Hydrogen typical operating requirements

Table 6. UTC-PSA Hydrogen Plant Typical Operating Requirement... 

Raw material and utilities Ethylene and hydrogen chloride selectivities of 98+% are typical with HC1 conversion of 99.8+%. Operating in an ethylene-rich environment, the process produces only about half as much CO and C02 as typical fluid-bed processes. Typical operating requirements per metric ton of EDC are ... 

Electrolyzers typically operate from grid-quality power, so a new variety of power control and conditioning equipment needs to be developed in order for electrolyzers to operate efficiently from renewable sources. The prospect exists for good efficiency in converting renewable power to hydrogen, insofar as electrolyzers require direct current and renewables generate direct current, so there are no losses associated with ac/dc conversion. 

Power requirements of portable hydrogen equipment such as cameras, mobile phones or laptop computers currently covered by batteries, typically of lithium ion type, could with a small fuel cell and some 10-20 g of directly or indirectly stored hydrogen prolong operational time by a factor of 5-10. A discussion of such options using direct methanol fuel cells is made in section 4.6. 

At maximum power, a typical fuel cell operating on hydrogen is only 50% efficient. This translates into 1W of thermal power that needs to be dissipated for every watt of electricity produced. A battery typically operates at an efficiency of 80%i or more. Therefore, the use of a fuel cell can increase the thermal load in an electronic device by 60-100%i. The fuel cell efficiency can be improved by operating the stack at a higher voltage. However, this requires oversizing the stack, which increases the mass and the volume of the power supply, and also, perhaps more significantly, increased cost. 

Several properties of cellulose phosphate have been evaluated. The material has good thermal stability and low hydrogen crossover, two requirements that are important to meet DOE fuel cell program targets. Further characterization of the material is required, especially the determination of proton conductivity. In addition, testing of the material in an MEA will allow the effect of acid stability and swelling properties of cellulose phosphate be evaluated under typical PEM fuel cell operating conditions. 

An accurate selection of the set of operating conditions ensures the best process performance. The main process variables (temperature, pressure, space velocity, and H2/oil ratio) are adjusted according to the specific HDT application. Table 13.3 shows typical operating conditions of various processes [59, 60]. Most of these processes are generally carried out in fixed-bed units, with the exception of ebullated-bed residue HCR. Naturally, the severity of the process increases with the heaviness of the feedstock. Distillate HDT is carried out at relatively mild conditions compared to residue HDT. HCR processes require more severe conditions than HDT and are much more demanding in terms of hydrogen supply. A brief discussion on the effect of these variables is presented later. 

The curves exhibited a linear relationship between voltage and current, which demonstrated reversibility, up to at least 1 A cm . At a typical operating current density of 0.2 A cm , electrochemical hydrogen pumping required relatively low voltages, i.e.. 

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