Commercial electrolyzers

There are no electrolyzers developed specifically for operation with wind turbines. However, the rapid response of electrochemical systems to power variations makes them suitable "loads" for wind turbines. Industrial electrolyzers are designed for continuous operation, mainly because their elevated investment cost requires high-capacity factors for reasonable payback times, but they are subject to a considerable number of current interruptions through their lifetime due to occasional power interruptions, accidental trips of safety systems, and planned stops for maintenance. Current interruptions are more frequent in specialty applications, where electrolyzers supply hydrogen "on demand." Therefore, the discontinuous use of the equipment is not new, and most commercial electrolyzers may be used in intermittent operation although a significant performance decrease is expected with time. In fact, it is not power variation, but current interruptions that may cause severe corrosion problems to the electrodes, if the latter are not protected by the application of a polarization current when idle. 

High pressure can increase efficiency anil this concept has been under development for many years. A commercial electrolyzer (Lurgii is available which operates at a pressure of 30 atmospheres and 90 C. requiring 3(HI amperes of electric current at 217 volts In the mid-1960s, bipolar cells of porous nickel electrodes were developed which operate at current densities of BIX) and 1600 amperes per square foot (11.09 square meler)... 

Table 2. Commercial electrolyzer manufacturers and selected performance data.

The primary intent of this work is to design, build and verify a system capable of accurately varying important system variables that are normally strictly monitored and controlled by the commercial electrolyzers containing the same PEME stack. The goal of the experimental characterization of the stack, under varying conditions and power, is to enable an optimized interconnection between the stack and RE source. Such a coupled system specifically designed with the RE source in mind would reduce the overall cost of independent stand alone systems and may eliminate the need for electrical storage components. 

Technology Brief Analysis of Current-Day Commercial Electrolyzers, NREL, Golden,... 

Occasionally, the market will swing the other way leaving chlorine in short supply. Fused sodium chloride is commercially electrolyzed in Down s cells to give chlorine and metallic sodium [11]. Sodium production in the U.S.A. has averaged 135,000-150,000 metric tonnes annually since 1968, which represents about a 2-3% contribution to the chlorine supply from this source. In the U.K., it is estimated that as much as 10% of the available chlorine arises from Down s cell technology. Potassium chloride solutions are also electrolyzed for commercial potassium hydroxide, but the contribution to the chlorine supply from this source is even less than from fused sodium chloride electrolysis. 

Some commercial electrolyzers sacrifice gas purity for electrical efficiency with closely spaced electrodes, only to have to add expensive purification equipment at the end of the process, which negates any cost efficiency at the production point. The more cost effective solution for purer gas production is to err on the side of separating the electrodes a bit more, and sacrifice a certain amount of electrical efficiency. 

An important design consideration was to maximize the efficient use of energy input from renewable energy power sources. Most commercial electrolyzers are designed to run off utility power grids with a rectified DC source. The electrode materials used in these electrolyzers reflect that particular type and quality of power source. 

We did run a quick comparison test with another electrolyzer. This particular electrolyzer weighed in at about 30 pounds, used sintered nickel plates, and was about three times as large as our P41. The P41 weighs a little more than a pound and was less than half the size of the commercial electrolyzer. 

We connected the electrolyzers to matching solar panels and watched the results. The P41 began gassing immediately, whereas the commercial electrolyzer took about a half hour to release its contents into the feed tubes. This fact pointed out design flaws in the commercial electrolyzer. 

Basically, in any electrolyzer you want the gas to get out of the reactor tank and away from the electrodes as fast as possible so that the gas does not interfere with the process. It was obvious at first glance that the commercial electrolyzer had gas pockets that had to be filled before the gas would be released. Even after the other electrolyzer was given time to come up to speed, it was visually evident that there was no contest. 

The P41 produced twice the gas that the commercial electrolyzer produced. We also noticed that the P41 performed extremely well under intermittent cloud cover as we had expected. Very sharp peaks and troughs in... 

Sharp peaks and troughs were evident in the other electrolyzer with minor atmospheric hindrances that vary from second to second and or minute to minute, such as moisture clouds or dust clouds. These are not perceptible to the naked eye, but never the less affect the power output of the PV panels and thus the gas production from the electrolyzer. Under these conditions, the P41 exhibited a rolling effect with a more consistent gas output, and with full cloud cover it was producing much more gas than the commercial electrolyzer. 

Commercial electrolyzers have been developed using both the bipolar and monopolar cell configuration. The cell unit is generally made of metal or corrosion resistant plastics. 

In a detailed laboratory investigation of the effect of cell variables on the deuterium separation factor in electrolysis of water, Brun and co-workers [B13] have found that a depends on the cathode material, electrolyte composition, and cell temperature, generally as follows. The separation factor is higher for an alkaline electrolyte than for an add. With KOH, at 15°C, a pure iron cathode gave the highest value reported, 13.2. The separation factor for mild steel, the material used in most commercial electrolyzers, was 12.2. Values as low as S were reported for tin, zinc, and platinized steel. At 2S°C the separation factor with a steel cathode was 10.6, and at 75°C it had dropped to 7.1. 

This means that the electrical energy required for electrolysis is reduced by about 56%. It has been reported that the voltage drop between electrodes attains 1.93-1.95 V at a current density of 30 A dm-2 in a semi-commercial electrolyzer.126 Further energy saving is possible in the chlor-alkali process. 

J.T. Keating, Effect of brine purity on performance of commercial electrolyzer, Soda Enso (Soda Chlorine), 1994, 45, 366-375 J.H. Austin, Operation in chlor-alkali plants, 3rd London International Chlorine Symposium, June, 5-7 1985. 

In order to lower the capital cost of the electrolyzer plant, it is necessary to operate at as high a current density as possible, i.e., often more than 500 mA cm Some commercial electrolyzers run at a current density as high as 3000 mA cm The drawbacks are a greater cell resistance, the need for a... 

Figure 7.5a, for example, illustrates the most direct implementation of the Combined PV-electrolysis configuratiOTi. Commercially available photovoltaic (PV) panels are coupled with separate commercial electrolyzer units, such as alkaline or PEM electrolyzers and appropriate power-conditioning equipment is utilized to load-match the processes. This is the clear path to near-term renewable solar hydrogen, but it is by no means inexpensive. Based on recent cost studies from the NREL, hydrogen production cost would exceed 10/kg for PV electricity cost at... 

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