PATENT
Patent number: 7964176
Issue date: Jun 21, 2011
Application number: 11/092,555
Inventors: Curtis L. Krause, Kevin H. Nguyen, Bhaskar Balasubramanian, Yunquan Liu, Jeroen Valensa, Michael J. Reinke, Mark G. Voss, Todd M. Bandhauer
Original Assignees: Chevron U.S.A. Inc., Modine Manufacturing Company
BACKGROUND OF THE INVENTION
1. Field of the Invention
2. Description of the Related Art
Hydrogen is being considered as an altemative fuel for transportation and power generation. However, hydrogen has a low volumetric density making the storage and transport of hydrogen both diflicult and costly. Thus, there is a need in the industry for eflicient, small scale, onsite hydrogen generation.
Hydrogen may be generated in a number of ways. The technology of choice for large, refinery scale hydrogen production is steam refonning of methane (natural gas) followed by a water gas shift reaction.
In steam reformation, methane and hydrogen are reacted to form a reformate that includes carbon monoxide and hydrogen. Then, in a subsequent water gas shift reaction, carbon monoxide and water can be reacted to form carbon dioxide and hydrogen.
This is a mature technology and is one of the more cost effective methods for producing hydrogen from natural gas for smaller-scale distributed hydrogen generation. However, when used to produce a transportation fuel, distributed hydrogen generation is not cost competitive with gasoline on a dollar per gallon basis. In order for distributed hydrogen generation via steam methane refonning to be practical and cost competitive, the hydrogen production efliciency must be improved.
The main contributor to the low efliciency of smaller-scale steam methane reforming is heat loss. Heat loss is greatly exacerbated when the process is scaled down from large refinery plant capacity hydrogen production (>100,000 kg/day) to production levels on the order of several hundreds of kg/day or less. The increased heat losses at small scale contribute directly to low production efficiency, higher operating costs, and ultimately a higher cost of hydrogen.
The production efficiency problem has been addressed to a certain extent through re-design of heat exchangers, modified catalyst formulations and improved heat management. For example, it is known in the art to embed cooling coils and other heat exchangers within reactor vessels (catalytic combustor, refonning reactor and water gas shift) for the purpose of directing heat flows out of the reactor to an external heat exchanger, reactor or temperature control system. This approach typically requires extensive piping, a separate heat exchange fluid, and active flow controls. It is also known to recover otherwise un-utilized heat by combusting or oxidizing a waste gas from a purification step or fuel cell in a catalytic combustor. However, such features also typically employ separate reactor vessels, extensive piping and controls. Moreover, the heat recovery and efliciencies of such systems are generally not maximized because of heat loss and added parasitic losses due to complex active control systems.
Additionally, the initial capital equipment cost to build a small scale steam methane reforming facility contributes to the process not being competitive. Further, these designs have typically not been able to be manufactured at low cost because they require elaborate balance of plant components for active control and monitoring of process parameters.
Thus, the improvements have not advanced the technology far enough to make it commercially feasible.
SUMMARY OF THE INVENTION
The present invention satisfies the objectives of providing a process and apparatus that improves the hydrogen production efliciency.
According to an aspect of the present invention, the process and apparatus utilize heat exchangers that thermally integrate the reaction steps such that heat generated by exothennic reactions, e.g., combustion and water gas shift, are arranged closely to the endothennic reaction, e.g., steam reformation, and heat sinks, e.g., cool methane, water and air, to minimize heat loss and maximize heat recovery. Effectively, this thermally integration eliminates excess piping throughout, reduces initial capital and operating costs, provides built-in passive temperature control, and improves hydrogen production efliciencies.
According to another aspect of the present invention, the process is thermally neutral, such that a supplemental fuel such as methane is no longer needed in order to achieve high reforming efficiency and conversion. This directly translates to lower operating costs.
According to another aspect of the present invention, the surface areas and flow configurations of the heat exchangers are designed such that they serve the dual purposes of heat recovery/pre-heating and passive temperature control of process streams. For example, a heat exchanger can preheat a steam and natural gas feed for the refonning reactor with heat derived from a heated reformate while yielding an optimum inlet reformate temperature for the water gas shift reactor. Also, a heat exchanger can cool the refonnate to a desired pressure swing adsorption unit operating temperature and utilize this heat to convert water to saturated steam and/or to preheat a combustion reactant such as air. This thennal pinching/passive temperature control technique not only simplifies and adds robustness to the process controls, but also eliminates control valves and various other moving parts throughout the apparatus as well as the need for external cooling. Thus, according to an aspect of the present invention, the only active control parameters of the process are setting and adjusting the air flow to the combustor and the natural gas and water flows to the reforming reactor. The uniqueness of this process flow design significantly drives down the capital cost of the system.
According to another aspect of the present invention, an annular design in a single vessel allows for operating the combustor and reforming reactor at two different pressure regimes without sacrificing heat loss.
In another aspect of the present invention, by directly coupling the heat generating combustion reaction with the endothermic steam refonning reaction, heat transfer is balanced between the two reactions, heat recovery is maximized, control of steam refonning temperature is simplified, and the apparatus has fewer parts and less connecting piping.
According to another aspect of the present invention, there are at least three heat transfers that are utilized in the process and apparatus. First, is a first heat transfer in order to preheat air and/or a combustion feed gas with heat derived from a shifted refonnate. A second heat transfer is directed to heating water, and optionally a methane-containing gas, with heat derived from an exhaust from a combustor and an unshifted reformate. A third heat transfer produces a cooled unshifted reformate by transferring heat to a refonning reactant.
Process for preparing hydrogen in a fuel processor assembly comprising: (a) preheating air with a shifted refonnate to form pre-heated air and cooled shifted reformate; (b) combusting the preheated air and the combustion feed gas in a catalytic combustor to form exhaust; (c) heating water with the exhaust of the catalytic combustor to form heated water; (d) heating a methane-containing gas and the heated water with an unshifted reformate to form steam, a heated methanecontaining gas and a cooled unshifted reformate; (e) reforming the steam and the heated methane-containing gas in a reforming reactor to form the unshifted reformate; (f) reacting the cooled unshifted reformate in the water gas shift reactor according to a water gas shift reaction to form the shifted reformate.
An apparatus for producing hydrogen comprising an annular arrangement comprising an annulus comprising a combustor, an intermediate amiulus comprising a reforming reactor and a water gas shift reactor disposed radially inward from the intermediate amiulus.
Free Full Text Source: http://www.google.com/patents/US7964176?dq=hydrogen+refinery
No comments:
Post a Comment