Reforming primary

Steam Reforming. In steam reforming, light hydrocarbon feeds ranging from natural gas to straight mn naphthas are converted to synthesis gas (H2, CO, CO2) by reaction with steam (qv) over a catalyst in a primary reformer furnace. This process is usually operated at 800—870°C and 2.17—2.86... 

Naphtha desulfurization is conducted in the vapor phase as described for natural gas. Raw naphtha is preheated and vaporized in a separate furnace. If the sulfur content of the naphtha is very high, after Co—Mo hydrotreating, the naphtha is condensed, H2S is stripped out, and the residual H2S is adsorbed on ZnO. The primary reformer operates at conditions similar to those used with natural gas feed. The nickel catalyst, however, requires a promoter such as potassium in order to avoid carbon deposition at the practical levels of steam-to-carbon ratios of 3.5—5.0. Deposition of carbon from hydrocarbons cracking on the particles of the catalyst reduces the activity of the catalyst for the reforming and results in local uneven heating of the reformer tubes because the firing heat is not removed by the reforming reaction. 

Gas-Heated Reforming. Gas-heated reforming is an extension of the combined reforming concept where the primary reformer is replaced by a heat-transfer device in which heat for the primary reforming reaction is recovered from the secondary reformer effluent. Various mechanical designs have been proposed which are variants of a shell-and-tube heat exchanger (12,13). 

In the catalytic steam reforming of natural gas (see Fig. 2), the hydrocarbon stream, principally methane, is desulfurized and, through the use of superheated steam (qv), contacts a nickel catalyst in the primary reformer at ca 3.04 MPa (30 atm) pressure and 800°C to convert methane to H2. 

The primary reformer is essentially a process furnace in which fuel is burned with air to indirectiy provide the heat of reaction to the catalyst contained within tubes. This area of the furnace is usually referred to as the radiant section, so named because this is the primary mechanism for heat transfer at the high (750—850°C) temperatures required by the process. Reforming pressures in the range 3 —4 MPa (30,000—40,000 atm) represent a reasonable compromise between cost and downstream compression requirements. 

Side reactions in the primary reformer are those which form carbon, an undesirable by-product. 

Excess Nitrogen Removal. A number of low energy processes use excess air in the secondary reformer in order to reduce the primary reformer duty. The surplus nitrogen so introduced has to be removed later in the process. 

Incorporation of a feed gas saturator cod in the convection section of the primary reformer allows for 100% vaporization of the process condensate. The steam is used as process steam in the reformer. 

Ammonia Plant 1. Where possible, use natural gas as the feedstock for the ammonia plant, to minimize air emissions. 2. Use hot process gas from the secondary reformer to heat the primary reformer tubes (the exchanger-reformer concept), thus reducing the need for natural 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 varies from 4-5 depending on natural gas composition (natural gas may contain ethane and heavier hydrocarbons) and the pressure used. 

The product gas from the primary reformer is a mixture of H2, CO, CO2, unreacted CH4, and steam. 

Figure 5-2. The ICI process for producing synthesis gas and ammonia (1) desulfurization, (2) feed gas saturator, (3) primary reformer, (4) secondary reformer, (5) shift converter, (6) methanator, (7) ammonia reactor.

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. 

Hycar (1) A reforming process for making syngas from light hydrocarbons, differing from the standard process in using two reactors. The second reactor (a convective reformer), operated in parallel with the primary reformer, preheats the feedstock. Developed by Uhde. 

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

Natural gas is reacted with steam on an Ni-based catalyst in a primary reformer to produce syngas at a residence time of several seconds, with an H2 CO ratio of 3 according to reaction (9.1). Reformed gas is obtained at about 930 °C and pressures of 15-30 bar. The CH4 conversion is typically 90-92% and the composition of the primary reformer outlet stream approaches that predicted by thermodynamic equilibrium for a CH4 H20 = 1 3 feed. A secondary autothermal reformer is placed just at the exit of the primary reformer in which the unconverted CH4 is reacted with O2 at the top of a refractory lined tube. The mixture is then equilibrated on an Ni catalyst located below the oxidation zone [21]. The main limit of the SR reaction is thermodynamics, which determines very high conversions only at temperatures above 900 °C. The catalyst activity is important but not decisive, with the heat transfer coefficient of the internal tube wall being the rate-limiting parameter [19, 20]. 

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). 

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