The worldwide demand for hydrogen has been increasing at rapid rates and its scope of industrial uses continues to expand. To meet such demand, hydrogen delivery systems have been developed which integrate multiple hydrogen production sources, typically large hydrogen plants, by connecting to a pipeline distribution system which transfers the hydrogen gas from points of production to points of use, typically after product compression to meet delivery pressure constraints. These pipeline and storage delivery systems are large, complex and designed to meet the varied requirements of multiple use points which include customers such as refineries, chemical plants, fertilizer plants, and other industrial users.
Automated control systems have been used to control the operation of hydrogen plants at both the individual plant level and the system level to address the various needs of the use points and maintain efficient plant operation. The variables addressed include demand swings; production requirements including feed and power costs; and operational requirements such as flow, pressure, emissions control, down time, and transportation constraints. Typically, individual hydrogen plants are optimized to meet variable demand by turning down the plants at low demand requirements to reduce production costs and turning them up at peak demands requirements. Such swings in production add excessive wear to the plants and can limit the extent of optimization that can be achieved. When multiple hydrogen plants are linked to an integrated gas delivery system that includes an underground hydrogen storage complex, the operational pressure of the pipeline can be controlled to minimize the impact on individual plants. It is also noted that real optimization can be achieved by looking at the entire system and understanding the relative shadow prices associated with each constraint imposed on the system.
Underground caverns or related storage sites have been used in the past for collecting inventories of gases, most commonly natural gas. For example, natural gas has been stored in various geological formations such as depleted reservoirs in oil and/or gas fields, aquifers, and salt cavern formations. More recently, hydrogen has been held in underground salt caverns and proposed for storage in these other geological formations.
High purity hydrogen (e.g. above 96% and preferably above 99%) storage within solution mined salt caverns presents several challenges. For example, storing large quantities (e.g., greater than 100 million standard cubic feet) of high purity gaseous hydrogen in underground caverns consisting of a minimum salt purity of 75% halite (NaCl) or greater without measurable losses is difficult based on the properties of hydrogen. Hydrogen is the smallest and lightest element within the periodic table of elements, having an atomic radius measuring 25 pm+/−5 pm.
Further, hydrogen is flammable, and therefore a very dangerous chemical if not handled properly. Salt caverns consist of salt that have various ranges of permeability (e.g., 0-23×10−6 Darcy) that if not controlled properly could easily allow gaseous hydrogen to permeate through the salt and escape to the surface of the formation. If the stored hydrogen within an underground salt formation was to escape and permeate through the salt formation to the surface, a dangerous situation could arise. Consequently, high purity hydrogen is typically considered one of the most difficult elements to contain within underground formations and there are currently very few hydrogen storage caverns in commercial use containing high purity hydrogen.
Hydrogen storage caverns have recently been integrated into pipeline distribution systems which include integration to hydrogen production sources. For example, see U.S. Pat. Nos. 7,078,011 B2, 8,690,476 B2 and 8,065,243 B2 which show or discuss hydrogen storage caverns integrated into pipeline systems. But the operation of the hydrogen production sources as disclosed therein were not integrated into the operation of the cavern. Secondly, the optimization approach did not address the extensive method of optimizing a contribution (or profit) margin in real-time subject to imposed system constraints. It has now been found that an integrated hydrogen system can be operated in a manner that optimizes the operation of each of the hydrogen sources, both individually and collectively, through the integrated use of the cavern. In addition, it has also been found that the operation of an underground high purity hydrogen storage cavern can be safeguarded against unexpected rises in pressure due to geologically induced creep closure, by relieving excess pressure formation by instantaneously withdrawing the stored hydrogen into a pipeline distribution system and decreasing the quantity of hydrogen being produced from the various hydrogen production sources co-located on the hydrogen pipeline system.
The present invention greatly increases the flexibility of the integrated supply operation and maximizes the profitability of the system while ensuring the efficient operation of the plants in a way not available without the use of the one or more underground hydrogen storage caverns. This coordinated operation of the entire integrated hydrogen supply system, including multiple hydrogen sources and one or more caverns, permits the operation of the individual hydrogen plants to be optimized to minimize the variable costs while continuing to meet the variable demand and pressure requirements of the multiple use points. Lastly, the coordinated operation of the integrated hydrogen storage and production sources in connection with the pipeline distribution system permits the enhanced operation of an underground hydrogen storage cavern and enables further optimization of hedging various hydrogen related feed stocks.