Hydrogen Recycling and On-site Generation
Higher transportation fuel costs, increasing electricity costs to operate hydrogen liquefiers and fewer liquid hydrogen producers with fewer liquid hydrogen plants operating in the U.S., combined with an increase in demand, have led to higher prices for hydrogen.
After the disruption caused by Hurricane Katrina to hydrogen production plants on the Gulf Coast, many users encountered a shortage of critical hydrogen and looked for alternatives to their current hydrogen supply. H2Gen, an Alexandria, Va.-based company, offers options for on-site hydrogen generation and, most interestingly, hydrogen recovery.
Hydrogen is a critical raw material that until recently was supplied almost exclusively through the major gas companies for users with consumption volumes that did not warrant a big, custom-built hydrogen-generation plant. This is particularly true for heat-treating applications where consumption levels are relatively low when compared to big users.
H2Gen has innovated and adapted established processes used in large-scale hydrogen-generation plants, steam-methane reforming (SMR) and pressure-swing adsorption (PSA) to be used in small-scale, complete packaged units that are readily transportable and easy to install.
Hydrogen Recovery - Recycling the H2 Instead of Venting or BurningThe most attractive product in the H2Gen line-up is a hydrogen recovery system that was developed for metallurgical applications. Instead of venting or burning hydrogen-containing process atmospheres, the Metallurgical Atmosphere Recycle System (MARSTM) recovers up to 88% of the hydrogen discharged from metallurgical atmospheres. This is particularly attractive for atmospheres with a closed process loop – with no contamination through ambient air – such as bell annealing or powder-metallurgy operations.
The core technology of the MARSTM system is a new method of removing condensable hydrocarbons and other impurities from the process atmosphere. These impurities consist of thermally degraded rolling oil in the case of bell-annealing applications or thermally degraded acrylic, alcohol and parrafin binders for powder metallurgy.
H2Gen uses a chemical-engineering-based approach to solve the oil separation problem. Once these heavy impurities are removed, the process atmosphere is sent for purification through a traditional PSA module. The adsorbent layers in the PSA module will be optimized to achieve a high recovery rate for a particular application.
Innovation in PSA Technology and DesignGas separation by PSA is a mature technology that is widely used in the chemical industry for air dehumidification, nitrogen/oxygen enrichment from air and hydrogen purification.
Adsorption is a surface phenomenon whereby selected molecules are retained on a porous material, referred to as an adsorbent, while the desired molecules are not. This results in a purified stream of the desired molecules leaving a PSA vessel packed with adsorbent while the undesired molecules are retained on the adsorbent.
Once the undesired molecules adsorb to almost all of the available surface area in the active PSA vessel, then valves are automatically switched to move the input-gas stream and output pure-gas stream to another clean PSA vessel. Meanwhile, the pressure of the contaminated PSA vessel is reduced, which causes the impurities to come back out of the porous adsorbent, regenerating the PSA vessel and allowing the adsorption process to continue in a cyclic manner.
In essence, PSA can be thought of as a “regenerative filter” with pressure as the driving force for the adsorption and desorption of unwanted molecules from the desired molecules. Tailoring the adsorbent packed within a PSA vessel, in addition to the sequence of pressure steps used for adsorption and regeneration, allows high-yield separations of the desired molecules to be achieved.
The breakthrough design of the H2Gen PSA system was formulated using Design For Manufacture and Assembly (DFMA) techniques – an integral step in the development of H2Gen’s product line.
H2Gen’s PSA module design is mechanically unique, and it employs:
- No welds in manufacture of the vessels subject to cyclic stresses
- No bending moments in the PSA vessels
- Extensive use of aluminum structural components not subject to hydrogen embrittlement
- Complete isolation of all bolting from the hydrogen process atmosphere
- Substantially smaller vessels and far lower inventory of flammable gases than traditional PSA plants
From Small to Large Gas Flows - Modular DesignCurrently, H2Gen manufactures 7-vessel and 8-vessel PSA modules that can perform three independent pressure equalization stages to maximize product recovery. This design allows the recovery of hydrogen to exceed 80% with 1 ppmv or less of total impurities in the product.
H2Gen can design high-yield PSA systems that can be tailored to each customer’s individual product requirements. The two base-module sizes can process almost 3,500 and 8,000 scfh of raw gas to produce 2,200 scfh and 6,000 scfh respectively of purified product. By grouping these PSA modules into banks, process capacity can increase into the many thousands of scfh.
For high-throughput applications, H2Gen offers a gas-filtration product line for processing 250,000 scfh of gas. Common applications convert syn-gas variants to pure hydrogen, but systems can be designed to separate and purify all types of gas streams.
Multiple skids can be used together to economically process nearly any flow stream. The auxiliary tanks required by such systems are far smaller than comparable site-erected plants.
The unique design of the manifold and adsorbent hold-down mechanism employed within the PSA vessel allows short cycle times to be used. This significantly reduces the size and cost of the system required to produce one unit amount of product gas in comparison to the traditional PSA suppliers.
First Field Application for Hydrogen RecoverySaving and recycling hydrogen with the H2Gen MARSTM system allows significant cost savings and increased usage of hydrogen atmospheres, letting users move up-market to handle more specialty alloys. With a purity of up to 99.999%, the cost for the recovered hydrogen can be as low as 10% compared to the cost of conventionally supplied hydrogen. The system is capable of handling flow rates in process atmosphere of close to 100,000 scfh.
Depending on the desired purity, over 80% of the hydrogen in the process atmosphere can be recovered using H2Gen’s system. For a typical purity requirement of 99.9% used in many metallurgical applications, the recovery rate is above 75%. Even at a higher purity level, the recovery rate is still above 65%.
In March 2007, H2Gen commissioned the first MARSTM installation at a bell-annealing facility in the U.S. The recovery rate was well above the expected 80%, and it is generating extremely low-cost hydrogen. The cost of the recovered hydrogen is below $0.10/ccf, significantly lowering the customer’s hydrogen cost, thus having a direct impact on the bottom line.
Figure 3 shows the typical recovery rate for a hydrogen-rich process atmosphere containing 96% H2, 2% CH4, 1% N2 and the remainder being CO and CO2 – a typical composition for annealing applications. To increase recovery rates of the MARSTM, the feedgas is pressurized above 160 psig.
Low-Cost On-site Hydrogen GenerationOther products marketed by H2Gen are compact steam-methane reformers (SMR) producing hydrogen from natural gas and water.
Several technical inventions have been applied in the design of the SMR units: a single reactor, a sulfur-tolerant catalyst, a highly efficient heat-exchange system and the PSA described above. The result is a very compact unit with a 7-foot x 9.5-foot (2m x 3m) footprint producing hydrogen with purity of 99.999%.
The thermal efficiency of the hydrogen generators is 71% HHV at nameplate production. But it can be as high as 78% at higher output, making this a very cost-efficient option for on-site hydrogen generation. Taking into account capital investment and operating cost, the all-in production costs for hydrogen can be 30%-50% lower compared to conventionally delivered hydrogen.
The output capacity of the hydrogen generators is 2,000 scfh for the HGM 2000 and 10,000 scfh for the HGM 10000. Due to their modular design, several units can be linked together to meet higher demand profiles. The company’s generators are used in a variety of applications, from metals manufacturing to pharmaceuticals and vehicle fueling.
With 10 commercial installations of the HGM 2000 over the past 18 months and seven additional units sold, H2Gen is fast increasing the number of its units in the field. The company is working on the deployment of the first HGM 10000, thus making them a leader for small-scale, on-site steam-methane reformers. IH
For more information: Richard S. Todd, Ph.D. is PSA development manager, Sumant K. Warty is director of sales and business development and Udo Dengel is international sales manager for H2Gen Innovations, Inc., 4740 Eisenhower Avenue, Alexandria, VA 22304; tel: 703-778-3113; fax: 703-212-4898; e-mail: email@example.com; web: www.h2gen.com
Additional related information may be found by searching for these (and other) key words/terms via BNP Media SEARCH at www.industrialheating.com: hydrogen generation, process gas, hydrogen embrittlement, annealing, powder metallurgy