency during steady state conditions. Moreover, the inventive control algorithm can prevent the thermal reformer system from experiencing stall, premature shutdown, and dangerous conditions such as overheating, over-pressurization, and over-speeding.
In accordance with many embodiments of the present invention, the present invention's computer program product is used in association with a reformer system in which: an autothermal reaction is performed to combine oxygen-containing gas (e.g., air), hydrocarbon (e.g., fuel), and steam and to produce a mixture containing hydrogen and carbon monoxide; a water-gas shift reaction is performed to combine steam with the mixture produced by the autothermal reaction and to produce a mixture containing hydrogen and carbon dioxide; membrane separation is performed of hydrogen from non-hydrogen ingredients of the mixture produced by the water-gas shift reaction so as to produce a permeate hydrogen stream; and, energy is produced using shaft rotation. The inventive computer program product includes a computer-useable medium having computer program logic recorded thereon for enabling the computer to maintain constancy of the permeate hydrogen stream at a permeate pressure setpoint. The computer program logic includes: means for enabling the computer to receive signals indicative of the pressure of the permeate hydrogen stream; means for enabling the computer to access control data; means for enabling the computer to process the received signals and the control data so as to determine the optimal permeate hydrogen stream output level, the optimal output level resulting in restoring the pressure of said permeate hydrogen stream to said permeate pressure setpoint; means for enabling the computer to transmit control signals to adjust the variables in accordance with the group of subordinate setpoints that corresponds to the optimal output level. The control data includes plural (at least three) output levels, on a scale from zero output to maximum output, of the permeate hydrogen stream. The control data further includes plural subordinate setpoints. Each output level has corresponding thereto a group of (e.g., five) subordinate setpoints. Each subordinate setpoint represents one of plural (e.g., five) variables, including: the mass flow rate of the oxygen-containing gas prior to the autothermal reaction; the mass flow rate of the hydrocarbon prior to the autothermal reaction; the mass flow rate of the steam prior to the autothermal reaction; the mass flow rate of the steam prior to the water-gas shift reaction; and, the speed of the shaft rotation. As the present invention is frequently practiced, cooling and compressing of the permeate hydrogen stream is performed in the reformer system so as to produce a delivery hydrogen stream. The computer program logic is further for enabling the computer to maintain constancy of the delivery hydrogen stream at a delivery pressure setpoint. The control data further includes the delivery pressure setpoint. The computer program logic further includes: means for enabling the computer to receive signals indicative of the pressure of the delivery hydrogen stream; and, means for enabling said computer to transmit control signals to adjust the pressure of the delivery hydrogen stream in accordance with the delivery pressure setpoint.
Various aspects of the present invention are disclosed in the following paper, incorporated herein by reference: Steven P. Miller, John M. Heinzel, John H. Kuseian, Donald J. Hoffman and Edward M. House, “A Dynamic Model of a Shipboard PEM Fuel Cell Reformer System with an Integrated Gas Turbine,” Proceedings of GT 2006, ASME Turbo Expo 2006: Power for Land, Sea, and Air, The 51st Annual Technical Congress & Exposition for the Worldwide Gas Turbine Community, May 8-11, 2006, Barcelona, Spain, American Society of Mechanical Engineers (ASME), GT2006-90739 (8 pages).
Other objects, advantages and features of the present invention will become apparent from the following detailed description of the present invention when considered in conjunction with the accompanying drawings.
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