Hydrogen is used in industrial-scale metallurgical processes to create a controlled, oxygen-free, reducing atmosphere. In many applications, the hydrogen is fed into furnaces and then almost immediately flared or vented to the atmosphere. Typical hydrogen-intensive processes of this nature include bright annealing, brazing, ore-reduction and powder-metal sintering, to name a few.
Given the increasing cost of delivered hydrogen, the current economic climate and increasing pressure to create “green” processes, hydrogen recycling is compelling. Approximately half of the 20 billion kilograms of hydrogen generated in the U.S. annually is sold into merchant markets in either liquid or gaseous form, much of which is used in heat-treating applications. Approximately 85% of the hydrogen production in the U.S. is derived from steam methane reforming, where carbon dioxide is a by-product of the hydrogen-generation process. Additional carbon emissions are produced as merchants compress and transport the hydrogen to the end-user location. The reduction in such emissions further reinforces the attractiveness of recycling.
Hydrogen cost can be a substantial percentage of operating expenses in heat-treating processes. The molecule costs on a kilogram basis, including transportation, range from ~$5 to $20, depending on how the hydrogen is generated and distributed (liquid or gaseous) and the level of purity required. Site consumption rates vary from site to site and are process-dependent with hundreds or even thousands of kilograms a day being common. A typical heat-treating furnace will use 100-300 kilograms of hydrogen daily. On-site hydrogen recycling can provide substantial cost and operational benefits in numerous heat-treating processes.
Electrochemical Hydrogen Recovery and Recycling
The electrochemical recycling system (Fig. 1) developed by H2Pump is significantly different than the more conventional approach that utilizes mechanical compressors. The heart of the “pumping” process (Fig. 2) is a catalyzed membrane, which is capable of ionically transporting hydrogen ions from the anode (hydrogen to be recycled) to the cathode (effluent).
Hydrogen – from any source – enters the anodic chamber, where it is oxidized to protons and electrons. An electrical power supply provides the driving force to transport the protons through the membrane, where they recombine to form “new” hydrogen at the cathode. Because only the membrane transports protons, there is a bulk purification effect as the impurities, along with a small quantity of hydrogen, are vented into the existing site’s exhaust system.
The amount of hydrogen driven through the device is controlled (up or down) by the amount of current applied to each cell that contains a catalyzed membrane. As a result, this method can be operated autonomously by control schemes that measure the amount of hydrogen in the waste stream, the flow rates, and other pertinent parameters and adjust the HRS™ operation and output accordingly.
With the electrochemical approach, hydrogen recovery and recycling rates can range from low to high volumes without sacrificing efficiency. H2Pump technology also inherently compresses the hydrogen non-mechanically without the generation of by-product heat. By controlling the flux rate, pressures as high as hundreds of psi can be generated with little increase in the power required. Cells containing individual membranes are stacked together in order to accommodate a given volume of exhaust gas. The resultant “stack” can be sized to cost effectively and economically process tens to thousands of kilograms of hydrogen daily.
The efficiency and operating costs of the approach are quite attractive. Electrochemical efficiencies when recovering approximately 90% of the hydrogen contained in the exhaust stream can be as high as 99%, while the entire system efficiency is typically greater than 80%. As the voltage required to operate the electrochemical pump is minimal on a per-cell basis (millivolts), a “stack” capable of processing 100 kg/day requires only slightly more than 30 volts.
Due to the nature of the electrochemical approach and the device’s patent-pending design, the HRS system is uniquely suited to extract hydrogen from industrial-process waste streams without impacting the furnace’s atmosphere or internal pressure. As a result, the recycler can be used with a host of furnaces that operate at atmospheric or near-atmospheric pressures. The HRS is not directly integrated with the furnace but rather into the existing exhaust and hydrogen distribution systems, thereby eliminating the potential of upsetting the heat-treating process.
The HRS system can handle a number of gaseous impurities commonly found in post-heat-treating gas streams. Gases such as carbon dioxide, ammonia, nitrogen, carbon monoxide and water vapor are typical in waste streams of annealing and brazing operations, most of which are generated from residual protective surface coatings (oils) or reactions with secondary gases such as nitrogen. The impurities are handled by a number of proprietary methods within the HRS. The final gas cleanup and drying stages are dependent on the customer’s process requirements. The HRS is capable of delivering 99.999% pure hydrogen with dew points well below -70˚C (-94˚F), often exceeding the original hydrogen feedstock quality.
The typical operating characteristics of the HRS-100™ 100-kg/day electrochemical recycling system are presented in the Table 1. In addition to being able to reclaim hydrogen on demand, the HRS controls allow for remote operation, monitoring, reporting and selected maintenance, with the end user having little to no involvement with the operation of the device.
Capital and Maintenance Costs Eliminated
In addition to the elimination of maintenance responsibilities, the customer is not burdened with the cost of the device. H2Pump assumes all capital costs for the HRS system, while the customer is only obligated to support the operation of the recycler (i.e. utilities and (minimal) site prep). Since the power consumption for the recycler is approximately 10 kWh/kg (with typical industrial electric rates of $0.10 kWh), a kilogram of hydrogen can be recovered and recycled for ~$1.00 ($0.25/100SCF). H2Pump’s approach has been well received because the customer begins saving process costs immediately after the installation of the HRS system. Because the reduction in hydrogen usage can be significant, H2Pump and the customer share in the savings via a Hydrogen Recycling Agreement (HRA).
Call to Action
The HRS™ technology will be commercially available in early 2013. Beta demonstration programs are currently under way and will continue to be pursued with interested prospective customers. IH
For more information: Marianne Morrison is director of sales and marketing (firstname.lastname@example.org), and Robert Hirsch, Ph.D., (Robert.email@example.com), is the systems engineer responsible for site assessment and integration. H2Pump LLC, 11 Northway Lane North, Latham, N.Y. 12110, tel: 518-783-2241, e-mail: firstname.lastname@example.org, website: www.h2pumpllc.com