Production of Hydrogen from Lpg

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2.5.1. Processing Steps of Hydrogen Production from LPG

Conventional process for producing hydrogen from light hydrocarbons involves the following process steps:

• Feed preparation
• Sulfur removal
• Steam reforming
• CO shift conversion
• Autothermal reforming
• Process gas cooling
• Synthesis gas purification (PSA pressure swing absorption) [5]

2.5.1.1. Sulfur Removal
LPG feed first passes through an ambient temperature sulfur adsorption vessel. The proprietary adsorbent in this vessel has been specifically designed to remove sulfur species native to LPG feeds as well as those sulfur compounds that are added as odorants for leak detection. The sulfur adsorbent has been proven effective in removing compounds ranging from H2S and mercaptans to thiophenes. Since sulfur is known to affect the performance of all reforming catalysts, removing the sulfur prior to entering the reforming section ensures the highest level of reforming catalyst performance and maximum catalyst life. [5]

2.5.1.2. Autothermal Reforming
During the reforming step, LPG feed is converted into a hydrogen rich product stream. At the entrance of the reforming catalyst bed, the feed, air and steam are mixed in proportions that are chosen to maximize hydrogen production from the given feedstock. The conversion takes place over a bi-functional catalyst that promotes both partial oxidation and steam reforming reactions in the same catalyst bed. This results in a direct transfer of heat within the catalyst bed and efficient production of hydrogen. The direct transfer of heat also means the process is responsive to changes in hydrogen demand requirements. [5]

3. Hydrogen Purification
Hydrogen purification is performed via the use of Pressure Swing Adsorption (PSA) technology. The PSA technology employed by HyRadix combines novel process hardware technology with proprietary adsorbents to attain a very high recovery of the product hydrogen. In addition, the process ensures removal of all of impurities such as water, CO, CO2, and CH4, which are harmful to end user industrial and fuel cell applications. This unique combination of technologies allows for a wide range of hydrogen purity control with the only product impurities being the inert components nitrogen and argon. [5]

2.5.1.4. Heat Integration
The heat integration step is key to achieving overall process efficiency. Heat is recovered from high temperature streams, such as the reactor section effluent or the PSA waste gas stream, and is used to preheat the feed streams to the reactor and generate steam for the reforming reaction. Additionally, any CO that remains in the PSA waste gas stream is converted to CO2 before the waste gas stream exits the unit. [5]

2.5.2. Pressure Swing Adsorption

Pressure Swing Adsorption (PSA) processes rely on the fact that under pressure gases tend to be attracted to solid surfaces, or adsorbed. The higher the pressure, the more gas is adsorbed; when the pressure is reduced, the gas is released, or desorbed. PSA processes can be used to separate gases in a mixture because different gases tend to be attracted to different solid surfaces more or less strongly. If a gas mixture such as air, for example, is passed under pressure through a vessel containing an adsorbent bed that attracts nitrogen more strongly than it does oxygen, part or all of the nitrogen will stay in the bed, and the gas coming out of the vessel will be enriched in oxygen. When the bed reaches the end of its capacity to adsorb nitrogen, it can be regenerated by reducing the pressure, thereby releasing the adsorbed nitrogen. It is then ready for another cycle of producing oxygen enriched air. [5]

This is exactly the process used in portable oxygen generators used by emphysema patients and others who require oxygen enriched air to breath. Aside from their ability to discriminate between different gases, adsorbents for...
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