Alternative Energy

For people who read my blog, they should have some basic knowledge on how to self-produce hydrogen for their car and if you have not read my blog before, please read some of my article at “How to DIY Hydrogen Fuel Cell? - Part 1″. 

In this topic, I will introduce another method to produce hydrogen in big scale and cheaper compared to electrolysis process called Steam Reforming. Steam Reforming is a method of producing hydrogen from hydrocarbons. Steam reforming converts methane (and other hydrocarbons in natural gas) into hydrogen and carbon monoxide by reaction with steam over a nickel catalyst.

The steam methane reforming (SMR) process consists of the following two steps:

1.   Reformation of Natural Gas
The first step of the SMR process involves methane reacting with steam at 750-800°C (1380-1470ºF) to produce a synthesis gas (syngas), a mixture primarily made up of hydrogen (H2) and carbon monoxide (CO).

2.   Shift Reaction
In the second step, known as a water gas shift (WGS) reaction, the carbon monoxide produced in the first reaction is reacted with steam over a catalyst to form hydrogen and carbon dioxide (CO2). This process occurs in two stages, consisting of a high temperature shift (HTS) at 350ºC (662ºF) and a low temperature shift (LTS) at 190-210ºC (374-410ºF). 

Steam Reforming Process

Hydrogen produced from the SMR process includes small quantities of carbon monoxide, carbon dioxide, and hydrogen sulfide as impurities and, depending on use, may require further purification. The primary steps for purification include:

• Feedstock purification – This process removes poisons, including sulfur (S) and chloride (Cl), to increase the life of the downstream steam reforming and other catalysts.
• Product purification – In a liquid absorption system, CO2 is removed. The product gas undergoes a methanation step to remove residual traces of carbon oxides. Newer SMR plants utilize a pressure swing absorption (PSA) unit instead, producing 99.99% pure product hydrogen.

High to ultra-high purity hydrogen may be needed for the durable and efficient operation of fuel cells. Impurities are believed to cause various problems in the current state-of-the-art fuel cell designs, including catalyst poisoning and membrane failure. As such, additional process steps may be required to purify the hydrogen to meet industry quality standards. Additional steps could also be needed if carbon capture and sequestration technologies are developed and utilized as part of this method of hydrogen production.

Source : www.getenergysmart.org