Water gas shift reactors

In the case of sulphur containing synthesis gases from a partial oxidation, amine scrubbing processes can be apphed as well in which the sulphuric components H2S and COS are scrubbed out together with CO2. In the case of higher sulphur contents (coal and heavy oil gasification) the sulphur components have to be removed selectively. A physical scrubhing process such as the so-called Rectisol 

To meet the requirements of the catalyst, additional steam is introduced before the second reactor lowering the stream temperature. 

The coupling of membrane separation modules and the conventional WGSR reactors through this kind of architecture results in a better overall efficiencies (97.5% as compared to 91% for the reference case). By this configuration, the fuel stream is enriched in H2 by the membrane reactor and requires only polishing by PSA. 

---

In a typical PAFC system, methane passes through a reformer with steam from the coolant loop of the water-cooled fuel cell. Heat for the reforming reaction is generated by combusting the depleted fuel. The reformed natural gas contains typically 60 percent H9, 20 percent CO, and 20 percent H9O. Because the platinum catalyst in the PAFC can tolerate only about 0.5 percent CO, this fuel mixture is passed through a water gas shift reactor before being fed to the fuel cell. 

The process begins with a gasification process that converts coal into carbon monoxide and hydrogen. Part of this gas is sent to a water-gas shift reactor to increase its hydrogen content. The purified syngas is then cryogenically separated into a carbon monoxide feed for the acetic anhydride plant and a hydrogen-rich stream for the synthesis of methanol. 

TonkovichA.L.ZilkaJ.L.PaMont, M.J. VangY. VegengP., Micro-channelchemicalreactorforfuelprocessing applications -1. Water gas shift reactor, Ghem.Eng.Sd. 54(1999)2947-2951. 

Fuel supply is usually from liquid hydrogen or pressurized gaseous hydrogen. For other fuels, a fuel processor is needed, which includes a reformer, water gas shift reactors and purification reactors, in order to decrease the amount of CO to an acceptable level (below a few tens of ppm), which would otherwise poison the platinum-based catalysts. This equipment is still heavy and bulky and limits the dynamic response of the fuel cell stack, particularly for the electric vehicle in some urban driving cycles. 

Advanced water-gas shift reactors using sulphur-tolerant catalysts to produce more hydrogen from synthesis gas at lower cost. 

A high temperature water-gas shift reactor 400°C) typically uses an iron oxide/chromia catalyst, while a low temperature shift reactor ( 200°C) uses a copper-based catalyst. Both low and high temperature shift reactors have superficial contact times (bas on the feed gases at STP) greater than 1 second (72). 

Fig. 10.2 Equilibrium CO concentrations in a WGS reaction showing how two (or more) water-gas shift reactors can be used in industrial applications.

Simulation of the Effect of Integrating Heat-exchange Capabilities into Water-gas Shift Reactors... 

A commercial Cu based catalyst supplied by Haldor-Topsoe was applied to the water-gas shift reaction. At 210 °C, a permeating flux of 4.5 Ndm3 nT2 s 1 was determined for pure hydrogen at a very low pressure drop of 0.2 bar. Then the membrane reactor was coupled with a conventional water-gas shift reactor. At 260-300 °C reaction temperature and a GHSV of 2 085 h 1, the maximum conversion achievable due to the thermodynamic equilibrium could be exceeded by this new technology by 5-10%. 

This system includes several mixing and heat exchange units. A concept for an integrated, microtechnology-based fuel processor was proposed by PNNF [8]. As examples for unit operations which may be included in future integrated systems the same publication mentions reactors for steam reforming and/or partial oxidation, water-gas shift reactors and preferential oxidation reactors for carbon monoxide conversions, heat exchangers, membranes or other separation components. 

Another process that is listed in Table 39 is the C02-free production of hydrogen via thermocatalytic decomposition of hydrocarbon fuels. The process involves a single-step decomposition (pyrolysis) of hydrocarbons over carbon catalysts in an air- and water-free environment. This approach eliminates the need for a water-gas shift reactor, CO2 removal and catalyst regeneration, which significantly simplifies the process60. 

At 850°C and a molar steam to carbon ratio of 9, the hydrogen yield was 90% of that possible for stoichiometric conversion during eight hours of the catalyst on-stream time. This yield could be 5-7% greater if a secondary water-gas shift reactor followed the reformer. 

Singh, C.P. Saraf, D.N. Simulation of High-Temperature Water-Gas Shift Reactors Ind. Eng. Chem. 

The required hydrogen needed for the hydrogenation of bio-oil can be produced through steam reforming of bio-oil over Ni-supported alumina catalysts [32], Hydrogen yields as high as 73% could be produced at 950°C without a low-temperature water-gas shift reactor [32],... 

Sulfur-tolerant catalysts for water-gas shift reactors are necessary to lower syngas processing costs. 

Carbon monoxide at 25°C and steam at 150°C are fed to a continuous water-gas shift reactor. The product gas, which contains 40.0mole% H , 40.0% CO2, and the balance H20(v). emerges at 500°C at a rate of 2.50 SCMH (standard cubic meters per hour) and goes to a condenser. The gas and liquid streams leaving the condenser are in equilibrium at 15 C and 1 atm. The liquid may be taken to be pure water (no dissolved gases). 

Kim, I.-W., T. F. Edgar, and N. H. Bell, Parameter estimation for a laboratory water-gas-shift reactor using a nonlinear error-in-variables method, Comput. Chem. Eng., 15, 361-367 (1991). 

Tonkovich, A.Y., Zilka, J.L., LaMont, M.J., Wang, Y., and Wegeng, R.S. MicroChannel reactors for fuel processing applications. I. Water gas shift reactor. Chemical Engineering Science, 1999, 54, 2947. 

Figure 7.12. MEMs SCT fuel processor. ATR, Autothermal Reformer WGSR, Water Gas Shift Reactor. See color insert.

Moe, J.M. Design of water-gas-shift reactors. Chemical Engineering Progress, 1962, 58, 33. 

---