Historically, the “make vs. buy” decision for obtaining hydrogen has been easy for most heat-treating companies. Generating hydrogen or other industrial gases at the point of use typically offers advantages in cost, purity and reliability of gas supply. However, the previously available options for on-site generation of hydrogen come at too high a price for medium and small users. The hefty capital investment required for a steam methane reformer – the process technology used in oil refineries and other large chemical plants that produces most of the hydrogen consumed worldwide today – makes it cost-effective only at production volumes far greater than the requirements of most heat-treating applications (Fig. 1). The only other on-site option for small and medium hydrogen users is electrolysis. The large amount of electricity required to produce hydrogen through electrolysis of water, however, makes this technology affordable only in areas of the world where electricity rates are very low or where hydrogen is not available from any other sources. Thus, for most heat-treating companies, the only practical means of obtaining hydrogen was to buy it in compressed gaseous or, where available, cryogenic liquid form from a local industrial-gas supplier or other distributor who delivers the gas by truck or pipeline.
Hydrogen Generators for Heat TreatmentResponding to increasing global demand for hydrogen in an ever-growing list of industrial applications, several equipment manufacturers have sought to develop hydrogen generators with output capacities in line with the needs of heat-treating companies and other industrial users. The design approach taken by a majority of these companies is to fabricate a scaled-down version of a high-volume steam methane reformer. These units, none of which are yet being used in full-scale industrial applications, retain many of the disadvantages of large-scale systems, including:
- Complex and costly system design
- Potential difficulties with integration into the customer’s existing plant
- Very high operating temperatures
- Slow start-up
- Large footprint
- Limited flow rate flexibility
- Discharge of low-quality fuel gases
Steam Methane Reforming vs. Catalytic Autothermal ReformingIn an effort to overcome these limitations, HyRadix Inc. pursued a different design concept in developing the Aptus® hydrogen generator. It incorporates innovations in catalyst selection, heat integration, sulfur removal and hydrogen purification. The resulting process, called catalytic autothermal reforming, differs from steam methane reforming in two important ways.
First, the reforming reaction in the generator occurs within a single catalyst bed, whereas conventional steam methane reforming is a two-step process – a reforming catalyst bed followed by a shift reactor. After entering the reforming chamber, the feedstock is combined with air and steam in the presence of a bifunctional catalyst that promotes both a partial oxidation reaction and a steam reforming reaction in the same bed. By the time the feedstock reaches the end of the catalyst bed, it has been converted into a hydrogen-rich syngas.
Second, heat needed for the reforming reaction comes from the exothermic partial oxidation reaction within the catalyst bed. Steam methane reforming requires an external fuel source to feed a flame inside a convection furnace to heat the reforming tubes. Because heat is generated where it is used (in catalytic autothermal reforming), heat transfer is extremely efficient (Fig. 2). Heat is also recovered from high-temperature waste-gas streams and is used to preheat the feedstock stream to the reactor and to generate steam for the reforming reaction. Steam methane reformers rely on an external heat source and typically require operating temperatures in excess of 850°C (1560°F). This mandates complex and costly system designs to meet the mechanical challenges of such temperatures where the catalytic autothermal reformer needs few exotic metals.
These advancements enable the new-technology hydrogen generator to deliver significant performance advantages compared to either large-scale or downsized steam methane reformers, including:
- Lower operating temperatures – The need for an external heat source to allow for a simpler operation is eliminated.
- Greater flexibility in hydrogen flow requirements – Rapid system start-up (as little as three hours for a cold start versus eight hours for steam methane reformers), efficient operation under turndown conditions as low as 25% of capacity and fast output ramp-up (from 25% of capacity to 100% in about 35 minutes) give it key advantages for applications with variable hydrogen demand.
- Easier installation – Costly and time-consuming site redesign and preparation are unnecessary. With a footprint of only 7 x 20 feet, the skid-mounted unit is small enough to fit easily into most existing heat-treating operations. Connecting the unit to electricity, water, feedstock input and hydrogen output lines complete the installation.
- Efficient system operation and monitoring – Hydrogen output is synchronized with the requirements of the downstream processes. The unit operates unattended and can be monitored remotely by the user and, if desired, off-site by the manufacturer.
- Feedstock flexibility – The Aptus design can be adapted for use with locally available feedstocks, including natural gas, liquid petroleum gas (LPG) blends, ethanol and other hydrocarbon-rich resources.
- Output flexibility – The subject unit is currently available in two output capacities: 50 Nm³/hour [1900 standard cubic feet per hour (scfh)] and 100 Nm³/hour (3800 scfh) with other sizes proposed for the future. Multiple units can be installed to cost-effectively achieve virtually any desired system capacity between 15 Nm³/hour and 600 Nm³/hour. The manufacturer’s engineers work closely with customers to tailor the unit and auxiliary equipment to deliver the required capacity, flow, pressure and purity of produced hydrogen.
ConclusionThe Aptus system provides heat-treating companies with a practical, affordable way to realize the benefits of on-site hydrogen generation while lowering total hydrogen costs and achieving unparalleled operational efficiency and flexibility.IH
For More Information:Contact David Cepla, vice president - business development, HyRadix Inc., 185 W. Oakton Street, Des Plaines, IL 60018; tel: (847) 391-1200: fax: (847) 391-2596; e-mail: firstname.lastname@example.org; web: www.hyradix.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, oxidation, catalyst, exothermic, steam methane reformer, natural gas, liquid petroleum gas
SIDEBAR: On-Site Hydrogen Generation Delivers Quality and Cuts Costs for Chinese Fastener ManufacturerInstalling a HyRadix Aptus® hydrogen generator at its new plant has enabled a Chinese fastener manufacturer to meet its specifications for hydrogen purity, pressure and flow rate while cutting total hydrogen costs by more than half and eliminating the risk of supply disruptions.
Hydrogen is used in heat treating of the steel-wire coils from which the manufacturer produces screws, bolts and other engineered fasteners. After the steel wire is extruded to the specified diameter, it is heat treated for several hours in a sealed bell-type annealing furnace to remove imperfections. A mix of nitrogen and hydrogen is continuously pumped into the furnace to prevent oxidation of the steel wire during heat treating. The hydrogen molecules bond chemically with any oxygen molecules present to form water vapor, which is vented from the furnace. After heat treating, the steel wire is cut to length and machined into finished fasteners.
Since natural gas was not available at the site, the hydrogen generator uses liquid petroleum gas (LPG) as the feedstock from which high-purity (99.95% pure) hydrogen is produced. The LPG is vaporized and compressed before entering the unit, which has a rated hydrogen capacity of 100 Nm³/hour (3,800 scf/hour) at 7 bar-g (100 psig). Hydrogen exiting the generator enters a buffer storage vessel that supplies hydrogen to the annealing furnaces. The Aptus system is configured to automatically adjust hydrogen production to the flow-rate requirements of the annealing furnaces, thus minimizing utility use during periods of lower hydrogen-flow requirements.
The fastener manufacturer handled site preparation and installation of the hydrogen generator. The manufacturer’s technical personnel connected the feedstock, cooling water, DI water, nitrogen, Ethernet and electricity inputs, conducted training, and supervised initial system operation and testing. The system has been operating since early fall 2006.
Although the existing system is sized to meet the fastener manufacturer’s hydrogen requirements for several years, the modular design of Aptus generators allows for fast and simple expansion as necessary to accommodate future growth.
All purity and performance specifications have been met, and cost savings from generating hydrogen on-site rather than purchasing it from an industrial-gas vendor have exceeded initial projections.