Reduced primary reforming

An incidental benefit of reducing the primary reformer load in this way is that the NOx emission is reduced because less firing is required, which produces a lower flue gas quantity. 

Some companies (for example, Jacobs, Foster - Wheeler, and Lurgi) have gone so far as to propose bypassing some of the natural gas around the primary reformer and feeding it straight to the secondary reformer, which then operates as a quasi-auto-thermal reformer. 

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Some reforming processes are designed for reduced primary reforming by moving some of the heat duty to the secondary reformer because of the marginal... 

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. 

Catalyst makers also succeeded in minimizing the activity reducing effect of the potassium in the alkalized catalysts [430], Pre-reduced primary reforming catalysts are now also marketed (ICI Katalco, Topsoe) [430], and splitloading of reformer tubes with more than one type of catalyst has now become very common. The benefitial effects concern pressure drop at increased plant load, carbon formation potential, catalyst activity, catalyst cost, and desired catalyst life. For example, a reformer tube may be loaded with 15 % alkali-free catalyst in pre-reduced form (top-section), 25 % unreduced alkali-promoted (middle section) and 60% alkali-free unreduced catalyst (bottom section). 

Installing a prereformer or rich-gas step is another possibility to reduce primary reformer duty and stack temperature of the flue gas [462]-[470], especially in LPG-and naphtha-based plants... 

Processes with reduced primary reformer firing and surplus process air... 

Processes with Reduced Primary Reformer Firing... 

ICI AMV Process. The ICI AMV process [1034], [1083], [1111] - [1122], also operates with reduced primary reforming (steam/carbon ratio 2.8) and a surplus of process air in the secondary reformer, which has a methane leakage of around 1 %. The nitrogen surplus is allowed to enter the synthesis loop, which operates at the very low pressure of 90 bar with an unusually large catalyst volume, the catalyst being a cobalt-enhanced version of the classical iron catalyst. The prototype was commissioned 1985 at Nitrogen Products (formerly CIL) in Canada, followed by additional plants in China. A flow sheet is shown in Figure 110. 

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. 

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. 

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. 

Emissions to the atmosphere are reduced significantly by eliminating the flue-gas from the primary reformer. NOx emissions may be reduced by 50% or more compared to conventional steam reforming. The level of NOx reductions depends on the extent of auxiliary combustion in the plant53. 

Convective Heat Transfer Reformers provide additional reforming capacity by using the heat contained in the primary reformer exit gases. Several designs are available, but not all have been commercialized. These units typically replace a portion or the entire duty of the waste heat boiler. So they significantly reduce the steam capability of the reformer. Potential increases in capacity of between 10% and 30% are possible. The modifications are capital intensive but relatively easy to implement170. 

The steam requirements in an ammonia unit can be reduced by lowering the steam-to-carbon ratio to the primary reformer. However a number of drawbacks can exist downstream in the I I I S and LTS reactors. The drawbacks include By-product formation in the HTS, Pressure drop buildup in the HTS, Reversible poisoning of the LTS catalyst, and Higher CO equilibrium concentrations exiting the HTS and LTS reactors. 

The gas-heated reformer (GHR) reduces the need for the high pressure steam system associated with the primary reformer and also minimizes or eliminates nitrogen oxide formation. The GHR is discussed in more detail in Chapter 5. 

Decreased Firing in the Primary Reformer. Decreased heat supply in the primary reformer means that the process outlet temperature is lowered to about 700°C, the firing efficiency increases, and the size and cost of the primary reformer are reduced. The milder operating conditions prolong catalyst life, catalyst tube life, and outlet header service life.53... 

The volume hourly space velocity, in comparison with the vaporized hydrocarbon feedstock, is normally around 1600 to 2000 h for primary reforming. In high-pressure treatment (2.5 to 3.10 Pa absolute), they reach 5000 In post-combustion, which serves to reduce the quantities of residual methane in the dry gas to 0.1 to 0.3 per cent, the volume hourly space velocities range from about 2500 to 3000... 

Table 25. Primary reforming-. Convenlia versus Reduced (low duty)...

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