Purification of syngas

Description The key features of the KBR Purifier Process are mild primary reforming, secondary reforming with excess air, cryogenic purification of syngas, and synthesis of ammonia over magnetite catalyst in a horizontal converter. 

Application To produce ammonia from hydrocarbon feedstocks using a high-pressure (HP) heat exchange-based steam reforming process integrated with cryogenic purification of syngas. 

With FI MH purification, hydrogen recovery does not strongly depend on reformate quality, and hence is the preferred option with ATRs and purification of syngas streams from renewable sources (e.g. biomass gasification or pyrolysis). 

New perspectives with respect to capital investment and operating costs of amine units, but also to their H2S/CD2 selectivity, are opened up by the so-called hindered canines about which more detailed publications first appeared in 1983 [2.19]. Their H2S/CO2 selectivity can be used to good advantage especially for the purification of syngas from coal. 

The required amount of catalyst is not proportional to the increase of yield of ammonia. In the past decades, the amount of catalyst required per ton of ammonia has been reducing. One reason is that the quality or purification of syngas is continuously improved. Another is that the heat stability and antitoxic property of catalysts is increased which prolong the usage life of the catalyst. At the same time, by reducing the pressure class in synthesis loop, the volume of catalyst used is increased significantly. 

Synthesis gas from the gasification of fossil fuels is contaminated by several gaseous compounds that would affect its further use in different ways. The purification steps depend on the type of syngas process and the feedstock. Table 22.9 illustrates how the synthesis gas stream can vary with different feedstocks. Figure 22.8 illustrates the different process steps that may occur before ammonia synthesis takes place.74... 

Purification of feed gas Stripping of syngas by molecular sieves and liq. NH3 -b KNH2 wash to remove impurities. 

Amide-amine solutions react vigorously with water and oxygenous impurities in syngas and form insoluble products. Hence, scrupulous purification of feed gas becomes inevitable. At high pressures, hydrogen reacts with methylamide catalyst [potassium methyla-mide (PMA) ] to form potassium hydride (KH), which is insoluble in amine. To circumvent this hydride precipitation and obtain a reasonable rate, an equimolar mixture of lithium methylamide (LMA) and PMA, called PLMA, was developed by Canadian workers. ... 

A typical layout of the steam-reforming section of a syngas plant with hydrocarbon feedstock is illustrated in Fig. 6. The first step is purification of the feedstock to remove sulfur so as to avoid poisoning of the downstream reformer catalysts. This is typically accomplished in a two-step process. In the first step, organic sulfur compoimds are converted into hydrogen sulfide by a hydrogenation catalyst. In the second step, H2S is absorbed by zinc oxide by the following reaction ... 

Clearly, the application of any type of membrane in the hot-end of the IGCC process can improve the conversion of CO if the membrane can selectively remove H2 or CO2 from the syngas. A highly selective membrane for H2 relative to the other syngas components is required to enhance equilibrium as well as to prevent the loss of valuable reactants and to minimize the need for further purification of the H2-rich permeate. 

Zeolites are also used in the non-cryogenic purification of hydrogen by the adsorption of water, CO2, N2 and hydrocarbons and in the removal of residual CO2 and H2O from syngas mixtures prepared by reforming natural gas according to the reaction CH4+H2O CO + 3H2. These processes are important... 

In addition to the processes described above, there are a number of other physical absorption processes which will not be discussed here in detail either because they can be reasonably used for the purification of methanol syngas from coal with economically justifiable expenditure only in exceptional cases, or because they have not yet been tested on an industrial scale. These processes include... 

The water gas shift (WGS) reaction is a key technology in the hydrogen purification processes of syngas obtained by steam reforming or partial oxidation of hydrocarbons ... 

Parsley, D., Ciora, R. J., Jr., Flowers, D. L., Laukaitaus, J., Chen, A., Liu, P. K. T., et al. (2014). Field evaluation of carbon molecular sieve membranes for the separation and purification of hydrogen from coal- and biomass-derived syngas. Journal of Membrane Science, 450, 81-92. 

The raw dust-free syngas from purification of coal and heavy hydrocarbons contains sulphur as COS and H2S (Table 1.18) according to the equilibrium (see Appendix 2). COS can be removed by a promoted zinc oxide [246]. 

Integration of Membrane and PSA Systems for the Purification of Hydrogen and Production of Oxo-alcohol Syngas... 

The adiabatic fixed-bed reactor with periodic flow reversal has three commercial applications, oxidation of SO2 for sulfuric acid production, oxidation of volatile organic compounds (VOCs) for purification of industrial exhaust gases, and NO, reduction by ammonia in industrial exhaust gases. Other possible future applications are steam reforming and partial oxidation of methane for syngas production, synthesis of methanol and ammonia, and catalytic dehydrogenations (Matros and Bunimovich, 1996). 

To enhance the output of high pressure steam produced by the waste heat boiler, the Uhde Company also proposed a sjmthesis loop with two converters and two waste heat boilers (Fig. 9.6) which were applied in the process with residual oil as raw materials and the cryogenic purification. The loop pressure is 16 MPa, the first converter has two beds, inter-cooled, radial-flow, and the outlet temperature of syngas is 473°C. The outlet gas goes through the waste heat boiler to by-produce high pressure steam then enters the second converter. 

The carbon oxides, particularly the dioxide, have been discussed in earlier chapters, principally Chapter 11. Recall that Joseph Priestley worked with fixed air to produce soda water. The carbonation of soft drinks is still the second leading use of CO2. (The leading use is of the solid as the refrigerant dry ice .) CO2 is produced by the complete combustion of hydrocarbons (p. 286) and plays a major role in the greenhouse effect (p. 369). Earlier we discussed the role of CO and CO2 in the production of syngas (p. 259) and the gasification of coal. In Chapter 6 (p. 132) we noted the utility of carbon monoxide (carbonyl) as a ligand in the Mondprocess for the purification of nickel. 

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