Hydrogen primary reforming

The first step in the production of synthesis gas is to treat natural gas to remove hydrogen sulfide. The purified gas is then mixed with steam and introduced to the first reactor (primary reformer). The reactor is constructed from vertical stainless steel tubes lined in a refractory furnace. The steam to natural gas ratio varies from 4-5 depending on natural gas composition (natural gas may contain ethane and heavier hydrocarbons) and the pressure used. 

Figure 8.21 shows the scheme for producing ammonia. First, the natural gas is desulfurized and then steam-reformed in the primary reformer into a mixture of unreacted methane (10-13 %), CO, CO2, and FI2 that is then combined with air, which contains the necessary nitrogen for the ammonia process, to react in a secondary reformer. Here the oxygen reacts with hydrogen and methane in strongly... 

Modern SMR plants (Figure 2.5b) incorporate a PSA unit for purifying hydrogen from C02, CO, and CH4 impurities (moisture is preliminarily removed from the process gas). The PSA unit consists of multiple (parallel) adsorption beds, most commonly filled with molecular sieves of suitable pore size it operates at the pressure of about 20 atm. The PSA off-gas is composed of (mol%) C02—55, H2—27, CH4—14, CO—3, N2—0.4, and some water vapor [11] and is burned as a fuel in the primary reformer furnace. Generally, SMR plants with PSA need only a HT-WGS stage, which may somewhat simplify the process. 

Figure 3.3 The primary reformer for methane conversion to carbon monoxide and hydrogen. (Courtesy of Solatia Inc., Luling, LA)...

The source of nitrogen for the synthesis gas has always been air, either supplied directly from a liquid-air separation plant or by burning a small amount of the hydrogen with air in the H2 gas. The need for air separation plants has been eliminated in modern ammonia plants by use of secondary reforming, where residual methane from the primary reformer is adiabatically reformed with sufficient air to produce a 3 1 mole ratio hydrogen-nitrogen synthesis gas. 

Synthesis Gas Preparation. The desulfurized natural gas mixed with steam is fed to the primary reformer, where it is reacted with steam in nickel-catalysl-lilled lubes to produce a major percentage of the hydrogen required. The principal reactions taking place are9... 

Here, the chosen domain for our case study is on-board hydrogen production to supply pure H2 to a fuel cell in an electrical car. Among the sequential catalytic reactions that take place for H2 production, the hydrogen purification units are located downstream, after the primary reforming of hydrocarbons into a CO-H2 mixture or Syngas units. They consist of Reaction (1) the water-gas shift (WGS) reaction and Reaction (2), the selective or preferential oxidation of CO in the presence of hydrogen (Selox). 

Application The ICIAMV process produces ammonia from hydrocarbon feedstocks. The AMV process concept offers excellent energy efficiency together with simplicity and reduced capital cost for plant capacities between 1,000 tpd and 1,750 tpd. Key features include reduced primary reformer duty, low-pressure synthesis loop and hydrogen recovery at synthesis loop pressure. 

After desulfurization, steam is added and the mixture heated to 480 to 550°C before it is fed into the primary reformer. The gas leaving the primary reformer contains between 7 and 10% methane. This is removed in so-called secondary reformers in which the gas leaving the primary reformer is partially burnt with air in nickel catalyst-filled shaft furnaces (autothermal process), whereupon the temperature increases to ca. 1000°C. Under these conditions the methane reacts with the steam reducing the methane content in the synthesis gas to ca. 0.5 mole %. The quantity of air is adjusted to give the nitrogen to hydrogen ratio required for the stoichiometry of the ammonia synthesis. 

Typically, the secondary reformer is a refractory-lined cylinder, the lower part of which is filled with a catalyst similar to that in the primary reformer. The upper part is the combustion chamber and the lower part continues the formation of carbon monoxide and hydrogen from the unbumed methane. The gases leave the secondary reformer at 950-1000°C, and are passed through a heat exchanger and cooled to 375°C. The intended reaction in this stage is the water-gas shift reaction ... 

Synthetic gas can be produced from a variety of feedstocks. Natural gas is the preferred feedstock when it is available from gas fields (nonassociated gas) or from oil wells (associated gas). The first step in the production of synthesis gas is to treat natural gas to remove hydrogen sulfide. The purified gas is then mixed with steam and introduced to the first reactor (primary reformer). The reactor is constructed from vertical stainless steel tubes lined in a refractory furnace. The steam to natural gas ratio is 4—5 depending on natural gas composition (natural gas may contain ethane and heavier hydrocarbons) and the pressure used. A promoted nickel-type catalyst contained in the reactor tubes is used at temperature and pressure ranges of 700 800°C and 30—50 atm, respectively. The product gas from the primary reformer is a mixture of H2, CO, C02, unreacted CH4, and steam. The main reforming reactions are ... 

Description The natural gas (1) is first desulfurized before entering a primary reformer (2), where it is reformed, reacting with steam to generate synthesis gas, i.e., hydrogen (H ), carbon monoxide (CO) and carbon dioxide (CO ). The reformed gas is cooled (3) by generating high-pressure (HP) steam, which provides heat for the methanol distillation columns (8). The cooled gas enters the synthesis gas compressor (4), where it is compressed to synthesis pressure. 

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