Manufacturers use synthesis gas, or “syngas” for fuel to produce electricity and as feedstock for production of industrial chemicals such as ammonia, methanol, and other hydrogen-rich compounds. Once isolated and purified, hydrogen from syngas is a major component in petrochemicals and oil refining. Syngas itself is a mixture primarily of hydrogen and carbon monoxide, created through the gasification of hydrocarbons in natural gas, coal, petroleum, biomass, and other feedstocks. Virtually all the hydrogen produced in the United States is produced from methane. And the cheapest, most available source of methane is natural gas.
Steam Methane Reforming
Steam methane reforming (SMR) accounts for about 95 percent of the industrial hydrogen produced domestically and about half the world’s production. The process begins with the introduction of superheated (1,300 to 1,800 degrees Fahrenheit) steam and natural gas into an array of vertically hanging tubes filled with nickel catalyst. As the mixture flows through the tubes, which are heated externally (the reaction is endothermic), the methane in the natural gas reacts with the water vapor to produce hydrogen and carbon monoxide:
CH4 + H2O < ——– > 3H2 + CO
Ensuring the feed mixture contains excess steam ensures the maximum production of hydrogen. Plentiful steam also enables the consumption of as much methane as possible. Methane in the product is an impurity and must be stripped from the gas later in the process. Nearly complete conversion of methane has the added benefit of preventing creation of elemental carbon, which can deposit on and foul the catalyst.
At present, the most widely used and cheapest method for hydrogen production is the steam reforming of methane (natural gas). This method includes about half of the world hydrogen production, and hydrogen price is about US$ 7 / GJ.
Below listed are several well-known companies which provide process technology and engineering of syngas / hydrogen production on the basis of steam reforming. The number in parenthesis shows the units installed worldwide approximately.
- Foster Wheeler (100)
- Lurgi (30)
- Linde (120)
- KBR (100)
- Uhde (60)
- Praxair (140)
- Haldor Topsoe (40)
- Technip (240)
- CB&I (175)
Water-Gas Shift Reaction
Another reason for incorporating relatively more steam than methane in the mixture is to encourage a secondary reaction for the recovery of additional hydrogen. In this process, the mixture passes through another set of tubes of iron-chromium catalyst in a fixed-bed reactor where the molecules in the water vapor are split into oxygen and hydrogen. The hydrogen is collected along with that produced in the SMR process. The oxygen bonds with the carbon monoxide from SMR to make carbon dioxide.
CO + H2O < ——– > CO2 + H2
Unlike the primary reaction, the water-gas shift reaction is exothermic, and the energy produced can be captured to partially fuel the steam-heating required in SMR.
Pressure Swing Adsorption
While steam methane reforming and water-gas shift reactions are quite efficient, complete reaction of methane is impossible because the reactions are subject to thermal equilibrium. This leaves some unreacted methane along with the carbon dioxide from the final product, some unreacted carbon monoxide, water vapor, and other contaminants in the gas mixture. As many operations require virtually pure hydrogen, the pressure swing adsorption process removes these contaminants.
This is accomplished by pumping the mixture through cylinders filled with specially treated beads to which the unwanted gasses adhere. Once the pristine hydrogen is pumped out of the cylinders, pressure can be lowered, releasing the contaminants from the beads. They then can be flushed from the chamber.
Numerous hydrogen PSA units have been installed worldwide. Leading technology licensors include:
- Air Products & Chemicals
A modern syngas / hydrogen plant typically has capacity range from 5 MMSCFD to 200 MMSCFD. For a 90 MMSCFD plant, the capital cost to build such a plant is estimated at approximately US$ 55 million nowadays. Average hydrogen production cost is US$ 1.60 per 1,000 standard cubic feet, or US$ 53 million per year to operate a plant of this capacity. This estimate is based on the following utility consumption.
Utilities consumption per 1,000 ft3 of contained hydrogen:
- Natural gas feed, million Btu LHV 317
- Natural gas fuel, million Btu LHV 126
- HP export steam, lbs 90
- Boiler feedwater, lbs 120
- Power, kWh 52
- Cooling water, gal 8
Low-cost feedstock and efficient conversion of hydrogen makes steam methane reforming from natural gas the most widely used process for syngas production. Phoenix Equipment sells used hydrogen and syngas plants, and hydrogen purification components that are immediately available for purchase and relocation. Buying a used plant can save you significant capital and drastically shorten the time required to build or expand manufacturing operations.